From ca314fbd2509439f708c56f34d0a85449a43fe73 Mon Sep 17 00:00:00 2001 From: Gerald Pfeifer Date: Tue, 7 Feb 2017 22:44:13 +0000 Subject: [PATCH] lwg-active.html: Remove. * doc/html/ext/lwg-active.html: Remove. * doc/html/ext/lwg-closed.html: Ditto. * doc/html/ext/lwg-defects.html: Ditto. * doc/Makefile.am (xml_extradir): Remove. (xml_extra): Ditto. (stamp-html-docbook-lwg): Remove recipe... (stamp-html-docbook-data): ...and its use here. * doc/Makefile.in: Regenerate. * doc/xml/manual/intro.xml: Shorten two paragraphs explaining the relationship to the upstream working group. Replace a local link to ../ext/lwg-active.html by the upstream one. Replace all reference to ../ext/lwg-defects.html by a new entity &DR; which refers to the upstream address. From-SVN: r245258 --- libstdc++-v3/ChangeLog | 18 + libstdc++-v3/doc/Makefile.am | 12 +- libstdc++-v3/doc/Makefile.in | 11 +- libstdc++-v3/doc/html/ext/lwg-active.html | 30172 ---- libstdc++-v3/doc/html/ext/lwg-closed.html | 42632 ------ libstdc++-v3/doc/html/ext/lwg-defects.html | 129794 ------------------ libstdc++-v3/doc/xml/manual/intro.xml | 286 +- 7 files changed, 160 insertions(+), 202765 deletions(-) delete mode 100644 libstdc++-v3/doc/html/ext/lwg-active.html delete mode 100644 libstdc++-v3/doc/html/ext/lwg-closed.html delete mode 100644 libstdc++-v3/doc/html/ext/lwg-defects.html diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index aedde084db67..1a10c3deabaa 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,21 @@ +2017-02-07 Gerald Pfeifer + + * doc/html/ext/lwg-active.html: Remove. + * doc/html/ext/lwg-closed.html: Ditto. + * doc/html/ext/lwg-defects.html: Ditto. + + * doc/Makefile.am (xml_extradir): Remove. + (xml_extra): Ditto. + (stamp-html-docbook-lwg): Remove recipe... + (stamp-html-docbook-data): ...and its use here. + * doc/Makefile.in: Regenerate. + + * doc/xml/manual/intro.xml: Shorten two paragraphs explaining + the relationship to the upstream working group. + Replace a local link to ../ext/lwg-active.html by the upstream one. + Replace all reference to ../ext/lwg-defects.html by a new entity + &DR; which refers to the upstream address. + 2017-02-07 Gerald Pfeifer * doc/xml/manual/status_cxx2017.xml: Fix link to N4284. diff --git a/libstdc++-v3/doc/Makefile.am b/libstdc++-v3/doc/Makefile.am index 6ea9da3c2992..7d0c52d96b5b 100644 --- a/libstdc++-v3/doc/Makefile.am +++ b/libstdc++-v3/doc/Makefile.am @@ -450,12 +450,6 @@ xml_image_generated = \ xml_images = ${xml_image_basic} ${xml_image_generated} -xml_extradir = ${glibcxx_srcdir}/doc/html/ext -xml_extra = \ - ${xml_extradir}/lwg-active.html \ - ${xml_extradir}/lwg-closed.html \ - ${xml_extradir}/lwg-defects.html - xml_noinst = \ ${xml_dir}/book.txml \ ${xml_dir}/chapter.txml \ @@ -538,11 +532,7 @@ stamp-html-docbook-images: stamp-html-docbook $(xml_images) $(INSTALL_DATA) $(xml_images) ${docbook_outdir}/html/images $(STAMP) stamp-html-docbook-images -stamp-html-docbook-lwg: stamp-html-docbook $(xml_extra) - $(INSTALL_DATA) $(xml_extra) ${docbook_outdir}/html/ext - $(STAMP) stamp-html-docbook-lwg - -stamp-html-docbook-data: stamp-html-docbook-images stamp-html-docbook-lwg +stamp-html-docbook-data: stamp-html-docbook-images $(STAMP) stamp-html-docbook-data # HTML, "chunked" into index plus chapters as separate pages diff --git a/libstdc++-v3/doc/Makefile.in b/libstdc++-v3/doc/Makefile.in index 9db085557852..281394debd04 100644 --- a/libstdc++-v3/doc/Makefile.in +++ b/libstdc++-v3/doc/Makefile.in @@ -539,11 +539,6 @@ xml_image_generated = \ ${xml_image_dir}/pbds_tree_text_lor_find.png xml_images = ${xml_image_basic} ${xml_image_generated} -xml_extradir = ${glibcxx_srcdir}/doc/html/ext -xml_extra = \ - ${xml_extradir}/lwg-active.html \ - ${xml_extradir}/lwg-closed.html \ - ${xml_extradir}/lwg-defects.html xml_noinst = \ ${xml_dir}/book.txml \ @@ -970,11 +965,7 @@ stamp-html-docbook-images: stamp-html-docbook $(xml_images) $(INSTALL_DATA) $(xml_images) ${docbook_outdir}/html/images $(STAMP) stamp-html-docbook-images -stamp-html-docbook-lwg: stamp-html-docbook $(xml_extra) - $(INSTALL_DATA) $(xml_extra) ${docbook_outdir}/html/ext - $(STAMP) stamp-html-docbook-lwg - -stamp-html-docbook-data: stamp-html-docbook-images stamp-html-docbook-lwg +stamp-html-docbook-data: stamp-html-docbook-images $(STAMP) stamp-html-docbook-data # HTML, "chunked" into index plus chapters as separate pages diff --git a/libstdc++-v3/doc/html/ext/lwg-active.html b/libstdc++-v3/doc/html/ext/lwg-active.html deleted file mode 100644 index 7da07e683d59..000000000000 --- a/libstdc++-v3/doc/html/ext/lwg-active.html +++ /dev/null @@ -1,30172 +0,0 @@ - - - -C++ Standard Library Active Issues List - - - - - - - - - - - - - - - - - - - - -
Doc. no.N4484
Date:2015-05-23
Project:Programming Language C++
Reply to:Marshall Clow <lwgchair@gmail.com>
-

C++ Standard Library Active Issues List (Revision R93)

-

Revised 2015-05-23 at 15:05:40 UTC

-

-

Reference ISO/IEC IS 14882:2014(E)

-

Also see:

- -

The purpose of this document is to record the status of issues - which have come before the Library Working Group (LWG) of the INCITS PL22.16 - and ISO WG21 C++ Standards Committee. Issues represent - potential defects in the ISO/IEC IS 14882:2014(E) document. -

- -

This document contains only library issues which are actively being - considered by the Library Working Group, i.e., issues which have a - status of New, Open, - Ready, or Review. - See Library Defect Reports List for issues considered defects - and Library Closed Issues List for issues considered closed.

- -

The issues in these lists are not necessarily formal ISO Defect - Reports (DR's). While some issues will eventually be elevated to - official Defect Report status, other issues will be disposed of in - other ways. See Issue Status.

- -

Prior to Revision 14, library issues lists existed in two slightly - different versions; a Committee Version and a Public - Version. Beginning with Revision 14 the two versions were combined - into a single version.

- -

This document includes [bracketed italicized notes] as a - reminder to the LWG of current progress on issues. Such notes are - strictly unofficial and should be read with caution as they may be - incomplete or incorrect. Be aware that LWG support for a particular - resolution can quickly change if new viewpoints or killer examples are - presented in subsequent discussions.

- -

For the most current official version of this document see - http://www.open-std.org/jtc1/sc22/wg21/. - Requests for further information about this document should include - the document number above, reference ISO/IEC 14882:2014(E), and be - submitted to Information Technology Industry Council (ITI), 1250 Eye - Street NW, Washington, DC 20005.

- -

Public information as to how to obtain a copy of the C++ Standard, - join the standards committee, submit an issue, or comment on an issue - can be found in the comp.std.c++ FAQ. -

- -

How to submit an issue

- -
    -
  1. -Mail your issue to the author of this list. -
    2. -
  2. -Specify a short descriptive title. If you fail to do so, the subject line of your -mail will be used as the issue title. -
    3. -
  3. -If the "From" on your email is not the name you wish to appear as issue submitter, -then specify issue submitter. -
    4. -
  4. -Provide a brief discussion of the problem you wish to correct. Refer to the latest -working draft or standard using [section.tag] and paragraph numbers where appropriate. -
    5. -
  5. -Provide proposed wording. This should indicate exactly how you want the standard -to be changed. General solution statements belong in the discussion area. This -area contains very clear and specific directions on how to modify the current -draft. If you are not sure how to word a solution, you may omit this part. -But your chances of a successful issue greatly increase if you attempt wording. -
    6. -
  6. -It is not necessary for you to use html markup. However, if you want to, you can -<ins>insert text like this</ins> and <del>delete text like -this</del>. The only strict requirement is to communicate clearly to -the list maintainer exactly how you want your issue to look. -
    7. -
  7. -It is not necessary for you to specify other html font/formatting -mark-up, but if you do the list maintainer will attempt to respect your -formatting wishes (as described by html markup, or other common idioms). -
    8. -
  8. -It is not necessary for you to specify open date or last modified date (the date -of your mail will be used). -
    9. -
  9. -It is not necessary for you to cross reference other issues, but you can if you -like. You do not need to form the hyperlinks when you do, the list maintainer will -take care of that. -
    10. -
  10. -One issue per email is best. -
    11. -
  11. -Between the time you submit the issue, and the next mailing deadline -(date at the top of the Revision History), you own this issue. -You control the content, the stuff that is right, the stuff that is -wrong, the format, the misspellings, etc. You can even make the issue -disappear if you want. Just let the list maintainer know how you want -it to look, and he will try his best to accommodate you. After the -issue appears in an official mailing, you no longer enjoy exclusive -ownership of it. -
    12. -
- - -

Revision History

- - -

Issue Status

- -

Issues reported to the LWG transition through a variety of statuses, - indicating their progress towards a resolution. Typically, most issues - will flow through the following stages. -

- -

New - The issue has not yet been - reviewed by the LWG. Any Proposed Resolution is purely a - suggestion from the issue submitter, and should not be construed as - the view of LWG.

- -

Open - The LWG has discussed the issue - but is not yet ready to move the issue forward. There are several - possible reasons for open status:

-
    -
  • Consensus may have not yet have been reached as to how to deal - with the issue.
    • -
  • Informal consensus may have been reached, but the LWG awaits - exact Proposed Resolution wording for review.
    • -
  • The LWG wishes to consult additional technical experts before - proceeding.
    • -
  • The issue may require further study.
    • -
- -

A Proposed Resolution for an open issue is still not be - construed as the view of LWG. Comments on the current state of - discussions are often given at the end of open issues in an italic - font. Such comments are for information only and should not be given - undue importance.

- -

Review - Exact wording of a - Proposed Resolution is now available for review on an issue - for which the LWG previously reached informal consensus.

- -

Ready - The LWG has reached consensus - that the issue is a defect in the Standard, the Proposed - Resolution is correct, and the issue is ready to forward to the - full committee for further action as a Defect Report (DR).

- -

Typically, an issue must have a proposed resolution in the currently - published issues list, whose wording does not change during LWG review, to - move to the Ready status.

- -

Voting - This status should not be seen - in a published issues list, but is a marker for use during meetings to - indicate an issues was Ready in the pre-meeting mailing, the Proposed - Resolution is correct, and the issue will be offered to the working - group at the end of the current meeting to apply to the current working - paper (WP) or to close in some other appropriate manner. This easily - distinguishes such issues from those moving to Ready status during the - meeting itself, that should not be forwarded until the next meeting. If - the issue does not move forward, it should fall back to one of the other - open states before the next list is published.

- -

Immediate - This status should not be - seen in a published issues list, but is a marker for use during meetings - to indicate an issues was not Ready in the pre-meeting mailing, but the - Proposed Resolution is correct, and the issue will be offered to - the working group at the end of the current meeting to apply to the - current working paper (WP) or to close in some other appropriate manner. - This status is used only rarely, typically for fixes that are both small - and obvious, and usually within a meeting of the expected publication of - a revised standard. If the issue does not move forward, it should fall - back to one of the other open states before the next list is published.

- -

In addition, there are a few ways to categorise and issue that remains - open to a resolution within the library, but is not actively being worked - on. -

- -

Deferred - The LWG has discussed the issue, - is not yet ready to move the issue forward, but neither does it deem the - issue significant enough to delay publishing a standard or Technical Report. - A typical deferred issue would be seeking to clarify wording that might be - technically correct, but easily mis-read.

- -

A Proposed Resolution for a deferred issue is still not be - construed as the view of LWG. Comments on the current state of - discussions are often given at the end of open issues in an italic - font. Such comments are for information only and should not be given - undue importance.

- -

Core - The LWG has discussed the issue, and feels - that some key part of resolving the issue is better handled by a cleanup of - the language in the Core part of the standard. The issue is passed to the Core - Working Group, which should ideally open a corresponding issue that can be - linked from the library issue. Such issues will be revisitted after Core have - made (or declined to make) any changes. -

- -

EWG - The LWG has discussed the issue, and wonder - that some key part of resolving the issue is better handled by some (hopefully - small) extension to the language. The issue is passed to the Evolution Working - Group, which should ideally open a corresponding issue that can be linked from - the library issue. Such issues will be revisitted after Evoltion have made (or - declined to make) any recommendations. Positive recommendations from EWG will - often mean the issue transition to Core status while we wait for some - proposed new feature to land in the working paper. -

- -

LEWG - The LWG has discussed the issue, and deemd - the issue is either an extension, however small, or changes the library design - in some fundamental way, and so has delegated the initial work to the Library - Evolution Working Group. -

- -

Ultimately, all issues should reach closure with one of the following statuses. -

- -

DR - (Defect Report) - The full WG21/PL22.16 - committee has voted to forward the issue to the Project Editor to be - processed as a Potential Defect Report. The Project Editor reviews - the issue, and then forwards it to the WG21 Convenor, who returns it - to the full committee for final disposition. This issues list - accords the status of DR to all these Defect Reports regardless of - where they are in that process.

- -

WP - (Working Paper) - The proposed resolution has not been - accepted as a Technical Corrigendum, but the full WG21/PL22.16 committee has voted to - apply the Defect Report's Proposed Resolution to the working paper.

- -

C++14 - (C++ Standard, as revised for 2014) - The full - WG21/PL22.16 committee has voted to accept the Defect Report's Proposed Resolution into - the published 2011 revision to the C++ standard, ISO/IEC IS 14882:2014(E).

- -

C++11 - (C++ Standard, as revised for 2011) - The full - WG21/PL22.16 committee has voted to accept the Defect Report's Proposed Resolution into - the published 2011 revision to the C++ standard, ISO/IEC IS 14882:2011(E).

- -

CD1 - (Committee Draft 2008) - The full - WG21/PL22.16 committee has voted to accept the Defect Report's Proposed - Resolution into the Fall 2008 Committee Draft.

- -

TC1 - (Technical Corrigenda 1) - The full - WG21/PL22.16 committee has voted to accept the Defect Report's Proposed - Resolution as a Technical Corrigenda. Action on this issue is thus - complete and no further action is possible under ISO rules.

- -

TRDec - (Decimal TR defect) - The LWG has voted to - accept the Defect Report's Proposed Resolution into the Decimal TR. Action on this - issue is thus complete and no further action is expected.

- -

Resolved - The LWG has reached consensus - that the issue is a defect in the Standard, but the resolution adopted to - resolve the issue came via some other mechanism than this issue in the - list - typically by applying a formal paper, occasionally as a side effect - of consolidating several interacting issue resolutions into a single issue.

- -

Dup - The LWG has reached consensus that - the issue is a duplicate of another issue, and will not be further - dealt with. A Rationale identifies the duplicated issue's - issue number.

- -

NAD - The LWG has reached consensus that - the issue is not a defect in the Standard.

- -

NAD Editorial - The LWG has reached consensus that - the issue can either be handled editorially, or is handled by a paper (usually - linked to in the rationale).

- -

Tentatively - This is a status qualifier. The issue has - been reviewed online, or at an unofficial meeting, but not in an official meeting, and - some support has been formed for the qualified status. Tentatively qualified issues may - be moved to the unqualified status and forwarded to full committee (if Ready) within the - same meeting. Unlike Ready issues, Tentatively Ready issues will be reviewed in - subcommittee prior to forwarding to full committee. When a status is qualified with - Tentatively, the issue is still considered active.

- -

Pending - This is a status qualifier. When prepended to a status this - indicates the issue has been processed by the committee, and a decision has been made to - move the issue to the associated unqualified status. However for logistical reasons the - indicated outcome of the issue has not yet appeared in the latest working paper.

- -

The following statuses have been retired, but may show up on older issues lists.

- -

NAD Future - In addition to the regular status, the - LWG believes that this issue should be revisited at the next revision of the standard. - That is now an ongoing task managed by the Library Evolution Working Group, and most - issues in this status were reopended with the status LEWG. -

- -

NAD Concepts - This status reflects an evolution - of the language during the development of C++11, where a new feature entered the - language, called concepts, that fundamentally changed the way templates would - be specified and written. While this language feature was removed towards the end of - the C++11 project, there is a clear intent to revisit this part of the language design. - During that development, a number of issues were opened against the updated library - related to use of that feature, or requesting fixes that would require exlicit use of - the concepts feature. All such issues have been closed with this status, and may be - revisitted should this or a similar language feature return for a future standard.

- -

Issues are always given the status of New when - they first appear on the issues list. They may progress to - Open or Review - while the LWG is actively working on them. When the LWG has reached consensus on - the disposition of an issue, the status will then change to - Dup, NAD, or - Ready as appropriate. Once the full PL22.16 committee - votes to forward Ready issues to the Project Editor, they are given the status of Defect - Report (DR). These in turn may become the basis for - Technical Corrigenda (TC1), an updated standard - (C++11, C++14), - or are closed without action other than a Record of Response - (Resolved) where the desired effect has already - been achieved by some other process. The intent of this LWG process is that only issues - which are truly defects in the Standard move to the formal ISO DR status. -

- - -

Active Issues

-
-

255. Why do basic_streambuf<>::pbump() and gbump() take an int?

-

Section: 27.6.3 [streambuf] Status: LEWG - Submitter: Martin Sebor Opened: 2000-08-12 Last modified: 2015-04-08

-

View all other issues in [streambuf].

-

View all issues with LEWG status.

-

Discussion:

-

-The basic_streambuf members gbump() and pbump() are specified to take an -int argument. This requirement prevents the functions from effectively -manipulating buffers larger than std::numeric_limits<int>::max() -characters. It also makes the common use case for these functions -somewhat difficult as many compilers will issue a warning when an -argument of type larger than int (such as ptrdiff_t on LLP64 -architectures) is passed to either of the function. Since it's often the -result of the subtraction of two pointers that is passed to the -functions, a cast is necessary to silence such warnings. Finally, the -usage of a native type in the functions signatures is inconsistent with -other member functions (such as sgetn() and sputn()) that manipulate the -underlying character buffer. Those functions take a streamsize argument. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-This is part of a bigger problem. If anyone cares enough, they should -write a paper solving the bigger problem of offset types in iostreams. -

-

-This is related to the paper about large file sizes. Beman has already -agreed to drop the section of that paper that deals with this. -

-

-int is big enough for reasonable buffers. -

-

-Move to NAD Future. -

-

-This is related to LWG 423. -

-
- - - -

Proposed resolution:

-

-Change the signatures of these functions in the synopsis of template -class basic_streambuf (27.5.2) and in their descriptions (27.5.2.3.1, p4 -and 27.5.2.3.2, p4) to take a streamsize argument. -

- -

-Although this change has the potential of changing the ABI of the -library, the change will affect only platforms where int is different -than the definition of streamsize. However, since both functions are -typically inline (they are on all known implementations), even on such -platforms the change will not affect any user code unless it explicitly -relies on the existing type of the functions (e.g., by taking their -address). Such a possibility is IMO quite remote. -

- -

-Alternate Suggestion from Howard Hinnant, c++std-lib-7780: -

- -

-This is something of a nit, but I'm wondering if streamoff wouldn't be a -better choice than streamsize. The argument to pbump and gbump MUST be -signed. But the standard has this to say about streamsize -(27.4.1/2/Footnote): -

- -

- [Footnote: streamsize is used in most places where ISO C would use - size_t. Most of the uses of streamsize could use size_t, except for - the strstreambuf constructors, which require negative values. It - should probably be the signed type corresponding to size_t (which is - what Posix.2 calls ssize_t). --- end footnote] -

- -

-This seems a little weak for the argument to pbump and gbump. Should we -ever really get rid of strstream, this footnote might go with it, along -with the reason to make streamsize signed. -

- - -

Rationale:

-

The LWG believes this change is too big for now. We may wish to -reconsider this for a future revision of the standard. One -possibility is overloading pbump, rather than changing the -signature.

-

[ -[2006-05-04: Reopened at the request of Chris (Krzysztof ?elechowski)] -]

- - - - - -
-

423. effects of negative streamsize in iostreams

-

Section: 27 [input.output] Status: LEWG - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [input.output].

-

View all issues with LEWG status.

-

Discussion:

- -

-A third party test suite tries to exercise istream::ignore(N) with -a negative value of N and expects that the implementation will treat -N as if it were 0. Our implementation asserts that (N >= 0) holds and -aborts the test. -

- -

-I can't find anything in section 27 that prohibits such values but I don't -see what the effects of such calls should be, either (this applies to -a number of unformatted input functions as well as some member functions -of the basic_streambuf template). -

- -

[ -2009-07 Frankfurt -]

- - -
-

-This is related to LWG 255. -

-

-Move to NAD Future. -

-
- - - -

Proposed resolution:

-

-I propose that we add to each function in clause 27 that takes an argument, -say N, of type streamsize a Requires clause saying that "N >= 0." The intent -is to allow negative streamsize values in calls to precision() and width() -but disallow it in calls to streambuf::sgetn(), istream::ignore(), or -ostream::write(). -

- -

[Kona: The LWG agreed that this is probably what we want. However, we - need a review to find all places where functions in clause 27 take - arguments of type streamsize that shouldn't be allowed to go - negative. Martin will do that review.]

- - - - - - -
-

484. Convertible to T

-

Section: 24.2.3 [input.iterators] Status: LEWG - Submitter: Chris Jefferson Opened: 2004-09-16 Last modified: 2015-04-08

-

View all other issues in [input.iterators].

-

View all issues with LEWG status.

-

Discussion:

-

From comp.std.c++:

- -

-I note that given an input iterator a for type T, -then *a only has to be "convertable to T", -not actually of type T. -

- -

Firstly, I can't seem to find an exact definition of "convertable to T". -While I assume it is the obvious definition (an implicit conversion), I -can't find an exact definition. Is there one?

- -

Slightly more worryingly, there doesn't seem to be any restriction on -the this type, other than it is "convertable to T". Consider two input -iterators a and b. I would personally assume that most people would -expect *a==*b would perform T(*a)==T(*b), however it doesn't seem that -the standard requires that, and that whatever type *a is (call it U) -could have == defined on it with totally different symantics and still -be a valid inputer iterator.

- -

Is this a correct reading? When using input iterators should I write -T(*a) all over the place to be sure that the object I'm using is the -class I expect?

- -

This is especially a nuisance for operations that are defined to be - "convertible to bool". (This is probably allowed so that - implementations could return say an int and avoid an unnessary - conversion. However all implementations I have seen simply return a - bool anyway. Typical implemtations of STL algorithms just write - things like while(a!=b && *a!=0). But strictly - speaking, there are lots of types that are convertible to T but - that also overload the appropriate operators so this doesn't behave - as expected.

- -

If we want to make code like this legal (which most people seem to - expect), then we'll need to tighten up what we mean by "convertible - to T".

- -

[Lillehammer: The first part is NAD, since "convertible" is - well-defined in core. The second part is basically about pathological - overloads. It's a minor problem but a real one. So leave open for - now, hope we solve it as part of iterator redesign.]

- - -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD Future. We agree there's an issue, but there is no -proposed solution at this time and this will be solved by concepts in -the future. -

- - - -

Proposed resolution:

- - -

Rationale:

-

[ -San Francisco: -]

- - -

-Solved by -N2758. -

- - - - - -
-

523. regex case-insensitive character ranges are unimplementable as specified

-

Section: 28 [re] Status: LEWG - Submitter: Eric Niebler Opened: 2005-07-01 Last modified: 2015-04-08

-

View other active issues in [re].

-

View all other issues in [re].

-

View all issues with LEWG status.

-

Discussion:

-

-A problem with TR1 regex is currently being discussed on the Boost -developers list. It involves the handling of case-insensitive matching -of character ranges such as [Z-a]. The proper behavior (according to the -ECMAScript standard) is unimplementable given the current specification -of the TR1 regex_traits<> class template. John Maddock, the author of -the TR1 regex proposal, agrees there is a problem. The full discussion -can be found at http://lists.boost.org/boost/2005/06/28850.php (first -message copied below). We don't have any recommendations as yet. -

-

--- Begin original message -- -

-

-The situation of interest is described in the ECMAScript specification -(ECMA-262), section 15.10.2.15: -

-

-"Even if the pattern ignores case, the case of the two ends of a range -is significant in determining which characters belong to the range. -Thus, for example, the pattern /[E-F]/i matches only the letters E, F, -e, and f, while the pattern /[E-f]/i matches all upper and lower-case -ASCII letters as well as the symbols [, \, ], ^, _, and `." -

-

-A more interesting case is what should happen when doing a -case-insentitive match on a range such as [Z-a]. It should match z, Z, -a, A and the symbols [, \, ], ^, _, and `. This is not what happens with -Boost.Regex (it throws an exception from the regex constructor). -

-

-The tough pill to swallow is that, given the specification in TR1, I -don't think there is any effective way to handle this situation. -According to the spec, case-insensitivity is handled with -regex_traits<>::translate_nocase(CharT) -- two characters are equivalent -if they compare equal after both are sent through the translate_nocase -function. But I don't see any way of using this translation function to -make character ranges case-insensitive. Consider the difficulty of -detecting whether "z" is in the range [Z-a]. Applying the transformation -to "z" has no effect (it is essentially std::tolower). And we're not -allowed to apply the transformation to the ends of the range, because as -ECMA-262 says, "the case of the two ends of a range is significant." -

-

-So AFAICT, TR1 regex is just broken, as is Boost.Regex. One possible fix -is to redefine translate_nocase to return a string_type containing all -the characters that should compare equal to the specified character. But -this function is hard to implement for Unicode, and it doesn't play nice -with the existing ctype facet. What a mess! -

-

--- End original message -- -

- -

[ -John Maddock adds: -]

- - -

-One small correction, I have since found that ICU's regex package does -implement this correctly, using a similar mechanism to the current -TR1.Regex. -

-

-Given an expression [c1-c2] that is compiled as case insensitive it: -

-

-Enumerates every character in the range c1 to c2 and converts it to it's -case folded equivalent. That case folded character is then used a key to a -table of equivalence classes, and each member of the class is added to the -list of possible matches supported by the character-class. This second step -isn't possible with our current traits class design, but isn't necessary if -the input text is also converted to a case-folded equivalent on the fly. -

-

-ICU applies similar brute force mechanisms to character classes such as -[[:lower:]] and [[:word:]], however these are at least cached, so the impact -is less noticeable in this case. -

-

-Quick and dirty performance comparisons show that expressions such as -"[X-\\x{fff0}]+" are indeed very slow to compile with ICU (about 200 times -slower than a "normal" expression). For an application that uses a lot of -regexes this could have a noticeable performance impact. ICU also has an -advantage in that it knows the range of valid characters codes: code points -outside that range are assumed not to require enumeration, as they can not -be part of any equivalence class. I presume that if we want the TR1.Regex -to work with arbitrarily large character sets enumeration really does become -impractical. -

-

-Finally note that Unicode has: -

-

-Three cases (upper, lower and title). -One to many, and many to one case transformations. -Character that have context sensitive case translations - for example an -uppercase sigma has two different lowercase forms - the form chosen depends -on context(is it end of a word or not), a caseless match for an upper case -sigma should match either of the lower case forms, which is why case folding -is often approximated by tolower(toupper(c)). -

-

-Probably we need some way to enumerate character equivalence classes, -including digraphs (either as a result or an input), and some way to tell -whether the next character pair is a valid digraph in the current locale. -

-

-Hoping this doesn't make this even more complex that it was already, -

- -

[ -Portland: Alisdair: Detect as invalid, throw an exception. -Pete: Possible general problem with case insensitive ranges. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-We agree that this is a problem, but we do not know the answer. -

-

-We are going to declare this NAD until existing practice leads us in some direction. -

-

-No objection to NAD Future. -

-

-Move to NAD Future. -

-
- - - -

Proposed resolution:

- - - - - -
-

532. Tuple comparison

-

Section: 20.4.2.7 [tuple.rel], TR1 6.1.3.5 [tr.tuple.rel] Status: LEWG - Submitter: David Abrahams Opened: 2005-11-29 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 348

-

Discussion:

-

-Where possible, tuple comparison operators <,<=,=>, and > ought to be -defined in terms of std::less rather than operator<, in order to -support comparison of tuples of pointers. -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -
-

-If we solve this for tuple we would have to solve it for pair -algorithms, etc. It is too late to do that at this time. Move to NAD Future. -

-
- - - -

Proposed resolution:

-

-change 6.1.3.5/5 from: -

- -

- Returns: The result of a lexicographical comparison between t and - u. The result is defined as: (bool)(get<0>(t) < get<0>(u)) || - (!(bool)(get<0>(u) < get<0>(t)) && ttail < utail), where rtail for - some tuple r is a tuple containing all but the first element of - r. For any two zero-length tuples e and f, e < f returns false. -

- -

-to: -

- -
-

- Returns: The result of a lexicographical comparison between t and - u. For any two zero-length tuples e and f, e < f returns false. - Otherwise, the result is defined as: cmp( get<0>(t), get<0>(u)) || - (!cmp(get<0>(u), get<0>(t)) && ttail < utail), where rtail for some - tuple r is a tuple containing all but the first element of r, and - cmp(x,y) is an unspecified function template defined as follows. -

-

- Where T is the type of x and U is the type of y: -

- -

- if T and U are pointer types and T is convertible to U, returns - less<U>()(x,y) -

- -

- otherwise, if T and U are pointer types, returns less<T>()(x,y) -

- -

- otherwise, returns (bool)(x < y) -

-
- -

[ -Berlin: This issue is much bigger than just tuple (pair, containers, -algorithms). Dietmar will survey and work up proposed wording. -]

- - - - -

Rationale:

-

-Recommend NAD. This will be fixed with the next revision of concepts. -

- -

[ -San Francisco: -]

- - -

-Solved by -N2770. -

- - - - - -
-

708. Locales need to be per thread and updated for POSIX changes

-

Section: 22 [localization] Status: LEWG - Submitter: Peter Dimov Opened: 2007-07-28 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The POSIX "Extended API Set Part 4," -

-

-http://www.opengroup.org/sib/details.tpl?id=C065 -

-

-introduces extensions to the C locale mechanism that -allow multiple concurrent locales to be used in the same application -by introducing a type locale_t that is very similar to -std::locale, and a number of _l functions that make use of it. -

-

-The global locale (set by setlocale) is now specified to be per- -process. If a thread does not call uselocale, the global locale is -in effect for that thread. It can install a per-thread locale by -using uselocale. -

-

-There is also a nice querylocale mechanism by which one can obtain -the name (such as "de_DE") for a specific facet, even for combined -locales, with no std::locale equivalent. -

-

-std::locale should be harmonized with the new POSIX locale_t -mechanism and provide equivalents for uselocale and querylocale. -

- -

[ -Kona (2007): Bill and Nick to provide wording. -]

- - -

[ -San Francisco: Bill and Nick still intend to provide wording, but this -is a part of the task to be addressed by the group that will look into -issue 860. -]

- - -

[ -2009-07 Frankfurt: -]

- - -
-

-It's our intention to stay in sync with WG14. If WG14 makes a decision -that requires a change in WG21 the issue will be reopened. -

-

-Move to NAD Future. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

760. The emplace issue

-

Section: 23.2 [container.requirements] Status: Tentatively NAD - Submitter: Paolo Carlini Opened: 2007-11-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In an emplace member function the function parameter pack may be bound -to a priori unlimited number of objects: some or all of them can be -elements of the container itself. Apparently, in order to conform to the -blanket statement 23.2 [container.requirements]/11, the -implementation must check all of them for that possibility. A possible -solution can involve extending the exception in 23.2 [container.requirements]/12 also to the emplace member. As a -side note, the push_back and push_front member -functions are luckily not affected by this problem, can be efficiently -implemented anyway. -

- -

[ -Related to 767 and to 2164 -]

- - -

[ -Bellevue: -]

- - -
-

-The proposed addition (13) is partially redundant with the existing -paragraph 12. Why was the qualifier "rvalues" added to paragraph 12? Why -does it not cover subelements and pointers? -

-

-Resolution: Alan Talbot to rework language, then set state to Review. -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-The problem is broader than emplace. The LWG doesn't -feel that it knows how to write wording that prohibits all of the -problematic use cases at this time. -

-

-NAD Future. -

-
- -

[2015-02 Cologne]

- -

-LWG believes that 2164 addresses this issue and therefore considers 760 as NAD. -

- - -

Proposed resolution:

-

-Add after 23.2 [container.requirements]/12: -

- -
-

--12- Objects passed to member functions of a container as rvalue -references shall not be elements of that container. No diagnostic -required. -

-

- --13- Objects bound to the function parameter pack of the -emplace member function shall not be elements or sub-objects of -elements of the container. No diagnostic required. - -

- -
- - - - - - -
-

839. Maps and sets missing splice operation

-

Section: 23.4 [associative], 23.5 [unord] Status: LEWG - Submitter: Alan Talbot Opened: 2008-05-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Splice is a very useful feature of list. This functionality is also very -useful for any other node based container, and I frequently wish it were -available for maps and sets. It seems like an omission that these -containers lack this capability. Although the complexity for a splice is -the same as for an insert, the actual time can be much less since the -objects need not be reallocated and copied. When the element objects are -heavy and the compare operations are fast (say a map<int, huge_thingy>) -this can be a big win. -

- -

-Suggested resolution: -

- -

-Add the following signatures to map, set, multimap, multiset, and the unordered associative containers: -

-
 
-void splice(list<T,Allocator>&& x);
-void splice(list<T,Allocator>&& x, const_iterator i);
-void splice(list<T,Allocator>&& x, const_iterator first, const_iterator last);
-
- -

-Hint versions of these are also useful to the extent hint is useful. -(I'm looking for guidance about whether hints are in fact useful.) -

- -
 
-void splice(const_iterator position, list<T,Allocator>&& x);
-void splice(const_iterator position, list<T,Allocator>&& x, const_iterator i);
-void splice(const_iterator position, list<T,Allocator>&& x, const_iterator first, const_iterator last);
-
- -

[ -Sophia Antipolis: -]

- - -
-

-Don't try to splice "list" into the other containers, it should be container-type. -

-

-forward_list already has splice_after. -

-

-Would "splice" make sense for an unordered_map? -

-

-Jens, Robert: "splice" is not the right term, it implies maintaining ordering in lists. -

-

-Howard: adopt? -

-

-Jens: absorb? -

-

-Alan: subsume? -

-

-Robert: recycle? -

-

-Howard: transfer? (but no direction) -

-

-Jens: transfer_from. No. -

-

-Alisdair: Can we give a nothrow guarantee? If your compare() and hash() doesn't throw, yes. -

-

-Daniel: For unordered_map, we can't guarantee nothrow. -

-
- -

[ -San Francisco: -]

- - -
-

-Martin: this would possibly outlaw an implementation technique that is -currently in use; caching nodes in containers. -

-

-Alan: if you cache in the allocator, rather than the individual -container, this proposal doesn't interfere with that. -

-

-Martin: I'm not opposed to this, but I'd like to see an implementation -that demonstrates that it works. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-NAD Future. -

- -

[ -2009-09-19 Howard adds: -]

- - -
-

-I'm not disagreeing with the NAD Future resolution. But when the future gets -here, here is a possibility worth exploring: -

- -
-

-Add to the "unique" associative containers: -

- -
-typedef details      node_ptr;
-
-node_ptr             remove(const_iterator p);
-pair<iterator, bool> insert(node_ptr&& nd);
-iterator             insert(const_iterator p, node_ptr&& nd);
-
- -

-And add to the "multi" associative containers: -

- -
-typedef details node_ptr;
-
-node_ptr remove(const_iterator p);
-iterator insert(node_ptr&& nd);
-iterator insert(const_iterator p, node_ptr&& nd);
-
- -

-Container::node_ptr is a smart pointer much like unique_ptr. -It owns a node obtained from the container it was removed from. It maintains a -reference to the allocator in the container so that it can properly deallocate -the node if asked to, even if the allocator is stateful. This being said, the -node_ptr can not outlive the container for this reason. -

- -

-The node_ptr offers "const-free" access to the node's -value_type. -

- -

-With this interface, clients have a great deal of flexibility: -

- -
    -
  • -A client can remove a node from one container, and insert it into another -(without any heap allocation). This is the splice functionality this issue -asks for. -
    • -
  • -A client can remove a node from a container, change its key or value, and insert -it back into the same container, or another container, all without the cost of -allocating a node. -
    • -
  • -If the Compare function is nothrow (which is very common), then this functionality -is nothrow unless modifying the value throws. And if this does throw, it does -so outside of the containers involved. -
    • -
  • -If the Compare function does throw, the insert function will have the -argument nd retain ownership of the node. -
    • -
  • -The node_ptr should be independent of the Compare parameter -so that a node can be transferred from set<T, C1, A> -to set<T, C2, A> (for example). -
    • -
- -

-Here is how the customer might use this functionality: -

- -
    -
  • -

    -Splice a node from one container to another: -

    -
    -m2.insert(m1.remove(i));
-
    -
    • - -
  • -

    -Change the "key" in a std::map without the cost of node reallocation: -

    -
    -auto p = m.remove(i);
-p->first = new_key;
-m.insert(std::move(p));
-
    -
    • - -
  • -

    -Change the "value" in a std::set without the cost of node reallocation: -

    -
    -auto p = s.remove(i);
-*p = new_value;
-s.insert(std::move(p));
-
    -
    • - -
  • -

    -Move a move-only or heavy object out of an associative container (as opposed to -the proposal in 1041): -

    -
    -MoveOnly x = std::move(*s.remove(i));
-
    -
      -
    1. -remove(i) transfers ownership of the node from the set to a temporary -node_ptr. -
      2. -
    2. -The node_ptr is dereferenced, and that non-const reference is sent to -move to cast it to an rvalue. -
      3. -
    3. -The rvalue MoveOnly is move constructed into x from -the node_ptr. -
      4. -
    4. -~node_ptr() destructs the moved-from MoveOnly and deallocates -the node. -
      5. -
    - -

    -Contrast this with the 1041 solution: -

    -
    -MoveOnly x = std::move(s.extract(i).first);
-
    - -

    -The former requires one move construction for x while the latter -requires two (one into the pair and then one into x). Either -of these constructions can throw (say if there is only a copy constructor for -x). With the former, the point of throw is outside of the container -s, after the element has been removed from the container. With the latter, -one throwing construction takes place prior to the removal of the element, and -the second takes place after the element is removed. -

    - -
    • -
- -

-The "node insertion" API maintains the API associated with inserting value_types -so the customer can use familiar techniques for getting an iterator to the -inserted node, or finding out whether it was inserted or not for the "unique" -containers. -

- -

-Lightly prototyped. No implementation problems. Appears to work great -for the client. -

- -
-
- - - -

Proposed resolution:

- - - - - -
-

851. simplified array construction

-

Section: 23.3.2 [array] Status: LEWG - Submitter: Benjamin Kosnik Opened: 2008-06-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-This is an issue that came up on the libstdc++ list, where a -discrepancy between "C" arrays and C++0x's std::array was pointed -out. -

- -

-In "C," this array usage is possible: -

- -
-int ar[] = {1, 4, 6};
-
- -

-But for C++, -

- -
-std::array<int> a = { 1, 4, 6 }; // error
-
- -

-Instead, the second parameter of the array template must be -explicit, like so: -

- -
-std::array<int, 3> a = { 1, 4, 6 };
-
- -

-Doug Gregor proposes the following solution, that assumes -generalized initializer lists. -

- -
-template<typename T, typename... Args>
-inline array<T, sizeof...(Args)> 
-make_array(Args&&... args) 
-{ return { std::forward<Args>(args)... };  }
-
- -

-Then, the way to build an array from a list of unknown size is: -

- -
-auto a = make_array<T>(1, 4, 6);
-
- -

[ -San Francisco: -]

- - -
-

-Benjamin: Move to Ready? -

-

-Bjarne: I'm not convinced this is useful enough to add, so I'd like us -to have time to reflect on it. -

-

-Alisdair: the constraints are wrong, they should be -

-
-template<ValueType T, ValueType... Args>
-requires Convertible<Args, T>...
-array<T, sizeof...(Args)> make_array(Args&&... args);
-
-

-Alidair: this would be useful if we had a constexpr version. -

-

-Bjarne: this is probably useful for arrays with a small number of -elements, but it's not clearly useful otherwise. -

-

-Consensus is to move to Open. -

-
- -

[ -2009-06-07 Daniel adds: -]

- - -
-

-I suggest a fix and a simplification of the current proposal: Recent -prototyping by -Howard showed, that a fix is required because narrowing conversion -8.5.4 [dcl.init.list]/6 b.3 -would severely limit the possible distribution of argument types, e.g. -the expression -make_array<double>(1, 2.0) is ill-formed, because the narrowing -happens inside the -function body where no constant expressions exist anymore. Furthermore -given e.g. -

-
-int f();
-double g();
-
-

-we probably want to support -

-
-make_array<double>(f(), g());
-
- -

-as well. To make this feasible, the currently suggested expansion -

- -
-{ std::forward<Args>(args)... }
-
- -

-needs to be replaced by -

- -
-{ static_cast<T>(std::forward<Args>(args))... }
-
- -

-which is safe, because we already ensure convertibility via the -element-wise Convertible<Args, T> requirement. Some other fixes are -necessary: The ValueType requirement for the function parameters -is invalid, because all lvalue arguments will deduce to an lvalue-reference, -thereby no longer satisfying this requirement. -

- -

-The suggested simplification is to provide a default-computed effective -type for the result array based on common_type and decay, in -unconstrained form: -

- -
-template<typename... Args>
-array<typename decay<typename common_type<Args...>::type>::type,
-sizeof...(Args)>
-make_array(Args&&... args);
-
- -

-The approach used below is similar to that of make_pair and make_tuple -using a symbol C to represent the decayed common type [Note: Special -handling of reference_wrapper types is intentionally not provided, because -our target has so satisfy ValueType, thus under the revised proposal only -an all-reference_wrapper-arguments would be well-formed and an array of -reference_wrapper will be constructed]. I do currently not suggest to -add new concepts reflecting decay and common_type, but an implementor will -need something like this to succeed. Note that we use a similar fuzziness for -make_pair and make_tuple currently. This fuzziness is not related to -the currently -missing Constructible<Vi, Ti&&> requirement for those functions. The following -proposal fixes that miss for make_array. If the corresponding C type -deduction is -explicitly wanted for standardization, here the implementation -

- -
-auto concept DC<typename... T> {
-  typename type = typename decay<typename common_type<T...>::type>::type;
-}
-
- -

-where C is identical to DC<Args...>::type in the proposed resolution below. -

-

-I intentionally added no further type relation between type and the concept -template parameters, but instead added this requirement below to make -the specification as transparent as possible. As written this concept is -satisfied, if the corresponding associated type exists. -

- -

Suggested Resolution:

- -
    -
  1. -

    -Add to the array synopsis in 23.3 [sequences]: -

    -
    -
-template<ReferentType... Args>
-requires ValueType<C> && IdentityOf<Args> && Constructible<C, Args&&>...
-array<C, sizeof...(Args)>
-make_array(Args&&... args);
-
-
    -
    2. - -
  2. -

    -Append after 23.3.2.9 [array.tuple] Tuple interface to class template array -the following new section: -

    -
    -

    -23.4.1.7 Array creation functions [array.creation] -

    - -
    -
-template<ReferentType... Args>
-requires ValueType<C> && IdentityOf<Args> && Constructible<C, Args&&>...
-array<C, sizeof...(Args)>
-make_array(Args&&... args);
-
    - -
    -

    -Let C be decay<common_type<Args...>::type>::type. -

    -

    -Returns: an array<C, sizeof...(Args)> initialized with -{ static_cast<C>(std::forward<Args>(args))... }. -

    -
    -
    - -
    3. - -
- -
- -

[ -2009-07 Frankfurt: -]

- - -
-

-The proposed resolution uses concepts. -

-

-Daniel to rewrite the proposed resolution. -

-

-Leave Open. -

-
- -

[ -2009-07-25 Daniel provides rewritten proposed resolution. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Argument for NAD future: everything about this could be added on. This -does not require changes to the existing text. -

- - - -

Proposed resolution:

- -
    -
  1. -

    -Add to the array synopsis in 23.3 [sequences]: -

    - -
    -template<class... Args>
-  array<CT, sizeof...(Args)>
-  make_array(Args&&... args);
-
    -
    2. - -
  2. -

    -Append after 23.3.2.9 [array.tuple] "Tuple interface to class template array" the -following new section: -

    - -
    -

    -XX.X.X.X Array creation functions [array.creation] -

    - -
    
-template<class... Args>
-array<CT, sizeof...(Args)>
-make_array(Args&&... args)
-
    - -
    -

    -Let CT be decay<common_type<Args...>::type>::type. -

    -

    -Returns: An array<CT, sizeof...(Args)> initialized with { -static_cast<CT>(std::forward<Args>(args))... }. -

    - -

    -[Example: -

    -
    
-int i = 0; int& ri = i;
-make_array(42u, i, 2.78, ri);
-
    -

    -returns an array of type -

    -
    
-array<double, 4>
-
    - -

    -—end example] -

    -
    -
    -
    3. - -
- - - - - - - - -
-

877. to throw() or to Throw: Nothing.

-

Section: 17 [library] Status: LEWG - Submitter: Martin Sebor Opened: 2008-08-23 Last modified: 2015-04-08

-

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-

Discussion:

-

- -Recent changes to -the working -draft have introduced a gratuitous inconsistency with the C++ 2003 -version of the specification with respect to exception guarantees -provided by standard functions. While the C++ 2003 standard -consistenly uses the empty exception specification, throw(), -to declare functions that are guaranteed not to throw exceptions, the -current working draft contains a number of "Throws: Nothing." -clause to specify essentially the same requirement. The difference -between the two approaches is that the former specifies the behavior -of programs that violate the requirement (std::unexpected() -is called) while the latter leaves the behavior undefined. - -

-

- -A survey of the working draft reveals that there are a total of 209 -occurrences of throw() in the library portion of the spec, -the majority in clause 18, a couple (literally) in 19, a handful in -20, a bunch in 22, four in 24, one in 27, and about a dozen in D.9. - -

-

- -There are also 203 occurrences of "Throws: Nothing." scattered -throughout the spec. - -

-

- -While sometimes there are good reasons to use the "Throws: -Nothing." approach rather than making use of throw(), these -reasons do not apply in most of the cases where this new clause has -been introduced and the empty exception specification would be a -better approach. - -

-

- -First, functions declared with the empty exception specification -permit compilers to generate better code for calls to such -functions. In some cases, the compiler might even be able to eliminate -whole chunks of user-written code when instantiating a generic -template on a type whose operations invoked from the template -specialization are known not to throw. The prototypical example are -the std::uninitialized_copy() -and std::uninitialized_fill() algorithms where the -entire catch(...) block can be optimized away. - -

-

- -For example, given the following definition of -the std::uninitialized_copy function template and a -user-defined type SomeType: - -

-
- 
-template <class InputIterator, class ForwardIterator>
-ForwardIterator
-uninitialized_copy (InputIterator first, InputIterator last, ForwardIterator res)
-{
-   typedef iterator_traits<ForwardIterator>::value_type ValueType;
-
-   ForwardIterator start = res;
-
-   try {
-       for (; first != last; ++first, ++res)
-           ::new (&*res) ValueType (*first);
-   }
-   catch (...) {
-       for (; start != res; --start)
-           (&*start)->~ValueType ();
-       throw;
-   }
-   return res;
-}
-
-struct SomeType {
-   SomeType (const SomeType&) throw ();
-}
-
-

- -compilers are able to emit the following efficient specialization -of std::uninitialized_copy<const SomeType*, SomeType*> -(note that the catch block has been optimized away): - -

-
- 
-template <> SomeType*
-uninitialized_copy (const SomeType *first, const SomeType *last, SomeType *res)
-{
-   for (; first != last; ++first, ++res)
-       ::new (res) SomeType (*first);
-
-   return res;
-}
-
-

- -Another general example is default constructors which, when decorated -with throw(), allow the compiler to eliminate the -implicit try and catch blocks that it otherwise must -emit around each the invocation of the constructor -in new-expressions. - -

-

- -For example, given the following definitions of -class MayThrow and WontThrow and the two -statements below: - -

-
- 
-struct MayThrow {
-   MayThrow ();
-};
-
-struct WontThrow {
-   WontThrow () throw ();
-};
-
-MayThrow  *a = new MayThrow [N];
-WontThrow *b = new WontThrow [N];
- -
-

- -the compiler generates the following code for the first statement: - -

-
- 
-MayThrow *a;
-{
-   MayThrow *first = operator new[] (N * sizeof (*a));
-   MayThrow *last  = first + N;
-   MayThrow *next  = first;
-   try {
-       for ( ; next != last; ++next)
-           new (next) MayThrow;
-   }
-   catch (...) {
-       for ( ; first != first; --next)
-           next->~MayThrow ();
-       operator delete[] (first);
-       throw;
-   }
-   a = first;
-}
-
-

- -but it is can generate much more compact code for the second statement: - -

-
- 
-WontThrow *b    = operator new[] (N * sizeof (*b));
-WontThrow *last = b + N;
-for (WontThrow *next = b; next != last; ++next)
-   new (next) WontThrow;
-
-
-

- -Second, in order for users to get the maximum benefit out of the new -std::has_nothrow_xxx traits when using standard library types -it will be important for implementations to decorate all non throwing -copy constructors and assignment operators with throw(). Note -that while an optimizer may be able to tell whether a function without -an explicit exception specification can throw or not based on its -definition, it can only do so when it can see the source code of the -definition. When it can't it must assume that the function may -throw. To prevent violating the One Definition Rule, -the std::has_nothrow_xxx trait must return the most -pessimistic guess across all translation units in the program, meaning -that std::has_nothrow_xxx<T>::value must evaluate to -false for any T whose xxx -(where xxx is default or copy ctor, or assignment operator) -is defined out-of-line. - -

-

- -Counterarguments: - -

-

- -During the discussion of this issue -on c++std-lib@accu.org -(starting with post c++std-lib-21950) the following arguments -in favor of the "Throws: Nothing." style have been made. - -

-
    -
  1. - -Decorating functions that cannot throw with the empty exception -specification can cause the compiler to generate suboptimal code for -the implementation of the function when it calls other functions that -aren't known to the compiler not to throw (i.e., that aren't decorated -with throw() even if they don't actually throw). This is a -common situation when the called function is a C or POSIX function. - -
    2. -
  2. - -Alternate, proprietary mechanisms exist (such as -GCC __attribute__((nothrow)) -or Visual -C++ __declspec(nothrow)) -that let implementers mark up non-throwing functions, often without -the penalty mentioned in (1) above. The C++ standard shouldn't -preclude the use of these potentially more efficient mechanisms. - -
    3. -
  3. - -There are functions, especially function templates, that invoke -user-defined functions that may or may not be -declared throw(). Declaring such functions with the empty -exception specification will cause compilers to generate suboptimal -code when the user-defined function isn't also declared not to throw. - -
    4. -
-

- -The answer to point (1) above is that implementers can (and some have) -declare functions with throw() to indicate to the compiler -that calls to the function can safely be assumed not to throw in order -to allow it to generate efficient code at the call site without also -having to define the functions the same way and causing the compiler -to generate suboptimal code for the function definition. That is, the -function is declared with throw() in a header but it's -defined without it in the source file. The throw() -declaration is suppressed when compiling the definition to avoid -compiler errors. This technique, while strictly speaking no permitted -by the language, is safe and has been employed in practice. For -example, the GNU C library takes this approach. Microsoft Visual C++ -takes a similar approach by simply assuming that no function with C -language linkage can throw an exception unless it's explicitly -declared to do so using the language extension throw(...). - -

-

- -Our answer to point (2) above is that there is no existing practice -where C++ Standard Library implementers have opted to make use of the -proprietary mechanisms to declare functions that don't throw. The -language provides a mechanism specifically designed for this -purpose. Avoiding its use in the specification itself in favor of -proprietary mechanisms defeats the purpose of the feature. In -addition, making use of the empty exception specification -inconsistently, in some areas of the standard, while conspicuously -avoiding it and making use of the "Throws: Nothing." form in -others is confusing to users. - -

-

- -The answer to point (3) is simply to exercise caution when declaring -functions and especially function templates with the empty exception -specification. Functions that required not to throw but that may call -back into user code are poor candidates for the empty exception -specification and should instead be specified using "Throws: -Nothing." clause. - -

- -

[ -2009-07 Frankfurt -]

- - -
-

-We need someone to do an extensive review. -

-

-NAD Future. -

-
- - -

Proposed resolution:

-

- -We propose two possible solutions. Our recommendation is to adopt -Option 1 below. - -

-

- -Option 1: - -

-

- -Except for functions or function templates that make calls back to -user-defined functions that may not be declared throw() -replace all occurrences of the "Throws: Nothing." clause with -the empty exception specification. Functions that are required not to -throw but that make calls back to user code should be specified to -"Throw: Nothing." - -

-

- -Option 2: - -

-

- -For consistency, replace all occurrences of the empty exception -specification with a "Throws: Nothing." clause. - -

- - - - -
-

933. Unique_ptr defect

-

Section: 20.8.1.2.5 [unique.ptr.single.modifiers] Status: LEWG - Submitter: Alisdair Meredith Opened: 2008-11-27 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.modifiers].

-

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-

Discussion:

-

-If we are supporting stateful deleters, we need an overload for -reset that -takes a deleter as well. -

- -
-void reset( pointer p, deleter_type d);
-
- -

-We probably need two overloads to support move-only deleters, and -this -sounds uncomfortably like the two constructors I have been ignoring -for -now... -

- -

[ -Batavia (2009-05): -]

- -
-

-Howard comments that we have the functionality via move-assigment. -

-

-Move to Open. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD Future. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

935. clock error handling needs to be specified

-

Section: 20.12.7 [time.clock] Status: LEWG - Submitter: Beman Dawes Opened: 2008-11-24 Last modified: 2015-04-08

-

View all issues with LEWG status.

-

Discussion:

-

-Each of the three clocks specified in Clocks 20.12.7 [time.clock] -provides the member function: -

- -
-static time_point now();
-
- -

-The semantics specified by Clock requirements 20.12.3 [time.clock.req] -make no mention of error handling. Thus the function may throw bad_alloc -or an implementation-defined exception (17.6.5.12 [res.on.exception.handling] -paragraph 4). -

- -

-Some implementations of these functions on POSIX, Windows, and -presumably on other operating systems, may fail in ways only detectable -at runtime. Some failures on Windows are due to supporting chipset -errata and can even occur after successful calls to a clock's now() -function. -

- -

-These functions are used in cases where exceptions are not appropriate -or where the specifics of the exception or cause of error need to be -available to the user. See -N2828, -Library Support for hybrid error -handling (Rev 1), for more specific discussion of use cases. Thus some change in -the interface of now is required. -

- -

-The proposed resolution has been implemented in the Boost version of the -chrono library. No problems were encountered. -

- -

[ -Batavia (2009-05): -]

- -
-

-We recommend this issue be deferred until the next Committee Draft -has been issued and the prerequisite paper has been accepted. -

-

-Move to Open. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD future. Too late to make this change without having already -accepted the hybrid error handling proposal. -

- - - -

Proposed resolution:

-

-Accept the proposed wording of -N2828, -Library Support for hybrid error handling (Rev 1). -

- -

-Change Clock requirements 20.12.3 [time.clock.req] as indicated: -

- -
-

--2- In Table 55 C1 and C2 denote clock types. t1 and -t2 are values returned by C1::now() where the call -returning t1 happens before (1.10) the call returning t2 and -both of these calls happen before C1::time_point::max(). -ec denotes an object of type error_code -(19.5.2.1 [syserr.errcode.overview]). -

- - - - - - - - - - - - - - - - - - - - - - - - -
Table 55 — Clock requirements
ExpressionReturn typeOperational semantics
.........
C1::now()C1::time_pointReturns a time_point object representing the current point in time. -
C1::now(ec)C1::time_pointReturns a time_point object representing the current point in time. -
-
- -

-Change class system_clock 20.12.7.1 [time.clock.system] as indicated: -

- -
-static time_point now(error_code& ec=throws());
-
- -

-Change class monotonic_clock X [time.clock.monotonic] as indicated: -

- -
-static time_point now(error_code& ec=throws());
-
- -

-Change class high_resolution_clock 20.12.7.3 [time.clock.hires] as indicated: -

- -
-static time_point now(error_code& ec=throws());
-
- - - - - - -
-

936. Mutex type overspecified

-

Section: 30.4.1 [thread.mutex.requirements] Status: LEWG - Submitter: Pete Becker Opened: 2008-12-05 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 961

-

Discussion:

- - - -

-30.4.1 [thread.mutex.requirements] describes the requirements for a type to be -a "Mutex type". A Mutex type can be used as the template argument for -the Lock type that's passed to condition_variable_any::wait (although -Lock seems like the wrong name here, since Lock is given a different -formal meaning in 30.4.2 [thread.lock]) and, although the WD doesn't quite say -so, as the template argument for lock_guard and unique_lock. -

- -

-The requirements for a Mutex type include: -

- -
    -
  • -m.lock() shall be well-formed and have [described] semantics, including a return type of void. -
    • -
  • -m.try_lock() shall be well-formed and have [described] semantics, including a return type of bool. -
    • -
  • -m.unlock() shall be well-formed and have [described] semantics, including a return type of void. -
    • -
- -

-Also, a Mutex type "shall not be copyable nor movable". -

- -

-The latter requirement seems completely irrelevant, and the three -requirements on return types are tighter than they need to be. For -example, there's no reason that lock_guard can't be instantiated with a -type that's copyable. The rule is, in fact, that lock_guard, etc. won't -try to copy objects of that type. That's a constraint on locks, not on -mutexes. Similarly, the requirements for void return types are -unnecessary; the rule is, in fact, that lock_guard, etc. won't use any -returned value. And with the return type of bool, the requirement should -be that the return type is convertible to bool. -

- -

[ -Summit: -]

- - -
-

-Move to open. Related to conceptualization and should probably be tackled as part of that. -

-
    -
  • -The intention is not only to place a constraint on what types such as -lock_guard may do with mutex types, but on what any code, including user -code, may do with mutex types. Thus the constraints as they are apply to -the mutex types themselves, not the current users of mutex types in the -standard. -
    • -
  • -This is a low priority issue; the wording as it is may be overly -restrictive but this may not be a real issue. -
    • -
-
- -

[ -Post Summit Anthony adds: -]

- - -
-

-Section 30.4.1 [thread.mutex.requirements] conflates the -requirements on a generic Mutex type (including user-supplied mutexes) -with the requirements placed on the standard-supplied mutex types in an -attempt to group everything together and save space. -

-

-When applying concepts to chapter 30, I suggest that the concepts -Lockable and TimedLockable embody the requirements for -*use* of a mutex type as required by -unique_lock/lock_guard/condition_variable_any. These should be -relaxed as Pete describes in the issue. The existing words in 30.4.1 [thread.mutex.requirements] are requirements on all of -std::mutex, std::timed_mutex, -std::recursive_mutex and std::recursive_timed_mutex, -and should be rephrased as such. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

961. Various threading bugs #11

-

Section: 30.4.1 [thread.mutex.requirements] Status: LEWG - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 936

-

Discussion:

-

-30.4.1 [thread.mutex.requirements] describes required member -functions of mutex types, and requires that they throw exceptions under -certain circumstances. This is overspecified. User-defined types can -abort on such errors without affecting the operation of templates -supplied by standard-library. -

- -

[ -Summit: -]

- -

-Move to open. Related to conceptualization and should probably be -tackled as part of that. -

- -

[ -2009-10 Santa Cruz: -]

- - -
-

-Would be OK to leave it as is for time constraints, could loosen later. -

- -

-Mark as NAD Future. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

1025. The library should provide more specializations for std::hash

-

Section: 20.9.13 [unord.hash] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

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-

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-

Discussion:

- -

Addresses UK 208 [CD1]

- -

-std::hash should be implemented for much more of the standard -library. In particular for pair, tuple and all the -standard containers. -

- - - -

Proposed resolution:

- - - - - -
-

1031. Need shared_ptr conversion to a unique_ptr

-

Section: 20.8.2.2 [util.smartptr.shared] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses US 78 [CD1]

- -

-There is presently no way to convert directly from a shared_ptr to a -unique_ptr. Add an interface that performs the conversion. -

- -

[ -Summit: -]

- - -

-We look forward to a paper on this topic. We recommend no action until a -paper is available. We believe that the shared pointer must use the default -deleter for the conversion to succeed. -

- -

[ -Peter Dimov adds: -]

- - -

-This is basically a request for shared_ptr<>::release in -disguise, with all the associated problems. Not a good idea. -

- -

[ -2009-07 post-Frankfurt: -]

- - -
-

-The rationale for the omission of a release() member function from shared_ptr is given in: -http://www.boost.org/doc/libs/1_39_0/libs/smart_ptr/shared_ptr.htm -

-

-The implementation of such a member is non-trivial (and maybe -impossible), because it would need to account for the deleter. -

-
- -

[ -2009-07-26 Howard sets to Tentatively NAD Future. -]

- - -
-

-I took an online poll and got 3 votes for NAD and 3 for NAD Future. Personally -I prefer NAD Future as this does refer to an extension that could conceivably be -considered beyond C++0X. -

- -

-However such an extension would need to solve a couple of problems: -

- -
    -
  1. What is the interface for such a conversion when the shared_ptr does -not have unique ownership? Throw an exception? Create a null unique_ptr? -Undefined behavior? -
    2. - -
  2. -

    -How does one handle custom deleters given to the shared_ptr constructor? -

    -

    -I do not believe it is possible to implement a general answer to this question. -The shared_ptr deleter is a run time (or construction time) characteristic. -The unique_ptr deleter is a compile time characteristic. In general one -can not know to what type of unqiue_ptr you are converting to. -

    -

    -One answer is for the user of the conversion to specify the deleter type and perhaps -throw an exception if the specification turns out to be incorrect. -

    -

    -Another answer is for the conversion to only be valid when the underlying deleter -is default_delete. We would probalby need to specify that this is indeed the -underlying deleter of a shared_ptr when a custom deleter is not given in -the constructor. -

    -
    3. -
- -

-At any rate, there are non-trivial design issues which would need to be implemented -and tested in the field for usability prior to standardization. -

-
- -

[ -2009 Santa Cruz: -]

- - -

-Moved to NAD Future. -

- - - -

Proposed resolution:

- - - - - -
-

1041. Add associative/unordered container functions that allow to extract elements

-

Section: 23.2.4 [associative.reqmts] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

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-

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-

Discussion:

- -

Addresses UK 239 [CD1]

- -

-It is not possible to take a move-only key out of an unordered -container, such as (multi)set or -(multi)map, or the new unordered containers. -

- -

-Add below a.erase(q), a.extract(q), with the following notation: -

-

-a.extract(q)>, Return type pair<key, iterator> -Extracts the element pointed to by q and erases it from the -set. Returns a pair containing the value pointed to by -q and an iterator pointing to the element immediately -following q prior to the element being erased. If no such -element exists,returns a.end(). -

- -

[ -Summit: -]

- - -

-We look forward to a paper on this topic. We recommend no action until a -paper is available. The paper would need to address exception safety. -

- -

[ -Post Summit Alisdair adds: -]

- - -

-Would value_type be a better return type than key_type? -

- -

[ -2009-07 post-Frankfurt: -]

- - -

-Leave Open. Alisdair to contact Chris Jefferson about this. -

- -

[ -2009-09-20 Howard adds: -]

- - -

-See the 2009-09-19 comment of 839 for an API which -accomplishes this functionality and also addresses several other use -cases which this proposal does not. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD Future. No consensus to make the change at this time. -

- - - -

Proposed resolution:

-

-In 23.2.4 [associative.reqmts] Table 85, add: -

- -
- - - - - - - - - - - - - - - - - - - - -
Table 85 -- Associative container requirements (in addition to container)
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
a.erase(q).........
a.extract(q)pair<key_type, iterator>Extracts the element pointed to by q and erases it from the set. -Returns a pair containing the value pointed to by q and an iterator -pointing to the element immediately following q prior to the element being -erased. If no such element -exists, returns a.end().amortized constant
-
- -

-In 23.2.5 [unord.req] Table 87, add: -

- -
- - - - - - - - - - - - - - - - - - - - -
Table 87 -- Unordered associative container requirements (in addition to container)
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
a.erase(q).........
a.extract(q)pair<key_type, iterator>Extracts the element pointed to by q and erases it from the set. -Returns a pair containing the value pointed to by q and an iterator -pointing to the element immediately following q prior to the element being -erased. If no such element -exists, returns a.end().amortized constant
-
- - - - - -
-

1052. reverse_iterator::operator-> should also support smart pointers

-

Section: 24.5.1.3.5 [reverse.iter.opref] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 281 [CD1]

- -

-The current specification for return value for reverse_iterator::operator-> -will always be a true pointer type, but reverse_iterator supports proxy -iterators where the pointer type may be some kind of 'smart pointer'. -

- -

[ -Summit: -]

- - -
-

-move_iterator avoids this problem by returning a value of the wrapped -Iterator type. -study group formed to come up with a suggested resolution. -

-

-move_iterator solution shown in proposed wording. -

-
- -

[ -2009-07 post-Frankfurt: -]

- - -

-Howard to deconceptize. Move to Review after that happens. -

- -

[ -2009-08-01 Howard deconceptized: -]

- - -

[ -2009-10 Santa Cruz: -]

- - -
-

-We can't think of any reason we can't just define reverse -iterator's pointer types to be the same as the underlying iterator's -pointer type, and get it by calling the right arrow directly. -

-

-Here is the proposed wording that was replaced: -

-
-template <class Iterator> 
-class reverse_iterator { 
-  ...
-  typedef typename iterator_traits<Iterator>::pointer pointer;
-
- -

-Change 24.5.1.3.5 [reverse.iter.opref]: -

- -
-pointer operator->() const;
-
-

-Returns: -

-&(operator*());
-this->tmp = current;
---this->tmp;
-return this->tmp;
-
-
-
- -
- -

[ -2010-03-03 Daniel opens: -]

- - -
-
    - -
  1. -There is a minor problem with the exposition-only declaration of the private -member deref_tmp which is modified in a const member function (and the -same problem occurs in the specification of operator*). The fix is to -make it a mutable member. -
    2. - -
  2. -

    -The more severe problem is that the resolution for some reasons -does not explain in the rationale why it was decided to differ from -the suggested fix (using deref_tmp instead of tmp) in the -[ 2009-10 Santa Cruz] comment: -

    - -
    -this->deref_tmp = current;
---this->deref_tmp;
-return this->deref_tmp;
-
    - -

    -combined with the change of -

    - -
    -typedef typename iterator_traits<Iterator>::pointer pointer;
-
    - -

    -to -

    - -
    -typedef Iterator pointer;
-
    - -

    -The problem of the agreed on wording is that the following rather -typical example, that compiled with the wording before 1052 had -been applied, won't compile anymore: -

    - -
    -#include <iterator>
-#include <utility>
-
-int main() {
-  typedef std::pair<int, double> P;
-  P op;
-  std::reverse_iterator<P*> ri(&op + 1);
-  ri->first; // Error
-}
-
    - -

    -Comeau online returns (if a correspondingly changed -reverse_iterator is used): -

    - -
    -"error: expression must have class type
-     return deref_tmp.operator->();
-            ^
-         detected during instantiation of "Iterator
-                   reverse_iterator<Iterator>::operator->() const [with
-                   Iterator=std::pair<int, double> *]""
-
    - -

    -Thus the change will break valid, existing code based -on std::reverse_iterator. -

    - -
    3. - -
- -

-IMO the suggestion proposed in the comment is a necessary fix, which harmonizes -with the similar specification of std::move_iterator and properly -reflects the recursive nature of the evaluation of operator-> -overloads. -

- -

-Suggested resolution: -

- -
    - -
  1. -

    -In the class template reverse_iterator synopsis of 24.5.1.1 [reverse.iterator] -change as indicated: -

    - -
    -namespace std {
-template <class Iterator>
-class reverse_iterator : public
-             iterator<typename iterator_traits<Iterator>::iterator_category,
-             typename iterator_traits<Iterator>::value_type,
-             typename iterator_traits<Iterator>::difference_type,
-             typename iterator_traits<Iterator>::pointer,
-             typename iterator_traits<Iterator>::reference> {
-public:
-  [..]
-  typedef typename iterator_traits<Iterator>::pointer pointer;
-  [..]
-protected:
-  Iterator current;
-private:
-  mutable Iterator deref_tmp; // exposition only
-};
-
    -
    2. - -
  2. -Change 24.5.1.3.5 [reverse.iter.opref]/1 as indicated: - -
    -pointer operator->() const;
-
    - -

    -1 Returns Effects: &(operator*()). -

    -deref_tmp = current;
---deref_tmp;
-return deref_tmp;
-
    -
    -
    - -
    3. - -
- -
- -

[ -2010 Pittsburgh: -]

- - -
-

-We prefer to make to use a local variable instead of deref_tmp within -operator->(). And although this means that the mutable -change is no longer needed, we prefer to keep it because it is needed for -operator*() anyway. -

- -

-Here is the proposed wording that was replaced: -

- -
-

-Change 24.5.1.3.5 [reverse.iter.opref]: -

- -
-pointer operator->() const;
-
- -

-Returns: -

-&(operator*());
-deref_tmp = current;
---deref_tmp;
-return deref_tmp::operator->();
-
- -
-
- - -
-
- -

[ -2010-03-10 Howard adds: -]

- - -
-

-Here are three tests that the current proposed wording passes, and no -other solution I've seen passes all three: -

- -
    -
  1. -

    -Proxy pointer support: -

    -
    -#include <iterator>
-#include <cassert>
-
-struct X { int m; };
-
-X x;
-
-struct IterX {
-    typedef std::bidirectional_iterator_tag iterator_category;
-    typedef X& reference;
-    struct pointer
-    {
-        pointer(X& v) : value(v) {}
-        X& value;
-        X* operator->() const {return &value;}
-    };
-    typedef std::ptrdiff_t difference_type;
-    typedef X value_type;
-    // additional iterator requirements not important for this issue
-    
-    reference operator*() const { return x; }
-    pointer operator->() const { return pointer(x); }
-    IterX& operator--() {return *this;}
-
-};
-
-int main()
-{
-    std::reverse_iterator<IterX> ix;
-    assert(&ix->m == &(*ix).m);
-}
-
    -
    2. -
  2. -

    -Raw pointer support: -

    -
    -#include <iterator>
-#include <utility>
-
-int main() {
-  typedef std::pair<int, double> P;
-  P op;
-  std::reverse_iterator<P*> ri(&op + 1);
-  ri->first; // Error
-}
-
    -
    3. -
  3. -

    -Caching iterator support: -

    -
    -#include <iterator>
-#include <cassert>
-
-struct X { int m; };
-
-struct IterX {
-    typedef std::bidirectional_iterator_tag iterator_category;
-    typedef X& reference;
-    typedef X* pointer;
-    typedef std::ptrdiff_t difference_type;
-    typedef X value_type;
-    // additional iterator requirements not important for this issue
-    
-    reference operator*() const { return value; }
-    pointer operator->() const { return &value; }
-    IterX& operator--() {return *this;}
-
-private:
-    mutable X value;
-};
-
-int main()
-{
-    std::reverse_iterator<IterX> ix;
-    assert(&ix->m == &(*ix).m);
-}
-
    -
    4. -
-
- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Future, rationale added. -

- - - - -

Rationale:

-

-The LWG did not reach a consensus for a change to the WP. -

- - -

Proposed resolution:

- -
    - -
  1. -

    -In the class template reverse_iterator synopsis of 24.5.1.1 [reverse.iterator] change as indicated: -

    - -
    -namespace std {
-template <class Iterator>
-class reverse_iterator : public
-             iterator<typename iterator_traits<Iterator>::iterator_category,
-             typename iterator_traits<Iterator>::value_type,
-             typename iterator_traits<Iterator>::difference_type,
-             typename iterator_traits<Iterator&>::pointer,
-             typename iterator_traits<Iterator>::reference> {
-public:
-  [..]
-  typedef typename iterator_traits<Iterator&>::pointer pointer;
-  [..]
-protected:
-  Iterator current;
-private:
-  mutable Iterator deref_tmp; // exposition only
-};
-
    -
    2. - -
  2. -Change 24.5.1.3.5 [reverse.iter.opref]/1 as indicated: - -
    -pointer operator->() const;
-
    - -

    -1 Returns Effects: &(operator*()). -

    -deref_tmp = current;
---deref_tmp;
-return deref_tmp;
-
    -
    -
    - -
    3. - -
- - - - - - - - - - -
-

1053. Unify algorithms with operator and function object variants

-

Section: 25 [algorithms] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [algorithms].

-

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-

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-

Discussion:

- -

Addresses UK 295 [CD1]

- -

-There is a level of redundancy in the library specification for many -algorithms that can be eliminated with the combination of concepts and -default parameters for function templates. Eliminating redundancy simplified -specification and reduces the risk of introducing accidental -inconsistencies. -

-

-Proposed resolution: Adopt -N2743. -

- -

[ -Summit: -]

- - -
-

-NAD, this change would break code that takes the address of an algorithm. -

-
- -

[ -Post Summit Alisdair adds: -]

- - -
-

-Request 'Open'. The issues in the paper go beyond just reducing -the number of signatures, but cover unifying the idea of the ordering -operation used by algorithms, containers and other library components. At -least, it takes a first pass at the problem. -

- -

-For me (personally) that was the more important part of the paper, and not -clearly addressed by the Summit resolution. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Too inventive, too late, would really need a paper. Moved to NAD Future. -

- - - -

Proposed resolution:

- - - - - -
-

1112. bitsets and new style for loop

-

Section: 20.6 [template.bitset] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-05-06 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-std::bitset is a homogeneous container-like sequence of bits, yet it does -not model the Range concept so cannot be used with the new for-loop syntax. -It is the only such type in the library that does NOT support the new for -loop. -

-

-The obvious reason is that bitset does not support iterators. -

-

-At least two reasonable solutions are available: -

-
    -
  1. -Add an iterator interface to bitset, bringing its interface close to that -of std::array -
    2. -
  2. -Provide an unspecified concept_map for Range<bitset>. -
    3. -
-

-The latter will still need some kind of iterator-like adapter for bitset, -but gives implementers greater freedom on the details. E.g. begin/end return -some type that simply invokes operator[] on the object it wraps, and -increments its index on operator++. A vendor can settle for InputIterator -support, rather than wrapping up a full RandomAccessIterator. -

-

-I have a mild preference for option (ii) as I think it is less work to -specify at this stage of the process, although (i) is probably more useful -in the long run. -

-

-Hmm, my wording looks a little woolly, as it does not say what the element -type of the range is. Do I get a range of bool, bitset<N>::reference, or -something else entirely? -

-

-I guess most users will assume the behaviour of reference, but expect to -work with bool. Bool is OK for read-only traversal, but you really need to -take a reference to a bitset::reference if you want to write back. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open. -We further recommend this be deferred until after the next Committee Draft. -

- -

[ -2009-05-25 Alisdair adds: -]

- - -
-

-I just stumbled over the Range concept_map for valarray and this should -probably set the precedent on how to write the wording. -

- -

[ -Howard: I've replaced the proposed wording with Alisdair's suggestion. -]

- - -
- -

[ -2009-07-24 Daniel modifies the proposed wording for non-concepts. -]

- - -

[ -2009-10 post-Santa Cruz: -]

- - -

-Mark as Tentatively NAD Future due to the loss of concepts. -

- - - -

Rationale:

-

-All concepts-related text has been removed from the draft. -

- - -

Proposed resolution:

-
    -
  1. -

    -Modify the section 20.6 [template.bitset] <bitset> synopsis by adding -the following at the end of the synopsis: -

    -
    -
-// XX.X.X bitset range access [bitset.range]
-template<size_t N> unspecified-1 begin(bitset<N>&);
-template<size_t N> unspecified-2 begin(const bitset<N>&);
-template<size_t N> unspecified-1 end(bitset<N>&);
-template<size_t N> unspecified-2 end(const bitset<N>&);
-
-
    -
    2. -
  2. -

    -Add a new section "bitset range access" [bitset.range] -after the current section 20.6.4 [bitset.operators] with the following series of -paragraphs: -

    -
    -

    - -1. In the begin and end function templates that follow, unspecified-1 -is a type that meets the requirements of a mutable random access -iterator (24.2.7 [random.access.iterators]) whose value_type is bool and -whose reference type is bitset<N>::reference. -unspecified-2 is a type that meets the requirements of a constant -random access iterator (24.2.7 [random.access.iterators]) whose value_type -is bool and whose reference type is bool. - -

    -
    -
-template<size_t N> unspecified-1 begin(bitset<N>&);
-template<size_t N> unspecified-2 begin(const bitset<N>&);
-
-
    -

    -2. Returns: an iterator referencing the first bit in the bitset. -

    - -
    
-template<size_t N> unspecified-1 end(bitset<N>&);
-template<size_t N> unspecified-2 end(const bitset<N>&);
-
    - -

    -3. Returns: an iterator referencing one past the last bit in the -bitset. -

    -
    -
    3. -
- - - - - - - - - - - - -
-

1120. New type trait - remove_all

-

Section: 20.10 [meta] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-05-23 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Sometimes it is necessary to remove all qualifiers from a type before -passing on to a further API. A good example would be calling the -tuple query APIs tuple_size or tuple_element -with a deduced type inside a function template. If the deduced type is -cv-qualified or a reference then the call will fail. The solution is to -chain calls to -remove_cv<remove_reference<T>::type>::type, and -note that the order matters. -

-

-Suggest it would be helpful to add a new type trait, -remove_all, that removes all top-level qualifiers from a type -i.e. cv-qualification and any references. Define the term in such a way -that if additional qualifiers are added to the language, then -remove_all is defined as stripping those as well. -

- -

[ -2009-10-14 Daniel adds: -]

- - -

-remove_all seems too generic, a possible alternative matching -the current naming style could be remove_cv_reference or -remove_reference_cv. It should also be considered whether this -trait should also remove 'extents', or pointer 'decorations'. Especially -if the latter situations are considered as well, it might be easier to -chose the name not in terms of what it removes (which might be -a lot), but in terms of it creates. In this case I could think -of e.g. extract_value_type. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Future. -

- - - -

Proposed resolution:

- - - - - -
-

1121. Support for multiple arguments

-

Section: 20.11.4 [ratio.arithmetic] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-05-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Both add and multiply could sensibly be called with more than two arguments. -The variadic template facility makes such declarations simple, and is likely -to be frequently wrapped by end users if we do not supply the variant -ourselves. -

-

-We deliberately ignore divide at this point as it is not transitive. -Likewise, subtract places special meaning on the first argument so I do not -suggest extending that immediately. Both could be supported with analogous -wording to that for add/multiply below. -

-

-Note that the proposed resolution is potentially incompatible with that -proposed for 921, although the addition of the typedef to ratio would be -equally useful. -

- -

[ -2009-10-30 Alisdair adds: -]

- - -
-

-The consensus of the group when we reviewed this in Santa Cruz was that -921 would proceed to Ready as planned, and the -multi-paramater add/multiply templates should be renamed as -ratio_sum and ratio_product to avoid the problem -mixing template aliases with partial specializations. -

- -

-It was also suggested to close this issue as NAD Future as it does not -correspond directly to any NB comment. NBs are free to submit a -specific comment (and re-open) in CD2 though. -

- -

-Walter Brown also had concerns on better directing the order of -evaluation to avoid overflows if we do proceed for 0x rather than TR1, -so wording may not be complete yet. -

- -

[ -Alisdair updates wording. -]

- - -
- -

[ -2009-10-30 Howard: -]

- - -

-Moved to Tentatively NAD Future after 5 positive votes on c++std-lib. -

- - - -

Rationale:

-

-Does not have sufficient support at this time. May wish to reconsider for a -future standard. -

- - -

Proposed resolution:

- -

-Add the following type traits to p3 20.11 [ratio] -

- -
-// ratio arithmetic
-template <class R1, class R2> struct ratio_add;
-template <class R1, class R2> struct ratio_subtract;
-template <class R1, class R2> struct ratio_multiply;
-template <class R1, class R2> struct ratio_divide;
-template <class R1, class ... RList> struct ratio_sum;
-template <class R1, class ... RList> struct ratio_product;
-
- -

-after 20.11.4 [ratio.arithmetic] p1: add -

- -
-template <class R1, class ... RList> struct ratio_sum; // declared, never defined
-
-template <class R1> struct ratio_sum<R1> : R1 {};
-
- -

-Requires: R1 is a specialization of class template ratio -

- -
-template <class R1, class R2, class ... RList> 
- struct ratio_sum<R1, R2, RList...>
-   : ratio_add< R1, ratio_sum<R2, RList...>> {
-};
-
- -

-Requires: R1 and each element in parmater pack -RList is a specialization of class template ratio -

-
- -

-after 20.11.4 [ratio.arithmetic] p3: add -

- -
-template <class R1, class ... RList> struct ratio_product; // declared, never defined
-
-template <class R1> struct ratio_product<R1> : R1 {};
-
- -

-Requires: R1 is a specialization of class template ratio -

- -
-template <class R1, class R2, class ... RList> 
- struct ratio_sum<R1, R2, RList...>
-   : ratio_add< R1, ratio_product<R2, RList...>> {
-};
-
- -

-Requires: R1 and each element in parmater pack -RList is a specialization of class template ratio -

-
- - - - - - - - -
-

1150. wchar_t, char16_t and char32_t filenames

-

Section: 27.9.1.14 [fstream] Status: LEWG - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all issues with LEWG status.

-

Discussion:

-

Addresses JP 73

- -

Description

-

It is a problem - from C++98, fstream cannot appoint a filename of wide - character string(const wchar_t and const wstring&).

-

Suggestion

-

Add - interface corresponding to wchar_t, char16_t and char32_t.

- -

[ -2009-07-01 Alisdair notes that this is a duplicate of 454 which has more -in-depth rationale. -]

- - -

[ -2009-09-21 Daniel adds: -]

- - -

-I suggest to mark this issue as NAD Future with the intend to -solve the issue with a single file path c'tor template assuming -a provision of a TR2 filesystem library. -

- -

[ -2009 Santa Cruz: -]

- - -

-NAD Future. This is a duplicate of 454. -

- - - -

Proposed resolution:

- - - - - -
-

1154. complex should accept integral types

-

Section: 26.4 [complex.numbers] Status: LEWG - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses FR 35

- -

Description

-

Instantiations of the class - template complex<> have to be allowed for integral - types, to reflect existing practice and ISO standards - (LIA-III).

- -

Suggestion

- -

[ -2009-10-26 Proposed wording in -N3002. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Future. Rationale added. -

- - - -

Rationale:

-

-There is no consensus for making this change at this time. -

- - -

Proposed resolution:

-Adopt -N3002. -

- - - - -
-

1169. num_get not fully compatible with strto*

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: Ready - Submitter: Cosmin Truta Opened: 2009-07-04 Last modified: 2015-05-22

-

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-

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-

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-

Discussion:

-

-As specified in the latest draft, -N2914, -num_get is still not fully compatible with the following C -functions: strtoul, strtoull, -strtof and -strtod. -

-

-In C, when conversion of a string to an unsigned integer type falls -outside the -representable range, strtoul and strtoull return -ULONG_MAX and ULLONG_MAX, respectively, -regardless -whether the input field represents a positive or a negative value. -On the other hand, the result of num_get conversion of -negative -values to unsigned integer types is zero. This raises a compatibility -issue. -

-

-Moreover, in C, when conversion of a string to a floating-point type falls -outside the representable range, strtof, strtod -and -strtold return ±HUGE_VALF, -±HUGE_VAL and ±HUGE_VALL, respectively. -On the other hand, the result of num_get conversion of such -out-of-range floating-point values results in the most positive/negative -representable value. -Although many C library implementations do implement HUGE_VAL -(etc.) as the highest representable (which is, usually, the infinity), -this isn't required by the C standard. The C library specification makes no -statement regarding the value of HUGE_VAL and friends, which -potentially raises the same compatibility issue as in the above case of -unsigned integers. -In addition, neither C nor C++ define symbolic constants for the maximum -representable floating-point values (they only do so only for the maximum -representable finite floating-point values), which raises a -usability -issue (it would be hard for the programmer to check the result of -num_get against overflow). -

-

-As such, we propose to adjust the specification of num_get to -closely follow the behavior of all of its underlying C functions. -

- - - -

[ -2010 Rapperswil: -]

- - -

-Some concern that this is changing the specification for an existing C++03 function, but it was -pointed out that this was underspecified as resolved by issue 23. This is clean-up for that -issue in turn. Some concern that we are trying to solve the same problem in both clause 22 and 27. -

-

-Bill: There's a change here as to whether val is stored to in an error case. -

-

-Pablo: Don't think this changes whether val is stored to or not, but changes the value that is stored. -

-

-Bill: Remembers having skirmishes with customers and testers as to whether val is stored to, and the resolution was not to store in error cases. -

-

-Howard: Believes since C++03 we made a change to always store in overflow. -

-

-Everyone took some time to review the issue. -

-

-Pablo: C++98 definitely did not store any value during an error condition. -

-

-Dietmar: Depends on the question of what is considered an error, and whether overflow is an error or not, which was the crux of LWG 23. -

-

-Pablo: Yes, but given the "zero, if the conversion function fails to convert the entire field", we are requiring every error condition to store. -

-

-Bill: When did this happen? -

-

-Alisdair: One of the last two or three meetings. -

-

-Dietmar: To store a value in case of failure is a very bad idea. -

-

-Move to Open, needs more study. -

-
- -

[2011-03-24 Madrid meeting]

- - -

Move to deferred

- -

[ -2011 Bloomington -]

- - -

-The proposed wording looks good, no-one sure why this was held back before. Move to Review. -

- - -

[2012,Kona]

- -

-Move to Open. -

-

-THe issues is what to do with -1. Should it match 'C' or do the "sane" thing. -A fix here changes behavior, but is probably what we want. -

-

-Pablo to provide wording, with help from Howard. -

- -

[2015-05-06 Lenexa: Move to Ready]

- -

STL: I like that this uses strtof, which I think is new in C99. that avoids truncation from using atof. I have another issue ...

-

MC: yes LWG 2403 (stof should call strtof)

-

PJP: the last line is horrible, you don't assign to err, you call setstate(ios_base::failbit). Ah, no, this is inside num_get so the caller does the setstate.

-

MC: we need all these words. are they the right words?

-

JW: I'd like to take a minute to check my impl. Technically this implies a change in behaviour (from always using strtold and checking the extracted floating point value, to using the right function). Oh, we already do exactly this.

-

MC: Move to Ready

-

6 in favor, none opposed, 1 abstention

- - -

Proposed resolution:

- -

-Change 22.4.2.1.2 [facet.num.get.virtuals] as follows: -

-
-

-Stage 3: -The sequence of chars accumulated in stage 2 (the field) is -converted to a numeric value by the rules of one of the functions declared in -the header <cstdlib>: -

-
    -
  • For a signed integer value, the function strtoll.
    • -
  • For an unsigned integer value, the function strtoull.
    • -
  • For a float value, the function - strtof.
    • -
  • For a double value, the function - strtod.
    • -
  • For a floating-point long double - value, the function strtold.
    • -
-

-The numeric value to be stored can be one of: -

-
    -
  • zero, if the conversion function fails to convert the entire field. - ios_base::failbit is assigned to err.
    • -
  • the most positive (or negative) representable value, if - the field to be converted to a signed integer type represents a - value too large positive (or negative) to be represented in - val. - ios_base::failbit is assigned to err.
    • -
  • the most negative representable value or zero for an unsigned integer - type, if the field represents a value too large negative to be represented - in val. - ios_base::failbit is assigned to err.
    • -
  • the most positive representable value, if the field to be converted to - an unsigned integer type represents a value that cannot be represented in - val.
    • -
  • the converted value, otherwise.
    • -
-

-The resultant numeric value is stored in val. -If the conversion function fails to convert the entire field, or if the -field represents a value outside the range of representable values, -ios_base::failbit is assigned to err. -

-
- - - - - - -
-

1173. "Equivalence" wishy-washiness

-

Section: 17 [library] Status: Open - Submitter: David Abrahams Opened: 2009-07-14 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Issue: The CopyConstructible requirements are wishy-washy. It requires -that the copy is "equivalent" to the original, but "equivalent" is never -defined. -

-

-I believe this to be an example of a more general lack of rigor around -copy and assignment, although I haven't done the research to dig up all -the instances. -

-

-It's a problem because if you don't know what CopyConstructible means, -you also don't know what it means to copy a pair of CopyConstructible -types. It doesn't prevent us from writing code, but it is a hole in our -ability to understand the meaning of copy. -

-

-Furthermore, I'm pretty sure that vector's copy constructor doesn't -require the elements to be EqualityComparable, so that table is actually -referring to some ill-defined notion of equivalence when it uses ==. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to "Open". Dave is right that this is a big issue. Paper D2987 -("Defining Move Special Member Functions", Bjarne Stroustrup and -Lawrence Crowl) touches on this but does not solve it. This issue is -discussed in Elements of Programming. -

- - -

[ -2010 Rapperswil: -]

- - -

-This issue is quite vague, so it is difficult to know if and when it has been resolved. -John Lakos wrote a paper covering this area a while back, and there is a real interest -in providing some sort of clean-up in the future. We need a more clearly draughted -issues with an addressable set of concerns, ideally with a paper proposing a resolution, -but for a future revision of the standard. Move to Tentatively NAD Future. -

- -

[ -Moved to NAD Future at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- - - - - -
-

1175. unordered complexity

-

Section: 23.2.5 [unord.req] Status: Open - Submitter: Pablo Halpern Opened: 2009-07-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-When I look at the unordered_* constructors, I think the complexity is poorly -described and does not follow the style of the rest of the standard. -

- -

-The complexity for the default constructor is specified as constant. -Actually, it is proportional to n, but there are no invocations of -value_type constructors or other value_type operations. -

- -

-For the iterator-based constructor the complexity should be: -

- -

-Complexity: exactly n calls to construct value_type -from InputIterator::value_type (where n = distance(f,l)). -The number of calls to key_equal::operator() is proportional to -n in the average case and n*n in the worst case. -

- -

[ -2010 Rapperswil: -]

- - -

-Concern that the current wording may require O(1) where that cannot be delivered. We need to look at -both the clause 23 requirements tables and the constructor description of each unordered container to be sure. -

-

-Howard suggests NAD Editorial as we updated the container requirement tables since this issue was written. -

-

-Daniel offers to look deeper, and hopefully produce wording addressing any outstanding concerns at the next meeting. -

-

-Move to Open. -

-
- -

[2011-02-26: Daniel provides wording]

- - -

I strongly suggest to clean-up the differences between requirement tables and individual -specifications. In the usual way, the most specific specifications wins, which is in this -case the wrong one. In regard to the concern expressed about missing DefaultConstructible -requirements of the value type I disagree: The function argument n is no size-control -parameter, but only some effective capacity parameter: No elements will be value-initialized -by these constructors. The necessary requirement for the value type, EmplaceConstructible -into *this, is already listed in Table 103 — Unordered associative container requirements. -Another part of the proposed resolution is the fact that there is an inconsistency of the -complexity counting when both a range and a bucket count is involved compared -to constructions where only bucket counts are provided: E.g. the construction X a(n); -has a complexity of n bucket allocations, but this part of the work is omitted for -X a(i, j, n);, even though it is considerable larger (in the average case) for -n ≫ distance(i, j). -

- -

[2011-03-24 Madrid meeting]

- - -

Move to deferred

- -

[ -2011 Bloomington -]

- - -

-The proposed wording looks good. Move to Review. -

- -

[2012, Kona]

- -

-Fix up some presentation issues with the wording, combining the big-O expressions into single -expressions rather than the sum of two separate big-Os. -

-

-Strike "constant or linear", prefer "linear in the number of buckets". -This allows for number of buckets being larger than requested n as well. -

-

-Default n to "unspecified" rather than "implementation-defined". It seems an un-necessary -burden asking vendors to document a quantity that is easily determined through the public API of -these classes. -

-

-Replace distance(f,l) with "number of elements in the range [f,l)" -

-

-Retain in Review with the updated wording -

- -

[2012, Portland: Move to Open]

- -

-The wording still does not call out Pablo's original concern, that the element constructor is called -no more than N times, and that the N squared term applies to moves during rehash. -

- -

-Inconsistent use of O(n)+O(N) vs. O(n+N), with a preference for the former. -

- -

-AJM to update wording with a reference to "no more than N element constructor calls". -

- -

-Matt concerned that calling out the O(n) requirements is noise, and dangerous noise in suggesting a precision -we do not mean. The cost of constructing a bucket is very different to constructing an element of user-supplied -type. -

- -

-AJM notes that if there are multiple rehashes, the 'n' complexity is probably not linear. -

- -

-Matt suggests back to Open, Pablo suggests potentially NAD if we keep revisitting without achieving a resolution. -

- -

-Matt suggests complexity we are concerned with is the number of operations, such as constructing elements, moving -nodes, and comparing/hashing keys. We are less concerned with constructing buckets, which are generally noise in -this bigger picture. -

- -

[2015-01-29 Telecon]

- -

-AM: essentially correct, but do we want to complicate the spec? -

-HH: Pablo has given us permission to NAD it -

-JM: when I look at the first change in the P/R I find it mildly disturbing that the existing wording says you have a -constant time constructor with a single element even if your n is 10^6, so I think adding this change makes people -aware there might be a large cost in initializing the hash table, even though it doesn't show up in user-visible constructions. -

-HH: one way to avoid that problem is make the default ctor noexcept. Then the container isn't allowed to create -an arbitrarily large hash table -

-AM: but this is the constructor where the user provides n -

-MC: happy with the changes, except I agree with the editorial recommendation to keep the two 𝒪s separate. -

-JW: yes, the constant 'k' is different in 𝒪(n) and 𝒪(N) -

-GR: do we want to talk about buckets at all -

-JM: yes, good to highlight that bucket construction might be a significant cost -

-HH: suggest we take the suggestion to split 𝒪(n+N) to 𝒪(n)+𝒪(N) and move to Tentatively Ready -

-GR: 23.2.1p2 says all complexity requirements are stated solely in terms of the number of operations on the contained -object, so we shouldn't be stating complexity in terms of the hash table initialization -

-HH: channeling Pete, there's an implicit "unless otherwise specified" everywhere. -

-VV: seem to be requesting modifications that render this not Tentatively Ready -

-GR: I think it can't be T/R -

-AM: make the editorial recommendation, consider fixing 23.2.1/3 to give us permission to state complexity in terms -of bucket initialization -

-HH: only set it to Review after we get new wording to review -

- -

[2015-02 Cologne]

- -

-Update wording, revisit later. -

- - - -

Proposed resolution:

-
    -

  1. Modify the following rows in Table 103 — Unordered associative container requirements to -add the explicit bucket allocation overhead of some constructions. As editorial recommendation it is -suggested not to shorten the sum 𝒪(n) + 𝒪(N) to -𝒪(n + N), because two different work units are involved.

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 103 — Unordered associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    …
    X(i, j, n, hf, eq)
    -X a(i, j, n, hf, eq) -    		X…
    -Effects: Constructs an empty container with at least n
    -buckets, using hf as the hash function and eq as the key
    -equality predicate, and inserts elements from [i, j) into it. -    		Average case 𝒪(n + N) (N is distance(i, j)),
    -worst case 𝒪(n) + 𝒪(N2)
    X(i, j, n, hf)
    -X a(i, j, n, hf) -    		X…
    -Effects: Constructs an empty container with at least n
    -buckets, using hf as the hash function and key_equal() as the key
    -equality predicate, and inserts elements from [i, j) into it. -    		Average case 𝒪(n + N) (N is distance(i, j)),
    -worst case 𝒪(n + N2)
    X(i, j, n)
    -X a(i, j, n) -    		X…
    -Effects: Constructs an empty container with at least n
    -buckets, using hasher() as the hash function and key_equal() as the key
    -equality predicate, and inserts elements from [i, j) into it. -    		Average case 𝒪(n + N) (N is distance(i, j)),
    -worst case 𝒪(n + N2)
    …
    -
    - -
    2. - -

  2. Modify 23.5.4.2 [unord.map.cnstr] p. 1-4 as indicated (The edits of p. 1 and p. 3 attempt to fix some -editorial oversight.):

    - -
    -explicit unordered_map(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-

    -1 Effects: Constructs an empty unordered_map using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_map. -max_load_factor() returns 1.0. -

    -

    -2 Complexity: ConstantLinear in the number of buckets. -

    -
    - -
    -template <class InputIterator>
-unordered_map(InputIterator f, InputIterator l,
-              size_type n = see below,
-              const hasher& hf = hasher(),
-              const key_equal& eql = key_equal(),
-              const allocator_type& a = allocator_type());
-

    -3 Effects: Constructs an empty unordered_map using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_map. -Then inserts elements from the range [f, l). max_load_factor() returns 1.0. -

    -

    -4 Complexity: Average case linear, worst case quadraticLinear in the number of buckets. -In the average case linear in N and in the worst case quadratic in N to insert -the elements, where N is equal to number of elements in the range [f,l). -

    -
    -
    3. - -

  3. Modify 23.5.5.2 [unord.multimap.cnstr] p. 1-4 as indicated (The edits of p. 1 and p. 3 attempt to fix some -editorial oversight.):

    - -
    -explicit unordered_multimap(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-

    -1 Effects: Constructs an empty unordered_multimap using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_multimap. -max_load_factor() returns 1.0. -

    -

    -2 Complexity: ConstantLinear in the number of buckets. -

    -
    - -
    -template <class InputIterator>
-unordered_multimap(InputIterator f, InputIterator l,
-                   size_type n = see below,
-                   const hasher& hf = hasher(),
-                   const key_equal& eql = key_equal(),
-                   const allocator_type& a = allocator_type());
-

    -3 Effects: Constructs an empty unordered_multimap using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_multimap. -Then inserts elements from the range [f, l). max_load_factor() returns 1.0. -

    -

    -4 Complexity: Average case linear, worst case quadraticLinear in the number of buckets. -In the average case linear in N and in the worst case quadratic in N to insert -the elements, where N is equal to number of elements in the range [f,l). -

    -
    -
    4. - -

  4. Modify 23.5.6.2 [unord.set.cnstr] p. 1-4 as indicated (The edits of p. 1 and p. 3 attempt to fix some -editorial oversight.):

    - -
    -explicit unordered_set(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-

    -1 Effects: Constructs an empty unordered_set using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_set. -max_load_factor() returns 1.0. -

    -

    -2 Complexity: ConstantLinear in the number of buckets. -

    -
    - -
    -template <class InputIterator>
-unordered_set(InputIterator f, InputIterator l,
-              size_type n = see below,
-              const hasher& hf = hasher(),
-              const key_equal& eql = key_equal(),
-              const allocator_type& a = allocator_type());
-

    -3 Effects: Constructs an empty unordered_set using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_set. -Then inserts elements from the range [f, l). max_load_factor() returns 1.0. -

    -

    -4 Complexity: Average case linear, worst case quadraticLinear in the number of buckets. -In the average case linear in N and in the worst case quadratic in N to insert -the elements, where N is equal to number of elements in the range [f,l). -

    -
    -
    5. - -

  5. Modify 23.5.7.2 [unord.multiset.cnstr] p. 1-4 as indicated (The edits of p. 1 and p. 3 attempt to fix some -editorial oversight.):

    - -
    -explicit unordered_multiset(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-

    -1 Effects: Constructs an empty unordered_multiset using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_multiset. -max_load_factor() returns 1.0. -

    -

    -2 Complexity: ConstantLinear in the number of buckets. -

    -
    - -
    -template <class InputIterator>
-unordered_multiset(InputIterator f, InputIterator l,
-                   size_type n = see below,
-                   const hasher& hf = hasher(),
-                   const key_equal& eql = key_equal(),
-                   const allocator_type& a = allocator_type());
-

    -3 Effects: Constructs an empty unordered_multiset using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -unspecifiedimpldefdefault number of buckets in unordered_multiset. -Then inserts elements from the range [f, l). max_load_factor() returns 1.0. -

    -

    -4 Complexity: Average case linear, worst case quadraticLinear in the number of buckets. -In the average case linear in N and in the worst case quadratic in N to insert -the elements, where N is equal to number of elements in the range [f,l). -

    -
    -
    6. - -
- - - - - -
-

1184. Feature request: dynamic bitset

-

Section: 23.3.6 [vector] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-07-29 Last modified: 2015-04-08

-

View all other issues in [vector].

-

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-

Discussion:

-

-Opened at Alisdair's request, steming from 96. -Alisdair recommends NAD Future. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Future. We want a heap allocated bitset, but we don't have one today and -don't have time to add one. -

- - - -

Proposed resolution:

- - - - - -
-

1188. Unordered containers should have a minimum load factor as well as a maximum

-

Section: 23.2.5 [unord.req], 23.5 [unord] Status: LEWG - Submitter: Matt Austern Opened: 2009-08-10 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

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-

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-

Discussion:

-

-Unordered associative containers have a notion of a maximum load factor: -when the number of elements grows large enough, the containers -automatically perform a rehash so that the number of elements per bucket -stays below a user-specified bound. This ensures that the hash table's -performance characteristics don't change dramatically as the size -increases. -

- -

-For similar reasons, Google has found it useful to specify a minimum -load factor: when the number of elements shrinks by a large enough, the -containers automatically perform a rehash so that the number of elements -per bucket stays above a user-specified bound. This is useful for two -reasons. First, it prevents wasting a lot of memory when an unordered -associative container grows temporarily. Second, it prevents amortized -iteration time from being arbitrarily large; consider the case of a hash -table with a billion buckets and only one element. (This was discussed -even before TR1 was published; it was TR issue 6.13, which the LWG -closed as NAD on the grounds that it was a known design feature. -However, the LWG did not consider the approach of a minimum load -factor.) -

- -

-The only interesting question is when shrinking is allowed. In principle -the cleanest solution would be shrinking on erase, just as we grow on -insert. However, that would be a usability problem; it would break a -number of common idioms involving erase. Instead, Google's hash tables -only shrink on insert and rehash. -

- -

-The proposed resolution allows, but does not require, shrinking in -rehash, mostly because a postcondition for rehash that involves the -minimum load factor would be fairly complicated. (It would probably have -to involve a number of special cases and it would probably have to -mention yet another parameter, a minimum bucket count.) -

- -

-The current behavior is equivalent to a minimum load factor of 0. If we -specify that 0 is the default, this change will have no impact on -backward compatibility. -

- - -

[ -2010 Rapperswil: -]

- - -

-This seems to a useful extension, but is too late for 0x. - -Move to Tentatively NAD Future. -

- -

[ -Moved to NAD Future at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Add two new rows, and change rehash's postcondition in the unordered -associative container requirements table in 23.2.5 [unord.req]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 87 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
-a.min_load_factor() - -float - -Returns a non-negative number that the container attempts to keep the -load factor greater than or equal to. The container automatically -decreases the number of buckets as necessary to keep the load factor -above this number. - -constant -
a.min_load_factor(z)voidPre: z shall be non-negative. Changes the container's minimum -load factor, using z as a hint. [Footnote: the minimum -load factor should be significantly smaller than the maximum. -If z is too large, the implementation may reduce it to a more sensible value.] - -constant -
a.rehash(n)void -Post: a.bucket_count() >= n, and a.size() <= a.bucket_count() -* a.max_load_factor(). [Footnote: It is intentional that the -postcondition does not mention the minimum load factor. -This member function is primarily intended for cases where the user knows -that the container's size will increase soon, in which case the container's -load factor will temporarily fall below a.min_load_factor().] - -a.bucket_cout > a.size() / a.max_load_factor() and a.bucket_count() ->= n. - - -Average case linear in a.size(), worst case quadratic. -
-
- -

-Add a footnote to 23.2.5 [unord.req] p12: -

- -
-

-The insert members shall not affect the validity of references to -container elements, but may invalidate all iterators to the container. -The erase members shall invalidate only iterators and references to the -erased elements. -

- -

-[A consequence of these requirements is that while insert may change the -number of buckets, erase may not. The number of buckets may be reduced -on calls to insert or rehash.] -

-
- -

-Change paragraph 13: -

- -

-The insert members shall not affect the validity of iterators if -(N+n) < z * B zmin * B <= (N+n) <= zmax * B, -where N is the number of elements in -the container prior to the insert operation, n is the number of -elements inserted, B is the container's bucket count, -zmin is the container's minimum load factor, -and zmax is the container's maximum load factor. -

- -

-Add to the unordered_map class synopsis in section 23.5.4 [unord.map], -the unordered_multimap class synopsis -in 23.5.5 [unord.multimap], the unordered_set class synopsis in -23.5.6 [unord.set], and the unordered_multiset class synopsis -in 23.5.7 [unord.multiset]: -

- -

-float min_load_factor() const;
-void min_load_factor(float z);
-
- -

-In 23.5.4.2 [unord.map.cnstr], 23.5.5.2 [unord.multimap.cnstr], 23.5.6.2 [unord.set.cnstr], and -23.5.7.2 [unord.multiset.cnstr], change: -

- -

-... max_load_factor() returns 1.0 and -min_load_factor() returns 0. -

- - - - - -
-

1201. Do we always want to unwrap ref-wrappers in make_tuple

-

Section: 20.4.2.4 [tuple.creation], 20.3 [pairs] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-09-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Spotting a recent thread on the boost lists regarding collapsing -optional representations in optional<optional<T>> instances, I wonder if -we have some of the same issues with make_tuple, and now make_pair? -

- -

-Essentially, if my generic code in my own library is handed a -reference_wrapper by a user, and my library in turn delegates some logic -to make_pair or make_tuple, then I am going to end up with a pair/tuple -holding a real reference rather than the intended reference wrapper. -

- -

-There are two things as a library author I can do at this point: -

- -
    -
  1. -document my library also has the same reference-wrapper behaviour as -std::make_tuple -
    2. -
  2. -roll my own make_tuple that does not unwrap rereferences, a lost -opportunity to re-use the standard library. -
    3. -
- -

-(There may be some metaprogramming approaches my library can use to wrap -the make_tuple call, but all will be significantly more complex than -simply implementing a simplified make_tuple.) -

- -

-Now I don't propose we lose this library facility, I think unwrapping -references will be the common behaviour. However, we might want to -consider adding another overload that does nothing special with -ref-wrappers. Note that we already have a second overload of -make_tuple in the library, called tie. -

- -

[ -2009-09-30 Daniel adds: -]

- - -
-

-I suggest to change the currently proposed paragraph for -make_simple_pair -

- -
-template<typename... Types>
-  pair<typename decay<Types>::type...> make_simple_pair(Types&&... t);
-
-
-

-Type requirements: sizeof...(Types) == 2. -Remarks: The program shall be ill-formed, if -sizeof...(Types) != 2. -

-

-... -

-
-
- -

-or alternatively (but with a slightly different semantic): -

- -
-

-Remarks: If sizeof...(Types) != 2, this function shall not -participate in overload resolution. -

-
- -

-to follow a currently introduced style and because the library does -not have yet a specific "Type requirements" element. If such thing -would be considered as useful this should be done as a separate -issue. Given the increasing complexity of either of these wordings -it might be preferable to use the normal two-argument-declaration -style again in either of the following ways: -

- -
    -
  1. -
    template<class T1, class T2>
-pair<typename decay<T1>::type, typename decay<T2>::type>
-make_simple_pair(T1&& t1, T2&& t2);
-
    -
    2. -
  2. -
    template<class T1, class T2>
-pair<V1, V2> make_simple_pair(T1&& t1, T2&& t2);
-
    -

    -Let V1 be typename decay<T1>::type and V2 be -typename decay<T2>::type. -

    -
    3. -
- -
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Mark as Tentatively NAD Future. -

- - - -

Rationale:

-

-Does not have sufficient support at this time. May wish to reconsider for a -future standard. -

- - -

Proposed resolution:

-

-Add the following function to 20.3 [pairs] and signature in -appropriate synopses: -

- -
-template<typename... Types>
-  pair<typename decay<Types>::type...> make_simple_pair(Types&&... t);
-
-
-

-Type requirements: sizeof...(Types) == 2. -

-

-Returns: pair<typename decay<Types>::type...>(std::forward<Types>(t)...). -

-
-
- -

[ -Draughting note: I chose a variadic representation similar to make_tuple -rather than naming both types as it is easier to read through the -clutter of metaprogramming this way. Given there are exactly two -elements, the committee may prefer to draught with two explicit template -type parameters instead -]

- - -

-Add the following function to 20.4.2.4 [tuple.creation] and -signature in appropriate synopses: -

- -
-template<typename... Types>
-  tuple<typename decay<Types>::type...> make_simple_tuple(Types&&... t);
-
-
-

-Returns: tuple<typename decay<Types>::type...>(std::forward<Types>(t)...). -

-
-
- - - - - -
-

1203. More useful rvalue stream insertion

-

Section: 27.7.3.9 [ostream.rvalue], 27.7.2.6 [istream.rvalue] Status: LEWG - Submitter: Howard Hinnant Opened: 2009-09-06 Last modified: 2015-04-08

-

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-

Discussion:

-

-27.7.3.9 [ostream.rvalue] was created to preserve the ability to insert -into (and extract from 27.7.2.6 [istream.rvalue]) rvalue streams: -

- -
-template <class charT, class traits, class T>
-  basic_ostream<charT, traits>&
-  operator<<(basic_ostream<charT, traits>&& os, const T& x);
-
-
-

-1 Effects: os << x -

-

-2 Returns: os -

-
-
- -

-This is good as it allows code that wants to (for example) open, write to, and -close an ofstream all in one statement: -

- -
-std::ofstream("log file") << "Some message\n";
-
- -

-However, I think we can easily make this "rvalue stream helper" even easier to -use. Consider trying to quickly create a formatted string. With the current -spec you have to write: -

- -
-std::string s = static_cast<std::ostringstream&>(std::ostringstream() << "i = " << i).str();
-
- -

-This will store "i = 10" (for example) in the string s. Note -the need to cast the stream back to ostringstream& prior to using -the member .str(). This is necessary because the inserter has cast -the ostringstream down to a more generic ostream during the -insertion process. -

- -

-I believe we can re-specify the rvalue-inserter so that this cast is unnecessary. -Thus our customer now has to only type: -

- -
-std::string s = (std::ostringstream() << "i = " << i).str();
-
- -

-This is accomplished by having the rvalue stream inserter return an rvalue of -the same type, instead of casting it down to the base class. This is done by -making the stream generic, and constraining it to be an rvalue of a type derived -from ios_base. -

- -

-The same argument and solution also applies to the inserter. This code has been -implemented and tested. -

- -

[ -2009 Santa Cruz: -]

- - -

-NAD Future. No concensus for change. -

- - - -

Proposed resolution:

-

-Change 27.7.2.6 [istream.rvalue]: -

- -
-template <class charT, class traits Istream, class T>
-  basic_istream<charT, traits>& Istream&&
-  operator>>(basic_istream<charT, traits> Istream&& is, T& x);
-
-
-

-1 Effects: is >> x -

-

-2 Returns: std::move(is) -

-

-3 Remarks: This signature shall participate in overload resolution if -and only if Istream is not an lvalue reference type and is derived from -ios_base. -

-
-
- -

-Change 27.7.3.9 [ostream.rvalue]: -

- -
-template <class charT, class traits Ostream, class T>
-  basic_ostream<charT, traits>& Ostream&&
-  operator<<(basic_ostream<charT, traits> Ostream&& os, const T& x);
-
-
-

-1 Effects: os << x -

-

-2 Returns: std::move(os) -

-

-3 Remarks: This signature shall participate in overload resolution if -and only if Ostream is not an lvalue reference type and is derived from -ios_base. -

-
-
- - - - - - -
-

1213. Meaning of valid and singular iterator underspecified

-

Section: 24.2 [iterator.requirements] Status: Open - Submitter: Daniel Krügler Opened: 2009-09-19 Last modified: 2015-05-08

-

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-

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-

Discussion:

-

-The terms valid iterator and singular aren't -properly defined. The fuzziness of those terms became even worse -after the resolution of 208 (including further updates by 278). In -24.2 [iterator.requirements] as of -N2723 -the standard says now: -

- -
-

-5 - These values are called past-the-end values. Values of an iterator i for -which the expression *i is defined are called dereferenceable. The library -never assumes that past-the-end values are dereferenceable. Iterators -can also have singular values that are not associated with any -container. [...] Results of most expressions are undefined for singular -values; the only exceptions are destroying an iterator that holds a -singular value and the assignment of a non-singular value to an iterator -that holds a singular value. [...] Dereferenceable values are always -non-singular. -

- -

-10 - An invalid iterator is an iterator that may be singular. -

-
- -

-First, issue 208 intentionally removed the earlier constraint that past-the-end -values are always non-singular. The reason for this was to support null -pointers as past-the-end iterators of e.g. empty sequences. But there -seem to exist different views on what a singular (iterator) value is. E.g. -according to the SGI definition -a null pointer is not a singular value: -

- -

-Dereferenceable iterators are always nonsingular, but the converse is -not true. -For example, a null pointer is nonsingular (there are well defined operations -involving null pointers) even thought it is not dereferenceable. -

- -

-and proceeds: -

- -

-An iterator is valid if it is dereferenceable or past-the-end. -

- -

-Even if the standard prefers a different meaning of singular here, the -change was incomplete, because by restricting feasible expressions of singular -iterators to destruction and assignment isn't sufficient for a past-the-end -iterator: Of-course it must still be equality-comparable and in general be a readable value. -

- -

-Second, the standard doesn't clearly say whether a past-the-end value is -a valid iterator or not. E.g. 20.7.12 [specialized.algorithms]/1 says: -

- -

-In all of the following algorithms, the formal template parameter ForwardIterator -is required to satisfy the requirements of a forward iterator (24.1.3) -[..], and is required to have the property that no exceptions are thrown from [..], or -dereference of valid iterators. -

- -

-The standard should make better clear what "singular pointer" and "valid -iterator" means. The fact that the meaning of a valid value -has a core language meaning doesn't imply that for an iterator concept -the term "valid iterator" has the same meaning. -

- -

-Let me add a final example: In X [allocator.concepts.members] of -N2914 -we find: -

- -
-pointer X::allocate(size_type n);
-
- -

-11 Returns: a pointer to the allocated memory. [Note: if n == 0, the return -value is unspecified. —end note] -

- -

-[..] -

- -
-void X::deallocate(pointer p, size_type n);
-
- -

-Preconditions: p shall be a non-singular pointer value obtained from a call -to allocate() on this allocator or one that compares equal to it. -

-
- -

-If singular pointer value would include null pointers this make the -preconditions -unclear if the pointer value is a result of allocate(0): Since the return value -is unspecified, it could be a null pointer. Does that mean that programmers -need to check the pointer value for a null value before calling deallocate? -

- -

[ -2010-11-09 Daniel comments: -]

- - -

-A later paper is in preparation. -

- -

[ -2010 Batavia: -]

- - -

-Doesn't need to be resolved for Ox -

- - -

[2014-02-20 Re-open Deferred issues as Priority 4]

- - -

-Consider to await the paper. -

- - -

Proposed resolution:

- - - - - -
-

1217. Quaternion support

-

Section: 26.4 [complex.numbers] Status: LEWG - Submitter: Ted Shaneyfelt Opened: 2009-09-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Concerning mathematically proper operation of the type: -

- -
-complex<complex<T> >
-
- -

-Generally accepted mathematical semantics of such a construct correspond -to quaternions through Cayly-Dickson construct -

- -
-(w+xi) + (y+zi) j
-
- -

-The proper implementation seems straightforward by adding a few -declarations like those below. I have included operator definition for -combining real scalars and complex types, as well, which seems -appropriate, as algebra of complex numbers allows mixing complex and -real numbers with operators. It also allows for constructs such as -complex<double> i=(0,1), x = 12.34 + 5*i; -

- -

-Quaternions are often used in areas such as computer graphics, where, -for example, they avoid the problem of Gimbal lock when rotating objects -in 3D space, and can be more efficient than matrix multiplications, -although I am applying them to a different field. -

- -
-/////////////////////////ALLOW OPERATORS TO COMBINE REAL SCALARS AND COMPLEX VALUES /////////////////////////
-template<typename T,typename S> complex<T> operator+(const complex<T> x,const S a) {
-    complex<T> result(x.real()+a, x.imag());
-    return result;
-}
-template<typename T,typename S> complex<T> operator+(const S a,const complex<T> x) {
-    complex<T> result(a+x.real(), x.imag());
-    return result;
-}
-template<typename T,typename S> complex<T> operator-(const complex<T> x,const S a) {
-    complex<T> result(x.real()-a, x.imag());
-    return result;
-}
-template<typename T,typename S> complex<T> operator-(const S a,const complex<T> x) {
-    complex<T> result(a-x.real(), x.imag());
-    return result;
-}
-template<typename T,typename S> complex<T> operator*(const complex<T> x,const S a) {
-    complex<T> result(x.real()*a, x.imag()*a);
-    return result;
-}
-template<typename T,typename S> complex<T> operator*(const S a,const complex<T> x) {
-    complex<T> result(a*x.real(), a*x.imag());
-    return result;
-}
-
-/////////////////////////PROPERLY IMPLEMENT QUATERNION SEMANTICS/////////////////////////
-template<typename T> double normSq(const complex<complex<T> >q) {
-    return q.real().real()*q.real().real()
-         + q.real().imag()*q.real().imag()
-         + q.imag().real()*q.imag().real()
-         + q.imag().imag()*q.imag().imag();
-}
-template<typename T> double norm(const complex<complex<T> >q) {
-    return sqrt(normSq(q));
-}
-/////// Cayley-Dickson Construction
-template<typename T> complex<complex<T> > conj(const complex<complex<T> > x) {
-    complex<complex<T> > result(conj(x.real()),-x.imag());
-    return result;
-}
-template<typename T> complex<complex<T> > operator*(const complex<complex<T> > ab,const complex<complex<T> > cd) {
-    complex<T> re(ab.real()*cd.real()-conj(cd.imag())*ab.imag());
-    complex<T> im(cd.imag()*ab.real()+ab.imag()*conj(cd.real()));
-    complex<complex<double> > q(re,im);
-    return q;
-}
-//// Quaternion division
-template<typename S,typename T> complex<complex<T> > operator/(const complex<complex<T> > q,const S a) {
-    return q * (1/a);
-}
-template<typename S,typename T> complex<complex<T> > operator/(const S a,const complex<complex<T> > q) {
-    return a*conj(q)/normSq(q);
-}
-template<typename T> complex<complex<T> > operator/(const complex<complex<T> > n, const complex<complex<T> > d) {
-    return n * (conj(d)/normSq(d));
-}
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Future. There is no consensus or time to move this into C++0X. -

- - - -

Proposed resolution:

- - - - - -
-

1235. Issue with C++0x random number proposal

-

Section: X [rand.concept.dist] Status: LEWG - Submitter: Matthias Troyer Opened: 2009-10-12 Last modified: 2015-04-08

-

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-

Discussion:

-

-There exist optimized, vectorized vendor libraries for the creation of -random number generators, such as Intel's MKL [1] and AMD's ACML [2]. In -timing tests we have seen a performance gain of a factor of up to 80 -(eighty) compared to a pure C++ implementation (in Boost.Random) when -using these generator to generate a sequence of normally distributed -random numbers. In codes dominated by the generation of random numbers -(we have application codes where random number generation is more than -50% of the CPU time) this factor 80 is very significant. -

- -

-To make use of these vectorized generators, we use a C++ class modeling -the RandomNumberEngine concept and forwarding the generation of random -numbers to those optimized generators. For example: -

- -
-namespace mkl {
- class mt19937 {.... };
-}
-
- -

-For the generation of random variates we also want to dispatch to -optimized vectorized functions in the MKL or ACML libraries. See this -example: -

- -
-mkl::mt19937 eng;
-std::normal_distribution<double> dist;
-
-double n = dist(eng);
-
- -

-Since the variate generation is done through the operator() of the -distribution there is no customization point to dispatch to Intel's or -AMD's optimized functions to generate normally distributed numbers based -on the mt19937 generator. Hence, the performance gain of 80 cannot be -achieved. -

- -

-Contrast this with TR1: -

- -
-mkl::mt19937 eng;
-std::tr1::normal_distribution<double> dist;
-std::tr1::variate_generator<mkl::mt19937,std::tr1::normal_distribution<double> > rng(eng,dist);
-double n = rng();
-
- -

-This - admittedly much uglier from an aestethic point of view - design -allowed optimization by specializing the variate_generator template for -mkl::mt19937: -

- -
-namespace std { namespace tr1 {
-
-template<>
-class variate_generator<mkl::mt19937,std::tr1::normal_distribution<double> > { .... };
-
-} }
-
- -

-A similar customization point is missing in the C++0x design and -prevents the optimized vectorized version to be used. -

- -

-Suggested resolution: -

- -

-Add a customization point to the distribution concept. Instead of the -variate_generator template this can be done through a call to a -free function generate_variate found by ADL instead of -operator() of the distribution: -

- -
-template <RandomNumberDistribution, class RandomNumberEngine>
-typename RandomNumberDistribution ::result_type
-generate_variate(RandomNumberDistribution const& dist, RandomNumberEngine& eng);
-
- -

-This function can be overloaded for optimized enginges like -mkl::mt19937. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Future. No time to add this feature for C++0X. -

- - - -

Proposed resolution:

- - - - - -
-

1238. defining algorithms taking iterator for range

-

Section: 25 [algorithms] Status: LEWG - Submitter: Alisdair Meredith Opened: 2009-10-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The library has many algorithms that take a source range represented by -a pair of iterators, and the start of some second sequence given by a -single iterator. Internally, these algorithms will produce undefined -behaviour if the second 'range' is not as large as the input range, but -none of the algorithms spell this out in Requires clauses, and there is -no catch-all wording to cover this in clause 17 or the front matter of -25. -

- -

-There was an attempt to provide such wording in paper -n2944 -but this -seems incidental to the focus of the paper, and getting the wording of -this issue right seems substantially more difficult than the simple -approach taken in that paper. Such wording will be removed from an -updated paper, and hopefully tracked via the LWG issues list instead. -

- -

-It seems there are several classes of problems here and finding wording -to solve all in one paragraph could be too much. I suspect we need -several overlapping requirements that should cover the desired range of -behaviours. -

- -

-Motivating examples: -

- -

-A good initial example is the swap_ranges algorithm. Here there is a -clear requirement that first2 refers to the start of a valid range at -least as long as the range [first1, last1). n2944 tries to solve this -by positing a hypothetical last2 iterator that is implied by the -signature, and requires distance(first2,last2) < distance(first1,last1). - This mostly works, although I am uncomfortable assuming that last2 is -clearly defined and well known without any description of how to obtain -it (and I have no idea how to write that). -

- -

-A second motivating example might be the copy algorithm. Specifically, -let us image a call like: -

- -
-copy(istream_iterator<int>(is),istream_iterator(),ostream_iterator<int>(os));
-
- -

-In this case, our input iterators are literally simple InputIterators, -and the destination is a simple OutputIterator. In neither case am I -happy referring to std::distance, in fact it is not possible for the -ostream_iterator at all as it does not meet the requirements. However, -any wording we provide must cover both cases. Perhaps we might deduce -last2 == ostream_iterator<int>{}, but that might not always be valid for -user-defined iterator types. I can well imagine an 'infinite range' -that writes to /dev/null and has no meaningful last2. -

- -

-The motivating example in n2944 is std::equal, and that seems to fall somewhere between the -two. -

- -

-Outlying examples might be partition_copy that takes two output -iterators, and the _n algorithms where a range is specified by a -specific number of iterations, rather than traditional iterator pair. -We should also not accidentally apply inappropriate constraints to -std::rotate which takes a third iterator that is not intended to be a -separate range at all. -

- -

-I suspect we want some wording similar to: -

- -

-For algorithms that operate on ranges where the end iterator of the -second range is not specified, the second range shall contain at least -as many elements as the first. -

- -

-I don't think this quite captures the intent yet though. I am not sure -if 'range' is the right term here rather than sequence. More awkwardly, -I am not convinced we can describe an Output sequence such as produce by -an ostream_iterator as "containing elements", at least not as a -precondition to the call before they have been written. -

- -

-Another idea was to describe require that the trailing iterator support -at least distance(input range) applications of operator++ and may be -written through the same number of times if a mutable/output iterator. -

- -

-We might also consider handling the case of an output range vs. an input -range in separate paragraphs, if that simplifies how we describe some of -these constraints. -

- -

[ -2009-11-03 Howard adds: -]

- - -

-Moved to Tentatively NAD Future after 5 positive votes on c++std-lib. -

- - -

Rationale:

-

-Does not have sufficient support at this time. May wish to reconsider for a -future standard. -

- - -

Proposed resolution:

- - - - - -
-

1242. Enable SCARY iterators

-

Section: 23 [containers] Status: LEWG - Submitter: Herb Sutter Opened: 2009-10-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-See N2980. -

- -

[ -2009-10 Santa Cruz -]

- - -

-The paper was lengthy discussed but considerable concern remained to add this feature to C++0x. -Strong consensus was found to consider it for C++1x, though. -

- - -

Proposed resolution:

-The LWG does not wish to make a change at this time. -

- - - - -
-

1282. A proposal to add std::split algorithm

-

Section: 25 [algorithms] Status: LEWG - Submitter: Igor Semenov Opened: 2009-12-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
    - -
  1. -

    -Motivation and Scope -

    -

    -Splitting strings into parts by some set of delimiters is an often task, but -there is no simple and generalized solution in C++ Standard. Usually C++ -developers use std::basic_stringstream<> to split string into -parts, but there are several inconvenient restrictions: -

    - -
      -
    • -we cannot explicitly assign the set of delimiters; -
      • -
    • -this approach is suitable only for strings, but not for other types of -containers; -
      • -
    • -we have (possible) performance leak due to string instantiation. -
      • -
    -
    2. - -
  2. -

    -Impact on the Standard -

    -

    -This algorithm doesn't interfere with any of current standard algorithms. -

    -
    3. - -
  3. -

    -Design Decisions -

    -

    -This algorithm is implemented in terms of input/output iterators. Also, there is -one additional wrapper for const CharType * specified delimiters. -

    -
    4. - -
  4. -

    -Example implementation -

    -
    -template< class It, class DelimIt, class OutIt >
-void split( It begin, It end, DelimIt d_begin, DelimIt d_end, OutIt out )
-{
-   while ( begin != end )
-   {
-       It it = std::find_first_of( begin, end, d_begin, d_end );
-       *out++ = std::make_pair( begin, it );
-       begin = std::find_first_of( it, end, d_begin, d_end,
-           std::not2( std::equal_to< typename It::value_type >() ) );
-   }
-}
-
-template< class It, class CharType, class OutIt >
-void split( It begin, It end, const CharType * delim, OutIt out )
-{
-   split( begin, end, delim, delim + std::strlen( delim ), out );
-}
-
    -
    5. - -
  5. -

    -Usage -

    -
    -std::string ss( "word1 word2 word3" );
-std::vector< std::pair< std::string::const_iterator, std::string::const_iterator > > v;
-split( ss.begin(), ss.end(), " ", std::back_inserter( v ) );
-
-for ( int i = 0; i < v.size(); ++i )
-{
-   std::cout << std::string( v[ i ].first, v[ i ].second ) << std::endl;
-}
-// word1
-// word2
-// word3
-
    -
    6. - -
- -

[ -2010-01-22 Moved to Tentatively NAD Future after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Rationale:

-

-The LWG is not considering completely new features for standardization at this -time. We would like to revisit this good suggestion for a future TR and/or -standard. -

- - -

Proposed resolution:

-

-Add to the synopsis in 25.1 [algorithms.general]: -

- -
-template< class ForwardIterator1, class ForwardIterator2, class OutputIterator >
-  void split( ForwardIterator1 first, ForwardIterator1 last,
-              ForwardIterator2 delimiter_first, ForwardIterator2 delimiter_last,
-              OutputIterator result );
-
-template< class ForwardIterator1, class CharType, class OutputIterator >
-  void split( ForwardIterator1 first, ForwardIterator1 last,
-              const CharType * delimiters, OutputIterator result );
-
- -

-Add a new section [alg.split]: -

- -
-template< class ForwardIterator1, class ForwardIterator2, class OutputIterator >
-  void split( ForwardIterator1 first, ForwardIterator1 last,
-              ForwardIterator2 delimiter_first, ForwardIterator2 delimiter_last,
-              OutputIterator result );
-
- -
-

-1. Effects: splits the range [first, last) into parts, using any -element of [delimiter_first, delimiter_last) as a delimiter. Results -are pushed to output iterator in the form of std::pair<ForwardIterator1, -ForwardIterator1>. Each of these pairs specifies a maximal subrange of -[first, last) which does not contain a delimiter. -

-

-2. Returns: nothing. -

-

-3. Complexity: Exactly last - first assignments. -

-
- -
-template< class ForwardIterator1, class CharType, class OutputIterator >
-  void split( ForwardIterator1 first, ForwardIterator1 last,
-              const CharType * delimiters, OutputIterator result );
-
- -
-

-1. Effects: split the range [first, last) into parts, using any -element of delimiters (interpreted as zero-terminated string) as a -delimiter. Results are pushed to output iterator in the form of -std::pair<ForwardIterator1, ForwardIterator1>. Each of these -pairs specifies a maximal subrange of [first, last) which does not -contain a delimiter. -

-

-2. Returns: nothing. -

-

-3. Complexity: Exactly last - first assignments. -

-
- -
- - - - - -
-

1289. Generic casting requirements for smart pointers

-

Section: 20.2 [utility] Status: LEWG - Submitter: Ion Gaztañaga Opened: 2009-12-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In section 17.6.3.5 [allocator.requirements], Table 40 — Allocator requirements, -the following expression is required for allocator pointers: -

- -
- - - - - - - - - - - - - - -
Table 40 — Allocator requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Default
static_cast<X::pointer>(w)X::pointerstatic_cast<X::pointer>(w) == p 
-
- -

-To achieve this expression, a smart pointer writer must introduce an explicit -conversion operator from smart_ptr<void> to -smart_ptr<T> so that -static_cast<pointer>(void_ptr) is a valid expression. -Unfortunately this explicit conversion weakens the safety of a smart pointer -since the following expression (invalid for raw pointers) would become valid: -

- -
-smart_ptr<void> smart_v = ...;
-smart_ptr<T> smart_t(smart_v);
-
- -

-On the other hand, shared_ptr also defines its own casting functions in -20.8.2.2.9 [util.smartptr.shared.cast], and although it's unlikely that a -programmer will use shared_ptr as allocator::pointer, having -two different ways to do the same cast operation does not seem reasonable. A -possible solution would be to replace static_cast<X::pointer>(w) -expression with a user customizable (via ADL) -static_pointer_cast<value_type>(w), and establish the -xxx_pointer_cast functions introduced by shared_ptr as the -recommended generic casting utilities of the standard. -

- -

-Unfortunately, we've experienced problems in Boost when trying to establish -xxx_pointer_cast as customization points for generic libraries (http://objectmix.com/c/40424-adl-lookup-explicit-template-parameters.html) -because these casting functions are called with explicit template parameters and -the standard says in 14.8.1 [temp.arg.explicit] p.8 "Explicit template -argument specification": -

- -

-8 ...But when a function template with explicit template arguments is used, the -call does not have the correct syntactic form unless there is a function -template with that name visible at the point of the call. If no such name is -visible, the call is not syntactically well-formed and argument-dependent lookup -does not apply. -

- -

-So we can do this: -

- -
-template<class BasePtr>
-void generic_ptr_swap(BasePtr p)
-{
-  //ADL customization point
-  swap(p, p);
-  //...
-}
-
- -

-but not the following: -

- -
-template<class BasePtr>
-void generic_ptr_algo(BasePtr p)
-{
-  typedef std::pointer_traits<BasePtr>::template
-     rebind<Derived> DerivedPtr;
-  DerivedPtr dp = static_pointer_cast<Derived>(p);
-}
-
- -

-The solution to make static_pointer_cast a customization point is to -add a generic declaration (no definition) of static_pointer_cast in a -namespace (like std) and apply "using -std::static_pointer_cast" declaration to activate ADL: -

- -
-namespace std{
-
-template<typename U, typename T>
-unspecified
-static_pointer_cast(T&&) = delete;
-
-}
-
-template<class BasePtr>
-void generic_ptr_algo(BasePtr p)
-{
-  typedef std::pointer_traits<BasePtr>::template
-     rebind<Derived> DerivedPtr;
-
-  //ADL applies because static_pointer_cast is made
-  //  visible according to [temp.arg.explicit]/8
-  using std::static_pointer_cast;
-
-  DerivedPtr dp = static_pointer_cast<Derived>(p);
-
-  //...
-}
-
- -

-A complete solution will need also the definition of -static_pointer_cast for raw pointers, and this definition has been -present in Boost (http://www.boost.org/boost/ -pointer_cast.hpp) for years. -

- -

[ -2010-03-26 Daniel made editorial adjustments to the proposed wording. -]

- - -

[ -Moved to NAD Future at 2010-11 Batavia -]

- -

-This is a new feature rather than a defect. -It can be added later: "this is such a hairy area that people will put up with changes" -

- - - -

Proposed resolution:

-

-Add to section 20.2 [utility] Utility components, Header -<utility> synopsis: -

- -
-// 20.3.X, generic pointer cast functions
-
-template<typename U, typename T>
-unspecified
-static_pointer_cast(T&&) = delete;
-
-template<typename U, typename T>
-unspecified
-dynamic_pointer_cast(T&&) = delete;
-
-template<typename U, typename T>
-unspecified
-const_pointer_cast(T&&) = delete;
-
-//Overloads for raw pointers
-template<typename U, typename T>
-auto static_pointer_cast(T* t) -> decltype(static_cast<U*>(t));
-
-template<typename U, typename T>
-auto dynamic_pointer_cast(T* t) -> decltype(dynamic_cast<U*>(t));
-
-template<typename U, typename T>
-auto const_pointer_cast(T* t) -> decltype(const_cast<U*>(t));
-
- -

-Add to section 20.2 [utility] Utility components, a new subclause -20.3.X Pointer cast utilities [pointer.cast]: -

- -
-

-20.3.X Pointer cast utilities [pointer.cast] -

- -

-1 The library defines generic pointer casting function templates so that template code -can explicitly make these names visible and activate argument-dependent lookup -for pointer cast calls. -

- -
-//Generic declarations
-template<typename U, typename T>
-unspecified
-static_pointer_cast(T&&) = delete;
-
-template<typename U, typename T>
-unspecified
-dynamic_pointer_cast(T&&) = delete;
-
-template<typename U, typename T>
-unspecified
-const_pointer_cast(T&&) = delete;
-
- -

-2 The library also defines overloads of these functions for raw pointers. -

- -
-//Overloads for raw pointers
-template<typename U, typename T>
-auto static_pointer_cast(T* t) -> decltype(static_cast<U*>(t));
-
- -

-Returns: static_cast<U*>(t) -

- -
-template<typename U, typename T>
-auto dynamic_pointer_cast(T* t) -> decltype(dynamic_cast<U*>(t));
-
- -

-Returns: dynamic_cast<U*>(t) -

- -
-template<typename U, typename T>
-auto const_pointer_cast(T* t) -> decltype(const_cast<U*>(t));
-
- -

-Returns: const_cast<U*>(t) -

- -

-[Example: -

- -
-#include <utility> //static_pointer_cast
-#include <memory>  //pointer_traits
-
-class Base{};
-class Derived : public Base{};
-
-template<class BasePtr>
-void generic_pointer_code(BasePtr b)
-{
-   typedef std::pointer_traits<BasePtr>::template
-      rebind<Derived> DerivedPtr;
-
-   using std::static_pointer_cast;
-   //ADL applies now that static_pointer_cast is visible
-   DerivedPtr d = static_pointer_cast<Derived>(b);
-}
-
- -

-— end example] -

- -
- -

-Replace in section 17.6.3.5 [allocator.requirements] Table 40 — Allocator -requirements, the following table entries for allocator pointers: -

- -
- - - - - - - - - - - - - - - - - - - - - - - -
Table 40 — Allocator requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Default
static_pointer_cast<X::pointerT>(w)X::pointerstatic_pointer_cast<X::pointerT>(w) == p 
static_pointer_cast<X::const_pointerconst T>(w)X::const_pointerstatic_pointer_cast<X::const_pointerconst T>(z) == q 
-
- - - - - - -
-

1317. make_hash

-

Section: 20.9.13 [unord.hash] Status: LEWG - Submitter: Nicolai M. Josuttis Opened: 2010-02-10 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

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-

Discussion:

-

-Currently, the library lacks a convenient way to provide a hash function that -can be used with the provided unordered containers to allow the usage of non -trivial element types. -

- -

-While we can easily declare an -

- -
-std::unordered_set<int>
-
- -

-or -

- -
-std::unordered_set<std::string>
-
- -

-we have no easy way to declare an unordered_set for a user defined -type. IMO, this is a big obstacle to use unordered containers in practice. Note -that in Java, the wide usage of HashMap is based on the fact that there -is always a default hash function provided. -

- -

-Of course, a default hash function implies the risk to provide poor hash -functions. But often even poor hash functions are good enough. -

- -

-While I really would like to see a default hash function, I don't propose it -here because this would probably introduce a discussion that's too big for this -state of C++0x. -

- -

-However, I strongly suggest at least to provide a convenience variadic template -function make_hash<>() to allow an easy definition of a (possibly -poor) hash function. -

- -

-As a consequence for a user-defined type such as -

- -
-class Customer {
-   friend class CustomerHash;
-   private:
-     string firstname;
-     string lastname;
-     long   no;
-   ...
- };
-
- -

-would allow to specify: -

- -
-class CustomerHash : public std::unary_function<Customer, std::size_t>
-{
-  public:
-    std::size_t operator() (const Customer& c) const  {
-       return make_hash(c.firstname,c.lastname,c.no);
-    }
-};
-
- -

-instead of: -

- -
-class CustomerHash : public std::unary_function<Customer, std::size_t>
-{
-  public:
-    std::size_t operator() (const Customer& c) const  {
-       return std::hash<std::string>()(c.firstname) +
-              std::hash<std::string>()(c.lastname) +
-              std::hash<long>()(c.no);
-    }
-};
-
- -

-Note that, in principle, we can either specify that -

- -

-make_hash returns the sum of a call of -std::hash<T>()(x) for each argument x of type -T -

- -

-or we can specify that -

- -

-make_hash provides a hash value for each argument, for which a -std::hash() function is provided -

- -

-with the possible note that the hash value may be poor or only a good hash value -if the ranges of all passed arguments is equally distributed. -

- -

-For my convenience, I propose wording that describes -the concrete implementation. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial, rationale added below. -]

- - - - -

Rationale:

-

-There is no consensus to make this change at this time. -

- - -

Proposed resolution:

-

-In Function objects 20.9 [function.objects] -in paragraph 2 at the end of the Header <functional> synopsis -insert: -

- -
-// convenience functions
-template <class T>
-  size_t make_hash (const T&);
-template <class T, class... Types>
-  size_t make_hash (const T&, const Types&...);
-
- -

-In Class template hash 20.9.13 [unord.hash] -add: -

- -
-

-20.7.16.1 Hash creation functions [hash.creation] -

- -
-template <class T>
-  size_t make_hash (const T& val);
-
- -

-Returns: hash<T>()(val); -

- -
-template <class T, class... Types>
-  size_t make_hash (const T& val, const Types&... args);
-
- -

-Returns: hash<T>()(val) + std::make_hash(args...) -

- -
- - - - - - -
-

1320. Header for iter_swap

-

Section: 24.3 [iterator.synopsis] Status: LEWG - Submitter: Alisdair Meredith Opened: 2010-02-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The iter_swap function template appears in the -<algorithm> header, yet its main use is in building further -algorithms, not calling existing ones. The main clients are implementers of data -structures and their iterators, so it seems most appropriate to place the -template in the <iterator> header instead. -

- -

-Note that this is not an issue for implementers of the standard library, as they -rarely use the standard headers directly, designing a more fine-grained set of -headers for their own internal use. This option is not available to customers -of the standard library. -

- -

-Note that we cannot remove iter_swap from <algorithm> -without breaking code, but there is no reason we cannot offer the same -declaration via two standard headers. Alternatively, require -<algorithm> to #include <iterator>, but -introducing the dependency on the iterator adaptors seems un-necessary. -

- -

[ -]

- - -

-Discussed possibly moving to <utility> but don't like that. Some not seeing this -as a defect, and want to keep it in <algorithm>. No one seems to feel strongly -about moving to <iterator>. -

- - -

Proposed resolution:

- -

-Add the declaration of iter_swap to the <iterator> -header synopsis (24.3 [iterator.synopsis]), with a note that it is -documented in clause 25 [algorithms]. -

- -
-...
-template <class T, size_t N> T* end(T (&array)[N]);
-
-// documented in 25 [algorithms]
-template<class ForwardIterator1, class ForwardIterator2>
-  void iter_swap(ForwardIterator1 a, ForwardIterator2 b);
-
- - - - - - -
-

1396. regex should support allocators

-

Section: 28.8 [re.regex] Status: LEWG - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1451

-

Discussion:

-

Addresses US-104, US-141

-

-std::basic_regex should have an allocator for all the -reasons that a std::string does. For example, I can use -boost::interprocess to put a string or vector -in shared memory, but not a regex. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Add allocators to regexes -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3171 -would solve this issue. -

- -

[2011-03-22 Madrid]

- - -

Close 1396 as NAD Future.

- - -

Rationale:

No consensus for a change at this time

- -

Proposed resolution:

- - - - - -
-

1406. Support hashing smart-pointers based on owner

-

Section: 20.8.2.2 [util.smartptr.shared] Status: LEWG - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses JP-5

-

-Hash support based on ownership sharing should be -supplied for shared_ptr and weak_ptr. -For two shared_ptr objects p and q, two distinct -equivalence relations can be defined. One is based on -equivalence of pointer values, which is derived from the -expression p.get() == q.get() (hereafter called address based -equivalence relation), the other is based on -equivalence of ownership sharing, which is derived from -the expression !p.owner_before(q) && !q.owner_before(p) -(hereafter called ownership-based equivalence relation). -These two equivalence relations are independent in -general. For example, a shared_ptr object created by the -constructor of the signature shared_ptr(shared_ptr<U> -const &, T *) could reveal a difference between these two -relations. Therefore, hash support based on each -equivalence relation should be supplied for shared_ptr. -However, while the standard library provides the hash -support for address-based one (20.9.11.6 paragraph 2), it -lacks the hash support for ownership-based one. In -addition, associative containers work well in combination -with the shared_ptr's ownership-based comparison but -unordered associative containers don't. This is -inconsistent. -

-

-For the case of weak_ptr, hash support for the ownership based -equivalence relation can be safely defined on -weak_ptrs, and even on expired ones. The absence of -hash support for the ownership-based equivalence -relation is fatal, especially for expired weak_ptrs. And the -absence of such hash support precludes some quite -effective use-cases, e.g. erasing the unordered_map entry -of an expired weak_ptr key from a customized deleter -supplied to shared_ptrs. -

-

-Hash support for the ownership-based equivalence -relation cannot be provided by any user-defined manner -because information about ownership sharing is not -available to users at all. Therefore, the only way to provide -ownership-based hash support is to offer it intrusively by -the standard library. -

-

-As far as we know, such hash support is implementable. -Typical implementation of such hash function could return -the hash value of the pointer of the counter object that is -internally managed by shared_ptr and weak_ptr. -

- -

[2010 Rapperswil:]

- -
-

No consensus to make this change at this time.

-
- - -

Proposed resolution:

-

-Add the following non-static member functions to -shared_ptr and weak_ptr class template; -

-

-Update [util.smartptr.shared], 20.9.11.2 paragraph 1 -

-
-namespace std{
-template<class T> class shared_ptr {
-public:
-...
-  size_t owner_hash() const;
-...
-};
-}
-
-

-Update [util.smartptr.weak], 20.9.11.3 paragraph 1 -

-
-namespace std{
-template<class T> class weak_ptr {
-public:
-...
-  size_t owner_hash() const;
-...
-};
-}
-
-

-These functions satisfy the following -requirements. Let p and q be objects of either -shared_ptr or weak_ptr, H be a hypothetical -function object type that satisfies the hash -requirements ([hash.requirements], 20.2.4) and h be an object of the -type H. The expression p.owner_hash() behaves -as if it were equivalent to the expression h(p). In -addition, h(p) == h(q) must become true if p and -q share ownership. -

- - - - - -
-

1422. vector<bool> iterators are not random access

-

Section: 23.3.7 [vector.bool] Status: LEWG - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-118

-

-vector<bool> iterators are not random access iterators -because their reference type is a special class, and not -bool &. All standard libary operations taking iterators -should treat this iterator as if it was a random access iterator, rather -than a simple input iterator. -

- -

[ -Resolution proposed in ballot comment -]

- -

-Either revise the iterator requirements to support proxy iterators -(restoring functionality that was lost when the Concept facility was -removed) or add an extra paragraph to the vector<bool> -specification requiring the library to treat vector<bool> -iterators as-if they were random access iterators, despite having the wrong -reference type. -

- -

[ -Rapperswil Review -]

- -

-The consensus at Rapperswil is that it is too late for full support for -proxy iterators, but requiring the library to respect vector<bool> -iterators as-if they were random access would be preferable to flagging -this container as deliberately incompatible with standard library algorithms. -

-

-Alisdair to write the note, which may become normative Remark depending -on the preferences of the project editor. -

- -

[ -Post-Rapperswil Alisdair provides wording -]

- -

-Initial wording is supplied, deliberately using Note in preference to -Remark although the author notes his preference for Remark. The -issue of whether iterator_traits<vector<bool>>::iterator_category -is permitted to report random_access_iterator_tag or must report -input_iterator_tag is not addressed. -

- -

[ -Old Proposed Resolution: -]

- -
-

-Insert a new paragraph into 23.3.7 [vector.bool] between p4 and p5: -

-

-[Note All functions in the library that take a pair of iterators to -denote a range shall treat vector<bool> iterators as-if they were -random access iterators, even though the reference type is not a -true reference.-- end note] -

-
- -

[ -2010-11 Batavia: -]

- -

-Closed as NAD Future, because the current iterator categories cannot correctly describe -vector<bool>::iterator. But saying that they are Random Access Iterators -is also incorrect, because it is not too hard to create a corresponding test that fails. -We should deal with the more general proxy iterator problem in the future, and see no -benefit to take a partial workaround specific to vector<bool> now. -

- - - -

Proposed resolution:

- - -

Rationale:

-

-No consensus to make this change at this time. -

- - - - - -
-

1459. Overlapping evaluations are allowed

-

Section: 29.3 [atomics.order] Status: LEWG - Submitter: Canada Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 1458

-

Discussion:

-

Addresses CA-21, GB-131

-

-29.4 [atomics.lockfree] p.8 states: -

-

-An atomic store shall only store a value that has -been computed from constants and program input values -by a finite sequence of program evaluations, such -that each evaluation observes the values of variables -as computed by the last prior assignment in the -sequence. -

-

-... but 1.9 [intro.execution] p.13 states: -

-

-If A is not sequenced before B and B is not -sequenced before A, then A and B are unsequenced. -[ Note: The execution of unsequenced -evaluations can overlap. — end note ] -

-

-Overlapping executions can make it impossible to -construct the sequence described in 29.4 [atomics.lockfree] p.8. We are not -sure of the intention here and do not offer a suggestion for -change, but note that 29.4 [atomics.lockfree] p.8 is the condition that prevents -out-of-thin-air reads. -

-

-For an example, suppose we have a function invocation -f(e1,e2). The evaluations of e1 and e2 can overlap. -Suppose that the evaluation of e1 writes y and reads x -whereas the evaluation of e2 reads y and writes x, with -reads-from edges as below (all this is within a single -thread). -

-
- e1           e2
-Wrlx y--   --Wrlx x
-      rf\ /rf
-         X
-        / \
-Rrlx x<-   ->Rrlx y
-
-

-This seems like it should be allowed, but there seems to -be no way to produce a sequence of evaluations with the -property above. -

-

-In more detail, here the two evaluations, e1 and e2, are -being executed as the arguments of a function and are -consequently not sequenced-before each other. In -practice we'd expect that they could overlap (as allowed -by 1.9 [intro.execution] p.13), with the two writes taking effect before the two -reads. However, if we have to construct a linear order of -evaluations, as in 29.4 [atomics.lockfree] p.8, then the execution above is not -permited. Is that really intended? -

- -

[ -Resolution proposed by ballot comment -]

- -

-Please clarify. -

- -

[2011-03-09 Hans comments:]

- - -

I'm not proud of 29.3 [atomics.order] p9 (formerly p8), and I agree with the comments that this -isn't entirely satisfactory. 29.3 [atomics.order] p9 was designed to preclude -out-of-thin-air results for races among memory_order_relaxed atomics, in spite of -the fact that Java experience has shown we don't really know how to do that adequately. In -the long run, we probably want to revisit this. -

-However, in the short term, I'm still inclined to declare this NAD, for two separate reasons: -

- -
    -

  1. 1.9 [intro.execution] p15 states: "If a side effect on a scalar -object is unsequenced relative to either another side -effect on the same scalar object or a value computation -using the value of the same scalar object, the behavior is undefined." -I think the examples presented here have undefined behavior as a result. -It's not completely clear to me whether examples can be constructed -that exhibit this problem, and don't have undefined behavior.

    2. - -

  2. This comment seems to be using a different meaning of "evaluation" -from what is used elsewhere in the standard. The sequence of evaluations -here doesn't have to consist of full expression evaluations. They -can be evaluations of operations like lvalue to rvalue conversion, -or individual assignments. In particular, the reads and writes -executed by e1 and e2 in the example could be treated as separate -evaluations for purposes of producing the sequence. -The definition of "sequenced before" in 1.9 [intro.execution] makes -little sense if the term "evaluation" is restricted to any notion -of complete expression. Perhaps we should add yet another note -to clarify this? 29.3 [atomics.order] p10 probably leads to -the wrong impression here. -

    -An alternative resolution would be to simply delete our flakey -attempt at preventing out-of-thin-air reads, by removing 29.3 [atomics.order] p9-11, -possibly adding a note that explains that we technically allow, -but strongly discourage them. If we were starting this from scratch -now, that would probably be my preference. But it seems like too drastic -a resolution at this stage. -

    3. -
- -

[2011-03-24 Madrid]

- -

-Moved to NAD Future -

- - - -

Proposed resolution:

- - - - - -
-

1484. Need a way to join a thread with a timeout

-

Section: 30.3.1 [thread.thread.class] Status: LEWG - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses US-183

- -

-There is no way to join a thread with a timeout. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add join_for and join_until. Or decide one should -never join a thread with a timeout since pthread_join doesn't have a -timeout version. -

- -

[ -2010 Batavia -]

- -

-The concurrency working group deemed this an extension beyond the scope of C++0x. -

-

Rationale:

The LWG does not wish to make a change at this time.

- - - -

Proposed resolution:

- - - - - -
-

1488. Improve interoperability between the C++0x and C1x threads APIs

-

Section: 30.4 [thread.mutex] Status: LEWG - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-185

- -

-Cooperate with WG14 to improve interoperability between -the C++0x and C1x threads APIs. In particular, C1x -mutexes should be conveniently usable with a C++0x -lock_guard. Performance overheads for this combination -should be considered. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Remove C++0x timed_mutex and -timed_recursive_mutex if that facilitates -development of more compatible APIs. -

- -

[ -2010 Batavia -]

- -

-The concurrency sub-group reviewed the options, and decided that closer harmony should wait until both standards are published. -

- -

Rationale:

-

-The LWG does not wish to make any change at this time. -

- - - - -

Proposed resolution:

- - - - - -
-

1493. Add mutex, recursive_mutex, is_locked function

-

Section: 30.4.1 [thread.mutex.requirements] Status: LEWG - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-189

- -

-mutex and recursive_mutex should have an is_locked() -member function. is_locked allows a user to test a lock -without acquiring it and can be used to implement a lightweight -try_try_lock. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add a member function: -

-
-bool is_locked() const;
-
-

-to std::mutex and std::recursive_mutex. These -functions return true if the current thread would -not be able to obtain a mutex. These functions do -not synchronize with anything (and, thus, can -avoid a memory fence). -

- -

[ -2010 Batavia -]

- -

-The Concurrency subgroup reviewed this issue and deemed it to be an extension to be handled after publishing C++0x. -

- -

Rationale:

The LWG does not wish to make a change at this time.

- - - -

Proposed resolution:

- - - - - -
-

1499. Condition variables preclude wakeup optimization

-

Section: 30.5 [thread.condition] Status: LEWG - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-193

- -

-Condition variables preclude a wakeup optimization. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Change condition_variable to allow such -optimization. See Appendix 1 - Additional Details -

- -

[ -2010 Batavia -]

- -

-The Concurrency subgroup reviewed the issue, and deemed it an extension to be handled after C++0x. -

- -

Rationale:

The LWG does not wish to make the change at this time.

- - - -

Proposed resolution:

- - - - - -
-

1521. Requirements on internal pointer representations in containers

-

Section: 23.2.1 [container.requirements.general] Status: LEWG - Submitter: Mike Spertus Opened: 2010-10-16 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-104, US-141

- -

-The standard doesn't say that containers should use abstract pointer -types internally. Both Howard and Pablo agree that this is the intent. -Further, it is necessary for containers to be stored, for example, in -shared memory with an interprocess allocator (the type of scenario that -allocators are intended to support). -

-

-In spite of the (possible) agreement on intent, it is necessary to make -this explicit: -

-

-An implementations may like to store the result of dereferencing the -pointer (which is a raw reference) as an optimization, but that prevents -the data structure from being put in shared memory, etc. In fact, a -container could store raw references to the allocator, which would be a -little weird but conforming as long as it has one by-value copy. -Furthermore, pointers to locales, ctypes, etc. may be there, which also -prevents the data structure from being put in shared memory, so we -should make explicit that a container does not store raw pointers or -references at all. -

- -

[ -Pre-batavia -]

- -

-This issue is being opened as part of the response to NB comments US-104/141. -See paper N3171 -in the pre-Batavia mailing. -

- -

[2011-03-23 Madrid meeting]

- - -

Deferred

- -

[ -2011 Batavia -]

- - -

-This may be an issue, but it is not clear. We want to gain a few years experience -with the C++11 allocator model to see if this is already implied by the existing -specification. -

- - - -

Proposed resolution:

-

-Add to the end of 23.2.1 [container.requirements.general] p. 8: -

-

-[..] In all container types defined in this Clause, the member get_allocator() returns -a copy of the allocator used to construct the container or, if that allocator has been replaced, -a copy of the most recent replacement. The container may not store internal objects whose -types are of the form T * or T & except insofar as they are part of the -item type or members. -

- - - - - -
-

2035. Output iterator requirements are broken

-

Section: 24.2.4 [output.iterators] Status: Open - Submitter: Daniel Krügler Opened: 2011-02-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

During the Pittsburgh meeting the proposal N3066 -became accepted because it fixed several severe issues related to the iterator specification. But the current working draft (N3225) -does not reflect all these changes. Since I'm unaware whether every correction can be done editorial, this issue is submitted to take -care of that. To give one example: All expressions of Table 108 — "Output iterator requirements" have a post-condition -that the iterator is incrementable. This is impossible, because it would exclude any finite sequence that is accessed by an output -iterator, such as a pointer to a C array. The N3066 wording changes did not have these effects. -

- -

[2011-03-01: Daniel comments:]

- - -

This issue has some overlap with the issue 2038 and I would prefer if we -could solve both at one location. I suggest the following approach: -

-
    -

  1. The terms dereferencable and incrementable could be defined in a more -general way not restricted to iterators (similar to the concepts HasDereference and -HasPreincrement from working draft N2914). But on the other hand, all current usages of -dereferencable and incrementable are involved with types that satisfy -iterator requirements. Thus, I believe that it is sufficient for C++0x to add corresponding definitions to -24.2.1 [iterator.requirements.general] and to let all previous usages of these terms refer to this -sub-clause. Since the same problem occurs with the past-the-end iterator, this proposal suggest providing -similar references to usages that precede its definition as well. -

    2. -

  2. We also need to ensure that all iterator expressions get either an operational semantics in -terms of others or we need to add missing pre- and post-conditions. E.g. we have the following -ones without semantics: -

    -*r++ = o // output iterator
-*r--     // bidirectional iterator
-

    -According to the SGI specification -these correspond to -

    -{ *r = o; ++r; }                         // output iterator
-{ reference tmp = *r; --r; return tmp; } // bidirectional iterator
-

    -respectively. Please note especially the latter expression for bidirectional iterator. It fixes a problem -that we have for forward iterator as well: Both these iterator categories provide stronger guarantees -than input iterator, because the result of the dereference operation is reference, and not -only convertible to the value type (The exact form from the SGI documentation does not correctly refer to -reference). -

    3. -
- -

[2011-03-14: Daniel comments and updates the suggested wording]

- - -

In addition to the before mentioned necessary changes there is another one need, which -became obvious due to issue 2042: forward_list<>::before_begin() returns -an iterator value which is not dereferencable, but obviously the intention is that it should -be incrementable. This leads to the conclusion that imposing dereferencable as a requirement -for the expressions ++r is wrong: We only need the iterator to be incrementable. A -similar conclusion applies to the expression --r of bidirectional iterators.

- -

[ -2011 Bloomington -]

- - -

-Consensus this is the correct direction, but there are (potentially) missing incrementable -preconditions on some table rows, and the Remarks on when an output iterator becomes dereferencable -are probably better handled outside the table, in a manner similar to the way we word for input -iterators. -

- -

-There was some concern about redundant pre-conditions when the operational semantic is defined in -terms of operations that have preconditions, and a similar level of concern over dropping such -redundancies vs. applying a consistent level of redundant specification in all the iterator tables. -Wording clean-up in either direction would be welcome. -

- -

[2011-08-18: Daniel adapts the proposed resolution to honor the Bloomington request]

- - -

-There is only a small number of further changes suggested to get rid of superfluous -requirements and essentially non-normative assertions. Operations should not have extra -pre-conditions, if defined by "in-terms-of" semantics, see e.g. a != b or a->m -for Table 107. Further, some remarks, that do not impose anything or say nothing new have been removed, -because I could not find anything helpful they provide. -E.g. consider the remarks for Table 108 for the operations dereference-assignment and -preincrement: They don't provide additional information say nothing surprising. With the -new pre-conditions and post-conditions it is implied what the remarks intend to say. -

- -

[ -2011-11-03: Some observations from Alexander Stepanov via c++std-lib-31405 -]

- - -

-The following sentence is dropped from the standard section on OutputIterators: -

-"In particular, the following two conditions should hold: first, any -iterator value should be assigned through before it is incremented -(this is, for an output iterator i, i++; i++; is not a valid code -sequence); second, any value of an output iterator may have at most -one active copy at any given time (for example, i = j; *++i = a; *j = b; -is not a valid code sequence)." -

- -

[ -2011-11-04: Daniel comments and improves the wording -]

- - -

-In regard to the first part of the comment, the intention of the newly proposed wording -was to make clear that for the expression -

-
-*r = o
-
-

-we have the precondition dereferenceable and the post-condition -incrementable. And for the expression -

-
-++r
-
-

-we have the precondition incrementable and the post-condition dereferenceable -or past-the-end. This should not allow for a sequence like i++; i++; -but I agree that it doesn't exactly say that. -

-In regard to the second point: To make this point clearer, I suggest to -add a similar additional wording as we already have for input iterator to the -"Assertion/note" column of the expression ++r: -

-"Post: any copies of the previous value of r are no longer -required to be dereferenceable or incrementable." -

-The proposed has been updated to honor the observations of Alexander Stepanov. -

- -

[2015-02 Cologne]

- -

-The matter is complicated, Daniel volunteers to write a paper. -

- - - -

Proposed resolution:

-
    -

  1. Add a reference to 24.2.1 [iterator.requirements.general] to the following parts of the -library preceding Clause 24 Iterators library: (I stopped from 23.2.5 [unord.req] on, because -the remaining references are the concrete containers)

    -
      -

    1. 17.6.3.2 [swappable.requirements] p5:

      - -

      --5- A type X satisfying any of the iterator requirements (24.2) is ValueSwappable if, -for any dereferenceable (24.2.1 [iterator.requirements.general]) object x of type -X, *x is swappable. -

      -
      2. - -

    2. 17.6.3.5 [allocator.requirements], Table 27 — "Descriptive variable definitions", -row with the expression c:

      - -

      -a dereferenceable (24.2.1 [iterator.requirements.general]) pointer of type C* -

      - -
      3. - -

    3. 20.7.3.2 [pointer.traits.functions]:

      -

      -Returns: The first template function returns a dereferenceable (24.2.1 [iterator.requirements.general]) -pointer to r obtained by calling Ptr::pointer_to(r); […] -

      -
      4. - -

    4. 21.4.3 [string.iterators] p. 2:

      -

      -Returns: An iterator which is the past-the-end value (24.2.1 [iterator.requirements.general]). -

      -
      5. - -

    5. 22.4.5.1.2 [locale.time.get.virtuals] p. 11:

      -
      -iter_type do_get(iter_type s, iter_type end, ios_base& f,
-  ios_base::iostate& err, tm *t, char format, char modifier) const;
-

      -Requires: t shall be dereferenceable (24.2.1 [iterator.requirements.general]). -

      -
      6. - -

    6. 23.2.1 [container.requirements.general] p. 6:

      - -

      -[…] end() returns an iterator which is the past-the-end (24.2.1 [iterator.requirements.general]) -value for the container. […] -

      -
      7. - -

    7. 23.2.3 [sequence.reqmts] p. 3:

      - -

      -[…] q denotes a valid dereferenceable (24.2.1 [iterator.requirements.general]) -const iterator to a, […] -

      -
      8. - -

    8. 23.2.4 [associative.reqmts] p. 8 (I omit intentionally one further reference in the same sub-clause):

      - -

      -[…] q denotes a valid dereferenceable (24.2.1 [iterator.requirements.general]) -const iterator to a, […] -

      -
      9. - -

    9. 23.2.5 [unord.req] p. 10 (I omit intentionally one further reference in the same sub-clause):

      - -

      -[…] q and q1 are valid dereferenceable (24.2.1 [iterator.requirements.general]) -const iterators to a, […] -

      -
      10. -
    - -
    2. -

  2. Edit 24.2.1 [iterator.requirements.general] p. 5 as indicated (The intent is to properly define -incrementable and to ensure some further library guarantee related to past-the-end iterator values):

    - -

    --5- Just as a regular pointer to an array guarantees that there is a pointer value pointing past the last element -of the array, so for any iterator type there is an iterator value that points past the last element of a -corresponding sequence. These values are called past-the-end values. Values of an iterator i for which the -expression *i is defined are called dereferenceable. Values of an iterator i for which the -expression ++i is defined are called incrementable. The library never assumes that -past-the-end values are dereferenceable or incrementable. Iterators can also have singular values -that are not associated with any sequence. […] -

    -
    3. - -

  3. Modify the column contents of Table 106 — "Iterator requirements", -24.2.2 [iterator.iterators], as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 106 — Iterator requirements
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    *rreference pre: r is dereferenceable.
    ++rX& pre: r is incrementable.
    -
    -
    4. - -

  4. Modify the column contents of Table 107 — "Input iterator requirements", -24.2.3 [input.iterators], as indicated [Rationale: The wording changes attempt -to define a minimal "independent" set of operations, namely *a and ++r, and -to specify the semantics of the remaining ones. This approach seems to be in agreement with the -original SGI specification -— end rationale]:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 107 — Input iterator requirements (in addition to Iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    a != bcontextually
    -convertible to bool    		!(a == b)pre: (a, b) is in the domain
    -of ==.     -
    *aconvertible to T pre: a is dereferenceable.
    -The expression
    -(void)*a, *a is equivalent
    -to *a.
    -If a == b and (a,b) is in
    -the domain of == then *a is
    -equivalent to *b. -
    a->m (*a).mpre: a is dereferenceable.
    ++rX& pre: r is dereferenceableincrementable.
    -post: r is dereferenceable or
    -r is past-the-end.
    -post: any copies of the
    -previous value of r are no
    -longer required either to be
    -dereferenceable, incrementable,
    -or to be in the domain of ==. -
    (void)r++ (void)++requivalent to (void)++r
    *r++convertible to T{ T tmp = *r;
    -++r;
    -return tmp; } -    		 
    -
    -
    5. - -
  5. -

    Modify the column contents of Table 108 — "Output iterator requirements", -24.2.4 [output.iterators], as indicated [Rationale: The wording changes attempt -to define a minimal "independent" set of operations, namely *r = o and ++r, -and to specify the semantics of the remaining ones. This approach seems to be in agreement with -the original SGI specification -— end rationale]:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 108 — Output iterator requirements (in addition to Iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    *r = oresult is not used pre: r is dereferenceable.
    -Remark: After this operation
    -r is not required to be
    -dereferenceable and any copies of
    -the previous value of r are no
    -longer required to be dereferenceable
    -or incrementable.
    -post: r is incrementable. -
    ++rX& pre: r is incrementable.
    -&r == &++r.
    -Remark: After this operation
    -r is not required to be
    -dereferenceable.
     -Remark: After this operation
    -r is not required to be
    -incrementable and any copies of
    -the previous value of r are no
    -longer required to be dereferenceable
    -or incrementable.
    -post: r is dereferenceable
    -or r is past-the-end    incrementable.
    -
    r++convertible to const X&{ X tmp = r;
    - ++r;
    - return tmp; }     -    		Remark: After this operation
    -r is not required to be
    -dereferenceable.
    -post: r is incrementable.     -
    *r++ = oresult is not used{ *r = o; ++r; }Remark: After this operation
    -r is not required to be
    -dereferenceable.
    -post: r is incrementable.     -
    -
    -
    6. - -

  6. Modify the column contents of Table 109 — "Forward iterator requirements", -24.2.5 [forward.iterators], as indicated [Rationale: Since the return type of the -expression *r++ is now guaranteed to be type reference, the implied operational -semantics from input iterator based on value copies is wrong — end rationale]

    - -
    - - - - - - - - - - - - - - - - - - - - - - - -
    Table 109 — Forward iterator requirements (in addition to input iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    r++convertible to const X&{ X tmp = r;
    - ++r;
    - return tmp; }     -    		 
    *r++reference{ reference tmp = *r;
    - ++r;
    - return tmp; }    		 
    -
    - -
    7. - -

  7. Modify the column contents of Table 110 — "Bidirectional iterator requirements", -24.2.6 [bidirectional.iterators], as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 110 — Bidirectional iterator requirements (in addition to forward iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    --rX& pre: there exists s such that
    -r == ++s.
    -post: r is dereferenceableincrementable.
    ---(++r) == r.
    ---r == --s implies r == s.
    -&r == &--r. -
    r--convertible to const X&{ X tmp = r;
    - --r;
    - return tmp; }     -    		 
    *r--reference{ reference tmp = *r;
    - --r;
    - return tmp; }    		 
    -
    -
    8. -
- - - - - -
-

2038. Missing definition for incrementable iterator

-

Section: 24.2.4 [output.iterators] Status: Open - Submitter: Pete Becker Opened: 2011-02-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

In comp.lang.c++, Vicente Botet raises the following questions:

- -

-"In "24.2.4 Output iterators" there are 3 uses of incrementable. I've -not found the definition. Could some one point me where it is defined? -

-Something similar occurs with dereferenceable. While the definition is -given in "24.2.1 In general" it is used several times before. -

-Shouldn't these definitions be moved to some previous section?" -

- -

He's right: both terms are used without being properly defined. -

-There is no definition of "incrementable". -

-While there is a definition of "dereferenceable", it is, in fact, a definition of -"dereferenceable iterator". "dereferenceable" is used throughout Clause 23 (Containers) -before its definition in Clause 24. In almost all cases it's referring to iterators, -but in 17.6.3.2 [swappable.requirements] there is a mention of "dereferenceable object"; in -17.6.3.5 [allocator.requirements] the table of Descriptive variable definitions refers to a -"dereferenceable pointer"; 20.7.3.2 [pointer.traits.functions] refers to a -"dereferenceable pointer"; in 22.4.5.1.2 [locale.time.get.virtuals]/11 (do_get) -there is a requirement that a pointer "shall be dereferenceable". In those specific cases -it is not defined. -

- -

[2011-03-02: Daniel comments:]

- - -

I believe that the currently proposed resolution of issue 2035 solves this -issue as well.

- -

[ -2011 Bloomington -]

- - -

-Agree with Daniel, this will be handled by the resolution of 2035. -

- - - -

Proposed resolution:

-

- - - - - -
-

2040. Missing type traits related to is_convertible

-

Section: 20.10 [meta] Status: LEWG - Submitter: Daniel Krügler Opened: 2011-03-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

When n3142 -was suggested, it concentrated on constructions, assignments, and destructions, but overlooked -to complement the single remaining compiler-support trait

- -
-template <class From, class To> struct is_convertible;
-
- -

with the no-throw and triviality related aspects as it had been done with the other -expression-based traits. Specifically, the current specification misses to add the -following traits: -

- -
-template <class From, class To> struct is_nothrow_convertible;
-template <class From, class To> struct is_trivially_convertible;
-
- -

In particular the lack of is_nothrow_convertible is severly restricting. This -was recently recognized when the proposal for decay_copy was prepared by -n3255. -There does not exist a portable means to define the correct conditional noexcept -specification for the decay_copy function template, which is declared as:

- -
-template <class T> 
-typename decay<T>::type decay_copy(T&& v) noexcept(???);
-
- -

The semantics of decay_copy bases on an implicit conversion which again -influences the overload set of functions that are viable here. In most circumstances -this will have the same effect as comparing against the trait -std::is_nothrow_move_constructible, but there is no guarantee for that being -the right answer. It is possible to construct examples, where this would lead -to the false result, e.g.

- -
-struct S {
-  S(const S&) noexcept(false);
- 
-  template<class T>
-  explicit S(T&&) noexcept(true);
-};
-
- -

std::is_nothrow_move_constructible will properly honor the explicit template -constructor because of the direct-initialization context which is part of the -std::is_constructible definition and will in this case select it, such that -std::is_nothrow_move_constructible<S>::value == true, but if we had -the traits is_nothrow_convertible, is_nothrow_convertible<S, S>::value -would evaluate to false, because it would use the copy-initialization context -that is part of the is_convertible definition, excluding any explicit -constructors and giving the opposite result.

- -

The decay_copy example is surely not one of the most convincing examples, but -is_nothrow_convertible has several use-cases, and can e.g. be used to express -whether calling the following implicit conversion function could throw an exception or not:

- -
-template<class T, class U>
-T implicit_cast(U&& u) noexcept(is_nothrow_convertible<U, T>::value) 
-{
-  return std::forward<U>(u);
-}
-
- -

Therefore I suggest to add the missing trait is_nothrow_convertible and for -completeness also the missing trait is_trivially_convertible to 20.10 [meta].

- -

[2011-03-24 Madrid meeting]

- - -

-Daniel K: This is a new feature so out of scope. -

-Pablo: Any objections to moving 2040 to Open? -

-No objections. -

- -

[Bloomington, 2011]

- -

-Move to NAD Future, this would be an extension to existing functionality. -

- - - -

Proposed resolution:

-
    -

  1. Ammend the following declarations to the header <type_traits> synopsis -in 20.10.2 [meta.type.synop]:

    - -
    -namespace std {
-  …
-  // 20.9.6, type relations:
-  template <class T, class U> struct is_same;
-  template <class Base, class Derived> struct is_base_of;
-  template <class From, class To> struct is_convertible;
-  template <class From, class To> struct is_trivially_convertible;
-  template <class From, class To> struct is_nothrow_convertible;
-
-  …
-}
-
    -
    2. - -

  2. Modify Table 51 — "Type relationship predicates" as indicated. The removal of the -remaining traces of the trait is_explicitly_convertible is an editorial -step, it was removed by n3047: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 51 — Type relationship predicates
    TemplateConditionComments
    …
    template <class From, class To>
    -struct is_convertible;    		see belowFrom and To shall be complete
    -types, arrays of unknown bound, or
    -(possibly cv-qualified) void
    -types.
    template <class From, class To>
    -struct is_explicitly_convertible;    		is_constructible<To, From>::valuea synonym for a two-argument
    -version of is_constructible.
    -An implementation may define it
    -as an alias template.
    template <class From, class To>
    -struct is_trivially_convertible;    		is_convertible<From,
    - To>::value     is true and the
    -conversion, as defined by
    -is_convertible, is known
    -to call no operation that is
    -not trivial ([basic.types], [special]).    		From and To shall be complete
    -types, arrays of unknown bound,
    -or (possibly cv-qualified) void
    -types.
    template <class From, class To>
    -struct is_nothrow_convertible;    		is_convertible<From,
    - To>::value     is true and the
    -conversion, as defined by
    -is_convertible, is known
    -not to throw any
    -exceptions ([expr.unary.noexcept]).    		From and To shall be complete
    -types, arrays of unknown bound,
    -or (possibly cv-qualified) void
    -types.
    …
    -
    - -
    3. -
- - - - - -
-

2051. Explicit tuple constructors for more than one parameter

-

Section: 20.4.2 [tuple.tuple], 20.4.2.1 [tuple.cnstr] Status: Open - Submitter: Ville Voutilainen Opened: 2011-05-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-One of my constituents wrote the following: -

--------snip------------ -

-So far the only use I've found for std::tuple is as an ad-hoc type to emulate -multiple return values. If the tuple ctor was made non-explicit one could -almost think C++ supported multiple return values especially when combined -with std::tie(). -

-
-// assume types line_segment and point
-// assume function double distance(point const&, point const&)
-
-std::tuple<point, point>
-closest_points(line_segment const& a, line_segment const& b) {
- point ax;
- point bx;
- /* some math */
-
- return {ax, bx};
-}
-
-
-double
-distance(line_segment const& a, line_segment const& b) {
- point ax;
- point bx;
- std::tie(ax, bx) = closest_points(a, b);
-
- return distance(ax, bx);
-}
-
-

--------snap---------- -

-See also the messages starting from lib-29330. -

-Some notes: -

-
    -
  1. pair allows such a return
    2. -
  2. a lambda with a deduced return type doesn't allow it for any type
    3. -
  3. decltype refuses {1, 2}
    4. -
-

-I would recommend making non-unary tuple constructors non-explicit. -

- -

[Bloomington, 2011]

- -

-Move to NAD Future, this would be an extension to existing functionality. -

- -

[Portland, 2012]

- -

-Move to Open at the request of the Evolution Working Group. -

- - - -

Proposed resolution:

- - - - - -
-

2055. std::move in std::accumulate and other algorithms

-

Section: 26.7 [numeric.ops] Status: LEWG - Submitter: Chris Jefferson Opened: 2011-01-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The C++0x draft says std::accumulate uses: acc = binary_op(acc, *i). -

-Eelis van der Weegen has pointed out, on the libstdc++ mailing list, that using -acc = binary_op(std::move(acc), *i) can lead to massive improvements (particularly, -it means accumulating strings is linear rather than quadratic). -

-Consider the simple case, accumulating a bunch of strings of length 1 (the same argument holds for other length buffers). -For strings s and t, s+t takes time length(s)+length(t), as you have to copy -both s and t into a new buffer. -

-So in accumulating n strings, step i adds a string of length i-1 to a string of length -1, so takes time i. -

-Therefore the total time taken is: 1+2+3+...+n = O(n2) -

-std::move(s)+t, for a "good" implementation, is amortized time length(t), like vector, -just copy t onto the end of the buffer. So the total time taken is: -

-1+1+1+...+1 (n times) = O(n). This is the same as push_back on a vector. -

-I'm trying to decide if this implementation might already be allowed. I suspect it might not -be (although I can't imagine any sensible code it would break). There are other algorithms -which could benefit similarly (inner_product, partial_sum and -adjacent_difference are the most obvious). -

-Is there any general wording for "you can use rvalues of temporaries"? -

-The reflector discussion starting with message c++std-lib-29763 came to the conclusion -that above example is not covered by the "as-if" rules and that enabling this behaviour -would seem quite useful. -

- -

[ -2011 Bloomington -]

- - -

-Moved to NAD Future. This would be a larger change than we would consider for a simple TC. -

- - - -

Proposed resolution:

- - - - - -
-

2062. Effect contradictions w/o no-throw guarantee of std::function swaps

-

Section: 20.9.12.2 [func.wrap.func], 20.9.12.2.2 [func.wrap.func.mod] Status: Open - Submitter: Daniel Krügler Opened: 2011-05-28 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Howard Hinnant observed in reflector message c++std-lib-30841 that 20.9.12.2 [func.wrap.func] -makes the member swap noexcept, even though the non-member swap is not noexcept. -

-The latter was an outcome of the discussions during the Batavia meeting and the Madrid meeting -involving LWG 1349, which seems to indicate that the remaining noexcept -specifier at the member swap is incorrect and should be removed. -

-But if we allow for a potentially throwing member swap of std::function, this causes -another conflict with the exception specification for the following member function: -

-
-template<class F> function& operator=(reference_wrapper<F> f) noexcept;
-

-Effects: function(f).swap(*this); -

-
-

-Note that in this example the sub-expression function(f) does not cause any problems, -because of the nothrow-guarantee given in 20.9.12.2.1 [func.wrap.func.con] p. 10. The problem -is located in the usage of the swap which could potentially throw given the general latitude. -

-So, either the Madrid meeting decision need to be revised (and both member and free swap of -std::function should be noexcept), or this function needs to be adapted as well, -e.g. by taking the exception-specification away or by changing the semantics. -

-One argument for "swap-may-throw" would be to allow for small-object optimization techniques -where the copy of the target may throw. But given the fact that the swap function has been guaranteed -to be "Throws: Nothing" from TR1 on, it seems to me that that there would still be opportunities to -perform small-object optimizations just restricted to the set of target copies that cannot throw. -

-In my opinion member swap of std::function has always been intended to be no-throw, because -otherwise there would be no good technical reason to specify the effects of several member -functions in terms of the "construct-swap" idiom (There are three functions that are defined -this way), which provides the strong exception safety in this case. I suggest to enforce that both -member swap and non-member swap of std::function are nothrow functions as it had been guaranteed -since TR1 on. -

- -

[ -2011 Bloomington -]

- -

-Dietmar: May not be swappable in the first place. -

-

-Alisdair: This is wide contact. Then we should be taking noexcept off instead of putting it on. This is preferred resolution. -

-

-Pablo: This is bigger issue. Specification of assignment in terms of swap is suspect to begin with. It is over specification. -How this was applied to string is a better example to work from. -

-

-Pablo: Two problems: inconsistency that should be fixed (neither should have noexcept), the other issues is that assignment -should not be specified in terms of swap. There are cases where assignment should succeed where swap would fail. This is easier -with string as it should follow container rules. -

-

-Action Item (Alisdair): There are a few more issues found to file. -

-

-Dave: This is because of allocators? The allocator makes this not work. -

-

-Howard: There is a type erased allocator in shared_ptr. There is a noexcept allocator in shared_ptr. -

-

-Pablo: shared_ptr is a different case. There are shared semantics and the allocator does move around. -A function does not have shared semantics. -

-

-Alisdair: Function objects think they have unique ownership. -

-

-Howard: In function we specify semantics with copy construction and swap. -

-

-Action Item (Pablo): Write this up better (why assignment should not be defined in terms of swap) -

-

-Howard: Not having trouble making function constructor no throw. -

-

-Dietmar: Function must allocate memory. -

-

-Howard: Does not put stuff that will throw on copy or swap in small object optimization. Put those on heap. -Storing allocator, but has to be no throw copy constructable. -

-

-Pablo: Are you allowed to or required to swap or move allocators in case or swap or move. -

-

-Dave: An allocator that is type erased should be different... -

-

-Pablo: it is -

-

-Dave: Do you need to know something about allocator types? But only at construction time. -

-

-Pablo: You could have allocators that are different types. -

-

-Dave: Swap is two ended operation. -

-

-Pablo: Opinion is that both have to say propagate on swap for them to swap. -

-

-John: It is not arbitrary. If one person says no. No is no. -

-

-Howard: Find noexcept swap to be very useful. Would like to move in that direction and bring container design along. -

-

-Dave: If you have something were allocator must not propagate you can detect that at construction time. -

-

-... -

-

-Pablo: Need to leave this open and discuss in smaller group. -

-

-Alisdair: Tried to add boost::any as TR2 proposal and ran into this issue. Only the first place where we run into -issues with type erased allocators. Suggest we move it to open. -

-

-Action Item: Move to open. -

-

-Action Item (Pablo works with Howard and Daniel): Address the more fundamental issue -(which may be multiple issues) and write up findings. -

- -

[ -Original resolution: -]

- -

This wording is relative to the FDIS.

-
    -

  1. Modify the header <functional> synopsis in 20.9 [function.objects] as indicated:

    -
    -namespace std {
-  […]
-
-  template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
-
-  […]
-}
-
    -
    2. - -

  2. Modify the class template function synopsis in 20.9.12.2 [func.wrap.func] as indicated:

    -
    -namespace std {
-  […]
-
-  // [func.wrap.func.alg], specialized algorithms:
-  template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
-
-  […]
-}
-
    -
    3. - -

  3. Modify 20.9.12.2.7 [func.wrap.func.alg] as indicated:

    -
    -template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>& f2) noexcept;
-

    --1- Effects: f1.swap(f2); -

    -
    4. - -
- -

[2014-02-28 (Post Issaquah), Pablo provides more information]

- - -

-For cross-referencing purposes: The resolution of this issue should be -harmonized with any resolution to LWG 2370, which addresses -inappropriate noexcepts in some function constructors. -

- -

We have the following choices:

- -
    -
  1. -

    swap() does not throw

    - -

    -Discussion: This definition is desirable, and allows assignment - to be implemented with the strong exception guarantee, but it does have - consequences: The implementation cannot use the small-object optimization - for a function-object F unless F is NothrowMovable - (nothrow-swappable is unimportant because F is not swapped with another F). - Note that many functors written before C++11 will not have move constructors decorated - with noexcept, so this limitation could affect a lot of code. -

    -

    -It is not clear what other implementation restrictions might be - needed. Allocators are required not to throw on move or copy. Is that - sufficient? -

    -
    -
    2. - -
  2. -

    swap() can throw

    - -
    -

    -Discussion: This definition gives maximum latitude to implementation to - use small-object optimization. However, the strong guarantee on assignment - is difficult to achieve. Should we consider giving up on the strong - guarantee? How much are we willing to pessimize code for exceptions? -

    -
    -
    3. -
  3. -

    swap() will not throw if both functions have NoThrowMoveable functors

    - -
    -

    -Discussion: This definition is similar to option 2, but gives slightly - stronger guarantees. Here, swap() can throw, but the programmer can - theoretically prevent that from happening. This should be straight-forward - to implement and gives the implementation a lot of latitude for - optimization. However, because this is a dynamic decision, the program is - not as easy to reason about. Also, the strong guarantee for assignment is - compromized as in option 2. -

    -
    -
    4. -
- - - - -

Proposed resolution:

- - - - - -
-

2070. allocate_shared should use allocator_traits<A>::construct

-

Section: 20.8.2.2.6 [util.smartptr.shared.create] Status: Open - Submitter: Jonathan Wakely Opened: 2011-07-11 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

-

-20.8.2.2.6 [util.smartptr.shared.create] says: -

-

--2- Effects: Allocates memory suitable for an object of type T and constructs an object in that memory -via the placement new expression ::new (pv) T(std::forward<Args>(args)...). The template -allocate_shared uses a copy of a to allocate memory. If an exception is thrown, the functions have -no effect. -

-

-This explicitly requires placement new rather than using -allocator_traits<A>::construct(a, (T*)pv, std::forward<Args>(args)...) -In most cases that would result in the same placement new expression, -but would allow more control over how the object is constructed e.g. -using scoped_allocator_adaptor to do uses-allocator construction, or -using an allocator declared as a friend to construct objects with no -public constructors. -

- -

[ -2011-08-16 Bloomington: -]

- -

-Agreed to fix in principle, but believe that make_shared and -allocate_shared have now diverged enough that their descriptions -should be separated. Pablo and Stefanus to provide revised wording. -

- -

Daniel's (old) proposed resolution:

-
-

This wording is relative to the FDIS.

- -
    -

  1. Change the following paragraphs of 20.8.2.2.6 [util.smartptr.shared.create] as indicated (The suggested -removal of the last sentence of p1 is not strictly required to resolve this issue, but is still recommended, -because it does not say anything new but may give the impression that it says something new): -

    -template<class T, class... Args> shared_ptr<T> make_shared(Args&&... args);
-template<class T, class A, class... Args>
-  shared_ptr<T> allocate_shared(const A& a, Args&&... args);
-
    -

    --1- Requires: For the template make_shared, tThe expression -::new (pv) T(std::forward<Args>(args)...), where pv -has type void* and points to storage suitable to hold an object of type T, shall be well -formed. For the template allocate_shared, the expression -allocator_traits<A>::construct(a, pt, std::forward<Args>(args)...), -where pt has type T* and points to storage suitable to hold an object -of type T, shall be well formed. A shall be an allocator ([allocator.requirements]). -The copy constructor and destructor of A shall not throw exceptions. -

    --2- Effects: Allocates memory suitable for an object of type T and constructs an object in -that memory. The template make_shared constructs the object via the placement new expression -::new (pv) T(std::forward<Args>(args)...). The template allocate_shared uses a copy -of a to allocate memory and constructs the object by calling allocator_traits<A>::construct(a, pt, -std::forward<Args>(args)...). If an exception is thrown, the functions have no effect. -

    --3- Returns: A shared_ptr instance that stores and owns the address of the newly constructed -object of type T. -

    --4- Postconditions: get() != 0 && use_count() == 1 -

    --5- Throws: bad_alloc, or, for the template make_shared, an exception thrown from -the constructor of T, or, for the template allocate_shared, an exception thrown from -A::allocate or from allocator_traits<A>::constructfrom the constructor of -T. -

    --6- Remarks: Implementations are encouraged, but not required, to perform no more than one memory -allocation. [ Note: This provides efficiency equivalent to an intrusive smart pointer. — end note ] -

    --7- [ Note: These functions will typically allocate more memory than sizeof(T) to allow for internal -bookkeeping structures such as the reference counts. — end note ] -

    -
    -
    2. -
-
- -

[2011-12-04: Jonathan and Daniel improve wording]

- - -

See also c++std-lib-31796

- - - - -

[2013-10-13, Ville]

- -

-This issue is related to 2089. -

- - -

[2014-02-15 post-Issaquah session : move to Tentatively NAD]

- -

-STL: This takes an allocator, but then ignores its construct. That's squirrely. -

-

-Alisdair: The convention is when you take an allocator, you use its construct. -

-

-STL: 23.2.1 [container.requirements.general]/3, argh! This fills me with despair, but I understand it now. -

-

-STL: Ok, this is some cleanup. -

-

-STL: You're requiring b to be of type A and not being rebound, is that an overspecification? -

-

-Pablo: Good point. Hmm, that's only a requirement on what must be well-formed. -

-

-STL: If it's just a well-formed requirement, then why not just use a directly? -

-

-Pablo: Yeah, the well-formed requirement is overly complex. It's not a real call, we could just use a directly. It makes it harder to read. -

-

-Alisdair: b should be an allocator in the same family as a. -

-

-Pablo: This is a well-formed requirement, I wonder if it's the capital A that's the problem here. It doesn't matter here, this is way too much wording. -

-

-Alisdair: It's trying to tie the constructor arguments into the allocator requirements. -

-

-Pablo: b could be struck, that's a runtime quality. The construct will work with anything that's in the family of A. -

-

-Alisdair: The important part is the forward of Args. -

-

-Pablo: A must be an allocator, and forward Args must work with that. -

-

-Alisdair: First let's nail down A. -

-

-Pablo: Then replace b with a, and strike the rest. -

-

-STL: You need pt's type, at least. -

-

-Pablo: There's nothing to be said about runtime constraints here, this function doesn't even take a pt. -

-

-STL: Looking at the Effects, I believe b is similarly messed up, we can use a2 to construct an object. -

-

-Alisdair: Or any allocator in the family of a. -

-

-STL: We say this stuff for the deallocate too, it should be lifted up. -

-

-STL: "owns the address" is weird. -

-

-Alisdair: shared_ptr owns pointers, although it does sound funky. -

-

-Walter: "to destruct" is ungrammatical. -

-

-STL: "When ownership is given up" is not what we usually say. -

-

-Alisdair: I think the Returns clause is the right place to say this. -

-

-STL: The right place to say this is shared_ptr's dtor, we don't want to use Core's "come from" convention. -

-

-Alisdair: I'm on the hook to draft cleaner wording. -

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change the following paragraphs of 20.8.2.2.6 [util.smartptr.shared.create] as indicated: -

    -
    -template<class T, class... Args> shared_ptr<T> make_shared(Args&&... args);
-template<class T, class A, class... Args>
-  shared_ptr<T> allocate_shared(const A& a, Args&&... args);
-
    -

    --1- Requires: The expression ::new (pv) T(std::forward<Args>(args)...), where pv -has type void* and points to storage suitable to hold an object of type T, shall be well -formed. A shall be an allocator (17.6.3.5 [allocator.requirements]). The copy constructor -and destructor of A shall not throw exceptions. -

    --2- Effects: Equivalent to -

    -
     
-return allocate_shared<T>(allocator<T>(), std::forward<Args>(args)...);
-
    -

    -Allocates memory suitable for an object of type T -and constructs an object in that memory via the placement new expression -::new (pv) T(std::forward<Args>(args)...). The template allocate_shared uses a copy -of a to allocate memory. If an exception is thrown, the functions have no effect. -

    --?- Remarks: An implementation may meet the effects (and the implied guarantees) without -creating the allocator object [Note: That is, user-provided specializations of std::allocator -may not be instantiated, the expressions ::new (pv) T(std::forward<Args>(args)...) and -pv->~T() may be evaluated directly — end note]. -

    --3- Returns: A shared_ptr instance that stores and owns the address of the newly constructed -object of type T. -

    --4- Postconditions: get() != 0 && use_count() == 1 -

    --5- Throws: bad_alloc, or an exception thrown from A::allocate or from the -constructor of T. -

    --6- Remarks: Implementations are encouraged, but not required, to perform no more than one memory -allocation. [Note: This provides efficiency equivalent to an intrusive smart pointer. — end note] -

    --7- [Note: These functions will typically allocate more memory than sizeof(T) to allow -for internal bookkeeping structures such as the reference counts. — end note] -

    -
    2. -

  2. -Add the following set of new paragraphs immediately following the previous paragraph 7 of -20.8.2.2.6 [util.smartptr.shared.create]: -

    -
    -template<class T, class A, class... Args>
-  shared_ptr<T> allocate_shared(const A& a, Args&&... args);
-
    -

    --?- Requires: The expressions -allocator_traits<A>::construct(b, pt, std::forward<Args>(args)...) and -allocator_traits<A>::destroy(b, pt) shall be well-formed and well-defined, -where b has type A and is a copy of a and where pt -has type T* and points to storage suitable to hold an object of type T. -A shall meet the allocator requirements (17.6.3.5 [allocator.requirements]). -

    --?- Effects: Uses an object a2 -of type allocator_traits<A>::rebind_alloc<unspecified> that compares equal to -a to allocate memory suitable for an object of type T. -Uses a copy b of type A from a to construct an object of type T in -that memory by calling allocator_traits<A>::construct(b, pt, std::forward<Args>(args)...). -If an exception is thrown, the function has no effect. -

    --?- Returns: A shared_ptr instance that stores and owns the address of the newly constructed -object of type T. When ownership is given up, the effects are as follows: Uses a copy b2 -of type A from a to destruct an object of type T by calling -allocator_traits<A>::destroy(b2, pt2) where pt2 has type T* -and refers to the newly constructed object. Then uses an object of type -allocator_traits<A>::rebind_alloc<unspecified> that compares equal to -a to deallocate the allocated memory. -

    --?- Postconditions: get() != 0 && use_count() == 1 -

    --?- Throws: Nothing unless memory allocation or allocator_traits<A>::construct -throws an exception. -

    --?- Remarks: Implementations are encouraged, but not required, to perform no more than one memory -allocation. [Note: Such an implementation provides efficiency equivalent to an intrusive smart -pointer. — end note] -

    --?- [Note: This function will typically allocate more memory than sizeof(T) to allow for internal -bookkeeping structures such as the reference counts. — end note] -

    -
    3. -
- - - - - -
-

2072. Unclear wording about capacity of temporary buffers

-

Section: 20.7.11 [temporary.buffer] Status: Ready - Submitter: Kazutoshi Satoda Opened: 2011-08-10 Last modified: 2015-05-08

-

View all other issues in [temporary.buffer].

-

View all issues with Ready status.

-

Discussion:

- -

-According to 20.7.11 [temporary.buffer] p1+2: - -

-template <class T>
-pair<T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
-

--1- Effects: Obtains a pointer to storage sufficient to store up to n adjacent T -objects. It is implementation-defined whether over-aligned types are supported (3.11). -

--2- Returns: A pair containing the buffer's address and capacity (in the units of sizeof(T)), -or a pair of 0 values if no storage can be obtained or if n <= 0. -

-

-I read this as prohibiting to return a buffer of which capacity is less than n, because -such a buffer is not sufficient to store n objects. -

-The corresponding description in SGI STL -is clear on this point, but I think it is a bit too verbose: -

- -

-(for the return value, a pair P) [...] the buffer pointed to by P.first is large enough -to hold P.second objects of type T. P.second is greater than or equal to 0, -and less than or equal to len. -

- -

-There seems to be two different targets of the "up to n" modification: -The capacity of obtained buffer, and the actual number that the caller -will store into the buffer. -

-First I read as the latter, and got surprised seeing that libstdc++ -implementation can return a smaller buffer. I started searching about -get_temporary_buffer(). After reading a quote from TC++PL at -stackoverflow, -I realized that the former is intended. -

-Such misinterpretation seems common: -

-
    -
  • The above question is likely started from same misinterpretation.
    • -

  • JIS standard (Japanese translation of ISO/IEC standard) says nothing - like "up to". I think the editor misinterpreted the original wording, - and omitted words for "up to" as it is redundant. (If a buffer is - sufficient to store n objects, it is also sufficient to store - up to n objects.)

    • -

  • Rogue Wave implementation doesn't return smaller buffer, instead, it - can return larger buffer on some circumstances. Apache - STDCXX is a derived version of that - implementation, and publicly accessible: -

    -

    -Specializations of the get_temporary_buffer() function template -attempt to allocate a region of storage sufficiently large to store at -least n adjacent objects of type T. -

    -

    -I know one commercial compiler package based on Rogue Wave implementation, -and its implementation is essentially same as the above. -

    -
    • -
- -

[2014-05-18, Daniel comments and suggests concrete wording]

- - -

-The provided wording attempts to clarify the discussed capacity freedom, but it also makes it clearer that the returned -memory is just "raw memory", which is currently not really clear. In addition the wording clarifies that the deallocating -return_temporary_buffer function does not throw exceptions, which I believe is the intention when the preconditions -of the functions are satisfied. Then, my understanding is that we can provide to return_temporary_buffer a -null pointer value if that was the value, get_temporary_buffer() had returned. Furthermore, as STL noticed, the current -wording seemingly allows multiple invocations of return_temporary_buffer with the same value returned by -get_temporary_buffer; this should be constrained similar to the wording we have for operator delete (unfortunately -we miss such wording for allocators). -

- -

[2015-05, Lenexa]

- -

-MC: move to ready? in favor: 14, opposed: 0, abstain: 0 -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -

  1. Change 20.7.11 [temporary.buffer] as indicated:

    - -
    -
    -template <class T>
-  pair<T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
-
    -
    -

    --1- Effects: Obtains a pointer to uninitialized, contiguous storage for N adjacent objects of type -T, for some non-negative number N.Obtains a pointer to storage sufficient -to store up to n adjacent T objects. It is implementation-defined whether over-aligned types are supported (3.11). -

    --?- Remarks: Calling get_temporary_buffer with a positive number n is a non-binding request to return -storage for n objects of type T. In this case, an implementation is permitted to return instead storage for a -non-negative number N of such objects, where N != n (including N == 0). [Note: The -request is non-binding to allow latitude for implementation-specific optimizations of its memory management. — end note]. -

    --2- Returns: If n <= 0 or if no storage could be obtained, returns a pair P such that P.first -is a null pointer value and P.second == 0; otherwise returns a pair P such that P.first refers to the -address of the uninitialized storage and P.second refers to its capacity N (in the units of -sizeof(T)).A pair containing the buffer's address and capacity (in the units of sizeof(T)), or a -pair of 0 values if no storage can be obtained or if n <= 0. -

    -
    - -
    -template <class T> void return_temporary_buffer(T* p);
-
    -
    -

    --3- Effects: Deallocates the buffer to which p pointsstorage referenced by p. -

    --4- Requires: The buffer shall have been previously allocated byp shall be a pointer value -returned by an earlier call to get_temporary_buffer which has not been invalidated by an intervening call to -return_temporary_buffer(T*). -

    --?- Throws: Nothing. -

    -
    - -
    -
    2. -
- - - - - - -
-

2077. Further incomplete constraints for type traits

-

Section: 20.10.4.3 [meta.unary.prop] Status: Open - Submitter: Daniel Krügler Opened: 2011-08-20 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with Open status.

-

Discussion:

- -

-The currently agreed on proposed wording for 2015 using -remove_all_extents<T>::type instead of the "an array of -unknown bound" terminology in the precondition should be extended to -some further entries especially in Table 49, notably the -is_*constructible, is_*assignable, and -is_*destructible entries. To prevent ODR violations, incomplete -element types of arrays must be excluded for value-initialization and -destruction for example. Construction and assignment has to be honored, -when we have array-to-pointer conversions or pointer conversions of -incomplete pointees in effect. -

- -

[2012, Kona]

- -

-The issue is that in three type traits, we are accidentally saying that in certain -circumstances the type must give a specified answer when given an incomplete type. -(Specifically: an array of unknown bound of incomplete type.) The issue asserts -that there's an ODR violation, since the trait returns false in that case but might -return a different version when the trait is completed. -

-

-Howard argues: no, there is no risk of an ODR violation. -is_constructible<A[]> must return false regardless of whether -A is complete, so there's no reason to forbid an array of unknown bound of -incomplete types. Same argument applies to is_assignable. General agreement -with Howard's reasoning. -

-

-There may be a real issue for is_destructible. None of us are sure what -is_destructible is supposed to mean for an array of unknown bound -(regardless of whether its type is complete), and the standard doesn't make it clear. -The middle column doesn't say what it's supposed to do for incomplete types. -

-

-In at least one implementation, is_destructible<A[]> does return true -if A is complete, which would result in ODR violation unless we forbid it for -incomplete types. -

-

-Move to open. We believe there is no issue for is_constructible or -is_assignable, but that there is a real issue for is_destructible. -

- - - -

Proposed resolution:

- - - - - -
-

2088. std::terminate problem

-

Section: 18.8.3 [exception.terminate] Status: Open - Submitter: Daniel Krügler Opened: 2011-09-25 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

- -

-Andrzej Krzemienski reported the following on comp.std.c++: -

-
-

-In N3290, which is to become the official standard, in 18.8.3.4 [terminate], -paragraph 1 reads -

-

-Remarks: Called by the implementation when exception handling must -be abandoned for any of several reasons (15.5.1), in effect immediately after -evaluating the throw-expression (18.8.3.1). May also be called directly by the -program. -

-

It is not clear what is "in effect". It was clear in previous drafts where paragraphs -1 and 2 read: -

-

-Called by the implementation when exception handling must be -abandoned for any of several reasons (15.5.1). May also be called directly -by the program. -

-Effects: Calls the terminate_handler function in effect -immediately after evaluating the throw-expression (18.8.3.1), if called by the -implementation, or calls the current terminate_handler function, -if called by the program. -

-
-

-It was changed by N3189. The same applies to function unexpected (D. 11.4, paragraph 1). -

-Assuming the previous wording is still intended, the wording can be read -"unless std::terminate is called by the program, we will use the handler -that was in effect immediately after evaluating the throw-expression". -

- This assumes that there is some throw-expression connected to every - situation that triggers the call to std::terminate. But this is not - the case: -

-
    -
  • - In case std::thread is assigned to or destroyed while being joinable - there is no throw-expression involved. -
    • -
  • - In case std::unexpected is called by the program, std::terminate is - triggered by the implementation - no throw-expression involved. -
    • -
  • - In case a destructor throws during stack unwinding we have two throw-expressions - involved. -
    • -
-

-Which one is referred to? -

-In case std::nested_exception::rethrow_nested is called for an object that has -captured no exception, there is no throw-expression involved directly (and may no throw -be involved even indirectly). -

-Next, 18.8.3.1 [terminate.handler], paragraph 2 says -

-

-Required behavior: A terminate_handler shall terminate execution -of the program without returning to the caller. -

-

-This seems to allow that the function may exit by throwing an -exception (because word "return" implies a normal return). -

-One could argue that words "terminate execution of the program" are sufficient, -but then why "without returning to the caller" would be mentioned. In -case such handler throws, noexcept specification in function std::terminate -is violated, and std::terminate would be called recursively - should -std::abort not be called in case of recursive std::terminate -call? On the other hand some controlled recursion could be useful, like in the -following technique. -

-
- -

-The here mentioned wording changes by N3189 in regard to 18.8.3.4 [terminate] p1 -were done for a better separation of effects (Effects element) and additional normative -wording explanations (Remarks element), there was no meaning change intended. Further, -there was already a defect existing in the previous wording, which was not updated when -further situations where defined, when std::terminate where supposed to be -called by the implementation. -

-The part -

-"in effect immediately after evaluating the throw-expression" -

-should be removed and the quoted reference to 18.8.3.1 [terminate.handler] -need to be part of the effects element where it refers to the current terminate_handler -function, so should be moved just after -

-"Effects: Calls the current terminate_handler function." -

-It seems ok to allow a termination handler to exit via an exception, but the -suggested idiom should better be replaced by a more simpler one based on -evaluating the current exception pointer in the terminate handler, e.g. -

-
-void our_terminate (void) {
-  std::exception_ptr p = std::current_exception();
-  if (p) {
-    ... // OK to rethrow and to determine it's nature
-  } else {
-    ... // Do something else
-  }
-}
-
- -

[2011-12-09: Daniel comments]

- - -

-A related issue is 2111. -

- - -

[2012, Kona]

- -

-Move to Open. -

-

-There is an interaction with Core issues in this area that Jens is already supplying wording -for. Review this issue again once Jens wording is available. -

-

-Alisdair to review clause 15.5 (per Jens suggestion) and recommend any changes, then integrate -Jens wording into this issue. -

- - - -

Proposed resolution:

- - - - - -
-

2089. std::allocator::construct should use uniform initialization

-

Section: 20.7.9.1 [allocator.members] Status: EWG - Submitter: David Krauss Opened: 2011-10-07 Last modified: 2015-04-08

-

View all other issues in [allocator.members].

-

View all issues with EWG status.

-

Discussion:

- -

-When the EmplaceConstructible (23.2.1 [container.requirements.general]/13) requirement is used -to initialize an object, direct-initialization occurs. Initializing an aggregate or using a std::initializer_list -constructor with emplace requires naming the initialized type and moving a temporary. This is a result of -std::allocator::construct using direct-initialization, not list-initialization (sometimes called "uniform -initialization") syntax. -

-Altering std::allocator<T>::construct to use list-initialization would, among other things, give -preference to std::initializer_list constructor overloads, breaking valid code in an unintuitive and -unfixable way — there would be no way for emplace_back to access a constructor preempted by -std::initializer_list without essentially reimplementing push_back. -

-
-std::vector<std::vector<int>> v;
-v.emplace_back(3, 4); // v[0] == {4, 4, 4}, not {3, 4} as in list-initialization
-
-

-The proposed compromise is to use SFINAE with std::is_constructible, which tests whether direct-initialization -is well formed. If is_constructible is false, then an alternative std::allocator::construct overload -is chosen which uses list-initialization. Since list-initialization always falls back on direct-initialization, the -user will see diagnostic messages as if list-initialization (uniform-initialization) were always being used, because -the direct-initialization overload cannot fail. -

-I can see two corner cases that expose gaps in this scheme. One occurs when arguments intended for -std::initializer_list satisfy a constructor, such as trying to emplace-insert a value of {3, 4} in -the above example. The workaround is to explicitly specify the std::initializer_list type, as in -v.emplace_back(std::initializer_list<int>(3, 4)). Since this matches the semantics as if -std::initializer_list were deduced, there seems to be no real problem here. -

-The other case is when arguments intended for aggregate initialization satisfy a constructor. Since aggregates cannot -have user-defined constructors, this requires that the first nonstatic data member of the aggregate be implicitly -convertible from the aggregate type, and that the initializer list have one element. The workaround is to supply an -initializer for the second member. It remains impossible to in-place construct an aggregate with only one nonstatic -data member by conversion from a type convertible to the aggregate's own type. This seems like an acceptably small -hole. -

-The change is quite small because EmplaceConstructible is defined in terms of whatever allocator is specified, -and there is no need to explicitly mention SFINAE in the normative text. -

- -

[2012, Kona]

- -

-Move to Open. -

-

-There appears to be a real concern with initializing aggregates, that can be performed only -using brace-initialization. There is little interest in the rest of the issue, given the existence -of 'emplace' methods in C++11. -

-

-Move to Open, to find an acceptable solution for intializing aggregates. There is the potential -that EWG may have an interest in this area of language consistency as well. -

- -

[2013-10-13, Ville]

- -

-This issue is related to 2070. -

- -

[2015-02 Cologne]

- -

-Move to EWG, Ville to write a paper. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 20.7.9.1 [allocator.members] p12 as indicated:

- -
-template <class U, class... Args>
-  void construct(U* p, Args&&... args);
-
-

-12 Effects: ::new((void *)p) U(std::forward<Args>(args)...) if is_constructible<U, Args...>::value -is true, else ::new((void *)p) U{std::forward<Args>(args)...} -

-
- - - - - - -
-

2095. promise and packaged_task missing constructors needed for uses-allocator construction

-

Section: 30.6.5 [futures.promise], 30.6.9 [futures.task] Status: Open - Submitter: Jonathan Wakely Opened: 2011-11-01 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with Open status.

-

Discussion:

- -

-This example is ill-formed according to C++11 because uses_allocator<promise<R>, A>::value is true, but -is_constructible<promise<R>, A, promise<R>&&>::value is false. Similarly for packaged_task. -

-
-#include <future>
-#include <memory>
-#include <tuple>
-
-using namespace std;
-
-typedef packaged_task<void()> task;
-typedef promise<void> prom;
-allocator<task> a;
-
-tuple<task, prom> t1{ allocator_arg, a };
-tuple<task, prom> t2{ allocator_arg, a, task{}, prom{} };
-
- -

[2012, Portland]

- -

-This is an allocator issue, and should be dealt with directly by LWG. -

- -

[2013-03-06]

- - -

-Jonathan suggests to make the new constructors non-explicit and makes some representational improvements. -

- - -

[2013-09 Chicago]

- -

-Move to deferred. -

-

-This issue has much in common with similar problems with std::function that are being addressed -by the polymorphic allocators proposal currently under evaluation in LEWG. Defer further discussion on -this topic until the final outcome of that paper and its proposed resolution is known. -

- -

[2014-02-20 Re-open Deferred issues as Priority 4]

- - - - -

Proposed resolution:

-

[This wording is relative to the FDIS.]

- - -
    -

  1. Add to 30.6.5 [futures.promise], class template promise synopsis, -as indicated:

    - -
    -namespace std {
-  template <class R>
-  class promise {
-  public:
-    promise();
-    template <class Allocator>
-    promise(allocator_arg_t, const Allocator& a);
-    template <class Allocator>
-    promise(allocator_arg_t, const Allocator& a, promise&& rhs) noexcept;
-    promise(promise&& rhs) noexcept;
-    promise(const promise& rhs) = delete;
-    ~promise();	
-    […]
-  };
-  […]
-}
-
    -
    2. - -

  2. Change 30.6.5 [futures.promise] as indicated:

    - -
    -promise(promise&& rhs) noexcept;
-template <class Allocator>
-promise(allocator_arg_t, const Allocator& a, promise&& rhs) noexcept;
-
    -

    --5- Effects: constructs a new promise object and transfers ownership of -the shared state of rhs (if any) to the newly-constructed object. -

    --6- Postcondition: rhs has no shared state. -

    --?- [Note: a is not used — end note] -

    -
    - -
    3. - -

  3. Add to 30.6.9 [futures.task], class template packaged_task synopsis, -as indicated:

    - -
    -namespace std {
-  template<class> class packaged_task; // undefined
-
-  template<class R, class... ArgTypes>
-  class packaged_task<R(ArgTypes...)> {
-  public:
-    // construction and destruction
-    packaged_task() noexcept;
-    template <class Allocator>
-      packaged_task(allocator_arg_t, const Allocator& a) noexcept;
-    template <class F>
-      explicit packaged_task(F&& f);
-    template <class F, class Allocator>
-      explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
-    ~packaged_task();
-	
-    // no copy
-    packaged_task(const packaged_task&) = delete;
-    template<class Allocator>
-      packaged_task(allocator_arg_t, const Allocator& a, const packaged_task&) = delete;
-    packaged_task& operator=(const packaged_task&) = delete;
-    
-    // move support
-    packaged_task(packaged_task&& rhs) noexcept;
-    template <class Allocator>
-      packaged_task(allocator_arg_t, const Allocator& a, packaged_task&& rhs) noexcept;
-    packaged_task& operator=(packaged_task&& rhs) noexcept;
-    void swap(packaged_task& other) noexcept;
-    […]
-  };
-  […]
-}
-
    -
    4. - -

  4. Change 30.6.9.1 [futures.task.members] as indicated:

    - -
    -packaged_task() noexcept;
-template <class Allocator>
-  packaged_task(allocator_arg_t, const Allocator& a) noexcept;
-
    -

    --1- Effects: constructs a packaged_task object with no shared state and no stored task. -

    --?- [Note: a is not used — end note] -

    -
    -

    […]

    -
    -packaged_task(packaged_task&& rhs) noexcept;
-template <class Allocator>
-  packaged_task(allocator_arg_t, const Allocator& a, packaged_task&& rhs) noexcept;
-
    -

    --5- Effects: constructs a new packaged_task object and transfers ownership of rhs's -shared state to *this, leaving rhs with no shared state. Moves the stored task from rhs -to *this. -

    --6- Postcondition: rhs has no shared state. -

    --?- [Note: a is not used — end note] -

    -
    - -
    5. -
- -
-
-

-

- - - - - - -
-

2101. Some transformation types can produce impossible types

-

Section: 20.10.7 [meta.trans] Status: Ready - Submitter: Daniel Krügler Opened: 2011-11-18 Last modified: 2015-05-08

-

View all issues with Ready status.

-

Discussion:

- -

-Table 53 — "Reference modifications" says in regard to the type trait -add_lvalue_reference (emphasize mine) -

- -
-

-If T names an object or function type then the member typedef type -shall name T&; -

-
- -

-The problem with this specification is that function types with cv-qualifier or ref-qualifier, -like -

-
-void() const
-void() &
-
-

-are also affected by the first part of the rule, but this would essentially mean, that -instantiating add_lvalue_reference with such a type would attempt to form -a type that is not defined in the C++ type system, namely -

-
-void(&)() const
-void(&)() &
-
-

-The general policy for TransformationTraits is to define always some meaningful -mapping type, but this does not hold for add_lvalue_reference, add_rvalue_reference, -and in addition to these two for add_pointer as well. The latter one would -attempt to form the invalid types -

-
-void(*)() const
-void(*)() &
-
-

-A possible reason why those traits were specified in this way is that in C++03 (and that means -for TR1), cv-qualifier were underspecified in the core language and several compilers -just ignored them during template instantiations. This situation became fixed by adopting -CWG issues 295 and -547. -

-While there is possibly some core language clarification needed (see reflector messages -starting from c++std-core-20740), it seems also clear that the library should fix the -specification. The suggested resolution follows the style of the specification of the -support concepts PointeeType and ReferentType defined in -N2914. -

- - -

[2012-02-10, Kona]

- -

-Move to NAD. -

-

-These cv- and ref-qualified function types are aberrations in the type system, and do -not represent any actual entity defined by the language. The notion of cv- and ref- -qualification applies only to the implicit *this reference in a member function. -

-

-However, these types can be produced by quirks of template metaprogramming, the question -remains what the library should do about it. For example, add_reference returns -the original type if passed a reference type, or a void type. Conversely, -add_pointer will return a pointer to the referenced type when passed a reference. -

-

-It is most likely that the 'right' answer in any case will depend on the context that the -question is being asked, in terms of forming these obscure types. The best the LWG can -do is allow an error to propagate back to the user, so they can provide their own meaningful -answer in their context - with additional metaprogramming on their part. The consensus is -that if anyone is dangerous enough with templates to get themselves into this problem, they -will also have the skills to resolve the problem themselves. This is not going to trip up -the non-expert developer. -

-

-Lastly, it was noted that this problem arises only because the language is inconsistent in -providing us these nonsense types that do no really represent anything in the language. -There may be some way Core or Evolution could give us a more consistent type system so that -the LWG does not need to invent an answer at all, should this question need resolving. This -is another reason to not specify anything at the LWG trait level at this time, leaving the -other working groups free to produce the 'right' answer that we can then follow without -changing the meaning of existing, well-defined programs. -

- -

[2012-02-10, post-Kona]

- -

-Move back to Open. Daniel is concerned that this is not an issue we can simply ignore, -further details to follow. -

- -

[2012-10-06, Daniel comments]

- -

-This issue really should be resolved as a defect: First, the argument that "forming these obscure types" -should "allow an error to propagate" is inconsistent with the exact same "obscure type" that would be formed -when std::add_lvalue_reference<void> wouldn't have an extra rules for void types, which -also cannot form references. The originally proposed resolution attempts to apply the same solution for the same -common property of void types and function types with cv-qualifiers or ref-qualifier. -These functions had the property of ReferentType during concept time (see -CWG 749 bullet three for the final -wording). -

-Core issue CWG 1417 has clarified -that any attempt to form a reference of a pointer to a function type with cv-qualifiers or -ref-qualifier is ill-formed. Unfortunately, many compilers don't implement this yet. -

-I also would like to warn about so-called "obscure" types: The problem is that these can occur as the side effect -of finding a best match overload of function templates, where this type is exactly correct for one of these -overloads, but causes a deep (not-sfinae-friendly) error for others where one of these traits are part of the -signature. -

-Existing experience with void types shows, that this extra rule is not so unexpected. Further, any usage -of the result types of these traits as argument types or return types of functions would make these ill-formed -(and in a template context would be sfinaed away), so the expected effects are rarely unnoticed. Checking -all existing explicit usages of the traits add_rvalue_reference, add_lvalue_reference, and -add_pointer didn't show any example where the error would be silent: add_rvalue_reference -is used to specify the return value of declval() and the instantiation of declval<void() const>() -would be invalid, because of the attempt to return a function type. Similarly, add_lvalue_reference -is used to specify the return type of unique_ptr<T>::operator*(). Again, any instantiation with -void() const wouldn't remain unnoticed. The trait add_pointer is used to specify the trait -std::decay and this is an interesting example, because it is well-formed when instantiated with void -types, too, and is heavily used throughout the library specification. All use-cases would not be negatively affected -by the suggested acceptance of function types with cv-qualifiers or ref-qualifier, because they involve -types that are either function arguments, function parameters or types were references are formed from. -

-The alternative would be to add an additional extra rule that doesn't define a type member 'type' when -we have a function type with cv-qualifiers or ref-qualifier. This is better than the -current state but it is not superior than the proposal to specify the result as the original type, because -both variants are sfinae-friendly. A further disadvantage of the "non-type" approach here would be that any -usage of std::decay would require special protection against these function types, because -instantiating std::decay<void() const> again would lead to a deep, sfinae-unfriendly error. -

-The following example demonstrates the problem: Even though the second f template is the best final -match here, the first one will be instantiated. During that process std::decay<T>::type -becomes instantiated as well and will raise a deep error, because as part of the implementation the trait -std::add_pointer<void() const> becomes instantiated: -

-
-#include <type_traits>
-
-template<class T>
-typename std::decay<T>::type f(T&& t);
-
-template<class T, class U>
-U f(U u);
-
-int main() {
-  f<void() const>(0);
-}
-
-

-When the here proposed resolution would be applied this program would be well-formed and selects the expected function. -

- -

-Previous resolution from Daniel [SUPERSEDED]: -

-
-
    -

  1. Change Table 53 — "Reference modifications" in 20.10.7.2 [meta.trans.ref] as indicated:

    - - - - - - - - - - - - - - - - - - - - - -
    Table 53 — Reference modifications
    TemplateComments
    -… -
    -template <class T>
    -struct
    -add_lvalue_reference;     -    		 -If T names an object type or if T names a function type that does not have
    -cv-qualifiers or a ref-qualifier     then the member typedef type
    -shall name T&; otherwise, if T names a type "rvalue reference to T1" then
    -the member typedef type shall name T1&; otherwise, type shall name T. -
    -template <class T>
    -struct
    -add_rvalue_reference;     -    		 -If T names an object type or if T names a function type that does not have
    -cv-qualifiers or a ref-qualifier     then the member typedef type
    -shall name T&&; otherwise, type shall name T. [Note: This rule reflects
    -the semantics of reference collapsing (8.3.2 [dcl.ref]). For example, when a type T
    -names a type T1&, the type add_rvalue_reference<T>::type is not an
    -rvalue reference. — end note] -
    - -
    2. - -

  2. Change Table 56 — "Pointer modifications" in 20.10.7.5 [meta.trans.ptr] as indicated:

    - - - - - - - - - - - - - - - - - -
    Table 56 — Pointer modifications
    TemplateComments
    -… -
    -template <class T>
    -struct add_pointer;     -    		 -The member typedef type shall name the same type as
    -If T names a function type that has cv-qualifiers or a ref-qualifier
    -then the member typedef type shall name T; otherwise, it
    -shall name the same type as     remove_reference<T>::type*. -
    - -
    3. -
-
- -

-The following revised proposed resolution defines - in the absence of a proper core language definition - a new -term referenceable type as also suggested by the resolution for LWG 2196 as an -umbrella of the negation of void types and function types with cv-qualifiers or ref-qualifier. -This simplifies and minimizes the requires wording changes. -

- -

[ -2013-09-26, Daniel synchronizes wording with recent draft -]

- - -

[ -2014-05-18, Daniel synchronizes wording with recent draft and comments -]

- - -

-My impression is that this urgency of action this issue attempts to point out is partly caused by the fact that even for -the most recent C++14 compilers the implementations have just recently changed to adopt the core wording. Examples for these -are bug reports to gcc or -clang. -

-Occasionally the argument has been presented to me that the suggested changes to the traits affected by this issue would -lead to irregularities compared to other traits, especially the lack of guarantee that add_pointer might not return -a pointer or that add_(l/r)value_reference might not return a reference type. I would like to point out that this -kind of divergence is actually already present in most add/remove traits: For example, we have no guarantee that -add_const returns a const type (Reference types or function types get special treatments), or that add_rvalue_reference -returns an rvalue-reference (e.g. when applied to an lvalue-reference type). -

-Zhihao Yuan brought to my attention, that the originally proposing paper -N1345 carefully discussed these design choices. -

- -

[2015-05, Lenexa]

- -

-MC: move to Ready: in favor: 16, opposed: 0, abstain: 1
-STL: have libstdc++, libc++ implemented this? we would need to change your implementation
-

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change Table 53 — "Reference modifications" in 20.10.7.2 [meta.trans.ref] as indicated:

    - - - - - - - - - - - - - - - - - - - - - -
    Table 53 — Reference modifications
    TemplateComments
    -… -
    -template <class T>
    -struct
    -add_lvalue_reference;     -    		 -If T names an object or function typea referenceable type
    -then the member typedef type
    -shall name T&; otherwise, if T names a type "rvalue reference to T1" then
    -the member typedef type shall name T1&; otherwise,     type shall name T.
    -[Note: This rule reflects the semantics of reference collapsing (8.3.2 [dcl.ref]). — end note] -
    -template <class T>
    -struct
    -add_rvalue_reference;     -    		 -If T names an object or function typea referenceable type
    -then the member typedef type
    -shall name T&&; otherwise, type shall name T. [Note: This rule reflects
    -the semantics of reference collapsing (8.3.2 [dcl.ref]). For example, when a type T
    -names a type T1&, the type add_rvalue_reference_t<T> is not an
    -rvalue reference. — end note] -
    - -
    2. - -

  2. Change Table 56 — "Pointer modifications" in 20.10.7.5 [meta.trans.ptr] as indicated:

    - - - - - - - - - - - - - - - - - -
    Table 56 — Pointer modifications
    TemplateComments
    -… -
    -template <class T>
    -struct add_pointer;     -    		 -If T names a referenceable type or a (possibly cv-qualified) void type then
     -Tthe member typedef type shall name the same type as
    -remove_reference_t<T>*; otherwise, type shall name T. -
    - -
    3. -
- - - - - -
-

2111. Which unexpected/terminate handler is called from the exception handling runtime?

-

Section: 18.8.3.4 [terminate], D.8.4 [unexpected] Status: Ready - Submitter: Howard Hinnant Opened: 2011-12-06 Last modified: 2015-05-08

-

View all other issues in [terminate].

-

View all issues with Ready status.

-

Discussion:

- -

-Prior to N3242, modified by N3189, we said this about unexpected(): -

- -

-Effects: Calls the unexpected_handler function in effect immediately after evaluating the throw-expression -(D.13.1), if called by the implementation, or calls the current unexpected_handler, if called by the program. -

- -

-and this about terminate(): -

- -

-Effects: Calls the terminate_handler function in effect immediately after evaluating the throw-expression (18.8.3.1), -if called by the implementation, or calls the current terminate_handler function, if called by the program. -

- -

-But now in both places we say: -

- -

-Calls the current unexpected_handler function. -

- -

-and: -

- -

-Calls the current terminate function. -

- -

-The difference is that in C++98/03 if a destructor reset a handler during stack unwinding, that new handler was -not called if the unwinding later led to unexpected() or terminate() being called. But these new -words say that this new handler is called. This is an ABI-breaking change in the way exceptions are handled. -Was this change intentional? -

-N3189 was mainly about introducing exception safety and getters for the handlers. I don't recall the issue of -which handler gets called being part of the discussion. -

-I propose that we revert to the C++98/03 behavior in this regard, lest ABI's such as the Itanium ABI are invalidated. -A mechanical way to do this is to revert bullets 9 and 12 of N3189. -

- -

[2011-12-09: Daniel comments]

- - -

-There was no such semantic change intended. It was an unfortunate side effect when trying to better separate different -responsibilities in the previous wording. -

-A related issue is 2088. -

- -

[2012-01-30: Howard comments]

- - -

-The C++98/03 wording is somewhat ambiguous: -

-

-Calls the terminate_handler function in effect immediately after evaluating the throw-expression... -

-

-There are potentially two throw-expressions being referred to here, and it is not clear if this sentence is referring to just the first or both: -

-
    -
  1. throw assignment-expression;
    2. -
  2. throw;
    3. -
-

-There is ample evidence in current implementations that it is understood that only -1. was meant. But clearly both 1 and 2 could have been meant. We need a clarification. Does an execution -of a rethrow (throw;) update which handlers can potentially be called? -

-
    -
  1. throw; // update handlers to get_xxx()?
    2. -
-

-My opinion: Go with existing practice, and clarify what that practice is, if surveys find that everyone -does the same thing. Gcc 4.2 and Apple do 1. only, and do not reset the handlers to the current handlers -on throw;. -

-If current practice is not unanimously one way or the other, I have no strong opinion. I have not found -a motivating use case for the use of any particular handler. Most applications set the handlers once at -the beginning of the program and then do not change them, and so will not be impacted by whatever decision -is made here. -

- -

[2014-02-15 Issaquah: Move to Review]

- - -

-STL: Original change in N3242 came from trying to make set/get exception handler thread safe. -The issue requests we revert to 98/03, which Howard notes was already ambiguous. -

- -

-Alisdair: Issue author thinks we made this change in C++11 without taking into account Itanium ABI, -which cannot implement the new semantic (without breaking compatibility). -

- -

-Alisdair: original change in N3242 was trying to solve the problem of which handler is called when -the handler is changing in another thread, but this turns out to be an issue in even the -single-threaded case. -

- -

-Pablo: despite wanting to make it thread safe, you are still changing a global -

- -

-STL and Marshall confirm that there is real implementation divergance on the question, so -we cannot pick just one behavior if we want to avoid breaking exisitng practice. -

- -

-Alisdair: not sure who to talk to across all library vendors to fix, need more information -for progress (IBM and Sun) -

- -

-STL: Howard did identify a problem with the wording as well: throw; is a throw expression, -but we typically want to re-activate the in-flight exception, not throw a new copy. -

- -

-Pablo: wondering why all of this wording is here (N3189)? It looks like we were trying to handle another thread -changing handler between a throw and terminate in current thread. -

- -

-Alisdair: Anything working with exception handling should have used only thread-local resources, but that ship has sailed. -We must account for the same exception object being re-thrown in multiple threads simultaneously, with no happens-before -relationships. -

- -

-Room: Why on earth would we care about exactly which way the program dies when the terminate calls are racing?! -

- -

-Pablo: Reasonable to set the handler once (in main) and never change it. -

- -

-Pablo: If willing to put lots of work into this, you could say at point of a throw these handlers become -thread local but that is overkill. We want destructors to be able to change these handlers (if only for backwards -compatibility). -

- -

-Alisdair: the "do it right" is to do something per thread, but that is more work than vendors will want to do. -Want to say setting handler while running multiple threads is unspecified. -

- -

-Pablo: possible all we need to do is say it is always the current handler -

- -

-STL: That prevents an implementation or single threaded program from calling a new handler after a throw, -probably should say if terminate is called by the implementation (during EH), any handler that was -current can be called. Leaves it up in the air as to when the handler is captured, supporting the diverging -existing practices. -

- -

-Jeffrey: use happens before terminology to avoid introducing races -

- -

-STL: Give this to concurrency? -

- -

-Jeffrey: It is in clause 18, generally LWG and not SG1 territory. -

- -

-Alisdair: Concerned about introducing happens before into fundamental exception handling since it would affect -single threaded performance as well. Want to give to concurrency or LEWG/EWG, we are into language design here. -

- -

-Jeffrey: suspect LEWG won't have a strong opinion. I don't want it to be ours!!! -

- -

-Pablo: Might be a case for core> -

- -

-Alisdair: Would be happier if at least one core person were in the discussion. -

- -

-STL: No sympathy for code that tries to guard the terminate handler. -

- -

-Alisdair: We are back to set it once, globally. Want to be clear that if set_terminate is called just once, -when EH is not active, and never changed again, then the user should get the handler from that specific call. -

- -

-AlisdairM: "unspecified which handler is called if an exception is active when set_terminate is called." -This supports existing behaviors, and guarantees which handler is called in non-conentious situations. Implicit -assumption that a funtion becomes a handler only after a successful call to set_handler, so we are not -leaving a door open to the implementation inventing entirely new handlers of its own. -

- -

-Consensus. -

- -

-Poll to confirm status as P1: new consensus is P3 -

- -

-Action: Alisdair provides new wording. Drop from P1 to P3, and move to Review. -

- -

[2015-05, Lenexa]

- -

-HH: we accidentally changed semantics of which handler gets called during exception unwinding. This was attempt to put it back. -Discovered implementations don't really do anything. […] Fine with unspecified behavior to move this week.
-STL/MC: observed different behavior
-STL: legitimizes all implementations and tells users to not do this
-Move to ready? 9/0/1 -

- - -

Proposed resolution:

- -

-Amend 18.8.3.4 [terminate] as indicated: -

- -[[noreturn]] void terminate() noexcept; -

-Remarks: Called by the implementation when exception handling must be abandoned for any of several reasons (15.5.1) -, in effect immediately after throwing the exception. May also be called directly by the program. -

- -

-Effects: Calls a terminate_handler function. It is unspecified which terminate_handler function will -be called if an exception is active during a call to set_terminate. Otherwise cCalls the current -terminate_handler function. [Note: A default terminate_handler is always considered a callable handler in -this context. — end note] -

- -

-Amend D.8.4 [unexpected] as indicated: -

- -[[noreturn]] void unexpected(); -

-Remarks: Called by the implementation when a function exits via an exception not allowed by its exception-specification -(15.5.2), in effect after evaluating the throw-expression (D.11.1). May also be called directly by the program. -

- -

-Effects: Calls an unexpected_handler function. It is unspecified which unexpected_handler -function will be called if an exception is active during a call to set_unexpected. Otherwise cCalls the current -unexpected_handler function. [Note: A default unexpected_handler is always considered a callable handler in -this context. — end note] -

- - - - - - -
-

2114. Incorrect "contextually convertible to bool" requirements

-

Section: 17.6.3.3 [nullablepointer.requirements], 24.2.3 [input.iterators], 24.2.7 [random.access.iterators], 25.1 [algorithms.general], 25.4 [alg.sorting], 30.2.1 [thread.req.paramname] Status: Open - Submitter: Daniel Krügler Opened: 2011-12-09 Last modified: 2015-05-22

-

View all issues with Open status.

-

Discussion:

- -

-As of 17.6.3.1 [utility.arg.requirements] Table 17/18, the return types of the expressions -

-
-a == b
-
-

-or -

-
-a < b
-
-

-for types satisfying the EqualityComparable or LessThanComparable -types, respectively, are required to be "convertible to bool" which corresponds to -a copy-initialization context. But several newer parts of the library that refer to -such contexts have lowered the requirements taking advantage of the new terminology of -"contextually convertible to bool" instead, which corresponds to a -direct-initialization context (In addition to "normal" direct-initialization constructions, -operands of logical operations as well as if or switch conditions also -belong to this special context). -

-One example for these new requirements are input iterators which satisfy EqualityComparable -but also specify that the expression -

-
-a != b
-
-

-shall be just "contextually convertible to bool". The same discrepancy -exists for requirement set NullablePointer in regard to several equality-related expressions. -

-For random access iterators we have -

-

-a < b contextually convertible to bool -

-

-as well as for all derived comparison functions, so strictly speaking we could have a random access -iterator that does not satisfy the LessThanComparable requirements, which looks like an -artifact to me. -

-Even if we keep with the existing requirements based on LessThanComparable or -EqualityComparable we still would have the problem that some current specifications -are actually based on the assumption of implicit convertibility instead of "explicit convertibility", e.g. -20.8.1.5 [unique.ptr.special] p3: -

-
-template <class T1, class D1, class T2, class D2>
-bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
-
-

--3- Returns: x.get() != y.get(). -

-
-

-Similar examples exist in 20.8.1.2.2 [unique.ptr.single.dtor] p2, 20.8.1.2.3 [unique.ptr.single.asgn] p9, -20.8.1.2.4 [unique.ptr.single.observers] p1+3+8, etc. -

-In all these places the expressions involving comparison functions (but not those of the conversion -of a NullablePointer to bool!) assume to be "convertible to bool". I think this -is a very natural assumption and all delegations of the comparison functions of some type X to some -other API type Y in third-party code does so assuming that copy-initialization semantics will -just work. -

-The actual reason for using the newer terminology can be rooted back to LWG 556. My hypotheses -is that the resolution of that issue also needs a slight correction. Why so? -

-The reason for opening that issue were worries based on the previous "convertible to bool" -wording. An expressions like "!pred(a, b)" might not be well-formed in those situations, because -operator! might not be accessible or might have an unusual semantics (and similarly for other logical -operations). This can indeed happen with unusual proxy return types, so the idea was that the evaluation of -Predicate, BinaryPredicate (25.1 [algorithms.general] p8+9), and Compare -(25.4 [alg.sorting] p2) should be defined based on contextual conversion to bool. -Unfortunately this alone is not sufficient: In addition, I think, we also want the predicates -to be (implicitly) convertible to bool! Without this wording, several conditions are plain wrong, -e.g. 25.2.5 [alg.find] p2, which talks about "pred(*i) != false" (find_if) and -"pred(*i) == false" (find_if_not). These expressions are not within a boolean context! -

-While we could simply fix all these places by proper wording to be considered in a "contextual conversion to -bool", I think that this is not the correct solution: Many third-party libraries already refer to -the previous C++03 Predicate definition — it actually predates C++98 and is as old as the -SGI specification. It seems to be a high price to -pay to switch to direct initialization here instead of fixing a completely different specification problem. -

-A final observation is that we have another definition for a Predicate in 30.2.1 [thread.req.paramname] p2: -

-

-If a parameter is Predicate, operator() applied to the actual template argument shall return a value that -is convertible to bool. -

-

-The problem here is not that we have two different definitions of Predicate in the standard — this -is confusing, but this fact alone is not a defect. The first (minor) problem is that this definition does not properly -apply to function objects that are function pointers, because operator() is not defined in a strict sense. -But the actually worse second problem is that this wording has the very same problem that has originally lead to -LWG 556! We only need to look at 30.5.1 [thread.condition.condvar] p15 to recognice this: -

-
-while (!pred())
-  wait(lock);
-
-

-The negation expression here looks very familiar to the example provided in LWG 556 and is sensitive -to the same "unusual proxy" problem. Changing the 30.2.1 [thread.req.paramname] wording to a corresponding -"contextual conversion to bool" wouldn't work either, because existing specifications rely on "convertible -to bool", e.g. 30.5.1 [thread.condition.condvar] p32+33+42 or 30.5.2 [thread.condition.condvarany] -p25+26+32+33. -

-To summarize: I believe that LWG 556 was not completely resolved. A pessimistic interpretation is, -that even with the current wording based on "contextually convertible to bool" the actual problem of that -issue has not been fixed. What actually needs to be required here is some normative wording that basically -expresses something along the lines of: -

-

-The semantics of any contextual conversion to bool shall be equivalent to the semantics of -any implicit conversion to bool. -

-

-This is still not complete without having concepts, but it seems to be a better approximation. Another way of solving -this issue would be to define a minimum requirements table with equivalent semantics. The proposed wording is a bit -simpler but attempts to express the same thing. -

- -

[2012, Kona]

- -

-Agree with Daniel that we potentially broke some C++03 user code, accept the changes striking -"contextually" from tables. Stefan to provide revised wording for section 25, and figure out -changes to section 30. -

-

-Move to open, and then to Review when updated wording from Stefan is available. -

- -

[2012-10-12, STL comments]

- - -
    -
  1. -

    -The current proposed resolution still isn't completely satisfying. It would certainly be possible for the Standard to -require these various expressions to be implicitly and contextually convertible to bool, but that would have -a subtle consequence (which, I will argue, is undesirable - regardless of the fact that it dates all the way back to -C++98/03). It would allow users to provide really wacky types to the Standard Library, with one of two effects: -

    -
      -
    1. -

      Standard Library implementations would have to go to great lengths to respect such wacky types, essentially using -static_cast<bool> when invoking any predicates or comparators. -

      -
      2. - -
    2. -

      -Otherwise, such wacky types would be de facto nonportable, because they would make Standard Library implementations -explode. -

      -
      3. -
    - -

    -Effect B is the status quo we're living with today. What Standard Library implementations want to do with pred(args) -goes beyond "if (pred(args))" (C++03), contextually converting pred(args) to bool (C++11), or -implicitly and contextually converting pred(args) to bool (the current proposed resolution). -Implementations want to say things like: -

    - -
    -if (pred(args))
-if (!pred(args))
-if (cond && pred(args))
-if (cond && !pred(args))
-
    - -

    -These are real examples taken from Dinkumware's implementation. There are others that would be realistic -("pred(args) && cond", "cond || pred(args)", etc.) -

    -Although negation was mentioned in this issue's Discussion section, and in LWG 556's, the current proposed -resolution doesn't fix this problem. Requiring pred(args) to be implicitly and contextually convertible to bool -doesn't prevent operator!() from being overloaded and returning std::string (as a wacky example). More -ominously, it doesn't prevent operator&&() and operator||() from being overloaded and destroying -short-circuiting. -

    - -
    2. - -
  2. -

    -I would like LWG input before working on Standardese for a new proposed resolution. Here's an outline of what I'd like to -do: -

    -
      -
    1. -

      -Introduce a new "concept" in 17.6.3 [utility.requirements], which I would call BooleanTestable in the -absence of better ideas. -

      -
      2. - -
    2. -

      -Centralize things and reduce verbosity by having everything simply refer to BooleanTestable when necessary. -I believe that the tables could say "Return type: BooleanTestable", while Predicate/BinaryPredicate/Compare -would need the incantation "shall satisfy the requirements of BooleanTestable". -

      -
      3. - -
    3. -

      -Resolve the tug-of-war between users (who occasionally want to do weird things) and implementers (who don't want to have -to contort their code) by requiring that: -

      -
        -
      1. -

        -Given a BooleanTestable x, x is both implicitly and contextually convertible to bool. -

        -
        2. - -
      2. -

        -Given a BooleanTestable x, !x is BooleanTestable. (This is intentionally "recursive".) -

        -
        3. - -
      3. -

        -Given a BooleanTestable x, bool t = x, t2(x), f = !x; has the postcondition t == t2 && t != f. -

        -
        4. - -
      4. -

        -Given a BooleanTestable x and a BooleanTestable y of possibly different types, "x && y" -and "x || y" invoke the built-in operator&&() and operator||(), triggering short-circuiting. -

        -
        5. - -
      5. -

        -bool is BooleanTestable. -

        -
        6. -
      - -
      4. - -
    - -

    - I believe that this simultaneously gives users great latitude to use types other than bool, while allowing - implementers to write reasonable code in order to get their jobs done. (If I'm forgetting anything that implementers - would want to say, please let me know.) -

    - -
    3. - -
  3. -

    -About requirement (I): As Daniel patiently explained to me, we need to talk about both implicit conversions and -contextual conversions, because it's possible for a devious type to have both "explicit operator bool()" -and "operator int()", which might behave differently (or be deleted, etc.). -

    -
    4. - -
  4. -

    -About requirement (IV): This is kind of tricky. What we'd like to say is, "BooleanTestable can't ever trigger -an overloaded logical operator". However, given a perfectly reasonable type Nice - perhaps even bool itself! - -other code (perhaps a third-party library) could overload operator&&(Nice, Evil). Therefore, I believe -that the requirement should be "no first use" - the Standard Library will ask for various BooleanTestable types -from users (for example, the result of "first != last" and the result of "pred(args)"), and as long -as they don't trigger overloaded logical operators with each other, everything is awesome. -

    -
    5. - - -
  5. -

    -About requirement (V): This is possibly redundant, but it's trivial to specify, makes it easier for users to understand -what they need to do ("oh, I can always achieve this with bool"), and provides a "base case" for requirement -(IV) that may or may not be necessary. Since bool is BooleanTestable, overloading -operator&&(bool, Other) (etc.) clearly makes the Other type non-BooleanTestable. -

    -
    6. -
- -Previous resolution from Daniel [SUPERSEDED]: -

-

-

This wording is relative to the FDIS.

- -
    -

  1. Change Table 25 — "NullablePointer requirements" in 17.6.3.3 [nullablepointer.requirements] -as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 25 — NullablePointer requirements
    ExpressionReturn typeOperational semantics
    -[…] -
    -a != b - -contextually convertible to bool - -!(a == b) -
    -a == np
    -np == a     -    		 -contextually convertible to bool - -a == P() -
    -a != np
    -np != a     -    		 -contextually convertible to bool - -!(a == np) -
    - -
    2. - -

  2. Change Table 107 — "Input iterator requirements" in 24.2.3 [input.iterators] -as indicated:

    - - - - - - - - - - - - - - - - - - - - - -
    Table 107 — Input iterator requirements (in addition to Iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    -a != b - -contextually convertible to bool - -!(a == b) - -pre: (a, b) is in the domain of ==. -
    -[…] -
    - -
    3. - -

  3. Change Table 111 — "Random access iterator requirements" in 24.2.7 [random.access.iterators] -as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 111 — Random access iterator requirements (in addition to bidirectional iterator)
    ExpressionReturn typeOperational semanticsAssertion/note
    pre-/post-condition
    -[…] -
    -a < b - -contextually convertible to bool - -b - a > 0 - -< is a total ordering relation -
    -a > b - -contextually convertible to bool - -b < a - -> is a total ordering relation opposite to <. -
    -a >= b - -contextually convertible to bool - -!(a < b) - -
    -a <= b - -contextually convertible to bool - -!(a > b) - -
    - -
    4. - -

  4. Change 25.1 [algorithms.general] p8+9 as indicated:

    - -
    -

    --8- The Predicate parameter is used whenever an algorithm expects a function object -(20.9 [function.objects]) that, when applied to the result of dereferencing the corresponding iterator, -returns a value testable as true. In other words, if an algorithm takes Predicate pred -as its argument and first as its iterator argument, it should work correctly in the construct -pred(*first) implicitly or contextually converted to bool (Clause 4 [conv]). -The function object pred shall not apply any non-constant function through the dereferenced iterator. -

    --9- The BinaryPredicate parameter is used whenever an algorithm expects a function object that when applied -to the result of dereferencing two corresponding iterators or to dereferencing an iterator and type -T when T is part of the signature returns a value testable as true. In other words, if an algorithm takes -BinaryPredicate binary_pred as its argument and first1 and first2 as its iterator arguments, it should -work correctly in the construct binary_pred(*first1, *first2) implicitly or contextually converted to -bool (Clause 4 [conv]). -BinaryPredicate always takes the first iterator's value_type as its first argument, that is, in those cases -when T value is part of the signature, it should work correctly in the construct binary_pred(*first1, value) -implicitly or contextually converted to bool (Clause 4 [conv]). binary_pred shall -not apply any non-constant function through the dereferenced iterators. -

    -
    -
    5. - -

  5. Change 25.4 [alg.sorting] p2 as indicated:

    - -
    -

    --2- Compare is a function object type (20.9 [function.objects]). The return value of the function -call operation applied to an object of type Compare, when implicitly or contextually converted -to bool (4 [conv]), yields true if the first argument of the call is less than the second, and -false otherwise. Compare comp is used throughout for algorithms assuming an ordering relation. It is assumed -that comp will not apply any non-constant function through the dereferenced iterator. -

    -
    -
    6. - -

  6. Change 30.2.1 [thread.req.paramname] p2 as indicated:

    - -
    -

    --2- If a parameter is Predicate, operator() applied to the actual template argument shall return a value that -is convertible to boolPredicate is a function object type (20.9 [function.objects]). -The return value of the function call operation applied to an object of type Predicate, when implicitly or -contextually converted to bool (4 [conv]), yields true if the corresponding test condition is -satisfied, and false otherwise. -

    -
    -
    7. - -
-
- -

[2014-05-20, Daniel suggests concrete wording based on STL's proposal]

- -

-The presented wording follows relatively closely STL's outline with the following notable exceptions: -

-
    -

  1. -A reference to BooleanTestable in table "Return Type" specifications seemed very unusual to me and -I found no "prior art" for this in the Standard. Instead I decided to follow the usual style to add a symbol -with a specific meaning to a specific paragraph that specifies symbols and their meanings. -

    2. -

  2. -STL's requirement IV suggested to directly refer to built-in operators && and ||. In my -opinion this concrete requirement isn't needed if we simply require that two BooleanTestable operands behave -equivalently to two those operands after conversion to bool (each of them). -

    3. -

  3. -I couldn't find a good reason to require normatively that type bool meets the requirements of BooleanTestable: My -assertion is that after having defined them, the result simply falls out of this. But to make this a bit clearer, I added -also a non-normative note to these effects. -

    4. -
- -

[2014-06-10, STL comments]

- -

-In the current wording I would like to see changed the suggested changes described by bullet #6: -

-
    -

  1. In 23.2.1 [container.requirements.general] p4 undo the suggested change

    2. -

  2. Then change the 7 occurrences of "convertible to bool" in the denoted tables to "bool".

    3. -
- -

[2015-05-05 Lenexa]

- -

STL: Alisdair wanted to do something here, but Daniel gave us updated wording.

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 17.6.3.1 [utility.arg.requirements] p1, Table 17 — "EqualityComparable requirements", and -Table 18 — "LessThanComparable requirements" as indicated:

    - -
    -

    --1- […] In these tables, T is an object or reference type to be supplied by a C++ program -instantiating a template; a, b, and c are values of type (possibly const) T; -s and t are modifiable lvalues of type T; u denotes an identifier; rv -is an rvalue of type T; and v is an lvalue of type (possibly const) T or an -rvalue of type const T; and BT denotes a type that meets the BooleanTestable -requirements ([booleantestable.requirements]). -

    -[…] -

    -
    - - - - - - - - - - - - - - -
    Table 17 — EqualityComparable requirements [equalitycomparable]
    ExpressionReturn typeRequirement
    -a == b - -convertible to
    -bool    BT -    		 -== is an equivalence relation, that is, it has the -following properties: […] -
    -
    -

    -[…] -

    -
    - - - - - - - - - - - - - - -
    Table 18 — LessThanComparable requirements [lessthancomparable]
    ExpressionReturn typeRequirement
    -a < b - -convertible to
    -bool    BT -    		 -< is a strict weak ordering relation (25.4 [alg.sorting]) -
    -
    - -
    - -
    2. - -

  2. Between 17.6.3.2 [swappable.requirements] and 17.6.3.3 [nullablepointer.requirements] insert a new sub-clause -as indicated:

    - -
    -?.?.?.? BooleanTestable requirements [booleantestable.requirements] -
    -

    --?- A BooleanTestable type is a boolean-like type that also supports conversions to bool. -A type B meets the BooleanTestable requirements if the expressions described in Table ?? are valid -and have the indicated semantics, and if B also satisfies all the other requirements of this sub-clause -[booleantestable.requirements]. -

    -An object b of type B can be implicitly converted to bool and can be contextually converted -to bool (Clause 4). The result values of both kinds of conversions shall be equivalent. -

    -[Example: The types bool, std::true_type, and std::bitset<>::reference are -BooleanTestable types. — end example] -

    -In Table ??, B2 and Bn denote types (possibly equal to B or to each other) that meet the -BooleanTestable requirements, b1 denotes a (possibly const) value of B, b2 -denotes a (possibly const) value of B2, and t1 denotes a value of type bool. -

    -
    -
    -
    3. - -

  3. Somewhere within the new sub-clause [booleantestable.requirements] insert the following new Table (?? denotes -the assigned table number):

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table ?? — BooleanTestable requirements [booleantestable]
    ExpressionReturn typeOperational semantics
    -bool(b1) - -bool - -Remarks: bool(b1) == t1 for every value
    -b1 implicitly converted to t1. -
    -!b1 - -Bn - -Remarks: bool(b1) == !bool(!b1) for
    -every value b1. -
    -b1 && b2 - -bool - -bool(b1) && bool(b2) -
    -b1 || b2 - -bool - -bool(b1) || bool(b2) -
    -
    - -
    4. - -

  4. Change 17.6.3.3 [nullablepointer.requirements] p5 and Table 25 — "NullablePointer requirements" as indicated:

    - -
    -

    -[…] -

    --5- In Table 25, u denotes an identifier, t denotes a non-const lvalue of type P, a -and b denote values of type (possibly const) P, and np denotes a value of type -(possibly const) std::nullptr_t, and BT denotes a type that meets the BooleanTestable -requirements ([booleantestable.requirements]). -

    -[…] -

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 25 — NullablePointer requirements [nullablepointer]
    ExpressionReturn typeOperational semantics
    -… -
    -a != b - -contextually convertible to boolBT - -[…] -
    -a == np
    -np == a -    		 -contextually convertible to boolBT - -[…] -
    -a != np
    -np != a -    		 -contextually convertible to boolBT - -[…] -
    -
    -
    -
    5. - -

  5. Change 20.4.2.7 [tuple.rel] as indicated;

    - -
    -
    -template<class... TTypes, class... UTypes>
-constexpr bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
    -
    -

    --1- Requires: For all i, where 0 <= i and i < sizeof...(TTypes), -get<i>(t) == get<i>(u) is a valid expression returning a type that is convertible to -boolmeets the BooleanTestable requirements ([booleantestable.requirements]). -sizeof...(TTypes) == sizeof...(UTypes). -

    -[…] -

    -
    -
    -template<class... TTypes, class... UTypes>
-constexpr bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
    -
    -

    --4- Requires: For all i, where 0 <= i and i < sizeof...(TTypes), -get<i>(t) < get<i>(u) and get<i>(u) < get<i>(t) are valid -expressions returning types that are convertible to -boolmeet the BooleanTestable requirements ([booleantestable.requirements]). -sizeof...(TTypes) == sizeof...(UTypes). -

    -[…] -

    -
    -
    -
    6. - -

  6. Change 23.2.1 [container.requirements.general], Table 96 — "Container requirements", and -Table 98 — "Optional container operations" as indicated:

    - -
    -

    --4- In Tables 96, 97, and 98 X denotes a container class containing objects of type T, a and -b denote values of type X, u denotes an identifier, r denotes a non-const value -of type X, and rv denotes a non-const rvalue of type X, and BT -denotes a type that meets the BooleanTestable requirements ([booleantestable.requirements]). -

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 96 — Container requirements
    ExpressionReturn type[…]
    -… -
    -a == b - -convertible to
    -bool    BT -    		 -[…] -
    -a != b - -convertible to
    -bool    BT -    		 -[…] -
    -… -
    -a.empty() - -convertible to
    -bool    BT -    		 -[…] -
    -
    -

    -[…] -

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 98 — Optional container requirements
    ExpressionReturn type[…]
    -… -
    -a < b - -convertible to
    -bool    BT -    		 -[…] -
    -a > b - -convertible to
    -bool    BT -    		 -[…] -
    -a <= b - -convertible to
    -bool    BT -    		 -[…] -
    -a >= b - -convertible to
    -bool    BT -    		 -[…] -
    -
    -
    -
    7. - -

  7. Change 24.2.1 [iterator.requirements.general], Table 107 — "Input iterator requirements", and -Table 111 — "Random access iterator requirements" as indicated:

    - -
    -

    --11- In the following sections, a and b denote values of type X or const X, -difference_type and reference refer to the types iterator_traits<X>::difference_type and -iterator_traits<X>::reference, respectively, n denotes a value of difference_type, u, -tmp, and m denote identifiers, r denotes a value of X&, t denotes -a value of value type T, o denotes a value of some type that is writable to the output iterator, and BT -denotes a type that meets the BooleanTestable requirements ([booleantestable.requirements]). -

    -
    - - - - - - - - - - - - - -
    Table 107 — Input iterator requirements
    ExpressionReturn type[…]
    -a != b - -contextually convertible to
    -bool    BT -    		 -[…] -
    -
    -

    -[…] -

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 111 — Random access iterator requirements
    ExpressionReturn type[…]
    -… -
    -a < b - -contextually convertible to
    -bool    BT -    		 -[…] -
    -a > b - -contextually convertible to
    -bool    BT -    		 -[…] -
    -a >= b - -contextually convertible to
    -bool    BT -    		 -[…] -
    -a <= b - -contextually convertible to
    -bool    BT -    		 -[…] -
    -
    -
    -
    8. - -

  8. Change 25.1 [algorithms.general] p8+p9 as indicated: [Drafting note: The wording change also fixes -(a) unusual wording forms used ("should work") which are unclear in which sense they are imposing normative requirements and -(b) the problem, that the current wording seems to allow that the predicate may mutate a call argument, if that is not a -dereferenced iterator. -Upon applying the new wording it became obvious that the wording has the effect that currently algorithms such as -adjacent_find, search_n, unique, and unique_copy are not correctly described -(because they have no iterator argument named first1), which could give raise to a new library issue. -— end drafting note]

    - -
    -

    --8- The Predicate parameter is used whenever an algorithm expects a function object (20.9) that, when applied -to the result of dereferencing the corresponding iterator, returns a value testable as true. In other words, -iIf an algorithm takes Predicate pred as its argument and first as its iterator argument, -it should work correctly in the construct pred(*first) contextually converted to -bool (Clause 4)the expression pred(*first) shall have a type that meets the BooleanTestable -requirements ( [booleantestable.requirements]). -The function object pred shall not apply any non-constant function through the dereferenced -iteratorits argument. -

    --9- The BinaryPredicate parameter is used whenever an algorithm expects a function object that when applied -to the result of dereferencing two corresponding iterators or to dereferencing an iterator and type -T when T is part of the signature returns a value testable as true. In other words, -iIf an algorithm takes BinaryPredicate binary_pred as its argument and first1 and -first2 as its iterator arguments, it should work correctly in the construct binary_pred(*first1, *first2) -contextually converted to bool (Clause 4)the expression binary_pred(*first1, *first2) shall -have a type that meets the BooleanTestable requirements ( [booleantestable.requirements]). -BinaryPredicate always takes the first iterator's value_type as its first argument, that is, in those cases -when T value is part of the signature, it should work correctly in the construct binary_pred(*first1, value) -contextually converted to bool (Clause 4)the expression binary_pred(*first1, value) shall have a -type that meets the BooleanTestable requirements ( [booleantestable.requirements]). binary_pred -shall not apply any non-constant function through the dereferenced iteratorsany of its arguments. -

    -
    -
    9. - -

  9. Change 25.4 [alg.sorting] p2 as indicated:

    - -
    -

    -[…] -

    --2- Compare is a function object type (20.9). The return value of the function call -operation applied to an object of type Compare, when contextually converted -to bool(Clause 4), yields true if the first argument of the call is less than the second, -and false otherwise. Compare comp is used throughout for algorithms assuming an ordering relation. -Let a and b denote two argument values whose types depend on the corresponding algorithm. Then the expression -comp(a, b) shall have a type that meets the BooleanTestable requirements ( [booleantestable.requirements]). -The return value of comp(a, b), converted to bool, yields true if the -first argument a is less than the second argument b, and false otherwise. It is assumed that -comp will not apply any non-constant function through the dereferenced iteratorany of its arguments. -

    -[…] -

    -
    -
    10. - -

  10. Change 27.5.4.2 [fpos.operations] and Table 127 — "Position type requirements" as indicated:

    - -
    -

    --1- Operations specified in Table 127 are permitted. In that table, -

    -
      -

    • P refers to an instance of fpos,

      • -

    • […]

      • -

    • o refers to a value of type streamoff,

      • -

    • BT refers to a type that meets the BooleanTestable requirements ([booleantestable.requirements]),

      • -

    • […]

      • -
    -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 127 — Position type requirements
    ExpressionReturn type[…]
    -… -
    -p == q - -convertible to boolBT - -[…] -
    -p != q - -convertible to boolBT - -[…] -
    -
    -
    -
    -
    -
    11. - -

  11. Change 30.2.1 [thread.req.paramname] p2 as indicated:

    - -
    -

    --2- If a parameter is Predicate, operator() applied to the actual template argument shall return a value that -is convertible to boolPredicate is a function object type (20.9 [function.objects]). -Let pred denote an lvalue of type Predicate. Then the expression pred() shall have a type that meets the -BooleanTestable requirements ( [booleantestable.requirements]). The return value of pred(), -converted to bool, yields true if the corresponding test condition is satisfied, and false otherwise. -

    -
    -
    12. -
- - - - - -
-

2115. Undefined behaviour for valarray assignments with mask_array index?

-

Section: 26.6.8 [template.mask.array] Status: Open - Submitter: Thomas Plum Opened: 2011-12-10 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

- -

-Recently I received a Service Request (SR) alleging that one of our testcases causes an -undefined behavior. The complaint is that 26.6.8 [template.mask.array] in C++11 -(and the corresponding subclause in C++03) are interpreted by some people to require that -in an assignment "a[mask] = b", the subscript mask and the rhs b -must have the same number of elements. -

-IMHO, if that is the intended requirement, it should be stated explicitly. -

-In any event, there is a tiny editorial cleanup that could be made: -

-In C++11, 26.6.8.1 [template.mask.array.overview] para 2 mentions -

-

-"the expression a[mask] = b;" -

-

-but the semicolon cannot be part of an expression. The correction could omit the -semicolon, or change the word "expression" to "assignment" or "statement". -

-Here is the text of the SR, slightly modified for publication: -

-
-

-Subject: SR01174 LVS _26322Y31 has undefined behavior [open] -

-[Client:]
-The test case t263.dir/_26322Y31.cpp seems to be illegal as it has an undefined -behaviour. I searched into the SRs but found SRs were not related to the topic -explained in this mail (SR00324, SR00595, SR00838). -

-
-const char vl[] = {"abcdefghijklmnopqrstuvwxyz"};
-const char vu[] = {"ABCDEFGHIJKLMNOPQRSTUVWXYZ"};
-const std::valarray<char> v0(vl, 27), vm5(vu, 5), vm6(vu, 6);
-std::valarray<char> x = v0;
-[…]
-const bool vb[] = {false, false, true, true, false, true};
-const std::valarray<bool> vmask(vb, 6);
-x = v0;
-x[vmask] = vm5;      // ***** HERE....
-steq(&x[0], "abABeCghijklmnopqrstuvwxyz");
-x2 = x[vmask];       // ***** ....AND HERE
-[…]
-
-

-This problem has already been discussed between [experts]: -See thread http://gcc.gnu.org/ml/libstdc++/2009-11/threads.html#00051 -Conclusion http://gcc.gnu.org/ml/libstdc++/2009-11/msg00099.html -

-[Plum Hall:]
-Before I log this as an SR, I need to check one detail with you. -

-I did read the email thread you mentioned, and I did find a citation (see INCITS ISO/IEC 14882-2003 -Section 26.3.2.6 on valarray computed assignments): -

-Quote: "If the array and the argument array do not have the same length, the behavior is undefined", -

-But this applies to computed assignment (*=, +=, etc), not to simple assignment. Here is the C++03 citation -re simple assignment: -

-26.3.2.2 valarray assignment [lib.valarray.assign] -

-
-valarray<T>& operator=(const valarray<T>&);
-
-

-1 Each element of the *this array is assigned the value of the corresponding element of the argument array. -The resulting behavior is undefined if the length of the argument array is not equal to the length of the -*this array. -

-
-

-In the new C++11 (N3291), we find ... -

-26.6.2.3 valarray assignment [valarray.assign] -

-
-valarray<T>& operator=(const valarray<T>& v);
-
-

-1 Each element of the *this array is assigned the value of the corresponding element of the argument -array. If the length of v is not equal to the length of *this, resizes *this to make -the two arrays the same length, as if by calling resize(v.size()), before performing the assignment. -

-
-

-So it looks like the testcase might be valid for C++11 but not for C++03; what do you think? -

-[Client:]
-I quite agree with you but the two problems I mentioned: -

-
-x[vmask] = vm5;      // ***** HERE....
-[…]
-x2 = x[vmask];       // ***** ....AND HERE
-
-

-refer to mask_array assignment hence target the C++03 26.3.8 paragraph. Correct? -

-[Plum Hall:]
-I mentioned the contrast between C++03 26.3.2.2 para 1 versus C++11 26.6.2.3 para 1. -

-But in C++03 26.3.8, I don't find any corresponding restriction. Could you quote the specific -requirement you're writing about? -

-[Client:]
-I do notice the difference between c++03 26.3.2.2 and c++11 26.6.2.3 about assignments between -different sized valarray and I perfectly agree with you. -

-But, as already stated, this is not a simple valarray assignment but a -mask_array assignment (c++03 26.3.8 / c++11 26.6.8). See c++11 quote below: -

-26.6.8 Class template mask_array
-26.6.8.1 Class template mask_array overview
-[....] -

-
    -

  1. This template is a helper template used by the mask subscript operator: -mask_array<T> valarray<T>::operator[](const valarray<bool>&). -

    2. -

  2. It has reference semantics to a subset of an array specified by a boolean mask. Thus, -the expression a[mask] = b; has the effect of assigning the elements of b -to the masked elements in a (those for which the corresponding element in mask is true.) -

    3. -
-

-26.6.8.2 mask_array assignment -

-
-void operator=(const valarray<T>&) const;
-const mask_array& operator=(const mask_array&) const;
-
-

-1 These assignment operators have reference semantics, assigning the values of the argument array -elements to selected elements of the valarray<T> object to which it refers. -

-
-

-In particular, [one of the WG21 experts] insisted on the piece "the elements of b". -

-That is why I reported the test t263.dir/_26322Y31.cpp having an undefined behaviour. -

-[Plum Hall:]
-OK, I can see that I will have to ask WG21; I will file an appropriate issue -with the Library subgroup. In the meantime, I will mark this testcase as "DISPUTED" -so that it is not required for conformance testing, until we get a definitive opinion. -

-
- -

[2012, Kona]

- -

-Moved to Open. -

-

-There appears to be a real need for clarification in the standard, and -implementations differ in their current interpretation. This will need -some research by implementers and a proposed resolution before further -discussion is likely to be fruitful. -

- - - -

Proposed resolution:

- - - - - -
-

2116. std::swap noexcept(what?)

-

Section: 20.10.4.3 [meta.unary.prop] Status: Open - Submitter: Dave Abrahams Opened: 2011-12-09 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with Open status.

-

Discussion:

- -

-IMO if we specified is_[nothrow_]constructible in terms of a variable -declaration whose validity requires destructibility, it is clearly a bug -in our specification and a failure to realize the actual original -intent. The specification should have been in terms of placement-new. -

-Daniel:
-At the time of the specification this was intended and the solution is -not done by removing the destruction semantics of is_constructible. -

-The design of is_constructible was also impacted by the previous -Constructible concept that explicitly contained destruction semantics, -because during conceptification of the library it turned out to simplify -the constraints in the library because you did not need to add -Destructible all the time. It often was implied but never spoken out -in C++03. -

-Pure construction semantics was considered as useful as well, so HasConstructor -did also exist and would surely be useful as trait as well. -

-Another example that is often overlooked: This also affects wrapper types like pair, -tuple, array that contain potentially more than one type: -This is easy to understand if you think of T1 having a deleted destructor -and T2 having a constructor that may throw: Obviously the compiler has -potentially need to use the destructor of T1 in the constructor -of std::pair<T1, T2> to ensure that the core language requirements -are satisfied (All previous fully constructed sub-objects must be destructed). -

-The core language also honors this fact in 12.8 [class.copy] p11: -

-

-A defaulted copy/move constructor for a class X is defined as deleted (8.4.3 [dcl.fct.def.delete]) -if X has:
-[…]
-— any direct or virtual base class or non-static data member of a type with a destructor that is deleted -or inaccessible from the defaulted constructor,
-[…] -

-

-Dave:
-This is about is_nothrow_constructible in particular. The fact that it is -foiled by not having a noexcept dtor is a defect. -

- -

[2012, Kona]

- -

-Move to Open. -

-

-is_nothrow_constructible is defined in terms of is_constructible, which is defined -by looking at a hypothetical variable and asking whether the variable definition is known not to -throw exceptions. The issue claims that this also examines the type's destructor, given the context, -and thus will return false if the destructor can potentially throw. At least one -implementation (Howard's) does return false if the constructor is noexcept(true) -and the destructor is noexcept(false). So that's not a strained interpretation. -The issue is asking for this to be defined in terms of placement new, instead of in terms -of a temporary object, to make it clearer that is_nothrow_constructible looks at the -noexcept status of only the constructor, and not the destructor. -

-

-Sketch of what the wording would look like: -

-

-require is_constructible, and then also require that a placement new operation -does not throw. (Remembering the title of this issue... What does this imply for swap? -

-

-If we accept this resolution, do we need any changes to swap? -

-

STL argues: no, because you are already forbidden from passing anything with a throwing -desturctor to swap. -

-

-Dietmar argues: no, not true. Maybe statically the destructor can conceivably throw for some -values, but maybe there are some values known not to throw. In that case, it's correct to -pass those values to swap. -

- - - -

Proposed resolution:

- - - - - -
-

2117. ios_base manipulators should have showgrouping/noshowgrouping

-

Section: 22.4.2.2.2 [facet.num.put.virtuals], 27.5.3.1.2 [ios::fmtflags], 27.5.6.1 [fmtflags.manip] Status: New - Submitter: Benjamin Kosnik Opened: 2011-12-15 Last modified: 2015-04-08

-

View all other issues in [facet.num.put.virtuals].

-

View all issues with New status.

-

Discussion:

- -

-Iostreams should include a manipulator to toggle grouping on/off for -locales that support grouped digits. This has come up repeatedly and -been deferred. See LWG 826 for the previous attempt. -

-If one is using a locale that supports grouped digits, then output -will always include the generated grouping characters. However, very -plausible scenarios exist where one might want to output the number, -un-grouped. This is similar to existing manipulators that toggle -on/off the decimal point, numeric base, or positive sign. -

-See some user commentary here. -

- - -

[21012, Kona]

- -

-Move to Open. -

-

-This is a feature request. -

-

-Walter is slightly uncomfortable with processing feature requests through the issues lists. -

-

-Alisdair says this is far from the first feature request that has come in from the issues list. -

-

-STL: The fact that you can turn off grouping on hex output is compelling. -

-

-Marshall: if we add this flag, we'll need to update tables 87-91 as well. -

-

-STL: If it has been implemented somewhere, and it works, we'd be glad to add it. -

-

-Howard: We need to say what the default is. -

-

-Alisdair sumarizes: -

-

-(1) We want clear wording that says what the effect is of turning the flag off; -

-

-(2) what the default values are, and -

-

-(3) how this fits into tables 87-90. (and 128) -

- -

[Issaquah 2014-02-10-12: Move to LEWG]

- -

-Since this issue was filed, we have grown a new working group that is better placed to handle feature requests. -

-

-We will track such issues with an LEWG status until we get feedback from the Library Evolution Working Group. -

- -

[Issaquah 2014-02-12: LEWG discussion]

- - - - - - -
Do we think this feature should exist?
SFFNASA
2 4100
- -

Think about the ABI break for adding a flag. But this could be -mitigated by putting the data into an iword instead of a flag.

- -

This needs to change Stage 2 in [facet.num.put.virtuals].

- -

Previous resolution, which needs the above corrections:

-
-

This wording is relative to the FDIS.

- -
    -
  1. -

    Insert in 22.4.2.2.2 [facet.num.put.virtuals] paragraph 5:

    - -

    -Stage 1: The first action of stage 1 is to determine a conversion specifier. The tables that describe -this determination use the following local variables -

    -
    -fmtflags flags = str.flags() ;
-fmtflags basefield = (flags & (ios_base::basefield));
-fmtflags uppercase = (flags & (ios_base::uppercase));
-fmtflags floatfield = (flags & (ios_base::floatfield));
-fmtflags showpos = (flags & (ios_base::showpos));
-fmtflags showbase = (flags & (ios_base::showbase));
-fmtflags showgrouping = (flags & (ios_base::showgrouping));
-
    -
    -
    2. - -

  2. Change header <ios> synopsis, 27.5.1 [iostreams.base.overview] as indicated:

    - -
    -#include <iosfwd>
-
-namespace std {
-  […]
-  // 27.5.6, manipulators:
-  […]
-  ios_base& showpoint     (ios_base& str);
-  ios_base& noshowpoint   (ios_base& str);
-  ios_base& showgrouping  (ios_base& str);
-  ios_base& noshowgrouping(ios_base& str);
-  ios_base& showpos       (ios_base& str);
-  ios_base& noshowpos     (ios_base& str);
-  […]
-}
-
    -
    3. - -

  3. Change class ios_base synopsis, 27.5.3 [ios.base] as indicated:

    - -
    -namespace std {
-  class ios_base {
-  public:
-  class failure;
-    // 27.5.3.1.2 fmtflags
-    typedef T1 fmtflags;
-    […]
-    static constexpr fmtflags showpoint = unspecified ;
-    static constexpr fmtflags showgrouping = unspecified ;
-    static constexpr fmtflags showpos = unspecified ;
-    […]
-  };
-}
-
    -
    4. - -

  4. Add a new entry to Table 122 — "fmtflags effects" as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 122 — fmtflags effects
    ElementEffect(s) if set
    -[…] -
    -showpoint - -generates a decimal-point character unconditionally in generated floatingpoint output -
    -showgrouping - -generates grouping characters unconditionally in generated output -
    -[…] -
    - -
    5. - -

  5. After 27.5.3.1.2 [ios::fmtflags] p12 insert the following:

    -
    -ios_base& showgrouping(ios_base& str);
-
    -

    --?- Effects: Calls str.setf(ios_base::showgrouping). -

    --?- Returns: str. -

    -
    -
    -ios_base& noshowgrouping(ios_base& str);
-
    -

    --?- Effects: Calls str.unsetf(ios_base::showgrouping). -

    --?- Returns: str. -

    -
    -
    -
    6. - -
- -
- - -

Proposed resolution:

- - - - - -
-

2119. Missing hash specializations for extended integer types

-

Section: 20.9.13 [unord.hash] Status: Ready - Submitter: Daniel Krügler Opened: 2011-12-16 Last modified: 2015-05-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

View all issues with Ready status.

-

Discussion:

- -

-According to the header <functional> synopsis 20.9 [function.objects] -and to the explicit description in 20.9.13 [unord.hash] class template -hash specializations shall be provided for all arithmetic types that are -not extended integer types. This is not explicitly mentioned, but neither the list -nor any normative wording does include them, so it follows by implication. -

-What are the reasons that extended integer types are excluded? E.g. for -numeric_limits corresponding specializations are required. I would -expect that an unordered_map with key type std::uintmax_t would -just work, but that depends now on whether this type is an extended integer type -or not. -

-This issue is not asking for also providing specializations for the -cv-qualified arithmetic types. While this is surely a nice-to-have feature, -I consider that restriction as a more secondary problem in practice. -

-The proposed resolution also fixes a problem mentioned in 2109 in regard -to confusing requirements on user-defined types and those on implementations. -

- -

[2012, Kona]

- -

-Move to Open. -

-

-Agreed that it's a real issue and that the proposed wording fixes it. However, the wording -change is not minimal and isn't consistent with the way we fixed hash wording elsewhere. -

-

Alisdair will provide updated wording. -

- -

[2014-05-06 Geoffrey Romer suggests alternative wording]

- - -

-Previous resolution from Daniel [SUPERSEDED]: -

-
-

This wording is relative to the FDIS.

- -

Change 20.9.13 [unord.hash] p2 as indicated:

- -
-template <> struct hash<bool>;
-template <> struct hash<char>;
-[…]
-template <> struct hash<long double>;
-template <class T> struct hash<T*>;
-
-

--2- Requires: the template specializations shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<functional> provides definitions for specializations of the -hash class template for each cv-unqualified arithmetic type. This -header also provides a definition for a partial specialization of the hash -class template for any pointer type. The requirements for the members of these -specializations are given in sub-clause 20.9.13 [unord.hash]. -

-
-
- -

[2015-05, Lenexa]

- -

-STL: the new PR is very simple and could resolve that nicely
-MC: the older PR is rather longish -

-
    -

  • anybody have any objections to this approach?

    • -

  • what people want to have as a status?

    • -
-

-STL: I want to have Ready
-MC: move to ready: in favor: 13, opposed: 0, abstain: 4 -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -

Change 20.9.13 [unord.hash] p1 as indicated:

- -

-The unordered associative containers defined in 23.5 use specializations of the class template hash as the -default hash function. For all object types Key for which there exists a specialization hash<Key>, -and for all integral and enumeration types (7.2) Key, the instantiation hash<Key> shall: […] -

- - - - - - -
-

2121. app for string streams

-

Section: 27.8.5.1 [stringstream.cons] Status: New - Submitter: Nicolai Josuttis Opened: 2012-01-15 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

- -

-This issue was raised while discussing issue 1448. -

-Note the following program: -

-
-string s("s1: 123456789");
-ostringstream s1(s, ios_base::out|ios_base::app);
-s1 << "hello";
-cout << s1.str() << endl;
-
-

-With g++4.x it prints: -

-
-s1: 123456789hello
-
-

-With VisualC++10 it prints: -

-
-hello23456789
-
-

-From my intuitive understanding the flag "app" should result in the output of g++4.x. -I also would read that from 27.5.3.1.4 [ios::openmode] claiming: -

-

-app   seek to end before each write -

-

-However in issue 1448 P.J.Plauger comments: -

-

-I think we should say nothing special about app at construction time (thus leaving the write pointer at the beginning of the buffer). -Leave implementers wiggle room to ensure subsequent append writes as they see fit, but don't change existing rules for initial seek -position. -

-

-Note that the flag ate on both platforms appends "hello" to s. -

- - - -

Proposed resolution:

- - - - - -
-

2127. Move-construction with raw_storage_iterator

-

Section: 20.7.10 [storage.iterator] Status: Ready - Submitter: Jonathan Wakely Opened: 2012-01-23 Last modified: 2015-05-08

-

View all other issues in [storage.iterator].

-

View all issues with Ready status.

-

Discussion:

- -

-Aliaksandr Valialkin pointed out that raw_storage_iterator only supports constructing -a new object from lvalues so cannot be used to construct move-only types: -

-
-template <typename InputIterator, typename T>
-void move_to_raw_buffer(InputIterator first, InputIterator last, T *raw_buffer)
-{
-  std::move(first, last, std::raw_storage_iterator<T *, T>(raw_buffer));
-}
-
-

-This could easily be solved by overloading operator= for rvalues. -

-Dave Abrahams: -

-raw_storage_iterator causes exception-safety problems when used with any -generic algorithm. I suggest leaving it alone and not encouraging its use. -

- -

[2014-11-11, Jonathan provides improved wording]

- -

-In Urbana LWG decided to explicitly say the value is constructed from an rvalue. -

- -Previous resolution from Jonathan [SUPERSEDED]: -

-

-

This wording is relative to N3337.

- -
    -

  1. Add a new signature to the synopsis in 20.7.10 [storage.iterator] p1:

    - -
    -namespace std {
-  template <class OutputIterator, class T>
-  class raw_storage_iterator
-    : public iterator<output_iterator_tag,void,void,void,void> {
-  public:
-    explicit raw_storage_iterator(OutputIterator x);
-
-    raw_storage_iterator<OutputIterator,T>& operator*();
-    raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
-    raw_storage_iterator<OutputIterator,T>& operator=(T&& element);
-    raw_storage_iterator<OutputIterator,T>& operator++();
-    raw_storage_iterator<OutputIterator,T> operator++(int);
-};
-}
-
    -
    2. - -

  2. Insert the new signature and a new paragraph before p4:

    - -
    -raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
-raw_storage_iterator<OutputIterator,T>& operator=(T&& element);
-
    -

    --?- Requires: For the first signature T shall be CopyConstructible. For -the second signature T shall be MoveConstructible. -

    --4- Effects: Constructs a value from element at the location to which the iterator points. -

    --5- Returns: A reference to the iterator. -

    -
    -
    3. -
-
- -

[2015-05, Lenexa]

- -

-MC: Suggestion to move it to Ready for incorporation on Friday
-MC: move to ready: in favor: 12, opposed: 0, abstain: 3 -

- - -

Proposed resolution:

-

This wording is relative to N4140.

- -
    -

  1. Add a new signature to the synopsis in 20.7.10 [storage.iterator] p1:

    - -
    -namespace std {
-  template <class OutputIterator, class T>
-  class raw_storage_iterator
-    : public iterator<output_iterator_tag,void,void,void,void> {
-  public:
-    explicit raw_storage_iterator(OutputIterator x);
-
-    raw_storage_iterator<OutputIterator,T>& operator*();
-    raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
-    raw_storage_iterator<OutputIterator,T>& operator=(T&& element);
-    raw_storage_iterator<OutputIterator,T>& operator++();
-    raw_storage_iterator<OutputIterator,T> operator++(int);
-};
-}
-
    -
    2. - -

  2. Insert a new paragraph before p4:

    - -
    -raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
-
    -

    --?- Requires: T shall be CopyConstructible. -

    --4- Effects: Constructs a value from element at the location to which the iterator points. -

    --5- Returns: A reference to the iterator. -

    -
    -
    3. - -

  3. Insert the new signature and a new paragraph after p5:

    - -
    -raw_storage_iterator<OutputIterator,T>& operator=(T&& element);
-
    -

    --?- Requires: T shall be MoveConstructible. -

    --?- Effects: Constructs a value from std::move(element) at the -location to which the iterator points. -

    --?- Returns: A reference to the iterator. -

    -
    -
    4. -
- - - - - - -
-

2133. Attitude to overloaded comma for iterators

-

Section: 17.6.5.4 [global.functions] Status: Ready - Submitter: Yakov Galka Opened: 2012-01-25 Last modified: 2015-05-08

-

View all other issues in [global.functions].

-

View all issues with Ready status.

-

Discussion:

-

-17.6.5.4 [global.functions] says -

-

-Unless otherwise specified, global and non-member functions in the standard library -shall not use functions from another namespace which are found through argument-dependent -name lookup (3.4.2). -

-

-This sounds clear enough. There are just two problems: -

-
    -

  1. -Both implementations I tested (VS2005 and GCC 3.4.3) do unqualified -calls to the comma operator in some parts of the library with operands -of user-defined types. -

    2. -
  2. -

    -The standard itself does this in the description of some algorithms. E.g. uninitialized_copy -is defined as: -

    -

    -Effects: -

    -
    -for (; first != last; ++result, ++first)
-  ::new (static_cast<void*>(&*result))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-
    -
    -
    -
    3. -
-

-If understood literally, it is required to call operator,(ForwardIterator, InputIterator). -

-For detailed discussion with code samples see -here. -

-Proposal: -

-
    -
  1. -Add an exception to the rule in 17.6.5.4 [global.functions] by permitting -the implementation to call the comma operator as much as it wants to. I doubt we want this. or -
    2. -
  2. -Fix the description of the said algorithms and perhaps add a note to 17.6.5.4 [global.functions] -that brings attention of the implementers to avoid this pitfall. -
    3. -
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-There are real questions here, that may require a paper to explore and answer properly. -

- -

[2014-05-18, Daniel comments and suggests concrete wording]

- - -

-Other issues, such as 2114 already follow a similar spirit as the one suggested by bullet 2 of the -issue submitter. I assert that consideration of possible user-provided overloads of the comma-operator were not intended -by the original wording and doing so afterwards would unnecessarily complicate a future conceptualization of the library -and would needlessly restrict implementations. -

-I don't think that a paper is needed to solve this issue, there is a simply way to ensure that the code-semantics -excludes consideration of user-provided comma operators. The provided wording below clarifies this by explicitly -casting the first argument of the operator to void. -

- -

[2015-05, Lenexa]

- -

-DK: is putting it in the middle the right place for it?
-STL: either works, but visually putting it in the middle is clearer, and for "++it1, ++i2, ++it3" it needs to be -done after the second comma, so "++it1, (void) ++i2, (void) ++it3" is better than "(void) ++it1, ++i2, (void) ++it3"
-ZY: for INVOKE yesterday we used static_cast<void> but here we're using C-style cast, why?
-STL: for INVOKE I want to draw attention that there's an intentional coercion to void because that's -the desired type. Here we only do it because that's the best way to prevent the problem, not because we specifically want a -void type.
-Move to Ready: 9 in favor, none opposed, 1 abstention -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.7.12.2 [uninitialized.copy] as indicated:

    - -
    -
    -template <class InputIterator, class ForwardIterator>
-  ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
-                                     ForwardIterator result);
-
    -
    -

    --1- Effects: -

    -
    -
    -for (; first != last; ++result, (void) ++first)
-  ::new (static_cast<void*>(&*result))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-
    -
    -

    -[…] -

    -
    - -
    -template <class InputIterator, class Size,class ForwardIterator>
-  ForwardIterator uninitialized_copy_n(InputIterator first, Size n,
-                                       ForwardIterator result);
-
    -
    -

    --3- Effects: -

    -
    -
    -for (; n > 0; ++result, (void) ++first, --n)
-  ::new (static_cast<void*>(&*result))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-
    -
    -
    - -
    -
    2. - -

  2. Change 25.4.8 [alg.lex.comparison] p3 as indicated:

    - -
    -
    -template<class InputIterator1, class InputIterator2>
-  bool
-    lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
-                            InputIterator2 first2, InputIterator2 last2);
-template<class InputIterator1, class InputIterator2, class Compare>
-  bool
-    lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
-                            InputIterator2 first2, InputIterator2 last2,
-                            Compare comp);
-
    -
    -

    --3- Remarks: […] -

    -
    -
    -for ( ; first1 != last1 && first2 != last2 ; ++first1, (void) ++first2) {
-  if (*first1 < *first2) return true;
-  if (*first2 < *first1) return false;
-}
-return first1 == last1 && first2 != last2;
-
    -
    -
    -
    - -
    3. -
- - - - - - -
-

2136. Postconditions vs. exceptions

-

Section: 17.5.1 [structure] Status: Open - Submitter: Jens Maurer Opened: 2012-03-08 Last modified: 2015-05-22

-

View all issues with Open status.

-

Discussion:

- -

-The front matter in clause 17 should clarify that postconditions will not hold if a -standard library function exits via an exception. Postconditions or guarantees that -apply when an exception is thrown (beyond the basic guarantee) are described in an -"Exception safety" section. -

- -

[ -2012-10 Portland: Move to Open -]

- - -

-Consensus that we do not clearly say this, and that we probably should. A likely -location to describe the guarantees of postconditions could well be a new -sub-clause following 17.6.4.11 [res.on.required] which serves the same purpose -for requires clauses. However, we need such wording before we can make -progress. -

- -

-Also, see 2137 for a suggestion that we want to see a paper resolving -both issues together. -

- -

[2015-05-06 Lenexa: EirkWF to write paper addressing 2136 and 2137]

- -

MC: Idea is to replace all such "If no exception" postconditions with "Exception safety" sections.

- - -

Proposed resolution:

- - - - - -
-

2137. Misleadingly constrained post-condition in the presence of exceptions

-

Section: 28.8.3 [re.regex.assign] Status: Open - Submitter: Jonathan Wakely Opened: 2012-03-08 Last modified: 2015-05-22

-

View all other issues in [re.regex.assign].

-

View all issues with Open status.

-

Discussion:

- -

-The post-conditions of basic_regex<>::assign 28.8.3 [re.regex.assign] p16 say: -

-

-If no exception is thrown, flags() returns -f and mark_count() returns the number of marked sub-expressions within the expression. -

-

-The default expectation in the library is that post-conditions only hold, if there is no failure -(see also 2136), therefore the initial condition should be removed to prevent any -misunderstanding. -

- -

[ -2012-10 Portland: Move to Open -]

- - -

-A favorable resolution clearly depends on a favorable resolution to 2136. -There is also a concern that this is just one example of where we would want to apply -such a wording clean-up, and which is really needed to resolve both this issue and -2136 is a paper providing the clause 17 wording that gives the guarantee -for postcondition paragaraphs, and then reviews clauses 18-30 to apply that -guarantee consistently. We do not want to pick up these issues piecemeal, as we risk -openning many issues in an ongoing process. -

- -

[2015-05-06 Lenexa: EirkWF to write paper addressing 2136 and 2137]

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
-template <class string_traits, class A>
-  basic_regex& assign(const basic_string<charT, string_traits, A>& s,
-    flag_type f = regex_constants::ECMAScript);
-
-

-[…] -

--15- Effects: Assigns the regular expression contained in the string s, interpreted according -the flags specified in f. If an exception is thrown, *this is unchanged. -

--16- Postconditions: If no exception is thrown, flags() returns f and -mark_count() returns the number of marked sub-expressions within the expression. -

-
-
- - - - - - -
-

2139. What is a user-defined type?

-

Section: 17.6.4.2.1 [namespace.std], 19.5 [syserr], 20.7.7.1 [allocator.uses.trait], 20.9.10.1 [func.bind.isbind], 20.9.10.2 [func.bind.isplace], 20.9.13 [unord.hash], 20.10.7.6 [meta.trans.other], 22.3.1 [locale], 22.4.1.4 [locale.codecvt], 28.12.1.4 [re.regiter.incr] Status: Open - Submitter: Loïc Joly Opened: 2012-03-08 Last modified: 2015-05-22

-

View all other issues in [namespace.std].

-

View all issues with Open status.

-

Discussion:

- -

-The expression "user-defined type" is used in several places in the standard, but I'm not sure what -it means. More specifically, is a type defined in the standard library a user-defined type? -

-From my understanding of English, it is not. From most of the uses of this term in the standard, it -seem to be considered as user defined. In some places, I'm hesitant, e.g. 17.6.4.2.1 [namespace.std] p1: -

-

-A program may add a template specialization for any standard library template to namespace std -only if the declaration depends on a user-defined type and the specialization meets the standard library -requirements for the original template and is not explicitly prohibited. -

-

-Does it mean we are allowed to add in the namespace std a specialization for -std::vector<std::pair<T, U>>, for instance? -

-Additional remarks from the reflector discussion: The traditional meaning of user-defined types refers -to class types and enum types, but the library actually means here user-defined types that are not -(purely) library-provided. Presumably a new term - like user-provided type - should be introduced -and properly defined. -

- -

[ -2012-10 Portland: Move to Deferred -]

- - -

-The issue is real, in that we never define this term and rely on a "know it when I see it" -intuition. However, there is a fear that any attempt to pin down a definition is more -likely to introduce bugs than solve them - getting the wording for this precisely correct -is likely far more work than we are able to give it. -

- -

-There is unease at simple closing as NAD, but not real enthusiasm to provide wording either. -Move to Deferred as we are not opposed to some motivated individual coming back with full -wording to review, but do not want to go out of our way to encourage someone to work on this -in preference to other issues. -

- -

[2014-02-20 Re-open Deferred issues as Priority 4]

- - -

[2015-03-05 Jonathan suggests wording]

- -

-I dislike the suggestion to change to "user-provided" type because I already find the -difference between user-declared / user-provided confusing for special member functions, -so I think it would be better to use a completely different term. The core language -uses "user-defined conversion sequence" and "user-defined literal" and -similar terms for things which the library provides, so I think we -should not refer to "user" at all to distinguish entities defined -outside the implementation from things provided by the implementation. -

-I propose "program-defined type" (and "program-defined specialization"), defined below. -The P/R below demonstrates the scope of the changes required, even if this name isn't adopted. -I haven't proposed a change for "User-defined facets" in [locale]. -

- -

[Lenexa 2015-05-06]

- -

RS, HT: The core language uses "user-defined" in a specific way, including library things but excluding core language things, let's use a different term.

-

MC: Agree.

-

RS: "which" should be "that", x2

-

RS: Is std::vector<MyType> a "program-defined type"?

-

MC: I think it should be.

-

TK: std::vector<int> seems to take the same path.

-

JW: std::vector<MyType> isn't program-defined, we don't need it to be, anything that depends on that also depends on =MyType.

-

TK: The type defined by an "explicit template specialization" should be a program-defined type.

-

RS: An implicit instantiation of a "program-defined partial specialization" should also be a program-defined type.

-

JY: This definition formatting is horrible and ugly, can we do better?

-

RS: Checking ISO directives.

-

RS: Define "program-defined type" and "program-defined specialization" instead, to get rid of the angle brackets.

-

JW redrafting.

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Add a new sub-clause to 17.3 [definitions]:

    - -

    17.3.? [defns.program.defined]

    -

    -program-defined -

    -<type> a class type or enumeration type which is not part of the C++ -standard library and not defined by the implementation. [Note: Types -defined by the implementation include extensions (1.4 [intro.compliance]) -and internal types used by the library. — end note] -

    -

    -program-defined -

    -<specialization> an explicit template specialization or partial -specialization which is not part of the C++ standard library and not -defined by the implementation. -

    -
    2. - -

  2. Change 17.6.4.2.1 [namespace.std] paragraph 1+2:

    - -

    --1- The behavior of a C++ program is undefined if it adds declarations or definitions to namespace std or to a -namespace within namespace std unless otherwise specified. A program may add a template specialization -for any standard library template to namespace std only if the declaration depends on a -userprogram-defined type and the specialization meets the standard library requirements for the -original template and is not explicitly prohibited. -

    --2- The behavior of a C++ program is undefined if it declares -

    -[…] -

    -A program may explicitly instantiate a template defined in the standard library only if the declaration -depends on the name of a userprogram-defined type and the instantiation meets the standard -library requirements for the original template. -

    -
    3. - -

  3. Change 19.5 [syserr] paragraph 4:

    - -

    --4- The is_error_code_enum and is_error_condition_enum may be specialized for -userprogram-defined types to indicate that such types are eligible for class error_code -and class error_condition automatic conversions, respectively. -

    -
    4. - -

  4. Change 20.7.7.1 [allocator.uses.trait] paragraph 1:

    - -

    --1- Remarks: automatically detects […]. A program may specialize this template to derive from -true_type for a userprogram-defined type T that does not have a nested -allocator_type but nonetheless can be constructed with an allocator where either: […] -

    -
    5. - -

  5. Change 20.9.10.1 [func.bind.isbind] paragraph 2:

    - -

    --2- Instantiations of the is_bind_expression template […]. A program may specialize -this template for a userprogram-defined type T to have a BaseCharacteristic -of true_type to indicate that T should be treated as a subexpression in a bind call. -

    -
    6. - -

  6. Change 20.9.10.2 [func.bind.isplace] paragraph 2:

    - -

    --2- Instantiations of the is_placeholder template […]. A program may specialize this template for a -userprogram-defined type T to have a BaseCharacteristic of -integral_constant<int, N> with N > 0 to indicate that T should be -treated as a placeholder type. -

    -
    7. - -

  7. Change 20.9.13 [unord.hash] paragraph 1:

    - -

    -The unordered associative containers defined in 23.5 use specializations of the class template hash […], -the instantiation hash<Key> shall: -

    -
      -

    • […]

      • -

    • […]

      • -

    • […]

      • -

    • […]

      • -

    • satisfy the requirement that the expression h(k), where h is an object of type -hash<Key> and k is an object of type Key, shall not throw an exception unless -hash<Key> is a userprogram-defined specialization that depends on at least one -userprogram-defined type.

      • -
    -
    8. - -

  8. Change 20.10.7.5 [meta.trans.ptr] Table 57 (common_type row):

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 57 — Other transformations
    TemplateConditionComments
    -… -
    -template <class... T>
    -struct common_type;     -    		 -  - -The member typedef type shall be
    -defined or omitted as specified below.
    -[…]. A program may
    -specialize this trait if at least one
    -template parameter in the
    -specialization is a userprogram-defined type.
    -[…] -
    -… -
    -
    - -
    9. - -

  9. Change 22.4.1.4 [locale.codecvt] paragraph 3:

    - -

    --3- The specializations required in Table 81 (22.3.1.1.1) […]. Other encodings can be converted -by specializing on a userprogram-defined stateT type.[…] -

    -
    10. - -

  10. Change 28.12.1.4 [re.regiter.incr] paragraph 8:

    - -

    --8- [Note: This means that a compiler may call an implementation-specific search function, in which case -a userprogram-defined specialization of regex_search will not be called. — -end note] -

    -
    11. -
- - - - - -
-

2146. Are reference types Copy/Move-Constructible/Assignable or Destructible?

-

Section: 17.6.3.1 [utility.arg.requirements] Status: Open - Submitter: Nikolay Ivchenkov Opened: 2012-03-23 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with Open status.

-

Discussion:

- -

-According to 17.6.3.1 [utility.arg.requirements] p1 -

-

-The template definitions in the C++ standard library refer to various named requirements whose details are set out in -tables 17-24. In these tables, T is an object or reference type to be supplied by a C++ program instantiating -a template; a, b, and c are values of type (possibly const) T; s -and t are modifiable lvalues of type T; u denotes an identifier; rv is an rvalue of -type T; and v is an lvalue of type (possibly const) T or an rvalue of type const T. -

-

-Is it really intended that T may be a reference type? If so, what should a, b, c, -s, t, u, rv, and v mean? For example, are "int &" and -"int &&" MoveConstructible? -

-As far as I understand, we can explicitly specify template arguments for std::swap and std::for_each. -Can we use reference types there? -

-
    -
  1. -
    -#include <iostream>
-#include <utility>
-
-int main()
-{
-  int x = 1;
-  int y = 2;
-  std::swap<int &&>(x, y); // undefined?
-  std::cout << x << " " << y << std::endl;
-}
-
    -
    2. -
  2. -
    -#include <algorithm>
-#include <iostream>
-#include <iterator>
-#include <utility>
-
-struct F
-{
-  void operator()(int n)
-  {
-    std::cout << n << std::endl;
-    ++count;
-  }
-  int count;
-} f;
-
-int main()
-{
-  int arr[] = { 1, 2, 3 };
-  auto&& result = std::for_each<int *, F &&>( // undefined?
-    std::begin(arr),
-    std::end(arr),
-    std::move(f));
-  std::cout << "count: " << result.count << std::endl;
-}
-
    -
    3. -
-

-Are these forms of usage well-defined? -

-Let's also consider the following constructor of std::thread: -

-
-template <class F, class ...Args>
-explicit thread(F&& f, Args&&... args);
-
-

-Requires: F and each Ti in Args shall satisfy the MoveConstructible requirements. -

-
-

-When the first argument of this constructor is an lvalue (e.g. a name of a global function), template argument for F -is deduced to be lvalue reference type. What should "MoveConstructible" mean with regard to an lvalue reference -type? Maybe the wording should say that std::decay<F>::type and each std::decay<Ti>::type (where -Ti is an arbitrary item in Args) shall satisfy the MoveConstructible requirements? -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-The questions raised by the issue are real, and should have a clear answer. -

- - - -

Proposed resolution:

- - - - - - -
-

2151. basic_string<>::swap semantics ignore allocators

-

Section: 21.4.1 [string.require] Status: Open - Submitter: Robert Shearer Opened: 2012-04-13 Last modified: 2015-04-08

-

View all other issues in [string.require].

-

View all issues with Open status.

-

Discussion:

- -

-In C++11, basic_string is not described as a "container", and is not governed by the allocator-aware -container semantics described in sub-clause 23.2 [container.requirements]; as a result, and -requirements or contracts for the basic_string interface must be documented in Clause -21 [strings]. -

-Sub-clause 21.4.6.8 [string::swap] defines the swap member function with no requirements, and -with guarantees to execute in constant time without throwing. Fulfilling such a contract is not reasonable -in the presence of unequal non-propagating allocators. -

-In contrast, 23.2.1 [container.requirements.general] p7 declares the behavior of member swap -for containers with unequal non-propagating allocators to be undefined. -

-Resolution proposal: -

-Additional language from Clause 23 [containers] should probably be copied to Clause -21 [strings]. I will refrain from an exactly recommendation, however, as I am raising further -issues related to the language in Clause 23 [containers]. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Alisdair has offered to provide wording. -

-

-Telecon notes that 23.2.1 [container.requirements.general]p13 says that string is an -allocator-aware container. -

- - - -

Proposed resolution:

- - - - - -
-

2152. Instances of standard container types are not swappable

-

Section: 17.6.3.2 [swappable.requirements], 23.2.1 [container.requirements.general] Status: Open - Submitter: Robert Shearer Opened: 2012-04-13 Last modified: 2015-04-08

-

View all other issues in [swappable.requirements].

-

View all issues with Open status.

-

Discussion:

- -

-Sub-clause 17.6.3.2 [swappable.requirements] defines two notions of swappability: a binary version defining -when two objects are swappable with one another, and a unary notion defining whether an object is -swappable (without qualification), with the latter definition requiring that the object satisfy the -former with respect to all values of the same type. -

-Let T be a container type based on a non-propagating allocator whose instances do not necessarily -compare equal. Then sub-clause 23.2.1 [container.requirements.general] p7 implies that no object t -of type T is swappable (by the unary definition). -

-Throughout the standard it is the unary definition of "swappable" that is listed as a requirement (with the -exceptions of 20.2.2 [utility.swap] p4, 20.3.2 [pairs.pair] p31, 20.4.2.3 [tuple.swap] p2, -25.3.3 [alg.swap] p2, and 25.3.3 [alg.swap] p6, which use the binary definition). This renders -many of the mutating sequence algorithms of sub-clause 25.3 [alg.modifying.operations], for example, -inapplicable to sequences of standard container types, even where every element of the sequence is swappable -with every other. -

-Note that this concern extends beyond standard containers to all future allocator-based types. -

-Resolution proposal: -

-I see two distinct straightforward solutions: -

-
    -
  1. Modify the requirements of algorithms from sub-clause 25.3 [alg.modifying.operations], and all other -places that reference the unary "swappable" definition, to instead use the binary "swappable with" definition -(over a domain appropriate to the context). The unary definition of "swappable" could then be removed from the -standard. -
    2. -
  2. Modify sub-clause 23.2.1 [container.requirements.general] such that objects of standard container types -are "swappable" by the unary definition. -
    3. -
-

-I favor the latter solution, for reasons detailed in the following issue. -

- -

[ -2012-10 Portland: Move to Open -]

- - -

-The issue is broader than containers with stateful allocotors, although they are the most obvious -example contained within the standard itself. The basic problem is that once you have a stateful -allocator, that does not propagate_on_swap, then whether two objects of this type can be -swapped with well defined behavior is a run-time property (the allocators compare equal) rather -than a simple compile-time property that can be deduced from the type. Strictly speaking, any -type where the nature of swap is a runtime property does not meet the swappable -requirements of C++11, although typical sequences of such types are going to have elements that -are all swappable with any other element in the sequence (using our other term of art -for specifying requirements) as the common case is a container of elements who all share the -same allocator. -

- -

-The heart of the problem is that the swappable requirments demand that any two objects -of the same type be swappable with each other, so if any two such objects would not -be swappable with each other, then the whole type is never swappable. Many -algorithms in clause 25 are specified in terms of swappable which is essentially an -overspecification as all they actually need is that any element in the sequence is swappable -with any other element in the sequence. -

- -

-At this point Howard joins the discussion and points out that the intent of introducing the -two swap-related terms was to support vector<bool>::reference types, and we are -reading something into the wording that was never intended. Consuses is that regardless of -the intent, that is what the words today say. -

- -

-There is some support to see a paper reviewing the whole of clause 25 for this issue, and -other select clauses as may be necessary. -

- -

-There was some consideration to introducing a note into the front of clause 25 to indicate -swappable requirements in the clause should be interpreted to allow such awkward -types, but ultimately no real enthusiasm for introducing a swappable for clause 25 -requirement term, especially if it confusingly had the same name as a term used with a -subtly different meaning through the rest of the standard. -

- -

-There was no enthusiasm for the alternate resolution of requiring containers with unequal -allocators that do not propagate provide a well-defined swap behavior, as it is not -believed to be possible without giving swap linear complexity for such values, -and even then would require adding the constraint that the container element types are -CopyConstructible. -

- -

-Final conclusion: move to open pending a paper from a party with a strong interest in -stateful allocators. -

- - - -

Proposed resolution:

- - - - - -
-

2153. Narrowing of the non-member swap contract

-

Section: 20.2.2 [utility.swap], 17.6.3.2 [swappable.requirements], 23.2.1 [container.requirements.general] Status: Open - Submitter: Robert Shearer Opened: 2012-04-13 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

- -

-Sub-clause 20.2.2 [utility.swap] defines a non-member 'swap' function with defined behavior for -all MoveConstructible and MoveAssignable types. It does not guarantee -constant-time complexity or noexcept in general, however this definition does -render all objects of MoveConstructible and MoveAssignable type swappable -(by the unary definition of sub-clause 17.6.3.2 [swappable.requirements]) in the absence of -specializations or overloads. -

-The overload of the non-member swap function defined in Table 96, however, -defines semantics incompatible with the generic non-member swap function, -since it is defined to call a member swap function whose semantics are -undefined for some values of MoveConstructible and MoveAssignable types. -

-The obvious (perhaps naive) interpretation of sub-clause 17.6.3.2 [swappable.requirements] is as a guide to -the "right" semantics to provide for a non-member swap function (called in -the context defined by 17.6.3.2 [swappable.requirements] p3) in order to provide interoperable -user-defined types for generic programming. The standard container types don't follow these guidelines. -

-More generally, the design in the standard represents a classic example of "contract narrowing". It -is entirely reasonable for the contract of a particular swap overload to provide more -guarantees, such as constant-time execution and noexcept, than are provided by the swap -that is provided for any MoveConstructible and MoveAssignable types, but it is not -reasonable for such an overload to fail to live up to the guarantees it provides for general types when -it is applied to more specific types. Such an overload or specialization in generic programming is akin -to an override of an inherited virtual function in OO programming: violating a superclass contract in a -subclass may be legal from the point of view of the language, but it is poor design and can easily lead -to errors. While we cannot prevent user code from providing overloads that violate the more general -swap contract, we can avoid doing so within the library itself. -

-My proposed resolution is to draw a sharp distinction between member swap functions, which provide -optimal performance but idiosyncratic contracts, and non-member swap functions, which should always -fulfill at least the contract of 20.2.2 [utility.swap] and thus render objects swappable. The member -swap for containers with non-propagating allocators, for example, would offer constant-time -guarantees and noexcept but would only offer defined behavior for values with allocators that compare -equal; non-member swap would test allocator equality and then dispatch to either member swap or -std::swap depending on the result, providing defined behavior for all values (and rendering the type -"swappable"), but offering neither the constant-time nor the noexcept guarantees. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-This topic deserves more attention than can be given in the telocon, and there is no proposed resolution. -

- - - -

Proposed resolution:

- - - - - -
-

2154. What exactly does compile-time complexity imply?

-

Section: 26.5.1.3 [rand.req.urng] Status: New - Submitter: John Salmon Opened: 2012-04-26 Last modified: 2015-04-08

-

View all other issues in [rand.req.urng].

-

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-

Discussion:

- -

-The expressions G::min() and G::max() in Table 116 in 26.5.1.3 [rand.req.urng] are specified -as having "compile-time" complexity. -

-It is not clear what, exactly, this requirement implies. If a URNG has a method: -

-
-static int min();
-
-

-then is the method required to have a constexpr qualifier? I believe the standard would benefit from -clarification of this point. -

- - - -

Proposed resolution:

- - - - - -
-

2155. Macro __bool_true_false_are_defined should be removed

-

Section: 18.10 [support.runtime] Status: Open - Submitter: Thomas Plum Opened: 2012-04-30 Last modified: 2015-05-08

-

View other active issues in [support.runtime].

-

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-

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-

Discussion:

- -

-Since C99, the C standard describes a macro named __bool_true_false_are_defined. -

-In the process of harmonizing C++11 with C99, this name became part of the C++ standard. -

-I propose that all mention of this name should be removed from the C and C++ standards. -

-Here's the problem: The name was originally proposed as a transition tool, so that the headers for a -project could contain lines like the following. -

-
-#if !defined(__bool_true_false_are_defined)
-#define bool int /* or whatever */
-#define true 1
-#define false 0
-#endif
-
-

-Then when the project was compiled by a "new" compiler that implemented bool as defined by the -evolving C++98 or C99 standards, those lines would be skipped; but when compiled by an "old" compiler that -didn't yet provide bool, true, and false, then the #define's would provide a -simulation that worked for most purposes. -

-It turns out that there is an unfortunate ambiguity in the name. One interpretation is as shown above, but -a different reading says "bool, true, and false are #define'd", i.e. that the meaning of the macro is to -assert that these names are macros (not built-in) ... which is true in C, but not in C++. -

-In C++11, the name appears in parentheses followed by a stray period, so -some editorial change is needed in any event: -

-18.10 [support.runtime] para 1: -

-

-Headers <csetjmp> (nonlocal jumps), <csignal> (signal handling), <cstdalign> -(alignment), <cstdarg> (variable arguments), <cstdbool> (__bool_true_false_are_defined). -<cstdlib> (runtime environment getenv(), system()), and <ctime> -(system clock clock(), time()) provide further compatibility with C code. -

-

-However, para 2 says -

-

-"The contents of these headers are the same as the Standard C library headers <setjmp.h>, -<signal.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>, -<stdlib.h>, and <time.h>, respectively, with the following -changes:", -

-

-and para 8 says -

-

-"The header <cstdbool> and the header <stdbool.h> shall -not define macros named bool, true, or false." -

-

-Thus para 8 doesn't exempt the C++ implementation from the arguably clear requirement of the C standard, to -provide a macro named __bool_true_false_are_defined defined to be 1. -

-Real implementations of the C++ library differ, so the user cannot count upon any consistency; furthermore, the -usefulness of the transition tool has faded long ago. -

-That's why my suggestion is that both C and C++ standards should eliminate any mention of -__bool_true_false_are_defined. In that case, the name belongs to implementers to provide, or not, as -they choose. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-While not strictly necessary, the clean-up look good. -

-

-We would like to hear from our C liaison before moving on this issue though. -

- -

[2015-05 Lenexa]

- -

-LWG agrees. Jonathan provides wording. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -
  1. -

    Edit the footnote on 17.6.1.2 [headers] p7:

    -
    -

    -176) In particular, including any of the standard headers <stdbool.h>, <cstdbool>, <iso646.h> or <ciso646> has no effect. -

    -
    -
    2. - -
  2. -

    Edit 18.10 [support.runtime] p1 as indicated (and remove the index entry for __bool_true_false_are_defined):

    - -
    -

    --1- Headers <csetjmp> (nonlocal jumps), <csignal> (signal handling), <cstdalign> (alignment), <cstdarg> (variable arguments), <cstdbool>, (__bool_true_false_are_defined). <cstdlib> (runtime environment getenv(), system()), and <ctime> (system clock clock(), time()) provide further compatibility with C code. -

    -
    -
    3. - -
  3. -

    Remove Table 38 — Header <cstdbool> synopsis [tab:support.hdr.cstdbool] from 18.10 [support.runtime]

    -
    - - - - -
    Table 38 — Header <cstdbool> synopsis
    TypeName(s)
    Macro:__bool_true_false_are_defined
    -
    -
    4. -
- - - - - - -
-

2156. Unordered containers' reserve(n) reserves for n-1 elements

-

Section: 23.2.5 [unord.req] Status: Ready - Submitter: Daniel James Opened: 2012-05-07 Last modified: 2015-05-22

-

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-

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-

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-

Discussion:

- -

-I think that unordered containers' reserve doesn't quite do what it should. I'd expect after calling -x.reserve(n) to be able to insert n elements without invalidating iterators. But as -the standard is written (I'm looking at n3376), I think the guarantee only holds for n-1 elements. -

-For a container with max_load_factor of 1, reserve(n) is equivalent to -rehash(ceil(n/1)), ie. rehash(n). rehash(n) requires that the bucket -count is >= n, so it can be n (Table 103). The rule is that insert -shall not affect the validity of iterators if (N + n) < z * B (23.2.5 [unord.req] p15). -But for this case the two sides of the equation are equal, so insert can affect the validity of iterators. -

- -

[2013-03-16 Howard comments and provides wording]

- - -

-Given the following: -

- -
-LF := load_factor()
-MLF := max_load_factor()
-S := size()
-B := bucket_count()
-
-LF == S/B
-
- -

-The container has an invariant: -

- -
-LF <= MLF
-
- -

-Therefore: -

- -
-MLF >= S/B
-S <= MLF * B
-B >= S/MLF
-
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Howard to provide rationale and potentally revised wording. -

- - -

[2012-02-12 Issaquah : recategorize as P3]

- -

-Jonathon Wakely: submitter is Boost.Hash maintainer. Think it's right. -

- -

-Marshall Clow: even if wrong it's more right than what we have now -

- -

-Geoffrey Romer: issue is saying rehash should not leave container in such a state that a notional insertion of zero elements should not trigger a rehash -

- -

-AJM: e.g. if you do a range insert from an empty range -

- -

-AJM: we don't have enough brainpower to do this now, so not priority zero -

- -

-Recategorised as P3 -

- -

[Lenexa 2015-05-06: Move to Ready]

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -
  1. -

    -In 23.2.5 [unord.req] Table 103 — Unordered associative container requirements, change the post-condition -in the row for a.rehash(n) to: -

    -
    -Post: a.bucket_count() >= a.size() / a.max_load_factor() and a.bucket_count() >= n. -
    -
    2. - -
  2. -

    -In 23.2.5 [unord.req]/p15 change -

    -
    -The insert and emplace members shall not affect the validity of iterators if -(N+n) <= z * B, where N is the number of elements in the container -prior to the insert operation, n is the number of elements inserted, B is the container's -bucket count, and z is the container's maximum load factor. -
    -
    3. - -
- - - - - -
-

2157. How does std::array<T,0> initialization work when T is not default-constructible?

-

Section: 23.3.2.8 [array.zero] Status: Open - Submitter: Daryle Walker Opened: 2012-05-08 Last modified: 2015-04-08

-

View all other issues in [array.zero].

-

View all issues with Open status.

-

Discussion:

- -

-Objects of std::array<T,N> are supposed to be initialized with aggregate initialization (when -not the destination of a copy or move). This clearly works when N is positive. What happens when N -is zero? To continue using an (inner) set of braces for initialization, a std::array<T,0> implementation -must have an array member of at least one element, and let default initialization take care of those secret elements. -This cannot work when T has a set of constructors and the default constructor is deleted from that set. -Solution: Add a new paragraph in 23.3.2.8 [array.zero]: -

-

-The unspecified internal structure of array for this case shall allow initializations like: -

-
-array<T, 0> a = { };
-
-

-and said initializations must be valid even when T is not default-constructible. -

- -

[2012, Portland: Move to Open]

- -

-Some discussion to understand the issue, which is that implementations currently have freedom to implement -an empty array by holding a dummy element, and so might not support value initialization, which is -surprising when trying to construct an empty container. However, this is not mandated, it is an unspecified -implementation detail. -

- -

-Jeffrey points out that the implication of 23.3.2.1 [array.overview] is that this initialization syntax -must be supported by empty array objects already. This is a surprising inference that was not -obvious to the room, but consensus is that the reading is accurate, so the proposed resolution is not necessary, -although the increased clarity may be useful. -

- -

-Further observation is that the same clause effectively implies that T must always be DefaultConstructible, -regardless of N for the same reasons - as an initializer-list may not supply enough values, and the -remaining elements must all be value initialized. -

- -

-Concern that we are dancing angels on the head of pin, and that relying on such subtle implications in wording is -not helpful. We need a clarification of the text in this area, and await wording. -

- -

[2015-02 Cologne]

- -

-DK: What was the outcome of Portland? AM: Initially we thought we already had the intended behaviour. -We concluded that T must always be DefaultConstructible, but I'm not sure why. GR: It's p2 in -std::array, "up to N". AM: That wording already implies that "{}" has to work when N -is zero. But the wording of p2 needs to be fixed to make clear that it does not imply that T must be -DefaultConstructible. -

-Conclusion: Update wording, revisit later. -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -

Add the following new paragraph between the current 23.3.2.8 [array.zero] p1 and p2:

- -

--1- array shall provide support for the special case N == 0. -

--?- The unspecified internal structure of array for this case shall allow initializations like: -

-
-array<T, 0> a = { };
-
-

-and said initializations must be valid even when T is not default-constructible. -

--2- In the case that N == 0, begin() == end() == unique value. The return value of -data() is unspecified. -

--3- The effect of calling front() or back() for a zero-sized array is undefined. -

--4- Member function swap() shall have a noexcept-specification which is equivalent to -noexcept(true). -

- - - - - -
-

2158. Conditional copy/move in std::vector

-

Section: 23.3.6.3 [vector.capacity] Status: New - Submitter: Nikolay Ivchenkov Opened: 2012-05-08 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

-There are various operations on std::vector that can cause elements of the vector to be -moved from one location to another. A move operation can use either rvalue or const lvalue as -argument; the choice depends on the value of !is_nothrow_move_constructible<T>::value && -is_copy_constructible<T>::value, where T is the element type. Thus, some operations -on std::vector (e.g. 'resize' with single parameter, 'reserve', 'emplace_back') should have -conditional requirements. For example, let's consider the requirement for 'reserve' in N3376 – -23.3.6.3 [vector.capacity]/2: -

-

-Requires: T shall be MoveInsertable into *this. -

-

-This requirement is not sufficient if an implementation is free to select copy constructor when -!is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value -evaluates to true. Unfortunately, is_copy_constructible cannot reliably determine whether -T is really copy-constructible. A class may contain public non-deleted copy constructor whose -definition does not exist or cannot be instantiated successfully (e.g., -std::vector<std::unique_ptr<int>> has copy constructor, but this type is not -copy-constructible). Thus, the actual requirements should be: -

-
    -

  • -if !is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value -then T shall be CopyInsertable into *this; -

    • -

  • -otherwise T shall be MoveInsertable into *this. -

    • -
-

-Maybe it would be useful to introduce a new name for such conditional requirement (in addition to -"CopyInsertable" and "MoveInsertable"). -

- - - -

Proposed resolution:

- - - - - -
-

2161. const equivalence of std::map

-

Section: 23.4 [associative], 23.5 [unord] Status: New - Submitter: Bjarne Stroustrup Opened: 2012-06-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

-As described in the reflector discussion c++std-core-21860 consider the following example: -

-
-map<const int, int> mci{};
-map<int, int> mi = mci; // ??
-mci[1] = 2;
-mi[1] = 2;
-
-

-Should it be required that the marked initialization is well-formed? As a possible solution -this could be realized by an alias template: -

-
-template <class K, class T>
-struct OriginalMap { […] };
-
-template <class K, class T>
-using ImprovedMap = OriginalMap<const K, T>;
-
- - - -

Proposed resolution:

- - - - - -
-

2164. What are the semantics of vector.emplace(vector.begin(), vector.back())?

-

Section: 23.3.6.5 [vector.modifiers], 23.2 [container.requirements] Status: New - Submitter: Howard Hinnant Opened: 2012-07-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

-Nikolay Ivchenkov recently brought the following example on the -std-discussion -newsgroup, asking whether the following program well-defined: -

-
-#include <iostream>
-#include <vector>
-
-int main()
-{
-  std::vector<int> v;
-  v.reserve(4);
-  v = { 1, 2, 3 };
-  v.emplace(v.begin(), v.back());
-  for (int x : v)
-    std::cout << x << std::endl;
-}
-
-

-Nikolay Ivchenkov: -

-I think that an implementation of vector's 'emplace' should initialize an intermediate object with -v.back() before any shifts take place, then perform all necessary shifts and finally replace the -value pointed to by v.begin() with the value of the intermediate object. So, I would expect the -following output: -

-
-3
-1
-2
-3
-
-

-GNU C++ 4.7.1 and GNU C++ 4.8.0 produce other results: -

-
-2
-1
-2
-3
-
-

-Howard Hinnant: -

-I believe Nikolay is correct that vector should initialize an intermediate object with v.back() -before any shifts take place. As Nikolay pointed out in another email, this appears to be the only way to -satisfy the strong exception guarantee when an exception is not thrown by T's copy constructor, -move constructor, copy assignment operator, or move assignment operator as specified by -23.3.6.5 [vector.modifiers]/p1. I.e. if the emplace construction throws, the vector must remain unaltered. -

-That leads to an implementation that tolerates objects bound to the function parameter pack of the emplace -member function may be elements or sub-objects of elements of the container. -

-My position is that the standard is correct as written, but needs a clarification in this area. Self-referencing -emplace should be legal and give the result Nikolay expects. The proposed resolution of LWG 760 -is not correct. -

- -

[2015-02 Cologne]

- -

-LWG agrees with the analysis including the assessment of LWG 760 and would appreciate a concrete wording proposal. -

- -

[2015-04-07 dyp comments]

- -

-The Standard currently does not require that creation of such -intermediate objects is legal. 23.2.3 [sequence.reqmts] Table 100 -— "Sequence container requirements" currently specifies: -

- -
- - - - - - - - - - - - - - - - - - - - - - -
Table 100 — Sequence container requirements
ExpressionReturn typeAssertion/note
pre-/post-condition
-… -
-a.emplace(p, args); - -iterator - -Requires: T is EmplaceConstructible into -X from args. For vector and deque, -T is also MoveInsertable into X and -MoveAssignable. […] -
-… -
-
- -

-The EmplaceConstructible concept is defined via -allocator_traits<A>::construct in 23.2.1 [container.requirements.general] p15.5 That's surprising to me -since the related concepts use the suffix Insertable if they -refer to the allocator. An additional requirement such as -std::is_constructible<T, Args...> is necessary to allow -creation of intermediate objects. -

- -

-The creation of intermediate objects also affects other functions, such -as vector.insert. Since aliasing the vector is only allowed for -the single-element forms of insert and emplace (see -526), the range-forms are not affected. Similarly, -aliasing is not allowed for the rvalue-reference overload. See also LWG -2266. -

- -

-There might be a problem with a requirement of -std::is_constructible<T, Args...> related to the issues -described in LWG 2461. For example, a scoped allocator -adapter passes additional arguments to the constructor of the value -type. This is currently not done in recent implementations of libstdc++ -and libc++ when creating the intermediate objects, they simply create -the intermediate object by perfectly forwarding the arguments. If such -an intermediate object is then moved to its final destination in the -vector, a change of the allocator instance might be required — -potentially leading to an expensive copy. One can also imagine worse -problems, such as run-time errors (allocators not comparing equal at -run-time) or compile-time errors (if the value type cannot be created -without the additional arguments). I have not looked in detail into this -issue, but I'd be reluctant adding a requirement such as -std::is_constructible<T, Args...> without further -investigation. -

- -

-It should be noted that the creation of intermediate objects currently -is inconsistent in libstdc++ vs libc++. For example, libstdc++ creates -an intermediate object for vector.insert, but not -vector.emplace, whereas libc++ does the exact opposite in this -respect. -

- -

-A live demo of the inconsistent creation of intermediate objects can be -found here. -

- - -

Proposed resolution:

- - - - - -
-

2165. std::atomic<X> requires X to be nothrow default constructible

-

Section: 29.5 [atomics.types.generic], 29.6 [atomics.types.operations] Status: Core - Submitter: Jonathan Wakely Opened: 2012-07-19 Last modified: 2015-04-09

-

View other active issues in [atomics.types.generic].

-

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-

View all issues with Core status.

-

Discussion:

- -

-As raised in c++std-lib-32781, this fails to compile even though the default constructor is not used: -

-
-#include <atomic>
-
-struct X {
-  X() noexcept(false) {}
-  X(int) { }
-};
-
-std::atomic<X> x(3);
-
-

This is because atomic<T>'s default constructor is declared to be non-throwing and -is explicitly-defaulted on its first declaration: -

-
-atomic() noexcept = default;
-
-

-This is ill-formed if the implicitly-declared default constructor would not be non-throwing. -

-Possible solutions: -

-
    -
  1. -Add nothrow default constructible to requirements for template argument of the generic atomic<T> -
    2. -
  2. -Remove atomic<T>::atomic() from the overload set if T is not nothrow default constructible. -
    3. -
  3. -Remove noexcept from atomic<T>::atomic(), allowing it to be -deduced (but the default constructor is intended to be always noexcept) -
    4. -
  4. -Do not default atomic<T>::atomic() on its first declaration (but makes the default constructor -user-provided and so prevents atomic<T> being trivial) -
    5. -
  5. -A core change to allow the mismatched exception specification if the default constructor isn't used -(see c++std-core-21990) -
    6. -
- -

[2012, Portland: move to Core]

- -

-Recommend referring to core to see if the constructor noexcept mismatch -can be resolved there. The issue is not specific to concurrency. -

- -

[2015-04-09 Daniel comments]

- -

-CWG issue 1778, which had -been created in behalf of this LWG issue, has been resolved as a defect. -

- - -

Proposed resolution:

- - - - - -
-

2166. Heap property underspecified?

-

Section: 25.4.6 [alg.heap.operations] Status: New - Submitter: Peter Sommerlad Opened: 2012-07-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-Another similar issue to the operator< vs greater in nth_element but not as direct occurs -in 25.4.6 [alg.heap.operations]: -

-

--1- A heap is a particular organization of elements in a range between two random access iterators -[a,b). Its two key properties are: -

-
    -
  1. There is no element greater than *a in the range and -
    2. -
  2. *a may be removed by pop_heap(), or a new element added by push_heap(), in -O(log(N)) time. -
    3. -
-
-

-As noted by Richard Smith, it seems that the first bullet should read: -

-

-*a is not less than any element in the range -

-

-Even better the heap condition could be stated here directly, instead of leaving it unspecified, i.e., -

-

-Each element at (a+2*i+1) and (a+2*i+2) is less than the element at (a+i), -if those elements exist, for i>=0. -

-

-But may be that was may be intentional to allow other heap organizations? -

-See also follow-up discussion of c++std-lib-32780. -

- -

- - - -

Proposed resolution:

- - - - - -
-

2173. The meaning of operator + in the description of the algorithms

-

Section: 25 [algorithms] Status: New - Submitter: Nikolay Ivchenkov Opened: 2012-08-01 Last modified: 2015-04-08

-

View other active issues in [algorithms].

-

View all other issues in [algorithms].

-

View all issues with New status.

-

Discussion:

- -

-According to 25.1 [algorithms.general]/12, -

-

-In the description of the algorithms operators + and - are used for some of the iterator categories -for which they do not have to be defined. In these cases the semantics of a+n is the same as that of -

-
-X tmp = a;
-advance(tmp, n);
-return tmp;
-
-
-

-There are several places where such operator + is applied to an output iterator — for example, see the -description of std::copy: -

-
-template<class InputIterator, class OutputIterator>
-OutputIterator copy(InputIterator first, InputIterator last,
-                    OutputIterator result);
-
-

--1- Effects: Copies elements in the range [first,last) into the range [result,result + (last - -first)) starting from first and proceeding to last. For each non-negative integer -n < (last - first), performs *(result + n) = *(first + n). -

-

-std::advance is not supposed to be applicable to output iterators, so we need a different method of description. -

-See also message c++std-lib-32908. -

- -

[2014-06-07 Daniel comments and provides wording]

- -

-The specification for output iterators is somewhat tricky, because here a sequence of increments is required to -be combined with intervening assignments to the dereferenced iterator. I tried to respect this -fact by using a conceptual assignment operation as part of the specification. -

-Another problem in the provided as-if-code is the question which requirements are imposed on n. Unfortunately, -the corresponding function advance is completely underspecified in this regard, so I couldn't borrow wording -from it. We cannot even assume here that n is the difference type of the iterator, because for output iterators there is -no requirements for this associated type to be defined. The presented wording attempts to minimize assumptions, but still -can be considered as controversial. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 25.1 [algorithms.general] around p12 as indicated:

    - -
    -

    --12- In the description of the algorithms operators + and - are used for some of the iterator categories for which -they do not have to be defined. In these cases the semantics of a+n is the same as that of -

    -
    -
    -X tmp = a;
-advance(tmp, n);
-return tmp;
-
    -
    -

    -when X meets the input iterator requirements (24.2.3 [input.iterators]), otherwise it is the same as that of -

    -
    -
    -X tmp = a;
-for (auto i = n; i; ++tmp, (void) --i) 
-  *tmp = Expr(i); 
-return tmp;
-
    -
    -

    -where Expr(i) denotes the n-i-th expression that is assigned to for the corresponding algorithm; -and that of b-a is the same as of -

    -
    -
    -return distance(a, b);
-
    -
    -
    -
    2. -
- - - - - -
-

2178. Allocator requirement changes not mentioned Annex C

-

Section: 17.6.3.5 [allocator.requirements], C.5 [diff.library] Status: Open - Submitter: Nevin Liber Opened: 2012-08-14 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Open status.

-

Discussion:

- -

-Given that a number of things were removed from the allocator requirements (reference, const_reference, -address() in 17.6.3.5 [allocator.requirements]), it seems that these incompatible changes should be -mentioned in Annex C.5 [diff.library], more specifically in [diff.cpp03]. -

- -

[ -2012-10 Portland: Move to Open -]

- - -

-It was clearly pointed out by Bill during the C++11 process that our change to allocator requirements -potentially broke 3rd party user containers written to expect C++03 allocators, or rather, an -allocator written to the minimal requirements of C++11 might not be guaranteed to work with a container -written to the previous rules. This was a trade-off in making allocaters easier to write by use of -the allocator_traits framework. -

- -

-This probably does merit a write-up in Annex C, and we look forward to seeing wording. Until then, -the best we can do is move the issue to Open. -

- - - -

Proposed resolution:

- - - - - -
-

2179. enable_shared_from_this and construction from raw pointers

-

Section: 20.8.2.5 [util.smartptr.enab], 20.8.2.2.1 [util.smartptr.shared.const] Status: Open - Submitter: Daniel Krügler Opened: 2012-08-16 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

- -

-On reflector message c++std-lib-32927, -Matt Austern asked whether the following example should be well-defined or not -

-
-struct X : public enable_shared_from_this<X> { };
-auto xraw = new X;
-shared_ptr<X> xp1(xraw);
-shared_ptr<X> xp2(xraw);
-
-

-pointing out that 20.8.2.2.1 [util.smartptr.shared.const] does not seem to allow it, since -xp1 and xp2 aren't allowed to share ownership, because each of them is required to have -use_count() == 1. Despite this wording it might be reasonable (and technical possible) -to implement that request. -

-On the other hand, there is the non-normative note in 20.8.2.5 [util.smartptr.enab] p11 (already part of TR1): -

-

-The shared_ptr constructors that create unique pointers -can detect the presence of an enable_shared_from_this base and assign the newly created shared_ptr -to its __weak_this member. -

-

-Now according to the specification in 20.8.2.2.1 [util.smartptr.shared.const] p3-7: -

-
-template<class Y> explicit shared_ptr(Y* p);
-
-

-the notion of creating unique pointers can be read to be included by this note, because the post-condition -of this constructor is unique() == true. Evidence for this interpretation seems to be weak, though. -

-Howard Hinnant presented the counter argument, that actually the following is an "anti-idiom" and it seems questionable -to teach it to be well-defined in any case: -

-
-auto xraw = new X;
-shared_ptr<X> xp1(xraw);
-shared_ptr<X> xp2(xraw);
-
-

-He also pointed out that the current post-conditions of the affected shared_ptr constructor -would need to be reworded. -

-It needs to be decided, which direction to follow. If this idiom seems too much broken to be supported, -the note could be improved. If it should be supported, the constructors in -20.8.2.2.1 [util.smartptr.shared.const] need a careful analysis to ensure that post-conditions -are correct. -

-Several library implementations currently do not support this example, instead they typically -cause a crash. Matt points out that there are currently no explicit requirements imposed on -shared_ptr objects to prevent them from owning the same underlying object without sharing the -ownership. It might be useful to add such a requirement. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-More discussion is needed to pick a direction to guide a proposed resolution. -

- -

[2013-05-09 Jonathan comments]

- -

-The note says the newly created shared_ptr is assigned to the weak_ptr member. It doesn't -say before doing that the shared_ptr should check if the weak_ptr is non-empty and possibly -share ownership with some other pre-existing shared_ptr. -

- - - -

Proposed resolution:

- - - - - -
-

2181. Exceptions from seed sequence operations

-

Section: 26.5.1.2 [rand.req.seedseq], 26.5.3 [rand.eng], 26.5.4 [rand.adapt] Status: Ready - Submitter: Daniel Krügler Opened: 2012-08-18 Last modified: 2015-05-22

-

View all other issues in [rand.req.seedseq].

-

View all issues with Ready status.

-

Discussion:

- -

-LWG issue 2180 points out some deficiences in regard to the specification of the library-provided -type std::seed_seq regarding exceptions, but there is another specification problem -in regard to general types satisfying the seed sequence constraints (named SSeq) as described in -26.5.1.2 [rand.req.seedseq]. -

-26.5.3 [rand.eng] p3 and 26.5.4.1 [rand.adapt.general] p3 say upfront: -

-

-Except where specified otherwise, no function described in this section -26.5.3 [rand.eng]/26.5.4 [rand.adapt] throws an exception. -

-

-This constraint causes problems, because the described templates in these sub-clauses depend on operations of -SSeq::generate() which is a function template, that depends both on operations provided by the -implementor of SSeq (e.g. of std::seed_seq), and those of the random access iterator type -provided by the caller. With class template linear_congruential_engine we have just one example for a user -of SSeq::generate() via: -

-
-template<class Sseq> 
-linear_congruential_engine<>::linear_congruential_engine(Sseq& q);
-
-template<class Sseq> 
-void linear_congruential_engine<>::seed(Sseq& q);
-
-

-None of these operations has an exclusion rule for exceptions. -

-As described in 2180 the wording for std::seed_seq should and can be fixed to ensure that -operations of seed_seq::generate() won't throw except from operations of the provided iterator range, -but there is no corresponding "safety belt" for user-provided SSeq types, since 26.5.1.2 [rand.req.seedseq] -does not impose no-throw requirements onto operations of seed sequences. -

- -
    - -

  1. -A quite radical step to fix this problem would be to impose general no-throw requirements on the expression -q.generate(rb,re) from Table 115, but this is not as simple as it looks initially, because this -function again depends on general types that are mutable random access iterators. Typically, we do not -impose no-throw requirements on iterator operations and this would restrict general seed sequences where -exceptions are not a problem. Furthermore, we do not impose comparable constraints for other expressions, -like that of the expression g() in Table 116 for good reasons, e.g. random_device::operator() -explicitly states when it throws exceptions. -

    2. - -

  2. -A less radical variant of the previous suggestion would be to add a normative requirement on the expression -q.generate(rb,re) from Table 115 that says: "Throws nothing if operations of rb and re -do not throw exceptions". Nevertheless we typically do not describe conditional Throws elements in proper -requirement sets elsewhere (Container requirements excluded, they just describe the containers from Clause 23) -and this may exclude resonable implementations of seed sequences that could throw exceptions under rare -situations. -

    3. - -

  3. -The iterator arguments provided to SSeq::generate() for operations in templates of 26.5.3 [rand.eng] and -26.5.4 [rand.adapt] are under control of implementations, so we could impose stricter exceptions requirements -on SSeq::generate() for SSeq types that are used to instantiate member templates in 26.5.3 [rand.eng] -and 26.5.4 [rand.adapt] solely. -

    4. - -

  4. -We simply add extra wording to the introductive parts of 26.5.3 [rand.eng] and 26.5.4 [rand.adapt] -that specify that operations of the engine (adaptor) templates that depend on a template parameter SSeq -throw no exception unless SSeq::generate() throws an exception. -

    5. -
- -

-Given these options I would suggest to apply the variant described in the fourth bullet. -

-The proposed resolution attempts to reduce a lot of the redundancies of requirements in the introductory paragraphs of -26.5.3 [rand.eng] and 26.5.4 [rand.adapt] by introducing a new intermediate sub-clause -"Engine and engine adaptor class templates" following sub-clause 26.5.2 [rand.synopsis]. This approach also -solves the problem that currently 26.5.3 [rand.eng] also describes requirements that apply for -26.5.4 [rand.adapt] (Constrained templates involving the Sseq parameters). -

- -

[2013-04-20, Bristol]

- - -

-Remove the first bullet point: -

-

-?- Throughout this sub-clause general requirements and conventions are described that apply to every class -template specified in sub-clause 26.5.3 [rand.eng] and 26.5.4 [rand.adapt]. Phrases of the form "in those -sub-clauses" shall be interpreted as equivalent to "in sub-clauses 26.5.3 [rand.eng] and 26.5.4 [rand.adapt]". -

-

-Replace "in those sub-clauses" with "in sub-clauses 26.5.3 [rand.eng] and 26.5.4 [rand.adapt]". -

-Find another place for the wording. -

-Daniel: These are requirements on the implementation not on the types. I'm not comfortable in moving it to another place -without double checking. -

-Improve the text (there are 4 "for"s): for copy constructors, for copy assignment operators, -for streaming operators, and for equality and inequality operators are not shown in the synopses. -

-Move the information of this paragraph to the paragraphs it refers to: -

-

-"-?- Descriptions are provided in those sub-clauses only for engine operations that are not described in -26.5.1.4 [rand.req.eng], for adaptor operations that are not described in 26.5.1.5 [rand.req.adapt], or for -operations where there is additional semantic information. In particular, declarations for copy constructors, for -copy assignment operators, for streaming operators, and for equality and inequality operators are not shown in the synopses." -

-

-Alisdair: I prefer duplication here than consolidation/reference to these paragraphs. -

-The room showed weakly favjust or for duplication. -

- -

-Previous resolution from Daniel [SUPERSEDED]: -

-
-
    -

  1. Add a new sub-clause titled "Engine and engine adaptor class templates" following sub-clause -26.5.2 [rand.synopsis] (but at the same level) and add one further sub-clause "General" as -child of the new sub-clause as follows: -

    -Engine and engine adaptor class templates [rand.engadapt] -

    -General [rand.engadapt.general] -

    -

    --?- Throughout this sub-clause general requirements and conventions are described that apply to every class -template specified in sub-clause 26.5.3 [rand.eng] and 26.5.4 [rand.adapt]. Phrases of the -form "in those sub-clauses" shall be interpreted as equivalent to "in sub-clauses 26.5.3 [rand.eng] and -26.5.4 [rand.adapt]". - -

    --?- Except where specified otherwise, the complexity of each function specified in those sub-clauses is constant. -

    --?- Except where specified otherwise, no function described in those sub-clauses throws an exception. -

    --?- Every function described in those sub-clauses that has a function parameter q of type -SSeq& for a template type parameter named SSeq that is different from type std::seed_seq -throws what and when the invocation of q.generate throws. -

    --?- Descriptions are provided in those sub-clauses only for engine operations that are not described in -26.5.1.4 [rand.req.eng], for adaptor operations that are not described in 26.5.1.5 [rand.req.adapt], -or for operations where there is additional semantic information. In particular, declarations for copy constructors, -for copy assignment operators, for streaming operators, and for equality and inequality operators -are not shown in the synopses. -

    --?- Each template specified in those sub-clauses requires one or more relationships, involving the value(s) of -its non-type template parameter(s), to hold. A program instantiating any of these templates is ill-formed if -any such required relationship fails to hold. -

    --?- For every random number engine and for every random number engine adaptor X defined in those -sub-clauses: -

    -
      -

    • -if the constructor -

      -
      -template <class Sseq> explicit X(Sseq& q);
-
      -

      -is called with a type Sseq that does not qualify as a seed sequence, then this constructor shall not -participate in overload resolution; -

      -
      • - -

    • -if the member function -

      -
      -template <class Sseq> void seed(Sseq& q);
-
      -

      -is called with a type Sseq that does not qualify as a seed sequence, then this function shall not -participate in overload resolution; -

      -
      • -
    -

    -The extent to which an implementation determines that a type cannot be a seed sequence is unspecified, -except that as a minimum a type shall not qualify as a seed sequence if it is implicitly convertible to -X::result_type. -

    -
    - -
    2. - -

  2. Edit the contents of sub-clause 26.5.3 [rand.eng] as indicated:

    - -

    --1- Each type instantiated from a class template specified in this section 26.5.3 [rand.eng] satisfies the -requirements of a random number engine (26.5.1.4 [rand.req.eng]) type and the general implementation -requirements specified in sub-clause [rand.engadapt.general]. -

    --2- Except where specified otherwise, the complexity of each function specified in this section 26.5.3 [rand.eng] -is constant. -

    --3- Except where specified otherwise, no function described in this section 26.5.3 [rand.eng] throws an exception. -

    --4- Descriptions are provided in this section 26.5.3 [rand.eng] only for engine operations that are not -described in 26.5.1.4 [rand.req.eng] […] -

    --5- Each template specified in this section 26.5.3 [rand.eng] requires one or more relationships, -involving the value(s) of its non-type template parameter(s), to hold. […] -

    --6- For every random number engine and for every random number engine adaptor X defined in this subclause -(26.5.3 [rand.eng]) and in sub-clause 26.5.3 [rand.eng]: […] -

    - -
    3. - -

  3. Edit the contents of sub-clause 26.5.4.1 [rand.adapt.general] as indicated:

    - -

    --1- Each type instantiated from a class template specified in this section 26.5.3 [rand.eng]26.5.4 [rand.adapt] satisfies the -requirements of a random number engine adaptor (26.5.1.5 [rand.req.adapt]) type and the general -implementation requirements specified in sub-clause [rand.engadapt.general]. -

    --2- Except where specified otherwise, the complexity of each function specified in this section 26.5.4 [rand.adapt] -is constant. -

    --3- Except where specified otherwise, no function described in this section 26.5.4 [rand.adapt] throws an exception. -

    --4- Descriptions are provided in this section 26.5.4 [rand.adapt] only for engine operations that are not -described in 26.5.1.5 [rand.req.adapt] […] -

    --5- Each template specified in this section 26.5.4 [rand.adapt] requires one or more relationships, involving -the value(s) of its non-type template parameter(s), to hold. […] -

    - -
    4. - -
-
- -

[2014-02-09, Daniel provides alternative resolution]

- - -

[Lenexa 2015-05-07: Move to Ready]

- -

LWG 2181 exceptions from seed sequence operations

-

STL: Daniel explained that I was confused. I said, oh, seed_seq says it can throw if the RanIt throws. Daniel says the RanIts are provided by the engine. Therefore if you give a seed_seq to an engine, it cannot throw, as implied by the current normative text. So what Daniel has in the PR is correct, if slightly unnecessary. It's okay to have explicitly non-overlapping Standardese even if overlapping would be okay.

-

Marshall: And this is a case where the std:: on seed_seq is a good thing.

-

STL: Meh.

-

STL: And that was my only concern with this PR. I like the latest PR much better than the previous.

-

Marshall: Yes. There's a drive-by fix for referencing the wrong section. Other than that, the two are the same.

-

STL: Alisdair wanted the repetition instead of centralization, and I agree.

-

Marshall: Any other opinions?

-

Jonathan: I'll buy it.

-

STL: For a dollar?

-

Hwrd: I'll buy that for a nickel.

-

Marshall: Any objections to Ready? I don't see a point in Immediate.

-

Jonathan: Absolutely agree.

-

Marshall: 7 for ready, 0 opposed, 0 abstain.

- -

[2014-05-22, Daniel syncs with recent WP]

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Edit the contents of sub-clause 26.5.3 [rand.eng] as indicated:

    - -

    --1- Each type instantiated from a class template specified in this section 26.5.3 [rand.eng] satisfies the -requirements of a random number engine (26.5.1.4 [rand.req.eng]) type. -

    --2- Except where specified otherwise, the complexity of each function specified in this section 26.5.3 [rand.eng] -is constant. -

    --3- Except where specified otherwise, no function described in this section 26.5.3 [rand.eng] throws an exception. -

    --?- Every function described in this section 26.5.3 [rand.eng] that has a function parameter q of -type Sseq& for a template type parameter named Sseq that is different from type std::seed_seq -throws what and when the invocation of q.generate throws. -

    --4- Descriptions are provided in this section 26.5.3 [rand.eng] only for engine operations that are not -described in 26.5.1.4 [rand.req.eng] or for operations where there is additional semantic information. In particular, -declarations for copy constructors, for copy assignment operators, for streaming operators, and -for equality operators, and inequality operators are not shown in the synopses. -

    --5- Each template specified in this section 26.5.3 [rand.eng] requires one or more relationships, -involving the value(s) of its non-type template parameter(s), to hold. A program instantiating any of these templates is -ill-formed if any such required relationship fails to hold. -

    --6- For every random number engine and for every random number engine adaptor X defined in this subclause -(26.5.3 [rand.eng]) and in sub-clause 26.5.4 [rand.adapt]: -

    -
      -

    • -if the constructor -

      -
      -template <class Sseq> explicit X(Sseq& q);
-
      -

      -is called with a type Sseq that does not qualify as a seed sequence, then this constructor shall not -participate in overload resolution; -

      -
      • -

    • -if the member function -

      -
      -template <class Sseq> void seed(Sseq& q);
-
      -

      -is called with a type Sseq that does not qualify as a seed sequence, then this function shall not -participate in overload resolution; -

      -
      • -
    -

    -The extent to which an implementation determines that a type cannot be a seed sequence is unspecified, -except that as a minimum a type shall not qualify as a seed sequence if it is implicitly convertible to -X::result_type. -

    -
    -
    2. - -

  2. Edit the contents of sub-clause 26.5.4.1 [rand.adapt.general] as indicated:

    - -

    --1- Each type instantiated from a class template specified in this section -26.5.3 [rand.eng]26.5.4 [rand.adapt] satisfies the requirements of a -random number engine adaptor (26.5.1.5 [rand.req.adapt]) type. -

    --2- Except where specified otherwise, the complexity of each function specified in this section 26.5.4 [rand.adapt] -is constant. -

    --3- Except where specified otherwise, no function described in this section 26.5.4 [rand.adapt] throws an exception. -

    --?- Every function described in this section 26.5.4 [rand.adapt] that has a function parameter q of -type Sseq& for a template type parameter named Sseq that is different from type std::seed_seq -throws what and when the invocation of q.generate throws. -

    --4- Descriptions are provided in this section 26.5.4 [rand.adapt] only for adaptor operations that are not -described in section 26.5.1.5 [rand.req.adapt] or for operations where there is additional semantic information. In particular, -declarations for copy constructors, for copy assignment operators, for streaming operators, and for -equality operators, and inequality operators are not shown in the synopses. -

    --5- Each template specified in this section 26.5.4 [rand.adapt] requires one or more relationships, involving -the value(s) of its non-type template parameter(s), to hold. A program instantiating any of these templates is ill-formed if -any such required relationship fails to hold. -

    -
    3. - -

  3. Edit the contents of sub-clause 26.5.8.1 [rand.dist.general] p2 as indicated: [Drafting note: These -editorial changes are just for consistency with those applied to 26.5.3 [rand.eng] and -26.5.4.1 [rand.adapt.general] — end drafting note]

    - -

    --2- Descriptions are provided in this section 26.5.8 [rand.dist] only for distribution operations that are not -described in 26.5.1.6 [rand.req.dist] or for operations where there is additional semantic information. In particular, -declarations for copy constructors, for copy assignment operators, for streaming operators, and for -equality operators, and inequality operators are not shown in the synopses. -

    -
    4. - -
- - - - - -
-

2183. Muddled allocator requirements for match_results constructors

-

Section: 28.10.1 [re.results.const], 28.10.6 [re.results.all] Status: New - Submitter: Pete Becker Opened: 2012-08-29 Last modified: 2015-04-08

-

View other active issues in [re.results.const].

-

View all other issues in [re.results.const].

-

View all issues with New status.

-

Discussion:

- -

-28.10.1 [re.results.const] p1 says: -

-

-In all match_results constructors, a copy of the Allocator argument shall be used for any memory -allocation performed by the constructor or member functions during the lifetime of the object. -

-

-There are three constructors: -

-
-match_results(const Allocator& = Allocator());
-match_results(const match_results& m);
-match_results(match_results&& m) noexcept;
-
-

-The second and third constructors do no have an Allocator argument, so despite the "all match_results -constructors", it is not possible to use "the Allocator argument" for the second and third constructors. -

-The requirements for those two constructors also does not give any guidance. The second constructor has no language -about allocators, and the third states that the stored Allocator value is move constructed from -m.get_allocator(), but doesn't require using that allocator to allocate memory. -

-The same basic problem recurs in 28.10.6 [re.results.all], which gives the required return value for -get_allocator(): -

-

-Returns: A copy of the Allocator that was passed to the object's constructor or, if that allocator -has been replaced, a copy of the most recent replacement. -

-

-Again, the second and third constructors do not take an Allocator, so there is nothing that meets this -requirement when those constructors are used. -

- - - -

Proposed resolution:

- - - - - -
-

2184. Muddled allocator requirements for match_results assignments

-

Section: 28.10.1 [re.results.const], 28.10.6 [re.results.all] Status: New - Submitter: Pete Becker Opened: 2012-08-29 Last modified: 2015-04-08

-

View other active issues in [re.results.const].

-

View all other issues in [re.results.const].

-

View all issues with New status.

-

Discussion:

- -

-The effects of the two assignment operators are specified in Table 141. Table 141 makes no mention of allocators, -so, presumably, they don't touch the target object's allocator. That's okay, but it leaves the question: -match_results::get_allocator() is supposed to return "A copy of the Allocator that was passed to the -object's constructor or, if that allocator has been replaced, a copy of the most recent replacement"; if assignment -doesn't replace the allocator, how can the allocator be replaced? -

- - - -

Proposed resolution:

- - - - - -
-

2189. Throwing swap breaks unordered containers' state

-

Section: 23.2.5.1 [unord.req.except] Status: Open - Submitter: Alisdair Meredith Opened: 2012-09-23 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

- -

-The hash functor and key-comparison functor of unordered containers are allowed to throw on swap. -

-

-23.2.5.1 [unord.req.except]p3 "For unordered associative containers, no swap function throws -an exception unless that exception is thrown by the swap of the container's Hash or Pred object (if any)." -

-

-In such a case we must offer the basic exception safety guarantee, where both objects are left in valid -but unspecified states, and no resources are leaked. This yields a corrupt, un-usable container if the -first swap succeeds, but the second fails by throwing, as the functors form a matched pair. -

-

-So our basic scenario is first, swap the allocators if the allocators propagate on swap, according to -allocator_traits. Next we swap the pointers to our internal hash table data structures, so that -they match the allocators that allocated them. (Typically, this operation cannot throw). Now our containers -are back in a safely destructible state if an exception follows. -

-

-Next, let's say we swap the hash functor, and that throws. We have a corrupt data structure, in that the -buckets are not correctly indexed by the correct functors, lookups will give unpredicatable results etc. -We can safely restore a usable state by forcibly clearing each container - which does not leak resources -and leaves us with two (empty but) usable containers. -

-

-Now let us assume that the hasher swap succeeds. Next we swap the equality comparator functor, and this -too could throw. The important point to bear in mind is that these two functors form an important pairing -- two objects that compare equal by the equality functor must also hash to the same value. If we swap -one without the other, we most likely leave the container in an unusable state, even if we clear out all -elements. -

-

-1. A colleague pointed out that the solution for this is to dynamically allocate the two functors, and then -we need only swap pointers, which is not a throwing operation. And if we don't want to allocate on default -construction (a common QoI request), we might consider moving to a dynamically allocated functors whenever -swap is called, or on first insertion. Of course, allocating memory in swap is a whole -new can of worms, but this does not really sound like the design we had intended. -

- -

-2. The simplest option is to say that we do not support hasher or equality functors that throw on ADL -swap. Note that the requirement is simply to not throw, rather than to be explicitly -marked as noexcept. Throwing functors are allowed, so long as we never use values that -would actually manifest a throw when used in an unordered container. -

- -

-Pablo went on to give me several more options, to be sure we have a full set to consider: -

-

-3. Disallow one or the other functor from throwing. In that case, the -possibly-throwing functor must be swapped first, then the other functor, -the allocator, and the data pointer(s) afterwards (in any order -- there -was a TC that allocator assignment and swap may not throw if the -corresponding propagation trait is true.). Of course, the question -becomes: which functor is allowed to throw and which one is not? -

-

-4. Require that any successful functor swap be reliably reversible. -This is very inventive. I know of no other place in the standard where -such a requirement is stated, though I have occasionally wanted such a -guarantee. -

-

-5. Allow a failed swap to leave the containers in a state where future -insertions may fail for reasons other than is currently allowed. -Specifically, if the hash and equality functors are out of sync, all -insertions will fail. Presumably some "incompletely swapped" exception -would be thrown. This is "slightly" inventive, although people have been -discussing "radioactive" states for a while. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

- - - -

Proposed resolution:

- - - - - - -
-

2191. Incorrect specification of match_results(match_results&&)

-

Section: 28.10.1 [re.results.const] Status: New - Submitter: Pete Becker Opened: 2012-10-02 Last modified: 2015-04-08

-

View other active issues in [re.results.const].

-

View all other issues in [re.results.const].

-

View all issues with New status.

-

Discussion:

- -

-28.10.1 [re.results.const]/3: "Move-constructs an object of class match_results satisfying the same -postconditions as Table 141." -

-

-Table 141 lists various member functions and says that their results should be the results of the corresponding member -function calls on m. But m has been moved from, so the actual requirement ought to be based on the -value that m had before the move construction, not on m itself. -

-

-In addition to that, the requirements for the copy constructor should refer to Table 141. -

-Ganesh: -

-Also, the requirements for move-assignment should refer to Table 141. Further it seems as if in Table 141 all phrases of -"for all integers n < m.size()" should be replaced by "for all unsigned integers -n < m.size()". -

- - - -

Proposed resolution:

- - - - - -
-

2192. Validity and return type of std::abs(0u) is unclear

-

Section: 26.8 [c.math] Status: Open - Submitter: Daniel Krügler Opened: 2012-10-02 Last modified: 2015-05-22

-

View other active issues in [c.math].

-

View all other issues in [c.math].

-

View all issues with Open status.

-

Discussion:

- -

-In C++03 the following two programs are invalid: -

-
  1. -
    -#include <cmath>
-
-int main() {
-  std::abs(0u);
-}
-
    -
    2. -
  2. -
    -#include <cstdlib>
-
-int main() {
-  std::abs(0u);
-}
-
    -
    3. -
-

-because none of the std::abs() overloads is a best match. -

-

-In C++11 the additional "sufficient overload" rule from 26.8 [c.math] p11 (see also LWG -2086) can be read to be applicable to the std::abs() overloads as well, which -can lead to the following possible conclusions: -

-

    -

  1. The program

    -
    -#include <type_traits>
-#include <cmath>
-
-static_assert(std::is_same<decltype(std::abs(0u)), double>(), "Oops");
-
-int main() {
-  std::abs(0u); // Calls std::abs(double)
-}
-
    -

    -is required to be well-formed, because of sub-bullet 2 ("[..] or an integer type [..]") of -26.8 [c.math] p11 (Note that the current resolution of LWG 2086 doesn't -fix this problem). -

    -
    2. -

  2. Any translation unit including both <cmath> and <cstdlib> -might be ill-formed because of two conflicting requirements for the return type of the overload -std::abs(int). -

    -
    3. -
-

- -

-It seems to me that at least the second outcome is not intended, personally I think that both -are unfortunate: In contrast to all other floating-point functions explicitly listed in sub-clause -26.8 [c.math], the abs overloads have a special and well-defined meaning for -signed integers and thus have explicit overloads returning a signed integral type. I also believe that -there is no problem accepting that std::fabs(0u) is well-defined with return type double, -because the leading 'f' clearly signals that we have a floating point function here. But the expected -return type of std::abs(0u) seems less than clear to me. A very reasonable answer could be that -this has the same type as its argument type, alternatively it could be a reasonably chosen signed -integer type, or a floating point type. It should also be noted, that the corresponding -"generic type function" rule set from C99/C1x in 7.25 p2+3 is restricted to the floating-point functions -from <math.h> and <complex.h>, so cannot be applied to the abs -functions (but to the fabs functions!). -

-Selecting a signed integer return type for unsigned input values can also problematic: The directly -corresponding signed integer type would give half of the possible argument values an implementation-defined -result value. Choosing the first signed integer value that can represent all positive values would solve this -problem for unsigned int, but there would be no clear answer for the input type std::uintmax_t. -

-

-Based on this it seems to me that the C++03 state in regard to unsigned integer values was the better -situation, alerting the user that this code is ambigious at the moment (This might be change with different core-language -rules as described in N3387). -

- -

[2013-04-20, Bristol]

- - -

-Resolution: leave as new and bring it back in Chicago. -

- -

[2013-09 Chicago]

- -

-This issue also relates to LWG 2294 -

-STL: these two issues should be bundled -

-Stefanus: do what Pete says, and add overloads for unsigned to return directly -

-STL: agree Consensus that this is an issue -

-Walter: motion to move to Open -

-STL: no wording for 2294 -

-Stefanus: move to open and note the 2 issues are related and should be moved together -

-Stefanus: add and define unsigned versions of abs() -

- -

[2014-02-03 Howard comments]

- -

-Defining abs() for unsigned integers is a bad idea. Doing so would turn compile time errors into run time errors, -especially in C++ where we have templates, and the types involved are not always apparent to the programmer at design time. -For example, consider: -

-
-template <class Int>
-Int
-analyze(Int x, Int y)
-{
-  // ...
-  if (std::abs(x - y) < threshold)
-  {
-    // ...
-  }
-  // ...
-}
-
-

-std::abs(expr) is often used to ask: Are these two numbers sufficiently close? When the assumption is that -the two numbers are signed (either signed integral, or floating point), the logic is sound. But when the same logic is -accidentally used with an arithmetic type not capable of representing negative numbers, and especially if unsigned overflow -will silently happen, then the logic is no longer correct: -

-
-auto i = analyze(20u, 21u);  // Today a compile time error
-    // But with abs(unsigned) becomes a run time error
-
-

-This is not idle speculation. Search the net for "abs unsigned" -here or -here. -

-In C++11, chrono durations and time_points are allowed to be based on unsigned integers. Taking the -absolute value of the difference of two such time_points would be easy to accidentally do (say in code templated on -time_points), and would certainly be a logic bug, caught at compile time unless we provide the error prone abs(unsigned). -

- -

[2015-02, Cologne]

- -

-GR: Do we want to make the changes to both <cmath> and <cstdlib>?
-AM: I think so; we should provide consistent overloads.
-GR: Then we're imposing restrictions on what users put in the global namespace.
-AM: I'm not so worried about that. Users already know not to use C library names.
-VV: So what are we going to do about unsigned integers? AM: We will say that they are ill-formed.
-AM: Does anyone volunteer to send updated wording to Daniel? GR, can you do it? GR: Sure.
-GR: To clarify: we want to make unsigned types ill-formed?
-AM: With promotion rank at least unsigned int.
-GR: And NL suggests to just list those types. -

-Conclusion: Merge the resolution into a single issue. -

- -Previous resolution from Daniel [SUPERSEDED]: -
-

This wording is relative to N3376.

- -
    -

  1. Change 26.8 [c.math] p11 as indicated:

    -

    --11- Moreover, except for the abs functions, there shall be additional overloads sufficient to ensure: -

    -[…] -

    -
    2. -
-
- -

[2015-03-03, Geoffrey Romer provides improved wording]

- -

-In the following I've drafted combined wording to resolve LWG 2192 and 2294. Note that the first -two paragraphs are taken verbatim from the P/R of LWG 2294, but the third is newly drafted: -

- -

[2015-05-05 Lenexa: Howard to draft updated wording]

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Insert the following new paragraphs after 26.8 [c.math] p7:

    -
    -

    --6- In addition to the int versions of certain math functions in <cstdlib>, C++ adds long -and long long overloaded versions of these functions, with the same semantics. -

    --7- The added signatures are: -

    -
    -
    -long abs(long); // labs()
-long long abs(long long); // llabs()
-ldiv_t div(long, long); // ldiv()
-lldiv_t div(long long, long long); // lldiv()
-
    -
    -

    --?- To avoid ambiguities, C++ also adds the following overloads of abs() to <cstdlib>, -with the semantics defined in <cmath>: -

    -
    -
    -float abs(float);
-double abs(double);
-long double abs(long double);
-
    -
    -

    --?- To avoid ambiguities, C++ also adds the following overloads of abs() to <cmath>, -with the semantics defined in <cstdlib>: -

    -
    -
    -int abs(int);
-long abs(long);
-long long abs(long long);
-
    -
    -

    --?- If abs() is called with an argument of unsigned integral type that cannot be converted to int -by integral promotion (4.5 [conv.prom]), the program is ill-formed. [Note: arguments that can be promoted -to int are permitted for compatibility with C. — end note] -

    -
    -
    2. -
- - - - - -
-

2195. Missing constructors for match_results

-

Section: 28.10 [re.results] Status: Open - Submitter: Daniel Krügler Opened: 2012-10-06 Last modified: 2015-05-22

-

View all other issues in [re.results].

-

View all issues with Open status.

-

Discussion:

- -

-The requirement expressed in 28.10 [re.results] p2 -

-

-The class template match_results shall satisfy the requirements of an allocator-aware container and of a -sequence container, as specified in 23.2.3 [sequence.reqmts], except that only operations defined for -const-qualified sequence containers are supported. -

-

-can be read to require the existence of the described constructors from as well, but they do not exist in the -synopsis. -

-The missing sequence constructors are: -

-
-match_results(initializer_list<value_type>);
-match_results(size_type, const value_type&);
-template<class InputIterator> match_results(InputIterator, InputIterator);
-
-

-The missing allocator-aware container constructors are: -

-
-match_results(const match_results&, const Allocator&);
-match_results(match_results&&, const Allocator&);
-
-

-It should be clarified, whether (a) constructors are an exception of above mentioned operations or (b) whether -at least some of them (like those accepting a match_results value and an allocator) should be added. -

-As visible in several places of the standard (including the core language), constructors seem usually to be considered -as "operations" and they certainly can be invoked for const-qualified objects. -

-The below given proposed resolution applies only the minimum necessary fix, i.e. it excludes constructors from -above requirement. -

- -

[2013-04-20, Bristol]

- - -

-Check current implementations to see what they do and, possibly, write a paper. -

- -

[2013-09 Chicago]

- -

-Ask Daniel to update the proposed wording to include the allocator copy and move constructors. -

- -

[2014-01-18 Daniel changes proposed resolution]

- -

-Previous resolution from Daniel [SUPERSEDED]: -

- -
-
    -

  1. Change 28.10 [re.results] p2 as indicated:

    -

    -The class template match_results shall satisfy the requirements of an allocator-aware container and of a -sequence container, as specified in 23.2.3 [sequence.reqmts], except that only operations defined for -const-qualified sequence containers that are not constructors are supported. -

    -
    2. -
-
- -

[2015-05-06 Lenexa]

- -

MC passes important knowledge to EF.

-

VV, RP: Looks good.

-

TK: Second form should be conditionally noexcept

-

JY: Sequence constructors are not here, but mentioned in the issue writeup. Why?

-

TK: That would have been fixed by the superseded wording.

-

JW: How does this interact with Mike Spertus' allocator-aware regexes? [...] Perhaps it doesn't.

-

JW: Can't create match_results, want both old and new resolution.

-

JY: It's problematic that users can't create these, but not this issue.

-

VV: Why conditional noexcept?

-

MC: Allocator move might throw.

-

JW: Update superseded wording to "only non-constructor operations that are"?

-

MC: Only keep superseded, but append "and the means of constructing match_results are limited to [...]"?

-

JY: Bullet 4 paragraph 2 needs to address the allocator constructor.

-

Assigned to JW for drafting.

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 28.10 [re.results] p4, class template match_results synopsis, as indicated:

    -
    -[…]
-// 28.10.1, construct/copy/destroy:
-explicit match_results(const Allocator& a = Allocator());
-match_results(const match_results& m);
-match_results(const match_results& m, const Allocator& a);
-match_results(match_results&& m) noexcept;
-match_results(match_results&& m, const Allocator& a) noexcept;
-[…]
-
    -
    2. - -

  2. Change 28.10.1 [re.results.const] as indicated: [Drafting note: Paragraph 6 as currently written, -makes not much sense, because the noexcept does not allow any exception to propagate. Further-on, the allocator requirements -do not allow for throwing move constructors. Deleting it seems to be near to editorial — end drafting note]

    -
    - -
    -match_results(const match_results& m);
-match_results(const match_results& m, const Allocator& a);
-
    -
    -

    --4- Effects: Constructs an object of class match_results, as a copy of m. -

    -
    - -
    -match_results(match_results&& m) noexcept;
-match_results(match_results&& m, const Allocator& a) noexcept;
-
    -
    -

    --5- Effects: Move-constructs an object of class match_results from m satisfying the same postconditions -as Table 142. AdditionallyFor the first form, the stored Allocator value is move constructed -from m.get_allocator(). -

    --6- Throws: Nothing if the allocator's move constructor throws nothing. -

    -
    - -
    -
    3. -
- - - - - - -
-

2198. max_load_factor(z) makes no strong guarantees, but bans useful behavior

-

Section: 23.2.5 [unord.req] Status: Open - Submitter: Alisdair Meredith Opened: 2012-10-09 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

View all other issues in [unord.req].

-

View all issues with Open status.

-

Discussion:

- -

-The user cannot specify a max_load_factor for their unordered container -at construction, it must be supplied after the event, when the container is -potentially not empty. The contract for this method is deliberately vague, not -guaranteeing to use the value supplied by the user, and any value actually used -will be used as a ceiling that the container will attempt to respect. -

-

-The only guarantee we have is that, if user requests a max_load_factor -that is less than the current load_factor, then the operation will take -constant time, thus outlawing an implementation that chooses to rehash and so -preserve as a class invariant that load_factor < max_load_factor. -

-

-Reasonable options conforming to the standard include ignoring the user's request -if the requested value is too low, or deferring the rehash to the next insert -operation and allowing the container to have a strange state (wrt max_load_factor) -until then - and there is still the question of rehashing if the next insert -is for a duplicate key in a unique container. -

-

-Given the deliberate vagueness of the current wording, to support a range of reasonable -(but not perfect) behaviors, it is not clear why the equally reasonable rehash -to restore the constraint should be outlawed. It is not thought that this is a performance -critical operation, where users will be repeatedly setting low load factors on populated -containers, in a tight or (less unlikely) an instant response scenario. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Alisdair to provide wording. -

- - - -

Proposed resolution:

- - - - - - -
-

2199. unordered containers are required to have an initial max load factor of 1.0

-

Section: 23.2.5 [unord.req] Status: Open - Submitter: Alisdair Meredith Opened: 2012-10-09 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

View all other issues in [unord.req].

-

View all issues with Open status.

-

Discussion:

- -

-The default constructor, allocator-aware constructor, and range-based constructors -for the unordered containers do not offer a means to control the initial -max_load_factor, so the standard mandates the value 1.0. This seems overly -restrictive, as there is plenty of research suggesting a value between 0.5 and 1.0 -is more often optimal for unique-key containers, and perhaps a slightly higher -value might be appropriate for multi-containers. -

-

-Rather than guess at the appropriate max_load_factor, it seems reasonable -that the standard should allow vendors to pick a value at their discretion, with -perhaps a note of advice. It is less clear whether the default value should be -implementation-defined or unspecified, given the ease of a user determining this -by querying this attribute immediately after construction. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Alisdair to provide wording. -

-

-Marshall: It seems to me that what you really want is to be able to pass a max load factor in the -constructor, but that's a different issue. -

-

-Alisdair agrees in principle, but concerned with adding yet more constructors to these classes. -

- - - -

Proposed resolution:

- - - - - - -
-

2201. Missing macro entries from C standard library

-

Section: C.5 [diff.library] Status: New - Submitter: Kevin McCarty Opened: 2012-02-03 Last modified: 2015-04-08

-

View all other issues in [diff.library].

-

View all issues with New status.

-

Discussion:

- -

-It seems that in C.5 [diff.library], Table 150 the following macros from 18.3.3 [c.limits], Table 31 -are missing: -

-
-LLONG_MIN 
-LLONG_MAX
-ULLONG_MAX
-
-

-In addition in C.5 [diff.library], Table 150 the following macros from 18.3.3 [c.limits], Table 32 -are missing: -

-
-DECIMAL_DIG 
-FLT_EVAL_METHOD
-
-

-Furtheron it seems that in C.5 [diff.library], Table 149/150 further macros are missing as well, e.g. -HUGE_VALF, INFINITY, etc. -

- -

[2014-02 Issaquah:]

- -

-This is an issue, all of C has not been updated for C99, C99 functions are missing, whole section needs to be overhauled. -

-The issue needs to be updated for functions and other missing items and when that happens the issue title is wrong and -needs to be adapted. -

- - - -

Proposed resolution:

- - - - - -
-

2202. Missing allocator support by async

-

Section: 30.6.8 [futures.async] Status: Deferred - Submitter: Detlef Vollmann Opened: 2012-10-19 Last modified: 2015-05-08

-

View all other issues in [futures.async].

-

Discussion:

- -

-promise, packaged_task, and async are the only -places where a shared state is actually supposed to be allocated. Accordingly, -promise and packaged_task are "allocator-aware". But -function template async provides no way to provide an allocator. -

- -

[2013-09 Chicago]

- -

-Matt: deprecate async -

-Nico: read my paper -

-Alisdair: defer issues to wait for polymorphic allocators -

-Alisdair: defer, active topic of research Deferred -

- -

[2014-02-20 Re-open Deferred issues as Priority 4]

- - -

[2015-05 Lenexa, SG1 response]

- -

-We want whatever status approximates: "will not fix; we're working on a replacement facility and don't want to add features to a broken one" -

- - -

Proposed resolution:

- - - - - -
-

2206. Inaccuracy in initializer_list constructor requirements

-

Section: 23.2.3 [sequence.reqmts], 23.2.4 [associative.reqmts], 23.2.5 [unord.req], 26.5.1.2 [rand.req.seedseq] Status: Open - Submitter: Jeffrey Yasskin Opened: 2012-10-21 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with Open status.

-

Discussion:

- -

-In 23.2.3 [sequence.reqmts] p3, we have "il designates an object of type -initializer_list<value_type>", and then several functions that take -'il' as an argument. However, an expression like {1, 2, 'a'} is not -an object of type initializer_list<int> unless it's used to initialize -an explicitly-typed variable of that type. I believe we want: -

-
-std::vector<int> v;
-v = {1, 2, 'a'};
-
-

-to compile portably, so we should say something different when defining 'il'. The -same phrasing happens in 23.2.4 [associative.reqmts], 23.2.5 [unord.req], and -26.5.1.2 [rand.req.seedseq]. -

-This may just be an editorial issue because the actual class synopses declare the functions -to take initializer_list<exact_type>. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-This is definitely not NAD -

-

-Should copy the suggested wording as the proposed resolution. -

- - - -

Proposed resolution:

- - - - - -
-

2208. std::reverse_iterator should be a literal type

-

Section: 24.5.1 [reverse.iterators] Status: New - Submitter: Jeffrey Yasskin Opened: 2012-10-30 Last modified: 2015-04-08

-

View all other issues in [reverse.iterators].

-

View all issues with New status.

-

Discussion:

- -

-std::reverse_iterator::reverse_iterator(Iterator) should be constexpr -so that other constexpr functions can return reverse_iterators. Of the -other methods, the other constructors, base(), operator+, operator-, -operator[], and the non-member operators can probably also be -constexpr. -

-operator* cannot be constexpr because it involves an assignment to a -member variable. Discussion starting with c++std-lib-33282 indicated -that it would be useful to make reverse_iterator a literal type -despite this restriction on its use at compile time. -

- - - -

Proposed resolution:

- - - - - -
-

2214. Clarify basic_ios::init call restrictions

-

Section: 27.5.5.2 [basic.ios.cons] Status: Open - Submitter: Andrey Semashev Opened: 2012-11-09 Last modified: 2015-04-08

-

View all other issues in [basic.ios.cons].

-

View all issues with Open status.

-

Discussion:

-

-There is an ambiguity in how std::basic_ios::init method (27.5.5.2 [basic.ios.cons]) -can be used in the derived class. The Standard only specify the state of the basic_ios -object after the call completes. However, in basic_ios default constructor description -(27.5.5.2 [basic.ios.cons]) there is this sentence: -

-

-Effects: Constructs an object of class basic_ios (27.5.3.7 [ios.base.cons]) -leaving its member objects uninitialized. The object shall be initialized by calling basic_ios::init -before its first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined. -

-

-This restriction hints that basic_ios::init should be called exactly -once before the object can be used or destroyed, because basic_ios::init -may not know whether it was called before or not (i.e. whether its members are actually -uninitialized or are initialized by the previous call to basic_ios::init). There -is no such restriction in the basic_ios::init preconditions so it is not clear whether it is -allowed to call basic_ios::init multiple times or not. -

-This problem has already affected publicly available implementations. -For example, Microsoft Visual C++ STL introduces a memory leak if -basic_ios::init is called multiple times, while GCC 4.7 and STLPort -reinitialize the basic_ios object correctly without memory leak or any -other undesired effects. There was a discussion of this issue on Boost -developers mailing list, -and there is a test case -that reproduces the problem. The test case is actually a bug report for my Boost.Log library, -which attempts to cache basic_ostream-derived objects internally to avoid expensive construction -and destruction. My stream objects allowed resetting the stream buffer pointers the stream -is attached to, without requiring to destroy and construct the stream. -

-My personal view of the problem and proposed resolution follows. -

-While apparently the intent of basic_ios::init is to provide a way to -initialize basic_ios after default construction, I see no reason to -forbid it from being called multiple times to reinitialize the stream. -Furthermore, it is possible to implement a conforming basic_ios that -does not have this restriction. -

-The quoted above section of the Standard that describes the effects of -the default constructor is misleading. The Standard does not mandate -any data members of basic_ios or ios_base (27.5.3 [ios.base]), which -it derives from. This means that the implementation is allowed to use -non-POD data members with default constructors that initialize the -members with particular default values. For example, in the case of -Microsoft Visual C++ STL the leaked memory is an std::locale instance -that is dynamically allocated during basic_ios::init, a raw pointer to -which is stored within ios_base. It is possible to store e.g. an -unique_ptr instead of a raw pointer as a member of ios_base, the smart -pointer will default initialize the underlying raw pointer on default -construction and automatically destroy the allocated object upon being -reset or destroyed, which would eliminate the leak and allow -basic_ios::init to be called multiple times. This leads to conclusion -that the default constructor of basic_ios cannot leave "its member -objects uninitialized" but instead performs default initialization of -the member objects, which would mean the same thing in case of POD types. -

-However, I feel that restricting ios_base and basic_ios members to -non-POD types is not acceptable. Since multiple calls to basic_ios::init are -not forbidden by the Standard, I propose to correct the basic_ios default -constructor description so that it is allowed to destroy basic_ios object -without calling basic_ios::init. This would imply that any raw members of -basic_ios and ios_base should be initialized to values suitable for -destruction (essentially, this means only initializing raw pointers to NULL). The new -wording could look like this: -

-

-Effects: Constructs an object of class basic_ios (27.5.3.7 [ios.base.cons]) -initializing its member objects to unspecified state, only suitable for basic_ios destruction. -The object shall be initialized by calling basic_ios::init before its first use; otherwise -the behavior is undefined. -

-

-This would remove the hint that basic_ios::init must be called exactly -once. Also, this would remove the requirement for basic_ios::init to -be called at all before the destruction. This is also an important issue because -the derived stream constructor may throw an exception before it manages to call -basic_ios::init (for example, if the streambuf constructor throws), and -in this case the basic_ios destructor has undefined behavior. -

-To my mind, the described modification is sufficient to resolve the issue. But to -emphasize the possibility to call basic_ios::init multiple times, a remark -or a footnote for basic_ios::init postconditions could be added to explicitly -state the semantics of calling it multiple times. The note could read as follows: -

-

-The function can be called multiple times during the object lifetime. Each subsequent -call reinitializes the object to the described in postconditions initial state. -

- -

[2013-04-20, Bristol]

- - -

-Alisdair: The current wording is unclear but the proposed resolution is wrong -

-Solution: Clarify that init must be called once and only once. Move then to review. -

- - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 27.5.5.2 [basic.ios.cons] as indicated:

    -
    -basic_ios();
-
    -
    -

    --2- Effects: Constructs an object of class basic_ios (27.5.3.7 [ios.base.cons]) -leaving its member objects uninitializedinitializing its member objects to unspecified state, -only suitable for basic_ios destruction. The object shall be initialized by calling -basic_ios::init before its first use or before it is destroyed, whichever comes first; -otherwise the behavior is undefined. -

    -
    -
    -void init(basic_streambuf<charT,traits>* sb);
-
    -

    -Postconditions: The postconditions of this function are indicated in Table 128. -

    --?- Remarks: The function can be called multiple times during the object lifetime. Each subsequent -call reinitializes the object to the described in postconditions initial state. -

    -
    -
    -
    2. -
- - - - - - -
-

2215. (unordered) associative container functors should be CopyConstructible

-

Section: 23.2.4 [associative.reqmts], 23.2.5 [unord.req] Status: Open - Submitter: Alisdair Meredith Opened: 2012-11-14 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with Open status.

-

Discussion:

-

-The requirements on the functors used to arrange elements in the various associative and -unordered containers are given by a set of expressions in tables 102 — Associative container -requirements, and 103 — Unordered associative container requirements. In keeping with Library -convention these expressions make the minimal requirements necessary on their types. For -example, we have the following 3 row extracts for the unordered containers: -

- - - - - - - - - - - - - - - - - - - - -
- Expression - - Assertion/note pre-/post-condition -
-
-X(n, hf, eq)
-X a(n, hf, eq)
-
- 		- Requires: hasher and key_equal are CopyConstructible. -
-
-X(n, hf)
-X a(n, hf)
-
- 		- Requires: hasher is CopyConstructible and - key_equal is DefaultConstructible. -
-
-X(n)
-X a(n)
-
- 		- Requires: hasher and key_equal are DefaultConstructible. -
- -

-However, the signature for each class template requires that the functors must effectively be -CopyConstructible for each of these expressions: -

- -
-template <class Key,
-          class T,
-          class Hash  = hash<Key>,
-          class Pred  = std::equal_to<Key>,
-          class Allocator = std::allocator<std::pair<const Key, T> > >
-class unordered_map
-{
-  ...
-
-  // construct/destroy/copy
-  explicit unordered_map(size_type n = see below,
-                         const hasher& hf = hasher(),
-                         const key_equal& eql = key_equal(),
-                         const allocator_type& a = allocator_type());
-
-  ...
-}
-
- -

-The letter of the standard can be honored as long as implementors recognize -their freedom to split this one signature into multiple overloads, so that -the documented default arguments (requiring a CopyConstructible functor) -are not actually passed as default arguments. -

-

-As we look into the requirements for the copy constructor and copy-assignment -operator, the requirements are even more vague, as the explicit requirements on -the functors are not called out, other than saying that the functors are copied. -

-

-Must the functors be CopyAssignable? Or is CopyConstructible -sufficient in this case? Do we require that the functors be Swappable -so that the copy-swap idiom can be deployed here? Note that a type that is both -CopyConstructible and CopyAssignable is still not guaranteed to -be Swappable as the user may delete the swap function for their -type in their own namespace, which would be found via ADL. -

-

-Some clean-up of the requirements table looks necessary, to at least document the -assignment behavior. In addition, we should have clear guidance on whether these -functors should always be CopyConstructible, as suggested by the class -template definitions, or if the requirement tables are correct and we should -explicitly split up the constructors in the (unordered) associative containers -to no longer use default (function) arguments to obtain their defaulted functors. -

-

-I recommend the simplest solution would be to always require that the functors -for (unordered) associative containers be CopyConstructible, above the -requirements tables themselves, so that the issue need not be addressed within -the tables. I suggest that the assignment operators for these containers add -the requirement that the functors be Swappable, rather than forwarding -the corresponding Assignable requirement. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Alisdair to propose wording. -

- -

[2014-06-08, Daniel comments]

- -

-The area of this issue partially overlaps what LWG 2227 addresses. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

2216. regex_replace(basic_string) allocator handling

-

Section: 28.11.4 [re.alg.replace] Status: New - Submitter: Jeffrey Yasskin Opened: 2012-11-26 Last modified: 2015-04-08

-

View all other issues in [re.alg.replace].

-

View all issues with New status.

-

Discussion:

- -
-template <class traits, class charT, class ST, class SA>
-  basic_string<charT, ST, SA>
-  regex_replace(const basic_string<charT, ST, SA>& s,
-      const basic_regex<charT, traits>& e,
-      const charT* fmt,
-      regex_constants::match_flag_type flags = 
-	    regex_constants::match_default);
-
-

-and friends are documented as -

-

-Constructs an empty string result of type basic_string<charT, ST, SA> -and calls regex_replace(back_inserter(result), s.begin(), s.end(), e, fmt, flags). -

-

-This appears to require the result to have a default-constructed -allocator, which isn't even possible for all allocator types. I -suspect the allocator should be copied from 's' instead. Possibly -there should be an additional defaulted argument to override the -allocator of the result. -

- - - -

Proposed resolution:

- - - - - -
-

2218. Unclear how containers use allocator_traits::construct()

-

Section: 23.2.1 [container.requirements.general] Status: Ready - Submitter: Jonathan Wakely Opened: 2012-11-27 Last modified: 2015-05-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with Ready status.

-

Discussion:

- -

-Firstly, 23.2.1 [container.requirements.general]/7 says a container's -allocator is used to obtain memory, but it isn't stated explicitly that the same -allocator is used to construct and destroy elements, as opposed to a value-initialized -allocator of the same type. -

-

-Secondly, 23.2.1 [container.requirements.general]/3 says elements "shall be -constructed using the allocator_traits<allocator_type>::construct -function and destroyed using the allocator_traits<allocator_type>::destroy function" and -23.2.1 [container.requirements.general]/13 defines CopyInsertable etc. in -terms of an allocator A which is identical to the container's allocator_type. -

-

-The intent of making construct() and destroy() function templates was -that containers would be permitted to use allocator_traits<A>::construct() instead of -allocator_traits<allocator_type>::construct(), where A is -allocator_traits<allocator_type>::rebind_alloc<U> for some other type -U. This allows node-based containers to store an allocator of the right type for -allocating nodes and to use the same object to construct elements in aligned storage within -those nodes, avoiding rebinding and copying the stored allocator every time an element needs -to be constructed. -

-It should be made clear that a possibly-rebound copy of the container's allocator is used for object -construction. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Jonathan: point 2 in the proposed resolution is definitely needed. -

- -

[2014-11-28, Jonathan improves wording]

- -

-In the first set of edits to paragraph 3 both pieces inserting "rebind_alloc<U>::" -should be replaced by "rebind_traits<U>::" -

-Otherwise it implies using the allocator's functions directly, but they might not exist and -it should be through the rebound traits type. -

- -

[2015-05, Lenexa]

- -

-STL: You want to permit but not require rebinding?
-Wakely: The current wording forces me to use the original allocator, not the rebound one.
-STL: Oh, I see. Yeah, we immediately rebind.
-Wakely: The edits clarify that we don't use some other allocator. The third diff is because the definitions of -EmplaceConstructible/etc. happen with the same types. The diff to the note is because it doesn't require the value -of the allocator was the one passed in.
-STL: After looking at this, I think I'm comfortable with the edits. The previous Standardese was nonsense so it's -pretty easy to improve upon.
-Marshall: Any other opinions?
-Marshall: Any objections to moving it to Ready? Review? Ready in Kona?
-Wakely: My preference would be Ready. We all know this is what we're doing anyways.
-Nevin: The intent won't change.
-STL: I think this is the right fix.
-Hwrd: I third Ready. Even if Jonathan retracts his.
-Marshall: Ready! -

- - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 23.2.1 [container.requirements.general] paragraph 3:

    -

    -For the components affected by this subclause that declare an allocator_type, objects stored in these -components shall be constructed using the allocator_traits<allocator_type>::rebind_traits<U>::construct -function and destroyed using the allocator_traits<allocator_type>::rebind_traits<U>::destroy -function (20.7.8.2 [allocator.traits.members]), where U is either allocator_type::value_type -or an internal type used by the container. These functions are called only for the container's element type, -not for internal types used by the container. [ Note: This means, for example, that a node-based container -might need to construct nodes containing aligned buffers and call construct to place the element into the buffer. -— end note ] -

    -
    2. - -

  2. Edit 23.2.1 [container.requirements.general] paragraph 7:

    -

    -[…] A copy of this allocator is used for any memory allocation and element construction performed, -by these constructors and by all member functions, during the lifetime of each container object or until the allocator -is replaced. […] -

    -
    3. - -

  3. Edit 23.2.1 [container.requirements.general] paragraph 13:

    -

    -[…] Given an allocator type A and given a container type X having an -allocator_type identical to A and a value_type identical to T -and an allocator_type identical to allocator_traits<A>::rebind_alloc<T> -and given an lvalue m of type A, a pointer p -of type T*, an expression v of type (possibly const) T, and an rvalue rv -of type T, the following terms are defined. -

    -[…] -

    -[ Note: A container calls allocator_traits<A>::construct(m, p, args) to construct an element -at p using args, with m == get_allocator(). The default construct in -std::allocator will call ::new((void*)p) T(args), but specialized allocators may choose a -different definition. — end note ] -

    -
    4. - -
- - - - - - -
-

2219. INVOKE-ing a pointer to member with a reference_wrapper as the object expression

-

Section: 20.9.2 [func.require] Status: Ready - Submitter: Jonathan Wakely Opened: 2012-11-28 Last modified: 2015-05-06

-

View other active issues in [func.require].

-

View all other issues in [func.require].

-

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-

Discussion:

- -

-The standard currently requires this to be invalid: -

-
-#include <functional>
-
-struct X { int i; } x;
-auto f = &X::i;
-auto t1 = std::ref(x);
-int i = std::mem_fn(f)(t1);
-
-

-The call expression on the last line is equivalent to INVOKE(f, std::ref(x)) -which according to 20.9.2 [func.require]p1 results in the invalid expression (*t1).*f -because reference_wrapper<X> is neither an object of type X nor a reference -to an object of type X nor a reference to an object of a type derived from X. -

-

-The same argument applies to pointers to member functions, and if they don't work with INVOKE -it becomes harder to do all sorts of things such as: -

-

-call_once(o, &std::thread::join, std::ref(thr)) -

-

-or -

-

-async(&std::list<int>::sort, std::ref(list)); -

-

-The definition of INVOKE should be extended to handle reference wrappers. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-The wording seems accurate, but verbose. If possible, we would like to define the kind of thing being -specified so carefully as one of a number of potential language constructs in a single place. It is -also possible that this clause is that single place. -

- -

[2013-04-18, Bristol]

- - -

Jonathan comments:

- -

In the proposed resolution in the first bullet (t1.*f) is not valid if t1 is a -reference_wrapper, so we probably need a separate bullet to handle the -reference_wrapper case.

- -

[2014-02-14, Issaquah, Mike Spertus supplies wording]

- - -

Previous resolution from Jonathan [SUPERSEDED]:

- -
- -

This wording is relative to N3485.

- -
    -

  1. Edit 20.9.2 [func.require]:

    -

    -Define INVOKE(f, t1, t2, ..., tN) as follows: -

    -
      -

    • -(t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is an object of type T or a reference to an object of type T or a reference -to an object of a type derived from T U or an object of type reference_wrapper<U> -or a reference to an object of type reference_wrapper<U> where U is either the type -T or a type derived from T; -

      -
      • - -

    • -((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is not one of the types described in the previous item; -

      • - -

    • -t1.*f when N == 1 and f is a pointer to member data of a class T and t1 -is an object of type T or a reference to an object of type T or a reference to an object of a -type derived from T U or an object of type reference_wrapper<U> -or a reference to an object of type reference_wrapper<U> where U is either the type -T or a type derived from T; -

      • - -

    • -(*t1).*f when N == 1 and f is a pointer to member data of a class T and t1 -is not one of the types described in the previous item; -

      • - -

    • -f(t1, t2, ..., tN) in all other cases. -

      • -
    - -
    - -
    2. -
- -
- -

[2014-10-01, STL adds discussion and provides an improved resolution]

- -

-Because neither t1.*f nor (*t1).*f will compile when t1 is reference_wrapper<U> -for any U, we don't need to inspect U carefully. We can bluntly detect all reference_wrappers -and use get() for them. -

-We would have to be more careful if we had to deal with pointers to members of reference_wrapper itself. -Fortunately, we don't. First, it doesn't have user-visible data members. Second, users technically can't take the -addresses of its member functions (this is a consequence of 17.6.5.5 [member.functions], the Implementer's Best Friend). -

-While we're in the neighborhood, I recommend simplifying and clarifying the wording used to detect base/derived objects. -

- -

Previous resolution from Mike Spertus [SUPERSEDED]:

- -
-

This wording is relative to N3936.

- -
    -

  1. Edit 20.9.2 [func.require]:

    -

    -Define INVOKE(f, t1, t2, ..., tN) as follows: -

    -
      -

    • -(t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is an object of type T or a reference to an object of type T or a reference -to an object of a type derived from T; -

      -
      • - -

    • - -(t1.get().*f)(t2, ..., tN) when f is a pointer to a member function -of class T -and t1 is an object of type reference_wrapper<U> where U -is either the type T or a type derived from T. - -

      -
      • - -

    • -((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is not one of the types described in the previous item; -

      • - - - -

    • -t1.*f when N == 1 and f is a pointer to member data of a class T and t1 -is an object of type T or a reference to an object of type T or a reference to an object of a -type derived from T; -

      • - -

    • - -t1.get().*f when N == 1 and f is a pointer to member data of a -class T and t1 is an object of type reference_wrapper<U> -where U is either the type T or a type derived from T. - -

      • - -

    • -(*t1).*f when N == 1 and f is a pointer to member data of a class T and t1 -is not one of the types described in the previous item; -

      • - -

    • -f(t1, t2, ..., tN) in all other cases. -

      • -
    - -
    - -
    2. -
-
- -

[2015-02, Cologne]

- -

-Waiting for implementation experience. -

- -

[2015-05, Lenexa]

- -

-STL: latest note from Cologne, waiting for implementation experience
-STL: don't think this is harder than anything else we do
-MC: it does involve mem_fn and invoke
-STL: my simplication was not to attempt fine-grained
-STL: can ignore pmf
-STL: can't invoke pmf to reference wrapper
-STL: wording dated back to TR1 when there was no decltype
-MC: should decay_t<decltype(t1)> be pulled out since it is in multiple places
-STL: it could be handled editorially
-STL: we fix function, bind, invoke
-STL: have not implemented this but believe it is fine
-MC: Eric F, you have worked in invoke
-EF: yes, looks ok
-MC: consensus move to ready -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.9.2 [func.require] p1 as depicted:

    -

    -Define INVOKE(f, t1, t2, ..., tN) as follows: -

    -
      -

    • -(t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is an object of type T or a reference to an object of type T or a reference -to an object of a type derived from Tis_base_of<T, decay_t<decltype(t1)>>::value -is true; -

      -
      • - -

    • -(t1.get().*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -decay_t<decltype(t1)> is a specialization of reference_wrapper; -

      • - -

    • -((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a class T and -t1 is not one of the types described in the previous itemdoes not satisfy the previous two -items; -

      • - -

    • -t1.*f when N == 1 and f is a pointer to member data of a class T and t1 -is an object of type T or a reference to an object of type T or a reference to an object of a -type derived from Tis_base_of<T, decay_t<decltype(t1)>>::value -is true; -

      • - -

    • -t1.get().*f when N == 1 and f is a pointer to member data of a class T and -decay_t<decltype(t1)> is a specialization of reference_wrapper; -

      • - -

    • -(*t1).*f when N == 1 and f is a pointer to member data of a class T and t1 -is not one of the types described in the previous itemdoes not satisfy the previous two items; -

      • - -

    • -f(t1, t2, ..., tN) in all other cases. -

      • -
    - -
    - -
    2. -
- - - - - - -
-

2220. Under-specification of operator== for regex_token_iterator

-

Section: 28.12.2.2 [re.tokiter.comp] Status: New - Submitter: Pete Becker Opened: 2012-11-21 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

- -

-Consider the following example: -

-
-std::string str0("x");
-std::regex rg0("a");
-std::regex_token_iterator it0(str0.begin(), str0.end(), rg0, -1); // points at "x" in str0
-std::string str1("x");
-std::regex rg1("b");
-std::regex_token_iterator it1(str1.begin(), str1.end(), rg1, -1); // points at "x" in str1
-
-

-28.12.2.2 [re.tokiter.comp] p1 says that it0.operator==(it1) returns true "if -*this and right are both suffix iterators and suffix == right.suffix"; both -conditions are satisfied in this example. It does not say that they must both be iterators -into the same sequence, nor does it say (as general iterator requirements do) that they must -both be in the domain of == in order for the comparison to be meaningful. It's a -simple statement: they're equal if the strings they point at compare equal. Given this being -a valid comparison, the obtained result of "true" looks odd. -

-The problem is that for iterator values prior to the suffix iterator, equality means the same -regular expression and the same matched sequence (both uses of "same" refer to identity, not equality); -for the suffix iterator, equality means that the matched sequences compare equal. -

- - - -

Proposed resolution:

- - - - - -
-

2221. No formatted output operator for nullptr

-

Section: 27.7.3 [output.streams] Status: New - Submitter: Matt Austern Opened: 2012-12-07 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

- -

-When I write -

-
-std::cout << nullptr << std::endl;
-
-

-I get a compilation error, "ambiguous overload for 'operator<<' in 'std::cout << nullptr'". -As far as I can tell, the compiler is right to issue that error. There are inserters for const void*, -const char*, const signed char*, and const unsigned char*, and none for -nullptr_t, so the expression really is ambiguous. -

-Proposed wording: -

-The obvious library solution is to add a nullptr_t overload, which would be defined something like -

-
-template<class C, class T>
-basic_ostream<C, T>& operator<<(basic_ostream<C, T>& os, nullptr_t) 
-{ 
-  return os << (void*) nullptr; 
-}
-
-

-We might also consider addressing this at a core level: add a special-case language rule that addresses all -cases where you write f(nullptr) and f is overloaded on multiple pointer types. (Perhaps -a tiebreaker saying that void* is preferred in such cases.) -

- - - -

Proposed resolution:

- - - - - -
-

2223. shrink_to_fit effect on iterator validity

-

Section: 23.3.6.3 [vector.capacity] Status: Open - Submitter: Juan Soulie Opened: 2012-12-17 Last modified: 2015-04-08

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

View all issues with Open status.

-

Discussion:

- -

-After the additions by 2033, it appears clear that the intended effect includes a reallocation and -thus the potential effect on iterators should be explicitly added to the text in order to not contradict -23.2.1 [container.requirements.general]/11, or at the very least, explicitly state that a reallocation may -happen. -

-Taking consistency with "reserve" into consideration, I propose: -

-
    -

  • -that the current "Remarks" are made its "Effect" instead, inserting "Reallocation happens at this point if and only -if the function effectively reduces the capacity." after the note on non-bindingness. -

    -
    • -

  • -adding a "Remarks" paragraph, similar to that of reserve: "Reallocation invalidates all the references, pointers, -and iterators referring to the elements in the sequence." -

    • -
-

-BTW, while we are at it, I believe the effect on iterators should also be explicitly stated in the other instance -a reallocation may happen: 23.3.6.5 [vector.modifiers]/1 — even if obvious, it only contradicts -23.2.1 [container.requirements.general]/11 implicitly. -

-I propose to also insert "Reallocation invalidates all the references, pointers, and iterators referring to the -elements in the sequence." at the appropriate location in its "Remarks". -

- -

[2012-12-19: Jonathan Wakely comments]

- - -

-The described problem also affects std::basic_string and std::deque. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

- -

[2013-04-18, Bristol]

- - -

Daniel extends the P/R.

- -

Rationale:

- -

The wording in 21.4.4 [string.capacity] combined with 21.4.1 [string.require] -seems to say the necessary things. We cannot impose all requirements as we do for vector, because -we want to allow the short-string-optimization.

- - -

[2014-02-15 post-Issaquah session]

- -

-STL: I think that shrink_to_fit should be a no-op when called twice. -

-

-STL: Do we ever define reallocation for deque? Nope, all mentions of "reallocation" are in vector. - We define what it means in vector::reserve(), but not for deque. -

-

-STL: Oh duh, they define reallocate in the PR. But I think we can do better here. -

-

-STL: Optimally, deque shrinking just allocates a new map of pointers, and drops empty blocks, but preserves pointers/references to elements. -

-

-Alisdair: That's like unordered containers, invalidating only iterators. -

-

-Pablo: It doesn't make sense to reduce capacity() to size(), because deque doesn't have capacity! -

-

-STL: For vector, "effectively reduces the capacity" is unnecessary, the capacity there is observable. -

-

-STL: There is a strong reason to provide an optimal shrink to fit for deque, since only the library implementer can do this. -

-

-STL: The other thing I don't like the repeated definition of reallocation for vector, we define it once and use it in a bunch of places. - At most we can lift it up to the vector synopsis. -

-

-STL: I'll write new wording. -

- -

[2014-10-01, STL adds discussion and provides new wording]

- -

-Compared to the previous proposed resolution: -

-
    -

  • -I'm changing basic_string's wording because (1) we should guarantee that capacity won't increase, (2) we should mention -that it's linear complexity, and (3) we can provide a better invalidation guarantee than 21.4.1 [string.require]/5. -(As previously noted, we already have the strong exception guarantee.) This introduces the term "reallocation" into -basic_string, but immediately explains what it means for iterator validity. As far as I can tell, the Small String -Optimization doesn't complicate the wording here; it's a reason why an implementation might not honor the request, but if -the capacity is reduced, we are definitely reallocating buffers and will invalidate everything (including when the destination -is the small buffer). -

    • -

  • -Between N3485 and N3936, deque's wording was updated to avoid talking about capacity() which it doesn't have. -Since the container's capacity is unobservable, I'm saying that invalidation is unconditional. -

    • -

  • -In vector's wording, I'm also guaranteeing that capacity won't increase, and that iterators/etc. remain valid if the -capacity is unchanged. -

    • -
-

-My wording doesn't directly say that shrink_to_fit() should be a no-op when called twice in a row. (Indirectly, -if the first call reduces capacity() to size(), the second call must preserve iterators/etc.) I considered -rewording the complexity to say "linear if reallocation happens", but that's potentially problematic (what if we copy almost -all N elements, then one throws and we have to unwind? There are no effects, so reallocation didn't happen, yet we -took longer than constant time). Implementers can always do better than the stated complexity bounds. -

-I chose not to modify deque's requirements, so implementations remain free to reallocate the elements themselves. -

-I didn't attempt to centralize vector's reallocation wording. That can be done editorially, if someone is sufficiently motivated. -

- -

Previous resolution from Juan Soulie/Daniel [SUPERSEDED]:

- -
-

This wording is relative to N3485.

- -
    -

  1. Keep 21.4.4 [string.capacity] around p14 unchanged, because we don't speak about -reallocations and we give the strong exception guarantee in 21.4.1 [string.require] (Invalidation -specification also at that place):

    -
    -void shrink_to_fit();
-
    -

    --14- Remarks: shrink_to_fit is a non-binding request to reduce capacity() to -size(). [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note ]. -

    -
    -
    2. - -

  2. Edit 23.3.3.3 [deque.capacity] around p7 as indicated:

    -
    -void shrink_to_fit();
-
    -

    --5- Requires: T shall be MoveInsertable into *this. -

    --?- Effects: shrink_to_fit is a non-binding request to reduce capacity() to -size(). [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note ] Reallocation happens at this point if and only -if the function effectively reduces the capacity. If an exception is thrown other than by the move constructor -of a non-CopyInsertable T there are no effects. -

    --6- Complexity: Linear in the size of the sequence. -

    --7- Remarks: shrink_to_fit is a non-binding request to reduce capacity() to -size(). [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note ] If an exception is thrown other than by the move constructor -of a non-CopyInsertable T there are no effects.Reallocation invalidates all -the references, pointers, and iterators referring to the elements in the sequence. -

    -
    -
    3. - -

  3. Edit 23.3.6.3 [vector.capacity] around p7 as indicated:

    -
    -void shrink_to_fit();
-
    -

    --7- Requires: T shall be MoveInsertable into *this. -

    --?- Effects: shrink_to_fit is a non-binding request to reduce capacity() to -size(). [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note ] Reallocation happens at this point if and only -if the function effectively reduces the capacity. If an exception is thrown other than by the move constructor -of a non-CopyInsertable T there are no effects. -

    --8- Complexity: Linear in the size of the sequence. -

    --9- Remarks: shrink_to_fit is a non-binding request to reduce capacity() to -size(). [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note ] If an exception is thrown other than by the move constructor -of a non-CopyInsertable T there are no effects.Reallocation invalidates all -the references, pointers, and iterators referring to the elements in the sequence. -

    -
    -
    4. - -

  4. Edit 23.3.6.5 [vector.modifiers] p1 as indicated:

    -
    -iterator insert(const_iterator position, const T& x);
-iterator insert(const_iterator position, T&& x);
-iterator insert(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-iterator insert(const_iterator position, InputIterator first, InputIterator last);
-iterator insert(const_iterator position, initializer_list<T>);
-template <class... Args> void emplace_back(Args&&... args);
-template <class... Args> iterator emplace(const_iterator position, Args&&... args);
-void push_back(const T& x);
-void push_back(T&& x);
-
    -

    --1- Remarks: Causes reallocation if the new size is greater than the old capacity. Reallocation -invalidates all the references, pointers, and iterators referring to the elements in the sequence. If -no reallocation happens, all the iterators and references before the insertion point remain valid. If an -exception is thrown other than by the copy constructor, move constructor, assignment operator, or move -assignment operator of T or by any InputIterator operation there are no effects. If an -exception is thrown by the move constructor of a non-CopyInsertable T, the effects are unspecified. -

    -
    -
    5. -
- -
- -

[2015-02, Cologne]

- -

-GR: I'm concerned that shrink_to_fit may cause reallocation without changing the capacity. […] -It's about correctness. The statement about invalidation is useless if I cannot detect whether reallocation has happened? -

-AM: It seems like the logic goes the other way round: It's the capacity change that causes reallocation, so if -there's no capacity change, there's no reallocation. But that's not quite how I'd like to say it... maybe this, : -"If capacity does not change, no reallocation occurs." -

-GR: Where does it actually say that reserve() invalidates? AM: It should say that in the container requirements. -VV: vector specifies in reserve that there's reallocation if and only if the capacity changes. GR: I can't find -anything in the container requirements about reserve. DK: No, it's specified for every container separately. -GR: It isn't specified for string. -

-GR: I'm noticing that the issue touches on shrink_to_fit for a bunch of containers. Anyway, I think the -reserve issue [re string] is in scope for this issue. This change is touching on a lot of members. -

-AM: Landing this change will provide clarity for what we should do with basic_string. GR: We're already asking -for changes; we should fix string as well. AM: If one of the changes is ready before the other, I'd like to land the -finished part first, but if both are ready for Lenexa, I'm equally happy to fix them in one go. -

-DK will reword this. -

-Conclusion: Update wording, revisit in Lenexa. -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 21.4.4 [string.capacity] p14 as depicted:

    - -
    -
    -void shrink_to_fit();
-
    -
    -

    --14- RemarksEffects: shrink_to_fit is a non-binding request to reduce -capacity() to size(). [Note: The request is non-binding to allow latitude for -implementation-specific optimizations. — end note] It does not increase capacity(), -but may reduce capacity() by causing reallocation. -

    --?- Complexity: Linear in the size of the sequence. -

    --?- Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the -elements in the sequence. If no reallocation happens, they remain valid. -

    -
    -
    -
    2. - -

  2. Change 23.3.3.3 [deque.capacity] p5-p7 as depicted:

    -
    -
    -void shrink_to_fit();
-
    -
    -

    --5- Requires: T shall be MoveInsertable into *this. -

    --?- Effects: shrink_to_fit is a non-binding request to reduce memory use but does not change -the size of the sequence. [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note] If an exception is thrown other than by the move constructor of a -non-CopyInsertable T there are no effects. -

    --6- Complexity: Linear in the size of the sequence. -

    --7- Remarks: shrink_to_fit is a non-binding request to reduce memory use but does not change the -size of the sequence. [Note: The request is non-binding to allow latitude for implementation-specific -optimizations. — end note]shrink_to_fit invalidates all the references, pointers, -and iterators referring to the elements in the sequence. -

    -
    -
    -
    3. - -

  3. Change 23.3.6.3 [vector.capacity] p7-p9 as depicted:

    -
    -
    -void shrink_to_fit();
-
    -
    -

    --7- Requires: T shall be MoveInsertable into *this. -

    --?- Effects: shrink_to_fit is a non-binding request to reduce capacity() to size(). -[Note: The request is non-binding to allow latitude for implementation-specific optimizations. — end note] -It does not increase capacity(), but may reduce capacity() by causing reallocation. If an exception is -thrown other than by the move constructor of a non-CopyInsertable T there are no effects. -

    --8- Complexity: Linear in the size of the sequence. -

    --9- Remarks: shrink_to_fit is a non-binding request to reduce capacity() to size(). -[Note: The request is non-binding to allow latitude for implementation-specific optimizations. — end -note] If an exception is thrown other than by the move constructor of a non-CopyInsertable T there -are no effects.Reallocation invalidates all the references, pointers, and iterators referring to the elements -in the sequence. If no reallocation happens, they remain valid. -

    -
    -
    -
    4. - -

  4. Change 23.3.6.5 [vector.modifiers] p1 as depicted:

    - -
    -

    --1- Remarks: Causes reallocation if the new size is greater than the old capacity. Reallocation invalidates all -the references, pointers, and iterators referring to the elements in the sequence. If no reallocation happens, -all the iterators and references before the insertion point remain valid. […] -

    -
    -
    5. -
- - - - - -
-

2224. Ambiguous status of access to non-live objects

-

Section: 17.6.4.10 [res.on.objects] Status: Tentatively Ready - Submitter: Geoffrey Romer Opened: 2012-12-17 Last modified: 2015-05-05

-

View all other issues in [res.on.objects].

-

Discussion:

- -

-The standard currently does not discuss when library objects may be accessed, except in a non-normative -note pertaining to synchronization in [res.on.objects], leaving it ambiguous whether single-threaded -code can access a library object during its construction or destruction. For example, there is a -reasonable question as to what happens if the deleter supplied to a unique_ptr transitively -accesses the unique_ptr itself during unique_ptr's destruction; a straightforward -reading suggests that this is permitted, and that the deleter will see the unique_ptr still -holding the originally stored pointer, but consensus on the LWG reflector indicates this was not the -intent (see discussion beginning with -c++std-lib-33362). -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Geoffrey will provide an example that clearly highlights the issue. -

- -

[2013-03-19 Geoffrey provides revised resolution and an example]

- - -

-I contend that the most straightforward reading of the current standard requires the following example code to print -"good" (because ~unique_ptr is not specified to modify the state of the internal pointer), but the consensus -on the reflector was that its behavior should be undefined. -

-This example also shows that, contrary to a comment in the telecon, the PR is not tautological. 12.7 [class.cdtor]/p4 -explicitly permits member function calls during destruction, so the behavior of this code is well-defined as far as -the core language is concerned, despite the fact that it accesses a library object after the end of the object's -lifetime. If we want this code to have undefined behavior, we need to specify that at the library level. -

- -
-#include <memory>
-#include <iostream>
-
-class A;
-
-struct B {
- std::unique_ptr<A> a;
-};
-
-struct A {
- B* b;
- ~A() {
-   if (b->a.get() == this) {
-     std::cout << "good" << std::endl;
-   }
- }
-};
-
-int main() {
- B b;
- b.a.reset(new A);
- b.a->b = &b;
-}
-
- -

-Previous resolution: -

-
-
    -

  1. Change the title of sub-clause 17.6.4.10 [res.on.objects] as indicated:

    -

    Shared objects and the libraryLibrary object access [res.on.objects]

    -
    2. - -

  2. Edit 17.6.4.10 [res.on.objects] p2 as indicated:

    -

    -2- [Note: In particular, the program is required to ensure that completion of the constructor -of any object of a class type defined in the standard library happens before any other member function -invocation on that object and, unless otherwise specified, to ensure that completion of any member function -invocation other than destruction on such an object happens before destruction of that object. This applies -even to objects such as mutexes intended for thread synchronization. — end note] -If an object of a standard library type is accessed outside of the object's lifetime (3.8 [basic.life]), -the behavior is undefined unless otherwise specified.

    -
    3. -
-
- -

[2014 Urbana]

- -

-STL: is this resolved by our change to the reeentrancy rules? [LWG 2414]
-GR: don't think that solves the multi-threaded case
-MC: I like changing the note to normative text
-GR: uses the magic "happens before" words, and "access" is magic too
-JW: I like this. strict improvement, uses the right wording we have to say this properly
-STL: I like the last sentence of the note, could we add that as a new note at the end?
-So add "[Note: This applies even to objects such as mutexes intended for thread synchronization.]" to the end and move to Ready -

- - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Change the title of sub-clause 17.6.4.10 [res.on.objects] as indicated:

    -

    Shared objects and the libraryLibrary object access [res.on.objects]

    -
    2. - -

  2. Edit 17.6.4.10 [res.on.objects] p2 as indicated: [Editorial remark: The motivation, is to -be more precise about the meaning of "outside the object's lifetime" in the presence of threads — end editorial -remark]

    -

    -2- [Note: In particular, the program is required to ensure that completion of the constructor -of any object of a class type defined in the standard library happens before any other member function -invocation on that object and, unless otherwise specified, to ensure that completion of any member function -invocation other than destruction on such an object happens before destruction of that object. This applies -even to objects such as mutexes intended for thread synchronization. — end note] -If an object of a standard library type is accessed, and the beginning of the object's lifetime -(3.8 [basic.life]) does not happen before the access, or the access does not happen before the end -of the object's lifetime, the behavior is undefined unless otherwise specified. [Note: This applies even to -objects such as mutexes intended for thread synchronization. — end note]

    -
    3. -
- - - - - - -
-

2226. wstring_convert methods do not take allocator instance

-

Section: 22.3.3.2.2 [conversions.string] Status: LEWG - Submitter: Glen Fernandes Opened: 2012-12-14 Last modified: 2015-04-08

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with LEWG status.

-

Discussion:

- -

-The wstring_convert class template, described in 22.3.3.2.2 [conversions.string], does not -support custom stateful allocators. It only supports custom stateless allocators. -

-The to_bytes member function returns basic_string<char, char_traits<char>, Byte_alloc> -but it does not take an instance of Byte_alloc to pass to the constructor of the basic_string. -

-Similarly the from_bytes member function returns basic_string<Elem, char_traits<Elem>, Wide_alloc> -but it does not take an instance of Wide_alloc to pass to the constructor of the basic_string. -

-This makes these two member functions and the wstring_convert class template not usable when Wide_alloc -or Byte_alloc are stateful allocators. -

- -

[2013-01-22, Glen provides wording]

- - -

[2013-03-15 Issues Teleconference]

- -

-Moved to NAD Future. -

-

-This is clearly an extension that the LEWG may want to take a look at, once we have more experience -with appropriate use of allocators with the C++11 model. -

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. In 22.3.3.2.2 [conversions.string]/2 and /6 "Class template wstring_convert synopsis" change the overloads -of the member function from_bytes() so that all four overloads take an additional parameter -which is an instance of Wide_alloc:

    - -
    -wide_string from_bytes(char byte, const Wide_alloc& alloc = Wide_alloc());
-wide_string from_bytes(const char *ptr, const Wide_alloc& alloc = Wide_alloc());
-wide_string from_bytes(const byte_string& str, const Wide_alloc& alloc = Wide_alloc());
-wide_string from_bytes(const char *first, const char *last, const Wide_alloc& alloc = Wide_alloc());
-
    -
    2. - -

  2. In 22.3.3.2.2 [conversions.string] /8 specify that this Wide_alloc allocator parameter is used to -construct the wide_string object returned from the function:

    - -

    --7- Effects: The first member function shall convert the single-element sequence byte to a wide string. -The second member function shall convert the null-terminated sequence beginning at ptr to a wide -string. The third member function shall convert the sequence stored in str to a wide string. The fourth -member function shall convert the sequence defined by the range [first, last) to a wide string. -

    --8- In all cases: -

    -
      -

    • If the cvtstate object was not constructed with an explicit value, it shall be set to its default value -(the initial conversion state) before the conversion begins. Otherwise it shall be left unchanged.

      • - -

    • The number of input elements successfully converted shall be stored in cvtcount.

      • - -

    • The Wide_alloc allocator parameter is used to construct the wide_string object returned -from the function.

      • -
    -
    3. - -

  3. In 22.3.3.2.2 [conversions.string]/2 and /12 "Class template wstring_convert synopsis" change the overloads -of the member function to_bytes() so that all four overloads take an additional parameter -which is an instance of Byte_alloc:

    - -
    -byte_string to_bytes(Elem wchar, const Byte_alloc& alloc = Byte_alloc());
-byte_string to_bytes(const Elem *wptr, const Byte_alloc& alloc = Byte_alloc());
-byte_string to_bytes(const wide_string& wstr, const Byte_alloc& alloc = Byte_alloc());
-byte_string to_bytes(const Elem *first, const Elem *last, const Byte_alloc& alloc = Byte_alloc());
-
    -
    4. - -

  4. In 22.3.3.2.2 [conversions.string] /13 specify that this Byte_alloc allocator parameter is used to -construct the byte_string object returned from the function:

    - -

    --12- Effects: The first member function shall convert the single-element sequence wchar to a byte string. -The second member function shall convert the null-terminated sequence beginning at wptr to a byte -string. The third member function shall convert the sequence stored in wstr to a byte string. The -fourth member function shall convert the sequence defined by the range [first, last) to a byte string. -

    --13- In all cases: -

    -
      -

    • If the cvtstate object was not constructed with an explicit value, it shall be set to its default value -(the initial conversion state) before the conversion begins. Otherwise it shall be left unchanged.

      • - -

    • The number of input elements successfully converted shall be stored in cvtcount.

      • - -

    • The Byte_alloc allocator parameter is used to construct the byte_string object returned -from the function.

      • -
    -
    5. - -
- - - - - -
-

2227. Stateful comparison objects in associative containers

-

Section: 23.2.4 [associative.reqmts] Status: Open - Submitter: Juan Soulie Opened: 2012-12-19 Last modified: 2015-05-22

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with Open status.

-

Discussion:

- -

-Table 102 in 23.2.4 [associative.reqmts]/8 states on expression a.key_comp() that it -"returns the comparison object out of which a was constructed". At the same time, -23.2.1 [container.requirements.general]/8 states (starting in the third line) that -"...Any Compare, Pred, or Hash objects belonging to a and b -shall be swappable and shall be exchanged by unqualified calls to non-member swap...". This is -problematic for any compliant implementation, since once swapped the container cannot return the comparison -object out of which it was constructed unless incurring in storing an otherwise needless object. -

-The simple solution is to correct that statement in Table 102, but I believe this is part of a larger problem -of underspecified behavior: The new standard has made an effort in regards to allocators and now fully -specifies what happens to stateful allocator objects. It has even specified what happens to stateful hasher -and key_equal members of unordered containers (they propagate), but it says nothing about stateful -comparison objects of (ordered) associative containers, except for the statement in -23.2.1 [container.requirements.general]/8 referred above and only related to swap. -

-For example, it is unclear to me what is specified to happen on an assignment: should the comparison object -be copied/moved along with the elements, or should the left-hand side object keep its own? -Maybe this has been intentionally left unspecified with the purpose of compatibility with C++98, which I -understand it specified that comparison objects were kept for the entire life of the container (like allocators) -— an unfortunate choice. But anyway, the segment of 23.2.1 [container.requirements.general] quoted -above seems to break any possible backwards compatibility with C++98 in this regard. -

-Therefore, taking into consideration consistency with how this is dealed with for unordered associative -containers, I propose that Table 102 is modified as follows: -

-
    -
  • -

    -The row for expression a.key_comp() is changed so that its "assertion/note pre-/post-condition" reads -"Returns a's comparison object." -

    -
    • - -
  • -

    -A new row is added at the appropriate location (which I believe would be after "X(il)" row), with: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -X(b)
    -X a(b)     -    		 -X - -Copy constructor. In addition to
    -the requirements of Table 96, copies
    -the comparison object. -    		 -Linear in b.size() -
    -a = b - -X& - -Copy assignment operator. In addition to
    -the requirements of Table 96, copies the
    -comparison object. -    		 -Linear in a.size() and b.size() -
    -
    - -
    • -
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

- -

[2013-04-18, Bristol]

- -

-STL: can't believe we don't specify this already. this is totally necessary -

-Alisdair: how does it do this? copy construction? assignment? -

-Also need it for move. -

-STL: we already specify this for constructing from a comparator, not during copy construction though. -

-Jonathan: don't like wording, should say "key_compare is CopyConstructible. Uses b.key_comp() -as a comparison object." -

-STL: we get it right for unordered! -

-Jonathan: can't wordsmith this now, but I think implementations do the right thing. -

-Alisdair: not sure what right thing is for moves. Also we say nothing about propagating allocators to functors. -

-

-Moved to Open. -

- -

[2015-02 Cologne]

- -

-TK: There's no need for fine-grained propagate/not-propagate control. If you don't want to propagate the predicate, you can -simply construct or insert from an iterator range. -

-VV: libstdc++ already implements the resolution of this issue. -

-GR: There are a couple of other problems. We don't specify move constructor and move assignment for maps. Those are just general. -

-TK: General container requirements already describe the semantics for {copy,move}-{construction,assignment}, so it doesn't -seem that there's room for choice in std::map assignments. unordered_map is different, though. -

-[Note: Check what general container requirements say about container equality.] -

-DK will draft wording. The decision is to unambiguously make all {copy,move}-{construction,assignment} operations endow the -LHS with the exact state of the RHS, including all predicates and hash function states. -

-Conclusion: Update wording, revisit later. -

- -

[2015-05-06 Lenexa: Waiting for updated wording]

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Change Table 102 as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -X(il) - - - -Same as X(il.begin(), il.end()). - -same as X(il.begin(), il.end()). -
    -X(b)
    -X a(b)     -    		 - - -Copy constructor. In addition to
    -the requirements of Table 96, copies
    -the comparison object.     -    		 -Linear in b.size() -
    -a = b - -X& - -Copy assignment operator. In addition to
    -the requirements of Table 96, copies the
    -comparison object.     -    		 -Linear in a.size() and b.size() -
    -… -
    -a.key_comp() - -X::key_compare - -rReturns thea's comparison object
    -out of which a was constructed. -    		 -constant -
    -
    - -
    2. - -
- - - - - - -
-

2232. [CD] The char_traits specializations should declare their length(), compare(), and -find() members constexpr

-

Section: 21.2.3 [char.traits.specializations] Status: LEWG - Submitter: Jeffrey Yasskin Opened: 2012-12-24 Last modified: 2015-04-08

-

View all other issues in [char.traits.specializations].

-

View all issues with LEWG status.

-

Discussion:

- -

Addresses ES 14, US 19

- -

-These functions have easy recursive constexpr implementations that, unfortunately, aren't efficient at runtime. -EWG is still figuring out how to solve this problem in general (e.g., -N3444 isn't sufficient to avoid -stack overflows in debug builds or to get the optimal assembly-based implementations at runtime), so users can't -portably solve this problem for themselves, but implementations can use compiler-specific techniques to choose -the right implementation inside their standard libraries. -

- -

-The LWG is still undecided about whether individual implementations can add constexpr to these functions, so we -need to add constexpr to the standard here for implementations to be able to improve this. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-There are a number of people who have a strong interest in this issue not available for the telecon. -

-

-It also plays at the heart of a discussion about library freedoms for constexpr and specifying -a library that may depend on unspecified compiler intrinsics to be implementable. -

- -

[2013-09 Chicago]

- -

-Moved to NAD Future. -

-

-While it is clear that this feature can be implemented using only C++14 constexpr features, -there is real concern that we cannot call the efficient, highly optimized, C implementations of these -functions under a C++14 constexpr implementation, nor implement similar ourselves as this -typically involves use of inline asm instructions. -

-

-Clang and libc++ have some experience of using intrinsics to try to address the performance issue, but -the current intrinsics are not general enough to support char_traits. The intrinsics support -only operations on character string literals, and the string literal is no longer visible as a -literal after passing as a const char * to the char_traits functions. -

-

-Additional concern was raised that these operations are unlikely to be useful anyway, as the only client -is basic_string which relies on dynamic memory allocation, and so cannot effectively be made a -literal type. Jeffrey then pointed out the pending string_view library that will also use -char_traits and would most certainly benefit from being a literal type. -

- -

-Given the choice of giving up performance on a critical library component, or requiring a compiler -intrinsic with only unsuccessful implementation experience, the consensus is to not reject this, unless -compelling implementation experience is demonstrated. NAD Future seems the appropriate resolution. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. In 21.2.3.1 [char.traits.specializations.char], 21.2.3.2 [char.traits.specializations.char16_t], -21.2.3.3 [char.traits.specializations.char32_t], and 21.2.3.4 [char.traits.specializations.wchar.t]:

    -
    -static constexpr int compare(const char_type* s1, const char_type* s2, size_t n);
-static constexpr size_t length(const char_type* s);
-static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a);
-
    -
    2. -
- - - - - - -
-

2234. assert() should allow usage in constant expressions

-

Section: 19.3 [assertions] Status: Open - Submitter: Daniel Krügler Opened: 2013-01-12 Last modified: 2015-05-22

-

View other active issues in [assertions].

-

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-

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-

Discussion:

-

-It is unclear from the current specification whether assert() expressions can be used in -(potential) constant expressions. As an example consider the implementation of a constexpr -function: -

- -
-#include <cassert>
-
-template<class T, unsigned N>
-struct array {
-  T data[N];
-  constexpr const T& operator[](unsigned i) const {
-    return assert(i < N), data[i];
-  }
-};
-
-int main() {
-  constexpr array<int, 3> ai = {1, 2, 3};
-  constexpr int i = ai[0];
-  int j = ai[0];
-  // constexpr int k = ai[5];
-}
-
- -

-The first question is whether this program is guaranteed well-formed? A second question is whether is would guaranteed to be -ill-formed, if we uncomment the last code line in main()? -

- -

-The wording in 19.3 [assertions] doesn't add anything significant to the C99 wording. From the C99 specification -(7.2 p1 and 7.2.1.1 p2) we get already some valuable guarantees: -

- -
    -

  • -The expression assert(e) is a void expression for all expressions e independent of -the definition of NDEBUG. -

    • -

  • -If NDEBUG is defined, assert(e) is equivalent to the expression void() -(or anything that cannot be distinguished from that). -

    • -
- -

-The current wording does not yet guarantee that assert expressions can be used in constant expressions, -but all tested implementations (gcc, MSVC) would already support this use-case. It seems to me that this should be possible -without giving assert a special meaning for the core language. -

-As a related comment it should be added, that there is a core language -proposal -that intents to relax some current constraints for constexpr functions and literal types. The most -interesting one (making void a literal types and allowing for expression-statements) would simplify the motivating -example implementation of operator[] to: -

-
-constexpr const T& operator[](unsigned i) const {
-  assert(i < N);
-  return data[i];
-};
-
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-We are still gaining experience with constexpr as a language feature, and there may -be work in Evolution that would help address some of these concerns. Defer discussion until -we have a group familiar with any evolutionary direction. -

- -

[2014-06-08, Daniel comments and suggests wording]

- -

-After approval of N3652, -void is now a literal type and constexpr functions can contain multiple statements, so -this makes the guarantee that assert expressions are per-se constexpr-friendly even more -relevant. A possible wording form could be along the lines of: -

-
-

-For every core constant expression e of scalar type that evaluates to true after being contextually -converted to bool, the expression assert(e) shall be a prvalue core constant expression of type -void. -

-
-

-Richard Smith pointed out some weaknesses of this wording form, for example it would not guarantee to require -the following example to work: -

-
-constexpr void check(bool b) { assert(b); }
-
-

-because b is not a core constant expression in this context. -

-He suggested improvements that lead to the wording form presented below (any defects mine). -

- -

[Lenexa 2015-05-05]

- -

MC : ran into this

-

Z : Is it guaranteed to be an expression?

-

MC : clarifies that assert runs at runtime, not sure what it does at compile time

-

STL : c standard guarantees its an expression and not a whole statement, so comma chaining it is ok

-

HH : Some implementations work as author wants it to

-

STL : also doing this as constexpr

-

DK/STL : discussing how this can actually work

-

HH : GCC 5 also implements it. We have implementor convergence

-

MC : Wants to do this without giving assert a special meaning

-

STL : NDEBUG being defined where assert appears is not how assert works. This is bug in wording. Should be "when assert is defined" or something like that. ... is a constant subexpression if NDEBUG is defined at the point where assert is last defined or redefined."

-

Would like to strike the "either" because ok if both debug or assertion is true. We want inclusive-or here

-

MC : is redefined needed?

-

STL : my mental model is its defined once and then redefined

-

HH : wants to up to P2

-

Z/STL : discussing how wording takes care of how/when assert is defined/redefefined

-

STL/WB : discussing whether to move to ready or review. -> Want to move it to ready.

-

ask for updated wording

-

p3 -> p2

-

plan to go to ready after checking wording

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Introduce the following new definition to the existing list in 17.3 [definitions]: [Drafting note: -If LWG 2296 is accepted before this issue, the accepted wording for the new definition should be used instead -— end drafting note]

    - -
    -

    -constant subexpression [defns.const.subexpr] -

    -an expression whose evaluation as subexpression of a conditional-expression CE (5.16 [expr.cond]) -would not prevent CE from being a core constant expression (5.20 [expr.const]). -

    -
    -
    2. - -

  2. Insert a new paragraph following 19.3 [assertions] p1 as indicated:

    - -
    -

    --?- An expression assert(E) is a constant subexpression ( [defns.const.subexpr]), if either -

    -
      -

    • NDEBUG is defined at the point where assert(E) appears, or

      • -

    • E contextually converted to bool (4 [conv]), is a constant subexpression -that evaluates to the value true.

      • -
    -
    -
    3. - -
- - - - - - -
-

2236. kill_dependency unconditionally noexcept

-

Section: 29.2 [atomics.syn], 29.3 [atomics.order] Status: SG1 - Submitter: Daniel Krügler Opened: 2013-01-19 Last modified: 2015-04-08

-

View all other issues in [atomics.syn].

-

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-

Discussion:

-

-The "magic" kill_dependency function is a function without any constraints on the template parameter T -and is specified as -

- -
-template <class T>
-T kill_dependency(T y) noexcept;
-
-

--14- Effects: The argument does not carry a dependency to the return value (1.10). -

--15- Returns: y. -

-
- -

-I wonder whether the unconditional noexcept is really intended here: -Assume we have some type U that has a potentially throwing move -constructor (or it has a potentially throwing copy constructor and no -move constructor), for any "normal" function template with the same -signature and the same effects (modulo the dependency magic) this -would mean that it cannot safely be declared noexcept because of the -return statement being part of the complete function call affected by -noexcept (The by-value function argument is irrelevant in this -context). In other words it seems that a function call such as -

- -
-struct S {
-  ...
-  S(const S& r) { if(some condition) throw Something(); }
-  ...
-};
-
-int main() {
-  S s1 = ...;
-  S s2 = std::kill_dependency(s1);
-}
-
- -

-would be required to call std::terminate if the copy constructor of S throws during the return -of std::kill_dependency. -

-To require copy elision for this already magic function would look like a low-hanging fruit to solve this problem, -but this case is not covered by current copy elision rules see 12.8 p31 b1: -

-"— in a return statement in a function with a class return type, when the expression is the name of a non-volatile -automatic object (other than a function or catch-clause parameter) with the same cv-unqualified type as the -function return type, the copy/move operation can be omitted by constructing the automatic object directly into the -function's return value". -

-Some options come into my mind: -

-
    -

  1. -Make the exception-specification a constrained one in regard via std::is_nothrow_move_constructible: -

    - -
    -template <class T>
-T kill_dependency(T y) noexcept(see below);
-
    - -

    -This is similar to the approach taken for function templates such as std::swap. -

    -
    2. - -

  2. -Use perfect forwarding (This needs further wording to correct the effects): -

    - -
    -template <class T>
-T&& kill_dependency(T&& y) noexcept;
-
    -
    3. - -

  3. -Impose constraints on the template arguments in regard to throwing exceptions while copying/moving. -

    4. - -

  4. -Keep the state as it is but possibly add a note about a call of std::terminate in above scenario. -

    5. -
- -

-A second problem is that the current wording is not clear whether it is well-defined to call the function with -types that are reference types, such as in the following example: -

- -
-#include <atomic>
-
-int main()
-{
-  int a = 12;
-  int& b = std::kill_dependency<int&>(a);
-}
-
- -

-It is unclear what kind of dependency is killed here. This is presumably a core language problem, but could -affect the possible resolutions of the problem. -

- -

[2014-11 Urbana]

- -

-Recommend using a revised example: -

-
-int lookup(class D* p) 
-{
-  class E* q = p->a.load(memory_order_consume);
-  int y = std::kill_dependency(q->y);
-}
-
- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- - - -

Proposed resolution:

- - - - - -
-

2237. <cuchar> macros

-

Section: 21.8 [c.strings] Status: New - Submitter: Jason Merrill Opened: 2013-01-29 Last modified: 2015-04-08

-

View other active issues in [c.strings].

-

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-

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-

Discussion:

-

-Apparently C1X changes __STDC_UTF_16__ and __STDC_UTF_32__ from macros -defined in uchar.h (and reflected in C++ by Table 79) to be predefined by the compiler. -Do we want to do the same? -

- - - -

Proposed resolution:

- - - - - -
-

2238. Problematic iterator-pair constructor of containers

-

Section: 21.8 [c.strings] Status: Open - Submitter: Johannes Schaub Opened: 2013-02-02 Last modified: 2015-04-08

-

View other active issues in [c.strings].

-

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-

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-

Discussion:

-

-The non-explicit nature of the iterator-pair constructor of containers, such a -

- -
-template <class InputIterator>
-vector(InputIterator first, InputIterator last, const Allocator& = Allocator());
-
- -

-can be selected in unexpected situations, leading to a hard runtime error, as demonstrated by the following example: -

- -
-#include <vector>
-
-void f(std::vector<char> v){ /* ... */}
-
-int main() {
-  f({"A", "B"});
-}
-
- -

-The actually intended initializer-list constructor isn't feasible here, so the best match is the constructor template -

- -
-template <class InputIterator>
-vector(InputIterator first, InputIterator last, const Allocator& = Allocator());
-
- -

-This compiles, but will result in code running amok. The potential trap (that cannot be easily detected by the -library implementation) could be reduced by making this constructor explicit. It would still have the effect to -be selected here, but the code would be ill-formed, so the programmer gets a clear meassage here. -

- -

[2014-06 Rapperswil]

- -

-JW: can't fix this, don't want to touch this, Do The Right Thing clause has been a source of tricky issues. -only really happens with string literals, that's the only way to create an array that isn't obviously an array -

-GR: want to see paper -

-AM: is it only string literals, or also UDLs? -

-STL: maybe, but we don't need to deal with that. This is only a problem in a very specific case -

-Leave as Open. -

- - - -

Proposed resolution:

- - - - - -
-

2241. <cstdalign> and #define of alignof

-

Section: 18.10 [support.runtime] Status: Open - Submitter: Richard Smith Opened: 2013-02-14 Last modified: 2015-04-08

-

View other active issues in [support.runtime].

-

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-

View all issues with Open status.

-

Discussion:

-

-According to 18.10 [support.runtime] p2: -

- -

-The contents of these headers are the same as the Standard C library headers [..], <stdalign.h>, [..] -

- -

-Since our base C standard is C99, which doesn't have a <stdalign.h>, the reference to a non-existing -C header is irritating (In this context <stdalign.h> doesn't refer to the deprecated C++ header -<stdalign.h> described in D.5 [depr.c.headers]). -

-Furthermore, it would be also important that it doesn not define a macro named alignof, which C11 also defines -in this header. -

-Currently we only have the following guarantee as part of 18.10 [support.runtime] p7: -

- -

-The header <cstdalign> and the header <stdalign.h> shall not define a macro named -alignas. -

- -

-It is unclear what the better strategy is: Striking the reference to <stdalign.h> in -18.10 [support.runtime] p2 or upgrading to C11 as new base C standard. -

- -

[2014-02-15 Issaquah]

- -

-STL: related to earlier issue on C4, 2201, and now we get a C11 header -

-

-JY: find _Alignof as keyword C11 FDIS has four defines in stdalign.h -

-

-AM: need paper for C11 as base library we should really do that -

-

-STL: really need vendor input -

-

-STL: don't think we need to do anything right now not P1 -

-

-AM: any objections to downscale to P2 (no objections) -

- - - -

Proposed resolution:

- - - - - -
-

2242. [uninitialized_]copy_n() defect

-

Section: 25.3.1 [alg.copy], 20.7.12.2 [uninitialized.copy] Status: New - Submitter: Sean Parent Opened: 2013-02-14 Last modified: 2015-04-08

-

View other active issues in [alg.copy].

-

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-

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-

Discussion:

-

-copy_n() and uninitialized_copy_n() only return the output iterator, and not the input iterator. -Likely the interface was simply copied from the original STL. Unfortunately the interface in the original STL contains a bug. -

-copy_n() and uninitialized_copy_n() must return the resulting input iterator as well as the output -iterator (I would suggest returning a pair). Without this, there is no way to continue reading from an actual input -iterator — and if it is really a forward iterator, it will cost n increments to get back to where you were. -

- - - -

Proposed resolution:

- - - - - -
-

2243. istream::putback problem

-

Section: 27.7.2.3 [istream.unformatted] Status: New - Submitter: Juan Soulie Opened: 2013-03-01 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

-

-In 27.7.2.3 [istream.unformatted] / 34, when describing putback, it says that "rdbuf->sputbackc()" -is called. The problem are not the obvious typos in the expression, but the fact that it may lead to different -interpretations, since nowhere is specified what the required argument to sputbackc is. -

-It can be guessed to be "rdbuf()->sputbackc(c)", but "rdbuf()->sputbackc(char_type())" or -just anything would be as conforming (or non-confoming) as the first guess. -

- - - -

Proposed resolution:

- - - - - -
-

2244. Issue on basic_istream::seekg

-

Section: 27.7.2.3 [istream.unformatted] Status: Ready - Submitter: Juan Soulie Opened: 2013-03-04 Last modified: 2015-05-22

-

View other active issues in [istream.unformatted].

-

View all other issues in [istream.unformatted].

-

View all issues with Ready status.

-

Discussion:

-

-When issue 1445 was resolved by adopting -N3168, it exposed the need to -modify both overloads of basic_istream::seekg (by inserting "the function clears eofbit," after "except that"), -but the fix applied to the text apparently forgets the second overload at 27.7.2.3 [istream.unformatted] p43. -

- -

[2013-10-17: Daniel provides concrete wording]

- - -

-It seems that the tiny sentence "SIMILARLY for 27.7.1.3/43 (seekg)." had been overlooked. I agree that the wording needs to be -applied here as well. -

- -

[2015-05-06 Lenexa: Move to Ready]

- -

MC: This was just missed when we added "the function first clears eofbit" to the other overload, Daniel agrees. Editing mistake.

-

Move to Ready, consensus.

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 27.7.2.3 [istream.unformatted] p43 as indicated:

    - -
    -basic_istream<charT,traits>& seekg(off_type off, ios_base::seekdir dir);
-
    -

    --43- Effects: Behaves as an unformatted input function (as described in 27.7.2.3, paragraph 1), except -that the function first clears eofbit, it does not count the number of characters extracted, -and does not affect the value returned by subsequent calls to gcount(). […] -

    -
    -
    2. -
- - - - - -
-

2245. packaged_task::reset() memory allocation

-

Section: 30.6.9.1 [futures.task.members] Status: Open - Submitter: Jonathan Wakely Opened: 2013-03-05 Last modified: 2015-05-08

-

View all other issues in [futures.task.members].

-

View all issues with Open status.

-

Discussion:

- -

-The effects of packaged_task::reset() result in memory allocation, but -don't allow a user to provide an allocator. -

-packaged_task::reset() needs to be overloaded like so: -

- -
-template<class Alloc>  
-void reset(const Alloc&);
-
- -

-Alternatively, the effects of reset() need to require the same allocator is used -as at construction, which would require the constructor to store the allocator for later use. -

-I like to remark that GCC at the moment uses the second option, i.e. the allocator passed to the constructor -(if any) is used to create the new shared state, because this didn't require any change to the -interface. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-No strong opinions in SG1, and this is really an LWG issue. Back to you. -

- - - -

Proposed resolution:

- - - - - -
-

2248. numeric_limits::is_iec559 misnamed

-

Section: 18.3.2 [limits] Status: New - Submitter: Pete Becker Opened: 2013-03-08 Last modified: 2015-04-08

-

View all other issues in [limits].

-

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-

Discussion:

- -

-This member should probably be named "is_ieee754". Or at least the standard should explain that IEC-559 no longer exists, -and that it's been superseded by IEEE-754. -

- - - -

Proposed resolution:

- - - - - -
-

2250. Follow-up On Library Issue 2207

-

Section: 20.6.1 [bitset.cons], 20.6.2 [bitset.members], 21.4.2 [string.cons], 21.4.6 [string.modifiers], 21.4.7 [string.ops] Status: Ready - Submitter: Frank Birbacher Opened: 2013-04-18 Last modified: 2015-05-08

-

View all other issues in [bitset.cons].

-

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-

Discussion:

- -

-Similar to LWG 2207 there are several other places where the "Requires" clause precludes the "Throws" condition. -Searching for the out_of_range exception to be thrown, the following have been found (based on the working draft -N3485): -

- -
    -

  1. 20.6.1 [bitset.cons] p3+4

    2. -

  2. 20.6.2 [bitset.members] p13+14 (set)

    3. -

  3. 20.6.2 [bitset.members] p19+20 (reset)

    4. -

  4. 20.6.2 [bitset.members] p27+28 (flip)

    5. -

  5. 20.6.2 [bitset.members] p41+42 (test)

    6. -

  6. 21.4.2 [string.cons] p3+4

    7. -

  7. 21.4.6.2 [string::append] p3+4

    8. -

  8. 21.4.6.3 [string::assign] p4+5

    9. -

  9. 21.4.6.4 [string::insert] p1+2, p5+6, p9+10 (partially)

    10. -

  10. 21.4.6.5 [string::erase] p1+2

    11. -

  11. 21.4.6.6 [string::replace] p1+2, p5+6, p9+10 (partially)

    12. -

  12. 21.4.6.7 [string::copy] p1+2

    13. -

  13. 21.4.7.8 [string::substr] p1+2

    14. -
- -

[2013-10-15: Daniel provides wording]

- - -

-In addition to the examples mentioned in the discussion, a similar defect exists for thread's join() -and detach functions (see 30.3.1.5 [thread.thread.member]). The suggested wording applies a similar fix for these -as well. -

- -

[2015-05, Lenexa]

- -

-STL : likes it
-DK : does it change behavior?
-Multiple : no
-Move to ready? Unanimous -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Modify 20.6.1 [bitset.cons] as indicated: [Editorial comment: The wording form used to ammend the -Throws element is borrowed from a similar style used in 21.4.6.6 [string::replace] p10]

    - -
    -template <class charT, class traits, class Allocator>
-explicit
-bitset(const basic_string<charT, traits, Allocator>& str,
-       typename basic_string<charT, traits, Allocator>::size_type pos = 0,
-       typename basic_string<charT, traits, Allocator>::size_type n =
-         basic_string<charT, traits, Allocator>::npos,
-         charT zero = charT('0'), charT one = charT('1'));
-
    -

    --3- Requires: pos <= str.size(). -

    --4- Throws: out_of_range if pos > str.size() or invalid_argument if an -invalid character is found (see below). -

    --5- Effects: Determines the effective length rlen of the initializing string as the smaller of n and -str.size() - pos. -

    -The function then throws invalid_argument if any of the rlen characters in str beginning at position -pos is other than zero or one. The function uses traits::eq() to compare the character values. -

    -[…] -

    -
    -
    2. - -

  2. Modify 20.6.2 [bitset.members] as indicated:

    - -
    -bitset<N>& set(size_t pos, bool val = true);
-
    -

    --13- Requires: pos is valid -

    --14- Throws: out_of_range if pos does not correspond to a valid bit position. -

    -[…] -

    -
    - -
    -bitset<N>& reset(size_t pos);
-
    -

    --19- Requires: pos is valid -

    --20- Throws: out_of_range if pos does not correspond to a valid bit position. -

    -[…] -

    -
    - -
    -bitset<N>& flip(size_t pos);
-
    -

    --27- Requires: pos is valid -

    --28- Throws: out_of_range if pos does not correspond to a valid bit position. -

    -[…] -

    -
    - -
    -bool test(size_t pos) const;
-
    -

    --41- Requires: pos is valid -

    --42- Throws: out_of_range if pos does not correspond to a valid bit position. -

    -[…] -

    -
    - -
    3. - -

  3. Modify 21.4.2 [string.cons] as indicated:

    - -
    -basic_string(const basic_string& str,
-             size_type pos, size_type n = npos,
-             const Allocator& a = Allocator());
-
    -

    --3- Requires: pos <= str.size() -

    --4- Throws: out_of_range if pos > str.size(). -

    -
    -
    4. - -

  4. Modify 21.4.4 [string.capacity] as indicated:

    - -
    -void resize(size_type n, charT c);
-
    -

    --6- Requires: n <= max_size() -

    --7- Throws: length_error if n > max_size(). -

    -
    -
    5. - -

  5. Modify 21.4.6.2 [string::append] as indicated:

    - -
    -basic_string&
-  append(const basic_string& str, size_type pos, size_type n = npos);
-
    -

    --3- Requires: pos <= str.size() -

    --4- Throws: out_of_range if pos > str.size(). -

    -
    -
    6. - -

  6. Modify 21.4.6.3 [string::assign] as indicated:

    - -
    -basic_string&
-  assign(const basic_string& str, size_type pos, 
-         size_type n = npos);
-
    -

    --5- Requires: pos <= str.size() -

    --6- Throws: out_of_range if pos > str.size(). -

    -
    -
    7. - -

  7. Modify 21.4.6.4 [string::insert] as indicated: [Editorial note: The first change suggestion is also a bug fix -of the current wording, because (a) the function has parameter pos1 but the semantics refers to pos and (b) -it is possible that this function can throw length_error, see p10]

    - -
    -basic_string&
-  insert(size_type pos1, const basic_string& str);
-
    -

    --1- Requires: pos <= size(). -

    --2- Throws: out_of_range if pos > size(). -

    --3- Effects: CallsEquivalent to: return insert(pos, str.data(), str.size());. -

    --4- Returns: *this. -

    -
    - -
    -basic_string&
-  insert(size_type pos1, const basic_string& str,
-         size_type pos2, size_type n = npos);
-
    -

    --5- Requires: pos1 <= size() and pos2 <= str.size(). -

    --6- Throws: out_of_range if pos1 > size() or pos2 > str.size(). -

    -[…] -

    -
    - -
    -basic_string&
-  insert(size_type pos, const charT* s, size_type n);
-
    -

    --9- Requires: s points to an array of at least n elements of charT and -pos <= size(). -

    --10- Throws: out_of_range if pos > size() or length_error if size() + n > max_size(). -

    -[…] -

    -
    - -
    -basic_string&
-  insert(size_type pos, const charT* s);
-
    -

    --13- Requires: pos <= size() and s points to an array of at least -traits::length(s) + 1 elements of charT. -

    --14- Effects: Equivalent to return insert(pos, s, traits::length(s));. -

    --15- Returns: *this. -

    -
    -
    8. - -

  8. Modify 21.4.6.5 [string::erase] as indicated:

    - -
    -basic_string& erase(size_type pos = 0, size_type n = npos);
-
    -

    --1- Requires: pos <= size() -

    --2- Throws: out_of_range if pos > size(). -

    -[…] -

    -
    -
    9. - -

  9. Modify 21.4.6.6 [string::replace] as indicated: [Editorial note: The first change suggestion is also a bug fix -of the current wording, because it is possible that this function can throw length_error, see p10]

    - -
    -basic_string&
-  replace(size_type pos1, size_type n1,
-          const basic_string& str);
-
    -

    --1- Requires: pos1 <= size(). -

    --2- Throws: out_of_range if pos1 > size(). -

    --3- Effects: CallsEquivalent to return replace(pos1, n1, str.data(), str.size());. -

    --4- Returns: *this. -

    -
    - -
    -basic_string&
-  replace(size_type pos1, size_type n1,
-          const basic_string& str,
-          size_type pos2, size_type n = npos);
-
    -

    --5- Requires: pos1 <= size() and pos2 <= str.size(). -

    --6- Throws: out_of_range if pos1 > size() or pos2 > str.size(). -

    -[…] -

    -
    - -
    -basic_string&
-  replace(size_type pos1, size_type n1, const charT* s, size_type n2);
-
    -

    --9- Requires: pos1 <= size() and s points to an array of at least n2 elements -of charT. -

    --10- Throws: out_of_range if pos1 > size() or length_error if the length of the resulting -string would exceed max_size() (see below). -

    -[…] -

    -
    - -
    -basic_string&
-  replace(size_type pos, size_type n, const charT* s);
-
    -

    --13- Requires: pos <= size() and s points to an array of at least -traits::length(s) + 1 elements of charT. -

    --14- Effects: Equivalent to return replace(pos, n, s, traits::length(s));. -

    --15- Returns: *this. -

    -
    - -
    10. - -

  10. Modify 21.4.6.7 [string::copy] as indicated:

    - -
    -size_type copy(charT* s, size_type n, size_type pos = 0) const;
-
    -

    --1- Requires: pos <= size() -

    --2- Throws: out_of_range if pos > size(). -

    -[…] -

    -
    -
    11. - -

  11. Modify 21.4.7.8 [string::substr] as indicated:

    - -
    -basic_string substr(size_type pos = 0, size_type n = npos) const;
-
    -

    --1- Requires: pos <= size() -

    --2- Throws: out_of_range if pos > size(). -

    -[…] -

    -
    -
    12. - -

  12. Modify 30.3.1.5 [thread.thread.member] as indicated:

    - -
    -void join();
-
    -

    --3- Requires: joinable() is true. -

    -[…] -

    --7- Throws: system_error when an exception is required (30.2.2). -

    --8- Error conditions: -

    -
      -

    • […]

      • -

    • invalid_argument — if the thread is not joinable.

      • -
    -
    - -
    -void detach();
-
    -

    --9- Requires: joinable() is true. -

    -[…] -

    --12- Throws: system_error when an exception is required (30.2.2). -

    --13- Error conditions: -

    -
      -

    • […]

      • -

    • invalid_argument — if the thread is not joinable.

      • -
    -
    -
    13. - -
- - - - - -
-

2253. [arrays.ts] dynarray should state which container requirements aren't met

-

Section: X [dynarray.overview] Status: Ready - Submitter: Jonathan Wakely Opened: 2013-04-23 Last modified: 2015-04-08

-

View all issues with Ready status.

-

Discussion:

-

Addresses: arrays.ts

- -

-X [dynarray.overview] p2 says: -

-
-

-"Unless otherwise specified, all dynarray operations have the same requirements and semantics as specified in -23.2 [container.requirements]." -

-
-

-Some differences from 23.2 [container.requirements] are not explicitly specified, including at -least the lack of a default constructor, copy assignment and swap member. -

-The wording could be similar to 23.3.2.1 [array.overview] which says "An array satisfies all of the requirements -of a container and of a reversible container (23.2 [container.requirements]), except that a default constructed -array object is not empty and that swap does not have constant complexity." -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswil]

- -

-This issue has been reopened as arrays-ts. -

- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- -

[2014/11 Urbana]

- -

-Held at Ready status, pending clarification of Arrays TS -

- - - -

Proposed resolution:

- -
    -

  1. Add to X [dynarray.overview] p2:

    -

    --2- A dynarray satisfies all of the requirements of a container and of a reversible container -(23.2 [container.requirements]), except for default construction, assignment and swap. Unless -otherwise specified, all dynarray operations have the same requirements and semantics as specified in -23.2 [container.requirements]. -

    -
    2. -
- - - - - - -
-

2254. [arrays.ts] Is dynarray an allocator-aware container?

-

Section: 23.2.1 [container.requirements.general] Status: Open - Submitter: Jonathan Wakely Opened: 2013-04-23 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with Open status.

-

Discussion:

-

Addresses: arrays.ts

- -

-23.2.1 [container.requirements.general] p3 says: -

-
-

-"All of the containers defined in this Clause and in (21.4) except array meet the additional requirements -of an allocator-aware container, as described in Table 99." -

-
-

-Is this true of dynarray? I believe the answer must be no because dynarray has no allocator_type, -and morally should be no, so that operations are defined in terms of std::allocator<T>, which p13 says -doesn't actually need to be used (which allows the elements to be default-initialized as is intended, rather than -"default-inserted into the container" using an allocator.) -

-The requirement that "each element is constructed with uses-allocator construction" provides roughly equivalent behaviour -to the "CopyInsertable into X" requirements for allocator-aware containers, allowing an allocator to -control construction of the dynarray elements. -

- -

[2013-09 Chicago]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as arrays-ts. -

- - - -

Proposed resolution:

- -
    -

  1. Change to 23.2.1 [container.requirements.general] p13:

    -

    --13- All of the containers defined in this Clause and in (21.4) except array and dynarray -meet the additional requirements of an allocator-aware container, as described in Table 99. -

    -
    2. -
- - - - - - -
-

2255. [arrays.ts] dynarray constructor ambiguity

-

Section: X [dynarray.cons] Status: Ready - Submitter: Jonathan Wakely Opened: 2013-04-23 Last modified: 2015-04-08

-

View all issues with Ready status.

-

Discussion:

-

Addresses: arrays.ts

- -

-These constructors can interact badly:: -

-
-template<class Alloc>
-  dynarray(size_type c, const Alloc& alloc);
-dynarray(size_type c, const T& v);
-
-

-Unless the second argument is a value of exactly the type T you will get the first constructor, i.e. -all of these will fail to compile: -

-
-dynarray<long> dlong(1, 1);   // 1 is not long
-dynarray<float> dflt(1, 1.0);  // 1.0 is not float
-dynarray<int*> dptr(1, nullptr);  // nullptr is not int*
-dynarray<void*> doh(1, 0);  // 0 is not void*
-
-

-The nullptr case is particularly annoying, a user trying to do the right thing by saying nullptr -instead of NULL still gets the wrong result. -

-The constructor taking an allocator requires that "Alloc shall meet the requirements for an Allocator" -but doesn't actually say "shall not participate in overload resolution unless ..." -

-I believe we have no precedent for using SFINAE to check "the requirements for an Allocator" because it's -a pretty complicated set of requirements. We could say it shall not participate in overload resolution if Alloc -is implicitly convertible to value_type. -

-Alternatively, we could follow the same approach used by other types that can be constructed with an unconstrained -allocator type and use std::allocator_arg_t as the first argument instead of adding an allocator after the -other arguments. -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswil]

- -

-This issue has been reopened as arrays-ts. -

- -

[2014-06-16 Rapperswil]

- -

-Move to Ready for alternative A -

- -Previous resolution [SUPERSEDED]: -

-

-
    -
  1. -

    -Either use the correct way to unambiguously call a constructor taking any type of allocator, i.e. change the -constructors to take dynarray(std::allocator_arg_t, const Alloc&, ...) by modifying both the synopsis -X [dynarray.overview] p2 and X [dynarray.cons] before p9 like so:

    - -
    -template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, size_type c, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, size_type c, const T& v, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, const dynarray& d, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, initializer_list<T>, const Alloc& alloc);
-
    - -
    2. - -

  2. or constrain the problematic constructor by adding a new paragraph to X [dynarray.cons]:

    -
    -template <class Alloc>
-  dynarray(size_type c, const Alloc& alloc);
-template <class Alloc>
-  dynarray(size_type c, const T& v, const Alloc& alloc);
-template <class Alloc>
-  dynarray(const dynarray& d, const Alloc& alloc);
-template <class Alloc>
-  dynarray(initializer_list<T>, const Alloc& alloc);
-
    -

    --9- Requires: Alloc shall meet the requirements for an Allocator (17.6.3.5 [allocator.requirements]). -

    --10- Effects: Equivalent to the preceding constructors except that each element is constructed with uses-allocator -construction (20.7.7.2 [allocator.uses.construction]). -

    --?- Remarks: The first constructor shall not participate in overload resolution unless Alloc is not -implicitly convertible to T. -

    -
    -
    3. -
-
- -

[2014/11 Urbana]

- -

-Held at Ready status, pending clarification of Arrays TS -

- - - -

Proposed resolution:

- -
    -
  1. -

    -Use the correct way to unambiguously call a constructor taking any type of allocator, i.e. change the -constructors to take dynarray(std::allocator_arg_t, const Alloc&, ...) by modifying both the synopsis -X [dynarray.overview] p2 and X [dynarray.cons] before p9 like so:

    - -
    -template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, size_type c, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, size_type c, const T& v, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, const dynarray& d, const Alloc& alloc);
-template <class Alloc>
-  dynarray(allocator_arg_t, const Alloc& a, initializer_list<T>, const Alloc& alloc);
-
    - -
    2. -
- - - - - - -
-

2256. On vector iterator invalidation

-

Section: 23.3.6.5 [vector.modifiers] Status: New - Submitter: Howard Hinnant Opened: 2013-04-29 Last modified: 2015-04-08

-

View other active issues in [vector.modifiers].

-

View all other issues in [vector.modifiers].

-

View all issues with New status.

-

Discussion:

- -

-23.3.6.5 [vector.modifiers]/p3 says: -

-
-iterator erase(const_iterator position);
-iterator erase(const_iterator first, const_iterator last);
-
-
-

-Effects: Invalidates iterators and references at or after the point of the erase. -

-
-

-Consider this example: -

-
-#include <vector>
-#include <cassert>
-
-int main()
-{
-  typedef std::vector<int> C;
-  C c = {1, 2, 3, 4};
-  C::iterator i = c.begin() + 1;
-  C::iterator j = c.end() - 1;
-  assert(*i == 2);
-  assert(*j == 4);
-  c.erase(c.begin());
-  assert(*i == 3); // Why is this not perfectly fine?!
-}
-
-

-Why has the iterator i been invalidated? It still refers to a perfectly reasonable, fully constructed object. -If vector::iterator were to be implemented as a pointer (which is legal), it is not possible for that last -line to do anything but run fine. -

-The iterator j on the other hand now points at end, and any iterators that may now point beyond end(), -into uninitialized memory, are clearly invalid. -

-But why do we say that an iterator that must point to a valid object is invalid? This looks to me like we -simply got sloppy in our specification. -

- - -

Proposed resolution:

- - - - - - -
-

2259. Issues in 17.6.5.5 rules for member functions

-

Section: 17.6.5.5 [member.functions] Status: Ready - Submitter: Richard Smith Opened: 2013-05-12 Last modified: 2015-05-08

-

View all other issues in [member.functions].

-

View all issues with Ready status.

-

Discussion:

-

-17.6.5.5 [member.functions] p2 says: -

- -

-"An implementation may declare additional non-virtual member function signatures within a class: -

-
    -

    by adding arguments with default values to a member function signature; [Footnote: Hence, the address of a member -function of a class in the C++ standard library has an unspecified type.] [Note: An implementation -may not add arguments with default values to virtual, global, or non-member functions. — end note]

    -

    by replacing a member function signature with default values by two or more member function signatures -with equivalent behavior; and

    -

    by adding a member function signature for a member function name."

    -
-
- -
    -
  1. -

    -This wording is not using the correct terminology. "by adding arguments with default values" presumably means -"by adding parameters with default arguments", and likewise throughout. -

    -
    2. -
  2. -

    -This paragraph only allows an implementation to declare "additional" signatures, but the first bullet is talking -about replacing a standard signature with one with additional parameters. -

    -
    3. -
  3. -

    -None of these bullets allows a member function with no ref-qualifier to be replaced by signatures with ref-qualifiers -(a situation which was just discussed on std-proposals), and likewise for cv-qualifiers. Presumably that is -not intentional, and such changes should be permissible. -

    -
    4. -
- -

-I think the first two items are probably editorial, since the intent is clear. -

- -

[2013-12-11 Richard provides concrete wording]

- -

-

- -

[2015-05, Lenexa]

- -

-JW: I don't like that this loses the footnote about the address of member functions having an unspecified type, -the footnote is good to be able to point to as an explicit clarification of one consequence of the normative wording.
-MC: so we want to keep the footnote
-STL: doesn't need to be a footnote, can be an inline Note
-JW: does this have any impact on our ability to add totally different functions with unrelated names, not described in -the standard?
-MC: no, the old wording didn't refer to such functions anyway
-Move to Ready and include in motion on Friday?
-9 in favor, 0 opposed, 2 abstention -

- - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Merge 17.6.5.5 [member.functions]p2+3 as indicated:

    - -
    -

    --2- An implementation may declare additional non-virtual member function signatures within a class: -

    -
      -

    • -by adding arguments with default values to a member function signature;188 [Note: An implementation -may not add arguments with default values to virtual, global, or non-member functions. — end note] -

      • -

    • -by replacing a member function signature with default values by two or more member function signatures -with equivalent behavior; and -

      • -

    • -by adding a member function signature for a member function name. -

      • -
    -

    --3- A call to a member function signature described in the C++ standard library behaves as if the implementation -declares no additional member function signatures.[Footnote: A valid C++ program always calls the expected library -member function, or one with equivalent behavior. An implementation may also define additional member functions -that would otherwise not be called by a valid C++ program.] For a non-virtual member function described -in the C++ standard library, an implementation may declare a different set of member function signatures, provided -that any call to the member function that would select an overload from the set of declarations described in this -standard behaves as if that overload were selected. [Note: For instance, an implementation may add parameters -with default values, or replace a member function with default arguments with two or more member functions with -equivalent behavior, or add additional signatures for a member function name. — end note] -

    - -
    -
    2. - -
- - - - - -
-

2260. Missing requirement for Allocator::pointer

-

Section: 17.6.3.5 [allocator.requirements] Status: Open - Submitter: Jonathan Wakely Opened: 2013-05-14 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Open status.

-

Discussion:

-

-For an allocator A<T> which defines A<T>::pointer to a class type, -i.e. not T*, I see no requirement that A<T>::pointer is convertible to -A<U>::pointer, even if T* is convertible to U*. Such conversions are -needed in containers to convert from e.g. ListNodeBase* to ListNode<T>*. -

- -

The obvious way to do such conversions appears to be -pointer_traits::pointer_to(), but that's ill-formed if the static -member function A<T>::pointer::pointer_to() doesn't exist and the -allocator requirements don't mention that function, so you need to -cast A<T>::pointer to A<T>::void_pointer then cast that to -A<U>::pointer. -

- -

-Is converting via void_pointer really intended, or are we missing a requirement that -pointer_traits<A<T>::pointer>::pointer_to() be well-formed? -

- -

Proposed resolution:

- -

Add to the Allocator requirements table the following requirement:

- -
-

-The expression pointer_traits<XX::pointer>::pointer_to(r) is well-defined. -

-
- -

[2013-09 Chicago]

- -

-Pablo to come back with Proposed Wording -

- - -

Proposed resolution:

-
    -

  1. -Edit Table 28 as indicated: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements (continued)
    ExpressionReturn typeAssertion/note pre-/post-conditionDefault
    -… -
    -static_cast<X::const_pointer>(z) - -X::const_pointer - -static_cast<X::const_pointer>(z) == q - -  -
    -pointer_traits<X::pointer>::pointer_to(r) - -X::pointer - -  - -  -
    -… -
    -
    - - -
    2. -
- - - - - -
-

2261. Are containers required to use their 'pointer' type internally?

-

Section: 23.2 [container.requirements] Status: New - Submitter: Jonathan Wakely Opened: 2013-05-14 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

View all other issues in [container.requirements].

-

View all issues with New status.

-

Discussion:

-

-Is a container C only supposed to refer to allocated memory (blocks of -contiguous storage, nodes, etc.) through objects of type C::pointer -rather than C::value_type*? -

- -

-I don't see anything explicitly requiring this, so a container could -immediately convert the result of get_allocator().allocate(1) to a -built-in pointer of type value_type* and only deal with the built-in -pointer until it needs to deallocate it again, but that removes most -of the benefit of allowing allocators to use custom pointer types. -

- -

[2014-06-12, Jonathan comments]

- -

-This issue is basically the same issue as LWG 1521, which agrees it's an issue, -to be dealt with in the future, so I request that 2261 not be closed as a dup -unless we reopen 1521. -

- - - -

Proposed resolution:

- - - - - -
-

2262. Requirement for unique_ptr<T>::get_deleter()(p) to be able to destroy the unique_ptr

-

Section: 20.8.1.2 [unique.ptr.single] Status: Open - Submitter: Rob Desbois Opened: 2013-05-15 Last modified: 2015-05-08

-

View all other issues in [unique.ptr.single].

-

View all issues with Open status.

-

Discussion:

-

-N3337 20.8.1.2.5 [unique.ptr.single.modifiers] contains 2 non-normative notes stating: -

- -
-

-[para 4]: "The order of these operations is significant because the call to get_deleter() -may destroy *this." -

-

-[para 5]: "The postcondition does not hold if the call to get_deleter() destroys *this since -this->get() is no longer a valid expression." -

-
- -

-It seems this wording was created to resolve 998 due to the possibility that a unique_ptr may be -destroyed through deletion of its stored pointer where that directly or indirectly refers to the same unique_ptr. -If unique_ptr is required to support circular references then it seems this must be normative text: an implementation -is currently allowed to operate on *this after the assignment and deletion specified in para 4, since this is only -'disallowed' by the non-normative note. -

- -

I propose the following draft rewording:

- -

-[para 4]: Effects: assigns p to the stored pointer, and then if the old value of the stored pointer, old_p, was not -equal to nullptr, calls get_deleter()(old_p). No operation shall be performed after the call to -get_deleter()(old_p) that requires *this to be valid, because the deletion may destroy *this if it is -referred to directly or indirectly by the stored pointer. [Note: The order of these operations is significant -because the call to get_deleter() may destroy *this. — end note] -

-[para 5]: Postconditions: If the call get_deleter()(old_p) destroyed *this, none. Otherwise, -get() == p. [Note: The postcondition does not hold if the call to get_deleter() -destroys *this since this->get() is no longer a valid expression. — end note] -

- -

-I expect it will also be necessary to amend the requirements for a deleter, so in addition: -

- -

-20.8.1.2 [unique.ptr.single] [para 1]: The default type for the template parameter D is default_delete. -A client-supplied template argument D shall be a function object type (20.10), lvalue-reference to function, or -lvalue-reference to function object type for which, given a value d of type D and a value ptr of type -unique_ptr<T, D>::pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer -as appropriate for that deleter. Where D is not an lvalue reference type, d(ptr) shall be valid if ptr -refers directly or indirectly to the invoking unique_ptr object. -

- -

[2013-10-05, Stephan T. Lavavej comments and provides alternative wording]

- -

-In Chicago, we determined that the original proposed change to 20.8.1.2 [unique.ptr.single]/1 was insufficient, because -d might be a reference to a deleter functor that's destroyed during self-destruction. -

-We believed that 20.8.1.2.5 [unique.ptr.single.modifiers]/4 was already sufficiently clear. The Standard occasionally prevents -implementations of X from doing various things, through the principle of "nothing allows X to fail in that situation". -For example, v.push_back(v[0]) is required to work for non-empty vectors because nothing allows that to fail. In this case, -the intent to allow self-destruction is already clear. -

-Additionally, we did not believe that 20.8.1.2.5 [unique.ptr.single.modifiers]/5 had to be changed. The current note is slightly -squirrely but it does not lead to confusion for implementers or users. -

- -

-Previous resolution from Rob Desbois: -

-
-
    -
  1. -

    -Edit 20.8.1.2 [unique.ptr.single] p1 as indicated: -

    -

    -The default type for the template parameter D is default_delete. -A client-supplied template argument D shall be a function object type (20.10), lvalue-reference to function, or -lvalue-reference to function object type for which, given a value d of type D and a value ptr of type -unique_ptr<T, D>::pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer -as appropriate for that deleter. Where D is not an lvalue reference type, d(ptr) shall be valid if ptr -refers directly or indirectly to the invoking unique_ptr object. -

    -
    2. - -
  2. -

    -Edit 20.8.1.2.5 [unique.ptr.single.modifiers] p4+5 as indicated: -

    -
    -void reset(pointer p = pointer()) noexcept;
-
    -

    --3- Requires: The expression get_deleter()(get()) shall be well formed, shall have well-defined behavior, -and shall not throw exceptions. -

    --4- Effects: assigns p to the stored pointer, and then if the old value of the stored pointer, old_p, was not -equal to nullptr, calls get_deleter()(old_p). No operation shall be performed after the call to -get_deleter()(old_p) that requires *this to be valid, because the deletion may destroy *this if it is -referred to directly or indirectly by the stored pointer. [Note: The order of these operations is significant -because the call to get_deleter() may destroy *this. — end note] -

    --5- Postconditions: If the call get_deleter()(old_p) destroyed *this, none. Otherwise, -get() == p. [Note: The postcondition does not hold if the call to get_deleter() -destroys *this since this->get() is no longer a valid expression. — end note] -

    -
    -
    3. -
- -
- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3691.

- -
    -
  1. -

    -Edit 20.8.1.2 [unique.ptr.single] p1 as indicated: -

    -

    -The default type for the template parameter D is default_delete. -A client-supplied template argument D shall be a function object type (20.10), lvalue-reference to function, or -lvalue-reference to function object type for which, given a value d of type D and a value ptr of type -unique_ptr<T, D>::pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer -as appropriate for that deleter. d(ptr) shall be valid even if it triggers the destruction of d or (if -D is an lvalue reference to function object type) the function object that d refers to. -

    -
    2. -
-
- -

[2015-05, Lenexa]

- -

-After some discussion in Lenexa there was some wavering on if the added sentence is necessary. Here is example code that -demonstrates why the extra sentence is necessary. In this example the call to d(ptr) is valid, however the deleter -references *this after destructing its element: -

-
-#include <cassert>
-#include <memory>
-#include <iostream>
-
-class Deleter
-{
-    int state_ = 0;
-
-    enum
-    {
-        destructed            = -4,
-        self_move_assigned    = -3,
-        move_assigned_from    = -2,
-        move_constructed_from = -1
-    };
-public:
-    ~Deleter() {state_ = destructed;}
-
-    Deleter() = default;
-    Deleter(Deleter const&) = default;
-    Deleter& operator=(Deleter const&) = default;
-
-    Deleter(Deleter&& a) noexcept
-        : state_(a.state_)
-    {a.state_ = move_constructed_from;}
-
-    Deleter& operator=(Deleter&& a) noexcept
-    {
-        if (this == &a)
-            state_ = self_move_assigned;
-        else
-        {
-            state_ = a.state_;
-            a.state_ = move_assigned_from;
-        }
-        return *this;
-    }
-
-    Deleter(int state)
-        : state_(state)
-    {
-        assert(state >= 0);
-    }
-
-    template <class T>
-    void
-    operator()(T* t) const
-    {
-        std::cout << "Deleter beginning operator()(T*)\n";
-        std::cout << "The deleter = " << *this << '\n';
-        std::cout << "Deleter about to destruct the X.\n";
-        delete t;
-        std::cout << "Deleter has destructed the X.\n";
-        std::cout << "The deleter = " << *this << '\n';
-        std::cout << "Deleter ending operator()(T*)\n";
-    }
-
-    friend
-    std::ostream&
-    operator<<(std::ostream& os, const Deleter& a)
-    {
-        switch (a.state_)
-        {
-        case destructed:
-            os << "**destructed**";
-            break;
-        case self_move_assigned:
-            os << "self_move_assigned";
-            break;
-        case move_assigned_from:
-            os << "move_assigned_from";
-            break;
-        case move_constructed_from:
-            os << "move_constructed_from";
-            break;
-        default:
-            os << a.state_;
-            break;
-        }
-        return os;
-    }
-};
-
-struct X
-{
-    Deleter deleter_{1};
-};
-
-int main()
-{
-    auto xp = new X;
-    {
-        std::unique_ptr<X, Deleter&> p(xp, xp->deleter_);
-        std::cout << "unique_ptr is constructed.\n";
-        std::cout << "The deleter = " << p.get_deleter() << '\n';
-        std::cout << "Destructing unique_ptr...\n";
-    }
-    std::cout << "unique_ptr is destructed.\n";
-}
-
-

-Which outputs: -

-
-
-unique_ptr is constructed.
-The deleter = 1
-Destructing unique_ptr...
-Deleter beginning operator()(T*)
-The deleter = 1
-Deleter about to destruct the X.
-Deleter has destructed the X.
-The deleter = **destructed**
-Deleter ending operator()(T*)
-unique_ptr is destructed.
-
-
-

-The line "The deleter = **destructed**" represents the deleter referencing itself after it has been destructed by the -d(ptr) expression, but prior to that call returning. -

-Suggested alternative to the current proposed wording: -

-
-

-The expression d(ptr) shall not refer to the object d after it executes ptr->~T(). -

-
- - - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -
  1. -

    -Edit 20.8.1.2 [unique.ptr.single] p1 as indicated: -

    -

    -The default type for the template parameter D is default_delete. -A client-supplied template argument D shall be a function object type (20.9), lvalue-reference to function, or -lvalue-reference to function object type for which, given a value d of type D and a value ptr of type -unique_ptr<T, D>::pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer -as appropriate for that deleter. The expression d(ptr) shall not refer to the object d after it executes -ptr->~T(). -

    -
    2. -
- - - - - - -
-

2264. [arrays.ts] std::dynarray defines its initializer-list constructor in terms of a non-existent constructor

-

Section: X [dynarray], 23.2 [container.requirements] Status: Open - Submitter: Povilas Kanapickas Opened: 2013-05-22 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

-

Addresses: arrays.ts

- -

-std::dynarray member listing at X [dynarray.overview] includes this constructor: -

- -
-dynarray(initializer_list<T>);
-
- -

-Also, X [dynarray.overview] p. 2 says: -

- -

-Unless otherwise specified, all dynarray operations have the same requirements and semantics as specified in 23.2. -

- -

-The constructor in question isn't mentioned in X [dynarray.cons] or anywhere else. This means requirements from -23.2 [container.requirements] apply. However, Table 100 in 23.2.3 [sequence.reqmts] says: -

- -

-X(il)               Equivalent to X(il.begin(), il.end()) -

- -

-std::dynarray does not provide this constructor. -

- -

-The proposed resolution below adds the missing constructor and a complementary constructor with an allocator parameter. -The new constructors, differently from the rest of containers, accept iterators that have forward iterator category. This -is needed because the size requirements must be known in order to allocate appropriately-sized storage. -

-An alternative resolution could be to properly specify the initializer-list constructor. -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as arrays-ts. -

- - - -

Proposed resolution:

- -
    -

  1. Add the following to the std::dynarray synopsis at X [dynarray.overview]:

    - -
    -namespace std {
-  template <class T>
-  class dynarray {
-    […]
-    // 23.3.4.2 construct/copy/destroy:
-    […]
-    template <class ForwardIterator>
-    dynarray(ForwardIterator first, ForwardIterator last);
-    template <class ForwardIterator, class Alloc>
-    dynarray(ForwardIterator first, ForwardIterator last, const Alloc& alloc);
-    […]
-  };
-}
-
    -
    2. - -

  2. Add the following to X [dynarray.cons] after p. 8:

    - -
    -template <class ForwardIterator>
-dynarray(ForwardIterator first, ForwardIterator last);
-
    -

    --?- Requires: T shall meet the CopyConstructible requirements. -

    --?- Effects: Allocates storage for distance(first, last) elements. -The distance(first, last) elements of the dynarray are direct-initialized (8.5 [dcl.init]) with the -corresponding elements from the range [first,last). May or may not invoke the global operator new. -

    --?- Complexity: distance(first, last). -

    --?- Throws: std::bad_array_length when the size requested is larger than implementable, std::bad_alloc -when there is insufficient memory. -

    -
    -
    3. - -

  3. Add the following to the list of constructors at X [dynarray.cons] before p. 9:

    -
    4. - -
    -template <class Alloc>
-dynarray(size_type c, const Alloc& alloc);
-template <class Alloc>
-dynarray(size_type c, const T& v, const Alloc& alloc);
-template <class Alloc>
-dynarray(const dynarray& d, const Alloc& alloc);
-template <class Alloc>
-dynarray(initializer_list<T>, const Alloc& alloc);
-template <class ForwardIterator, class Alloc>
-dynarray(ForwardIterator first, ForwardIterator last, const Alloc& alloc);
-
    -
- - - - - - -
-

2265. 29.3p9 appears to rule out some acceptable executions

-

Section: 29.3 [atomics.order] Status: Open - Submitter: Brian Demsky Opened: 2013-06-17 Last modified: 2015-05-08

-

View other active issues in [atomics.order].

-

View all other issues in [atomics.order].

-

View all issues with Open status.

-

Discussion:

-

-I believe that the following variation on IRIW should admit executions in -which c1 = d1 = 5 and c2 = d2 = 0. If this is allowed, then what is sequence of -program evaluations for 29.3 [atomics.order] p9 that justifies the store to z? It seems that -29.3 [atomics.order] p9 should not allow this execution because one of the stores to x or y has -to appear earlier in the sequence, each of the fetch_adds reads the previous load in the thread (and thus must -appear later in the sequence), and 29.3 [atomics.order] p9 states that each load must read from the last prior -assignment in the sequence. -

- -
-atomic_int x;
-atomic_int y;
-atomic_int z;
-int c1, c2, d1, d2;
-
-static void a(void* obj)
-{
-  atomic_store_explicit(&x, 5, memory_order_relaxed); 
-}
-
-static void b(void* obj)
-{
-  atomic_store_explicit(&y, 5, memory_order_relaxed); 
-}
-
-static void c(void* obj)
-{
-  c1 = atomic_load_explicit(&x, memory_order_relaxed);
-  // this could also be an atomic load if the address depends on c1:
-  c2 = atomic_fetch_add_explicit(&y, c1, memory_order_relaxed);  
-}
-
-static void d(void* obj)
-{
-  d1 = atomic_load_explicit(&y, memory_order_relaxed);
-  d2 = atomic_fetch_add_explicit(&x, d1, memory_order_relaxed); 
-}
-
-int user_main(int argc, char** argv)
-{
-  thrd_t t1, t2, t3, t4;
-
-  atomic_init(&x, 0);
-  atomic_init(&y, 0);
-
-  printf("Main thread: creating 4 threads\n");
-  thrd_create(&t1, (thrd_start_t)&a, NULL);
-  thrd_create(&t2, (thrd_start_t)&b, NULL);
-  thrd_create(&t3, (thrd_start_t)&c, NULL);
-  thrd_create(&t4, (thrd_start_t)&d, NULL);
-
-  thrd_join(t1);
-  thrd_join(t2);
-  thrd_join(t3);
-  thrd_join(t4);
-  printf("c1=%d c2=%d\n",c1,c2);
-  printf("d1=%d d2=%d\n",d1,d2);
-
-  // Can this store write 1000 (i.e., c1=d1=5, c2=d2=0)?
-  atomic_store(&z, (c1+d1)*100+c2+d2);
-
-  printf("Main thread is finished\n");
-
-  return 0;
-}
-
- -

-It seems that the easiest fix is to allow a load in 29.3 [atomics.order] p9 to read from any prior -store in the evaluation order. -

-That said, I would personally advocate the following: -It seems to me that C/C++ atomics are in a bit of different situation than Java -because: -

-
    -

  1. People are expected to use relaxed C++ atomics in potentially racy -situations, so it isn't clear that semantics as complicated as the JMM's -causality would be sane. -

    2. -

  2. People who use C/C++ atomics are likely to be experts and use them in a -very controlled fashion. I would be really surprised if compilers would find -any real wins by optimizing the use of atomics. -

    3. -
-

-Why not do something like: -

-There is satisfaction DAG of all program evaluations. Each evaluation -observes the values of variables as computed by some prior assignment in -the DAG. -

-There is an edge x->y between two evaluations x and y if: -

-
    -

  1. the evaluation y observes a value computed by the evaluation x or -

    2. -

  2. the evaluation y is an atomic store, the evaluation x is an atomic load, and -there is a condition branch c that may depend (intrathread dependence) on x -and x-sb->c and c-sb->y. -

    3. -
-

-This seems to allow reordering of relaxed atomics that processors do without -extra fence instructions, allows most reorderings by the compiler, and gets -rid of satisfaction cycles. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- - -

[2015-05 Lenexa, SG1 response]

- -

-This was partially addressed (weasel-worded) in C++14 (See N3786). -The remainder is an open research problem. N3710 outlines a "solution" that doesn't have a consensus behind it because it costs performance. We have no better solution at the moment. -

- - -

Proposed resolution:

- - - - - -
-

2267. partial_sort_copy underspecified for ranges of two different types

-

Section: 25.4.1.4 [partial.sort.copy] Status: New - Submitter: Matt Austern Opened: 2013-06-26 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

-

-The signature of this function is: -

- -
-template<class InputIterator, class RandomAccessIterator>
-RandomAccessIterator
-partial_sort_copy(InputIterator first, InputIterator last,
-                  RandomAccessIterator result_first,
-                  RandomAccessIterator result_last);
-
-
- -

-(and the usual overload for an explicitly provided comparison function). The standard says nothing about requirements -in the case where the input type (iterator_traits<InputIterator>::value_type) and the output type -(iterator_traits<RandomAccessIterator>::value_type) are different. -

-Presumably the input type must be convertible to the output type. What's less clear is what the requirements are on -the comparison operator. Does the algorithm only perform comparisons on two values of the output type, or does it also -perform comparisons on values of the input type, or might it even perform heterogeneous comparisons? -

- - - -

Proposed resolution:

- - - - - -
-

2269. Container iterators and argument-dependent lookup

-

Section: 23.2.1 [container.requirements.general] Status: New - Submitter: Matt Austern Opened: 2013-06-26 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with New status.

-

Discussion:

-

-Consider the following code snippet: -

- -
-#include <vector>
-#include <algorithm>
-
-int main() {
-  std::vector<int> v1(100, 3);
-  std::vector<int> v2(100);
-  copy(v1.begin(), v1.end(), v2.begin());
-}
-
- -

-It compiles without error on my desktop. Is it required to? I can't find evidence from the standard that it is. -In my test std::copy was found by argument-dependent lookup because the implementation I used made -std::vector<int>::iterator a user-defined type defined in namespace std. But the standard -only requires std::vector<int>::iterator to be an implementation specified random access iterator -type. I can't find anything requiring it to be a user-defined type at all (and in fact there are reasonable implementation -where it isn't), let alone a user defined type defined in a specific namespace. -

- -

-Since the defining namespace of container iterators is visible to users, should the standard say anything about what -that namespace is? -

- - - -

Proposed resolution:

- - - - - -
-

2273. regex_match ambiguity

-

Section: 28.11.2 [re.alg.match] Status: Open - Submitter: Howard Hinnant Opened: 2013-07-14 Last modified: 2015-04-08

-

View all other issues in [re.alg.match].

-

View all issues with Open status.

-

Discussion:

-

-28.11.2 [re.alg.match] p2 in describing regex_match says: -

-
-

--2- Effects: Determines whether there is a match between the regular expression e, and all of -the character sequence [first,last). The parameter flags is used to control how the expression -is matched against the character sequence. Returns true if such a match exists, false otherwise. -

-
- -

-It has come to my attention that different people are interpreting the first sentence of p2 in different ways: -

- -
    -

  1. -If a search of the input string using the regular expression e matches the entire input string, -regex_match should return true. -

    2. -

  2. -Search the input string using the regular expression e. Reject all matches that do not match the -entire input string. If a such a match is found, return true. -

    3. -
- -

-The difference between these two subtly different interpretations is found using the following ECMAScript example: -

- -
-std::regex re("Get|GetValue");
-
- -

-Using regex_search, this re can never match the input string "GetValue", because ECMA -specifies that alternations are ordered, not greedy. As soon as "Get" is matched in the left alternation, -the matching algorithm stops. -

-Using definition 1, regex_match would return false for an input string of "GetValue". -

-However definition 2 alters the grammar and appears equivalent to augmenting the regex with a trailing '$', -which is an anchor that specifies, reject any matches which do not come at the end of the input sequence. -So, using definition 2, regex_match would return true for an input string of "GetValue". -

-My opinion is that it would be strange to have regex_match return true for a string/regex -pair that regex_search could never find. I.e. I favor definition 1. -

-John Maddock writes: -

-The intention was always that regex_match would reject any match candidate which didn't match the entire -input string. So it would find GetValue in this case because the "Get" alternative had already -been rejected as not matching. Note that the comparison with ECMA script is somewhat moot, as ECMAScript defines -the regex grammar (the bit we've imported), it does not define anything like regex_match, nor do we import -from ECMAScript the behaviour of that function. So IMO the function should behave consistently regardless of the -regex dialect chosen. Saying "use awk regexes" doesn't cut it, because that changes the grammar in other ways. -

-(John favors definition 2). -

-We need to clarify 28.11.2 [re.alg.match]/p2 in one of these two directions. -

- -

[2014-06-21, Rapperswil]

- -

-AM: I think there's a clear direction and consensus we agree with John Maddock's position, and if noone else -thinks we need the other function I won't ask for it. -

-Marshall Clow and STL to draft. -

- - - -

Proposed resolution:

- - - - - -
-

2276. Missing requirement on std::promise::set_exception

-

Section: 30.6 [futures] Status: Open - Submitter: Jonathan Wakely Opened: 2013-07-30 Last modified: 2015-05-08

-

View all other issues in [futures].

-

View all issues with Open status.

-

Discussion:

-

-The standard does not specify the behaviour of this program: -

- -
-#include <future>
-#include <cassert>
-
-struct NonTrivial
-{
-  NonTrivial() : init(true) { }
-  ~NonTrivial() { assert(init); }
-  bool init;
-};
-
-int main()
-{
-  std::promise<NonTrivial> p;
-  auto f = p.get_future();
-  p.set_exception(std::exception_ptr());
-  f.get();
-}
-
- -

-The standard doesn't forbid making the state ready with a null -exception_ptr, so what should get() return? There's no stored -exception to throw, but it can't return a value because none was initialized. -

-A careful reading of the standard shows 30.6.4 [futures.state] p8 says -"A shared state is ready only if it holds a value or an exception -ready for retrieval." One can infer from the fact that set_exception() -makes the state ready that it must store a value or exception, so -cannot store "nothing", but that isn't explicit. -

-The promise::set_exception() and promise::set_exception_at_thread_exit() -members should require p != nullptr or should state the type of exception thrown -if p is null. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-SG1 provides P/R and requests move to SG1-OK status: Add Requires clauses for promise (30.6.5 [futures.promise]) set_exception (before p18) and set_exception_at_thread_exit (before p24): Requires: p is not null. -

- - -

Proposed resolution:

-

-This wording is relative to N4431. -

-Add Requires clauses for promise (30.6.5 [futures.promise]) set_exception (before p18) and -set_exception_at_thread_exit (before p24): Requires: p is not null. - -
    -

  1. Change 30.6.5 [futures.promise] as depicted:

    - -
    -
    -void set_exception(exception_ptr p);
-
    -
    -

    --??- Requires: p is not null. -

    -

    --18- Effects: atomically stores the exception pointer p in the shared state and makes that state ready (30.6.4). -

    -
    -
    - -
    -
    -void set_exception_at_thread_exit(exception_ptr p);
-
    -
    -

    --??- Requires: p is not null. -

    -

    --24- Effects: Stores the exception pointer p in the shared state without making that state ready immediately. […] -

    -
    -
    -
- - - - - - -
-

2277. [arrays.ts] <dynarray> is missing in 24.7/1

-

Section: 24.7 [iterator.range] Status: Open - Submitter: Cassio Neri Opened: 2013-07-31 Last modified: 2015-04-08

-

View other active issues in [iterator.range].

-

View all other issues in [iterator.range].

-

View all issues with Open status.

-

Discussion:

-

Addresses: arrays.ts

- -

-Section 24.7 [iterator.range] p1 specifies header files that, in addition to -<iterator>, make available the function templates in 24.7 -(begin, end, etc.) but it fails to mention -<dynarray>. This seems to be just an oversight. -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as arrays-ts. -

- - - -

Proposed resolution:

- -

This wording is relative to N3691.

- -
    -

  1. Modify 24.7 [iterator.range] p1 as indicated:

    - -

    --1- In addition to being available via inclusion of the <iterator> header, the function templates in 24.7 are -available when any of the following headers are included: <array>, <deque>, -<dynarray>, -<forward_list>, <list>, <map>, <regex>, -<set>, <string>, <unordered_map>, <unordered_set>, -and <vector>. -

    -
    2. -
- - - - - -
-

2286. stringbuf::underflow() underspecified

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: New - Submitter: Sergey Zubkov Opened: 2013-08-29 Last modified: 2015-04-08

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View all other issues in [stringbuf.virtuals].

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-

Discussion:

-

-In 27.8.2.4 [stringbuf.virtuals]/1, basic_stringbuf::underflow() is specified to unconditionally -return traits::eof() when a read position is not available. -

-The semantics of basic_stringbuf require, and existing libraries implement it so that this function makes -a read position available if possible to do so, e.g. if some characters were inserted into the stream since the -last call to overflow(), resulting in pptr() > egptr(). Compare to the conceptually similar -D.7.1.3 [depr.strstreambuf.virtuals]/15. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    - -

  1. Change 27.8.2.4 [stringbuf.virtuals] as indicated:

    - -
    -
    -int_type underflow();
-
    -

    --1- Returns: If the input sequence has a read position available or the function makes a read position available -(as described below), returns traits::to_int_type(*gptr()). Otherwise, returns traits::eof(). Any -character in the underlying buffer which has been initialized is considered to be part of the input sequence. -

    --?- The function can make a read position available only if (mode & ios_base::in) != 0 and if the write -next pointer pptr() is not null and is greater than the current read end pointer egptr(). To make a read -position available, the function alters the read end pointer egptr() to equal pptr(). -

    -
    -
    2. - -
- - - - - -
-

2289. constexpr guarantees of defaulted functions still insufficient

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Section: 20.3.2 [pairs.pair], 20.4.2.1 [tuple.cnstr], 20.12.5 [time.duration] Status: Open - Submitter: Daniel Krügler Opened: 2013-09-09 Last modified: 2015-05-22

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View all other issues in [pairs.pair].

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-

Discussion:

-

-During the acceptance of N3471 and -some similar constexpr papers, specific wording was added to pair, tuple, and other templates -that were intended to impose implementation constraints that ensure that the observable constexpr "character" -of a defaulted function template is solely determined by the required expressions of the user-provided types when instantiated, -for example: -

- -

-The defaulted move and copy constructor, respectively, of pair shall be a constexpr function if and only if -all required element-wise initializations for copy and move, respectively, would satisfy the requirements for -a constexpr function. -

- -

-This wording doesn't require enough, especially since the core language via CWG 1358 does now support constexpr -function template instantiations, even if such function cannot appear in a constant expression (as specified in 5.20 [expr.const]) -or as a constant initializer of that object (as specified in 3.6.2 [basic.start.init]). The wording should be -improved and should require valid uses in constant expressions and as constant initializers instead. -

- -

[Lenexa 2015-05-05]

- -

STL : notice order of move/copy and copy/move with "respectively".

-

General word-smithing; ask for updated wording

-

Are we happy with this with changes we are suggesting?

-

unanimous

- - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 20.3.2 [pairs.pair] p2 as indicated:

    - -
    -

    --2- The defaulted move and copy constructor, respectively, of pair shall be a constexpr function if and only if -all required element-wise initializations for copy and move, respectively, would satisfy the requirements for -a constexpr functionAn invocation of the move or copy constructor of pair shall be a constant expression -(5.20 [expr.const]) if all required element-wise initializations would be constant expressions. An invocation of the -move or copy constructor of pair shall be a constant initializer for that pair object (3.6.2 [basic.start.init]) -if all required element-wise initializations would be constant initializers for the respective subobjects. -

    -
    -
    2. - -

  2. Change 20.4.2.1 [tuple.cnstr] p2 as indicated:

    - -
    -

    --2- The defaulted move and copy constructor, respectively, of tuple shall be a constexpr function if -and only if all required element-wise initializations for copy and move, respectively, would satisfy the requirements for -a constexpr function. The defaulted move and copy constructor of tuple<> shall be constexpr -functionsAn invocation of the move or copy constructor of tuple shall be a constant expression (5.20 [expr.const]) -if all required element-wise initializations would be constant expressions. An invocation of the move or copy constructor of -tuple shall be a constant initializer for that tuple object (3.6.2 [basic.start.init]) if all -required element-wise initializations would be constant initializers for the respective subobjects. An invocation of the -move or copy constructor of tuple<> shall be a constant expression, or a constant initializer for that -tuple<> object, respectively, if the function argument would be constant expression. -

    -
    -
    3. - -

  3. Change 20.12.5 [time.duration] p7 as indicated:

    - -
    -

    --7- Remarks: The defaulted copy constructor of duration shall be a constexpr function if and only if -the required initialization of the member rep_ for copy and move, respectively, would satisfy the -requirements for a constexpr function.An invocation of the copy constructor of duration shall -be a constant expression (5.20 [expr.const]) if the required initialization of the member rep_ would be a constant expression. -An invocation of the copy constructor of duration shall be a constant initializer for that duration object -(3.6.2 [basic.start.init]) if the required initialization of the member rep_ would be constant initializers -for this subobject. -

    -
    -
    4. - -
- - - - - -
-

2290. Top-level "SFINAE"-based constraints should get a separate definition in Clause 17

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Section: 20.10 [meta] Status: New - Submitter: Daniel Krügler Opened: 2013-09-02 Last modified: 2015-05-22

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View other active issues in [meta].

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Discussion:

-

-The current library specification uses at several places wording that is intended to refer to -core language template deduction failure at the top-level of expressions (aka "SFINAE"), for example: -

- -

-The expression declval<T>() = declval<U>() is well-formed when treated as an unevaluated operand (Clause 5). -Access checking is performed as if in a context unrelated to T and U. Only the validity of the immediate context -of the assignment expression is considered. [Note: The compilation of the expression can result in side effects -such as the instantiation of class template specializations and function template specializations, the generation of -implicitly-defined functions, and so on. Such side effects are not in the "immediate context" and can result in the program -being ill-formed. — end note] -

- -

-Similar wording can be found in the specification of result_of, is_constructible, and is_convertible, -being added to resolve an NB comment by LWG 1390 and 1391 through -N3142. -

-This wording is necessary to limit speculative compilations needed to implement these traits, but it is also lengthy and repetitive. -

- -

[2014-05-19, Daniel suggests a descriptive term]

- -

-constrictedly well-formed expression: -

-An expression e depending on a set of types A1, ..., An which is well-formed when treated as -an unevaluated operand (Clause 5). Access checking is performed as if in a context unrelated to A1, ..., -An. Only the validity of the immediate context of e is considered. [Note: The compilation of -the expression can result in side effects such as the instantiation of class template specializations and function -template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the -"immediate context" and can result in the program being ill-formed. — end note] -

- -

[2014-05-20, Richard and Jonathan suggest better terms]

- -

-Richard suggested "locally well-formed" -

-Jonathan suggested "contextually well-formed" and then "The expression ... is valid in a contrived argument -deduction context" -

- -

[2014-06-07, Daniel comments and improves wording]

- -

-The 2014-05-19 suggestion did only apply to expressions, but there are two important examples that are not expressions, but instead -are involving an object definition (std::is_constructible) and a function definition -(std::is_convertible), respectively, instead. Therefore I suggest to rephrase the usage of "expression" into "program -construct" in the definition of Jonathan's suggestion of "valid in a contrived argument deduction context". -

-I would like to point out that given the new definition of "valid in a contrived argument deduction context", there are several other -places of the Library specification that could take advantage of this wording to improve the existing specification, such as -20.9.12.2 [func.wrap.func] p2, most functions in 20.7.8.2 [allocator.traits.members], and the **Insertable, -EmplaceConstructible, and Erasable definitions in 23.2.1 [container.requirements.general], but given that -these are not fully described in terms of the aforementioned wording yet, I would recommend to fix them by a separate issue -once the committee has agreed on following the suggestion presented by this issue. -

- -

[2015-05-05 Lenexa: Move to Open]

- -

...

-

MC: I think we like the direction but it isn't quite right: it needs some work

-

JW: I'm prepared to volunteer to move that further, hopefully with the help of Daniel

-

Roger Orr: should this be Core wording because it doesn't really have anything to do with libraries - the term could then just be used here

-

AM: Core has nothing to deal with that, though

-

HT: it seems there is nothing to imply that allows dropping out with an error - maybe that's a separate issue

-

MC: I'm not getting what you are getting at: could you write an issue? - any objection to move to Open?

-

...

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Add the following new definition to 17.3 [definitions] as indicated:

    - -

    -valid in a contrived argument deduction context [defns.valid.contr.context] -

    -A program construct c depending on a set of types A1, ..., An, and treated as -an unevaluated operand (Clause 5) when c is an expression, which is well-formed. -Access checking is performed as if in a context unrelated to A1, ..., An. -Only the validity of the immediate context (14.8.2 [temp.deduct]) of c is considered. -[Note: The compilation of c can result in side effects such as the instantiation of class template -specializations and function template specializations, the generation of implicitly-defined functions, and so on. -Such side effects are not in the "immediate context" and can result in the program being ill-formed. — -end note]. -

    -
    2. - -

  2. Change Table 49 ("Type property predicates") as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 49 — Type property predicates
    TemplateConditionPreconditions
    -… -
    -template <class T, class U>
    -struct is_assignable;     -    		 -The expression -declval<T>() =
    -declval<U>()     is valid in a
    -contrived argument deduction context
    -([defns.valid.contr.context]) for types
    -T and U.     -well-formed when treated
    -as an unevaluated operand
    -(Clause 5). Access
    -checking is performed as if
    -in a context unrelated to T
    -and U. Only the validity of
    -the immediate context of
    -the assignment expression
    -is considered. [Note: The
    -compilation of the
    -expression can result in
    -side effects such as the
    -instantiation of class
    -template specializations
    -and function template
    -specializations, the
    -generation of
    -implicitly-defined
    -functions, and so on. Such
    -side effects are not in the
    -"immediate context" and
    -can result in the program
    -being ill-formed. — end
    -note]     -    		 -[…] -
    -… -
    -
    - -
    3. - -

  3. Change 20.10.4.3 [meta.unary.prop] p7 as indicated:

    - -

    --7- Given the following function prototype: -

    -
    -template <class T>
-  add_rvalue_reference_t<T> create() noexcept;
-
    -

    -the predicate condition for a template specialization is_constructible<T, Args...> shall be satisfied -if and only if the following variable definition would be well-formed for some invented -variable t would be valid in a contrived argument deduction context ([defns.valid.contr.context]) for -types T and Args...: -

    -
    -T t(create<Args>()...);
-
    -

    -[Note: These tokens are never interpreted as a function declaration. — end note] Access checking is -performed as if in a context unrelated to T and any of the Args. Only the validity of the immediate context -of the variable initialization is considered. [Note: The evaluation of the initialization can result in side -effects such as the instantiation of class template specializations and function template specializations, the -generation of implicitly-defined functions, and so on. Such side effects are not in the "immediate context" -and can result in the program being ill-formed. — end note] -

    -
    -
    4. - -

  4. Change Table 57 ("Other transformations") as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 57 — Other transformations
    TemplateConditionComments
    -… -
    -template <class Fn, class... ArgTypes>
    -struct result_of<Fn(ArgTypes...)>;     -    		 -[…] - -If the expression
    -INVOKE(declval<Fn>(),
    -declval<ArgTypes>()...)     is
    -valid in a contrived argument deduction
    -context ([defns.valid.contr.context]) for types
    -Fn and ArgTypes...     -well
    -formed when treated as an
    -unevaluated operand (Clause 5)    , the
    -member typedef type shall name the
    -type
    -decltype(INVOKE(declval<Fn>(),
    -declval<ArgTypes>()...))    ;
    -otherwise, there shall be no member
    -type. Access checking is performed as
    -if in a context unrelated to Fn and
    -ArgTypes. Only the validity of the
    -immediate context of the expression is
    -considered. [Note: The compilation of
    -the expression can result in side
    -effects such as the instantiation of
    -class template specializations and
    -function template specializations, the
    -generation of implicitly-defined
    -functions, and so on. Such side effects
    -are not in the "immediate context"
    -and can result in the program being
    -ill-formed. — end note]     -
    -… -
    -
    - -
    5. - -

  5. Change 20.10.6 [meta.rel] p4 as indicated:

    - -

    --4- Given the following function prototype: -

    -
    -template <class T>
-  add_rvalue_reference_t<T> create() noexcept;
-
    -

    -the predicate condition for a template specialization is_convertible<From, To> shall be satisfied if and -only if the return expression in the following code would be well-formedvalid in a contrived argument -deduction context ([defns.valid.contr.context]) for types To and From, including any implicit conversions -to the return type of the function: -

    -
    -To test() {
-  return create<From>();
-}
-
    -

    -[Note: This requirement gives well defined results for reference types, void types, array types, and -function types. — end note] Access checking is performed as if in a context unrelated to To -and From. Only the validity of the immediate context of the expression of the return-statement (including conversions to -the return type) is considered. [Note: The evaluation of the conversion can result in side effects such as -the instantiation of class template specializations and function template specializations, the generation of -implicitly-defined functions, and so on. Such side effects are not in the "immediate context" and can result -in the program being ill-formed. — end note] -

    -
    -
    6. - -
- - - - - -
-

2292. Find a better phrasing for "shall not participate in overload resolution"

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Section: 17.5.1.4 [structure.specifications] Status: New - Submitter: Jeffrey Yasskin Opened: 2013-09-03 Last modified: 2015-04-08

-

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-

Discussion:

-

-The C++14 CD has 25 sections including the phrase "X shall not -participate in overload resolution ...". Most of these uses are double -negatives, which are hard to interpret. "shall not ... unless" tends -to be the easiest to read, since the condition is true when the -function is available, but we also have a lot of "if X is not Y, then -Z shall not participate", which actually means "You can call Z if X is -Y." The current wording is also clumsy and long-winded. We should find -a better and more concise phrasing. -

-As an initial proposal, I'd suggest using "X is enabled if and only if Y" in prose -and adding an "Enabled If: ..." element to 17.5.1.4 [structure.specifications]. -

-Daniel: -

-I suggest to name this new specification element for 17.5.1.4 [structure.specifications] -as "Template Constraints:" instead, because the mentioned wording form was intentionally provided -starting with LWG 1237 to give implementations more freedom to realize the -concrete constraints. Instead of the original std::enable_if-based specifications -we can use better forms of "SFINAE" constraints today and it eases the path to possible language-based -constraints in the future. -

- - - -

Proposed resolution:

- - - - - -
-

2294. <cstdlib> should declare abs(double)

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Section: 26.8 [c.math] Status: Open - Submitter: Pete Becker Opened: 2013-09-04 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

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-

Discussion:

-

-… and abs(float) and abs(long double). And <cmath> should declare -abs(int), abs(long), and abs(long long). -

-As things currently stand, this program is illegal: -

-
-#include <cstdlib>
-
-int main() {
-  double d = -1.23;
-  double dd = std::abs(d);
-  return 0;
-}
-
-

-The call is ambiguous because of the various integer overloads, that's because <cstdlib> provides -abs(int) but not abs(double). -

-This lead one commenter on Stackoverflow to state that abs is dangerous, and to recommend using fabs instead. -

-In general, it makes sense to declare overloaded functions that take user-defined types in the same header as the -definition of the user-defined types; it isn't necessary to declare all of the overloads in the same place. But -here we're not dealing with any user-defined types; we're dealing with builtin types, which are always defined; -all of the overloads should be defined in the same place, to avoid mysterious problems like the one in the code above. -

-The standard library has six overloads for abs: -

-
-int abs(int);  // <cstdlib>
-long abs(long); // <cstdlib>
-long long abs(long long); // <cstdlib>
-
-float abs(float); // <cmath>
-double abs(double); // <cmath>
-long double abs(long double); // <cmath>
-
-

-These should all be declared in both headers. -

-I have no opinion on <stdlib.h> and <math.h>. -

- -

[2013-09 Chicago]

- -

-This issue is related to LWG 2192 -

-Move to open -

- -

[2014-02-13 Issaquah — Nicolai Josuttis suggest wording]

- - -

[2015-03-03, Geoffrey Romer provides improved wording]

- -

-See proposed resolution of LWG 2192. -

- -Previous resolution from Nicolai [SUPERSEDED]: -
-
    -

  1. Edit 26.8 [c.math] after p7 as indicated:

    - -

    --6- In addition to the int versions of certain math functions in <cstdlib>, C++ adds long and long long -overloaded versions of these functions, with the same semantics. -

    --7- The added signatures are: -

    -
    -long abs(long);                    // labs()
-long long abs(long long);          // llabs()
-ldiv_t div(long, long);            // ldiv()
-lldiv_t div(long long, long long); // lldiv()
-
    -

    --?- To avoid ambiguities, C++ also adds the following overloads of abs() to <cstdlib>, -with the semantics defined in <cmath>: -

    -
    -float abs(float);
-double abs(double);
-long double abs(long double);
-
    -

    --?- To avoid ambiguities, C++ also adds the following overloads of abs() to <cmath>, -with the semantics defined in <cstdlib>: -

    -
    -int abs(int);
-long abs(long);
-long long abs(long long);
-
    -
    -
    2. -
-
- - - -

Proposed resolution:

-

-See proposed resolution of LWG 2192. -

- - - - - -
-

2295. Locale name when the provided Facet is a nullptr

-

Section: 22.3.1.2 [locale.cons] Status: New - Submitter: Juan Soulie Opened: 2013-09-04 Last modified: 2015-04-08

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-

Discussion:

-

-22.3.1.2 [locale.cons] p14 ends with: -

-

-"[…] If f is null, the resulting object is a copy of other." -

-

-but the next line p15 says: -

-

-"Remarks: The resulting locale has no name." -

-

-But both can't be true when other has a name and f is null. -

-I've tried it on two implementations (MSVC,GCC) and they are inconsistent with each other on this. -

-

-Daniel Krügler: -

-As currently written, the Remarks element applies unconditionally for all cases and thus should -"win". The question arises whether the introduction of this element by LWG 424 had actually intended -to change the previous Note to a Remarks element. In either case the wording should be improved -to clarify this special case. -

- - - -

Proposed resolution:

- - - - - -
-

2296. std::addressof should be constexpr

-

Section: 20.7.12.1 [specialized.addressof] Status: Review - Submitter: Daryle Walker Opened: 2013-09-08 Last modified: 2015-05-08

-

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-

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-

Discussion:

-

-I'm writing a function that needs to be constexpr and I wanted to take the address of its input. I was -thinking of using std::addressof to be safe, but it isn't currently constexpr. A -sample implementation -couldn't be constexpr under the C++11 rules, though. -

-Daniel Krügler: -

-Indeed the core language clarified by CWG 1312 -and by CWG 1384, that such emulations of std::addressof -implementations are not valid in constant expressions, therefore it seems more like a defect than a feature request to ask for -the guarantee that std::addressof is a constexpr function. It should be added that a similar requirement -already exists for offsetof indirectly via the C99 standard as of 7.17 p3: -

-
-

-The macros are […] -

-
-offsetof(type, member-designator)
-
-

-which expands to an integer constant expression that has type size_t […] -

-
- -

-combined with the noted property in C++11 that: -

- -

-"offsetof is required to work as specified even if unary operator& -is overloaded for any of the types involved" -

- -

-Therefore implementations should already be able without heroic efforts to realize this functionality by -some intrinsic. The wording needs at least to ensure that for any lvalue core constant expression e -the expression std::addressof(e) is a core constant expression. -

- -

[2013-09 Chicago]

- -

-

- -

[2014-06-08, Daniel improves wording]

- -

-It has been ensured that the wording is in sync with the recent working paper and the usage of "any" has been -improved to say "every" instead (the fix is similar to that applied by LWG 2150). -

- -

-Previous resolution from Daniel [SUPERSEDED]: -

-
-
    -

  1. Change header <memory> synopsis, 20.7.2 [memory.syn] as indicated:

    - -
    -namespace std {
-  […]
-  // 20.7.12 [specialized.algorithms], specialized algorithms:
-  template <class T> constexpr T* addressof(T& r) noexcept;
-  […]
-}
-
    -
    2. - -

  2. Change 20.7.12.1 [specialized.addressof] as indicated:

    - -
    -template <class T> constexpr T* addressof(T& r) noexcept;
-
    -

    --1- Returns: The actual address of the object or function referenced by r, even in the presence of an -overloaded operator&. -

    --?- Remarks: For every lvalue core constant expression e (5.20 [expr.const]), the expression -std::addressof(e) is a core constant expression. -

    -
    -
    - -
    3. -
-
- -

[2014-06-09, further improvements]

- -

-A new wording form is now used similar to the approach used by LWG 2234, which -is a stricter way to impose the necessary implementation requirements. -

- -

[2015-05, Lenexa]

- -

- STL: the intent of this change is good; I think the wording is good
-- I'm a bit worried about asking for a compiler hook
-- if every implementer says: yes they can do it we should be good
-EB: there is missing the word "a" before "subexpression" (in multiple places)
-MC: the editor should do - we rely on our editors
-MC: move to Review with a note stating that we wait for implementation experience first
-- in favor: 13, opposed: 0, abstain: 2 -HB: N4430 will bring something which is addressing this issue
-MC: good we didn't go to ready then -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Introduce the following new definition to the existing list in 17.3 [definitions]: [Drafting note: -If LWG 2234 is accepted before this issue, the accepted wording for the new definition should be used instead -— end drafting note]

    - -
    -

    -constant subexpression [defns.const.subexpr] -

    -an expression whose evaluation as subexpression of a conditional-expression CE (5.16 [expr.cond]) -would not prevent CE from being a core constant expression (5.20 [expr.const]). -

    -
    -
    2. - -

  2. Change header <memory> synopsis, 20.7.2 [memory.syn] as indicated:

    - -
    -namespace std {
-  […]
-  // 20.7.12 [specialized.algorithms], specialized algorithms:
-  template <class T> constexpr T* addressof(T& r) noexcept;
-  […]
-}
-
    -
    3. - -

  3. Change 20.7.12.1 [specialized.addressof] as indicated:

    - -
    -template <class T> constexpr T* addressof(T& r) noexcept;
-
    -

    --1- Returns: The actual address of the object or function referenced by r, even in the presence of an -overloaded operator&. -

    --?- Remarks: An expression std::addressof(E) is a constant subexpression ( [defns.const.subexpr]), -if E is an lvalue constant subexpression. -

    -
    -
    - -
    4. -
- - - - - - -
-

2303. Explicit instantiation of std::vector<UserType> broken?

-

Section: 18.6.1.3 [new.delete.placement] Status: New - Submitter: Daniel Krügler Opened: 2013-09-18 Last modified: 2015-04-08

-

View all other issues in [new.delete.placement].

-

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-

Discussion:

-

-The library gives explicit permission in 17.6.4.2.1 [namespace.std] p2 that user code may explicitly instantiate -a library template provided that the instantiations depend on at least one user-defined type: -

- -

-A program may explicitly instantiate a template defined in the standard library only if the declaration -depends on the name of a user-defined type and the instantiation meets the standard library requirements -for the original template. -

- -

-But it seems that the C++11 library is not specified in a way that guarantees such an instantiation to be well-formed -if the minimum requirements of the library is not satisfied. -

-For example, in general, the first template parameter of std::vector is not required to be -DefaultConstructible in general, but due to the split of the single C++03 member function -with default argument -

-
-void resize(size_type sz, T c = T());
-
-

-into -

-
-void resize(size_type sz);
-void resize(size_type sz, const T& c);
-
-

-the effect is now that for a type ND that is not DefaultConstructible, such as -

-
-struct NP { 
-  NP(int); 
-};
-
-

-the explicit instantiation of std::vector<ND> is no longer well-formed, because the attempt to -instantiate the single-argument overload of resize cannot not succeed, because this function imposes -the DefaultInsertable requirements and given the default allocator this effectively requires -DefaultConstructible. -

-

-But DefaultConstructible is not the only point, what about CopyConstructible versus -MoveConstructible alone? It turns out that currently the second resize overload -would fail during an explicit instantiation for a type like -

-
-struct MO { 
-  MO() = default; 
-  MO(MO&&) = default; 
-};
-
-

-because it imposes CopyInsertable requirements that end up being equivalent to the CopyConstructible -requirements for the default allocator. -

-Technically a library can solve these issues: For special member functions by defining them in some base class, for others -by transforming them effectively into a function template due to the great feature of default template arguments for -function templates (At the very moment the validity of the latter approach depends on a resolution of core language issue -CWG 1635, though). E.g. the here mentioned -resize functions of std::vector could be prevented from instantiation by defining them like this -with an implementation: -

-
-template<class = void>
-void resize(size_type sz) { […] }
-template<class = void>
-void resize(size_type sz, const T& c) { […] }
-
-

-In this case, these functions could also be defined in a base class, but the latter approach won't work in all cases. -

-Basically such an implementation is required to constrain all member functions that are not covered by the general -requirements imposed on the actual library template parameters. I tested three different C++11 library implementations -and but none could instantiate for example std::list, std::vector, or std::deque with -value types that are not DefaultConstructible or only MoveConstructible. -

- -

-This issue is raised to clarify the current situation in regard to the actual requirements imposed on user-provided -types that are used to explicitly instantiate Library-provided templates. For example, the current Container requirements -impose very little requirements on the actual value type and it is unclear to which extend library implementations have -to respect that. -

-The minimum solution of this issue should be to at least realize that there is no fundamental requirement on -DefaultConstructible for value types of library containers, because we have since C++03 the general -statement of 17.6.3.1 [utility.arg.requirements] ("In general, a default constructor is not required."). -It is unclear whether CopyConstructible should be required for an explicit instantiation request, but -given the careful introduction of move operations in the library it would seem astonishing that a -MoveConstructible type wouldn't suffice for value types of the container types. -

-In any case I can envision at least two approaches to solve this issue: -

-
    -
  1. -

    -As indicated in LWG 2292, those function could get an explicit "Template Constraints:" -element, albeit this promises more than needed to solve this issue. -

    -
    2. -
  2. -

    -The library could introduce a completely new element form, such as "Instantiation Constraints:" that -would handle this situation for explicit instantiation situations. This would allow for simpler techniques -to solve the issue when explicit instantiation is required compared to the first bullet, because it would not -(necessarily) guarantee SFINAE-friendly expression-wellformedness, such as inspecting the expression -std::declval<std::vector<ND>&>.resize(0) in an unevaluated context. -

    -
    3. -
- -

-It should be noted that the 2013-08-27 comment to LWG 2193 could be resolved by a similar solution -as indicated in this issue here. -

- - -

Proposed resolution:

- - - - - -
-

2307. Should the Standard Library use explicit only when necessary?

-

Section: 23 [containers] Status: Open - Submitter: Zhihao Yuan Opened: 2013-09-26 Last modified: 2015-04-08

-

View other active issues in [containers].

-

View all other issues in [containers].

-

View all issues with Open status.

-

Discussion:

-

-LWG 2193 yields explicit for default ctors to allow {}, but not for -all cases of uniform initialization. For example: -

-
-explicit vector(size_type count, const Allocator& alloc = Allocator());
-
-

-This prevents {n, alloc()}. Although this use is relatively rare, -but the behavior is inconsistent with that of -

-
-vector(size_type count, const T& value, const Allocator& alloc = Allocator());
-
- -

[Urbana 2014-11-07: Move to Open]

- - - - -

Proposed resolution:

- - - - - -
-

2309. mutex::lock() should not throw device_or_resource_busy

-

Section: 30.4.1.2 [thread.mutex.requirements.mutex] Status: Open - Submitter: Detlef Vollmann Opened: 2013-09-27 Last modified: 2015-05-08

-

View all other issues in [thread.mutex.requirements.mutex].

-

View all issues with Open status.

-

Discussion:

-

-As discussed during the Chicago meeting in -SG1 -the only reasonable reasons for throwing device_or_resource_busy seem to be: -

-
    -

  • -The thread currently already holds the mutex, the mutex is not recursive, and the implementation detects this. -In this case resource_deadlock_would_occur should be thrown. -

    • -

  • -Priority reasons. At least std::mutex (and possibly all standard mutex types) -should not be setup this way, otherwise we have real problems with condition_variable::wait(). -

    • -
- -

[2014-06-17 Rapperswil]

- -

-Detlef provides wording -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-We believe we were already done with it. Should be in SG1-OK status. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 30.4.1.2 [thread.mutex.requirements.mutex] as indicated:

    - -

    --13- Error conditions: -

    -
      -

    • operation_not_permitted — if the thread does not have the privilege to perform the operation.

      • -

    • resource_deadlock_would_occur — if the implementation detects that a deadlock would occur.

      • -

    • device_or_resource_busy — if the mutex is already locked and blocking is not possible.

      • -
    -
    -
    2. -
- - - - - -
-

2310. Public exposition only member in std::array

-

Section: 23.3.2.1 [array.overview] Status: Open - Submitter: Jonathan Wakely Opened: 2013-09-30 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

-

-23.3.2.1 [array.overview] shows std::array with an "exposition only" data member, elems. -

-The wording in 17.5.2.3 [objects.within.classes] that defines how -"exposition only" is used says it applies to private members, but -std::array::elems (or its equivalent) must be public in order for -std::array to be an aggregate. -

-If the intention is that std::array::elems places requirements on the -implementation to provide "equivalent external behavior" to a public -array member, then 17.5.2.3 [objects.within.classes] needs to cover public -members too, or some other form should be used in 23.3.2.1 [array.overview]. -

- -

[Urbana 2014-11-07: Move to Open]

- - - - -

Proposed resolution:

- - - - - -
-

2312. tuple's constructor constraints need to be phrased more precisely

-

Section: 20.4.2.1 [tuple.cnstr] Status: Open - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-05-06

-

View other active issues in [tuple.cnstr].

-

View all other issues in [tuple.cnstr].

-

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-

Discussion:

-

-Consider the following code: -

-
-void meow(tuple<long, long>) { puts("Two"); }
-
-void meow(tuple<long, long, long>) { puts("Three"); }
-
-tuple<int, int, int> t(0, 0, 0);
-
-meow(t);
-
-

-This should compile and print "Three" because tuple<long, long>'s constructor from -const tuple<int, int, int>& should remove itself from overload resolution. -Implementations sensibly do this, but the Standard doesn't actually say it! -

-In this case, Types is "long, long" and UTypes is "int, int, int". 20.4.2.1 [tuple.cnstr]/3 -says "let i be in the range [0,sizeof...(Types)) in order", which is [0, 2). Then /17 says -"Remark: This constructor shall not participate in overload resolution unless const Ui& is implicitly -convertible to Ti for all i." Interpreted literally, this is true! /15 says -"Requires: sizeof...(Types) == sizeof...(UTypes)." but requiring the sizes to be identical doesn't help. -Only the special phrase "shall not participate in overload resolution unless" mandates SFINAE/enable_if machinery. -

-The wording that we need is almost available in the Requires paragraphs, except that the Requires paragraphs say -"is_constructible" while the Remark paragraphs say "is implicitly convertible", which is the correct thing for the SFINAE -constraints to check. My proposed resolution is to unify the Requires and Remark paragraphs, after which there -will be no need for Requires (when a constructor participates in overload resolution if and only if X is true, -then there's no need for it to Require that X is true). -

-Note: 20.10.4.3 [meta.unary.prop]/6 specifies is_constructible<To, From> and 20.10.6 [meta.rel]/4 specifies -is_convertible<From, To>. Both are specified in terms of -"template <class T> typename add_rvalue_reference<T>::type create();". -Therefore, passing From and From&& is equivalent, regardless of whether From is an object type, -an lvalue reference, or an rvalue reference. -

-Also note that 20.4.2.1 [tuple.cnstr]/3 defines T0 and T1 so we don't need to repeat their definitions. -

- -

[2014-10-05, Daniel comments]

- -

-This issue is closely related to LWG 2419. -

- -

[2015-02, Cologne]

- -

-AM: Howard wants to do something in this space and I want to wait for him to get a paper in. -

-Postponed. -

- -

[2015-05, Lenexa]

- -

-MC: handled by Daniel's tuple paper N4387
-STL: look at status after N4387 applied. -

-

[2015-05-05, Daniel comments]

- -

-N4387 doesn't touch these area intentionally. I agree with Howard that a different option exists that would introduce -a TupleLike concept. Some implementations currently take advantage of this choice and this P/R would forbid them, which seems -unfortunate to me. -

- - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 20.4.2.1 [tuple.cnstr] as indicated:

    - -
    -template <class... UTypes>
-  explicit constexpr tuple(UTypes&&... u);
-
    -

    --8- Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, Ui&&>::value is true -for all i. -

    -[…] -

    --10- Remark: This constructor shall not participate in overload resolution unless each type in UTypes is -implicitly convertible to its corresponding type in Typessizeof...(Types) == sizeof...(UTypes) and -both is_constructible<Ti, Ui>::value and is_convertible<Ui, Ti>::value are true for all i. -

    -
    -

    -[…] -

    -
    -
    -template <class... UTypes>
-  constexpr tuple(const tuple<UTypes...>& u);
-
    -

    --15- Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, const Ui&>::value is true -for all i. -

    -[…] -

    --17- Remark: This constructor shall not participate in overload resolution unless const Ui& is implicitly -convertible to Tisizeof...(Types) == sizeof...(UTypes) and -both is_constructible<Ti, const Ui&>::value and is_convertible<const Ui&, Ti>::value are -true for all i. -

    -
    -
    -
    -template <class... UTypes>
-  constexpr tuple(tuple<UTypes...>&& u);
-
    -

    --18- Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, Ui&&>::value is true -for all i. -

    -[…] -

    --20- Remark: This constructor shall not participate in overload resolution unless each type in UTypes is -implicitly convertible to its corresponding type in Typessizeof...(Types) == sizeof...(UTypes) and -both is_constructible<Ti, Ui>::value and is_convertible<Ui, Ti>::value are true for all i. -

    -
    -
    -
    -template <class U1, class U2> constexpr tuple(const pair<U1, U2>& u);
-
    -

    --21- Requires: sizeof...(Types) == 2. is_constructible<T0, const U1&>::value is true for the first -type T0 in Types and is_constructible<T1, const U2&>::value is true for the second type T1 in -Types. -

    -[…] -

    --23- Remark: This constructor shall not participate in overload resolution unless const U1& is implicitly -convertible to T0 and const U2& is implicitly convertible to T1sizeof...(Types) == 2 -&& is_constructible<T0, const U1&>::value && is_constructible<T1, const U2&>::value && -is_convertible<const U1&, T0>::value && is_convertible<const U2&, T1>::value is true. -

    -
    -
    -
    -template <class U1, class U2> constexpr tuple(pair<U1, U2>&& u);
-
    -

    --24- Requires: sizeof...(Types) == 2. is_constructible<T0, U1&&>::value is true for the first -type T0 in Types and is_constructible<T1, U2&&>::value is true for the second type T1 in -Types. -

    -[…] -

    --26- Remark: This constructor shall not participate in overload resolution unless U1 is implicitly convertible -to T0 and U2 is implicitly convertible to T1sizeof...(Types) == 2 -&& is_constructible<T0, U1>::value && is_constructible<T1, U2>::value && -is_convertible<U1, T0>::value && is_convertible<U2, T1>::value is true. -

    -
    -
    -
    2. - -
- - - - - -
-

2318. basic_string's wording has confusing relics from the copy-on-write era

-

Section: 21.4 [basic.string] Status: New - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with New status.

-

Discussion:

-

-21.4.4 [string.capacity]/8 specifies basic_string::resize(n, c) with: -

-

-Effects: Alters the length of the string designated by *this as follows: -

-
    -

  • -If n <= size(), the function replaces the string designated by *this with a string of length n whose -elements are a copy of the initial elements of the original string designated by *this. -

    -
    • -

  • -If n > size(), the function replaces the string designated by *this with a string of length n whose -first size() elements are a copy of the original string designated by *this, and whose remaining elements are all -initialized to c. -

    -
    • -
-
-

-This wording is a relic of the copy-on-write era. In addition to being extremely confusing, it has undesirable implications. -Saying "replaces the string designated by *this with a string of length n whose elements are a copy" suggests -that the trimming case can reallocate. Reallocation during trimming should be forbidden, like vector. -

-At least 7 paragraphs are affected: 21.4.4 [string.capacity]/8, 21.4.6.2 [string::append]/9, -21.4.6.3 [string::assign]/3 and /10, 21.4.6.4 [string::insert]/11, 21.4.6.5 [string::erase]/4, and -21.4.6.6 [string::replace]/11 say "replaces the string [designated/controlled] by *this". (21.4.6.7 [string::copy]/3 -is different — it "replaces the string designated by s".) -

-Of the affected paragraphs, resize() and erase() are the most important to fix because they should forbid -reallocation during trimming. -

- - -

Proposed resolution:

- - - - - -
-

2321. Moving containers should (usually) be required to preserve iterators

-

Section: 23.2.1 [container.requirements.general] Status: Open - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with Open status.

-

Discussion:

-

-23.2.1 [container.requirements.general]/10 says that unless otherwise specified, "no swap() function invalidates -any references, pointers, or iterators referring to the elements of the containers being swapped. [Note: The end() -iterator does not refer to any element, so it may be invalidated. — end note]". However, move constructors and move -assignment operators aren't given similar invalidation guarantees. The guarantees need several exceptions, so I do not believe -that blanket language like /11 "Unless otherwise specified (either explicitly or by defining a function in terms of other functions), -invoking a container member function or passing a container as an argument to a library function shall not invalidate iterators to, -or change the values of, objects within that container." is applicable. -

- -

[2014-02-13 Issaquah]

- -

-General agreeement on intent, several wording nits and additional paragraphs to hit. -

-

-STL to provide updated wording. Move to Open. -

- -

[2015-02, Cologne]

- -

-AM: in the proposed wording, I'd like to mention that the iterators now refer to elements of a different container. -I think we're saying something like this somewhere. JY: There's some wording like that for swap I think. TK: It's also in -list::splice(). DK to JY: 23.2.1p9. -

-VV: The issue says that STL was going to propose new wording. Has he done that? AM: I believe we're looking at that. -GR: The request touches on multiple paragraphs, and this PR has only one new paragraph, so this looks like it's not up-to-date. -MC: This was last updated a year ago in Issaquah. -

-Conclusion: Skip, not up to date. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. In 23.2.1 [container.requirements.general]/10 change as indicated:

    - -

    --10- Unless otherwise specified (see 23.2.4.1, 23.2.5.1, 23.3.3.4, and 23.3.7.5) all container types defined in this -Clause meet the following additional requirements: -

    -
      -

    • -[…] -

      • -

    • -no copy constructor or assignment operator of a returned iterator throws an exception. -

      • -

    • -no move constructor (or move assignment operator when -allocator_traits<allocator_type>::propagate_on_container_move_assignment::value is true) of a container -(except for array) invalidates any references, pointers, or iterators referring to the elements of the source container. -[Note: The end() iterator does not refer to any element, so it may be invalidated. — end note] -

      • -

    • -no swap() function throws an exception. -

      • -

    • -no swap() function invalidates any references, pointers, or iterators referring to the elements of the -containers being swapped. [Note: The end() iterator does not refer to any element, so it may be -invalidated. — end note] -

      • -
    -
    -
    2. - -
- - - - - - -
-

2326. uniform_int_distribution<unsigned char> should be permitted

-

Section: 26.5.1.1 [rand.req.genl] Status: New - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

-

-26.5.1.1 [rand.req.genl]/1 says: "Throughout this subclause 26.5, the effect of instantiating a template [...] that has a -template type parameter named IntType is undefined unless the corresponding template argument is cv-unqualified -and is one of short, int, long, long long, unsigned short, unsigned int, -unsigned long, or unsigned long long." 26.5.8.2.1 [rand.dist.uni.int] specifies -template<class IntType = int> class uniform_int_distribution, so this forbids -uniform_int_distribution<char/signed char/unsigned char>. -

-I am not aware of anything in <random> that works with 16-bit integers but fails with 8-bit integers, so I suspect -that IntType and UIntType could simply be extended to permit the char family. Alternatively, this -change could be limited to uniform_int_distribution alone, where it is definitely safe. A <random> expert -should decide which change is best. -

- -

[2015-04-04 Geoffrey provides wording]

- -

- I think it's time to call the question; it's just silly that we have a random number library with no natural way to generate - random bytes. However, I don't think it's sufficient to fix only uniform_int_distribution, or even all of IntType. - At a bare minimum we need to also fix independent_bits_engine (arguably the cleanest way of generating a random byte) - and that's specified in terms of UIntType. -

- The wording provided below is equivalent to adding unsigned char to item "f" and adding signed char and - unsigned char to item "e". That means it still excludes char, but I'm OK with that. If you want to generate - a 1-byte number, you should probably pick a signedess, and if you want to generate a raw byte, the "true" raw byte type is - unsigned char. This also excludes extended integral types and wide char types, which seem like nice-to-haves at best. - I have no objection to supporting any of those types; I just picked this to simplify the wording and hopefully maximize consensus. - Note that if we want to broaden IntType to permit any integral type, we'll need to decide if we want to exclude bool. -

-For reference, IntType is used as a parameter of the following templates: -

-
-
-uniform_int_distribution
-binomial_distribution
-geometric_distribution
-negative_binomial_distribution
-poisson_distribution
-discrete_distribution
-
-
-

-and UIntType is used as a parameter of the following templates: -

-
-
-linear_congruential_engine
-mersenne_twister_engine
-subtract_with_carry_engine
-independent_bits_engine
-
-
- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change in 26.5.1.1 [rand.req.genl] p1 as indicated:

    - -

    --1- Throughout this subclause 26.5, the effect of instantiating a template: -

    -
      -

    1. […]

      2. -

    2. that has a template type parameter named IntType is undefined unless the corresponding template -argument is cv-unqualified and is a standard integer type (3.9.1 [basic.fundamental])one of -short, int, long, long long, unsigned short, unsigned int, -unsigned long, or unsigned long long.

      3. -

    3. that has a template type parameter named UIntType is undefined unless the corresponding template -argument is cv-unqualified and is a standard unsigned integer type (3.9.1 [basic.fundamental])one -of unsigned short, unsigned int, unsigned long, or unsigned long long.

      4. -
    -
    2. -
- - - - - -
-

2328. Rvalue stream extraction should use perfect forwarding

-

Section: 27.7.2.6 [istream.rvalue] Status: Review - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-05-22

-

View other active issues in [istream.rvalue].

-

View all other issues in [istream.rvalue].

-

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-

Discussion:

-

-27.7.2.6 [istream.rvalue] declares operator>>(basic_istream<charT, traits>&& is, T& x). -However, 27.7.2.2.3 [istream::extractors]/7 declares operator>>(basic_istream<charT,traits>& in, charT* s), -plus additional overloads for unsigned char* and signed char*. This means that -"return_rvalue_istream() >> &arr[0]" won't compile, because T& won't bind to the rvalue &arr[0]. -

- -

[2014-02-12 Issaquah : recategorize as P3]

- - -

-Jonathan Wakely: Bill was certain the change is right, I think so with less certainty -

- -

-Jeffrey Yaskin: I think he's right, hate that we need this -

- -

-Jonathan Wakely: is this the security issue Jeffrey raised on lib reflector? -

- -

-Move to P3 -

- -

[2015-05-06 Lenexa: Move to Review]

- - -

WEB, MC: Proposed wording changes one signature (in two places) to take a forwarding reference.

-

TK: Should be consistent with an istream rvalue?

-

MC: This is the case where you pass the stream by rvalue reference.

-

RP: I would try it before standardizing.

-

TK: Does it break anything?

-

RP, TK: It will take all arguments, will be an exact match for everything.

-

RS, TK: This adapts streaming into an rvalue stream to make it act like streaming into an lvalue stream.

-

RS: Should this really return the stream by lvalue reference instead of by rvalue reference? => new LWG issue.

-

RP: Security issue?

-

MC: No. That's istream >> char*, C++ version of gets(). Remove it, as we did for gets()? => new LWG issue.

-

RS: Proposed resolution looks correct to me.

-

MC: Makes me (and Jonathan Wakely) feel uneasy.

-

Move to Review, consensus.

- - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 27.7.1 [iostream.format.overview], header <istream> synopsis, as indicated:

    - -
    -namespace std {
-  […]
-  template <class charT, class traits, class T>
-    basic_istream<charT, traits>&
-    operator>>(basic_istream<charT, traits>&& is, T&& x);
-}
-
    -
    2. - -

  2. Edit 27.7.2.6 [istream.rvalue] as indicated:

    - -
    -template <class charT, class traits, class T>
-  basic_istream<charT, traits>&
-  operator>>(basic_istream<charT, traits>&& is, T&& x);
-
    -

    --1- Effects: is >>x std::forward<T>(x) -

    --2- Returns: is -

    -
    -
    3. -
- - - - - -
-

2331. regex_constants::collate's effects are inaccurately summarized

-

Section: 28.5.1 [re.synopt] Status: Open - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-05-08

-

View other active issues in [re.synopt].

-

View all other issues in [re.synopt].

-

View all issues with Open status.

-

Discussion:

-

-The table in 28.5.1 [re.synopt]/1 says that regex_constants::collate "Specifies that character ranges of the form -"[a-b]" shall be locale sensitive.", but 28.13 [re.grammar]/14 says that it affects individual character comparisons -too. -

- -

[2012-02-12 Issaquah : recategorize as P3]

- - -

-Marshall Clow: 28.13/14 only applies to ECMAScript -

- -

-All: we're unsure -

- -

-Jonathan Wakely: we should ask John Maddock -

- -

-Move to P3 -

- -

[2014-5-14, John Maddock response]

- -

-The original intention was the original wording: namely that collate only made character ranges locale sensitive. -To be frank it's a feature that's probably hardly ever used (though I have no real hard data on that), and is a leftover -from early POSIX standards which required locale sensitive collation for character ranges, and then later changed -to implementation defined if I remember correctly (basically nobody implemented locale-dependent collation). -

-So I guess the question is do we gain anything by requiring all character-comparisons to go through the locale when this bit -is set? Certainly it adds a great deal to the implementation effort (it's not what Boost.Regex has ever done). I guess the -question is are differing code-points that collate identically an important use case? I guess there might be a few Unicode -code points that do that, but I don't know how to go about verifying that. -

-STL: -

-If this was unintentional, then 28.5.1 [re.synopt]/1's table should be left alone, while 28.13 [re.grammar]/14 -should be changed instead. -

-Jeffrey Yasskin: -

-This page -mentions that [V] in Swedish should match "W" in a perfect world. -

-However, the most recent version of TR18 retracts -both language-specific loose matches and language-specific ranges -because "for most full-featured regular expression engines, it is -quite difficult to match under code point equivalences that are not -1:1" and "tailored ranges can be quite difficult to implement -properly, and can have very unexpected results in practice. For -example, languages may also vary whether they consider lowercase below -uppercase or the reverse. This can have some surprising results: [a-Z] -may not match anything if Z < a in that locale." -

-ECMAScript doesn't include collation at all. -

-IMO, +1 to changing 28.13 instead of 28.5.1. It seems like we'd be on -fairly solid ground if we wanted to remove regex_constants::collate -entirely, in favor of named character classes, but of course that's -not for this issue. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. In 28.5.1 [re.synopt]/1, Table 138 — "syntax_option_type effects", change as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - -
    Table 138 — syntax_option_type effects
    ElementEffect(s) if set
    -… -
    -collate - -Specifies that character ranges of the form "[a-b]"comparisons and character range comparisons -shall be locale sensitive. -
    -… -
    -
    -
    2. -
- - - - - -
-

2334. atomic's default constructor requires "uninitialized" state even for types with non-trivial default-constructor

-

Section: 29.6.5 [atomics.types.operations.req] Status: SG1 - Submitter: Daniel Krügler Opened: 2013-10-03 Last modified: 2015-04-08

-

View other active issues in [atomics.types.operations.req].

-

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-

View all issues with SG1 status.

-

Discussion:

-

-According to 29.6.5 [atomics.types.operations.req] p4, -

-
-A ::A () noexcept = default;
-
-

-Effects: leaves the atomic object in an uninitialized state. [Note: These semantics ensure compatibility -with C. — end note] -

-
-

-This implementation requirement is OK for POD types, like int, but 29.5 [atomics.types.generic] p1 -intentionally allows template arguments of atomic with a non-trivial default constructor ("The type of the template argument -T shall be trivially copyable (3.9)"), so this wording can be read in a way that makes the behaviour of the following code -undefined: -

-
-#include <atomic>
-#include <iostream>
-
-struct S {
-  S() noexcept : v(42) {}
-  int v;
-};
-
-int main() {
-  std::atomic<S> as; // Default-initialization
-  std::cout << as.load().v << std::endl; // ?
-}
-
-

-For a user-defined emulation of atomic the expected outcome would be defined and the program would output "42", -but existing implementations differ and the result value is a "random number" for at least one implementation. This seems -very surprising to me. -

-To realize that seemingly existing requirement, an implementation is either required to violate normal language rules internally -or to perform specific bit-randomization-techniques after the normal default-initialization that called the default constructor -of S. -

-According to my understanding, the non-normative note in 29.6.5 [atomics.types.operations.req] p4 is intended to -refer to types that are valid C-types, but the example type S is not such a type. -

-To make the mental model of atomic's default constructor more intuitive for user-code, I suggest to clarify the wording -to have the effects of default-initialization instead. The current state seems more like an unintended effect of imprecise -language used here and has some similarities to wording that was incorrectly used to specify atomic_flag initialization -as described by LWG 2159. -

- -

[2014-05-17, Daniel comments and provides alternative wording]

- - -

-The current wording was considered controversial as expressed by reflector discussions. To me, the actual problem is not newly -introduced by that wording, but instead is already present in basically all paragraphs specifying semantics of atomic types, -since the wording never clearly distinguishes the value of the actual atomic type A and the value of the "underlying", -corresponding non-atomic type C. The revised proposed wording attempts to improve the current ambiguity of these two -kinds of values. -

- -Previous resolution from Daniel [SUPERSEDED]: -

-

-

This wording is relative to N3691.

- -
    -

  1. Modify 29.6.5 [atomics.types.operations.req] p4 as indicated: [Editorial note: There is no exposition-only -member in atomic, which makes it a bit hard to specify what actually is initialized, but the usage of the term "value" -seems consistent with similar wording used to specify the effects of the atomic load functions]

    - -
    -A ::A () noexcept = default;
-
    -

    --4- Effects: leaves the atomic object in an uninitialized stateThe value of the atomic object -is default-initialized (8.5 [dcl.init]). [Note: These semantics ensure compatibility -with C. — end note] -

    -
    -
    2. - -
-
- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Modify 29.6.5 [atomics.types.operations.req] p2 as indicated: [Editorial note: This is a near-to editorial -change not directly affecting this issue, but atomic_address does no longer exist and the pointed to definition is -relevant in the context of this issue resolution.] -

    -
    -

    --2- In the following operation definitions: -

    -
      -

    • an A refers to one of the atomic types.

      • -

    • a C refers to its corresponding non-atomic type. The atomic_address atomic type corresponds to the -void* non-atomic type.

      • -

    • […]

      • -
    -
    -
    2. - -

  2. Modify 29.6.5 [atomics.types.operations.req] p4 and the following as indicated: [Editorial note: There -is no exposition-only member in atomic, which makes it a bit hard to specify what actually is initialized, but -the introductory wording of 29.6.5 [atomics.types.operations.req] p2 b2 defines: "a C refers to its -corresponding non-atomic type." which helps to specify the semantics in terms of "the C value referred to by the -atomic object"]

    - -
    -
    -A::A() noexcept = default;
-
    -
    -

    --4- Effects: leaves the atomic object in an uninitialized stateDefault-initializes (8.5 [dcl.init]) -the C value referred to by the atomic object. [Note: These semantics ensure compatibility with C. -— end note] -

    -
    - -
    -constexpr A::A(C desired) noexcept;
-
    -
    -

    --5- Effects: Direct-iInitializes the C value referred to by the atomic object -with the value desired. Initialization is not an atomic operation (1.10). […] -

    -[…] -

    -
    - -
    -void atomic_init(volatile A* object, C desired) noexcept;
-void atomic_init(A* object, C desired) noexcept;
-
    -
    -

    --8- Effects: Non-atomically initializes the C value referred to by *object with value -desired. […] -

    -
    - -
    -void atomic_store(volatile A* object, C desired) noexcept;
-[…]
-void A::store(C desired, memory_order order = memory_order_seq_cst) noexcept;
-
    -
    -

    --9- […] -

    --10- Effects: Atomically replaces the C value pointed to by -object or by this with the value of desired. […] -

    -[…] -

    -
    - -
    -C atomic_load(const volatile A* object) noexcept;
-[…]
-C A::load(memory_order order = memory_order_seq_cst) const noexcept;
-
    -
    -

    --13- […] -

    --14- […] -

    --15- Returns: Atomically returns the C value pointed to by object or by this. -

    -[…] -

    -
    - -
    -C atomic_exchange(volatile A* object, C desired) noexcept;
-[…]
-C A::exchange(C desired, memory_order order = memory_order_seq_cst) noexcept;
-
    -
    -

    --18- Effects: Atomically replaces the C value pointed to by object or by this with desired. […] -

    --19- Returns: Atomically returns the C value pointed to by object or by this -immediately before the effects. -

    -[…] -

    -
    - -
    -C atomic_fetch_key(volatile A* object, M operand) noexcept;
-[…]
-C A::fetch_key(M operand, memory_order order = memory_order_seq_cst) noexcept;
-
    -
    -

    --28- Effects: Atomically replaces the C value pointed to by object or by this with -the result of the computation applied to the C value pointed to by object or by this and -the given operand. […] -

    --29- Returns: Atomically, returns the C value pointed to by object -or by this immediately before the effects. -

    -[…] -

    -
    - -
    -
    3. - -

  3. Modify 29.7 [atomics.flag] p5 and the following as indicated:

    - -
    -
    -bool atomic_flag_test_and_set(volatile atomic_flag* object) noexcept;
-[…]
-bool atomic_flag::test_and_set(memory_order order = memory_order_seq_cst) noexcept;
-
    -
    -

    --5- Effects: Atomically sets the bool value pointed to by object or by this to true. -[…] -

    --6- Returns: Atomically, returns the bool value of thepointed -to by object or by this immediately before the effects. -

    -
    - -
    -void atomic_flag_clear(volatile atomic_flag* object) noexcept;
-[…]
-void atomic_flag::clear(memory_order order = memory_order_seq_cst) noexcept;
-
    -
    -

    --7- […] -

    --8- Effects: Atomically sets the bool value pointed to by object or by this to false. -[…] -

    -
    - -
    - -
    4. -
- - - - - -
-

2335. array<array<int, 3>, 4> should be layout-compatible with int[4][3]

-

Section: 23.3.2 [array] Status: New - Submitter: Jeffrey Yasskin Opened: 2013-10-04 Last modified: 2015-04-08

-

View other active issues in [array].

-

View all other issues in [array].

-

View all issues with New status.

-

Discussion:

-

-In order to replace some uses of C arrays with std::array, we need it -to be possible to cast from a std::array<> to an equivalent C array. -Core wording doesn't appear to be in quite the right state to allow -casting, but if we specify that appropriate types are -layout-compatible, we can at least write: -

-
-union {
-  array<array<array<int, 2>, 3>, 4> arr;
-  int carr[4][3][2];
-};
-
-

-to view memory as the other type: C++14 CD [class.mem]p18. -

-I believe it's sufficient to add "array<T, N> shall be -layout-compatible (3.9 [basic.types]) with T[N]." to -23.3.2.1 [array.overview], but we might also need some extension to -9.2 [class.mem] to address the possibility of layout-compatibility -between struct and array types. -

-I checked that libc++ on MacOS already implements this, although it -would be good for someone else to double-check; I haven't checked any -other standard libraries. -

- - - -

Proposed resolution:

- - - - - -
-

2336. is_trivially_constructible/is_trivially_assignable traits are always false

-

Section: 20.10.4.3 [meta.unary.prop] Status: Ready - Submitter: Daniel Krügler Opened: 2013-10-01 Last modified: 2015-05-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with Ready status.

-

Discussion:

-

-In 20.10.4.3 [meta.unary.prop] we have traits to allow testing for triviality of specific operations, such as -is_trivially_constructible and is_trivially_assignable (and their derived forms), which are specified -in terms of the following initialization and assignment, respectively: -

-
-T t(create<Args>()...);
-
-declval<T>() = declval<U>()
-
-

-The wording that describes the way how triviality is deduced, is in both cases of the same form: -

-

-[… ] and the variable definition/assignment, as defined by is_constructible/is_assignable, is known -to call no operation that is not trivial (3.9, 12). -

-

-The problematic part of this wording is that both definitions are specified in terms of an "object construction" function -create or declval, respectively, (The former being a conceptual function, the latter being a library function), -but for none of these functions we can assume that they could be considered as trivial — only special member functions can -have this property and none of these is one. This problem became obvious, when the similar issue LWG 2298 -in regard to is_nothrow_constructible was opened. -

-A possible approach to solve this specification problem is to make a blanket statement for sub-clause 20.10.4.3 [meta.unary.prop] -that these helper functions are considered trivial for the purpose of defining these traits. -

-Using this kind of wording technique can also be used to get rid of the additional helper function template create, which -is currently needed for the is_convertible and the is_constructible traits, because both traits are specified in -terms of contexts where technically the corresponding "object construction" function would be considered as odr-used. This is problematic, -because these traits are defined in terms of well-formed code and odr-using declval would make the program ill-formed (see -20.2.5 [declval]). So extending above blanket statement to consider std::declval<T>() as not odr-used -in the context of the corresponding trait definition would allow for replacing create by declval. -

- -

[2015-05, Lenexa]

- -

-STL: would you consider moving the change to 20.10 as editorial or are you uncomfortable with it?
-JW: this sounds a viable editorial change
-VV: I guarantee you that moving it doesn't change anything
-MC: how about this: we move it to Ready as is and if we conclude moving it is editorial we can do it and if not open an issue
-STL: I would like to guarantee that the lifting happens
-JW: I do that! If it goes in I move it up
-MC: move to Ready: in favor: 15, opposed: 0, abstain: 1 -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Add a new paragraph after 20.10.4.3 [meta.unary.prop] p3 as indicated: [Editorial note: The first change in -20.10.4.3 [meta.unary.prop] p3 is recommended, because technically a Clause is always a "main chapter" — such as -Clause 20 — but every child of a Clause or sub-clause is a sub-clause]

    - -
    -

    -[…] -

    --3- For all of the class templates X declared in this Clausesub-clause, instantiating that -template with a template-argument that is a class template specialization may result in the implicit instantiation of the -template argument if and only if the semantics of X require that the argument must be a complete type. -

    --?- For the purpose of defining the templates in this sub-clause, a function call expression -declval<T>() for any type T is considered to be a trivial (3.9 [basic.types], 12 [special]) -function call that is not an odr-use (3.2 [basic.def.odr]) of declval in the context of the corresponding definition -notwithstanding the restrictions of 20.2.5 [declval]. -

    -[…] -

    -
    -
    2. - -

  2. Modify 20.10.4.3 [meta.unary.prop] p7 as indicated:

    - -
    -

    --7- Given the following function prototype: -

    -
    -template <class T>
-  typename add_rvalue_reference<T>::type create();
-
    -

    -tThe predicate condition for a template specialization is_constructible<T, Args...> -shall be satisfied if and only if the following variable definition would be well-formed for some invented variable t: -

    -
    -T t(createdeclval<Args>()...);
-
    -

    -[…] -

    -
    -
    3. - -

  3. Add a new paragraph after 20.10.6 [meta.rel] p2 as indicated: [Editorial note: Technically we don't need -the guarantee of "a trivial function call" for the type relationship predicates at the very moment, but it seems more robust and -consistent to have the exact same guarantee here as well] -

    -
    -

    -[…] -

    --2- […] -

    --?- For the purpose of defining the templates in this sub-clause, a function call expression -declval<T>() for any type T is considered to be a trivial (3.9 [basic.types], 12 [special]) -function call that is not an odr-use (3.2 [basic.def.odr]) of declval in the context of the corresponding definition -notwithstanding the restrictions of 20.2.5 [declval]. -

    -[…] -

    -
    -
    4. - -

  4. Modify 20.10.6 [meta.rel] p4 as indicated:

    - -
    -

    --4- Given the following function prototype: -

    -
    -template <class T>
-  typename add_rvalue_reference<T>::type create();
-
    -

    -tThe predicate condition for a template specialization is_convertible<From, To> -shall be satisfied if and only if the return expression in the following code would be well-formed, including any implicit -conversions to the return type of the function: -

    -
    -To test() {
-  return createdeclval<From>();
-}
-
    -

    -[…] -

    -
    -
    5. - -
- - - - - - -
-

2337. shared_ptr operator*() should not be noexcept

-

Section: 20.8.2.2.5 [util.smartptr.shared.obs] Status: Tentatively NAD - Submitter: Stephan T. Lavavej Opened: 2013-10-05 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.obs].

-

View all issues with Tentatively NAD status.

-

Discussion:

-

-20.8.1.2.4 [unique.ptr.single.observers]/3: "pointer operator->() const noexcept; Requires: get() != nullptr." -

-20.8.2.2.5 [util.smartptr.shared.obs]/2: "T& operator*() const noexcept; Requires: get() != 0." -

-20.8.2.2.5 [util.smartptr.shared.obs]/5: "T* operator->() const noexcept; Requires: get() != 0." -

-Narrow-contract functions should not be noexcept. -

- -

[2014-02-15 Issaquah]

- -

-Issue is contentious, raise to P2. -

- -

[2015-02 Cologne]

- -

-AM: This ship has sailed. JM: What's the issue? AM: operator-> has narrow contract and should never have had -noexcept. DK: Not quite. We explicitly called out that for shared_ptr this is fine. You said so in your -"narrow contract" paper. GR: This would be a fairly major regression in the design of {unique,shared}_ptr -over raw pointers; raw pointer dereferencing is noexcept. It's not a performance regression but a usability regression. -AM: Do we expect users to query noexpect on dereference expressions? Room: Yes. VV: We don't just expect it, we have -seen it. JM: Yes, users may be querying something like noexcept(x->y) and expect to be checking y, but -silently end up checking x->. -

-Close as NAD, with explanation from GR. -

- -Previous resolution [SUPERSEDED]: -
-

This wording is relative to N3691.

- -
    -

  1. In 20.8.1.2 [unique.ptr.single]/1, class template unique_ptr synopsis for single objects, change as indicated:

    - -
    -pointer operator->() const noexcept;
-
    -
    2. - -

  2. In 20.8.1.2.4 [unique.ptr.single.observers] change as indicated:

    - -
    -pointer operator->() const noexcept;
-
    -

    --3- Requires: get() != nullptr. -

    --4- Returns: get(). -

    --?- Throws: Nothing. -

    --5- Note: use typically requires that T be a complete type. -

    -
    -
    3. - -

  3. In 20.8.2.2 [util.smartptr.shared]/1, class template shared_ptr synopsis, change as indicated:

    - -
    -T& operator*() const noexcept;
-T* operator->() const noexcept;
-
    -
    4. - -

  4. In 20.8.2.2.5 [util.smartptr.shared.obs] change as indicated:

    - -
    -T& operator*() const noexcept;
-
    -

    --2- Requires: get() != 0. -

    --3- Returns: *get(). -

    --?- Throws: Nothing. -

    --4- Remarks: When T is void, it is unspecified whether this member function is declared. -If it is declared, it is unspecified what its return type is, except that the declaration (although not necessarily the -definition) of the function shall be well formed. -

    -
    - -
    -T* operator->() const noexcept;
-
    -

    --5- Requires: get() != 0. -

    --6- Returns: get(). -

    --?- Throws: Nothing. -

    -
    -
    5. - -
-
- -

[2015-03-03, Geoffrey provides rationale]

- -

-Rationale: -

-
-

-It is by design that these members are noexcept, and changing that now would be a substantial regression in functionality. -These classes were designed to substitute for plain pointers as transparently as possible, so since those operations are effectively -noexcept on plain pointers, they should be noexcept on unique_ptr and shared_ptr as well. -This matters in practice because we expect these members to be used fairly often inside the noexcept operator, and such -code could be broken by this change. These design considerations override our general policy against noexcept for -narrow-contract functions. -

-It is notable that N3279, which proposed this policy, did not propose striking noexcept from these operations. It's not -clear if the omission of operator* and operator-> was an oversight, or an intentional reflection of the above -considerations. N3279 was based on N3248 by the same authors, which states that: -

-
-

-"Most applications of noexcept for unique_ptr and shared_ptr are on functions with wide contracts. -However, there are preconditions on the atomic access functions, so these should lose the specification." -

-
-
- - - -

Proposed resolution:

- - - - - -
-

2338. [re.traits]/7 expects of locale facets something not guaranteed by [locale.facet]/4

-

Section: 28.7 [re.traits], 22.3.1.1.2 [locale.facet] Status: Open - Submitter: Sergey Zubkov Opened: 2013-10-15 Last modified: 2015-05-22

-

View all other issues in [re.traits].

-

View all issues with Open status.

-

Discussion:

-

-28.7 [re.traits]/7, begins with "if typeid(use_facet<collate<charT> >) == typeid(collate_byname<charT>)", -which appears to be pseudocode with the intention to convey that the collate facet has not been replaced by the user. Cf. the wording in -N1429 "there is no portable way to implement -transform_primary in terms of std::locale, since even if the sort key format returned by -std::collate_byname<>::transform is known and can be converted into a primary sort key, the user can still -install their own custom std::collate implementation into the locale object used, and that can use any sort key -format they see fit.". -

-Taken literally, 28.7 [re.traits]/7 appears to imply that named locales are required to hold their collate facets with -dynamic type std::collate_byname<charT>, which is in fact true in some implementations (e.g libc++), but not others -(e.g. libstdc++). This does not follow from the description of _byname in 22.3.1.1.2 [locale.facet]/4, which is only -required to provide equivalent semantics, to the named locale's facet, not to actually be one. -

- - -

[2015-05-06 Lenexa: Move to Open]

- - -

MC, RP: Consequence of failing to follow the rule is UB.

-

MC: Tightening of requirements.

-

RP: It should be this way, we just didn't impose it before.

-

MC: Second change is a bug fix, original code didn't work.

-

TK: Doesn't seem to make things worse.

-

Bring up in larger group tomorrow.

-

JW arrives.

-

JW: libstdc++ violates this due to two std::string ABIs.

-

JW: This prevents installing a type derived from Facet_byname, constrains the implementor from using a smarter derived class version.

-

JW: Can't look at facet id to detect replacement, because replacements have the same id.

-

RP: Can you give it multiple ids through multiple inheritance?

-

JW: No, the facet mechanism wouldn't like that.

-

JW: We should also ask Martin Sebor, he's implemented this stuff recently.

-

MC: Sounds like this resolution doesn't work, need a better solution.

-

JW: Write in words "if the facet has not been replaced by the user", the implementation knows how to detect that, but not like this.

-

RP: User RE traits need to detect this too.

-

JW: =(

-

Move to Open, JW will invite Martin Sebor to join LWG for discussion.

-

Later ...

-

JW: This is not needed for user specializations after all.

-

MC: Agree, [re.traits]/7 only applies to the stdlib traits.

-

NM: Effects: doesn't make sense.

-

JW, NM, Martin Sebor to come up with new wording.

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Modify 22.3.1.1.2 [locale.facet]/4 as indicated:

    - -

    -For some standard facets a standard "..._byname" class, derived from it, implements the virtual function -semantics equivalent toprovided by that facet of the locale constructed by locale(const char*) -with the same name. -Each such facet provides a constructor that takes a const char* argument, which names the locale, and a -refs argument, which is passed to the base class constructor. Each such facet also provides a constructor -that takes a string argument str and a refs argument, which has the same effect as calling the first -constructor with the two arguments str.c_str() and refs. If there is no "..._byname" -version of a facet, the base class implements named locale semantics itself by reference to other facets. For any -locale loc constructed by locale(const char*) and facet Facet that has a corresponding standard -Facet_byname class, typeid(use_facet<Facet>(loc)) == typeid(Facet_byname). -

    -
    2. - -

  2. Modify 28.7 [re.traits]/7 as indicated:

    - -
    -template <class ForwardIterator>
-  string_type transform_primary(ForwardIterator first, ForwardIterator last) const;
-
    -

    --7- Effects: if typeid(use_facet<collate<charT> >(getloc())) == typeid(collate_byname<charT>) -and the form of the sort key returned by collate_byname<charT>::transform(first, last) is known and -can be converted into a primary sort key then returns that key, otherwise returns an empty string. -

    -
    -
    3. - -
- - - - - -
-

2342. User conversion to wchar_t const* or to wchar_t not invoked for operator<<

-

Section: 27.7.3.1 [ostream] Status: New - Submitter: Alf P. Steinbach Opened: 2013-10-29 Last modified: 2015-04-08

-

View all other issues in [ostream].

-

View all issues with New status.

-

Discussion:

-

-For wide streams argument types wchar_t const* and wchar_t are supported only as template parameters. -User defined conversions are not considered for template parameter matching. Hence inappropriate overloads of -operator<< are selected when an implicit conversion is required for the argument, which is inconsistent -with the behavior for char const* and char, is unexpected, and is a useless result. -

-Demonstration: -

-
-#include <iostream>
-
-struct Byte_string
-{ 
-  operator char const*() const { return "Hurray, it works!"; } 
-};
-
-struct Wide_string
-{ 
-  operator wchar_t const*() const { return L"Hurray, it works!"; } 
-};
-
-struct Byte_ch
-{ 
-  operator char() const { return 'X'; } 
-};
-
-struct Wide_ch
-{ 
-  operator wchar_t() const { return L'X'; } 
-};
-
-auto main() -> int
-{
-  using namespace std;
-  wcout << "'X' as char value   : " << Byte_ch() << endl;
-  wcout << "'X' as wchar_t value: " << Wide_ch() << endl;
-  wcout << "Byte string pointer : " << Byte_string() << endl;
-  wcout << "Wide string pointer : " << Wide_string() << endl;
-}
-
-

-Example output: -

-
-'X' as char value   : X
-'X' as wchar_t value: 88
-Byte string pointer : Hurray, it works!
-Wide string pointer : 000803C8
-
- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 27.7.3.1 [ostream], class template basic_ostream synopsis, as indicated:

    - -
    -namespace std {
-[…]
-
-// 27.7.3.6.4 character inserters
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
-                                          charT);
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
-                                          char);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
-                                         char);
-template<class traits>
-  basic_ostream<wchar_t,traits>& operator<<(basic_ostream<wchar_t,traits>&,
-                                            wchar_t);
-[…]
-
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
-                                          const charT*);
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&,
-                                          const char*);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,
-                                         const char*);
-template<class traits>
-  basic_ostream<wchar_t,traits>& operator<<(basic_ostream<wchar_t,traits>&,
-                                            const wchar_t*);
-[…]
-}
-
-
    -
    2. - -

  2. Modify 27.7.3.6.4 [ostream.inserters.character] as indicated: [Drafting note: -The replacement of os by out in p1 and the insertion of "out." in p4 -just fix two obvious typos — end drafting note]

    - -
    -template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          charT c);
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          char c);
-// specialization
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         char c);
-template<class traits>
-  basic_ostream<wchar_t,traits>& operator<<(basic_ostream<wchar_t,traits>& out,
-                                            wchar_t c);
-
-// signed and unsigned
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                          signed char c);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                          unsigned char c);
-
    -

    --1- Effects: Behaves as a formatted output function (27.7.3.6.1 [ostream.formatted.reqmts]) of out. -Constructs a character sequence seq. If c has type char and the character type of the stream -is not char, then seq consists of out.widen(c); otherwise seq consists of c. -Determines padding for seq as described in 27.7.3.6.1 [ostream.formatted.reqmts]. Inserts seq into -out. Calls osout.width(0). -

    --2- Returns: out. -

    -
    -
    -template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          const charT* s);
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          const char* s);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const char* s);
-template<class traits>
-  basic_ostream<wchar_t,traits>& operator<<(basic_ostream<wchar_t,traits>& out,
-                                            const wchar_t* s);
-											
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const signed char* s);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const unsigned char* s);
-
    -

    --3- Requires: s shall not be a null pointer. -

    --4- Effects: Behaves like a formatted inserter (as described in 27.7.3.6.1 [ostream.formatted.reqmts]) of out. -Creates a character sequence seq of n characters starting at s, each widened using out.widen() -(27.5.5.3), where n is the number that would be computed as if by: -

    -
      -

    • -traits::length(s) for the following overloads: -

        -

      • -where the first argument is of type basic_ostream<charT, traits>& -and the second is of type const charT*, -

        • -

      • -and also for the overload where the first argument is of type -basic_ostream<char, traits>& and the second is of type const char*, -

        • -

      • -where the first argument is of type -basic_ostream<wchar_t, traits>& and the second is of type const wchar_t*, -

        • -
      -

      • -

    • -std::char_traits<char>::length(s) for the overload where the first argument is of type -basic_ostream<charT, traits>& and the second is of type const char*, -

      • -

    • -traits::length(reinterpret_cast<const char*>(s)) for the other two overloads. -

      • -
    -

    -Determines padding for seq as described in 27.7.3.6.1 [ostream.formatted.reqmts]. Inserts seq into -out. Calls out.width(0). -

    --5- Returns: out. -

    -
    -
    3. - -
- - - - - -
-

2343. Is the value of the ECMA-262 RegExp object's multiline property really false?

-

Section: 28.13 [re.grammar] Status: New - Submitter: Nayuta Taga Opened: 2013-10-30 Last modified: 2015-05-22

-

View all other issues in [re.grammar].

-

View all issues with New status.

-

Discussion:

-

-In the following "Multiline" is the value of the ECMA-262 RegExp object's multiline property. -

-In ECMA-262, -there are some definitions that relate to Multiline: -

-
    -

  • -ECMA-262 15.10.2.6: -

    -
    -

    -If Multiline is true, ^ matches just after LineTerminator. -

    -If Multiline is false, ^ does not match just after LineTerminator. -

    -If Multiline is true, $ matches just before LineTerminator. -

    -If Multiline is false, $ does not match just before LineTerminator. -

    -
    -
    • -
  • -

    -ECMA-262 15.10.4.1, 15.10.7.4: -

    -

    -By default, Multiline is false. -

    -
    • -
-

-So, the C++11 standard says that Multiline is false. As it is false, -^ matches only the beginning of the string, and $ matches only the end -of the string. -

-However, two flags are defined in 28.5.2 [re.matchflag] Table 139: -

-
-

-match_not_bol: the character ^ in the regular expression shall not match [first,first). -

-match_not_eol: the character "$" in the regular expression shall not match [last,last). -

-
-

-As Multiline is false, the match_not_bol and the match_not_eol are -meaningless because they only make ^ and $ match none. -

-In my opinion, Multiline should be true. -

-FYI, Multiline of the existing implementations are as follows: -

-Multiline=false: -

-
    -

  • -libstdc++ r206594 -

    • -

  • -libc++ r199174 -

    • -
-

-Multiline=true: -

-
    -

  • -Visual Studio Express 2013 -

    • -

  • -boost 1.55 -

    • -
- -

[2015-05-22, Daniel comments]

- -

-This issue interacts with LWG 2503. -

- - - -

Proposed resolution:

- - - - - -
-

2348. charT('1') is not the wide equivalent of '1'

-

Section: 20.6 [template.bitset], 27.7.6 [quoted.manip] Status: Open - Submitter: Zhihao Yuan Opened: 2013-12-02 Last modified: 2015-05-22

-

View other active issues in [template.bitset].

-

View all other issues in [template.bitset].

-

View all issues with Open status.

-

Discussion:

-

-Example: char16_t('1') != u'1' is possible. -

-The numeric value of char16_t is defined to be Unicode -code point, which is same to the ASCII value and UTF-8 for -7-bit chars. However, char is not guaranteed to have an -encoding which is compatible with ASCII. For example, '1' in EBCDIC is 241. -

-I found three places in the standard casting narrow char -literals: bitset::bitset, bitset::to_string and quoted. -

-PJ confirmed this issue and says he has a solution used -in their <filesystem> implementation, and he may want to -propose it to the standard. -

-The solution in my mind, for now, is to make those default -arguments magical, where the "magic" can be implemented -with a C11 _Generic selection (works in clang): -

-
-#define _G(T, literal) _Generic(T{}, \
-      char: literal, \
-      wchar_t: L ## literal, \
-      char16_t: u ## literal, \
-      char32_t: U ## literal)
-
-  _G(char16_t, '1') == u'1'
-
- -

[Lenexa 2015-05-05: Move to Open]

- -

Ask for complete PR (need quoted, to string, et al.)

-

Will then take it up again

-

Expectation is that this is correct way to fix this

- - -

Proposed resolution:

-

This wording is relative to N3797.

- -[Drafting note: This is a sample wording fixing only one case; - I'm just too lazy to copy-paste it before we discussed whether - the solution is worth and sufficient (for example, should the - other `charT`s like `unsigned char` just don't compile without - supplying those arguments? I hope so). — end drafting note] - -
    -

  1. Modify 20.6 [template.bitset] p1, class template bitset synopsis, as indicated:

    - -
    -namespace std {
-  template <size_t N> class bitset {
-  public:
-    […]
-    template<class charT, class traits, class Allocator>
-      explicit bitset(
-        const basic_string<charT,traits,Allocator>& str,
-        typename basic_string<charT,traits,Allocator>::size_type pos = 0,
-        typename basic_string<charT,traits,Allocator>::size_type n =
-          basic_string<charT,traits,Allocator>::npos,
-          charT zero = charT('0')see below, charT one = charT('1')see below);
-     […]
-  };
-  […]
-}
-
    -
    2. - -

  2. Modify 20.6.1 [bitset.cons] as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-explicit 
-bitset(const basic_string<charT, traits, Allocator>& str,
-       typename basic_string<charT, traits, Allocator>::size_type pos = 0,
-       typename basic_string<charT, traits, Allocator>::size_type n =
-         basic_string<charT, traits, Allocator>::npos,
-         charT zero = charT('0')see below, charT one = charT('1')see below);
-
    -

    --?- The default values of zero and one compare equal to the -character literals 0 and 1 of type charT, respectively. -

    --3- Requires:: pos <= str.size(). -

    -[…] -

    -
    -
    3. - -
- - - - - - -
-

2349. Clarify input/output function rethrow behavior

-

Section: 27.7.2.2.1 [istream.formatted.reqmts] Status: Open - Submitter: Zhihao Yuan Opened: 2013-12-06 Last modified: 2015-05-22

-

View all other issues in [istream.formatted.reqmts].

-

View all issues with Open status.

-

Discussion:

-

-The formatted input function requirement says in 27.7.2.2.1 [istream.formatted.reqmts]: -

-

-"If an exception is thrown during input then ios::badbit is turned on -in *this's error state. If (exceptions()&badbit) != 0 then the exception -is rethrown." -

-

-while some formatted function may throw an exception from basic_ios::clear, for example -in 20.6.4 [bitset.operators] p6: -

-

-"If no characters are stored in str, calls is.setstate(ios_base::failbit) (which may -throw ios_base::failure)" -

-

-So should this exception be considered as "an exception [...] thrown -during input"? And here is an implementation divergence (or you -can read the following as "a bug libc++ only has" :) -

-
-cin.exceptions(ios_base::failbit);
-bitset<N> b;
-try {
-  cin >> b;  // type 'a' and return
-} catch (...)
-{}
-
-

-Now cin.rdstate() is just failbit in libstdc++ (and Dinkumware, by -PJ), but failbit & badbit libc++. Similar difference found in other -places, like eofbit & badbid after std::getline. -

-PJ and Matt both agree that the intention (of badbit + rethrow) is -"to signify an exception arising in user code, not the iostreams package". -

-In addition, I found the following words in unformatted input -function's requirements (27.7.2.3 [istream.unformatted]): -

-

-If an exception is thrown during input then ios::badbit is turned on -in *this's error state. (Exceptions thrown from basic_ios<>::clear() -are not caught or rethrown.) If (exceptions()&badbit) != 0 then the -exception is rethrown. -

-

-The content within the parenthesis is added by LWG defect 61, -and does fix the ambiguity. However, it only fixed the 1 of 4 -requirements, and it lost some context (the word "rethrown" is not -seen before this sentence within this section). -

- -

[Lenexa 2015-05-07: Marshall to research and report]

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -[Drafting note: The editor is kindly asked to introduce additional spaces at the following marked occurrences of -operator& — end drafting note] - -
    -

  1. Modify 27.7.2.2.1 [istream.formatted.reqmts] p1 as indicated:

    - -

    --1- Each formatted input function begins execution by constructing an object of class sentry with the noskipws -(second) argument false. If the sentry object returns true, when converted to a value of type bool, the -function endeavors to obtain the requested input. If an exception, other than the ones thrown from clear(), if any, -is thrown during input then ios::badbit -is turned on[Footnote 314] in *this's error state. If (exceptions() & badbit) != 0 -then the exception is rethrown. -In any case, the formatted input function destroys the sentry object. If no exception has been thrown, it returns *this. -

    -
    2. - -

  2. Modify 27.7.3.6.1 [ostream.formatted.reqmts] p1 as indicated:

    - -

    --1- Each formatted output function begins execution by constructing an object of class sentry. If this object -returns true when converted to a value of type bool, the function endeavors to generate the requested -output. If the generation fails, then the formatted output function does setstate(ios_base::failbit), -which might throw an exception. If an exception, other than the ones thrown from clear(), if any, is thrown -during output, then ios::badbit is turned on[Footnote 327] -in *this's error state. If (exceptions() & badbit) != 0 then the exception is rethrown. -Whether or not -an exception is thrown, the sentry object is destroyed before leaving the formatted output function. If no -exception is thrown, the result of the formatted output function is *this. -

    -
    3. - -

  3. Modify 27.7.3.7 [ostream.unformatted] p1 as indicated:

    - -

    --1- Each unformatted output function begins execution by constructing an object of class sentry. If this object -returns true, while converting to a value of type bool, the function endeavors to generate the requested -output. If an exception, other than the ones thrown from clear(), if any, is thrown during output, -then ios::badbit is turned on[Footnote 330] in *this's error state. -If (exceptions() & badbit) != 0 then the exception is rethrown. In any case, the unformatted output -function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified -for the unformatted output function. -

    -
    4. - -

  4. Modify 27.7.2.3 [istream.unformatted] p1 as indicated:

    - -

    --1- Each unformatted input function begins execution by constructing an object of class sentry with the default -argument noskipws (second) argument true. If the sentry object returns true, when converted to a value -of type bool, the function endeavors to obtain the requested input. Otherwise, if the sentry constructor exits -by throwing an exception or if the sentry object returns false, when converted to a value of type bool, the -function returns without attempting to obtain any input. In either case the number of extracted characters -is set to 0; unformatted input functions taking a character array of non-zero size as an argument shall also -store a null character (using charT()) in the first location of the array. If an exception, other than the -ones thrown from clear(), if any, is thrown during input -then ios::badbit is turned on[Footnote 317] in *this's error state. (Exceptions thrown from -basic_ios<>::clear() are not caught or rethrown.) If (exceptions() & badbit) != 0 -then the exception is rethrown. It also counts the number of characters extracted. If no exception has been thrown it ends -by storing the count in a member object and returning the value specified. In any event the sentry object is destroyed -before leaving the unformatted input function. -

    -
    5. - -
- - - - - - -
-

2352. Is a default-constructed std::seed_seq intended to produce a predictable .generate()?

-

Section: 26.5.7.1 [rand.util.seedseq] Status: New - Submitter: Thomas Plum Opened: 2013-12-02 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with New status.

-

Discussion:

-

-With respect to class seed_seq 26.5.7.1 [rand.util.seedseq], is a default-constructed -std::seed_seq intended to produce a predictable .generate() sequence? -

-Implementations differ. -

- - - -

Proposed resolution:

- - - - - -
-

2353. std::next is over-constrained

-

Section: 24.4.4 [iterator.operations] Status: Ready - Submitter: Eric Niebler Opened: 2013-12-24 Last modified: 2015-05-22

-

View all other issues in [iterator.operations].

-

View all issues with Ready status.

-

Discussion:

-

-In LWG 1011, std::next and std::prev were changed -from accepting InputIterator to accepting -ForwardIterator. This needlessly excludes perfectly legitimate use -cases. Consider the following hypothetical range-based implementation of -drop, which creates a view of a range without the first n elements: -

-
-template<typename Distance, typename InputRange>
-iterator_range<range_iterator_t<InputRange>>
-drop(Distance n, InputRange& rng)
-{
-  return make_iterator_range(
-    std::next(std::begin(rng), n),
-    std::end(rng)
-  );
-}
-
-

-I believe this to be a legitimate use case that is currently outlawed by -the standard without cause. See the discussion beginning at -c++std-lib-35313 -for an in-depth discussion of the issue, in which -Howard Hinnant agreed that it was a defect. -

-(Some discussion then ensued about whether an overload should be added -that only accepts rvalue InputIterators to avoid the surprise that issue -1011 sought to address. I make no such attempt, nor do I believe it to -be necessary.) -

-Suggested resolution: -

-Back out the resolution of 1011. -

- -

[Lenexa 2015-05-07: Move to Ready]

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Change 24.3 [iterator.synopsis], header <iterator> synopsis, and 24.4.4 [iterator.operations] -before p.6 as indicated:

    - -
    -template <class ForwardInputIterator>
-  ForwardInputIterator next(ForwardInputIterator x,
-    typename std::iterator_traits<ForwardInputIterator>::difference_type n = 1);
-
    -
    2. - -
- - - - - -
-

2358. Apparently-bogus definition of is_empty type trait

-

Section: 20.10.4.3 [meta.unary.prop] Status: New - Submitter: Richard Smith Opened: 2014-02-01 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with New status.

-

Discussion:

-

-The 'Condition' for std::is_empty is listed as: -

-

-"T is a class type, but not a union type, with no non-static data members other than bit-fields of length 0, -no virtual member functions, no virtual base classes, and no base class B for which is_empty<B>::value -is false." -

-

-This is incorrect: there is no such thing as a non-static data member that is a bit-field of length 0, since bit-fields of -length 0 must be unnamed, and unnamed bit-fields are not members (see 9.6 [class.bit] p2). -

-It also means that classes such as: -

-
-struct S {
- int : 3;
-};
-
-

-are empty (because they have no non-static data members). There's implementation divergence on the value of -is_empty<S>::value. -

-I'm not sure what the purpose of is_empty is (or how it could be useful), but if it's desirable for the above type to -not be treated as empty, something like this could work: -

-

-"T is a class type, but not a union type, with no non-static data members other than, no unnamed -bit-fields of non-zero length 0, no virtual member functions, no virtual base classes, and no base class -B for which is_empty<B>::value is false." -

-

-and if the above type should be treated as empty, then this might be appropriate: -

-

-"T is a class type, but not a union type, with no (named) non-static data members other than bit-fields of -length 0, no virtual member functions, no virtual base classes, and no base class B for which -is_empty<B>::value is false." -

- - - -

Proposed resolution:

- - - - - -
-

2362. unique, associative emplace() should not move/copy the mapped_type constructor arguments when no insertion happens

-

Section: 23.2.4 [associative.reqmts], 23.2.5 [unord.req] Status: New - Submitter: Jeffrey Yasskin Opened: 2014-02-15 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with New status.

-

Discussion:

-

-a_uniq.emplace(args) is specified as: -

- -

-Effects: Inserts a value_type object t constructed with
-std::forward<Args>(args)... if and only if there is no element in the
-container with key equivalent to the key of t. The bool component of
-the returned pair is true if and only if the insertion takes place,
-and the iterator component of the pair points to the element with key
-equivalent to the key of t. -

- -

-However, we occasionally find code of the form: -

- -
-std::unique_ptr<Foo> p(new Foo);
-auto res = m.emplace("foo", std::move(p));
-
- -

-where we'd like to avoid destroying the Foo if the insertion doesn't -take place (if the container already had an element with the specified key). -

-N3873 includes -a partial solution to this in the form of a new emplace_stable member function, but LEWG's -discussion strongly agreed that we'd rather have emplace() Just Work: -

-Should map::emplace() be guaranteed not to move/copy its arguments if the insertion doesn't happen? -

-SF: 8 F: 3 N: 0 A: 0 SA: 0 -

-This poll was marred by the fact that we didn't notice or call out -that emplace() must construct the key before doing the lookup, and it -must not then move the key after it determines whether an insert is -going to happen, and the mapped_type instance must live next to the key. -

-The very similar issue 2006 was previously marked NAD, with -N3178 as -discussion. However, given LEWG's interest in the alternate behavior, -we should reopen the question in this issue. -

-We will need a paper that describes how to implement this before we can make more progress. -

- - - -

Proposed resolution:

- - - - - -
-

2363. Defect in 30.4.1.4.1 [thread.sharedtimedmutex.class]

-

Section: 30.4.1.5.1 [thread.sharedtimedmutex.class] Status: Open - Submitter: Richard Smith Opened: 2014-02-16 Last modified: 2015-05-08

-

View all issues with Open status.

-

Discussion:

-

-30.4.1.5.1 [thread.sharedtimedmutex.class] paragraph 2: -

-

The class shared_timed_mutex shall satisfy all of the -SharedTimedMutex requirements (30.4.1.4). It shall be a standard layout class (Clause 9). -

-

-There's no SharedTimedMutex requirements; this name doesn't appear anywhere else in the standard. (Prior to N3891, -this was SharedMutex, which was equally undefined.) -

-I assume this concept should be defined somewhere? -

-Also, n3891 changes 30.4.1.5 [thread.sharedtimedmutex.requirements] from defining "shared mutex type" to defining -"shared timed mutex type", but its paragraph 2 still talks about "shared mutex type". Is that OK? I think you could argue -that it's clear enough what it means, but presumably it should use the term that paragraph 1 defined. -

-30.4.2.3 [thread.lock.shared] paragraph 1 talks about the "shared mutex requirements", which again is a term that isn't -defined, and presumably means "the requirements on a shared timed mutex type" or similar (maybe if SharedMutex or -SharedTimedMutex were defined it could be reused here). -

- -

[2014-05-22, Daniel comments]

- -

-As for SharedTimedMutex, there exists a similar problem in regard to TimedMutex referred to in -30.4.1.3.1 [thread.timedmutex.class] p2 and in 30.4.1.3.2 [thread.timedmutex.recursive] p2, but nowhere defined. -

-Another problem is, that according to 30.4.1.2.1 [thread.mutex.class] p3, "The class mutex shall satisfy all the -Mutex requirements (30.4.1 [thread.mutex.requirements]).", but there are no concrete Mutex requirements, -30.4.1 [thread.mutex.requirements] — titled as "Mutex requirements" — describes mutex types, -timed mutex types, and shared timed mutex types. -

- -

[2014-06-08, Daniel comments and provides wording]

- -

-The presented wording adds to the existing mutex types, timed mutex types, and shared timed mutex types -terms a new set of corresponding MutexType, TimedMutexType, and SharedTimedMutexType requirements. -

-The reason for the change of requirement names is two-fold: First, the new name better matches the intention to have a concrete -name for the requirements imposed on the corresponding mutex types (This kind of requirement deviate from the more general -Lockable requirements, which are not restricted to a explicitly enumerated set of library types). Second, using -**MutexType over **Mutex provides the additional advantage that it reduces the chances of confusing named -requirements from template parameters named Mutex (such as for unique_lock or shared_lock). -

-Nonetheless the here presented wording has one unfortunate side-effect: Once applied it would have the effect that types -used to instantiate std::shared_lock cannot be user-defined shared mutex types due to 30.4.2.3 [thread.lock.shared]. -The reason is based on the currently lack of an existing SharedLockable requirement set, which would complete the -existing BasicLockable and Lockable requirements (which are "real" requirements). This restriction is not -actually a problem introduced by the provided resolution but instead one that existed before but becomes more obvious now. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-Thanks to Daniel, and please put it in SG1-OK status. Perhaps open another issue for the remaining problem Daniel points out? -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 30.4.1.2 [thread.mutex.requirements.mutex] as indicated:

    - -

    --1- The mutex types are the standard library types std::mutex, std::recursive_mutex, std::timed_mutex, -std::recursive_timed_mutex, and std::shared_timed_mutex. They shall meet the MutexType -requirements set out in this section. In this description, m denotes an object of a mutex type. -

    -
    2. - -

  2. Change 30.4.1.2.1 [thread.mutex.class] as indicated:

    - -

    --3- The class mutex shall satisfy all the MutexType requirements -(30.4.1.2 [thread.mutex.requirements.mutex]30.4.1 [thread.mutex.requirements]). -It shall be a standard-layout class (Clause 9). -

    -
    3. - -

  3. Change 30.4.1.2.2 [thread.mutex.recursive] as indicated:

    - -

    --2- The class recursive_mutex shall satisfy all the MutexMutexType requirements -(30.4.1.2 [thread.mutex.requirements.mutex]30.4.1 [thread.mutex.requirements]). -It shall be a standard-layout class (Clause 9). -

    -
    4. - -

  4. Change 30.4.1.3 [thread.timedmutex.requirements] as indicated:

    - -

    --1- The timed mutex types are the standard library types std::timed_mutex, std::recursive_timed_mutex, -and std::shared_timed_mutex. They shall meet the TimedMutexType requirements set out below. -In this description, m denotes an object of a mutex type, rel_time denotes an object of an instantiation of -duration (20.12.5), and abs_time denotes an object of an instantiation of time_point (20.12.6). -

    -
    5. - -

  5. Change 30.4.1.3.1 [thread.timedmutex.class] as indicated:

    - -

    --2- The class timed_mutex shall satisfy all of the TimedMutexType requirements -(30.4.1.3 [thread.timedmutex.requirements]). It shall be a standard-layout class (Clause 9). -

    -
    6. - -

  6. Change 30.4.1.3.2 [thread.timedmutex.recursive] as indicated:

    - -

    --2- The class recursive_timed_mutex shall satisfy all of the TimedMutexType requirements -(30.4.1.3 [thread.timedmutex.requirements]). It shall be a standard-layout class (Clause 9). -

    -
    7. - -

  7. Change 30.4.1.5 [thread.sharedtimedmutex.requirements] as indicated: [Drafting note: The reference to the -timed mutex types requirements has been moved after introducing the new requirement set to ensure that -SharedTimedMutexType refine TimedMutexType.]

    - -
    -

    --1- The standard library type std::shared_timed_mutex is a shared timed mutex type. Shared timed mutex -types shall meet the SharedTimedMutexType requirements of timed mutex types -(30.4.1.3 [thread.timedmutex.requirements]), and additionally shall meet the requirements set out below. In this -description, m denotes an object of a mutex type, rel_type denotes -an object of an instantiation of duration (20.12.5), and abs_time denotes an object of an instantiation of -time_point (20.12.6). -

    --?- The shared timed mutex types shall meet the TimedMutexType requirements (30.4.1.3 [thread.timedmutex.requirements]). -

    -
    -
    8. - -

  8. Change 30.4.1.5.1 [thread.sharedtimedmutex.class] as indicated:

    - -

    --2- The class shared_timed_mutex shall satisfy all of the SharedTimedMutexType requirements -(30.4.1.5 [thread.sharedtimedmutex.requirements]). It shall be a standard-layout class (Clause 9). -

    -
    9. - -

  9. Change 30.4.2.3 [thread.lock.shared] as indicated: [Drafting note: Once -N3995 has been applied, the following -reference should be changed to the new SharedMutexType requirements ([thread.sharedmutex.requirements]) or -even better to some new SharedLockable requirements (to be defined) — end drafting note]

    - -

    --1- […] The supplied Mutex type shall meet the shared mutexSharedTimedMutexType requirements -(30.4.1.5 [thread.sharedtimedmutex.requirements]). -

    --2- [Note: shared_lock<Mutex> meets the TimedLockable requirements -(30.2.5.4). — end note] -

    -
    10. -
- - - - - - -
-

2366. istreambuf_iterator end-of-stream equality

-

Section: 24.6.3 [istreambuf.iterator] Status: New - Submitter: Hyman Rosen Opened: 2014-02-19 Last modified: 2015-04-08

-

View all other issues in [istreambuf.iterator].

-

View all issues with New status.

-

Discussion:

-

-Given the following code, -

-
-#include <sstream>
-
-std::stringbuf buf;
-std::istreambuf_iterator<char> begin(&buf);
-std::istreambuf_iterator<char> end;
-
-

-it is not clear from the wording of the Standard whether begin.equal(end) -must be true. In at least one implementation it is not (CC: Sun C++ 5.10 SunOS_sparc Patch 128228-25 2013/02/20) and in at least -one implementation it is (gcc version 4.3.2 x86_64-unknown-linux-gnu). -

-24.6.3 [istreambuf.iterator] says that end is an end-of-stream iterator since it was default -constructed. It also says that an iterator becomes equal to an end-of-stream -iterator when end of stream is reached by sgetc() having returned eof(). -24.6.3.5 [istreambuf.iterator::equal] says that equal() returns true iff both iterators are end of stream -or not end of stream. But there seems to be no requirement that equal check for end-of-stream by calling sgetc(). -

-Jiahan Zi at BloombergLP discovered this issue through his code failing to -work correctly. Dietmar Kühl has opined in a private communication that -the iterators should compare equal. -

- - - -

Proposed resolution:

- - - - - -
-

2367. pair and tuple are not correctly implemented for is_constructible with no args

-

Section: 20.10.4.3 [meta.unary.prop] Status: Ready - Submitter: Howard Hinnant Opened: 2014-02-19 Last modified: 2015-05-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with Ready status.

-

Discussion:

-

-Consider: -

-
-struct X
-{
-  X() = delete;
-};
-
-int main()
-{
-  typedef std::pair<int, X> P;
-  static_assert(!std::is_constructible<P>::value, "");
-  static_assert(!std::is_default_constructible<P>::value, "");
-  typedef std::tuple<int, X> T;
-  static_assert(!std::is_constructible<T>::value, "");
-  static_assert(!std::is_default_constructible<T>::value, "");
-}
-
-

-For me these static_asserts fail. And worse than that, even asking the question fails (as opposed to gets the wrong answer): -

-
-assert(!std::is_constructible<P>::value);
-
-

-In file included from test.cpp:2: -

-
-error:
-      call to deleted constructor of 'X'
-   pair() : first(), second() {}
-                     ^
-note: function has been explicitly marked deleted here
-    X() = delete;
-    ^
-1 error generated.
-
-

-This can be solved by specializing is_constructible on pair and tuple for zero Args: -

-
-template <class T, class U>
-struct is_constructible<pair<T, U>>
-  : integral_constant<bool, is_default_constructible<T>::value &&
-                            is_default_constructible<U>::value>
-{};
-
-template <class ...T>
-struct is_constructible<tuple<T...>>
-  : integral_constant<bool,
-                      __all<is_default_constructible<T>::value...>::value>
-{};
-
-

-Now everything just works. -

- -

[2014-05-14, Daniel comments]

- - -

-The proposed resolution is incomplete, because it wouldn't work for cv-qualified objects of -pair or for references of them during reference-initialization. -

-I would like to point out that the approach suggested in N3739 -can be easily extended to solve the problem without need to muddle with specializing is_constructible: -

-
-template<class U1 = T1, class U2 = T2,
-  typename enable_if<
-    is_default_constructible<U1>::value && is_default_constructible<U2>::value
-  , bool>::type = false
->
-constexpr pair();
-
-

-The new wording proposal represents an alternative wording change that I would strongly prefer. -

- -Previous resolution from Howard [SUPERSEDED]: -

-

-

This wording is relative to N3936.

- -
    -

  1. Add to 20.3.3 [pairs.spec]:

    - -
    -
    -template <class T, class U>
-struct is_constructible<pair<T, U>>
-  : integral_constant<bool, is_default_constructible<T>::value &&
-                            is_default_constructible<U>::value>
-{};
-
    -
    -
    2. - -

  2. Add to 20.4.2.9 [tuple.special]:

    - -
    -
    -template <class ...T>
-struct is_constructible<tuple<T...>>
-  : integral_constant<bool, see below>
-{};
-
    -

    --?- The second argument to integral_constant shall be true if for each T, -is_default_constructible<T>::value is true. -

    -
    -
    -
    3. -
-
- -

[2015-05, Lenexa]

- -

-STL: I object to this resolution due to British spelling of behavior
-JW: we already have other places of this spelling
-VV: the easy resolution is to remove the notes
-MC: if that's all we want to change: put it in and make the editorial change of removing the note
-VV: the other paper doesn't make any of these changes so it would be consistent
-JW: this make me want even more the features of having constructors doing the Right Thing -- I haven't written up the request to do something like that
-VV: so it would be an aggregate reflecting the properties of the constituting types
-JW: I should write that up
-MC: any objection to move to ready? in favor: 16, opposed: 0, abstain: 1 -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.3.2 [pairs.pair] around p3 as indicated:

    - -
    -constexpr pair();
-
    -
    -

    --3- Requires: is_default_constructible<first_type>::value is true and -is_default_constructible<second_type>::value is true. -

    --4- Effects: Value-initializes first and second. -

    --?- Remarks: This constructor shall not participate in overload resolution unless -is_default_constructible<first_type>::value is true and -is_default_constructible<second_type>::value is true. [Note: This behaviour can be implemented -by a constructor template with default template arguments — end note]. -

    -
    -
    -
    2. - -

  2. Change 20.4.2.1 [tuple.cnstr] around p4 as indicated:

    - -
    -constexpr tuple();
-
    -
    -

    --4- Requires: is_default_constructible<Ti>::value is true for all i. -

    --5- Effects: Value initializes each element. -

    --?- Remarks: This constructor shall not participate in overload resolution unless -is_default_constructible<Ti>::value is true for all i. [Note: This behaviour can -be implemented by a constructor template with default template arguments — end note]. -

    -
    -
    -
    3. -
- - - - - - -
-

2368. Replacing global operator new

-

Section: 18.6.1 [new.delete] Status: New - Submitter: Stephen Clamage Opened: 2014-02-20 Last modified: 2015-04-08

-

View all other issues in [new.delete].

-

View all issues with New status.

-

Discussion:

-

-Section 18.6.1 [new.delete] and subsections shows: -

-
-void* operator new(std::size_t size);
-void* operator new[](std::size_t size);
-
-

-That is, without exception-specifications. (Recall that C++03 specified these functions with throw(std::bad_alloc).) -

-Section 17.6.5.12 [res.on.exception.handling] the end of paragraph 4 says: -

-

-Any other functions defined in the C++ standard library that do not have an exception-specification may throw implementation-defined -exceptions unless otherwise specified. An implementation may strengthen this implicit exception-specification by adding an explicit one. -

-

-For example, an implementation could provide C++03-compatible declarations of operator new. -

-Programmers are allowed to replace these operator new functions. But how can you write the definition of these functions when -the exception specification can vary among implementations? For example, the declarations -

-
-void* operator new(std::size_t size) throw(std::bad_alloc);
-void* operator new(std::size_t size);
-
-

-are not compatible. -

-From what I have been able to determine, gcc has a hack for the special case of operator new to ignore the differences in -(at least) the two cases I show above. But can users expect all compilers to quietly ignore the incompatibility? -

-The blanket permission to add any explicit exception specification could cause a problem for any user-overridable function. -Different implementations could provide incompatible specifications, making portable code impossible to write. -

- - - -

Proposed resolution:

- - - - - -
-

2370. Operations involving type-erased allocators should not be noexcept in std::function

-

Section: 20.9.12.2 [func.wrap.func] Status: Open - Submitter: Pablo Halpern Opened: 2014-02-27 Last modified: 2015-05-05

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with Open status.

-

Discussion:

-

-The following constructors in 20.9.12.2 [func.wrap.func] are declared noexcept, even -though it is not possible for an implementation to guarantee that they will not throw: -

- -
-template <class A> function(allocator_arg_t, const A&) noexcept;
-template <class A> function(allocator_arg_t, const A&, nullptr_t) noexcept;
-
- -

-In addition, the following functions are guaranteed not to throw if the target -is a function pointer or a reference_wrapper: -

- -
-template <class A> function(allocator_arg_t, const A& a, const function& f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
- -

-In all of the above cases, the function object might need to allocate memory -(an operation that can throw) in order to hold a copy of the type-erased -allocator itself. The first two constructors produce an empty function -object, but the allocator is still needed in case the object is later assigned -to. In this case, we note that the propagation of allocators on assignment is -underspecified for std::function. There are three possibilities: -

- -
    -

  1. The allocator is never copied on copy-assignment, moved on move-assignment, or swapped on swap.

    -
    2. - -

  2. The allocator is always copied on copy-assignment, moved on move-assignment, and swapped on swap.

    -
    3. - -

  3. Whether or not the allocator is copied, moved, or swapped is determined at - run-time based on the propagate_on_container_copy_assignment and - propagate_on_container_move_assignment traits of the allocators at - construction of the source function, the target function, or both.

    -
    4. -
- -

-Although the third option seems to be the most consistent with existing -wording in the containers section of the standard, it is problematic in a -number of respects. To begin with, the propagation behavior is determined at -run time based on a pair of type-erased allocators, instead of at compile -time. Such run-time logic is not consistent with the rest of the standard -and is hard to reason about. Additionally, there are two allocator types -involved, rather than one. Any set of rules that attempts to rationally -interpret the propagation traits of both allocators is likely to be arcane -at best, and subtly wrong for some set of codes at worst. -

- -

-The second option is a non-starter. Historically, and in the vast majority of -existing code, an allocator does not change after an object is constructed. -The second option, if adopted, would undermine the programmer's ability to -construct, e.g., an array of function objects, all using the same allocator. -

- -

-The first option is (in Pablo's opinion) the simplest and best. It is -consistent with historical use of allocators, is easy to understand, and -requires minimal wording. It is also consistent with the wording in N3916, -which formalizes type-erased allocators. -

- -

-For cross-referencing purposes: The resolution of this issue should be -harmonized with any resolution to LWG 2062, which questions the noexcept -specification on the following member functions of std::function: -

- -
-template <class F> function& operator=(reference_wrapper<F>) noexcept;
-void swap(function&) noexcept;
-
- -

[2015-05, Lenexa]

- -

-MC: change to P3 and status to open. -

-STL: note that noexcept is an issue and large chunks of allocator should be destroyed. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.9.12.2 [func.wrap.func], class template function synopsis, as indicated:

    - -
    -template <class A> function(allocator_arg_t, const A&) noexcept;
-template <class A> function(allocator_arg_t, const A&, nullptr_t) noexcept;
-
    -
    2. - -

  2. Change 20.9.12.2.1 [func.wrap.func.con] as indicated:

    - -
    -

    --1- When any function constructor that takes a first argument of type allocator_arg_t is invoked, the second -argument shall have a type that conforms to the requirements for Allocator (Table 17.6.3.5). A copy of the -allocator argument is used to allocate memory, if necessary, for the internal data structures of the constructed -function object. For the remaining constructors, an instance of allocator<T>, for some suitable type -T, is used to allocate memory, if necessary, for the internal data structures of the constructed function object. -

    - -
    -function() noexcept;
-template <class A> function(allocator_arg_t, const A&) noexcept;
-
    - -
    -

    --2- Postconditions: !*this. -

    -
    - -
    -function(nullptr_t) noexcept;
-template <class A> function(allocator_arg_t, const A&, nullptr_t) noexcept;
-
    - -

    --3- Postconditions: !*this. -

    - -
    -function(const function& f);
-template <class A> function(allocator_arg_t, const A& a, const function& f);
-
    - -

    --4- Postconditions: !*this if !f; otherwise, *this targets a copy of f.target(). -

    - -

    --5- Throws: shall not throw exceptions if f's target is a callable object passed -via reference_wrapper or a function pointer. Otherwise, may throw bad_alloc -or any exception thrown by the copy constructor of the stored callable -object. [Note: Implementations are encouraged to avoid the use of -dynamically allocated memory for small callable objects, for example, where -f's target is an object holding only a pointer or reference to an object and -a member function pointer. — end note] -

    - -
    -template <class A> function(allocator_arg_t, const A& a, const function& f);
-
    - -

    --?- Postconditions: !*this if !f; otherwise, *this targets a copy of f.target(). -

    - -
    -function(function&& f);
-template <class A> function(allocator_arg_t, const A& a, function&& f);
-
    - -

    --6- Effects: If !f, *this has no target; otherwise, move-constructs the target -of f into the target of *this, leaving f in a valid state with an -unspecified value. If an allocator is not specified, the constructed function will use the same allocator as f. -

    - -
    -template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
    - -
    -

    --7- Requires: F shall be CopyConstructible. -

    --8- Remarks: These constructors shall not participate in overload resolution unless f is Callable (20.9.11.2) -for argument types ArgTypes... and return type R. -

    - -

    --9- Postconditions: !*this if any of the following hold: -

    -
      -

    • f is a null function pointer value.

      • -

    • f is a null member pointer value.

      • -

    • F is an instance of the function class template, and !f

      • -
    - -

    --10- Otherwise, *this targets a copy of f initialized with std::move(f). -[Note: Implementations are encouraged to avoid the use of dynamically -allocated memory for small callable objects, for example, where f's target -is an object holding only a pointer or reference to an object and a member -function pointer. — end note] -

    - -

    --11- Throws: shall not throw exceptions when an allocator is not specified -and f is a function pointer or a reference_wrapper<T> for some -T. Otherwise, may throw bad_alloc or any exception thrown by F's copy or -move constructor or by A's allocate function. -

    -
    - -
    -
    3. - -
- - - - - -
-

2372. Assignment from int to std::string

-

Section: 21.4 [basic.string] Status: LEWG - Submitter: Andrzej Krzemieński Opened: 2014-03-13 Last modified: 2015-05-22

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with LEWG status.

-

Discussion:

-

-The following code works in C++: -

-
-int i = 300;
-std::string threeHundred;
-threeHundred = i;
-
-

-"Works" == "Compiles and doesn't have an undefined behavior". But it may not be obvious and in fact misleading what it does. -This assignment converts an int to char and then uses string's assignment from char. While -the assignment from char can be considered a feature, being able to assign from an int looks like a safety gap. Someone -may believe C++ works like "dynamically typed" languages and expect a lexical conversion to take place. -

-Ideally the assignment from char could be deprecated and later removed, but as a less intrusive alternative one could -consider adding a SFINAEd deleted function template: -

-
-template <typename IntT> // enable if is_integral<IntT>::value
-basic_string& operator=(IntT) = delete;
-
- -

[Lenexa 2015-06-06: Move to LEWG]

- -

RS: std::string x('0' + n); broken by this.

-

MC: This is an extension, move to LEWG.

-

Move to LEWG, consensus.

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. To 21.4 [basic.string], class template basic_string synopsis, add as indicated:

    - -
    -basic_string& operator=(const basic_string& str);
-basic_string& operator=(basic_string&& str) noexcept;
-basic_string& operator=(const charT* s);
-basic_string& operator=(charT c);
-template <class IntT> basic_string& operator=(IntT i) = delete;
-basic_string& operator=(initializer_list<charT>);
-
    -
    2. - -

  2. Add after 21.4.2 [string.cons] p26 as indicated:

    - -
    -
    -basic_string& operator=(charT c);
-
    -
    -

    --26- Returns: *this = basic_string(1,c). -

    -
    - -
    -template <class IntT> basic_string& operator=(IntT i) = delete;
-
    -
    -

    --?- Remarks: This signature shall not participate in overload resolution unless is_integral<T>::value is -true. -

    -
    -
    - -
    3. - -
- - - - - -
-

2375. Is [iterator.requirements.general]/9 too broadly applied?

-

Section: 24.2.1 [iterator.requirements.general] Status: New - Submitter: Marshall Clow Opened: 2014-03-25 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

-

-24.2.1 [iterator.requirements.general] p9 says: -

-

-Destruction of an iterator may invalidate pointers and references previously obtained from that iterator. -

-

-But the resolution of LWG issue 2360 specifically advocates returning *--temp; where temp is a -local variable. -

-And 24.2.5 [forward.iterators] p6 says: -

-

-If a and b are both dereferenceable, then a == b if and only if *a and *b are bound -to the same object. -

-

-which disallows "stashing" iterators (i.e, iterators that refer to data inside themselves). -

-So, I suspect that the restriction in p9 should only apply to input iterators, and can probably be moved into -24.2.3 [input.iterators] instead of 24.2.1 [iterator.requirements.general]. -

- -

[2014-05-22, Daniel comments]

- - -

-Given that forward iterators (and beyond) are refinements of input iterator, moving this constraint to input iterators won't help -much because it would still hold for all refined forms. -

- - - -

Proposed resolution:

- - - - - -
-

2379. Obtaining native handle of the current thread

-

Section: 30.2.3 [thread.req.native], 30.3.2 [thread.thread.this] Status: Open - Submitter: Matt Austern Opened: 2014-03-31 Last modified: 2015-05-08

-

View all issues with Open status.

-

Discussion:

-

-Class thread contains an implementation-defined type thread::native_handle_type, and an implementation-defined -function thread::native_handle() that returns a value of that type. The presence and semantics of those members is -implementation-defined; the intention is that they can be used for interoperability with libraries that rely on operating system -specific features. (Posix libraries that accept arguments of type pthread_t, for example.) -

-Unfortunately, there appears to be no native handle support for the equivalent of pthread_self(). We can use -this_thread::get_id() to obtain the thread::id of the current thread, but there is no mechanism for converting -a thread::id to a thread::native_handle. -

-Proposed wording: -

-In 30.3.2 [thread.thread.this] add: -

-
-thread::native_handle_type native_handle(); // See 30.2.3
-
-

- to the this_thread namespace synopsis. -

-Rationale: -

-Informally, we could address this issue either by adding a new function in this_thread or by providing a mechanism for converting -between thread::id and thread::native_handle. I propose the former because it seems more localized, and doesn't involve -saying anything more about implementation defined native functionality than we currently do. -

-It's intentional that the proposed resolution adds a declaration of native_handle() without adding a paragraph explaining what -it does. This is because everything about native_handle() is implementation-defined. The standard does the same thing in -30.3.1.5 [thread.thread.member]. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-Strong "don't care" reaction from SG1, after pointing out that this only matters in non-portable code, which can call pthread_self() or the like anyway, but the change also doesn't add any non-trivial implementation requirements. This defused initial strong opinions on both sides. Since this is essentially a feature request, we did not have sufficient consensus to proceed at this point. There was a feeling we should reconsider after making more sense out of the much more general TLS issues we have been discussing. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 30.2.3 [thread.req.native] p1 as indicated:

    - -
    -

    --1- Several classes described in this Clause have membersThis Clause includes several members named -native_handle_type and native_handle. The presence of these members and their semantics is -implementation-defined. […] -

    -
    -
    2. - -

  2. In 30.3 [thread.threads], header <thread> synopsis, add:

    - -
    -
    -namespace std {
-  […]
-  namespace this_thread {
-    thread::id get_id() noexcept;
-    thread::native_handle_type native_handle();
-    […]
-  }
-}
-
    -
    -
    3. - -

  3. In 30.3.2 [thread.thread.this] add:

    -
    -
    -namespace std {
-  namespace this_thread {
-    thread::id get_id() noexcept;
-    thread::native_handle_type native_handle(); // See 30.2.3 [thread.req.native]
-    […]
-  }
-}
-
    -
    -
    4. -
- - - - - - -
-

2380. May <cstdlib> provide long ::abs(long) and long long ::abs(long long)?

-

Section: 17.6.1.2 [headers] Status: Ready - Submitter: Richard Smith Opened: 2014-03-31 Last modified: 2015-05-05

-

View all other issues in [headers].

-

View all issues with Ready status.

-

Discussion:

-

-D.5 [depr.c.headers] p3 says: -

-

-[Example: The header <cstdlib> assuredly provides its declarations and definitions within the namespace -std. It may also provide these names within the global namespace. The header <stdlib.h> assuredly -provides the same declarations and definitions within the global namespace, much as in the C Standard. It -may also provide these names within the namespace std. — end example] -

-

-This suggests that <cstdlib> may provide ::abs(long) and ::abs(long long). But this seems like -it might contradict the normative wording of 17.6.1.2 [headers] p4: -

-

-Except as noted in Clauses 18 through 30 and Annex D, the contents of each header cname shall be the same -as that of the corresponding header name.h, as specified in the C standard library (1.2) or the C Unicode -TR, as appropriate, as if by inclusion. In the C++ standard library, however, the declarations (except for -names which are defined as macros in C) are within namespace scope (3.3.6) of the namespace std. It is -unspecified whether these names are first declared within the global namespace scope and are then injected -into namespace std by explicit using-declarations (7.3.3). -

-

-Note that this allows <cstdlib> to provide ::abs(int), but does not obviously allow ::abs(long) -nor ::abs(long long), since they are not part of the header stdlib.h as specified in the C standard library. -

-26.8 [c.math] p7 adds signatures std::abs(long) and std::abs(long long), but not in a way that seems -to allow ::abs(long) and ::abs(long long) to be provided. -

-I think the right approach here would be to allow <cstdlib> to either provide no ::abs declaration, or -to provide all three declarations from namespace std, but it should not be permitted to provide only int abs(int). -Suggestion: -

-Change in 17.6.1.2 [headers] p4: -

-

-[…]. It is unspecified whether these names (including any overloads added in Clauses 18 through 30 and Annex D) -are first declared within the global namespace scope and are then injected into namespace std by explicit using-declarations -(7.3.3). -

- -

[2015-05, Lenexa]

- -

-MC: do we need to defer this?
-PJP: just need to get my mind around it, already playing dirty games here, my reaction is just do it as it will help C++
-STL: this is safe
-TP: would be surprising if using abs didn't bring in all of the overloads
-MC: that's Richard's argument
-MC: move to ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Modify 17.6.1.2 [headers] p4 as indicated:

    - -

    -Except as noted in Clauses 18 through 30 and Annex D, the contents of each header cname shall be the same -as that of the corresponding header name.h, as specified in the C standard library (1.2) or the C Unicode -TR, as appropriate, as if by inclusion. In the C++ standard library, however, the declarations (except for -names which are defined as macros in C) are within namespace scope (3.3.6) of the namespace std. It is -unspecified whether these names (including any overloads added in Clauses 18 through 30 and Annex D) are first -declared within the global namespace scope and are then injected into namespace std by explicit using-declarations (7.3.3). -

    -
    2. -
- - - - - - -
-

2381. Inconsistency in parsing floating point numbers

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: New - Submitter: Marshall Clow Opened: 2014-04-30 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

View all other issues in [facet.num.get.virtuals].

-

View all issues with New status.

-

Discussion:

-

-In 22.4.2.1.2 [facet.num.get.virtuals] we have: -

-

-Stage 3: The sequence of chars accumulated in stage 2 (the field) is converted to a numeric value by the -rules of one of the functions declared in the header <cstdlib>: -

-
    -

  • For a signed integer value, the function strtoll.

    • -

  • For an unsigned integer value, the function strtoull.

    • -

  • For a floating-point value, the function strtold.

    • -
-
-

-This implies that for many cases, this routine should return true: -

-
-bool is_same(const char* p) 
-{
-  std::string str{p};
-  double val1 = std::strtod(str.c_str(), nullptr);
-  std::stringstream ss(str);
-  double val2;
-  ss >> val2;
-  return std::isinf(val1) == std::isinf(val2) &&                 // either they're both infinity
-         std::isnan(val1) == std::isnan(val2) &&                 // or they're both NaN
-         (std::isinf(val1) || std::isnan(val1) || val1 == val2); // or they're equal
-}
-
-

-and this is indeed true, for many strings: -

-
-assert(is_same("0"));
-assert(is_same("1.0"));
-assert(is_same("-1.0"));
-assert(is_same("100.123"));
-assert(is_same("1234.456e89"));
-
-

-but not for others -

-
-assert(is_same("0xABp-4")); // hex float
-assert(is_same("inf"));
-assert(is_same("+inf"));
-assert(is_same("-inf"));
-assert(is_same("nan"));
-assert(is_same("+nan"));
-assert(is_same("-nan"));
-
-assert(is_same("infinity"));
-assert(is_same("+infinity"));
-assert(is_same("-infinity"));
-
-

-These are all strings that are correctly parsed by std::strtod, but not by the stream extraction operators. -They contain characters that are deemed invalid in stage 2 of parsing. -

-If we're going to say that we're converting by the rules of strtold, then we should accept all the things that -strtold accepts. -

- - - -

Proposed resolution:

- - - - - -
-

2383. Overflow cannot be ill-formed for chrono::duration integer literals

-

Section: 20.12.5.8 [time.duration.literals] Status: Open - Submitter: Jonathan Wakely Opened: 2014-05-16 Last modified: 2015-04-08

-

View all issues with Open status.

-

Discussion:

-

-20.12.5.8 [time.duration.literals] p3 says: -

-

-If any of these suffixes are applied to an integer literal and the -resulting chrono::duration value cannot be represented in the result -type because of overflow, the program is ill-formed. -

-

-Ill-formed requires a diagnostic at compile-time, but there is no way -to detect the overflow from unsigned long long to the signed -duration<>::rep type. -

-Overflow could be detected if the duration integer literals were -literal operator templates, otherwise overflow can either be undefined -or a run-time error, not ill-formed. -

- -

[Urbana 2014-11-07: Move to Open]

- - - - -

Proposed resolution:

- - - - - -
-

2384. Allocator's deallocate function needs better specification

-

Section: 17.6.3.5 [allocator.requirements] Status: Ready - Submitter: Daniel Krügler Opened: 2014-05-19 Last modified: 2015-05-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Ready status.

-

Discussion:

-

-According to Table 28, 17.6.3.5 [allocator.requirements], an Allocator's deallocate -function is specified as follows: -

-

-All n T objects in the area -pointed to by p shall be -destroyed prior to this call. n -shall match the value passed to -allocate to obtain this -memory. Does not throw -exceptions. [Note: p shall not be -singular. — end note] -

-

-This wording is confusing in regard to the following points: -

-
    -

  1. This specification does not make clear that the result of an allocate -call can only be returned once to the deallocate function. This is much -clearer expressed for operator delete (18.6.1.1 [new.delete.single] p12, emphasis mine):

    -

    -Requires: ptr shall be a null pointer or its value shall be a value returned -by an earlier call to the (possibly replaced) operator new(std::size_t) or -operator new(std::size_t,const std::nothrow_t&) which has not been invalidated -by an intervening call to operator delete(void*). -

    -
    2. -

  2. The intended meaning of that wording was to say that deallocate shall accept every result value -that had been returned by a corresponding call to allocate, this includes also a possible result of a -null pointer value, which is possible ("[Note: If n == 0, the return value is unspecified. -— end note]"). Unfortunately the deallocate function uses a non-normative note ("p shall not be -singular.") which refers to the fuzzy term singular, that is one of the most unclear and misunderstood terms -of the library, as pointed out in 1213. The occurrence of this term has lead to the possible understanding, -that this function would never allow null pointer values. Albeit for allocators the intention had not been to require the support -in general that a null pointer value can be provided to deallocate (as it is allowed for std::free -and operator delete), the mental model was that every returned value of allocate shall be an -acceptable argument type of the corresponding deallocate function. -

    -
    3. -
- -

-This issue is not intending to enforce a specific meaning of singular iterator values, but the assertion is -that this note does more harm than good. In addition to wording from operator delete there is no longer any need -to obfuscate the normative wording. -

- -

[2014-05-24 Alisdair comments]

- - -

-Now that I am reading it very precisely, there is another mis-stated assumption -as a precondition for deallocate: -

-

-All n T objects in the area pointed to by p shall be destroyed prior to this call. -

-

-This makes a poor assumption that every possible object in the allocated buffer -was indeed constructed, but this is often not the case, e.g., a vector that is not -filled to capacity. We should require calling the destructor for only those objects -actually constructed in the buffer, which may be fewer than n, or even 0. -

-I wonder if we really require all objects to be destroyed before calling deallocate -though. Are we really so concerned about leaking objects that might not manage -resources? Should this not be the proper concern of the library managing the -objects and memory? -

- -

[2014-06-05 Daniel responds and improves wording]

- - -

-I fully agree with the last comment and I think that this requirement should be removed. We have no such -requirements for comparable functions such as operator delete or return_temporary_buffer(), -and this wording seems to be a wording rudiment that exists since C++98. -

- -

[2015-05, Lenexa]

- -

-Marshall: What do people think about this?
-PJP: Sure.
-Wakely: Love it.
-Marshall: Ready?
-Everyone agrees.
-

- - -

Proposed resolution:

- -

This wording is relative to N3936.

- -
    -

  1. Change Table 28 ("Allocator requirements") as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements
    ExpressionReturn typeAssertion/note
    pre-/post-condition    		Default
    -… -
    -a.deallocate(p,n) - -(not used) - -Pre: p shall be a value returned by an earlier
    -call to allocate which has not been invalidated by
    -an intervening call to deallocate. n shall
    -match the value passed to allocate to obtain this
    -memory.     All n T objects in the area pointed to by
    -p shall be destroyed prior to this call.
    -Throws: Nothing.n
    -shall match the value passed to
    -allocate to obtain this
    -memory. Does not throw
    -exceptions. [Note: p shall not
    -be singular. — end note]     -    		 -  -
    -… -
    -
    - -
    2. -
- - - - - - -
-

2385. function::assign allocator argument doesn't make sense

-

Section: 20.9.12.2 [func.wrap.func] Status: Ready - Submitter: Pablo Halpern Opened: 2014-05-23 Last modified: 2015-05-07

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with Ready status.

-

Discussion:

-

-The definition of function::assign in N3936 is: -

-
-template<class F, class A>
-  void assign(F&& f, const A& a);
-
-
-

-Effects: function(allocator_arg, a, std::forward<F>(f)).swap(*this) -

-
-
-

-This definition is flawed in several respects: -

-
    -

  1. The interface implies that the intent is to replace the allocator in *this -with the specified allocator, a. Such functionality is unique in the -standard and is problematic when creating, e.g. a container of function -objects, all using the same allocator.

    -
    2. -

  2. The current definition of swap() makes it unclear whether the objects being -swapped can have different allocators. The general practice is that -allocators must be equal in order to support swap, and this practice is -reinforced by the proposed library TS. Thus, the definition of assign would -have undefined behavior unless the allocator matched the allocator already -within function. -

    -
    3. -

  3. -The general rule for members of function is to supply the allocator before -the functor, using the allocator_arg prefix. Supplying the allocator as a -second argument, without the allocator_arg prefix is error prone and -confusing. -

    4. -
- -

-I believe that this ill-conceived interface was introduced in the effort to -add allocators to parts of the standard where it had been missing, when we -were unpracticed in the right way to accomplish that. Allocators were added -to function at a time when the allocator model was in flux and it was the -first class in the standard after shared_ptr to use type-erased allocators, so -it is not surprising to see some errors in specification here. (shared_ptr is -a special case because of its shared semantics, and so is not a good model.) -

-The main question is whether this member should be specified with better -precision or whether it should be deprecated/removed. The only way I can see to -give a "reasonable" meaning to the existing interface is to describe it in -terms of destroying and re-constructing *this: -

-
-function temp(allocator_arg, a, std::forward<F>(f));
-this->~function();
-::new(this) function(std::move(temp));
-
-

-(The temp variable is needed for exception safety). The ugliness of this -specification underscores the ugliness of the concept. What is the purpose of -this member other than to reconstruct the object from scratch, a facility that -library classes do not generally provide? Programmers are always free to -destroy and re-construct objects — there is no reason why function should -make that especially easy. -

-I propose, therefore, that we make no attempt at giving the current interface -a meaningful definition of questionable utility, but simply get rid of it -all together. This leaves us with only two questions: -

-
    -

  1. Should we deprecate the interface or just remove it?

    2. -

  2. Should we replace it with an assign(f) member that doesn't take an -allocator?

    3. -
-

-Of these four combinations of binary answers to the above questions, I think -the ones that make the most sense are (remove, no) and (deprecate, yes). The -proposed new interface provides nothing that operator= does not already -provide. However, if the old (deprecated) interface remains, then having the -new interface will guide the programmer away from it. -

-The proposed wording below assumes deprecation. If we choose removal, then -there is no wording needed; simply remove the offending declaration and -definition. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3936.

- -
    -

  1. Change class template function synopsis, 20.9.12.2 [func.wrap.func], as indicated:

    - -
    -
    -template<class R, class... ArgTypes>
-class function<R(ArgTypes...)> {
-  […]
-  // 20.9.11.2.2, function modifiers:
-  void swap(function&) noexcept;
-  template<class F, class A> void assign(F&&, const A&);
-  […]
-};
-
    -
    -
    2. - -

  2. Change 20.9.12.2.2 [func.wrap.func.mod] as indicated:

    - -
    -
    -template<class F, class A> void assign(F&& f, const A& a);
-
    -
    -

    -Effects: *this = forward<F>(f);function(allocator_arg, a, std::forward<F>(f)).swap(*this) -

    -
    -
    -
    3. - -

  3. To deprecation section [depr.function.objects], add the following new sub-clause:

    - -
    -

    -Old assign member of polymorphic function wrappers [depr.function.objects.assign] -

    -
    -
    -namespace std{
-  template<class R, class... ArgTypes>
-  class function<R(ArgTypes...)> {
-    // remainder unchanged
-    template<class F, class A> void assign(F&& f, const A& a);
-    […]
-  };
-}
-
    -
    -

    -The two-argument form of assign is defined as follows: -

    -
    -template<class F, class A> void assign(F&& f, const A& a);
-
    -
    -

    -Requires: a shall be equivalent to the allocator used to construct *this. -

    -Effects: this->assign(forward<F>(f)); -

    -
    - -
    -
    4. -
-
- -

[2015-05, Lenexa]

- -

-STL: I would ask, does anybody oppose removing this outright?
-Wakely: I don't even have this signature.
-Hwrd: And I think this doesn't go far enough, even more should be removed. This is a step in the right direction.
-PJP: I'm in favor of removal.
-Wakely: We've already got TS1 that has a new function that does it right. We could wait for feedback on that. -I think this issue should be taken now.
-Marshall: Then the goal will be to move to ready. -

- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Change class template function synopsis, 20.9.12.2 [func.wrap.func], as indicated:

    - -
    -
    -template<class R, class... ArgTypes>
-class function<R(ArgTypes...)> {
-  […]
-  // 20.9.12.2.2, function modifiers:
-  void swap(function&) noexcept;
-  template<class F, class A> void assign(F&&, const A&);
-  […]
-};
-
    -
    -
    2. - -

  2. Change 20.9.12.2.2 [func.wrap.func.mod] as indicated:

    - -
    -
    -template<class F, class A> 
-  void assign(F&& f, const A& a);
-
    -
    -

    --2- Effects: function(allocator_arg, a, std::forward<F>(f)).swap(*this) -

    -
    -
    -
    3. - -
- - - - - -
-

2391. basic_string is missing non-const data()

-

Section: 21.4 [basic.string] Status: LEWG - Submitter: Michael Bradshaw Opened: 2014-05-27 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with LEWG status.

-

Discussion:

-

-Regarding 21.4 [basic.string], std::basic_string<charT>::data() returns a const charT* -21.4.7.1 [string.accessors]. While this method is convenient, it doesn't quite match std::array<T>::data() -23.3.2.5 [array.data] or std::vector<T>::data() 23.3.6.4 [vector.data], both of which provide two -versions (that return T* or const T*). An additional data() method can be added to -std::basic_string that returns a charT* so it can be used in similar situations that std::array and -std::vector can be used. Without a non-const data() method, std::basic_string has to be treated -specially in code that is otherwise oblivious to the container type being used. -

-Adding a charT* return type to data() would be equivalent to doing &str[0] or &str.front(). -

-Small discussion on the issue can be found here -and in the std-discussion thread -(which didn't get too much attention). -

-This requires a small change to std::basic_string's definition in 21.4 [basic.string] to add the method to -std::basic_string, and another small change in 21.4.7.1 [string.accessors] to define the new method. -

- -

[2015-02 Cologne]

- -

-Back to LEWG. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change class template basic_string synopsis, 21.4 [basic.string], as indicated:

    -
    -
    -namespace std {
-  template<class charT, class traits = char_traits<charT>,
-  class Allocator = allocator<charT> >
-  class basic_string {
-  public:
-    […]
-    // 21.4.7, string operations:
-    const charT* c_str() const noexcept;
-    const charT* data() const noexcept;
-    charT* data() noexcept;
-    allocator_type get_allocator() const noexcept;
-    […]
-  };
-}
-
    -
    - -
    2. - -

  2. Add the following sequence of paragraphs following 21.4.7.1 [string.accessors] p3, as indicated:

    -
    -
    -charT* data() noexcept;
-
    -
    -

    --?- Returns: A pointer p such that p + i == &operator[](i) for each i in [0,size()]. -

    --?- Complexity: Constant time. -

    --?- Requires: The program shall not alter the value stored at p + size(). -

    -
    -
    -
    3. -
- - - - - -
-

2392. "character type" is used but not defined

-

Section: 17.3 [defns.ntcts], 22.3.1.1.1 [locale.category], 27.2.2 [iostreams.limits.pos], 27.7.3.6.1 [ostream.formatted.reqmts], 27.7.3.6.4 [ostream.inserters.character] Status: New - Submitter: Jeffrey Yasskin Opened: 2014-06-01 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

-

-The term "character type" is used in 17.3 [defns.ntcts], 22.3.1.1.1 [locale.category], -27.2.2 [iostreams.limits.pos], 27.7.3.6.1 [ostream.formatted.reqmts], and -27.7.3.6.4 [ostream.inserters.character], but the core language only defines -"narrow character types" (3.9.1 [basic.fundamental]). -

-"wide-character type" is used in 22.5 [locale.stdcvt], but the core -language only defines a "wide-character set" and "wide-character literal". -

- - -

Proposed resolution:

- - - - - -
-

2393. std::function's Callable definition is broken

-

Section: 20.9.12.2 [func.wrap.func] Status: Open - Submitter: Daniel Krügler Opened: 2014-06-03 Last modified: 2015-04-08

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with Open status.

-

Discussion:

-

-The existing definition of std::function's Callable requirements provided in 20.9.12.2 [func.wrap.func] -p2, -

-

-A callable object f of type F is Callable for argument types ArgTypes and return type -R if the expression INVOKE(f, declval<ArgTypes>()..., R), considered as an unevaluated operand -(Clause 5), is well formed (20.9.2). -

-

-is defective in several aspects: -

-
    -

  1. The wording can be read to be defined in terms of callable objects, not of callable types.

    -
    2. -

  2. Contrary to that, 20.9.12.2.5 [func.wrap.func.targ] p2 speaks of "T shall be a type that is Callable -(20.9.11.2) for parameter types ArgTypes and return type R."

    -
    3. -

  3. -The required value category of the callable object during the call expression (lvalue or rvalue) strongly depends on -an interpretation of the expression f and therefore needs to be specified unambiguously. -

    4. -
-

-The intention of original proposal -(see IIIa. Relaxation of target requirements) was to refer to both types and values ("we say that the function object f -(and its type F) is Callable […]"), but that mental model is not really deducible from the -existing wording. An improved type-dependence wording would also make the sfinae-conditions specified in 20.9.12.2.1 [func.wrap.func.con] -p8 and p21 ("[…] shall not participate in overload resolution unless f is Callable (20.9.11.2) -for argument types ArgTypes... and return type R.") easier to interpret. -

-My understanding always had been (see e.g. Howard's code example in the 2009-05-01 comment in LWG 815), that -std::function invokes the call operator of its target via an lvalue. The required value-category is relevant, -because it allows to reflect upon whether an callable object such as -

-
-struct RVF 
-{
-  void operator()() const && {}
-};
-
-

-would be a feasible target object for std::function<void()> or not. -

-Clarifying the current Callable definition seems also wise to make a future transition to language-based concepts -easier. A local fix of the current wording is simple to achieve, e.g. by rewriting it as follows: -

-

-A callable object f of type (20.9.1 [func.def]) F is Callable -for argument types ArgTypes and return type R if the expression INVOKE(fdeclval<F&>(), -declval<ArgTypes>()..., R), considered as an unevaluated operand (Clause 5), is well formed (20.9.2). -

-

-It seems appealing to move such a general Callable definition to a more "fundamental" place (e.g. as another -paragraph of 20.9.1 [func.def]), but the question arises, whether such a more general concept should impose -the requirement that the call expression is invoked on an lvalue of the callable object — such a -special condition would also conflict with the more general definition of the result_of trait, which -is defined for either lvalues or rvalues of the callable type Fn. In this context I would like to point out that -"Lvalue-Callable" is not the one and only Callable requirement in the library. Counter examples are -std::thread, call_once, or async, which depend on "Rvalue-Callable", because they -all act on functor rvalues, see e.g. 30.3.1.2 [thread.thread.constr]: -

-

-[…] The new thread of execution executes INVOKE(DECAY_COPY(std::forward<F>(f)), -DECAY_COPY(std::forward<Args>(args))...) […] -

-

-For every callable object F, the result of DECAY_COPY is an rvalue. These implied rvalue function calls are -no artifacts, but had been deliberately voted for by a Committee decision (see LWG 2021, 2011-06-13 comment) -and existing implementations respect these constraints correctly. Just to give an example, -

-
-#include <thread>
-
-struct LVF 
-{
-  void operator()() & {}
-};
-
-int main()
-{
-  LVF lf;
-  std::thread t(lf);
-  t.join();
-}
-
-

-is supposed to be rejected. -

-The below presented wording changes are suggested to be minimal (still local to std::function), but the used approach -would simplify a future (second) conceptualization or any further generalization of Callable requirements of the Library. -

- -

[2015-02 Cologne]

- -

-Related to N4348. Don't touch with a barge pole. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.9.12.2 [func.wrap.func] p2 as indicated:

    - -

    --2- A callable object f of type (20.9.1 [func.def]) F is Lvalue-Callable -for argument types ArgTypes and return type R if the expression INVOKE(fdeclval<F&>(), -declval<ArgTypes>()..., R), considered as an unevaluated operand (Clause 5), is well formed (20.9.2). -

    -
    2. - -

  2. Change 20.9.12.2.1 [func.wrap.func.con] p8+p21 as indicated:

    - -
    -
    -template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
    -
    -

    -[…] -

    --8- Remarks: These constructors shall not participate in overload resolution unless fF is -Lvalue-Callable (20.9.11.2) for argument types ArgTypes... and return type R. -

    -
    -

    -[…] -

    -
    -template<class F> function& operator=(F&& f);
-
    -
    -

    -[…] -

    --21- Remarks: This assignment operator shall not participate in overload resolution unless -declval<typename decay<F>::type&>()decay_t<F> is -Lvalue-Callable (20.9.11.2) for argument types ArgTypes... and return type R. -

    -
    - -
    -
    3. - -

  3. Change 20.9.12.2.5 [func.wrap.func.targ] p2 as indicated: [Editorial comment: Instead of adapting the preconditions -for the naming change I recommend to strike it completely, because the target() functions do not depend on it; the -corresponding wording exists since its initial proposal -and it seems without any advantage to me. Assume that some template argument T is provided, which does not -satisfy the requirements: The effect will be that the result is a null pointer value, but that case can happen in other (valid) situations -as well. — end comment]

    - -
    -template<class T> T* target() noexcept;
-template<class T> const T* target() const noexcept;
-
    -
    -

    --2- Requires: T shall be a type that is Callable (20.9.11.2) for parameter types -ArgTypes and return type R. -

    --3- Returns: If target_type() == typeid(T) a pointer to the stored function target; otherwise a null -pointer. -

    -
    -
    -
    4. -
- - - - - -
-

2394. locale::name specification unclear — what is implementation-defined?

-

Section: 22.3.1.3 [locale.members] Status: New - Submitter: Richard Smith Opened: 2014-06-09 Last modified: 2015-04-08

-

View all other issues in [locale.members].

-

View all issues with New status.

-

Discussion:

-

-22.3.1.3 [locale.members] p5 says: -

-

-Returns: The name of *this, if it has one; otherwise, the string "*". If *this has a name, then -locale(name().c_str()) is equivalent to *this. Details of the contents of the resulting string are -otherwise implementation-defined. -

-

-So… what is implementation-defined here, exactly? The first sentence completely defines the behavior of this function -in all cases. -

-Also, the second sentence says (effectively) that all locales with the same name are equivalent: given L1 and L2 -that have the same name N, they are both equivalent to locale(N), and since there is no definition of -"equivalent" specific to locale, I assume it's the normal transitive equivalence property, which would imply that -L1 is equivalent to L2. I'm not sure why this central fact is in the description of locale::name, nor -why it's written in this roundabout way. -

- - -

Proposed resolution:

- - - - - -
-

2398. type_info's destructor shouldn't be required to be virtual

-

Section: 18.7.1 [type.info] Status: Open - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-05-22

-

View all other issues in [type.info].

-

View all issues with Open status.

-

Discussion:

-

-type_info's destructor is depicted as being virtual, which is nearly unobservable to users (since they can't construct -or copy this class, they can't usefully derive from it). However, it's technically observable (via is_polymorphic and -has_virtual_destructor). It also imposes real costs on implementations, requiring them to store one vptr per -type_info object, when RTTI space consumption is a significant concern. -

-Making this implementation-defined wouldn't affect users (who can observe this only if they're specifically looking for it) and -wouldn't affect implementations who need virtual here, but it would allow other implementations to drop virtual -and improve their RTTI space consumption. -

-Richard Smith: -

-It's observable in a few other ways. -

-
-std::map<void*, something> m;
-m[dynamic_cast<void*>(&typeid(blah))] = stuff;
-
-

-... is broken by this change, because you can't dynamic_cast a non-polymorphic class type to void*. -

-
-type_info& f();
-typeid(f());
-
-

-... evaluates f() at runtime without this change, and might not do so with this change. -

-These are probably rare things, but I can imagine at least some forms of the latter being used in SFINAE tricks. -

- -

[Lenexa 2015-05-05: Move to Open]

- -

Marshall to poll LEWG for their opinion

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 18.7.1 [type.info] as indicated:

    - -
    -
    -namespace std {
-  class type_info {
-  public:
-    virtualsee below ~type_info();
-    […]
-  };
-}
-
    -

    --1- The class type_info describes type information generated by the implementation. Objects of this class -effectively store a pointer to a name for the type, and an encoded value suitable for comparing two types for -equality or collating order. The names, encoding rule, and collating sequence for types are all unspecified -and may differ between programs. Whether ~type_info() is virtual is implementation-defined. -

    -
    -
    2. -
- - - - - -
-

2402. basic_string(const basic_string& str, size_type pos, size_type n = npos) shouldn't use Allocator()

-

Section: 21.4.2 [string.cons] Status: Open - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-05-22

-

View all other issues in [string.cons].

-

View all issues with Open status.

-

Discussion:

-

-21.4.2 [string.cons] p3 specifies: -

-
-
-basic_string(const basic_string& str, size_type pos, size_type n = npos, const Allocator& a = Allocator());
-
-

-But this implies that basic_string(str, pos) and basic_string(str, pos, n) use Allocator() -instead of getting an allocator from str. -

-21.4.1 [string.require] p3 says "The Allocator object used shall be obtained as described in 23.2.1." -23.2.1 [container.requirements.general] p8 says "Copy constructors for these container types obtain an allocator -by calling allocator_traits<allocator_type>::select_on_container_copy_construction on the allocator -belonging to the container being copied.", but this isn't exactly a copy constructor. Then it talks about move constructors -(which this definitely isn't), and finally says that "All other constructors for these container types take a -const allocator_type& argument. […] A copy of this allocator is used for any memory allocation performed". -

-
- -

[2015-05-06 Lenexa: move to Open]

- -

STL: there an allocator right there in str, why default-construct one

-

STL: my fix, which may not be right, splits out functions with and without allocators

-

JW: there are other ways to propagate the allocator from str to the new object

-

PJP: hard to get motivated about this one

-

JW: I think this is not a copy operation, this is init'ing a string from a range of characters which happens to originate in a string. It makes it inconsistent with the similar ctor taking a const char pointer, and if we had a std::string_view we wouldn't even have this ctor, and it wouldn't be possible to propagate the allocator.

-

STL: but people with stateful allocators want it to propagate

-

JW: I think the people using stateful allocators will alter the default behaviour of select_on_container_copy_construction so that it doesn't propagate, but will return a default-constructed one (to ensure a stateful allocator referring to a stack buffer doesn't leak to a region where the stack buffer has gone). So for those people, your proposed change does nothing, it changes one default-constructed allocator to a call to select_on_container_copy_construction which returns a default-constructed allocator. For other people who have different stateful allocators they can still provide the right allocator (whatever that may be) by passing it in.

-

STL: OK, that's convincing.

-

PJP: I agree with Jonathan

-

JW: would like to run both our arguments by Pablo in case I'm totally misrepresenting the expected users of allocator-traits stuff

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 21.4 [basic.string] p5, class template basic_string synopsis, as indicated:

    - -
    -
    -[…]
-// 21.4.2, construct/copy/destroy:
-[…]
-basic_string(basic_string&& str) noexcept;
-basic_string(const basic_string& str, size_type pos, size_type n = npos);
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-            const Allocator& a = Allocator());
-[…]
-
    -
    -
    2. - -

  2. Change 21.4.2 [string.cons] around p3 as indicated:

    - -
    -
    -basic_string(const basic_string& str, 
-             size_type pos, size_type n = npos);
-basic_string(const basic_string& str, 
-             size_type pos, size_type n = npos,
-             const Allocator& a = Allocator());
-
    -
    -

    -[…] -

    --5- Effects: Constructs an object of class basic_string and determines the effective length rlen of the -initial string value as the smaller of n and str.size() - pos, as indicated in Table 65. The first constructor -obtains an allocator by calling allocator_traits<allocator_type>::select_on_container_copy_construction on the -allocator belonging to str. -

    -Table 65 — basic_string(const basic_string&, size_type, size_type) and -basic_string(const basic_string&, size_type, size_type, const Allocator&) effects -

    -
    -
    -
    3. -
- - - - - -
-

2412. promise::set_value() and promise::get_future() should not race

-

Section: 30.6.5 [futures.promise], 30.6.9.1 [futures.task.members] Status: SG1 - Submitter: Jonathan Wakely Opened: 2014-06-23 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with SG1 status.

-

Discussion:

-

-The following code has a data race according to the standard: -

-
-
-std::promise<void> p;
-std::thread t{ []{
-  p.get_future().wait();
-}};
-p.set_value();
-t.join();
-
-
-

-The problem is that both promise::set_value() and -promise::get_future() are non-const member functions which modify the -same object, and we only have wording saying that the set_value() and -wait() calls (i.e. calls setting and reading the shared state) are -synchronized. -

-The calls don't actually access the same memory locations, so the -standard should allow it. My suggestion is to state that calling -get_future() does not conflict with calling the various functions that -make the shared state ready, but clarify with a note that this does -not imply any synchronization or "happens before", only being free -from data races. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 30.6.5 [futures.promise] around p12 as indicated:

    - -
    -
    -future<R> get_future();
-
    -
    -

    --12- Returns: A future<R> object with the same shared state as *this. -

    --?- Synchronization: Calls to this function do not conflict (1.10 [intro.multithread]) -with calls to set_value, set_exception, set_value_at_thread_exit, or -set_exception_at_thread_exit. [Note: Such calls need not be synchronized, but implementations -must ensure they do not introduce data races. — end note] -

    --13- Throws: future_error if *this has no shared state or if get_future has already been called on a -promise with the same shared state as *this. -

    --14- Error conditions: […] -

    -
    -
    -
    2. - -

  2. Change 30.6.9.1 [futures.task.members] around p13 as indicated:

    - -
    -
    -future<R> get_future();
-
    -
    -

    --13- Returns: A future<R> object that shares the same shared state as *this. -

    --?- Synchronization: Calls to this function do not conflict (1.10 [intro.multithread]) -with calls to operator() or make_ready_at_thread_exit. [Note: Such calls need not be -synchronized, but implementations must ensure they do not introduce data races. — end note] -

    --14- Throws: a future_error object if an error occurs. -

    --15- Error conditions: […] -

    -
    -
    -
    3. - -
- - - - - -
-

2413. assert macro is overconstrained

-

Section: 19.3 [assertions] Status: New - Submitter: David Krauss Opened: 2014-06-25 Last modified: 2015-04-08

-

View other active issues in [assertions].

-

View all other issues in [assertions].

-

View all issues with New status.

-

Discussion:

-

-When NDEBUG is defined, assert must expand exactly to the token sequence ((void)0), with no -whitespace (C99 §7.2/1 and also C11 §7.2/1). This is a lost opportunity to pass the condition along to the optimizer. -

-The user may observe the token sequence using the stringize operator or discriminate it by making a matching #define -directive. There is little chance of practical code doing such things. It's reasonable to allow any expansion that is a void -expression with no side effects or semantic requirements, for example, an extension keyword or an attribute-specifier finagled -into the context. -

-Conforming optimizations would still be limited to treating the condition as hint, not a requirement. Nonconformance on this -point is quite reasonable though, given user preferences. Anyway, it shouldn't depend on preprocessor quirks. -

-As for current practice, Darwin OS <assert.h> provides a GCC-style compiler hint __builtin_expect but only in -debug mode. Shouldn't release mode preserve hints? -

-Daniel: -

-The corresponding resolution should take care not to conflict with the intention behind LWG 2234. -

- - -

Proposed resolution:

- - - - - -
-

2414. Member function reentrancy should be implementation-defined

-

Section: 17.6.5.8 [reentrancy] Status: Open - Submitter: Stephan T. Lavavej Opened: 2014-07-01 Last modified: 2015-05-05

-

View all other issues in [reentrancy].

-

View all issues with Open status.

-

Discussion:

-

-N3936 17.6.5.8 [reentrancy]/1 talks about "functions", but that doesn't address the scenario of calling different member -functions of a single object. Member functions often have to violate and then re-establish invariants. For example, vectors -often have "holes" during insertion, and element constructors/destructors/etc. shouldn't be allowed to observe the vector -while it's in this invariant-violating state. The [reentrancy] Standardese should be extended to cover member functions, -so that implementers can either say that member function reentrancy is universally prohibited, or selectively allowed for -very specific scenarios. -

-(For clarity, this issue has been split off from LWG 2382.) -

- -

[2014-11-03 Urbana]

- -

-AJM confirmed with SG1 that they had no special concerns with this issue, and LWG should retain ownership. -

-AM: this is too overly broad as it also covers calling the exact same member function on a different object
-STL: so you insert into a map, and copying the value triggers another insertion into a different map of the same type
-GR: reentrancy seems to imply the single-threaded case, but needs to consider the multi-threaded case -

-Needs more wording. -

-

-Move to Open -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 17.6.5.8 [reentrancy] p1 as indicated:

    -
    -

    --1- Except where explicitly specified in this standard, it is implementation-defined which functions (including different -member functions called on a single object) in the Standard C++ library may be recursively reentered. -

    -
    -
    2. -
- - - - - -
-

2417. [fund.ts] std::experimental::optional::operator< and LessThanComparable requirement

-

Section: X [optional.relops], X [optional.comp_with_t] Status: LEWG - Submitter: Daniel Krügler Opened: 2014-06-20 Last modified: 2015-04-08

-

View all issues with LEWG status.

-

Discussion:

-

Addresses: fund.ts

-

-Currently, std::experimental::optional::operator== imposes the EqualityComparable requirement which provides -two guarantees: It ensures that operator!= can rely on the equivalence-relation property and more importantly, that -the BooleanTestable requirements suggested by issue 2114 are automatically implied. -

-std::experimental::optional::operator< doesn't provide a LessThanComparable requirement, but there was quite -an historic set of changes involved with that family of types: As of -N3527 -this operator was defined in terms of operator< of the contained type T and imposed the LessThanComparable -requirement. In the final acceptance step of optional by the committee, the definition was expressed in terms of std::less -and the LessThanComparable requirement had been removed. -

-The inconsistency between operator== and operator< should be removed. One possible course of action would be -to add the LessThanComparable to std::experimental::optional::operator<. The EqualityComparable requirement -of operator== could also be removed, but in that case both operators would at least need to require the BooleanTestable -requirements (see 2114) for the result type of T's operator== and operator<. -

-Arguably, corresponding operators for pair and tuple do not impose LessThanComparable (nor -EqualityComparable), albeit the definition of the "derived" relation functions depend on properties ensured by -LessThanComparable. According to the SGI definition, the intention was -to imposed both EqualityComparable and LessThanComparable. If this is not intended, the standard should clarify -this position. -

- -

[2015-02 Cologne]

- -

-VV, DK, JY discuss why and when LessThanComparable was removed. AM: Move to LEWG. Please tell LWG when you look at it. -

- - -

Proposed resolution:

- - - - - -
-

2419. Clang's libc++ extension to std::tuple

-

Section: 20.4.2.1 [tuple.cnstr] Status: LEWG - Submitter: Akim Demaille Opened: 2014-07-11 Last modified: 2015-04-08

-

View other active issues in [tuple.cnstr].

-

View all other issues in [tuple.cnstr].

-

View all issues with LEWG status.

-

Discussion:

-

-The issue has been submitted after exchanges with the clang++ team -as a consequence of two PR I sent: -

-Issue 20174 -

-Issue 20175 -

-The short version is shown in the program below: -

-
-
-#include <iostream>
-#include <tuple>
-
-struct base
-{
-  void out(const std::tuple<char, char>& w) const
-  {
-    std::cerr << "Tuple: " << std::get<0>(w) << std::get<1>(w) << '\n';
-  }
-};
-
-struct decorator
-{
-  base b_;
-
-  template <typename... Args>
-  auto
-  out(Args&&... args)
-    -> decltype(b_.out(args...))
-  {
-    return b_.out(args...);
-  }
-
-  void out(const char& w)
-  {
-    std::cerr << "char: " << w << '\n';
-  }
-};
-
-int main()
-{
-  decorator d{base{}};
-  char l = 'a';
-  d.out(l);
-}
-
-
-

-This is a stripped down version of a real world case where I -wrap objects in decorators. These decorators contributes some -functions, and forward all the rest of the API to the wrapped -object using perfect forwarding. There can be overloaded names. -

-Here the inner object provides an -

-
-out(const std::tuple<char, char>&) -> void
-
-

-function, and the wrappers, in addition to perfect forwarding, -provides -

-
-out(const char&) -> void
-
-

-The main function then call out(l) where l is a char lvalue. -

-With (GCC's) libstdc++ I get the expected result: the char -overload is run. With (clang++'s) libc++ it is the tuple -version which is run. -

-
-$ g++-mp-4.9 -std=c++11 bar.cc && ./a.out
-char: a
-$ clang++-mp-3.5 -std=c++11 bar.cc -Wall && ./a.out
-Tuple: a
-
-

-It turns out that this is the result of an extension of std::tuple -in libc++ where they accept constructors with fewer values that -tuple elements. -

-The purpose of this issue is to ask the standard to forbid -that this extension be allowed to participate in overload resolution. -

- -

[2014-10-05, Daniel comments]

- -

-This issue is closely related to LWG 2312. -

- -

[2014-11 Urbana]

- -

-Moved to LEWG. -

-

-Extensions to tuple's design are initially a question for LEWG. -

- - -

Proposed resolution:

- - - - - -
-

2421. Non-specification of handling zero size in std::align [ptr.align]

-

Section: 20.7.5 [ptr.align] Status: New - Submitter: Melissa Mears Opened: 2014-08-06 Last modified: 2015-04-08

-

View all other issues in [ptr.align].

-

View all issues with New status.

-

Discussion:

-

-The specification of std::align does not appear to specify what happens when the value of the size -parameter is 0. (The question of what happens when alignment is 0 is mentioned in another Defect Report, 2377; -it would change the behavior to be undefined rather than potentially implementation-defined.) -

-The case of size being 0 is interesting because the result is ambiguous. Consider the following code's output: -

-
-
-#include <cstdio>
-#include <memory>
-
-int main()
-{
-  alignas(8) char buffer[8];
-  void *ptr = &buffer[1];
-  std::size_t space = sizeof(buffer) - sizeof(char[1]);
-
-  void *result = std::align(8, 0, ptr, space);
-
-  std::printf("%d %td\n", !!result, result ? (static_cast<char*>(result) - buffer) : std::ptrdiff_t(-1));
-}
-
-
-

-There are four straightforward answers as to what the behavior of std::align with size 0 should be: -

-
    -

  1. The behavior is undefined because the size is invalid.

    2. -

  2. The behavior is implementation-defined. This seems to be the status quo, with current implementations using #3.

    3. -

  3. Act the same as size == 1, except that if size == 1 would fail but would be defined and succeed -if space were exactly 1 larger, the result is a pointer to the byte past the end of the ptr buffer. That is, the -"aligned" version of a 0-byte object can be one past the end of an allocation. Such pointers are, of course, valid when not -dereferenced (and a "0-byte object" shouldn't be), but whether that is desired is not specified in the Standard's definition -of std::align, it appears. The output of the code sample is "1 8" in this case.

    4. -

  4. Act the same as size == 1; this means that returning "one past the end" is not a possible result. In this case, -the code sample's output is "0 -1".

    5. -
-

-The two compilers I could get working with std::align, Visual Studio 2013 and Clang 3.4, implement #3. (Change %td to -%Id on Visual Studio 2013 and earlier. 2014 and later will have %td.) -

- - -

Proposed resolution:

- - - - - -
-

2422. std::numeric_limits<T>::is_modulo description: "most machines" errata

-

Section: 18.3.2.4 [numeric.limits.members] Status: Open - Submitter: Melissa Mears Opened: 2014-08-06 Last modified: 2015-05-22

-

View all other issues in [numeric.limits.members].

-

View all issues with Open status.

-

Discussion:

-

-The seemingly non-normative (?) paragraph 61 (referring to N3936) describing how "most machines" define -std::numeric_limits<T>::is_modulo in [numeric.limits.members] appears to have some issues, in my opinion. -

-
-

--61- On most machines, this is false for floating types, true for unsigned integers, and true -for signed integers. -

-
-

-Issues I see: -

-
    -

  1. Very minor: change clause 2 to "this is false for floating point types". Other uses of the term -say "floating point types" rather than just "floating types" — see nearby is_iec559, tinyness_before, -etc.

    2. -

  2. is_modulo must be true for unsigned integers in order to be compliant with the Standard; -this is not just for "most machines". For reference, this requirement is from [basic.fundamental] paragraph 4 with its -footnote 48.

    3. -

  3. Depending on the definition of "most machines", is_modulo could be false for most machines' signed -integer types. GCC, Clang and Visual Studio, the 3 most popular C++ compilers by far, by default treat signed integer overflow -as undefined.

    4. -
-

-As an additional note regarding the definition of is_modulo, it seems like it should be explicitly mentioned that -on an implementation for which signed integer overflow is undefined, is_modulo shall be false for signed -integer types. It took bugs filed for all three of these compilers before they finally changed (or planned to change) -is_modulo to false for signed types. -

- -

[2014-12 telecon]

- -

-HH: agree with the proposal, don't like the phrasing
-AM: second note feels a bit wooly
-WB: not even happy with the first note, notes shouldn't say "shall"
-JW: the original isn't very prescriptive because "on most machines" is not something the standard controls.
-AM: "On most machines" should become a note too?
-AM: first note is repeating something defined in core, shouldn't say it normatively here. Change "shall" to "is"?
-MC: don't like "signed integer overflow is left undefined" ... it's just plain undefined.
-AM: implementations can define what they do in that case and provide guarantees.
-WB: in paragraph 61, would like to see "this" replaced by "is_modulo"
-AM: Move to Open -

- -

[2015-05-05 Lenexa]

- -

Marshall: I will contact the submitter to see if she can re-draft the Proposed Resolution

- - -

Proposed resolution:

-
    -

  1. Edit 18.3.2.4 [numeric.limits.members] around p60 as indicated:

    - -
    -
    -static constexpr bool is_modulo;
-
    -

    --60- True if the type is modulo.(footnote) A type is modulo if, for any operation involving +, -, or * -on values of that type whose result would fall outside the range [min(),max()], the value returned differs from -the true value by an integer multiple of max() - min() + 1. -

    --??- [Note: is_modulo shall be true for unsigned integer types (3.9.1 [basic.fundamental]). — -end note] -

    --??- [Note: is_modulo shall be false for types for which overflow is undefined on the implementation, -because such types cannot meet the modulo requirement. Often, signed integer overflow is left undefined on implementations. — -end note] -

    --61- On most machines, this is false for floating point types, true for unsigned integers, -and true for signed integers. -

    --62- Meaningful for all specializations. -

    -
    -
    2. -
- - - - - -
-

2423. Missing specification slice_array, gslice_array, mask_array, indirect_array copy constructor

-

Section: 26.6.5 [template.slice.array], 26.6.7 [template.gslice.array], 26.6.8 [template.mask.array], 26.6.9 [template.indirect.array] Status: New - Submitter: Akira Takahashi Opened: 2014-08-12 Last modified: 2015-04-08

-

View all other issues in [template.slice.array].

-

View all issues with New status.

-

Discussion:

-

-I found a missing specification of the copy constructor of the following class templates: -

-
    -

  • slice_array (26.6.5 [template.slice.array])

    • -

  • gslice_array (26.6.7 [template.gslice.array])

    • -

  • mask_array (26.6.8 [template.mask.array])

    • -

  • indirect_array (26.6.9 [template.indirect.array])

    • -
- - -

Proposed resolution:

-
    -

  1. Before 26.6.5.2 [slice.arr.assign] insert a new sub-clause as indicated:

    - -

    --?- slice_array constructors [slice.arr.cons] -

    -
    -
    -slice_array(const slice_array&);
-
    -

    --?- Effects: The constructed slice refers to the same valarray<T> object to which -the argument slice refers. -

    -
    -
    2. - -

  2. Before 26.6.7.2 [gslice.array.assign] insert a new sub-clause as indicated:

    - -

    --?- gslice_array constructors [gslice.array.cons] -

    -
    -
    -gslice_array(const gslice_array&);
-
    -

    --?- Effects: The constructed slice refers to the same valarray<T> object to which -the argument slice refers. -

    -
    -
    3. - -

  3. Before 26.6.8.2 [mask.array.assign] insert a new sub-clause as indicated:

    - -

    --?- mask_array constructors [mask.array.cons] -

    -
    -
    -mask_array(const mask_array&);
-
    -

    --?- Effects: The constructed slice refers to the same valarray<T> object to which -the argument slice refers. -

    -
    -
    4. - -

  4. Before 26.6.9.2 [indirect.array.assign] insert a new sub-clause as indicated:

    - -

    --?- indirect_array constructors [indirect.array.cons] -

    -
    -
    -indirect_array(const indirect_array&);
-
    -

    --?- Effects: The constructed slice refers to the same valarray<T> object to which -the argument slice refers. -

    -
    -
    5. -
- - - - - -
-

2424. 29.5 should state that atomic types are not trivially copyable

-

Section: 29.5 [atomics.types.generic] Status: Review - Submitter: Jens Maurer Opened: 2014-08-14 Last modified: 2015-05-22

-

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-

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-

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-

Discussion:

-

-Otherwise, one could use memcpy to save and restore the value according to 3.9p2. -

-It seems the core language rules in 9 [class]p6 with 12.8 [class.copy]p12 -(trivial copy constructor) etc. and 8.4.2 [dcl.fct.def.default]p5 (user-provided) say -that the atomic types are trivially copyable, which is bad. We shouldn't rely on future core -changes in that area and simply say in the library section 29.5 [atomics.types.generic] -that these very special types are not trivially copyable. -

- -

[2014-11 Urbana]

- -

-Lawrence:Definition of "trivially copyable" has been changing. -

-

-Doesn't hurt to add proposed change, even if the sentence is redundant -

-

-Move to Review. -

- -

[2015-02 Cologne]

- -

-GR has a minor problem with the style of the wording. VV has major issues with implementability. -

- -

[2015-03-22, Jens Maurer responses to Cologne discussion]

- -

-A library implementation could provide a partial specialization for is_trivially_copyable<atomic<T>>, -to ensure that any such type query would return false. -

-Assuming such a specialization would be provided, how could a conforming program observe that per -language rules an atomic specialization would actually be trivially copyable if there -is no way to call the (deleted) copy constructor or copy assignment operator? -

-The sole effect of the suggested addition of the constraining sentence is that it would make a user program -non-conforming that attempts to invoke memcpy (and the like) on atomic types, since that -would invoke undefined behaviour. -

- -

[2015-05 Lenexa, SG1 response]

- -

-SG1 is fine with P/R (and agrees it's needed), but LWG may want to -check the details; it's not entirely an SG1 issue. -

- -

[2015-05-05 Lenexa]

- -

Marshall: This was discussed on the telecon. Alisdair was going to write something to Mike and send it to Core.

-

Hwrd: Core says that deleted copies are trivially copyable, which makes no sense to Library people.

-

STL: There doesn't appear to be a Core issue about it.

- - -

Proposed resolution:

-
    -

  1. Change 29.5 [atomics.types.generic]p3 as indicated:

    - -
    -

    -Specializations and instantiations of the atomic template shall have a deleted copy constructor, a deleted -copy assignment operator, and a constexpr value constructor. They are not trivially copyable -types (3.9 [basic.types]). -

    -
    -
    2. -
- - - - - -
-

2426. Issue about compare_exchange

-

Section: 29.6.5 [atomics.types.operations.req] Status: Open - Submitter: Hans Boehm Opened: 2014-08-25 Last modified: 2015-05-08

-

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-

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-

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-

Discussion:

-

-The standard is either ambiguous or misleading about the nature of accesses through the expected argument -to the compare_exchange_* functions in 29.6.5 [atomics.types.operations.req]p21. -

-It is unclear whether the access to expected is itself atomic (intent clearly no) and exactly when the implementation -is allowed to read or write it. These affect the correctness of reasonable code. -

-Herb Sutter, summarizing a complaint from Duncan Forster wrote: -

-
-

-Thanks Duncan, -

-I think we have a bug in the standardese wording and the implementations are -legal, but let's check with the designers of the feature. -

-Let me try to summarize the issue as I understand it: -

-
    -

  1. -What I think was intended: Lawrence, I believe you championed having -compare_exchange_* take the expected value by reference, and update -expected on failure to expose the old value, but this was only for convenience -to simplify the calling loops which would otherwise always have to write an -extra "reload" line of code. Lawrence, did I summarize your intent correctly? -

    2. -

  2. -What I think Duncan is trying to do: However, it turns out that, now that -expected is an lvalue, it has misled(?) Duncan into trying to use the success of -compare_exchange_* to hand off ownership of expected itself to another -thread. For that to be safe, if the compare_exchange_* succeeds then the -thread that performed it must no longer read or write from expected else his -technique contains a race. Duncan, did I summarize your usage correctly? Is -that the only use that is broken? -

    3. -

  3. -What the standard says: I can see why Duncan thinks the standard supports -his use, but I don't think this was intended (I don't remember this being -discussed but I may have been away for that part) and unless you tell me this -was intended I think it's a defect in the standard. From 29.6.5 [atomics.types.operations.req]/21: -

    -

    --21- Effects: Atomically, compares the contents of the memory pointed to by -object or by this for equality with that in expected, and if true, replaces the -contents of the memory pointed to by object or by this with that in desired, and -if false, updates the contents of the memory in expected with the contents of -the memory pointed to by object or by this. […] -

    -

    -I think we have a wording defect here in any case, because the "atomically" -should not apply to the entire sentence — I'm pretty sure we never intended the -atomicity to cover the write to expected. -

    -As a case in point, borrowing from Duncan's mail below, I think the following -implementation is intended to be legal: -

    -
    -inline int _Compare_exchange_seq_cst_4(volatile _Uint4_t *_Tgt, _Uint4_t *_Exp, _Uint4_t _Value)
-{ /* compare and exchange values atomically with
-     sequentially consistent memory order */
-  int _Res;
-  _Uint4_t _Prev = _InterlockedCompareExchange((volatile long *)_Tgt, _Value, *_Exp);
-  if (_Prev == *_Exp) //!!!!! Note the unconditional read from *_Exp here
-    _Res = 1;
-  else
-  { /* copy old value */
-    _Res = 0;
-    *_Exp = _Prev;
-  }
-  return (_Res);
-}
-
    -

    -I think this implementation is intended to be valid — I think the only code that -could be broken with the "!!!!!" read of *_Exp is Duncan's use of treating -a.compare_exchange_*(expected, desired) == true as implying expected got -handed off, because then another thread could validly be using *_Exp — but we -never intended this use, right? -

    -
    4. -
-
-

-In a different thread Richard Smith wrote about the same problem: -

-
-

-The atomic_compare_exchange functions are described as follows: -

-

-"Atomically, compares the contents of the memory pointed to by object or by this -for equality with that in expected, and if true, replaces the contents of the memory pointed to -by object or by this with that in desired, and if false, updates the contents -of the memory in expected with the contents of the memory pointed to by object or by -this. Further, if the comparison is true, memory is affected according to the value of success, -and if the comparison is false, memory is affected according to the value of failure." -

-

-I think this is less clear than it could be about the effects of these operations on *expected in the failure case: -

-
    -

  1. We have "Atomically, compares […] and updates the contents of the memory in expected […]". -The update to the memory in expected is clearly not atomic, and yet this wording parallels the success case, -in which the memory update is atomic. -

    2. -

  2. The wording suggests that memory (including *expected) is affected according to the value of failure. -In particular, the failure order could be memory_order_seq_cst, which might lead someone to incorrectly think they'd -published the value of *expected.

    3. -
-

-I think this can be clarified with no change in meaning by reordering the wording a little: -

-

-"Atomically, compares the contents of the memory pointed to by object or by this for equality with that in -expected, and if true, replaces the contents of the memory pointed to by object or by this with -that in desired, and if. If the comparison is true, memory is affected according to the value of -success, and if the comparison is false, memory is affected according to the value of failure. Further, -if the comparison is false, updatesreplaces the contents of the memory in expected with -the contents ofvalue that was atomically read from the memory pointed to by object or by -this. Further, if the comparison is true, memory is affected according to the value of success, and -if the comparison is false, memory is affected according to the value of failure." -

-
-

-Jens Maurer add: -

-
-

-I believe this is an improvement. -

-I like to see the following additional improvements: -

-
    -

  • -"contents of the memory" is strange phrasing, which doesn't say how large the -memory block is. Do we compare the values or the value representation of the lvalue -*object (or *this)? -

    • -

  • -29.3 [atomics.order] defines memory order based on the "affected memory location". It would be -better to say something like "If the comparison is true, the memory synchronization order for the -affected memory location *object is […]" -

    • -
-
-

-There was also a discussion thread involving Herb Sutter, Hans Boehm, and Lawrence Crowl, resulting in proposed -wording along the lines of: -

-
-
-

--21- Effects: Atomically with respect to expected and the memory pointed -to by object or by this, compares the contents of the memory pointed -to by object or by this for equality with that in expected, and if and -only if true, replaces the contents of the memory pointed to by object -or by this with that in desired, and if and only if false, updates the -contents of the memory in expected with the contents of the memory pointed to by -object or by this. -

-
-

-At the end of paragraph 23, perhaps add -

-
-

-[Example: Because the expected value is updated only on failure, -code releasing the memory containing the expected value on success -will work. E.g. list head insertion will act atomically and not -have a data race in the following code. -

-
-do {
-  p->next = head; // make new list node point to the current head
-} while(!head.compare_exchange_weak(p->next, p)); // try to insert
-
-

-— end example] -

-
-
-

-Hans objected that this still gives the misimpression that the update to expected is atomic. -

- -

[2014-11 Urbana]

- -

-Proposed resolution was added after Redmond. -

-

-Recommendations from SG1: -

-
    -
  1. Change wording to if trueif and only if true, and change if falseif and only if false.
    2. -
  2. If they want to add "respect to" clause, say "respect to object or this".
    3. -
  3. In example, load from head should be "head.load(memory_order_relaxed)", because people are going to use example as example of good code.
    4. -
- -

-(wording edits not yet applied) -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-We believed we were done with it, but it was kicked back to us, with the wording we suggested not yet applied. It may have been that our suggestions were unclear. Was that the concern? -

- - - -

Proposed resolution:

- -
    -

  1. Edit 29.6.5 [atomics.types.operations.req] p21 as indicated:

    - -
    -

    --21- Effects: Retrieves the value in expected. It then aAtomically, -compares the contents of the memory pointed to by object or by this for equality with that -inpreviously retrieved from expected, and if true, replaces the contents of the -memory pointed to by object or by this with that in desired, and if false, -updates the contents of the memory in expected with the contents of the memory pointed to by object -or by this. Further, if. If and only if the comparison is true, memory is affected according to the value of -success, and if the comparison is false, memory is affected according to the value of failure. -When only one memory_order argument is supplied, the value of success is order, -and the value of failure is order except that a value of memory_order_acq_rel -shall be replaced by the value memory_order_acquire and a value of memory_order_release shall -be replaced by the value memory_order_relaxed. If the comparison is false then, after the atomic -operation, the contents of the memory in expected are replaced by the value read from object or -by this during the atomic comparison. If the operation returns true, these operations are -atomic read-modify-write operations (1.10) on the memory pointed to by this or -object. Otherwise, these operations are atomic load operations on that memory. -

    -
    -
    2. - -

  2. Add the following example to the end of 29.6.5 [atomics.types.operations.req] p23:

    - -
    -

    --23- [Note: […] — end note] [Example: […] — end example] -

    -[Example: Because the expected value is updated only on failure, -code releasing the memory containing the expected value -on success will work. E.g. list head insertion will act atomically -and would not introduce a data race in the following code: -

    -
    -
    
-do {
-  p-i>next = head; // make new list node point to the current head
-} while(!head.compare_exchange_weak(p->next, p)); // try to insert
-
    -
    -

    -— end example] -

    -
    -
    3. -
- - - - - - -
-

2430. Heterogeneous container lookup should be enabled using meta-function instead of nested type

-

Section: 23.2.4 [associative.reqmts] Status: LEWG - Submitter: Tomasz Kamiński Opened: 2014-07-14 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Currently the heterogeneous lookup in associative container are -enabled by presence of is_transparent nested type in the comparator -type (23.2.4 [associative.reqmts]). This complicates the definition -of call wrapper types that want to define is_transparent if they wrap -a callable type that defines is_transparent, and requires the target -to be a complete type in cases where an incomplete type would otherwise be ok. -

-Another problem is that users cannot add the is_transparent member to -a third-party comparison type that they do not control, even if they -know it supports heterogeneous comparisons. -

-If the associative containers used a trait instead of checking for an -is_transparent member type then it would avoid the requirement for -complete types, and would allow customization of the trait without -modifying the comparator type. This would also be consistent with the -traits is_placeholder and is_bind_expression. -

-For backward compatibility with the existing design, the default -implementation of the is_transparent trait could depend on the -presence of the is_transparent nested type. -

- -

[2014-11 Urbana]

- -

Move to LEWG

-

-Request for a new metafunction should first be responded to by LEWG. -

- - -

Proposed resolution:

- - - - - -
-

2431. Missing regular expression traits requirements

-

Section: 28.3 [re.req] Status: New - Submitter: Jonathan Wakely Opened: 2014-09-30 Last modified: 2015-04-08

-

View all issues with New status.

-

Discussion:

-

-The requirements on the traits class in 28.3 [re.req] do not say whether a -regular expression traits class is required to be DefaultConstructible, -CopyConstructible, CopyAssignable etc. -

-The std::regex_traits class appears to be all of the above, but can -basic_regex assume that for user-defined traits classes? -

-Should the following statements all leave u in equivalent states? -

-
-X u{v};
-X u; u = v;
-X u; u.imbue(v.getloc();
-
-

-Whether they are equivalent has implications for basic_regex copy construction and -assignment. -

- - -

Proposed resolution:

- - - - - -
-

2432. initializer_list assignability

-

Section: 18.9 [support.initlist] Status: EWG - Submitter: David Krauss Opened: 2014-09-30 Last modified: 2015-05-22

-

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-

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-

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-

Discussion:

-

-std::initializer_list::operator= 18.9 [support.initlist] is horribly broken and it needs deprecation: -

-
-std::initializer_list<foo> a = {{1}, {2}, {3}};
-a = {{4}, {5}, {6}};
-// New sequence is already destroyed.
-
-

-Assignability of initializer_list isn't explicitly specified, but most implementations supply a default assignment -operator. I'm not sure what 17.5 [description] says, but it probably doesn't matter. -

- -

[Lenexa 2015-05-05: Send to EWG as discussed in Telecon]

- - - -

Proposed resolution:

- -
    -

  1. Edit 18.9 [support.initlist] p1, class template initializer_list synopsis, as indicated:

    - -
    -
    -namespace std {
-  template<class E> class initializer_list {
-  public:
-    […]
-    constexpr initializer_list() noexcept;
-  
-    initializer_list(const initializer_list&) = default;
-    initializer_list(initializer_list&&) = default;
-    initializer_list& operator=(const initializer_list&) = delete;
-    initializer_list& operator=(initializer_list&&) = delete;
-    
-    constexpr size_t size() const noexcept;
-    […]
-  };
-  […]
-}
-
    -
    - -
    2. -
- - - - - - -
-

2435. reference_wrapper::operator()'s Remark should be deleted

-

Section: 20.9.4.4 [refwrap.invoke] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-08

-

View all issues with Ready status.

-

Discussion:

-

-20.9.4.4 [refwrap.invoke]/2 is no longer useful. (It was originally TR1 2.1.2.4 [tr.util.refwrp.invoke]/2.) -First, we already have the As If Rule (1.9 [intro.execution]/1) and the STL Implementers Can Be Sneaky Rule -(17.6.5.5 [member.functions]). Second, with variadic templates and other C++11/14 tech, this can be implemented -exactly as depicted. -

- -

[2015-05, Lenexa]

- -

-DK: I don't see a defect here
-STL: the issue is that the standard is overly verbose, we don't need this sentence. It's redundant.
-MC: does anyone think this paragraph has value?
-JW: it has negative value. reading it makes me wonder if there's some reason I would want to provide a set of overloaded -functions, maybe there's some problem with doing it the obvious way that I'm not clever enough to see.
-Move to Ready status: 8 in favor, none against. -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 20.9.4.4 [refwrap.invoke] p2 as depicted:

    - -
    -
    -template <class... ArgTypes>
-  result_of_t<T&(ArgTypes&&...)>
-    operator()(ArgTypes&&... args) const;
-
    -
    -

    --1- Returns: INVOKE(get(), std::forward<ArgTypes>(args)...). (20.9.2) -

    --2- Remark: operator() is described for exposition only. Implementations are not required to provide an -actual reference_wrapper::operator(). Implementations are permitted to support reference_wrapper function -invocation through multiple overloaded operators or through other means. -

    -
    -
    -
    2. -
- - - - - - -
-

2436. Comparators for associative containers should always be CopyConstructible

-

Section: 23.2.4 [associative.reqmts], 23.2.5 [unord.req] Status: LEWG - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with LEWG status.

-

Discussion:

-

-The associative container requirements attempt to permit comparators that are DefaultConstructible -but non-CopyConstructible. However, the Standard contradicts itself. 23.4.4.1 [map.overview] depicts -map() : map(Compare()) { } which requires both DefaultConstructible and CopyConstructible. -

-Unlike fine-grained element requirements (which are burdensome for implementers, but valuable for users), such -fine-grained comparator requirements are both burdensome for implementers (as the Standard's self-contradiction -demonstrates) and worthless for users. We should unconditionally require CopyConstructible comparators. -(Note that DefaultConstructible should remain optional; this is not problematic for implementers, and -allows users to use lambdas.) -

-Key equality predicates for unordered associative containers are also affected. However, 17.6.3.4 [hash.requirements]/1 -already requires hashers to be CopyConstructible, so 23.2.5 [unord.req]'s redundant wording should -be removed. -

- -

[2015-02, Cologne]

- -

-GR: I prefer to say "Compare" rather than "X::key_compare", since the former is what the user supplies. -JY: It makes sense to use "Compare" when we talk about requirements but "key_compare" when we use it. -

-AM: We're adding requirements here, which is a breaking change, even though nobody will ever have had a non-CopyConstructible -comparator. But the simplification is probably worth it. -

-GR: I don't care about unmovable containers. But I do worry that people might want to move they comparators. MC: How do -you reconcile that with the function that says "give me the comparator"? GR: That one returns by value? JY: Yes. [To MC] -You make it a requirement of that function. [To GR] And it [the key_comp() function] is missing its requirements. -We need to add them everywhere. GR: map already has the right requirements. -

-JM: I dispute this. If in C++98 a type wasn't copyable, it had some interesting internal state, but in C++98 you wouldn't -have been able to pass it into the container since you would have had to make a copy. JY: No, you could have -default-constructed it and never moved it, e.g. a mutex. AM: So, it's a design change, but one that we should make. -That's probably an LEWG issue. AM: There's a contradiction in the Standard here, and we need to fix it one way or another. -

-Conclusion: Move to LEWG -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 23.2.4 [associative.reqmts] Table 102 as indicated (Editorial note: For "expression" X::key_compare -"defaults to" is redundant with the class definitions for map/etc.):

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -X::key_compare - -Compare - -defaults to less<key_type>
    -Requires: key_compare is CopyConstructible. -    		 -compile time -
    -… -
    -X(c)
    -X a(c);     -    		 - -Requires: key_compare is CopyConstructible.
    -Effects: Constructs an empty -container. Uses a copy of c as -a comparison object. -    		 -constant -
    -… -
    -X(i,j,c)
    -X a(i,j,c);     -    		 - -Requires: key_compare is CopyConstructible.
    -value_type is EmplaceConstructible into X from *i.
    -Effects: Constructs […] -    		 -[…] -
    -… -
    -
    2. - -

  2. Change 23.2.5 [unord.req] Table 103 as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 103 — Unordered associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -X::key_equal - -Pred - -Requires: Pred is CopyConstructible.
    -Pred shall be a binary predicate that takes two arguments of type Key.
    -Pred is an equivalence relation. -    		 -compile time -
    -… -
    -X(n, hf, eq)
    -X a(n, hf, eq);     -    		 -X - -Requires: hasher and key_equal are CopyConstructible.
    -Effects: Constructs […] -    		 -[…] -
    -… -
    -X(n, hf)
    -X a(n, hf);     -    		 -X - -Requires: hasher is CopyConstructible and
    -key_equal is DefaultConstructible
    -Effects: Constructs […] -    		 -[…] -
    -… -
    -X(i, j, n, hf, eq)
    -X a(i, j, n, hf, eq);     -    		 -X - -Requires: hasher and key_equal are CopyConstructible.
    -value_type is EmplaceConstructible into X from *i.
    -Effects: Constructs […] -    		 -[…] -
    -… -
    -X(i, j, n, hf)
    -X a(i, j, n, hf);     -    		 -X - -Requires: hasher is CopyConstructible and
    -key_equal is DefaultConstructible
    -value_type is EmplaceConstructible into X from *i.
    -Effects: Constructs […] -    		 -[…] -
    -… -
    -
    3. -
- - - - - - -
-

2441. Exact-width atomic typedefs should be provided

-

Section: 29.5 [atomics.types.generic] Status: Open - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-08

-

View other active issues in [atomics.types.generic].

-

View all other issues in [atomics.types.generic].

-

View all issues with Open status.

-

Discussion:

-

-<atomic> doesn't provide counterparts for <inttypes.h>'s most useful typedefs, possibly -because they're quasi-optional. We can easily fix this. -

- -

[2014-11, Urbana]

- -

-Typedefs were transitional compatibility hack. Should use _Atomic macro or template. -E.g. _Atomic(int8_t). BUT _Atomic disappeared!

- -

-Detlef will look for _Atomic macro. If missing, will open issue. -

- -

[2014-11-25, Hans comments]

- -

-There is no _Atomic in C++. This is related to the much more general unanswered question of whether C++17 -should reference C11, C99, or neither. -

- -

[2015-02 Cologne]

- -

-AM: I think this is still an SG1 issue; they need to deal with it before we do. -

- -

[2015-05 Lenexa, SG1 response]

- -

-Move to SG1-OK status. This seems like an easy short-term fix. We probably need a paper on C/C++ atomics compatibility to deal with _Atomic, but that's a separable issue. -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 29.5 [atomics.types.generic] p8 as depicted:

    - -
    -

    --8- There shall be atomic typedefs corresponding to the typedefs in the header <inttypes.h> as specified in -Table 147. atomic_intN_t, atomic_uintN_t, atomic_intptr_t, and -atomic_uintptr_t shall be defined if and only if intN_t, uintN_t, intptr_t, -and uintptr_t are defined, respectively. -

    -
    2. - -

  2. Change 29.6.5 [atomics.types.operations.req], Table 147 ("atomic <inttypes.h> -typedefs"), as depicted:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 147 — atomic <inttypes.h> typedefs
    Atomic typedef<inttypes.h> type
    -atomic_int8_t - -int8_t -
    -atomic_uint8_t - -uint8_t -
    -atomic_int16_t - -int16_t -
    -atomic_uint16_t - -uint16_t -
    -atomic_int32_t - -int32_t -
    -atomic_uint32_t - -uint32_t -
    -atomic_int64_t - -int64_t -
    -atomic_uint64_t - -uint64_t -
    -… -
    -
    -
    3. -
- - - - - - -
-

2443. std::array member functions should be constexpr

-

Section: 23.3.2 [array] Status: LEWG - Submitter: Peter Sommerlad Opened: 2014-10-06 Last modified: 2015-04-08

-

View other active issues in [array].

-

View all other issues in [array].

-

View all issues with LEWG status.

-

Discussion:

-

-When experimenting with C++14 relaxed constexpr functions I made the observation that I couldn't -use std::array to create a table of data at compile time directly using loops in a function. -However, a simple substitute I could use instead: -

-
-
-template <typename T, size_t n>
-struct ar {
-  T a[n];
-  constexpr ar() : a{{}}{}
-  constexpr auto data() const { return &a[0];}
-  constexpr T const & operator[](size_t i) const { return a[i]; }
-  constexpr T & operator[](size_t i) { return a[i]; }
-};
-
-template <size_t n>
-using arr = ar<size_t, n>; // std::array<size_t, n>;
-
-template <size_t n>
-constexpr auto make_tab(){
-  arr<n> result;
-  for(size_t i=0; i < n; ++i)
-    result[i] = (i+1)*(i+1); // cannot define operator[] for mutable array...
-  return result;
-}
-
-template <size_t n>
-constexpr auto squares=make_tab< n>();
-
-int main() {
-  int dummy[squares<5>[3]];
-}
-
-
-

-Therefore, I suggest that all member functions of std::array should be made constexpr -to make the type usable in constexpr functions. -

-Wording should be straight forward, may be with the exception of fill, which would require -fill_n to be constexpr as well. -

- -

[2014-11 Urbana]

- -

Move to LEWG

-

-The extent to which constexpr becomes a part of the Library design is a policy -matter best handled initially by LEWG. -

- - -

Proposed resolution:

- - - - - -
-

2444. Inconsistent complexity for std::sort_heap

-

Section: 25.4.6.4 [sort.heap] Status: Open - Submitter: François Dumont Opened: 2014-10-07 Last modified: 2015-05-22

-

View all issues with Open status.

-

Discussion:

-

-While creating complexity tests for the GNU libstdc++ implementation I -stumbled across a surprising requirement for the std::sort_heap algorithm. -

-In 25.4.6.4 [sort.heap] p3 the Standard states: -

-

-Complexity: At most N log(N) comparisons (where N == last - first). -

-

-As stated on the libstdc++ mailing list by Marc Glisse sort_heap can be implemented by N calls to -pop_heap. As max number of comparisons of pop_heap is 2 * log(N) then sort_heap -max limit should be 2 * log(1) + 2 * log(2) + .... + 2 * log(N) that is to say 2 * log(N!). -In terms of log(N) we can also consider that this limit is also cap by 2 * N * log(N) -which is surely what the Standard wanted to set as a limit. -

-This is why I would like to propose to replace paragraph 3 by: -

-

-Complexity: At most 2N log(N) comparisons (where N == last - first). -

- -

[2015-02 Cologne]

- -

-Marshall will research the maths and report back in Lenexa. -

- -

[2015-05-06 Lenexa]

- -

STL: I dislike exact complexity requirements, they prevent one or two extra checks in debug mode. Would it be better to say O(N log(N)) not at most?

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
  1. -

    -In 25.4.6.4 [sort.heap] p3 the Standard states: -

    -
    -
    -template<class RandomAccessIterator>
-  void sort_heap(RandomAccessIterator first, RandomAccessIterator last);
-template<class RandomAccessIterator, class Compare>
-  void sort_heap(RandomAccessIterator first, RandomAccessIterator last,
-                 Compare comp);
-
    -

    -[…] -

    --3- Complexity: At most 2N log(N) comparisons (where N == last - first). -

    -
    -
    2. -
- - - - - -
-

2445. "Stronger" memory ordering

-

Section: 20.8.2.6 [util.smartptr.shared.atomic], 29.6.5 [atomics.types.operations.req] Status: SG1 - Submitter: JF Bastien Opened: 2014-10-08 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.atomic].

-

View all issues with SG1 status.

-

Discussion:

-

-The definitions of compare and exchange in 20.8.2.6 [util.smartptr.shared.atomic] p32 and -29.6.5 [atomics.types.operations.req] p20 state: -

-

-Requires: The failure argument shall not be memory_order_release nor memory_order_acq_rel. -The failure argument shall be no stronger than the success argument. -

-

-The term "stronger" isn't defined by the standard. -

-It is hinted at by 29.6.5 [atomics.types.operations.req] p21: -

-

-When only one memory_order argument is supplied, the value of success is order, and the -value of failure is order except that a value of memory_order_acq_rel shall be replaced -by the value memory_order_acquire and a value of memory_order_release shall be replaced by the -value memory_order_relaxed. -

-

-Should the standard define a partial ordering for memory orders, where consume and acquire are incomparable with release? -

- -

[2014-11 Urbana]

- -

-Move to SG1. -

- - -

Proposed resolution:

- - - - - -
-

2446. Unspecialized std::tuple_size should be defined

-

Section: 20.4.1 [tuple.general] Status: LEWG - Submitter: Nevin Liber Opened: 2014-10-10 Last modified: 2015-04-08

-

View all issues with LEWG status.

-

Discussion:

-

-In 20.4.1 [tuple.general] paragraph 2, the unspecialized std::tuple_size is undefined. It would -be a lot more useful with SFINAE if it were defined as an empty struct; that way, it can be used with enable_if -for determining whether or not it is valid to use tuple_size, tuple_element and get on the -corresponding data structure. -

- -

[2014-11 Urbana]

- -

Moved to LEWG 42.

-

-This request goes beyond simply making an API respond well to SFINAE, but coupling that with an -implication for other tuple APIs. The proper place for such design discussions is LEWG. -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 20.4.1 [tuple.general] p2, header <tuple> synopsis, as indicated

    -
    -
    -[…]
-// 20.4.2.5, tuple helper classes:
-template <class T> class tuple_size; // undefined
-[…]
-
    -
    -
    2. - -

  2. Change 20.4.2.5 [tuple.helper] as indicated

    -
    -
    -[…]
-template <class T> struct tuple_size { };
-[…]
-
    -
    -
    3. -
- - - - - -
-

2447. Allocators and volatile-qualified value types

-

Section: 17.6.3.5 [allocator.requirements] Status: Ready - Submitter: Daniel Krügler Opened: 2014-10-16 Last modified: 2015-05-22

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Ready status.

-

Discussion:

-

-According to Table 27 — "Descriptive variable definitions" which is used to define the symbols used in the -allocator requirements table within 17.6.3.5 [allocator.requirements] we have the following constraints for -the types T, U, C: -

-

-any non-const object type (3.9) -

-

-This wording can be read to allow instead a volatile-qualified value type such as volatile int. -

-The nearest-by way of fixing this would be to add "non-volatile" as additional constraint to this table -row. -

-Another choice would be to think of requiring that allocators must be capable to handle any cv-qualified -value types. This would make all currently existing allocators non-conforming that can't handle cv-qualified -value types, so I'm not suggesting to follow that route. -

-A less radical step would be to allow cv-qualified types just for C (which is used to specify the -functions construct and destroy and where does not even exist any requirement that C actually -is related to the value type of the allocator at all). This seemingly extension would be harmless because as of p8 of the -same sub-clause "An allocator may constrain the types on which it can be instantiated and the arguments for which its -construct member may be called." -

-This differs from the requirements imposed on the types T and U which both refer to value types of allocators. -

-The proposed wording attempts to separate the two classes of requirements. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

-This wording is relative to N4140. -

- -
    -

  1. Change 17.6.3.5 [allocator.requirements], Table 27 — "Descriptive variable definitions", as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - -
    Table 27 — Descriptive variable definitions
    VariableDefinition
    -T, U, C - -any non-constconst and non-volatile object type (3.9) -
    -C - -any object type -
    -… -
    -
    -
    2. - -

  2. Change 17.6.3.5 [allocator.requirements] p8 as indicated: (This wording change is intended to -fix an obvious asymmetry between construct and destroy which I believe is not intended)

    - -

    --8- An allocator may constrain the types on which it can be instantiated and the arguments for which its -construct or destroy members may be called. If a type cannot be -used with a particular allocator, the allocator class or the call to construct or destroy -may fail to instantiate. -

    -
    3. -
- -
- -

[2014-11, Urbana]

- -

-JW: say "cv-unqualified" instead?
-JW: very nervous about allowing construct on const-types, because of the cast to (non-const) void*
-MA: should we just make the minimal fix?
-STL: don't break C out for special treatment
-New proposed resolution: just change "non-const" to "cv-unqualified". Keep addition of destroy later. -

- -

[2015-02 Cologne]

- -

-GR: It makes me nervous that someone at some point decided to not add "non-volatile".
-AM: That was over ten years ago. It was a deliberate, minuted choice to support volatile. We are now reversing that decision. -It would be good to poll our vendors, none of which are in the room. This is a bit more work than we expect of a P0 issue.
-VV: libstdc++ and libc++ seem to support volatile template parameters for the standard allocator.
-AM: To clarify, the proposed resolution here would remove the requirement to support volatile. Implementations could still -choose to support volatile.
-DK: I'm happy to drop this and open a new issue in regard to the destroy member specification.
-AM: I just think this is harder than a P0. Let's reprioritize. -

- -

[2015-04-01 Daniel comments]

- -

-The less controversial part of the issue related to constraints imposed on destroy has be handed over to the new -issue 2470. -

- -

[2015-05-06 Lenexa: Move to Ready]

- - - -

Proposed resolution:

-

-This wording is relative to N4431. -

- -
    -

  1. Change 17.6.3.5 [allocator.requirements], Table 27 — "Descriptive variable definitions", as indicated:

    -
    - - - - - - - - - - - - - - - - -
    Table 27 — Descriptive variable definitions
    VariableDefinition
    -T, U, C - -any non-constcv-unqualified object type (3.9) -
    -… -
    -
    -
    2. -
- - - - - -
-

2449. vector::insert invalidates end()?

-

Section: 23.3.6.5 [vector.modifiers] Status: New - Submitter: Marc Glisse Opened: 2014-10-21 Last modified: 2015-04-08

-

View other active issues in [vector.modifiers].

-

View all other issues in [vector.modifiers].

-

View all issues with New status.

-

Discussion:

-

-this issue is based on the discussion here. -

-23.3.6.5 [vector.modifiers] says about vector::insert: "If no reallocation happens, all the iterators and references -before the insertion point remain valid." This doesn't seem to guarantee anything about the iterator at the point of insertion. -

-The question comes from people asking if the following is valid, assuming a sufficient call to reserve() was done first: -

-
-v.insert(v.end(), v.begin(), v.end());
-
-

-It could fail for an implementation using a sentinel for the end of the vector, but I don't know of any (it would be quite -inconvenient). And for any implementation using a simple position as iterator (pointer (possibly in a wrapper), or base+offset), -this is needlessly restrictive. The fact that this alternative: -

-
-v.insert(v.end(), &v[0], &v[0]+v.size())
-
-

-is arguably valid (again assuming a large enough reserve()) makes it a bit confusing that the first version isn't -(23.2.3 [sequence.reqmts] has a precondition that iterator arguments to insert() do not point into the sequence, -but vector::insert is more refined and seems to give enough guarantees that it cannot fail). -

-Then we might as well say that vector iterators act as positions, and that after a reallocation-free operation an -iterator points to the same position, whatever may be there now… -

- - -

Proposed resolution:

- - - - - -
-

2450. (greater|less|greater_equal|less_equal)<void> do not yield a total order for pointers

-

Section: 20.9.6 [comparisons] Status: Open - Submitter: Joaquín M López Muñoz Opened: 2014-10-30 Last modified: 2015-05-06

-

View other active issues in [comparisons].

-

View all other issues in [comparisons].

-

View all issues with Open status.

-

Discussion:

-

-less<void>::operator(t, u) (and the same applies to the rest of void specializations for standard -comparison function objects) returns t < u even if t and u are pointers, which by -5.9 [expr.rel]/3 is undefined except if both pointers point to the same array or object. This might be -regarded as a specification defect since the intention of N3421 is that less<> can substitute for -less<T> in any case where the latter is applicable. less<void> can be rewritten in -the following manner to cope with pointers: -

-
-template<> struct less<void>
-{
-
-  typedef unspecified is_transparent;
-
-  template <class T, class U>
-  struct pointer_overload : std::is_pointer<std::common_type_t<T, U>>
-  {};
-
-  template <
-    class T, class U,
-    typename std::enable_if<!pointer_overload<T, U>::value>::type* = nullptr
-  >
-  auto operator()(T&& t, U&& u) const
-    -> decltype(std::forward<T>(t) < std::forward<U>(u))
-  {
-    return std::forward<T>(t) < std::forward<U>(u);
-  } 
-
-  template <
-    class T, class U,
-    typename std::enable_if<pointer_overload<T, U>::value>::type* = nullptr
-  >
-  auto operator()(T&& t, U&& u) const
-    -> decltype(std::declval<std::less<std::common_type_t<T, U>>>()(std::forward<T>(t), std::forward<U>(u)))
-  {
-    std::less<std::common_type_t<T, U>> l;
-    return l(std::forward<T>(t), std::forward<U>(u));
-  }
-
-};
-
- -
-

-This wording is relative to N4140. -

- -
    -

  1. Change 20.9.6 [comparisons] p14 as indicated:

    -

    --14- For templates greater, less, greater_equal, and less_equal, the specializations -for any pointer type yield a total order, even if the built-in operators <, >, <=, ->= do not. For template specializations greater<void>, less<void>, -greater_equal<void>, and less_equal<void>, the call operator with arguments whose common -type CT is a pointer yields the same value as the corresponding comparison function object class -specialization for CT. -

    -
    2. -
-
- -

[2015-02, Cologne]

- -

-AM: Is there any way this will be resolved elsewhere? VV: No. AM: Then we should bite the bullet and deal with it here. -

-MC: These diamond operators are already ugly. Making them more ugly isn't a big problem. -

-JY found some issue with types that are convertible, and will reword. -

-Jeffrey suggests improved wording. -

- -

[2015-05, Lenexa]

- -

-STL: when diamond functions designed, this was on purpose
-STL: this does go against the original design
-STL: library is smarter and can give a total order
-MC: given that the original design rejected this, give back to LEWG
-STL: original proposal did not talk about total order
-STL: don't feel strongly about changing the design
-STL: no objections to taking this issue with some wording changes if people want it
-MC: not happy with wording, comparing pointers — what does that mean?
-STL: needs careful attention to wording
-STL: want to guarantee that nullptr participates in total ordering
-STL: all hooks into composite pointer type
-MC: move from new to open with better wording
-STL: to check updates to issue after Lenexa -

- - -

Proposed resolution:

-

-This wording is relative to N4296. -

- -
    -

  1. Change 20.9.6 [comparisons] p14 as indicated:

    -

    --14- For templates greater, less, greater_equal, and less_equal, the specializations -for any pointer type yield a total order, even if the built-in operators <, >, <=, ->= do not. For template specializations greater<void>, less<void>, -greater_equal<void>, and less_equal<void>, if the call operator calls a built-in operator -comparing pointers, the call operator yields a total order. -

    -
    2. -
- - - - - -
-

2451. [fund.ts] optional<T> should 'forward' T's implicit conversions

-

Section: X [optional.object] Status: LEWG - Submitter: Geoffrey Romer Opened: 2014-10-31 Last modified: 2015-04-08

-

View all issues with LEWG status.

-

Discussion:

-

Addresses: fund.ts

-

-Code such as the following is currently ill-formed (thanks to STL for the compelling example): -

-
-optional<string> opt_str = "meow";
-
-

-This is because it would require two user-defined conversions (from const char* to string, -and from string to optional<string>) where the language permits only one. This is -likely to be a surprise and an inconvenience for users. -

-optional<T> should be implicitly convertible from any U that is implicitly convertible -to T. This can be implemented as a non-explicit constructor template optional(U&&), -which is enabled via SFINAE only if is_convertible_v<U, T> and is_constructible_v<T, U>, -plus any additional conditions needed to avoid ambiguity with other constructors (see -N4064, particularly the -"Odd" example, for why is_convertible and is_constructible are both needed; thanks to Howard -Hinnant for spotting this). -

-In addition, we may want to support explicit construction from U, which would mean providing a corresponding -explicit constructor with a complementary SFINAE condition (this is the single-argument case of the "perfect -initialization" pattern described in N4064). -

- - - -

Proposed resolution:

- - - - - -
-

2452. is_constructible, etc. and default arguments

-

Section: 20.10 [meta] Status: Core - Submitter: Hubert Tong Opened: 2014-11-04 Last modified: 2015-04-08

-

View other active issues in [meta].

-

View all other issues in [meta].

-

View all issues with Core status.

-

Discussion:

-

-The BaseCharacteristic for is_constructible is defined in terms of the well-formedness -of a declaration for an invented variable. The well-formedness of the described declaration itself may -change for the same set of arguments because of the introduction of default arguments. -

-In the following program, there appears to be conflicting definitions of a specialization of -std::is_constructible; however, it seems that this situation is caused without a user violation -of the library requirements or the ODR. There is a similar issue with is_convertible, result_of -and others. -

-a.cc: -

-
-#include <type_traits>
-struct A { A(int, int); };
-const std::false_type& x1 = std::is_constructible<A, int>();
-
-int main() { }
-
-

-b.cc: -

-
-#include <type_traits>
-struct A { A(int, int); };
-
-inline A::A(int, int = 0) { }
-
-const std::true_type& x2 = std::is_constructible<A, int>();
-
-

-Presumably this program should invoke undefined behaviour, but the Library specification doesn't -say that. -

- -

[2015-02 Cologne]

- -

-Core wording should say "this kind of thing is ill-formed, no diagnostic required" -

- - -

Proposed resolution:

- - - - - -
-

2453. [iterator.range] and now [iterator.container] aren't available via <initializer_list>

-

Section: 18.9 [support.initlist], 24.7 [iterator.range], 24.8 [iterator.container] Status: New - Submitter: Richard Smith Opened: 2014-11-11 Last modified: 2015-04-08

-

View other active issues in [support.initlist].

-

View all other issues in [support.initlist].

-

View all issues with New status.

-

Discussion:

-

-These sections define helper functions, some of which apply to initializer_list<T>. And they're -available if you include one of a long list of header files, many of which include <initializer_list>. -But they are not available if you include <initializer_list>. This seems very odd. -

-
-#include <initializer_list>
-auto x = {1, 2, 3};
-const int *p = data(x); // error, undeclared
-#include <vector>
-const int *q = data(x); // ok
-
- - -

Proposed resolution:

- - - - - -
-

2456. Incorrect exception specifications for 'swap' throughout library

-

Section: 20.2 [utility], 20.3.2 [pairs.pair], 20.4 [tuple], 23.3.2 [array], 23.6.3 [queue], 23.6.4 [priority.queue], 23.6.5 [stack] Status: Open - Submitter: Richard Smith Opened: 2014-11-14 Last modified: 2015-05-05

-

View other active issues in [utility].

-

View all other issues in [utility].

-

View all issues with Open status.

-

Discussion:

-

-We have this antipattern in various library classes: -

-
-void swap(priority_queue& q) noexcept(
-    noexcept(swap(c, q.c)) && noexcept(swap(comp, q.comp)))
-
-

-This doesn't work. The unqualified lookup for 'swap' finds the member named 'swap', and that suppresses ADL, -so the exception specification is always ill-formed because you can't call the member 'swap' with two arguments. -

-Relevant history on the core language side: -

-This used to be ill-formed due to 3.3.7 [basic.scope.class] p1 rule 2: "A name N used in a class -S shall refer to the same declaration in its context and when re-evaluated in the completed scope of S. -No diagnostic is required for a violation of this rule." -

-Core issue 1330 introduced delay-parsing for exception specifications. Due to the 3.3.7 [basic.scope.class] rules, -this shouldn't have changed the behavior of any conforming programs. But it changes the behavior in the non-conforming -case from "no diagnostic required" to "diagnostic required", so implementations that implement core issue 1330 are now -required to diagnose the ill-formed declarations in the standard library. -

-Suggested resolution: -

-Add an is_nothrow_swappable trait, and use it throughout the library in place of these noexcept expressions. -

- -

[2015-02, Cologne]

- -

-No action for now; we intend to have papers for Lenexa. -

- -

[2015-05, Lenexa]

- -

-Move to Open. -

-Daniel: A first paper (N4426) exists -to suggest some ways of solving this issue. -

- - -

Proposed resolution:

- - - - - -
-

2457. std::begin() and std::end() do not support multi-dimensional arrays correctly

-

Section: 24.7 [iterator.range] Status: New - Submitter: Janez Žemva Opened: 2014-11-16 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The following code: -

-
-#include <algorithm>
-#include <iterator>
-#include <iostream>
-#include <cassert>
-
-int main() 
-{
-  int a[2][3][4] = { { { 1,  2,  3,  4}, { 5,  6,  7,  8}, { 9, 10, 11, 12} },
-                     { {13, 14, 15, 16}, {17, 18, 19, 20}, {21, 22, 23, 24} } };
-  int b[2][3][4];
-
-  assert(std::distance(std::begin(a), std::end(a)) == 2 * 3 * 4);
-  std::copy(std::begin(a), std::end(a), std::begin(b));
-  std::copy(std::begin(b), std::end(b), std::ostream_iterator<int>(std::cout, ","));
-}
-
-

-does not compile. -

-A possible way to remedy this would be to add the following overloads of -begin, end, rbegin, and rend to 24.7 [iterator.range], -relying on recursive evaluation: -

-
-namespace std {
-
-  template <typename T, size_t M, size_t N>
-  constexpr remove_all_extents_t<T>*
-  begin(T (&array)[M][N])
-  {
-    return begin(*array);
-  }
-  
-  template <typename T, size_t M, size_t N>
-  constexpr remove_all_extents_t<T>*
-  end(T (&array)[M][N])
-  {
-    return end(array[M - 1]);
-  }
-
-  template <typename T, size_t M, size_t N>
-  reverse_iterator<remove_all_extents_t<T>*>
-  rbegin(T (&array)[M][N])
-  {
-    return decltype(rbegin(array))(end(array[M - 1]));
-  }
-  
-  template <typename T, size_t M, size_t N>
-  reverse_iterator<remove_all_extents_t<T>*>
-  rend(T (&array)[M][N])
-  {
-    return decltype(rend(array))(begin(*array));
-  }
-
-}
-
- - -

Proposed resolution:

- - - - - -
-

2460. LWG issue 2408 and value categories

-

Section: 20.10.7.6 [meta.trans.other], 24.4.1 [iterator.traits] Status: New - Submitter: Richard Smith Opened: 2014-11-19 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-LWG issue 2408 changes the meat of the specification of common_type to compute: -

-

-[..] the type, if any, of an unevaluated conditional expression (5.16) whose first operand is an -arbitrary value of type bool, whose second operand is an xvalue of type T1, -and whose third operand is an xvalue of type T2. -

-

-This has an effect on the specification that I think was unintended. It used to be the case that -common_type<T&, U&&> would consider the type of a conditional between an -lvalue of type T and an xvalue of type U. It's now either invalid (because there is -no such thing as an xvalue of reference type) or considers the type of a conditional between an xvalue -of type T and an xvalue of type U, depending on how you choose to read it. -

-Put another way, this has the effect of changing the usual definition from: -

-
-typedef decay_t<decltype(true ? declval<T>() : declval<U>())> type;
-
-

-to: -

-
-typedef decay_t<decltype(true ? declval<remove_reference_t<T>>() : declval<remove_reference_t<U>>())> type;
-
-

-It also makes common_type underspecified in the case where one of the operands is of type void; -in that case, the resulting type depends on whether the expression is a throw-expression, which is not -specified (but used to be). -

-Also on the subject of this wording: the changes to 24.4.1 [iterator.traits] say that -iterator_traits<T> "shall have no members" in some cases. That's wrong. It's a class type; -it always has at least a copy constructor, a copy assignment operator, and a destructor. Plus this -removes the usual library liberty to add additional members with names that don't collide with normal -usage (for instance, if a later version of the standard adds members, they can't be present here as a -conforming extension). Perhaps this should instead require that the class doesn't have members with any -of those five names? That's what 2408 does for common_type's type member. -

- - -

Proposed resolution:

- - - - - -
-

2461. Interaction between allocators and container exception safety guarantees

-

Section: 17.6.3.5 [allocator.requirements], 23.3.6.3 [vector.capacity], 23.3.6.5 [vector.modifiers] Status: New - Submitter: dyp Opened: 2014-12-06 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-When resizing a vector, the accessibility and exception specification of the value type's -constructors determines whether the elements are copied or moved to the new buffer. -However, the copy/move is performed via the allocator's construct member function, which is -assumed, but not required, to call the copy/move constructor and propagate only exceptions -from the value type's copy/move constructor. The issue might also affect other classes. -

-The current wording in N4296 relevant here is from Table 28 — "Allocator requirements" in -17.6.3.5 [allocator.requirements]: -

-
- - - - - - - - - - - - - - - - - - - - - - - - -
Table 28 — Allocator requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Default
-… -
-a.construct(c, args) - -(not used) - -Effect: Constructs an object of type C at c - -::new ((void*)c) C(forward<Args>(args)...) -
-… -
-
-

-and from 17.6.3.5 [allocator.requirements] p9: -

-

-An allocator may constrain the types on which it can be instantiated and the arguments for which its -construct member may be called. If a type cannot be used with a particular allocator, the allocator class -or the call to construct may fail to instantiate. -

-

-I conclude the following from the wording: -

-
    -

  1. The allocator is not required to call the copy constructor if the -arguments (args) is a single (potentially const) lvalue of the value -type. Similarly for a non-const rvalue + move constructor. See also -23.2.1 [container.requirements.general] p15 which seems to try to require -this, but is not sufficient: -That paragraph specifies the semantics of the allocator's operations, -but not which constructors of the value type are used, if any. -

    2. -
  2. -

    The allocator may throw exceptions in addition to the exceptions propagated by -the constructors of the value type; it can also propagate exceptions from constructors -other than a copy/move constructor. -

    -
    3. -
-

-This leads to an issue with the wording of the exception safety guarantees for vector modifiers in -23.3.6.5 [vector.modifiers] p1: -

-
-

-[…] -

-
-void push_back(const T& x);
-void push_back(T&& x);
-
-
-

-Remarks: Causes reallocation if the new size is greater than the old capacity. If no -reallocation happens, all the iterators and references before the insertion point remain valid. -If an exception is thrown other than by the copy constructor, move constructor, assignment -operator, or move assignment operator of T or by any InputIterator operation there are -no effects. - -If an exception is thrown while inserting a single element at the end and T -is CopyInsertable or is_nothrow_move_constructible<T>::value -is true, there are no effects. Otherwise, if an exception is thrown by the move constructor of a -non-CopyInsertable T, the effects are unspecified. - -

-
-
-

-The wording leads to the following problem: -Copy and move assignment are invoked directly from vector. -For intermediary objects (see 2164), -vector also directly invokes the copy and move constructor of the value type. -However, construction of the actual element within the buffer is invoked via the allocator abstraction. -As discussed above, the allocator currently is not required to call a copy/move constructor. -If is_nothrow_move_constructible<T>::value is true for some value type T, -but the allocator uses modifying operations for MoveInsertion that do throw, -the implementation is required to ensure that "there are no effects", -even if the source buffer has been modified. -

-Similarly, the vector capacity functions specify exception safety guarantees -referring to the move constructor of the value type. For example, vector::resize in 23.3.6.3 [vector.capacity] p14: -

-
-Remarks: If an exception is thrown other than by the move constructor of a -non-CopyInsertable T there are no effects. -
-

-The wording leads to the same issue as described above. -

-Code example: -

-
-
-template<class T>
-class allocator;
-
-class pot_reg_type // a type which creates
-                   // potentially registered instances
-{
-private:
-  friend class allocator<pot_reg_type>;
-  struct register_t {};
-
-  static std::set<pot_reg_type*>& get_registry()
-  {
-    static std::set<pot_reg_type*> registry;
-    return registry;
-  }
-  void enregister() noexcept(false)
-  {
-    get_registry().insert(this);
-  }
-  void deregister()
-  {
-    get_registry().erase(this);
-  }
-
-public:
-  pot_reg_type(void               ) noexcept(true) {}
-  pot_reg_type(pot_reg_type const&) noexcept(true) {}
-  pot_reg_type(pot_reg_type&&     ) noexcept(true) {}
-
-private:
-  pot_reg_type(register_t                     ) noexcept(false)
-  { enregister(); }
-  pot_reg_type(register_t, pot_reg_type const&) noexcept(false)
-  { enregister(); }
-  pot_reg_type(register_t, pot_reg_type&&     ) noexcept(false)
-  { enregister(); }
-};
-
-template<class T>
-class allocator
-{
-public:
-  using value_type = T;
-
-  value_type* allocate(std::size_t p)
-  { return (value_type*) ::operator new(p); }
-
-  void deallocate(value_type* p, std::size_t)
-  { ::operator delete(p); }
-
-  void construct(pot_reg_type* pos)
-  {
-    new((void*)pos) pot_reg_type((pot_reg_type::register_t()));
-  }
-  void construct(pot_reg_type* pos, pot_reg_type const& source)
-  {
-    new((void*)pos) pot_reg_type(pot_reg_type::register_t(), source);
-  }
-
-  template<class... Args>
-  void construct(T* p, Args&&... args)
-  {
-    new((void*)p) T(std::forward<Args>(args)...);
-  }
-}; 
-
-
-

-The construct member function template is only required for rebinding, -which can be required e.g. to store additional debug information in -the allocated memory (e.g. VS2013). -

-Even though the value type has an accessible and noexcept(true) move -constructor, this allocator won't call that constructor for rvalue arguments. -In any case, it does not call a constructor for which vector has formulated its -requirements. An exception thrown by a constructor called by this allocator is not -covered by the specification in 23.3.6.5 [vector.modifiers] and therefore is -guaranteed not to have any effect on the vector object when resizing. -

-For an example how this might invalidate the exception safety -guarantees, see this post on the std-discussion mailing list. -

-Another problem arises for value types whose constructors are private, -but may be called by the allocator e.g. via friendship. -Those value types are not MoveConstructible -(is_move_constructible is false), yet they can be MoveInsertable. -It is not possible for vector to create intermediary objects (see 2164) of such a type -by directly using the move constructor. -Current implementations of the single-element forms of vector::insert and vector::emplace -do create intermediary objects by directly calling one of the value type's constructors, -probably to allow inserting objects from references that alias other elements of the container. -As far as I can see, Table 100 — "Sequence container requirements" in 23.2.3 [sequence.reqmts] -does not require that the creation of such intermediare objects can be performed -by containers using the value type's constructor directly. -It is unclear to me if the allocator's construct function could be used to create those -intermediary objects, given that they have not been allocated by the allocator. -

-Two possible solutions: -

-
    -

  1. -Add the following requirement to the allocator_traits::construct function: -If the parameter pack args consists of a single parameter of the type -value_type&&, -the function may only propagate exceptions if is_nothrow_move_constructible<value_type>::value -is false. -

    -Requiring alloctor_traits::construct to call a true copy/move constructor -of the value type breaks std::scoped_allocator_adapter, -as pointed out by Casey Carter in a post on the std-discussion mailing list. -

    2. -
  2. -

    -Change vector's criterion whether to move or copy when resizing: -

    -Instead of testing the value type's constructors via -is_move_constructible, check the value of -noexcept( allocator_traits<Allocator>::construct(alloc, ptr, rval) ) -where -alloc is an lvalue of type Allocator, -ptr is an expression of type allocator_traits<Allocator>::pointer -and -rval is a non-const rvalue of type value_type. -

    -
    3. -
-

-A short discussion of the two solutions: -

-Solution 1 allows keeping is_nothrow_move_constructible<value_type> -as the criterion for vector to decide between copying and moving when resizing. -It restricts what can be done inside the construct member function of allocators, -and requires implementers of allocators to pay attention to the value types used. -One could conceive allocators checking the following with a static_assert: -If the value type is_nothrow_move_constructible, -then the constructor actually called for MoveInsertion within the construct -member function is also declared as noexcept. -

-Solution 2 requires changing both the implementation of the default -allocator (add a conditional noexcept) and vector (replace -is_move_constructible with an allocator-targeted check). -It does not impose additional restrictions on the allocator (other than -23.2.1 [container.requirements.general] p15), -and works nicely even if the move constructor of a MoveInsertable type is private or deleted -(the allocator might be a friend of the value type). -

-In both cases, an addition might be required to provide the basic exception safety guarantee. -A short discussion on this topic can be found - -in the std-discussion mailing list. -Essentially, if allocator_traits<Allocator>::construct throws an exception, -the object may or may not have been constructed. -Two solutions are mentioned in that discussion: -

-
    -

  1. -allocator_traits<Allocator>::construct needs to tell its caller -whether or not the construction was successful, in case of an exception. -

    2. -

  2. -If allocator_traits<Allocator>::construct propagates an exception, -it shall either not have constructed an object at the specified location, -or that object shall have been destroyed -(or it shall ensure otherwise that no resources are leaked). -

    3. -
- - - -

Proposed resolution:

- - - - - -
-

2462. std::ios_base::failure is overspecified

-

Section: 27.5.3 [ios.base], 27.5.3.1.1 [ios::failure] Status: Ready - Submitter: Jonathan Wakely Opened: 2014-12-15 Last modified: 2015-05-22

-

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-

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-

Discussion:

-

-27.5.3 [ios.base] defines ios_base::failure as a nested class: -

-
-
-namespace std {
-  class ios_base {
-  public:
-    class failure;
-    […]
-  };
-  […]
-}
-
-
-

-This means it is valid to use an elaborated-type-specifier to -refer to ios_base::failure: -

-
-
-using F = class std::ios_base::failure;
-throw F();
-
-
-

-Therefore implementations are not permitted to define -ios_base::failure as a typedef e.g. -

-
-
- class ios_base {
- public:
-#if __cplusplus < 201103L
-   class failure_cxx03 : public exception {...};
-   typedef failure_cxx03 failure;
-#else
-   class failure_cxx11 : public system_error {...};
-   typedef failure_cxx11 failure;
-#endif
-   […]
- };
-
-
-

-This constrains implementations, making it harder to manage the ABI -change to ios_base::failure between C++03 and C++11. -

- -

[2015-05-06 Lenexa: Move to Ready]

- -

JW: the issue is that users are currently allowed to write "class failure" with an elaborated-type-specifier and it must be well-formed, I want the freedom to make that type a typedef, so they can't necessarily use an elaborated-type-specifier (which there is no good reason to use anyway)

-

JW: ideally I'd like this everywhere for all nested classes, but that's a paper not an issue, I only need this type fixed right now.

-

RD: is a synonym the same as an alias?

-

JW: dcl.typedef says a typedef introduces a synonym for another type, so I think this is the right way to say this

-

JW: I already shipped this last month

-

PJP: we're going to have to break ABIs again some time, we need all the wiggle room we can get to make that easier. This helps.

-

MC: do we want this at all? Ready?

-

9 in favor, none opose or abstaining

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change the synopsis in 27.5.3 [ios.base] as indicated:

    - -
    -
    -namespace std {
-  class ios_base {
-  public:
-    class failure; // see below
-    […]
-  };
-  […]
-};
-
    -
    -
    2. - -

  2. Change 27.5.3 [ios.base] paragraph 1:

    - -
    -

    -ios_base defines several member types: -

    -
      -

    • a class failuretype failure, defined as either -a class derived from system_error or a synonym for a class derived from -system_error;

      • -
    -
    -
    3. - -

  3. Change 27.5.3.1.1 [ios::failure] paragraph 1:

    -
    -

    --1- An implementation is permitted to define ios_base::failure as -a synonym for a class with equivalent functionality to class ios_base::failure shown -in this subclause. [Note: When ios_base::failure is a synonym for another type -it shall provide a nested type failure, to emulate the injected class name. — -end note] The class failure defines the base class for the types of all -objects thrown as exceptions, by functions in the iostreams library, to report errors detected -during stream buffer operations. -

    -
    -
    4. -
- - - - - -
-

2465. SFINAE-friendly common_type is nearly impossible to specialize -correctly and regresses key functionality

-

Section: 20.10.7.6 [meta.trans.other] Status: New - Submitter: Eric Niebler Opened: 2015-01-12 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-I think there's a defect regarding common_type and its specializations. -Unless I've missed it, there is nothing preventing folks from -instantiating common_type with cv-qualified types or reference types. In -fact, the wording in N3797 explicitly mentions cv void, so presumably at -least cv qualifications are allowed. -

-Users are given license to specialize common_type when at least of of -the types is user-defined. (A separate issue is the meaning of -user-defined. In core, I believe this is any class/struct/union/enum, -but in lib, I think it means any type not defined in std, right?) There -is at least one place in the standard that specializes common_type -(time.traits.specializations) on time_point and duration. But the -specializations are only for non-cv-qualified and non-reference -specializations of time_point and duration. -

-If the user uses, say, common_type<duration<X,Y> const, duration<A,B> -const>, they're not going to get the behavior they expect. -

-Suggest we clarify the requirements of common_type's template -parameters. Also, perhaps we can add blanket wording that common_type<A -[cv][&], B [cv][&]> is required to be equivalent to -common_type<A,B> (if that is in fact the way we intent this to work). -

-Also, the change to make common_type SFINAE-friendly regressed key -functionality, as noted by Agustín K-ballo Bergé in -c++std-lib-37178. -Since decay_t is not applied until the very end of the type computation, -user specializations are very likely to to be found. -

-Agustín says: -

-
-

-Consider the following snippet: -

-
-
-struct X {};
-struct Y { explicit Y(X){} };
-
-namespace std {
-  template<> struct common_type<X, Y> { typedef Y type; };
-  template<> struct common_type<Y, X> { typedef Y type; };
-}
-
-static_assert(is_same<common_type_t<X, Y>, Y>()); // (A)
-static_assert(is_same<common_type_t<X, Y, Y>, Y>()); // (B)
-static_assert(is_same<common_type_t<X, X, Y>, Y>()); // (C)
-
-
-

-Under the original wording, all three assertion holds. Under the current wording, -

-
    -

  • (A) picks the user-defined specialization, so the assertion holds.

    • - -

  • (B) goes to the third bullet and, ignoring the user-defined specialization, looks for -decltype(true ? declval<X>() : declval<Y>()); since it is ill-formed -there is no common type.

    • - -

  • (C) goes to the third bullet and yields common_type_t<X&&, Y>, which again misses -the user-defined specialization.

    • -
-
-

-The discussion following c++std-lib-35636 -seemed to cohere around the idea that the primary common_type specialization should have the effect -of stripping top-level ref and cv qualifiers by applying std::decay_t to its arguments and, -if any of them change as a result of that transformation, re-dispatching to common_type on those transformed -arguments, thereby picking up any user-defined specializations. This change to common_type would make -the specializations in time.traits.specializations sufficient. -

-Suggested wording: -

-I'm afraid I don't know enough to suggest wording. But for exposition, -the following is my best shot at implementing the suggested resolution. -I believe it also fixes the regression noted by Agustín K-ballo Bergé in -c++std-lib-37178. -

-
-
-namespace detail
-{
-    template<typename T, typename U>
-    using default_common_t =
-        decltype(true? std::declval<T>() : std::declval<U>());
-
-    template<typename T, typename U, typename Enable = void>
-    struct common_type_if
-    {};
-
-    template<typename T, typename U>
-    struct common_type_if<T, U,
-      void_t<default_common_t<T, U>>>
-    {
-      using type = decay_t<default_common_t<T, U>>;
-    };
-
-    template<typename T, typename U,
-       typename TT = decay_t<T>, typename UU = decay_t<U>>
-    struct common_type2
-      : common_type<TT, UU> // Recurse to catch user specializations
-    {};
-
-    template<typename T, typename U>
-    struct common_type2<T, U, T, U>
-      : common_type_if<T, U>
-    {};
-
-    template<typename Meta, typename Enable = void>
-    struct has_type
-      : std::false_type
-    {};
-
-    template<typename Meta>
-    struct has_type<Meta, void_t<typename Meta::type>>
-      : std::true_type
-    {};
-
-    template<typename Meta, typename...Ts>
-    struct common_type_recurse
-      : common_type<typename Meta::type, Ts...>
-    {};
-
-    template<typename Meta, typename...Ts>
-    struct common_type_recurse_if
-      : std::conditional<
-          has_type<Meta>::value,
-          common_type_recurse<Meta, Ts...>,
-          empty
-        >::type
-    {};
-}
-
-template<typename ...Ts>
-struct common_type
-{};
-
-template<typename T>
-struct common_type<T>
-{
-  using type = std::decay_t<T>;
-};
-
-template<typename T, typename U>
-struct common_type<T, U>
-  : detail::common_type2<T, U>
-{};
-
-template<typename T, typename U, typename... Vs>
-struct common_type<T, U, Vs...>
-  : detail::common_type_recurse_if<common_type<T, U>, Vs...>
-{};
-
-
- - -

Proposed resolution:

- - - - - -
-

2466. allocator_traits::max_size() default behavior is incorrect

-

Section: 17.6.3.5 [allocator.requirements], 20.7.8.2 [allocator.traits.members] Status: Ready - Submitter: Howard Hinnant Opened: 2015-01-17 Last modified: 2015-05-08

-

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-

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-

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-

Discussion:

-

-Table 28 — "Allocator requirements" says that default behavior for a.max_size() is -numeric_limits<size_type>::max(). And this is consistent with the matching statement -for allocator_traits in 20.7.8.2 [allocator.traits.members]/p7: -

-
-
-static size_type max_size(const Alloc& a) noexcept;
-
-
-

-Returns: a.max_size() if that expression is well-formed; otherwise, -numeric_limits<size_type>::max(). -

-
-
-

-However, when allocating memory, an allocator must allocate n*sizeof(value_type) bytes, for example: -

-
-
-value_type*
-allocate(std::size_t n)
-{
-  return static_cast<value_type*>(::operator new (n * sizeof(value_type)));
-}
-
-
-

-When n == numeric_limits<size_type>::max(), n * sizeof(value_type) is guaranteed -to overflow except when sizeof(value_type) == 1. -

-A more useful default would be numeric_limits<size_type>::max() / sizeof(value_type). -

- -

[2015-05, Lenexa]

- -

-Marshall: Is this the right solution?
-PJP: I think it's gilding the lily.
-STL: I think this is right, and it doesn't interact with the incomplete container stuff because it's in a member function.
-Marshall: Objections to this?
-STL: Spaces around binary operators.
-Hwrd: It's completely wrong without spaces.
-Marshall: All in favor of Ready?
-Lots. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 17.6.3.5 [allocator.requirements], Table 28 — "Allocator requirements", as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements
    ExpressionReturn typeAssertion/note
    pre-/post-condition    		Default
    -… -
    -a.max_size() - -X::size_type - -the largest value that can
    -meaningfully be passed to
    -X::allocate() -    		 -numeric_limits<size_type>::max()/sizeof(value_type) -
    -… -
    -
    - -
    2. - -

  2. Change 20.7.8.2 [allocator.traits.members]/p7 as indicated:

    - -
    -
    -static size_type max_size(const Alloc& a) noexcept;
-
    -
    -

    -Returns: a.max_size() if that expression is well-formed; otherwise, -numeric_limits<size_type>::max()/sizeof(value_type). -

    -
    -
    - -
    3. -
- - - - - -
-

2468. Self-move-assignment of library types

-

Section: 17.6.4.9 [res.on.arguments], 17.6.3.1 [utility.arg.requirements], 17.6.5.15 [lib.types.movedfrom], 23.2.1 [container.requirements.general] Status: New - Submitter: Matt Austern Opened: 2015-01-22 Last modified: 2015-04-08

-

View all other issues in [res.on.arguments].

-

View all issues with New status.

-

Discussion:

-

-Suppose we write -

-
-
-vector<string> v{"a", "b", "c", "d"};
-v = move(v);
-
-
-

-What should be the state of v be? The standard doesn't say anything specific about self-move-assignment. -There's relevant text in several parts of the standard, and it's not clear how to reconcile them. -

-17.6.4.9 [res.on.arguments] writes that, for all functions in the standard library, unless explicitly stated -otherwise, "If a function argument binds to an rvalue reference parameter, the implementation may assume that this -parameter is a unique reference to this argument." The MoveAssignable requirements table in -17.6.3.1 [utility.arg.requirements] writes that, given t = rv, t's state is equivalent to -rv's from before the assignment and rv's state is unspecified (but valid). For containers -specifically, the requirements table in 23.2.1 [container.requirements.general] says that, given a = rv, -a becomes equal to what rv was before the assignment (and doesn't say anything about rv's -state post-assignment). -

-Taking each of these pieces in isolation, without reference to the other two: -

-
    -

  • 17.6.4.9 [res.on.arguments] would clearly imply that the effect of v = move(v) is undefined.

    • -

  • 17.6.3.1 [utility.arg.requirements] would clearly imply that v = move(v) has defined behavior. -It might be read to imply that this is a no-op, or might be read to imply that it leaves v in a valid but -unspecified state; I'm not sure which reading is more natural.

    • -

  • 23.2.1 [container.requirements.general] would clearly imply that v = move(v) is a no-op.

    • -
-

-It's not clear from the text how to put these pieces together, because it's not clear which one takes precedence. -Maybe 17.6.4.9 [res.on.arguments] wins (it imposes an implicit precondition that isn't mentioned in the -MoveAssignable requirements, so v = move(v) is undefined), or maybe -23.2.1 [container.requirements.general] wins (it explicitly gives additional guarantees for -Container::operator= beyond what's guaranteed for library functions in general, so v = move(v) -is a no-op), or maybe something else. -

-On the existing implementations that I checked, for what it's worth, v = move(v) appeared to clear the vector; -it didn't leave the vector unchanged and it didn't cause a crash. -

-Proposed wording: -

-Informally: change the MoveAssignable and Container requirements tables (and any other requirements tables -that mention move assignment, if any) to make it explicit that x = move(x) is defined behavior and it leaves -x in a valid but unspecified state. That's probably not what the standard says today, but it's probably what -we intended and it's consistent with what we've told users and with what implementations actually do. -

- - -

Proposed resolution:

- - - - - -
-

2469. Wrong specification of Requires clause of operator[] for map and unordered_map

-

Section: 23.4.4.3 [map.access], 23.5.4.3 [unord.map.elem] Status: Ready - Submitter: Tomasz Kamiński Opened: 2015-01-21 Last modified: 2015-05-08

-

View all other issues in [map.access].

-

View all issues with Ready status.

-

Discussion:

-

-The "Requires:" clause for the operator[] for the unordered_map and map, are defining -separate requirements for insertability into container of mapped_type and key_type. -

-23.4.4.3 [map.access] p2: // T& operator[](const key_type& x); -

-Requires: key_type shall be CopyInsertable and mapped_type shall be DefaultInsertable -into *this. -

-23.4.4.3 [map.access] p6: // T& operator[](key_type&& x) -

-Requires: mapped_type shall be DefaultInsertable into *this. -

-23.5.4.3 [unord.map.elem] p1: // mapped_type& operator[](const key_type& k); -mapped_type& operator[](key_type&& k); -

-Requires: mapped_type shall be DefaultInsertable into *this. For the first operator, -key_type shall be CopyInsertable into *this. For the second operator, key_type shall -be MoveConstructible. -

-Definition of the appropriate requirements: 23.2.1 [container.requirements.general] p15. -

-T is DefaultInsertable into X means that the following expression is well-formed: //p15.1 -

-allocator_traits<A>::construct(m, p) -

-T is MoveInsertable into X means that the following expression is well-formed: //p15.3 -

-allocator_traits<A>::construct(m, p, rv) -

-T is CopyInsertable into X means that, in addition to T being MoveInsertable -into X, the following expression is well-formed: //p15.4 -

-allocator_traits<A>::construct(m, p, v) -

-In the context of above definition the requirement "key_type shall be CopyInsertable into *this" -would mean that the key element of the pair<const key_type, mapped_type> (value_type of the map) -should be constructed using separate call to the construct method, the same applies for the mapped_type. -Such behavior is explicitly prohibited by 23.2.1 [container.requirements.general] p3. -

-

-For the components affected by this sub-clause that declare an allocator_type, objects stored in these -components shall be constructed using the allocator_traits<allocator_type>::construct function and -destroyed using the allocator_traits<allocator_type>::destroy function (20.7.8.2). These functions -are called only for the container's element type, not for internal types used by the container. -

-

-It clearly states that element_type of the map, must be constructed using allocator for value type, which -disallows using of separate construction of first and second element, regardless of the fact if it can be actually -performed without causing undefined behavior. -

-That means that the MoveInsertable and similar requirements may only be expressed in terms of value_type, -not its members types. -

- -

[2015-02 Cologne]

- -

-This issue is related to 2464. -

-GR: Effects should say "returns ...". DK: Or just have a Returns clause? MC: A Returns clause is a directive to implementers. -

-TK/DK: This PR fails to address the requirements about which it complained in the first place. DK: I can reword this. TK can help. -

- -

[2015-03-29, Daniel provides improved wording]

- -

-The revised wording fixes the proper usage of the magic "Equivalent to" wording, which automatically induces Requires:, -Returns:, and Complexity: elements (and possibly more). This allows us to strike all the remaining -elements, because they fall out from the semantics of the wording defined by 2464. In particular it is important -to realize that the wording form -

-
-

-value_type shall be EmplaceConstructible into map from piecewise_construct, -forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...) -

-
-

-degenerates for the empty pack expansion args to: -

-
-

-value_type shall be EmplaceConstructible into map from piecewise_construct, -forward_as_tuple(k), forward_as_tuple() -

-
-

-which again means that such a pair construction (assuming std::allocator) would copy k -into member first and would value-initialize member second. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N4296.

- -

Accept resolution of the issue issue 2464 and define operator[] as follows -(This would also address issue 2274):

- -
    -

  1. Change 23.4.4.3 [map.access] as indicated:

    - -
    -
    -T& operator[](const key_type& x);
-
    -

    --1- Effects: If there is no key equivalent to x in the map, inserts value_type(x, T()) -into the mapEquivalent to: try_emplace(x).first->second. -

    -[…] -

    -
    -
    -T& operator[](key_type&& x);
-
    -
    -

    --5- Effects: If there is no key equivalent to x in the map, inserts value_type(std::move(x), T()) -into the mapEquivalent to: try_emplace(move(x)).first->second. -

    -
    -
    -
    2. - -

  2. Change 23.5.4.3 [unord.map.elem] as indicated:

    - -
    -
    -mapped_type& operator[](const key_type& k);
-mapped_type& operator[](key_type&& k);
-
    -
    -

    -[…] -

    --2- Effects: If the unordered_map does not already contain an element whose key is equivalent to k, -the first operator inserts the value value_type(k, mapped_type()) and the second operator inserts the -value value_type(std::move(k), mapped_type())For the first operator, equivalent to: -try_emplace(k).first->second; for the second operator, equivalent to: -try_emplace(move(k)).first->second. -

    -
    -
    -
    3. -
-
- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N4296.

- -

Accept resolution of the issue issue 2464 and define operator[] as follows -(This would also address issue 2274):

- -
    -

  1. Change 23.4.4.3 [map.access] as indicated:

    - -
    -
    -T& operator[](const key_type& x);
-
    -

    --1- Effects: If there is no key equivalent to x in the map, inserts value_type(x, T()) -into the map.Equivalent to: return try_emplace(x).first->second; -

    --2- Requires: key_type shall be CopyInsertable and mapped_type shall be -DefaultInsertable into *this. -

    --3- Returns: A reference to the mapped_type corresponding to x in *this. -

    --4- Complexity: Logarithmic. -

    -
    -
    -T& operator[](key_type&& x);
-
    -
    -

    --5- Effects: If there is no key equivalent to x in the map, inserts value_type(std::move(x), T()) -into the map.Equivalent to: return try_emplace(move(x)).first->second; -

    --6- Requires: mapped_type shall be DefaultInsertable into *this. -

    --7- Returns: A reference to the mapped_type corresponding to x in *this. -

    --8- Complexity: Logarithmic. -

    -
    -
    -
    2. - -

  2. Change 23.5.4.3 [unord.map.elem] as indicated:

    - -
    -
    -mapped_type& operator[](const key_type& k);
-mapped_type& operator[](key_type&& k);
-
    -
    -

    --1- Requires: mapped_type shall be DefaultInsertable into *this. For the first operator, -key_type shall be CopyInsertable into *this. For the second operator, key_type shall -be MoveConstructible. -

    --2- Effects: If the unordered_map does not already contain an element whose key is equivalent to k, -the first operator inserts the value value_type(k, mapped_type()) and the second operator inserts the -value value_type(std::move(k), mapped_type())For the first operator, equivalent to: -

    -
    -
     
-return try_emplace(k).first->second;
-
    -
    -

    -for the second operator, equivalent to: -

    -
    -
    -return try_emplace(move(k)).first->second;
-
    -
    -

    --3- Returns: A reference to x.second, where x is the (unique) element whose key is equivalent to -k. -

    --4- Complexity: Average case 𝒪(1), worst case 𝒪(size()). -

    -
    -
    -
    3. -
-
- - -

Proposed resolution:

-

This wording is relative to N4431.

- -

Accept resolution of the issue issue 2464 and define operator[] as follows -(This would also address issue 2274):

- -
    -

  1. Change 23.4.4.3 [map.access] as indicated:

    - -
    -
    -T& operator[](const key_type& x);
-
    -

    --1- Effects: If there is no key equivalent to x in the map, inserts value_type(x, T()) -into the map.Equivalent to: return try_emplace(x).first->second; -

    --2- Requires: key_type shall be CopyInsertable and mapped_type shall be -DefaultInsertable into *this. -

    --3- Returns: A reference to the mapped_type corresponding to x in *this. -

    --4- Complexity: Logarithmic. -

    -
    -
    -T& operator[](key_type&& x);
-
    -
    -

    --5- Effects: If there is no key equivalent to x in the map, inserts value_type(std::move(x), T()) -into the map.Equivalent to: return try_emplace(move(x)).first->second; -

    --6- Requires: mapped_type shall be DefaultInsertable into *this. -

    --7- Returns: A reference to the mapped_type corresponding to x in *this. -

    --8- Complexity: Logarithmic. -

    -
    -
    -
    2. - -

  2. Change 23.5.4.3 [unord.map.elem] as indicated:

    - -
    -
    -mapped_type& operator[](const key_type& k);
-mapped_type& operator[](key_type&& k);
-
    -
    -

    --1- Requires: mapped_type shall be DefaultInsertable into *this. For the first operator, -key_type shall be CopyInsertable into *this. For the second operator, key_type shall -be MoveConstructible. -

    --2- Effects: Equivalent to return try_emplace(k).first->second;If the unordered_map -does not already contain an element whose key is equivalent to k, -the first operator inserts the value value_type(k, mapped_type()) and the second operator inserts the -value value_type(std::move(k), mapped_type()) -

    -

    --3- Returns: A reference to x.second, where x is the (unique) element whose key is equivalent to -k. -

    --4- Complexity: Average case 𝒪(1), worst case 𝒪(size()). -

    -
    - -
    -mapped_type& operator[](key_type&& k);
-
    -
    -

    --?- Effects: Equivalent to return try_emplace(move(k)).first->second; -

    -
    - -
    -
    3. -
- - - - - -
-

2471. copy_n's number of InputIterator increments unspecified

-

Section: 25.3.1 [alg.copy] Status: New - Submitter: Jonathan Wakely Opened: 2015-01-28 Last modified: 2015-05-04

-

View other active issues in [alg.copy].

-

View all other issues in [alg.copy].

-

View all issues with New status.

-

Discussion:

-

-It's unspecified how many times copy_n increments the InputIterator. -uninitialized_copy_n is specified to increment it exactly n times, -which means if an istream_iterator is used then the next character -after those copied is read from the stream and then discarded, losing data. -

-I believe all three of Dinkumware, libc++ and libstdc++ implement -copy_n with n - 1 increments of the InputIterator, which avoids reading -and discarding a character when used with istream_iterator, but is -inconsistent with uninitialized_copy_n and causes surprising behaviour -with istreambuf_iterator instead, because copy_n(in, 2, copy_n(in, 2, -out)) is not equivalent to copy_n(in, 4, out) -

- - -

Proposed resolution:

- - - - - -
-

2472. Heterogeneous comparisons in the standard library can result in ambiguities

-

Section: 20.4.2.7 [tuple.rel], 20.7.9.2 [allocator.globals], 20.8.1.5 [unique.ptr.special], 20.8.2.2.7 [util.smartptr.shared.cmp], 20.12.5.6 [time.duration.comparisons], 20.12.6.6 [time.point.comparisons], 20.13.5 [scoped.adaptor.operators], 24.5.1.3.13 [reverse.iter.op==], 24.5.3.3.13 [move.iter.op.comp] Status: New - Submitter: Richard Smith Opened: 2015-02-07 Last modified: 2015-05-04

-

View other active issues in [tuple.rel].

-

View all other issues in [tuple.rel].

-

View all issues with New status.

-

Discussion:

-

-The standard library specifies a lot of heterogeneous comparison operators. For instance: -

-
-
-template<class... TTypes, class... UTypes>
-constexpr bool operator!=(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-
-

-This has an unfortunate consequence: -

-
-
-#include <tuple>
-#include <utility>
-
-using namespace std::rel_ops;
-std::tuple<int> a(0);
-bool b = a != a;
-
-
-

-The last line here is ill-formed due to ambiguity: it might be rel_ops::operator!=, and it might be the -heterogeneous tuple operator!=. These are not partially ordered, because they have different constraints: -rel_ops requires the types to match, whereas the tuple comparison requires both types to be tuples (but not -to match). The same thing happens for user code that defines its own unconstrained -'template<typename T> operator!=(const T&, const T&)' rather than using rel_ops. -

-One straightforward fix would be to add a homogeneous overload for each heterogeneous comparison: -

-
-
-template<class... TTypes>
-constexpr bool operator!=(const tuple<TTypes...>&, const tuple<TTypes...>&);
-
-

-This is then unambiguously chosen over the other options in the preceding case. FWIW, libstdc++ already does this -in some cases. -

-
- - -

Proposed resolution:

- - - - - -
-

2473. basic_filebuf's relation to C FILE semantics

-

Section: 27.9.1.5 [filebuf.virtuals] Status: Ready - Submitter: Aaron Ballman Opened: 2015-02-09 Last modified: 2015-05-08

-

View all other issues in [filebuf.virtuals].

-

View all issues with Ready status.

-

Discussion:

-

-The restrictions on reading and writing a sequence controlled by an object of class -basic_filebuf<charT, traits> are the same as for reading and writing with -the Standard C library FILEs. One of the restrictions placed by C is on the behavior of -a stream that is opened for input and output. See the C99 standard, 7.19.5.3p6 for more -details, but the gist is that when opened in update mode, reads and writes must have an -intervening file positioning or flushing call to not trigger UB. -

- -

-27.9.1.5 [filebuf.virtuals] p13 specifies that basic_filebuf::seekoff() calls -std::fseek(). However, there is no mention of std::fseek() in -basic_filebuf::seekpos(), and no mention of std::fflush() in -basic_filebuf::sync(), which seem like an oversight. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N4296.

- -
    -
  1. -

    Change 27.9.1.5 [filebuf.virtuals] p16 as follows [Editorial note: A footnote referring to fseek is not needed, -because this is already covered by the existing footnote 334]:

    -
    -

    --16- Alters the file position, if possible, to correspond to the position stored in sp (as described below). -Altering the file position performs as follows: -

    -
      -

    1. if (om & ios_base::out) != 0, then update the output sequence and write any unshift sequence;

      2. -

    2. set the file position to sp as if by calling std::fseek(file, sp, SEEK_SET);

      3. -

    3. if (om & ios_base::in) != 0, then update the input sequence;

      4. -
    -

    -where om is the open mode passed to the last call to open(). The operation fails if -is_open() returns false. -

    -
    -
    2. - -
  2. -

    Change 27.9.1.5 [filebuf.virtuals] p19 as follows and add a new footnote that mimics comparable footnotes in -27.9.1.4 [filebuf.members] and 27.9.1.5 [filebuf.virtuals]:

    -
    -

    --19- Effects: If a put area exists, calls filebuf::overflow to write the characters to the file, then -flushes the file as if by calling std::fflush(file) [Footnote: The function signature fflush(FILE*) -is declared in <cstdio> (27.9.2).]. If a get area exists, the effect is implementation-defined. -

    -
    -
    3. -
-
- -

[2015-05, Lenexa]

- -

-Aaron provides improved wording by removing the params from std::fseek() due to the concerns -regarding the parameters on systems where fseek uses 32-bit parameters. -

-Second wording improvement, replacing the new one see below. It -

-
    -

  1. drops the std::

    2. -

  2. drops the footnote for fflush

    3. -

  3. replaces fseek with fsetpos

    4. -
- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N4431.

- -
    -
  1. -

    Change 27.9.1.5 [filebuf.virtuals] p16 as follows [Editorial note: A footnote referring to fseek is not needed, -because this is already covered by the existing footnote 334]:

    -
    -

    --16- Alters the file position, if possible, to correspond to the position stored in sp (as described below). -Altering the file position performs as follows: -

    -
      -

    1. if (om & ios_base::out) != 0, then update the output sequence and write any unshift sequence;

      2. -

    2. set the file position to sp as if by a call to std::fseek;

      3. -

    3. if (om & ios_base::in) != 0, then update the input sequence;

      4. -
    -

    -where om is the open mode passed to the last call to open(). The operation fails if -is_open() returns false. -

    -
    -
    2. - -
  2. -

    Change 27.9.1.5 [filebuf.virtuals] p19 as follows and add a new footnote that mimics comparable footnotes in -27.9.1.4 [filebuf.members] and 27.9.1.5 [filebuf.virtuals]:

    -
    -

    --19- Effects: If a put area exists, calls filebuf::overflow to write the characters to the file, then -flushes the file as if by calling std::fflush(file) [Footnote: The function signature fflush(FILE*) -is declared in <cstdio> (27.9.2).]. If a get area exists, the effect is implementation-defined. -

    -
    -
    3. -
-
- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -
  1. -

    Change 27.9.1.5 [filebuf.virtuals] p16 as follows [Editorial note: A footnote referring to fseek is not needed, -because this is already covered by the existing footnote 334]:

    -
    -

    --16- Alters the file position, if possible, to correspond to the position stored in sp (as described below). -Altering the file position performs as follows: -

    -
      -

    1. if (om & ios_base::out) != 0, then update the output sequence and write any unshift sequence;

      2. -

    2. set the file position to sp as if by a call to fsetpos;

      3. -

    3. if (om & ios_base::in) != 0, then update the input sequence;

      4. -
    -

    -where om is the open mode passed to the last call to open(). The operation fails if -is_open() returns false. -

    -
    -
    2. - -
  2. -

    Change 27.9.1.5 [filebuf.virtuals] p19 as follows and add a new footnote that mimics comparable footnotes in -27.9.1.4 [filebuf.members] and 27.9.1.5 [filebuf.virtuals]:

    -
    -

    --19- Effects: If a put area exists, calls filebuf::overflow to write the characters to the file, then -flushes the file as if by calling fflush(file). If a get area exists, the effect is implementation-defined. -

    -
    -
    3. -
- - - - - -
-

2474. <cmath> functions unfriendly to integral_constant arguments

-

Section: 26.8 [c.math] Status: New - Submitter: Matheus Izvekov Opened: 2015-02-13 Last modified: 2015-05-04

-

View other active issues in [c.math].

-

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-

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-

Discussion:

-

-Using numeric wrappers with <cmath> functions is currently troublesome. -Code such as: "std::exp2(std::integral_constant<int, 5>{})" will fail to -compile because of ambiguity. -

-Arguments which are implicitly convertible to an arithmetic type should be accepted whenever -the latter would be accepted. -

-David Krauss pointed out that some issue may present itself with numeric libraries which provide <cmath> -equivalents in their own namespace which are not more specialized than the ones provided in <cmath>. -If the changes proposed are implemented, then cases where the user brings those into scope through ADL might become ambiguous. -

-It's hard to assess how much breakage this would cause in the wild, and how much work it would take to fix. -Should this be determined to be a problem, it's possible to make the new behaviour optional, and disabled by -default for all user-defined types. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -
  1. -

    Change 26.8 [c.math] p11 b2 as indicated:

    -
    -

    --11- Moreover, there shall be additional overloads sufficient to ensure: -

    -
      -

    1. […]

      2. -

    2. Otherwise, if any arithmetic argument corresponding to a double parameter has type double or -an integer typea type which is not floating-point, but which is implicitly convertible to double, -then all arithmetic arguments corresponding to double parameters are effectively cast to double.

      3. -

    3. […]

      4. -
    -
    -
    2. -
- - - - - -
-

2475. Allow overwriting of std::basic_string terminator with charT() to allow -cleaner interoperation with legacy APIs

-

Section: 21.4.5 [string.access] Status: New - Submitter: Matt Weber Opened: 2015-02-21 Last modified: 2015-05-04

-

View all other issues in [string.access].

-

View all issues with New status.

-

Discussion:

-

-It is often desirable to use a std::basic_string object as a buffer when interoperating with libraries -that mutate null-terminated arrays of characters. In many cases, these legacy APIs write a null terminator at -the specified end of the provided buffer. Providing such a function with an appropriately-sized -std::basic_string results in undefined behavior when the charT object at the size() -position is overwritten, even if the value remains unchanged. -

-Absent the ability to allow for this, applications are forced into pessimizations such as: providing -appropriately-sized std::vectors of charT for interoperating with the legacy API, and then -copying the std::vector to a std::basic_string; providing an oversized std::basic_string -object and then calling resize() later. -

-A trivial example: -

-
-
-#include <string>
-#include <vector>
-
-void legacy_function(char *out, size_t count) {
-  for (size_t i = 0; i < count; ++i) {
-    *out++ = '0' + (i % 10);
-  }
-  *out = '\0'; // if size() == count, this results in undefined behavior
-}
-
-int main() {
-  std::string s(10, '\0');
-  legacy_function(&s[0], s.size()); // undefined behavior
-
-  std::vector<char> buffer(11);
-  legacy_function(&buffer[0], buffer.size() - 1);
-  std::string t(&buffer[0], buffer.size() - 1); // potentially expensive copy
-
-  std::string u(11, '\0');
-  legacy_function(&u[0], u.size() - 1);
-  u.resize(u.size() - 1); // needlessly complicates the program's logic
-}
-
-
-

-A slight relaxation of the requirement on the returned object from the element access operator would -allow for this interaction with no semantic change to existing programs. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -
  1. -

    Edit 21.4.5 [string.access] as indicated:

    -
    -
    -const_reference operator[](size_type pos) const;
-reference operator[](size_type pos);
-
    -
    -

    --1- Requires: […] -

    --2- Returns: *(begin() + pos) if pos < size(). Otherwise, returns a reference to an object of type -charT with value charT(), where modifying the object to any value other than charT() -leads to undefined behavior. -

    -[…] -

    -
    -
    -
    2. -
- - - - - -
-

2476. scoped_allocator_adaptor is not assignable

-

Section: 20.13.1 [allocator.adaptor.syn] Status: Ready - Submitter: Jonathan Wakely Opened: 2015-03-02 Last modified: 2015-05-08

-

View all issues with Ready status.

-

Discussion:

-

-The class definition in 20.13.1 [allocator.adaptor.syn] declares a move -constructor, which means that the copy assignment operator is defined -as deleted, and no move assignment operator is declared. -

-This means a scoped_allocator_adaptor is not assignable, and a -container using scoped_allocator_adaptor<A...> may not be -CopyAssignable or MoveAssignable (depending on the -propagate_on_container_xxxx_assignment traits of the outer and inner -allocator types). -

- -

[2015-04-03 Howard comments]

- -

-If the contained allocators are not assignable, I think we need the ability of = default to automagically become -= delete. My concern is that is_copy_assignable<scoped_allocator_adaptor<CustomAllocator>>::value -get the right answer for both cases: -

-
    -

  1. is_copy_assignable<CustomAllocator>::value is true.

    2. -

  2. is_copy_assignable<CustomAllocator>::value is false.

    3. -
-

-If we allow the vendor to declare and provide the copy assignment operator, the chance of getting #2 correct goes to zero. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N4296.

- -
    -
  1. -

    Add to the synopsis in 20.13.1 [allocator.adaptor.syn]/1 [Editorial remark: The proposed wording -does not explicitly specify the semantics of the added copy/move assignment operators, based on -17.5.2.2 [functions.within.classes] p1, which says: -

    -"For the sake of exposition, Clauses 18 through 30 and Annex D do not describe copy/move constructors, -assignment operators, or (non-virtual) destructors with the same apparent semantics as those that can be -generated by default (12.1, 12.4, 12.8)." -

    -— end remark]: -

    -
    -
    -[…]
-template <class OuterA2>
-  scoped_allocator_adaptor(
-    scoped_allocator_adaptor<OuterA2, InnerAllocs...>&& other) noexcept;
-
-scoped_allocator_adaptor& operator=(const scoped_allocator_adaptor&);
-scoped_allocator_adaptor& operator=(scoped_allocator_adaptor&&);
-
-~scoped_allocator_adaptor();
-[…]
-
    -
    -
    2. -
-
- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -
  1. -

    Add to the synopsis in 20.13.1 [allocator.adaptor.syn]/1: -

    -
    -
    -[…]
-template <class OuterA2>
-  scoped_allocator_adaptor(
-    scoped_allocator_adaptor<OuterA2, InnerAllocs...>&& other) noexcept;
-
-scoped_allocator_adaptor& operator=(const scoped_allocator_adaptor&) = default;
-scoped_allocator_adaptor& operator=(scoped_allocator_adaptor&&) = default;
-
-~scoped_allocator_adaptor();
-[…]
-
    -
    -
    2. -
- - - - - -
-

2477. Inconsistency of wordings in std::vector::erase() and std::deque::erase()

-

Section: 23.3.3.4 [deque.modifiers], 23.3.6.5 [vector.modifiers] Status: Ready - Submitter: Anton Savin Opened: 2015-03-03 Last modified: 2015-05-08

-

View all other issues in [deque.modifiers].

-

View all issues with Ready status.

-

Discussion:

-

-In the latest draft N4296, and in all drafts up to at least N3337: -

-23.3.3.4 [deque.modifiers]/5 (regarding deque::erase()): -

-
-

-Complexity: The number of calls to the destructor is the same as the number of elements erased, but -the number of calls to the assignment operator is no more -than the lesser of the number of elements before the erased elements and the number of elements after the erased elements. -

-
-

-23.3.6.5 [vector.modifiers]/4 (regarding vector::erase()): -

-
-

-Complexity: The destructor of T is called the number of times equal to the number of the elements -erased, but the move assignment operator of T is called -the number of times equal to the number of elements in the vector after the erased elements. -

-
-

-Is there any reason for explicit mentioning of move assignment for std::vector::erase()? -Shouldn't these two wordings be the same with this regard? -

-Also, for std::deque, it's not clear from the text which destructors and assignment operators are called. -

- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 23.3.3.4 [deque.modifiers]/5 to:

    - -

    --5- Complexity: The number of calls to the destructor of T is the same as the number of -elements erased, but the number of calls to the assignment operator of T is no more than the -lesser of the number of elements before the erased elements and the number of elements after the erased elements. -

    -
    2. - -

  2. Change 23.3.6.5 [vector.modifiers]/4 to:

    - -

    --4- Complexity: The destructor of T is called the number of times equal to the number of the elements -erased, but the move assignment operator of T is called the number of times equal to the number of -elements in the vector after the erased elements. -

    -
    3. -
- - - - - - -
-

2478. Unclear how wstring_convert uses cvtstate

-

Section: 22.3.3.2.2 [conversions.string] Status: New - Submitter: Jonathan Wakely Opened: 2015-03-04 Last modified: 2015-05-04

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with New status.

-

Discussion:

-

-How do wstring_convert::from_bytes and wstring_convert::to_bytes use -the cvtstate member? -

-Is it passed to the codecvt member functions? Is a copy of it passed -to the member functions? "Otherwise it shall be left unchanged" -implies a copy is used, but if that's really what's intended there are -simpler ways to say so. -

- - -

Proposed resolution:

- - - - - -
-

2479. Unclear how wbuffer_convert uses cvtstate

-

Section: 22.3.3.2.3 [conversions.buffer] Status: New - Submitter: Jonathan Wakely Opened: 2015-03-04 Last modified: 2015-05-04

-

View other active issues in [conversions.buffer].

-

View all other issues in [conversions.buffer].

-

View all issues with New status.

-

Discussion:

-

-How does wbuffer_convert use the cvtstate member? -

-Is the same conversion state object used for converting both the get -and put areas? That means a read which runs out of bytes halfway -through a multibyte character will leave some shift state in cvtstate, -which would then be used by a following write, even though the shift -state of the get area is unrelated to the put area. -

- - -

Proposed resolution:

- - - - - -
-

2480. Error handling of wbuffer_convert unclear

-

Section: 22.3.3.2.3 [conversions.buffer] Status: New - Submitter: Jonathan Wakely Opened: 2015-03-04 Last modified: 2015-05-04

-

View other active issues in [conversions.buffer].

-

View all other issues in [conversions.buffer].

-

View all issues with New status.

-

Discussion:

-

-If a codecvt conversion returns codecvt_base::error should that be -treated as EOF? An exception? Should all the successfully converted -characters before a conversion error be available to the users of the -wbuffer_convert and/or the internal streambuf, or does a conversion -error lose information? -

- - -

Proposed resolution:

- - - - - -
-

2481. wstring_convert should be more precise regarding "byte-error string" etc.

-

Section: 22.3.3.2.2 [conversions.string] Status: New - Submitter: Jonathan Wakely Opened: 2015-03-04 Last modified: 2015-05-04

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with New status.

-

Discussion:

-

-Paragraph 4 of 22.3.3.2.2 [conversions.string] introduces byte_err_string -as "a byte string to display on errors". What does display mean? The string is returned -on error, it's not displayed anywhere. -

-Paragraph 14 says "Otherwise, if the object was constructed with a -byte-error string, the member function shall return the byte-error -string." The term byte-error string is not used anywhere else. -

-Paragraph 17 talks about storing "default values in byte_err_string". -What default value? Is "Hello, world!" allowed? If it means -default-construction it should say so. If paragraph 14 says it won't -be used what does it matter how it's initialized? The end of the -paragraph refers to storing "byte_err in byte_err_string". This should -be more clearly related to the wording in paragraph 14. -

-It might help if the constructor (and destructor) was specified before -the other member functions, so it can more formally define the -difference between being "constructed with a byte-error string" and -not. -

-All the same issues apply to the wide_err_string member. -

- - -

Proposed resolution:

- - - - - -
-

2483. throw_with_nested() should use is_final

-

Section: 18.8.6 [except.nested] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

View other active issues in [except.nested].

-

View all other issues in [except.nested].

-

View all issues with Ready status.

-

Discussion:

-

-When N2559 was voted into the Working Paper, -it said "This function template must take special case to handle non-class types, unions and [[final]] classes that cannot -be derived from, and [...]". However, its Standardese didn't handle final classes, and this was never revisited. Now that -we have is_final, we can achieve this proposal's original intention. -

-Additionally, we need to handle the case where U is nested_exception itself. is_base_of's wording -handles this and ignores cv-qualifiers. (Note that is_class detects "non-union class type".) -

- -

[2015-05, Lenexa]

- -

-STL, MC and JW already do this
-MC: move to Ready, bring to motion on Friday
-7 in favor, none opposed -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 18.8.6 [except.nested] as depicted:

    - -
    -
    -template <class T> [[noreturn]] void throw_with_nested(T&& t);
-
    -
    -

    --6- Let U be remove_reference_t<T>. -

    --7- Requires: U shall be CopyConstructible. -

    --8- Throws: if U is a non-union class type not derived from -nested_exceptionis_class<U>::value && !is_final<U>::value && -!is_base_of<nested_exception, U>::value is true, an exception of unspecified type that -is publicly derived from both U and nested_exception and constructed from -std::forward<T>(t), otherwise std::forward<T>(t). -

    -
    -
    -
    2. -
- - - - - - -
-

2484. rethrow_if_nested() is doubly unimplementable

-

Section: 18.8.6 [except.nested] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

View other active issues in [except.nested].

-

View all other issues in [except.nested].

-

View all issues with Ready status.

-

Discussion:

-

-rethrow_if_nested() wants to determine "If the dynamic type of e is publicly and unambiguously derived -from nested_exception", but 5.2.7 [expr.dynamic.cast] specifies that dynamic_cast has a couple -of limitations. -

-First, nonpolymorphic inputs. These could be non-classes, or nonpolymorphic classes. The Standardese handles non-classes, -although implementers need special logic. (If E is int, the dynamic type can't possibly derive from -nested_exception. Implementers need to detect this and avoid dynamic_cast, which would be ill-formed -due to 5.2.7 [expr.dynamic.cast]/2.) The Standardese is defective when E is a nonpolymorphic class. -Consider the following example: -

-
-
-struct Nonpolymorphic { };
-struct MostDerived : Nonpolymorphic, nested_exception { };
-MostDerived md;
-const Nonpolymorphic& np = md;
-rethrow_if_nested(np);
-
-
-

-According to 1.3 [defns.dynamic.type], the dynamic type of np is MostDerived. However, it's -physically impossible to discover this, and attempting to do so will lead to an ill-formed dynamic_cast -(5.2.7 [expr.dynamic.cast]/6). The Standardese must be changed to say that if E is nonpolymorphic, nothing happens. -

-Second, statically good but dynamically bad inputs. Consider the following example: -

-
-
-struct Nested1 : nested_exception { };
-struct Nested2 : nested_exception { };
-struct Ambiguous : Nested1, Nested2 { };
-Ambiguous amb;
-const Nested1& n1 = amb;
-rethrow_if_nested(n1);
-
-
-

-Here, the static type Nested1 is good (i.e. publicly and unambiguously derived from nested_exception), but -the dynamic type Ambiguous is bad. The Standardese currently says that we have to detect the dynamic badness, but -dynamic_cast won't let us. 5.2.7 [expr.dynamic.cast]/3 and /5 are special cases (identity-casting and upcasting, -respectively) that activate before the "run-time check" behavior that we want (/6 and below). Statically good inputs succeed -(regardless of the dynamic type) and statically bad inputs are ill-formed (implementers must use type traits to avoid this). -

-It might be possible to implement this with clever trickery involving virtual base classes, but implementers shouldn't be asked -to do that. It would definitely be possible to implement this with a compiler hook (a special version of dynamic_cast), -but implementers shouldn't be asked to do so much work for such an unimportant case. (This case is pathological because the -usual way of adding nested_exception inheritance is throw_with_nested(), which avoids creating bad inheritance.) -The Standardese should be changed to say that statically good inputs are considered good. -

-Finally, we want is_base_of's "base class or same class" semantics. If the static type is nested_exception, -we have to consider it good due to dynamic_cast's identity-casting behavior. And if the dynamic type is -nested_exception, it is definitely good. -

- -

[2015-05, Lenexa]

- -

-WB: so the is_polymorphic trait must be used?
-STL and JW: yes, that must be used to decide whether to try using dynamic_cast or not.
-JW: I'd already made this fix in our implementation
-STL: the harder case also involves dynamic_cast. should not try using dynamic_cast if we can -statically detect it is OK, doing the dynamic_cast might fail.
-STL: finally, want "is the same or derived from" behaviour of is_base_of
-WB: should there be an "else no effect" at the end? We have "Otherwise, if ..." and nothing saying what if the condition is false.
-TP I agree.
-MC: move to Ready and bring to motion on Friday
-7 in favor, none opposed -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 18.8.6 [except.nested] as depicted:

    - -
    -
    -template <class E> void rethrow_if_nested(const E& e);
-
    -
    -

    --9- Effects: If E is not a polymorphic class type, there is no effect. Otherwise, if the static -type or the dynamic type of e is nested_exception or is publicly and unambiguously -derived from nested_exception, calls dynamic_cast<const nested_exception&>(e).rethrow_nested(). -

    -
    -
    -
    2. -
- - - - - - -
-

2485. get() should be overloaded for const tuple&&

-

Section: 20.4.2.6 [tuple.elem] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

View all other issues in [tuple.elem].

-

View all issues with Ready status.

-

Discussion:

-

-const rvalues are weird, but they're part of the type system. Consider the following code: -

-
-
-#include <functional>
-#include <string>
-#include <tuple>
-
-using namespace std; 
-
-string str1() { return "one"; }
-const string str2() { return "two"; }
-tuple<string> tup3() { return make_tuple("three"); }
-const tuple<string> tup4() { return make_tuple("four"); }
-
-int main() {
-  // cref(str1()); // BAD, properly rejected
-  // cref(str2()); // BAD, properly rejected
-  // cref(get<0>(tup3())); // BAD, properly rejected
-  cref(get<0>(tup4())); // BAD, but improperly accepted!
-}
-
-
-

-As tuple is a fundamental building block (and the only convenient way to have variadic data members), it should -not open a hole in the type system. get() should imitate 5.2.5 [expr.ref]'s rules for accessing data members. -(This is especially true for pair, where both get<0>() and .first are available.) -

-While we're in the neighborhood, we can dramatically simplify the wording here. All we need to do is follow -20.4.2.6 [tuple.elem]/9's example of saying "Returns: A reference to STUFF", and allow implementers to figure out how -to achieve that with the given return types. -

- -

[2015-05, Lenexa]

- -

-TP: for the existing overloads there's no change to the code, just descriptions?
-STL: right.
-JW: I love it
-MC: in favor of moving to Ready and bringing up for vote on Friday
-7 in favor, none opposed -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.2 [utility]/2 "Header <utility> synopsis" as depicted:

    - -
    -
    -[…]
-template<size_t I, class T1, class T2>
-  constexpr tuple_element_t<I, pair<T1, T2>>&
-    get(pair<T1, T2>&) noexcept;
-template<size_t I, class T1, class T2>
-  constexpr tuple_element_t<I, pair<T1, T2>>&&
-    get(pair<T1, T2>&&) noexcept;
-template<size_t I, class T1, class T2>
-  constexpr const tuple_element_t<I, pair<T1, T2>>&
-    get(const pair<T1, T2>&) noexcept;
-template<size_t I, class T1, class T2>
-  constexpr const tuple_element_t<I, pair<T1, T2>>&&
-    get(const pair<T1, T2>&&) noexcept;
-template <class T, class U>
-  constexpr T& get(pair<T, U>& p) noexcept;
-template <class T, class U>
-  constexpr const T& get(const pair<T, U>& p) noexcept;
-template <class T, class U>
-  constexpr T&& get(pair<T, U>&& p) noexcept;
-template <class T, class U>
-  constexpr const T&& get(const pair<T, U>&& p) noexcept;
-template <class T, class U>
-  constexpr T& get(pair<U, T>& p) noexcept;
-template <class T, class U>
-  constexpr const T& get(const pair<U, T>& p) noexcept;
-template <class T, class U>
-  constexpr T&& get(pair<U, T>&& p) noexcept;
-template <class T, class U>
-  constexpr const T&& get(const pair<U, T>&& p) noexcept;
-[…]
-
    -
    -
    2. - -

  2. Change 20.4.1 [tuple.general]/2 "Header <tuple> synopsis" as depicted:

    - -
    -
    -[…]
-// 20.4.2.6, element access:
-template <size_t I, class... Types>
-constexpr tuple_element_t<I, tuple<Types...>>&
-get(tuple<Types...>&) noexcept;
-template <size_t I, class... Types>
-constexpr tuple_element_t<I, tuple<Types...>>&&
-get(tuple<Types...>&&) noexcept;
-template <size_t I, class... Types>
-constexpr const tuple_element_t<I, tuple<Types...>>&
-get(const tuple<Types...>&) noexcept;
-template <size_t I, class... Types>
-constexpr const tuple_element_t<I, tuple<Types...>>&&
-get(const tuple<Types...>&&) noexcept;
-template <class T, class... Types>
-constexpr T& get(tuple<Types...>& t) noexcept;
-template <class T, class... Types>
-constexpr T&& get(tuple<Types...>&& t) noexcept;
-template <class T, class... Types>
-constexpr const T& get(const tuple<Types...>& t) noexcept;
-template <class T, class... Types>
-constexpr const T&& get(const tuple<Types...>&& t) noexcept;
-[…]
-
    -
    -
    3. - -

  3. Change 23.3.1 [sequences.general]/2 "Header <array> synopsis" as depicted:

    - -
    -
    -[…]
-template <size_t I, class T, size_t N>
-constexpr T& get(array<T, N>&) noexcept;
-template <size_t I, class T, size_t N>
-constexpr T&& get(array<T, N>&&) noexcept;
-template <size_t I, class T, size_t N>
-constexpr const T& get(const array<T, N>&) noexcept;
-template <size_t I, class T, size_t N>
-constexpr const T&& get(const array<T, N>&&) noexcept;
-[…]
-
    -
    -
    4. - -

  4. Change 20.3.4 [pair.astuple] as depicted:

    - -
    -
    -template<size_t I, class T1, class T2>
-constexpr tuple_element_t<I, pair<T1, T2>>&
-get(pair<T1, T2>& p) noexcept;
-template<size_t I, class T1, class T2>
-constexpr const tuple_element_t<I, pair<T1, T2>>&
-get(const pair<T1, T2>& p) noexcept;
-
    -
    -

    --3- Returns: If I == 0 returns p.first; if I == 1 returns p.second; -otherwise the program is ill-formed. -

    -
    -
    -template<size_t I, class T1, class T2>
-constexpr tuple_element_t<I, pair<T1, T2>>&&
-get(pair<T1, T2>&& p) noexcept;
-template<size_t I, class T1, class T2>
-constexpr const tuple_element_t<I, pair<T1, T2>>&&
-get(const pair<T1, T2>&& p) noexcept;
-
    -
    -

    --4- Returns: If I == 0 returns a reference to -std::forward<T1&&>(p.first); if I == 1 -returns a reference to std::forward<T2&&>(p.second); -otherwise the program is ill-formed. -

    -
    -
    -template <class T, class U>
-constexpr T& get(pair<T, U>& p) noexcept;
-template <class T, class U>
-constexpr const T& get(const pair<T, U>& p) noexcept;
-
    -
    -

    --5- Requires: T and U are distinct types. Otherwise, the program is ill-formed. -

    --6- Returns: get<0>(p); -

    -
    -
    -template <class T, class U>
-constexpr T&& get(pair<T, U>&& p) noexcept;
-template <class T, class U>
-constexpr const T&& get(const pair<T, U>&& p) noexcept;
-
    -
    -

    --7- Requires: T and U are distinct types. Otherwise, the program is ill-formed. -

    --8- Returns: A reference to p.first.get<0>(std::move(p)); -

    -
    -
    -template <class T, class U>
-constexpr T& get(pair<U, T>& p) noexcept;
-template <class T, class U>
-constexpr const T& get(const pair<U, T>& p) noexcept;
-
    -
    -

    --9- Requires: T and U are distinct types. Otherwise, the program is ill-formed. -

    --10- Returns: get<1>(p); -

    -
    -
    -template <class T, class U>
-constexpr T&& get(pair<U, T>&& p) noexcept;
-template <class T, class U>
-constexpr const T&& get(const pair<U, T>&& p) noexcept;
-
    -
    -

    --11- Requires: T and U are distinct types. Otherwise, the program is ill-formed. -

    --12- Returns: A reference to p.second.get<1>(std::move(p)); -

    -
    -
    -
    5. - -

  5. Change 20.4.2.6 [tuple.elem] as depicted:

    - -
    -
    -template <size_t I, class... Types>
-  constexpr tuple_element_t<I, tuple<Types...> >& get(tuple<Types...>& t) noexcept;
-
    -
    -

    --1- Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

    --2- Returns: A reference to the Ith element of t, where indexing is zero-based. -

    -
    -
    -template <size_t I, class... Types>
-  constexpr tuple_element_t<I, tuple<Types...> >&& get(tuple<Types...>&& t) noexcept; // Note A
-
    -
    -

    --3- Effects: Equivalent to return std::forward<typename tuple_element<I, tuple<Types...> >::type&&>(get<I>(t)); -

    --4- Note: if a T in Types is some reference type X&, the return type is X&, not -X&&. However, if the element type is a non-reference type T, the return type is T&&. -

    -
    -
    -template <size_t I, class... Types>
-  constexpr tuple_element_t<I, tuple<Types...> > const& get(const tuple<Types...>& t) noexcept; // Note B
-template <size_t I, class... Types>
-  constexpr const tuple_element_t<I, tuple<Types...> >&& get(const tuple<Types...>&& t) noexcept;  
-
    -
    -

    --5- Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

    --6- Returns: A const reference to the Ith element of t, where indexing is zero-based. -

    --?- [Note A: if a T in Types is some reference type X&, the return type is X&, -not X&&. However, if the element type is a non-reference type T, the return type is T&&. -— end note] -

    --7- [Note B: Constness is shallow. If a T in Types is some reference type X&, -the return type is X&, not const X&. However, if the element type is non-reference type T, -the return type is const T&. This is consistent with how constness is defined to work for member variables of -reference type. — end note] -

    -
    -
    -template <class T, class... Types>
-  constexpr T& get(tuple<Types...>& t) noexcept;
-template <class T, class... Types>
-  constexpr T&& get(tuple<Types...>&& t) noexcept;
-template <class T, class... Types>
-  constexpr const T& get(const tuple<Types...>& t) noexcept;
-template <class T, class... Types>
-  constexpr const T&& get(const tuple<Types...>&& t) noexcept;
-
    -
    -

    --8- Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed. -

    --9- Returns: A reference to the element of t corresponding to the type T in Types.... -

    -[…] -

    -
    -
    -
    6. - -

  6. Change 23.3.2.9 [array.tuple] as depicted:

    - -
    -
    -template <size_t I, class T, size_t N>
-  constexpr T& get(array<T, N>& a) noexcept;
-
    -
    -

    --3- Requires: I < N. The program is ill-formed if I is out of bounds. -

    --4- Returns: A reference to the Ith element of a, where indexing is zero-based. -

    -
    -
    -template <size_t I, class T, size_t N>
-  constexpr T&& get(array<T, N>&& a) noexcept;
-
    -
    -

    --5- Effects: Equivalent to return std::move(get<I>(a)); -

    -
    -
    -template <size_t I, class T, size_t N>
-  constexpr const T& get(const array<T, N>& a) noexcept;
-template <size_t I, class T, size_t N>
-  constexpr const T&& get(const array<T, N>&& a) noexcept;
-
    -
    -

    --6- Requires: I < N. The program is ill-formed if I is out of bounds. -

    --7- Returns: A const reference to the Ith element of a, where indexing is zero-based. -

    -
    -
    -
    7. - - -
- - - - - - -
-

2486. mem_fn() should be required to use perfect forwarding

-

Section: 20.9.2 [func.require] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

View other active issues in [func.require].

-

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-

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-

Discussion:

-

-20.9.2 [func.require]/4 defines "simple call wrapper" and "forwarding call wrapper". Only mem_fn() is -specified to be a "simple call wrapper", by 20.9.11 [func.memfn]/1: "A simple call wrapper (20.9.1) fn -such that the expression fn(t, a2, ..., aN) is equivalent to INVOKE(pm, t, a2, ..., aN) (20.9.2)." -

-This suggests, but doesn't outright state, that perfect forwarding is involved. It matters for PMFs like -R (T::*)(Arg) where Arg is passed by value — if the mem_fn() wrapper's function call -operator takes Arg by value, an extra copy/move will be observable. We should require perfect forwarding here. -

- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.9.2 [func.require] as depicted [Editorial remark: This simply adds "A simple call wrapper -is a forwarding call wrapper", then moves the sentence. — end of remark]:

    - -
    -

    --4- Every call wrapper (20.9.1) shall be MoveConstructible. A simple call wrapper is a call wrapper that is -CopyConstructible and CopyAssignable and whose copy constructor, move constructor, and assignment -operator do not throw exceptions. A forwarding call wrapper is a call wrapper that can be called with -an arbitrary argument list and delivers the arguments to the wrapped callable object as references. This -forwarding step shall ensure that rvalue arguments are delivered as rvalue-references and lvalue arguments -are delivered as lvalue-references. A simple call wrapper is a forwarding call wrapper that is CopyConstructible -and CopyAssignable and whose copy constructor, move constructor, and assignment operator do not throw exceptions. -[Note: In a typical implementation […] — end note] -

    -
    -
    2. - -
- - - - - - -
-

2487. bind() should be const-overloaded, not cv-overloaded

-

Section: 20.9.10.3 [func.bind.bind] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

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-

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-

Discussion:

-

-The Standard currently requires bind() to return something with a cv-overloaded function call operator. -const is great, but volatile is not. First, the Library almost always ignores volatile's -existence (with <type_traits> and <atomic> being rare exceptions). Second, implementations -typically store bound arguments in a tuple, but get() isn't overloaded for volatile tuple. Third, -when a bound argument is a reference_wrapper, we have to call tid.get(), but that won't compile for a -volatile reference_wrapper. Finally, const and volatile don't always have to be handled symmetrically -— for example, lambda function call operators are const by default, but they can't ever be volatile. -

-Implementers shouldn't be required to provide cv-overloading here. (They can provide it as a conforming extension if -they want.) -

- -

[2015-05, Lenexa]

- -

-JW: why would a reference_wrapper be volatile?
-STL: if a bound argument is a reference_wrapper then in a volatile-qualified operator() that -member will be volatile so you can't call get() on it
-STL: worded like this it's a conforming extension to kep overloading on volatile
-HH: libc++ doesn't overload on volatile
-JW: libstdc++ does overload for volatile
-MC: move to Ready and bring motion on Friday
-10 in favor, none opposed -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.9.10.3 [func.bind.bind] as depicted:

    - -
    -
    -template<class F, class... BoundArgs>
-  unspecified bind(F&& f, BoundArgs&&... bound_args);
-
    -
    -

    --2- Requires: is_constructible<FD, F>::value shall be true. For each Ti -in BoundArgs, is_constructible<TiD, Ti>::value shall be true. -INVOKE(fd, w1, w2, ..., wN) (20.9.2) shall be a valid expression for some values w1, w2, -..., wN, where N == sizeof...(bound_args). The cv-qualifiers cv of the call -wrapper g, as specified below, shall be neither volatile nor const volatile. -

    -[…] -

    -
    -
    -template<class R, class F, class... BoundArgs>
-  unspecified bind(F&& f, BoundArgs&&... bound_args);
-
    -
    -

    --6- Requires: is_constructible<FD, F>::value shall be true. For each Ti -in BoundArgs, is_constructible<TiD, Ti>::value shall be true. -INVOKE(fd, w1, w2, ..., wN) shall be a valid expression for some values w1, w2, -..., wN, where N == sizeof...(bound_args). The cv-qualifiers cv of the call -wrapper g, as specified below, shall be neither volatile nor const volatile. -

    -[…] -

    -
    -
    -
    2. - -
- - - - - - -
-

2489. mem_fn() should be noexcept

-

Section: 20.9.11 [func.memfn] Status: Ready - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-08

-

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-

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-

Discussion:

-

-mem_fn() is wide contract and doesn't do anything that could throw exceptions, so it should be marked noexcept. -

-Note that mem_fn() is perfectly happy to wrap a null PMF/PMD, it just can't be invoked later. This is exactly like -std::function, which can be constructed from null PMFs/PMDs. Therefore, mem_fn() will remain wide contract forever. -

- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.9 [function.objects] p2 "Header <functional> synopsis" as depicted:

    - -
    -
    -[…]
-// 20.9.11, member function adaptors:
-template<class R, class T> unspecified mem_fn(R T::*) noexcept;
-[…]
-
    -
    -
    2. - -

  2. Change 20.9.11 [func.memfn] as depicted:

    - -
    -
    -template<class R, class T> unspecified mem_fn(R T::* pm) noexcept;
-
    -
    -

    -[…] -

    --4- Throws: Nothing. -

    -
    -
    -
    3. -
- - - - - - -
-

2490. <regex> needs lots of noexcept

-

Section: 28 [re] Status: New - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-04

-

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-

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-

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-

Discussion:

-

-Only 4 functions are marked noexcept in all of Clause 28. Many more need to be marked — for example, -regex_error::code(), basic_regex::swap(), and sub_match::length(). -

- - - -

Proposed resolution:

- - - - - -
-

2491. std::less<T*> in constant expression

-

Section: 20.9.6 [comparisons] Status: New - Submitter: Agustín K-ballo Bergé Opened: 2015-04-01 Last modified: 2015-05-04

-

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-

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-

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-

Discussion:

-

-It is not entirely clear if and when the specializations of std::less (and friends) for pointer types -can be used in a constant expression. Consider the following code: -

-
-#include <functional>
-
-struct foo {};
-foo x, y;
-constexpr bool b = std::less<foo*>{}(&x, &y); // [1]
-
-foo z[] = {{}, {}};
-constexpr bool ba = std::less<foo*>{}(&z[0], &z[1]); // [2]
-
-

-Comparing the address of unrelated objects is not a constant expression since the result is unspecified, so -it could be expected for [1] to fail and [2] to succeed. However, std::less specialization for pointer -types is well-defined and yields a total order, so it could just as well be expected for [1] to succeed. Finally, -since the implementation of such specializations is not mandated, [2] could fail as well (This could happen, if -an implementation would provide such a specialization and if that would use built-in functions that would not be -allowed in constant expressions, for example). In any case, the standard should be clear so as to avoid -implementation-defined constexpr-ness. -

- - - -

Proposed resolution:

- - - - - -
-

2492. Clarify requirements for comp

-

Section: 25.4 [alg.sorting] Status: Ready - Submitter: Anton Savin Opened: 2015-04-14 Last modified: 2015-05-08

-

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-

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-

Discussion:

-

-N4296 25.4 [alg.sorting]/3 reads: -

-

-For all algorithms that take Compare, there is a version that uses operator< instead. That is, -comp(*i,*j) != false defaults to *i < *j != false. For algorithms other than those described in -25.4.3 to work correctly, comp has to induce a strict weak ordering on the values. -

-

-So it's not specified clearly what happens if comp or operator< don't induce a strict weak ordering. -Is it undefined or implementation-defined behavior? It seems that it should be stated more clearly that the behavior is -undefined. -

- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Change 25.4 [alg.sorting]/3 to the following:

    -
    -

    -For all algorithms that take Compare, there is a version that uses operator< instead. That is, comp(*i, -*j) != false defaults to *i < *j != false. For algorithms other than those described in 25.4.3 to work -correctly, comp shallhas to induce a strict weak ordering on the values. -

    -
    -
    2. -
- - - - - -
-

2493. initializer_list supports incomplete classes

-

Section: 18.9 [support.initlist] Status: New - Submitter: David Krauss Opened: 2015-04-27 Last modified: 2015-05-04

-

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-

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-

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-

Discussion:

-

-The typical use-case of std::initializer_list<T> is for a pass-by-value parameter of T's constructor. -However, this contravenes 17.6.4.8 [res.on.functions]/2.5 because initializer_list doesn't specifically allow -incomplete types (as do for example std::unique_ptr (20.8.1 [unique.ptr]/5) and -std::enable_shared_from_this (20.8.2.5 [util.smartptr.enab]/2)). -

-A resolution would be to copy-paste the relevant text from such a paragraph. -

- - - -

Proposed resolution:

- - - - - -
-

2494. [fund.ts.v2] ostream_joiner needs noexcept

-

Section: X [iterator.ostream.joiner] Status: Ready - Submitter: Nate Wilson Opened: 2015-05-03 Last modified: 2015-05-08

-

View all issues with Ready status.

-

Discussion:

-

Addresses: fund.ts.v2

-

-In Library Fundamentals 2 -N4481, -[iterator.ostream.joiner], all operations are no-ops other than the assignment operator. -

-So, they should be marked as noexcept. -

- -

[2015-05, Lenexa]

- -

-Move to Immediate. -

- - -

Proposed resolution:

-

This wording is relative to N4481 in regard to fundamental-ts-2 changes.

- -
    -

  1. Change class template ostream_joiner synopsis, [iterator.ostream.joiner] p2, as indicated:

    - -
    -
    -namespace std {
-namespace experimental {
-inline namespace fundamentals_v2 {
-
-template <class DelimT, class charT = char, class traits = char_traits<charT> >
-  class ostream_joiner {
-  public:
-    […]
-    ostream_joiner<DelimT, charT,traits>& operator*() noexcept;
-    ostream_joiner<DelimT, charT,traits>& operator++() noexcept;
-    ostream_joiner<DelimT, charT,traits>& operator++(int) noexcept;
-    […]
-  };
-
-} // inline namespace fundamentals_v2
-} // namespace experimental
-} // namespace std
-
    -
    -
    2. - -

  2. Change [iterator.ostream.joiner.ops] p3+5, as indicated:

    - -
    -
    -ostream_joiner<DelimT, charT, traits>& operator*() noexcept;
-
    -

    -[…] -

    -
    -ostream_joiner<DelimT, charT, traits>& operator++() noexcept;
-ostream_joiner<DelimT, charT, traits>& operator++(int) noexcept;
-
    -
    - -
    3. -
- - - - - -
-

2495. There is no such thing as an Exception Safety element

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: New - Submitter: Jonathan Wakely Opened: 2015-05-05 Last modified: 2015-05-20

-

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-

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-

Discussion:

-

-20.8.2.2.1 [util.smartptr.shared.const] includes several "Exception safety" -elements, but that is not one of the elements defined in 17.5.1.4 -17.5.1.4 [structure.specifications]. We should either define what it means, or -just move those sentences into the Effects: clause. -

- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Change 20.8.2.2.1 [util.smartptr.shared.const] as follows:

    - -
    -
    -template<class Y> explicit shared_ptr(Y* p);
-
    -
    -

    -[…] -

    --4- Effects: Constructs a shared_ptr object that owns the pointer p. If an exception -is thrown, delete p is called. -

    -[…] -

    --7- Exception safety: If an exception is thrown, delete p is called. -

    -
    -
    -template <class Y, class D> shared_ptr(Y* p, D d);
-template <class Y, class D, class A> shared_ptr(Y* p, D d, A a);
-template <class D> shared_ptr(nullptr_t p, D d);
-template <class D, class A> shared_ptr(nullptr_t p, D d, A a);
-
    -
    -

    -[…] -

    --9- Effects: Constructs a shared_ptr object that owns the object p and the deleter d. -The second and fourth constructors shall use a copy of a to allocate memory for internal use. If an exception -is thrown, d(p) is called. -

    -[…] -

    --12- Exception safety: If an exception is thrown, d(p) is called. -

    -
    -[…] -
    -template <class Y> explicit shared_ptr(const weak_ptr<Y>& r);
-
    -
    -

    -[…] -

    --24- Effects: Constructs a shared_ptr object that shares ownership with r and stores a copy of the pointer -stored in r. If an exception is thrown, the constructor has no effect. -

    -[…] -

    --27- Exception safety: If an exception is thrown, the constructor has no effect. -

    -
    -
    -template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
-
    -
    -

    -[…] -

    --29- Effects: Equivalent to shared_ptr(r.release(), r.get_deleter()) when D is not a reference type, -otherwise shared_ptr(r.release(), ref(r.get_deleter())). If an exception is thrown, the constructor has no effect. -

    --30- Exception safety: If an exception is thrown, the constructor has no effect. -

    -
    -
    -
    2. - -
- - - - - -
-

2496. Certain hard-to-avoid errors not in the immediate context are not allowed to be triggered by -the evaluation of type traits

-

Section: 20.10.4.3 [meta.unary.prop] Status: New - Submitter: Hubert Tong Opened: 2015-05-07 Last modified: 2015-05-20

-

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-

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-

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-

Discussion:

-

-I do not believe that the wording in 20.10.4.3 [meta.unary.prop] paragraph 3 allows for the following program to be ill-formed: -

-
-
-#include <type_traits>
-
-template <typename T> struct B : T { };
-template <typename T> struct A { A& operator=(const B<T>&); };
-
-std::is_assignable<A<int>, int> q;
-
-
-

-In particular, I do not see where the wording allows for the "compilation of the expression" -declval<T>() = declval<U>() to occur as a consequence of instantiating std::is_assignable<T, U> -(where T and U are, respectively, A<int> and int in the example code). -

-Instantiating A<int> as a result of requiring it to be a complete type does not trigger the instantiation of -B<int>; however, the "compilation of the expression" in question does. -

- - -

Proposed resolution:

- - - - - -
-

2497. Use of uncaught_exception()

-

Section: 27.7.3.4 [ostream::sentry] Status: New - Submitter: Roger Orr Opened: 2015-05-08 Last modified: 2015-05-20

-

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-

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-

Discussion:

-

-In the current 27.7.3.4 [ostream::sentry], p4 refers to the now deprecated std::uncaught_exception(): -D.9 [depr.uncaught]. -

-
-

-If ((os.flags() & ios_base::unitbuf) && !uncaught_exception() && os.good()) is true, calls -os.rdbuf()->pubsync(). -

-
-

-This needs to be changed, for example to use std::uncaught_exceptions() and to capture the value on entry and -compare with the saved value on exit. -

- - -

Proposed resolution:

- - - - - -
-

2498. operator>>(basic_istream&&, T&&) returns basic_istream&, but should probably return -basic_istream&&

-

Section: 27.7.2.6 [istream.rvalue] Status: New - Submitter: Richard Smith Opened: 2015-05-08 Last modified: 2015-05-20

-

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-

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-

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-

Discussion:

-

-Consider: -

-
-
-auto& is = make_istream() >> x; // oops, istream object is already gone
-
-
-

-With a basic_istream&& return type, the above would be ill-formed, and generally we'd -preserve the value category properly. -

- - -

Proposed resolution:

- - - - - -
-

2499. operator>>(basic_istream&, CharT*) makes it hard to avoid buffer overflows

-

Section: 27.7.2.2.3 [istream::extractors] Status: New - Submitter: Richard Smith Opened: 2015-05-08 Last modified: 2015-05-21

-

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-

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-

Discussion:

-

-We removed gets() (due to an NB comment and C11 — bastion of backwards compatibility — doing the same). -Should we remove this too? -

-Unlike gets(), there are legitimate uses: -

-
-
-char buffer[32];
-char text[32] = // ...
-ostream_for_buffer(text) >> buffer; // ok, can't overrun buffer
-
-
-

-… but the risk from constructs like "std::cin >> buffer" seems to outweigh the benefit. -

-The issue had been discussed on the library reflector starting around -c++std-lib-35541. -

- - -

Proposed resolution:

- - - - - -
-

2500. [fund.ts.v2] fundts.memory.smartptr.shared.obs/6 should apply to cv-unqualified void

-

Section: X [memory.smartptr.shared.obs] Status: New - Submitter: Jeffrey Yasskin Opened: 2015-05-11 Last modified: 2015-05-20

-

View all issues with New status.

-

Discussion:

-

Addresses: fund.ts.v2

-

-S. B. Tam reported this here. -

-N3920 changed operator*() in -[util.smartptr.shared.obs] as: -

-
-

-Remarks: When T is an array type or cv-qualified void, it -is unspecified whether this member function is declared. … -

-
-

-This excludes cv-unqualified void, which is probably unintended. -

- - -

Proposed resolution:

-
    -

  1. In the library -fundamentals v2, [memory.smartptr.shared.obs] p2, change as indicated:

    -
    -

    -Remarks: When T is an array type or (possibly cv-qualified) -void, it is unspecified whether this -member function is declared. If it is declared, it is unspecified what -its return type is, except that the declaration (although not -necessarily the definition) of the function shall be well formed. -

    -
    -
    2. -
- - - - - -
-

2501. std::function requires POCMA/POCCA

-

Section: 20.9.12.2 [func.wrap.func] Status: New - Submitter: David Krauss Opened: 2015-05-20 Last modified: 2015-05-22

-

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-

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-

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-

Discussion:

-

-The idea behind propagate_on_container_move_assignment is that you can keep an allocator attached to a container. -But it's not really designed to work with polymorphism, which introduces the condition where the current allocator is non-POCMA -and the RHS of assignment, being POCMA, wants to replace it. If function were to respect the literal meaning, any would-be -attached allocator is at the mercy of every assignment operation. So, std::function is inherently POCMA, and passing -a non-POCMA allocator should be ill-formed. -

-The other alternative, and the status quo, is to ignore POCMA and assume it is true. This seems just dangerous enough to outlaw. -It is, in theory, possible to properly support POCMA as far as I can see, albeit with difficulty and brittle results. It would -require function to keep a throwing move constructor, which otherwise can be noexcept. -

-The same applies to propagate_on_container_copy_assignment. This presents more difficulty because std::allocator -does not set this to true. Perhaps it should. For function to respect this would require inspecting the POCCA of the source allocator, -slicing the target from the erasure of the source, slicing the allocation from the erasure of the destination, and performing a -copy with the destination's allocator with the source's target. This comes out of the blue for the destination allocator, which -might not support the new type anyway. Theoretically possible, but brittle and not very practical. Again, current implementations -quietly ignore the issue but this isn't very clean. -

-The following code example is intended to demonstrate the issue here: -

-
-#include <functional>
-#include <iostream>
-#include <vector>
-
-template <typename T>
-struct diag_alloc 
-{
-  std::string name;
-
-  T* allocate(std::size_t n) const 
-  {
-    std::cout << '+' << name << '\n';
-    return static_cast<T*>(::operator new(n * sizeof(T)));
-  }
-  
-  void deallocate(T* p, std::size_t) const 
-  {
-    std::cout << '-' << name << '\n';
-    return ::operator delete(p);
-  }
-
-  template <typename U>
-  operator diag_alloc<U>() const { return {name}; }
-
-  friend bool operator==(const diag_alloc& a, const diag_alloc& b)
-  { return a.name == b.name; }
-  
-  friend bool operator!=(const diag_alloc& a, const diag_alloc& b)
-  { return a.name != b.name; }
-
-  typedef T value_type;
-  
-  template <typename U>
-  struct rebind { typedef diag_alloc<U> other; };
-};
-
-int main() {
-  std::cout << "VECTOR\n";
-  std::vector<int, diag_alloc<int>> foo({1, 2}, {"foo"}); // +foo
-  std::vector<int, diag_alloc<int>> bar({3, 4}, {"bar"}); // +bar
-
-  std::cout << "move\n";
-  foo = std::move(bar); // no message
-
-  std::cout << "more foo\n";
-  foo.reserve(40); // +foo -foo
-  std::cout << "more bar\n";
-  bar.reserve(40); // +bar -bar
-
-  std::cout << "\nFUNCTION\n";
-  int bigdata[100];
-  auto bigfun = [bigdata]{};
-  typedef decltype(bigfun) ft;
-  std::cout << "make fizz\n";
-  std::function<void()> fizz(std::allocator_arg, diag_alloc<ft>{"fizz"}, bigfun); // +fizz
-  std::cout << "another fizz\n";
-  std::function<void()> fizz2;
-  fizz2 = fizz; // +fizz as if POCCA
-  std::cout << "make buzz\n";
-  std::function<void()> buzz(std::allocator_arg, diag_alloc<ft>{"buzz"}, bigfun); // +buzz
-  std::cout << "move\n";
-  buzz = std::move(fizz); // -buzz as if POCMA
-
-  std::cout << "\nCLEANUP\n";
-}
-
- - -

Proposed resolution:

- - - - - -
-

2502. std::function does not use allocator::construct

-

Section: 20.9.12.2 [func.wrap.func] Status: New - Submitter: David Krauss Opened: 2015-05-20 Last modified: 2015-05-21

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with New status.

-

Discussion:

-

-It is impossible for std::function to construct its target object using the construct method of a type-erased -allocator. More confusingly, it is possible when the allocator and the target are created at the same time. The means -of target construction should be specified. -

- - -

Proposed resolution:

- - - - - -
-

2503. multiline option should be added to syntax_option_type

-

Section: 28.5.1 [re.synopt] Status: New - Submitter: Nozomu Katō Opened: 2015-05-22 Last modified: 2015-05-22

-

View other active issues in [re.synopt].

-

View all other issues in [re.synopt].

-

View all issues with New status.

-

Discussion:

-

-The specification of ECMAScript defines the Multiline property for its -RegExp and the regular expressions ^ and $ behave differently according -to the value of this property. Thus, this property should be available -also in the ECMAScript compatible engine in std::regex. -

- -

[2015-05-22, Daniel comments]

- -

-This issue interacts somewhat with LWG 2343. -

- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Change 28.5.1 [re.synopt] as indicated:

    - -
    -namespace std::regex_constants {
-  typedef T1 syntax_option_type;
-  constexpr syntax_option_type icase = unspecified ;
-  constexpr syntax_option_type nosubs = unspecified ;
-  constexpr syntax_option_type optimize = unspecified ;
-  constexpr syntax_option_type collate = unspecified ;
-  constexpr syntax_option_type ECMAScript = unspecified ;
-  constexpr syntax_option_type basic = unspecified ;
-  constexpr syntax_option_type extended = unspecified ;
-  constexpr syntax_option_type awk = unspecified ;
-  constexpr syntax_option_type grep = unspecified ;
-  constexpr syntax_option_type egrep = unspecified ;
-  constexpr syntax_option_type multiline = unspecified ;
-}
-
    -
    2. - -

  2. Change 28.5.2 [re.matchflag], Table 138 — "syntax_option_type effects" as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - -
    Table 138 — syntax_option_type effects
    ElementEffect(s) if set
    -… -
    -multiline - -Specifies that ^ shall match the beginning of a line -and $ shall match the end of a line, if the ECMAScript engine is -selected. -
    -… -
    -
    - -
    3. -
- - - - - - - diff --git a/libstdc++-v3/doc/html/ext/lwg-closed.html b/libstdc++-v3/doc/html/ext/lwg-closed.html deleted file mode 100644 index b01c109c7448..000000000000 --- a/libstdc++-v3/doc/html/ext/lwg-closed.html +++ /dev/null @@ -1,42632 +0,0 @@ - - - -C++ Standard Library Closed Issues List - - - - - - - - - - - - - - - - - - - - -
Doc. no.N4486
Date:2015-05-23
Project:Programming Language C++
Reply to:Marshall Clow <lwgchair@gmail.com>
-

C++ Standard Library Closed Issues List (Revision R93)

-

Revised 2015-05-23 at 15:05:40 UTC

-

-

Reference ISO/IEC IS 14882:2014(E)

-

Also see:

- - -

This document contains only library issues which have been closed - by the Library Working Group as duplicates or not defects. That is, - issues which have a status of Dup or - NAD. See the Library Active Issues List active issues and more - information. See the Library Defect Reports List for issues considered - defects. The introductory material in that document also applies to - this document.

- -

Revision History

- - -

Closed Issues

-
-

2. Auto_ptr conversions effects incorrect

-

Section: X [auto.ptr.conv] Status: NAD - Submitter: Nathan Myers Opened: 1997-12-04 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

Paragraph 1 in "Effects", says "Calls -p->release()" where it clearly must be "Calls -p.release()". (As it is, it seems to require using -auto_ptr<>::operator-> to refer to X::release, assuming that -exists.)

- - -

Proposed resolution:

-

Change 20.10.4.3 [meta.unary.prop] paragraph 1 Effects from -"Calls p->release()" to "Calls p.release()".

- - -

Rationale:

-

Not a defect: the proposed change is already found in the standard. -[Originally classified as a defect, later reclassified.]

- - - - - -
-

4. Basic_string size_type and difference_type should be implementation defined

-

Section: 21.4 [basic.string] Status: NAD - Submitter: Beman Dawes Opened: 1997-11-16 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with NAD status.

-

Discussion:

-

In Morristown we changed the size_type and difference_type typedefs -for all the other containers to implementation defined with a -reference to 23.2 [container.requirements]. This should probably also have been -done for strings.

- - -

Rationale:

-

Not a defect. [Originally classified as a defect, later -reclassified.] basic_string, unlike the other standard library -template containers, is severely constrained by its use of -char_traits. Those types are dictated by the traits class, and are far -from implementation defined.

- - - - - -
-

6. File position not an offset unimplementable

-

Section: 27.5.4 [fpos] Status: NAD - Submitter: Matt Austern Opened: 1997-12-15 Last modified: 2015-04-08

-

View all other issues in [fpos].

-

View all issues with NAD status.

-

Discussion:

-

Table 88, in I/O, is too strict; it's unimplementable on systems -where a file position isn't just an offset. It also never says just -what fpos<> is really supposed to be. [Here's my summary, which -Jerry agrees is more or less accurate. "I think I now know what -the class really is, at this point: it's a magic cookie that -encapsulates an mbstate_t and a file position (possibly represented as -an fpos_t), it has syntactic support for pointer-like arithmetic, and -implementors are required to have real, not just syntactic, support -for arithmetic." This isn't standardese, of course.]

- - -

Rationale:

-

Not a defect. The LWG believes that the Standard is already clear, -and that the above summary is what the Standard in effect says.

- - - - - -
-

10. Codecvt<>::do unclear

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: Dup - Submitter: Matt Austern Opened: 1998-01-14 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.byname].

-

View all issues with Dup status.

-

Duplicate of: 19

-

Discussion:

-

Section 22.2.1.5.2 says that codecvt<>::do_in and do_out -should return the value noconv if "no conversion was -needed". However, I don't see anything anywhere that defines what -it means for a conversion to be needed or not needed. I can think of -several circumstances where one might plausibly think that a -conversion is not "needed", but I don't know which one is -intended here.

- - -

Rationale:

- - - - - - -
-

12. Way objects hold allocators unclear

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: Angelika Langer Opened: 1998-02-23 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with NAD status.

-

Discussion:

-

I couldn't find a statement in the standard saying whether the allocator object held by -a container is held as a copy of the constructor argument or whether a pointer of -reference is maintained internal. There is an according statement for compare objects and -how they are maintained by the associative containers, but I couldn't find anything -regarding allocators.

- -

Did I overlook it? Is it an open issue or known defect? Or is it deliberately left -unspecified?

- - -

Rationale:

-

Not a defect. The LWG believes that the Standard is already -clear.  See 23.2 [container.requirements], paragraph 8.

- - - - - -
-

43. Locale table correction

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: Dup - Submitter: Brendan Kehoe Opened: 1998-06-01 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.byname].

-

View all issues with Dup status.

-

Duplicate of: 33

-

Discussion:

- - -

Rationale:

- - - - - - -
-

45. Stringstreams read/write pointers initial position unclear

-

Section: 27.8.4 [ostringstream] Status: NAD - Submitter: Matthias Mueller Opened: 1998-05-27 Last modified: 2015-04-08

-

View all other issues in [ostringstream].

-

View all issues with NAD status.

-

Discussion:

-

In a comp.lang.c++.moderated Matthias Mueller wrote:

- -

"We are not sure how to interpret the CD2 (see 27.3 [iostream.forward], 27.8.4.1 [ostringstream.cons], 27.8.2.1 [stringbuf.cons]) -with respect to the question as to what the correct initial positions -of the write and  read pointers of a stringstream should -be."

- -

"Is it the same to output two strings or to initialize the stringstream with the -first and to output the second?"

- -

[PJ Plauger, Bjarne Stroustrup, Randy Smithey, Sean Corfield, and -Jerry Schwarz have all offered opinions; see reflector messages -lib-6518, 6519, 6520, 6521, 6523, 6524.]

- - - - -

Rationale:

-

The LWG believes the Standard is correct as written. The behavior -of stringstreams is consistent with fstreams, and there is a -constructor which can be used to obtain the desired effect. This -behavior is known to be different from strstreams.

- - - - - -
-

58. Extracting a char from a wide-oriented stream

-

Section: 27.7.2.2.3 [istream::extractors] Status: NAD - Submitter: Matt Austern Opened: 1998-07-01 Last modified: 2015-04-08

-

View all other issues in [istream::extractors].

-

View all issues with NAD status.

-

Discussion:

-

27.6.1.2.3 has member functions for extraction of signed char and -unsigned char, both singly and as strings. However, it doesn't say -what it means to extract a char from a -basic_streambuf<charT, Traits>.

- -

basic_streambuf, after all, has no members to extract a char, so -basic_istream must somehow convert from charT to signed char or -unsigned char. The standard doesn't say how it is to perform that -conversion.

- - -

Rationale:

-

The Standard is correct as written. There is no such extractor and -this is the intent of the LWG.

- - - - -
-

65. Underspecification of strstreambuf::seekoff

-

Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD - Submitter: Matt Austern Opened: 1998-08-18 Last modified: 2015-04-08

-

View all other issues in [depr.strstreambuf.virtuals].

-

View all issues with NAD status.

-

Discussion:

-

The standard says how this member function affects the current -stream position. (gptr or pptr) However, it does not -say how this member function affects the beginning and end of the -get/put area.

- -

This is an issue when seekoff is used to position the get pointer -beyond the end of the current read area. (Which is legal. This is -implicit in the definition of seekhigh in D.7.1, paragraph 4.) -

- - -

Rationale:

-

The LWG agrees that seekoff() is underspecified, but does not wish -to invest effort in this deprecated feature.

- - - - - -
-

67. Setw useless for strings

-

Section: 21.4.8.9 [string.io] Status: Dup - Submitter: Steve Clamage Opened: 1998-07-09 Last modified: 2015-04-08

-

View all other issues in [string.io].

-

View all issues with Dup status.

-

Duplicate of: 25

-

Discussion:

-

In a comp.std.c++ posting Michel Michaud wrote: What -should be output by:

- -
   string text("Hello");
-   cout << '[' << setw(10) << right << text << ']';
-
- -

Shouldn't it be:

- -
   [     Hello]
- -

Another person replied: Actually, according to the FDIS, the width -of the field should be the minimum of width and the length of the -string, so the output shouldn't have any padding. I think that this is -a typo, however, and that what is wanted is the maximum of the -two. (As written, setw is useless for strings. If that had been the -intent, one wouldn't expect them to have mentioned using its value.) -

- -

It's worth pointing out that this is a recent correction anyway; -IIRC, earlier versions of the draft forgot to mention formatting -parameters whatsoever.

- - -

Rationale:

- - - - - - -
-

72. Do_convert phantom member function

-

Section: 22.4.1.4 [locale.codecvt] Status: Dup - Submitter: Nathan Myers Opened: 1998-08-24 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

View all issues with Dup status.

-

Duplicate of: 24

-

Discussion:

-

In 22.4.1.4 [locale.codecvt] par 3, and in 22.4.1.4.2 [locale.codecvt.virtuals] par 8, a nonexistent member function -"do_convert" is mentioned. This member was replaced with -"do_in" and "do_out", the proper referents in the -contexts above.

- - -

Rationale:

- - - - - -
-

73. is_open should be const

-

Section: 27.9.1 [fstreams] Status: NAD - Submitter: Matt Austern Opened: 1998-08-27 Last modified: 2015-04-08

-

View all other issues in [fstreams].

-

View all issues with NAD status.

-

Discussion:

-

Classes basic_ifstream, basic_ofstream, and -basic_fstream all have a member function is_open. It -should be a const member function, since it does nothing but -call one of basic_filebuf's const member functions.

- - -

Rationale:

-

Not a defect. This is a deliberate feature; const streams would be -meaningless.

- - - - -
-

77. Valarray operator[] const returning value

-

Section: 26.6.2.4 [valarray.access] Status: Dup - Submitter: Levente Farkas Opened: 1998-09-09 Last modified: 2015-04-08

-

View all other issues in [valarray.access].

-

View all issues with Dup status.

-

Duplicate of: 389

-

Discussion:

-

valarray:
-
-    T operator[] (size_t) const;
-
-why not
-
-    const T& operator[] (size_t) const;
-
-as in vector ???
-
-One can't copy even from a const valarray eg:
-
-    memcpy(ptr, &v[0], v.size() * sizeof(double));
-
-[I] find this bug in valarray is very difficult.

- - -

Rationale:

-

The LWG believes that the interface was deliberately designed that -way. That is what valarray was designed to do; that's where the -"value array" name comes from. LWG members further comment -that "we don't want valarray to be a full STL container." -26.6.2.4 [valarray.access] specifies properties that indicate "an -absence of aliasing" for non-constant arrays; this allows -optimizations, including special hardware optimizations, that are not -otherwise possible.

- - - - - -
-

81. Wrong declaration of slice operations

-

Section: 26.6.5 [template.slice.array], 26.6.7 [template.gslice.array], 26.6.8 [template.mask.array], 26.6.9 [template.indirect.array] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [template.slice.array].

-

View all issues with NAD status.

-

Discussion:

-

Isn't the definition of copy constructor and assignment operators wrong? -       Instead of

- -
      slice_array(const slice_array&); 
-      slice_array& operator=(const slice_array&);
- -

IMHO they have to be

- -
      slice_array(const slice_array<T>&); 
-      slice_array& operator=(const slice_array<T>&);
- -

Same for gslice_array.

- - -

Rationale:

-

Not a defect. The Standard is correct as written.

- - - - -
-

82. Missing constant for set elements

-

Section: 23.2.4 [associative.reqmts] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with NAD status.

-

Discussion:

-

Paragraph 5 specifies:

- -

-For set and multiset the value type is the same as the key type. For -map and multimap it is equal to pair<const Key, T>. -

- -

Strictly speaking, this is not correct because for set and multiset -the value type is the same as the constant key type.

- - -

Rationale:

-

Not a defect. The Standard is correct as written; it uses a -different mechanism (const &) for set and -multiset. See issue 103 for a related -issue.

- - - - -
-

84. Ambiguity with string::insert()

-

Section: 21.4.5 [string.access] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [string.access].

-

View all issues with NAD status.

-

Discussion:

-

If I try

-
    s.insert(0,1,' ');
- -

  I get an nasty ambiguity. It might be

-
    s.insert((size_type)0,(size_type)1,(charT)' ');
- -

which inserts 1 space character at position 0, or

-
    s.insert((char*)0,(size_type)1,(charT)' ')
- -

which inserts 1 space character at iterator/address 0 (bingo!), or

-
    s.insert((char*)0, (InputIterator)1, (InputIterator)' ')
- -

which normally inserts characters from iterator 1 to iterator ' -'. But according to 23.1.1.9 (the "do the right thing" fix) -it is equivalent to the second. However, it is still ambiguous, -because of course I mean the first!

- - -

Rationale:

-

Not a defect. The LWG believes this is a "genetic -misfortune" inherent in the design of string and thus not a -defect in the Standard as such .

- - - - -
-

85. String char types

-

Section: 21 [strings] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [strings].

-

View all issues with NAD status.

-

Discussion:

-

The standard seems not to require that charT is equivalent to -traits::char_type. So, what happens if charT is not equivalent to -traits::char_type?

- - -

Rationale:

-

There is already wording in 21.2 [char.traits] paragraph 3 that -requires them to be the same.

- - - - -
-

87. Error in description of string::compare()

-

Section: 21.4.6.8 [string::swap] Status: Dup - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [string::swap].

-

View all issues with Dup status.

-

Duplicate of: 5

-

Discussion:

-

The following compare() description is obviously a bug:

- -
-int compare(size_type pos, size_type n1, 
-            charT *s, size_type n2 = npos) const;
-
- -

because without passing n2 it should compare up to the end of the -string instead of comparing npos characters (which throws an -exception)

- - -

Rationale:

- - - - - -
-

88. Inconsistency between string::insert() and string::append()

-

Section: 21.4.6.4 [string::insert], 21.4.6.2 [string::append] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [string::insert].

-

View all issues with NAD status.

-

Discussion:

-

Why does

-
  template<class InputIterator> 
-       basic_string& append(InputIterator first, InputIterator last);
- -

return a string, while

-
  template<class InputIterator> 
-       void insert(iterator p, InputIterator first, InputIterator last);
- -

returns nothing ?

- - -

Rationale:

-

The LWG believes this stylistic inconsistency is not sufficiently -serious to constitute a defect.

- - - - -
-

89. Missing throw specification for string::insert() and string::replace()

-

Section: 21.4.6.4 [string::insert], 21.4.6.6 [string::replace] Status: Dup - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [string::insert].

-

View all issues with Dup status.

-

Duplicate of: 83

-

Discussion:

-

All insert() and replace() members for strings with an iterator as -first argument lack a throw specification. The throw -specification should probably be: length_error if size exceeds -maximum.

- - -

Rationale:

-

Considered a duplicate because it will be solved by the resolution -of issue 83.

- - - - - -
-

93. Incomplete Valarray Subset Definitions

-

Section: 26.6 [numarray] Status: NAD - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

View all other issues in [numarray].

-

View all issues with NAD status.

-

Discussion:

-

You can easily create subsets, but you can't easily combine them -with other subsets. Unfortunately, you almost always needs an -explicit type conversion to valarray. This is because the standard -does not specify that valarray subsets provide the same operations as -valarrays.

- -

For example, to multiply two subsets and assign the result to a third subset, you can't -write the following:

- -
va[slice(0,4,3)] = va[slice(1,4,3)] * va[slice(2,4,3)];
- -

Instead, you have to code as follows:

- -
va[slice(0,4,3)] = static_cast<valarray<double> >(va[slice(1,4,3)]) * 
-                   static_cast<valarray<double> >(va[slice(2,4,3)]);
- -

This is tedious and error-prone. Even worse, it costs performance because each cast -creates a temporary objects, which could be avoided without the cast.

- - -

Proposed resolution:

-

Extend all valarray subset types so that they offer all valarray operations.

- - -

Rationale:

-

This is not a defect in the Standard; it is a request for an extension.

- - - - -
-

94. May library implementors add template parameters to Standard Library classes?

-

Section: 17.6.5 [conforming] Status: NAD - Submitter: Matt Austern Opened: 1998-01-22 Last modified: 2015-04-08

-

View all other issues in [conforming].

-

View all issues with NAD status.

-

Discussion:

-

Is it a permitted extension for library implementors to add template parameters to -standard library classes, provided that those extra parameters have defaults? For example, -instead of defining template <class T, class Alloc = allocator<T> > class -vector; defining it as template <class T, class Alloc = allocator<T>, -int N = 1> class vector;

- -

The standard may well already allow this (I can't think of any way that this extension -could break a conforming program, considering that users are not permitted to -forward-declare standard library components), but it ought to be explicitly permitted or -forbidden.

- -

comment from Steve Cleary via comp.std.c++:

-
-

I disagree [with the proposed resolution] for the following reason: -consider user library code with template template parameters. For -example, a user library object may be templated on the type of -underlying sequence storage to use (deque/list/vector), since these -classes all take the same number and type of template parameters; this -would allow the user to determine the performance tradeoffs of the -user library object. A similar example is a user library object -templated on the type of underlying set storage (set/multiset) or map -storage (map/multimap), which would allow users to change (within -reason) the semantic meanings of operations on that object.

-

I think that additional template parameters should be forbidden in -the Standard classes. Library writers don't lose any expressive power, -and can still offer extensions because additional template parameters -may be provided by a non-Standard implementation class:

-
 
-   template <class T, class Allocator = allocator<T>, int N = 1>
-   class __vector
-   { ... };
-   template <class T, class Allocator = allocator<T> >
-   class vector: public __vector<T, Allocator>
-   { ... };
-
- -
- - - -

Proposed resolution:

-

Add a new subclause [presumably 17.4.4.9] following 17.6.5.12 [res.on.exception.handling]:

- -
-

17.4.4.9 Template Parameters

A specialization of a - template class described in the C++ Standard Library behaves the - same as if the implementation declares no additional template - parameters.

Footnote: Additional template parameters with - default values are thus permitted.

-
- -

Add "template parameters" to the list of subclauses at -the end of 17.6.5 [conforming] paragraph 1.

- -

[Kona: The LWG agreed the standard needs clarification. After -discussion with John Spicer, it seems added template parameters can be -detected by a program using template-template parameters. A straw vote -- "should implementors be allowed to add template -parameters?" found no consensus ; 5 - yes, 7 - no.]

- - - - -

Rationale:

-

-There is no ambiguity; the standard is clear as written. Library -implementors are not permitted to add template parameters to standard -library classes. This does not fall under the "as if" rule, -so it would be permitted only if the standard gave explicit license -for implementors to do this. This would require a change in the -standard. -

- -

-The LWG decided against making this change, because it would break -user code involving template template parameters or specializations -of standard library class templates. -

- - - - - -
-

95. Members added by the implementation

-

Section: 17.6.5.5 [member.functions] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [member.functions].

-

View all issues with NAD status.

-

Discussion:

-

In 17.3.4.4/2 vs 17.3.4.7/0 there is a hole; an implementation could add virtual -members a base class and break user derived classes.

- -

Example:

- -
- 
// implementation code:
-struct _Base { // _Base is in the implementer namespace
-        virtual void foo ();
-};
-class vector : _Base // deriving from a class is allowed
-{ ... };
-
-// user code:
-class vector_checking : public vector 
-{
-        void foo (); // don't want to override _Base::foo () as the 
-                     // user doesn't know about _Base::foo ()
-};
-
- - -

Proposed resolution:

-

Clarify the wording to make the example illegal.

- - -

Rationale:

-

This is not a defect in the Standard.  The example is already -illegal.  See 17.6.5.5 [member.functions] paragraph 2.

- - - - -
-

96. Vector<bool> is not a container

-

Section: 23.3.6 [vector] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [vector].

-

View all issues with NAD status.

-

Discussion:

-

vector<bool> is not a container as its reference and -pointer types are not references and pointers.

- -

Also it forces everyone to have a space optimization instead of a -speed one.

- -

See also: 99-0008 == N1185 Vector<bool> is -Nonconforming, Forces Optimization Choice.

- -

[In Santa Cruz the LWG felt that this was Not A Defect.]

- - -

[In Dublin many present felt that failure to meet Container -requirements was a defect. There was disagreement as to whether -or not the optimization requirements constituted a defect.]

- - -

[The LWG looked at the following resolutions in some detail: -
-     * Not A Defect.
-     * Add a note explaining that vector<bool> does not meet -Container requirements.
-     * Remove vector<bool>.
-     * Add a new category of container requirements which -vector<bool> would meet.
-     * Rename vector<bool>.
-
-No alternative had strong, wide-spread, support and every alternative -had at least one "over my dead body" response.
-
-There was also mention of a transition scheme something like (1) add -vector_bool and deprecate vector<bool> in the next standard. (2) -Remove vector<bool> in the following standard.]

- - -

[Modifying container requirements to permit returning proxies -(thus allowing container requirements conforming vector<bool>) -was also discussed.]

- - -

[It was also noted that there is a partial but ugly workaround in -that vector<bool> may be further specialized with a customer -allocator.]

- - -

[Kona: Herb Sutter presented his paper J16/99-0035==WG21/N1211, -vector<bool>: More Problems, Better Solutions. Much discussion -of a two step approach: a) deprecate, b) provide replacement under a -new name. LWG straw vote on that: 1-favor, 11-could live with, 2-over -my dead body. This resolution was mentioned in the LWG report to the -full committee, where several additional committee members indicated -over-my-dead-body positions.]

- - -

Discussed at Lillehammer. General agreement that we should - deprecate vector<bool> and introduce this functionality under - a different name, e.g. bit_vector. This might make it possible to - remove the vector<bool> specialization in the standard that comes - after C++0x. There was also a suggestion that - in C++0x we could additional say that it's implementation defined - whether vector<bool> refers to the specialization or to the - primary template, but there wasn't general agreement that this was a - good idea.

- -

We need a paper for the new bit_vector class.

- -

[ -Batavia: -]

- -

-The LWG feels we need something closer to SGI's bitvector to ease migration -from vector<bool>. Although some of the funcitonality from -N2050 -could well be used in such a template. The concern is easing the API migration for those -users who want to continue using a bit-packed container. Alan and Beman to work. -

- -

[ -Post Summit Alisdair adds: -]

- - -
-

-vector<bool> is now a conforming container under the revised terms of C++0x, -which supports containers of proxies. -

-

-Recommend NAD. -

-

-Two issues remain: -

-

-i/ premature optimization in the specification. -There is still some sentiment that deprecation is the correct way to go, -although it is still not clear what it would mean to deprecate a single -specialization of a template. -

-

-Recommend: Create a new issue for the discussion, leave as Open. -

-

-ii/ Request for a new bitvector class to guarantee the optimization, perhaps -with a better tuned interface. -

-

-This is a clear extension request that may be handled via a future TR. -

-
- -

[ -Batavia (2009-05): -]

- -

-We note that most of this issue has become moot over time, -and agree with Alisdair's recommendations. -Move to NAD Future for reconsideration of part (ii). -

- -

[ -2009-07-29 Alisdair reopens: -]

- - -
-

-This infamous issue was closed as NAD Future when concepts introduced -support for proxy iterators, so the only remaining requirement was to -provide a better type to support bitsets of dynamic length. I fear we -must re-open this issue until the post-concept form of iterators is -available, and hopefully will support the necessary proxy functionality -to allow us to close this issue as NAD. -

- -

-I recommend we spawn a separate issue (1184) requesting a dynamic length bitset -and pre-emptively file it as NAD Future. It is difficult to resolve #96 -when it effectively contains two separate sub-issues. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD, and give rationale. -

- - - -

Proposed resolution:

-

-We now have: -N2050 -and -N2160. -

- - - -

Rationale:

-

-We want to support proxy iterators but that is going to be separate -work. Don't want to see this issue come back in these kinds of terms. -We're interested in a separate container, and proxy iterators, but both -of those are separate issues. -

-

-We've looked at a lot of ways to fix this that would be close to this, -but those things would break existing code. Attempts to fix this -directly have not been tractable, and removing it has not been -tractable. Therefore we are closing. -

- - - - - -
-

97. Insert inconsistent definition

-

Section: 23 [containers] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View other active issues in [containers].

-

View all other issues in [containers].

-

View all issues with NAD status.

-

Discussion:

-

insert(iterator, const value_type&) is defined both on -sequences and on set, with unrelated semantics: insert here (in -sequences), and insert with hint (in associative containers). They -should have different names (B.S. says: do not abuse overloading).

- - -

Rationale:

-

This is not a defect in the Standard. It is a genetic misfortune of -the design, for better or for worse.

- - - - -
-

99. Reverse_iterator comparisons completely wrong

-

Section: 24.5.1.3.13 [reverse.iter.op==] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

The <, >, <=, >= comparison operator are wrong: they -return the opposite of what they should.

- -

Note: same problem in CD2, these were not even defined in CD1. SGI -STL code is correct; this problem is known since the Morristown -meeting but there it was too late

- - -

Rationale:

-

This is not a defect in the Standard. A careful reading shows the Standard is correct -as written. A review of several implementations show that they implement -exactly what the Standard says.

- - - - -
-

100. Insert iterators/ostream_iterators overconstrained

-

Section: 24.5.2 [insert.iterators], 24.6.4 [ostreambuf.iterator] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [insert.iterators].

-

View all issues with NAD status.

-

Discussion:

-

Overspecified For an insert iterator it, the expression *it is -required to return a reference to it. This is a simple possible -implementation, but as the SGI STL documentation says, not the only -one, and the user should not assume that this is the case.

- - -

Rationale:

-

The LWG believes this causes no harm and is not a defect in the -standard. The only example anyone could come up with caused some -incorrect code to work, rather than the other way around.

- - - - - -
-

101. No way to free storage for vector and deque

-

Section: 23.3.6 [vector], 23.3.2 [array] Status: NAD Editorial - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [vector].

-

View all issues with NAD Editorial status.

-

Discussion:

-

Reserve can not free storage, unlike string::reserve

- -

[ -2010-02-13 Alisdair adds: -]

- - -
-

-This issue has been revisited and addressed (755, 850). This issues should be reclassified to NAD Editorial to reflect -this action. -

-
- - - -

Rationale:

-

This is not a defect in the Standard. The LWG has considered this -issue in the past and sees no need to change the Standard. Deque has -no reserve() member function. For vector, shrink-to-fit can be -expressed in a single line of code (where v is -vector<T>): -

- -
-

vector<T>(v).swap(v);  // shrink-to-fit v

-
- - - - - -
-

102. Bug in insert range in associative containers

-

Section: 23.2.4 [associative.reqmts] Status: Dup - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with Dup status.

-

Duplicate of: 264

-

Discussion:

-

Table 69 of Containers say that a.insert(i,j) is linear if [i, j) is ordered. It seems -impossible to implement, as it means that if [i, j) = [x], insert in an associative -container is O(1)!

- - -

Proposed resolution:

-

N+log (size()) if [i,j) is sorted according to value_comp()

- - -

Rationale:

-

Subsumed by issue 264.

- - - - - -
-

104. Description of basic_string::operator[] is unclear

-

Section: 21.4.4 [string.capacity] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [string.capacity].

-

View all issues with NAD status.

-

Discussion:

-

It is not clear that undefined behavior applies when pos == size () -for the non const version.

- - -

Proposed resolution:

-

Rewrite as: Otherwise, if pos > size () or pos == size () and -the non-const version is used, then the behavior is undefined.

- - -

Rationale:

-

The Standard is correct. The proposed resolution already appears in -the Standard.

- - - - -
-

105. fstream ctors argument types desired

-

Section: 27.9 [file.streams] Status: Dup - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all issues with Dup status.

-

Duplicate of: 454

-

Discussion:

- - -

fstream ctors take a const char* instead of string.
-fstream ctors can't take wchar_t

- -

An extension to add a const wchar_t* to fstream would make the -implementation non conforming.

- - -

Rationale:

-

This is not a defect in the Standard. It might be an -interesting extension for the next Standard.

- - - - -
-

107. Valarray constructor is strange

-

Section: 26.6.2 [template.valarray] Status: NAD - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

View all other issues in [template.valarray].

-

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-

Discussion:

-

The order of the arguments is (elem, size) instead of the normal -(size, elem) in the rest of the library. Since elem often has an -integral or floating point type, both types are convertible to each -other and reversing them leads to a well formed program.

- - -

Proposed resolution:

-

Inverting the arguments could silently break programs. Introduce -the two signatures (const T&, size_t) and (size_t, const T&), -but make the one we do not want private so errors result in a -diagnosed access violation. This technique can also be applied to STL -containers.

- - -

Rationale:

-

The LWG believes that while the order of arguments is unfortunate, -it does not constitute a defect in the standard. The LWG believes that -the proposed solution will not work for valarray<size_t> and -perhaps other cases.

- - - - -
-

111. istreambuf_iterator::equal overspecified, inefficient

-

Section: 24.6.3.5 [istreambuf.iterator::equal] Status: NAD - Submitter: Nathan Myers Opened: 1998-10-15 Last modified: 2015-04-08

-

View all other issues in [istreambuf.iterator::equal].

-

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-

Discussion:

-

The member istreambuf_iterator<>::equal is specified to be -unnecessarily inefficient. While this does not affect the efficiency -of conforming implementations of iostreams, because they can -"reach into" the iterators and bypass this function, it does -affect users who use istreambuf_iterators.

- -

The inefficiency results from a too-scrupulous definition, which -requires a "true" result if neither iterator is at eof. In -practice these iterators can only usefully be compared with the -"eof" value, so the extra test implied provides no benefit, -but slows down users' code.

- -

The solution is to weaken the requirement on the function to return -true only if both iterators are at eof.

- -

[ -Summit: -]

- - -

-Reopened by Alisdair. -

- -

[ -Post Summit Daniel adds: -]

- - -
-

-Recommend NAD. The proposed wording would violate the axioms of -concept requirement EqualityComparable axioms as part of concept InputIterator -and more specifically it would violate the explicit wording of -24.2.3 [input.iterators]/7: -

- -

-If two iterators a and b of the same type are equal, then either a -and b are both dereferenceable or else neither is dereferenceable. -

- -

[ -2009-07 Frankfurt -]

- - -

-Agree NAD. -

- -
- - - -

Proposed resolution:

-

Replace 24.6.3.5 [istreambuf.iterator::equal], paragraph 1,

- -
-

-1- Returns: true if and only if both iterators are at end-of-stream, or neither is at - end-of-stream, regardless of what streambuf object they use.

-
- -

with

- -
-

-1- Returns: true if and only if both iterators are at - end-of-stream, regardless of what streambuf object they use.

-
- - - -

Rationale:

-

It is not clear that this is a genuine defect. Additionally, the -LWG was reluctant to make a change that would result in -operator== not being a equivalence relation. One consequence of -this change is that an algorithm that's passed the range [i, i) -would no longer treat it as an empty range.

- - - - - -
-

113. Missing/extra iostream sync semantics

-

Section: 27.7.2.1 [istream], 27.7.2.3 [istream.unformatted] Status: NAD - Submitter: Steve Clamage Opened: 1998-10-13 Last modified: 2015-04-08

-

View all other issues in [istream].

-

View all issues with NAD status.

-

Discussion:

-

In 27.6.1.1, class basic_istream has a member function sync, described in 27.6.1.3, -paragraph 36.

- -

Following the chain of definitions, I find that the various sync functions have defined -semantics for output streams, but no semantics for input streams. On the other hand, -basic_ostream has no sync function.

- -

The sync function should at minimum be added to basic_ostream, for internal -consistency.

- -

A larger question is whether sync should have assigned semantics for input streams.

- -

Classic iostreams said streambuf::sync flushes pending output and attempts to return -unread input characters to the source. It is a protected member function. The filebuf -version (which is public) has that behavior (it backs up the read pointer). Class -strstreambuf does not override streambuf::sync, and so sync can't be called on a -strstream.

- -

If we can add corresponding semantics to the various sync functions, we should. If not, -we should remove sync from basic_istream.

- - -

Rationale:

-

A sync function is not needed in basic_ostream because the flush function provides the -desired functionality.

- -

As for the other points, the LWG finds the standard correct as written.

- - - - - -
-

116. bitset cannot be constructed with a const char*

-

Section: 20.6 [template.bitset] Status: Dup - Submitter: Judy Ward Opened: 1998-11-06 Last modified: 2015-04-08

-

View other active issues in [template.bitset].

-

View all other issues in [template.bitset].

-

View all issues with Dup status.

-

Duplicate of: 778

-

Discussion:

- - - -

The following code does not compile with the EDG compiler:

- -
- 
#include <bitset>
-using namespace std;
-bitset<32> b("111111111");
-
- -

If you cast the ctor argument to a string, i.e.:

- -
- 
bitset<32> b(string("111111111"));
-
- -

then it will compile. The reason is that bitset has the following templatized -constructor:

- -
- 
template <class charT, class traits, class Allocator>
-explicit bitset (const basic_string<charT, traits, Allocator>& str, ...);
-
- -

According to the compiler vendor, Steve Adamcyk at EDG, the user -cannot pass this template constructor a const char* and -expect a conversion to basic_string. The reason is -"When you have a template constructor, it can get used in -contexts where type deduction can be done. Type deduction basically -comes up with exact matches, not ones involving conversions." -

- -

I don't think the intention when this constructor became -templatized was for construction from a const char* to no -longer work.

- - -

Proposed resolution:

-

Add to 20.6 [template.bitset] a bitset constructor declaration

- -
- 
explicit bitset(const char*);
-
- -

and in Section 20.6.1 [bitset.cons] add:

- -
- 
explicit bitset(const char* str);
-

Effects:
-     Calls bitset((string) str, 0, string::npos);

-
- - -

Rationale:

-

Although the problem is real, the standard is designed that way so -it is not a defect. Education is the immediate workaround. A future -standard may wish to consider the Proposed Resolution as an -extension.

- - - - - -
-

121. Detailed definition for ctype<wchar_t> specialization

-

Section: 22.3.1.1.1 [locale.category] Status: NAD - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [locale.category].

-

View all issues with NAD status.

-

Discussion:

-

Section 22.1.1.1.1 has the following listed in Table 51: ctype<char> , -ctype<wchar_t>.

- -

Also Section 22.4.1.1 [locale.ctype] says:

- -
-

The instantiations required in Table 51 (22.1.1.1.1) namely ctype<char> and - ctype<wchar_t> , implement character classing appropriate to the implementation's - native character set.

-
- -

However, Section 22.4.1.3 [facet.ctype.special] -only has a detailed description of the ctype<char> specialization, not the -ctype<wchar_t> specialization.

- - -

Proposed resolution:

-

Add the ctype<wchar_t> detailed class description to Section -22.4.1.3 [facet.ctype.special].

- - -

Rationale:

-

Specialization for wchar_t is not needed since the default is acceptable.

- - - - - -
-

128. Need open_mode() function for file stream, string streams, file buffers, and string  buffers

-

Section: 27.8 [string.streams], 27.9 [file.streams] Status: NAD - Submitter: Angelika Langer Opened: 1999-02-22 Last modified: 2015-04-08

-

View all other issues in [string.streams].

-

View all issues with NAD status.

-

Discussion:

-

The following question came from Thorsten Herlemann:

- -
-

You can set a mode when constructing or opening a file-stream or - filebuf, e.g. ios::in, ios::out, ios::binary, ... But how can I get - that mode later on, e.g. in my own operator << or operator - >> or when I want to check whether a file-stream or - file-buffer object passed as parameter is opened for input or output - or binary? Is there no possibility? Is this a design-error in the - standard C++ library?

-
- -

It is indeed impossible to find out what a stream's or stream -buffer's open mode is, and without that knowledge you don't know -how certain operations behave. Just think of the append mode.

- -

Both streams and stream buffers should have a mode() function that returns the -current open mode setting.

- -

[ -post Bellevue: Alisdair requested to re-Open. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-Neither Howard nor Bill has received a customer request for this. -

-

-No consensus for change. The programmer can save this information to the side. -

-

-Moved to NAD. -

-
- - - -

Proposed resolution:

-

For stream buffers, add a function to the base class as a non-virtual function -qualified as const to 27.6.3 [streambuf]:

- -

    openmode mode() const;

- -

    Returns the current open mode.

- -

With streams, I'm not sure what to suggest. In principle, the mode -could already be returned by ios_base, but the mode is only -initialized for file and string stream objects, unless I'm overlooking -anything. For this reason it should be added to the most derived -stream classes. Alternatively, it could be added to basic_ios -and would be default initialized in basic_ios<>::init().

- - -

Rationale:

-

This might be an interesting extension for some future, but it is -not a defect in the current standard. The Proposed Resolution is -retained for future reference.

- - - - - -
-

131. list::splice throws nothing

-

Section: 23.3.5.5 [list.ops] Status: NAD - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with NAD status.

-

Discussion:

-

What happens if a splice operation causes the size() of a list to grow -beyond max_size()?

- - -

Rationale:

-

Size() cannot grow beyond max_size(). 

- - - - - -
-

135. basic_iostream doubly initialized

-

Section: 27.7.2.5.1 [iostream.cons] Status: NAD - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-1- Effects Constructs an object of class basic_iostream, assigning -initial values to the base classes by calling -basic_istream<charT,traits>(sb) (lib.istream) and -basic_ostream<charT,traits>(sb) (lib.ostream)

- -

The called for basic_istream and basic_ostream constructors call -init(sb). This means that the basic_iostream's virtual base class is -initialized twice.

- - -

Proposed resolution:

-

Change 27.6.1.5.1, paragraph 1 to:

- -

-1- Effects Constructs an object of class basic_iostream, assigning -initial values to the base classes by calling -basic_istream<charT,traits>(sb) (lib.istream).

- - -

Rationale:

-

The LWG agreed that the init() function is called -twice, but said that this is harmless and so not a defect in the -standard.

- - - - -
-

138. Class ctype_byname<char> redundant and misleading

-

Section: 22.4.1.4 [locale.codecvt] Status: NAD - Submitter: Angelika Langer Opened: 1999-03-18 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

View all issues with NAD status.

-

Discussion:

-

Section 22.4.1.4 [locale.codecvt] specifies that -ctype_byname<char> must be a specialization of the ctype_byname -template.

- -

It is common practice in the standard that specializations of class templates are only -mentioned where the interface of the specialization deviates from the interface of the -template that it is a specialization of. Otherwise, the fact whether or not a required -instantiation is an actual instantiation or a specialization is left open as an -implementation detail.

- -

Clause 22.2.1.4 deviates from that practice and for that reason is misleading. The -fact, that ctype_byname<char> is specified as a specialization suggests that there -must be something "special" about it, but it has the exact same interface as the -ctype_byname template. Clause 22.2.1.4 does not have any explanatory value, is at best -redundant, at worst misleading - unless I am missing anything.

- -

Naturally, an implementation will most likely implement ctype_byname<char> as a -specialization, because the base class ctype<char> is a specialization with an -interface different from the ctype template, but that's an implementation detail and need -not be mentioned in the standard.

- -

[ -Summit: -]

- - -

-Reopened by Alisdair. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved to NAD. -

- - - -

Rationale:

-

The standard as written is mildly misleading, but the correct fix -is to deal with the underlying problem in the ctype_byname base class, -not in the specialization. See issue 228.

- - - - -
-

140. map<Key, T>::value_type does not satisfy the assignable requirement

-

Section: 23.4.4 [map] Status: NAD Editorial - Submitter: Mark Mitchell Opened: 1999-04-14 Last modified: 2015-04-08

-

View all other issues in [map].

-

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-

Discussion:

-
-

23.2 [container.requirements]
-
- expression         return type -      pre/post-condition
- -------------     -----------      - -------------------
- X::value_type    T -                    - T is assignable
-
- 23.4.4 [map]
-
- A map satisfies all the requirements of a container.
-
- For a map<Key, T> ... the value_type is pair<const Key, T>.

-
- -

There's a contradiction here. In particular, `pair<const Key, -T>' is not assignable; the `const Key' cannot be assigned -to. So,  map<Key, T>::value_type does not satisfy the -assignable requirement imposed by a container.

- -

[See issue 103 for the slightly related issue of -modification of set keys.]

- - - -

Rationale:

-

The LWG believes that the standard is inconsistent, but that this -is a design problem rather than a strict defect. May wish to -reconsider for the next standard.

- - - - -
-

143. C .h header wording unclear

-

Section: D.5 [depr.c.headers] Status: NAD - Submitter: Christophe de Dinechin Opened: 1999-05-04 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

[depr.c.headers] paragraph 2 reads:

- -
- -

Each C header, whose name has the form name.h, behaves as if each -name placed in the Standard library namespace by the corresponding -cname header is also placed within the namespace scope of the -namespace std and is followed by an explicit using-declaration -(_namespace.udecl_)

- -
- -

I think it should mention the global name space somewhere...  -Currently, it indicates that name placed in std is also placed in -std...

- -

I don't know what is the correct wording. For instance, if struct -tm is defined in time.h, ctime declares std::tm. However, the current -wording seems ambiguous regarding which of the following would occur -for use of both ctime and time.h:

- -
- 
// version 1:
-namespace std {
-        struct tm { ... };
-}
-using std::tm;
-
-// version 2:
-struct tm { ... };
-namespace std {
-        using ::tm;
-}
-
-// version 3:
-struct tm { ... };
-namespace std {
-        struct tm { ... };
-}
-
- -

I think version 1 is intended.

- -

[Kona: The LWG agreed that the wording is not clear. It also -agreed that version 1 is intended, version 2 is not equivalent to -version 1, and version 3 is clearly not intended. The example below -was constructed by Nathan Myers to illustrate why version 2 is not -equivalent to version 1.

- -

Although not equivalent, the LWG is unsure if (2) is enough of -a problem to be prohibited. Points discussed in favor of allowing -(2):

- -
-
    -
  • It may be a convenience to implementors.
    • -
  • The only cases that fail are structs, of which the C library - contains only a few.
    • -
-
- -

]

- -

Example:

- -
- -
#include <time.h>
-#include <utility>
-
-int main() {
-    std::tm * t;
-    make_pair( t, t ); // okay with version 1 due to Koenig lookup
-                       // fails with version 2; make_pair not found
-    return 0;
-}
- -
- - -

Proposed resolution:

- -

Replace D.5 [depr.c.headers] paragraph 2 with:

- -
- -

Each C header, whose name has the form name.h, behaves as if each -name placed in the Standard library namespace by the corresponding -cname header is also placed within the namespace scope of the -namespace std by name.h and is followed by an explicit -using-declaration (_namespace.udecl_) in global scope.

- -
- - - -

Rationale:

-

The current wording in the standard is the result of a difficult -compromise that averted delay of the standard. Based on discussions -in Tokyo it is clear that there is no still no consensus on stricter -wording, so the issue has been closed. It is suggested that users not -write code that depends on Koenig lookup of C library functions.

- - - - -
-

145. adjustfield lacks default value

-

Section: 27.5.5.2 [basic.ios.cons] Status: NAD - Submitter: Angelika Langer Opened: 1999-05-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

There is no initial value for the adjustfield defined, although -many people believe that the default adjustment were right. This is a -common misunderstanding. The standard only defines that, if no -adjustment is specified, all the predefined inserters must add fill -characters before the actual value, which is "as if" the -right flag were set. The flag itself need not be set.

- -

When you implement a user-defined inserter you cannot rely on right -being the default setting for the adjustfield. Instead, you must be -prepared to find none of the flags set and must keep in mind that in -this case you should make your inserter behave "as if" the -right flag were set. This is surprising to many people and complicates -matters more than necessary.

- -

Unless there is a good reason why the adjustfield should not be -initialized I would suggest to give it the default value that -everybody expects anyway.

- - - -

Rationale:

-

This is not a defect. It is deliberate that the default is no bits -set. Consider Arabic or Hebrew, for example. See 22.4.2.2.2 [facet.num.put.virtuals] paragraph 19, Table 61 - Fill padding.

- - - - -
-

157. Meaningless error handling for pword() and iword()

-

Section: 27.5.3.5 [ios.base.storage] Status: Dup - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View all other issues in [ios.base.storage].

-

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-

Duplicate of: 41

-

Discussion:

-

According to paragraphs 2 and 4 of 27.5.3.5 [ios.base.storage], the -functions iword() and pword() "set the -badbit (which might throw an exception)" on -failure. ... but what does it mean for ios_base to set the -badbit? The state facilities of the IOStream library are -defined in basic_ios, a derived class! It would be possible -to attempt a down cast but then it would be necessary to know the -character type used...

- - -

Rationale:

- - - - - -
-

162. Really "formatted input functions"?

-

Section: 27.7.2.2.3 [istream::extractors] Status: Dup - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 60

-

Discussion:

-

It appears to be somewhat nonsensical to consider the functions -defined in the paragraphs 1 to 5 to be "Formatted input -function" but since these functions are defined in a section -labeled "Formatted input functions" it is unclear to me -whether these operators are considered formatted input functions which -have to conform to the "common requirements" from 27.7.2.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not just -ws, would skip whitespace unless noskipws is set -(... but setting noskipws using the manipulator syntax would -also skip whitespace :-)

- -

See also issue 166 for the same problem in formatted -output

- - -

Rationale:

- - - - - -
-

163. Return of gcount() after a call to gcount

-

Section: 27.7.2.3 [istream.unformatted] Status: Dup - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 60

-

Discussion:

-

It is not clear which functions are to be considered unformatted -input functions. As written, it seems that all functions in 27.7.2.3 [istream.unformatted] are unformatted input functions. However, it does not -really make much sense to construct a sentry object for -gcount(), sync(), ... Also it is unclear what -happens to the gcount() if eg. gcount(), -putback(), unget(), or sync() is called: -These functions don't extract characters, some of them even -"unextract" a character. Should this still be reflected in -gcount()? Of course, it could be read as if after a call to -gcount() gcount() return 0 (the last -unformatted input function, gcount(), didn't extract any -character) and after a call to putback() gcount() -returns -1 (the last unformatted input function -putback() did "extract" back into the -stream). Correspondingly for unget(). Is this what is -intended? If so, this should be clarified. Otherwise, a corresponding -clarification should be used.

- - -

Rationale:

- - - - - -
-

166. Really "formatted output functions"?

-

Section: 27.7.3.6.3 [ostream.inserters] Status: Dup - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

Duplicate of: 60

-

Discussion:

-

From 27.7.3.6.1 [ostream.formatted.reqmts] it appears that all the functions -defined in 27.7.3.6.3 [ostream.inserters] have to construct a -sentry object. Is this really intended?

- -

This is basically the same problem as issue 162 but -for output instead of input.

- - -

Rationale:

- - - - - -
-

177. Complex operators cannot be explicitly instantiated

-

Section: 26.4.6 [complex.ops] Status: NAD - Submitter: Judy Ward Opened: 1999-07-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

A user who tries to explicitly instantiate a complex non-member operator will -get compilation errors. Below is a simplified example of the reason why. The -problem is that iterator_traits cannot be instantiated on a non-pointer type -like float, yet when the compiler is trying to decide which operator+ needs to -be instantiated it must instantiate the declaration to figure out the first -argument type of a reverse_iterator operator.

-
namespace std {
-template <class Iterator> 
-struct iterator_traits
-{
-    typedef typename Iterator::value_type value_type;
-};
-
-template <class T> class reverse_iterator;
-
-// reverse_iterator operator+
-template <class T> 
-reverse_iterator<T> operator+
-(typename iterator_traits<T>::difference_type, const reverse_iterator<T>&);
-
-template <class T> struct complex {};
-
-// complex operator +
-template <class T>
-complex<T> operator+ (const T& lhs, const complex<T>& rhs) 
-{ return complex<T>();} 
-}
-
-// request for explicit instantiation
-template std::complex<float> std::operator+<float>(const float&, 
-     const std::complex<float>&);
-

See also c++-stdlib reflector messages: lib-6814, 6815, 6816.

- - -

Rationale:

-

Implementors can make minor changes and the example will -work. Users are not affected in any case.

According to John -Spicer, It is possible to explicitly instantiate these operators using -different syntax: change "std::operator+<float>" to -"std::operator+".

- -

The proposed resolution of issue 120 is that users will not be able -to explicitly instantiate standard library templates. If that -resolution is accepted then library implementors will be the only ones -that will be affected by this problem, and they must use the indicated -syntax.

- - - - -
-

178. Should clog and cerr initially be tied to cout?

-

Section: 27.4.2 [narrow.stream.objects] Status: NAD - Submitter: Judy Ward Opened: 1999-07-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 27.3.1 says "After the object cerr is initialized, -cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as -required for ios_base::init (lib.basic.ios.cons). It doesn't say -anything about the the state of clog. So this means that calling -cerr.tie() and clog.tie() should return 0 (see Table 89 for -ios_base::init effects). -

-

-Neither of the popular standard library implementations -that I tried does this, they both tie cerr and clog -to &cout. I would think that would be what users expect. -

- - -

Rationale:

-

The standard is clear as written.

-

27.3.1/5 says that "After the object cerr is initialized, cerr.flags() -& unitbuf is nonzero. Its state is otherwise the same as required for -ios_base::init (27.4.4.1)." Table 89 in 27.4.4.1, which gives the -postconditions of basic_ios::init(), says that tie() is 0. (Other issues correct -ios_base::init to basic_ios::init().)

- - - - -
-

188. valarray helpers missing augmented assignment operators

-

Section: 26.6.2.7 [valarray.cassign] Status: NAD - Submitter: Gabriel Dos Reis Opened: 1999-08-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

26.5.2.6 defines augmented assignment operators -valarray<T>::op=(const T&), but fails to provide -corresponding versions for the helper classes. Thus making the -following illegal:

-
-
#include <valarray>
-
-int main()
-{
-std::valarray<double> v(3.14, 1999);
-
-v[99] *= 2.0; // Ok
-
-std::slice s(0, 50, 2);
-
-v[s] *= 2.0; // ERROR
-}
-
-

I can't understand the intent of that omission. It makes the -valarray library less intuitive and less useful.

- - -

Rationale:

-

Although perhaps an unfortunate -design decision, the omission is not a defect in the current -standard.  A future standard may wish to add the missing -operators.

- - - - -
-

190. min() and max() functions should be std::binary_functions

-

Section: 25.4.7 [alg.min.max] Status: NAD - Submitter: Mark Rintoul Opened: 1999-08-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Both std::min and std::max are defined as template functions. This -is very different than the definition of std::plus (and similar -structs) which are defined as function objects which inherit -std::binary_function.
-
- This lack of inheritance leaves std::min and std::max somewhat useless in standard library algorithms which require -a function object that inherits std::binary_function.

- -

[ -post Bellevue: Alisdair requested to re-Open. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-C++0x has lambdas to address this problem now. -

-

-Moved to NAD. -

-
- - - -

Rationale:

-

Although perhaps an unfortunate design decision, the omission is not a defect -in the current standard.  A future standard may wish to consider additional -function objects.

- - - - -
-

191. Unclear complexity for algorithms such as binary search

-

Section: 25.4.3 [alg.binary.search] Status: NAD - Submitter: Nico Josuttis Opened: 1999-10-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The complexity of binary_search() is stated as "At most -log(last-first) + 2 comparisons", which seems to say that the -algorithm has logarithmic complexity. However, this algorithms is -defined for forward iterators. And for forward iterators, the need to -step element-by-element results into linear complexity. But such a -statement is missing in the standard. The same applies to -lower_bound(), upper_bound(), and equal_range(). 
-
-However, strictly speaking the standard contains no bug here. So this -might considered to be a clarification or improvement. -

- - -

Rationale:

-

The complexity is expressed in terms of comparisons, and that -complexity can be met even if the number of iterators accessed is -linear. Paragraph 1 already says exactly what happens to -iterators.

- - - - -
-

192. a.insert(p,t) is inefficient and overconstrained

-

Section: 23.2.4 [associative.reqmts] Status: NAD - Submitter: Ed Brey Opened: 1999-06-06 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 233

-

Discussion:

-

As defined in 23.1.2, paragraph 7 (table 69), a.insert(p,t) suffers from -several problems:

- - - - - - - - - - - - - -
expressionreturn typepre/post-conditioncomplexity
a.insert(p,t)iteratorinserts t if and only if there is no element with key equivalent to the key of - t in containers with unique keys; always inserts t in containers with equivalent - keys. always returns the iterator pointing to the element with key equivalent to - the key of t . iterator p is a hint pointing to where the insert should start to search.logarithmic in general, but amortized constant if t is inserted right after p .
-

1. For a container with unique keys, only logarithmic complexity is -guaranteed if no element is inserted, even though constant complexity is always -possible if p points to an element equivalent to t.

-

2. For a container with equivalent keys, the amortized constant complexity -guarantee is only useful if no key equivalent to t exists in the container. -Otherwise, the insertion could occur in one of multiple locations, at least one -of which would not be right after p.

-

3. By guaranteeing amortized constant complexity only when t is inserted -after p, it is impossible to guarantee constant complexity if t is inserted at -the beginning of the container. Such a problem would not exist if amortized -constant complexity was guaranteed if t is inserted before p, since there is -always some p immediately before which an insert can take place.

-

4. For a container with equivalent keys, p does not allow specification of -where to insert the element, but rather only acts as a hint for improving -performance. This negates the added functionality that p would provide if it -specified where within a sequence of equivalent keys the insertion should occur. -Specifying the insert location provides more control to the user, while -providing no disadvantage to the container implementation.

- - -

Proposed resolution:

-

In 23.2.4 [associative.reqmts] paragraph 7, replace the row in table 69 -for a.insert(p,t) with the following two rows:

- - - - - - - - - - - - - - - - - - - -
expressionreturn typepre/post-conditioncomplexity
a_uniq.insert(p,t)iteratorinserts t if and only if there is no element with key equivalent to the - key of t. returns the iterator pointing to the element with key equivalent - to the key of t.logarithmic in general, but amortized constant if t is inserted right - before p or p points to an element with key equivalent to t.
a_eq.insert(p,t)iteratorinserts t and returns the iterator pointing to the newly inserted - element. t is inserted right before p if doing so preserves the container - ordering.logarithmic in general, but amortized constant if t is inserted right - before p.
- - - -

Rationale:

-

Too big a change.  Furthermore, implementors report checking -both before p and after p, and don't want to change this behavior.

- - - - - -
-

194. rdbuf() functions poorly specified

-

Section: 27.5.5 [ios] Status: NAD - Submitter: Steve Clamage Opened: 1999-09-07 Last modified: 2015-04-08

-

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-

Discussion:

-

In classic iostreams, base class ios had an rdbuf function that returned a -pointer to the associated streambuf. Each derived class had its own rdbuf -function that returned a pointer of a type reflecting the actual type derived -from streambuf. Because in ARM C++, virtual function overrides had to have the -same return type, rdbuf could not be virtual.

-

In standard iostreams, we retain the non-virtual rdbuf function design, and -in addition have an overloaded rdbuf function that sets the buffer pointer. -There is no need for the second function to be virtual nor to be implemented in -derived classes.

-

Minor question: Was there a specific reason not to make the original rdbuf -function virtual?

-

Major problem: Friendly compilers warn about functions in derived classes -that hide base-class overloads. Any standard implementation of iostreams will -result in such a warning on each of the iostream classes, because of the -ill-considered decision to overload rdbuf only in a base class.

-

In addition, users of the second rdbuf function must use explicit -qualification or a cast to call it from derived classes. An explicit -qualification or cast to basic_ios would prevent access to any later overriding -version if there was one.

-

What I'd like to do in an implementation is add a using- declaration for the -second rdbuf function in each derived class. It would eliminate warnings about -hiding functions, and would enable access without using explicit qualification. -Such a change I don't think would change the behavior of any valid program, but -would allow invalid programs to compile:

-
- 
 filebuf mybuf;
- fstream f;
- f.rdbuf(mybuf); // should be an error, no visible rdbuf
-
-

I'd like to suggest this problem as a defect, with the proposed resolution to -require the equivalent of a using-declaration for the rdbuf function that is not -replaced in a later derived class. We could discuss whether replacing the -function should be allowed.

- - -

Rationale:

-

For historical reasons, the standard is correct as written. There is a subtle difference between the base -class rdbuf() and derived class rdbuf(). The derived -class rdbuf() always returns the original streambuf, whereas the base class - rdbuf() will return the "current streambuf" if that has been changed by the variant you mention.

- -

Permission is not required to add such an extension. See -17.6.5.5 [member.functions].

- - - - -
-

196. Placement new example has alignment problems

-

Section: 18.6.1.3 [new.delete.placement] Status: Dup - Submitter: Herb Sutter Opened: 1998-12-15 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 114

-

Discussion:

-

The example in 18.6.1.3 [new.delete.placement] paragraph 4 reads:

- -
- -

[Example: This can be useful for constructing an object at a known address:
-
-   char place[sizeof(Something)];
-   Something* p = new (place) Something();
-
-end example]

- -
- -

This example has potential alignment problems.

- - -

Rationale:

- - - - - -
-

197. max_size() underspecified

-

Section: 17.6.3.5 [allocator.requirements], 23.2 [container.requirements] Status: NAD - Submitter: Andy Sawyer Opened: 1999-10-21 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Must the value returned by max_size() be unchanged from call to call?

- -

Must the value returned from max_size() be meaningful?

- -

Possible meanings identified in lib-6827:

- -

1) The largest container the implementation can support given "best -case" conditions - i.e. assume the run-time platform is "configured to -the max", and no overhead from the program itself. This may possibly -be determined at the point the library is written, but certainly no -later than compile time.
-
-2) The largest container the program could create, given "best case" -conditions - i.e. same platform assumptions as (1), but take into -account any overhead for executing the program itself. (or, roughly -"storage=storage-sizeof(program)"). This does NOT include any resource -allocated by the program. This may (or may not) be determinable at -compile time.
-
-3) The largest container the current execution of the program could -create, given knowledge of the actual run-time platform, but again, -not taking into account any currently allocated resource. This is -probably best determined at program start-up.
-
-4) The largest container the current execution program could create at -the point max_size() is called (or more correctly at the point -max_size() returns :-), given it's current environment (i.e. taking -into account the actual currently available resources). This, -obviously, has to be determined dynamically each time max_size() is -called.

- - -

Proposed resolution:

- - -

Rationale:

-

max_size() isn't useful for very many things, and the existing - wording is sufficiently clear for the few cases that max_size() can - be used for. None of the attempts to change the existing wording - were an improvement.

- -

It is clear to the LWG that the value returned by max_size() can't - change from call to call.

- - - - - - -
-

203. basic_istream::sentry::sentry() is uninstantiable with ctype<user-defined type>

-

Section: 27.7.2.1.3 [istream::sentry] Status: NAD - Submitter: Matt McClure and Dietmar Kühl Opened: 2000-01-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

27.6.1.1.2 Paragraph 4 states:

-
-

To decide if the character c is a whitespace character, the constructor - performs ''as if'' it executes the following code fragment: 

- 
const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc());
-if (ctype.is(ctype.space,c)!=0)
-// c is a whitespace character.
-
- -

But Table 51 in 22.1.1.1.1 only requires an implementation to -provide specializations for ctype<char> and -ctype<wchar_t>. If sentry's constructor is implemented using -ctype, it will be uninstantiable for a user-defined character type -charT, unless the implementation has provided non-working (since it -would be impossible to define a correct ctype<charT> specialization -for an arbitrary charT) definitions of ctype's virtual member -functions.

- -

-It seems the intent the standard is that sentry should behave, in -every respect, not just during execution, as if it were implemented -using ctype, with the burden of providing a ctype specialization -falling on the user. But as it is written, nothing requires the -translation of sentry's constructor to behave as if it used the above -code, and it would seem therefore, that sentry's constructor should be -instantiable for all character types. -

- -

-Note: If I have misinterpreted the intent of the standard with -respect to sentry's constructor's instantiability, then a note should -be added to the following effect: -

- -

-An implementation is forbidden from using the above code if it renders -the constructor uninstantiable for an otherwise valid character -type. -

- -

In any event, some clarification is needed.

- - - -

Rationale:

-

It is possible but not easy to instantiate on types other than char -or wchar_t; many things have to be done first. That is by intention -and is not a defect.

- - - - -
-

204. distance(first, last) when "last" is before "first"

-

Section: 24.4.4 [iterator.operations] Status: NAD - Submitter: Rintala Matti Opened: 2000-01-28 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Section 24.3.4 describes the function distance(first, last) (where first and -last are iterators) which calculates "the number of increments or -decrements needed to get from 'first' to 'last'".

-

The function should work for forward, bidirectional and random access -iterators, and there is a requirement 24.3.4.5 which states that "'last' -must be reachable from 'first'".

-

With random access iterators the function is easy to implement as "last -- first".

-

With forward iterators it's clear that 'first' must point to a place before -'last', because otherwise 'last' would not be reachable from 'first'.

-

But what about bidirectional iterators? There 'last' is reachable from -'first' with the -- operator even if 'last' points to an earlier position than -'first'. However, I cannot see how the distance() function could be implemented -if the implementation does not know which of the iterators points to an earlier -position (you cannot use ++ or -- on either iterator if you don't know which -direction is the "safe way to travel").

-

The paragraph 24.3.4.1 states that "for ... bidirectional iterators they -use ++ to provide linear time implementations". However, the ++ operator is -not mentioned in the reachability requirement. Furthermore 24.3.4.4 explicitly -mentions that distance() returns the number of increments _or decrements_, -suggesting that it could return a negative number also for bidirectional -iterators when 'last' points to a position before 'first'.

-

Is a further requirement is needed to state that for forward and -bidirectional iterators "'last' must be reachable from 'first' using the ++ -operator". Maybe this requirement might also apply to random access -iterators so that distance() would work the same way for every iterator -category?

- - -

Rationale:

-

"Reachable" is defined in the standard in X [iterator.concepts] paragraph 6. -The definition is only in terms of operator++(). The LWG sees no defect in -the standard.

- - - - -
-

205. numeric_limits unclear on how to determine floating point types

-

Section: 18.3.2.4 [numeric.limits.members] Status: NAD - Submitter: Steve Cleary Opened: 2000-01-28 Last modified: 2015-04-08

-

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-

Discussion:

-

In several places in 18.3.2.4 [numeric.limits.members], a member is -described as "Meaningful for all floating point types." -However, no clear method of determining a floating point type is -provided.

- -

In 18.3.2.7 [numeric.special], paragraph 1 states ". . . (for -example, epsilon() is only meaningful if is_integer is -false). . ." which suggests that a type is a floating point type -if is_specialized is true and is_integer is false; however, this is -unclear.

- -

When clarifying this, please keep in mind this need of users: what -exactly is the definition of floating point? Would a fixed point or -rational representation be considered one? I guess my statement here -is that there could also be types that are neither integer or -(strictly) floating point.

- - -

Rationale:

-

It is up to the implementor of a user define type to decide if it is a -floating point type.

- - - - -
-

207. ctype<char> members return clause incomplete

-

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: Dup - Submitter: Robert Klarer Opened: 1999-11-02 Last modified: 2015-04-08

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-

Duplicate of: 153

-

Discussion:

-

-The widen and narrow member functions are described -in 22.2.1.3.2, paragraphs 9-11. In each case we have two overloaded -signatures followed by a Returns clause. The Returns -clause only describes one of the overloads. -

- - -

Proposed resolution:

-

Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] -paragraph 10 from:

-

    Returns: do_widen(low, high, to).

- -

to:

-

    Returns: do_widen(c) or do_widen(low, high, to), -respectively.

- -

Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] paragraph 11 -from:

-

    Returns: do_narrow(low, high, to).

- -

to:

-

    Returns: do_narrow(c) or do_narrow(low, high, to), -respectively.

- - -

Rationale:

-

Subsumed by issue 153, which addresses the same -paragraphs.

- - - - - - -
-

213. Math function overloads ambiguous

-

Section: 26.8 [c.math] Status: NAD - Submitter: Nico Josuttis Opened: 2000-02-26 Last modified: 2015-04-08

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-

Discussion:

-

Due to the additional overloaded versions of numeric functions for -float and long double according to Section 26.5, calls such as int x; -std::pow (x, 4) are ambiguous now in a standard conforming -implementation. Current implementations solve this problem very -different (overload for all types, don't overload for float and long -double, use preprocessor, follow the standard and get -ambiguities).

This behavior should be standardized or at least -identified as implementation defined.

- - -

Rationale:

-

These math issues are an -understood and accepted consequence of the design. They have -been discussed several times in the past. Users must write casts -or write floating point expressions as arguments.

- - - - -
-

215. Can a map's key_type be const?

-

Section: 23.2.4 [associative.reqmts] Status: NAD - Submitter: Judy Ward Opened: 2000-02-29 Last modified: 2015-04-08

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Discussion:

-

A user noticed that this doesn't compile with the Rogue Wave library because -the rb_tree class declares a key_allocator, and allocator<const int> is -not legal, I think:

-
- 
map < const int, ... > // legal?
-
-

which made me wonder whether it is legal for a map's key_type to be const. In -email from Matt Austern he said:

-
-

I'm not sure whether it's legal to declare a map with a const key type. I -hadn't thought about that question until a couple weeks ago. My intuitive -feeling is that it ought not to be allowed, and that the standard ought to say -so. It does turn out to work in SGI's library, though, and someone in the -compiler group even used it. Perhaps this deserves to be written up as an issue -too.

-
- - -

Rationale:

-

The "key is assignable" requirement from table 69 in -23.2.4 [associative.reqmts] already implies the key cannot be const.

- - - - -
-

216. setbase manipulator description flawed

-

Section: 27.7.4 [std.manip] Status: Dup - Submitter: Hyman Rosen Opened: 2000-02-29 Last modified: 2015-04-08

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-

Duplicate of: 193

-

Discussion:

-

27.7.4 [std.manip] paragraph 5 says:

-
-
smanip setbase(int base);
-

Returns: An object s of unspecified type such that if out is an -(instance of) basic_ostream then the expression out<<s behaves -as if f(s) were called, in is an (instance of) basic_istream then the -expression in>>s behaves as if f(s) were called. Where f can be -defined as:

-
ios_base& f(ios_base& str, int base)
-{
-  // set basefield
-  str.setf(n == 8 ? ios_base::oct :
-                n == 10 ? ios_base::dec :
-                n == 16 ? ios_base::hex :
-                  ios_base::fmtflags(0), ios_base::basefield);
-  return str;
-}
-
-

There are two problems here. First, f takes two parameters, so the -description needs to say that out<<s and in>>s behave as if f(s,base) -had been called. Second, f is has a parameter named base, but is written as if -the parameter was named n.

-

Actually, there's a third problem. The paragraph has grammatical errors. -There needs to be an "and" after the first comma, and the "Where -f" sentence fragment needs to be merged into its preceding sentence. You -may also want to format the function a little better. The formatting above is -more-or-less what the Standard contains.

- - -

Rationale:

-

The resolution of this defect is subsumed by the proposed resolution for -issue 193.

- -

[Tokyo: The LWG agrees that this is a defect and notes that it -occurs additional places in the section, all requiring fixes.]

- - - - - - - - -
-

218. Algorithms do not use binary predicate objects for default comparisons

-

Section: 25.4 [alg.sorting] Status: NAD - Submitter: Pablo Halpern Opened: 2000-03-06 Last modified: 2015-04-08

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Discussion:

-

Many of the algorithms take an argument, pred, of template parameter type -BinaryPredicate or an argument comp of template parameter type Compare. These -algorithms usually have an overloaded version that does not take the predicate -argument. In these cases pred is usually replaced by the use of operator== and -comp is replaced by the use of operator<.

-

This use of hard-coded operators is inconsistent with other parts of the -library, particularly the containers library, where equality is established -using equal_to<> and ordering is established using less<>. Worse, -the use of operator<, would cause the following innocent-looking code to have -undefined behavior:

-
- 
vector<string*> vec;
-sort(vec.begin(), vec.end());
-
-

The use of operator< is not defined for pointers to unrelated objects. If -std::sort used less<> to compare elements, then the above code would be -well-defined, since less<> is explicitly specialized to produce a total -ordering of pointers.

- - -

Rationale:

-

This use of operator== and operator< was a very deliberate, conscious, and -explicitly made design decision; these operators are often more efficient. The -predicate forms are available for users who don't want to rely on operator== and -operator<.

- - - - -
-

219. find algorithm missing version that takes a binary predicate argument

-

Section: 25.2.5 [alg.find] Status: NAD - Submitter: Pablo Halpern Opened: 2000-03-06 Last modified: 2015-04-08

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-

Discussion:

-

The find function always searches for a value using operator== to compare the -value argument to each element in the input iterator range. This is inconsistent -with other find-related functions such as find_end and find_first_of, which -allow the caller to specify a binary predicate object to be used for determining -equality. The fact that this can be accomplished using a combination of find_if -and bind_1st or bind_2nd does not negate the desirability of a consistent, -simple, alternative interface to find.

- -

[ -Summit: -]

- - -

-Reopened by Alisdair. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-The same thing can be achieved using find_if (as noted in the issue). -

-

-Moved to NAD. -

-
- - - -

Proposed resolution:

-
-

In section 25.2.5 [alg.find], add a second prototype for find -(between the existing prototype and the prototype for find_if), as -follows:

-
    template<class InputIterator, class T, class BinaryPredicate>
-      InputIterator find(InputIterator first, InputIterator last,
-                         const T& value, BinaryPredicate bin_pred);
-

Change the description of the return from:

-
-

Returns: The first iterator i in the range [first, last) for which the following corresponding - conditions hold: *i == value, pred(*i) != false. Returns last if no such iterator is found.

-
-

 to:

-
-

Returns: The first iterator i in the range [first, last) for which the following  - corresponding condition holds: *i == value, bin_pred(*i,value) != false, pred(*) - != false. Return last if no such iterator is found.

-
-
- - -

Rationale:

-

This is request for a pure extension, so it is not a defect in the -current standard.  As the submitter pointed out, "this can -be accomplished using a combination of find_if and bind_1st or -bind_2nd".

- - - - -
-

236. ctype<char>::is() member modifies facet

-

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: Dup - Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2015-04-08

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-

Duplicate of: 28

-

Discussion:

-

The description of the is() member in paragraph 4 of 22.4.1.3.2 [facet.ctype.char.members] is broken: According to this description, the -second form of the is() method modifies the masks in the -ctype object. The correct semantics if, of course, to obtain -an array of masks. The corresponding method in the general case, -ie. the do_is() method as described in 22.4.1.1.2 [locale.ctype.virtuals] paragraph 1 does the right thing.

- - -

Proposed resolution:

-

Change paragraph 4 from

-

- The second form, for all *p in the range [low, high), assigns - vec[p-low] to table()[(unsigned char)*p]. -

-

to become

-

- The second form, for all *p in the range [low, high), assigns - table()[(unsigned char)*p] to vec[p-low]. -

- - -

Rationale:

- - - - - -
-

244. Must find's third argument be CopyConstructible?

-

Section: 25.2.5 [alg.find] Status: NAD - Submitter: Andrew Koenig Opened: 2000-05-02 Last modified: 2015-04-08

-

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-

Discussion:

-

Is the following implementation of find acceptable?

- -
-        template<class Iter, class X>
-        Iter find(Iter begin, Iter end, const X& x)
-        {
-            X x1 = x;           // this is the crucial statement
-            while (begin != end && *begin != x1)
-                ++begin;
-            return begin;
-        }
-
- -

If the answer is yes, then it is implementation-dependent as to -whether the following fragment is well formed:

- -
-        vector<string> v;
-
-        find(v.begin(), v.end(), "foo");
-
- -

At issue is whether there is a requirement that the third argument -of find be CopyConstructible. There may be no problem here, but -analysis is necessary.

- - -

Rationale:

-

There is no indication in the standard that find's third argument -is required to be Copy Constructible. The LWG believes that no such -requirement was intended. As noted above, there are times when a user -might reasonably pass an argument that is not Copy Constructible.

- - - - -
-

245. Which operations on istream_iterator trigger input operations?

-

Section: 24.6.1 [istream.iterator] Status: NAD - Submitter: Andrew Koenig Opened: 2000-05-02 Last modified: 2015-04-08

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-

Discussion:

-

I do not think the standard specifies what operation(s) on istream -iterators trigger input operations. So, for example:

- -
-        istream_iterator<int> i(cin);
-
-        int n = *i++;
-
- -

I do not think it is specified how many integers have been read -from cin. The number must be at least 1, of course, but can it be 2? -More?

- - -

Rationale:

-

The standard is clear as written: the stream is read every time -operator++ is called, and it is also read either when the iterator is -constructed or when operator* is called for the first time. In the -example above, exactly two integers are read from cin.

- -

There may be a problem with the interaction between istream_iterator -and some STL algorithms, such as find. There are no guarantees about -how many times find may invoke operator++.

- - - - -
-

246. a.insert(p,t) is incorrectly specified

-

Section: 23.2.4 [associative.reqmts] Status: Dup - Submitter: Mark Rodgers Opened: 2000-05-19 Last modified: 2015-04-08

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-

Duplicate of: 233

-

Discussion:

-

Closed issue 192 raised several problems with the specification of -this function, but was rejected as Not A Defect because it was too big -a change with unacceptable impacts on existing implementations. -However, issues remain that could be addressed with a smaller change -and with little or no consequent impact.

- -
    -

  1. The specification is inconsistent with the original - proposal and with several implementations.

    - -

    The initial implementation by Hewlett Packard only ever looked - immediately before p, and I do not believe there was any - intention to standardize anything other than this behavior. - Consequently, current implementations by several leading - implementors also look immediately before p, and will only insert - after p in logarithmic time. I am only aware of one implementation - that does actually look after p, and it looks before p as well. It - is therefore doubtful that existing code would be relying on the - behavior defined in the standard, and it would seem that fixing - this defect as proposed below would standardize existing - practice.

    2. - -

  2. - The specification is inconsistent with insertion for sequence - containers.

    - -

    This is difficult and confusing to teach to newcomers. All - insert operations that specify an iterator as an insertion location - should have a consistent meaning for the location represented by - that iterator.

    3. - -

  3. As specified, there is no way to hint that the insertion - should occur at the beginning of the container, and the way to hint - that it should occur at the end is long winded and unnatural.

    - -

    For a container containing n elements, there are n+1 possible - insertion locations and n+1 valid iterators. For there to be a - one-to-one mapping between iterators and insertion locations, the - iterator must represent an insertion location immediately before - the iterator.

    4. - -

  4. When appending sorted ranges using insert_iterators, - insertions are guaranteed to be sub-optimal.

    - -

    In such a situation, the optimum location for insertion is - always immediately after the element previously inserted. The - mechanics of the insert iterator guarantee that it will try and - insert after the element after that, which will never be correct. - However, if the container first tried to insert before the hint, - all insertions would be performed in amortized constant - time.

    5. -
- - -

Proposed resolution:

-

In 23.1.2 [lib.associative.reqmts] paragraph 7, table 69, make -the following changes in the row for a.insert(p,t):

- -

assertion/note pre/post condition: -
Change the last sentence from

-

- "iterator p is a hint pointing to where the insert should - start to search." -

-

to

-

- "iterator p is a hint indicating that immediately before p - may be a correct location where the insertion could occur." -

- -

complexity:
-Change the words "right after" to "immediately before".

- - -

Rationale:

- - - - - -
-

249. Return Type of auto_ptr::operator=

-

Section: X [auto.ptr] Status: NAD - Submitter: Joseph Gottman Opened: 2000-06-30 Last modified: 2015-04-08

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-

Discussion:

-

According to section 20.4.5, the function -auto_ptr::operator=() returns a reference to an auto_ptr. -The reason that operator=() usually returns a reference is to -facilitate code like

- -
-    int x,y,z;
-    x = y = z = 1;
-
- -

However, given analogous code for auto_ptrs,

-
-    auto_ptr<int> x, y, z;
-    z.reset(new int(1));
-    x = y = z;
-
- -

the result would be that z and y would both be set to -NULL, instead of all the auto_ptrs being set to the same value. -This makes such cascading assignments useless and counterintuitive for -auto_ptrs.

- - -

Proposed resolution:

-

Change auto_ptr::operator=() to return void instead -of an auto_ptr reference.

- - -

Rationale:

-

The return value has uses other than cascaded assignments: a user can -call an auto_ptr member function, pass the auto_ptr to a -function, etc. Removing the return value could break working user -code.

- - - - -
-

257. STL functional object and iterator inheritance.

-

Section: X [depr.base], 24.4.2 [iterator.basic] Status: NAD - Submitter: Robert Dick Opened: 2000-08-17 Last modified: 2015-04-08

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-

Discussion:

-

-According to the November 1997 Draft Standard, the results of deleting an -object of a derived class through a pointer to an object of its base class are -undefined if the base class has a non-virtual destructor. Therefore, it is -potentially dangerous to publicly inherit from such base classes. -

- -

Defect: -
-The STL design encourages users to publicly inherit from a number of classes -which do nothing but specify interfaces, and which contain non-virtual -destructors. -

- -

Attribution: -
-Wil Evers and William E. Kempf suggested this modification for functional -objects. -

- - -

Proposed resolution:

-

-When a base class in the standard library is useful only as an interface -specifier, i.e., when an object of the class will never be directly -instantiated, specify that the class contains a protected destructor. This -will prevent deletion through a pointer to the base class without performance, -or space penalties (on any implementation I'm aware of). -

- -

-As an example, replace... -

- -
-    template <class Arg, class Result>
-    struct unary_function {
-            typedef Arg    argument_type;
-            typedef Result result_type;
-    };
-
- -

-... with... -

- -
-    template <class Arg, class Result>
-    struct unary_function {
-            typedef Arg    argument_type;
-            typedef Result result_type;
-    protected:
-            ~unary_function() {}
-    };
-
- -

-Affected definitions: -
-  20.3.1 [lib.function.objects] -- unary_function, binary_function -
-  24.3.2 [lib.iterator.basic] -- iterator -

- - -

Rationale:

-

-The standard is clear as written; this is a request for change, not a -defect in the strict sense. The LWG had several different objections -to the proposed change. One is that it would prevent users from -creating objects of type unary_function and -binary_function. Doing so can sometimes be legitimate, if users -want to pass temporaries as traits or tag types in generic code. -

- - - - - -
-

267. interaction of strstreambuf::overflow() and seekoff()

-

Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD - Submitter: Martin Sebor Opened: 2000-10-05 Last modified: 2015-04-08

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-

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-

Discussion:

-

-It appears that the interaction of the strstreambuf members overflow() -and seekoff() can lead to undefined behavior in cases where defined -behavior could reasonably be expected. The following program -demonstrates this behavior: -

- -
-    #include <strstream>
-
-    int main ()
-    {
-         std::strstreambuf sb;
-         sb.sputc ('c');
-
-         sb.pubseekoff (-1, std::ios::end, std::ios::in);
-         return !('c' == sb.sgetc ());
-    }
-
- -

-D.7.1.1, p1 initializes strstreambuf with a call to basic_streambuf<>(), -which in turn sets all pointers to 0 in 27.5.2.1, p1. -

- -

-27.5.2.2.5, p1 says that basic_streambuf<>::sputc(c) calls -overflow(traits::to_int_type(c)) if a write position isn't available (it -isn't due to the above). -

- -

-D.7.1.3, p3 says that strstreambuf::overflow(off, ..., ios::in) makes at -least one write position available (i.e., it allows the function to make -any positive number of write positions available). -

- -

-D.7.1.3, p13 computes newoff = seekhigh - eback(). In D.7.1, p4 we see -seekhigh = epptr() ? epptr() : egptr(), or seekhigh = epptr() in this -case. newoff is then epptr() - eback(). -

- -

-D.7.1.4, p14 sets gptr() so that gptr() == eback() + newoff + off, or -gptr() == epptr() + off holds. -

- -

-If strstreambuf::overflow() made exactly one write position available -then gptr() will be set to just before epptr(), and the program will -return 0. Buf if the function made more than one write position -available, epptr() and gptr() will both point past pptr() and the -behavior of the program is undefined. -

- - -

Proposed resolution:

- - -

Change the last sentence of D.7.1 [depr.strstreambuf] paragraph 4 from

- -

- Otherwise, seeklow equals gbeg and seekhigh is either pend, if - pend is not a null pointer, or gend. -

- -

to become

- -

- Otherwise, seeklow equals gbeg and seekhigh is either gend if - 0 == pptr(), or pbase() + max where max is the maximum value of - pptr() - pbase() ever reached for this stream. -

- -

[ - pre-Copenhagen: Dietmar provided wording for proposed resolution. -]

- - -

[ - post-Copenhagen: Fixed a typo: proposed resolution said to fix - 4.7.1, not D.7.1. -]

- - - - -

Rationale:

-

This is related to issue 65: it's not clear what it -means to seek beyond the current area. Without resolving issue 65 we can't resolve this. As with issue 65, -the library working group does not wish to invest time nailing down -corner cases in a deprecated feature.

- - - - - -
-

269. cstdarg and unnamed parameters

-

Section: 18.8 [support.exception] Status: NAD - Submitter: J. Stephen Adamczyk Opened: 2000-10-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-One of our customers asks whether this is valid C++: -

- -
-   #include <cstdarg>
-
-   void bar(const char *, va_list);
-
-   void
-   foo(const char *file, const char *, ...)
-   {
-     va_list ap;
-     va_start(ap, file);
-     bar(file, ap);
-     va_end(ap);
-   }
-
- -

-The issue being whether it is valid to use cstdarg when the final -parameter before the "..." is unnamed. cstdarg is, as far -as I can tell, inherited verbatim from the C standard. and the -definition there (7.8.1.1 in the ISO C89 standard) refers to "the -identifier of the rightmost parameter". What happens when there -is no such identifier? -

- -

-My personal opinion is that this should be allowed, but some tweak -might be required in the C++ standard. -

- - -

Rationale:

-

-Not a defect, the C and C++ standards are clear. It is impossible to -use varargs if the parameter immediately before "..." has no -name, because that is the parameter that must be passed to va_start. -The example given above is broken, because va_start is being passed -the wrong parameter. -

- -

-There is no support for extending varargs to provide additional -functionality beyond what's currently there. For reasons of C/C++ -compatibility, it is especially important not to make gratuitous -changes in this part of the C++ standard. The C committee has already -been requested not to touch this part of the C standard unless -necessary. -

- - - - -
-

277. Normative encouragement in allocator requirements unclear

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: Matt Austern Opened: 2000-11-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In 20.1.5, paragraph 5, the standard says that "Implementors are -encouraged to supply libraries that can accept allocators that -encapsulate more general memory models and that support non-equal -instances." This is intended as normative encouragement to -standard library implementors. However, it is possible to interpret -this sentence as applying to nonstandard third-party libraries. -

- - -

Proposed resolution:

-

-In 20.1.5, paragraph 5, change "Implementors" to -"Implementors of the library described in this International -Standard". -

- - -

Rationale:

-

The LWG believes the normative encouragement is already -sufficiently clear, and that there are no important consequences -even if it is misunderstood.

- - - - - -
-

279. const and non-const iterators should have equivalent typedefs

-

Section: 23.2 [container.requirements] Status: NAD - Submitter: Steve Cleary Opened: 2000-11-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

-This came from an email from Steve Cleary to Fergus in reference to -issue 179. The library working group briefly discussed -this in Toronto and believes it should be a separate issue. -

- -

-Steve said: "We may want to state that the const/non-const iterators must have -the same difference type, size_type, and category." -

- -

-(Comment from Judy) -I'm not sure if the above sentence should be true for all -const and non-const iterators in a particular container, or if it means -the container's iterator can't be compared with the container's -const_iterator unless the above it true. I suspect the former. -

- - -

Proposed resolution:

-

-In Section: 23.2 [container.requirements], -table 65, in the assertion/note pre/post condition for X::const_iterator, -add the following: -

- -
-

-typeid(X::const_iterator::difference_type) == typeid(X::iterator::difference_type) -

- -

-typeid(X::const_iterator::size_type) == typeid(X::iterator::size_type) -

- -

-typeid(X::const_iterator::category) == typeid(X::iterator::category) -

-
- - -

Rationale:

-

Going through the types one by one: Iterators don't have a -size_type. We already know that the difference types are -identical, because the container requirements already say that the -difference types of both X::iterator and X::const_iterator are both -X::difference_type. The standard does not require that X::iterator -and X::const_iterator have the same iterator category, but the LWG -does not see this as a defect: it's possible to imagine cases in which -it would be useful for the categories to be different.

- -

It may be desirable to require X::iterator and X::const_iterator to -have the same value type, but that is a new issue. (Issue 322.)

- - - - - - -
-

287. conflicting ios_base fmtflags

-

Section: 27.5.3.2 [fmtflags.state] Status: NAD - Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The Effects clause for ios_base::setf(fmtflags fmtfl) says -"Sets fmtfl in flags()". What happens if the user first calls -ios_base::scientific and then calls ios_base::fixed or vice-versa? -This is an issue for all of the conflicting flags, i.e. ios_base::left -and ios_base::right or ios_base::dec, ios_base::hex and ios_base::oct. -

- -

-I see three possible solutions: -

- -
    -
  1. Set ios_base::failbit whenever the user specifies a conflicting -flag with one previously explicitly set. If the constructor is -supposed to set ios_base::dec (see discussion below), then -the user setting hex or oct format after construction will not -set failbit.
    2. -
  2. The last call to setf "wins", i.e. it clears any conflicting -previous setting.
    3. -
  3. All the flags that the user specifies are set, but when actually -interpreting them, fixed always override scientific, right always -overrides left, dec overrides hex which overrides oct.
    4. -
- -

-Most existing implementations that I tried seem to conform to resolution #3, -except that when using the iomanip manipulator hex or oct then that always -overrides dec, but calling setf(ios_base::hex) doesn't. -

- -

-There is a sort of related issue, which is that although the ios_base -constructor says that each ios_base member has an indeterminate value -after construction, all the existing implementations I tried explicitly set -ios_base::dec. -

- - -

Proposed resolution:

- - -

Rationale:

-

-adjustfield, basefield, and floatfield -are each multi-bit fields. It is possible to set multiple bits within -each of those fields. (For example, dec and -oct). These fields are used by locale facets. The LWG -reviewed the way in which each of those three fields is used, and -believes that in each case the behavior is well defined for any -possible combination of bits. See for example Table 58, in 22.4.2.2.2 [facet.num.put.virtuals], noting the requirement in paragraph 6 of that -section. -

-

-Users are advised to use manipulators, or else use the two-argument -version of setf, to avoid unexpected behavior. -

- - - - - -
-

289. <cmath> requirements missing C float and long double versions

-

Section: 26.8 [c.math] Status: NAD - Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

- In ISO/IEC 9899:1990 Programming Languages C we find the following - concerning <math.h>: -

- -

- 7.13.4 Mathematics <math.h> -
- The names of all existing functions declared in the <math.h> - header, suffixed with f or l, are reserved respectively for - corresponding functions with float and long double arguments - are return values. -

- -

- For example, float sinf(float) - is reserved. -

- -

- In the C99 standard, <math.h> must contain declarations - for these functions. -

- -

-So, is it acceptable for an implementor to add these prototypes to the -C++ versions of the math headers? Are they required? -

- - -

Proposed resolution:

-

-Add these Functions to Table 80, section 26.5 and to Table 99, -section C.2: -

- -
-    acosf asinf atanf atan2f ceilf cosf coshf 
-    expf fabsf floorf fmodf frexpf ldexpf 
-    logf log10f modff powf sinf sinhf sqrtf 
-    tanf tanhf 
-    acosl asinl atanl atan2l ceill cosl coshl 
-    expl fabsl floorl fmodl frexpl ldexpl 
-    logl log10l modfl powl sinl sinhl sqrtl 
-    tanl tanhl
-
- -

-There should probably be a note saying that these functions -are optional and, if supplied, should match the description in -the 1999 version of the C standard. In the next round -of C++ standardization they can then become mandatory. -

- - -

Rationale:

-

The C90 standard, as amended, already permits (but does not -require) these functions, and the C++ standard incorporates the -C90 standard by reference. C99 is not an issue, because it is -never referred to by the C++ standard.

- - - - - -
-

290. Requirements to for_each and its function object

-

Section: 25.2.4 [alg.foreach] Status: NAD - Submitter: Angelika Langer Opened: 2001-01-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The specification of the for_each algorithm does not have a -"Requires" section, which means that there are no -restrictions imposed on the function object whatsoever. In essence it -means that I can provide any function object with arbitrary side -effects and I can still expect a predictable result. In particular I -can expect that the function object is applied exactly last - first -times, which is promised in the "Complexity" section. -

- -

I don't see how any implementation can give such a guarantee -without imposing requirements on the function object. -

- -

Just as an example: consider a function object that removes -elements from the input sequence. In that case, what does the -complexity guarantee (applies f exactly last - first times) mean? -

- -

One can argue that this is obviously a nonsensical application and -a theoretical case, which unfortunately it isn't. I have seen -programmers shooting themselves in the foot this way, and they did not -understand that there are restrictions even if the description of the -algorithm does not say so. -

-

[Lillehammer: This is more general than for_each. We don't want - the function object in transform invalidiating iterators - either. There should be a note somewhere in clause 17 (17, not 25) - saying that user code operating on a range may not invalidate - iterators unless otherwise specified. Bill will provide wording.]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-Moved to NAD. -

-

-It was felt that the current description is adequate, and that there are -limits to what the standard can reasonably say to prohibit perverse uses -of the library. -

-
- - - -

Proposed resolution:

- - - - - - -
-

293. Order of execution in transform algorithm

-

Section: 25.3.4 [alg.transform] Status: NAD - Submitter: Angelika Langer Opened: 2001-01-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

This issue is related to issue 242. In case that the resolution -proposed for issue 242 is accepted, we have have the following -situation: The 4 numeric algorithms (accumulate and consorts) as well -as transform would allow a certain category of side effects. The -numeric algorithms specify that they invoke the functor "for -every iterator i in the range [first, last) in order". transform, -in contrast, would not give any guarantee regarding order of -invocation of the functor, which means that the functor can be invoked -in any arbitrary order. -

- -

Why would that be a problem? Consider an example: say the -transformator that is a simple enumerator ( or more generally -speaking, "is order-sensitive" ). Since a standard -compliant implementation of transform is free to invoke the enumerator -in no definite order, the result could be a garbled enumeration. -Strictly speaking this is not a problem, but it is certainly at odds -with the prevalent understanding of transform as an algorithms that -assigns "a new _corresponding_ value" to the output -elements. -

- -

All implementations that I know of invoke the transformator in -definite order, namely starting from first and proceeding to last - -1. Unless there is an optimization conceivable that takes advantage of -the indefinite order I would suggest to specify the order, because it -eliminate the uncertainty that users would otherwise have regarding -the order of execution of their potentially order-sensitive function -objects. -

- - -

Proposed resolution:

-

In section 25.2.3 - Transform [lib.alg.transform] change:

-

--1- Effects: Assigns through every iterator i in the range [result, -result + (last1 - first1)) a new corresponding -value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + -(i - result), *(first2 + (i - result))). -

-

to:

-

--1- Effects: Computes values by invoking the operation op or binary_op -for every iterator in the range [first1, last1) in order. Assigns through -every iterator i in the range [result, result + (last1 - first1)) a new -corresponding -value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + -(i - result), *(first2 + (i - result))). -

- - -

Rationale:

-

For Input Iterators an order is already guaranteed, because -only one order is possible. If a user who passes a Forward -Iterator to one of these algorithms really needs a specific -order of execution, it's possible to achieve that effect by -wrapping it in an Input Iterator adaptor.

- - - - - -
-

299. Incorrect return types for iterator dereference

-

Section: 24.2.6 [bidirectional.iterators], 24.2.7 [random.access.iterators] Status: NAD Editorial - Submitter: John Potter Opened: 2001-01-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In section 24.2.6 [bidirectional.iterators], -Table 75 gives the return type of *r-- as convertible to T. This is -not consistent with Table 74 which gives the return type of *r++ as -T&. *r++ = t is valid while *r-- = t is invalid. -

- -

-In section 24.2.7 [random.access.iterators], -Table 76 gives the return type of a[n] as convertible to T. This is -not consistent with the semantics of *(a + n) which returns T& by -Table 74. *(a + n) = t is valid while a[n] = t is invalid. -

- -

-Discussion from the Copenhagen meeting: the first part is -uncontroversial. The second part, operator[] for Random Access -Iterators, requires more thought. There are reasonable arguments on -both sides. Return by value from operator[] enables some potentially -useful iterators, e.g. a random access "iota iterator" (a.k.a -"counting iterator" or "int iterator"). There isn't any obvious way -to do this with return-by-reference, since the reference would be to a -temporary. On the other hand, reverse_iterator takes an -arbitrary Random Access Iterator as template argument, and its -operator[] returns by reference. If we decided that the return type -in Table 76 was correct, we would have to change -reverse_iterator. This change would probably affect user -code. -

- -

-History: the contradiction between reverse_iterator and the -Random Access Iterator requirements has been present from an early -stage. In both the STL proposal adopted by the committee -(N0527==94-0140) and the STL technical report (HPL-95-11 (R.1), by -Stepanov and Lee), the Random Access Iterator requirements say that -operator[]'s return value is "convertible to T". In N0527 -reverse_iterator's operator[] returns by value, but in HPL-95-11 -(R.1), and in the STL implementation that HP released to the public, -reverse_iterator's operator[] returns by reference. In 1995, the -standard was amended to reflect the contents of HPL-95-11 (R.1). The -original intent for operator[] is unclear. -

- -

-In the long term it may be desirable to add more fine-grained -iterator requirements, so that access method and traversal strategy -can be decoupled. (See "Improved Iterator Categories and -Requirements", N1297 = 01-0011, by Jeremy Siek.) Any decisions -about issue 299 should keep this possibility in mind. -

- -

Further discussion: I propose a compromise between John Potter's -resolution, which requires T& as the return type of -a[n], and the current wording, which requires convertible to -T. The compromise is to keep the convertible to T -for the return type of the expression a[n], but to also add -a[n] = t as a valid expression. This compromise "saves" the -common case uses of random access iterators, while at the same time -allowing iterators such as counting iterator and caching file -iterators to remain random access iterators (iterators where the -lifetime of the object returned by operator*() is tied to the -lifetime of the iterator). -

- -

-Note that the compromise resolution necessitates a change to -reverse_iterator. It would need to use a proxy to support -a[n] = t. -

- -

-Note also there is one kind of mutable random access iterator that -will no longer meet the new requirements. Currently, iterators that -return an r-value from operator[] meet the requirements for a -mutable random access iterator, even though the expression a[n] = -t will only modify a temporary that goes away. With this proposed -resolution, a[n] = t will be required to have the same -operational semantics as *(a + n) = t. -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-09-18 Alisdair adds: -]

- - -
-

-Why can't we write through the reference returned from operator[] on a -random access iterator? -

- -

-Recommended solution: -

- -

-In table Table 104 — Random access iterator requirements, replace -

- -

-a[n] : convertible to const T & -T& if X is mutable, otherwise convertible to const T& -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave Open. Alisdair to spearhead a paper on revivification. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

- -

-In section 24.1.4 [lib.bidirectdional.iterators], change the return -type in table 75 from "convertible to T" to -T&. -

- -

-In section 24.1.5 [lib.random.access.iterators], change the -operational semantics for a[n] to " the r-value of -a[n] is equivalent to the r-value of *(a + -n)". Add a new row in the table for the expression a[n] = t -with a return type of convertible to T and operational semantics of -*(a + n) = t. -

- -

[Lillehammer: Real problem, but should be addressed as part of - iterator redesign]

- - - - -

Rationale:

-

[ -San Francisco: -]

- - -

-Solved by -N2758. -

- - - - - - - -
-

302. Need error indication from codecvt<>::do_length

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: NAD - Submitter: Gregory Bumgardner Opened: 2001-01-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The effects of codecvt<>::do_length() are described in -22.2.1.5.2, paragraph 10. As implied by that paragraph, and clarified -in issue 75, codecvt<>::do_length() must -process the source data and update the stateT argument just -as if the data had been processed by codecvt<>::in(). -However, the standard does not specify how do_length() would -report a translation failure, should the source sequence contain -untranslatable or illegal character sequences. -

- -

-The other conversion methods return an "error" result value -to indicate that an untranslatable character has been encountered, but -do_length() already has a return value (the number of source -characters that have been processed by the method). -

- - -

Proposed resolution:

-

-This issue cannot be resolved without modifying the interface. An exception -cannot be used, as there would be no way to determine how many characters -have been processed and the state object would be left in an indeterminate -state. -

- -

-A source compatible solution involves adding a fifth argument to length() -and do_length() that could be used to return position of the offending -character sequence. This argument would have a default value that would -allow it to be ignored: -

- -
-  int length(stateT& state, 
-             const externT* from, 
-             const externT* from_end, 
-             size_t max,
-             const externT** from_next = 0);
-
-  virtual
-  int do_length(stateT& state, 
-                const externT* from, 
-                const externT* from_end, 
-                size_t max,
-                const externT** from_next);
-
- -

-Then an exception could be used to report any translation errors and -the from_next argument, if used, could then be used to retrieve the -location of the offending character sequence. -

- - -

Rationale:

-

The standard is already clear: the return value is the number of -"valid complete characters". If it encounters an invalid sequence of -external characters, it stops.

- - - - - -
-

304. Must *a return an lvalue when a is an input iterator?

-

Section: X [iterator.concepts] Status: NAD - Submitter: Dave Abrahams Opened: 2001-02-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-We all "know" that input iterators are allowed to produce -values when dereferenced of which there is no other in-memory copy. -

- -

-But: Table 72, with a careful reading, seems to imply that this can only be -the case if the value_type has no members (e.g. is a built-in type). -

- -

The problem occurs in the following entry:

- -
-  a->m     pre: (*a).m is well-defined
-           Equivalent to (*a).m
-
- -

-*a.m can be well-defined if *a is not a reference -type, but since operator->() must return a pointer for -a->m to be well-formed, it needs something to return a -pointer to. This seems to indicate that *a must be -buffered somewhere to make a legal input iterator. -

- -

I don't think this was intentional.

- - -

Rationale:

-

The current standard is clear and consistent. Input iterators that - return rvalues are in fact implementable. They may in some cases - require extra work, but it is still possible to define an operator-> - in such cases: it doesn't have to return a T*, but may return a - proxy type. No change to the standard is justified.

- - - - - -
-

309. Does sentry catch exceptions?

-

Section: 27.7 [iostream.format] Status: NAD - Submitter: Martin Sebor Opened: 2001-03-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The descriptions of the constructors of basic_istream<>::sentry -(27.7.2.1.3 [istream::sentry]) and basic_ostream<>::sentry -(27.7.3.4 [ostream::sentry]) do not explain what the functions do in -case an exception is thrown while they execute. Some current -implementations allow all exceptions to propagate, others catch them -and set ios_base::badbit instead, still others catch some but let -others propagate. -

- -

-The text also mentions that the functions may call setstate(failbit) -(without actually saying on what object, but presumably the stream -argument is meant). That may have been fine for -basic_istream<>::sentry prior to issue 195, since -the function performs an input operation which may fail. However, -issue 195 amends 27.7.2.1.3 [istream::sentry], p2 to -clarify that the function should actually call setstate(failbit | -eofbit), so the sentence in p3 is redundant or even somewhat -contradictory. -

- -

-The same sentence that appears in 27.7.3.4 [ostream::sentry], p3 -doesn't seem to be very meaningful for basic_istream<>::sentry -which performs no input. It is actually rather misleading since it -would appear to guide library implementers to calling -setstate(failbit) when os.tie()->flush(), the only called function, -throws an exception (typically, it's badbit that's set in response to -such an event). -

- -

Additional comments from Martin, who isn't comfortable with the - current proposed resolution (see c++std-lib-11530)

- -

-The istream::sentry ctor says nothing about how the function -deals with exemptions (27.6.1.1.2, p1 says that the class is -responsible for doing "exception safe"(*) prefix and suffix -operations but it doesn't explain what level of exception -safety the class promises to provide). The mockup example -of a "typical implementation of the sentry ctor" given in -27.6.1.1.2, p6, removed in ISO/IEC 14882:2003, doesn't show -exception handling, either. Since the ctor is not classified -as a formatted or unformatted input function, the text in -27.6.1.1, p1 through p4 does not apply. All this would seem -to suggest that the sentry ctor should not catch or in any -way handle exceptions thrown from any functions it may call. -Thus, the typical implementation of an istream extractor may -look something like [1]. -

- -

-The problem with [1] is that while it correctly sets ios::badbit -if an exception is thrown from one of the functions called from -the sentry ctor, if the sentry ctor reaches EOF while extracting -whitespace from a stream that has eofbit or failbit set in -exceptions(), it will cause an ios::failure to be thrown, which -will in turn cause the extractor to set ios::badbit. -

- -

-The only straightforward way to prevent this behavior is to -move the definition of the sentry object in the extractor -above the try block (as suggested by the example in 22.2.8, -p9 and also indirectly supported by 27.6.1.3, p1). See [2]. -But such an implementation will allow exceptions thrown from -functions called from the ctor to freely propagate to the -caller regardless of the setting of ios::badbit in the stream -object's exceptions(). -

- -

-So since neither [1] nor [2] behaves as expected, the only -possible solution is to have the sentry ctor catch exceptions -thrown from called functions, set badbit, and propagate those -exceptions if badbit is also set in exceptions(). (Another -solution exists that deals with both kinds of sentries, but -the code is non-obvious and cumbersome -- see [3].) -

- -

-Please note that, as the issue points out, current libraries -do not behave consistently, suggesting that implementors are -not quite clear on the exception handling in istream::sentry, -despite the fact that some LWG members might feel otherwise. -(As documented by the parenthetical comment here: -http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1480.html#309) -

- -

-Also please note that those LWG members who in Copenhagen -felt that "a sentry's constructor should not catch exceptions, -because sentries should only be used within (un)formatted input -functions and that exception handling is the responsibility of -those functions, not of the sentries," as noted here -http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2001/n1310.html#309 -would in effect be either arguing for the behavior described -in [1] or for extractors implemented along the lines of [3]. -

- -

-The original proposed resolution (Revision 25 of the issues -list) clarifies the role of the sentry ctor WRT exception -handling by making it clear that extractors (both library -or user-defined) should be implemented along the lines of -[2] (as opposed to [1]) and that no exception thrown from -the callees should propagate out of either function unless -badbit is also set in exceptions(). -

- - -

[1] Extractor that catches exceptions thrown from sentry:

- -
-
-struct S { long i; };
-
-istream& operator>> (istream &strm, S &s)
-{
-    ios::iostate err = ios::goodbit;
-    try {
-        const istream::sentry guard (strm, false);
-        if (guard) {
-            use_facet<num_get<char> >(strm.getloc ())
-                .get (istreambuf_iterator<char>(strm),
-                      istreambuf_iterator<char>(),
-                      strm, err, s.i);
-        }
-    }
-    catch (...) {
-        bool rethrow;
-        try {
-            strm.setstate (ios::badbit);
-            rethrow = false;
-        }
-        catch (...) {
-            rethrow = true;
-        }
-        if (rethrow)
-            throw;
-    }
-    if (err)
-        strm.setstate (err);
-    return strm;
-}
-
-
- -

[2] Extractor that propagates exceptions thrown from sentry:

- -
-
-istream& operator>> (istream &strm, S &s)
-{
-    istream::sentry guard (strm, false);
-    if (guard) {
-        ios::iostate err = ios::goodbit;
-        try {
-            use_facet<num_get<char> >(strm.getloc ())
-                .get (istreambuf_iterator<char>(strm),
-                      istreambuf_iterator<char>(),
-                      strm, err, s.i);
-        }
-        catch (...) {
-            bool rethrow;
-            try {
-                strm.setstate (ios::badbit);
-                rethrow = false;
-            }
-            catch (...) {
-                rethrow = true;
-            }
-            if (rethrow)
-                throw;
-        }
-        if (err)
-            strm.setstate (err);
-    }
-    return strm;
-}
-
-
- -

-[3] Extractor that catches exceptions thrown from sentry -but doesn't set badbit if the exception was thrown as a -result of a call to strm.clear(). -

- -
-
-istream& operator>> (istream &strm, S &s)
-{
-    const ios::iostate state = strm.rdstate ();
-    const ios::iostate except = strm.exceptions ();
-    ios::iostate err = std::ios::goodbit;
-    bool thrown = true;
-    try {
-        const istream::sentry guard (strm, false);
-        thrown = false;
-        if (guard) {
-            use_facet<num_get<char> >(strm.getloc ())
-                .get (istreambuf_iterator<char>(strm),
-                      istreambuf_iterator<char>(),
-                      strm, err, s.i);
-        }
-    }
-    catch (...) {
-        if (thrown && state & except)
-            throw;
-        try {
-            strm.setstate (ios::badbit);
-            thrown = false;
-        }
-        catch (...) {
-            thrown = true;
-        }
-        if (thrown)
-            throw;
-    }
-    if (err)
-        strm.setstate (err);
-
-    return strm;
-}
-
-
- -

-[Pre-Berlin] Reopened at the request of Paolo Carlini and Steve Clamage. -

- -

-[Pre-Portland] A relevant newsgroup post: -

- -

-The current proposed resolution of issue #309 -(http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#309) is -unacceptable. I write commerical software and coding around this -makes my code ugly, non-intuitive, and requires comments referring -people to this very issue. Following is the full explanation of my -experience. -

-

-In the course of writing software for commercial use, I constructed -std::ifstream's based on user-supplied pathnames on typical POSIX -systems. -

-

-It was expected that some files that opened successfully might not read -successfully -- such as a pathname which actually refered to a -directory. Intuitively, I expected the streambuffer underflow() code -to throw an exception in this situation, and recent implementations of -libstdc++'s basic_filebuf do just that (as well as many of my own -custom streambufs). -

-

-I also intuitively expected that the istream code would convert these -exceptions to the "badbit' set on the stream object, because I had not -requested exceptions. I refer to 27.6.1.1. P4. -

-

-However, this was not the case on at least two implementations -- if -the first thing I did with an istream was call operator>>( T& ) for T -among the basic arithmetic types and std::string. Looking further I -found that the sentry's constructor was invoking the exception when it -pre-scanned for whitespace, and the extractor function (operator>>()) -was not catching exceptions in this situation. -

-

-So, I was in a situation where setting 'noskipws' would change the -istream's behavior even though no characters (whitespace or not) could -ever be successfully read. -

-

-Also, calling .peek() on the istream before calling the extractor() -changed the behavior (.peek() had the effect of setting the badbit -ahead of time). -

-

-I found this all to be so inconsistent and inconvenient for me and my -code design, that I filed a bugzilla entry for libstdc++. I was then -told that the bug cannot be fixed until issue #309 is resolved by the -committee. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Moved to NAD. -

-

-See the rationale in the issue. Paolo, who requested that the issue be -reopened, agreed with the rationale. -

-
- - - -

Proposed resolution:

- - -

Rationale:

-

The LWG agrees there is minor variation between implementations, - but believes that it doesn't matter. This is a rarely used corner - case. There is no evidence that this has any commercial importance - or that it causes actual portability problems for customers trying - to write code that runs on multiple implementations.

- - - - - -
-

313. set_terminate and set_unexpected question

-

Section: 18.8.3.4 [terminate] Status: NAD - Submitter: Judy Ward Opened: 2001-04-03 Last modified: 2015-04-08

-

View all other issues in [terminate].

-

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-

Discussion:

-

-According to section 18.7.3.3 of the standard, std::terminate() is -supposed to call the terminate_handler in effect immediately after -evaluating the throw expression. -

- -

-Question: what if the terminate_handler in effect is itself -std::terminate? -

- -

For example:

- -
-  #include <exception>
-
-  int main () {
-      std::set_terminate(std::terminate);
-      throw 5;
-      return 0;
-  }
-
- -

-Is the implementation allowed to go into an infinite loop? -

- -

-I think the same issue applies to std::set_unexpected. -

- - -

Proposed resolution:

- - -

Rationale:

-

Infinite recursion is to be expected: users who set the terminate -handler to terminate are explicitly asking for terminate -to call itself.

- - - - - -
-

314. Is the stack unwound when terminate() is called?

-

Section: 18.8.3.4 [terminate] Status: NAD - Submitter: Detlef Vollmann Opened: 2001-04-11 Last modified: 2015-04-08

-

View all other issues in [terminate].

-

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-

Discussion:

- -

-The standard appears to contradict itself about whether the stack is -unwound when the implementation calls terminate(). -

- -

From 18.7.3.3p2:

-

- Calls the terminate_handler function in effect immediately - after evaluating the throw-expression (lib.terminate.handler), - if called by the implementation [...] -

- -

So the stack is guaranteed not to be unwound.

- -

But from 15.3p9:

-

- [...]whether or not the stack is unwound before this call - to terminate() is implementation-defined (except.terminate). -

- -

-And 15.5.1 actually defines that in most cases the stack is unwound. -

- - -

Proposed resolution:

- - -

Rationale:

-

There is definitely no contradiction between the core and library -clauses; nothing in the core clauses says that stack unwinding happens -after terminate is called. 18.7.3.3p2 does not say anything -about when terminate() is called; it merely specifies which -terminate_handler is used.

- - - - - -
-

323. abs() overloads in different headers

-

Section: 26.8 [c.math] Status: NAD - Submitter: Dave Abrahams Opened: 2001-06-04 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

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-

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-

Discussion:

-

Currently the standard mandates the following overloads of -abs():

- -
-    abs(long), abs(int) in <cstdlib>
-
-    abs(float), abs(double), abs(long double) in <cmath>
-
-    template<class T> T abs(const complex<T>&) in <complex>
-
-    template<class T> valarray<T> abs(const valarray<T>&); in <valarray>
-
- -

-The problem is that having only some overloads visible of a function -that works on "implicitly inter-convertible" types is dangerous in -practice. The headers that get included at any point in a translation -unit can change unpredictably during program -development/maintenance. The wrong overload might be unintentionally -selected. -

- -

-Currently, there is nothing that mandates the simultaneous visibility -of these overloads. Indeed, some vendors have begun fastidiously -reducing dependencies among their (public) headers as a QOI issue: it -helps people to write portable code by refusing to compile unless all -the correct headers are #included. -

- -

The same issue may exist for other functions in the library.

- -

Redmond: PJP reports that C99 adds two new kinds of abs: complex, -and int_max_abs.

- -

Related issue: 343.

- -

[ -Bellevue: -]

- - -

-The situation is not sufficiently severe to warrant a change. -

- - - - -

Rationale:

-

The programs that could potentially be broken by this situation are - already fragile, and somewhat contrived: For example, a user-defined - class that has conversion overloads both to long and - to float. If x is a value of such a class, then - abs(x) would give the long version if the user - included <cstdlib>, the float version if the user - included <cmath>, and would be diagnosed as ambiguous at - compile time if the user included both headers. The LWG couldn't - find an example of a program whose meaning would be changed (as - opposed to changing it from well-formed to ill-formed) simply by - adding another standard header.

- -

Since the harm seems minimal, and there don't seem to be any simple - and noninvasive solutions, this is being closed as NAD. It is - marked as "Future" for two reasons. First, it might be useful to - define an <all> header that would include all - Standard Library headers. Second, we should at least make sure that - future library extensions don't make this problem worse.

- - - - - -
-

326. Missing typedef in moneypunct_byname

-

Section: 22.4.6.4 [locale.moneypunct.byname] Status: NAD - Submitter: Martin Sebor Opened: 2001-07-05 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

The definition of the moneypunct facet contains the typedefs char_type -and string_type. Only one of these names, string_type, is defined in -the derived facet, moneypunct_byname.

- - -

Proposed resolution:

-

For consistency with the numpunct facet, add a typedef for -char_type to the definition of the moneypunct_byname facet in -22.4.6.4 [locale.moneypunct.byname].

- - -

Rationale:

-

The absence of the typedef is irrelevant. Users can still access -the typedef, because it is inherited from the base class.

- - - - - -
-

330. Misleading "exposition only" value in class locale definition

-

Section: 22.3.1 [locale] Status: NAD - Submitter: Martin Sebor Opened: 2001-07-15 Last modified: 2015-04-08

-

View all other issues in [locale].

-

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-

Discussion:

-

-The "exposition only" value of the std::locale::none constant shown in -the definition of class locale is misleading in that it on many -systems conflicts with the value assigned to one if the LC_XXX -constants (specifically, LC_COLLATE on AIX, LC_ALL on HP-UX, LC_CTYPE -on Linux and SunOS). This causes incorrect behavior when such a -constant is passed to one of the locale member functions that accept a -locale::category argument and interpret it as either the C LC_XXX -constant or a bitmap of locale::category values. At least three major -implementations adopt the suggested value without a change and -consequently suffer from this problem. -

- -

-For instance, the following code will (presumably) incorrectly copy facets -belonging to the collate category from the German locale on AIX: -

- -
-  std::locale l (std::locale ("C"), "de_DE", std::locale::none);
-
- - -

Rationale:

-

The LWG agrees that it may be difficult to implement locale member -functions in such a way that they can take either category -arguments or the LC_ constants defined in <cctype>. In light of -this requirement (22.3.1.1.1 [locale.category], paragraph 2), and in light -of the requirement in the preceding paragraph that it is possible to -combine category bitmask elements with bitwise operations, -defining the category elements is delicate, -particularly if an implementor is constrained to work with a -preexisting C library. (Just using the existing LC_ constants would -not work in general.) There's no set of "exposition only" values that -could give library implementors proper guidance in such a delicate -matter. The non-normative example we're giving is no worse than -any other choice would be.

- -

See issue 347.

- - - - - -
-

332. Consider adding increment and decrement operators to std::fpos< T >

-

Section: 27.5.4 [fpos] Status: NAD - Submitter: PremAnand M. Rao Opened: 2001-08-27 Last modified: 2015-04-08

-

View all other issues in [fpos].

-

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-

Discussion:

-

-Increment and decrement operators are missing from -Table 88 -- Position type requirements in 27.5.4 [fpos]. -

- - -

Proposed resolution:

-

-Table 88 (section 27.4.3) -- Position type requirements -be updated to include increment and decrement operators. -

- -
-expression        return type     operational    note
-
-++p               fpos&           p += O(1)
-p++               fpos            { P tmp = p;
-                                    ++p;
-                                    return tmp; }
---p               fpos&           p -= O(1)
-p--               fpos            { P tmp = p;
-                                    --p;
-                                    return tmp; }
-
- - - -

Rationale:

-

The LWG believes this is a request for extension, not a defect -report. Additionally, nobody saw a clear need for this extension; -fpos is used only in very limited ways.

- - - - - -
-

342. seek and eofbit

-

Section: 27.7.2.3 [istream.unformatted] Status: NAD - Submitter: Howard Hinnant Opened: 2001-10-09 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

-

I think we have a defect.

- -

According to lwg issue 60 which is now a dr, the -description of seekg in 27.7.2.3 [istream.unformatted] paragraph 38 now looks -like:

- -

-Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1), except that it does not count the number of characters -extracted and does not affect the value returned by subsequent calls to -gcount(). After constructing a sentry object, if fail() != true, -executes rdbuf()->pubseekpos( pos). -

- -

And according to lwg issue 243 which is also now a dr, -27.6.1.3, paragraph 1 looks like:

- -

-Each unformatted input function begins execution by constructing an -object of class sentry with the default argument noskipws (second) -argument true. If the sentry object returns true, when converted to a -value of type bool, the function endeavors to obtain the requested -input. Otherwise, if the sentry constructor exits by throwing an -exception or if the sentry object returns false, when converted to a -value of type bool, the function returns without attempting to obtain -any input. In either case the number of extracted characters is set to -0; unformatted input functions taking a character array of non-zero -size as an argument shall also store a null character (using charT()) -in the first location of the array. If an exception is thrown during -input then ios::badbit is turned on in *this'ss error state. If -(exception()&badbit)!= 0 then the exception is rethrown. It also counts -the number of characters extracted. If no exception has been thrown it -ends by storing the count in a member object and returning the value -specified. In any event the sentry object is destroyed before leaving -the unformatted input function. -

- -

And finally 27.6.1.1.2/5 says this about sentry:

- -

-If, after any preparation is completed, is.good() is true, ok_ != false -otherwise, ok_ == false. -

- -

-So although the seekg paragraph says that the operation proceeds if -!fail(), the behavior of unformatted functions says the operation -proceeds only if good(). The two statements are contradictory when only -eofbit is set. I don't think the current text is clear which condition -should be respected. -

- -

Further discussion from Redmond:

- -

PJP: It doesn't seem quite right to say that seekg is -"unformatted". That makes specific claims about sentry that -aren't quite appropriate for seeking, which has less fragile failure -modes than actual input. If we do really mean that it's unformatted -input, it should behave the same way as other unformatted input. On -the other hand, "principle of least surprise" is that seeking from EOF -ought to be OK.

- -

-Pre-Berlin: Paolo points out several problems with the proposed resolution in -Ready state: -

- -
    -
  • It should apply to both overloads of seekg.
    • -
  • tellg has similar issues, except that it should not call clear().
    • -
  • The point about clear() seems to apply to seekp().
    • -
  • Depending on the outcome of 419 -if the sentry -sets failbit when it finds eofbit already set, then -you can never seek away from the end of stream.
    • -
- -

[ -2009-07 Frankfurt -]

- - -
-

-Moved to NAD. Will reopen if proposed resolution is supplied. -

-
- - - -

Proposed resolution:

- -

Change 27.7.2.3 [istream.unformatted] to:

-

-Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1), except that it does not count the number of characters -extracted, does not affect the value returned by subsequent calls to -gcount(), and does not examine the value returned by the sentry -object. After constructing a sentry object, if fail() != -true, executes rdbuf()->pubseekpos(pos). In -case of success, the function calls clear(). -In case of failure, the function calls setstate(failbit) -(which may throw ios_base::failure). -

- -

[Lillehammer: Matt provided wording.]

- - - - -

Rationale:

-

In C, fseek does clear EOF. This is probably what most users would - expect. We agree that having eofbit set should not deter a seek, - and that a successful seek should clear eofbit. Note - that fail() is true only if failbit - or badbit is set, so using !fail(), rather - than good(), satisfies this goal.

- - - - - -
-

344. grouping + showbase

-

Section: 22.4.2 [category.numeric] Status: NAD - Submitter: Howard Hinnant Opened: 2001-10-13 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-When both grouping and showbase are active and the basefield is octal, -does the leading 0 participate in the grouping or not? For example, -should one format as: 0,123,456 or 0123,456? -

-

-An analogy can be drawn with hexadecimal. It appears that 0x123,456 is -preferred over 0x,123,456. However, this analogy is not universally -accepted to apply to the octal base. The standard is not clear on how -to format (or parse) in this manner. -

- -

Proposed resolution:

-

-Insert into 22.4.3.1.2 [facet.numpunct.virtuals] paragraph 3, just before the last -sentence: -

-

-The leading hexadecimal base specifier "0x" does not participate in -grouping. The leading '0' octal base specifier may participate in -grouping. It is unspecified if the leading '0' participates in -formatting octal numbers. In parsing octal numbers, the implementation -is encouraged to accept both the leading '0' participating in the -grouping, and not participating (e.g. 0123,456 or 0,123,456). -

- -

Rationale:

-

-The current behavior may be unspecified, but it's not clear that it -matters. This is an obscure corner case, since grouping is usually -intended for the benefit of humans and oct/hex prefixes are usually -intended for the benefit of machines. There is not a strong enough -consensus in the LWG for action. -

- - - - -
-

348. Minor issue with std::pair operator<

-

Section: 20.3 [pairs] Status: Dup - Submitter: Andy Sawyer Opened: 2001-10-23 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Duplicate of: 532

-

Discussion:

- - -

-The current wording of 20.2.2 [lib.pairs] p6 precludes the use of -operator< on any pair type which contains a pointer. -

- - -

Proposed resolution:

-

In 20.3 [pairs] paragraph 6, replace:

-
-    Returns: x.first < y.first || (!(y.first < x.first) && x.second <
-        y.second).
-
-

With:

-
-    Returns: std::less<T1>()( x.first, y.first ) ||
-             (!std::less<T1>()( y.first, x.first) && 
-             std::less<T2>()( x.second, y.second ) )
-
- - - -

Rationale:

-

This is an instance of a much more general problem. If we want - operator< to translate to std::less for pairs of pointers, where - do we draw the line? The same issue applies to individual - pointers, smart pointer wrappers, std::vector<T*>, and so - on.

- -

Andy Koenig suggests that the real issue here is that we aren't - distinguishing adequately between two different orderings, a - "useful ordering" and a "canonical ordering" that's used just - because we sometimes need some ordering without caring much - which ordering it is. Another example of the later is typeinfo's - before.

- - - - - - -
-

350. allocator<>::address

-

Section: 20.7.9.1 [allocator.members], 17.6.3.5 [allocator.requirements], 17.6.1.1 [contents] Status: Dup - Submitter: Nathan Myers Opened: 2001-10-25 Last modified: 2015-04-08

-

View all other issues in [allocator.members].

-

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-

Duplicate of: 634

-

Discussion:

-

See c++std-lib-9006 and c++std-lib-9007. This issue is taken -verbatim from -9007.

- -

-The core language feature allowing definition of operator&() applied -to any non-builtin type makes that operator often unsafe to use in -implementing libraries, including the Standard Library. The result -is that many library facilities fail for legal user code, such as -the fragment

-
-  class A { private: A* operator&(); };
-  std::vector<A> aa;
-
-  class B { };
-  B* operator&(B&) { return 0; }
-  std::vector<B> ba;
-
- -

-In particular, the requirements table for Allocator (Table 32) specifies -no semantics at all for member address(), and allocator<>::address is -defined in terms of unadorned operator &. -

- - - -

Proposed resolution:

-

-In 20.6.1.1, Change the definition of allocator<>::address from:

-

- Returns: &x -

- -

to:

- -

- Returns: The value that the built in operator&(x) would return if not - overloaded. -

- -

-In 20.1.6, Table 32, add to the Notes column of the a.address(r) and -a.address(s) lines, respectively: -

- -
-  allocator<T>::address(r)
-  allocator<T>::address(s)
-
- -

In addition, in clause 17.4.1.1, add a statement:

- -

- The Standard Library does not apply operator& to any type for which - operator& may be overloaded. -

- - - -

Rationale:

-

The LWG believes both examples are ill-formed. The contained type -is required to be CopyConstructible (17.6.3.1 [utility.arg.requirements]), and that -includes the requirement that &t return the usual types and -values. Since allocators are intended to be used in conjunction with -containers, and since the CopyConstructible requirements appear to -have been written to deal with the concerns of this issue, the LWG -feels it is NAD unless someone can come up with a well-formed example -exhibiting a problem.

- -

It may well be that the CopyConstructible requirements are too - restrictive and that either the container requirements or the - CopyConstructive requirements should be relaxed, but that's a far - larger issue. Marking this issue as "future" as a pointer to that - larger issue.

- - - - - -
-

351. unary_negate and binary_negate: struct or class?

-

Section: 20.9 [function.objects] Status: NAD Editorial - Submitter: Dale Riley Opened: 2001-11-12 Last modified: 2015-04-08

-

View all other issues in [function.objects].

-

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-

Discussion:

-

-In 20.9 [function.objects] the header <functional> synopsis declares -the unary_negate and binary_negate function objects as struct. -However in 20.9.9 [negators] the unary_negate and binary_negate -function objects are defined as class. Given the context, they are -not "basic function objects" like negate, so this is either a typo or -an editorial oversight. -

- -

[Taken from comp.std.c++]

- - - -

Proposed resolution:

-

Change the synopsis to reflect the useage in 20.9.9 [negators]

- -

[Curaçao: Since the language permits "struct", the LWG -views this as NAD. They suggest, however, that the Project Editor -might wish to make the change as editorial.]

- - - - - - - -
-

356. Meaning of ctype_base::mask enumerators

-

Section: 22.4.1 [category.ctype] Status: NAD - Submitter: Matt Austern Opened: 2002-01-23 Last modified: 2015-04-08

-

View all other issues in [category.ctype].

-

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-

Discussion:

- -

What should the following program print?

- -
-  #include <locale>
-  #include <iostream>
-
-  class my_ctype : public std::ctype<char>
-  {
-    typedef std::ctype<char> base;
-  public:
-    my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
-    {
-      std::copy(base::classic_table(), base::classic_table() + base::table_size,
-                my_table);
-      my_table[(unsigned char) '_'] = (base::mask) (base::print | base::space);
-    }
-  private:
-    mask my_table[base::table_size];
-  };
-
-  int main()
-  {
-    my_ctype ct;
-    std::cout << "isspace: " << ct.is(std::ctype_base::space, '_') << "    "
-              << "isalpha: " << ct.is(std::ctype_base::alpha, '_') << std::endl;
-  }
-
- -

The goal is to create a facet where '_' is treated as whitespace.

- -

On gcc 3.0, this program prints "isspace: 1 isalpha: 0". On -Microsoft C++ it prints "isspace: 1 isalpha: 1".

- -

-I believe that both implementations are legal, and the standard does not -give enough guidance for users to be able to use std::ctype's -protected interface portably.

- -

-The above program assumes that ctype_base::mask enumerators like -space and print are disjoint, and that the way to -say that a character is both a space and a printing character is to or -those two enumerators together. This is suggested by the "exposition -only" values in 22.4.1 [category.ctype], but it is nowhere specified in -normative text. An alternative interpretation is that the more -specific categories subsume the less specific. The above program -gives the results it does on the Microsoft compiler because, on that -compiler, print has all the bits set for each specific -printing character class. -

- -

From the point of view of std::ctype's public interface, there's no -important difference between these two techniques. From the point of -view of the protected interface, there is. If I'm defining a facet -that inherits from std::ctype<char>, I'm the one who defines the -value that table()['a'] returns. I need to know what combination of -mask values I should use. This isn't so very esoteric: it's exactly -why std::ctype has a protected interface. If we care about users -being able to write their own ctype facets, we have to give them a -portable way to do it. -

- -

-Related reflector messages: -lib-9224, lib-9226, lib-9229, lib-9270, lib-9272, lib-9273, lib-9274, -lib-9277, lib-9279. -

- -

Issue 339 is related, but not identical. The -proposed resolution if issue 339 says that -ctype_base::mask must be a bitmask type. It does not say that the -ctype_base::mask elements are bitmask elements, so it doesn't -directly affect this issue.

- -

More comments from Benjamin Kosnik, who believes that -that C99 compatibility essentially requires what we're -calling option 1 below.

- -
-
-I think the C99 standard is clear, that isspace -> !isalpha.
---------
-
-#include <locale>
-#include <iostream>
-
-class my_ctype : public std::ctype<char>
-{
-private:
-  typedef std::ctype<char> base;
-  mask my_table[base::table_size];
-
-public:
-  my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
-  {
-    std::copy(base::classic_table(), base::classic_table() + base::table_size,
-              my_table);
-    mask both = base::print | base::space;
-    my_table[static_cast<mask>('_')] = both;
-  }
-};
-
-int main()
-{
-  using namespace std;
-  my_ctype ct;
-  cout << "isspace: " << ct.is(ctype_base::space, '_') << endl;
-  cout << "isprint: " << ct.is(ctype_base::print, '_') << endl;
-
-  // ISO C99, isalpha iff upper | lower set, and !space.
-  // 7.5, p 193
-  // -> looks like g++ behavior is correct.
-  // 356 -> bitmask elements are required for ctype_base
-  // 339 -> bitmask type required for mask
-  cout << "isalpha: " << ct.is(ctype_base::alpha, '_') << endl;
-}
-
-
- - - -

Proposed resolution:

-

Informally, we have three choices:

-
    -
  1. Require that the enumerators are disjoint (except for alnum and -graph)
    2. -
  2. Require that the enumerators are not disjoint, and specify which -of them subsume which others. (e.g. mandate that lower includes alpha -and print)
    3. -
  3. Explicitly leave this unspecified, which the result that the above -program is not portable.
    4. -
- -

Either of the first two options is just as good from the standpoint -of portability. Either one will require some implementations to -change.

- - -

Rationale:

-

The LWG agrees that this is a real ambiguity, and that both -interpretations are conforming under the existing standard. However, -there's no evidence that it's causing problems for real users. Users -who want to define ctype facets portably can test the ctype_base masks -to see which interpretation is being used.

- - - - - -
-

357. <cmath> float functions cannot return HUGE_VAL

-

Section: 26.8 [c.math] Status: NAD Editorial - Submitter: Ray Lischner Opened: 2002-02-26 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

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-

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-

Discussion:

-

-The float versions of the math functions have no meaningful value to return -for a range error. The long double versions have a value they can return, -but it isn't necessarily the most reasonable value. -

- -

-Section 26.5 [lib.c.math], paragraph 5, says that C++ "adds float and long -double overloaded versions of these functions, with the same semantics," -referring to the math functions from the C90 standard. -

- -

-The C90 standard, in section 7.5.1, paragraph 3, says that functions return -"the value of the macro HUGE_VAL" when they encounter a range error. -Section 7.5, paragraph 2, defines HUGE_VAL as a macro that "expands to a -positive double expression, not necessarily representable as a float." -

- -

-Therefore, the float versions of the math functions have no way to -signal a range error. [Curaçao: The LWG notes that this isn't -strictly correct, since errno is set.] The semantics require that they -return HUGE_VAL, but they cannot because HUGE_VAL might not be -representable as a float. -

- -

-The problem with long double functions is less severe because HUGE_VAL is -representable as a long double. On the other hand, it might not be a "huge" -long double value, and might fall well within the range of normal return -values for a long double function. Therefore, it does not make sense for a -long double function to return a double (HUGE_VAL) for a range error. -

- - -

Proposed resolution:

-

Curaçao: C99 was faced with a similar problem, which they fixed by -adding HUGE_VALF and HUGE_VALL in addition to HUGE_VAL.

- -

C++ must also fix, but it should be done in the context of the -general C99 based changes to C++, not via DR. Thus the LWG in Curaçao -felt the resolution should be NAD, FUTURE, but the issue is being held -open for one more meeting to ensure LWG members not present during the -discussion concur.

- - -

Rationale:

-

Will be fixed as part of more general work in the TR.

- - - - - -
-

361. num_get<>::do_get (..., void*&) checks grouping

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: NAD - Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-22.2.2.2.2, p12 specifies that thousands_sep is to be inserted only -for integral types (issue 282 suggests that this should be done for -all arithmetic types). -

- -

-22.2.2.1.2, p12 requires that grouping be checked for all extractors -including that for void*. -

- -

-I don't think that's right. void* values should not be checked for -grouping, should they? (Although if they should, then num_put needs -to write them out, otherwise their extraction will fail.) -

- - -

Proposed resolution:

-

-Change the first sentence of 22.2.2.2.2, p12 from -

-

- Digit grouping is checked. That is, the positions of discarded - separators is examined for consistency with - use_facet<numpunct<charT> >(loc).grouping(). - If they are not consistent then ios_base::failbit is assigned - to err. -

- -

to

-

- Except for conversions to void*, digit grouping is checked... -

- - - -

Rationale:

-

This would be a change: as it stands, the standard clearly - specifies that grouping applies to void*. A survey of existing - practice shows that most existing implementations do that, as they - should.

- - - - - -
-

366. Excessive const-qualification

-

Section: 27 [input.output] Status: NAD - Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The following member functions are declared const, yet return non-const -pointers. We believe they are should be changed, because they allow code -that may surprise the user. See document N1360 for details and -rationale. -

- -

[Santa Cruz: the real issue is that we've got const member -functions that return pointers to non-const, and N1360 proposes -replacing them by overloaded pairs. There isn't a consensus about -whether this is a real issue, since we've never said what our -constness policy is for iostreams. N1360 relies on a distinction -between physical constness and logical constness; that distinction, or -those terms, does not appear in the standard.]

- - - - -

Proposed resolution:

-

In 27.4.4 and 27.4.4.2

-

Replace

-
-  basic_ostream<charT,traits>* tie() const;
-
-

with

-
-  basic_ostream<charT,traits>* tie();
-  const basic_ostream<charT,traits>* tie() const;
-
- -

and replace

-
-  basic_streambuf<charT,traits>* rdbuf() const;
-
-

with

-
-  basic_streambuf<charT,traits>* rdbuf();
-  const basic_streambuf<charT,traits>* rdbuf() const;
-
- -

In 27.5.2 and 27.5.2.3.1

-

Replace

-
-  char_type* eback() const;
-
-

with

-
-  char_type* eback();
-  const char_type* eback() const;
-
- -

Replace

-
-  char_type gptr() const;
-
-

with

-
-  char_type* gptr();
-  const char_type* gptr() const;
-
- -

Replace

-
-  char_type* egptr() const;
-
-

with

-
-  char_type* egptr();
-  const char_type* egptr() const;
-
- -

In 27.5.2 and 27.5.2.3.2

-

Replace

-
-  char_type* pbase() const;
-
-

with

-
-  char_type* pbase();
-  const char_type* pbase() const;
-
- -

Replace

-
-  char_type* pptr() const;
-
-

with

-
-  char_type* pptr();
-  const char_type* pptr() const;
-
- -

Replace

-
-  char_type* epptr() const;
-
-

with

-
-  char_type* epptr();
-  const char_type* epptr() const;
-
- -

In 27.7.2, 27.7.2.2, 27.7.3 27.7.3.2, 27.7.4, and 27.7.6

-

Replace

-
-  basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
-
-

with

-
-  basic_stringbuf<charT,traits,Allocator>* rdbuf();
-  const basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
-
- -

In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13

-

Replace

-
-  basic_filebuf<charT,traits>* rdbuf() const;
-
-

with

-
-  basic_filebuf<charT,traits>* rdbuf();
-  const basic_filebuf<charT,traits>* rdbuf() const;
-
- - -

Rationale:

-

The existing specification is a bit sloppy, but there's no - particular reason to change this other than tidiness, and there are - a number of ways in which streams might have been designed - differently if we were starting today. There's no evidence that the - existing constness policy is harming users. We might consider - a different constness policy as part of a full stream redesign.

- - - - - -
-

367. remove_copy/remove_copy_if and Input Iterators

-

Section: 25.3.8 [alg.remove] Status: NAD - Submitter: Anthony Williams Opened: 2002-05-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-remove_copy and remove_copy_if (25.3.8 [alg.remove]) permit their -input range to be marked with Input Iterators. However, since two -operations are required against the elements to copy (comparison and -assigment), when the input range uses Input Iterators, a temporary -copy must be taken to avoid dereferencing the iterator twice. This -therefore requires the value type of the InputIterator to be -CopyConstructible. If the iterators are at least Forward Iterators, -then the iterator can be dereferenced twice, or a reference to the -result maintained, so the temporary is not required. -

- - -

Proposed resolution:

-

-Add "If InputIterator does not meet the requirements of forward -iterator, then the value type of InputIterator must be copy -constructible. Otherwise copy constructible is not required." to -25.3.8 [alg.remove] paragraph 6. -

- - -

Rationale:

-

The assumption is that an input iterator can't be dereferenced - twice. There's no basis for that assumption in the Standard.

- - - - - -
-

368. basic_string::replace has two "Throws" paragraphs

-

Section: 21.4.6.6 [string::replace] Status: NAD Editorial - Submitter: Beman Dawes Opened: 2002-06-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-21.4.6.6 [string::replace] basic_string::replace, second -signature, given in paragraph 1, has two "Throws" paragraphs (3 and -5). -

- -

-In addition, the second "Throws" paragraph (5) includes specification -(beginning with "Otherwise, the function replaces ...") that should be -part of the "Effects" paragraph. -

- - -

Proposed resolution:

- - -

Rationale:

-

This is editorial. Both "throws" statements are true. The bug is - just that the second one should be a sentence, part of the "Effects" - clause, not a separate "Throws". The project editor has been - notified.

- - - - - -
-

372. Inconsistent description of stdlib exceptions

-

Section: 17.6.5.12 [res.on.exception.handling], 18.7.1 [type.info] Status: NAD - Submitter: Randy Maddox Opened: 2002-07-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Paragraph 3 under clause 17.6.5.12 [res.on.exception.handling], Restrictions on -Exception Handling, states that "Any other functions defined in the -C++ Standard Library that do not have an exception-specification may -throw implementation-defined exceptions unless otherwise specified." -This statement is followed by a reference to footnote 178 at the -bottom of that page which states, apparently in reference to the C++ -Standard Library, that "Library implementations are encouraged (but -not required) to report errors by throwing exceptions from (or derived -from) the standard exceptions."

- -

These statements appear to be in direct contradiction to clause -18.7.1 [type.info], which states "The class exception defines the -base class for the types of objects thrown as exceptions by the C++ -Standard library components ...".

- -

Is this inconsistent?

- - - -

Proposed resolution:

- - -

Rationale:

-

Clause 17 is setting the overall library requirements, and it's - clear and consistent. This sentence from Clause 18 is descriptive, - not setting a requirement on any other class. -

- - - - - -
-

374. moneypunct::frac_digits returns int not unsigned

-

Section: 22.4.6.3.1 [locale.moneypunct.members], 22.4.6.3.2 [locale.moneypunct.virtuals] Status: NAD - Submitter: Ray Lischner Opened: 2002-08-08 Last modified: 2015-04-08

-

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-

Discussion:

-

-In section 22.4.6.3.1 [locale.moneypunct.members], frac_digits() returns type -"int". This implies that frac_digits() might return a negative value, -but a negative value is nonsensical. It should return "unsigned". -

- -

-Similarly, in section 22.4.6.3.2 [locale.moneypunct.virtuals], do_frac_digits() -should return "unsigned". -

- - - -

Proposed resolution:

- - -

Rationale:

-

Regardless of whether the return value is int or unsigned, it's -always conceivable that frac_digits might return a nonsensical -value. (Is 4294967295 really any better than -1?) The clients of -moneypunct, the get and put facets, can and do perform range -checks.

- - - - - -
-

377. basic_string::insert and length_error

-

Section: 21.4.6.4 [string::insert] Status: NAD - Submitter: Ray Lischner Opened: 2002-08-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 21.4.6.4 [string::insert], paragraph 4, contains the following, -"Then throws length_error if size() >= npos - rlen." -

- -

-Related to DR 83, this sentence should probably be removed. -

- - -

Proposed resolution:

- - -

Rationale:

This requirement is redundant but correct. No change is -needed.

- - - - -
-

378. locale immutability and locale::operator=()

-

Section: 22.3.1 [locale] Status: Dup - Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 31

-

Discussion:

-

-I think there is a problem with 22.1.1, p6 which says that -

-
-    -6- An instance of locale is immutable; once a facet reference
-        is obtained from it, that reference remains usable as long
-        as the locale value itself exists.
-
-

-and 22.1.1.2, p4: -

-
-    const locale& operator=(const locale& other) throw();
-
-    -4- Effects: Creates a copy of other, replacing the current value.
-
-

-How can a reference to a facet obtained from a locale object remain -valid after an assignment that clearly must replace all the facets -in the locale object? Imagine a program such as this -

-
-    std::locale loc ("de_DE");
-    const std::ctype<char> &r0 = std::use_facet<std::ctype<char> >(loc);
-    loc = std::locale ("en_US");
-    const std::ctype<char> &r1 = std::use_facet<std::ctype<char> >(loc);
-
-

-Is r0 really supposed to be preserved and destroyed only when loc goes -out of scope? -

- - -

Proposed resolution:

-

[Summer '04 mid-meeting mailing: Martin and Dietmar believe this - is a duplicate of issue 31 and recommend that it be - closed. -]

- - - - - - -
-

382. codecvt do_in/out result

-

Section: 22.4.1.4 [locale.codecvt] Status: NAD - Submitter: Martin Sebor Opened: 2002-08-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It seems that the descriptions of codecvt do_in() and do_out() leave -sufficient room for interpretation so that two implementations of -codecvt may not work correctly with the same filebuf. Specifically, -the following seems less than adequately specified: -

- -
    -
  1. - the conditions under which the functions terminate -
    2. -
  2. - precisely when the functions return ok -
    3. -
  3. - precisely when the functions return partial -
    4. -
  4. - the full set of conditions when the functions return error -
    5. -
- -
    -
  1. - 22.4.1.4.2 [locale.codecvt.virtuals], p2 says this about the effects of the - function: ...Stops if it encounters a character it cannot - convert... This assumes that there *is* a character to - convert. What happens when there is a sequence that doesn't form a - valid source character, such as an unassigned or invalid UNICODE - character, or a sequence that cannot possibly form a character - (e.g., the sequence "\xc0\xff" in UTF-8)? -
    2. -
  2. - Table 53 says that the function returns codecvt_base::ok - to indicate that the function(s) "completed the conversion." - Suppose that the source sequence is "\xc0\x80" in UTF-8, - with from pointing to '\xc0' and (from_end==from + 1). - It is not clear whether the return value should be ok - or partial (see below). -
    3. -
  3. - Table 53 says that the function returns codecvt_base::partial - if "not all source characters converted." With the from pointers - set up the same way as above, it is not clear whether the return - value should be partial or ok (see above). -
    4. -
  4. - Table 53, in the row describing the meaning of error mistakenly - refers to a "from_type" character, without the symbol from_type - having been defined. Most likely, the word "source" character - is intended, although that is not sufficient. The functions - may also fail when they encounter an invalid source sequence - that cannot possibly form a valid source character (e.g., as - explained in bullet 1 above). -
    5. -
-

-Finally, the conditions described at the end of 22.4.1.4.2 [locale.codecvt.virtuals], p4 don't seem to be possible: -

-

- "A return value of partial, if (from_next == from_end), - indicates that either the destination sequence has not - absorbed all the available destination elements, or that - additional source elements are needed before another - destination element can be produced." -

-

-If the value is partial, it's not clear to me that (from_next -==from_end) could ever hold if there isn't enough room -in the destination buffer. In order for (from_next==from_end) to -hold, all characters in that range must have been successfully -converted (according to 22.4.1.4.2 [locale.codecvt.virtuals], p2) and since there are no -further source characters to convert, no more room in the -destination buffer can be needed. -

-

-It's also not clear to me that (from_next==from_end) could ever -hold if additional source elements are needed to produce another -destination character (not element as incorrectly stated in the -text). partial is returned if "not all source characters have -been converted" according to Table 53, which also implies that -(from_next==from) does NOT hold. -

-

-Could it be that the intended qualifying condition was actually -(from_next != from_end), i.e., that the sentence was supposed -to read -

-

- "A return value of partial, if (from_next != from_end),..." -

-

-which would make perfect sense, since, as far as I understand it, -partial can only occur if (from_next != from_end)? -

-

[Lillehammer: Defer for the moment, but this really needs to be - fixed. Right now, the description of codecvt is too vague for it to - be a useful contract between providers and clients of codecvt - facets. (Note that both vendors and users can be both providers and - clients of codecvt facets.) The major philosophical issue is whether - the standard should only describe mappings that take a single wide - character to multiple narrow characters (and vice versa), or whether - it should describe fully general N-to-M conversions. When the - original standard was written only the former was contemplated, but - today, in light of the popularity of utf8 and utf16, that doesn't - seem sufficient for C++0x. Bill supports general N-to-M conversions; - we need to make sure Martin and Howard agree.]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-codecvt is meant to be a 1-to-N to N-to-1 conversion. It does not work -well for N-to-M conversions. wbuffer_convert now exists, and handles -N-to-M cases. Also, there is a new specialization of codecvt that -permits UTF-16 <-> UTF-8 conversions. -

-

-NAD without prejudice. Will reopen if proposed resolution is supplied. -

-
- - - -

Proposed resolution:

- - - - -
-

385. Does call by value imply the CopyConstructible requirement?

-

Section: 17 [library] Status: NAD - Submitter: Matt Austern Opened: 2002-10-23 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Many function templates have parameters that are passed by value; -a typical example is find_if's pred parameter in -25.2.5 [alg.find]. Are the corresponding template parameters -(Predicate in this case) implicitly required to be -CopyConstructible, or does that need to be spelled out explicitly? -

- -

-This isn't quite as silly a question as it might seem to be at first -sight. If you call find_if in such a way that template -argument deduction applies, then of course you'll get call by value -and you need to provide a copy constructor. If you explicitly provide -the template arguments, however, you can force call by reference by -writing something like find_if<my_iterator, -my_predicate&>. The question is whether implementation -are required to accept this, or whether this is ill-formed because -my_predicate& is not CopyConstructible. -

- -

-The scope of this problem, if it is a problem, is unknown. Function -object arguments to generic algorithms in clauses 25 [algorithms] -and 26 [numerics] are obvious examples. A review of the whole -library is necessary. -

-

[ -This is really two issues. First, predicates are typically passed by -value but we don't say they must be Copy Constructible. They should -be. Second: is specialization allowed to transform value arguments -into references? References aren't copy constructible, so this should -not be allowed. -]

- -

[ -2007-01-12, Howard: First, despite the note above, references are -copy constructible. They just aren't assignable. Second, this is very -closely related to 92 and should be consistent with that. -That issue already says that implementations are allowed to copy -function objects. If one passes in a reference, it is copyable, but -susceptible to slicing if one passes in a reference to a base. Third, -with rvalue reference in the language one only needs to satisfy -MoveConstructible to pass an rvalue "by value". Though the function -might still copy the function object internally (requiring -CopyConstructible). Finally (and fwiw), if we wanted to, it is easy to -code all of the std::algorithms such that they do not copy function -objects internally. One merely passes them by reference internally if -desired (this has been fully implemented and shipped for several years). - If this were mandated, it would reverse 92, allowing -function objects to reliably maintain state. E.g. the example in 92 would reliably remove only the third element. -]

- - - -

Proposed resolution:

-

-Recommend NAD. -

- - -

Rationale:

-

-Generic algorithms will be marked with concepts and these will imply a requirement -of MoveConstructible (not CopyConstructible). The signature of the function will -then precisely describe and enforce the precise requirements. -

- - - - - -
-

388. Use of complex as a key in associative containers

-

Section: 26.4 [complex.numbers] Status: NAD - Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Practice with std::complex<> and the associative containers -occasionally reveals artificial and distracting issues with constructs -resembling: std::set<std::complex<double> > s; -

- -

-The main reason for the above to fail is the absence of an appropriate -definition for std::less<std::complex<T> >. That in turn comes from -the definition of the primary template std::less<> in terms of -operator<. -

- -

-The usual argument goes as follows: Since there is no ordering over -the complex field compatible with field operations it makes little -sense to define a function operator< operating on the datatype -std::complex<T>. That is fine. However, that reasoning does not carry -over to std::less<T> which is used, among other things, by associative -containers as an ordering useful to meet complexity requirements. -

- -

Related issue: 348.

- -

[ -Pre Bellevue: Reopened at the request of Alisdair. -]

- - -

[ -Bellevue: -]

- - -

-This is a request for a design change, and not a defect in the standard. -It is in scope to consider, but the group feels that it is not a change -that we need to do. Is there a total ordering for floating point values, -including NaN? There is not a clear enough solution or big enough -problem for us to solve. Solving this problem would require solving the -problem for floating point, which is equally unclear. The LWG noted that -users who want to put objects into an associative container for which -operator< isn't defined can simply provide their own comparison -function object. NAD -

- - -

Proposed resolution:

-

Informally: Add a specialization of std::less for std::complex.

- - -

Rationale:

-

Discussed in Santa Cruz. An overwhelming majority of the LWG -believes this should not be treated a DR: it's a request for a design -change, not a defect in the existing standard. Most people (10-3) -believed that we probably don't want this change, period: as with -issue 348, it's hard to know where to draw the line. -The LWG noted that users who want to put objects into an associative -container for which operator< isn't defined can simply -provide their own comparison function object.

- - - - - -
-

390. CopyConstructible requirements too strict

-

Section: 17.6.3.1 [utility.arg.requirements] Status: NAD Editorial - Submitter: Doug Gregor Opened: 2002-10-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The CopyConstructible requirements in Table 30 state that for an -object t of type T (where T is CopyConstructible), the expression &t -returns the address of t (with type T*). This requirement is overly -strict, in that it disallows types that overload operator& to not -return a value of type T*. This occurs, for instance, in the Boost.Lambda library, where -operator& is overloaded for a Boost.Lambda function object to return -another function object. -

- -

Example:

- -
-  std::vector<int> u, v;
-  int x;
-  // ...
-  std::transform(u.begin(), u.end(), std::back_inserter(v), _1 * x);
-
- -

-_1 * x returns an unnamed function object with operator& overloaded to -not return T* , therefore rendering the std::transform call ill-formed. -However, most standard library implementations will compile this code -properly, and the viability of such binder libraries is severely hindered -by the unnecessary restriction in the CopyConstructible requirements. -

- -

-For reference, the address of an object can be retrieved without using -the address-of operator with the following function template: -

- -
-  template <typename T> T* addressof(T& v)
-  {
-    return reinterpret_cast<T*>(
-         &const_cast<char&>(reinterpret_cast<const volatile char &>(v)));
-  }
-
- -

-Note: this relates directly to library issue 350, which -will need to be reexamined if the CopyConstructible requirements -change. -

- - -

Proposed resolution:

-

-Remove the last two rows of Table 30, eliminating the requirements -that &t and &u return the address of t and u, respectively. -

- - -

Rationale:

-

This was a deliberate design decision. Perhaps it should be - reconsidered for C++0x.

- - - - - -
-

392. 'equivalence' for input iterators

-

Section: 24.2.3 [input.iterators] Status: NAD - Submitter: Corwin Joy Opened: 2002-12-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-In section 24.2.3 [input.iterators] table 72 - -'Input Iterator Requirements' we have as a postcondition of *a: -"If a==b and (a, b) is in the domain of == then *a is equivalent to *b". -

- -

-In section 24.6.3.5 [istreambuf.iterator::equal] it states that -"istreambuf_iterator::equal returns true if and only if both iterators -are at end-of-stream, or neither is at end-of-stream, regardless of -what streambuf object they use." (My emphasis). -

- -

-The defect is that either 'equivalent' needs to be more precisely -defined or the conditions for equality in 24.6.3.5 [istreambuf.iterator::equal] -are incorrect. (Or both). -

- -

Consider the following example:

-
-   #include <iostream>
-   #include <fstream>
-   #include <iterator>
-   using namespace std;
-
-   int main() {
-    ifstream file1("file1.txt"), file2("file2.txt");
-    istreambuf_iterator<char> f1(file1), f2(file2);
-    cout << "f1 == f2 : " << boolalpha << (f1 == f2) << endl;
-    cout << "f1 = " << *f1 << endl;
-    cout << "f2 = " << *f2 << endl;
-    return 0;
-   }
-
- -

Now assuming that neither f1 or f2 are at the end-of-stream then -f1 == f2 by 24.6.3.5 [istreambuf.iterator::equal].

- -

However, it is unlikely that *f1 will give the same value as *f2 except -by accident.

- -

So what does *f1 'equivalent' to *f2 mean? I think the standard should -be clearer on this point, or at least be explicit that this does not -mean that *f1 and *f2 are required to have the same value in the case -of input iterators.

- - -

Proposed resolution:

- - -

Rationale:

The two iterators aer not in the domain of ==

- - - - - - -
-

393. do_in/do_out operation on state unclear

-

Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: NAD Editorial - Submitter: Alberto Barbati Opened: 2002-12-24 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.virtuals].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-this DR follows the discussion on the previous thread "codecvt::do_in -not consuming external characters". It's just a clarification issue -and not a request for a change. -

-

-Can do_in()/do_out() produce output characters without consuming input -characters as a result of operation on state? -

- - -

Proposed resolution:

-

-Add a note at the end of 22.4.1.4.2 [locale.codecvt.virtuals], -paragraph 3: -

- -

-[Note: As a result of operations on state, it can return ok or partial -and set from_next == from and to_next != to. --end note] -

- - -

Rationale:

-

-The submitter believes that standard already provides an affirmative -answer to the question. However, the current wording has induced a few -library implementors to make the incorrect assumption that -do_in()/do_out() always consume at least one internal character when -they succeed. -

- -

-The submitter also believes that the proposed resolution is not in -conflict with the related issue 76. Moreover, by explicitly allowing -operations on state to produce characters, a codecvt implementation -may effectively implement N-to-M translations without violating the -"one character at a time" principle described in such issue. On a side -note, the footnote in the proposed resolution of issue 76 that -informally rules out N-to-M translations for basic_filebuf should be -removed if this issue is accepted as valid. -

- - -

[ -Kona (2007): The proposed resolution is to add a note. Since this is -non-normative, the issue is editorial, but we believe that the note is -correct. Proposed Disposition: NAD, Editorial -]

- - - - - - -
-

394. behavior of formatted output on failure

-

Section: 27.7.3.6.1 [ostream.formatted.reqmts] Status: NAD - Submitter: Martin Sebor Opened: 2002-12-27 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-There is a contradiction in Formatted output about what bit is -supposed to be set if the formatting fails. On sentence says it's -badbit and another that it's failbit. -

-

-27.6.2.5.1, p1 says in the Common Requirements on Formatted output -functions: -

-
-     ... If the generation fails, then the formatted output function
-     does setstate(ios::failbit), which might throw an exception.
-
-

-27.6.2.5.2, p1 goes on to say this about Arithmetic Inserters: -

-

- ... The formatting conversion occurs as if it performed the - following code fragment: -

-
-     bool failed =
-         use_facet<num_put<charT,ostreambuf_iterator<charT,traits>
-         > >
-         (getloc()).put(*this, *this, fill(), val). failed();
-
-     ... If failed is true then does setstate(badbit) ...
-
-

-The original intent of the text, according to Jerry Schwarz (see -c++std-lib-10500), is captured in the following paragraph: -

-

-In general "badbit" should mean that the stream is unusable because -of some underlying failure, such as disk full or socket closure; -"failbit" should mean that the requested formatting wasn't possible -because of some inconsistency such as negative widths. So typically -if you clear badbit and try to output something else you'll fail -again, but if you clear failbit and try to output something else -you'll succeed. -

-

-In the case of the arithmetic inserters, since num_put cannot -report failure by any means other than exceptions (in response -to which the stream must set badbit, which prevents the kind of -recoverable error reporting mentioned above), the only other -detectable failure is if the iterator returned from num_put -returns true from failed(). -

-

-Since that can only happen (at least with the required iostream -specializations) under such conditions as the underlying failure -referred to above (e.g., disk full), setting badbit would seem -to be the appropriate response (indeed, it is required in -27.6.2.5.2, p1). It follows that failbit can never be directly -set by the arithmetic (it can only be set by the sentry object -under some unspecified conditions). -

-

-The situation is different for other formatted output functions -which can fail as a result of the streambuf functions failing -(they may do so by means other than exceptions), and which are -then required to set failbit. -

-

-The contradiction, then, is that ostream::operator<<(int) will -set badbit if the disk is full, while operator<<(ostream&, -char) will set failbit under the same conditions. To make the behavior -consistent, the Common requirements sections for the Formatted output -functions should be changed as proposed below. -

-

[Kona: There's agreement that this is a real issue. What we - decided at Kona: 1. An error from the buffer (which can be detected - either directly from streambuf's member functions or by examining a - streambuf_iterator) should always result in badbit getting set. - 2. There should never be a circumstance where failbit gets set. - That represents a formatting error, and there are no circumstances - under which the output facets are specified as signaling a - formatting error. (Even more so for string output that for numeric - because there's nothing to format.) If we ever decide to make it - possible for formatting errors to exist then the facets can signal - the error directly, and that should go in clause 22, not clause 27. - 3. The phrase "if generation fails" is unclear and should be - eliminated. It's not clear whether it's intended to mean a buffer - error (e.g. a full disk), a formatting error, or something else. - Most people thought it was supposed to refer to buffer errors; if - so, we should say so. Martin will provide wording.]

- - -

[ -2009-07 Frankfurt -]

- - -

-NAD. This issue is already fixed. -

- - - -

Proposed resolution:

- - -

Rationale:

- - - - - - -
-

397. ostream::sentry dtor throws exceptions

-

Section: 27.7.3.4 [ostream::sentry] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2015-04-08

-

View all other issues in [ostream::sentry].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-17.4.4.8, p3 prohibits library dtors from throwing exceptions. -

-

-27.6.2.3, p4 says this about the ostream::sentry dtor: -

- 
-    -4- If ((os.flags() & ios_base::unitbuf) && !uncaught_exception())
-        is true, calls os.flush().
-
-

-27.6.2.6, p7 that describes ostream::flush() says: -

- 
-    -7- If rdbuf() is not a null pointer, calls rdbuf()->pubsync().
-        If that function returns ?-1 calls setstate(badbit) (which
-        may throw ios_base::failure (27.4.4.3)).
-
-

-That seems like a defect, since both pubsync() and setstate() can -throw an exception. -

-

[ -The contradiction is real. Clause 17 says destructors may never -throw exceptions, and clause 27 specifies a destructor that does -throw. In principle we might change either one. We're leaning -toward changing clause 17: putting in an "unless otherwise specified" -clause, and then putting in a footnote saying the sentry destructor -is the only one that can throw. PJP suggests specifying that -sentry::~sentry() should internally catch any exceptions it might cause. -]

- - -

[ -See 418 and 622 for related issues. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-Move to Review. Add "Throws: nothing" to the specification of ostream::sentry::~sentry(). -

-
- -

[ -2009-10-13 Daniel adds: -]

- - -

-The proposed resolution of 835 is written to match the outcome -of this issue. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Open. Our intent is to solve this issue with 835. -

- -

[ -2010-03-06 Martin updates wording. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Editorial. -

- - - -

Rationale:

-

-Solved by 835. -

- - -

Proposed resolution:

-

-Add after 27.7.3.4 [ostream::sentry] p17: -

- -
-
-~sentry();
-
-
-

--17- If (os.flags() & ios_base::unitbuf) -is true, calls os.flush(). -

- -

-Throws: Nothing. -

-
-
- - - - - -
-

398. effects of end-of-file on unformatted input functions

-

Section: 27.7.3.4 [ostream::sentry] Status: NAD - Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2015-04-08

-

View all other issues in [ostream::sentry].

-

View all issues with NAD status.

-

Discussion:

-

-While reviewing unformatted input member functions of istream -for their behavior when they encounter end-of-file during input -I found that the requirements vary, sometimes unexpectedly, and -in more than one case even contradict established practice (GNU -libstdc++ 3.2, IBM VAC++ 6.0, STLPort 4.5, SunPro 5.3, HP aCC -5.38, Rogue Wave libstd 3.1, and Classic Iostreams). -

-

-The following unformatted input member functions set eofbit if they -encounter an end-of-file (this is the expected behavior, and also -the behavior of all major implementations): -

- 
-    basic_istream<charT, traits>&
-    get (char_type*, streamsize, char_type);
-
-

- Also sets failbit if it fails to extract any characters. -

- 
-    basic_istream<charT, traits>&
-    get (char_type*, streamsize);
-
-

- Also sets failbit if it fails to extract any characters. -

- 
-    basic_istream<charT, traits>&
-    getline (char_type*, streamsize, char_type);
-
-

- Also sets failbit if it fails to extract any characters. -

- 
-    basic_istream<charT, traits>&
-    getline (char_type*, streamsize);
-
-

- Also sets failbit if it fails to extract any characters. -

- 
-    basic_istream<charT, traits>&
-    ignore (int, int_type);
-
- 
-    basic_istream<charT, traits>&
-    read (char_type*, streamsize);
-
-

- Also sets failbit if it encounters end-of-file. -

- 
-    streamsize readsome (char_type*, streamsize);
-
- -

-The following unformated input member functions set failbit but -not eofbit if they encounter an end-of-file (I find this odd -since the functions make it impossible to distinguish a general -failure from a failure due to end-of-file; the requirement is -also in conflict with all major implementation which set both -eofbit and failbit): -

- 
-    int_type get();
-
- 
-    basic_istream<charT, traits>&
-    get (char_type&);
-
-

-These functions only set failbit of they extract no characters, -otherwise they don't set any bits, even on failure (I find this -inconsistency quite unexpected; the requirement is also in -conflict with all major implementations which set eofbit -whenever they encounter end-of-file): -

- 
-    basic_istream<charT, traits>&
-    get (basic_streambuf<charT, traits>&, char_type);
-
- 
-    basic_istream<charT, traits>&
-    get (basic_streambuf<charT, traits>&);
-
-

-This function sets no bits (all implementations except for -STLport and Classic Iostreams set eofbit when they encounter -end-of-file): -

- 
-    int_type peek ();
-
-

Informally, what we want is a global statement of intent saying - that eofbit gets set if we trip across EOF, and then we can take - away the specific wording for individual functions. A full review - is necessary. The wording currently in the standard is a mishmash, - and changing it on an individual basis wouldn't make things better. - Dietmar will do this work.

- -

[ -2009-07 Frankfurt -]

- - -

-Moved to NAD. See 27.7.2.1 [istream] p3. -

- - - -

Proposed resolution:

- - - - -
-

399. volations of unformatted input function requirements

-

Section: 27.7.2.3 [istream.unformatted] Status: NAD - Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

View all other issues in [istream.unformatted].

-

View all issues with NAD status.

-

Discussion:

-

-The Effects clauses for the two functions below violate the -general requirements on unformatted input functions outlined -in 27.6.1.3: they do not begin by constructing a sentry object. -Instead, they begin by calling widen ('\n'), which may throw -an exception. The exception is then allowed to propagate from -the unformatted input function irrespective of the setting of -exceptions(). -

-

-Note that in light of 27.6.1.1, p3 and p4, the fact that the -functions allow exceptions thrown from widen() to propagate -may not strictly speaking be a defect (but the fact that the -functions do not start by constructing a sentry object still -is). However, since an exception thrown from ctype<charT> -::widen() during any other input operation (say, from within -a call to num_get<charT>::get()) will be caught and cause -badbit to be set, these two functions should not be treated -differently for the sake of consistency. -

- - -

Proposed resolution:

- - -

Rationale:

-

-Not a defect. The standard is consistent, and the behavior required -by the standard is unambiguous. Yes, it's theoretically possible for -widen to throw. (Not that this will happen for the default ctype -facet or for most real-world replacement ctype facets.) Users who -define ctype facets that can throw, and who care about this behavior, -can use alternative signatures that don't call widen. -

- - - - - - -
-

408. Is vector<reverse_iterator<char*> > forbidden?

-

Section: 24.2 [iterator.requirements] Status: NAD Editorial - Submitter: Nathan Myers Opened: 2003-06-03 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

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-

Discussion:

-

-I've been discussing iterator semantics with Dave Abrahams, and a -surprise has popped up. I don't think this has been discussed before. -

- -

-X [iterator.concepts] says that the only operation that can be performed on "singular" -iterator values is to assign a non-singular value to them. (It -doesn't say they can be destroyed, and that's probably a defect.) -Some implementations have taken this to imply that there is no need -to initialize the data member of a reverse_iterator<> in the default -constructor. As a result, code like -

-
-  std::vector<std::reverse_iterator<char*> > v(7);
-  v.reserve(1000);
-
-

-invokes undefined behavior, because it must default-initialize the -vector elements, and then copy them to other storage. Of course many -other vector operations on these adapters are also left undefined, -and which those are is not reliably deducible from the standard. -

- -

-I don't think that 24.1 was meant to make standard-library iterator -types unsafe. Rather, it was meant to restrict what operations may -be performed by functions which take general user- and standard -iterators as arguments, so that raw pointers would qualify as -iterators. However, this is not clear in the text, others have come -to the opposite conclusion. -

- -

-One question is whether the standard iterator adaptors have defined -copy semantics. Another is whether they have defined destructor -semantics: is -

-
-  { std::vector<std::reverse_iterator<char*> >  v(7); }
-
-

-undefined too? -

- -

-Note this is not a question of whether algorithms are allowed to -rely on copy semantics for arbitrary iterators, just whether the -types we actually supply support those operations. I believe the -resolution must be expressed in terms of the semantics of the -adapter's argument type. It should make clear that, e.g., the -reverse_iterator<T> constructor is actually required to execute -T(), and so copying is defined if the result of T() is copyable. -

- -

-Issue 235, which defines reverse_iterator's default -constructor more precisely, has some relevance to this issue. -However, it is not the whole story. -

- -

-The issue was whether -

-
-  reverse_iterator() { }
-
-

-is allowed, vs. -

-
-  reverse_iterator() : current() { }
-
- -

-The difference is when T is char*, where the first leaves the member -uninitialized, and possibly equal to an existing pointer value, or -(on some targets) may result in a hardware trap when copied. -

- -

-8.5 paragraph 5 seems to make clear that the second is required to -satisfy DR 235, at least for non-class Iterator argument -types. -

- -

-But that only takes care of reverse_iterator, and doesn't establish -a policy for all iterators. (The reverse iterator adapter was just -an example.) In particular, does my function -

-
-  template <typename Iterator>
-    void f() { std::vector<Iterator>  v(7); } 
-
-

-evoke undefined behavior for some conforming iterator definitions? -I think it does, now, because vector<> will destroy those singular -iterator values, and that's explicitly disallowed. -

- -

-24.1 shouldn't give blanket permission to copy all singular iterators, -because then pointers wouldn't qualify as iterators. However, it -should allow copying of that subset of singular iterator values that -are default-initialized, and it should explicitly allow destroying any -iterator value, singular or not, default-initialized or not. -

- -

Related issues: 407, 1012

-

[ -We don't want to require all singular iterators to be copyable, -because that is not the case for pointers. However, default -construction may be a special case. Issue: is it really default -construction we want to talk about, or is it something like value -initialization? We need to check with core to see whether default -constructed pointers are required to be copyable; if not, it would be -wrong to impose so strict a requirement for iterators. -]

- - -

[ -2009-05-10 Alisdair provided wording. -]

- - -

-The comments regarding destroying singular iterators have already been -resolved. That just leaves copying (with moving implied). -

- -

[ -2009-07 Frankfurt -]

- - -
-

-This is related to LWG 1012. -

-

-Note that there is a bug in the proposed resolution to LWG 1012. The -change to [reverse.iter.con] should be modified so that the word -"default" in the second sentence of the Effects clause is replaced by -"value." -

-

-We believe that the proposed fix to LWG 1012 (now corrected) is -sufficient to solve the problem for reverse_iterator. However, Alisdair -pointed out that LWG 1012 does not solve the general problem for authors -of iterator adaptors. -

-

-There are some problems with the proposed resolution. The phrase "safely -copyable" is not a term of art. Also, it mentions a -DefaultConstructible? concept. -

-

-Move to Review after Alisdair updates the wording. -

-
- -

[ -2009-07-31 Alisdair revised wording: -]

- - -

[ -2009-08-17 Alisdair and Daniel collaborate on slightly revised wording. -This issue depends upon 724 -]

- - -

[ -2009-10-14 Daniel adds: -]

- - -

-There is a clear dependency on 1213, because the term "singular", -which is used as part of the resolution, is not properly defined yet. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Open. Alisdair will provide improved wording to make -this have "value semantics" and otherwise behave like a valid iterator. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

-

-Add a new paragrpah to Iterator concepts 24.2 [iterator.requirements] after para 5 (the one describing -singular iterators) -

-
-

-Just as a regular pointer to an array guarantees that there is a pointer -value pointing past the last element of the array, so for any iterator -type there is an iterator value that points past the last element of a -corresponding container. These values are called past-the-end values. -Values of an iterator i for which the expression *i is defined are called -dereferenceable. The library never assumes that past-the-end values are -dereferenceable. Iterators can also have singular values that are not -associated with any container. [Example: After the declaration of an -uninitialized pointer x (as with int* x;), x must always be assumed to -have a singular value of a pointer. — end example] Results of most -expressions are undefined for singular values; the only exceptions are -destroying an iterator that holds a singular value and the assignment of -a non-singular value to an iterator that holds a singular value. In this -case the singular value is overwritten the same way as any other value. -Dereferenceable values are always non-singular. -

-

-After value-initialization, any iterator that satisfies the -DefaultConstructible requirements ([defaultconstructible]) shall not introduce undefined behaviour -when used as the -source of a copy or move operation, even if it would -otherwise be singular. [Note: This guarantee is not offered for -default-initialization (8.5 [dcl.init]), although the distinction only -matters for types with trivial default constructors such as pointers. — -end note] -

- - -
- - - - - - -
-

417. what does ctype::do_widen() return on failure

-

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: NAD - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [locale.ctype.virtuals].

-

View all issues with NAD status.

-

Discussion:

-

-The Effects and Returns clauses of the do_widen() member function of -the ctype facet fail to specify the behavior of the function on failure. -That the function may not be able to simply cast the narrow character -argument to the type of the result since doing so may yield the wrong value -for some wchar_t encodings. Popular implementations of ctype<wchar_t> that -use mbtowc() and UTF-8 as the native encoding (e.g., GNU glibc) will fail -when the argument's MSB is set. There is no way for the the rest of locale -and iostream to reliably detect this failure. -

-

[Kona: This is a real problem. Widening can fail. It's unclear - what the solution should be. Returning WEOF works for the wchar_t - specialization, but not in general. One option might be to add a - default, like narrow. But that's an incompatible change. - Using traits::eof might seem like a good idea, but facets - don't have access to traits (a recurring problem). We could - have widen throw an exception, but that's a scary option; - existing library components aren't written with the assumption - that widen can throw.]

- - -

[ -2009-07 Frankfurt -]

- - -

-NAD. The behavior is specified for all of the facets that an -implementation is required to provide, for the basic character set. -

- - - -

Proposed resolution:

- - - - -
-

418. exceptions thrown during iostream cleanup

-

Section: 27.5.3.1.6 [ios::Init] Status: NAD - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [ios::Init].

-

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-

Discussion:

-

-The dtor of the ios_base::Init object is supposed to call flush() on the -6 standard iostream objects cout, cerr, clog, wcout, -wcerr, and wclog. -This call may cause an exception to be thrown. -

- -

-17.4.4.8, p3 prohibits all library destructors from throwing exceptions. -

- -

-The question is: What should this dtor do if one or more of these calls -to flush() ends up throwing an exception? This can happen quite easily -if one of the facets installed in the locale imbued in the iostream -object throws. -

-

[Kona: We probably can't do much better than what we've got, so - the LWG is leaning toward NAD. At the point where the standard - stream objects are being cleaned up, the usual error reporting - mechanism are all unavailable. And exception from flush at this - point will definitely cause problems. A quality implementation - might reasonably swallow the exception, or call abort, or do - something even more drastic.]

- - -

[ -See 397 and 622 for related issues. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-Moved to NAD, no consensus for change. -

- - - -

Proposed resolution:

- - - - -
-

421. is basic_streambuf copy-constructible?

-

Section: 27.6.3.1 [streambuf.cons] Status: NAD - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [streambuf.cons].

-

View all issues with NAD status.

-

Discussion:

-

-The reflector thread starting with c++std-lib-11346 notes that the class -template basic_streambuf, along with basic_stringbuf and basic_filebuf, -is copy-constructible but that the semantics of the copy constructors -are not defined anywhere. Further, different implementations behave -differently in this respect: some prevent copy construction of objects -of these types by declaring their copy ctors and assignment operators -private, others exhibit undefined behavior, while others still give -these operations well-defined semantics. -

- -

-Note that this problem doesn't seem to be isolated to just the three -types mentioned above. A number of other types in the library section -of the standard provide a compiler-generated copy ctor and assignment -operator yet fail to specify their semantics. It's believed that the -only types for which this is actually a problem (i.e. types where the -compiler-generated default may be inappropriate and may not have been -intended) are locale facets. See issue 439. -

- -

[ -2009-07 Frankfurt -]

- - -

-NAD. Option B is already in the Working Draft. -

- - - -

Proposed resolution:

-

-27.5.2 [lib.streambuf]: Add into the synopsis, public section, just above the destructor declaration: -

- -
-
-basic_streambuf(const basic_streambuf& sb);
-basic_streambuf& operator=(const basic_streambuf& sb);
-
-
- -

Insert after 27.5.2.1, paragraph 2:

-
-
-basic_streambuf(const basic_streambuf& sb);
-
- -

Constructs a copy of sb.

-

Postcondtions:

-
-                eback() == sb.eback()
-                gptr()  == sb.gptr()
-                egptr() == sb.egptr()
-                pbase() == sb.pbase()
-                pptr()  == sb.pptr()
-                epptr() == sb.epptr()
-                getloc() == sb.getloc()
-
- -
-basic_streambuf& operator=(const basic_streambuf& sb);
-
- -

Assigns the data members of sb to this.

- -

Postcondtions:

-
-                eback() == sb.eback()
-                gptr()  == sb.gptr()
-                egptr() == sb.egptr()
-                pbase() == sb.pbase()
-                pptr()  == sb.pptr()
-                epptr() == sb.epptr()
-                getloc() == sb.getloc()
-
- -

Returns: *this.

-
- -

27.7.1 [lib.stringbuf]:

- -

Option A:

- -
-

Insert into the basic_stringbuf synopsis in the private section:

- -
-basic_stringbuf(const basic_stringbuf&);             // not defined
-basic_stringbuf& operator=(const basic_stringbuf&);  // not defined
-
-
- -

Option B:

- -
-

Insert into the basic_stringbuf synopsis in the public section:

- -
-basic_stringbuf(const basic_stringbuf& sb);
-basic_stringbuf& operator=(const basic_stringbuf& sb);
-
- -

27.7.1.1, insert after paragraph 4:

- -
basic_stringbuf(const basic_stringbuf& sb);
- -

-Constructs an independent copy of sb as if with sb.str(), and with the openmode that sb was constructed with. -

- -

Postcondtions:

-
-               str() == sb.str()
-               gptr()  - eback() == sb.gptr()  - sb.eback()
-               egptr() - eback() == sb.egptr() - sb.eback()
-               pptr()  - pbase() == sb.pptr()  - sb.pbase()
-               getloc() == sb.getloc()
-
- -

-Note: The only requirement on epptr() is that it point beyond the initialized range if an -output sequence exists. There is no requirement that epptr() - pbase() == sb.epptr() - sb.pbase(). -

- -
basic_stringbuf& operator=(const basic_stringbuf& sb);
-

-After assignment the basic_stringbuf has the same state as if it were initially copy constructed -from sb, except that the basic_stringbuf is allowed to retain any excess capacity it -might have, which may in turn effect the value of epptr(). -

-
- -

27.8.1.1 [lib.filebuf]

- -

Insert at the bottom of the basic_filebuf synopsis:

- -
-
-private:
-  basic_filebuf(const basic_filebuf&);             // not defined
-  basic_filebuf& operator=(const basic_filebuf&);  // not defined
-
-
-

[Kona: this is an issue for basic_streambuf itself and for its - derived classes. We are leaning toward allowing basic_streambuf to - be copyable, and specifying its precise semantics. (Probably the - obvious: copying the buffer pointers.) We are less sure whether - the streambuf derived classes should be copyable. Howard will - write up a proposal.]

- - -

[Sydney: Dietmar presented a new argument against basic_streambuf - being copyable: it can lead to an encapsulation violation. filebuf - inherits from streambuf. Now suppose you inherit a my_hijacking_buf - from streambuf. You can copy the streambuf portion of a filebuf to a - my_hijacking_buf, giving you access to the pointers into the - filebuf's internal buffer. Perhaps not a very strong argument, but - it was strong enough to make people nervous. There was weak - preference for having streambuf not be copyable. There was weak - preference for having stringbuf not be copyable even if streambuf - is. Move this issue to open for now. -]

- - -

[ -2007-01-12, Howard: -Rvalue Reference Recommendations for Chapter 27 -recommends protected copy constructor and assignment for basic_streambuf with the same semantics -as would be generated by the compiler. These members aid in derived classes implementing move semantics. -A protected copy constructor and copy assignment operator do not expose encapsulation more so than it is -today as each data member of a basic_streambuf is already both readable and writable by derived -classes via various get/set protected member functions (eback(), setp(), etc.). Rather -a protected copy constructor and copy assignment operator simply make the job of derived classes implementing -move semantics less tedious and error prone. -]

- - - - -

Rationale:

-

-27.5.2 [lib.streambuf]: The proposed basic_streambuf copy constructor -and assignment operator are the same as currently implied by the lack -of declarations: public and simply copies the data members. This -resolution is not a change but a clarification of the current -standard. -

- -

-27.7.1 [lib.stringbuf]: There are two reasonable options: A) Make -basic_stringbuf not copyable. This is likely the status-quo of -current implementations. B) Reasonable copy semantics of -basic_stringbuf can be defined and implemented. A copyable -basic_streambuf is arguably more useful than a non-copyable one. This -should be considered as new functionality and not the fixing of a -defect. If option B is chosen, ramifications from issue 432 are taken -into account. -

- -

-27.8.1.1 [lib.filebuf]: There are no reasonable copy semantics for -basic_filebuf. -

- - - - - - -
-

424. normative notes

-

Section: 17.5.1.2 [structure.summary] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

- -

-The text in 17.3.1.1, p1 says: -
- -"Paragraphs labelled "Note(s):" or "Example(s):" are informative, other -paragraphs are normative." -
- -The library section makes heavy use of paragraphs labeled "Notes(s)," -some of which are clearly intended to be normative (see list 1), while -some others are not (see list 2). There are also those where the intent -is not so clear (see list 3). -

- -List 1 -- Examples of (presumably) normative Notes: -
- -20.7.9.1 [allocator.members], p3,
-20.7.9.1 [allocator.members], p10,
-21.4.2 [string.cons], p11,
-22.3.1.2 [locale.cons], p11,
-23.3.3.4 [deque.modifiers], p2,
-25.4.7 [alg.min.max], p3,
-26.4.6 [complex.ops], p15,
-27.6.3.4.3 [streambuf.virt.get], p7.
-
- -List 2 -- Examples of (presumably) informative Notes: -
- -18.6.1.3 [new.delete.placement], p3,
-21.4.6.6 [string::replace], p14,
-22.4.1.4.2 [locale.codecvt.virtuals], p3,
-25.2.4 [alg.foreach], p4,
-26.4.5 [complex.member.ops], p1,
-27.5.3.5 [ios.base.storage], p6.
-
- -List 3 -- Examples of Notes that are not clearly either normative -or informative: -
- -22.3.1.2 [locale.cons], p8,
-22.3.1.5 [locale.statics], p6,
-27.6.3.4.5 [streambuf.virt.put], p4.
-
- -None of these lists is meant to be exhaustive. -

- -

[Definitely a real problem. The big problem is there's material - that doesn't quite fit any of the named paragraph categories - (e.g. Effects). Either we need a new kind of named - paragraph, or we need to put more material in unnamed paragraphs - jsut after the signature. We need to talk to the Project Editor - about how to do this. -]

- - -

[ -Bellevue: Specifics of list 3: First 2 items correct in std (22.1.1.2, -22.1.1.5) Third item should be non-normative (27.5.2.4.5), which Pete -will handle editorially. -]

- - -

[ -post San Francisco: Howard: reopened, needs attention. -]

- - -

[Pete: I changed the paragraphs marked "Note" and "Notes" to use "Remark" and "Remarks". -Fixed as editorial. This change has been in the WD since the post-Redmond mailing, in 2004. -Recommend NAD.]

- - -

[ -Batavia: We feel that the references in List 2 above should be changed from Remarks -to Notes. We also feel that those items in List 3 need to be double checked for -the same change. Alan and Pete to review. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-A spot-check of List 2 suggests the issue is still relevant, -and a review of List 3 still seems called-for. -

-

-Move to NAD Editorial. -

-
- - - -

Proposed resolution:

- - - - -
-

429. typo in basic_ios::clear(iostate)

-

Section: 27.5.5.4 [iostate.flags] Status: Dup - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [iostate.flags].

-

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-

Duplicate of: 412

-

Discussion:

-

- -The Effects clause in 27.4.4.3, p5 describing the effects of a call to -the ios_base member function clear(iostate state) says that the function -only throws if the respective bits are already set prior to the function -call. That's obviously not the intent. If it was, a call to clear(badbit) -on an object for which (rdstate() == goodbit && exceptions() == badbit) -holds would not result in an exception being thrown. - -

- -

Proposed resolution:

-

- -The text ought to be changed from -
- -"If (rdstate() & exceptions()) == 0, returns. ..." -
- -to -
- -"If (state & exceptions()) == 0, returns. ..." -

- - -

Rationale:

- - - - - - -
-

433. Contradiction in specification of unexpected()

-

Section: D.8.4 [unexpected] Status: NAD - Submitter: Vyatcheslav Sysoltsev Opened: 2003-09-29 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-Clause 15.5.2 [except.unexpected] paragraph 1 says that "void unexpected(); -is called (18.7.2) immediately after completing the stack unwinding -for the former function", but 18.7.2.4 (Effects) says that "void -unexpected(); . . . Calls the unexpected_handler function in effect -immediately after evaluating the throwexpression (18.7.2.2),". Isn't -here a contradiction: 15.5.2 requires stack have been unwound when in -void unexpected() and therefore in unexpected_handler but 18.7.2.4 -claims that unexpected_handler is called "in effect immediately" after -evaluation of throw expression is finished, so there is no space left -for stack to be unwound therefore? I think the phrase "in effect -immediately" should be removed from the standard because it brings -ambiguity in understanding. -

- - -

Proposed resolution:

- - -

Rationale:

-

There is no contradiction. The phrase "in effect immediately" is - just to clarify which handler is to be called.

- - - - - -
-

437. Formatted output of function pointers is confusing

-

Section: 27.7.3.6.2 [ostream.inserters.arithmetic] Status: NAD - Submitter: Ivan Godard Opened: 2003-10-24 Last modified: 2015-04-08

-

View all other issues in [ostream.inserters.arithmetic].

-

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-

Discussion:

-

-Given: -

-
-void f(int) {}
-void(*g)(int) = f;
-cout << g;
-
- -

-(with the expected #include and usings), the value printed is a rather -surprising "true". Rather useless too. -

- -

The standard defines:

- -
ostream& operator<<(ostream&, void*);
- -

which picks up all data pointers and prints their hex value, but does -not pick up function pointers because there is no default conversion -from function pointer to void*. Absent that, we fall back to legacy -conversions from C and the function pointer is converted to bool. -

- -

There should be an analogous inserter that prints the address of a - function pointer.

- - -

Proposed resolution:

- - -

Rationale:

-

This is indeed a wart, but there is no good way to solve it. C - doesn't provide a portable way of outputting the address of a - function point either.

- - - - - -
-

439. Should facets be copyable?

-

Section: 22.4 [locale.categories] Status: NAD - Submitter: Matt Austern Opened: 2003-11-02 Last modified: 2015-04-08

-

View all other issues in [locale.categories].

-

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-

Discussion:

-

The following facets classes have no copy constructors described in - the standard, which, according to the standard, means that they are - supposed to use the compiler-generated defaults. Default copy - behavior is probably inappropriate. We should either make these - classes uncopyable or else specify exactly what their constructors do.

- -

Related issue: 421.

- -
-        ctype_base
-        ctype
-        ctype_byname
-        ctype<char>
-        ctype_byname<char>
-        codecvt_base
-        codecvt
-        codecvt_byname
-        num_get
-        num_put
-        numpunct
-        numpunct_byname
-        collate
-        collate_byname
-        time_base
-        time_get
-        time_get_byname
-        time_put
-        time_put_byname
-        money_get
-        money_put
-        money_base
-        moneypunct
-        moneypunct_byname
-        messages_base
-        messages
-        messages_byname
-
- - - -

Proposed resolution:

- - -

Rationale:

-

The copy constructor in the base class is private.

- - - - - -
-

440. Should std::complex use unqualified transcendentals?

-

Section: 26.4.8 [complex.transcendentals] Status: NAD - Submitter: Matt Austern Opened: 2003-11-05 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-Operations like pow and exp on -complex<T> are typically implemented in terms of -operations like sin and cos on T. -Should implementations write this as std::sin, or as plain -unqualified sin? -

- -

The issue, of course, is whether we want to use -argument-dependent lookup in the case where T is a -user-defined type. This is similar to the issue of valarray -transcendentals, as discussed in issue 226.

- -

This issue differs from valarray transcendentals in two important -ways. First, "the effect of instantiating the template -complex for types other than float, double or long double is -unspecified." (26.4.1 [complex.syn]) Second, the standard does not -dictate implementation, so there is no guarantee that a particular -real math function is used in the implementation of a particular -complex function.

- - - -

Proposed resolution:

- - -

Rationale:

-

If you instantiate std::complex for user-defined types, all bets -are off.

- - - - - -
-

446. Iterator equality between different containers

-

Section: 24.2 [iterator.requirements], 23.2 [container.requirements] Status: NAD Editorial - Submitter: Andy Koenig Opened: 2003-12-16 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

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-

Discussion:

-

-What requirements does the standard place on equality comparisons between -iterators that refer to elements of different containers. For example, if -v1 and v2 are empty vectors, is v1.end() == v2.end() -allowed to yield true? Is it allowed to throw an exception? -

- -

-The standard appears to be silent on both questions. -

-

[Sydney: The intention is that comparing two iterators from -different containers is undefined, but it's not clear if we say that, -or even whether it's something we should be saying in clause 23 or in -clause 24. Intuitively we might want to say that equality is defined -only if one iterator is reachable from another, but figuring out how -to say it in any sensible way is a bit tricky: reachability is defined -in terms of equality, so we can't also define equality in terms of -reachability. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-Daniel volunteered to work on this. -

- -

[ -2009-09-20 Daniel provided wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as Open. Alisdair has volunteered to refine the wording. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

-

-Insert a new paragraph between 24.2 [iterator.requirements]/7+8: -

- -
-

-[..] The result of the application of functions in the library to invalid -ranges is undefined. -

- -

The result of directly or indirectly evaluating any comparison function -or the binary - operator with two iterator values as arguments that -were obtained -from two different ranges r1 and r2 (including their past-the-end values) which -are not subranges of one common range is undefined, unless explicitly -described otherwise. -

- -
- - - - - - -
-

447. Wrong template argument for time facets

-

Section: 22.3.1.1.1 [locale.category] Status: Dup - Submitter: Pete Becker Opened: 2003-12-26 Last modified: 2015-04-08

-

View all other issues in [locale.category].

-

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-

Duplicate of: 327

-

Discussion:

-

-22.1.1.1.1/4, table 52, "Required Instantiations", lists, among others: -

-
-    time_get<char,InputIterator>
-    time_get_byname<char,InputIterator>
-    time_get<wchar_t,OutputIterator>
-    time_get_byname<wchar_t,OutputIterator>
-
- -

-The second argument to the last two should be InputIterator, not -OutputIterator. -

- - -

Proposed resolution:

-

-Change the second template argument to InputIterator. -

- - -

Rationale:

- - - - - - -
-

450. set::find is inconsistent with associative container requirements

-

Section: 23.4.6 [set] Status: Dup - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

View all other issues in [set].

-

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-

Duplicate of: 214

-

Discussion:

-

map/multimap have:

- -
-    iterator find(const key_type& x) const;
-    const_iterator find(const key_type& x) const;
-
- -

-which is consistent with the table of associative container requirements. -But set/multiset have: -

-
-    iterator find(const key_type&) const;
-
- -

-set/multiset should look like map/multimap, and honor the requirements -table, in this regard. -

- - -

Proposed resolution:

- - -

Rationale:

- - - - - - -
-

451. Associative erase should return an iterator

-

Section: 23.2.4 [associative.reqmts], 23.4 [associative] Status: Dup - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 130

-

Discussion:

-

map/multimap/set/multiset have:

-
-    void erase(iterator);
-    void erase(iterator, iterator);
-
- -

But there's no good reason why these can't return an iterator, as for -vector/deque/list:

-
-    iterator erase(iterator);
-    iterator erase(iterator, iterator);
-
- - - -

Proposed resolution:

-

-Informally: The table of associative container requirements, and the -relevant template classes, should return an iterator designating the -first element beyond the erased subrange. -

- - -

Rationale:

- - - - - - -
-

452. locale::combine should be permitted to generate a named locale

-

Section: 22.3.1.3 [locale.members] Status: NAD - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

View all other issues in [locale.members].

-

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-

Discussion:

-
-template<class Facet>
-    locale::combine(const locale&) const;
-
-

-is obliged to create a locale that has no name. This is overspecification -and overkill. The resulting locale should follow the usual rules -- it -has a name if the locale argument has a name and Facet is one of the -standard facets. -

- -

[ - Sydney and post-Sydney (see c++std-lib-13439, c++std-lib-13440, - c++std-lib-13443): agreed that it's overkill to say that the locale - is obligated to be nameless. However, we also can't require it to - have a name. At the moment, locale names are based on categories - and not on individual facets. If a locale contains two different - facets of different names from the same category, then this would - not fit into existing naming schemes. We need to give - implementations more freedom. Bill will provide wording. -]

- - - - -

Rationale:

-

After further discussion the LWG decided to close this as NAD. - The fundamental problem is that names right now are per-category, - not per-facet. The combine member function works at the - wrong level of granularity.

- - - - - -
-

454. basic_filebuf::open should accept wchar_t names

-

Section: 27.9.1.4 [filebuf.members] Status: NAD - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

View all other issues in [filebuf.members].

-

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-

Duplicate of: 105

-

Discussion:

-
-    basic_filebuf *basic_filebuf::open(const char *, ios_base::open_mode);
-
- -

should be supplemented with the overload:

- -
-    basic_filebuf *basic_filebuf::open(const wchar_t *, ios_base::open_mode);
-
- -

-Depending on the operating system, one of these forms is fundamental and -the other requires an implementation-defined mapping to determine the -actual filename. -

- -

[Sydney: Yes, we want to allow wchar_t filenames. Bill will - provide wording.]

- - -

[ -In Toronto we noted that this is issue 5 from -N1569. -]

- -

-How does this interact with the newly-defined character types, and how -do we avoid interface explosion considering std::string overloads that -were added? Propose another solution that is different than the -suggestion proposed by PJP. -

-

-Suggestion is to make a member template function for basic_string (for -char, wchar_t, u16char, u32char instantiations), and then just keep a -const char* member. -

-

-Goal is to do implicit conversion between character string literals to -appropriate basic_string type. Not quite sure if this is possible. -

-

-Implementors are free to add specific overloads for non-char character -types. -

- -

[ -Martin adds pre-Sophia Antipolis: -]

- - -

-Please see issue 454: problems and solutions. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Beman is concerned that making these changes to basic_filebuf is not -usefully changed unless fstream is also changed; this also only handles -wchar_t and not other character types. -

-

-The TR2 filesystem library is a more complete solution, but is not available soon. -

-
- -

[ -Martin adds: please reference -N2683 for -problems and solutions. -]

- - - - -

Proposed resolution:

- -

Change from:

-
-
-basic_filebuf<charT,traits>* open(
-    const char* s,
-    ios_base::openmode mode );
-
- -

-Effects: If is_open() != false, returns a null pointer. -Otherwise, initializes the filebuf as required. It then -opens a file, if possible, whose name is the NTBS s ("as if" -by calling std::fopen(s,modstr)).

-
- -

to:

- -
-
-basic_filebuf<charT,traits>* open(
-    const char* s,
-    ios_base::openmode mode );
-
-basic_filebuf<charT,traits>* open(
-    const wchar_t* ws,
-    ios_base::openmode mode );
-
- -

-Effects: If is_open() != false, returns a null pointer. -Otherwise, initializes the filebuf as required. It then -opens a file, if possible, whose name is the NTBS s ("as if" -by calling std::fopen(s,modstr)). -For the second signature, the NTBS s is determined from the -WCBS ws in an implementation-defined manner. -

- -

-(NOTE: For a system that "naturally" represents a filename -as a WCBS, the NTBS s in the first signature may instead -be mapped to a WCBS; if so, it follows the same mapping -rules as the first argument to open.) -

-
- - - -

Rationale:

-

-Slightly controversial, but by a 7-1 straw poll the LWG agreed to move -this to Ready. The controversy was because the mapping between wide -names and files in a filesystem is implementation defined. The -counterargument, which most but not all LWG members accepted, is that -the mapping between narrow files names and files is also -implemenation defined.

- -

[Lillehammer: Moved back to "open" status, at Beman's urging. -(1) Why just basic_filebuf, instead of also basic_fstream (and -possibly other things too). (2) Why not also constructors that take -std::basic_string? (3) We might want to wait until we see Beman's -filesystem library; we might decide that it obviates this.]

- - -

[ -post Bellevue: -]

- - -
-

-Move again to Ready. -

-

-There is a timing issue here. Since the filesystem library will not be -in C++0x, this should be brought forward. This solution would remain -valid in the context of the proposed filesystem. -

-

-This issue has been kicking around for a while, and the wchar_t addition -alone would help many users. Thus, we suggest putting this on the -reflector list with an invitation for someone to produce proposed -wording that covers basic_fstream. In the meantime, we suggest that the -proposed wording be adopted as-is. -

-

-If more of the Lillehammer questions come back, they should be -introduced as separate issues. -

-
- -

[ -San Francisco: -]

- - -

-Some existing implementations provide overload already. Expected -filesystem "path" object overloads neatly, without surprises; implying -NAD. -

- - - - - - - -
-

458. 24.1.5 contains unintended limitation for operator-

-

Section: 24.2.7 [random.access.iterators] Status: NAD - Submitter: Daniel Frey Opened: 2004-02-27 Last modified: 2015-04-08

-

View all other issues in [random.access.iterators].

-

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-

Discussion:

-

-In 24.1.5 [lib.random.access.iterators], table 76 the operational -semantics for the expression "r -= n" are defined as "return r += -n". -This means, that the expression -n must be valid, which is not the case -for unsigned types. -

- -

[ -Sydney: Possibly not a real problem, since difference type is required -to be a signed integer type. However, the wording in the standard may -be less clear than we would like. -]

- - -

[ -Post Summit Alisdair adds: -]

- - -
-

-This issue refers to a requirements table we have removed. -

-

-The issue might now relate to 24.2.7 [random.access.iterators] p5. -However, the rationale in the issue already recognises that the -difference_type must be signed, so this really looks NAD. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-We agree with Alisdair's observations. -

-

-Move to NAD. -

-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-Need to look at again without concepts. -

-

-There was a question about this phrase in the discussion: "the -expression -n must be valid, which is not the case for unsigned types." -If n is an object of the iterator difference_type (eg ptrdiff_t), -then it is never unsigned. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-The group reviewed the wording in the draft and agreed that n is of -difference type, the difference type is signed, and the current wording -is correct. Moved to NAD. -

- - - -

Proposed resolution:

-

-To remove this limitation, I suggest to change the -operational semantics for this column to: -

-
-    { Distance m = n;
-      if (m >= 0)
-        while (m--) --r;
-      else
-        while (m++) ++r;
-      return r; }
-
- - - - - - -
-

459. Requirement for widening in stage 2 is overspecification

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: NAD - Submitter: Martin Sebor Opened: 2004-03-16 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

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-

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-

Discussion:

-

When parsing strings of wide-character digits, the standard - requires the library to widen narrow-character "atoms" and compare - the widened atoms against the characters that are being parsed. - Simply narrowing the wide characters would be far simpler, and - probably more efficient. The two choices are equivalent except in - convoluted test cases, and many implementations already ignore the - standard and use narrow instead of widen.

- -

-First, I disagree that using narrow() instead of widen() would -necessarily have unfortunate performance implications. A possible -implementation of narrow() that allows num_get to be implemented -in a much simpler and arguably comparably efficient way as calling -widen() allows, i.e. without making a virtual call to do_narrow every -time, is as follows: -

- -
-  inline char ctype<wchar_t>::narrow (wchar_t wc, char dflt) const
-  {
-      const unsigned wi = unsigned (wc);
-
-      if (wi > UCHAR_MAX)
-          return typeid (*this) == typeid (ctype<wchar_t>) ?
-                 dflt : do_narrow (wc, dflt);
-
-      if (narrow_ [wi] < 0) {
-         const char nc = do_narrow (wc, dflt);
-         if (nc == dflt)
-             return dflt;
-         narrow_ [wi] = nc;
-      }
-
-      return char (narrow_ [wi]);
-  }
-
- -

-Second, I don't think the change proposed in the issue (i.e., to use -narrow() instead of widen() during Stage 2) would be at all -drastic. Existing implementations with the exception of libstdc++ -currently already use narrow() so the impact of the change on programs -would presumably be isolated to just a single implementation. Further, -since narrow() is not required to translate alternate wide digit -representations such as those mentioned in issue 303 to -their narrow equivalents (i.e., the portable source characters '0' -through '9'), the change does not necessarily imply that these -alternate digits would be treated as ordinary digits and accepted as -part of numbers during parsing. In fact, the requirement in 22.4.1.1.2 [locale.ctype.virtuals], p13 forbids narrow() to translate an alternate -digit character, wc, to an ordinary digit in the basic source -character set unless the expression -(ctype<charT>::is(ctype_base::digit, wc) == true) holds. This in -turn is prohibited by the C standard (7.25.2.1.5, 7.25.2.1.5, and -5.2.1, respectively) for charT of either char or wchar_t. -

- -

[Sydney: To a large extent this is a nonproblem. As long as -you're only trafficking in char and wchar_t we're only dealing with a -stable character set, so you don't really need either 'widen' or -'narrow': can just use literals. Finally, it's not even clear whether -widen-vs-narrow is the right question; arguably we should be using -codecvt instead.]

- - -

[ -2009-07 Frankfurt -]

- - -

-NAD. The standard is clear enough as written. -

- - - -

Proposed resolution:

-

Change stage 2 so that implementations are permitted to use either -technique to perform the comparison:

-
    -
  1. call widen on the atoms and compare (either by using - operator== or char_traits<charT>::eq) the input with - the widened atoms, or
    2. -
  2. call narrow on the input and compare the narrow input - with the atoms
    3. -
  3. do (1) or (2) only if charT is not char or wchar_t, - respectively; i.e., avoid calling widen or narrow - if it the source and destination types are the same
    4. -
- - - - - -
-

462. Destroying objects with static storage duration

-

Section: 3.6.3 [basic.start.term], 18.4 [cstdint] Status: NAD - Submitter: Bill Plauger Opened: 2004-03-23 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-3.6.3 Termination spells out in detail the interleaving of static -destructor calls and calls to functions registered with atexit. To -match this behavior requires intimate cooperation between the code -that calls destructors and the exit/atexit machinery. The former -is tied tightly to the compiler; the latter is a primitive mechanism -inherited from C that traditionally has nothing to do with static -construction and destruction. The benefits of intermixing destructor -calls with atexit handler calls is questionable at best, and very -difficult to get right, particularly when mixing third-party C++ -libraries with different third-party C++ compilers and C libraries -supplied by still other parties. -

- -

-I believe the right thing to do is defer all static destruction -until after all atexit handlers are called. This is a change in -behavior, but one that is likely visible only to perverse test -suites. At the very least, we should permit deferred destruction -even if we don't require it. -

- -

[If this is to be changed, it should probably be changed by CWG. - At this point, however, the LWG is leaning toward NAD. Implementing - what the standard says is hard work, but it's not impossible and - most vendors went through that pain years ago. Changing this - behavior would be a user-visible change, and would break at least - one real application.]

- - -

[ -Batavia: Send to core with our recommendation that we should permit deferred -destruction but not require it. -]

- - -

[ -Howard: The course of action recommended in Batavia would undo LWG -issue 3 and break current code implementing the "phoenix -singleton". Search the net for "phoenix singleton atexit" to get a feel -for the size of the adverse impact this change would have. Below is -sample code which implements the phoenix singleton and would break if -atexit is changed in this way: -]

- - -
-#include <cstdlib>
-#include <iostream>
-#include <type_traits>
-#include <new>
-
-class A
-{
-    bool alive_;
-    A(const A&);
-    A& operator=(const A&);
-public:
-    A() : alive_(true) {std::cout << "A()\n";}
-    ~A() {alive_ = false; std::cout << "~A()\n";}
-    void use()
-    {
-        if (alive_)
-            std::cout << "A is alive\n";
-        else
-            std::cout << "A is dead\n";
-    }
-};
-
-void deallocate_resource();
-
-// This is the phoenix singleton pattern
-A& get_resource(bool create = true)
-{
-    static std::aligned_storage<sizeof(A), std::alignment_of<A>::value>::type buf;
-    static A* a;
-    if (create)
-    {
-        if (a != (A*)&buf)
-        {
-            a = ::new (&buf) A;
-            std::atexit(deallocate_resource);
-        }
-    }
-    else
-    {
-        a->~A();
-        a = (A*)&buf + 1;
-    }
-    return *a;
-}
-
-void deallocate_resource()
-{
-    get_resource(false);
-}
-
-void use_A(const char* message)
-{
-    A& a = get_resource();
-    std::cout << "Using A " << message << "\n";
-    a.use();
-}
-
-struct B
-{
-    ~B() {use_A("from ~B()");}
-};
-
-B b;
-
-int main()
-{
-    use_A("from main()");
-}
-
- -

-The correct output is: -

- -
-A()
-Using A from main()
-A is alive
-~A()
-A()
-Using A from ~B()
-A is alive
-~A()
-
- -

[ -Bellevue: Confirmed no interaction with quick_exit. -Strong feeling against mandating the change. Leaning towards NAD rather than permitting the change, -as this would make common implementations of pheonix-singleton pattern implementation defined, as noted by Howard. -Bill agrees issue is no longer serious, and accepts NAD. -]

- - - - -

Proposed resolution:

-

-

- - - - - -
-

463. auto_ptr usability issues

-

Section: X [auto.ptr] Status: NAD - Submitter: Rani Sharoni Opened: 2003-12-07 Last modified: 2015-04-08

-

View all other issues in [auto.ptr].

-

View all issues with NAD status.

-

Discussion:

- -

-TC1 CWG DR #84 effectively made the template<class Y> operator auto_ptr<Y>() -member of auto_ptr (20.4.5.3/4) obsolete. -

- -

-The sole purpose of this obsolete conversion member is to enable copy -initialization base from r-value derived (or any convertible types like -cv-types) case: -

-
-#include <memory>
-using std::auto_ptr;
-
-struct B {};
-struct D : B {};
-
-auto_ptr<D> source();
-int sink(auto_ptr<B>);
-int x1 = sink( source() ); // #1 EDG - no suitable copy constructor
-
- -

-The excellent analysis of conversion operations that was given in the final -auto_ptr proposal -(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1997/N1128.pdf) -explicitly specifies this case analysis (case 4). DR #84 makes the analysis -wrong and actually comes to forbid the loophole that was exploited by the -auto_ptr designers. -

- -

-I didn't encounter any compliant compiler (e.g. EDG, GCC, BCC and VC) that -ever allowed this case. This is probably because it requires 3 user defined -conversions and in fact current compilers conform to DR #84. -

- -

-I was surprised to discover that the obsolete conversion member actually has -negative impact of the copy initialization base from l-value derived -case:

-
-auto_ptr<D> dp;
-int x2 = sink(dp); // #2 EDG - more than one user-defined conversion applies
-
- -

-I'm sure that the original intention was allowing this initialization using -the template<class Y> auto_ptr(auto_ptr<Y>& a) constructor (20.4.5.1/4) but -since in this copy initialization it's merely user defined conversion (UDC) -and the obsolete conversion member is UDC with the same rank (for the early -overloading stage) there is an ambiguity between them. -

- -

-Removing the obsolete member will have impact on code that explicitly -invokes it: -

-
-int y = sink(source().operator auto_ptr<B>());
-
- -

-IMHO no one ever wrote such awkward code and the reasonable workaround for -#1 is: -

-
-int y = sink( auto_ptr<B>(source()) );
-
- -

-I was even more surprised to find out that after removing the obsolete -conversion member the initialization was still ill-formed: -int x3 = sink(dp); // #3 EDG - no suitable copy constructor -

- -

-This copy initialization semantically requires copy constructor which means -that both template conversion constructor and the auto_ptr_ref conversion -member (20.4.5.3/3) are required which is what was explicitly forbidden in -DR #84. This is a bit amusing case in which removing ambiguity results with -no candidates. -

- -

-I also found exception safety issue with auto_ptr related to auto_ptr_ref: -

-
-int f(auto_ptr<B>, std::string);
-auto_ptr<B> source2();
-
-// string constructor throws while auto_ptr_ref
-// "holds" the pointer
-int x4 = f(source2(), "xyz"); // #4
-
- -

-The theoretic execution sequence that will cause a leak: -

-
    -
  1. call auto_ptr<B>::operator auto_ptr_ref<B>()
    2. -
  2. call string::string(char const*) and throw
    3. -
- -

-According to 20.4.5.3/3 and 20.4.5/2 the auto_ptr_ref conversion member -returns auto_ptr_ref<Y> that holds *this and this is another defect since -the type of *this is auto_ptr<X> where X might -be different from Y. Several library vendors (e.g. SGI) implement -auto_ptr_ref<Y> with Y* as member which -is much more reasonable. Other vendor implemented auto_ptr_ref as -defectively required and it results with awkward and catastrophic code: -int oops = sink(auto_ptr<B>(source())); // warning recursive on all control paths -

- -

-Dave Abrahams noticed that there is no specification saying that -auto_ptr_ref copy constructor can't throw. -

- -

-My proposal comes to solve all the above issues and significantly simplify -auto_ptr implementation. One of the fundamental requirements from -auto_ptr is that it can be constructed in an intuitive manner (i.e. -like ordinary pointers) but with strict ownership semantics which yield that source -auto_ptr in initialization must be non-const. My idea is to add additional -constructor template with sole propose to generate ill-formed, diagnostic -required, instance for const auto_ptr arguments during instantiation of -declaration. This special constructor will not be instantiated for other -types which is achievable using 14.8.2/2 (SFINAE). Having this constructor -in hand makes the constructor template<class Y> auto_ptr(auto_ptr<Y> const&) -legitimate since the actual argument can't be const yet non const r-value -are acceptable. -

- -

-This implementation technique makes the "private auxiliary class" -auto_ptr_ref obsolete and I found out that modern C++ compilers (e.g. EDG, -GCC and VC) consume the new implementation as expected and allow all -intuitive initialization and assignment cases while rejecting illegal cases -that involve const auto_ptr arguments. -

- -

The proposed auto_ptr interface:

- -
-namespace std {
-    template<class X> class auto_ptr {
-    public:
-        typedef X element_type;
-
-        // 20.4.5.1 construct/copy/destroy:
-        explicit auto_ptr(X* p=0) throw();
-        auto_ptr(auto_ptr&) throw();
-        template<class Y> auto_ptr(auto_ptr<Y> const&) throw();
-        auto_ptr& operator=(auto_ptr&) throw();
-        template<class Y> auto_ptr& operator=(auto_ptr<Y>) throw();
-        ~auto_ptr() throw();
-
-        // 20.4.5.2 members:
-        X& operator*() const throw();
-        X* operator->() const throw();
-        X* get() const throw();
-        X* release() throw();
-        void reset(X* p=0) throw();
-
-    private:
-        template<class U>
-        auto_ptr(U& rhs, typename
-unspecified_error_on_const_auto_ptr<U>::type = 0);
-    };
-}
-
- -

-One compliant technique to implement the unspecified_error_on_const_auto_ptr -helper class is using additional private auto_ptr member class template like -the following: -

-
-template<typename T> struct unspecified_error_on_const_auto_ptr;
-
-template<typename T>
-struct unspecified_error_on_const_auto_ptr<auto_ptr<T> const>
-{ typedef typename auto_ptr<T>::const_auto_ptr_is_not_allowed type; };
-
- -

-There are other techniques to implement this helper class that might work -better for different compliers (i.e. better diagnostics) and therefore I -suggest defining its semantic behavior without mandating any specific -implementation. IMO, and I didn't found any compiler that thinks otherwise, -14.7.1/5 doesn't theoretically defeat the suggested technique but I suggest -verifying this with core language experts. -

- -

Further changes in standard text:

-

Remove section 20.4.5.3

- -

Change 20.4.5/2 to read something like: -Initializing auto_ptr<X> from const auto_ptr<Y> will result with unspecified -ill-formed declaration that will require unspecified diagnostic.

- -

Change 20.4.5.1/4,5,6 to read:

- -
template<class Y> auto_ptr(auto_ptr<Y> const& a) throw();
-

4 Requires: Y* can be implicitly converted to X*.

-

5 Effects: Calls const_cast<auto_ptr<Y>&>(a).release().

-

6 Postconditions: *this holds the pointer returned from a.release().

- -

Change 20.4.5.1/10

-
-template<class Y> auto_ptr& operator=(auto_ptr<Y> a) throw();
-
-

-10 Requires: Y* can be implicitly converted to X*. The expression delete -get() is well formed. -

- -

LWG TC DR #127 is obsolete.

- -

-Notice that the copy constructor and copy assignment operator should remain -as before and accept non-const auto_ptr& since they have effect on the form -of the implicitly declared copy constructor and copy assignment operator of -class that contains auto_ptr as member per 12.8/5,10: -

-
-struct X {
-    // implicit X(X&)
-    // implicit X& operator=(X&)
-    auto_ptr<D> aptr_;
-};
-
- -

-In most cases this indicates about sloppy programming but preserves the -current auto_ptr behavior. -

- -

-Dave Abrahams encouraged me to suggest fallback implementation in case that -my suggestion that involves removing of auto_ptr_ref will not be accepted. -In this case removing the obsolete conversion member to auto_ptr<Y> and -20.4.5.3/4,5 is still required in order to eliminate ambiguity in legal -cases. The two constructors that I suggested will co exist with the current -members but will make auto_ptr_ref obsolete in initialization contexts. -auto_ptr_ref will be effective in assignment contexts as suggested in DR -#127 and I can't see any serious exception safety issues in those cases -(although it's possible to synthesize such). auto_ptr_ref<X> semantics will -have to be revised to say that it strictly holds pointer of type X and not -reference to an auto_ptr for the favor of cases in which auto_ptr_ref<Y> is -constructed from auto_ptr<X> in which X is different from -Y (i.e. assignment from r-value derived to base). -

- -

[Redmond: punt for the moment. We haven't decided yet whether we - want to fix auto_ptr for C++-0x, or remove it and replace it with - move_ptr and unique_ptr.]

- - -

[ -Oxford 2007: Recommend NAD. We're just going to deprecate it. It still works for simple use cases -and people know how to deal with it. Going forward unique_ptr is the recommended -tool. -]

- - -

[ -2007-11-09: Reopened at the request of David Abrahams, Alisdair Meredith and Gabriel Dos Reis. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-This is a complicated issue, so we agreed to defer discussion until -later in the week so that interested parties can read up on it. -

- -

[ -2009-10-04 Daniel adds: -]

- - -
-

-I suggest to close this issue as NAD. The reasons are two-fold: First, the -suggested proposed resolution uses no longer appropriate language means -to solve this issue, which has the effect that the recommended resolution is -another - but better - form of hack. Second, either following the suggested -resolution or the now more natural alternative via the added member set -

- -
-template<class Y> auto_ptr(auto_ptr<Y>&&) throw();
-template<class Y> auto_ptr& operator=(auto_ptr<Y>&&) throw();
-
- -

-would still have a non-zero probability to break user-code that actively -references auto_ptr_ref. This risk seems to indicate that a -decision which would not touch the current spec of auto_ptr at -all (but deprecating it) and instead recommending to use -unique_ptr for new code instead might have the best -cost-benefit ratio. IMO the current solution of 1100 can -be considered as an active user-support for this transition. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. Alisdair will open a new issue (1247) with -proposed wording to handle auto_ptr_ref. -

- - - -

Proposed resolution:

-

-Change the synopsis in X [auto.ptr]: -

- -
-namespace std { 
-  template <class Y> struct auto_ptr_ref {};
-
-  // exposition only
-  template <class T> struct constant_object;
-
-  // exposition only
-  template <class T>
-  struct cannot_transfer_ownership_from
-    : constant_object<T> {};
-
-  template <class X> class auto_ptr { 
-  public: 
-    typedef X element_type; 
-
-    // D.9.1.1 construct/copy/destroy: 
-    explicit auto_ptr(X* p =0) throw(); 
-    auto_ptr(auto_ptr&) throw(); 
-    template<class Y> auto_ptr(auto_ptr<Y> const&) throw(); 
-    auto_ptr& operator=(auto_ptr&) throw(); 
-    template<class Y> auto_ptr& operator=(auto_ptr<Y>&) throw();
-    auto_ptr& operator=(auto_ptr_ref<X> r) throw();
-    ~auto_ptr() throw(); 
-
-    // D.9.1.2 members: 
-    X& operator*() const throw();
-    X* operator->() const throw();
-    X* get() const throw();
-    X* release() throw();
-    void reset(X* p =0) throw();
-
-    // D.9.1.3 conversions:
-    auto_ptr(auto_ptr_ref<X>) throw();
-    template<class Y> operator auto_ptr_ref<Y>() throw();
-    template<class Y> operator auto_ptr<Y>() throw();
-
-    // exposition only
-    template<class U>
-    auto_ptr(U& rhs, typename cannot_transfer_ownership_from<U>::error = 0);
-  }; 
-
-  template <> class auto_ptr<void> 
-  { 
-  public: 
-    typedef void element_type; 
-  }; 
-
-}
-
- -

-Remove X [auto.ptr.conv]. -

- -

-Change X [auto.ptr], p3: -

- -

-The auto_ptr provides a semantics of strict ownership. An -auto_ptr owns the object it holds a pointer to. Copying an -auto_ptr copies the pointer and transfers ownership to the -destination. If more than one auto_ptr owns the same object at -the same time the behavior of the program is undefined. Templates -constant_object and cannot_transfer_ownership_from, -and the final constructor of auto_ptr are for exposition only. -For any types X and Y, initializing -auto_ptr<X> from const auto_ptr<Y> is -ill-formed, diagnostic required. [Note: The uses of -auto_ptr include providing temporary exception-safety for -dynamically allocated memory, passing ownership of dynamically allocated -memory to a function, and returning dynamically allocated memory from a -function. auto_ptr does not meet the CopyConstructible -and Assignable requirements for Standard Library container -elements and thus instantiating a Standard Library container with an -auto_ptr results in undefined behavior. -- end note] -

- -

-Change [auto.ptr.cons], p5: -

- -
-
-template<class Y> auto_ptr(auto_ptr<Y> const& a) throw();
-
-
-

-Requires: Y* can be implicitly converted to X*. -

-

-Effects: Calls const_cast<auto_ptr<Y>&>(a).release(). -

-

-Postconditions: *this holds the pointer returned from a.release(). -

-
-
- -

-Change [auto.ptr.cons], p10: -

- -
-
-template<class Y> auto_ptr& operator=(auto_ptr<Y>& a) throw();
-
-
-

-Requires: Y* can be implicitly converted to X*. -The expression delete get() is well formed. -

-

-Effects: Calls reset(a.release()). -

-

-Returns: *this. -

-
-
- - - - - - -
-

466. basic_string ctor should prevent null pointer error

-

Section: 21.4.1 [string.require] Status: NAD - Submitter: Daniel Frey Opened: 2004-06-10 Last modified: 2015-04-08

-

View all other issues in [string.require].

-

View all issues with NAD status.

-

Discussion:

-

-Today, my colleagues and me wasted a lot of time. After some time, I -found the problem. It could be reduced to the following short example: -

- -
-  #include <string>
-  int main() { std::string( 0 ); }
-
- -

The problem is that the tested compilers (GCC 2.95.2, GCC 3.3.1 and -Comeau online) compile the above without errors or warnings! The -programs (at least for the GCC) resulted in a SEGV.

- -

I know that the standard explicitly states that the ctor of string -requires a char* which is not zero. STLs could easily detect the above -case with a private ctor for basic_string which takes a single 'int' -argument. This would catch the above code at compile time and would not -ambiguate any other legal ctors.

- -

[Redmond: No great enthusiasm for doing this. If we do, - however, we want to do it for all places that take charT* - pointers, not just the single-argument constructor. The other - question is whether we want to catch this at compile time (in which - case we catch the error of a literal 0, but not an expression whose - value is a null pointer), at run time, or both. - Recommend NAD. Relegate this functionality to debugging implementations.]

- - -

[ -Post Summit: Alisdair requests this be re-opened as several new language facilities are -designed to solve exactly this kind of problem. -]

- - -

[ -Batavia (2009-05): -]

- -

-We are unable to achieve consensus on an approach to a resolution. -There is some sentiment for treating this as a QOI matter. -It is also possible -that when string is brought into the concepts world, -this issue might be addressed in that context. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-We considered three options: -

- -
    -
  • The proposed resolution.
    • -
  • NAD
    • -
  • Interpret a null pointer as the empty string.
    • -
- -

-The consensus was NAD. -

-
- - - -

Proposed resolution:

-

-Add to the synopsis in 21.4 [basic.string] -

- -
-basic_string( nullptr_t ) = delete;
-
- - - - - -
-

470. accessing containers from their elements' special functions

-

Section: 23 [containers] Status: NAD - Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2015-04-08

-

View other active issues in [containers].

-

View all other issues in [containers].

-

View all issues with NAD status.

-

Discussion:

- -

-The standard doesn't prohibit the destructors (or any other special -functions) of containers' elements invoked from a member function -of the container from "recursively" calling the same (or any other) -member function on the same container object, potentially while the -container is in an intermediate state, or even changing the state -of the container object while it is being modified. This may result -in some surprising (i.e., undefined) behavior. -

- -

Read email thread starting with c++std-lib-13637 for more.

- - - -

Proposed resolution:

- -

Add to Container Requirements the following new paragraph:

- -
-    Unless otherwise specified, the behavior of a program that
-    invokes a container member function f from a member function
-    g of the container's value_type on a container object c that
-    called g from its mutating member function h, is undefined.
-    I.e., if v is an element of c, directly or indirectly calling
-    c.h() from v.g() called from c.f(), is undefined.
-
- -

[Redmond: This is a real issue, but it's probably a clause 17 - issue, not clause 23. We get the same issue, for example, if we - try to destroy a stream from one of the stream's callback functions.]

- - - - -

Rationale:

-

-Recommend NAD. We agree this is an issue, but not a defect. -We believe that there is no wording we can put in the standard -that will cover all cases without introducing unfortunate -corner cases. -

- - - - - -
-

472. Missing "Returns" clause in std::equal_range

-

Section: 25.4.3.3 [equal.range] Status: Dup - Submitter: Prateek R Karandikar Opened: 2004-06-30 Last modified: 2015-04-08

-

View all other issues in [equal.range].

-

View all issues with Dup status.

-

Duplicate of: 270

-

Discussion:

-

-There is no "Returns:" clause for std::equal_range, which returns non-void. -

- - -

Proposed resolution:

- - -

Rationale:

-

Fixed as part of issue 270.

- - - - - - -
-

476. Forward Iterator implied mutability

-

Section: 24.2.5 [forward.iterators] Status: NAD - Submitter: Dave Abrahams Opened: 2004-07-09 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

View all issues with NAD status.

-

Discussion:

- -

24.1/3 says:

-

- Forward iterators satisfy all the requirements of the input and - output iterators and can be used whenever either kind is specified -

- -

-The problem is that satisfying the requirements of output iterator -means that you can always assign *something* into the result of -dereferencing it. That makes almost all non-mutable forward -iterators non-conforming. I think we need to sever the refinement -relationship between forward iterator and output iterator. -

- -

Related issue: 200. But this is not a dup.

- - - -

Proposed resolution:

- - -

Rationale:

-

Yes, 24.1/3 does say that. But it's introductory material. The -precise specification is in 24.1.3, and the requrements table there is -right. We don't need to fine-tune introductory wording. (Especially -since this wording is likely to be changed as part of the iterator -overhaul.)

- - - - - -
-

477. Operator-> for const forward iterators

-

Section: 24.2.5 [forward.iterators] Status: Dup - Submitter: Dave Abrahams Opened: 2004-07-11 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

View all issues with Dup status.

-

Duplicate of: 478

-

Discussion:

-

-The Forward Iterator requirements table contains the following: -

-
- expression  return type         operational  precondition
-                                  semantics
-  ==========  ==================  ===========  ==========================
-  a->m        U& if X is mutable, (*a).m       pre: (*a).m is well-defined.
-              otherwise const U&
-
-  r->m        U&                  (*r).m       pre: (*r).m is well-defined.
-
- -

-The first line is exactly right. The second line is wrong. Basically -it implies that the const-ness of the iterator affects the const-ness -of referenced members. But Paragraph 11 of [lib.iterator.requirements] says: -

- -

- In the following sections, a and b denote values of type const X, n - denotes a value of the difference type Distance, u, tmp, and m - denote identifiers, r denotes a value of X&, t denotes a value of - value type T, o denotes a value of some type that is writable to - the output iterator. -

- -

AFAICT if we need the second line at all, it should read the same -as the first line.

- -

Related issue: 478

- - -

Proposed resolution:

- - -

Rationale:

-

The LWG agrees that this is a real problem. Marked as a DUP - because the LWG chose to adopt the solution proposed in - 478. -

- - - - - -
-

479. Container requirements and placement new

-

Section: 23.2 [container.requirements] Status: Dup - Submitter: Herb Sutter Opened: 2004-08-01 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

View all other issues in [container.requirements].

-

View all issues with Dup status.

-

Duplicate of: 580

-

Discussion:

-

Nothing in the standard appears to make this program ill-formed:

- -
-  struct C {
-    void* operator new( size_t s ) { return ::operator new( s ); }
-    // NOTE: this hides in-place and nothrow new
-  };
-
-  int main() {
-    vector<C> v;
-    v.push_back( C() );
-  }
-
- -

Is that intentional? We should clarify whether or not we intended - to require containers to support types that define their own special - versions of operator new.

- -

[ -Lillehammer: A container will definitely never use this overridden -operator new, but whether it will fail to compile is unclear from the -standard. Are containers supposed to use qualified or unqualified -placement new? 20.4.1.1 is somewhat relevant, but the standard -doesn't make it completely clear whether containers have to use -Allocator::construct(). If containers don't use it, the details of how -containers use placement new are unspecified. That is the real bug, -but it needs to be fixed as part of the allocator overhaul. Weak -support that the eventual solution should make this code well formed. -]

- - - - -

Proposed resolution:

- - - - - - - -
-

480. unary_function and binary_function should have protected nonvirtual destructors

-

Section: X [depr.base] Status: NAD - Submitter: Joe Gottman Opened: 2004-08-19 Last modified: 2015-04-08

-

View all other issues in [depr.base].

-

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-

Discussion:

-

The classes std::unary_function and std::binary_function are both -designed to be inherited from but contain no virtual functions. This -makes it too easy for a novice programmer to write code like -binary_function<int, int, int> *p = new plus<int>; delete p;

- -

There are two common ways to prevent this source of undefined -behavior: give the base class a public virtual destructor, or give it -a protected nonvirtual destructor. Since unary_function and -binary_function have no other virtual functions, (note in particular -the absence of an operator()() ), it would cost too much to give them -public virtual destructors. Therefore, they should be given protected -nonvirtual destructors.

- - -

Proposed resolution:

-

Change Paragraph 20.3.1 of the Standard from

-
-    template <class Arg, class Result>
-    struct unary_function {
-        typedef Arg argument_type;
-        typedef Result result_type;
-    };
-
-    template <class Arg1, class Arg2, class Result>
-    struct binary_function {
-        typedef Arg1 first_argument_type;
-        typedef Arg2 second_argument_type;
-        typedef Result result_type;
-    };
-
- -

to

-
-    template <class Arg, class Result>
-        struct unary_function {
-        typedef Arg argument_type;
-        typedef Result result_type;
-    protected:
-        ~unary_function() {}
-    };
-
-    template <class Arg1, class Arg2, class Result>
-    struct binary_function {
-        typedef Arg1 first_argument_type;
-        typedef Arg2 second_argument_type;
-        typedef Result result_type;
-    protected:
-        ~binary_function() {}
-    };
-
- - -

Rationale:

-

The LWG doesn't believe the existing definition causes anybody any - concrete harm.

- - - - - -
-

481. unique's effects on the range [result, last)

-

Section: 25.3.9 [alg.unique] Status: NAD - Submitter: Andrew Koenig Opened: 2004-08-30 Last modified: 2015-04-08

-

View all other issues in [alg.unique].

-

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-

Discussion:

-

-The standard says that unique(first, last) "eliminates all but the -first element from every consecutive group of equal elements" in -[first, last) and returns "the end of the resulting range". So a -postcondition is that [first, result) is the same as the old [first, -last) except that duplicates have been eliminated. -

- -

What postconditions are there on the range [result, last)? One - might argue that the standard says nothing about those values, so - they can be anything. One might also argue that the standard - doesn't permit those values to be changed, so they must not be. - Should the standard say something explicit one way or the other?

- - - -

Proposed resolution:

-

-

- - -

Rationale:

-

We don't want to make many guarantees about what's in [result, -end). Maybe we aren't being quite explicit enough about not being -explicit, but it's hard to think that's a major problem.

- - - - - -
-

483. Heterogeneous equality and EqualityComparable

-

Section: 25.2 [alg.nonmodifying], 25.3 [alg.modifying.operations] Status: Dup - Submitter: Peter Dimov Opened: 2004-09-20 Last modified: 2015-04-08

-

View all issues with Dup status.

-

Duplicate of: 283

-

Discussion:

-

c++std-lib-14262

- -

[lib.alg.find] requires T to be EqualityComparable:

- -
-template <class InputIterator, class T>
-   InputIterator find(InputIterator first, InputIterator last,
-                      const T& value);
-
- -

-However the condition being tested, as specified in the Effects -clause, is actually *i == value, where i is an InputIterator. -

- -

-The two clauses are in agreement only if the type of *i is T, but this -isn't necessarily the case. *i may have a heterogeneous comparison -operator that takes a T, or a T may be convertible to the type of *i. -

- -

Further discussion (c++std-lib-14264): this problem affects a - number of algorithsm in clause 25, not just find. We - should try to resolve this problem everywhere it appears.

- - -

Proposed resolution:

- -

[lib.alg.find]:

-

- Remove [lib.alg.find]/1. -

- -

[lib.alg.count]:

-

- Remove [lib.alg.count]/1. -

- -

[lib.alg.search]:

-

- Remove "Type T is EqualityComparable (20.1.1), " from [lib.alg.search]/4. -

- -

[lib.alg.replace]:

- -
-

- Remove [lib.alg.replace]/1. - Replace [lb.alg.replace]/2 with: -

- -

- For every iterator i in the range [first, last) for which *i == value - or pred(*i) holds perform *i = new_value. -

- -

- Remove the first sentence of /4. - Replace the beginning of /5 with: -

- -

- For every iterator i in the range [result, result + (last - - first)), assign to *i either... -

- -

(Note the defect here, current text says assign to i, not *i).

-
- -

[lib.alg.fill]:

- -
-

- Remove "Type T is Assignable (23.1), " from /1. - Replace /2 with: -

- -

- For every iterator i in the range [first, last) or [first, first + n), - perform *i = value. -

-
- -

[lib.alg.remove]:

-

- Remove /1. - Remove the first sentence of /6. -

- - - -

Rationale:

-

Duplicate of (a subset of) issue 283.

- - - - - - -
-

486. min/max CopyConstructible requirement is too strict

-

Section: 25.4.7 [alg.min.max] Status: Dup - Submitter: Dave Abrahams Opened: 2004-10-13 Last modified: 2015-04-08

-

View all other issues in [alg.min.max].

-

View all issues with Dup status.

-

Duplicate of: 281

-

Discussion:

-

A straightforward implementation of these algorithms does not need to -copy T.

- - -

Proposed resolution:

-

drop the the words "and CopyConstructible" from paragraphs 1 and 4

- - -

Rationale:

- - - - - - -
-

487. Allocator::construct is too limiting

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: Dhruv Matani Opened: 2004-10-17 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with NAD status.

-

Discussion:

-

-The standard's version of allocator::construct(pointer, -const_reference) severely limits what you can construct using this -function. Say you can construct a socket from a file descriptor. Now, -using this syntax, I first have to manually construct a socket from -the fd, and then pass the constructed socket to the construct() -function so it will just to an uninitialized copy of the socket I -manually constructed. Now it may not always be possible to copy -construct a socket eh! So, I feel that the changes should go in the -allocator::construct(), making it: -

-
-    template<typename T>
-    struct allocator{
-      template<typename T1>
-      void construct(pointer T1 const& rt1);
-    };
-
- -

-Now, the ctor of the class T which matches the one that takes a T1 can -be called! Doesn't that sound great? -

- - -

Proposed resolution:

- - -

Rationale:

-

NAD. STL uses copying all the time, and making it possible for - allocators to construct noncopyable objects is useless in the - absence of corresponding container changes. We might consider this - as part of a larger redesign of STL.

- - - - - -
-

489. std::remove / std::remove_if wrongly specified

-

Section: 25.3.8 [alg.remove] Status: NAD - Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2015-04-08

-

View all other issues in [alg.remove].

-

View all issues with NAD status.

-

Discussion:

-

In Section 25.2.7 [lib.alg.remove], paragraphs 1 to 5 describe the -behavior of the mutating sequence operations std::remove and -std::remove_if. However, the wording does not reflect the intended -behavior [Note: See definition of intended behavior below] of these -algorithms, as it is known to the C++ community [1]. -

- - - -

1) Analysis of current wording:

- - -

25.2.7 [lib.alg.remove], paragraph 2:

- -

Current wording says: -"Effects: Eliminates all the elements referred to by iterator i in the -range [first, last) for which the following corresponding conditions -hold: *i == value, pred(*i) != false."

- -

-This sentences expresses specifically that all elements denoted by the -(original) range [first, last) for which the corresponding condition -hold will be eliminated. Since there is no formal definition of the term -"eliminate" provided, the meaning of "eliminate" in everyday language -implies that as postcondition, no element in the range denoted by -[first, last) will hold the corresponding condition on reiteration over -the range [first, last). -

- -

-However, this is neither the intent [Note: See definition of intended -behavior below] nor a general possible approach. It can be easily proven -that if all elements of the original range[first, last) will hold the -condition, it is not possible to substitute them by an element for which -the condition will not hold. -

- - -

25.2.7 [lib.alg.remove], paragraph 3:

- -

-Current wording says: -"Returns: The end of the resulting range." -

- -

-The resulting range is not specified. In combination with 25.2.7 -[lib.alg.remove], paragraph 2, the only reasonable interpretation of -this so-called resulting range is the range [first,last) - thus -returning always the ForwardIterator 'last' parameter. -

- - -

-25.2.7 [lib.alg.remove], paragraph 4: -

- -

-Current wording says: -"Notes: Stable: the relative order of the elements that are not removed -is the same as their relative order in the original range" -

- -

-This sentences makes use of the term "removed", which is neither -specified, nor used in a previous paragraph (which uses the term -"eliminate"), nor unamgiuously separated from the name of the algorithm. -

- - -

2) Description of intended behavior:

- -

-For the rest of this Defect Report, it is assumed that the intended -behavior was that all elements of the range [first, last) which do not -hold the condition *i == value (std::remove) or pred(*i) != false -(std::remove_if)], call them s-elements [Note: s...stay], will be placed -into a contiguous subrange of [first, last), denoted by the iterators -[first, return value). The number of elements in the resulting range -[first, return value) shall be equal to the number of s-elements in the -original range [first, last). The relative order of the elements in the -resulting subrange[first, return value) shall be the same as the -relative order of the corresponding elements in the original range. It -is undefined whether any elements in the resulting subrange [return -value, last) will hold the corresponding condition, or not. -

- -

-All implementations known to the author of this Defect Report comply -with this intent. Since the intent of the behavior (contrary to the -current wording) is also described in various utility references serving -the C++ community [1], it is not expected that fixing the paragraphs -will influence current code - unless the code relies on the behavior as -it is described by current wording and the implementation indeed -reflects the current wording, and not the intent. -

- - - -

3) Proposed fixes:

- - -

Change 25.2.7 [lib.alg.remove], paragraph 2 to:

- -

-"Effect: Places all the elements referred to by iterator i in the range -[first, last) for which the following corresponding conditions hold : -!(*i == value), pred(*i) == false into the subrange [first, k) of the -original range, where k shall denote a value of type ForwardIterator. It -is undefined whether any elements in the resulting subrange [k, last) -will hold the corresponding condition, or not." -

- -

Comments to the new wording:

- -

-a) "Places" has no special meaning, and the everyday language meaning -should fit. -b) The corresponding conditions were negated compared to the current -wording, becaue the new wording requires it. -c) The wording "of the original range" might be redundant, since any -subrange starting at 'first' and containing no more elements than the -original range is implicitly a subrange of the original range [first, -last). -d) The iterator k was introduced instead of "return value" in order to -avoid a cyclic dependency on 25.2.7/3. The wording ", where k shall -denote a value of type ForwardIterator" might be redundant, because it -follows implicitly by 25.2.7/3. -e) "Places" does, in the author's opinion, explicitly forbid duplicating -any element holding the corresponding condition in the original range -[first, last) within the resulting range [first, k). If there is doubt -this term might be not unambiguous regarding this, it is suggested that -k is specified more closely by the following wording: "k shall denote a -value of type ForwardIterator [Note: see d)] so that k - first is equal -to the number of elements in the original range [first, last) for which -the corresponding condition did hold". This could also be expressed as a -separate paragraph "Postcondition:" -f) The senctence "It is undefined whether any elements in the resulting -subrange [k, last) will hold the corresponding condition, or not." was -added consciously so the term "Places" does not imply if the original -range [first, last) contains n elements holding the corresponding -condition, the identical range[first, last) will also contain exactly n -elements holding the corresponding condition after application of the -algorithm. -

- -

-Change 25.2.7 [lib.alg.remove], paragraph 3 to: - -"Returns: The iterator k." -

- -

-Change 25.2.7 [lib.alg.remove], paragraph 4 to: - -"Notes: Stable: the relative order of the elements that are placed into -the subrange [first, return value) shall be the same as their relative -order was in the original range [first, last) prior to application of -the algorithm." -

- -

-Comments to the new wording: -

- -

-a) the wording "was ... prior to application of the algorithm" is used -to explicitly distinguish the original range not only by means of -iterators, but also by a 'chronological' factor from the resulting range -[first, return value). It might be redundant. -

- -

-[1]: -The wording of these references is not always unambiguous, and provided -examples partially contradict verbal description of the algorithms, -because the verbal description resembles the problematic wording of -ISO/IEC 14882:2003. -

- - -

Proposed resolution:

- - -

Rationale:

-

The LWG believes that the standard is sufficiently clear, and that - there is no evidence of any real-world confusion about this point.

- - - - - -
-

490. std::unique wrongly specified

-

Section: 25.3.9 [alg.unique] Status: NAD - Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2015-04-08

-

View all other issues in [alg.unique].

-

View all issues with NAD status.

-

Discussion:

-

In Section 25.2.8 [lib.alg.unique], paragraphs 1 to 3 describe the -behavior of the mutating sequence operation std::unique. However, the -wording does not reflect the intended behavior [Note: See definition of -intended behavior below] of these algorithms, as it is known to the C++ -community [1].

- - - -

1) Analysis of current wording:

- - -

25.2.8 [lib.alg.unique], paragraph 1:

- -

-Current wording says: -"Effects: Eliminates all but the first element from every consecutive -group of equal elements referred to by the iterator i in the range -[first, last) for which the following corresponding conditions hold: *i -== *(i - 1) or pred(*i, *(i -1)) != false" -

- -

-This sentences expresses specifically that all elements denoted by the -(original) range [first, last) which are not but the first element from -a consecutive group of equal elements (where equality is defined as *i -== *(i - 1) or pred(*i, *(i - 1)) ! = false) [Note: See DR 202], call -them r-elements [Note: r...remove], will be eliminated. Since there is -no formal definition of the term "eliminate" provided, it is undefined -how this "elimination" takes place. But the meaning of "eliminate" in -everyday language seems to disallow explicitly that after application of -the algorithm, any r-element will remain at any position of the range -[first, last) [2]. -

- -

-Another defect in the current wording concerns the iterators used to -compare two elements for equality: The current wording contains the -expression "(i - 1)", which is not covered by 25/9 [Note: See DR -submitted by Thomas Mang regarding invalid iterator arithmetic -expressions]. -

- - -

-25.2.8 [lib.alg.unique], paragraph 2: -

-

Current wording says: -"Returns: The end of the resulting range."

- -

-The resulting range is not specified. In combination with 25.2.8 -[lib.alg.unique], paragraph 1, one reasonable interpretation (in the -author's opinion even the only possible interpretation) of this -so-called resulting range is the range [first, last) - thus returning -always the ForwardIterator 'last' parameter. -

- -

2) Description of intended behavior:

- -

-For the rest of this Defect Report, it is assumed that the intended -behavior was that all elements denoted by the original range [first, -last) which are the first element from a consecutive group of elements -for which the corresponding conditions: *(i-1) == *i (for the version of -unique without a predicate argument) or pred(*(i-1), *i) ! = false (for -the version of unique with a predicate argument) [Note: If such a group -of elements consists of only a single element, this is also considered -the first element] [Note: See resolutions of DR 202], call them -s-elements [Note: s...stay], will be placed into a contiguous subrange -of [first, last), denoted by the iterators [first, return value). The -number of elements in the resulting range [first, return value) shall be -equal to the number of s-elements in the original range [first, last). -Invalid iterator arithmetic expressions are expected to be resolved as -proposed in DR submitted by Thomas Mang regarding invalid iterator -arithmetic expressions. It is also assumed by the author that the -relative order of the elements in the resulting subrange [first, return -value) shall be the same as the relative order of the corresponding -elements (the s-elements) in the original range [Note: If this was not -intended behavior, the additional proposed paragraph about stable order -will certainly become obsolete]. -Furthermore, the resolutions of DR 202 are partially considered. -

- -

-All implementations known to the author of this Defect Report comply -with this intent [Note: Except possible effects of DR 202]. Since this -intent of the behavior (contrary to the current wording) is also -described in various utility references serving the C++ community [1], -it is not expected that fixing the paragraphs will influence current -code [Note: Except possible effects of DR 202] - unless the code relies -on the behavior as it is described by current wording and the -implementation indeed reflects the current wording, and not the intent. -

- - - -

3) Proposed fixes:

- -

-Change 25.2.8 [lib.alg.unique], paragraph 1 to: -

- -

-"Effect: Places the first element from every consecutive group of -elements, referred to by the iterator i in the range [first, last), for -which the following conditions hold: *(i-1) == *i (for the version of -unique without a predicate argument) or pred(*(i -1), *i) != false (for -the version of unique with a predicate argument), into the subrange -[first, k) of the original range, where k shall denote a value of type -ForwardIterator." -

- -

Comments to the new wording:

- -

-a) The new wording was influenced by the resolutions of DR 202. If DR -202 is resolved in another way, the proposed wording need also -additional review. -b) "Places" has no special meaning, and the everyday language meaning -should fit. -c) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -d) The wording "(for the version of unique without a predicate -argument)" and "(for the version of unique with a predicate argument)" -was added consciously for clarity and is in resemblence with current -23.2.2.4 [lib.list.ops], paragraph 19. It might be considered redundant. -e) The wording "of the original range" might be redundant, since any -subrange starting at first and containing no more elements than the -original range is implicitly a subrange of the original range [first, -last). -f) The iterator k was introduced instead of "return value" in order to -avoid a cyclic dependency on 25.2.8 [lib.alg.unique], paragraph 2. The -wording ", where k shall denote a value of type ForwardIterator" might -be redundant, because it follows implicitly by 25.2.8 [lib.alg.unique], -paragraph 2. -g) "Places" does, in the author's opinion, explicitly forbid duplicating -any s-element in the original range [first, last) within the resulting -range [first, k). If there is doubt this term might be not unambiguous -regarding this, it is suggested that k is specified more closely by the -following wording: "k shall denote a value of type ForwardIterator -[Note: See f)] so that k - first is equal to the number of elements in -the original range [first, last) being the first element from every -consecutive group of elements for which the corresponding condition did -hold". This could also be expressed as a separate paragraph -"Postcondition:". -h) If it is considered that the wording is unclear whether it declares -the element of a group which consists of only a single element -implicitly to be the first element of this group [Note: Such an -interpretation could eventually arise especially in case last - first == -1] , the following additional sentence is proposed: "If such a group of -elements consists of only a single element, this element is also -considered the first element." -

- -

-Change 25.2.8 [lib.alg.unique], paragraph 2 to: -"Returns: The iterator k." -

- -

-Add a separate paragraph "Notes:" as 25.2.8 [lib.alg.unique], paragraph -2a or 3a, or a separate paragraph "Postcondition:" before 25.2.8 -[lib.alg.unique], paragraph 2 (wording inside {} shall be eliminated if -the preceding expressions are used, or the preceding expressions shall -be eliminated if wording inside {} is used): -

- -

-"Notes:{Postcondition:} Stable: the relative order of the elements that -are placed into the subrange [first, return value {k}) shall be the same -as their relative order was in the original range [first, last) prior to -application of the algorithm." -

- -

Comments to the new wording:

- -

-a) It is assumed by the author that the algorithm was intended to be -stable. -In case this was not the intent, this paragraph becomes certainly -obsolete. -b) The wording "was ... prior to application of the algorithm" is used -to explicitly distinguish the original range not only by means of -iterators, but also by a 'chronological' factor from the resulting range -[first, return value). It might be redundant. -

- -

-25.2.8 [lib.alg.unique], paragraph 3: -

-

See DR 239.

- -

-4) References to other DRs: -

- -

-See DR 202, but which does not address any of the problems described in -this Defect Report [Note: This DR is supposed to complement DR 202]. -See DR 239. -See DR submitted by Thomas Mang regarding invalid iterator arithmetic -expressions. -

- -

-[1]: -The wording of these references is not always unambiguous, and provided -examples partially contradict verbal description of the algorithms, -because the verbal description resembles the problematic wording of -ISO/IEC 14882:2003. -

- -

-[2]: -Illustration of conforming implementations according to current wording: -

- -

-One way the author of this DR considers how this "elimination" could be -achieved by a conforming implementation according to current wording is -by substituting each r-element by _any_ s-element [Note: s...stay; any -non-r-element], since all r-elements are "eliminated". -

- -

-In case of a sequence consisting of elements being all 'equal' [Note: -See DR 202], substituting each r-element by the single s-element is the -only possible solution according to current wording. -

- - -

Proposed resolution:

- - -

Rationale:

-

The LWG believes the standard is sufficiently clear. No -implementers get it wrong, and changing it wouldn't cause any code to -change, so there is no real-world harm here.

- - - - - -
-

491. std::list<>::unique incorrectly specified

-

Section: 23.3.5.5 [list.ops] Status: NAD - Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with NAD status.

-

Discussion:

-

In Section 23.3.5.5 [list.ops], paragraphs 19 to 21 describe the -behavior of the std::list<T, Allocator>::unique operation. However, the -current wording is defective for various reasons.

- - - -

-1) Analysis of current wording: -

- -

23.3.5.5 [list.ops], paragraph 19:

- -

-Current wording says: -"Effects: Eliminates all but the first element from every consecutive -group of equal elements referred to by the iterator i in the range -[first + 1, last) for which *i == *(i - 1) (for the version of unique -with no argument) or pred(*i, *(i -1)) (for the version of unique with a -predicate argument) holds."

- -

-This sentences makes use of the undefined term "Eliminates". Although it -is, to a certain degree, reasonable to consider the term "eliminate" -synonymous with "erase", using "Erase" in the first place, as the -wording of 23.3.5.5 [list.ops], paragraph 15 does, would be clearer.

- -

-The range of the elements referred to by iterator i is "[first + 1, -last)". However, neither "first" nor "last" is defined.

- -

-The sentence makes three times use of iterator arithmetic expressions ( -"first + 1", "*i == *(i - 1)", "pred(*i, *(i -1))" ) which is not -defined for bidirectional iterator [see DR submitted by Thomas Mang -regarding invalid iterator arithmetic expressions].

- -

-The same problems as pointed out in DR 202 (equivalence relation / order -of arguments for pred()) apply to this paragraph.

- -

-23.3.5.5 [list.ops], paragraph 20: -

- -

-Current wording says: -"Throws: Nothing unless an exception in thrown by *i == *(i-1) or -pred(*i, *(i - 1))"

- -

-The sentence makes two times use of invalid iterator arithmetic -expressions ( "*i == *(i - 1)", "pred(*i, *(i -1))" ). -

-

-[Note: Minor typos: "in" / missing dot at end of sentence.] -

- -

-23.3.5.5 [list.ops], paragraph 21:

- -

-Current wording says: -"Complexity: If the range (last - first) is not empty, exactly (last - -first) - 1 applications of the corresponding predicate, otherwise no -application of the predicate.

- -

-See DR 315 regarding "(last - first)" not yielding a range.

- -

-Invalid iterator arithmetic expression "(last - first) - 1" left .

- - -

2) Description of intended behavior:

- -

-For the rest of this Defect Report, it is assumed that "eliminate" is -supposed to be synonymous to "erase", that "first" is equivalent to an -iterator obtained by a call to begin(), "last" is equivalent to an -iterator obtained by a call to end(), and that all invalid iterator -arithmetic expressions are resolved as described in DR submitted by -Thomas Mang regarding invalid iterator arithmetic expressions.

- -

-Furthermore, the resolutions of DR 202 are considered regarding -equivalence relation and order of arguments for a call to pred.

- -

-All implementations known to the author of this Defect Report comply -with these assumptions, apart from the impact of the alternative -resolution of DR 202. Except for the changes implied by the resolutions -of DR 202, no impact on current code is expected.

- -

-3) Proposed fixes:

- -

-Change 23.3.5.5 [list.ops], paragraph 19 to:

- -

-"Effect: Erases all but the first element from every consecutive group -of elements, referred to by the iterator i in the range [begin(), -end()), for which the following conditions hold: *(i-1) == *i (for the -version of unique with no argument) or pred(*(i-1), *i) != false (for -the version of unique with a predicate argument)."

- -

-Comments to the new wording:

- -

-a) The new wording was influenced by DR 202 and the resolutions -presented there. If DR 202 is resolved in another way, the proposed -wording need also additional review. -b) "Erases" refers in the author's opinion unambiguously to the member -function "erase". In case there is doubt this might not be unamgibuous, -a direct reference to the member function "erase" is suggested [Note: -This would also imply a change of 23.3.5.5 [list.ops], paragraph -15.]. -c) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -d) The wording "(for the version of unique with no argument)" and "(for -the version of unique with a predicate argument)" was kept consciously -for clarity. -e) "begin()" substitutes "first", and "end()" substitutes "last". The -range need adjustment from "[first + 1, last)" to "[begin(), end())" to -ensure a valid range in case of an empty list. -f) If it is considered that the wording is unclear whether it declares -the element of a group which consists of only a single element -implicitly to be the first element of this group [Note: Such an -interpretation could eventually arise especially in case size() == 1] , -the following additional sentence is proposed: "If such a group of -elements consists of only a single element, this element is also -considered the first element."

- -

-Change 23.3.5.5 [list.ops], paragraph 20 to:

- -

-"Throws: Nothing unless an exception is thrown by *(i-1) == *i or -pred(*(i-1), *i)."

- -

-Comments to the new wording:

- -

-a) The wording regarding the conditions is identical to proposed -23.3.5.5 [list.ops], paragraph 19. If 23.3.5.5 [list.ops], -paragraph 19 is resolved in another way, the proposed wording need also -additional review. -b) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -c) Typos fixed.

- -

-Change 23.3.5.5 [list.ops], paragraph 21 to:

- -

-"Complexity: If empty() == false, exactly size() - 1 applications of the -corresponding predicate, otherwise no applications of the corresponding -predicate."

- -

-Comments to the new wording:

- -

-a) The new wording is supposed to also replace the proposed resolution -of DR 315, which suffers from the problem of undefined "first" / "last". -

- -

-5) References to other DRs:

- -

See DR 202. -See DR 239. -See DR 315. -See DR submitted by Thomas Mang regarding invalid iterator arithmetic -expressions.

- - - -

Proposed resolution:

- - -

Rationale:

-

"All implementations known to the author of this Defect Report -comply with these assumption", and "no impact on current code is -expected", i.e. there is no evidence of real-world confusion or -harm.

- - - - - -
-

492. Invalid iterator arithmetic expressions

-

Section: 17.5.1.4 [structure.specifications] Status: NAD - Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2015-04-08

-

View all other issues in [structure.specifications].

-

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-

Discussion:

-

Various clauses other than clause 25 make use of iterator arithmetic not -supported by the iterator category in question. -Algorithms in clause 25 are exceptional because of 25 [lib.algorithms], -paragraph 9, but this paragraph does not provide semantics to the -expression "iterator - n", where n denotes a value of a distance type -between iterators.

- -

1) Examples of current wording:

- -

Current wording outside clause 25:

- -

-23.2.2.4 [lib.list.ops], paragraphs 19-21: "first + 1", "(i - 1)", -"(last - first)" -23.3.1.1 [lib.map.cons], paragraph 4: "last - first" -23.3.2.1 [lib.multimap.cons], paragraph 4: "last - first" -23.3.3.1 [lib.set.cons], paragraph 4: "last - first" -23.3.4.1 [lib.multiset.cons], paragraph 4: "last - first" -24.4.1 [lib.reverse.iterators], paragraph 1: "(i - 1)" -

- -

-[Important note: The list is not complete, just an illustration. The -same issue might well apply to other paragraphs not listed here.]

- -

None of these expressions is valid for the corresponding iterator -category.

- -

Current wording in clause 25:

- -

-25.1.1 [lib.alg.foreach], paragraph 1: "last - 1" -25.1.3 [lib.alg.find.end], paragraph 2: "[first1, last1 - -(last2-first2))" -25.2.8 [lib.alg.unique], paragraph 1: "(i - 1)" -25.2.8 [lib.alg.unique], paragraph 5: "(i - 1)" -

- -

-However, current wording of 25 [lib.algorithms], paragraph 9 covers -neither of these four cases:

- -

Current wording of 25 [lib.algorithms], paragraph 9:

- -

-"In the description of the algorithms operator + and - are used for some -of the iterator categories for which they do not have to be defined. In -these cases the semantics of a+n is the same as that of

-
-{X tmp = a;
-advance(tmp, n);
-return tmp;
-}
-
-

and that of b-a is the same as of return distance(a, b)"

- -

-This paragrpah does not take the expression "iterator - n" into account, -where n denotes a value of a distance type between two iterators [Note: -According to current wording, the expression "iterator - n" would be -resolved as equivalent to "return distance(n, iterator)"]. Even if the -expression "iterator - n" were to be reinterpreted as equivalent to -"iterator + -n" [Note: This would imply that "a" and "b" were -interpreted implicitly as values of iterator types, and "n" as value of -a distance type], then 24.3.4/2 interfers because it says: "Requires: n -may be negative only for random access and bidirectional iterators.", -and none of the paragraphs quoted above requires the iterators on which -the algorithms operate to be of random access or bidirectional category. -

- -

2) Description of intended behavior:

- -

-For the rest of this Defect Report, it is assumed that the expression -"iterator1 + n" and "iterator1 - iterator2" has the semantics as -described in current 25 [lib.algorithms], paragraph 9, but applying to -all clauses. The expression "iterator1 - n" is equivalent to an -result-iterator for which the expression "result-iterator + n" yields an -iterator denoting the same position as iterator1 does. The terms -"iterator1", "iterator2" and "result-iterator" shall denote the value of -an iterator type, and the term "n" shall denote a value of a distance -type between two iterators.

- -

-All implementations known to the author of this Defect Report comply -with these assumptions. -No impact on current code is expected.

- -

3) Proposed fixes:

- - -

Change 25 [lib.algorithms], paragraph 9 to:

- -

-"In the description of the algorithms operator + and - are used for some -of the iterator categories for which they do not have to be defined. In -this paragraph, a and b denote values of an iterator type, and n denotes -a value of a distance type between two iterators. In these cases the -semantics of a+n is the same as that of

-
-{X tmp = a;
-advance(tmp, n);
-return tmp;
-}
-
-

,the semantics of a-n denotes the value of an iterator i for which the -following condition holds: -advance(i, n) == a, -and that of b-a is the same as of -return distance(a, b)". -

- -

Comments to the new wording:

- -

-a) The wording " In this paragraph, a and b denote values of an iterator -type, and n denotes a value of a distance type between two iterators." -was added so the expressions "b-a" and "a-n" are distinguished regarding -the types of the values on which they operate. -b) The wording ",the semantics of a-n denotes the value of an iterator i -for which the following condition holds: advance(i, n) == a" was added -to cover the expression 'iterator - n'. The wording "advance(i, n) == a" -was used to avoid a dependency on the semantics of a+n, as the wording -"i + n == a" would have implied. However, such a dependency might well -be deserved. -c) DR 225 is not considered in the new wording. -

- -

-Proposed fixes regarding invalid iterator arithmetic expressions outside -clause 25:

- -

-Either -a) Move modified 25 [lib.algorithms], paragraph 9 (as proposed above) -before any current invalid iterator arithmetic expression. In that case, -the first sentence of 25 [lib.algorithms], paragraph 9, need also to be -modified and could read: "For the rest of this International Standard, -...." / "In the description of the following clauses including this -...." / "In the description of the text below ..." etc. - anyways -substituting the wording "algorithms", which is a straight reference to -clause 25. -In that case, 25 [lib.algorithms] paragraph 9 will certainly become -obsolete. -Alternatively, -b) Add an appropiate paragraph similar to resolved 25 [lib.algorithms], -paragraph 9, to the beginning of each clause containing invalid iterator -arithmetic expressions. -Alternatively, -c) Fix each paragraph (both current wording and possible resolutions of -DRs) containing invalid iterator arithmetic expressions separately. -

- -

5) References to other DRs:

- -

-See DR 225. -See DR 237. The resolution could then also read "Linear in last - -first". -

- -

[ -Bellevue: -]

- - -

-Keep open and ask Bill to provide wording. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -

-This issue is related to 997. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Hinnant: this isn't going to change any user's code or any vendor's implementation. -

-

-No objection to "NAD without prejudice." If anyone proposes a -resolution, the LWG will consider it. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

- -

[Lillehammer: Minor issue, but real. We have a blanket statement -about this in 25/11. But (a) it should be in 17, not 25; and (b) it's -not quite broad enough, because there are some arithmetic expressions -it doesn't cover. Bill will provide wording.]

- - - - - - - -
-

493. Undefined Expression in Input Iterator Note Title

-

Section: 24.2.3 [input.iterators] Status: NAD - Submitter: Chris Jefferson Opened: 2004-12-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

1) In 24.1.1/3, the following text is currently present.

- -

"Note: For input iterators, a==b does not imply ++a=++b (Equality does -not guarantee the substitution property or referential transparency)."

- -

However, when in Table 72, part of the definition of ++r is given as:

- -

"pre: r is dereferenceable. -post: any copies of the previous value of r are no longer required -either to be dereferenceable ..."

- -

While a==b does not imply that b is a copy of a, this statement should -perhaps still be made more clear.

- -

2) There are no changes to intended behaviour

- -

-3) This Note should be altered to say "Note: For input iterators a==b, -when its behaviour is defined ++a==++b may still be false (Equality does -not guarantee the substitution property or referential transparency).

- - - -

Proposed resolution:

- - -

Rationale:

-

This is descriptive text, not normative, and the meaning is clear.

- - - - - -
-

494. Wrong runtime complexity for associative container's insert and delete

-

Section: 23.2.4 [associative.reqmts] Status: NAD - Submitter: Hans B os Opened: 2004-12-19 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

According to [lib.associative.reqmts] table 69, the runtime comlexity -of insert(p, t) and erase(q) can be done in amortized constant time.

- -

It was my understanding that an associative container could be -implemented as a balanced binary tree.

- -

For inser(p, t), you 'll have to iterate to p's next node to see if t -can be placed next to p. Furthermore, the insertion usually takes -place at leaf nodes. An insert next to the root node will be done at -the left of the root next node

- -

So when p is the root node you 'll have to iterate from the root to -its next node, which takes O(log(size)) time in a balanced tree.

- -

If you insert all values with insert(root, t) (where root is the -root of the tree before insertion) then each insert takes O(log(size)) -time. The amortized complexity per insertion will be O(log(size)) -also.

- -

For erase(q), the normal algorithm for deleting a node that has no -empty left or right subtree, is to iterate to the next (or previous), -which is a leaf node. Then exchange the node with the next and delete -the leaf node. Furthermore according to DR 130, erase should return -the next node of the node erased. Thus erasing the root node, -requires iterating to the next node.

- -

Now if you empty a map by deleting the root node until the map is -empty, each operation will take O(log(size)), and the amortized -complexity is still O(log(size)).

- -

The operations can be done in amortized constant time if iterating -to the next node can be done in (non amortized) constant time. This -can be done by putting all nodes in a double linked list. This -requires two extra links per node. To me this is a bit overkill since -you can already efficiently insert or erase ranges with erase(first, -last) and insert(first, last).

- - - -

Proposed resolution:

- - -

Rationale:

-

Only "amortized constant" in special circumstances, and we believe - that's implementable. That is: doing this N times will be O(N), not - O(log N).

- - - - - -
-

499. Std. doesn't seem to require stable_sort() to be stable!

-

Section: 25.4.1.2 [stable.sort] Status: NAD Editorial - Submitter: Prateek Karandikar Opened: 2005-04-12 Last modified: 2015-04-08

-

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-

Discussion:

-

-17.3.1.1 Summary

- -

-1 The Summary provides a synopsis of the category, and introduces the -first-level subclauses. Each subclause also provides a summary, listing -the headers specified in the subclause and the library entities -provided in each header. -

-

-2 Paragraphs labelled "Note(s):" or "Example(s):" are informative, -other paragraphs are normative. -

- -

So this means that a "Notes" paragraph wouldn't be normative.

- -

-25.3.1.2 stable_sort -

-
-template<class RandomAccessIterator> 
-void stable_sort(RandomAccessIterat or first, RandomAccessIterator last); 
-
-template<class RandomAccessIterator, class Compare> 
-void stable_sort(RandomAccessIterat or first, RandomAccessIterator last, Compare comp);
-
-

-1 Effects: Sorts the elements in the range [first, last). -

-

-2 Complexity: It does at most N(log N)^2 (where N == last - first) -comparisons; if enough extra memory is available, it is N log N. -

-

-3 Notes: Stable: the relative order of the equivalent elements is -preserved. -

- -

-The Notes para is informative, and nowhere else is stability mentioned above. -

- -

-Also, I just searched for the word "stable" in my copy of the Standard. -and the phrase "Notes: Stable: the relative order of the elements..." -is repeated several times in the Standard library clauses for -describing various functions. How is it that stability is talked about -in the informative paragraph? Or am I missing something obvious? -

- - -

Proposed resolution:

-

-

- - -

Rationale:

-

-This change has already been made. -

- - - - - -
-

500. do_length cannot be implemented correctly

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: NAD - Submitter: Krzysztof Żelechowski Opened: 2005-05-24 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.byname].

-

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-

Discussion:

-
    -
  1. codecvt::do_length is of type int;
    2. -
  2. it is assumed to be sort-of returning from_next - from of type ptrdiff_t;
    3. -
  3. ptrdiff_t cannot be cast to an int without data loss.
    4. -
-

-Contradiction. -

- - -

Proposed resolution:

-

-

- - - - - -
-

501. Proposal: strengthen guarantees of lib.comparisons

-

Section: X [depr.base] Status: NAD - Submitter: Me <anti_spam_email2003@yahoo.com> Opened: 2005-06-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-"For templates greater, less, greater_equal, and less_equal, -the specializations for any pointer type yield a total order, even if -the built-in operators <, >, <=, >= do not." -

- -

-The standard should do much better than guarantee that these provide a -total order, it should guarantee that it can be used to test if memory -overlaps, i.e. write a portable memmove. You can imagine a platform -where the built-in operators use a uint32_t comparison (this tests for -overlap on this platform) but the less<T*> functor is allowed to be -defined to use a int32_t comparison. On this platform, if you use -std::less with the intent of making a portable memmove, comparison on -an array that straddles the 0x7FFFFFFF/0x8000000 boundary can give -incorrect results. -

- - -

Proposed resolution:

-

-Add a footnote to 20.5.3/8 saying: -

- -

-Given a p1 and p2 such that p1 points to N objects of type T and p2 -points to M objects of type T. If [p1,p1+N) does not overlap [p2,p2+M), -less returns the same value when comparing all pointers in [p1,p1+N) to -all pointers in [p2,p2+M). Otherwise, there is a value Q and a value R -such that less returns the same value when comparing all pointers in -[p1,p1+Q) to all pointers in [p2,p2+R) and an opposite value when -comparing all pointers in [p1+Q,p1+N) to all pointers in [p2+R,p2+M). -For the sake of completeness, the null pointer value (4.10) for T is -considered to be an array of 1 object that doesn't overlap with any -non-null pointer to T. less_equal, greater, greater_equal, equal_to, -and not_equal_to give the expected results based on the total ordering -semantics of less. For T of void, treat it as having similar semantics -as T of char i.e. less<cv T*>(a, b) gives the same results as less<cv -void*>(a, b) which gives the same results as less<cv char*>((cv -char*)(cv void*)a, (cv char*)(cv void*)b). -

- -

-I'm also thinking there should be a footnote to 20.5.3/1 saying that if -A and B are similar types (4.4/4), comp<A>(a,b) returns the same value -as comp<B>(a,b) (where comp is less, less_equal, etc.). But this might -be problematic if there is some really funky operator overloading going -on that does different things based on cv (that should be undefined -behavior if somebody does that though). This at least should be -guaranteed for all POD types (especially pointers) that use the -built-in comparison operators. -

- - - -

Rationale:

-

-less is already required to provide a strict weak ordering which is good enough -to detect overlapping memory situations. -

- - - - - -
-

502. Proposition: Clarification of the interaction between a facet and an iterator

-

Section: 22.3.1.1.1 [locale.category] Status: NAD - Submitter: Christopher Conrade Zseleghovski Opened: 2005-06-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Motivation: -

- -

-This requirement seems obvious to me, it is the essence of code modularity. -I have complained to Mr. Plauger that the Dinkumware library does not -observe this principle but he objected that this behaviour is not covered in -the standard. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-No objection to NAD, Fixed. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

-Append the following point to 22.1.1.1.1: -

- -

-6. The implementation of a facet of Table 52 parametrized with an -InputIterator/OutputIterator should use that iterator only as character -source/sink respectively. -For a *_get facet, it means that the value received depends only on the -sequence of input characters and not on how they are accessed. -For a *_put facet, it means that the sequence of characters output depends -only on the value to be formatted and not of how the characters are stored. -

- -

[ -Berlin: Moved to Open, Need to clean up this area to make it clear -locales don't have to contain open ended sets of facets. Jack, Howard, -Bill. -]

- - - - - - - -
-

503. more on locales

-

Section: 22.4 [locale.categories] Status: NAD - Submitter: P.J. Plauger Opened: 2005-06-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-a) In 22.2.1.1 para. 2 we refer to "the instantiations required in Table -51" to refer to the facet *objects* associated with a locale. And we -almost certainly mean just those associated with the default or "C" -locale. Otherwise, you can't switch to a locale that enforces a different -mapping between narrow and wide characters, or that defines additional -uppercase characters. -

- -

-b) 22.2.1.5 para. 3 (codecvt) has the same issues. -

- -

-c) 22.2.1.5.2 (do_unshift) is even worse. It *forbids* the generation of -a homing sequence for the basic character set, which might very well need -one. -

- -

-d) 22.2.1.5.2 (do_length) likewise dictates that the default mapping -between wide and narrow characters be taken as one-for-one. -

- -

-e) 22.2.2 para. 2 (num_get/put) is both muddled and vacuous, as far as -I can tell. The muddle is, as before, calling Table 51 a list of -instantiations. But the constraint it applies seems to me to cover -*all* defined uses of num_get/put, so why bother to say so? -

- -

-f) 22.2.3.1.2 para. 1(do_decimal_point) says "The required instantiations -return '.' or L'.'.) Presumably this means "as appropriate for the -character type. But given the vague definition of "required" earlier, -this overrules *any* change of decimal point for non "C" locales. -Surely we don't want to do that. -

- -

-g) 22.2.3.1.2 para. 2 (do_thousands_sep) says "The required instantiations -return ',' or L','.) As above, this probably means "as appropriate for the -character type. But this overrules the "C" locale, which requires *no* -character ('\0') for the thousands separator. Even if we agree that we -don't mean to block changes in decimal point or thousands separator, -we should also eliminate this clear incompatibility with C. -

- -

-h) 22.2.3.1.2 para. 2 (do_grouping) says "The required instantiations -return the empty string, indicating no grouping." Same considerations -as for do_decimal_point. -

- -

-i) 22.2.4.1 para. 1 (collate) refers to "instantiations required in Table -51". Same bad jargon. -

- -

-j) 22.2.4.1.2 para. 1 (do_compare) refers to "instantiations required -in Table 51". Same bad jargon. -

- -

-k) 22.2.5 para. 1 (time_get/put) uses the same muddled and vacuous -as num_get/put. -

- -

-l) 22.2.6 para. 2 (money_get/put) uses the same muddled and vacuous -as num_get/put. -

- -

-m) 22.2.6.3.2 (do_pos/neg_format) says "The instantiations required -in Table 51 ... return an object of type pattern initialized to -{symbol, sign, none, value}." This once again *overrides* the "C" -locale, as well as any other locale." -

- -

-3) We constrain the use_facet calls that can be made by num_get/put, -so why don't we do the same for money_get/put? Or for any of the -other facets, for that matter? -

- -

-4) As an almost aside, we spell out when a facet needs to use the ctype -facet, but several also need to use a codecvt facet and we don't say so. -

-

[ -Berlin: Bill to provide wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-No objection to NAD. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

504. Integer types in pseudo-random number engine requirements

-

Section: 26.5.1 [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD Editorial - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In [tr.rand.req], Paragraph 2 states that "... s is a value of integral type, -g is an ... object returning values of unsigned integral type ..." -

- - -

Proposed resolution:

-

-In 5.1.1 [tr.rand.req], Paragraph 2 replace -

- -

-... s is a value of integral type, g is an lvalue of a type other than X that -defines a zero-argument function object returning values of unsigned integral type -unsigned long int, -... -

- -

-In 5.1.1 [tr.rand.seq], Table 16, replace in the line for X(s) -

- -

-creates an engine with the initial internal state -determined by static_cast<unsigned long>(s) -

- -

[ -Mont Tremblant: Both s and g should be unsigned long. -This should refer to the constructor signatures. Jens provided wording post Mont Tremblant. -]

- - -

[ -Berlin: N1932 adopts the proposed resolution: see 26.3.1.3/1e and Table 3 row 2. Moved -to Ready. -]

- - - - -

Rationale:

-

-Jens: Just requiring X(unsigned long) still makes it possible -for an evil library writer to also supply a X(int) that does something -unexpected. The wording above requires that X(s) always performs -as if X(unsigned long) would have been called. I believe that is -sufficient and implements our intentions from Mont Tremblant. I -see no additional use in actually requiring a X(unsigned long) -signature. u.seed(s) is covered by its reference to X(s), same -arguments. -

- - -

[ -Portland: Subsumed by N2111. -]

- - - - - -
-

506. Requirements of Distribution parameter for variate_generator

-

Section: 26.5 [rand], TR1 5.1.3 [tr.rand.var] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 3 requires that template argument U (which corresponds to template -parameter Engine) satisfy all uniform random number generator requirements. -However, there is no analogous requirement regarding the template argument -that corresponds to template parameter Distribution. We believe there should -be, and that it should require that this template argument satisfy all random -distribution requirements. -

- - -

Proposed resolution:

-

-Consequence 1: Remove the precondition clauses [tr.rand.var]/16 and /18. -

-

-Consequence 2: Add max() and min() functions to those distributions that -do not already have them. -

- -

[ -Mont Tremblant: Jens reccommends NAD, min/max not needed everywhere. -Marc supports having min and max to satisfy generic programming interface. -]

- - - - -

Rationale:

-

Berlin: N1932 makes this moot: variate_generator has been eliminated.

- - - - - -
-

509. Uniform_int template parameters

-

Section: 26.5.8.2 [rand.dist.uni], TR1 5.1.7.1 [tr.rand.dist.iunif] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In [tr.rand.dist.iunif] the uniform_int distribution currently has a single -template parameter, IntType, used as the input_type and as the result_type -of the distribution. We believe there is no reason to conflate these types -in this way. -

- - -

Proposed resolution:

-

-We recommend that there be a second template parameter to -reflect the distribution's input_type, and that the existing first template -parameter continue to reflect (solely) the result_type: -

-
-template< class IntType = int, UIntType = unsigned int >
-class uniform_int
-{
-public:
-  // types
-  typedef  UIntType  input_type;
-  typedef  IntType   result_type;
-
- -

[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]

- - - - - - - -
-

510. Input_type for bernoulli_distribution

-

Section: 26.5.8.3 [rand.dist.bern], TR1 5.1.7.2 [tr.rand.dist.bern] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-In [tr.rand.dist.bern] the distribution currently requires; -

-
-typedef  int  input_type;
-
- - -

Proposed resolution:

-

-We believe this is an unfortunate choice, and recommend instead: -

-
-typedef  unsigned int  input_type;
-
- -

[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]

- - - - - - - -
-

511. Input_type for binomial_distribution

-

Section: 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Unlike all other distributions in TR1, this binomial_distribution has an -implementation-defined input_type. We believe this is an unfortunate choice, -because it hinders users from writing portable code. It also hinders the -writing of compliance tests. We recommend instead: -

-
-typedef  RealType  input_type;
-
-

-While this choice is somewhat arbitrary (as it was for some of the other -distributions), we make this particular choice because (unlike all other -distributions) otherwise this template would not publish its RealType -argument and so users could not write generic code that accessed this -second template parameter. In this respect, the choice is consistent with -the other distributions in TR1. -

-

-We have two reasons for recommending that a real type be specified instead. -One reason is based specifically on characteristics of binomial distribution -implementations, while the other is based on mathematical characteristics of -probability distribution functions in general. -

-

-Implementations of binomial distributions commonly use Stirling approximations -for values in certain ranges. It is far more natural to use real values to -represent these approximations than it would be to use integral values to do -so. In other ranges, implementations reply on the Bernoulli distribution to -obtain values. While TR1's bernoulli_distribution::input_type is specified as -int, we believe this would be better specified as double. -

-

-This brings us to our main point: The notion of a random distribution rests -on the notion of a cumulative distribution function, which in turn mathematically -depends on a continuous dependent variable. Indeed, such a distribution function -would be meaningless if it depended on discrete values such as integers - and this -remains true even if the distribution function were to take discrete steps. -

-

-Although this note is specifically about binomial_distribution::input_type, -we intend to recommend that all of the random distributions input_types be -specified as a real type (either a RealType template parameter, or double, -as appropriate). -

-

-Of the nine distributions in TR1, four already have this characteristic -(uniform_real, exponential_distribution, normal_distribution, and -gamma_distribution). We have already argued the case for the binomial the -remaining four distributions. -

-

-In the case of uniform_int, we believe that the calculations to produce an -integer result in a specified range from an integer in a different specified -range is best done using real arithmetic. This is because it involves a -product, one of whose terms is the ratio of the extents of the two ranges. -Without real arithmetic, the results become less uniform: some numbers become -more (or less) probable that they should be. This is, of course, undesireable -behavior in a uniform distribution. -

-

-Finally, we believe that in the case of the bernoulli_distribution (briefly -mentioned earlier), as well as the cases of the geometric_distribution and the -poisson_distribution, it would be far more natural to have a real input_type. -This is because the most natural computation involves the random number -delivered and the distribution's parameter p (in the case of bernoulli_distribution, -for example, the computation is a comparison against p), and p is already specified -in each case as having some real type. -

- - -

Proposed resolution:

-
-typedef  RealType  input_type;
-
- -

[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]

- - - - - - -
-

512. Seeding subtract_with_carry_01 from a single unsigned long

-

Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 8 specifies the algorithm by which a subtract_with_carry_01 engine -is to be seeded given a single unsigned long. This algorithm is seriously -flawed in the case where the engine parameter w (also known as word_size) -exceeds 31 [bits]. The key part of the paragraph reads: -

-

-sets x(-r) ... x(-1) to (lcg(1)*2**(-w)) mod 1 -

-

-and so forth. -

-

-Since the specified linear congruential engine, lcg, delivers numbers with -a maximum of 2147483563 (just a shade under 31 bits), then when w is, for -example, 48, each of the x(i) will be less than 2**-17. The consequence -is that roughly the first 400 numbers delivered will be conspicuously -close to either zero or one. -

-

-Unfortunately, this is not an innocuous flaw: One of the predefined engines -in [tr.rand.predef], namely ranlux64_base_01, has w = 48 and would exhibit -this poor behavior, while the original N1378 proposal states that these -pre-defined engines are intended to be of "known good properties." -

- - -

Proposed resolution:

-

-In 5.1.4.4 [tr.rand.eng.sub1], replace the "effects" clause for -void seed(unsigned long value = 19780503) by -

- -

-Effects: If value == 0, sets value to 19780503. In any -case, with a linear congruential generator lcg(i) having parameters -mlcg = 2147483563, alcg = 40014, -clcg = 0, and lcg(0) = value, -sets carry(-1) and x(-r) … x(-1) -as if executing

- -

-linear_congruential<unsigned long, 40014, 0, 2147483563> lcg(value);
-seed(lcg);
-
- -

-to (lcg(1) · 2-w) mod 1 -… (lcg(r) · 2-w) mod 1, -respectively. If x(-1) == 0, sets carry(-1) = 2-w, -else sets carry(-1) = 0.

-
- -

[ -Jens provided revised wording post Mont Tremblant. -]

- - -

[ -Berlin: N1932 adopts the originally-proposed resolution of the issue. -Jens's supplied wording is a clearer description of what is -intended. Moved to Ready. -]

- - - - -

Rationale:

-

-Jens: I'm using an explicit type here, because fixing the -prose would probably not qualify for the (with issue 504 even -stricter) requirements we have for seed(Gen&). -

- -

[ -Portland: Subsumed by N2111. -]

- - - - - - -
-

513. Size of state for subtract_with_carry_01

-

Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 3 begins: -

-

-The size of the state is r. -

-

-However, this is not quite consistent with the remainder of the paragraph -which specifies a total of nr+1 items in the textual representation of -the state. We recommend the sentence be corrected to match: -

-

-The size of the state is nr+1. -

-

-To give meaning to the coefficient n, it may be also desirable to move -n's definition from later in the paragraph. Either of the following -seem reasonable formulations: -

-

-With n=..., the size of the state is nr+1. -

-

-The size of the state is nr+1, where n=... . -

- - - -

Proposed resolution:

-

[ -Jens: I plead for "NAD" on the grounds that "size of state" is only -used as an argument for big-O complexity notation, thus -constant factors and additions don't count. -]

- - -

[ -Berlin: N1932 adopts the proposed NAD. -]

- - - - - - - -
-

514. Size of state for subtract_with_carry

-

Section: 26.5.3.3 [rand.eng.sub], TR1 5.1.4.3 [tr.rand.eng.sub] Status: NAD Editorial - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

Discussion:

-

-Paragraph 2 begins: -

-

-The size of the state is r. -

-

-However, the next sentence specifies a total of r+1 items in the textual -representation of the state, r specific x's as well as a specific carry. -This makes a total of r+1 items that constitute the size of the state, -rather than r. -

- - -

Proposed resolution:

-

-We recommend the sentence be corrected to match: -

-

- The size of the state is r+1. -

- -

[ -Jens: I plead for "NAD" on the grounds that "size of state" is only -used as an argument for big-O complexity notation, thus -constant factors and additions don't count. -]

- - -

[ -Berlin: N1932 adopts the proposed NAD. -]

- - - - - - - -
-

515. Random number engine traits

-

Section: 26.5.2 [rand.synopsis], TR1 5.1.2 [tr.rand.synopsis] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-To accompany the concept of a pseudo-random number engine as defined in Table 17, -we propose and recommend an adjunct template, engine_traits, to be declared in -[tr.rand.synopsis] as: -

-
-template< class PSRE >
-class engine_traits;
-
-

-This template's primary purpose would be as an aid to generic programming involving -pseudo-random number engines. Given only the facilities described in tr1, it would -be very difficult to produce any algorithms involving the notion of a generic engine. -The intent of this proposal is to provide, via engine_traits<>, sufficient -descriptive information to allow an algorithm to employ a pseudo-random number engine -without regard to its exact type, i.e., as a template parameter. -

-

-For example, today it is not possible to write an efficient generic function that -requires any specific number of random bits. More specifically, consider a -cryptographic application that internally needs 256 bits of randomness per call: -

-
-template< class Eng, class InIter, class OutIter >
-void crypto( Eng& e, InIter in, OutIter out );
-
-

-Without knowning the number of bits of randomness produced per call to a provided -engine, the algorithm has no means of determining how many times to call the engine. -

-

-In a new section [tr.rand.eng.traits], we proposed to define the engine_traits -template as: -

-
-template< class PSRE >
-class engine_traits
-{
-  static  std::size_t  bits_of_randomness = 0u;
-  static  std::string  name()  { return "unknown_engine"; }
-  // TODO: other traits here
-};
-
-

-Further, each engine described in [tr.rand.engine] would be accompanied by a -complete specialization of this new engine_traits template. -

- - - -

Proposed resolution:

-

[ -Berlin: Walter: While useful for implementation per TR1, N1932 has no need for this -feature. Recommend close as NAD. -]

- - - -

Rationale:

-

-Recommend NAD, -N1932, -N2111 -covers this. Already in WP. -

- - - - - -
-

516. Seeding subtract_with_carry_01 using a generator

-

Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 6 says: -

-

-... obtained by successive invocations of g, ... -

-

-We recommend instead: -

-

-... obtained by taking successive invocations of g mod 2**32, ... -

-

-as the context seems to require only 32-bit quantities be used here. -

- - -

Proposed resolution:

-

-Berlin: N1932 adopts the proposed resultion: see 26.3.3.4/7. Moved to Ready. -

- -

[ -Portland: Subsumed by N2111. -]

- - - - - - -
-

517. Should include name in external representation

-

Section: 26.5.1 [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The last two rows of Table 16 deal with the i/o requirements of an engine, -specifying that the textual representation of an engine's state, -appropriately formatted, constitute the engine's external representation. -

-

-This seems adequate when an engine's type is known. However, it seems -inadequate in the context of generic code, where it becomes useful and -perhaps even necessary to determine an engine's type via input. -

-

-

- - -

Proposed resolution:

-

-We therefore recommend that, in each of these two rows of Table 16, the -text "textual representation" be expanded so as to read "engine name -followed by the textual representation." -

- -

[ -Berlin: N1932 considers this NAD. This is a QOI issue. -]

- - - - - - - -
-

526. Is it undefined if a function in the standard changes in parameters?

-

Section: 23.2.3 [sequence.reqmts] Status: NAD - Submitter: Chris Jefferson Opened: 2005-09-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Problem: There are a number of places in the C++ standard library where -it is possible to write what appear to be sensible ways of calling -functions, but which can cause problems in some (or all) -implementations, as they cause the values given to the function to be -changed in a way not specified in standard (and therefore not coded to -correctly work). These fall into two similar categories. -

- -

-1) Parameters taken by const reference can be changed during execution -of the function -

- -

-Examples: -

- -

-Given std::vector<int> v: -

-

-v.insert(v.begin(), v[2]); -

-

-v[2] can be changed by moving elements of vector -

- - -

-Given std::list<int> l: -

-

-l.remove(*l.begin()); -

-

-Will delete the first element, and then continue trying to access it. -This is particularily vicious, as it will appear to work in almost all -cases. -

- -

-2) A range is given which changes during the execution of the function: -Similarly, -

- -

-v.insert(v.begin(), v.begin()+4, v.begin()+6); -

- -

-This kind of problem has been partly covered in some cases. For example -std::copy(first, last, result) states that result cannot be in the range -[first, last). However, does this cover the case where result is a -reverse_iterator built from some iterator in the range [first, last)? -Also, std::copy would still break if result was reverse_iterator(last + -1), yet this is not forbidden by the standard -

- -

-Solution: -

- -

-One option would be to try to more carefully limit the requirements of -each function. There are many functions which would have to be checked. -However as has been shown in the std::copy case, this may be difficult. -A simpler, more global option would be to somewhere insert text similar to: -

- -

-If the execution of any function would change either any values passed -by reference or any value in any range passed to a function in a way not -defined in the definition of that function, the result is undefined. -

- -

-Such code would have to at least cover chapters 23 and 25 (the sections -I read through carefully). I can see no harm on applying it to much of -the rest of the standard. -

- -

-Some existing parts of the standard could be improved to fit with this, -for example the requires for 25.2.1 (Copy) could be adjusted to: -

- -

-Requires: For each non-negative integer n < (last - first), assigning to -*(result + n) must not alter any value in the range [first + n, last). -

- -

-However, this may add excessive complication. -

- -

-One other benefit of clearly introducing this text is that it would -allow a number of small optimisations, such as caching values passed -by const reference. -

- -

-Matt Austern adds that this issue also exists for the insert and -erase members of the ordered and unordered associative containers. -

- -

[ -Berlin: Lots of controversey over how this should be solved. Lots of confusion -as to whether we're talking about self referencing iterators or references. -Needs a good survey as to the cases where this matters, for which -implementations, and how expensive it is to fix each case. -]

- - - - -

Proposed resolution:

- - -

Rationale:

-

-Recommend NAD. -

-
    -
  • vector::insert(iter, value) is required to work because the standard -doesn't give permission for it not to work.
    • -
  • list::remove(value) is required to work because the standard -doesn't give permission for it not to work.
    • -
  • vector::insert(iter, iter, iter) is not required to work because -23.2.3 [sequence.reqmts], p4 says so.
    • -
  • copy has to work, except where 25.3.1 [alg.copy] says -it doesn't have to work. While a language lawyer can tear this wording apart, -it is felt that the wording is not prone to accidental interpretation.
    • -
  • The current working draft provide exceptions for the unordered associative -containers similar to the containers requirements which exempt the member -template insert functions from self referencing.
    • -
- - - - - -
-

528. const_iterator iterator issue when they are the same type

-

Section: 23.5 [unord], TR1 6.3.4 [tr.unord.unord] Status: NAD - Submitter: Paolo Carlini Opened: 2005-10-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-while implementing the resolution of issue 6.19 I'm noticing the -following: according to 6.3.4.3/2 (and 6.3.4.5/2), for unordered_set and -unordered_multiset: -

- -

- "The iterator and const_iterator types are both const types. It is -unspecified whether they are the same type" -

- -

-Now, according to the resolution of 6.19, we have overloads of insert -with hint and erase (single and range) both for iterator and -const_iterator, which, AFAICS, can be meaningful at the same time *only* -if iterator and const_iterator *are* in fact different types. -

-

-Then, iterator and const_iterator are *required* to be different types? -Or that is an unintended consequence? Maybe the overloads for plain -iterators should be added only to unordered_map and unordered_multimap? -Or, of course, I'm missing something? -

- - - -

Proposed resolution:

-

-Add to 6.3.4.3p2 (and 6.3.4.5p2): -

-

-2 ... The iterator and const_iterator types are both const -constant iterator types. -It is unspecified whether they are the same type. -

- -

-Add a new subsection to 17.4.4 [lib.conforming]: -

- -
-

-An implementation shall not supply an overloaded function - signature specified in any library clause if such a signature - would be inherently ambiguous during overload resolution - due to two library types referring to the same type. -

-

- [Note: For example, this occurs when a container's iterator - and const_iterator types are the same. -- end note] -

-
- -

[ -Post-Berlin: Beman supplied wording. -]

- - - - -

Rationale:

-Toronto: The first issue has been fixed by N2350 (the insert and erase members -are collapsed into one signature). Alisdair to open a separate issue on the -chapter 17 wording. -

- - - - -
-

529. The standard encourages redundant and confusing preconditions

-

Section: 17.6.4.11 [res.on.required] Status: NAD Editorial - Submitter: David Abrahams Opened: 2005-10-25 Last modified: 2015-04-08

-

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-

Discussion:

-

-17.4.3.8/1 says: -

- -

-Violation of the preconditions specified in a function's -Required behavior: paragraph results in undefined behavior unless the -function's Throws: paragraph specifies throwing an exception when the -precondition is violated. -

- -

-This implies that a precondition violation can lead to defined -behavior. That conflicts with the only reasonable definition of -precondition: that a violation leads to undefined behavior. Any other -definition muddies the waters when it comes to analyzing program -correctness, because precondition violations may be routinely done in -correct code (e.g. you can use std::vector::at with the full -expectation that you'll get an exception when your index is out of -range, catch the exception, and continue). Not only is it a bad -example to set, but it encourages needless complication and redundancy -in the standard. For example: -

- -
-  21 Strings library 
-  21.3.3 basic_string capacity
-
-  void resize(size_type n, charT c);
-
-  5 Requires: n <= max_size()
-  6 Throws: length_error if n > max_size().
-  7 Effects: Alters the length of the string designated by *this as follows:
-
- -

-The Requires clause is entirely redundant and can be dropped. We -could make that simplifying change (and many others like it) even -without changing 17.4.3.8/1; the wording there just seems to encourage -the redundant and error-prone Requires: clause. -

- -

[ -Batavia: Alan and Pete to work. -]

- - -

[ -Bellevue: NAD Editorial, this group likes -N2121, -Pete agrees, accepting it is Pete's business. -General agreement that precondition violations are synonymous with UB. -]

- - - -

Proposed resolution:

-

-1. Change 17.4.3.8/1 to read: -

- -

-Violation of the preconditions specified in a function's -Required behavior: paragraph results in undefined behavior -unless the function's Throws: paragraph specifies throwing -an exception when the precondition is violated. -

- -

-2. Go through and remove redundant Requires: clauses. Specifics to be - provided by Dave A. -

- -

[ -Berlin: The LWG requests a detailed survey of part 2 of the proposed resolution. -]

- - -

[ -Alan provided the survey -N2121. -]

- - - - - - - -
-

536. Container iterator constructor and explicit convertibility

-

Section: 23.2 [container.requirements] Status: Dup - Submitter: Joaquín M López Muñoz Opened: 2005-12-17 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 589

-

Discussion:

-

-The iterator constructor X(i,j) for containers as defined in 23.1.1 and -23.2.2 does only require that i and j be input iterators but -nothing is said about their associated value_type. There are three -sensible -options: -

-
    -
  1. iterator's value_type is exactly X::value_type (modulo cv).
    2. -
  2. iterator's value_type is *implicitly* convertible to X::value_type.
    3. -
  3. iterator's value_type is *explicitly* convertible to X::value_type.
    4. -
-

-The issue has practical implications, and stdlib vendors have -taken divergent approaches to it: Dinkumware follows 2, -libstdc++ follows 3. -

-

-The same problem applies to the definition of insert(p,i,j) for -sequences and insert(i,j) for associative contianers, as well as -assign. -

- -

[ -The following added by Howard and the example code was originally written by -Dietmar. -]

- -

-Valid code below? -

- -
-#include <vector> 
-#include <iterator> 
-#include <iostream> 
-
-struct foo 
-{ 
-    explicit foo(int) {} 
-}; 
-
-int main() 
-{ 
-    std::vector<int> v_int; 
-    std::vector<foo> v_foo1(v_int.begin(), v_int.end()); 
-    std::vector<foo> v_foo2((std::istream_iterator<int>(std::cin)), 
-                             std::istream_iterator<int>()); 
-} 
-
-

[ -Berlin: Some support, not universal, for respecting the explicit qualifier. -]

- - - - -

Proposed resolution:

- - - - - - -
-

544. minor NULL problems in C.2

-

Section: C.5 [diff.library] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2005-11-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-According to C.2.2.3, p1, "the macro NULL, defined in any of <clocale>, -<cstddef>, <cstdio>, <cstdlib>, <cstring>, <ctime>, -or <cwchar>." This is consistent with the C standard. -

-

-However, Table 95 in C.2 fails to mention <clocale> and <cstdlib>. -

-

-In addition, C.2, p2 claims that "The C++ Standard library provides -54 standard macros from the C library, as shown in Table 95." While -table 95 does have 54 entries, since a couple of them (including the -NULL macro) are listed more than once, the actual number of macros -defined by the C++ Standard Library may not be 54. -

- - -

Proposed resolution:

-

-I propose we add <clocale> and <cstdlib> to Table 96 and remove the -number of macros from C.2, p2 and reword the sentence as follows: -

-

-The C++ Standard library provides 54 standard macros from -defines a number macros corresponding to those defined by the C -Standard library, as shown in Table 96. -

- -

[ -Portland: Resolution is considered editorial. It will be incorporated into the WD. -]

- - - - - - - -
-

546. _Longlong and _ULonglong are integer types

-

Section: TR1 5.1.1 [tr.rand.req] Status: NAD - Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-The TR sneaks in two new integer types, _Longlong and _Ulonglong, in [tr.c99]. -The rest of the TR should use that type. I believe this affects two places. -First, the random number requirements, 5.1.1/10-11, lists all of the types with -which template parameters named IntType and UIntType may be instantiated. -_Longlong (or "long long", assuming it is added to C++0x) should be added to the -IntType list, and UIntType (again, or "unsigned long long") should be added to -the UIntType list. Second, 6.3.2 lists the types for which hash<> is -required to be instantiable. _Longlong and _Ulonglong should be added to that -list, so that people may use long long as a hash key. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-We are not going to fix TR1. -

-

-The paper "long long goes to the library" addresses the integration of -long long into the C++0x library. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

547. division should be floating-point, not integer

-

Section: 26.5 [rand], TR1 5.1 [tr.rand] Status: NAD - Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2015-04-08

-

View all other issues in [rand].

-

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-

Discussion:

-

-Paragraph 10 describes how a variate generator uses numbers produced by an -engine to pass to a generator. The sentence that concerns me is: "Otherwise, if -the value for engine_value_type::result_type is true and the value for -Distribution::input_type is false [i.e. if the engine produces integers and the -engine wants floating-point values], then the numbers in s_eng are divided by -engine().max() - engine().min() + 1 to obtain the numbers in s_e." Since the -engine is producing integers, both the numerator and the denominator are -integers and we'll be doing integer division, which I don't think is what we -want. Shouldn't we be performing a conversion to a floating-point type first? -

- - -

Proposed resolution:

- - -

Rationale:

-

-Recommend NAD as the affected section is now gone and so the issue is moot. -N2111. -

- - - - - -
-

548. May random_device block?

-

Section: 26.5.6 [rand.device], TR1 5.1.6 [tr.rand.device] Status: NAD - Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Class random_device "produces non-deterministic random numbers", using some -external source of entropy. In most real-world systems, the amount of available -entropy is limited. Suppose that entropy has been exhausted. What is an -implementation permitted to do? In particular, is it permitted to block -indefinitely until more random bits are available, or is the implementation -required to detect failure immediately? This is not an academic question. On -Linux a straightforward implementation would read from /dev/random, and "When -the entropy pool is empty, reads to /dev/random will block until additional -environmental noise is gathered." Programmers need to know whether random_device -is permitted to (or possibly even required to?) behave the same way. -

- -

[ -Berlin: Walter: N1932 considers this NAD. Does the standard specify whether std::cin -may block? -]

- - -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423 (NAD). -

- - - - - -
-

549. Undefined variable in binomial_distribution

-

Section: 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD Editorial - Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 1 says that "A binomial distributon random distribution produces -integer values i>0 with p(i) = (n choose i) * p*i * (1-p)^(t-i), where t and -p are the parameters of the distribution. OK, that tells us what t, p, and i -are. What's n? -

- - -

Proposed resolution:

-

-Berlin: Typo: "n" replaced by "t" in N1932: see 26.3.7.2.2/1. -

- -

[ -Portland: Subsumed by N2111. -]

- - - - - - -
-

553. very minor editorial change intptr_t / uintptr_t

-

Section: 18.4.1 [cstdint.syn], TR1 8.22.1 [tr.c99.cstdint.syn] Status: NAD Editorial - Submitter: Paolo Carlini Opened: 2006-01-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In the synopsis, some types are identified as optional: int8_t, int16_t, -and so on, consistently with C99, indeed. -

-

-On the other hand, intptr_t and uintptr_t, are not marked as such and -probably should, consistently with C99, 7.18.1.4. -

- - -

Proposed resolution:

-

-Change 18.4.1 [cstdint.syn]: -

- -
-...
-typedef signed integer type intptr_t;    // optional
-...
-typedef unsigned integer type uintptr_t;    // optional
-...
-
- - - -

Rationale:

-Recommend NAD and fix as editorial with the proposed resolution. -

- - - - -
-

554. Problem with lwg DR 184 numeric_limits<bool>

-

Section: 18.3.2.7 [numeric.special] Status: NAD - Submitter: Howard Hinnant Opened: 2006-01-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I believe we have a bug in the resolution of: -lwg 184 -(WP status). -

- -

-The resolution spells out each member of numeric_limits<bool>. -The part I'm having a little trouble with is: -

-
-static const bool traps = false;
-
- -

-Should this not be implementation defined? Given: -

- -
-int main()
-{
-     bool b1 = true;
-     bool b2 = false;
-     bool b3 = b1/b2;
-}
-
- -

-If this causes a trap, shouldn't numeric_limits<bool>::traps be -true? -

- - -

Proposed resolution:

-

-Change 18.2.1.5p3: -

- -

--3- The specialization for bool shall be provided as follows:

-
-namespace std { 
-   template <> class numeric_limits<bool> {
-      ...
-      static const bool traps = false implementation-defined;
-      ...
-   };
-}
-
-
- -

[ -Redmond: NAD because traps refers to values, not operations. There is no bool -value that will trap. -]

- - - - - - - -
-

555. TR1, 8.21/1: typo

-

Section: TR1 8.21 [tr.c99.boolh] Status: NAD Editorial - Submitter: Paolo Carlini Opened: 2006-02-02 Last modified: 2015-04-08

-

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-

Discussion:

-

-This one, if nobody noticed it yet, seems really editorial: -s/cstbool/cstdbool/ -

- - -

Proposed resolution:

-

-Change 8.21p1: -

-

--1- The header behaves as if it defines the additional macro defined in -<cstdbool> by including the header <cstdbool>. -

- -

[ -Redmond: Editorial. -]

- - - - - - - -
-

557. TR1: div(_Longlong, _Longlong) vs div(intmax_t, intmax_t)

-

Section: 18.4 [cstdint], TR1 8.22 [tr.c99.cstdint] Status: NAD Editorial - Submitter: Paolo Carlini Opened: 2006-02-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I'm seeing a problem with such overloads: when, _Longlong == intmax_t == -long long we end up, essentially, with the same arguments and different -return types (lldiv_t and imaxdiv_t, respectively). Similar issue with -abs(_Longlong) and abs(intmax_t), of course. -

-

-Comparing sections 8.25 and 8.11, I see an important difference, -however: 8.25.3 and 8.25.4 carefully describe div and abs for _Longlong -types (rightfully, because not moved over directly from C99), whereas -there is no equivalent in 8.11: the abs and div overloads for intmax_t -types appear only in the synopsis and are not described anywhere, in -particular no mention in 8.11.2 (at variance with 8.25.2). -

-

-I'm wondering whether we really, really, want div and abs for intmax_t... -

- - - -

Proposed resolution:

- - - -

[ -Portland: no consensus. -]

- - -

Rationale:

-

[ -Batavia, Bill: The <cstdint> synopsis in TR1 8.11.1 [tr.c99.cinttypes.syn] contains: -]

- -
-intmax_t imaxabs(intmax_t i);
-intmax_t abs(intmax_t i);
-
-imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
-imaxdiv_t div(intmax_t numer, intmax_t denom);
-
- -

[ -and in TR1 8.11.2 [tr.c99.cinttypes.def]: -]

- - -

-The header defines all functions, types, and macros the same as C99 -subclause 7.8. -

- -

[ -This is as much definition as we give for most other C99 functions, -so nothing need change. We might, however, choose to add the footnote: -]

- - -

-[Note: These overloads for abs and div may well be equivalent to -those that take long long arguments. If so, the implementation is -responsible for avoiding conflicting declarations. -- end note] -

- -

[ -Bellevue: NAD Editorial. Pete must add a footnote, as described below. -]

- - -
-

[ -Looks like a real problem. Dietmar suggests div() return a template -type. Matt: looks like imaxdiv_t is loosly defined. Can it be a typedef -for lldiv_t when _Longlong == intmax_t? PJP seems to agree. We would -need a non-normative note declaring that the types lldiv_t and imaxdiv_t -may not be unique if intmax_t==_longlong. -]

- -
- - - - - - -
-

558. lib.input.iterators Defect

-

Section: 24.2.3 [input.iterators] Status: NAD Editorial - Submitter: David Abrahams Opened: 2006-02-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
-

- 24.1.1 Input iterators [lib.input.iterators] -

-

- 1 A class or a built-in type X satisfies the requirements of an - input iterator for the value type T if the following expressions are - valid, where U is the type of any specified member of type T, as - shown in Table 73. -

-
-

-There is no capital U used in table 73. There is a lowercase u, but -that is clearly not meant to denote a member of type T. Also, there's -no description in 24.1.1 of what lowercase a means. IMO the above -should have been...Hah, a and b are already covered in 24.1/11, so maybe it -should have just been: -

- - -

Proposed resolution:

-

-Change 24.1.1p1: -

-

--1- A class or a built-in type X satisfies the requirements of an -input iterator for the value type T if the following expressions -are valid, where U is the type of any specified member of type -T, as shown in Table 73. -

- -

[ -Portland: Editorial. -]

- - - - - - - -
-

560. User-defined allocators without default constructor

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: Sergey P. Derevyago Opened: 2006-02-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

1. The essence of the problem.

-

-User-defined allocators without default constructor are not explicitly -supported by the standard but they can be supported just like std::vector -supports elements without default constructor. -

-

-As a result, there exist implementations that work well with such allocators -and implementations that don't. -

- -

2. The cause of the problem.

-

-1) The standard doesn't explicitly state this intent but it should. In -particular, 20.1.5p5 explicitly state the intent w.r.t. the allocator -instances that compare non-equal. So it can similarly state the intent w.r.t. -the user-defined allocators without default constructor. -

-

-2) Some container operations are obviously underspecified. In particular, -21.3.7.1p2 tells: -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator> operator+(
-    const charT* lhs,
-    const basic_string<charT,traits,Allocator>& rhs
-  );
-
-

-Returns: basic_string<charT,traits,Allocator>(lhs) + rhs. -

-
-

-That leads to the basic_string<charT,traits,Allocator>(lhs, Allocator()) call. -Obviously, the right requirement is: -

-

-Returns: basic_string<charT,traits,Allocator>(lhs, rhs.get_allocator()) + rhs. -

-

-It seems like a lot of DRs can be submitted on this "Absent call to -get_allocator()" topic. -

- -

3. Proposed actions.

-

-1) Explicitly state the intent to allow for user-defined allocators without -default constructor in 20.1.5 Allocator requirements. -

-

-2) Correct all the places, where a correct allocator object is available -through the get_allocator() call but default Allocator() gets passed instead. -

-

4. Code sample.

-

-Let's suppose that the following memory pool is available: -

-
-class mem_pool {
-      // ...
-      void* allocate(size_t size);
-      void deallocate(void* ptr, size_t size);
-};
-
-

-So the following allocator can be implemented via this pool: -

-
-class stl_allocator {
-      mem_pool& pool;
-
- public:
-      explicit stl_allocator(mem_pool& mp) : pool(mp) {}
-      stl_allocator(const stl_allocator& sa) : pool(sa.pool) {}
-      template <class U>
-      stl_allocator(const stl_allocator<U>& sa)  : pool(sa.get_pool()) {}
-      ~stl_allocator() {}
-
-      pointer allocate(size_type n, std::allocator<void>::const_pointer = 0)
-      {
-       return (n!=0) ? static_cast<pointer>(pool.allocate(n*sizeof(T))) : 0;
-      }
-
-      void deallocate(pointer p, size_type n)
-      {
-       if (n!=0) pool.deallocate(p, n*sizeof(T));
-      }
-
-      // ...
-};
-
-

-Then the following code works well on some implementations and doesn't work on -another: -

-
-typedef basic_string<char, char_traits<char>, stl_allocator<char> > 
-  tl_string;
-mem_pool mp;
-tl_string s1("abc", stl_allocator<int>(mp));
-printf("(%s)\n", ("def"+s1).c_str());
-
-

-In particular, on some implementations the code can't be compiled without -default stl_allocator() constructor. -

-

-The obvious way to solve the compile-time problems is to intentionally define -a NULL pointer dereferencing default constructor -

-
-stl_allocator() : pool(*static_cast<mem_pool*>(0)) {}
-
-

-in a hope that it will not be called. The problem is that it really gets -called by operator+(const char*, const string&) under the current 21.3.7.1p2 -wording. -

- - -

Proposed resolution:

-

-

- - -

Rationale:

-

-Recommend NAD. operator+() with string already requires the desired -semantics of copying the allocator from one of the strings (lhs when there is a choice). -

- - - - - -
-

568. log2 overloads missing

-

Section: TR1 8.16.4 [tr.c99.cmath.over] Status: NAD - Submitter: Paolo Carlini Opened: 2006-03-07 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-log2 is missing from the list of "additional overloads" in TR1 8.16.4 [tr.c99.cmath.over] p1. -

- -

-Hinnant: This is a TR1 issue only. It is fixed in the current (N2135) WD. -

- -

[ -Batavia (2009-05): -]

- -

-We agree this has been fixed in the Working Draft. -Move to NAD. -

- - -

Proposed resolution:

-

-Add log2 to the list of functions in TR1 8.16.4 [tr.c99.cmath.over] p1. -

- - - - - -
-

569. Postcondition for basic_ios::clear(iostate) incorrectly stated

-

Section: 27.5.5.4 [iostate.flags] Status: Dup - Submitter: Seungbeom Kim Opened: 2006-03-10 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 272

-

Discussion:

-

-Section: 27.4.4.3 [lib.iostate.flags] -

-

-Paragraph 4 says: -

-
-
-void clear(iostate state = goodbit);
-
-

-Postcondition: If rdbuf()!=0 then state == rdstate(); -otherwise rdstate()==state|ios_base::badbit. -

-
- -

-The postcondition "rdstate()==state|ios_base::badbit" is parsed as -"(rdstate()==state)|ios_base::badbit", which is probably what the -committee meant. -

- - - - -

Rationale:

- - - - - - -
-

570. Request adding additional explicit specializations of char_traits

-

Section: 21.2 [char.traits] Status: NAD - Submitter: Jack Reeves Opened: 2006-04-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Currently, the Standard Library specifies only a declaration for template class -char_traits<> and requires the implementation provide two explicit -specializations: char_traits<char> and char_traits<wchar_t>. -I feel the Standard should require explicit specializations for all built-in -character types, i.e. char, wchar_t, unsigned char, -and signed char. -

-

-I have put together a paper -(N1985) -that describes this in more detail and -includes all the necessary wording. -

-

[ -Portland: Jack will rewrite -N1985 -to propose a primary template that will work with other integral types. -]

- -

[ -Toronto: issue has grown with addition of char16_t and char32_t. -]

- - -

[ -post Bellevue: -]

- - -
-

-We suggest that Jack be asked about the status of his paper, and if it -is not forthcoming, the work-item be assigned to someone else. If no one -steps forward to do the paper before the next meeting, we propose to -make this NAD without further discussion. We leave this Open for now, -but our recommendation is NAD. -

-

-Note: the issue statement should be updated, as the Toronto comment has -already been resolved. E.g., char_traits specializations for char16_t -and char32_t are now in the working paper. -

-
- -

[ -Sophia Antipolis: -]

- - -

-Nobody has submitted the requested paper, so we move to NAD, as suggested by the decision at the last meeting. -

- - -

Proposed resolution:

- - - - - -
-

571. Update C90 references to C99?

-

Section: 1.2 [intro.refs] Status: NAD Editorial - Submitter: Beman Dawes Opened: 2006-04-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-1.2 Normative references [intro.refs] of the WP currently refers to ISO/IEC -9899:1990, Programming languages - C. Should that be changed to ISO/IEC -9899:1999? -

-

-What impact does this have on the library? -

- - -

Proposed resolution:

-

-In 1.2/1 [intro.refs] of the WP, change: -

-
-
    -
  • ISO/IEC 9899:19901999 + TC1 + TC2, Programming languages - C
    • -
-
- - - -

Rationale:

-Recommend NAD, fixed editorially. -

- - - - -
-

572. Oops, we gave 507 WP status

-

Section: 26.5 [rand], TR1 5.1 [tr.rand] Status: NAD - Submitter: Howard Hinnant Opened: 2006-04-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In Berlin, as a working group, we voted in favor of N1932 which makes issue 507 moot: -variate_generator has been eliminated. Then in full committee we voted to give -this issue WP status (mistakenly). -

- - -

Proposed resolution:

-

-Strike the proposed resolution of issue 507. -

-

[ -post-Portland: Walter and Howard recommend NAD. The proposed resolution of 507 no longer -exists in the current WD. -]

- - - -

Rationale:

-

-NAD. Will be moot once -N2135 -is adopted. -

- - - - - -
-

573. C++0x file positioning should handle modern file sizes

-

Section: 27.5.4 [fpos] Status: NAD - Submitter: Beman Dawes Opened: 2006-04-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-There are two deficiencies related to file sizes: -

-
    -
  1. It doesn't appear that the Standard Library is specified in - a way that handles modern file sizes, which are often too - large to be represented by an unsigned long.
    2. - -
  2. The std::fpos class does not currently have the ability to - set/get file positions.
    3. -
-

-The Dinkumware implementation of the Standard Library as shipped with the Microsoft compiler copes with these issues by: -

-
    -
  1. Defining fpos_t be long long, which is large enough to - represent any file position likely in the foreseeable future.
    2. - -
  2. Adding member functions to class fpos. For example, -
    -fpos_t seekpos() const;
-
    -
    3. -
-

-Because there are so many types relating to file positions and offsets (fpos_t, -fpos, pos_type, off_type, streamoff, streamsize, -streampos, wstreampos, and perhaps more), it is difficult to know if -the Dinkumware extensions are sufficient. But they seem a useful starting place for -discussions, and they do represent existing practice. -

- -

[ -Kona (2007): We need a paper. It would be nice if someone proposed -clarifications to the definitions of pos_type and off_type. Currently -these definitions are horrible. Proposed Disposition: Open -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-This is the subject of paper N2926. -

-

-If we choose to take any action, we will move the paper, so the issue can be closed. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

579. erase(iterator) for unordered containers should not return an iterator

-

Section: 23.2.5 [unord.req] Status: NAD - Submitter: Joaquín M López Muñoz Opened: 2006-06-13 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses ES-2

- -

-See -N2023 -for full discussion. -

- -

[ -2009-12-11 Paolo opens: -]

- - -

-I'm asking for DR 579 to be re-opened, basing on recent discussions on the -library reflector, see Message c++std-lib-26040 and replies. -

- -

[ -2010-02-07 Paolo updates wording. -]

- - -

-As pointed out by Chris in c++std-lib-26040, that an -erase(unordered_container, iterator) returning an iterator can -easily implemented in user code, if needed; that actually returning an -iterator costs nothing for the overload taking two iterators, -thus that proposed change is only for consistency; that -forward_list::erase_after also returns void (for different -reasons, granted, but isn't that any "erase" function in the containers -uniformly returns an iterator); that, also in thread started by Chris' -message, Alberto pointed out that the proxy idea isn't a good one; that users -both of the GNU and Boost implementations are reporting serious performance -problems with the current version returning an iterator. -

- -

[ -2010-02-07 Original wording saved here: -]

- - -
-

-Option 1: -

- -

-The problem can be eliminated by omitting the requirement that a.erase(q) return an -iterator. This is, however, in contrast with the equivalent requirements for other -standard containers. -

- -

-Option 2: -

- -

-a.erase(q) can be made to compute the next iterator only when explicitly requested: -the technique consists in returning a proxy object implicitly convertible to iterator, so -that -

- -
-iterator q1=a.erase(q);
-
- -

-works as expected, while -

- -
-a.erase(q);
-
- -

-does not ever invoke the conversion-to-iterator operator, thus avoiding the associated -computation. To allow this technique, some sections of TR1 along the line "return value -is an iterator..." should be changed to "return value is an unspecified object implicitly -convertible to an iterator..." Although this trick is expected to work transparently, it can -have some collateral effects when the expression a.erase(q) is used inside generic -code. -

- -
- -

[ -2010-03-27 Joaquín adds: -]

- - -
-

-Signature of iterator erase(const_iterator) should be changed to void -erase(const_iterator). If this is not viable an acceptable tradeoff -could be to make the return type of erase(const_iterator) -implementation defined. -

- -

-The standard should allow implementations of unordered associative -containers using either singly or doubly linked lists. -N2023 -proves that singly-linked lists implementations cannot provide the required -complexity for iterator erase(const_iterator). Thus, some action is -needed to allow both implementations. -

- -

-Option 1: Changing the required complexity from O(1) to O(log n). This option -merely masks a design flaw. Users are forcefully penalized for what they don't -use (the returned iterator). Besides, they would have to learn about the -pathological (yet very real) situations where using erase can lead to -quadratic performance. Two out of these three objections remain even if some -alternative member function like void quick_erase(const_iterator) is -thrown in to the interface. -

- -

-Some objections have been expressed to changing return type of erase to -void, arguing that it would break current existing practice with -standard library implementations based on doubly-linked lists, where the problem -does not occur. However implementations based on drafts should not block the -resolution of a serious design issue, more so when the issue will hurt future -users of C++, as it's happening already. -

- -

-Option 2: Make erase return type implementation defined. There's -a possible tradeoff with the objectors above consisting in changing the -signature to implementation defined erase(iterator), so that -returning an iterator is indeed a valid extension. To this it can be argued that -this would make implementantions returning an iterator look as somehow promoting -proprietary extensions: this in my opinion is not a valid argument since those -implementations are already extending the required interface by -providing bidirectional iterators (just forward iterators are required). -

-
- -

[ -2010 Rapperswil: -]

- - -
-

-The issue was lengthy discussed and implementation experience was demonstrated that a non-void return -type is implementable for both single-linked and double-linked lists without loss of efficiency. -

- -

-By a 12-1-1-0 poll voted to keep the return type of erase as iterator instead of -void and a second 0-0-3-10 poll rejected the additional proposal to add a -quick_erase returning void, thus LWG decided for NAD. -

-
- - -

Rationale:

- -

-No consensus for a change. -

- - - -

Proposed resolution:

- - - - - -
-

580. unused allocator members

-

Section: 23.2.1 [container.requirements.general] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2006-06-14 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 479

-

Discussion:

-

- -C++ Standard Library templates that take an allocator as an argument -are required to call the allocate() and -deallocate() members of the allocator object to obtain -storage. However, they do not appear to be required to call any other -allocator members such as construct(), -destroy(), address(), and -max_size(). This makes these allocator members less than -useful in portable programs. - -

-

- -It's unclear to me whether the absence of the requirement to use these -allocator members is an unintentional omission or a deliberate -choice. However, since the functions exist in the standard allocator -and since they are required to be provided by any user-defined -allocator I believe the standard ought to be clarified to explictly -specify whether programs should or should not be able to rely on -standard containers calling the functions. - -

-

- -I propose that all containers be required to make use of these -functions. - -

-

[ -Batavia: We support this resolution. Martin to provide wording. -]

- -

[ -pre-Oxford: Martin provided wording. -]

- - -

[ -2009-04-28 Pablo adds: -]

- - -

-N2554 -(scoped allocators), -N2768 -(allocator concepts), and -N2810 -(allocator defects), address all of these points EXCEPT max_size(). -So, I would add a note to that affect and re-class the defect as belonging -to section 23.2.1 [container.requirements.general]. -

- -

[ -2009-07 Frankfurt -]

- - -

-The comment in the description of this issue that this "would be" -rendered editorial by the adoption of N2257 is confusing. It appears -that N2257 was never adopted. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Editorial. Addressed by -N2982. -

- - - -

Proposed resolution:

-

- -Specifically, I propose to change 23.2 [container.requirements], -p9 as follows: - -

-
-

--9- Copy constructors for all container types defined in this clause -that are parametrized on Allocator copy -anthe allocator argument from their respective -first parameters. - -All other constructors for these container types take an -const Allocator& argument (20.1.6), an -allocator whose value_type is the same as the container's -value_type. - -A copy of this argument isshall be used for any -memory allocation and deallocation performed, -by these constructors and by all member functions, during -the lifetime of each container object. Allocation shall be -performed "as if" by calling the allocate() member -function on a copy of the allocator object of the appropriate type -New Footnote), and deallocation "as if" by calling -deallocate() on a copy of the same allocator object of -the corresponding type. - -A copy of this argument shall also be used to construct and -destroy objects whose lifetime is managed by the container, including -but not limited to those of the container's value_type, -and to obtain their address. All objects residing in storage -allocated by a container's allocator shall be constructed "as if" by -calling the construct() member function on a copy of the -allocator object of the appropriate type. The same objects shall be -destroyed "as if" by calling destroy() on a copy of the -same allocator object of the same type. The address of such objects -shall be obtained "as if" by calling the address() member -function on a copy of the allocator object of the appropriate -type. - -Finally, a copy of this argument shall be used by its container -object to determine the maximum number of objects of the container's -value_type the container may store at the same time. The -container member function max_size() obtains this number -from the value returned by a call to -get_allocator().max_size(). - -In all container types defined in this clause that are -parametrized on Allocator, the member -get_allocator() returns a copy of the -Allocator object used to construct the -container.258) -

-

-New Footnote: This type may be different from Allocator: -it may be derived from Allocator via -Allocator::rebind<U>::other for the appropriate -type U. -

-
-

- -The proposed wording seems cumbersome but I couldn't think of a better -way to describe the requirement that containers use their -Allocator to manage only objects (regardless of their -type) that persist over their lifetimes and not, for example, -temporaries created on the stack. That is, containers shouldn't be -required to call Allocator::construct(Allocator::allocate(1), -elem) just to construct a temporary copy of an element, or -Allocator::destroy(Allocator::address(temp), 1) to -destroy temporaries. - -

- - -

[ -Howard: This same paragraph will need some work to accommodate 431. -]

- - -

[ -post Oxford: This would be rendered NAD Editorial by acceptance of -N2257. -]

- - - - - -
-

582. specialized algorithms and volatile storage

-

Section: 20.7.12.2 [uninitialized.copy] Status: NAD - Submitter: Martin Sebor Opened: 2006-06-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Related to 1029

-

- -The specialized algorithms [lib.specialized.algorithms] are specified -as having the general effect of invoking the following expression: - -

- 
-
-new (static_cast<void*>(&*i))
-    typename iterator_traits<ForwardIterator>::value_type (x)
-
-
-

- -This expression is ill-formed when the type of the subexpression -&*i is some volatile-qualified T. - -

- -

[ -Batavia: Lack of support for proposed resolution but agree there is a -defect. Howard to look at wording. Concern that move semantics -properly expressed if iterator returns rvalue. -]

- - - -

[ -2009-06-17 Pablo adds: -]

- - -
- -

Propose that Issue 582 be closed NAD.

-

-Issue 582 asks that uninitialized_copy, -uninitialized_fill, and uninitialized_fill_n should be -well-formed if the result type is volatile. My feeling is that the -standard does not, and should not, guarantee any useful behavior when -constructors are invoked on volatile storage, so making it syntactically -legal to call uninitialized_copy on volatile storage is not useful. A -possible editorial change would be to put my previous sentence into a -non-normative note. -

-

-Note that the three sections starting with 20.7.12.2 [uninitialized.copy] do not -yet have concepts. Here's a first crack at the first one: -

-
-template <InputIterator InIter, OutputIterator OutIter>
-requires ExplicitConvertible<HasDereference<OutIter::reference>::result,
-                             OutIter::value_type&>
-      && Convertible<OutIter::value_type*, void*>
-      && ExplicitConvertible<OutIter::value_type, InIter::reference>
-  OutIter uninitialized_copy(InIter first, InIter last, OutIter result);
-
-
-

-Effects: -

-
-while (first != last) {
-  typedef OutIter::value_type value_type;
-  value_type& outRef = static_cast<value_type&>(*result++);
-  ::new (static_cast<void*>(addressof(outRef))) value_type(*first++);
-}
-
-
- -
- -

-Notes: -

-
    -
  1. This definition is actually LESS constrained than in C++03 because -there is no requirement that the result be a forward iterator. -
    2. -
  2. -If -OutIter returns a proxy type with an overloaded operator&, this -definition probably won't compile. Lifting this limitation while -allowing value_type to have an overloaded operator& would be hard, but -is probably possible with careful overloading. I'm not sure it's worth -it. -
    3. -
  3. -This definition retains the prohibition on the use of volatile types for the result. -
    4. -
- -
- -

[ -2009-07 Frankfurt -]

- - -
-

-We don't deal with volatile in the library. -

-

-Jim: should we state that explicitly somewhere? -

-

-Beman: you might argue that clause 17 should say something about -volatile. However, if you want to raise we argument, we should open it -as a separate issue and consult with experts on concurrency. -

-

-Hinnant: actually, some library components do handle volatile, so we'd -need to be very careful about what we say in clause 17. -

-

-No objection to NAD. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

- -In order to allow these algorithms to operate on volatile storage I -propose to change the expression so as to make it well-formed even for -pointers to volatile types. Specifically, I propose the following -changes to clauses 20 and 24. Change 20.6.4.1, p1 to read: - -

- 
-
-Effects:
-
-typedef typename iterator_traits<ForwardIterator>::pointer    pointer;
-typedef typename iterator_traits<ForwardIterator>::value_type value_type;
-
-for (; first != last; ++result, ++first)
-    new (static_cast<void*>(const_cast<pointer>(&*result))
-        value_type (*first);
-
-
-

- -change 20.6.4.2, p1 to read - -

- 
-
-Effects:
-
-typedef typename iterator_traits<ForwardIterator>::pointer    pointer;
-typedef typename iterator_traits<ForwardIterator>::value_type value_type;
-
-for (; first != last; ++result, ++first)
-    new (static_cast<void*>(const_cast<pointer>(&*first))
-        value_type (*x);
-
-
-

- -and change 20.6.4.3, p1 to read - -

- 
-
-Effects:
-
-typedef typename iterator_traits<ForwardIterator>::pointer    pointer;
-typedef typename iterator_traits<ForwardIterator>::value_type value_type;
-
-for (; n--; ++first)
-    new (static_cast<void*>(const_cast<pointer>(&*first))
-        value_type (*x);
-
-
-

- -In addition, since there is no partial specialization for -iterator_traits<volatile T*> I propose to add one -to parallel such specialization for <const T*>. Specifically, I -propose to add the following text to the end of 24.3.1, p3: - -

-

- -and for pointers to volatile as - -

- 
-
-namespace std {
-template<class T> struct iterator_traits<volatile T*> {
-typedef ptrdiff_t difference_type;
-typedef T value_type;
-typedef volatile T* pointer;
-typedef volatile T& reference;
-typedef random_access_iterator_tag iterator_category;
-};
-}
-
-
-

- -Note that the change to iterator_traits isn't necessary -in order to implement the specialized algorithms in a way that allows -them to operate on volatile strorage. It is only necesassary in order -to specify their effects in terms of iterator_traits as -is done here. Implementations can (and some do) achieve the same -effect by means of function template overloading. - -

- - - - -
-

583. div() for unsigned integral types

-

Section: 26.8 [c.math] Status: NAD - Submitter: Beman Dawes Opened: 2006-06-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-There is no div() function for unsigned integer types. -

-

-There are several possible resolutions. The simplest one is noted below. Other -possibilities include a templated solution. -

- - -

Proposed resolution:

-

-Add to 26.7 [lib.c.math] paragraph 8: -

- -
-struct udiv_t div(unsigned, unsigned);
-struct uldiv_t div(unsigned long, unsigned long);
-struct ulldiv_t div(unsigned long long, unsigned long long);
-
- - - -

Rationale:

-Toronto: C99 does not have these unsigned versions because -the signed version exist just to define the implementation-defined behavior -of signed integer division. Unsigned integer division has no implementation-defined -behavior and thus does not need this treatment. -

- - - - -
-

584. missing int pow(int,int) functionality

-

Section: 26.8 [c.math] Status: NAD - Submitter: Beman Dawes Opened: 2006-06-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-There is no pow() function for any integral type. -

- - -

Proposed resolution:

-

-Add something like: -

- -
-template< typename T>
-T power( T x, int n );
-// requires: n >=0
-
- - -

Rationale:

-Toronto: We already have double pow(integral, integral) from 26.8 [c.math] p11. -

- - - - -
-

585. facet error reporting

-

Section: 22.4 [locale.categories] Status: NAD - Submitter: Martin Sebor, Paolo Carlini Opened: 2006-06-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -Section 22.2, paragraph 2 requires facet get() members -that take an ios_base::iostate& argument, -err, to ignore the (initial) value of the -argument, but to set it to ios_base::failbit in case of a -parse error. - -

-

- -We believe there are a few minor problems with this blanket -requirement in conjunction with the wording specific to each -get() member function. - -

-

- -First, besides get() there are other member functions -with a slightly different name (for example, -get_date()). It's not completely clear that the intent of -the paragraph is to include those as well, and at least one -implementation has interpreted the requirement literally. - -

-

- -Second, the requirement to "set the argument to -ios_base::failbit suggests that the functions are not -permitted to set it to any other value (such as -ios_base::eofbit, or even ios_base::eofbit | -ios_base::failbit). - -

-

- -However, 22.2.2.1.2, p5 (Stage 3 of num_get parsing) and -p6 (bool parsing) specifies that the do_get -functions perform err |= ios_base::eofbit, which -contradicts the earlier requirement to ignore err's initial -value. - -

-

- -22.2.6.1.2, p1 (the Effects clause of the money_get -facet's do_get member functions) also specifies that -err's initial value be used to compute the final -value by ORing it with either ios_base::failbit or -withios_base::eofbit | ios_base::failbit. - -

- -

[ -2009-07 Frankfurt -]

- - -

-Move to NAD. -

- - - -

Proposed resolution:

-

- -We believe the intent is for all facet member functions that take an -ios_base::iostate& argument to: - -

-
    -
  • - -ignore the initial value of the err argument, - -
    • -
  • - -reset err to ios_base::goodbit prior -to any further processing, - -
    • -
  • - -and set either ios_base::eofbit, or -ios_base::failbit, or both in err, as -appropriate, in response to reaching the end-of-file or on parse -error, or both. - -
    • -
-

- -To that effect we propose to change 22.2, p2 as follows: - -

-

- -The put() members make no provision for error -reporting. (Any failures of the OutputIterator argument must be -extracted from the returned iterator.) Unless otherwise -specified, the get() members that -take an ios_base::iostate& argument whose value -they ignore, but set to ios_base::failbit in case of a parse -error., err, start by evaluating -err = ios_base::goodbit, and may subsequently set -err to either ios_base::eofbit, or -ios_base::failbit, or ios_base::eofbit | -ios_base::failbit in response to reaching the end-of-file or in -case of a parse error, or both, respectively. - -

- - -

[ -Kona (2007): We need to change the proposed wording to clarify that the -phrase "the get members" actually denotes get(), get_date(), etc. -Proposed Disposition: Open -]

- - - - -
-

587. iststream ctor missing description

-

Section: D.7.2.1 [depr.istrstream.cons] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2006-06-22 Last modified: 2015-04-08

-

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-

Discussion:

-

- -The iststream(char*, streamsize) ctor is in the class -synopsis in D.7.2 but its signature is missing in the description -below (in D.7.2.1). - -

- - -

Proposed resolution:

-

- -This seems like a simple editorial issue and the missing signature can -be added to the one for const char* in paragraph 2. - -

- -

[ -post Oxford: Noted that it is already fixed in -N2284 -]

- - - - - - -
-

588. requirements on zero sized tr1::arrays and other details

-

Section: 23.3.2 [array] Status: NAD - Submitter: Gennaro Prota Opened: 2006-07-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The wording used for section 23.2.1 [lib.array] seems to be subtly -ambiguous about zero sized arrays (N==0). Specifically: -

-

-* "An instance of array<T, N> stores N elements of type T, so that -[...]" -

-

-Does this imply that a zero sized array object stores 0 elements, i.e. -that it cannot store any element of type T? The next point clarifies -the rationale behind this question, basically how to implement begin() -and end(): -

-

-* 23.2.1.5 [lib.array.zero], p2: "In the case that N == 0, begin() == -end() == unique value." -

-

-What does "unique" mean in this context? Let's consider the following -possible implementations, all relying on a partial specialization: -

-
-a)
-    template< typename T >
-    class array< T, 0 > {
-    
-        ....
-
-        iterator begin()
-        { return iterator( reinterpret_cast< T * >( this ) ); }
-        ....
-
-    };
-
-

-This has been used in boost, probably intending that the return value -had to be unique to the specific array object and that array couldn't -store any T. Note that, besides relying on a reinterpret_cast, has -(more than potential) alignment problems. -

-
-b)
-    template< typename T >
-    class array< T, 0 > {
-    
-        T t;
-
-        iterator begin()
-        { return iterator( &t ); }
-        ....
-
-    };
-
-

-This provides a value which is unique to the object and to the type of -the array, but requires storing a T. Also, it would allow the user to -mistakenly provide an initializer list with one element. -

-

-A slight variant could be returning *the* null pointer of type T -

-
-    return static_cast<T*>(0);
-
-

-In this case the value would be unique to the type array<T, 0> but not -to the objects (all objects of type array<T, 0> with the same value -for T would yield the same pointer value). -

-

-Furthermore this is inconsistent with what the standard requires from -allocation functions (see library issue 9). -

-

-c) same as above but with t being a static data member; again, the -value would be unique to the type, not to the object. -

-

-d) to avoid storing a T *directly* while disallowing the possibility -to use a one-element initializer list a non-aggregate nested class -could be defined -

-
-    struct holder { holder() {} T t; } h;
-
-

-and then begin be defined as -

-
- iterator begin() { return &h.t; }
-
-

-But then, it's arguable whether the array stores a T or not. -Indirectly it does. -

-

------------------------------------------------------ -

-

-Now, on different issues: -

-

-* what's the effect of calling assign(T&) on a zero-sized array? There -seems to be only mention of front() and back(), in 23.2.1 [lib.array] -p4 (I would also suggest to move that bullet to section 23.2.1.5 -[lib.array.zero], for locality of reference) -

-

-* (minor) the opening paragraph of 23.2.1 [lib.array] wording is a bit -inconsistent with that of other sequences: that's not a problem in -itself, but compare it for instance with "A vector is a kind of -sequence that supports random access iterators"; though the intent is -obvious one might argue that the wording used for arrays doesn't tell -what an array is, and relies on the reader to infer that it is what -the <array> header defines. -

-

-* it would be desiderable to have a static const data member of type -std::size_t, with value N, for usage as integral constant expression -

-

-* section 23.1 [lib.container.requirements] seem not to consider -fixed-size containers at all, as it says: "[containers] control -allocation and deallocation of these objects [the contained objects] -through constructors, destructors, *insert and erase* operations" -

-

-* max_size() isn't specified: the result is obvious but, technically, -it relies on table 80: "size() of the largest possible container" -which, again, doesn't seem to consider fixed size containers -

- -

[ -2009-05-29 Daniel adds: -]

- - -
-
    -
  1. -

    -star bullet 1 ("what's the effect of calling assign(T&) on a -zero-sized array?[..]"); -

    -

    -assign has been renamed to fill and the semantic of fill is now -defined in terms of -the free algorithm fill_n, which is well-defined for this situation. -

    -
    2. -
  2. -

    -star bullet 3 ("it would be desiderable to have a static const data -member..."): -

    -

    -It seems that tuple_size<array<T, N> >::value as of 23.3.2.9 [array.tuple] does -provide this functionality now. -

    -
    3. -
-
- -

[ -2009-07 Frankfurt -]

- - -
-

-Alisdair to address by the next meeting, or declare NAD. -

-

-Moved to Tentatively NAD. -

-
- -

[ -2009 Santa Cruz: -]

- - -

-Moved to NAD. -

- - - -

Proposed resolution:

-

-

- - -

[ -Kona (2007): requirements on zero sized tr1::arrays and other details -Issue 617: std::array is a sequence that doesn't satisfy the sequence -requirements? Alisdair will prepare a paper. Proposed Disposition: Open -]

- - - - - -
-

590. Type traits implementation latitude should be removed for C++0x

-

Section: 20.10 [meta], TR1 4.9 [tr.meta.req] Status: NAD Editorial - Submitter: Beman Dawes Opened: 2006-08-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-20.4.9 [lib.meta.req], Implementation requirements, provides latitude for type -traits implementers that is not needed in C++0x. It includes the wording: -

- -

-[Note: the latitude granted to implementers in this clause is temporary, -and is expected to be removed in future revisions of this document. -- end note] -

- -

-Note: -N2157: Minor Modifications to the type traits Wording -also has the intent of removing this wording from the WP. -

- - - -

Proposed resolution:

-

-Remove 20.4.9 [lib.meta.req] in its entirety from the WP. -

- -

[ -post-Oxford: Recommend NAD Editorial. This resolution is now in the -current working draft. -]

- - - - - - - -
-

591. Misleading "built-in

-

Section: 18.3.2.4 [numeric.limits.members] Status: NAD Editorial - Submitter: whyglinux Opened: 2006-08-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-18.2.1.2 numeric_limits members [lib.numeric.limits.members] -Paragraph 7: -

-

-"For built-in integer types, the number of non-sign bits in the -representation." -

- -

-26.1 Numeric type requirements [lib.numeric.requirements] -Footnote: -

- -

-"In other words, value types. These include built-in arithmetic types, -pointers, the library class complex, and instantiations of valarray for -value types." -

- -

-Integer types (which are bool, char, wchar_t, and the signed and -unsigned integer types) and arithmetic types (which are integer and -floating types) are all built-in types and thus there are no -non-built-in (that is, user-defined) integer or arithmetic types. Since -the redundant "built-in" in the above 2 sentences can mislead that -there may be built-in or user-defined integer and arithmetic types -(which is not correct), the "built-in" should be removed. -

- - -

Proposed resolution:

-

-18.2.1.2 numeric_limits members [lib.numeric.limits.members] -Paragraph 7: -

-

-"For built-in integer types, the number of non-sign bits in the -representation." -

- -

-26.1 Numeric type requirements [lib.numeric.requirements] -Footnote: -

- -

-"In other words, value types. These include built-in arithmetic types, -pointers, the library class complex, and instantiations of valarray for -value types." -

- - -

Rationale:

-

-Recommend NAD / Editorial. The proposed resolution is accepted as editorial. -

- - - - - -
-

592. Incorrect treatment of rdbuf()->close() return type

-

Section: 27.9.1.9 [ifstream.members] Status: NAD Editorial - Submitter: Christopher Kohlhoff Opened: 2006-08-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I just spotted a minor problem in 27.8.1.7 -[lib.ifstream.members] para 4 and also 27.8.1.13 -[lib.fstream.members] para 4. In both places it says: -

-
-
-void close();
-
-

-Effects: Calls rdbuf()->close() and, if that function returns false, ... -

-
-

-However, basic_filebuf::close() (27.8.1.2) returns a pointer to the -filebuf on success, null on failure, so I think it is meant to -say "if that function returns a null pointer". Oddly, it is -correct for basic_ofstream. -

- - -

Proposed resolution:

-

-Change 27.9.1.9 [ifstream.members], p5: -

- -

-Effects: Calls rdbuf()->close() and, if that function -fails (returns false a null pointer), -calls setstate(failbit) (which may throw ios_base::failure -(27.4.4.3)). -

- -

-Change 27.9.1.17 [fstream.members], p5: -

- -

-Effects: Calls rdbuf()->close() and, if that function -fails (returns false a null pointer), -calls setstate(failbit) (which may throw ios_base::failure -(27.4.4.3)). -

- - - -

[ -Kona (2007): Proposed Disposition: NAD, Editorial -]

- - - - - -
-

597. Decimal: The notion of 'promotion' cannot be emulated by user-defined types.

-

Section: TRDecimal 3.2 [trdec.types.types] Status: NAD - Submitter: Daveed Vandevoorde Opened: 2006-04-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In a private email, Daveed writes: -

-
-

-I am not familiar with the C TR, but my guess is that the -class type approach still won't match a built-in type -approach because the notion of "promotion" cannot be -emulated by user-defined types. -

-

-Here is an example: -

-
-
-
-         struct S {
-           S(_Decimal32 const&);  // Converting constructor
-         };
-         void f(S);
-
-         void f(_Decimal64);
-
-         void g(_Decimal32 d) {
-           f(d);
-         }
-
- -
-

-If _Decimal32 is a built-in type, the call f(d) will likely -resolve to f(_Decimal64) because that requires only a -promotion, whereas f(S) requires a user-defined conversion. -

-

-If _Decimal32 is a class type, I think the call f(d) will be -ambiguous because both the conversion to _Decimal64 and the -conversion to S will be user-defined conversions with neither -better than the other. -

-
-

-Robert comments: -

-

-In general, a library of arithmetic types cannot exactly emulate the behavior of the intrinsic numeric types. There are several ways to tell whether an implementation of the decimal types uses compiler intrinisics or a library. For example: -

-
-                 _Decimal32 d1;
-                 d1.operator+=(5);  // If d1 is a builtin type, this won't compile.
-
-

-In preparing the decimal TR, we have three options: -

-
    -
  1. require that the decimal types be class types
    2. -
  2. require that the decimal types be builtin types, like float and double
    3. -
  3. specify a library of class types, but allow enough implementor latitude that a conforming implementation could instead provide builtin types
    4. -
-

-We decided as a group to pursue option #3, but that approach implies that implementations may not agree on the semantics of certain use cases (first example, above), or on whether certain other cases are well-formed (second example). Another potentially important problem is that, under the present definition of POD, the decimal classes are not POD types, but builtins will be. -

-

-Note that neither example above implies any problems with respect to C-to-C++ compatibility, since neither example can be expressed in C. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Decimal numeric types may either be builtin types or library types. We -only intend to specify the common subset of behaviors of the two -implementation approaches. The front matter of the Decimal TR says this -explicitly. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

- - - - - -
-

606. Decimal: allow narrowing conversions

-

Section: TRDecimal 3.2 [trdec.types.types] Status: NAD - Submitter: Martin Sebor Opened: 2006-06-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In c++std-lib-17205, Martin writes: -

-

-...was it a deliberate design choice to make narrowing assignments ill-formed while permitting narrowing compound assignments? For instance: -

-
-      decimal32 d32;
-      decimal64 d64;
-
-      d32 = 64;     // error
-      d32 += 64;    // okay
-
-

-In c++std-lib-17229, Robert responds: -

-

-It is a vestige of an old idea that I forgot to remove from the paper. Narrowing assignments should be permitted. The bug is that the converting constructors that cause narrowing should not be explicit. Thanks for pointing this out. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-The current state of the Decimal TR is the result of a deliberate design -decision that has been examined many times. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-1. In "3.2.2 Class decimal32" synopsis, remove the explicit specifier from the narrowing conversions: -

-
-                // 3.2.2.2 conversion from floating-point type:
-                explicit decimal32(decimal64 d64);
-                explicit decimal32(decimal128 d128);
-
-

-2. Do the same thing in "3.2.2.2. Conversion from floating-point type." -

-

-3. In "3.2.3 Class decimal64" synopsis, remove the explicit specifier from the narrowing conversion: -

-
-                // 3.2.3.2 conversion from floating-point type:
-                explicit decimal64(decimal128 d128);
-
-

-4. Do the same thing in "3.2.3.2. Conversion from floating-point type." -

- -

[ -Redmond: We prefer explicit conversions for narrowing and implicit for widening. -]

- - - - - - -
-

614. std::string allocator requirements still inconsistent

-

Section: 21.4 [basic.string] Status: NAD - Submitter: Bo Persson Opened: 2006-12-05 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-This is based on N2134, where 21.3.1/2 states: -"... The Allocator object used shall be a copy of the Allocator object -passed to the basic_string object's constructor or, if the constructor does -not take an Allocator argument, a copy of a default-constructed Allocator -object." -

-

-Section 21.3.2/1 lists two constructors: -

-
-basic_string(const basic_string<charT,traits,Allocator>& str );
-
-basic_string(const basic_string<charT,traits,Allocator>& str ,
-             size_type pos , size_type n = npos,
-             const Allocator& a = Allocator());
-
-

-and then says "In the first form, the Allocator value used is copied from -str.get_allocator().", which isn't an option according to 21.3.1. -

-

[ -Batavia: We need blanket statement to the effect of: -]

- - -
    -
  1. If an allocator is passed in, use it, or,
    2. -
  2. If a string is passed in, use its allocator.
    3. -
-

[ -Review constructors and functions that return a string; make sure we follow these -rules (substr, operator+, etc.). Howard to supply wording. -]

- - -

[ -Bo adds: The new container constructor which takes only a size_type is not -consistent with 23.2 [container.requirements], p9 which says in part: -]

- - -

-All other constructors for these container types take an -Allocator& argument (20.1.2), an allocator whose value type -is the same as the container's value type. A copy of this argument is -used for any memory allocation performed, by these constructors and by -all member functions, during the lifetime of each container object. -

- -

[ -post Bellevue: We re-confirm that the issue is real. Pablo will provide wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-Move to NAD. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

615. Inconsistencies in Section 21.4

-

Section: 21.8 [c.strings] Status: NAD Editorial - Submitter: Bo Persson Opened: 2006-12-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In the current draft N2134, 21.4/1 says -

-

-"Tables 59,228) 60, 61, 62,and 63 229) 230) describe headers <cctype>, -<cwctype>, <cstring>, <cwchar>, and <cstdlib> (character conversions), -respectively." -

-

-Here footnote 229 applies to table 62, not table 63. -

-

-Also, footnote 230 lists the new functions in table 63, "atoll, strtoll, -strtoull, strtof, and strtold added by TR1". However, strtof is not present -in table 63. -

- - -

Proposed resolution:

-

-

- - -

Rationale:

-

-Recommend NAD, editorial. Send to Pete. -

- - - - - -
-

617. std::array is a sequence that doesn't satisfy the sequence requirements?

-

Section: 23.3.2 [array] Status: NAD - Submitter: Bo Persson Opened: 2006-12-30 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The <array> header is given under 23.3 [sequences]. -23.3.2 [array]/paragraph 3 says: -

-

-"Unless otherwise specified, all array operations are as described in -23.2 [container.requirements]". -

-

-However, array isn't mentioned at all in section 23.2 [container.requirements]. -In particular, Table 82 "Sequence requirements" lists several operations (insert, erase, clear) -that std::array does not have in 23.3.2 [array]. -

-

-Also, Table 83 "Optional sequence operations" lists several operations that -std::array does have, but array isn't mentioned. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-The real issue seems to be different than what is described here. -Non-normative text says that std::array is a sequence container, but -there is disagreement about what that really means. There are two -possible interpretations: -

-
    -
  1. -a sequence container is one that satisfies all sequence container requirements -
    2. -
  2. -a sequence container is one that satisfies some of the sequence -container requirements. Any operation that the container supports is -specified by one or more sequence container requirements, unless that -operation is specifically singled out and defined alongside the -description of the container itself. -
    3. -
-

-Move to Tentatively NAD. -

-
- -

[ -2009-07-15 Loïc Joly adds: -]

- - -
-

-The section 23.2.3 [sequence.reqmts]/1 states that array is a sequence. 23.2.3 [sequence.reqmts]/3 -introduces table 83, named Sequence container requirements. This seems -to me to be defining the requirements for all sequences. However, array -does not follow all of this requirements (this can be read in the array -specific section, for the standard is currently inconsistent). -

- -

-Proposed resolution 1 (minimal change): -

-
-

-Say that array is a container, that in addition follows only some of the -sequence requirements, as described in the array section: -

- -

-The library provides five three basic kinds of sequence containers: array, -vector, -forward_list, list, and deque. In addition, array -and forward_list follows some of the requirements -of sequences, as described in their respective sections. -

- -
- -

-Proposed resolution 2 (most descriptive description, no full wording provided): -

-

-Introduce the notion of a Fixed Size Sequence, with it requirement table -that would be a subset of the current Sequence container. array would be -the only Fixed Size Sequence (but dynarray is in the queue for TR2). -Sequence requirements would now be requirements in addition to Fixed -Size Sequence requirements (it is currently in addition to container). -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to NAD Editorial -

- -

[ -2009 Santa Cruz: -]

- - -

-This will require a lot of reorganization. Editor doesn't think this is really -an issue, since the description of array can be considered as overriding -what's specified about sequences. Move to NAD. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

626. new Remark clauses not documented

-

Section: 17.5.1.4 [structure.specifications] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -The Remark clauses newly introduced into the Working Paper -(N2134) -are not mentioned in 17.5.1.4 [structure.specifications] where we list the -meaning of Effects, Requires, and other clauses (with -the exception of Notes which are documented as informative in -17.5.1.2 [structure.summary], p2, and which they replace in many cases). - -

-

- -Propose add a bullet for Remarks along with a brief description. - -

-

[ -Batavia: Alan and Pete to work. -]

- - -

[ -Bellevue: Already resolved in current working paper. -]

- - - -

Proposed resolution:

-

-

- - - - - -
-

627. Low memory and exceptions

-

Section: 18.6.1.1 [new.delete.single] Status: NAD - Submitter: P.J. Plauger Opened: 2007-01-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I recognize the need for nothrow guarantees in the exception reporting -mechanism, but I strongly believe that implementors also need an escape hatch -when memory gets really low. (Like, there's not enough heap to construct and -copy exception objects, or not enough stack to process the throw.) I'd like to -think we can put this escape hatch in 18.6.1.1 [new.delete.single], -operator new, but I'm not sure how to do it. We need more than a -footnote, but the wording has to be a bit vague. The idea is that if -new can't allocate something sufficiently small, it has the right to -abort/call terminate/call unexpected. -

- -

[ -Bellevue: NAD. 1.4p2 specifies a program must behave correctly "within -its resource limits", so no further escape hatch is necessary. -]

- - - -

Proposed resolution:

-

-

- - - - - -
-

631. conflicting requirements for BinaryPredicate

-

Section: 25 [algorithms] Status: NAD - Submitter: James Kanze Opened: 2007-01-31 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The general requirements for BinaryPredicate (in 25 [algorithms]/8) contradict the implied specific requirements for -some functions. In particular, it says that: -

- -

-[...] if an algorithm takes BinaryPredicate binary_pred -as its argument and first1 and first2 as its -iterator arguments, it should work correctly in the construct if -(binary_pred (*first1 , *first2 )){...}. -BinaryPredicate always takes the first iterator type as its -first argument, that is, in those cases when T value is -part of the signature, it should work correctly in the context of if -(binary_pred (*first1 , value)){...}. -

- -

-In the description of upper_bound (25.4.3.2 [upper.bound]/2), however, the use is described as -"!comp(value, e)", where e is an -element of the sequence (a result of dereferencing -*first). -

- -

-In the description of lexicographical_compare, we have both -"*first1 < *first2" and "*first2 -< *first1" (which presumably implies "comp( -*first1, *first2 )" and "comp( *first2, -*first1 )". -

- -

-Logically, the BinaryPredicate is used as an ordering -relationship, with the semantics of "less than". Depending on the -function, it may be used to determine equality, or any of the inequality -relationships; doing this requires being able to use it with either -parameter first. I would thus suggest that the requirement be: -

- -

-Alternatively, one could specify an order for each function. IMHO, this -would be more work for the committee, more work for the implementors, -and of no real advantage for the user: some functions, such as -lexicographical_compare or equal_range, will still require both -functions, and it seems like a much easier rule to teach that both -functions are always required, rather than to have a complicated list of -when you only need one, and which one. -

- -

[ -Toronto: Moved to Open. ConceptGCC seems to get lower_bound -and upper_bound to work withoutt these changes. -]

- - -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Review. The small problem with the "iterator type" -will be fixed. The cited functions (lower_bound, uppwer_bound, -equal_range) don't actually use BinaryPredicate , and where it is used, -it is consistent with [algorithm]/8, so the main complaint of the issue -is moot. -

- -

[ -2010-01-16 Beman clarified wording. -]

- - -

[ -2010-01-31: Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - - -

Rationale:

-

[ -post San Francisco: -]

- - -
-

-Solved by -N2759. -

-
- -

-2010-01-31: The draft standard is well specified as is, and this specification -is desired. Issues 556 and 870 solve the remaining -unclearness regarding the meaning of BinaryPredicate. -

- - - -

Proposed resolution:

-

Change 25 [algorithms] paragraph 8 as indicated:

- -
- -

-8 The BinaryPredicate parameter is used whenever an algorithm expects a -function object that when applied to the result of dereferencing two -corresponding iterators or to dereferencing an iterator and type T when -T is part of the signature returns a value testable as true. -BinaryPredicate always takes the first iterator value_type as -one of its arguments; which argument is unspecified. In other words, -if If an algorithm takes BinaryPredicate binary_pred -as its argument and first1 and first2 as its iterator -arguments, it should work correctly both in the construct if -(binary_pred(*first1, *first2)){...} and if (binary_pred (*first2, -*first1)){...}. BinaryPredicate always takes the first -iterator type as its first argument, that is, in In those cases -when T value is part of the signature, it should work correctly in the -context of if (binary_pred(*first1, value)){...} and of if -(binary_pred (value, *first1)){...}. binary_pred shall -not apply any non-constant function through the dereferenced iterators. -[Note: if the two types are not identical, and neither is -convertable to the other, this may require that the BinaryPredicate be -a functional object with two overloaded operator()() functions. -— end note] -

- -
- - - - - - -
-

632. Time complexity of size() for std::set

-

Section: 23.2 [container.requirements] Status: NAD - Submitter: Lionel B Opened: 2007-02-01 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-A recent news group discussion: -

-
-

-Anyone know if the Standard has anything to say about the time complexity -of size() for std::set? I need to access a set's size (not -to know if it is empty!) heavily during an algorithm and was thus wondering -whether I'd be better off tracking the size "manually" or whether that'd be pointless. -

-

-That would be pointless. size() is O(1). -

-

-Nit: the standard says "should" have constant time. Implementations may take -license to do worse. I know that some do this for std::list<> as a part of -some trade-off with other operation. -

- -

-I was aware of that, hence my reluctance to use size() for std::set. -

-

-However, this reason would not apply to std::set<> as far as I can see. -

-

-Ok, I guess the only option is to try it and see... -

-
- -

-If I have any recommendation to the C++ Standards Committee it is that -implementations must (not "should"!) document clearly[1], where known, the -time complexity of *all* container access operations. -

-

-[1] In my case (gcc 4.1.1) I can't swear that the time complexity of size() -for std::set is not documented... but if it is it's certainly well hidden -away. -

- -

[ -Kona (2007): This issue affects all the containers. We'd love to see a -paper dealing with the broad issue. We think that the complexity of the -size() member of every container -- except possibly list -- should be -O(1). Alan has volunteered to provide wording. -]

- - -

[ -Bellevue: -]

- - -

-Mandating O(1) size will not fly, too many implementations would be -invalidated. Alan to provide wording that toughens wording, but that -does not absolutely mandate O(1). -

- -

[ -Batavia (2009-05): -]

- -

-We observed that the wording "should" (in note a) has no effect. -Howard prefers that O(1) size be mandated. -It is not clear that this issue can be resolved to everyone's satisfaction, -but Alan will provide wording nonetheless. -

- -

[ -2009-07 Frankfurt -]

- - -

-Fixed by paper N2923. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

633. Return clause mentions undefined "type()"

-

Section: 20.9.12.2.5 [func.wrap.func.targ] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-02-03 Last modified: 2015-04-08

-

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-

Discussion:

-

-20.9.12.2.5 [func.wrap.func.targ], p4 says: -

-

-Returns: If type() == typeid(T), a pointer to the stored -function target; otherwise a null pointer. -

- -
    -
  1. -There exists neither a type, a typedef type, nor member -function type() in class template function nor in the global or -std namespace. -
    2. -
  2. -Assuming that type should have been target_type(), -this description would lead to false results, if T = cv -void due to returns clause 20.9.12.2.5 [func.wrap.func.targ], p1. -
    3. -
- - - -

Proposed resolution:

-

-Change 20.9.12.2.5 [func.wrap.func.targ], p4: -

- -

-Returns: If type() target_type() == typeid(T) && typeid(T) != -typeid(void), a pointer to the stored function target; -otherwise a null pointer. -

- -

[ -Pete: Agreed. It's editorial, so I'll fix it. -]

- - - - - - - -
-

636. 26.5.2.3 valarray::operator[]

-

Section: 26.6.2.4 [valarray.access] Status: NAD Editorial - Submitter: Bo Persson Opened: 2007-02-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The signature of the const operator[] has been changed to return a const -reference. -

-

-The description in paragraph 1 still says that the operator returns by -value. -

-

[ -Pete recommends editorial fix. -]

- - - -

Proposed resolution:

-

-

- - - - - -
-

637. [c.math]/10 inconsistent return values

-

Section: 26.8 [c.math] Status: NAD Editorial - Submitter: Bo Persson Opened: 2007-02-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-26.8 [c.math], paragraph 10 has long lists of added signatures for float and long double -functions. All the signatures have float/long double return values, which is -inconsistent with some of the double functions they are supposed to -overload. -

- - -

Proposed resolution:

-

-Change 26.8 [c.math], paragraph 10, -

- -
-float int ilogb(float);
-float long lrint(float);
-float long lround(float);
-float long long llrint(float);
-float long long llround(float);
-
-long double int ilogb(long double);
-long double long lrint(long double);
-long double long lround(long double);
-long double long long llrint(long double);
-long double long long llround(long double);
-
- - - - - -
-

639. Still problems with exceptions during streambuf IO

-

Section: 27.7.2.2.3 [istream::extractors], 27.7.3.6.3 [ostream.inserters] Status: NAD - Submitter: Daniel Krügler Opened: 2007-02-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-There already exist two active DR's for the wording of 27.7.2.2.3 [istream::extractors]/13 -from 14882:2003(E), namely 64 and 413. -

- -

-Even with these proposed corrections, already maintained in N2134, -I have the feeling, that the current wording does still not properly -handle the "exceptional" situation. The combination of para 14 -

- -

-"[..] Characters are extracted and inserted until -any of the following occurs: -

-

-[..] -

-

-- an exception occurs (in which case the exception is caught)." -

- -

-and 15 -

- -

-"If the function inserts no characters, it calls setstate(failbit), -which -may throw ios_base::failure (27.4.4.3). If it inserted no characters -because it caught an exception thrown while extracting characters -from *this and failbit is on in exceptions() (27.4.4.3), then the -caught -exception is rethrown." -

- -

-both in N2134 seems to imply that any exception, which occurs -*after* at least one character has been inserted is caught and lost -for -ever. It seems that even if failbit is on in exceptions() rethrow is -not -allowed due to the wording "If it inserted no characters because it -caught an exception thrown while extracting". -

- -

-Is this behaviour by design? -

- -

-I would like to add that its output counterpart in 27.7.3.6.3 [ostream.inserters]/7-9 -(also -N2134) does not demonstrate such an exception-loss-behaviour. -On the other side, I wonder concerning several subtle differences -compared to input:: -

-

-1) Paragraph 8 says at its end: -

- -

-"- an exception occurs while getting a character from sb." -

- -

-Note that there is nothing mentioned which would imply that such -an exception will be caught compared to 27.7.2.2.3 [istream::extractors]/14. -

- -

-2) Paragraph 9 says: -

- -

-"If the function inserts no characters, it calls setstate(failbit) -(which -may throw ios_base::failure (27.4.4.3)). If an exception was thrown -while extracting a character, the function sets failbit in error -state, -and if failbit is on in exceptions() the caught exception is -rethrown." -

- -

-The sentence starting with "If an exception was thrown" seems to -imply that such an exception *should* be caught before. -

- - -

Proposed resolution:

-

-(a) In 27.7.2.2.3 [istream::extractors]/15 (N2134) change the sentence -

- -

-If the function inserts no characters, it calls -setstate(failbit), which may throw ios_base::failure -(27.4.4.3). If it inserted no characters because it caught an -exception thrown while extracting characters from *this -an exception was thrown while extracting a character from -*this, the function sets failbit in error state, -and failbit is on in exceptions() (27.4.4.3), then the -caught exception is rethrown. -

- -

-(b) In 27.7.3.6.3 [ostream.inserters]/8 (N2134) change the sentence: -

- -
-

-Gets characters from sb and inserts them in *this. -Characters are read from sb and inserted until any of the -following occurs: -

-
    -
  • end-of-file occurs on the input sequence;
    • -
  • inserting in the output sequence fails (in which case the character to be inserted is not extracted);
    • -
  • an exception occurs while getting a character from sb (in which -case the exception is caught).
    • -
-
- - - -

Rationale:

-This extractor is described as a formatted input function so the -exception behavior is already specified. There is additional behavior -described in this section that applies to the case in which failbit is -set. This doesn't contradict the usual exception behavior for formatted -input functions because that applies to the case in which badbit is set. -

- - - - -
-

641. Editorial fix for 27.6.4 (N2134)

-

Section: 27.7.5 [ext.manip] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-02-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The function f in para 4 (27.7.5 [ext.manip]) references an unknown strm -in the following line: -

- -
-mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
-
- - -

Proposed resolution:

-

-Change 27.7.5 [ext.manip], p4: -

- -
-mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
-
- -

[ -Oxford: Editorial. -]

- - - - - - - -
-

642. Invalidated fstream footnotes in N2134

-

Section: 27.9.1.9 [ifstream.members], 27.9.1.13 [ofstream.members] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-02-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The standard wording of N2134 has extended the 14882:2003(E) -wording for the ifstream/ofstream/fstream open function to fix -a long standing problem, see 409. -

- -

-Now it's properly written as -

- -

-"If that function does not return a null pointer calls clear(), -otherwise -calls setstate(failbit)[..]" -

- -

-instead of the previous -

- -

-"If that function returns a null pointer, calls setstate(failbit)[..] -

- -

-While the old footnotes saying -

- -

-"A successful open does not change the error state." -

- -

-where correct and important, they are invalid now for ifstream and -ofstream (because clear *does* indeed modify the error state) and -should be removed (Interestingly fstream itself never had these, -although -they where needed for that time). -

- - -

Proposed resolution:

-

-In 27.9.1.9 [ifstream.members], remove footnote: -

- -

-334) A successful open does not change the error state. -

- -

-In 27.9.1.13 [ofstream.members], remove footnote: -

- -

-335) A successful open does not change the error state. -

- - - - - - -
-

644. Possible typos in 'function' description

-

Section: 20.9.12.2 [func.wrap.func] Status: NAD - Submitter: Bo Persson Opened: 2007-02-25 Last modified: 2015-04-08

-

View other active issues in [func.wrap.func].

-

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-

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-

Discussion:

-

-20.9.12.2 [func.wrap.func] -

-

-The note in paragraph 2 refers to 'undefined void operators', while the -section declares a pair of operators returning bool. -

- -

[ -Post-Sophia Antipolis: -]

- - -

-Changed from Pending WP to Open. This issue was voted to WP at the same time the operators were -changed from private to deleted. The two issues stepped on each other. What do we want the return -type of these deleted functions to be? -

- -

[ -2009-05-02 Daniel adds: -]

- - -
-

-I suggest harmonizing this issue with similar classes. E.g. in -20.8.2.3 [util.smartptr.weak] bool return values for -

-
-template <class Y> bool operator<(weak_ptr<Y> const&) const = delete;
-template <class Y> bool operator<=(weak_ptr<Y> const&) const = delete;
-template <class Y> bool operator>(weak_ptr<Y> const&) const = delete;
-template <class Y> bool operator>=(weak_ptr<Y> const&) const = delete;
-
- -

-are used and basically all newer provided deleted copy assignment operators -of type X use the canonical return type X& instead of void. Since the note -mentioned in the issue description has now already been changed to -

-

-deleted overloads close possible hole in the type system -

-

-it seems to be of even lesser need to perform the change. Therefore -I recommend declaring the issue as NAD. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-We agree with Daniel's recommendation. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-Change 20.9.12.2 [func.wrap.func] -

- -
-...
-private:
-   // 20.9.12.2 [func.wrap.func], undefined operators:
-   template<class Function2> bool void operator==(const function<Function2>&);
-   template<class Function2> bool void operator!=(const function<Function2>&);
-};
-
- -

-Change 20.9.12.2 [func.wrap.func] -

- -
-template<class Function2> bool void operator==(const function<Function2>&);
-template<class Function2> bool void operator!=(const function<Function2>&);
-
- - - - - -
-

645. Missing members in match_results

-

Section: 28.10 [re.results] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2015-04-08

-

View all other issues in [re.results].

-

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-

Discussion:

-

-According to the description given in 28.10 [re.results]/2 the class template -match_results "shall satisfy the requirements of a Sequence, [..], -except that only operations defined for const-qualified Sequences -are supported". -Comparing the provided operations from 28.10 [re.results]/3 with the -sequence/container tables 80 and 81 one recognizes the following -missing operations: -

- -

-1) The members -

- -
-const_iterator rbegin() const;
-const_iterator rend() const;
-
- -

-should exists because 23.1/10 demands these for containers -(all sequences are containers) which support bidirectional -iterators. Aren't these supported by match_result? This is not -explicitely expressed, but it's somewhat implied by two arguments: -

-

-(a) Several typedefs delegate to -iterator_traits<BidirectionalIterator>. -

-

-(b) The existence of const_reference operator[](size_type n) const -implies even random-access iteration. -I also suggest, that match_result should explicitly mention, -which minimum iterator category is supported and if this does -not include random-access the existence of operator[] is -somewhat questionable. -

-

-2) The new "convenience" members -

-
-const_iterator cbegin() const;
-const_iterator cend() const;
-const_iterator crbegin() const;
-const_iterator crend() const;
-
-

-should be added according to tables 80/81. -

- - -

Proposed resolution:

-

-Add the following members to the match_results synopsis after end() in 28.10 [re.results] -para 3: -

- -
-const_iterator cbegin() const; 
-const_iterator cend() const;
-
- -

-In section 28.10.4 [re.results.acc] change: -

- -
-
-const_iterator begin() const;
-const_iterator cbegin() const;
-
-
-

--7- Returns: A starting iterator that enumerates over all the sub-expressions stored in *this. -

-
- -
-const_iterator end() const;
-const_iterator cend() const;
-
-
-

--8- Returns: A terminating iterator that enumerates over all the sub-expressions stored in *this. -

-
-
- - - -

[ -Kona (2007): Voted to adopt proposed wording in -N2409 -except removing the entry in the table container requirements. Moved to Review. -]

- - -

[ -Bellevue: Proposed wording now in the WP. -]

- - - - - -
-

647. Inconsistent regex_search params

-

Section: 28.11.3 [re.alg.search] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

-

-28.11.3 [re.alg.search]/5 declares -

- -
-template <class iterator, class charT, class traits>
-bool regex_search(iterator first, iterator last,
-                  const basic_regex<charT, traits>& e,
-                  regex_constants::match_flag_type flags =
-                      regex_constants::match_default);
-
- -

-where it's not explained, which iterator category -the parameter iterator belongs to. This is inconsistent -to the preceding declaration in the synopsis section -28.4 [re.syn], which says: -

- -
-template <class BidirectionalIterator, class charT, class traits>
-bool regex_search(BidirectionalIterator first, BidirectionalIterator last,
-                  const basic_regex<charT, traits>& e,
-                  regex_constants::match_flag_type flags =
-                      regex_constants::match_default);
-
- - -

Proposed resolution:

-

-In 28.11.3 [re.alg.search]/5 replace all three occurences of param "iterator" with -"BidirectionalIterator" -

- -
-template <class iterator BidirectionalIterator, class charT, class traits>
-  bool regex_search(iterator BidirectionalIterator first, iterator BidirectionalIterator last, 
-                    const basic_regex<charT, traits>& e, 
-                    regex_constants::match_flag_type flags = 
-                      regex_constants::match_default);
-
-

--6- Effects: Behaves "as if" by constructing an object what of -type match_results<iterator -BidirectionalIterator> and then returning the result -of regex_search(first, last, what, e, flags). -

-
- - -

Rationale:

-Applied to working paper while issue was still in New status. -

- - - - -
-

648. regex_iterator c'tor needs clarification/editorial fix

-

Section: 28.12.1.1 [re.regiter.cnstr] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-03-03 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

-

-In 28.12.1.1 [re.regiter.cnstr]/2 the effects paragraph starts with: -

- -
-

-Effects: Initializes begin and end to point to the beginning and the -end of the target sequence, sets pregex to &re, sets flags to f,[..] -

- -

-There are two issues with this description: -

- -
    -
  1. -The meaning of very first part of this quote is unclear, because -there is no target sequence provided, instead there are given two -parameters a and b, both of type BidirectionalIterator. The mentioned -part does not explain what a and b represent. -
    2. -
  2. -There does not exist any parameter f, but instead a parameter -m in the constructor declaration, so this is actually an editorial -fix. -
    3. -
- - -

Proposed resolution:

-

-In 28.12.1.1 [re.regiter.cnstr]/2 change the above quoted part by -

- -

-Effects: Initializes begin and end to point to -the beginning and the end of the target sequence designated by the -iterator range [a, b), sets pregex to -&re, sets flags to f -m, then calls regex_search(begin, end, match, -*pregex, flags). If this call returns false the -constructor sets *this to the end-of-sequence iterator. -

- - - - - -
-

649. Several typos in regex_token_iterator constructors

-

Section: 28.12.2.1 [re.tokiter.cnstr] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-03-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In 28.12.2.1 [re.tokiter.cnstr]/1+2 both the constructor declaration -and the following text shows some obvious typos: -

-

-1) The third constructor form is written as -

-
-template <std::size_t N>
-  regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, 
-                       const regex_type& re, 
-                       const int (&submatches)[R], 
-                       regex_constants::match_flag_type m = 
-                         regex_constants::match_default);
-
- -

-where the dimensions of submatches are specified by an -unknown value R, which should be N. -

-

-2) Paragraph 2 of the same section says in its last sentence: -

- -

-The third constructor initializes the member subs to hold a -copy of the sequence of integer values pointed to by the iterator range -[&submatches, &submatches + R). -

- -

-where again R must be replaced by N. -

- -

-3) Paragraph 3 of the same section says in its first sentence: -

- -

-Each constructor then sets N to 0, and -position to position_iterator(a, b, re, f). -

- -

-where a non-existing parameter "f" is mentioned, which must be -replaced -by the parameter "m". -

- - -

Proposed resolution:

-

-Change 28.12.2.1 [re.tokiter.cnstr]/1: -

-
-template <std::size_t N>
-  regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, 
-                       const regex_type& re, 
-                       const int (&submatches)[R N], 
-                       regex_constants::match_flag_type m = 
-                         regex_constants::match_default);
-
- -

-Change 28.12.2.1 [re.tokiter.cnstr]/2: -

- -

-Effects: The first constructor initializes the member -subs to hold the single value submatch. The second -constructor initializes the member subs to hold a copy of the -argument submatches. The third constructor initializes the -member subs to hold a copy of the sequence of integer values -pointed to by the iterator range [&submatches, &submatches + -R N). -

- -

-Change 28.12.2.1 [re.tokiter.cnstr]/3: -

- -

-Each constructor then sets N to 0, and -position to position_iterator(a, b, re, f -m). If position is not an end-of-sequence -iterator the constructor sets result to the address of the -current match. Otherwise if any of the values stored in subs is -equal to -1 the constructor sets *this to a suffix -iterator that points to the range [a, b), otherwise the -constructor sets *this to an end-of-sequence iterator. -

- - - - - - -
-

653. Library reserved names

-

Section: 1.2 [intro.refs] Status: NAD - Submitter: Alisdair Meredith Opened: 2007-03-08 Last modified: 2015-04-08

-

View all other issues in [intro.refs].

-

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-

Discussion:

-

-

-
-

-1.2 [intro.refs] Normative references -

- -

-The following standards contain provisions which, through reference in -this text, constitute provisions of this Interna- tional Standard. At -the time of publication, the editions indicated were valid. All -standards are subject to revision, and parties to agreements based on -this International Standard are encouraged to investigate the -possibility of applying the most recent editions of the standards -indicated below. Members of IEC and ISO maintain registers of currently -valid International Standards. -

- -
    -
  • Ecma International, ECMAScript Language Specification, Standard -Ecma-262, third edition, 1999.
    • -
  • ISO/IEC 2382 (all parts), Information technology - Vocabulary
    • -
  • ISO/IEC 9899:1990, Programming languages - C
    • -
  • ISO/IEC 9899/Amd.1:1995, Programming languages - C, AMENDMENT 1: C -Integrity
    • -
  • ISO/IEC 9899:1999, Programming languages - C
    • -
  • ISO/IEC 9899:1999/Cor.1:2001 Programming languages - C
    • -
  • ISO/IEC 9899:1999/Cor.2:2004 Programming languages - C
    • -
  • ISO/IEC 9945:2003, Information Technology-Portable Operating System -Interface (POSIX)
    • -
  • ISO/IEC 10646-1:1993 Information technology - Universal Multiple-Octet -Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual -Plane
    • -
-
- -

-I'm not sure how many of those reserve naming patterns that might affect -us, but I am equally sure I don't own a copy of any of these to check! -

-

-The point is to list the reserved naming patterns, rather than the -individual names themselves - although we may want to list C keywords -that are valid identifiers in C++ but likely to cause trouble in shared -headers (e.g. restrict) -

- -

[ -Kona (2007): Recommend NAD. No one has identified a specific defect, just the possibility of one. -]

- - -

[ -Post-Kona: Alisdair request Open. A good example of the problem was a -discussion of the system error proposal, where it was pointed out an all-caps -identifier starting with a capital E conflicted with reserved macro names for -both Posix and C. I had absolutely no idea of this rule, and suspect I was -not the only one in the room.
-
-Resolution will require someone with access to all the listed documents to -research their respective name reservation rules, or people with access to -specific documents add their rules to this issue until the list is complete. -]

- - -

[ -Bellevue: Wording is aleady present in various standards, and no-one has come forward with wording. -Suggest a formal paper rather than a defect report is the correct way to proceed. -]

- - - - -

Proposed resolution:

- - - - - -
-

656. Typo in subtract_with_carry_engine declaration

-

Section: 26.5.2 [rand.synopsis] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-26.5.2 [rand.synopsis] the header <random> synopsis -contains an unreasonable closing curly brace inside the -subtract_with_carry_engine declaration. -

- - -

Proposed resolution:

-

-Change the current declaration in 26.5.2 [rand.synopsis] -

- -
-template <class UIntType, size_t w}, size_t s, size_t r>
-class subtract_with_carry_engine;
-
- - -

[ -Pete: Recommends editorial. -]

- - - - - -
-

657. unclear requirement about header inclusion

-

Section: 17.6.2.2 [using.headers] Status: NAD - Submitter: Gennaro Prota Opened: 2007-03-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-17.6.2.2 [using.headers] states: -

- -

-A translation unit shall include a header only outside of any -external declaration or definition, [...] -

- -

-I see three problems with this requirement: -

- -
    -

  1. The C++ standard doesn't define what an "external declaration" or -an "external definition" are (incidentally the C99 standard does, and -has a sentence very similar to the above regarding header inclusion). -

    -I think the intent is that the #include directive shall lexically -appear outside *any* declaration; instead, when the issue was pointed -out on comp.std.c++ at least one poster interpreted "external -declaration" as "declaration of an identifier with external linkage". -If this were the correct interpretation, then the two inclusions below -would be legal: -

    -
    -  // at global scope
-  static void f()
-  {
-# include <cstddef>
-  }
-
-  static void g()
-  {
-# include <stddef.h>
-  }
-
    -

    -(note that while the first example is unlikely to compile correctly, -the second one may well do) -

    2. - -

  2. as the sentence stands, violations will require a diagnostic; is -this the intent? It was pointed out on comp.std.c++ (by several -posters) that at least one way to ensure a diagnostic exists: -

    -

    - [If there is an actual file for each header,] one simple way - to implement this would be to insert a reserved identifier - such as __begin_header at the start of each standard header. - This reserved identifier would be ignored for all other - purposes, except that, at the appropriate point in phase 7, if - it is found inside an external definition, a diagnostic is - generated. There's many other similar ways to achieve the same - effect. -

    -

    --James Kuyper, on comp.std.c++ -

    3. - -

  3. is the term "header" meant to be limited to standard headers? -Clause 17 is all about the library, but still the general question is -interesting and affects one of the points in the explicit namespaces -proposal (n1691): -

    -

    - Those seeking to conveniently enable argument-dependent - lookups for all operators within an explicit namespace - could easily create a header file that does so: -

    -    namespace mymath::
-    {
-        #include "using_ops.hpp"
-    }
-
    -
    4. -
- - -

Proposed resolution:

-

-

- - -

Rationale:

-We believe that the existing language does not cause any real confusion -and any new formulation of the rules that we could come up with are -unlikely to be better than what's already in the standard. -

- - - - -
-

662. Inconsistent handling of incorrectly-placed thousands separators

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: NAD - Submitter: Cosmin Truta Opened: 2007-04-05 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-From Section 22.4.2.1.2 [facet.num.get.virtuals], paragraphs 11 and 12, it is implied -that the value read from a stream must be stored -even if the placement of thousands separators does not conform to the -grouping() specification from the numpunct facet. -Since incorrectly-placed thousands separators are flagged as an extraction -failure (by the means of failbit), we believe it is better not -to store the value. A consistent strategy, in which any kind of extraction -failure leaves the input item intact, is conceptually cleaner, is able to avoid -corner-case traps, and is also more understandable from the programmer's point -of view. -

-

-Here is a quote from "The C++ Programming Language (Special Edition)" -by B. Stroustrup (Section D.4.2.3, pg. 897): -

-

-"If a value of the desired type could not be read, failbit is set in r. -[...] An input operator will use r to determine how to set the state of its -stream. If no error was encountered, the value read is assigned through v; -otherwise, v is left unchanged." -

-

-This statement implies that rdstate() alone is sufficient to -determine whether an extracted value is to be assigned to the input item -val passed to do_get. However, this is in disagreement -with the current C++ Standard. The above-mentioned assumption is true in all -cases, except when there are mismatches in digit grouping. In the latter case, -the parsed value is assigned to val, and, at the same time, err -is assigned to ios_base::failbit (essentially "lying" about the -success of the operation). Is this intentional? The current behavior raises -both consistency and usability concerns. -

-

-Although digit grouping is outside the scope of scanf (on which -the virtual methods of num_get are based), handling of grouping -should be consistent with the overall behavior of scanf. The specification of -scanf makes a distinction between input failures and matching -failures, and yet both kinds of failures have no effect on the input items -passed to scanf. A mismatch in digit grouping logically falls in -the category of matching failures, and it would be more consistent, and less -surprising to the user, to leave the input item intact whenever a failure is -being signaled. -

-

-The extraction of bool is another example outside the scope of -scanf, and yet consistent, even in the event of a successful -extraction of a long but a failed conversion from -long to bool. -

-

-Inconsistency is further aggravated by the fact that, when failbit is set, -subsequent extraction operations are no-ops until failbit is -explicitly cleared. Assuming that there is no explicit handling of -rdstate() (as in cin>>i>>j) it is -counter-intuitive to be able to extract an integer with mismatched digit -grouping, but to be unable to extract another, properly-formatted integer -that immediately follows. -

-

-Moreover, setting failbit, and selectively assigning a value to -the input item, raises usability problems. Either the strategy of -scanf (when there is no extracted value in case of failure), or -the strategy of the strtol family (when there is always an -extracted value, and there are well-defined defaults in case of a failure) are -easy to understand and easy to use. On the other hand, if failbit -alone cannot consistently make a difference between a failed extraction, and a -successful but not-quite-correct extraction whose output happens to be the same -as the previous value, the programmer must resort to implementation tricks. -Consider the following example: -

-
-    int i = old_i;
-    cin >> i;
-    if (cin.fail())
-        // can the value of i be trusted?
-        // what does it mean if i == old_i?
-        // ...
-
-

-Last but not least, the current behvaior is not only confusing to the casual -reader, but it has also been confusing to some book authors. Besides -Stroustrup's book, other books (e.g. "Standard C++ IOStreams and Locales" by -Langer and Kreft) are describing the same mistaken assumption. Although books -are not to be used instead of the standard reference, the readers of these -books, as well as the people who are generally familiar to scanf, -are even more likely to misinterpret the standard, and expect the input items -to remain intact when a failure occurs. -

- - -

Proposed resolution:

- -

-Change 22.4.2.1.2 [facet.num.get.virtuals]: -

- -
-

-Stage 3: The result of stage 2 processing can be one of -

-
    -
  • A sequence of chars has been accumulated in stage 2 that is converted (according to the rules of scanf) to a value of the type of val. This value is stored in val and ios_base::goodbit is stored in err.
    • - -
  • The sequence of chars accumulated in stage 2 would have caused scanf to report an input failure. ios_base::failbit is assigned to err.
    • -
-

-In the first case, Ddigit grouping is checked. That is, the positions of discarded separators is examined for consistency with use_facet<numpunct<charT> >(loc).grouping(). If they are not consistent then ios_base::failbit is assigned to err. Otherwise, the value that was converted in stage 2 is stored in val and ios_base::goodbit is stored in err. -

-
- - -

Rationale:

-post-Toronto: Changed from New to NAD at the request of the author. The preferred solution of -N2327 -makes this resolution obsolete. -

- - - - -
-

663. Complexity Requirements

-

Section: 17.5.1.4 [structure.specifications] Status: NAD - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-17.5.1.4 [structure.specifications] para 5 says -

- -

--5- Complexity requirements specified in the library -clauses are upper bounds, and implementations that provide better -complexity guarantees satisfy the requirements. -

- -

-The following -objection has been raised: -

- -

-The library clauses suggest general -guidelines regarding complexity, but we have been unable to discover -any absolute hard-and-fast formulae for these requirements. Unless -or until the Library group standardizes specific hard-and-fast -formulae, we regard all the complexity requirements as subject to a -"fudge factor" without any intrinsic upper bound. -

- -

-[Plum ref -_23213Y31 etc] -

- - -

Proposed resolution:

-

-

- - -

Rationale:

-Kona (2007): No specific instances of underspecification have been -identified, and big-O notation always involves constant factors. -

- - - - -
-

667. money_get's widened minus sign

-

Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: NAD - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all other issues in [locale.money.get.virtuals].

-

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-

Discussion:

-

-22.4.6.1.2 [locale.money.get.virtuals], para 1 says: -

- -

-The result is returned as an integral value -stored in units or as a sequence of digits possibly preceded by a -minus sign (as produced by ct.widen(c) where c is '-' or in the range -from '0' through '9', inclusive) stored in digits. -

- -

-The following -objection has been raised: -

- -

-Some implementations interpret this to mean that a facet derived from -ctype<wchar_t> can provide its own member do_widen(char) -which produces e.g. L'@' for the "widened" minus sign, and that the -'@' symbol will appear in the resulting sequence of digits. Other -implementations have assumed that one or more places in the standard permit the -implementation to "hard-wire" L'-' as the "widened" minus sign. Are -both interpretations permissible, or only one? -

- -

-[Plum ref _222612Y14] -

- -

-Furthermore: if ct.widen('9') produces L'X' (a non-digit), does a -parse fail if a '9' appears in the subject string? [Plum ref _22263Y33] -

- -

[ -Kona (2007): Bill and Dietmar to provide proposed wording. -]

- - -

[ -post Bellevue: Bill adds: -]

- - -

-The Standard is clear that the minus sign stored in digits is ct.widen('-'). -The subject string must contain characters c in the set [-0123456789] -which are translated by ct.widen(c) calls before being stored in digits; -the widened characters are not relevant to the parsing of the subject string. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with Bill's comment above, -in line with the first of the interpretations offered in the issue. -Move to NAD. -

- - -

Proposed resolution:

-

-

- - - - - -
-

668. money_get's empty minus sign

-

Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: NAD - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all other issues in [locale.money.get.virtuals].

-

View all issues with NAD status.

-

Discussion:

-

-22.4.6.1.2 [locale.money.get.virtuals], para 3 says: -

- -

-If pos or neg is empty, the sign component is -optional, and if no sign is detected, the result is given the sign -that corresponds to the source of the empty string. -

- -

-The following objection has been raised: -

- -

-A negative_sign of "" means "there is no -way to write a negative sign" not "any null sequence is a negative -sign, so it's always there when you look for it". -

- -

-[Plum ref _222612Y32] -

- -

[ -Kona (2007): Bill to provide proposed wording and interpretation of existing wording. -]

- - -

-Related to 669. -

- -

[ -2009-05-17 Howard adds: -]

- - -
-

-I disagree that a negative_sign of "" means "there is no way to -write a negative sign". The meaning requires the sentences of 22.4.6.1.2 [locale.money.get.virtuals] p3 following that quoted above to be -taken into account: -

- -

--3- ... If pos or neg is empty, the sign component is -optional, and if no sign is detected, the result is given the sign that -corresponds to the source of the empty string. Otherwise, the character -in the indicated position must match the first character of pos -or neg, and the result is given the corresponding sign. If the -first character of pos is equal to the first character of -neg, or if both strings are empty, the result is given a -positive sign. -

- -

-So a negative_sign of "" means "there is no way to write a -negative sign" only when positive_sign is also "". However -when negative_sign is "" and postive_sign.size() > -0, then one writes a negative value by not writing the -postive_sign in the position indicated by -money_base::sign. -For example: -

- -
-pattern = {symbol, sign, value, none}
-positive_sign = "+"
-negative_sign = ""
-$123   // a negative value, using optional sign
-$+123  // a positive value
-$-123  // a parse error
-
- -

-And: -

- -
-pattern = {symbol, sign, value, none}
-positive_sign = ""
-negative_sign = ""
-$123   // a positive value, no sign possible
-$+123  // a parse error
-$-123  // a parse error
-
- - -

-And (regarding 669): -

- -
-pattern = {symbol, sign, value, none}
-positive_sign = "-"
-negative_sign = "-"
-$123   // a parse error, sign is mandatory
-$+123  // a parse error
-$-123  // a positive value
-
- - -

-The text seems both unambiguous and clear to me. I recommend NAD for -both this issue and 669. However I would have no -objection to adding examples such as those above. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-This discussion applies equally to issue 669 (q.v.). -Howard has added examples above, -and recommends either NAD or a resolution that adds his (or similar) examples -to the Working Paper. -

-

-Alan would like to rewrite paragraph 3. -

-

-We recommend moving to NAD. -Anyone who feels strongly about adding the examples -is invited to submit corresponding wording. -We further recommend issue 669 be handled identically. -

-
- -

[ -2009-07-14 Alan reopens with improved wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-No consensus for closing as NAD. Leave in Review. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD. Agreed that the original assessment as NAD was correct. -

- - - -

Proposed resolution:

-

-Change 22.4.6.1.2 [locale.money.get.virtuals] p3: -

- -

--3- If the first character (if any) in the string pos returned by -mp.positive_sign() or the string neg returned by -mp.negative_sign() is recognized in the position indicated by -sign in the format pattern, it is consumed and any remaining characters -in the string are required after all the other format components. -[Example: If showbase is off, then for a neg -value of "()" and a currency symbol of "L", in "(100 L)" the "L" is -consumed; but if neg is "-", the "L" in "-100 L" is not -consumed. -- end example] If pos or neg is -empty, the sign component is optional, and if no sign is detected, the -result is given the sign that corresponds to the source of the empty -string. Otherwise, the character in the indicated position must match -the first character of pos or neg, and the result is -given the corresponding sign. If the first character of pos is -equal to the first character of neg, or if both strings are -empty, the result is given a positive sign. - -The sign pattern strings pos and neg are returned by -mp.positive_sign() and mp.negative_sign() respectively. A sign pattern -is matched if its first character is recognized in s in the position -indicated by sign in the format pattern, or if the pattern is empty and -there is no sign recognized in s. A match is required to occur. If both -patterns are matched, the result is given a positive sign, otherwise the -result is given the sign corresponding to the matched pattern. -If the pattern contains more than one character, the characters after the first -must be matched in s after all other format components. -If any sign -characters are matched, s is consumed up to and including those characters. -[Example: If showbase is off, then for a neg -value of "()" and a currency symbol of "L", in -"(100 L)" the entire string is consumed; but for a neg -value of "-", in "-100 L", the string is consumed -through the second "0" (the space and "L" are not consumed). — end -example] -

- - - - - -
-

669. Equivalent postive and negative signs in money_get

-

Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: NAD - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all other issues in [locale.money.get.virtuals].

-

View all issues with NAD status.

-

Discussion:

-

-22.4.6.1.2 [locale.money.get.virtuals], para 3 sentence 4 says: -

- -

-If the first character of pos is equal to the first character of neg, -or if both strings are empty, the result is given a positive sign. -

- -

-One interpretation is that an input sequence must match either the -positive pattern or the negative pattern, and then in either event it -is interpreted as positive. The following objections has been raised: -

- -

-The input can successfully match only a positive sign, so the negative -pattern is an unsuccessful match. -

- -

-[Plum ref _222612Y34, 222612Y51b] -

- -

[ -Bill to provide proposed wording and interpretation of existing wording. -]

- - -

[ -2009-05-17 See Howard's comments in related issue 668. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-This discussion applies equally to issue 668 (q.v.). -Howard has added examples there, -and recommends either NAD or a resolution that adds his (or similar) examples -to the Working Paper. -

-

-We recommend moving to NAD. -Anyone who feels strongly about adding the examples -is invited to submit corresponding wording. -We further recommend issue 668 be handled identically. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

670. money_base::pattern and space

-

Section: 22.4.6.3 [locale.moneypunct] Status: Dup - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all issues with Dup status.

-

Duplicate of: 836

-

Discussion:

-

-22.4.6.3 [locale.moneypunct], para 2 says: -

- -

-The value space indicates that at least one space is required at -that position. -

- -

-The following objection has been raised: -

- -

-Whitespace is optional when matching space. (See 22.4.6.1.2 [locale.money.get.virtuals], para 2.) -

- -

-[Plum ref _22263Y22] -

- -

[ -Kona (2007): Bill to provide proposed wording. We agree that C++03 is -ambiguous, and that we want C++0X to say "space" means 0 or more -whitespace characters on input. -]

- - - - -

Proposed resolution:

- - - - - -
-

683. regex_token_iterator summary error

-

Section: 28.12.2 [re.tokiter] Status: NAD Editorial - Submitter: Eric Niebler Opened: 2007-06-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-28.12.2 [re.tokiter], p3 says: -

-
-

-After it is constructed, the iterator finds and stores a value -match_results<BidirectionalIterator> position and sets the -internal count N to zero. -

-
- -

-Should read: -

- -
-

-After it is constructed, the iterator finds and stores a value -match_resultsregex_iterator<BidirectionalIterator, charT, traits> -position and sets the internal count N to zero. -

-
- -

[ -John adds: -]

- - -

-Yep, looks like a typo/administrative fix to me. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

684. Unclear which members of match_results should be used in comparison

-

Section: 28.10 [re.results] Status: NAD Editorial - Submitter: Nozomu Katoo Opened: 2007-05-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In 28.4 [re.syn] of N2284, two template functions -are declared here: -

-
-// 28.10, class template match_results: 
-  <snip>
-// match_results comparisons 
-  template <class BidirectionalIterator, class Allocator> 
-    bool operator== (const match_results<BidirectionalIterator, Allocator>& m1, 
-                     const match_results<BidirectionalIterator, Allocator>& m2); 
-  template <class BidirectionalIterator, class Allocator> 
-    bool operator!= (const match_results<BidirectionalIterator, Allocator>& m1, 
-                     const match_results<BidirectionalIterator, Allocator>& m2); 
-
-// 28.10.6, match_results swap:
-
- -

-But the details of these two bool operator functions (i.e., which members of -match_results should be used in comparison) are not described in any -following sections. -

- -

[ -John adds: -]

- - -

-That looks like a bug: operator== should return true only if -the two objects refer to the same match - ie if one object was constructed as a -copy of the other. -

- -

[ -Kona (2007): Bill and Pete to add minor wording to that proposed in -N2409. -]

- - - -

Proposed resolution:

-

-Add a new section after 28.10.7 [re.results.swap], which reads: -

-

-28.10.7 match_results non-member functions. -

- -
-
-template<class BidirectionalIterator, class Allocator> 
-  bool operator==(const match_results<BidirectionalIterator, Allocator>& m1, 
-                  const match_results<BidirectionalIterator, Allocator>& m2);
-
-
-

-Returns: true only if the two objects refer to the same match. -

-
-
- -
-
-template<class BidirectionalIterator, class Allocator> 
-  bool operator!=(const match_results<BidirectionalIterator, Allocator>& m1, 
-                  const match_results<BidirectionalIterator, Allocator>& m2);
-
-
-

-Returns: !(m1 == m2). -

-
-
- -
-
-template<class BidirectionalIterator, class Allocator> 
-  void swap(match_results<BidirectionalIterator, Allocator>& m1, 
-            match_results<BidirectionalIterator, Allocator>& m2);
-
-
-

-Returns: m1.swap(m2). -

-
-
- - -

[ -Bellevue: Proposed wording now in WP. -]

- - - - - -
-

686. unique_ptr and shared_ptr fail to specify non-convertibility to int for unspecified-bool-type

-

Section: 20.8.1.2.4 [unique.ptr.single.observers], 20.8.2.2.5 [util.smartptr.shared.obs] Status: NAD - Submitter: Beman Dawes Opened: 2007-06-14 Last modified: 2015-04-08

-

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-

Discussion:

-

-The standard library uses the operator unspecified-bool-type() const idiom in -five places. In three of those places (20.9.12.2.3 [func.wrap.func.cap], function capacity -for example) the returned value is constrained to disallow -unintended conversions to int. The standardese is -

-

-The return type shall not be convertible to int. -

-

-This constraint is omitted for unique_ptr and shared_ptr. It should be added for those. -

- -

[ -Bellevue: -]

- - -

-Close as NAD. Accepting paper -N2435 -makes it irrelevant. -

- - - -

Proposed resolution:

-

-To the Returns paragraph for operator unspecified-bool-type() -const of 20.8.1.2.4 [unique.ptr.single.observers] paragraph 11 and 20.8.2.2.5 [util.smartptr.shared.obs] paragraph 16, add the sentence: -

-

-The return type shall not be convertible to int. -

- - -

[ -Kona (2007): Uncertain if nullptr will address this issue. -]

- - - - - -
-

690. abs(long long) should return long long

-

Section: 26.8 [c.math] Status: NAD Editorial - Submitter: Niels Dekker Opened: 2007-06-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Quoting the latest draft (n2135), 26.8 [c.math]: -

- -
-

-The added signatures are: -

-
-long abs(long); // labs()
-long abs(long long); // llabs()
-
-
-

-Shouldn't abs(long long) have long long as return type? -

- - -

Proposed resolution:

-

-Change 26.8 [c.math]: -

-
-long long abs(long long); // llabs()
-
- - -

Rationale:

-Had already been fixed in the WP by the time the LWG reviewed this. -

- - - - -
-

701. assoc laguerre poly's

-

Section: TR1 5.2.1.1 [tr.num.sf.Lnm] Status: NAD - Submitter: Christopher Crawford Opened: 2007-06-30 Last modified: 2015-04-08

-

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-

Discussion:

-

-I see that the definition the associated Laguerre -polynomials TR1 5.2.1.1 [tr.num.sf.Lnm] has been corrected since -N1687. -However, the draft standard only specifies ranks of integer value m, -while the associated Laguerre polynomials are actually valid for real -values of m > -1. In the case of non-integer values of m, the -definition Ln(m) = (1/n!)exx-m (d/dx)n (e-xxm+n) -must be used, which also holds for integer values of m. See -Abramowitz & Stegun, 22.11.6 for the general case, and 22.5.16-17 for -the integer case. In fact fractional values are most commonly used in -physics, for example to m = +/- 1/2 to describe the harmonic -oscillator in 1 dimension, and 1/2, 3/2, 5/2, ... in 3 -dimensions. -

-

-If I am correct, the calculation of the more general case is no -more difficult, and is in fact the function implemented in the GNU -Scientific Library. I would urge you to consider upgrading the -standard, either adding extra functions for real m or switching the -current ones to double. -

- -

[ -Batavia (2009-05): -]

- -
-

-We understand the issue, and have opted not to extend as recommended. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

702. Restriction in associated Legendre functions

-

Section: TR1 5.2.1.2 [tr.num.sf.Plm] Status: NAD - Submitter: Christopher Crawford Opened: 2007-06-30 Last modified: 2015-04-08

-

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-

Discussion:

-

-One other small thing, in TR1 5.2.1.2 [tr.num.sf.Plm], the restriction should be -|x| <= 1, not x >= 0.

- -

[ -Batavia (2009-05): -]

- -
-

-The error has been corrected in the pending IS. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

707. null pointer constant for exception_ptr

-

Section: 18.8.5 [propagation] Status: NAD - Submitter: Jens Maurer Opened: 2007-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-From the Toronto Core wiki: -

- -

-What do you mean by "null pointer constant"? How do you guarantee that -exception_ptr() == 1 doesn't work? Do you even want to prevent that? -What's the semantics? What about void *p = 0; exception_ptr() == p? -Maybe disallow those in the interface, but how do you do that with -portable C++? Could specify just "make it work". -

- -

-Peter's response: -

- -

-null pointer constant as defined in 4.10 [conv.ptr]. Intent is "just make it -work", can be implemented as assignment operator taking a unique pointer -to member, as in the unspecified bool type idiom. -

- -

[ -Bellevue: -]

- - -
-

-Original implementation was possible using the "unspecified-null-pointer" idiom, similar to unspecified-bool. -

-

-Even simpler now with nullptr_t. -

-

-NAD Rationale : null pointer constant is a perfectly defined term, and -while API is clearly implementable there is no need to spell out -implementation details. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

717. Incomplete valarray::operator[] specification in [valarray.access]

-

Section: 26.6.2.4 [valarray.access] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-08-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Since the return type of valarray's operator[] const overload has been -changed to const T& as described in 389 several paragraphs of -the section 26.6.2.4 [valarray.access] are now -incompletely -specified, because many requirements and guarantees should now also -apply to the const overload. Most notably, the address and reference -guarantees should be extended to the const overload case. -

- - -

Proposed resolution:

-

-Change 26.6.2.4 [valarray.access]: -

- -
-

--1- When applied to a constant array, the subscript operator returns a -reference to the corresponding element of the array. When applied to a -non-constant array, tThe subscript operator returns a -reference to the corresponding element of the array. -

- -

--3- The expression &a[i+j] == &a[i] + j evaluates as true for all size_t i -and size_t j such that i+j is less -than the length of the non-constant array a. -

- -

--4- Likewise, the expression &a[i] != &b[j] evaluates -as true for any two non-constant arrays a and -b and for any size_t i and size_t j such that -i is less than the length of a and j is less -than the length of b. This property indicates an absence of -aliasing and may be used to advantage by optimizing -compilers.281) -

- -

--5- The reference returned by the subscript operator for an non-constant array is guaranteed to be valid until -the member function resize(size_t, T) (26.5.2.7) is called for that array or until the lifetime -of that array ends, whichever happens first. -

- -
- - - - - - -
-

718. basic_string is not a sequence

-

Section: 21.4 [basic.string] Status: NAD Editorial - Submitter: Bo Persson Opened: 2007-08-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Paragraph 21.4 [basic.string]/3 states: -

- -
-

-The class template basic_string conforms to the requirements for a -Sequence (23.1.1) and for a Reversible Container (23.1). -

-
- -

-First of all, 23.2.3 [sequence.reqmts] is no longer "Sequence" but "Sequence container". -Secondly, after the resent changes to containers (emplace, push_back, -const_iterator parameters to insert and erase), basic_string is not -even close to conform to the current requirements. -

- -

[ -Bellevue: -]

- - -
-
    -
  • emplace, for example, may not make sense for strings. Is also likely suboptimal
    • -
  • with concepts do we need to maintain string as sequence container?
    • -
  • One approach might be to say something like: string is a sequence except it doesn't have these functions
    • -
-
    -
  • basic_string already has push_back
    • -
  • const_iterator parameters to insert and erase should be added to basic_string
    • -
  • this leaves emplace to handle -- we have the following options: -
      -
    • option 1: add it to string even though it's optional
      • -
    • option 2: make emplace optional to sequences (move from table 89 to 90)
      • -
    • option 3: say string not sequence (the proposal),
      • -
    • option 4: add an exception to basic string wording.
      • -
    -
    • -
-

General consensus is to suggest option 2.

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to NAD Editorial -

- - - -

Proposed resolution:

-

-Remove this sentence, in recognition of the fact that basic_string is -not just a vector-light for literal types, but something quite -different, a string abstraction in its own right. -

- - - - - -
-

721. wstring_convert inconsistensies

-

Section: 22.3.3.2.2 [conversions.string] Status: NAD - Submitter: Bo Persson Opened: 2007-08-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Paragraph 3 says that the Codecvt template parameter shall meet the -requirements of std::codecvt, even though std::codecvt itself cannot -be used (because of a protected destructor). -

- -

-How are we going to explain this code to beginning programmers? -

- -
-template<class I, class E, class S>
-struct codecvt : std::codecvt<I, E, S>
-{
-    ~codecvt()
-    { }
-};
-
-void main()
-{
-    std::wstring_convert<codecvt<wchar_t, char, std::mbstate_t> > compiles_ok;
-    
-    std::wstring_convert<std::codecvt<wchar_t, char, std::mbstate_t> >   not_ok;
-}
-
- -

[ -San Francisco: -]

- - -

-Bill will propose a resolution. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-codecvt isn't intended for beginning programmers. This is a regrettable -consequence of the original design of the facet. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

725. Optional sequence container requirements column label

-

Section: 23.2.3 [sequence.reqmts] Status: NAD Editorial - Submitter: David Abrahams Opened: 2007-09-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Table 90: (Optional sequence container operations) states the -"assertion note pre/post-condition" of operator[] to be -

- -
-*(a.begin() + n)
-
- -

-Surely that's meant to be "operational semantics?" -

- - - -

Proposed resolution:

-
- - - - - -
Table 90: Optional sequence container operations
expression return type assertion/note
pre/post-condition
operational semantics		 container
-
- - - - - - -
-

726. Missing regex_replace() overloads

-

Section: 28.11.4 [re.alg.replace] Status: NAD - Submitter: Stephan T. Lavavej Opened: 2007-09-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Two overloads of regex_replace() are currently provided: -

- -
-template <class OutputIterator, class BidirectionalIterator, 
-    class traits, class charT> 
-  OutputIterator 
-  regex_replace(OutputIterator out, 
-                BidirectionalIterator first, BidirectionalIterator last, 
-                const basic_regex<charT, traits>& e, 
-                const basic_string<charT>& fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
- 
-template <class traits, class charT> 
-  basic_string<charT> 
-  regex_replace(const basic_string<charT>& s, 
-                const basic_regex<charT, traits>& e, 
-                const basic_string<charT>& fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
- -
    -
  1. Overloads taking const charT * are provided for regex_match() and -regex_search(), but not regex_replace(). This is inconsistent.
    2. -
  2. -

    The absence of const charT * overloads prevents ordinary-looking code from compiling, such as:

    - -
    -const string s("kitten");
-const regex r("en");
-cout << regex_replace(s, r, "y") << endl;
-
    - -

    -The compiler error message will be something like "could not deduce -template argument for 'const std::basic_string<_Elem> &' from 'const -char[1]'". -

    - -

    -Users expect that anything taking a basic_string<charT> can also take a -const charT *. In their own code, when they write a function taking -std::string (or std::wstring), they can pass a const char * (or const -wchar_t *), thanks to basic_string's implicit constructor. Because the -regex algorithms are templated on charT, they can't rely on -basic_string's implicit constructor (as the compiler error message -indicates, template argument deduction fails first). -

    - -

    -If a user figures out what the compiler error message means, workarounds -are available - but they are all verbose. Explicit template arguments -could be given to regex_replace(), allowing basic_string's implicit -constructor to be invoked - but charT is the last template argument, not -the first, so this would be extremely verbose. Therefore, constructing -a basic_string from each C string is the simplest workaround. -

    -
    3. - -
  3. -There is an efficiency consideration: constructing basic_strings can -impose performance costs that could be avoided by a library -implementation taking C strings and dealing with them directly. -(Currently, for replacement sources, C strings can be converted into -iterator pairs at the cost of verbosity, but for format strings, there -is no way to avoid constructing a basic_string.) -
    4. -
- -

[ -Sophia Antipolis: -]

- - -

-We note that Boost already has these overloads. However, the proposed -wording is provided only for 28.11.4 [re.alg.replace]; wording is needed for the synopsis -as well. We also note that this has impact on match_results::format, -which may require further overloads. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Daniel to tweak for us. -

- -

[ -2009-07-25 Daniel tweaks both this issue and 727. -]

- - -
-

-This is solved by the proposed resolution of 727. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave Open. Though we believe this is solved by the proposed resolution -to 727. -

- -

[ -2010-01-27 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Rationale:

-

-Solved by 727. -

- - -

Proposed resolution:

- -

-Provide additional overloads for regex_replace(): one additional -overload of the iterator-based form (taking const charT* fmt), and three -additional overloads of the convenience form (one taking const charT* -str, another taking const charT* fmt, and the third taking both const -charT* str and const charT* fmt). 28.11.4 [re.alg.replace]: -

- -
-
-template <class OutputIterator, class BidirectionalIterator, 
-    class traits, class charT> 
-  OutputIterator 
-  regex_replace(OutputIterator out, 
-                BidirectionalIterator first, BidirectionalIterator last, 
-                const basic_regex<charT, traits>& e, 
-                const basic_string<charT>& fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-template <class OutputIterator, class BidirectionalIterator, 
-    class traits, class charT> 
-  OutputIterator 
-  regex_replace(OutputIterator out, 
-                BidirectionalIterator first, BidirectionalIterator last, 
-                const basic_regex<charT, traits>& e, 
-                const charT* fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-

...

-
-template <class traits, class charT> 
-  basic_string<charT> 
-  regex_replace(const basic_string<charT>& s, 
-                const basic_regex<charT, traits>& e, 
-                const basic_string<charT>& fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-template <class traits, class charT> 
-  basic_string<charT> 
-  regex_replace(const basic_string<charT>& s, 
-                const basic_regex<charT, traits>& e, 
-                const charT* fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-template <class traits, class charT> 
-  basic_string<charT> 
-  regex_replace(const charT* s, 
-                const basic_regex<charT, traits>& e, 
-                const basic_string<charT>& fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-template <class traits, class charT> 
-  basic_string<charT> 
-  regex_replace(const charT* s, 
-                const basic_regex<charT, traits>& e, 
-                const charT* fmt, 
-                regex_constants::match_flag_type flags = 
-                  regex_constants::match_default);
-
-
- - - - - - -
-

729. Problem in [rand.req.eng]/3

-

Section: 26.5.1.4 [rand.req.eng] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

View all other issues in [rand.req.eng].

-

View all issues with NAD status.

-

Discussion:

-

-The 3rd table row in 26.5.1.4 [rand.req.eng]/3 requires random number engines to accept any -arithmetic type as a seed, which is then casted to the engine's result_type and subsequently -used for seeding the state of the engine. The requirement stated as "Creates an engine with -initial state determined by static_cast<X::result_type>(s)" forces random number engines -to either use a seeding method that completely depends on the result_type (see the discussion -of seeding for the mersenne_twister_engine in point T2 above) or at least to throw away "bits -of randomness" in the seed value if the result_type is smaller than the seed type. This seems -to be inappropriate for many modern random number generators, in particular F2-linear or -cryptographic ones, which operate on an internal bit array that in principle is independent of the -type of numbers returned. -

- -

-Possible resolution: I propose to change the wording to a version similar to "Creates an -engine with initial state determined by static_cast<UintType>(s), where UintType is an -implementation specific unsigned integer type." -

- -

-Additionally, the definition of s in 26.5.1.4 [rand.req.eng]/1 c) could be restricted to unsigned integer types. -

- -

-Similarly, the type of the seed in 26.5.1.5 [rand.req.adapt]/3 e) could be left unspecified. -

- -

-See N2424 -for further discussion. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-In reply to the discussion in -N2424 -regarding this issue: -

-

-The descriptions of all engines and engine adaptors given in sections -26.5.3 [rand.eng] and 26.5.4 [rand.adapt] already specify the concrete -types of the integer arguments for seeding. Hence, relaxing the general -requirement in 26.5.1.4 [rand.req.eng] would not affect portability and -reproducibility of the standard library. Furthermore, it is not clear to -me what exactly the guarantee "with initial state determined by -static_cast<X::result_type>(s)" is useful for. On the other hand, -relaxing the requirement would allow developers to implement other -random number engines that do not have to cast all arithmetic seed -arguments to their result_types. -

-
- -

[ -Bellevue: -]

- - -

-Propose close NAD for the reasons given in N2424. -

- - - - -

Proposed resolution:

-

-See N2424 -for further discussion. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-Change row 3 of table 105 "Random number engine requirements" in 26.5.1.4 [rand.req.eng]/3 -

- -

-Creates an engine with initial state determined by -static_cast<X::result_type>(s) -

- -

-Similarly, change 26.5.1.5 [rand.req.adapt]/3 e) -

- -

-When X::X is invoked with an X::result_type value s -of arithmetic type (3.9.1), ... -

- -
- - - - - - -
-

730. Comment on [rand.req.adapt]/3 e)

-

Section: 26.5.1.5 [rand.req.adapt] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

Discussion:

-

-If an engine adaptor is invoked with an argument of type seed_seq, then all base -engines are specified to be seeded with this seed_seq. As seed_seq's randomization method is -qualified as constant, this procedure will ef fectively initialize all base engines with the same seed -(though the resulting state might still dif fer to a certain degree if the engines are of different types). -It is not clear whether this mode of operation is in general appropriate, hence -- as far as the -stated requirements are of general nature and not just specific to the engine adaptors provided by -the library -- it might be better to leave the behaviour unspecified, since the current definition of -seed_seq does not allow for a generally satisfying specification. -

- -

-Posssible resolution: [As above] -

- -

-See N2424 -for further discussion. -

- -

[ -Bellevue: -]

- - -

-Close NAD for the reasons given in N2424. -

- - - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

731. proposal for a customizable seed_seq

-

Section: 26.5.7.1 [rand.util.seedseq] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The proper way to seed random number engines seems to be the most frequently -discussed issue of the 26.5 [rand] proposal. While the new seed_seq approach is already rather -general and probably sufficient for most situations, it is unlikely to be optimal in every case (one -problem was pointed out in point T5 above). In some situations it might, for instance, be better to -seed the state with a cryptographic generator. -

-

-In my opinion this is a pretty strong argument for extending the standard with a simple facility to -customize the seeding procedure. This could, for example, be done with the following minimal -changes: -

- -

-Possible resolution: -

- -
    -
  1. -Turn the interface specification of 26.5.7.1 [rand.util.seedseq]/2 into a "SeedSeq" requirement, where the -exact behaviour of the constructors and the randomize method are left unspecified and where the -const qualification for randomize is removed. Classes implementing this interface are additionally -required to specialize the traits class in c). -
    2. -
  2. -Provide the class seed_seq as a default implementation of the SeedSeq interface. -
    3. -
  3. -

    -Supplement the seed_seq with a traits class -

    -
    -template <typename T> 
-struct is_seed_seq { static const bool value = false; }
-
    -

    and the specialization

    -
    -template <> 
-struct is_seed_seq<seed_seq> { static const bool value = true; }
-
    -

    which users can supplement with further specializations.

    -
    4. -
  4. -Change 26.5.1.4 [rand.req.eng]/1 d) to "q is an lvalue of a type that fulfils the SeedSeq requirements", and -modify the constructors and seed methods in 26.5.3 [rand.eng] appropriately (the actual implementation -could be done using the SFINAE technique). -
    5. -
- -

[ -Bellevue: -]

- - -

-See N2424. Close NAD but note that "conceptizing" the library may cause -this problem to be solved by that route. -

- - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

733. Comment on [rand.req.dist]/9

-

Section: 26.5.1.6 [rand.req.dist] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

Discussion:

-

-The requirement "P shall have a declaration of the form typedef X distribution_- -type" effectively makes the use of inheritance for implementing distributions very inconvenient, -because the child of a distribution class in general will not satisfy this requirement. In my opinion -the benefits of having a typedef in the parameter class pointing back to the distribution class are -not worth the hassle this requirement causes. [In my code base I never made use of the nested -typedef but on several occasions could have profited from being able to use simple inheritance for -the implementation of a distribution class.] -

- -

-Proposed resolution: I propose to drop this requirement. -

- -

[ -Bellevue: -]

- - -

-Close NAD for the reasons given in N2424. In practice it is not inconvenient to meet these requirements. -

- - - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

735. Unfortunate naming

-

Section: 26.5.8.3.2 [rand.dist.bern.bin], 26.5.8.3.4 [rand.dist.bern.negbin] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

Discussion:

-

-In my opinion the choice of name for the t parameter of the binomial_distribution -is very unfortunate. In virtually every internet reference, book and software implementation -this parameter is called n instead, see for example Wikipedia, Mathworld, Evans et al. (1993) -Statistical Distributions, 2nd E., Wiley, p. 38, the R statistical computing language, p. 926, -Mathematica and Matlab. -

- -

-Similarly, the choice of k for the parameter of the negative binomial distributions is rather unusual. -The most common choice for the negative binomial distribution seems to be r instead. -

- -

-Choosing unusual names for the parameters causes confusion among users and makes the -interface unnecessarily inconvenient to use. -

- -

-Possible resolution: For these reasons, I propose to change the name of the respective parameters -to n and r. -

- -

[ -Bellevue: -]

- - -

-In N2424. NAD It has been around for a while. It is hardly universal, -there is prior art, and this would confuse people. -

- - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

736. Comment on [rand.dist.samp.discrete]

-

Section: 26.5.8.6.1 [rand.dist.samp.discrete] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
    -
  1. -The specification for discrete_distribution requires the member probabilities() -to return a vector of standardized probabilities, which forces the implementation every time to -divide each probability by the sum of all probabilities, as the sum will in practice almost never be -exactly 1.0. This is unnecessarily inef ficient as the implementation would otherwise not need to -compute the standardized probabilities at all and could instead work with the non-standardized -probabilities and the sum. If there was no standardization the user would just get back the -probabilities that were previously supplied to the distribution object, which to me seems to be the -more obvious solution. -
    2. -
  2. -The behaviour of discrete_distribution is not specified in case the number of given -probabilities is larger than the maximum number representable by the IntType. -
    3. -
- -

-Possible resolution: I propose to change the specification such that the non-standardized -probabilities need to be returned and that an additional requirement is included for the number -of probabilities to be smaller than the maximum of IntType. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-In reply to the discussion in -N2424 -of this issue: -

-

-Rescaled floating-point parameter vectors can not be expected to compare -equal because of the limited precision of floating-point numbers. -My proposal would at least guarantee that a parameter -vector (of type double) passed into the distribution would compare equal -with the one returned by the probabilities() method. Furthermore, I do -not understand why "the changed requirement would lead to a significant -increase in the amount of state in the distribution object". A typical -implementation's state would increase by exactly one number: the sum of -all probabilities. The textual representation for serialization would -not need to grow at all. Finally, the proposed replacement "0 < n <= -numeric_limits<IntType>::max() + 1" makes the implementation -unnecessarily complicated, "0 < n <= numeric_limits<IntType>::max()" -would be better. -

-
- -

[ -Bellevue: -]

- - -
-

-In N2424. We agree with the observation and the proposed resolution to -part b). We recommend the wording n > 0 be replaced with 0 < n -numeric_limits::max() + 1. However, we disagree with part a), as it -would interfere with the definition of parameters' equality. Further, -the changed requirement would lead to a significant increase in the -amount of state of the distribution object. -

- -

-As it stands now, it is convenient, and the changes proposed make it -much less so. -

- -

-NAD. Part a the current behavior is desirable. Part b, any constructor -can fail, but the rules under which it can fail do not need to be listed -here. -

-
- - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-In 26.5.8.6.1 [rand.dist.samp.discrete]: -

- -

-Proposed wording a): -

- -
-

-Change in para. 2 -

- -

-Constructs a discrete_distribution object with n=1 and p0 = w0 = 1 -

- -

-and change in para. 5 -

- -

-Returns: A vector<double> whose size member returns n and whose -operator[] member returns pk -the weight wk as a double value -when invoked with argument k for k = 0, -..., n-1 -

- -
- -

-Proposed wording b): -

- -
-

-Change in para. 3: -

- -

-If firstW == lastW, let the sequence w have length n = 1 and consist -of the single value w0 = 1. Otherwise, [firstW,lastW) shall form a -sequence w of length n > 0 -such that 0 < n <= numeric_limits<IntType>::max(), -and *firstW shall yield a value w0 -convertible to double. [Note: The values wk are commonly known -as the weights . -- end note] -

- -
- -
- - - - - -
-

737. Comment on [rand.dist.samp.pconst]

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
    -
  1. -The discussion in point T11 above regarding probabilities() similarly applies -to the method densities() of piecewise_constant_distribution. -
    2. -
  2. -

    -The design of the constructor -

    -
    -template <class InputIteratorB, class InputIteratorW> 
-piecewise_constant_distribution( InputIteratorB firstB, InputIteratorB lastB, 
-                                 InputIteratorW firstW);
-
    -

    -is unnecessarily unsafe, as there is no separate end-iterator given for the weights. I can't see -any performance or convenience reasons that would justify the risks inherent in such a function -interface, in particular the risk that input error might go unnoticed. -

    -
    3. -
- -

-Possible resolution: I propose to add an InputIteratorW lastW argument to the interface. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- -

-In reply to the discussion in -N2424 -I'd like to make the same comments as for 736. -

- -

[ -Bellevue: -]

- - -

-In N2424. There is already precedent elsewhere in the library. Follows existing convention. NAD. -

- - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-In 26.5.8.6.2 [rand.dist.samp.pconst]: -

- -

-Proposed wording a) -

- -
-

-Change in para. 2 -

-

-Constructs a piecewise_constant_distribution object with n = 1, p0 = w0 = 1, -b0 = 0, and b1 = 1 -

- -

-and change in para. 5 -

- -

-A vector<result_type> whose size member returns n and whose operator[] -member returns pk -the weight wk as a double value -when invoked with argument k for k = 0, ..., n-1 -

- -
- -

-Proposed wording b) -

- -
-

-Change both occurrences of -

- -
-"piecewise_constant_distribution(InputIteratorB firstB, InputIteratorB lastB,
-                                 InputIteratorW firstW, InputIteratorW lastW)
-
- -

-and change in para. 3 -

- -

-the length of the sequence w starting from firstW shall be at least n, -*firstW shall return a value w0 that is convertible to double, and any -wk for k >= n shall be ignored by the distribution -[firstW, lastW) shall form a sequence w of length n whose leading element -w0 shall be convertible to double -

- -
- - -
- - - - - - -
-

738. Editorial issue in [rand.adapt.disc]/3

-

Section: 26.5.4.2 [rand.adapt.disc] Status: NAD Editorial - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Since the template parameter p and r are of type size_t, the member n in the class -exposition should have type size_t, too. -

- - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

739. Defect in [rand.util.canonical]/3

-

Section: 26.5.7.2 [rand.util.canonical] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The complexity of generate_canonical is specified to be "exactly k=max(1, ceil(b/log2 -R)) invocations of g". This terms involves a logarithm that is not rounded and hence can not (in -general) be computed at compile time. As this function template is performance critical, I propose -to replace ceil(b/log2 R) with ceil(b/floor(log2 R)). -

- -

-See N2424 -for further discussion. -

- -

[ -Bellevue: -]

- - -

-In N2424. Close NAD as described there. -

- - - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- - - - - -
-

741. Const-incorrect get_deleter function for shared_ptr

-

Section: 20.8.2.2.10 [util.smartptr.getdeleter] Status: NAD - Submitter: Daniel Krügler Opened: 2007-09-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The following issue was raised by Alf P. Steinbach in c.l.c++.mod: -

- -

-According to the recent draft N2369, both the header memory synopsis -of 20.7 [memory] and 20.8.2.2.10 [util.smartptr.getdeleter] declare: -

- -
-template<class D, class T> D* get_deleter(shared_ptr<T> const& p);
-
- -

-This allows to retrieve the pointer to a mutable deleter of a const -shared_ptr (if that owns one) and therefore contradicts the usual -philosophy that associated functors are either read-only (e.g. -key_comp or value_comp of std::map) or do at least reflect -the mutability of the owner (as seen for the both overloads of -unique_ptr::get_deleter). -Even the next similar counter-part of get_deleter - the two -overloads of function::target in the class template function -synopsis 20.9.12.2 [func.wrap.func] or in 20.9.12.2.5 [func.wrap.func.targ] - do -properly mirror the const-state of the owner. -

- -

Possible proposed resolutions:

- -

-Replace the declarations of get_deleter in the header <memory> -synopsis of 20.7 [memory] and in 20.8.2.2.10 [util.smartptr.getdeleter] by one of the -following alternatives (A) or (B): -

- -
    -
  1. -Provide only the immutable variant. This would reflect the -current praxis of container::get_allocator(), map::key_comp(), or -map::value_comp. - -
    -template<class D, class T> const D* get_deleter(shared_ptr<T> const& p);
-
    -
    2. -
  2. -Just remove the function. -
    3. -
- -

-Alberto Ganesh Barbati adds: -

- -
    -
  1. -

    -Replace it with two functions: -

    -
    -template <class D, class T> D get_deleter(shared_ptr<T> const&);
-template <class D, class T> bool has_deleter(shared_ptr<T> const&);
-
    - -

    -The first one would throw if D is the wrong type, while the latter would -never throw. This approach would reflect the current praxis of -use_facet/has_facet, with the twist of returning the deleter by value as -container::get_allocator() do. -

    -
    2. -
- -

-Peter Dimov adds: -

- -
-

-My favorite option is "not a defect". A, B and C break useful code. -

-
- -

[ -Bellevue: -]

- - -

-Concern this is similar to confusing "pointer to const" with "a constant pointer". -

- - -

Proposed resolution:

-

-

- - - - - -
-

745. copy_exception API slices.

-

Section: 18.8.5 [propagation] Status: NAD - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It could be I did not understand the design rationale, but I thought -copy_exception would produce an exception_ptr to the most-derived (dynamic) -type of the passed exception. Instead it slices, which appears to be less -useful, and a likely source of FAQ questions in the future. -

-

-(Peter Dimov suggests NAD) -

- -

[ -Bellevue: -]

- - -
-

-How could this be implemented in a way that the dynamic type is cloned? -

-

-The feature is designed to create an exception_ptr from an object whose -static type is identical to the dynamic type and thus there is no -slicing involved. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

747. We have 3 separate type traits to identify classes supporting no-throw operations

-

Section: 20.10.4.3 [meta.unary.prop] Status: NAD - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-We have 3 separate type traits to identify classes supporting no-throw -operations, which are very useful when trying to provide exception safety -guarantees. However, I'm not entirely clear on what the current wording -requires of a conforming implementation. To quote from -has_nothrow_default_constructor: -

-

-or T is a class type with a default constructor that is known not to throw -any exceptions -

-

-What level of magic do we expect to deduce if this is known? -

-

-E.g. -

- -
-struct test{
- int x;
- test() : x() {}
-};
-
-

-Should I expect a conforming compiler to - assert( has_nothrow_constructor<test>::value ) -

-

-Is this a QoI issue? -

-

-Should I expect to 'know' only if-and-only-if there is an inline definition -available? -

-

-Should I never expect that to be true, and insist that the user supplies an -empty throw spec if they want to assert the no-throw guarantee? -

-

-It would be helpful to maybe have a footnote explaining what is required, -but right now I don't know what to suggest putting in the footnote. -

-

-(agreement since is that trivial ops and explicit no-throws are required. -Open if QoI should be allowed to detect further) -

- -

[ -Bellevue: -]

- - -

-This looks like a QoI issue. -In the case of trivial and nothrow it is known. Static analysis of the program is definitely into QoI. -Move to OPEN. Need to talk to Core about this. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-This is QoI. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

748. The is_abstract type trait is defined by reference to 10.4.

-

Section: 20.10.4.3 [meta.unary.prop] Status: NAD - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-I am trying to decide is a pure virtual function is a necessary as well as -sufficient requirement to be classified as abstract? -

-

-For instance, is the following (non-polymorphic) type considered abstract? -

-
-struct abstract {
-protected:
- abstract(){}
- abstract( abstract const & ) {}
- ~abstract() {}
-};
-
-

-(Suggested that this may be NAD, with an editorial fix-up from Pete on the -core wording to make clear that abstract requires a pure virtual function) -

- - -

Proposed resolution:

-

-Core has clarified that the definition abstract is adequate. Issue withdrawn by submitter. NAD. -

- - - - - -
-

750. The current definition for is_convertible requires that the type be -implicitly convertible, so explicit constructors are ignored.

-

Section: 20.10.6 [meta.rel] Status: Dup - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 719

-

Discussion:

-

-With the pending arrival of explicit conversion functions though, I'm -wondering if we want an additional trait, is_explictly_convertible? -

- -

[ -Bellevue: -]

- - -

-Alisdair is considering preparing a paper listing a number of missing -type traits, and feels that it might be useful to handle them all -together rather than piecemeal. This would affect issue 719 and 750. -These two issues should move to OPEN pending AM paper on type traits. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Duplicate of 719 (for our purposes). -

- -

[ -Addressed in N2947. -]

- - - - -

Proposed resolution:

- - - - - - -
-

751. change pass-by-reference members of vector<bool> to pass-by-value?

-

Section: 23.3.7 [vector.bool] Status: NAD - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

View all other issues in [vector.bool].

-

View all issues with NAD status.

-

Discussion:

-

-A number of vector<bool> members take const bool& as arguments. -Is there any chance we could change them to pass-by-value or would I -be wasting everyone's time if wrote up an issue? -

- -

[ -post Bellevue: -]

- - -
-

-As we understand it, the original requester (Martin Sebor) would like -for implementations to be permitted to pass-by-value. Alisdair suggests -that if this is to be resolved, it should be resolved more generally, -e.g. in other containers as well. -

-

-We note that this would break ABI. However, we also suspect that this -might be covered under the "as-if" rule in section 1.9. -

-

-Many in the group feel that for vector<bool>, this is a "don't care", -and that at this point in the process it's not worth the bandwidth. -

-

-Issue 679 -- which was in ready status pre-Bellevue and is -now in the working paper -- is related to this, though not a duplicate. -

-

-Moving to Open with a task for Alisdair to craft a informative note to -be put whereever appropriate in the WP. This note would clarify places -where pass-by-const-ref can be transformed to pass-by-value under the -as-if rule. -

-
- -

[ -San Francisco: -]

- - -
-

-This is really a clause 17 issue, rather than something specific to vector<bool>. -

-

-Move to Open. Alisdair to provide a resolution. Alternately, Howard can -close this as NAD and then open a new issue to handle the general issue -(rather than the vector<bool> one). -

-

-Howard: Haven't yet opened new issue. Lacking wording for it. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-NAD. Insufficient motivation to make any changes. -

- - -

Proposed resolution:

-

-

- - - - - -
-

754. Ambiguous return clause for std::uninitialized_copy

-

Section: 20.7.12.2 [uninitialized.copy] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2007-10-15 Last modified: 2015-04-08

-

View all other issues in [uninitialized.copy].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-14882-2003, [lib.uninitialized.copy] is currently written as follows: -

- -
-
-template <class InputIterator, class ForwardIterator>
-  ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
-                                     ForwardIterator result);
-
-
-

--1- Effects: -

-
-for (; first != last; ++result, ++first)
-  new (static_cast<void*>(&*result))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-
-

--2- Returns: result -

-
-
- -

-similarily for N2369, and its corresponding section -20.7.12.2 [uninitialized.copy]. -

- -

-It's not clear to me what the return clause is supposed to mean, I see -two -possible interpretations: -

- -
    -
  1. -The notion of result is supposed to mean the value given by the -function parameter result [Note to the issue editor: Please use italics for -result]. -This seems somewhat implied by recognizing that both the function -parameter -and the name used in the clause do have the same italic font. -
    2. -
  2. -The notion of "result" is supposed to mean the value of result -after the -preceding effects clause. This is in fact what all implementations I -checked -do (and which is probably it's intend, because it matches the -specification of std::copy). -
    3. -
- -

-The problem is: I see nothing in the standard which grants that this -interpretation -is correct, specifically [lib.structure.specifications] or -17.5.1.4 [structure.specifications] -resp. do not clarify which "look-up" rules apply for names found in -the elements -of the detailed specifications - Do they relate to the corresponding -synopsis or -to the effects clause (or possibly other elements)? Fortunately most -detailed -descriptions are unambigious in this regard, e.g. this problem does -not apply -for std::copy. -

- - - -

Proposed resolution:

-

-Change the wording of the return clause to say (20.7.12.2 [uninitialized.copy]): -

- -
-

--2- Returns: The value of result after effects have taken place. -

-
- - -

[ -Bellevue: -]

- - -

-Resolution: NAD editorial -- project editor to decide if change is -worthwhile. Concern is that there are many other places this might -occur. -

- - - - -
-

757. Typo in the synopsis of vector

-

Section: 23.3.6 [vector] Status: NAD Editorial - Submitter: Paolo Carlini Opened: 2007-11-04 Last modified: 2015-04-08

-

View all other issues in [vector].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-In the synopsis 23.3.6 [vector], there is the signature: -

- -
-void insert(const_iterator position, size_type n, T&& x);
-
- -

-instead of: -

- -
-iterator insert(const_iterator position, T&& x);
-
- -

-23.3.6.5 [vector.modifiers] is fine. -

- - - -

Proposed resolution:

-

-Change the synopsis in 23.3.6 [vector]: -

- -
-iterator insert(const_iterator position, const T& x); 
-iterator insert(const_iterator position, T&& x);
-void     insert(const_iterator position, size_type n, const T& x); 
-void     insert(const_iterator position, size_type n, T&& x);
-
- - - - - -
-

763. Renaming emplace() overloads

-

Section: 23.2.4 [associative.reqmts] Status: NAD - Submitter: Sylvain Pion Opened: 2007-12-04 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with NAD status.

-

Discussion:

-

-The associative containers provide 2 overloads of emplace(): -

- -
-template <class... Args> pair<iterator, bool> emplace(Args&&... args);
-template <class... Args> iterator emplace(const_iterator position, Args&&... args);
-
- -

-This is a problem if you mean the first overload while passing -a const_iterator as first argument. -

- -

[ -Related to 767 -]

- - -

[ -Bellevue: -]

- - -

-This can be disambiguated by passing "begin" as the first argument in -the case when the non-default choice is desired. We believe that desire -will be rare. -

- -

[For related discussion see 1302]

- - -

-LWG N2680 -renamed one of the overloads to emplace_hint. -

- -

-Resolution: Change state to NAD. -

- - -

Proposed resolution:

-

-Rename one of the two overloads. -For example to emplace_here, hint_emplace... -

- - - - - -
-

764. equal_range on unordered containers should return a pair of local_iterators

-

Section: 23.2.5 [unord.req] Status: NAD - Submitter: Joe Gottman Opened: 2007-11-29 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

View all other issues in [unord.req].

-

View all issues with NAD status.

-

Discussion:

-

- A major attribute of the unordered containers is that iterating -though them inside a bucket is very fast while iterating between buckets -can be much slower. If an unordered container has a low load factor, -iterating between the last iterator in one bucket and the next iterator, -which is in another bucket, is O(bucket_count()) which may be much -larger than O(size()). -

-

- If b is an non-const unordered container of type B and k is an -object of it's key_type, then b.equal_range(k) currently returns -pair<B::iterator, B::iterator>. Consider the following code: -

- -
-B::iterator lb, ub;
-tie(lb, ub) = b.equal_range(k);
-for (B::iterator it = lb; it != ub; ++it) {
-        // Do something with *it
-}
-
- -

-If b.equal_range(k) returns a non-empty range (i.e. b contains at least -on element whose key is equivalent to k), then every iterator in the -half-open range [lb, ub) will be in the same bucket, but ub will likely -either be in a different bucket or be equal to b.end(). In either case, -iterating between ub - 1 and ub could take a much longer time than -iterating through the rest of the range. -

-

-If instead of returning pair<iterator, iterator>, equal_range were to -return pair<local_iterator, local_iterator>, then ub (which, like lb, -would now be a local_iterator) could be guaranteed to always be in the -same bucket as lb. In the cases where currently ub is equal to b.end() -or is in a different bucket, ub would be equal to b.end(b.bucket(key)). - This would make iterating between lb and ub much faster, as every -iteration would be constant time. -

- -

[ -Bellevue: -]

- - -

-The proposed resolution breaks consistency with other container types -for dubious benefit, and iterators are already constant time. -

- - - -

Proposed resolution:

-

-Change the entry for equal_range in Table 93 (23.2.5 [unord.req]) as follows: -

- - - - - - - - - - - -
expression return type assertion/note pre/post-condition complexity
b.equal_range(k)pair<local_iterator,local_iterator>; pair<const_local_iterator,const_local_iterator> for const b.Returns a range containing all elements with keys equivalent to k. Returns make_pair(b.end(b.bucket(key)),b.end(b.bucket(key))) if no such elements exist.Average case Θ(b.count(k)). Worst case Θ(b.size()).
- - - - - -
-

773. issues with random

-

Section: 26.5.8.2 [rand.dist.uni] Status: NAD - Submitter: P.J. Plauger Opened: 2008-01-14 Last modified: 2015-04-08

-

View all other issues in [rand.dist.uni].

-

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-

Discussion:

-
    -
  1. -26.5.8.2.1 [rand.dist.uni.int] uniform_int constructor has changed the default -max constructor parameter from 9 (in TR1) to max(). The value -is arbitrary at best and shouldn't be lightly changed because -it breaks backward compatibility. -
    2. - -
  2. -26.5.8.2.1 [rand.dist.uni.int] uniform_int has a parameter param that you can -provide on construction or operator(), set, and get. But there -is not even a hint of what this might be for. -
    3. - -
  3. -26.5.8.2.2 [rand.dist.uni.real] uniform_real. Same issue as #2. -
    4. -
- -

[ -Bellevue: -]

- - -

-NAD. Withdrawn. -

- - -

Proposed resolution:

-

-

- - - - - -
-

784. unique_lock::release

-

Section: 30.4.2.2.3 [thread.lock.unique.mod] Status: NAD - Submitter: Constantine Sapuntzakis Opened: 2008-02-02 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-unique_lock::release will probably lead to many mistakes where people -call release instead of unlock. I just coded such a mistake using the -boost pre-1.35 threads library last week. -

- -

-In many threading libraries, a call with release in it unlocks the -lock (e.g. ReleaseMutex in Win32, java.util.concurrent.Semaphore). -

- -

-I don't call unique_lock::lock much at all, so I don't get to see the -symmetry between ::lock and ::unlock. I usually use the constructor to -lock the mutex. So I'm left to remember whether to call release or -unlock during the few times I need to release the mutex before the scope -ends. If I get it wrong, the compiler doesn't warn me. -

- -

-An alternative name for release may be disown. -

- -

-This might be a rare case where usability is hurt by consistency with -the rest of the C++ standard (e.g. std::auto_ptr::release). -

- -

[ -Bellevue: -]

- - -

-Change a name from release to disown. However prior art uses the release -name. Compatibility with prior art is more important that any possible -benefit such a change might make. We do not see the benefit for -changing. NAD -

- - -

Proposed resolution:

-

-Change the synopsis in 30.4.2.2 [thread.lock.unique]: -

- -
-template <class Mutex> 
-class unique_lock 
-{ 
-public:
-   ...
-   mutex_type* release disown();
-   ...
-};
-
- -

-Change 30.4.2.2.3 [thread.lock.unique.mod]: -

- -
-mutex_type *release disown();
-
- - - - - -
-

785. Random Number Requirements in TR1

-

Section: TR1 5.1.4.5 [tr.rand.eng.disc], TR1 5.1.4.6 [tr.rand.eng.xor] Status: NAD - Submitter: John Maddock Opened: 2008-01-15 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-Table 16 of TR1 requires that all Pseudo Random Number generators have a -

- -
-seed(integer-type s)
-
- -

-member function that is equivalent to: -

- -
-mygen = Generator(s)
-
- -

-But the generators xor_combine and discard_block have no such seed member, only the -

- -
-template <class Gen>
-seed(Gen&);
-
- -

-member, which will not accept an integer literal as an argument: something that appears to violate the intent of Table 16. -

- -

-So... is this a bug in TR1? -

- -

-This is a real issue BTW, since the Boost implementation does adhere to the requirements of Table 16, while at least one commercial implementation does not and follows a strict adherence to sections 5.1.4.5 and 5.1.4.6 instead. -

- -

[ -Jens adds: -]

- - -

-Both engines do have the necessary -constructor, therefore the omission of the seed() member -functions appears to be an oversight. -

- -

[ -Post Summit Daniel adds: -]

- - -

-Recommend NAD: xor_combine does no longer exist and discard_block[_engine] -has now the required seed overload accepting a result_type, which shall be an -unsigned integral type. -

- -

[ -Batavia (2009-05): -]

- -

-Move to NAD as recommended. -

- - -

Proposed resolution:

-

-NAD Recommended. -

- - - - - -
-

790. xor_combine::seed not specified

-

Section: X [rand.adapt.xor] Status: NAD - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.adapt.xor].

-

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-

Discussion:

-

-xor_combine::seed(result_type) and seed(seed_seq&) don't say what -happens to each of the sub-engine seeds. (Should probably do the same -to both, unlike TR1.) -

- -

[ -Bellevue: -]

- - -

-Overcome by the previous proposal. NAD mooted by resolution of 789. -

- - - -

Proposed resolution:

- - - - - -
-

791. piecewise_constant_distribution::densities has wrong name

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: NAD - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.pconst].

-

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-

Discussion:

-

-piecewise_constant_distribution::densities() should be probabilities(), -just like discrete_distribution. (There's no real use for weights divided -by areas.) -

- -

[ -Bellevue: -]

- - -
-

-Fermilab does not agree with this summary. As defined in the equation in -26.4.8.5.2/4, the quantities are indeed probability densities not -probabilities. Because we view this distribution as a parameterization -of a *probability density function*, we prefer to work in terms of -probability densities. -

- -

-We don't think this should be changed. -

- -

-If there is a technical argument about why the implementation dealing -with these values can't be as efficient as one dealing with -probabilities, we might reconsider. We don't care about this one member -function being somewhat more or less efficient; we care about the size -of the distribution object and the speed of the calls to generate -variates. -

-
- - - -

Proposed resolution:

- -

-Change synopsis in 26.5.8.6.2 [rand.dist.samp.pconst]: -

- -
-template <class RealType = double> 
-class piecewise_constant_distribution 
-{ 
-public:
-    ...
-    vector<double> densities probabilities() const;
-    ...
-};
-
- -

-Change 26.5.8.6.2 [rand.dist.samp.pconst]/6: -

- -
-vector<double> densities probabilities() const;
-
- - - - - - -
-

795. general_pdf_distribution should be dropped

-

Section: X [rand.dist.samp.genpdf] Status: Dup - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.genpdf].

-

View all issues with Dup status.

-

Duplicate of: 732

-

Discussion:

-

-general_pdf_distribution should be dropped. (It's a research topic in -adaptive numerical integration.) -

- -

[ -Stephan Tolksdorf notes: -]

- - -

-This appears to be a duplicate of 732. -

- - -

Proposed resolution:

- - - - - - -
-

796. ranlux48_base returns wrong value

-

Section: 26.5.5 [rand.predef] Status: NAD - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.predef].

-

View all issues with NAD status.

-

Discussion:

-

-The 10,000th value returned by ranlux48_base is supposed to be -61839128582725. We get 192113843633948. (Note that the underlying -generator was changed in Kona.) -

- -

[ -Bellevue: -]

- - -

-Submitter withdraws defect. -

- - - -

Proposed resolution:

-

-Change 26.5.5 [rand.predef]/p5: -

- -
-
-typedef subtract_with_carry_engine<uint_fast64_t, 48, 5, 12> 
-        ranlux48_base; 
-
-

-Required behavior: The 10000th consecutive invocation of a default-constructed -object of type ranlux48_base shall produce the value -61839128582725 192113843633948. -

-
- - - - - -
-

797. ranlux48 returns wrong value

-

Section: 26.5.5 [rand.predef] Status: NAD - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.predef].

-

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-

Discussion:

-

-The 10,000th value returned by ranlux48 is supposed to be -249142670248501. We get 88229545517833. (Note that this depends -on ranlux48_base.) -

-

[ -Bellevue: -]

- - -

-Submitter withdraws defect. -

- - - -

Proposed resolution:

-

-Change 26.5.5 [rand.predef]/p6: -

- -
-
-typedef discard_block_engine<ranlux48_base, 389, 11> 
-        ranlux48
-
-

-Required behavior: The 10000th consecutive invocation of a default-constructed -object of type ranlux48 shall produce the value -249142670248501 88229545517833. -

-
- - - - - -
-

799. [tr.rand.eng.mers] and [rand.eng.mers]

-

Section: 26.5.3.2 [rand.eng.mers], TR1 5.1.4.2 [tr.rand.eng.mers] Status: NAD - Submitter: Stephan Tolksdorf Opened: 2008-02-18 Last modified: 2015-04-08

-

View all other issues in [rand.eng.mers].

-

View all issues with NAD status.

-

Discussion:

-

-TR1 5.1.4.2 [tr.rand.eng.mers](10) requires that operator== for the mersenne_twister -returns true if and only if the states of two mersenne_twisters, -consisting each of n integers between 0 and 2w - 1, are completely -equal. This is a contradiction with TR1 5.1.1 [tr.rand.req](3) because the given -definition of the state also includes the lower r bits of x(i-n), which -will never be used to generate a random number. If two mersenne_twisters -only differ in the lower bits of x(i-n) they will not compare equal, -although they will produce an identical sequence of random numbers. -

- -

-26.5.3.2 [rand.eng.mers] in the latest C++ draft does not specify the behaviour -of operator== but uses a similar definition of the state and, just like -TR1 5.1.4.2 [tr.rand.eng.mers], requires the textual representation of a -mersenne_twister_engine to consist of Xi-n to Xi-1, including the -lower bits of Xi-n. This leads to two problems: First, the -unsuspecting implementer is likely to erroneously compare the lower r -bits of Xi-n in operator==. Second, if only the lower r bits differ, -two mersenne_twister_engines will compare equal (if correctly -implemented) but have different textual representations, which -conceptually is a bit ugly. -

- -

-I propose that a paragraph or footnote is added to 26.5.3.2 [rand.eng.mers] which -clarifies that the lower r bits of Xi-n are not to be compared in -operator== and operator!=. It would only be consequent if furthermore -the specification for the textual respresentation was changed to -Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), ..., Xi-1 or -something similar. -

- -

-These changes would likely have no practical effect, but would allow an -implementation that does the right thing to be standard-conformant. -

- -

[ -Bellevue: -]

- - -
-

-Fermi Lab has no objection to the proposed change. However it feels that -more time is needed to check the details, which would suggest a change -to REVIEW. -

-

-Bill feels that this is NAD, not enough practical importance to abandon -the simple definition of equality, and someone would have to do a lot -more study to ensure that all cases are covered for a very small -payback. The submitter admits that "These changes would likely have no -practical effect,", and according to Plum's razor this means that it is -not worth the effort! -

-

-Revisted: Agree that the fact that there is no practical difference means that no change can be justified. -

-
- - -

Proposed resolution:

-

-In 26.5.3.2 [rand.eng.mers]: -

- -
-

-Insert at the end of para 2.: -

- -

-[Note: The lower r bits of Xi-n do not influence -the state transition and hence should not be compared when comparing two -mersenne_twister_engine objects. -- end note] -

- -

-In para 5. change: -

- -

-The textual representation of xi consists of the values of -Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), -..., Xi-1, in that order. -

-
- - - - - -
-

802. knuth_b returns wrong value

-

Section: 26.5.5 [rand.predef] Status: NAD - Submitter: P.J. Plauger Opened: 2008-02-20 Last modified: 2015-04-08

-

View all other issues in [rand.predef].

-

View all issues with NAD status.

-

Discussion:

-

-The 10,000th value returned by knuth_b is supposed to be -1112339016. We get 2126698284. -

- - -

Proposed resolution:

-

-Change 26.5.5 [rand.predef]/p8: -

- -
-
-typedef shuffle_order_engine<minstd_rand0, 256> 
-        knuth_b; 
-
-

-Required behavior: The 10000th consecutive invocation of a default-constructed -object of type knuth_b shall produce the value -1112339016 2126698284. -

-
- - -

[ -Bellevue: Submitter withdraws defect. "We got the wrong value for entirely the right reasons". NAD. -]

- - - - - -
-

812. unsolicited multithreading considered harmful?

-

Section: 25.4.1 [alg.sort] Status: NAD Editorial - Submitter: Paul McKenney Opened: 2008-02-27 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

-

-Multi-threading is a good thing, but unsolicited multi-threading can -potentially be harmful. For example, sort() performance might be -greatly increased via a multithreaded implementation. However, such -a multithreaded implementation could result in concurrent invocations -of the user-supplied comparator. This would in turn result in problems -given a caching comparator that might be written for complex sort keys. -Please note that this is not a theoretical issue, as multithreaded -implementations of sort() already exist. -

-

-Having a multithreaded sort() available is good, but it should not -be the default for programs that are not explicitly multithreaded. -Users should not be forced to deal with concurrency unless they have -asked for it. -

- -

[ -This may be covered by -N2410 -Thread-Safety in the Standard Library (Rev 1). -]

- - - -

Proposed resolution:

-

-

- - -

Rationale:

-This is already covered by 17.6.5.6/20 in N2723. -

- - - - -
-

822. Object with explicit copy constructor no longer CopyConstructible

-

Section: 17.6.3.1 [utility.arg.requirements] Status: NAD - Submitter: James Kanze Opened: 2008-04-01 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with NAD status.

-

Discussion:

-

-I just noticed that the following program is legal in C++03, but -is forbidden in the current draft: -

- -
-#include <vector>
-#include <iostream>
-
-class Toto
-{
-public:
-    Toto() {}
-    explicit Toto( Toto const& ) {}
-} ;
-
-int
-main()
-{
-    std::vector< Toto > v( 10 ) ;
-    return 0 ;
-}
-
- -

-Is this change intentional? (And if so, what is the -justification? I wouldn't call such code good, but I don't see -any reason to break it unless we get something else in return.) -

- -

[ -San Francisco: -]

- - -

-The subgroup that looked at this felt this was a good change, but it may -already be handled by incoming concepts (we're not sure). -

- -

[ -Post Summit: -]

- - -
-

-Alisdair: Proposed resolution kinda funky as these tables no longer -exist. Move from direct init to copy init. Clarify with Doug, recommends -NAD. -

-

-Walter: Suggest NAD via introduction of concepts. -

-

-Recommend close as NAD. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Need to look at again without concepts. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-Move to Ready with original proposed resolution. -

-

[Howard: Original proposed resolution restored.]

- -
- -

[ -2010-11 Batavia: -]

- -

-This issue was re-reviewed in relation to [another issue, number to follow], -and the verdict was reversed. Explicit copy and move constructors are rare -beasts, and the ripple effect of this fix was far more difficult to contain -than simply saying such types do not satisfy the MoveConstructible -and CopyConstructible requirements. -

- -
-

-In 17.6.3.1 [utility.arg.requirements] change Table 33: MoveConstructible requirements [moveconstructible]: -

- -
- - - - - - - - - - -
expressionpost-condition
T t(rv) = rvt is equivalent to the value of rv before the construction
...
-
- -

-In 17.6.3.1 [utility.arg.requirements] change Table 34: CopyConstructible requirements [copyconstructible]: -

- -
- - - - - - - - - - -
expressionpost-condition
T t(u) = uthe value of u is unchanged and is equivalent to t
...
-
- -
- - - -

Proposed resolution:

-Resolved by n3215. -

- - - - -
-

826. Equivalent of %'d, or rather, lack thereof?

-

Section: 22.4.2.2 [locale.nm.put] Status: NAD - Submitter: Peter Dimov Opened: 2008-04-07 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-In the spirit of printf vs iostream... -

- -

-POSIX printf says that %'d should insert grouping characters (and the -implication is that in the absence of ' no grouping characters are -inserted). The num_put facet, on the other hand, seems to always insert -grouping characters. Can this be considered a defect worth fixing for -C++0x? Maybe ios_base needs an additional flag? -

- -

[ -Pablo Halpern: -]

- - -

-I'm not sure it constitutes a defect, but I would be in favor of adding -another flag (and corresponding manipulator). -

- -

[ -Martin Sebor: -]

- - -

-I don't know if it qualifies as a defect but I agree that there -should be an easy way to control whether the thousands separator -should or shouldn't be inserted. A new flag would be in line with -the current design of iostreams (like boolalpha, showpos, or -showbase). -

- -

[ -Sophia Antipolis: -]

- - -

-This is not a part of C99. LWG suggests submitting a paper may be appropriate. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

830. Incomplete list of char_traits specializations

-

Section: 21.2 [char.traits] Status: NAD Editorial - Submitter: Dietmar Kühl Opened: 2008-04-23 Last modified: 2015-04-08

-

View all other issues in [char.traits].

-

View all issues with NAD Editorial status.

-

Discussion:

-

- Paragraph 4 of 21.2 [char.traits] mentions that this - section specifies two specializations (char_traits<char> - and (char_traits<wchar_t>). However, there are actually - four specializations provided, i.e. in addition to the two above also - char_traits<char16_t> and char_traits<char32_t>). - I guess this was just an oversight and there is nothing wrong with just - fixing this. -

- -

[ -Alisdair adds: -]

- -

-char_traits< char16/32_t > -should also be added to <ios_fwd> in 27.3 [iostream.forward], and all the specializations -taking a char_traits parameter in that header. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Idea of the issue is ok. -

-

-Alisdair to provide wording, once that wording arrives, move to review. -

- -
- -

[ -2009-05-04 Alisdair adds: -]

- - -
-

-The main point of the issue was resolved editorially in -N2723, -so we are -close to NAD Editorial. -However, exploring the issue we found a second tweak was necessary for -<iosfwd> and that is still outstanding, so here are the words I am long -overdue delivering: -

- -

[ -Howard: I've put Alisdair's words into the proposed wording section and -moved the issue to Review. -]

- - -
- -

[ -Original proposed wording. -]

- - -
- -

- Replace paragraph 4 of 21.2 [char.traits] by: -

-
-

- This subclause specifies a struct template, char_traits<charT>, - and four explicit specializations of it, char_traits<char>, - char_traits<char16_t>, char_traits<char32_t>, and - char_traits<wchar_t>, all of which appear in the header - <string> and satisfy the requirements below. -

-
-
- -

[ -Batavia (2009-05): -]

- -

-We agree. Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Change Forward declarations 27.3 [iostream.forward]: -

- -
-

-Header <iosfwd> synopsis -

-
-namespace std {
-   template<class charT> class char_traits;
-   template<> class char_traits<char>;
-   template<> class char_traits<char16_t>;
-   template<> class char_traits<char32_t>;
-   template<> class char_traits<wchar_t>;
-...
-}
-
-
- - - - - -
-

831. wrong type for not_eof()

-

Section: 21.2.3 [char.traits.specializations] Status: NAD Editorial - Submitter: Dietmar Kühl Opened: 2008-04-23 Last modified: 2015-04-08

-

View all other issues in [char.traits.specializations].

-

View all issues with NAD Editorial status.

-

Discussion:

-

- In Table 56 (Traits requirements) the not_eof() member function - is using an argument of type e which denotes an object of - type X::int_type. However, the specializations in - 21.2.3 [char.traits.specializations] all use char_type. - This would effectively mean that the argument type actually can't - represent EOF in the first place. I'm pretty sure that the type used - to be int_type which is quite obviously the only sensible - argument. -

-

- This issue is close to being editorial. I suspect that the proposal - changing this section to include the specializations for char16_t - and char32_t accidentally used the wrong type. -

- - -

Proposed resolution:

-

- In 21.2.3.1 [char.traits.specializations.char], - 21.2.3.2 [char.traits.specializations.char16_t], - 21.2.3.3 [char.traits.specializations.char32_t], and - [char.traits.specializations.wchar_t] correct the - argument type from char_type to int_type. -

- - -

Rationale:

-Already fixed in WP. -

- - - - -
-

832. Applying constexpr to System error support

-

Section: 19.5 [syserr] Status: NAD - Submitter: Beman Dawes Opened: 2008-05-14 Last modified: 2015-04-08

-

View all other issues in [syserr].

-

View all issues with NAD status.

-

Discussion:

-

-Initialization of objects of class error_code -(19.5.2 [syserr.errcode]) and class -error_condition (19.5.3 [syserr.errcondition]) can be made simpler and more reliable by use of -the new constexpr feature -[N2349] -of C++0x. Less code will need to be -generated for both library implementations and user programs when -manipulating constant objects of these types. -

- -

-This was not proposed originally because the constant expressions -proposal was moving into the standard at about the same time as the -Diagnostics Enhancements proposal -[N2241], -and it wasn't desirable to -make the later depend on the former. There were also technical concerns -as to how constexpr would apply to references. Those concerns are now -resolved; constexpr can't be used for references, and that fact is -reflected in the proposed resolution. -

- -

-Thanks to Jens Maurer, Gabriel Dos Reis, and Bjarne Stroustrup for clarification of constexpr requirements. -

- -

-LWG issue 804 is related in that it raises the question of whether the -exposition only member cat_ of class error_code (19.5.2 [syserr.errcode]) and class -error_condition (19.5.3 [syserr.errcondition]) should be presented as a reference or pointer. -While in the context of 804 that is arguably an editorial question, -presenting it as a pointer becomes more or less required with this -proposal, given constexpr does not play well with references. The -proposed resolution thus changes the private member to a pointer, which -also brings it in sync with real implementations. -

- -

[ -Sophia Antipolis: -]

- - -

-On going question of extern pointer vs. inline functions for interface. -

- -

[ -Pre-San Francisco: -]

- - -
-

-Beman Dawes reports that this proposal is unimplementable, and thus NAD. -

-

-Implementation would require constexpr objects of classes derived -from class error_category, which has virtual functions, and that is -not allowed by the core language. This was determined when trying to -implement the proposal using a constexpr enabled compiler provided -by Gabriel Dos Reis, and subsequently verified in discussions with -Gabriel and Jens Maurer. -

- -
- - -

Proposed resolution:

-

-The proposed wording assumes the LWG 805 proposed wording has been -applied to the WP, resulting in the former posix_category being renamed -generic_category. If 805 has not been applied, the names in this -proposal must be adjusted accordingly. -

- -

-Change 19.5.1.1 [syserr.errcat.overview] Class -error_category overview error_category synopsis as -indicated: -

- -
-const error_category& get_generic_category();
-const error_category& get_system_category();
-
-static extern const error_category&* const generic_category = get_generic_category();
-static extern const error_category&* const native_category system_category = get_system_category();
-
- -

-Change 19.5.1.5 [syserr.errcat.objects] Error category objects as indicated: -

- -
-
-extern const error_category&* const get_generic_category();
-
-

-Returns: A reference generic_category shall point -to an a statically initialized object of a type derived from -class error_category. -

- -

-Remarks: The object's default_error_condition and equivalent virtual -functions shall behave as specified for the class error_category. The -object's name virtual function shall return a pointer to the string -"GENERIC". -

- -
-extern const error_category&* const get_system_category();
-
- -

-Returns: A reference system_category shall point -to an a statically -initialized object of a type derived from class error_category. -

- -

-Remarks: The object's equivalent virtual functions shall behave as -specified for class error_category. The object's name virtual function -shall return a pointer to the string "system". The object's -default_error_condition virtual function shall behave as follows: -

- -

-If the argument ev corresponds to a POSIX errno value posv, the function -shall return error_condition(posv, generic_category). Otherwise, the -function shall return error_condition(ev, system_category). What -constitutes correspondence for any given operating system is -unspecified. [Note: The number of potential system error codes is large -and unbounded, and some may not correspond to any POSIX errno value. -Thus implementations are given latitude in determining correspondence. --- end note] -

-
- -

-Change 19.5.2.1 [syserr.errcode.overview] Class error_code overview as indicated: -

- -
-class error_code {
-public:
-  ...;
-  constexpr error_code(int val, const error_category&* cat);
-  ...
-  void assign(int val, const error_category&* cat);
-  ...
-  const error_category&* category() const;
-  ...
-private:
-  int val_;                    // exposition only
-  const error_category&* cat_; // exposition only
-
- -

-Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors as indicated: -

- -
-
-constexpr error_code(int val, const error_category&* cat);
-
-

-Effects: Constructs an object of type error_code. -

-

-Postconditions: val_ == val and cat_ == cat. -

-

-Throws: Nothing. -

-
- -

-Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as indicated: -

- -
-
-void assign(int val, const error_category&* cat);
-
-

-Postconditions: val_ == val and cat_ == cat. -

-

-Throws: Nothing. -

-
- -

-Change 19.5.2.4 [syserr.errcode.observers] Class error_code observers as indicated: -

- -
-
-const error_category&* category() const;
-
- -

-Returns: cat_. -

-

-Throws: Nothing. -

-
- -

-Change 19.5.3.1 [syserr.errcondition.overview] Class error_condition overview as indicated: -

- -
-
-class error_condition {
-public:
-  ...;
-  constexpr error_condition(int val, const error_category&* cat);
-  ...
-  void assign(int val, const error_category&* cat);
-  ...
-  const error_category&* category() const;
-  ...
-private:
-  int val_;                    // exposition only
-  const error_category&* cat_; // exposition only
-
-
- -

-Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition constructors as indicated: -

- -
-
-constexpr error_condition(int val, const error_category&* cat);
-
-

-Effects: Constructs an object of type error_condition. -

-

-Postconditions: val_ == val and cat_ == cat. -

-

-Throws: Nothing. -

-
- -

-Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition modifiers as indicated: -

- -
-
-void assign(int val, const error_category&* cat);
-
-

-Postconditions: val_ == val and cat_ == cat. -

-

-Throws: Nothing. -

-
- -

-Change 19.5.3.4 [syserr.errcondition.observers] Class error_condition observers as indicated: -

- -
-
-const error_category&* category() const;
-
-

-Returns: cat_. -

-

-Throws: Nothing. -

-
- -

-Throughout 19.5 [syserr] System error support, change "category()." to "category()->". -Appears approximately six times. -

- -

-[Partially Editorial] In 19.5.4 [syserr.compare] Comparison operators, -paragraphs 2 and 4, change "category.equivalent(" to -"category()->equivalent(". -

- -

-Change 19.5.6.1 [syserr.syserr.overview] Class system_error overview as indicated: -

- -
-public:
-  system_error(error_code ec, const string& what_arg);
-  system_error(error_code ec);
-  system_error(int ev, const error_category&* ecat,
-      const string& what_arg);
-  system_error(int ev, const error_category&* ecat);
-
- -

-Change 19.5.6.2 [syserr.syserr.members] Class system_error members as indicated: -

- -
-
-system_error(int ev, const error_category&* ecat, const string& what_arg);
-
-
-

-Effects: Constructs an object of class system_error. -

-

-Postconditions: code() == error_code(ev, ecat) and -strcmp(runtime_error::what(), what_arg.c_str()) == 0. -

-
- -
-system_error(int ev, const error_category&* ecat);
-
-
-

-Effects: Constructs an object of class system_error. -

-

-Postconditions: code() == error_code(ev, ecat) and -strcmp(runtime_error::what(), "") == 0. -

-
-
- - - -

Rationale:

-

[ -San Francisco: -]

- - -

-NAD because Beman said so. -

- - - - - -
-

833. Freestanding implementations header list needs review for C++0x

-

Section: 17.6.1.3 [compliance] Status: NAD - Submitter: Beman Dawes Opened: 2008-05-14 Last modified: 2015-04-08

-

View all other issues in [compliance].

-

View all issues with NAD status.

-

Discussion:

-

-Once the C++0x standard library is feature complete, the LWG needs to -review 17.6.1.3 [compliance] Freestanding implementations header list to -ensure it reflects LWG consensus. -

- -

[ -San Francisco: -]

- - -
-

-This is a placeholder defect to remind us to review the table once we've -stopped adding headers to the library. -

-

-Three new headers that need to be added to the list: -

-
-<initializer_list> <concept> <iterator_concepts>
-
-

-<iterator_concepts>, in particular, has lots of stuff -that isn't needed, so maybe the stuff that is needed should be broken -out into a separate header. -

-

-Robert: What about reference_closure? It's currently in -<functional>. -

-
- -

[ -Post Summit Daniel adds: -]

- - -
-
    -
  1. -The comment regarding reference_closure seems moot since it was just -recently decided to remove that. -
    2. -
  2. -A reference to proposal -N2814 -("Fixing freestanding") should be added. This -paper e.g. proposes to add only <initializer_list> to the include list -of freestanding. -
    3. -
-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-Addressed by paper -N2814. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

- - - - - -
-

837. - basic_ios::copyfmt() overly loosely specified -

-

Section: 27.5.5.3 [basic.ios.members] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

View all issues with NAD Editorial status.

-

Discussion:

-

- -The basic_ios::copyfmt() member function is specified in 27.5.5.3 [basic.ios.members] to have the following effects: - -

-

- -Effects: If (this == &rhs) does -nothing. Otherwise assigns to the member objects of *this -the corresponding member objects of rhs, except that -

-
    -
  • - -rdstate() and rdbuf() are left unchanged; - -
    • -
  • - -exceptions() is altered last by -calling exceptions(rhs.except) - -
    • -
  • - -the contents of arrays pointed at by pword -and iword are copied not the pointers themselves - -
    • -
-
-

- -Since the rest of the text doesn't specify what the member objects -of basic_ios are this seems a little too loose. - -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

- -I propose to tighten things up by adding a Postcondition clause -to the function like so: - -

-

- Postconditions: -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
copyfmt() postconditions
ElementValue
rdbuf()unchanged
tie()rhs.tie()
rdstate()unchanged
exceptions()rhs.exceptions()
flags()rhs.flags()
width()rhs.width()
precision()rhs.precision()
fill()rhs.fill()
getloc()rhs.getloc()
-
-

- -The format of the table follows Table 117 (as -of N2588): basic_ios::init() -effects. - -

-

- -The intent of the new table is not to impose any new requirements or -change existing ones, just to be more explicit about what I believe is -already there. - -

- - - - -
-

840. pair default template argument

-

Section: 20.3 [pairs] Status: NAD - Submitter: Thorsten Ottosen Opened: 2008-05-23 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

View all issues with NAD status.

-

Discussion:

-

-I have one issue with std::pair. Well, it might just be a very annoying -historical accident, but why is there no default template argument for -the second template argument? This is so annoying when the type in -question is looong and hard to write (type deduction with auto won't -help those cases where we use it as a return or argument type). -

- - -

Proposed resolution:

-

-Change the synopsis in 20.2 [utility] to read: -

- -
-template <class T1, class T2 = T1> struct pair;
-
- -

-Change 20.3 [pairs] to read: -

- -
-namespace std {
- template <class T1, class T2 = T1>
- struct pair {
-   typedef T1 first_type;
-   typedef T2 second_type;
-   ...
-
- - -

Rationale:

-std::pair is a heterogeneous container. -

- - - - -
-

841. cstdint.syn inconsistent with C99

-

Section: 18.4.1 [cstdint.syn] Status: NAD Editorial - Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2015-04-08

-

View all other issues in [cstdint.syn].

-

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-

Discussion:

-

- -In specifying the names of macros and types defined in -header <stdint.h>, C99 makes use of the -symbol N to accommodate unusual platforms with -word sizes that aren't powers of two. C99 -permits N to take on any positive integer value -(including, for example, 24). - -

-

- -In cstdint.syn Header <cstdint> -synopsis, C++ on the other hand, fixes the value -of N to 8, 16, 32, and 64, and specifies only -types with these exact widths. - -

-

- -In addition, paragraph 1 of the same section makes use of a rather -informal shorthand notation to specify sets of macros. When -interpreted strictly, the notation specifies macros such -as INT_8_MIN that are not intended to be specified. - -

-

- -Finally, the section is missing the usual table of symbols defined -in that header, making it inconsistent with the rest of the -specification. - -

- -

Proposed resolution:

-

- -I propose to use the same approach in the C++ spec as C99 uses, that -is, to specify the header synopsis in terms of "exposition only" types -that make use of the symbol N to denote one or -more of a theoretically unbounded set of widths. - -

-

- -Further, I propose to add a new table to section listing the symbols -defined in the header using a more formal notation that avoids -introducing inconsistencies. - -

-

- -To this effect, in cstdint.syn -Header <cstdint> synopsis, replace both the -synopsis and paragraph 1 with the following text: - -

-
-

-

-
    -
  1. - -In the names defined in the <cstdint> header, the -symbol N represents a positive decimal integer -with no leading zeros (e.g., 8 or 24, but not 0, 04, or 048). With the -exception of exact-width types, macros and types for values -of N in the set of 8, 16, 32, and 64 are -required. Exact-width types, and any macros and types for values -of N other than 8, 16, 32, and 64 are -optional. However, if an implementation provides integer types with -widths of 8, 16, 32, or 64 bits, the corresponding exact-width types -and macros are required. - -
    2. -
- 
-namespace std {
-
-   // required types
-
-   // Fastest minimum-width integer types
-   typedef signed integer type   int_fast8_t;
-   typedef signed integer type   int_fast16_t;
-   typedef signed integer type   int_fast32_t;
-   typedef signed integer type   int_fast64_t;
-
-   typedef unsigned integer type uint_fast8_t;
-   typedef unsigned integer type uint_fast16_t;
-   typedef unsigned integer type uint_fast32_t;
-   typedef unsigned integer type uint_fast64_t;
-
-   // Minimum-width integer types
-   typedef signed integer type   int_least8_t;
-   typedef signed integer type   int_least16_t;
-   typedef signed integer type   int_least32_t;
-   typedef signed integer type   int_least64_t;
-
-   typedef unsigned integer type uint_least8_t;
-   typedef unsigned integer type uint_least16_t;
-   typedef unsigned integer type uint_least32_t;
-   typedef unsigned integer type uint_least64_t;
-
-   // Greatest-width integer types
-   typedef signed integer type   intmax_t;
-   typedef unsigned integer type uintmax_t;
-
-   // optionally defined types
-
-   // Exact-width integer types
-   typedef signed integer type   intN_t;
-   typedef unsigned integer type uintN_t;
-
-   // Fastest minimum-width integer types for values
-   // of N other than 8, 16, 32, and 64
-   typedef signed integer type   uint_fastN_t;
-   typedef unsigned integer type uint_fastN_t;
-
-   // Minimum-width integer types for values
-   // of N other than 8, 16, 32, and 64
-   typedef signed integer type   uint_leastN_t;
-   typedef unsigned integer type uint_leastN_t;
-
-   // Integer types capable of holding object pointers
-   typedef signed integer type   intptr_t;
-   typedef signed integer type   intptr_t;
-
-}
-
-

- -[Note to editor: Remove all of the existing paragraph 1 from cstdint.syn.] - -

-

- Table ??: Header <cstdint> synopsis -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
TypeName(s)
Macros:INTN_MININTN_MAXUINTN_MAX
INT_FASTN_MININT_FASTN_MAXUINT_FASTN_MAX
INT_LEASTN_MININT_LEASTN_MAXUINT_LEASTN_MAX
INTPTR_MININTPTR_MAXUINTPTR_MAX
INTMAX_MININTMAX_MAXUINTMAX_MAX
PTRDIFF_MINPTRDIFF_MAXPTRDIFF_MAX
SIG_ATOMIC_MINSIG_ATOMIC_MAXSIZE_MAX
WCHAR_MINWCHAR_MAX
WINT_MINWINT_MAX
INTN_C()UINTN_C()
INTMAX_C()UINTMAX_C()
Types:intN_tuintN_t
int_fastN_tuint_fastN_t
int_leastN_tuint_leastN_t
intptr_tuintptr_t
intmax_tuintmax_t
-
- - - - - -
-

849. missing type traits to compute root class and derived class of types in a class hierachy

-

Section: 20.10.7.6 [meta.trans.other] Status: NAD - Submitter: Thorsten Ottosen Opened: 2008-06-05 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with NAD status.

-

Discussion:

-

-The type traits library contains various traits to dealt with -polymorphic types, e.g. std::has_virtual_destructor, std::is_polymorphic -and std::is_base_of. However, there is no way to compute the unique -public base class of a type if such one exists. Such a trait could be -very useful if one needs to instantiate a specialization made for the -root class whenever a derived class is passed as parameter. For example, -imagine that you wanted to specialize std::hash for a class -hierarchy---instead of specializing each class, you could specialize the -std::hash<root_class> and provide a partial specialization that worked -for all derived classes. -

- -

-This ability---to specify operations in terms of their equivalent in the -root class---can be done with e.g. normal functions, but there is, -AFAIK, no way to do it for class templates. Being able to access -compile-time information about the type-hierachy can be very powerful, -and I therefore also suggest traits that computes the directly derived -class whenever that is possible. -

- -

-If the computation can not be done, the traits should fall back on an -identity transformation. I expect this gives the best overall usability. -

- - -

Proposed resolution:

-

-Add the following to the synopsis in 20.10.2 [meta.type.synop] under "other transformations": -

- -
-template< class T > struct direct_base_class;
-template< class T > struct direct_derived_class;
-template< class T > struct root_base_class;
-
- -

-Add three new entries to table 51 (20.10.7.6 [meta.trans.other]) with the following content -

- -
- - - - - - - - - - - - - - - - - - - -
TemplateConditionComments
template< class T > struct direct_base_class;T shall be a complete type.The member typedef type shall equal the accessible unambiguous direct base class of T. -If no such type exists, the member typedef type shall equal T.
template< class T > struct direct_derived_class;T shall be a complete type.The member typedef type shall equal the unambiguous type which has T -as an accessible unambiguous direct base class. If no such type exists, the member typedef -type shall equal T.
template< class T > struct root_base_class;T shall be a complete type.The member typedef type shall equal the accessible unambiguous most indirect base class of -T. If no such type exists, the member typedef type shall equal T.
-
- - - -

Rationale:

-2008-9-16 San Francisco: Issue pulled by author prior to being reviewed by the LWG. -

- - - - -
-

855. capacity() and reserve() for deque?

-

Section: 23.3.3.3 [deque.capacity] Status: NAD - Submitter: Hervé Brönnimann Opened: 2008-06-11 Last modified: 2015-04-08

-

View all other issues in [deque.capacity].

-

View all issues with NAD status.

-

Discussion:

-

-The main point is that capacity can be viewed as a mechanism to -guarantee the validity of iterators when only push_back/pop_back -operations are used. For vector, this goes with reallocation. For -deque, this is a bit more subtle: capacity() of a deque may shrink, -whereas that of vector doesn't. In a circular buffer impl. of the -map, as Howard did, there is very similar notion of capacity: as long -as size() is less than B * (total size of the map - 2), it is -guaranteed that no iterator is invalidated after any number of -push_front/back and pop_front/back operations. But this does not -hold for other implementations. -

-

-Still, I believe, capacity() can be defined by size() + how many -push_front/back minus pop_front/back that can be performed before -terators are invalidated. In a classical impl., capacity() = size() -+ the min distance to either "physical" end of the deque (i.e., -counting the empty space in the last block plus all the blocks until -the end of the map of block pointers). In Howard's circular buffer -impl., capacity() = B * (total size of the map - 2) still works with -this definition, even though the guarantee could be made stronger. -

-

-A simple picture of a deque: -

-
-A-----|----|-----|---F+|++++|++B--|-----|-----Z
-
-

-(A,Z mark the beginning/end, | the block boundaries, F=front, B=back, -and - are uninitialized, + are initialized) -In that picture: capacity = size() + min(dist(A,F),dist(B,Z)) = min -(dist(A,B),dist(F,Z)). -

-

-Reserve(n) can grow the map of pointers and add possibly a number of -empty blocks to it, in order to guarantee that the next n-size() -push_back/push_front operations will not invalidate iterators, and -also will not allocate (i.e. cannot throw). The second guarantee is -not essential and can be left as a QoI. I know well enough existing -implementations of deque (sgi/stl, roguewave, stlport, and -dinkumware) to know that either can be implemented with no change to -the existing class layout and code, and only a few modifications if -blocks are pre-allocated (instead of always allocating a new block, -check if the next entry in the map of block pointers is not zero). -

-

-Due to the difference with vector, wording is crucial. Here's a -proposed wording to make things concrete; I tried to be reasonably -careful but please double-check me: -

- -

[ -San Francisco: -]

- - -
-

-Hans: should the Returns clause for capacity read "1 Returns: A lower -bound..." rather than "1 Returns: An upper bound..." -

-

-Howard: maybe what's needed is capacity_front and capacity_back. In -fact, I think I implemented a deque that had these members as -implementation details. -

-
- - - -

Proposed resolution:

- -

-Add new signatures to synopsis in 23.3.3 [deque]: -

- -
-size_type capacity() const;
-bool reserve(size_type n);
-
- -

-Add new signatures to 23.3.3.3 [deque.capacity]: -

- -
-
-size_type capacity() const;
-
-
-

-1 Returns: An upper bound on n + max(n_f - m_f, n_b - m_b) such -that, for any sequence of n_f push_front, m_f pop_front, n_b -push_back, and m_b pop_back operations, interleaved in any order, -starting with the current deque of size n, the deque does not -invalidate any of its iterators except to the erased elements. -

-

-2 Remarks: Unlike a vector's capacity, the capacity of a deque can -decrease after a sequence of insertions at both ends, even if none of -the operations caused the deque to invalidate any of its iterators -except to the erased elements. -

-
-
- -
-
-bool reserve(size_type n);
-
-
-

-2 Effects: A directive that informs a deque of a planned sequence of -push_front, pop_front, push_back, and pop_back operations, so that it -can manage iterator invalidation accordingly. After reserve(), -capacity() is greater or equal to the argument of reserve if this -operation returns true; and equal to the previous value of capacity() -otherwise. If an exception is thrown, there are no effects. -

-

-3 Returns: true if iterators are invalidated as a result of this -operation, and false otherwise. -

-

-4 Complexity: It does not change the size of the sequence and takes -at most linear time in n. -

-

-5 Throws: length_error if n > max_size(). -

-

-6 Remarks: It is guaranteed that no invalidation takes place during a -sequence of insert or erase operations at either end that happens -after a call to reserve() except to the erased elements, until the -time when an insertion would make max(n_f-m_f, n_b-m_b) larger than -capacity(), where n_f is the number of push_front, m_f of pop_front, -n_b of push_back, and m_b of pop_back operations since the call to -reserve(). -

-

-7 An implementation is free to pre-allocate buffers so as to -offer the additional guarantee that no exception will be thrown -during such a sequence other than by the element constructors. -

-
-
- -

-And 23.3.3.4 [deque.modifiers] para 1, can be enhanced: -

- -

-1 Effects: An insertion in the middle of the deque invalidates all the iterators and references to elements of the -deque. An insertion at either end of the deque invalidates all the iterators to the deque, -unless provisions have been made with reserve, -but has no effect on the validity of references to elements of the deque. -

- - -

Rationale:

-

Complication outweighs the benefit.

- - - - - -
-

862. Impossible complexity for 'includes'

-

Section: 25.4.5.1 [includes] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2008-07-02 Last modified: 2015-04-08

-

View all other issues in [includes].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-In 25.4.5.1 [includes] the complexity is "at most -1 comparisons" if passed -two empty ranges. I don't know how to perform a negative number of -comparisions! -

- -

-This same issue also applies to: -

- -
    -
  • set_union
    • -
  • set_intersection
    • -
  • set_difference
    • -
  • set_symmetric_difference
    • -
  • merge
    • -
- -

[ -2009-03-30 Beman adds: -]

- - -

-Suggest NAD. The complexity of empty ranges is -1 in other places in the -standard. See 25.4.4 [alg.merge] merge and -inplace_merge, and forward_list merge, for example. -The time and effort to find and fix all places in the standard where -empty range[s] result in negative complexity isn't worth the very -limited benefit. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -
-

-I'm not happy with NAD if we can find a simple solution. -

-

-How about adding a rider somewhere in clause 17 suggesting that complexities -that specify a negative number of operations are treated as specifying zero -operations? That should generically solve the issue without looking for -further cases. -

-
- -

[ -Batavia (2009-05): -]

- -

-Pete to provide "straightforward" wording. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Recommend NAD. -

- - - - - -
-

863. What is the state of a stream after close() succeeds

-

Section: 27.9.1 [fstreams] Status: NAD - Submitter: Steve Clamage Opened: 2008-07-08 Last modified: 2015-04-08

-

View all other issues in [fstreams].

-

View all issues with NAD status.

-

Discussion:

-

-Suppose writing to an [o]fstream fails and you later close the stream. -The overflow() function is called to flush the buffer (if it exists). -Then the file is unconditionally closed, as if by calling flcose. -

-

-If either overflow or fclose fails, close() reports failure, and clearly -the stream should be in a failed or bad state. -

-

-Suppose the buffer is empty or non-existent (so that overflow() does not -fail), and fclose succeeds. The close() function reports success, but -what is the state of the stream? -

- -

[ -Batavia (2009-05): -]

- -
-

-Tom's impression is that the issue is about the failbit, etc. -

-

-Bill responds that the stream is now closed, -and any status bits remain unchanged. -

-

-See the description of close() in 27.9.1.17 [fstream.members]. -

-

-We prefer not to add wording to say that nothing changes. -Move to NAD. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

864. Defect in atomic wording

-

Section: 29.6 [atomics.types.operations] Status: NAD Editorial - Submitter: Anthony Williams Opened: 2008-07-10 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-There's an error in 29.6 [atomics.types.operations]/p9: -

- -
-
-C atomic_load(const volatile A * object);
-C atomic_load_explicit(const volatile A * object, memory_order);
-C A ::load(memory_order order = memory_order_seq_cst) const volatile;
-
-
-

-Requires: The order argument shall not be memory_order_acquire nor -memory_order_acq_rel. -

-
-
- -

-I believe that this should state -

-

-shall not be memory_order_release. -

- -

-There's also an error in 29.6 [atomics.types.operations]/p17: -

- -

-... When only one memory_order argument is supplied, the value of success -is order, and -the value of failure is order except that a value of -memory_order_acq_rel shall be replaced by the value -memory_order_require ... -

-

-I believe this should state -

-

-shall be replaced by the value memory_order_acquire ... -

- - -

Proposed resolution:

-

-Change 29.6 [atomics.types.operations]/p9: -

- -
-
-C atomic_load(const volatile A * object);
-C atomic_load_explicit(const volatile A * object, memory_order);
-C A ::load(memory_order order = memory_order_seq_cst) const volatile;
-
-
-

-Requires: The order argument shall not be memory_order_acquire -memory_order_release nor memory_order_acq_rel. -

-
-
- -

-Change 29.6 [atomics.types.operations]/p17: -

- -

-... When only one memory_order argument is supplied, the value of success -is order, and -the value of failure is order except that a value of -memory_order_acq_rel shall be replaced by the value -memory_order_require memory_order_acquire ... -

- - - -

Rationale:

-

Already fixed by the time the LWG processed it.

- - - - - -
-

867. Valarray and value-initialization

-

Section: 26.6.2.2 [valarray.cons] Status: NAD Editorial - Submitter: Alberto Ganesh Barbati Opened: 2008-07-20 Last modified: 2015-04-08

-

View all other issues in [valarray.cons].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-From 26.6.2.2 [valarray.cons], paragraph 2: -

- -
-explicit  valarray(size_t);
-
-

-The array created by this constructor has a length equal to the value of the argument. The elements -of the array are constructed using the default constructor for the instantiating type T. -

-
- -

-The problem is that the most obvious Ts for valarray are float -and double, they don't have a default constructor. I guess the intent is to value-initialize -the elements, so I suggest replacing: -

- -

-The elements of the array are constructed using the default constructor for the instantiating type T. -

-

-with -

-

-The elements of the array are value-initialized. -

- -

-There is another reference to the default constructor of T in the non-normative note in paragraph 9. -That reference should also be replaced. (The normative wording in paragraph 8 refers to T() -and so it doesn't need changes). -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Change 26.6.2.2 [valarray.cons], paragraph 2: -

- -
-
-explicit  valarray(size_t);
-
-

-The array created by this constructor has a length equal to the value of the argument. The elements -of the array are constructed using the default constructor for the instantiating type T -value-initialized (8.5 [dcl.init]). -

-
- -

-Change 26.6.2.8 [valarray.members], paragraph 9: -

- -

-[Example: If the argument has the value -2, the first two elements of the result will be constructed using the -default constructor -value-initialized (8.5 [dcl.init]); -the third element of the result will be assigned the value of the first element of the argument; etc. -- end example] -

- - - - - - -
-

873. signed integral type and unsigned integral type are not clearly defined

-

Section: 3.9.1 [basic.fundamental] Status: NAD Editorial - Submitter: Travis Vitek Opened: 2008-06-30 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

-

- Neither the term "signed integral type" nor the term "unsigned - integral type" is defined in the core language section of the - standard, therefore the library section should avoid its use. The - terms signed integer type and unsigned integer type are - indeed defined (in 3.9.1 [basic.fundamental]), thus the usages should be - replaced accordingly. -

- -

- Note that the key issue here is that "signed" + "integral type" != - "signed integral type". - - The types bool, char, char16_t, - char32_t and wchar_t are all listed as - integral types, but are neither of signed integer type or - unsigned integer type. According to 3.9 [basic.types] p7, a synonym for - integral type is integer type. - - Given this, one may choose to assume that an integral type that - can represent values less than zero is a signed integral type. - Unfortunately this can cause ambiguities. - - As an example, if T is unsigned char, the - expression make_signed<T>::type, is supposed to - name a signed integral type. There are potentially two types that - satisfy this requirement, namely signed char and - char (assuming CHAR_MIN < 0). -

- -

[ -San Francisco: -]

- - -

-Plum, Sebor to review. -

- -

[ -Post Summit Daniel adds: -]

- - -

-The proposed resolution needs to be "conceptualized". Currently we have -in [concept.support] only concept IntegralType -for all "integral types", thus indeed the current Container -concept and Iterator concepts are sufficiently satisfied with "integral -types". If the changes are applied, we might ask core for concept -BilateralIntegerType and add proper restrictions to the library -concepts. -

- - - -

Proposed resolution:

-

- I propose to use the terms "signed integer type" and "unsigned integer - type" in place of "signed integral type" and "unsigned integral type" - to eliminate such ambiguities. -

- -

- The proposed change makes it absolutely clear that the difference - between two pointers cannot be char or wchar_t, - but could be any of the signed integer types. - 5.7 [expr.add] paragraph 6... -

-
-

-

-
    -
  1. - When two pointers to elements of the same array object are - subtracted, the result is the difference of the subscripts of - the two array elements. The type of the result is an - implementation-defined signed integral - typesigned integer type; this type shall be the - same type that is defined as std::ptrdiff_t in the - <cstdint> header (18.1)... -
    2. -
-
- -

- The proposed change makes it clear that X::size_type and - X::difference_type cannot be char or - wchar_t, but could be one of the signed or unsigned integer - types as appropriate. - 17.6.3.5 [allocator.requirements] table 40... -

-

- Table 40: Allocator requirements -

- - - - - - - - - - - - - - - - - - - - -
expressionreturn typeassertion/note/pre/post-condition
X::size_type - unsigned integral type - unsigned integer type - a type that can represent the size of the largest object in - the allocation model.
X::difference_type - signed integral type - signed integer type - a type that can represent the difference between any two - pointers in the allocation model.
-
- -

- The proposed change makes it clear that make_signed<T>::type - must be one of the signed integer types as defined in 3.9.1. Ditto for - make_unsigned<T>type and unsigned integer types. - 20.10.7.3 [meta.trans.sign] table 48... -

-

- Table 48: Sign modifications -

- - - - - - - - - - - - - - - - - -
TemplateComments
- template <class T> struct make_signed; - - If T names a (possibly cv-qualified) signed - integral typesigned integer type (3.9.1) then - the member typedef type shall name the type - T; otherwise, if T names a (possibly - cv-qualified) unsigned integral typeunsigned - integer type then type shall name the - corresponding signed integral typesigned - integer type, with the same cv-qualifiers as - T; otherwise, type shall name the - signed integral typesigned integer type - with the smallest rank (4.13) for which sizeof(T) == - sizeof(type), with the same cv-qualifiers as - T. - - Requires: T shall be a (possibly - cv-qualified) integral type or enumeration but not a - bool type. -
- template <class T> struct make_unsigned; - - If T names a (possibly cv-qualified) - unsigned integral typeunsigned integer - type (3.9.1) then the member typedef type - shall name the type T; otherwise, if - T names a (possibly cv-qualified) signed - integral typesigned integer type then - type shall name the corresponding unsigned - integral typeunsigned integer type, with the - same cv-qualifiers as T; otherwise, - type shall name the unsigned integral - typeunsigned integer type with the smallest - rank (4.13) for which sizeof(T) == sizeof(type), - with the same cv-qualifiers as T. - - Requires: T shall be a (possibly - cv-qualified) integral type or enumeration but not a - bool type. -
-
- - -

- Note: I believe that the basefield values should probably be - prefixed with ios_base:: as they are in 22.4.2.2.2 [facet.num.put.virtuals] - - The listed virtuals are all overloaded on signed and unsigned integer - types, the new wording just maintains consistency. - - 22.4.2.1.2 [facet.num.get.virtuals] table 78... -

-

- Table 78: Integer Conversions -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Statestdio equivalent
basefield == oct%o
basefield == hex%X
basefield == 0%i
signed integral typesigned integer - type%d
unsigned integral typeunsigned integer - type%u
-
- - - -

- Rationale is same as above. - 22.4.2.2.2 [facet.num.put.virtuals] table 80... -

-

- Table 80: Integer Conversions -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Statestdio equivalent
basefield == ios_base::oct%o
(basefield == ios_base::hex) && - !uppercase%x
(basefield == ios_base::hex)%X
basefield == 0%i
for a signed integral typesigned integer - type%d
for a unsigned integral typeunsigned integer - type%u
-
- - -

- 23.2 [container.requirements] table 80... -

-

- Table 89: Container requirements -

- - - - - - - - - - - - - - - - - - - - - - - - - - -
expressionreturn typeoperational semanticsassertion/note/pre/post-conditioncomplexity
X::difference_typesigned integral typesigned integer type is identical to the difference type of X::iterator - and X::const_iteratorcompile time
X::size_typeunsigned integral typeunsigned integer type size_type can represent any non-negative value of - difference_typecompile time
-
- -

- X [iterator.concepts] paragraph 1... -

-

- Iterators are a generalization of pointers that allow a C++ program to - work with different data structures (containers) in a uniform manner. - To be able to construct template algorithms that work correctly and - efficiently on different types of data structures, the library - formalizes not just the interfaces but also the semantics and - complexity assumptions of iterators. All input iterators - i support the expression *i, resulting in a - value of some class, enumeration, or built-in type T, - called the value type of the iterator. All output iterators - support the expression *i = o where o is a - value of some type that is in the set of types that are - writable to the particular iterator type of i. All - iterators i for which the expression (*i).m - is well-defined, support the expression i->m with the - same semantics as (*i).m. For every iterator type - X for which equality is defined, there is a corresponding - signed integral type signed integer type called - the difference type of the iterator. -

- -

- I'm a little unsure of this change. Previously this paragraph would - allow instantiations of linear_congruential_engine on - char, wchar_t, bool, and other types. The - new wording prohibits this. - 26.5.3.1 [rand.eng.lcong] paragraph 2... -

-

- The template parameter UIntType shall denote an - unsigned integral typeunsigned integer type - large enough to store values as large as m - 1. If the - template parameter m is 0, the modulus m - used throughout this section 26.4.3.1 is - numeric_limits<result_type>::max() plus 1. [Note: - The result need not be representable as a value of type - result_type. --end note] Otherwise, the following - relations shall hold: a < m and c < - m. -

- -

- Same rationale as the previous change. - X [rand.adapt.xor] paragraph 6... -

-

- Both Engine1::result_type and - Engine2::result_type shall denote (possibly different) - unsigned integral typesunsigned integer types. - The member result_type shall denote either the type - Engine1::result_type or the type Engine2::result_type, - whichever provides the most storage according to clause 3.9.1. -

- -

- 26.5.7.1 [rand.util.seedseq] paragraph 7... -

-

- Requires:RandomAccessIterator shall meet the - requirements of a random access iterator (24.1.5) such that - iterator_traits<RandomAccessIterator>::value_type - shall denote an unsigned integral typeunsigned integer - type capable of accomodating 32-bit quantities. -

- -

- By making this change, integral types that happen to have a signed - representation, but are not signed integer types, would no longer be - required to use a two's complement representation. This may go against - the original intent, and should be reviewed. - 29.6 [atomics.types.operations] paragraph 24... -

-

- Remark: For signed integral typessigned integer - types, arithmetic is defined using two's complement - representation. There are no undefined results. For address types, the - result may be an undefined address, but the operations otherwise have - no undefined behavior. -

- - - - - - -
-

879. Atomic load const qualification

-

Section: 29 [atomics] Status: NAD Editorial - Submitter: Alexander Chemeris Opened: 2008-08-24 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-The atomic_address type and atomic<T*> specialization provide atomic -updates to pointers. However, the current specification requires -that the types pointer be to non-const objects. This restriction -is unnecessary and unintended. -

- -

[ -Summit: -]

- -

-Move to review. Lawrence will first check with Peter whether the -current examples are sufficient, or whether they need to be expanded to -include all cases. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Lawrence will handle all issues relating to atomics in a single paper. -

-

-LWG will defer discussion on atomics until that paper appears. -

-

-Move to Open. -

-
- -

[ -2009-08-17 Handled by -N2925. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Editorial. Solved by -N2992. -

- - - -

Proposed resolution:

-

-Add const qualification to the pointer values of the atomic_address -and atomic<T*> specializations. E.g. -

- -
-typedef struct atomic_address {
-   void store(const void*, memory_order = memory_order_seq_cst) volatile;
-   void* exchange( const void*, memory_order = memory_order_seq_cst) volatile;
-   bool compare_exchange( const void*&, const void*,
-                          memory_order, memory_order) volatile;
-   bool compare_exchange( const void*&, const void*,
-                          memory_order = memory_order_seq_cst ) volatile;
-   void* operator=(const void*) volatile;
-} atomic_address;
-
-void atomic_store(volatile atomic_address*, const void*);
-void atomic_store_explicit(volatile atomic_address*, const void*,
-                          memory_order);
-void* atomic_exchange(volatile atomic_address*, const void*);
-void* atomic_exchange_explicit(volatile atomic_address*, const void*,
-                              memory_order);
-bool atomic_compare_exchange(volatile atomic_address*,
-                            const void**, const void*);
-bool atomic_compare_exchange_explicit(volatile atomic_address*,
-                                     const void**, const void*,
-                                     memory_order, memory_order);
-
- - - - - -
-

887. issue with condition::wait_...

-

Section: 30.5.1 [thread.condition.condvar] Status: NAD - Submitter: Lawrence Crowl Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

View all issues with NAD status.

-

Discussion:

-

-The Posix/C++ working group has identified an inconsistency between -Posix and the C++ working draft in that Posix requires the clock to be -identified at creation, whereas C++ permits identifying the clock at the -call to wait. The latter cannot be implemented with the former. -

- -

[ -San Francisco: -]

- - -
-

-Howard recommends NAD with the following explanation: -

- -

-The intent of the current wording is for the condtion_variable::wait_until -be able to handle user-defined clocks as well as clocks the system knows about. -This can be done by providing overloads for the known clocks, and another -overload for unknown clocks which synchs to a known clock before waiting. -For example: -

- -
-template <class Duration>
-bool
-condition_variable::wait_until(unique_lock<mutex>& lock,
-                               const chrono::time_point<chrono::system_clock, Duration>& abs_time)
-{
-    using namespace chrono;
-    nanoseconds d = __round_up<nanoseconds>(abs_time.time_since_epoch());
-    __do_timed_wait(lock.mutex()->native_handle(), time_point<system_clock, nanoseconds>(d));
-    return system_clock::now() < abs_time;
-}
-
-template <class Clock, class Duration>
-bool
-condition_variable::wait_until(unique_lock<mutex>& lock,
-                               const chrono::time_point<Clock, Duration>& abs_time)
-{
-    using namespace chrono;
-    system_clock::time_point    s_entry = system_clock::now();
-    typename Clock::time_point  c_entry = Clock::now();
-    nanoseconds dn = __round_up<nanoseconds>(abs_time.time_since_epoch() -
-                                              c_entry.time_since_epoch());
-    __do_timed_wait(lock.mutex()->native_handle(), s_entry + dn);
-    return Clock::now() < abs_time;
-}
-
- -

-In the above example, system_clock is the only clock which the underlying -condition variable knows how to deal with. One overload just passes that clock -through. The second overload (approximately) converts the unknown clock into -a system_clock time_point prior to passing it down to the native -condition variable. -

- -

-On Posix systems vendors are free to add implementation defined constructors which -take a clock. That clock can be stored in the condition_variable, and converted -to (or not as necessary) as shown above. -

- -

-If an implementation defined constructor takes a clock (for example), then part -of the semantics for that implementation defined ctor might include that a -wait_until using a clock other than the one constructed with results -in an error (exceptional condition) instead of a conversion to the stored clock. -Such a design is up to the vendor as once an implementation defined ctor is used, -the vendor is free to specifiy the behavior of waits and/or notifies however -he pleases (when the cv is constructed in an implementation defined manner). -

-
- -

[ -Post Summit: -]

- - -
-

-"POSIX people will review the proposed NAD resolution at their upcoming NY -meeting. -

- -

-See the minutes at: http://wiki.dinkumware.com/twiki/bin/view/Posix/POSIX-CppBindingWorkingGroupNewYork2009. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Move to NAD. -

- -

[ -2009-07-18 Detlef reopens the issue: -]

- - -
-

-On Friday afternoon in Frankfurt is was decided that 887 is NAD. -This decision was mainly based on a sample implementation presented -by Howard that implemented one clock on top of another. -Unfortunately this implementation doesn't work for the probably most -important case where a system has a monotonic clock and a real-time -clock (or "wall time" clock): -

-

-If the underlying "system_clock" is a monotonic clock, and -the program waits on the real-time clock, and the real-time clock -is set forward, the wait will unblock too late. -

- -

-If the underlying "system_clock" is a real-time clock, and the -program waits on the monotonic clock, and the real-time clock -is set back, the wait again will unblock too late. -

- -

-Sorry that I didn't remember this on Friday, but it was Friday -afternoon after a busy week... -

- -

-So as the decision was made on a wrong asumption, I propose to re-open -the issue. -

-
- -

[ -2009-07-26 Howard adds: -]

- - -
-

-Detlef correctly argues that condition_variable::wait_until could -return "too late" in the context of clocks being adjusted during the wait. I agree -with his logic. But I disagree that this makes this interface unimplementable -on POSIX. -

- -

-The POSIX spec also does not guarantee that pthread_cond_timedwait does -not return "too late" when clocks are readjusted during the wait. Indeed, the -POSIX specification lacks any requirements at all concerning how soon -pthread_cond_timedwait returns after a time out. This is evidently a -QOI issue by the POSIX standard. Here is a quote of the most relevant normative -text concerning pthread_cond_timedwait found -here. -

- -

-The pthread_cond_timedwait() function shall be equivalent to -pthread_cond_wait(), except that an error is returned if the absolute -time specified by abstime passes (that is, system time equals or exceeds -abstime) before the condition cond is signaled or broadcasted, or if the -absolute time specified by abstime has already been passed at the time -of the call. -

- -

-I.e. the POSIX specification speaks of the error code returned in case of a time -out, but not on the timeliness of that return. -

- -

-Might this simply be an oversight, or minor defect in the POSIX specification? -

- -

-I do not believe so. This same section goes on to say in non-normative -text: -

- -

-For cases when the system clock is advanced discontinuously by an -operator, it is expected that implementations process any timed wait -expiring at an intervening time as if that time had actually occurred. -

- -

-Here is non-normative wording encouraging the implementation to ignore an advancing -underlying clock and subsequently causing an early (spurious) return. There is -no wording at all which addresses Detlef's example of a "late return". With -pthread_cond_timedwait this would be caused by setting the system clock -backwards. It seems reasonable to assume, based on the wording that is already -in the POSIX spec, that again, the discontinuously changed clock would be ignored -by pthread_cond_timedwait. -

- -

-A noteworthy difference between pthread_cond_timedwait and -condition_variable::wait_until is that the POSIX spec appears to -say that ETIMEDOUT should be returned if pthread_cond_timedwait -returns because of timeout signal, whether or not the system clock was discontinuously -advanced during the wait. In contrast condition_variable::wait_until -always returns: -

- -
-Clock::now() < abs_time
-
- -

-That is, the C++ spec requires that the clock be rechecked (detecting discontinuous -adjustments during the wait) at the time of return. condition_variable::wait_until -may indeed return early or late. But regardless it will return a value -reflecting timeout status at the time of return (even if clocks have been adjusted). -Of course the clock may be adjusted after the return value is computed but before the client has -a chance to read the result of the return. Thus there are no iron-clad guarantees -here. -

- -

-condition_variable::wait_until (and pthread_cond_timedwait) -is little more than a convenience function for making sure -condition_variable::wait doesn't hang for an unreasonable amount of -time (where the client gets to define "unreasonable"). I do not think it -is in anyone's interest to try to make it into anything more than that. -

- -

-I maintain that this is a useful and flexible specification in the spirit of -C++, and is implementable on POSIX. The implementation technique described above -is a reasonable approach. There may also be higher quality approaches. This -specification, like the POSIX specification, gives a wide latitude for QOI. -

- -

-I continue to recommend NAD, but would not object to a clarifying note regarding -the behavior of condition_variable::wait_until. At the moment, I do -not have good wording for such a note, but welcome suggestions. -

- -
- -

[ -2009-09-30: See N2969. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-The LWG is in favor of Detlef to supply revision which adopts Option 2 from -N2969 -but is modified by saying that system_clock must be available for wait_until. -

- -

[ -2010-02-11 Anthony provided wording. -]

- - -

[ -2010-02-22 Anthony adds: -]

- - -
-

-I am strongly against -N2999. -

- -

-Firstly, I think that the most appropriate use of a timed wait on a condition -variable is with a monotonic clock, so it ought to be guaranteed to be available -on systems that support such a clock. Also, making the set of supported clocks -implementation defined essentially kills portability around the use of -user-defined clocks. -

- -

-I also think that wait_for is potentially useful, and trivially -implementable given a working templated wait_until and a monotonic -clock. -

- -

-I also disagree with many of Detlef's points in the rationale. In a system with -hard latency limits there is likely to be a monotonic clock, otherwise you have -no way of measuring against these latency limits since the system_clock -may change arbitrarily. In such systems, you want to be able to use -wait_for, or wait_until with a monotonic clock. -

- -

-I disagree that the wait_* functions cannot be implemented correctly on -top of POSIX: I have done so. The only guarantee in the working draft is that -when the function returns certain properties are true; there is no guarantee -that the function will return immediately that the properties are true. -My resolution to issue 887 makes this clear. How small the latency is is QoI. -

- -

-On systems without a monotonic clock, you cannot measure the problem since the -system clock can change arbitrarily so any timing calculations you make may be -wrong due to clock changes. -

- -

-On systems with a monotonic clock, you can choose to use it for your condition -variables. If you are waiting against a system_clock::time_point then -you can check the clock when waking, and either return as a timeout or spurious -wake depending on whether system_clock::now() is before or after the -specified time_point. -

- -

-Windows does provide condition variables from Vista onwards. I choose -not to use them, but they are there. If people are concerned about -implementation difficulty, the Boost implementation can be used for most -purposes; the Boost license is pretty liberal in that regard. -

- -

-My preferred resolution to issue 887 is currently the PR in the issues list. -

-
- -

[ -2010 Pittsburgh: -]

- - -
-

-There is no consensus for moving the related paper -N2999 -into the WP. -

-

-There was support for moving this issue as proposed to Ready, but the support -was insufficient to call a consensus. -

-

-There was consensus for moving this issue to NAD as opposed to leaving it open. -Rationale added. -

-
- - - -

Rationale:

-

-The standard as written is sufficiently implementable and self consistent. -

- - -

Proposed resolution:

-

-Add a new paragraph after 30.2.4 [thread.req.timing]p3: -

- -
-

-3 The resolution of timing provided by an implementation depends on both -operating system and hardware. The finest resolution provided by an -implementation is called the native resolution. -

- -

-If a function in this clause takes a timeout argument, and the time point or -elapsed time specified passes before the function returns, the latency between -the timeout occurring and the function returning is unspecified [Note: -Implementations should strive to keep such latency as small as possible, but -portable code should not rely on any specific upper limits — end -note] -

-
- - - - - -
-

892. Forward_list issues...

-

Section: 23.3.4.6 [forwardlist.ops] Status: NAD Editorial - Submitter: Ed Smith-Rowland Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-I was looking at the latest draft on forward_list. Especially the splice methods. -

-

-The first one splices a whole list after a given iterator in this. The name is splice_after. -I think in 23.3.4.6 [forwardlist.ops] paragraph 40 -change: -

-

-Effect: Insert the contents of x before after position, ... -

- -

-A deeper issue involves the complexity. forward_list has no size and we -don't know when we've reached the end except to walk up to it. To -splice we would need to hook the end of the source list to the item -after position in this list. This would involve walking length of the -source list until we got to the last dereference-able element in source. -There's no way we could do this in O(1) unless we stored a bogus end in -forward_list. -

-

-OTOH, the last version of splice_after with iterator ranges we could do -in O(1) because we know how to hook the end of the source range to ... -

-

-Unless I'm misconceiving the whole thing. Which is possible. I'll look at it again. -

-

-I'm pretty sure about the first part though. -

- -

[ -San Francisco: -]

- - -
-

-This issue is more complicated than it looks. -

-

-paragraph 47: replace each (first, last) with (first, last] -

-

-add a statement after paragraph 48 that complexity is O(1) -

-

-remove the complexity statement from the first overload of splice_after -

-

-We may have the same problems with other modifiers, like erase_after. -Should it require that all iterators in the range (position, last] be -dereferenceable? -

-

-We do, however, like the proposed changes and consider them Editorial. -Move to NAD Editorial, Pending. Howard to open a new issue to handle the -problems with the complexity requirements. -

-

-Opened 897. -

-
- - -

Proposed resolution:

-

-In 23.3.4.6 [forwardlist.ops] paragraph 40 -change: -

-

-Effect: Insert the contents of x before after position, ... -

- - - - - -
-

895. "Requires:" on std::string::at et al

-

Section: 17.5.1.4 [structure.specifications] Status: Dup - Submitter: James Dennett Opened: 2008-09-16 Last modified: 2015-04-08

-

View all other issues in [structure.specifications].

-

View all issues with Dup status.

-

Duplicate of: 625

-

Discussion:

-

-Per discussion, we need an issue open to cover looking at "Requires" -clauses which are not constraints on user code, such as that on -std::basic_string::at. -

- -

[ -2009-07 Frankfurt -]

- - -

- Alan to address in paper. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

901. insert iterators can move from lvalues

-

Section: 24.5.2.5 [insert.iterator] Status: NAD - Submitter: Alisdair Meredith Opened: 2008-09-24 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

Addresses UK 282

- -

-The requires clause on the const T & overloads in -back_insert_iterator/front_insert_iterator/insert_iterator mean that the -assignment operator will implicitly move from lvalues of a move-only type. -

-

-Suggested resolutions are: -

-
    -
  1. -Add another overload with a negative constraint on copy-constructible -and flag it "= delete". -
    2. -
  2. -Drop the copy-constructible overload entirely and rely on perfect -forwarding to catch move issues one level deeper. -
    3. -
  3. -This is a fundamental problem in move-syntax that relies on the -presence of two overloads, and we need to look more deeply into this -area as a whole - do not solve this issue in isolation. -
    4. -
- -

[ -Post Summit, Alisdair adds: -]

- - -
-

-Both comment and issue have been resolved by the adoption of -N2844 -(rvalue references safety fix) at the last meeting. -

- -

-Suggest resolve as NAD Editorial with a reference to the paper. -

-
- -

[ -Batavia (2009-05): -]

- -

-We agree that this has been resolved in the latest Working Draft. -Move to NAD. -

- - -

Proposed resolution:

-

-Recommend NAD, addressed by N2844. -

- - - - - -
-

902. Regular is the wrong concept to constrain numeric_limits

-

Section: 18.3.2 [limits] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2008-09-24 Last modified: 2015-04-08

-

View all other issues in [limits].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses FR 32 and DE 16

- -

-numeric_limits has functions specifically designed to return NaNs, which -break the model of Regular (via its axioms.) While floating point types -will be acceptible in many algorithms taking Regular values, it is not -appopriate for this specific API and we need a less refined constraint. -

- -

FR 32:

- -

-The definition of numeric_limits<> as requiring a regular -type is both conceptually wrong and operationally illogical. As we -pointed before, this mistake needs to be corrected. For example, the -template can be left unconstrained. In fact this reflects a much more -general problem with concept_maps/axioms and their interpretations. It -appears that the current text heavily leans toward experimental academic -type theory. -

- -

DE 16:

- -

-The class template numeric_limits should not specify the Regular concept -requirement for its template parameter, because it contains functions -returning NaN values for floating-point types; these values violate the -semantics of EqualityComparable. -

- -

[ -Summit: -]

- - -

-Move to Open. Alisdair and Gaby will work on a solution, along with the new -treatment of axioms in clause 14. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

903. back_insert_iterator issue

-

Section: 24.5.2.1 [back.insert.iterator] Status: NAD - Submitter: Dave Abrahams Opened: 2008-09-19 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-I just noticed this; don't know how far the problem(?) extends or -whether it's new or existing: back_insert_iterator's operator* is not -const, so you can't dereference a const one. -

- -

[ -Post Summit Daniel adds: -]

- - -
-

-If done, this change should be applied for front_insert_iterator, -insert_iterator, ostream_iterator, and ostreambuf_iterator as well. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-Alisdair notes that these all are output iterators. -Howard points out that ++*i -would no longer work if we made this change. -

-

-Move to NAD. -

-
- -

[ -2009-05-25 Daniel adds: -]

- - -
    -
  1. -If 1009 is accepted, OutputIterator does no longer support post increment. -
    2. -
  2. -To support backward compatibility a second overload of operator* -can be added. -Note that the HasDereference concept (and the HasDereference part of concept -Iterator) was specifically refactored to cope with optional const -qualification and -to properly reflect the dual nature of built-in operator* as of -13.5.8 [over.literal]/6. -
    3. -
- - -

Proposed resolution:

- - - - - -
-

905. Mutex specification questions

-

Section: 30.4.1.2.1 [thread.mutex.class] Status: Dup - Submitter: Herb Sutter Opened: 2008-09-18 Last modified: 2015-04-08

-

View all other issues in [thread.mutex.class].

-

View all issues with Dup status.

-

Duplicate of: 893

-

Discussion:

-

-A few questions on the current WP, -N2723: -

-

-30.4.1 [thread.mutex.requirements]/24 says an expression -mut.unlock() "Throws: Nothing." I'm assuming that, per 17.6.4.11 [res.on.required], errors that violate the precondition "The -calling thread shall own the mutex" opens the door for throwing an -exception anyway, such as to report unbalanced unlock operations and -unlocking from a thread that does not have ownership. Right? -

-

-30.4.1.2.1 [thread.mutex.class]/3 (actually numbered paragraph "27" -in the WP; this is just a typo I think) says -

-
-

-The behavior of a program is undefined if: -

-
    -
  • it destroys a mutex object owned by any thread,
    • -
  • a thread that owns a mutex object calls lock() or try_lock() on that object, or
    • -
  • a thread terminates while owning a mutex object.
    • -
-
- -

-As already discussed, I think the second bullet should be removed, and -such a lock() or try_lock() should fail with an -exception or returning false, respectively. -

-

-A potential addition to the list would be -

-
    -
  • a thread unlocks a mutex it does not have ownership of.
    • -
-

-but without that the status quo text endorses the technique of the -program logically transferring ownership of a mutex to another thread -with correctness enforced by programming discipline. Was that intended? -

- -

[ -Summit: -]

- - -
-

-Two resolutions: "not a defect" and "duplicate", as follows: -

-
    -
  • -30.4.1 [thread.mutex.requirements]/24: NAD. If the precondition -fails the program has undefined behaviour and therefore an -implementation may throw an exception already. -
    • -
  • -30.4.1.2.1 [thread.mutex.class]/3 bullet 2: Already addressed by issue 893. -
    • -
  • -30.4.1.2.1 [thread.mutex.class]/3 proposed addition: NAD. This is -already covered by the mutex requirements, which have ownership as a -Precondition. -
    • -
-
- - -

Proposed resolution:

- - - - - - -
-

906. ObjectType is the wrong concept to constrain initializer_list

-

Section: 18.9 [support.initlist] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2015-04-08

-

View other active issues in [support.initlist].

-

View all other issues in [support.initlist].

-

View all issues with NAD Concepts status.

-

Discussion:

-

-The currently proposed constraint on initializer_list's element type -E is that is has to meet ObjectType. This is an underspecification, -because both core language and library part of initializer_list -make clear, that it references an implicitly allocated array: -

-

-8.5.4 [dcl.init.list]/4: -

-

-When an initializer list is implicitly converted to a -std::initializer_list<E>, the object passed is constructed as if the -implementation allocated an array of N elements of type E, where -N is the number of elements in the initializer list.[..] -

- -

-18.9 [support.initlist]/2. -

- -

-An object of type initializer_list<E> provides access to an array of -objects of type const E.[..] -

- -

-Therefore, E needs to fulfill concept ValueType (thus excluding -abstract class types). This stricter requirement should be added -to prevent deep instantiation errors known from the bad old times, -as shown in the following example: -

- -
-// Header A: (Should concept-check even in stand-alone modus)
-
-template <DefaultConstructible T>
-requires MoveConstructible<T>
-void generate_and_do_3(T a) {
-  std::initializer_list<T> list{T(), std::move(a), T()};
-  ...
-}
-
-void do_more();
-void do_more_or_less();
-
-template <DefaultConstructible T>
-requires MoveConstructible<T>
-void more_generate_3() {
-  do_more();
-  generate_and_do_3(T());
-}
-
-template <DefaultConstructible T>
-requires MoveConstructible<T>
-void something_and_generate_3() {
-  do_more_or_less();
-  more_generate_3();
-}
-
-// Test.cpp
-
-#include "A.h"
-
-class Abstract {
-public:
-  virtual ~Abstract();
-  virtual void foo() = 0; // abstract type
-  Abstract(Abstract&&){} // MoveConstructible
-  Abstract(){} // DefaultConstructible
-};
-
-int main() {
-  // The restricted template *accepts* the argument, but
-  // causes a deep instantiation error in the internal function
-  // generate_and_do_3:
-  something_and_generate_3<Abstract>();
-}
-
- -

-The proposed stricter constraint does not minimize the aim to -support more general containers for which ObjectType would be -sufficient. If such an extended container (lets assume it's still a -class template) provides a constructor that accepts an initializer_list -only this constructor would need to be restricted on ValueType: -

- -
-template<ObjectType T>
-class ExtContainer {
-public:
-  requires ValueType<T>
-  ExtContainer(std::initializer_list<T>);
-  ...
-};
-
- -

[ -Batavia (2009-05): -]

- -

-Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Need to look at again without concepts. -

- - - -

Proposed resolution:

-
    -
  1. -In 18.9 [support.initlist]/p.1 replace in "header <initializer_list> synopsis" -the constraint "ObjectType" in the template parameter list by the -constraint "ValueType". -
    2. -
- - - - - - -
-

910. Effects of MoveAssignable

-

Section: 17.6.3.1 [utility.arg.requirements] Status: NAD Concepts - Submitter: Alberto Ganesh Barbati Opened: 2008-09-29 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 150

- -

-The description of the effect of operator= in the MoveAssignable -concept, given in paragraph 7 is: -

- -
-result_type  T::operator=(T&&  rv);  // inherited from HasAssign<T, T&&>
-
- -

-Postconditions: the constructed T object is equivalent to the value of -rv before the assignment. [Note: there is no -requirement on the value of rv after the assignment. --end note] -

-
- -

-The sentence contains a typo (what is the "constructed T object"?) -probably due to a cut&paste from MoveConstructible. Moreover, the -discussion of LWG issue 675 shows that the postcondition is too generic -and might not reflect the user expectations. An implementation of the -move assignment that just calls swap() would always fulfill the -postcondition as stated, but might have surprising side-effects in case -the source rvalue refers to an object that is not going to be -immediately destroyed. See LWG issue 900 for another example. Due to -the sometimes intangible nature of the "user expectation", it seems -difficult to have precise normative wording that could cover all cases -without introducing unnecessary restrictions. However a non-normative -clarification could be a very helpful warning sign that swapping is not -always the correct thing to do. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -
-

-Issue 910 is exactly the reason BSI advanced the Editorial comment UK-150. -

-

-The post-conditions after assignment are at a minimum that the object -referenced by rv must be safely destructible, and the transaction should not -leak resources. Ideally it should be possible to simply assign rv a new -valid state after the call without invoking undefined behaviour, but any -other use of the referenced object would depend upon additional guarantees -made by that type. -

-
- -

[ -2009-05-09 Howard adds: -]

- - -
-

-The intent of the rvalue reference work is that the moved from rv is -a valid object. Not one in a singular state. If, for example, the moved from -object is a vector, one should be able to do anything on that moved-from -vector that you can do with any other vector. However you would -first have to query it to find out what its current state is. E.g. it might have capacity, -it might not. It might have a non-zero size, it might not. But regardless, -you can push_back on to it if you want. -

- -

-That being said, most standard code is now conceptized. That is, the concepts -list the only operations that can be done with templated types - whether or not -the values have been moved from. -

- -

-Here is user-written code which must be allowed to be legal: -

-
-#include <vector>
-#include <cstdio>
-
-template <class Allocator>
-void
-inspect(std::vector<double, Allocator>&& v)
-{
-    std::vector<double, Allocator> result(move(v));
-    std::printf("moved from vector has %u size and %u capacity\n", v.size(), v.capacity());
-    std::printf("The contents of the vector are:\n");
-    typedef typename std::vector<double, Allocator>::iterator I;
-    for (I i = v.begin(), e = v.end(); i != e; ++i)
-        printf("%f\n", *i);
-}
-
-int main()
-{
-    std::vector<double> v1(100, 5.5);
-    inspect(move(v1));
-}
-
- -

-The above program does not treat the moved-from vector as singular. It -only treats it as a vector with an unknown value. -

-

-I believe the current proposed wording is consistent with my view on this. -

-
- -

[ -Batavia (2009-05): -]

- -

-We agree that the proposed resolution -is an improvement over the current wording. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Need to look at again without concepts. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Walter will consult with Dave and Doug. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-We believe this is handled by the resolution to issue 1204, -but there is to much going on in this area to be sure. Defer for now. -

- -

[ -2010-01-23 Moved to Tentatively NAD Concepts after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Rationale:

-

-The current MoveAssignable requirements say everything that can be said -in general. Each std-defined type has a more detailed specification of move -assignment. -

- - -

Proposed resolution:

-

-In [concept.copymove], replace the postcondition in paragraph 7 with: -

- -

-Postconditions: *this is equivalent to the value of rv before the -assignment. [Note: there is no requirement on the value of rv after the -assignment, but the -effect should be unsurprising to the user even in case rv is not -immediately destroyed. This may require that resources previously owned -by *this are released instead of transferred to rv. -- end note] -

- - - - - -
-

912. Array swap needs to be conceptualized

-

Section: 25.3.3 [alg.swap] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2008-10-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-With the adaption of 809 -we have a new algorithm swap for C-arrays, which needs to be conceptualized. -

- -

[ -Post Summit Daniel adds: -]

- - -

-Recommend as NAD Editorial: The changes have already been applied to the WP -N2800. -

- -

[ -Batavia (2009-05): -]

- -

-Move to NAD; the changes have already been made. -

- - -

Proposed resolution:

-

-Replace in 25.3.3 [alg.swap] before p. 3 until p. 4 by -

- -
-template <class ValueType T, size_t N>
-requires Swappable<T>
-void swap(T (&a)[N], T (&b)[N]);
-
-
-

-Requires: T shall be Swappable. -

-

-Effects: swap_ranges(a, a + N, b); -

-
-
- - - - - - -
-

913. Superfluous requirements for replace algorithms

-

Section: 25.3.5 [alg.replace] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2008-10-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-(A) 25.3.5 [alg.replace]/1: -

- -

-Requires: The expression *first = new_value shall be valid. -

- -

-(B) 25.3.5 [alg.replace]/4: -

- -

-Requires: The results of the expressions *first and new_value shall -be writable to the result output iterator.[..] -

- -

-Since conceptualization, the quoted content of these clauses is covered -by the existing requirements -

- -

-(A) OutputIterator<Iter, const T&> -

- -

-and -

- -

-(B) OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&> -

- -

-resp, and thus should be removed. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-
    -
  1. -

    -Remove 25.3.5 [alg.replace]/1. -

    -
    -template<ForwardIterator Iter, class T> 
-  requires OutputIterator<Iter, Iter::reference> 
-        && OutputIterator<Iter, const T&> 
-        && HasEqualTo<Iter::value_type, T> 
-  void replace(Iter first, Iter last, 
-               const T& old_value, const T& new_value); 
-
-template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> 
-  requires OutputIterator<Iter, Iter::reference> 
-        && OutputIterator<Iter, const T&> 
-        && CopyConstructible<Pred> 
-  void replace_if(Iter first, Iter last, 
-                  Pred pred, const T& new_value);
-
    -

    -1 Requires: The expression *first = new_value shall be valid. -

    -
    -
    2. -
  2. -

    -25.3.5 [alg.replace]/4: Remove the sentence "The results of the -expressions *first and -new_value shall be writable to the result output iterator.". -

    -
    -template<InputIterator InIter, typename OutIter, class T> 
-  requires OutputIterator<OutIter, InIter::reference> 
-        && OutputIterator<OutIter, const T&> 
-        && HasEqualTo<InIter::value_type, T> 
-  OutIter replace_copy(InIter first, InIter last, 
-                       OutIter result, 
-                       const T& old_value, const T& new_value);
-
-template<InputIterator InIter, typename OutIter,
-         Predicate<auto, InIter::value_type> Pred, class T> 
-  requires OutputIterator<OutIter, InIter::reference> 
-        && OutputIterator<OutIter, const T&> 
-        && CopyConstructible<Pred> 
-  OutIter replace_copy_if(InIter first, InIter last, 
-                          OutIter result, 
-                          Pred pred, const T& new_value);
-
    -

    -4 Requires: The results of the expressions *first and -new_value shall be writable to the result output -iterator. The ranges [first,last) and [result,result + -(last - first)) shall not overlap. -

    -
    -
    3. -
- - - - - -
-

914. Superfluous requirement for unique

-

Section: 25.3.9 [alg.unique] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2008-10-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-25.3.9 [alg.unique]/2: "Requires: The comparison function shall be an -equivalence relation." -

- -

-The essence of this is already covered by the given requirement -

- -
-EquivalenceRelation<auto, Iter::value_type> Pred
-
- -

-and should thus be removed. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Remove 25.3.9 [alg.unique]/2 -

- -
-template<ForwardIterator Iter>
-  requires OutputIterator<Iter, Iter::reference>
-        && EqualityComparable<Iter::value_type>
-  Iter unique(Iter first, Iter last);
-
-template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred>
-  requires OutputIterator<Iter, RvalueOf<Iter::reference>::type>
-        && CopyConstructible<Pred>
-  Iter unique(Iter first, Iter last,
-               Pred pred);
-
-
-

-1 Effects: ... -

-

-2 Requires: The comparison function shall be an equivalence relation. -

-
-
- - - - - -
-

915. minmax with initializer_list should return -pair of T, not pair of const T&

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Section: 25.4.7 [alg.min.max] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It seems that the proposed changes for -N2772 -were not clear enough in -this point: -

- -

-25.4.7 [alg.min.max], before p.23 + p.24 + before p. 27 + p. 28 say that the return -type of the minmax overloads with an initializer_list is -pair<const T&, const T&>, -which is inconsistent with the decision for the other min/max overloads which take -a initializer_list as argument and return a T, not a const T&. -Doing otherwise for minmax would easily lead to unexpected life-time -problems by using minmax instead of min and max separately. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-08-18 Daniel adds: -]

- - -

-Recommend NAD since the proposed changes have already been performed -as part of editorial work of -N2914. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Can't find initializer_list form of minmax anymore, only variadic -version. Seems like we had an editing clash with concepts. Leave Open, -at least until editorial issues resolved. Bring this to Editor's attention. -

- -

[ -2010 Pittsburgh: Pete to reapply -N2772. -]

- - - - -

Rationale:

-Solved by reapplying -N2772. -

- -

Proposed resolution:

-
    -
  1. -

    -In 25 [algorithms]/2, header <algorithm> synopsis change as indicated: -

    - -
    -template<classLessThanComparable T>
-requires CopyConstructible<T>
-pair<const T&, const T&>
-minmax(initializer_list<T> t);
-
-template<class T, classStrictWeakOrder<auto, T> Compare>
-requires CopyConstructible<T>
-pair<const T&, const T&>
-minmax(initializer_list<T> t, Compare comp);
-
    -
    2. -
  2. -

    -In 25.4.7 [alg.min.max] change as indicated (Begin: Just before p.20): -

    -
    -template<classLessThanComparable T>
-  requires CopyConstructible<T>
-  pair<const T&, const T&>
-  minmax(initializer_list<T> t);
-
    -
    -

    --20- Requires: T is LessThanComparable and -CopyConstructible. -

    -

    --21- Returns: pair<const T&, const -T&>(x, y) where x is the -smallest value and y the largest value in the initializer_list. -

    -
    - -

    [..]

    -
    -template<class T, classStrictWeakOrder<auto, T> Compare>
-  requires CopyConstructible<T>
-  pair<const T&, const T&>
-  minmax(initializer_list<T> t, Compare comp);
-
    - -
    -

    --24- Requires: type T is LessThanComparable and CopyConstructible. -

    -

    --25- Returns: pair<const T&, const -T&>(x, y) where x is the -smallest value and y largest value in the initializer_list. -

    -
    -
    -
    3. -
- - - - - - -
-

916. Redundant move-assignment operator of pair should be removed

-

Section: 20.3 [pairs] Status: NAD - Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

see also 917.

- -

-The current WP provides the following assignment operators for pair -in 20.3 [pairs]/1: -

- -
    -
  1. -
    -template<class U , class V>
-requires HasAssign<T1, const U&> && HasAssign<T2, const V&>
-pair& operator=(const pair<U , V>& p);
-
    -
    2. -
  2. -
    -requires MoveAssignable<T1> && MoveAssignable<T2> pair& operator=(pair&& p );
-
    -
    3. -
  3. -
    -template<class U , class V>
-requires HasAssign<T1, RvalueOf<U>::type> && HasAssign<T2, RvalueOf<V>::type>
-pair& operator=(pair<U , V>&& p);
-
    -
    4. -
- -

-It seems that the functionality of (2) is completely covered by (3), therefore -(2) should be removed. -

- -

[ -Batavia (2009-05): -]

- -
-

-Bill believes the extra assignment operators are necessary for resolving -ambiguities, but that does not mean it needs to be part of the specification. -

-

-Move to Open. -We recommend this be looked at in the context of the ongoing work -related to the pair templates. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Leave this open pending the removal of concepts from the WD. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD, see issue 801. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 20.3 [pairs] p. 1, class pair and just before p. 13 remove the declaration: -

    - -
    -requires MoveAssignable<T1> && MoveAssignable<T2> pair& operator=(pair&& p );
-
    -
    2. - -
  2. -Remove p.13+p.14 -
    3. - -
- - - - - -
-

917. Redundant move-assignment operator of tuple should be removed

-

Section: 20.4.2.1 [tuple.cnstr] Status: NAD - Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

see also 916.

-

-N2770 (and thus now the WP) removed the -non-template move-assignment operator from tuple's class definition, -but the latter individual member description does still provide this -operator. Is this (a) an oversight and can it (b) be solved as part of an -editorial process? -

- -

[ -Post Summit Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-We believe that the proposed resolution's part 1 is editorial. -

-

-Regarding part 2, we either remove the specification as proposed, -or else add back the declaration to which the specification refers. -Alisdair and Bill prefer the latter. -It is not immediately obvious whether the function is intended to be present. -

-

-We recommend that the Project Editor restore the missing declaration -and that we keep part 2 of the issue alive. -

-

-Move to Open. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Leave this open pending the removal of concepts from the WD. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD, see issue 801. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 20.4.2 [tuple.tuple], class tuple just before member swap please -change as indicated: -

    -

    [ -This fixes an editorial loss between N2798 to N2800 -]

    - -
    -template <class... UTypes>
-requires HasAssign<Types, const UTypes&>...
-tuple& operator=(const pair<UTypes...>&);
-
-template <class... UTypes>
-requires HasAssign<Types, RvalueOf<UTypes>::type>...
-tuple& operator=(pair<UTypes...>&&);
-
    -
    2. -
  2. -

    -In 20.4.2.1 [tuple.cnstr], starting just before p. 11 please remove -as indicated: -

    - -
    -requires MoveAssignable<Types>... tuple& operator=(tuple&& u);
-
    -
    -

    --11- Effects: Move-assigns each element of u to the corresponding -element of *this. -

    -

    --12- Returns: *this. -

    -
    -
    -
    3. -
- - - - - -
-

918. Swap for tuple needs to be conceptualized

-

Section: 20.4.2.3 [tuple.swap] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2015-04-08

-

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-

Discussion:

-

-Issue 522 was accepted after tuple had been conceptualized, -therefore this step needs to be completed. -

- -

[ -Post Summit Daniel adds -]

- - -

-This is now NAD Editorial (addressed by -N2844) -except for item 3 in the proposed wording. -

- -

[ -2009-05-01 Daniel adds: -]

- - -

-As of the recent WP -(N2857), -this issue is now completely covered by editorial changes (including the third bullet), -therefore I unconditionally recommend NAD. -

- -

[ -Batavia (2009-05): -]

- -
-

-We observed that all the proposed changes have already been applied to the -Working Draft, rendering this issue moot. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-
    -
  1. -

    -In both 20.4.1 [tuple.general]/2 and 20.4.2.9 [tuple.special] change -

    - -
    -template <class Swappable... Types>
-void swap(tuple<Types...>& x, tuple<Types...>& y);
-
    - -
    2. - -
  2. -

    -In 20.4.2 [tuple.tuple], class tuple definition and in -20.4.2.3 [tuple.swap], change -

    - -
    -requires Swappable<Types>...void swap(tuple&);
-
    - -
    3. - -
  3. -

    -In 20.4.2.3 [tuple.swap] remove the current requires-clause, which says: -

    - -

    -Requires: Each type in Types shall be Swappable -

    -
    4. - -
- - - - - - -
-

919. (forward_)list specialized remove algorithms are over constrained

-

Section: 23.3.4.6 [forwardlist.ops], 23.3.5.5 [list.ops] Status: NAD - Submitter: Daniel Krügler Opened: 2008-10-06 Last modified: 2015-04-08

-

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-

Discussion:

-

-The signatures of forwardlist::remove and list::remove -defined in 23.3.4.6 [forwardlist.ops] before 11 + 23.3.5.5 [list.ops] before 15: -

- -
-requires EqualityComparable<T> void remove(const T& value);
-
- -

-are asymmetric to their predicate variants (which only require -Predicate, not EquivalenceRelation) and with the free algorithm -remove (which only require HasEqualTo). Also, nothing in the -pre-concept WP -N2723 -implies that EqualityComparable should -be the intended requirement. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution, -but would like additional input from concepts experts. -

-

-Move to Review. -

-
- -

[ -2009-07-21 Alisdair adds: -]

- - -

-Current rationale and wording for this issue is built around concepts. I -suggest the issue reverts to Open status. I believe there is enough of -an issue to review after concepts are removed from the WP to re-examine -the issue in Santa Cruz, rather than resolve as NAD Concepts. -

- -

[ -2009-10-10 Daniel adds: -]

- - -

-Recommend NAD: The concept-free wording as of -N2960 -has no longer the -over-specified requirement -EqualityComparable for the remove function that uses ==. In fact, now -the same test conditions exists -as for the free algorithm remove (25.3.8 [alg.remove]). The error was -introduced in the process of conceptifying. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD, solved by the removal of concepts. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Replace in 23.3.4.6 [forwardlist.ops] before 11 and in 23.3.5.5 [list.ops] before 15 -

    - -
    -requires EqualityComparable<T> HasEqualTo<T, T> void remove(const T& value);
-
    -
    2. -
- - - - - - -
-

926. Sequentially consistent fences, relaxed operations and modification order

-

Section: 29.3 [atomics.order] Status: NAD Editorial - Submitter: Anthony Williams Opened: 2008-10-19 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses UK 313

- -

-There was an interesting issue raised over on comp.programming.threads -today regarding the following example -

- -
-// Thread 1:
-x.store(1, memory_order_relaxed);           // SX
-atomic_thread_fence(memory_order_seq_cst);  // F1
-y.store(1, memory_order_relaxed);           // SY1
-atomic_thread_fence(memory_order_seq_cst);  // F2
-r1 = y.load(memory_order_relaxed);          // RY
-
-// Thread 2:
-y.store(0, memory_order_relaxed);          // SY2
-atomic_thread_fence(memory_order_seq_cst); // F3
-r2 = x.load(memory_order_relaxed);         // RX
-
- -

-is the outcome r1 == 0 and r2 == 0 possible? -

-

-I think the intent is that this is not possible, but I am not sure the -wording guarantees that. Here is my analysis: -

-

-Since all the fences are SC, there must be a total order between them. -F1 must be before F2 in that order since they are in -the same thread. Therefore F3 is either before F1, -between F1 and F2 or after F2. -

-

-If F3 is after F2, then we can apply 29.3 [atomics.order]p5 from -N2798: -

- -

-For atomic operations A and B on an atomic object -M, where A modifies M and B takes -its value, if there are memory_order_seq_cst fences X -and Y such that A is sequenced before X, -Y is sequenced before B, and X precedes -Y in S, then B observes either the effects of -A or a later modification of M in its modification -order. -

- -

-In this case, A is SX, B is RX, the -fence X is F2 and the fence Y is F3, -so RX must see 1. -

-

-If F3 is before F2, this doesn't apply, but -F3 can therefore be before or after F1. -

-

-If F3 is after F1, the same logic applies, but this -time the fence X is F1. Therefore again, RX -must see 1. -

-

-Finally we have the case that F3 is before F1 -in the SC ordering. There are now no guarantees about RX, and -RX can see r2==0. -

-

-We can apply 29.3 [atomics.order]p5 again. This time, -A is SY2, B is RY, X is -F3 and Y is F1. Thus RY must observe -the effects of SY2 or a later modification of y in its -modification order. -

-

-Since SY1 is sequenced before RY, RY must -observe the effects of SY1 or a later modification of -y in its modification order. -

-

-In order to ensure that RY sees (r1==1), we must see -that SY1 is later in the modification order of y than -SY2. -

-

-We're now skating on thin ice. Conceptually, SY2 happens-before -F3, F3 is SC-ordered before F1, F1 -happens-before SY1, so SY1 is later in the -modification order M of y, and RY must see -the result of SY1 (r1==1). However, I don't think the -words are clear on that. -

- -

[ -Post Summit Hans adds: -]

- - -
-

-In my (Hans') view, our definition of fences will always be weaker than -what particular hardware will guarantee. Memory_order_seq_cst fences -inherently don't guarantee sequential consistency anyway, for good -reasons (e.g. because they can't enforce a total order on stores). - Hence I don't think the issue demonstrates a gross failure to achieve -what we intended to achieve. The example in question is a bit esoteric. - Hence, in my view, living with the status quo certainly wouldn't be a -disaster either. -

-

-In any case, we should probably add text along the lines of the -following between p5 and p6 in 29.3 [atomics.order]: -

-

-[Note: Memory_order_seq_cst only ensures sequential consistency for a -data-race-free program that uses exclusively memory_order_seq_cst -operations. Any use of weaker ordering will invalidate this guarantee -unless extreme care is used. In particular, memory_order_seq_cst fences -only ensure a total order for the fences themselves. They cannot, in -general, be used to restore sequential consistency for atomic operations -with weaker ordering specifications.] -

- -

-Also see thread beginning at c++std-lib-23271. -

- -
- -

[ -Herve's correction: -]

- -
-

-Minor point, and sorry for the knee jerk reaction: I admit to having -no knowledge of Memory_order_seq_cst, but my former boss (John Lakos) -has ingrained an automatic introspection on the use of "only". I -think you meant: -

- -

-[Note: Memory_order_seq_cst ensures sequential consistency only -for . . . . In particular, memory_order_seq_cst fences ensure a -total order only for . . . -

-

-Unless, of course, Memory_order_seq_cst really do nothing but ensure -sequential consistency for a data-race-free program that uses -exclusively memory_order_seq_cst operations. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Editorial. Solved by -N2992. -

- - - -

Proposed resolution:

-

-Add a new paragraph after 29.3 [atomics.order]p5 that says -

- -

-For atomic operations A and B on an atomic object -M, where A and B modify M, if there -are memory_order_seq_cst fences X and Y such -that A is sequenced before X, Y is sequenced -before B, and X precedes Y in S, -then B occurs later than A in the modifiction order of -M. -

- - - - - -
-

927. Dereferenceable should be HasDereference

-

Section: X [allocator.concepts] Status: NAD Concepts - Submitter: Pablo Halpern Opened: 2008-10-23 Last modified: 2015-04-08

-

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-

Discussion:

-

-X [allocator.concepts] contains a reference to a concept named -Dereferenceable. No such concept exists. -

- -

[ -Daniel adds 2009-02-14: -]

- - -

-The proposal given in the paper -N2829 -would automatically resolve this issue. -

- - -

[ -Batavia (2009-05): -]

- -
-

-This particular set of changes has already been made. -There are two related changes later on (and possibly also an earlier Example); -these can be handled editorially. -

-

-Move to NAD Editorial. -

-
- - -

Proposed resolution:

-

-Change all uses of the concept Dereferenceable to -HasDereference in X [allocator.concepts]. -

- - - - - -
-

928. Wrong concepts used for tuple's comparison operators

-

Section: 20.4.2.7 [tuple.rel] Status: NAD Concepts - Submitter: Joe Gottman Opened: 2008-10-28 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In the latest working draft for C++0x, tuple's operator== and operator< -are declared as -

- -
-template<class... TTypes, class... UTypes> 
-  requires EqualityComparable<TTypes, UTypes>... 
-  bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
- -

-and -

- -
-template<class... TTypes, class... UTypes> 
-  requires LessThanComparable<TTypes, UTypes>... 
-  bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
- -

-But the concepts EqualityComparable and LessThanComparable only take one -parameter, not two. Also, even if LessThanComparable could take two -parameters, the definition of tuple::operator<() should also require -

- -
-LessThanComparable<UTypes, TTypes>... // (note the order) 
-
- -

-since the algorithm for tuple::operator< is the following (pseudo-code) -

- -
-for (size_t N = 0; N < sizeof...(TTypes); ++N) { 
-    if (get<N>(t) < get<N>(u) return true; 
-    else if ((get<N>(u) < get<N>(t)) return false; 
-} 
-
-return false; 
-
- -

-Similar problems hold for tuples's other comparison operators. -

- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- - - -

Proposed resolution:

-

-In 20.4.1 [tuple.general] and 20.4.2.7 [tuple.rel] change: -

- -
-template<class... TTypes, class... UTypes>
-  requires EqualityComparableHasEqualTo<TTypes, UTypes>...
-  bool operator==(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-template<class... TTypes, class... UTypes>
-  requires LessThanComparableHasLess<TTypes, UTypes>... && HasLess<UTypes, TTypes>...
-  bool operator<(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-template<class... TTypes, class... UTypes>
-  requires EqualityComparableHasEqualTo<TTypes, UTypes>...
-  bool operator!=(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-template<class... TTypes, class... UTypes>
-  requires LessThanComparableHasLess<UTTypes, TUTypes>... && HasLess<UTypes, TTypes>...
-  bool operator>(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-template<class... TTypes, class... UTypes>
-  requires LessThanComparableHasLess<UTTypes, TUTypes>... && HasLess<UTypes, TTypes>...
-  bool operator<=(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
-template<class... TTypes, class... UTypes>
-  requires LessThanComparableHasLess<TTypes, UTypes>... && HasLess<UTypes, TTypes>...
-  bool operator>=(const tuple<TTypes...>&, const tuple<UTypes...>&);
-
- - - - - -
-

930. Access to std::array data as built-in array type

-

Section: 23.3.2 [array] Status: NAD - Submitter: Niels Dekker Opened: 2008-11-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

-The Working Draft (N2798) allows access to the elements of -std::array by its data() member function: -

- -
- -
23.2.1.4 array::data [array.data]
-
- T *data();
- const T *data() const;
-
-
  1. - Returns: elems. -
-
- -

-Unfortunately, the result of std::array::data() cannot be bound -to a reference to a built-in array of the type of array::elems. -And std::array provides no other way to get a reference to -array::elems. -This hampers the use of std::array, for example when trying to -pass its data to a C style API function: -

- -
- // Some C style API function. 
- void set_path( char (*)[MAX_PATH] );
-
- std::array<char,MAX_PATH> path;
- set_path( path.data() );  // error
- set_path( &(path.data()) );  // error
-
- -

-Another example, trying to pass the array data to an instance of another -C++ class: -

- -
- // Represents a 3-D point in space.
- class three_d_point {
- public:
-   explicit three_d_point(const double (&)[3]); 
- };
-
- const std::array<double,3> coordinates = { 0, 1, 2 };
- three_d_point point1( coordinates.data() );  // error.
- three_d_point point2( *(coordinates.data()) );  // error.
-
- -

-A user might be tempted to use std::array::elems instead, but -doing so isn't recommended, because std::array::elems is "for -exposition only". Note that Boost.Array users might already use -boost::array::elems, as its documentation doesn't explicitly -state that boost::array::elems is for exposition only: -http://www.boost.org/doc/libs/1_36_0/doc/html/boost/array.html -

-

-I can think of three options to solve this issue: -

-
  1. -Remove the words "exposition only" from the definition of -std::array::elems, as well as the note saying that "elems is -shown for exposition only." -
  2. -Change the signature of std::array::data(), so that it would -return a reference to the built-in array, instead of a pointer to its -first element. -
  3. -Add extra member functions, returning a reference to the built-in array. -
-

-Lawrence Crowl wrote me that it might be better to leave -std::array::elems "for exposition only", to allow alternate -representations to allocate the array data dynamically. This might be -of interest to the embedded community, having to deal with very limited -stack sizes. -

-

-The second option, changing the return type of -std::array::data(), would break backward compatible to current -Boost and TR1 implementations, as well as to the other contiguous -container (vector and string) in a very subtle way. -For example, the following call to std::swap currently swap two -locally declared pointers (data1, data2), for any container -type T that has a data() member function. When -std::array::data() is changed to return a reference, the -std::swap call may swap the container elements instead. -

- -
- template <typename T>
- void func(T& container1, T& container2)
- {
-   // Are data1 and data2 pointers or references?
-   auto data1 = container1.data();
-   auto data2 = container2.data();
-
-   // Will this swap two local pointers, or all container elements?
-   std::swap(data1, data2);
- }
-
- -

-The following concept is currently satisfied by all contiguous -containers, but it no longer is for std::array, when -array::data() -is changed to return a reference (tested on ConceptGCC Alpha 7): -

- -
- auto concept ContiguousContainerConcept<typename T>
- {
-   typename value_type = typename T::value_type;
-   const value_type * T::data() const;
- }
-
- -

-Still it's worth considering having std::array::data() return a -reference, because it might be the most intuitive option, from a user's -point of view. Nicolai Josuttis (who wrote boost::array) -mailed me that he very much prefers this option. -

-

-Note that for this option, the definition of data() would also -need to be revised for zero-sized arrays, as its return type cannot be a -reference to a zero-sized built-in array. Regarding zero-sized array, -data() could throw an exception. Or there could be a partial -specialization of std::array where data() returns -T* or gets removed. -

-

-Personally I prefer the third option, adding a new member function to -std::array, overloaded for const and non-const access, -returning a reference to the built-in array, to avoid those compatible -issues. I'd propose naming the function std::array::c_array(), -which sounds intuitive to me. Note that boost::array already -has a c_array() member, returning a pointer, but Nicolai told -me that this one is only there for historical reasons. (Otherwise a name -like std::array::native_array() or -std::array::builtin_array() would also be fine with me.) -According to my proposed resolution, a zero-sized std::array does not need -to have c_array(), while it is still required to have -data() functions. -

- -

[ -Post Summit: -]

- - -
- -

-Alisdair: Don't like p4 suggesting implementation-defined behaviour. -

-

-Walter: What about an explicit conversion operator, instead of adding -the new member function? -

-

-Alisdair: Noodling about: -

-
-template<size_t N, ValueType T>
-struct array
-{
-  T elems[N];
-
-// fantasy code starts here
-
-// crazy decltype version for grins only
-//requires True<(N>0)>
-//explict operator decltype(elems) & () { return elems; }
-
-// conversion to lvalue ref
-requires True<(N>0)>
-explict operator T(&)[N] () & { return elems; }
-
-// conversion to const lvalue ref
-requires True<(N>0)>
-explict operator const T(&)[N] () const & { return elems; }
-
-// conversion to rvalue ref using ref qualifiers
-requires True<(N>0)>
-explict operator T(&&)[N] () && { return elems; }
-
-// fantasy code ends here
-
-explicit operator bool() { return true; }
-};
-
- -

-This seems legal but odd. Jason Merrill says currently a CWG issue 613 -on the non-static data member that fixes the error that current G++ -gives for the non-explicit, non-conceptualized version of this. Verdict -from human compiler: seems legal. -

-

-Some grumbling about zero-sized arrays being allowed and supported. -

-

-Walter: Would this address the issue? Are we inclined to go this route? -

-

-Alan: What would usage look like? -

-
-// 3-d point in space
-struct three_d_point
-{
-  explicit three_d_point(const double (&)[3]);
-};
-
-void sink(double*);
-
-const std::array<double, 3> coordinates = { 0, 1, 2 };
-three_d_point point1( coordinates.data() ); //error
-three_d_point point2( *(coordinates.data()) ); // error
-three_d_point point3( coordinates ); // yay!
-
-sink(cooridinates); // error, no conversion
-
- -

-Recommended Open with new wording. Take the required clause and add the -explicit conversion operators, not have a typedef. At issue still is use -decltype or use T[N]. In favour of using T[N], even though use of -decltype is specially clever. -

- -
- -

[ -Post Summit, further discussion in the thread starting with c++std-lib-23215. -]

- - -

[ -2009-07 post-Frankfurt (Saturday afternoon group): -]

- - -
-

-The idea to resolve the issue by adding explicit conversion operators -was abandoned, because it would be inconvenient to use, especially when -passing the array to a template function, as mentioned by Daniel. So we -reconsidered the original proposed resolution, which appeared -acceptable, except for its proposed changes to 23.3.2.8 [array.zero], which -allowed c_array_type and c_array() to be absent for a zero-sized array. -Alisdair argued that such wording would disallow certain generic use -cases. New wording for 23.3.2.8 [array.zero] was agreed upon (Howard: and -is reflected in the proposed resolution). -

-

-Move to Review -

-
- -

[ -2009-07-31 Alisdair adds: -]

- - -
-

-I will be unhappy voting the proposed resolution for 930 past review -until we have implementation experience with reference qualifiers. -Specifically, I want to understand the impact of the missing overload -for const && (if any.) -

- -

-If we think the issue is important enough it might be worthwhile -stripping the ref qualifiers for easy progress next meeting, and opening -yet another issue to put them back with experience. -

- -

-Recommend deferring any decision on splitting the issue until we get LWG -feedback next meeting - I may be the lone dissenting voice if others are -prepared to proceed without it. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. There was not enough consensus that this was sufficiently -useful. There are known other ways to do this, such as small inline -conversion functions. -

- - - -

Proposed resolution:

-

-Add to the template definition of array, 23.3.2 [array]/3: -

- -
-

-typedef T c_array_type[N];
-c_array_type & c_array() &;
-c_array_type && c_array() &&;
-const c_array_type & c_array() const &;
-
-
-
- -

-Add the following subsection to 23.3.2 [array], after 23.3.2.5 [array.data]: -

- -
-
23.2.1.5 array::c_array [array.c_array]
- 

-c_array_type & c_array() &;
-c_array_type && c_array() &&;
-const c_array_type & c_array() const &;
-
-
-

-Returns: elems. -

-
- -
- - - -

-Change Zero sized arrays 23.3.2.8 [array.zero]: -

- -
- -

-2- ...

- -

-The type c_array_type is unspecified for a zero-sized array. -

- -

--3- The effect of calling c_array(), front(), or -back() for a zero-sized array is implementation defined. -

-
- - - - - - -
-

937. Atomics for standard typedef types

-

Section: 29 [atomics] Status: NAD Editorial - Submitter: Clark Nelson Opened: 2008-12-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses US 89

- -
-

-The types in the table "Atomics for standard typedef types" should be -typedefs, not classes. These semantics are necessary for compatibility -with C. -

- -

-Change the classes to typedefs. -

-
- -

-N2427 -specified different requirements for atomic analogs of fundamental -integer types (such as atomic_int) and for atomic analogs of <cstdint> -typedefs (such as atomic_size_t). Specifically, atomic_int et al. were -specified to be distinct classes, whereas atomic_size_t et al. were -specified to be typedefs. Unfortunately, in applying -N2427 -to the WD, that distinction was erased, and the atomic analog of every <cstdint> -typedef is required to be a distinct class. -

- -

-It shouldn't be required that the atomic analog of every <cstdint> -typedef be a typedef for some fundamental integer type. After all, -<cstdint> is supposed to provide standard names for extended integer -types. So there was a problem in -N2427, -which certainly could have been -interpreted to require that. But the status quo in the WD is even worse, -because it's unambiguously wrong. -

- -

-What is needed are words to require the existence of a bunch of type -names, without specifying whether they are class names or typedef names. -

- -

[ -Summit: -]

- - -
-

-Change status to NAD, editorial. See US 89 comment notes above. -

-

-Direct the editor to turn the types into typedefs as proposed in the -comment. Paper approved by committee used typedefs, this appears to have -been introduced as an editorial change. Rationale: for compatibility -with C. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

941. Ref-qualifiers for assignment operators

-

Section: 17 [library] Status: NAD - Submitter: Niels Dekker Opened: 2008-12-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The assignment and equality operators = and == are easily confused, just -because of their visual similarity, and in this case a simple typo can cause -a serious bug. When the left side of an operator= is an rvalue, it's -highly unlikely that the assignment was intended by the programmer: -

-
-if ( func() = value )  // Typical typo: == intended!
-
-

-Built-in types don't support assignment to an rvalue, but unfortunately, -a lot of types provided by the Standard Library do. -

-

-Fortunately the language now offers a syntax to prevent a certain member -function from having an rvalue as *this: by adding a ref-qualifier (&) -to the member function declaration. Assignment operators are explicitly -mentioned as a use case of ref-qualifiers, in "Extending Move Semantics -To *this (Revision 1)", -N1821 by Daveed -Vandevoorde and Bronek Kozicki -

-

-Hereby I would like to propose adding ref-qualifiers to all appropriate -assignment operators in the library. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open. -We recommend this be deferred until after the next Committee Draft. -

- -

[ -Frankfurt 2009-07: -]

- - -
-

-The LWG declined to move forward with -N2819. -

-

-Moved to NAD. -

-
- - -

Proposed resolution:

-

-A proposed resolution is provided by the paper on this subject, -N2819, -Ref-qualifiers for assignment operators of the Standard Library -

- - - - - -
-

942. Atomics synopsis typo

-

Section: 29 [atomics] Status: Dup - Submitter: Holger Grund Opened: 2008-12-19 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 880

-

Discussion:

- - - -

-I'm looking at 29 [atomics] and can't really make sense of a couple of things. -

-

-Firstly, there appears to be a typo in the <cstdatomic> synopsis: -

- -
-

-The atomic_exchange overload taking an atomic_address -is missing the second parameter: -

- -
-void* atomic_exchange(volatile atomic_address*);
-
- -

-should be -

- -
-void* atomic_exchange(volatile atomic_address*, void*);
-
- -

-Note, that this is not covered by 880 "Missing atomic exchange parameter", -which only talks about the atomic_bool. -

-
- - - -

Proposed resolution:

-

-Change the synopsis in 29 [atomics]/2: -

- -
-void* atomic_exchange(volatile atomic_address*, void*);
-
- - - - - - -
-

945. system_clock::rep not specified

-

Section: 20.12.7.1 [time.clock.system] Status: NAD Editorial - Submitter: Pete Becker Opened: 2008-12-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In 20.12.7.1 [time.clock.system], the declaration of system_clock::rep says "see -below", but there is nothing below that describes it. -

- -

[ -Howard adds: -]

- - -
-

-This note refers to: -

- -

--2- system_clock::duration::min() < system_clock::duration::zero() shall be true. -

- -

-I.e. this is standardeze for "system_clock::rep is signed". -Perhaps an editorial note along the lines of: -

- -

--2- system_clock::duration::min() < system_clock::duration::zero() -shall be true. [Note: system_clock::rep shall be signed. -- end note]. -

- -

-? -

- -
- -

[ -Batavia (2009-05): -]

- -

-We agree with the direction of the proposed resolution. -Move to NAD Editorial. -

- - - -

Proposed resolution:

-

-Add a note to 20.12.7.1 [time.clock.system], p2: -

-

--2- system_clock::duration::min() < system_clock::duration::zero() -shall be true. [Note: system_clock::rep shall be signed. -- end note]. -

- - - - - -
-

946. duration_cast improperly specified

-

Section: 20.12.5.7 [time.duration.cast] Status: NAD - Submitter: Pete Becker Opened: 2008-12-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-20.12.5.7 [time.duration.cast]/3: -

-

-.... All intermediate computations shall be -carried out in the widest possible representation... . -

- -

-So ignoring floating-point types for the moment, all this arithmetic has to be done -using the implementation's largest integral type, even if both arguments -use int for their representation. This seems excessive. And it's not at -all clear what this means if we don't ignore floating-point types. -

- -

-This issue is related to 952. -

- -

[ -Howard adds: -]

- - -
-

-The intent of this remark is that intermediate computations are carried out -using: -

- -
-common_type<typename ToDuration::rep, Rep, intmax_t>::type
-
- -

-The Remark was intended to be clarifying prose supporting the rather algorithmic description -of the previous paragraph. I'm open to suggestions. Perhaps the entire paragraph -3 (Remarks) would be better dropped? -

-
- -

[ -Batavia (2009-05): -]

- -
-

-We view this as a specific case of issue 952, -and should be resolved when that issue is resolved. -

-

-Move to NAD. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

952. Various threading bugs #2

-

Section: 20.12.5.7 [time.duration.cast] Status: NAD Editorial - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-20.12.5.7 [time.duration.cast] specifies an implementation and imposes -requirements in text (and the implementation doesn't satisfy all of the -text requirements). Pick one. -

- -

-This issue is related to 946. -

- -

[ -2009-05-10 Howard adds: -]

- - -
-

-The Remarks paragraph is an English re-statement of the preceeding -Returns clause. It was meant to be clarifying and motivating, not -confusing. I'm not aware with how the Remarks contradicts the Returns clause -but I'm ok with simply removing the Remarks. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-Pete suggests that this could be resolved -by rephrasing the Remarks to Notes. -

-

-Move to NAD Editorial. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

955. Various threading bugs #5

-

Section: 20.12.3 [time.clock.req] Status: NAD - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-20.12.3 [time.clock.req] requires that a clock type have a member -typedef named time_point that names an instantiation of the -template time_point, and a member named duration that -names an instantiation of the template duration. This mixing of -levels is confusing. The typedef names should be different from the -template names. -

- -

[ -Post Summit, Anthony provided proposed wording. -]

- - -

[ -2009-05-04 Howard adds: -]

- - -
-

-The reason that the typedef names were given the same name as the class templates -was so that clients would not have to stop and think about whether they were -using the clock's native time_point / duration or the class -template directly. In this case, one person's confusion is another person's -encapsulation. The detail that sometimes one is referring to the clock's -native types, and sometimes one is referring to an independent type is -purposefully "hidden" because it is supposed to be an unimportant -detail. It can be confusing to have to remember when to type duration -and when to type duration_type, and there is no need to require the -client to remember something like that. -

- -

-For example, here is code that I once wrote in testing out the usability of -this facility: -

- -
-template <class Clock, class Duration>
-void do_until(const std::chrono::time_point<Clock, Duration>& t)
-{
-    typename Clock::time_point now = Clock::now();
-    if (t > now)
-    {
-        typedef typename std::common_type
-        <
-            Duration,
-            typename std::chrono::system_clock::duration
-        >::type CD;
-        typedef std::chrono::duration<double, std::nano> ID;
-
-        CD d = t - now;
-        ID us = duration_cast<ID>(d);
-        if (us < d)
-            ++us;
-        ...
-    }
-}
-
- -

-I see no rationale to require the client to append _type to some -of those declarations. It seems overly burdensome on the author of do_until: -

- -
-template <class Clock, class Duration>
-void do_until(const std::chrono::time_point<Clock, Duration>& t)
-{
-    typename Clock::time_point_type now = Clock::now();
-    if (t > now)
-    {
-        typedef typename std::common_type
-        <
-            Duration,
-            typename std::chrono::system_clock::duration_type
-        >::type CD;
-        typedef std::chrono::duration<double, std::nano> ID;
-
-        CD d = t - now;
-        ID us = duration_cast<ID>(d);
-        if (us < d)
-            ++us;
-        ...
-    }
-}
-
- -

-Additionally I'm fairly certain that this suggestion hasn't been implemented. -If it had, it would have been discovered that it is incomplete. time_point -also has a nested type (purposefully) named duration. -

-

-That is, the current proposed wording would put the WP into an inconsistent state. -

-

-In contrast, -the current WP has been implemented and I've received very favorable feedback -from people using this interface in real-world code. -

- -
- -

[ -Batavia (2009-05): -]

- -
-

-Bill agrees that distinct names should be used for distinct kinds of entities. -

-

-Walter would prefer not to suffix type names, -especially for such well-understood terms as "duration". -

-

-Howard reminds us that the proposed resolution is incomplete, per his comment -in the issue. -

-

-Move to Open. -

-
- -

[ -2009-06-07 Howard adds: -]

- - -
-

-Not meaning to be argumentative, but we have a decade of positive experience -with the precedent of using the same name for the nested type as an external -class representing an identical concept. -

- -
-template<class Category, class T, class Distance = ptrdiff_t,
-         class Pointer = T*, class Reference = T&>
-struct iterator
-{
-    ...
-};
-
-template <BidirectionalIterator Iter>
-class reverse_iterator
-{
-    ...
-};
-
-template <ValueType T, Allocator Alloc = allocator<T> >
-    requires NothrowDestructible<T>
-class list
-{
-public:
-    typedef implementation-defined     iterator;
-    ...
-    typedef reverse_iterator<iterator> reverse_iterator;
-    ...
-};
-
- -

-I am aware of zero complaints regarding the use of iterator -and reverse_iterator as nested types of the containers despite these -names also having related meaning at namespace std scope. -

- -

-Would we really be doing programmers a favor by renaming these nested types? -

- -
-template <ValueType T, Allocator Alloc = allocator<T> >
-    requires NothrowDestructible<T>
-class list
-{
-public:
-    typedef implementation-defined     iterator_type;
-    ...
-    typedef reverse_iterator<iterator> reverse_iterator_type;
-    ...
-};
-
- -

-I submit that such design contributes to needless verbosity which ends up -reducing readability. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. No concensus for changing the WP. -

- - - -

Proposed resolution:

-

-Change 20.12 [time]: -

- -
-...
-template <class Clock, class Duration = typename Clock::duration_type> class time_point;
-...
-
- -

-Change 20.12.3 [time.clock.req]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 45 -- Clock requirements
ExpressionReturn typeOperational semantics
.........
C1::duration_typechrono::duration<C1::rep, C1::period>The native duration type of the clock.
C1::time_point_typechrono::time_point<C1> or chrono::time_point<C2, C1::duration_type<The native time_point type of the clock. Different clocks may share a time_point_type -definition if it is valid to -compare their time_point_types by -comparing their respective -duration_types. C1 and C2 shall -refer to the same epoch.
.........
C1::now()C1::time_point_typeReturns a time_point_type object -representing the current point -in time. -
-
- -

-Change 20.12.7.1 [time.clock.system]: -

- -
-

--1- Objects of class system_clock represent wall clock time from the system-wide realtime clock. -

- -
-class system_clock { 
-public: 
-  typedef see below rep; 
-  typedef ratio<unspecified, unspecified> period; 
-  typedef chrono::duration<rep, period> duration_type; 
-  typedef chrono::time_point<system_clock> time_point_type; 
-  static const bool is_monotonic = unspecified ; 
-
-  static time_point_type now(); 
-
-  // Map to C API 
-  static time_t to_time_t (const time_point_type& t); 
-  static time_point_type from_time_t(time_t t); 
-};
-
- -

--2- system_clock::duration_type::min() < system_clock::duration_type::zero() shall be true. -

- -
-time_t to_time_t(const time_point_type& t);
-
- -

--3- Returns: A time_t object that represents the same -point in time as t when both values are truncated to the -coarser of the precisions of time_t and time_point_type. -

- -
-time_point_type from_time_t(time_t t);
-
- -

--4- Returns: A time_point_type object that represents the same point -in time as t when both values are truncated to the coarser of the -precisions of time_t and time_point_type. -

-
- -

-Change X [time.clock.monotonic]: -

- -
-class monotonic_clock { 
-public: 
-  typedef unspecified                                rep; 
-  typedef ratio<unspecified , unspecified>           period; 
-  typedef chrono::duration<rep, period>              duration_type; 
-  typedef chrono::time_point<unspecified , duration_type> time_point_type; 
-  static const bool is_monotonic =                   true; 
-
-  static time_point_type now();
-};
-
- -

-Change 20.12.7.3 [time.clock.hires]: -

- -
-class high_resolution_clock { 
-public: 
-  typedef unspecified                                rep; 
-  typedef ratio<unspecified , unspecified>           period; 
-  typedef chrono::duration<rep, period>              duration_type; 
-  typedef chrono::time_point<unspecified , duration_type> time_point_type; 
-  static const bool is_monotonic =                   true; 
-
-  static time_point_type now();
-};
-
- - - - - - -
-

959. Various threading bugs #9

-

Section: 30.5.1 [thread.condition.condvar] Status: NAD - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar]: condition_variable::wait_for -is required to compute the absolute time by adding the duration value to -chrono::monotonic_clock::now(), but monotonic_clock is not required to -exist. -

- -

[ -Summit: -]

- - -

-Move to open. Associate with LWG 859 and any other monotonic-clock -related issues. -

- -

[ -2009-08-01 Howard adds: -]

- - -

-I believe that 859 (currently Ready) addresses this issue, and -that this issue should be marked NAD, solved by 859 (assuming -it moves to WP). -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave open, but expect to be fixed by N2969 revision that Detlef is writing. -

- -

[ -2009-11-18 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - - -

Proposed resolution:

-

-

- - -

Rationale:

-

-condition_variable::wait_for no longer refers to -monotonic_clock, so this issue is moot. -

- - - - - -
-

969. What happened to Library Issue 475?

-

Section: 25.2.4 [alg.foreach] Status: NAD Editorial - Submitter: Stephan T. Lavavej Opened: 2009-01-12 Last modified: 2015-04-08

-

View all other issues in [alg.foreach].

-

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-

Discussion:

-

-Library Issue 475 has CD1 status, but the non-normative note in -N2723 -was removed in -N2798 -(25.2.4 [alg.foreach] in both drafts). -

- -

[ -Batavia (2009-05): -]

- -

-Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Restore the non-normative note. It might need to be expressed in terms of concepts. -

- - - - - -
-

971. Spurious diagnostic conversion function

-

Section: 19.5.2.5 [syserr.errcode.nonmembers] Status: NAD - Submitter: Beman Dawes Opened: 2009-01-19 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-Anthony Williams raised the question in c++std-lib-22987 "why is there -std::make_error_code(std::errc)? What purpose does this serve?" -

-

-The function make_error_code(errc e) is not required, since -make_error_condition(errc e) is the function that is needed for errc -conversions. make_error_code(errc e) appears to be a holdover from my -initial confusion over the distinction between POSIX and operating -systems that conform to the POSIX spec. -

- -

[ -Post Summit: -]

- - -

-Recommend Review. -

- -

[ -Batavia (2009-05): -]

- -

-The designer of the facility (Christopher Kohlhoff) -strongly disagrees that there is an issue here, -and especially disagrees with the proposed resolution. -Bill would prefer to be conservative and not apply this proposed resolution. -Move to Open, and recommend strong consideration for NAD status. -

- -

[ -2009-05-21 Beman adds: -]

- - -

-My mistake. Christopher and Bill are correct and the issue should be -NAD. The function is needed by users. -

- -

[ -2009-07-21 Christopher Kohlhoff adds rationale for make_error_code: -]

- - -
-

-Users (and indeed library implementers) may need to use the -errc codes in portable code. For example: -

- -
-void do_foo(error_code& ec)
-{
-#if defined(_WIN32)
-  // Windows implementation ...
-#elif defined(linux)
-  // Linux implementation ...
-#else
-  // do_foo not supported on this platform
-  ec = make_error_code(errc::not_supported);
-#endif
-}
-
-
- -

[ -2009 Santa Cruz: -]

- - -

-Moved to NAD. -

- - - -

Proposed resolution:

-

-Change System error support 19.5 [syserr], Header <system_error> -synopsis, as indicated: -

- -
-error_code make_error_code(errc e);
-error_condition make_error_condition(errc e);
-
- -

-Delete from Class error_code non-member functions -19.5.2.5 [syserr.errcode.nonmembers]: -

- -
-error_code make_error_code(errc e);
-
-

-Returns: error_code(static_cast<int>(e), -generic_category). -

-
- - - - - - -
-

972. The term "Assignable" undefined but still in use

-

Section: 17 [library] Status: NAD Editorial - Submitter: Niels Dekker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Previous versions of the Draft had a table, defining the Assignable -requirement. For example -N2134 -Table 79, "Assignable requirements". But I guess the term "Assignable" -is outdated by now, because the current Committee Draft provides -MoveAssignable, CopyAssignable, and TriviallyCopyAssignable concepts -instead. And as far as I can see, it no longer has a definition of -Assignable. (Please correct me if I'm wrong.) Still the word -"Assignable" is used in eight places in the Draft, -N2800. -

- -

-Are all of those instances of "Assignable" to be replaced by "CopyAssignable"? -

- -

[ -Batavia (2009-05): -]

- -

-Move to NAD Editorial. -

- - -

Proposed resolution:

- -

-Change Exception Propagation 18.8.5 [propagation]: -

-

-exception_ptr shall be DefaultConstructible, CopyConstructible, -CopyAssignable and EqualityComparable. -

- -

-Change Class template reference_wrapper 20.9.4 [refwrap]: -

-

-reference_wrapper<T> is a CopyConstructible and CopyAssignable -wrapper around a reference to an object of type T. -

-

-Change Placeholders 20.9.10.4 [func.bind.place]: -

-

-It is implementation defined whether placeholder types are CopyAssignable. -CopyAssignable placeholders' copy assignment operators shall not throw exceptions. -

-

-Change Class template shared_ptr 20.8.2.2 [util.smartptr.shared]: -

-

-Specializations of shared_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable... -

-

-Change Class template weak_ptr 20.8.2.3 [util.smartptr.weak]: -

-

-Specializations of weak_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable... -

-

-Change traits typedefs 21.2.2 [char.traits.typedefs] (note: including deletion of reference to 23.1!): -

-

-Requires: state_type shall meet the requirements of CopyAssignable -(23.1), CopyConstructible (20.1.8), and DefaultConstructible types. -

-

-Change Class seed_seq 26.5.7.1 [rand.util.seedseq] (note again: including deletion of reference to 23.1!): -

-

-In addition to the requirements set forth below, instances of -seed_seq shall meet the requirements of CopyConstructible (20.1.8) and of CopyAssignable (23.1). -

- -

-Note: The proposed resolution of this issue does not deal with the -instance of the term "Assignable" in X [auto.ptr], as this is dealt -with more specifically by LWG 973, "auto_ptr characteristics", submitted -by Maarten Hilferink. -

- - - - - - -
-

973. auto_ptr characteristics

-

Section: X [auto.ptr] Status: NAD Editorial - Submitter: Maarten Hilferink Opened: 2009-01-21 Last modified: 2015-04-08

-

View all other issues in [auto.ptr].

-

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-

Discussion:

-

-I think that the Note of X [auto.ptr], paragraph 3 needs a rewrite -since "Assignable" is no longer defined as a concept. -The relationship of auto_ptr with the new CopyAssignable, MoveAssignable, - and MoveConstructible concepts should be clarified. -Furthermore, since the use of auto_ptr is depreciated anyway, - we can also omit a description of its intended use. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the intent of the proposed resolution. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Change X [auto.ptr], paragraph 3: -

- -

-The auto_ptr provides a semantics of strict ownership. An -auto_ptr owns the ob ject it holds a pointer to. Copying an -auto_ptr copies the pointer and transfers ownership to the -destination. If more than one auto_ptr owns the same ob ject at -the same time the behavior of the program is undefined. [Note: -The uses of auto_ptr include providing temporary -exception-safety for dynamically allocated memory, passing ownership of -dynamically allocated memory to a function, and returning dynamically -allocated memory from a function. -auto_ptr does not meet the -CopyConstructible and Assignable requirements for -standard library container elements and thus instantiating a standard -library container with an auto_ptr results in undefined -behavior. -

-Instances of auto_ptr shall -meet the MoveConstructible and MoveAssignable -requirements, but do not meet the CopyConstructible and -CopyAssignable requirements. --- end note] -

- - - - - -
-

977. insert iterators inefficient for expensive to move types

-

Section: 24.5.2 [insert.iterators] Status: NAD - Submitter: Howard Hinnant Opened: 2009-02-02 Last modified: 2015-04-08

-

View all other issues in [insert.iterators].

-

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-

Discussion:

-

-The new concepts for the insert iterators mandate an extra copy when -inserting an lvalue: -

- -
-requires CopyConstructible<Cont::value_type>
-  back_insert_iterator<Cont>& 
-  operator=(const Cont::value_type& value);
-
-

--1- Effects: push_back(*container, Cont::value_type(value)); -

-
- -

-The reason is to convert value into an rvalue because the current -BackInsertionContainer concept only handles push_back-ing -rvalues: -

- -
-concept BackInsertionContainer<typename C> : Container<C> { 
-  void push_back(C&, value_type&&); 
-}
-
- -

-Without the conversion of value to an rvalue, the assignment operator -fails to concept check. -

- -

-A solution is to modify the BackInsertionContainer concept so that -the client can pass in the parameter type for push_back similar to -what is already done for the OutputIterator concept: -

- -
-concept BackInsertionContainer<typename C, typename Value = C::value_type&&>
-  : Container<C> { 
-     void push_back(C&, Value); 
-}
-
- -

-This allows the assignment operator to be adjusted appropriately: -

- -
-requires BackInsertionContainer<Cont, Cont::value_type const&> &&
-         CopyConstructible<Cont::value_type>
-  back_insert_iterator<Cont>& 
-  operator=(const Cont::value_type& value);
-
-

--1- Effects: push_back(*container, value); -

-
- -

[ -We may want to propagate this fix to other concepts such as StackLikeContainer. -]

- - -

[ -Solution and wording collaborated on by Doug and Howard. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Howard notes that "these operations behaved efficiently until concepts were added." -

-

-Alisdair is uncertain that the proposed resolution is syntactically correct. -

-

-Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD, solved by the removal of concepts. -

- - - -

Proposed resolution:

-

-Change [container.concepts.free]: -

- -
-
-concept FrontInsertionContainer<typename C, typename Value = C::value_type&&>
-    : Container<C> { 
-  void push_front(C&, value_type&& Value); 
-
-  axiom FrontInsertion(C c, value_type Value x) { 
-    x == (push_front(c, x), front(c)); 
-  } 
-}
-
- -

...

- -
-concept BackInsertionContainer<typename C, typename Value = C::value_type&&>
-    : Container<C> { 
-  void push_back(C&, value_type&& Value); 
-}
-
- -

...

- -
-concept InsertionContainer<typename C, typename Value = C::value_type&&>
-    : Container<C> { 
-  iterator insert(C&, const_iterator, value_type&& Value); 
-
-  axiom Insertion(C c, const_iterator position, value_type Value v) { 
-    v == *insert(c, position, v); 
-  } 
-}
-
- -
- -

-Change [container.concepts.member]: -

- -
-
-auto concept MemberFrontInsertionContainer<typename C, typename Value = C::value_type&&>
-    : MemberContainer<C> { 
-  void C::push_front(value_type&& Value); 
-
-  axiom MemberFrontInsertion(C c, value_type Value x) { 
-    x == (c.push_front(x), c.front()); 
-  } 
-}
-
- -

...

- -
-auto concept MemberBackInsertionContainer<typename C, typename Value = C::value_type&&>
-    : MemberContainer<C> { 
-  void C::push_back(value_type&& Value); 
-}
-
- -

...

- -
-auto concept MemberInsertionContainer<typename C, typename Value = C::value_type&&>
-    : MemberContainer<C> { 
-  iterator C::insert(const_iterator, value_type&& Value); 
-
-  axiom MemberInsertion(C c, const_iterator position, value_type Value v) { 
-    v == *c.insert(position, v); 
-  } 
-}
-
-
- -

-Change [container.concepts.maps]: -

- -
-
-template <MemberFrontInsertionContainer C, typename Value = C::value_type&&> 
-concept_map FrontInsertionContainer<C, Value> { 
-  typedef Container<C>::value_type value_type;
-
-  void push_front(C& c, value_type&& Value v) { c.push_front(static_cast<value_type&& Value>(v)); } 
-}
-
- -

...

- -
-template <MemberBackInsertionContainer C, typename Value = C::value_type&&> 
-concept_map BackInsertionContainer<C, Value> { 
-  typedef Container<C>::value_type value_type;
-
-  void push_back(C& c, value_type&& Value v) { c.push_back(static_cast<value_type&& Value>(v)); } 
-}
-
- -

...

- -
-template <MemberInsertionContainer C, typename Value = C::value_type&&> 
-concept_map InsertionContainer<C, Value> { 
-  typedef Container<C>::value_type value_type;
-  Container<C>::iterator insert(C& c, Container<C>::const_iterator i, value_type&& Value v) 
-  { return c.insert(i, static_cast<value_type&& Value>(v)); } 
-}
-
- -
- -

-Change 24.5.2.1 [back.insert.iterator]: -

- -
-template <BackInsertionContainer Cont> 
-class back_insert_iterator {
-  ...
-  requires BackInsertionContainer<Cont, const Cont::value_type&>
-           CopyConstructible<Cont::value_type>
-    back_insert_iterator<Cont>& 
-      operator=(const Cont::value_type& value);
-  ...
-
- -

-Change 24.5.2.2.2 [back.insert.iter.op=]: -

- -
-
-requires BackInsertionContainer<Cont, const Cont::value_type&>
-         CopyConstructible<Cont::value_type>
-  back_insert_iterator<Cont>& 
-    operator=(const Cont::value_type& value);
-
-

--1- Effects: push_back(*container, Cont::value_type(value)); -

-
- -

-Change 24.5.2.3 [front.insert.iterator]: -

- -
-template <FrontInsertionContainer Cont> 
-class front_insert_iterator {
-  ...
-  requires FrontInsertionContainer<Cont, const Cont::value_type&>
-           CopyConstructible<Cont::value_type>
-    front_insert_iterator<Cont>& 
-      operator=(const Cont::value_type& value);
-  ...
-
- -

-Change 24.5.2.4.2 [front.insert.iter.op=]: -

- -
-
-requires FrontInsertionContainer<Cont, const Cont::value_type&>
-         CopyConstructible<Cont::value_type>
-  front_insert_iterator<Cont>& 
-    operator=(const Cont::value_type& value);
-
-

--1- Effects: push_front(*container, Cont::value_type(value)); -

-
- -

-Change 24.5.2.5 [insert.iterator]: -

- -
-template <InsertionContainer Cont> 
-class insert_iterator {
-  ...
-  requires InsertionContainer<Cont, const Cont::value_type&>
-           CopyConstructible<Cont::value_type>
-    insert_iterator<Cont>& 
-      operator=(const Cont::value_type& value);
-  ...
-
- -

-Change 24.5.2.6.2 [insert.iter.op=]: -

- -
-
-requires InsertionContainer<Cont, const Cont::value_type&>
-         CopyConstructible<Cont::value_type>
-  insert_iterator<Cont>& 
-    operator=(const Cont::value_type& value);
-
-
-

--1- Effects: -

-
-iter = insert(*container, iter, Cont::value_type(value)); 
-++iter;
-
-
-
- - - - - - -
-

979. Bad example

-

Section: 24.5.3 [move.iterators] Status: NAD Editorial - Submitter: Howard Hinnant Opened: 2009-02-03 Last modified: 2015-04-08

-

View all other issues in [move.iterators].

-

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-

Discussion:

-

-24.5.3 [move.iterators] has an incorrect example: -

- -
-

--2- [Example: -

- -
-set<string> s; 
-// populate the set s 
-vector<string> v1(s.begin(), s.end());          // copies strings into v1 
-vector<string> v2(make_move_iterator(s.begin()), 
-                  make_move_iterator(s.end())); // moves strings into v2
-
- -

--- end example] -

-
- -

-One can not move from a set because the iterators return const -references. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. Move to NAD Editorial. -

- - - -

Proposed resolution:

-

-Change 24.5.3 [move.iterators]/2: -

- -
-

--2- [Example: -

- -
-setlist<string> s; 
-// populate the setlist s 
-vector<string> v1(s.begin(), s.end());          // copies strings into v1 
-vector<string> v2(make_move_iterator(s.begin()), 
-                  make_move_iterator(s.end())); // moves strings into v2
-
- -

--- end example] -

-
- - - - - -
-

980. mutex lock() missing error conditions

-

Section: 30.4.1 [thread.mutex.requirements] Status: NAD - Submitter: Ion Gaztañaga Opened: 2009-02-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-POSIX 2008 adds two return values for pthread_mutex_xxxlock(): -EOWNERDEAD (owner_dead) and ENOTRECOVERABLE -(state_not_recoverable). In the first case the mutex is locked, -in the second case the mutex is not locked. -

- -

-Throwing an exception in the first case can be incompatible with the use -of Locks, since the Lock::owns_lock() will be false when the lock is -being destroyed. -

- -

-Consider: -

- -
-//Suppose mutex.lock() throws "owner_dead"
-unique_lock ul(&mutex);
-//mutex left locked if "owner_dead" is thrown
-
- -

-Throwing an exception with owner_dead might be also undesirable if -robust-mutex support is added to C++ and the user has the equivalent of -pthread_mutex_consistent() to notify the user has fixed the corrupted -data and the mutex state should be marked consistent. -

- -
    -
  1. -For state_not_recoverable add it to the list of Error conditions: -
    2. -
  2. -For owner_dead, no proposed resolution. -
    3. -
- -

[ -Summit: -]

- - -

-Not a defect. Handling these error conditions is an implementation -detail and must be handled below the C++ interface. -

- - - -

Proposed resolution:

- -

-Add to 30.4.1 [thread.mutex.requirements], p12: -

- -
-

--12- Error conditions: -

- -
    -
  • -operation_not_permitted -- if the thread does not have the necessary permission to change -the state of the mutex. -
    • -
  • -resource_deadlock_would_occur -- if the current thread already owns the mutex and is able -to detect it. -
    • -
  • -device_or_resource_busy -- if the mutex is already locked and blocking is not possible. -
    • -
  • -state_not_recoverable -- if the state protected by the mutex is not recoverable. -
    • -
-
- - - - - -
-

988. Reflexivity meaningless?

-

Section: X [concept.comparison] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-02-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-X [concept.comparison] p2: -

-

-Due to the subtle meaning of == inside axioms, the Reflexivity axiom does -not do anything as written. It merely states that a value is substitutable -with itself, rather than asserting a property of the == operator. -

- -

-Original proposed resolution: -

- -

-Change the definition of Reflexivity in X [concept.comparison]: -

- -
-axiom Reflexivity(T a) { (a == a) == true; }
-
- -

[ -Post Summit: -]

- - -
-

-Alisdair: I was wrong. -

-

-Recommend NAD. -

-
- - - -

Proposed resolution:

-

-NAD. -

- - - - - -
-

989. late_check and library

-

Section: 17 [library] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-02-24 Last modified: 2015-04-08

-

View other active issues in [library].

-

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-

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-

Discussion:

-

-The example in 6.9p2 shows how late_check blocks inhibit concept_map lookup -inside a constrained context, and so inhibit concept map adaption by users -to meet template requirements. -

-

-Do we need some text in clause 17 prohibitting use of late_check in library -template definitions unless otherwise documented? -

- -

[ -Doug adds: -]

- - -

-We need something like this, but it should be a more general statement -about implementations respecting the concept maps provided by the -user. Use of late_check is one way in which implementations can -subvert the concept maps provided by the user, but there are other -ways as well ("pattern-based" overloading, tricks with "auto" concept -maps and defaulted associated type arguments). -

- -

[ -Batavia (2009-05): -]

- - -

-Move to Open, pending proposed wording from Alisdair and/or Doug for further review. -

- - -

Proposed resolution:

- - - - - -
-

992. Allow implementations to implement C library in the global namespace

-

Section: 17.6.1.1 [contents] Status: NAD - Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2015-04-08

-

View all other issues in [contents].

-

View all issues with NAD status.

-

Discussion:

-

Addresses UK-169 [CD1]

-

-This phrasing contradicts later freedom to implement the C standard -library portions in the global namespace as well as std. (17.6.2.3p4) -

- -

[ -Batavia (2009-05): -]

- -

-The proposed wording seems to go too far. -Move back to Open. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-Howard to add NB reference to the description of this issue. -

-

-Move to NAD. This comment is informative and not normative by the use of -the word "are" instead of the word "shall." -

-

-A note linking to Annex D would help clarify the intention, here. -

-

-Robert to Open a separate issue proposing that the standard C headers be -undeprecated, for the purpose of clarifying the standard. -

-
- -

[ -2009-07-22 Bill modified the proposed wording with a clarifying footnote. -]

- - - - -

Proposed resolution:

-

-Add a footnote to 17.6.1.1 [contents], p2: -

- -
-

--2- All library entities except macros, operator new and operator -delete are defined within the namespace std or namespaces -nested within namespace std*. -

- -

-*The C standard library headers D.5 [depr.c.headers] also define -names within the global namespace, while the C++ headers for -C library facilities 17.6.1.2 [headers] may also define names within -the global namespace. -

-
- - - - - - -
-

995. Operational Semantics Unclear

-

Section: 17.5.1.3 [structure.requirements] Status: NAD - Submitter: David Abrahams Opened: 2009-03-06 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-As a practical matter there's disagreement on the meaning of operational -semantics. If the text in 17.5.1.3 [structure.requirements]p4 isn't -clear, it should be clarified. However, it's not clear whether the -disagreement is merely due to people not being aware of the text. -

- -

[ -Batavia (2009-05): -]

- -

-Agree with the recommended NAD resolution. -

- - -

Proposed resolution:

-

-Recommend NAD. The text in 17.5.1.3 [structure.requirements] is -perfectly clear. -

- - - - - -
-

996. Move operation not well specified

-

Section: 17 [library] Status: NAD - Submitter: David Abrahams Opened: 2009-03-06 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-There are lots of places in the standard where we talk about "the move -constructor" but where we mean "the move operation," i.e. T( move( x ) ). -

-

-We also don't account for whether that operation modifies x or not, and -we need to. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, pending proposed wording from Dave for further -review. -

- - - -

[ -2010 Rapperswil: -]

- - -

-Move to NAD. We define what we expect from a moved-from object in Table 34 [movesconstructible]. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

1000. adjacent_find is over-constrained

-

Section: 25.2.8 [alg.adjacent.find] Status: NAD Concepts - Submitter: Chris Jefferson Opened: 2009-03-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Addresses UK 296 -

- -

-adjacent_find in C++03 allows an arbitrary predicate, but in C++0x -EqualityComparable/EquivalenceRelation is required. This forbids a -number of use cases, including: -

-
- - - - - - - - - -
-adjacent_find(begin, end, less<double>) - -Find the first -place where a range is not ordered in decreasing order - in use to check -for sorted ranges. -
-adjacent_find(begin, end, DistanceBiggerThan(6) ) ) - -Find the first -place in a range where values differ by more than a given value - in use -to check an algorithm which produces points in space does not generate -points too far apart. -
-
- -

-A number of books use predicate which are not equivalence relations in -examples, including "Thinking in C++" and "C++ Primer". -

- -

-Adding the requirement that the predicate is an EquivalenceRelation -does not appear to open up any possibility for a more optimised algorithm. -

- - - -

Proposed resolution:

-

-Change the definition of adjacent_find in the synopsis of 25 [algorithms] -and 25.2.8 [alg.adjacent.find] to: -

- -
-template<ForwardIterator Iter> 
-  requires EqualityComparableHasEqualTo<Iter::value_type, Iter::value_type>
-  Iter adjacent_find(Iter first, Iter last);
-
-template<ForwardIterator Iter, EquivalenceRelationPredicate<auto, Iter::value_type, Iter::value_type> Pred> 
-  requires CopyConstructible<Pred> 
-  Iter adjacent_find(Iter first, Iter last, Pred pred);
-
- - - - - -
-

1001. Pointers, concepts and headers

-

Section: 17 [library] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 78

- -

-Related to 1063. -

- -

-This is effectively an extension of LWG issue 343. -

-

-We know there is an increasing trend (encouraged by conformance testers and -some users) that each library header should supply no more than required to -satisfy the synopsis in the standard. This is typically achieved by -breaking larger headers into smaller subsets, and judicious use of forward -declarations. -

-

-If we apply this policy to C++0x (per -N2800) -it will be very surprising for -people using library algorithms over ranges defined by pointers that they -must #include <iterator_concepts> for their code to compile again. That is -because pointers do not satisfy any of the iterator concepts without the -concept_map supplied in this header. -

-

-Therefore, I suggest we should require all library headers that make use of -iterator concepts are specifically required to #include <iterator_concepts>. -

-

-At a minimum, the list of headers would be: (assuming all are constrained by -concepts) -

-
-algorithm
-array
-deque
-forward_list
-initializer_list
-iterator
-locale
-list
-map
-memory          // if 1029 is adopted
-memory_concepts
-numeric
-random
-regex
-set
-string
-tuple
-unordered_map
-unordered_set
-utility
-vector
-
- -

[ -Ganesh adds: -]

- - -
-

-The same problems exists for <memory_concepts> and -<container_concepts>. -

-

-In order to compile <vector> you just need the -definitions of the concepts in <memory_concepts>, the -concept maps defined there are not necessary. Yet, from the user point -of view, if the concept map template for AllocatableElement are -not in scope, <vector> is pretty useless. Same for -<tuple> and ConstructibleWithAllocator. -

-

-Similarly, <queue> is not very useful if the concept map -template for QueueLikeContainer is not in scope, although the -definition of concept alone is theoretically sufficient. -

-

-There's a pattern here: if a concept has concept maps "attached", they -should never be separated. -

-
- -

[ -Beman provided the proposed resolution for the May 2009 mailing. He -comments: -]

- - -
- -

Initially I tried to specify exactly what header should include what other -headers. This was verbose, error prone, hard to maintain, and appeared to add -little value compared to just stating the general rule.

- -
- -

[ -Batavia (2009-05): -]

- -
-

-Pete believes the proposed wording overconstrains implementers. -Instead of specifying the mechanism, -he prefers a solution that spells out what needs to be declared, -rather than how those declarations are to be provided, -e.g., -

-

-A C++ header shall provide the names -that are required to be defined in that header. -

-

-Bill suggests approaching the wording from a programmer's perspective. -We may want to consider promising that certain widely-used headers -(e.g., the concept headers) are included when needed by other headers. -He feels, however, there is nothing broken now, -although we may want to consider "something nicer." -

-

-Move to Open status. -

- -
- -

[ -2009-06-16 Beman updated the proposed resolution: -]

- - -
-
    -
  • The mechanism is no longer specified, as requested in Batavia.
    • -
  • The footnote has been removed since it specified mechanism and also did - not reflect existing practice.
    • -
  • A sentence was added that makes it clear that the existing practice is - permitted.
    • -
-
- -

[ -2009-07-15 Beman updated the proposed resolution: -]

- - -

[ -2009-07-17 Beman updated the proposed resolution based on feedback from the LWG in Frankfurt: -]

- - -
-
    -
  • Strike two pieces of text considered unnecessary.
    • -
  • Change "definitions" to "declarations and definitions" in two places.
    • -
  • Wording tightened slightly.
    • -
-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-Revised Proposed Resolution: -

-

-A C++ header may include other C++ headers. A C++ header shall provide -the declarations and definitions that appear in its synopsis (3.2 -[basic.def.odr]). A C++ header shown in its synopsis as including other -C++ headers shall provide the declarations and definitions that appear -in the synopses of those other headers. -

-

-Alisdair: Does this address the BSI comment? -

-Beman: There were several overlapping comments. I tried to handle them -all with one resolution. -

-Alisdair: I'd prefer to see this closed as NAD and have this resolution -be the subject of some other, new issue. -

-Move to NAD Concepts. Howard to open a new issue (1178) in Ready state with the -Proposed Resolution above. Beman will write up a discussion for the new -issue. -

-
- - - -

Proposed resolution:

-

Change 17.6.5.2 [res.on.headers], Headers, paragraph 1, as indicated:

- -
- -

-A C++ header may include other C++ -headers.[footnote] A C++ header shall provide -the declarations and definitions that appear in its synopsis -(3.2 [basic.def.odr]). A C++ header shown in its synopsis as including -other C++ headers shall provide the same declarations and definitions as -if those other headers were included. -

- -

[footnote] C++ headers must include a C++ header that contains - any needed definition (3.2).

-
- - - - - - -
-

1002. Provide bulk include headers

-

Section: 17.6.1.2 [headers] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [headers].

-

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-

Discussion:

- -

Addresses UK-170 [CD1]

- -

-One of goals of C++0x is to make language easier to teach and for -'incidental' programmers. The fine-grained headers of the C++ library -are valuable in large scale systems for managing dependencies and -optimising build times, but overcomplicated for simple development and -tutorials. Add additional headers to support the whole library through a -single include statement. -

- -

[ -Batavia (2009-05): -]

- -

-We do not all agree that this is an issue, -but we agree that if it needs solving this is the right way to do it. -Move to Tentatively Ready. -

- -

[ -2009-07-06 Beman notes: -]

- - -
-

-This issue -adds a header <std>. -

-

-There is a paper to be looked at, -N2905 -Aggregation headers, that adds -a header <std-all> that is the same thing except it excludes -deprecated headers. -N2905 -also proposes a second aggregation header. -

-

-Seems like this issue should be held in abeyance until the LWG has had -a chance to look at N2905. -

-
- -

[ -2009-07-06 Howard: I've pulled this issue back to Review. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-No consensus for change. -

- - - -

Proposed resolution:

-

-Insert a new paragraph in 17.6.1.2 [headers] between p4 and p5 -

-

-An additional header <std> shall have the effect of -supplying the entire standard library. [Note: for example, it -might be implemented as a file with an #include statement for each of the -headers listed in tables 13 and 14. -- end note] -

- - - - - -
-

1003. Require more useful headers for freestanding implementations

-

Section: 17.6.1.3 [compliance] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses JP 23 [CD1]

- -

-There is a freestanding implementation including -<type_traits>, <array>, -<ratio>, lately added to Table 13, C++ library headers. -Programmers think them useful and hope that these headers are also added -to Table 15, C++ headers for freestanding implementations, that shows -the set of headers which a freestanding implementation shall include at -least. -

- -

Original proposed resolution

- -

-Add <type_traits>, <array>, -<ratio> to Table 15. -

- -

[ -Summit: -]

- - -
-

- The <array> header has far too many dependencies to require for a -free-standing implementation. -

-

-The <ratio> header would be useful, has no dependencies, but is not -strictly necessary. -

-

-The <type_traits> header is fundamentally a core language facility with a -library interface, so should be supported. -

- -

-(it is anticipated the resolution will come via an update to paper -N2814) -(see also LWG 833) -

-
- -

[ -Batavia (2009-05): -]

- -

-Leave in Review status pending a paper on freestanding implementations -by Martin Tasker. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-Move this to NAD. -

-

-We considered all of the listed headers, and found a compelling case -only for the inclusion of <type_traits> in the list of headers required -of a freestanding implementation. -

-

-See Martin Tasker's paper -Fixing Freestanding -which provides the wording to include <type_traits> into freestanding -implementations. -

-
- - - -

Proposed resolution:

-

-Add <type_traits> to Table 15. -

- - - - - -
-

1005. numeric_limits partial specializations not concept enabled

-

Section: 18.3.2.3 [numeric.limits] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

Discussion:

- -

Addresses JP 26

- -

-numeric_limits [partial specializations] does not use concept. -

- -

[ -Summit: -]

- - -

-Alisdair will provide a solution as part of treatment of axioms and LWG 902. -

- -

[ -Post Summit: -]

- - -

-Alisdair recommends NAD as the partial specializations are already -constrained by requirements on the primary template. -

- -

[ -Batavia (2009-05): -]

- -

-The Working Draft does not in general repeat a primary template's constraints -in any specializations. -Move to NAD. -

- -

[ -2009-05-25 Howard adds: -]

- - -

-A c++std-lib thread starting at c++std-lib-23880 has cast doubt that NAD is the -correct resolution of this issue. Indeed the discussion also casts doubt that -the current proposed wording is the correct resolution as well. Personally I'm -inclined to reset the status to Open. However I'm reverting the status to -that which it had prior to the Batavia recommendation. I'm setting back to Review. -

- - -

Proposed resolution:

-

-Change 18.3.2.3 [numeric.limits]: -

- -
-template<class Regular T> class numeric_limits<const T>;
-template<class Regular T> class numeric_limits<volatile T>;
-template<class Regular T> class numeric_limits<const volatile T>;
-
- - - - - - -
-

1007. throw_with_nested not concept enabled

-

Section: 18.8.6 [except.nested] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses JP 29

- -

-throw_with_nested does not use concept. -

- -

[ -Summit: -]

- - -

-Agreed. -

- - - -

Proposed resolution:

- -

-Alisdair initially proposed wording in -N2619. -

-

-We are awaiting an updated paper based on feedback from the San Francisco -review. -

- - - - - -
-

1008. nested_exception wording unclear

-

Section: 18.8.6 [except.nested] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses JP 31

- -

-It is difficult to understand in which case nested_exception is applied. -

- -

[ -Summit: -]

- - -

-Alisdair will add an example in an update to -N2619. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-It doesn't appear that N2619 really addresses this. Alisdair to propose wording. -

- -

[ -2010 Pittsburgh: -]

- - -

-Mark issue 1008 as NAD, the type is adequately described. -

- - - -

Rationale:

-

-nested_exception is intended to be inherited from by exception classes -that are to be thrown during the handling of another exception, i.e. -when translating from one exception type to another. nested_exception -allows the originally thrown exception to be easily retained in that -scenario. -

- - -

Proposed resolution:

- - - - - -
-

1009. InputIterator post-increment dangerous

-

Section: 24.2.2 [iterator.iterators] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 251

- -

-The post-increment operator is dangerous for a general InputIterator. -The multi-pass guarantees that make it meaningful are defined as part of -the ForwardIterator refinement. Any change will affect only constrained -templates that have not yet been written, so should not break existing -user iterators which remain free to add these operations. This change -will also affect the generalised OutputIterator, although there is no -percieved need for the post-increment operator in this case either. -

- -

[ -2009-07-28 Alisdair adds: -]

- - -

-We still think the issue is relevant, but needs totally rewording in -non-concept language. We would like to see the issue retained as Open, -rather than deferred as NAD Concepts. Review status is no longer -appropriate. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD. Without concepts we do not feel that input iterator post increment -is broken. -

- - - -

Proposed resolution:

-

-Change 24.2.2 [iterator.iterators]: -

- -
-concept Iterator<typename X> : Semiregular<X> { 
-  MoveConstructible reference = typename X::reference; 
-  MoveConstructible postincrement_result;
-
-  requires HasDereference<postincrement_result>;
-
-  reference operator*(X&&); 
-  X& operator++(X&); 
-  postincrement_result operator++(X&, int);
-}
-
- -

...

-
-postincrement_result operator++(X& r, int);
-
- -

--3- Effects: equivalent to { X tmp = r; ++r; return tmp; }. -

- -
- -

-Change 24.2.3 [input.iterators]: -

- -
-
-concept InputIterator<typename X> : Iterator<X>, EqualityComparable<X> { 
-  ObjectType value_type = typename X::value_type; 
-  MoveConstructible pointer = typename X::pointer; 
-
-  SignedIntegralLike difference_type = typename X::difference_type; 
-
-  requires IntegralType<difference_type> 
-        && Convertible<reference, const value_type &>; 
-        && Convertible<pointer, const value_type*>; 
-
-  requires Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;
-
-  pointer operator->(const X&); 
-}
-
-
- -

-Change 24.2.4 [output.iterators]: -

- -
-
-auto concept OutputIterator<typename X, typename Value> { 
-  requires Iterator<X>; 
-
-  typename reference = Iterator<X>::reference; 
-  typename postincrement_result = Iterator<X>::postincrement_result;
-  requires SameType<reference, Iterator<X>::reference> 
-        && SameType<postincrement_result, Iterator<X>::postincrement_result>
-        && Convertible<postincrement_result, const X&>
-        && HasAssign<reference, Value> 
-        && HasAssign<HasDereference<postincrement_result>::result_type, Value>;
-}
-
-
- -

-Change 24.2.5 [forward.iterators]: -

- -

[ -See 1084 which is attempting to change this same area in a compatible -way. -]

- - -
-
-concept ForwardIterator<typename X> : InputIterator<X>, Regular<X> { 
-  requires Convertible<postincrement_result, const X&>;
-
-  MoveConstructible postincrement_result;
-  requires HasDereference<postincrement_result>
-        && Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;
-
-  postincrement_result operator++(X&, int);
-
-  axiom MultiPass(X a, X b) { 
-    if (a == b) *a == *b; 
-    if (a == b) ++a == ++b; 
-  } 
-}
-
- -
-

-4- ...

-
- -
-postincrement_result operator++(X& r, int);
-
- -
-

--5- Effects: equivalent to { X tmp = r; ++r; return tmp; }. -

-
- -
- - - - - - -
-

1010. operator-= should use default in concept

-

Section: 24.2.7 [random.access.iterators] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 263

- -

-This requirement on operator-= would be better expressed as a default -implementation in the concept, with a matching axiom. -

- -

[ -Batavia (2009-05): -]

- -

-The proposed resolution should also remove -paragraph 5 and the declaration that precedes it. -Further, we should provide an axiom -that captures the desired semantics. -This may be a broader policy to be applied. -Move to Open. -

- - -

Proposed resolution:

-

-Change 24.2.7 [random.access.iterators]: -

- -
-concept RandomAccessIterator<typename X> : BidirectionalIterator<X>, LessThanComparable<X> {
-  ...
-  X& operator-=(X& x, difference_type n) { return x += -n; }
-  ...
-}
-
- - - - - - -
-

1013. Remove IsSameType hold-over constraints

-

Section: 25.4.7 [alg.min.max] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 305

- -

-The negative requirement on IsSameType is a hold-over from an earlier -draught with a variadic template form of min/max algorith. It is no -longer necessary. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-We believe this is NAD, but this needs to be reviewed against the -post-remove-concepts draft. -

- - - -

Proposed resolution:

-

-Change 25 [algorithms]: -

- -
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  const T& min(const T& a, const T& b, Compare comp);
-...
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  const T& max(const T& a, const T& b, Compare comp);
-...
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
-
- -

-Change 25.4.7 [alg.min.max], p1, p9 and p17: -

- -
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  const T& min(const T& a, const T& b, Compare comp);
-...
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  const T& max(const T& a, const T& b, Compare comp);
-...
-template<class T, StrictWeakOrder<auto, T> Compare>
-  requires !SameType<T, Compare> && CopyConstructible<Compare>
-  pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
-
- - - - - - -
-

1015. C++ programs - but not users - need to provide support concept_maps

-

Section: X [concept.transform] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 199

- -

-The requirement that programs do not supply concept_maps should -probably be users do not supply their own concept_map -specializations. The program will almost certainly supply -concept_maps - the standard itself supplies a specialization -for RvalueOf references. Note that the term program is -defined in 3.5 [basic.link]p1 and makes no account of the -standard library being treated differently to user written code. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -
-

-The same problem is present in the words added for the -LvalueReference/RvalueReference concepts last meeting. -

-

-With three subsections requiring the same constraint, I'm wondering if there -is a better way to organise this section. -Possible 20.2.1 -> 20.2.3 belong in the fundamental concepts clause in - [concept.support]? While they can be implemented purely as a -library feature without additional compiler support, they are pretty -fundamental and we want the same restriction on user-concept maps as is -mandated there. -

-
- -

[ -Batavia (2009-05): -]

- -

-We agree with the issue, -but believe the wording needs further improvement. -We want to investigate current definitions for nomenclature such as -"user" and "program." -Move to Open pending the recommended investigation. -

- - -

Proposed resolution:

-

-Change X [concept.transform] p2: -

- -

--2- A program user shall not provide concept maps for -any concept in 20.1.1. -

- -

-Change [concept.true] p2: -

- -

--2- Requires: a program user shall not -provide a concept map for the True concept. -

- -

-Change [concept.classify] p2: -

- -

--2- Requires: a programuser shall not provide concept -maps for any concept in this section. -

- - - - - - -
-

1016. Provide LessThanComparable and EqualityComparable for FloatingPointType

-

Section: X [concept.comparison] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses JP 33

- -

-LessThanComparable and EqualityComparable don't correspond to NaN. -

- -

Original proposed resolution:

- -

-Apply concept_map to these concepts at FloatingPointType. -

- -

[ -Post Summit, Alisdair adds: -]

- - -
-

-I don't understand the proposed resolution - there is no such thing as a -'negative' concept_map, and these concepts are auto concepts that match -float/double etc. Also not clear how we are supposed to match values to -concepts. -

-

-Recommend NAD and treat as a subset of issue 902. -

-
- - - -

Proposed resolution:

-

-Recommend NAD. -

- - - - - -
-

1017. Floating-point types should not satisfy Regular

-

Section: X [concept.regular] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

Discussion:

- -

Addresses US 66

- -

-Application of the Regular concept to floating-point types appears to be -controversial (see long discussion on std-lib reflector). -

- -

Original proposed resolution:

- -

-State that the Regular concept does not apply to floating-point types. -

- -

[ -Summit: -]

- - -
-

-Recommend that we handle the same as JP 33 / 1016. -

-
- -

[ -Post Summit, Alisdair adds: -]

- - -
-

-Recommend Open, and review after resolution of 902 and revised axiom -feature. -

-
- - - -

Proposed resolution:

- - - - - -
-

1018. Trait specifications should be expressed in terms of concepts

-

Section: 20.10 [meta] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses US 70 [CD1]

- -

-Specifications now expressed via narrative text are more accurately and -clearly expressed via executable code. -

-

-Wherever concepts are available that directly match this section's type -traits, express the traits in terms of the concepts instead of via -narrative text. Where the type traits do not quite match the -corresponding concepts, bring the two into alignment so as to avoid two -nearly-identical notions. -

- -

[ -Summit: -]

- - -
-

-We think that this is a good idea, but it requires a lot of work. If someone -submits a paper proposing specific changes, we would be happy to review it -at the next meeting. -

-
- - - -

Proposed resolution:

- - - - - -
-

1020. Restore aligned_union

-

Section: 20.10.7.6 [meta.trans.other] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses UK 204 [CD1]

- -

-It is not possible to create a variant union based on a parameter pack -expansion, e.g. to implement a classic discriminated union template. -

- -

Original proposed resolutuion:

- -

-Restore aligned_union template that was removed by LWG issue 856. -

- -

[ -Summit: -]

- - -

-Agree. The need for aligned_union is compelling enough to reinstate. -

- -

[ -Post Summit, Alisdair adds: -]

- - -

-Paper -N2843 -proposes an extension to the [[align]] attribute -that further diminishes the need for this template. Recommend NAD. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark NAD as suggested. -

- - - -

Proposed resolution:

- - - - - -
-

1022. Pointer-safety API has nothing to do with smart pointers

-

Section: 20.7.4 [util.dynamic.safety] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 212 [CD1]

- -

-The pointer-safety API is nothing to do with smart pointers, so does not -belong in 20.8.2 [util.smartptr]. In fact it is a set of language -support features are really belongs in clause 18 [language.support], -with the contents declared in a header that deals with language-support -of memory management. -

- -

[ -Summit: -]

- - -

-Agree in principle, but not with the proposed resolution. We believe it -belongs either a subsection of either 20 [utilities] or -20.7 [memory] as part of the general reorganization of -20 [utilities]. The declaration should stay in <memory>. -

- - - -

Proposed resolution:

- - - - - -
-

1023. Unclear inheritance relation for std::function

-

Section: 20.9.12.2 [func.wrap.func] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses DE 22 [CD1]

- -

Related to issue 1114.

- -

-The conditions for deriving from std::unary_function and -std::binary_function are unclear: The condition would also be satisfied if -ArgTypes were std::vector<T1>, because it (arguably) -"contains" T1. -

- -

[ -Summit: -]

- - -

-Agree. std::reference_wrapper has the same structure, and we -suggest that std::function be presented in the same way as -std::reference_wrapper. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -

-Phrasing should be "publicly and unambiguously derived from" and probably back in -reference_wrapper too. Updated wording supplied. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed wording. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

-(no changes to <functional> synopsis required) -

- -

-Change synopsis in Class template function 20.9.12.2 [func.wrap.func]: -

- -
-template<Returnable R, CopyConstructible... ArgTypes> 
-class function<R(ArgTypes...)> 
-  : public unary_function<T1, R>      // iff sizeof...(ArgTypes) == 1 and see below
-                                      // ArgTypes contains T1
-  : public binary_function<T1, T2, R> // iff sizeof...(ArgTypes) == 2 and see below
-                                      // ArgTypes contains T1 and T2
-{
-   ...
-
- -

-Add new p1/p2 before 20.9.12.2.1 [func.wrap.func.con]: -

- -
-

-The template instantiation function<R(T1)> shall be publicly and -unambiguously derived from -std::unary_function<T1,R> if and only if the template type parameter -is a function type taking one argument of type T1 and returning R. -

- -

-The template instantiation function<R(T1,T2)> shall be publicly and -unambiguously derived from -std::binary_function<T1,T2,R> if and only if the template type -parameter is a function type taking two arguments of type T1 and T2 and -returning R. -

- -
-explicit function();
-
-
- - - - - - -
-

1024. std::function constructors overly generous

-

Section: 20.9.12.2 [func.wrap.func] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses JP 39 [CD1]

- -

-There are no requires corresponding to F of std::function. -

- -

[ -2009-05-01 Daniel adds: -]

- - -

-1070 removes the second constructor. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -If issue 1070 is accepted, -the changes to the second constructor -in this issue are moot. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Constructors have no definition. -

- - - -

Proposed resolution:

-

-Correct as follows in 20.9.12.2 [func.wrap.func] (class definition) -

- -
- template<class F, Allocator Alloc>
-   requires ConstructibleWithAllocator<F, Alloc>
-     && call=Callable<F, ArgTypes...>
-     && Convertible<call::result_type, R>
-   function(allocator_arg_t, const Alloc&, F);
- template<class F, Allocator Alloc>
-   requires ConstructibleWithAllocator<F,Alloc>
-     && call=Callable<F, ArgTypes...>
-     && Convertible<call::result_type, R>
-   function(allocator_arg_t, const Alloc&, F&&);
-
- - - - - - -
-

1026. Smart pointers need to be concept-constrained templates

-

Section: 20.7 [memory] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 209 [CD1]

- -

-Smart pointers cannot be used in constrained templates. -

- -

[ -Summit: -]

- - -

-We look forward to a paper on this topic. We recommend no action until a -paper is available. We understand that a paper is forthcoming. -

- -

[ -Peter Dimov adds: -]

- - -

-shared_ptr<T> and weak_ptr<T> support all -types T for which T* is valid. In other words, a -possible (partial) resolution is to change class T to -PointeeType T for shared_ptr, weak_ptr and -possibly enable_shared_from_this. -

- - - -

Proposed resolution:

- - - - - -
-

1027. std::allocator needs to be a concept-constrained template

-

Section: 20.7.9 [default.allocator] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 213 [CD1]

- -

-std::allocator should be constrained to simplify its use on constrained -contexts. This library component models allocation from free store via the -new operator so choose constraints to -match. The Allocator concept allows for a wider variety of allocators that -users may choose to supply if their allocation model does not require -operator new, without impacting the -requirements of this template. -

- -

-Suggested direction: -

-

-The primary allocator template should be constrained to require -ObjectType<T> and FreeStoreAllocatable<T>. -Further operations to be constrained as required. -

- -

[ -Summit: -]

- - -

-Agree as stated. A future paper will address additional related issues. -

- - - -

Proposed resolution:

- - - - - -
-

1028. raw_storage_iterator needs to be a concept-constrained template

-

Section: 20.7.10 [storage.iterator] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 214 [CD1]

- -

-raw_storage_iterator needs constraining as an iterator adaptor to be safely -used in constrained templates -

- -

[ -Summit: -]

- - -

-We look forward to a paper on this topic. We recommend no action until a -paper is available. -

- -

[ -Post Summit Alisdair provided wording and rationale. -]

- - - - -

Proposed resolution:

-

-20.7 [memory] p2 -

-

-Update the synopsis for <memory> -

-
-// 20.7.8, raw storage iterator:
-template <class ForwardIterator OutputIterator, class ObjectType T> 
-  requires OutputIterator< OutIter, T >
-    class raw_storage_iterator;
-
-template <ForwardIterator OutIter, ObjectType T> 
-  requires OutputIterator< OutIter, T >
-  concept_map Iterator<raw_storage_iterator< OutIter, T > > { }
-
- - -

-20.7.10 [storage.iterator] p1 -

-

-Replace class template definition with: -

-
-namespace std { 
-  template <class ForwardIterator OutputIterator, class ObjectType T> 
-    requires OutputIterator< OutIter, T >
-  class raw_storage_iterator 
-    : public iterator<output_iterator_tag,void,void,void,void> { 
-  public: 
-    explicit raw_storage_iterator(OutputIterator x); 
-
-    raw_storage_iterator<OutputIterator,T>& operator*(); 
-    raw_storage_iterator<OutputIterator,T>& operator=(const T& element); 
-    raw_storage_iterator<OutputIterator,T>& operator++(); 
-    raw_storage_iterator<OutputIterator,T> operator++(int); 
-  }; 
-
-  template <ForwardIterator OutIter, ObjectType T> 
-    requires OutputIterator< OutIter, T >
-    concept_map Iterator<raw_storage_iterator< OutIter, T > > { }
-}
-
- - -

Rationale:

-

-raw_storage_iterator has to adapt a ForwardIterator, -rather than just an InputIterator for two reasons: -

- -
    -
  1. -The initial iterator passed by value is expected to remain valid, -pointing to the initialized region of memory. -
    2. -
  2. -to avoid breaking the declaration of post-increment operator which would -require some kind of proxy formulation to support generalised InputIterators. -
    3. -
- - - - - - -
-

1029. Specialized algorithms for memory management need to be concept-constrained templates

-

Section: 20.7.12 [specialized.algorithms] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 210 [CD1]

- -

Related to 582

- -

-Specialized algorithms for memory management need requirements to be -easily usable in constrained templates. -

- -

[ -Summit: -]

- - -

-We look forward to a paper on this topic. We recommend no action until a -paper is available. -

- -

[ -Post Summit Alisdair provided wording. -]

- - -

[ -Post Summit: -]

- - -
-

-Daniel adds: -

- -
-
    -
  1. -I suggest Size should require IntegralLike and not UnsignedIntegralLike, -because otherwise simple int-literals could not be provided as arguments -and it would conflict with other algorithms that only require IntegralLike. -
    2. -
  2. -

    -The current for-loop-test relies on evaluation in boolean context which is -not provided by ArithmeticLike and it's refinements. I propose to change the -corresponding for-loop-headers to: -

    -
      -
    1. -for uninitialized_copy_n: for ( ; n > Size(0); ++result, ++first, --n) { -
      2. -
    2. -for uninitialized_fill_n: for (; n > Size(0); ++first, --n) { -
      3. -
    -
    3. -
-
- -

-Alisdair adds: -

-

-For the record I agree with Daniel's suggestion. -

- -
- - - -

Proposed resolution:

-

-20.7 [memory] p2 -

-

-Update the synopsis for <memory> -

-
-template <class InputIterator InIter,
-         class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
-   requires ForwardIterator<OutIter>
-   ForwardIterator OutIter
-   uninitialized_copy(InputIterator InIter first, InputIterator InIter last, 
-                      ForwardIterator OutIter result);
-
-template <class InputIterator InIter,
-          class IntegralLike Size,
-          class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
-  requires ForwardIterator<OutIter>
-  ForwardIterator OutIter
-  uninitialized_copy_n(InputIterator InIter first, Size n, 
-                       ForwardIterator OutIter result);
-
-template <class ForwardIterator Iter, class ObjectType T>
-  requires Constructible< Iter::value_type, const T& >
-  void uninitialized_fill(ForwardIterator Iter first, ForwardIterator Iter last, 
-                          const T& x);
-
-template <class ForwardIterator Iter, class IntegralLike Size, class ObjectType T> 
-  requires Constructible< Iter::value_type, const T& >
-  void
-  uninitialized_fill_n(ForwardIterator Iter first, Size n, const T& x);
-
- -

-Update as follows: -

- -

-uninitialized_copy 20.7.12.2 [uninitialized.copy] -

- -
-template <class InputIterator InIter,
-         class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
-   requires ForwardIterator<OutIter>
-   ForwardIterator OutIter
-   uninitialized_copy(InputIterator InIter first, InputIterator InIter last, 
-                      ForwardIterator OutIter result);
-
- -
-

--1- Effects: -

-
-for (; first != last; ++result, ++first)  {
-   new (static_cast<void*>(&*result))
-       typename iterator_traits<ForwardIterator> OutIter::value_type(*first);
-}
-
- -

--2- Returns: result -

- -
- -
-template <class InputIterator InIter,
-          class IntegralLike Size,
-          class ForwardIterator OutputIterator<auto, InIter::reference> OutIter> 
-  requires ForwardIterator<OutIter>
-  ForwardIterator OutIter
-  uninitialized_copy_n(InputIterator InIter first, Size n, 
-                       ForwardIterator OutIter result);
-
- -
-

--3- Effects: -

-
-for ( ; n > Size(0); ++result, ++first, --n) {
-   new (static_cast<void*>(&*result))
-       typename iterator_traits<ForwardIterator> OutIter::value_type(*first);
-}
-
-

--4- Returns: result -

-
- -
- - -

-uninitialized_fill 20.7.12.3 [uninitialized.fill] -

- -
-template <class ForwardIterator Iter, class ObjectType T>
-  requires Constructible< Iter::value_type, const T& >
-  void uninitialized_fill(ForwardIterator Iter first, ForwardIterator Iter last, 
-                          const T& x);
-
- -
-

--1- Effects: -

-
-for (; first != last; ++first) {
-   new ( static_cast<void*>( &*first) ) 
-       typename iterator_traits<ForwardIterator> Iter::value_type(x);
-}
-
-
-
- - -

-uninitialized_fill_n 20.7.12.4 [uninitialized.fill.n] -

- -
-template <class ForwardIterator Iter, class IntegralLike Size, class ObjectType T> 
-  requires Constructible< Iter::value_type, const T& >
-  void
-  uninitialized_fill_n(ForwardIterator Iter first, Size n, const T& x);
-
- -
-

--1- Effects: -

-
-for (; n-- > Size(0); ++first, --n) {
-   new ( static_cast<void*>( &*first) ) 
-       typename iterator_traits<ForwardIterator> Iter::value_type(x);
-}
-
-
-
- - - - - - -
-

1032. Tome utility templates need to be concept-constrained

-

Section: 20.12 [time] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses JP 45 [CD1]

- -

-Rep, Period, Clock and Duration -don't correspond to concept. -

-
-template <class Rep, class Period = ratio<1>> class duration; 
-template <class Clock, class Duration = typename Clock::duration> class time_point; 
-
-

-Make concept for Rep, Period, Clock and Duration. -Fix 20.12 [time] and wait_until -and wait_for's template parameter at 30 [thread]. -

- -

[ -Summit: -]

- - -

-We agree that this section needs concepts. We look forward to a paper on -this topic. We recommend no action until a paper is available. -

- - - -

Proposed resolution:

- - - - - -
-

1035. <array>::swap can invalidate references, pointers, and iterators

-

Section: 23.2.1 [container.requirements.general] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses UK 226 [CD1]

- -

-<array> must be added to this list. In particular it -doesn't satisfy: - no swap() function invalidates any -references, pointers, or iterators referring to the elements of the -containers being swapped. and probably doesn't satisfy: - no -swap() function throws an exception. -

-

-If <array> remains a container, this will have to also -reference array, which will then have to say which of these -points it satisfies. -

- -

[ -Summit: -]

- - -

-Agree. The proposed resolution is incomplete. Further work required. -

- -

[ -2009-05-01 Daniel adds: -]

- - -

-Issue 1099 also suggests adding move constructor to this. -

- -

[ -2009-07 post-Frankfurt: -]

- - -

-Howard is to draft a note that explains what happens to references. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. No consensus for change. -

- - - -

[ -2009-08-01 Howard provided wording. -]

- - -

Proposed resolution:

-

-Add a paragraph to 23.3.2.3 [array.special]: -

- -
-template <Swappable T, size_t N> void swap(array<T,N>& x, array<T,N>& y);
-
-
-

-Effects: -

-
-swap_ranges(x.begin(), x.end(), y.begin());
-
- -

-[Note: -Outstanding iterators, references and pointers may be invalidated. -— end note] -

-
-
- - - - - -
-

1036. Remove iterator specification that is redundant due to concept constraints

-

Section: 23.2.3 [sequence.reqmts] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 231 [CD1]

- -

-p9-p11 are redundant now that Concepts define what it means to be an -Iterator and guide overload resolution accordingly. -

- -

[ -Summit: -]

- - -

-Agree with issue and change to 23.2.3 [sequence.reqmts]. The -changes required to 21 [strings] will be part of the general -concept support for that clause. -

- - - -

Proposed resolution:

-

-Strike 23.2.3 [sequence.reqmts]p9-11. Make sure std::basic_string -has constraints similar to -std::vector to meet this old guarantee. -

- - - - - -
-

1042. Provide ContiguousStorage concept and apply it to corresponding containers

-

Section: 23.3 [sequences] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 244 [CD1]

- -

-The validity of the expression &a[n] == &a[0] + n is contingent on -operator& doing the "right thing" (as captured by the CopyConstructible -requirements in table 30 in C++2003). However this constraint has been -lost in the Concepts of C++0x. This applies to vector and array (it -actually applies to string also, but that's a different chapter, so I'll -file a separate comment there and cross-reference). -

- -

-Suggested solution: -

- -

-Define a ContiguousStorage and apply it to -vector, array and string. -

- -

[ -Summit: -]

- - -

-Agree with the issue but not the details of the proposed solution. Walter to -provide wording for the new concept. -

- -

[ -Post Summit Alisdair adds: -]

- - -

-Another LWG subgroup wondered if this concept should extend to complex<T>, -and so not be built on the container concept at all? -

- -

[ -2009-07 post-Frankfurt: -]

- - -

-Leave Open, pending a post-Concepts Working Draft. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark issue 1042 as NAD, in rationale state that this was solved by removal of concepts. -

- - - -

Proposed resolution:

-

-Add to <container_concepts> synopsis in [container.concepts] -

- -
-concept< typename C > ContiguousStorageContainer see below;
-
- -

-Add a new section to the end of [container.concepts] -

- -
-

-23.1.6.x ContiguousStorageContainer concept [container.concepts.contiguous] -

- -
-concept ContiguousStorageContainer< typename C >
-  : Container<C>
-{
-  value_type* data(C&);
-
-  axiom Contiguity(C& c, size_type i) {
-    if( i < size(c) ) {
-         addressof( * (data(c) + i) )
-      == addressof( * advance(data(c), i) );
-    }
-  }
-}
-
- -

-The ContiguousStorageContainer concept describes a container whose elements -are allocated in a single region of memory, and are stored sequentially -without intervening padding other than to meet alignment requirements. -For example, the elements may be stored in a -single array of suitable length. -

- -
-value_type * data( C& );
-
- -

-Returns: a pointer to the first element in the region of storage. -Result is unspecified for an empty container. -

- -
- -

-Change 23.3.2 [array] p1: -

- -

--1- The header <array> defines a class template for -storing fixed-size sequences of objects. An array supports -random access iterators. An instance of array<T, N> -stores N elements of type T, so that size() == -N is an invariant. The elements of an array are stored -contiguously, meaning that if a is an -array<T, N> then it obeys the identity &a[n] -== &a[0] + n for all 0 <= n < N -satisfies the concept ContiguousStorageContainer< array<T, -N>>. -

- -

-Add to the synopsis in 23.3.2 [array]: -

- -
-    ...
-    T * data(); 
-    const T * data() const; 
-  };
-
-  template< typename T, size_t N >
-    concept_map ContiguousStorageContainer< array<T, N>> {};
-} 
-
- -

-Change 23.3.6 [vector] p1: -

- -

-A vector is a sequence container that supports random access -iterators. In addition, it supports (amortized) constant time insert and -erase operations at the end; insert and erase in the middle take linear -time. Storage management is handled automatically, though hints can be -given to improve efficiency. The elements of a vector are stored -contiguously, meaning that if v is a -vector<T, Alloc> (where T is some -type other than bool), then it obeys the -identity &v[n] == &v[0] + n for all 0 <= n < -v.size() satisfies the concept ContiguousStorageContainer< -vector< T, Alloc>>. -

- -

-Add at the end of the synopsis in 23.3.6 [vector] p2: -

- -
-template< typename T, typename A >
-  requires !SameType< T, bool >
-  concept_map ContiguousStorageContainer< vector<T, A>> {};
-
- - - -

Rationale:

-

Solved by removal of concepts.

- - - - - -
-

1051. Specify subscript operation return types of reverse_iterator and move_iterator

-

Section: 24.5.1.3.12 [reverse.iter.opindex], 24.5.3.3.12 [move.iter.op.index] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 279 [CD1]

- -

-The reason the return type became unspecified is LWG issue 386. This -reasoning no longer applies as there are at least two ways to get the right -return type with the new language facilities added since the previous -standard. -

- -

-Proposal: Specify the return type using either decltype or the Iter concept_map. -

- -

[ -Summit: -]

- - -
-

-Under discussion. This is a general question about all iterator -adapters. -

-
- -

[ -Howard adds post Summit: -]

- - -

-I am requesting test cases to demonstrate a position. -

- -

[ -2009-07-24 Daniel adds: -]

- - -
-

-I recommend NAD. Without concepts we can no longer -restrict this member in a trivial way. Using decltype the -declaration would be along the lines of -

-
-static const Iter& __base(); // not defined
-auto operator[](difference_type n) const -> decltype(__base()[-n-1]);
-
- -

-but once reverse_iterator is instantiated for some given type -Iter which cannot form a well-formed expression __base()[-n-1] -this would cause an ill-formed function declaration, diagnostic -required, and no silent SFINAE elimination. -

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to NAD. -

- -

[ -2009-10-22 Daniel adds: -]

- - -
-

-IMO, my original comment regarding ill-formedness of the described -construction is still correct, but I must add that I should weaken my -assertion "Without concepts we can no longer restrict this member in -a trivial way". -

- -

-In fact with the existence of default template arguments for function -templates it is not too hard to implement this like as follows, which -shows that we can indeed simulate to some sense constrained -member functions in C++0x. -

- -

-My example does not really proof that the specification is easy, but -it should be possible. I assume that the implementation would not -be ABI compatible, though. -

- -

-It is now your own decision how to proceed ;-) -

- -
-#include <type_traits>
-#include <cstddef>
-
-template<class T>
-typename std::add_rvalue_reference<T>::type declval();
-
-template<class It>
-struct reverse_iterator {
-    It base;
-    
-    typedef std::ptrdiff_t difference_type;
-    
-    template<class U = It, class Res =
-     decltype(declval<const U&>()[declval<difference_type>()])
-    >
-    Res operator[](difference_type n) const  {
-        return base[-n-1];
-    }    
-};
-
-struct MyIter {
-};
-
-int main() {
-    reverse_iterator<int*> ri;
-    ri[0] = 2;
-    reverse_iterator<MyIter> ri2;
-}
-
- -

-The above declaration could be simplified, but the ideal solution -

- -
-template<class U = It>
-  decltype(declval<const U&>()[declval<difference_type>()])
-     operator[](difference_type n) const;
-
- -

-does not work yet on gcc 4.4.1. -

- -
- - - - -

Proposed resolution:

- - - - - -
-

1056. Must all Engines and Distributions be Streamable?

-

Section: 26.5 [rand] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [rand].

-

View all issues with NAD status.

-

Discussion:

- -

-Both the concepts RandomNumberEngine and RandomNumberDistribution have -requirements to be InputStreamable and OutputStreamable. -

-

-I have no problems leaving the WP in an inconsistent state on the best-faith -assumption these concepts will be provided later, however disagree with the -proposers that these constraints are not separable, orthogonal to the basic -concepts of generating random number distributions. -

-

-These constraints should be dropped, and applied to specific algorithms as -needed. -

-

-If a more refined concept (certainly deemed useful by the proposers) is -proposed there is no objection, but the basic concept should not require -persistence via streaming. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open. -

- -

[ -2009-05-31 Alisdair adds: -]

- - -
-

-Working on constraining the stream iterators, I have a few more observations -to make on the concepts proposed while constraining the random number -facility. -

-

-While I still believe the concerns are orthogonal, I don't believe the -existing constraints go far enough either! The goal we want to achieve is -not that a RandomNumberEngine / RandomNumberDistribution supports the stream -operators, but that it is Serializable. I.e. there is a relationship -between the insert and extract operations that guarantees to restore the -state of the original object. This implies a coupling of the concepts -together in a broader concept (Serializable) with at least one axiom to -assert the semantics. -

-

-One problem is that istream and ostream may be fundamentally different -types, although we can hook a relation if we are prepared to drop down to -the char type and char_traits template parameters. Doing so ties us to a -form of serialization that demands implementation via the std iostreams -framework, which seems overly prescriptive. I believe the goal is generally -to support serialization without regard to how it is expressed - although -this is getting even more inventive in terms of concepts we do not have -today. -

-
- -

[ -2009-11-03 Alisdair adds: -]

- - -
-

-I can't find the record in the wiki minutes, but it was agreed at both -Frankfurt and Santa Cruz that this issue is NAD. -

-

-The agreement in SC was that I would provide you with the rationale (see -below) to include when moving to NAD. -

-
- -

[ -2009-11-03 Howard adds: -]

- - -

-Moved to Tentatively NAD after 5 positive votes on c++std-lib. -

- - -

Proposed resolution:

- - -

Rationale:

-

-The issue suggests a more refined concept should be used if we want to -require streaming, to separate concerns from the basic -RandomNumberEngine behaviour. In Frankfurt it was observed -that RandomNumberEngine is that more refined concept, -and the basic concept used in the framework is -UniformRandomNumberGenerator, which it refines. -

- -

-We concur, and expect this to have no repurcussions re-writing this -clause now concepts are removed. -

- - - - - -
-

1057. RandomNumberEngineAdaptor

-

Section: 26.5 [rand] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [rand].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

-The RandomNumberEngineAdaptor concept breaks precedent in the -way the library has been specified by grouping requirements into a -concept that is never actually used in the library. -

-

-This is undoubtedly a very helpful device for documentation, but we are not -comfortable with the precedent - especially as we have rejected national -body comments on the same grounds. -

-

-Suggest either removing the concept, or providing an algorithm/type that -requires this concept in their definition (such as a factory function to -create new engines). -

-

-The preference is to create a single new algorithm and retain the value of -the existing documentation. -

- -

[ -Batavia (2009-05): -]

- -
-

-Walter points out that it is unlikely that any algorithm would ever -require this concept, but that the concept nonetheless is useful as -documentation, and (via concept maps) as a means of checking specific adapters. -

-

-Alisdair disagrees as to the concept's value as documentation. -

-

-Marc points out that the RandomNumberDistribution -is also a concept not used elsewhere in the Standard. -

-

-Pete agrees that a policy of not inventing concepts -that aren't used in the Standard is a good starting point, -but should not be used as a criterion for rejecting a concept. -

-

-Move to Open. -

-
- - -

Proposed resolution:

- - - - - -
-

1058. New container issue

-

Section: 23.2.3 [sequence.reqmts] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with NAD Editorial status.

-

Discussion:

- -

-Sequence containers 23.2.3 [sequence.reqmts]: -

- -

-The return value of new calls added to table 83 are not specified. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to NAD Editorial. -

-
- - -

Proposed resolution:

-

-Add after p6 23.2.3 [sequence.reqmts]: -

- -
-

--6- ... -

-

-The iterator returned from a.insert(p,rv) points to the copy of rv -inserted into a. -

-

-The iterator returned from a.emplace(p, args) points to the new -element constructed from args inserted into a. -

-
- - - - - -
-

1059. Usage of no longer existing FunctionType concept

-

Section: 20.9.12.2 [func.wrap.func] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2009-03-13 Last modified: 2015-04-08

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

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-

Discussion:

-

-Due to a deliberate core language decision, the earlier called -"foundation" concept std::FunctionType had been removed in -N2773 -shortly -before the first "conceptualized" version of the WP -(N2798) -had been -prepared. This caused a break of the library, which already used this -concept in the adapted definition of std::function -(20.9 [function.objects]/2, header <functional> synopsis and -20.9.12.2 [func.wrap.func]). -

-

-A simple fix would be to either (a) make std::function's primary template -unconstrained or to (b) add constraints based on existing (support) concepts. -A more advanced fix would (c) introduce a new library concept. -

-

-The big disadvantage of (a) is, that users can define templates which -cause compiler errors during instantiation time because of under-constrainedness -and would thus violate the basic advantage of constrained -code. -

-

-For (b), the ideal constraints for std::function's template parameter would -be one which excludes everything else but the single provided partial -specialization that matches every "free function" type (i.e. any function -type w/o cv-qualifier-seq and w/o ref-qualifier). -Expressing such a type as as single requirement would be written as -

-
-template<typename T>
-requires ReferentType<T> // Eliminate cv void and function types with cv-qual-seq
-                         //   or ref-qual (depending on core issue #749)
-      && PointeeType<T>  // Eliminate reference types
-      && !ObjectType<T>  // Eliminate object types
-
-

-Just for completeness approach (c), which would make sense, if the -library has more reasons to constrain for free function types: -

-
-auto concept FreeFunctionType<typename T>
-  : ReferentType<T>, PointeeType<T>, MemberPointeeType<T>
-{
-  requires !ObjectType<T>;
-}
-
-

-I mention that approach because I expect that free function types belong -to the most natural type categories for every days coders. Potential -candidates in the library are addressof and class template packaged_task. -

- -

[ -Batavia (2009-05): -]

- -
-

-Alisdair would prefer to have a core-supported FunctionType concept -in order that any future changes be automatically correct -without need for a library solution to catch up; -he points to type traits as a precedent. -Further, he believes that a published concept can't in the future -be changed. -

-

-Bill feels this category of entity would change sufficiently slowly -that he would be willing to take the risk. -

-

-Of the discussed solutions, we tend toward option (c). -We like the idea of having a complete taxonomy of native types, -and perhaps erred in trimming the set. -

-

-We would like to have this issue reviewed by Core and would like -their feedback. Move to Open. -

-
- - -

Proposed resolution:

-
    -
  1. -

    -Change in 20.9 [function.objects]/2, Header <functional> synopsis: -

    -
    -// 20.6.16 polymorphic function wrappers:
-class bad_function_call;
-template<FunctionTypeReferentType F>
-requires PointeeType<F> && !ObjectType<F>
-class function; // undefined
-
    -
    2. -
  2. -

    -Change in 20.9.12.2 [func.wrap.func]: -

    -
    -namespace std {
-template<FunctionTypeReferentType F>
-requires PointeeType<F> && !ObjectType<F>
-class function; // undefined
-
    -
    3. -
- - - - - -
-

1060. Embedded nulls in NTBS

-

Section: 17.5.2.1.4.1 [byte.strings] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-13 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

- -

-Definition of null-terminated sequences allow for embedded nulls. This is -surprising, and probably not supportable with the intended use cases. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the issue, but believe this can be handled editorially. -Move to NAD Editorial. -

- - - -

Proposed resolution:

- - - - - -
-

1061. Bad indexing for tuple access to pair (Editorial?)

-

Section: 20.3.4 [pair.astuple] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-03-13 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

- -

-The definition of get implies that get must return the second element if -given a negative integer. -

- -

[ -Batavia (2009-05): -]

- -

-Move to NAD Editorial. -

- - - -

Proposed resolution:

-

-20.3.4 [pair.astuple] p5: -

- -
-template<int size_t I, class T1, class T2> 
-  requires True<(I < 2)> 
-  const P& get(const pair<T1, T2>&);
-
-
- - - - - - -
-

1062. Missing insert_iterator for stacks/queues

-

Section: 24.5.2 [insert.iterators] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-13 Last modified: 2015-04-08

-

View all other issues in [insert.iterators].

-

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-

Discussion:

- -

-It is odd that we have an iterator to insert into a vector, but not an -iterator to insert into a vector that is adapted as a stack. The standard -container adapters all have a common interface to push and pop so it should -be simple to create an iterator adapter to complete the library support. -

- -

-We should provide an AdaptedContainer concept supporting push and pop -operations. Create a new insert iterator and factory function that inserts -values into the container by calling push. -

- -

[ -Batavia (2009-05): -]

- -
-

-Walter recommends NAD Future. -

-

-Move to Open, and recommend deferring the issue until after the next -Committee Draft is issued. -

-
- -

[ -2009-07-29 Howard moves to Tentatively NAD Future. -]

- - -

-A poll on the LWG reflector voted unanimously to move this issue to Tentatively NAD Future. -

- -

[ -2009 Santa Cruz: -]

- - -

-Moved to NAD. The intent of these adapters are to restrict the interfaces. -

- - - -

Proposed resolution:

- - - - - -
-

1063. 03 iterator compatibilty

-

Section: X [iterator.backward] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-15 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

- -

-Which header must a user #include to obtain the library-supplied -concept_maps declared in this paragraph? -

- -

-This is important information, as existing user code will break if this -header is not included, and we should make a point of mandating this header -is #include-d by library headers likely to make use of it, notably -<algorithm>. See issue 1001 for more details. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the direction of the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-We believe this is NAD Concepts, but this needs to be reviewed against the -post-remove-concepts draft. -

- - -

Proposed resolution:

-

Change [depr.lib.iterator.primitives], Iterator primitives, as -indicated:

- -
-

To simplify the use of iterators and provide backward compatibility with - previous C++ Standard Libraries, - the library provides several classes and functions. Unless otherwise - specified, these classes and functions shall be defined in header <iterator>.

-
-

Change X [iterator.backward], Iterator backward compatibility, as -indicated:

-
-

The library provides concept maps that allow iterators specified with - iterator_traits to interoperate with - algorithms that require iterator concepts. These concept maps shall be - defined in the same header that defines the iterator. [Example:

-
- - - - - -
-

1064. Term "object state" should not refer to classes

-

Section: 17.3 [defns.obj.state] Status: NAD - Submitter: Howard Hinnant Opened: 2009-03-15 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

- -

Addresses UK 152 [CD1]

- -

-Object state is using a definition of object (instance of a class) from -outside the standard, rather than the 'region of storage' definiton in -1.8 [intro.object]p1 -

- -

[ -Summit: -]

- -

-We think we're removing this; See X [func.referenceclosure.cons]. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. This will not affect user or implementer code -

- - - -

Proposed resolution:

-

-

- - - - - -
-

1067. simplified wording for inner_product

-

Section: 26.7 [numeric.ops] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-17 Last modified: 2015-04-08

-

View all other issues in [numeric.ops].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

-One of the motivating examples for introducing requirements-aliases was to -simplify the wording of the inner_product requirements. As the paper -adopting the feature and constrained wording for the library went through in -the same meeting, it was not possible to make the change at the time. The -simpler form should be adopted now though. Similarly, most the other -numerical algorithms can benefit from a minor cleanup. -

-

-Note that in each case, the second more generalised form of the algorithm -does not benefit, as there are already named constraints supplied by the -template type parameters. -

- -

[ -2009-05-02 Daniel adds: -]

- - -
-

-one part of the suggested resolution suggests the removal of the -MoveConstructible<T> requirement from -inner_product. According to 26.7.3 [inner.product] -

- -

-Computes its result by initializing the accumulator acc with the -initial value init -

- -

-this step requires at least MoveConstructible. -

- -

-Therefore I strongly suggest to take this removal back (Note also -that the corresponding overload with a functor argument still has -the same MoveConstructible<T> requirement). -

-
- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution as amended by Daniel's suggestion -to restore MoveConstructible, -reflected in the updated proposed resolution below. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-Change in 26.7 [numeric.ops] and 26.7.2 [accumulate]: -

- -
-template <InputIterator Iter, MoveConstructible T>
- requires add = HasPlus<T, Iter::reference>
-       && HasAssign<T, HasPlus<T, Iter::reference> add::result_type>
- T accumulate(Iter first, Iter last, T init);
-
- -

-Change in 26.7 [numeric.ops] and 26.7.3 [inner.product]: -

- -
-template <InputIterator Iter1, InputIterator Iter2, MoveConstructible T>
-  requires mult = HasMultiply<Iter1::reference, Iter2::reference>
-        && add = HasPlus<T, HasMultiply<Iter1::reference, Iter2::reference> mult::result_type>
-        && HasAssign< 
-             T,
-             HasPlus<T,
-                     HasMultiply<Iter1::reference, Iter2::reference>::result_type> add::result_type>
-  T inner_product(Iter1 first1, Iter1 last1, Iter2 first2, T init);
-
- -

-Change in 26.7 [numeric.ops] and 26.7.4 [partial.sum]: -

- -
-template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter>
-  requires add = HasPlus<InIter::value_type, InIter::reference>
-        && HasAssign<InIter::value_type,
-                     HasPlus<InIter::value_type, InIter::reference> add::result_type>
-        && Constructible<InIter::value_type, InIter::reference>
-  OutIter partial_sum(InIter first, InIter last, OutIter result);
-
- -

-Change in 26.7 [numeric.ops] and 26.7.5 [adjacent.difference]: -

- -
-template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter>
-  requires sub = HasMinus<InIter::value_type, InIter::value_type>
-        && Constructible<InIter::value_type, InIter::reference>
-        && OutputIterator<OutIter, HasMinus<InIter::value_type, InIter::value_type> sub::result_type>
-        && MoveAssignable<InIter::value_type>
-  OutIter adjacent_difference(InIter first, InIter last, OutIter result);
-
- - - - - - -
-

1068. class random_device should be movable

-

Section: 26.5.6 [rand.device] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-18 Last modified: 2015-04-08

-

View all other issues in [rand.device].

-

View all issues with NAD status.

-

Discussion:

- -

-class random_device should be movable. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, and recommend this issue be deferred until after the next -Committee Draft is issued. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Leave open. Walter to provide drafting as part of his planned paper. -

- -

[ -2010 Pittsburgh: Moved to NAD. -]

- - - - -

Rationale:

-

-WP is correct as written. -

- - -

Proposed resolution:

- - - - - -
-

1069. class seed_seq should support efficient move operations

-

Section: 26.5.7.1 [rand.util.seedseq] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-03-18 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with NAD status.

-

Discussion:

- -

-class seed_seq should support efficient move operations. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, and recommend this issue be deferred until after the next -Committee Draft is issued. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Leave open. Walter to provide drafting as part of his planned paper. -

- -

[ -2010 Pittsburgh: -]

- - -

-seed_seq is explicitly not copyable, so, much like LWG issue -1068, LWG issue 1069 could be marked NAD to be consistent -with this. -

- - - -

Proposed resolution:

- - - - - -
-

1072. Is std::hash a constrained template or not?

-

Section: 20.9.13 [unord.hash] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

-Is std::hash a constrained template or not? -

-

-According to class template hash 20.9.13 [unord.hash], the definition is: -

- -
-template <class T>
-struct hash : public std::unary_function<T, std::size_t> {
-  std::size_t operator()(T val) const;
-};
-
- -

-And so unconstrained. -

-

-According to the <functional> synopsis in p2 Function objects -20.9 [function.objects] the template is declared as: -

- -
-template <ReferentType T> struct hash;
-
- -

-which would make hash a constrained template. -

- -

[ -2009-03-22 Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Alisdair is not certain that Daniel's proposed resolution is sufficient, -and recommends we leave the hash template unconstrained for now. -

-

-Recommend that the Project Editor make the constrained declaration consistent -with the definition in order to make the Working Paper internally consistent, -and that the issue then be revisited. -

-

-Move to Open. -

-
- - -

Proposed resolution:

- -

-[To the editor: This resolution is merge-compatible to the -resolution of 1078] -

- -
    -
  1. -

    -In 20.9 [function.objects]/2, header <functional> synopsis, change as indicated: -

    - -
    -// 20.6.17, hash function base template:
-template <ReferentType T> struct hash; // undefined
-
    -
    2. -
  2. -

    -In 20.9.13 [unord.hash]/1 change as indicated: -

    -
    -namespace std {
- template <class T>
- struct hash : public std::unary_function<T, std::size_t> {
- std::size_t operator()(T val) const;
- };
- template <ReferentType T> struct hash; // undefined
-}
-
    -
    3. -
  3. -

    -In 20.9.13 [unord.hash]/2 change as indicated: -

    - -

    --2- For all library-provided specializations, the template -instantiation hash<T> - shall provide a public operator() with return type std::size_t to -satisfy the concept - requirement Callable<const hash<T>, const T&>. If T is an object -type or reference to - object, hash<T> shall be publicly derived from -std::unary_function<T, std::size_t>. - The return value of operator() is unspecified, except that -equal arguments - shall yield the same result. operator() shall not throw exceptions. -

    -
    4. -
  4. -

    -In 18.7 [support.rtti]/1, header <typeinfo> synopsis change as indicated: -

    -
    -namespace std {
-  class type_info;
-  class type_index;
-  template <classReferentType T> struct hash;
-
    -
    5. -
- - - - - -
-

1074. concept map broken by N2840

-

Section: X [allocator.element.concepts] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

- -

-p7 Allocator-related element concepts X [allocator.element.concepts] -

- -

-The changes to the AllocatableElement concept mean this concept_map -specialization no longer matches the original concept: -

- -
-template <Allocator Alloc, class T, class ... Args>
-  requires HasConstructor<T, Args...>
-    concept_map AllocatableElement<Alloc, T, Args&&...> {
-      void construct_element(Alloc& a, T* t, Args&&... args) {
-        Alloc::rebind<T>(a).construct(t, forward(args)...);
-      }
-    }
-
- -

[ -2009-03-23 Pablo adds: -]

- - -

-Actually, this is incorrect, -N2840 -says. "In section -X [allocator.element.concepts] paragraph 8, modify the definition of the -AllocatableElement concept and eliminate the related concept map:" but -then neglects to include the red-lined text of the concept map that was -to be eliminated. Pete also missed this, but I caught it he asked me to -review his edits. Pete's updated WP removes the concept map entirely, -which was the original intent. The issue is, therefore, moot. Note, as -per my presentation of -N2840 -in summit, construct() no longer has a -default implementation. This regrettable fact was deemed (by David -Abrahams, Doug, and myself) to be preferable to the complexity of -providing a default implementation that would not under-constrain a more -restrictive allocator (like the scoped allocators). -

- -

[ -2009-05-01 Daniel adds: -]

- -
-

-it seems to me that #1074 should be resolved as a NAD, because the -current WP has already removed the previous AllocatableElement concept map. -It introduced auto concept AllocatableElement instead, but as of -X [allocator.element.concepts]/7 this guy contains now -

-
-requires FreeStoreAllocatable<T>;
-void Alloc::construct(T*, Args&&...);
-
-
- -

[ -Batavia (2009-05): -]

- -
-

-The affected code is no longer part of the Working Draft. -

-

-Move to NAD. -

-
- - -

Proposed resolution:

-

-Change X [allocator.element.concepts]: -

- -
-template <Allocator Alloc, class T, class ... Args>
-  requires HasConstructor<T, Args...>
-    concept_map AllocatableElement<Alloc, T, Args&&...> {
-      void construct_element(Alloc& a, T* t, Args&&... args) {
-        Alloc::rebind<T>(a).construct(t, forward(args)...);
-      }
-    }
-
- - - - - - -
-

1076. unary/binary_negate need constraining and move support

-

Section: 20.9.9 [negators] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-03-20 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

-The class templates unary/binary_negate need constraining and move support. -

-

-Ideally these classes would be deprecated, allowing unary/binary_function to -also be deprecated. However, until a generic negate adaptor is introduced -that can negate any Callable type, they must be supported so should be -constrained. Likewise, they should be movable, and support adopting a -move-only predicate type. -

-

-In order to preserve ABI compatibility, new rvalue overloads are supplied in -preference to changing the existing pass-by-const-ref to pass-by-value. -

-

-Do not consider the issue of forwarding mutable lvalues at this point, -although remain open to another issue on the topic. -

- -

[ -2009-05-01 Daniel adds: -]

- -
-

-IMO the currently proposed resolution needs some updates -because it is ill-formed at several places: -

- -
    -
  1. -

    -In concept AdaptableUnaryFunction change -

    -
    -typename X::result_type;
-typename X::argument_type;
-
    -

    -to -

    -
    -Returnable result_type = typename X::result_type;
-typename argument_type = typename X::argument_type;
-
    -

    -[The replacement "Returnable result_type" instead of "typename -result_type" is non-editorial, but maybe you prefer that as well] -

    -
    2. -
  2. -

    -In concept AdaptableBinaryFunction change -

    -
    -typename X::result_type;
-typename X::first_argument_type;
-typename X::second_argument_type;
-
    -

    -to -

    -
    -Returnable result_type = typename X::result_type;
-typename first_argument_type = typename X::first_argument_type;
-typename second_argument_type = typename X::second_argument_type;
-
    -

    -[The replacement "Returnable result_type" instead of "typename -result_type" is non-editorial, but maybe you prefer that as well.] -

    -
    3. - -
  3. -

    -In class unary/binary_function -

    -
      -
    1. -I suggest to change "ReturnType" to "Returnable" in both cases. -
      2. -
    2. -I think you want to replace the remaining occurrences of "Predicate" by "P" -(in both classes in copy/move from a predicate) -
      3. -
    -
    4. -
  4. -

    -I think you need to change the proposed signatures of not1 and not2, because -they would still remain unconstrained: To make them constrained at least a -single requirement needs to be added to enable requirement implication. This -could be done via a dummy ("requires True<true>") or just explicit as follows: -

    -
      -
    1. -
      -template <AdaptableUnaryFunction P>
-requires Predicate< P, P::argument_type>
-unary_negate<P> not1(const P&& pred);
-template <AdaptableUnaryFunction P>
-requires Predicate< P, P::argument_type >
-unary_negate<P> not1(P&& pred);
-
      -

      --3- Returns: unary_negate<P>(pred). -

      -
      -

      -[Don't we want a move call for the second overload as in -

      -
      -unary_negate<P>(std::move(pred))
-
      -

      -in the Returns clause ?] -

      -
      2. -
    2. -
      -template <AdaptableBinaryFunction P>
-requires Predicate< P, P::first_argument_type, P::second_argument_type >
-binary_negate<P> not2(const P& pred);
-template <AdaptableBinaryFunction P>
-requires Predicate< P, P::first_argument_type, P::second_argument_type >
-binary_negate<P> not2(P&& pred);
-
      -

      --5- Returns: binary_negate<P>(pred). -

      -

      -[Don't we want a move call for the second overload as in -

      -
      -binary_negate<P>(std::move(pred))
-
      -

      -in the Returns clause ?] -

      -
      3. -
    -
    5. -
-
- -

[ -Batavia (2009-05): -]

- -
-

-There is concern that complicating the solution -to preserve the ABI seems unnecessary, -since we're not in general preserving the ABI. -

-

-We would prefer a separate paper consolidating all Clause 20 -issues that are for the purpose of providing constrained versions -of the existing facilities. -

-

-Move to Open. -

-
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Leave open pending the potential move constructor paper. Note that -we consider the "constraining" part NAD Concepts. -

- -

[ -2010-01-31 Alisdair removes the current proposed wording from the proposed -wording section because it is based on concepts. That wording is proposed here: -]

- - -
-

-Add new concepts where appropriate:: -

- -
-auto concept AdaptableUnaryFunction< typename X > {
-  typename X::result_type;
-  typename X::argument_type;
-}
-
-auto concept AdaptableBinaryFunction< typename X > {
-  typename X::result_type;
-  typename X::first_argument_type;
-  typename X::second_argument_type;
-}
-
- -

-Revise as follows: -

- -

-Base [base] (Only change is constrained Result) -

- -
-

--1- The following classes are provided to simplify the typedefs of the -argument and result types: -

-
-namespace std {
-  template <class Arg, class ReturnType Result>
-  struct unary_function {
-     typedef Arg    argument_type;
-     typedef Result result_type;
-  };
-
-  template <class Arg1, class Arg2, class ReturnType Result>
-  struct binary_function {
-     typedef Arg1   first_argument_type;
-     typedef Arg2   second_argument_type;
-     typedef Result result_type;
-  };
-}
-
- -

-Negators 20.9.9 [negators]: -

- -
-

--1- Negators not1 and not2 take a unary and a binary predicate, -respectively, and return their complements (5.3.1). -

- -
-template <class AdaptableUnaryFunction Predicate>
-  requires Predicate< P, P::argument_type >
-  class unary_negate
-    : public unary_function<typename Predicate::argument_type,bool> {
-  public:
-    unary_negate(const unary_negate & ) = default;
-    unary_negate(unary_negate && );
-
-    requires CopyConstructible< P >
-       explicit unary_negate(const Predicate& pred); 
-    requires MoveConstructible< P >
-       explicit unary_negate(Predicate && pred);
-
-    bool operator()(const typename Predicate::argument_type& x) const;
-  };
-
-

--2 operator() returns !pred(x). -

- -
-template <class Predicate>
-  unary_negate<Predicate> not1(const Predicate&amp; pred);
-template <class Predicate>
-  unary_negate<Predicate> not1(Predicate&& pred);
-
-

--3- Returns: unary_negate<Predicate>(pred). -

- -
-template <class AdaptableBinaryFunction Predicate >
-  requires Predicate< P, P::first_argument_type, P::second_argument_type >
-  class binary_negate
-    : public binary_function<typename Predicate::first_argument_type,
-                              typename Predicate::second_argument_type, bool> {
-  public:
-    biary_negate(const binary_negate & ) = default;
-    binary_negate(binary_negate && );
-
-    requires CopyConstructible< P >
-       explicit binary_negate(const Predicate& pred);
-    requires MoveConstructible< P >
-       explicit binary_negate(const Predicate& pred);
-
-    bool operator()(const typename Predicate::first_argument_type& x,
-                    const typename Predicate::second_argument_type& y) const;
-  };
-
-

--4- operator() returns !pred(x,y). -

- -
-template <class Predicate>
-  binary_negate<Predicate> not2(const Predicate& pred);
-template <class Predicate>
-  binary_negate<Predicate> not2(Predicate&& pred);
-
- -

--5- Returns: binary_negate<Predicate>(pred). -

-
- -
- - -

[ -2010 Rapperswil: -]

- - -

-Move to NAD Concepts. The move-semantic part has been addressed by a core language change, -which implicitly generates appropriate move constructors and move-assignment operators. -

- - - -

Proposed resolution:

- - - - - -
-

1077. Nonesense tuple declarations

-

Section: 20.4.2 [tuple.tuple] Status: NAD Editorial - Submitter: Pete Becker Opened: 2009-03-20 Last modified: 2015-04-08

-

View all other issues in [tuple.tuple].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-Class template tuple 20.4.2 [tuple.tuple]: -

- -
-template <class... UTypes>
-  requires Constructible<Types, const UTypes&>...
-template <class... UTypes>
-  requires Constructible<Types, RvalueOf<UTypes>::type>...
-
- -

-Somebody needs to look at this and say what it should be. -

- -

[ -2009-03-21 Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -

-The resolution looks correct; move to NAD Editorial. -

- - -

Proposed resolution:

-

-In 20.4.2 [tuple.tuple], class tuple, change as indicated: -

- -
-template <class... UTypes>
-  requires Constructible<Types, const UTypes&>...
-  tuple(const pair<UTypes...>&);
-template <class... UTypes>
-  requires Constructible<Types, RvalueOf<UTypes>::type>...
-  tuple(pair<UTypes...>&&);
-
- -

-[NB.: The corresponding prototypes do already exist in 20.4.2.1 [tuple.cnstr]/7+8] -

- - - - - -
-

1078. DE-17: Remove class type_index

-

Section: 20.14 [type.index] Status: NAD Concepts - Submitter: Doug Gregor Opened: 2009-03-20 Last modified: 2015-04-08

-

View all other issues in [type.index].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses DE 17

- -

-DE-17: -

-

-The class type_index should be removed; it provides no additional -functionality beyond providing appropriate concept maps. -

- -

[ -2009-03-31 Peter adds: -]

- - -
-

-It is not true, in principle, that std::type_index provides no utility -compared to bare std::type_info*. -

-

-std::type_index can avoid the lifetime issues with type_info when the -DLL that has produced the type_info object is unloaded. A raw -type_info* does not, and cannot, provide any protection in this case. -A type_index can (if the implementor so chooses) because it can wrap a -smart (counted or even cloning) pointer to the type_info data that is -needed for name() and before() to work. -

-
- - - -

Proposed resolution:

-

Modify the header <typeinfo> synopsis in - 18.7 [support.rtti]p1 as follows:

- -
-namespace std { 
-  class type_info; 
-  class type_index;
-  template <class T> struct hash;
-  template<> struct hash<type_indexconst type_info *> : public std::unary_function<type_indexconst type_info *, size_t> {
-    size_t operator()(type_indexconst type_info * indext) const;
-  };
-  concept_map LessThanComparable<const type_info *> see below
-  class bad_cast; 
-  class bad_typeid;
-}
-
- -

Add the following new subsection

-
-

-18.7.1.1 Template specialization hash<const type_info *> -[type.info.hash]

- -
-size_t operator()(const type_info *x) const;
-
-
    -
  1. Returns: x->hash_code()
    2. -
-
- -

Add the following new subsection

-
-

18.7.1.2 type_info concept map [type.info.concepts]

- - -
-concept_map LessThanComparable<const type_info *> {
-  bool operator<(const type_info *x, const type_info *y) { return x->before(*y); }
-  bool operator<=(const type_info *x, const type_info *y) { return !y->before(*x); }
-  bool operator>(const type_info *x, const type_info *y) { return y->before(*x); }
-  bool operator>=(const type_info *x, const type_info *y) { return !x->before(*y); }
-}
-
-
    -
  1. Note: provides a well-defined ordering among - type_info const pointers, which makes such pointers - usable in associative containers (23.4).
    2. -
-
- -

Remove section 20.14 [type.index]

- - - - - -
-

1080. Concept ArithmeticLike should provide explicit boolean conversion

-

Section: X [concept.arithmetic] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2009-03-21 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

-Astonishingly, the current concept ArithmeticLike as specified in -X [concept.arithmetic] does not provide explicit conversion -to bool although this is a common property of arithmetic types -(4.12 [conv.bool]). Recent proposals that introduced such types -(integers of arbitrary precision, -n2143, -decimals -n2732 -indirectly -via conversion to long long) also took care of such a feature. -

-

-Adding such an explicit conversion associated function would also -partly solve a currently invalid effects clause in library, which bases -on this property, 24.2.7 [random.access.iterators]/2: -

-
-{ difference_type m = n;
- if (m >= 0) while (m--) ++r;
- else while (m++) --r;
- return r; }
-
- -

-Both while-loops take advantage of a contextual conversion to bool -(Another problem is that the >= comparison uses the no -longer supported existing implicit conversion from int to IntegralLike). -

- -

Original proposed resolution:

-
    -
  1. -

    -In X [concept.arithmetic], add to the list of less refined -concepts one further concept: -

    - -
    -concept ArithmeticLike<typename T>
-  : Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>,
-    HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>,
-    HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>,
-    HasPostdecrement<T>,
-    HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>,
-    HasMultiplyAssign<T, const T&>,
-    HasDivideAssign<T, const T&>, ExplicitlyConvertible<T, bool> {
-
    -
    2. -
  2. -

    -In 24.2.7 [random.access.iterators]/2 change the current effects clause -as indicated [The proposed insertion fixes the problem that the previous -implicit construction from integrals has been changed to an explicit -constructor]: -

    -
    -{ difference_type m = n;
- if (m >= difference_type(0)) while (m--) ++r;
- else while (m++) --r;
- return r; }
-
    -
    3. -
- -

[ -Batavia (2009-05): -]

- -
-

-We agree that arithmetic types ought be convertible to bool, -and we therefore agree with the proposed resolution's paragraph 1. -

-

-We do not agree that the cited effects clause is invalid, -as it expresses intent rather than specific code. -

-

-Move to Review, pending input from concepts experts. -

-
- - - -

Proposed resolution:

-

-In X [concept.arithmetic], add to the list of less refined -concepts one further concept: -

- -
-concept ArithmeticLike<typename T>
-  : Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>,
-    HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>,
-    HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>,
-    HasPostdecrement<T>,
-    HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>,
-    HasMultiplyAssign<T, const T&>,
-    HasDivideAssign<T, const T&>, ExplicitlyConvertible<T, bool> {
-
- - - - - -
-

1081. basic_string needs to be a concept-constrained template

-

Section: 21 [strings] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [strings].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 216, JP 46, JP 48 [CD1]

- -

-All the containers use concepts for their iterator usage, exect for -basic_string. This needs fixing. -

- -

-Use concepts for iterator template parameters throughout the chapter. -

- -

[ -Summit: -]

- -

-NB comments to be handled by Dave Abrahams and Howard Hinnant with -advice from PJP: UK216 (which duplicates) JP46, JP48. JP46 supplies -extensive proposed wording; start there. -

- - -

Proposed resolution:

- - - - - -
-

1082. codecvt needs to be a concept-constrained template

-

Section: 22 [localization] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [localization].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses JP 49 [CD1]

- -

-codecvt does not use concept. For example, create CodeConvert -concept and change as follows. -

- -
-template<CodeConvert Codecvt, class Elem = wchar_t>
-  class wstring_convert {
-
- -

[ -Summit: -]

- -

-To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger. -

- - -

Proposed resolution:

- - - - - -
-

1083. InputIterator and OutputIterator template parameters need to be concept constraints

-

Section: 22 [localization] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [localization].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses JP 52, JP 53 [CD1]

- -

-InputIterator does not use concept. -

- -

-OutputIterator does not use concept. -

- -

-Comments include proposed wording. -

- -

[ -Summit: -]

- -

-To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger. -

- - -

Proposed resolution:

- - - - - -
-

1084. Concept ForwardIterator should provide default implementation for post-increment

-

Section: 24.2.5 [forward.iterators] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 250 [CD1]

- -

-A default implementation should be supplied for the post-increment -operator to simplify implementation of iterators by users. -

- -

-Copy the Effects clause into the concept description as the default -implementation. Assumes a default value for postincrement_result. -

- -

[ -Summit: -]

- -

-Howard will open an issue. -

- -

[ -2009-06-07 Daniel adds: -]

- - -

-This issue cannot currently be resolved as suggested, because -that would render auto-detection of the return type -postincrement_result invalid, see [concept.map.assoc]/4+5. The -best fix would be to add a default type to that associated type, but -unfortunately any default type will prevent auto-deduction of types of -associated functions as quoted above. A corresponding core issue -is in preparation. -

- - -

Proposed resolution:

-

[ -This wording assumes the acceptance of UK 251 / 1009. Both -wordings change the same paragraphs. -]

- - -

-Change 24.2.5 [forward.iterators]: -

- -
-
-concept ForwardIterator<typename X> : InputIterator<X>, Regular<X> { 
-
-  MoveConstructible postincrement_result;
-  requires HasDereference<postincrement_result>
-        && Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;
-
-  postincrement_result operator++(X& r, int); {
-     X tmp = r;
-     ++r;
-     return tmp;
-  }
-
-  axiom MultiPass(X a, X b) { 
-    if (a == b) *a == *b; 
-    if (a == b) ++a == ++b; 
-  } 
-}
-
- - - - - - -
-

1085. BidirectionalIterator concept should provide default implementation for post-decrement

-

Section: 24.2.6 [bidirectional.iterators] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [bidirectional.iterators].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 258 [CD1]

- -

-A default implementation should be supplied for the post-decrement -operator to simplify implementation of iterators by users. -

- -

-Copy the Effects clause into the concept description as the default -implementation. Assumes a default value for postincrement_result. -

- -

[ -Summit: -]

- -

-Howard will open an issue. -

- -

[ -2009-06-07 Daniel adds: -]

- - -

-This issue cannot currently be resolved as suggested, because -that would render auto-detection of the return type -postdecrement_result invalid, see 1084. -

- - -

Proposed resolution:

- -

-Change 24.2.6 [bidirectional.iterators]: -

- -
-
-concept BidirectionalIterator<typename X> : ForwardIterator<X> { 
-  MoveConstructible postdecrement_result; 
-  requires HasDereference<postdecrement_result> 
-        && Convertible<HasDereference<postdecrement_result>::result_type, const value_type&> 
-        && Convertible<postdecrement_result, const X&>; 
-  X& operator--(X&); 
-  postdecrement_result operator--(X& r, int); {
-     X tmp = r;
-     --r;
-     return tmp;
-  }
-}
-
- - - - - - -
-

1086. Stream iterators need to be concept-constrained templates

-

Section: 24.6 [stream.iterators] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 284 [CD1]

- -

-The stream iterators need constraining with concepts/requrires clauses. -

- -

[ -Summit: -]

- -

-We agree. To be handled by Howard, Martin and PJ. -

- - -

Proposed resolution:

- - - - - -
-

1087. Incorrect OutputIterator concept requirements for replace algorithms

-

Section: 25.3.5 [alg.replace] Status: NAD Concepts - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [alg.replace].

-

View all issues with NAD Concepts status.

-

Discussion:

-

Addresses UK 301 [CD1]

- -

-replace and replace_if have the requirement: OutputIterator<Iter, -Iter::reference> Which implies they need to copy some values in the -range the algorithm is iterating over. This is not however the case, the -only thing that happens is const T&s might be copied over existing -elements (hence the OutputIterator<Iter, const T&>. -

- -

-Remove OutputIterator<Iter, Iter::reference> from replace -and replace_if. -

- -

[ -Summit: -]

- -

-We agree. To be handled by Howard. -

- - -

Proposed resolution:

-

-Change in [algorithms.syn] and 25.3.5 [alg.replace]: -

- -
-template<ForwardIterator Iter, class T> 
-  requires OutputIterator<Iter, Iter::reference> 
-        && OutputIterator<Iter, const T&> 
-        && HasEqualTo<Iter::value_type, T> 
-  void replace(Iter first, Iter last, 
-               const T& old_value, const T& new_value); 
-
-template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> 
-  requires OutputIterator<Iter, Iter::reference> 
-        && OutputIterator<Iter, const T&> 
-        && CopyConstructible<Pred> 
-  void replace_if(Iter first, Iter last,
-                  Pred pred, const T& new_value);
-
- - - - - -
-

1091. Multimap description confusing

-

Section: 23.4.5.3 [multimap.modifiers] Status: NAD - Submitter: LWG Opened: 2009-03-22 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

- -

Addresses UK 246

-

-The content of this sub-clause is purely trying to describe in words the -effect of the requires clauses on these operations, now that we have -Concepts. As such, the description is more confusing than the signature -itself. The semantic for these functions is adequately covered in the -requirements tables in 23.2.4 [associative.reqmts]. -

- -

[ -Beman adds: -]

- - -

-Pete is clearly right that -this one is technical rather than editorial. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Review. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD, solved by removing concepts. -

- - - -

Proposed resolution:

-

-Strike 23.4.5.3 [multimap.modifiers] entirely -(but do NOT strike these signatures from the class template definition!). -

- - - - - -
-

1092. Class template integral_constant should be a constrained template

-

Section: 20.10.3 [meta.help] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [meta.help].

-

View all issues with NAD Concepts status.

-

Discussion:

-

-A first step to change the type traits predicates to constrained templates is to -constrain their common base template integral_constant. This can be done, -without enforcing depending classes to be constrained as well, but not -vice versa -without brute force late_check usages. The following proposed resolution depends -on the resolution of LWG issue 1019. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, pending a paper that looks at constraints -for the entirety of the type traits -and their relationship to the foundation concepts. -We recommend this be deferred -until after the next Committee Draft is issued. -

- - -

Proposed resolution:

-
    -
  1. -

    -In 20.10.2 [meta.type.synop], Header <type_traits> -synopsis change as indicated: -

    -
    -namespace std {
-// 20.5.3, helper class:
-template <classIntegralConstantExpressionType T, T v> struct integral_constant;
-
    -
    2. -
  2. -

    -In 20.10.3 [meta.help] change as indicated: -

    -
    -template <classIntegralConstantExpressionType T, T v>
-struct integral_constant {
-  static constexpr T value = v;
-  typedef T value_type;
-  typedef integral_constant<T,v> type;
-  constexpr operator value_type() { return value; }
-};
-
    -
    3. -
- - - - - -
-

1096. unconstrained rvalue ref parameters

-

Section: 17 [library] Status: NAD Concepts - Submitter: David Abrahams Opened: 2009-03-21 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD Concepts status.

-

Discussion:

-

-TODO: Look at all cases of unconstrained rvalue ref parameters and check -that concept req'ts work when T deduced as reference. -

- -

- We found some instances where that was not done correctly and we figure - the possibility of deducing T to be an lvalue reference was probably - overlooked elsewhere. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, pending proposed wording from Dave for further review. -

- - -

Proposed resolution:

-

-

- - - - - -
-

1099. Various issues

-

Section: 17 [library] Status: NAD - Submitter: David Abrahams Opened: 2009-03-21 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD status.

-

Discussion:

-

-Notes -

-
-

-[2009-03-21 Sat] p. 535 at the top we need MoveConstructible V1, -MoveConstructible V2 (where V1,V2 are defined on 539). Also make_tuple -on 550 -

- -
-

-CD-1 reads: -

- -
-template <MoveConstructible T1, MoveConstructible T2> 
-pair<V1, V2> make_pair(T1&&, T2&&); 
-
- -

-Actually I'm guessing we need something like MoveConstructible<V1,T1>, -i.e. "V1 can be constructed from an rvalue of type T1." -

- -

-Ditto for make_tuple -

-
- -

-[2009-03-21 Sat] p1183 thread ctor, and in general, we need a way to -talk about "copiable from generalized rvalue ref argument" for cases -where we're going to forward and copy. -

-
-

- This issue may well be quite large. Language in para 4 about "if - an lvalue" is wrong because types aren't expressions. -

- -
-

-Maybe we should define the term "move" so we can just say in the -effects, "f is moved into the newly-created thread" or something, and -agree (and ideally document) that saying "f is moved" implies -

- -
-F x(move(f))
-
- -

-is required to work. That would cover both ctors at once. -

-
- -

- p1199, call_once has all the same issues. -

-
-

-[2009-03-21 Sat] p869 InputIterator pointer type should not be required -to be convertible to const value_type*, rather it needs to have a -operator-> of its own that can be used for the value type. -

- -

-This one is serious and unrelated to the move issue. -

- -

-[2009-03-21 Sat] p818 stack has the same problem with default ctor. -

-

-[2009-03-21 Sat] p816 priority_queue has the same sorts of problems as queue, only more so -

-
-   requires MoveConstructible<Cont> 
-     explicit priority_queue(const Compare& x = Compare(), Cont&& = Cont()); 
-
-

- Don't require MoveConstructible when default constructing Cont. - Also missing semantics for move ctor. -

-
-

- [2009-03-21 Sat] Why are Allocators required to be CopyConstructible as - opposed to MoveConstructible? -

-

- [2009-03-21 Sat] p813 queue needs a separate default ctor (Cont needn't - be MoveConstructible). No documented semantics for move c'tor. Or - *any* of its 7 ctors! -

-

- [2009-03-21 Sat] std::array should have constructors for C++0x, - consequently must consider move construction. -

- -

[ -2009-05-01 Daniel adds: -]

- - -

-This could be done as part of 1035, which already handles -deviation of std::array from container tables. -

- -

- [2009-03-21 Sat] p622 all messed up. -

-
-

- para 8 "implementation-defined" is the wrong term; should be "see - below" or something. -

- para 12 "will be selected" doesn't make any sense because we're not - talking about actual arg types. -

- paras 9-13 need to be totally rewritten for concepts. -

-
- -

- [2009-03-21 Sat] Null pointer comparisons (p587) have all become - unconstrained. Need to fix that -

- [2009-03-21 Sat] mem_fun_t etc. definition doesn't match declaration. - We think CopyConstructible is the right reqt. -

- make_pair needs Constructible<V1, T1&&> requirements! -

- make_tuple needs something similar -

- tuple bug in synopsis: -

-
-   template <class... UTypes>
-   requires Constructible<Types, const UTypes&>...
-   template <class... UTypes>
-   requires Constructible<Types, RvalueOf<UTypes>::type>...
-
-

- Note: removal of MoveConstructible requirements in std::function makes - these routines unconstrained! -

-
- -

[ -2009-05-02 Daniel adds: -]

- - -

-This part of the issue is already covered by 1077. -

- -

- these unique_ptr constructors are broken [ I think this is covered in "p622 all messed up" ] -

-
- unique_ptr(pointer p, implementation-defined d);
- unique_ptr(pointer p, implementation-defined d);
-
-

- multimap range constructor should not have MoveConstructible<value_type> requirement. -

-

- same with insert(..., P&&); multiset has the same issue, as do - unordered_multiset and unordered_multimap. Review these! -

- -
- -

[ -Batavia (2009-05): -]

- -

-Move to Open, pending proposed wording from Dave for further review. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Tentatively NAD. We are not sure what has been addressed and what hasn't. -Recommend closing unless someone sorts this out into something more readable. -

- - - -

Rationale:

-

-The issue(s) at hand not adequately communicated. -

- - -

Proposed resolution:

-

-

- - - - - -
-

1101. unique requirements

-

Section: 25.3.9 [alg.unique] Status: NAD Editorial - Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2015-04-08

-

View all other issues in [alg.unique].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-From Message c++std-core-14160 Howard wrote: -

- -

-It was the intent of the rvalue reference proposal for unique to only require MoveAssignable: -N1860. -

- -

-And Pete replied: -

- -

-That was overridden by the subsequent changes made for concepts in -N2573, -which reimposed the C++03 requirements. -

- -

-My impression is that this overwrite was a simple (unintentional) mistake. -Wording below to correct it. -

- -

[ -Batavia (2009-05): -]

- -
-

-Howard notes this issue resolves a discrepancy between the synopsis -and the description. -

-

-Move to NAD Editorial. -

-
- - -

Proposed resolution:

-

-Change 25.3.9 [alg.unique]: -

- -
-template<ForwardIterator Iter> 
-  requires OutputIterator<Iter, RvalueOf<Iter::reference>::type> 
-        && EqualityComparable<Iter::value_type> 
-  Iter unique(Iter first, Iter last); 
-
-template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred> 
-  requires OutputIterator<Iter, RvalueOf<Iter::reference>::type> 
-        && CopyConstructible<Pred> 
-  Iter unique(Iter first, Iter last, Pred pred);
-
- -

-Note that the synopsis in [algorithms.syn] is already correct. -

- - - - - - -
-

1102. std::vector's reallocation policy still unclear

-

Section: 23.3.6.3 [vector.capacity] Status: NAD - Submitter: Daniel Krügler Opened: 2009-04-20 Last modified: 2015-04-08

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

View all issues with NAD status.

-

Discussion:

-

-I have the impression that even the wording of current draft -N2857 -does insufficiently express the intent of vector's -reallocation strategy. This has produced not too old library -implementations which release memory in the clear() function -and even modern articles about C++ programming cultivate -the belief that clear is allowed to do exactly this. A typical -example is something like this: -

- -
-const int buf_size = ...;
-std::vector<T> buf(buf_size);
-for (int i = 0; i < some_condition; ++i) {
-  buf.resize(buf_size);
-  write_or_read_data(buf.data());
-  buf.clear(); // Ensure that the next round get's 'zeroed' elements
-}
-
-

-where still the myth is ubiquitous that buf might be -allowed to reallocate it's memory *inside* the for loop. -

-

-IMO the problem is due to the fact, that -

- -
    -
  1. -the actual memory-reallocation stability of std::vector -is explained in 23.3.6.3 [vector.capacity]/3 and /6 which -are describing just the effects of the reserve -function, but in many examples (like above) there -is no explicit call to reserve involved. Further-more -23.3.6.3 [vector.capacity]/6 does only mention insertions -and never mentions the consequences of erasing -elements. -
    2. -
  2. -

    -the effects clause of std::vector's erase overloads in -23.3.6.5 [vector.modifiers]/4 is silent about capacity changes. This -easily causes a misunderstanding, because the counter -parting insert functions described in 23.3.6.5 [vector.modifiers]/2 -explicitly say, that -

    -

    -Causes reallocation if the new size is greater than the -old capacity. If no reallocation happens, all the iterators -and references before the insertion point remain valid. -

    -

    -It requires a complex argumentation chain about four -different places in the standard to provide the - possibly -weak - proof that calling clear() also does never change -the capacity of the std::vector container. Since std::vector -is the de-facto replacement of C99's dynamic arrays this -type is near to a built-in type and it's specification should -be clear enough that usual programmers can trust their -own reading. -

    -
    3. -
- -

[ -Batavia (2009-05): -]

- -
-

-Bill believes paragraph 1 of the proposed resolution is unnecessary -because it is already implied (even if tortuously) by the current wording. -

-

-Move to Review. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. Rationale: there is no consensus to clarify the standard, -general consensus that the standard is correct as written. -

- - - -

Proposed resolution:

-

[ -This is a minimum version. I also -suggest that the wording explaining the allocation strategy -of std::vector in 23.3.6.3 [vector.capacity]/3 and /6 is moved into -a separate sub paragraph of 23.3.6.3 [vector.capacity] before -any of the prototype's are discussed, but I cannot provide -reasonable wording changes now -]

- - -
    -
  1. -

    -Change 23.3.6.3 [vector.capacity]/6 as follows: -

    -

    -It is guaranteed that no reallocation takes place during -insertions or erasures that happen after a call -to reserve() until the time when an insertion would make -the size of the vector greater than the value of capacity(). -

    -
    2. -
  2. -

    -Change 23.3.6.5 [vector.modifiers]/4 as follows: -

    -

    -Effects: The capacity shall remain unchanged and no reallocation shall -happen. -Invalidates iterators and references at or after the point -of the erase. -

    -
    3. -
- - - - - -
-

1105. Shouldn't Range be an auto concept

-

Section: X [iterator.concepts.range] Status: NAD Concepts - Submitter: David Abrahams Opened: 2009-04-23 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

- -

[ -2009-04-26 Herb adds: -]

- - -
-

-Here's a common example: We have many ISV customers who have built lots of -in-house STL-like containers. Imagine that, for the past ten years, the user -has been happily using his XYZCorpContainer<T> that has begin() and end() -and an iterator typedef, and indeed satisfies nearly all of Container, -though maybe not quite all just like valarray. The user upgrades to a -range-enabled version of a library, and now lib_algo( xyz.begin(), xyz.end()); -no longer works -- compiler error. -

-

-Even though XYZCorpContainer matches the pre-conceptized version of the -algorithm, and has been working for years, it appears the user has to write -at least this: -

-
-template<class T> concept_map Range<XYZCorpContainer<T>> {};
-
-template<class T> concept_map Range<const XYZCorpContainer<T>> {};
-
-

-Is that correct? -

-

-But he may actually have to write this as we do for initializer list: -

-
-template<class T>
-concept_map Range<XYZCorpContainer<T>> {
-   typedef T* iterator;
-   iterator begin(XYZCorpContainer<T> c) { return c.begin(); }
-   iterator end(XYZCorpContainer<T> c) { return c.end(); }
-};
-
-template<class T>
-concept_map Range<const XYZCorpContainer<T>> {
-   typedef T* iterator;
-   iterator begin(XYZCorpContainer<T> c) { return c.begin(); }
-   iterator end(XYZCorpContainer<T> c) { return c.end(); }
-};
-
- -
- -

[ -2009-04-28 Alisdair adds: -]

- - -
-

-I recommend NAD, although remain concerned about header organisation. -

-

-A user container will satisfy the MemberContainer concept, which IS auto. -There is a concept_map for all MemberContainers to Container, and then a -further concept_map for all Container to Range, so the stated problem is not -actually true. User defined containers will automatically match the Range -concept without explicitly declaring a concept_map. -

-

-The problem is that they should now provide an additional two headers, -<iterator_concepts> and <container_concepts>. - The only difference from -making Range an auto concept would be this reduces to a single header, -<iterator_concepts>. -

-

-I am strongly in favour of any resolution that tackles the issue of -explicitly requiring concept headers to make these concept maps available. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-We observe there is a recent paper by Bjarne that overlaps this issue. -

-

-Alisdair continues to recommend NAD. -

-

-Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -

-
- - -

Proposed resolution:

- - - - - -
-

1107. constructor shared_future(unique_future) by value?

-

Section: 30.6.7 [futures.shared_future] Status: NAD Editorial - Submitter: Thomas J. Gritzan Opened: 2009-04-03 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

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-

Discussion:

-

-In the shared_future class definition in 30.6.7 [futures.shared_future] -the move constructor -that constructs a shared_future from an unique_future receives the -parameter by value. In paragraph 3, the same constructor receives it as -const value. -

- -

-I think that is a mistake and the constructor should take a r-value -reference: -

- -
-shared_future(unique_future<R>&& rhs);
-
- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-Move to Tentatively Ready. -

-
- -

[ -2009-07-05 Daniel notes: -]

- - -

-The proposed change has already been incorported into the current working draft -N2914. -

- - - -

Proposed resolution:

-

-Change the synopsis in 30.6.7 [futures.shared_future]: -

- -
-shared_future(unique_future<R>&& rhs);
-
- -

-Change the definition of the constructor in 30.6.7 [futures.shared_future]: -

- -
-shared_future(const unique_future<R>&& rhs);
-
- - - - - - -
-

1109. std::includes should require CopyConstructible predicate

-

Section: 25.4.5.1 [includes] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-04-28 Last modified: 2015-04-08

-

View all other issues in [includes].

-

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-

Discussion:

-

-All the set operation algorithms require a CopyConstructible predicate, with -the exception of std::includes. This looks like a typo as much as anything, -given the general library requirement that predicates are copy -constructible, and wording style of other set-like operations. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to NAD Editorial. -

- - -

Proposed resolution:

-

-Change [algorithms.syn] and 25.4.5.1 [includes]: -

- -
-template<InputIterator Iter1, InputIterator Iter2,
-         typename CopyConstructible Compare>
-  requires Predicate<Compare, Iter1::value_type, Iter2::value_type>
-        && Predicate<Compare, Iter2::value_type, Iter1::value_type>
-  bool includes(Iter1 first1, Iter1 last1,
-                Iter2 first2, Iter2 last2,
-                Compare comp);
-
- - - - - -
-

1111. associative containers underconstrained

-

Section: 23.4 [associative] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-04-29 Last modified: 2015-04-08

-

View other active issues in [associative].

-

View all other issues in [associative].

-

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-

Discussion:

-

-According to table 87 (n2857) the expression X::key_equal for an unordered -container shall return a value of type Pred, where Pred is an equivalence -relation. -

- -

-However, all 4 containers constrain Pred to be merely a Predicate, -and not EquivalenceRelation. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Review. -

-
- - -

Proposed resolution:

-

-For ordered containers, replace -

-
-Predicate<auto, Key, Key> Compare = less<Key>
-
-

-with -

-
-StrictWeakOrder<auto, Key, Key> Compare = less<Key>
-
- -

-For unordered containers, replace -

-
-Predicate<auto, Key, Key> Compare = less<Key>
-
-

-with -

-
-EquivalenceRelation<auto, Key, Key> Compare = less<Key>
-
-

-As in the following declarations: -

- -
-

-Associative containers 23.4 [associative] -

-

- 1 Headers <map> and <set>: -

-

- Header <map> synopsis -

-
-   namespace std {
-     template <ValueType Key, ValueType T,
-               PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-               Allocator Alloc = allocator<pair<const Key, T> > >
-       requires NothrowDestructible<Key> && NothrowDestructible<T>
-             && CopyConstructible<Compare>
-             && AllocatableElement<Alloc, Compare, const Compare&>
-             && AllocatableElement<Alloc, Compare, Compare&&>
-     class map;
-
-     ...
-
-     template <ValueType Key, ValueType T,
-               PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-               Allocator Alloc = allocator<pair<const Key, T> > >
-       requires NothrowDestructible<Key> && NothrowDestructible<T>
-             && CopyConstructible<Compare>
-             && AllocatableElement<Alloc, Compare, const Compare&>
-             && AllocatableElement<Alloc, Compare, Compare&&>
-     class multimap;
-
-     ...
-
-   }
-
- -

- Header <set> synopsis -

-
-   namespace std {
-     template <ValueType Key, PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-               Allocator Alloc = allocator<Key> >
-       requires NothrowDestructible<Key> && CopyConstructible<Compare>
-             && AllocatableElement<Alloc, Compare, const Compare&>
-             && AllocatableElement<Alloc, Compare, Compare&&>
-     class set;
-
-     ...
-
-     template <ValueType Key, PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-               Allocator Alloc = allocator<Key> >
-       requires NothrowDestructible<Key> && CopyConstructible<Compare>
-             && AllocatableElement<Alloc, Compare, const Compare&>
-             && AllocatableElement<Alloc, Compare, Compare&&>
-     class multiset;
-
-     ...
-
-   }
-
- -

- 23.4.1p2 Class template map [map] -

-
- namespace std {
-   template <ValueType Key, ValueType T,
-             PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && CopyConstructible<Compare>
-           && AllocatableElement<Alloc, Compare, const Compare&>
-           && AllocatableElement<Alloc, Compare, Compare&&>
-   class map {
-     ...
-   };
- }
-
- - -

- 23.4.2p2 Class template multimap [multimap] -

-
- namespace std {
-   template <ValueType Key, ValueType T,
-             PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && CopyConstructible<Compare>
-           && AllocatableElement<Alloc, Compare, const Compare&>
-           && AllocatableElement<Alloc, Compare, Compare&&>
-   class multimap {
-     ...
-   };
- }
-
- - -

- 23.4.3p2 Class template set [set] -

-
- namespace std {
-   template <ValueType Key, PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-             Allocator Alloc = allocator<Key> >
-     requires NothrowDestructible<Key> && CopyConstructible<Compare>
-           && AllocatableElement<Alloc, Compare, const Compare&>
-           && AllocatableElement<Alloc, Compare, Compare&&>
-   class set {
-     ...
-   };
- }
-
- - -

- 23.4.4p2 Class template multiset [multiset] -

-
- namespace std {
-   template <ValueType Key, PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>,
-             Allocator Alloc = allocator<Key> >
-     requires NothrowDestructible<Key> && CopyConstructible<Compare>
-           && AllocatableElement<Alloc, Compare, const Compare&>
-           && AllocatableElement<Alloc, Compare, Compare&&>
-   class multiset {
-     ...
-   };
- }
-
- -

- 23.5 Unordered associative containers [unord] -

-

- 1 Headers <unordered_map> and <unordered_set>: -

-

- Header <unordered_map> synopsis -

-
- namespace std {
-   // 23.5.1, class template unordered_map:
-   template <ValueType Key,
-             ValueType T,
-             Callable<auto, const Key&> Hash = hash<Key>,
-             PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-     class unordered_map;
-
-   // 23.5.2, class template unordered_multimap:
-   template <ValueType Key,
-             ValueType T,
-             Callable<auto, const Key&> Hash = hash<Key>,
-             PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-     class unordered_multimap;
-
-   ...
- }
-
- -

- Header <unordered_set> synopsis -

-
- namespace std {
-   // 23.5.3, class template unordered_set:
-   template <ValueType Value,
-             Callable<auto, const Value&> Hash = hash<Value>,
-             PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>,
-             Allocator Alloc = allocator<Value> >
-     requires NothrowDestructible<Value>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-     class unordered_set;
-
-   // 23.5.4, class template unordered_multiset:
-   template <ValueType Value,
-             Callable<auto, const Value&> Hash = hash<Value>,
-             PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>,
-             Allocator Alloc = allocator<Value> >
-     requires NothrowDestructible<Value>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-     class unordered_multiset;
-
-   ...
- }
-
- -

- 23.5.1p3 Class template unordered_map [unord.map] -

-
- namespace std {
-   template <ValueType Key,
-             ValueType T,
-             Callable<auto, const Key&> Hash = hash<Key>,
-             PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-   class unordered_map
-   {
-     ...
-   };
- }
-
- -

- 23.5.2p3 Class template unordered_multimap [unord.multimap] -

-
- namespace std {
-   template <ValueType Key,
-             ValueType T,
-             Callable<auto, const Key&> Hash = hash<Key>,
-             PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>,
-             Allocator Alloc = allocator<pair<const Key, T> > >
-     requires NothrowDestructible<Key> && NothrowDestructible<T>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-   class unordered_multimap
-   {
-     ...
-   };
- }
-
- -

- 23.5.3p3 Class template unordered_set [unord.set] -

-
- namespace std {
-   template <ValueType Value,
-             Callable<auto, const Value&> Hash = hash<Value>,
-             PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>,
-             Allocator Alloc = allocator<Value> >
-     requires NothrowDestructible<Value>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-   class unordered_set
-   {
-     ...
-   };
- }
-
-

- 23.5.4p3 Class template unordered_multiset [unord.multiset] -

-
- namespace std {
-   template <ValueType Value,
-             Callable<auto, const Value&> Hash = hash<Value>,
-             PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>,
-             Allocator Alloc = allocator<Value> >
-     requires NothrowDestructible<Value>
-           && SameType<Hash::result_type, size_t>
-           && CopyConstructible<Hash> && CopyConstructible<Pred>
-           && AllocatableElement<Alloc, Pred, const Pred&>
-           && AllocatableElement<Alloc, Pred, Pred&&>
-           && AllocatableElement<Alloc, Hash, const Hash&>
-           && AllocatableElement<Alloc, Hash, Hash&&>
-   class unordered_multiset
-   {
-     ...
-   };
- }
-
- -
- - - - - - -
-

1115. va_copy missing from Standard macros table

-

Section: C.5 [diff.library] Status: NAD Editorial - Submitter: Miles Zhao Opened: 2009-05-23 Last modified: 2015-04-08

-

View all other issues in [diff.library].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-In "Table 122 — Standard macros" of C.5 [diff.library], which lists the 56 macros -inherited from C library, va_copy seems to be missing. But in -"Table 21 — Header <cstdarg> synopsis" (18.10 [support.runtime]), there is. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Mark as Tentatively NAD Editorial, if Pete disagrees, Howard -will move to Tentatively Ready -

- - - -

Proposed resolution:

-

-Add va_copy to Table 122 -- Standard macros in C.5 [diff.library]. -

- - - - - -
-

1119. tuple query APIs do not support references

-

Section: 20.4.2.5 [tuple.helper] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-05-23 Last modified: 2015-04-08

-

View all other issues in [tuple.helper].

-

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-

Discussion:

-

-The tuple query APIs tuple_size and -tuple_element do not support references-to-tuples. This can be -annoying when a template deduced a parameter type to be a reference, -which must be explicitly stripped with remove_reference before calling -these APIs. -

-

-I am not proposing a resolution at this point, as there is a -combinatorial explosion with lvalue/rvalue references and -cv-qualification (see previous issue) that suggests some higher -refactoring is in order. This might be something to kick back over to -Core/Evolution. -

-

-Note that we have the same problem in numeric_limits. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Open. Alisdair to provide wording. -

- - -

[ -2010 Rapperswil: -]

- - -

-Move to NAD. This is an extension after the FCD, without a clear motivation. -May consider as NAD Future if motivating examples come forward. -

- - - -

Proposed resolution:

- - - - - -
-

1124. Invalid definition of concept RvalueOf

-

Section: X [concept.transform] Status: NAD Concepts - Submitter: Daniel Krügler Opened: 2009-05-28 Last modified: 2015-04-08

-

View all other issues in [concept.transform].

-

View all issues with NAD Concepts status.

-

Discussion:

-

-A recent news group -article -points to several defects in the -specification of reference-related concepts. -

-

-One problem of the concept RvalueOf as currently defined in -X [concept.transform]: -

- -
-concept RvalueOf<typename T> {
- typename type = T&&;
- requires ExplicitlyConvertible<T&,type> && Convertible<T&&,type>;
-}
-
-template<typename T> concept_map RvalueOf<T&> {
- typedef T&& type;
-}
-
- -

-is that if T is an lvalue-reference, the requirement -Convertible<T&&,type> isn't satisfied for -lvalue-references, because after reference-collapsing in the concept -definition we have Convertible<T&,type> in this case, -which isn't satisfied in the concept map template and also is not the -right constraint either. I think that the reporter is right that -SameType requirements should do the job and that we also should -use the new RvalueReference concept to specify a best matching -type requirement. -

- - -

Proposed resolution:

-

-In X [concept.transform] before p. 4 change as indicated: -

- -
-auto concept RvalueOf<typename T> {
-  typenameRvalueReference type = T&&;
-  requires ExplicitlyConvertible<T&, type> && Convertible<T&&, type>SameType<T&, type&>;
-}
-
- - - - - -
-

1125. ostream_iterator does not work with movable types

-

Section: 24.6.2.2 [ostream.iterator.ops] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-ostream_iterator has not been updated to support moveable types, in a -similar manner to the insert iterators. -Note that this is not a problem for ostreambuf_iterator, as the types it is -restricted to dealing with do not support extra-efficient moving. -

- -

[ -2009-11-10 Howard adds: -]

- - -

-Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale -added below. -

- - -

Proposed resolution:

-

-Add second operator= overload to class template ostream_iterator -in 24.6.2 [ostream.iterator], para 2: -

- -
-ostream_iterator<T,charT,traits>& operator=(const T& value);
-ostream_iterator<T,charT,traits>& operator=(T&& value);
-
- -

-Add a new paragraph: in 24.6.2.2 [ostream.iterator.ops]: -

- -
-
-ostream_iterator& operator=(T&& value);
-
-
-

--2- Effects: -

-
-*out_stream << std::move(value);
-if(delim != 0)
-  *out_stream << delim;
-return (*this);
-
-
-
- - - -

Rationale:

-

-Several objections to move forward with this issue were voiced in the thread -starting with c++std-lib-25438. Among them is that we know of no motivating -use case to make streaming rvalues behave differently than streaming const -lvalues. -

- - - - - -
-

1127. rvalue references and iterator traits

-

Section: 24.4.1 [iterator.traits] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2015-04-08

-

View all other issues in [iterator.traits].

-

View all issues with NAD Concepts status.

-

Discussion:

-

-The deprecated support for iterator_traits and legacy (unconstrained) -iterators features the (exposition only) concept: -

- -
-concept IsReference<typename T> { } // exposition only
-template<typename T> concept_map IsReference<T&> { }
-
-

-Now this looks exactly like the LvalueReference concept recently added to -clause 20, so I wonder if we should use that instead? -Then I consider the lack of rvalue-reference support, which means that -move_iterator would always flag as merely supporting the input_iterator_tag -category. This suggests we retain the exposition concept, but add a second -concept_map to support rvalue references. -

-

-I would suggest adding the extra concept_map is the right way forward, but -still wonder if the two exposition-only concepts in this clause might be -worth promoting to clause 20. That question might better be answered with a -fuller investigation of type_trait/concept unification though. -

- - -

Proposed resolution:

-

-In Iterator traits 24.4.1 [iterator.traits] para 4 add: -

- -
-concept IsReference<typename T> { } // exposition only
-template<typename T> concept_map IsReference<T&> { }
-template<typename T> concept_map IsReference<T&&> { }
-
- - - - - - -
-

1128. Missing definition of iterator_traits<T*>

-

Section: X [iterator.syn] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

-The <iterator> header synopsis declares a partial specialization of -iterator_traits to support pointers, X [iterator.syn]. The implication -is that specialization will be described in D10, yet it did not follow the -rest of the deprecated material into this clause. -

-

-However, this is not as bad as it first seems! -There are partial specializations of iterator_traits for types that satisfy -the various Iterator concepts, and there are concept_maps for pointers to -explicitly support the RandomAccessIterator concept, so the required -template will be present - just not in the manner advertised. -

-

-I can see two obvious solutions: -

- -
    -
  1. -Restore the iterator_traits<T*> partial specialization in D.10 -
    2. -
  2. -Remove the declaration of iterator_traits<T*> from 24.3 synopsis -
    3. -
-

-I recommend option (ii) in the wording below -

-

-Option (ii) could be extended to strike all the declarations of deprecated -material from the synopsis, as it is effectively duplicating D.10 anyway. -This is the approach taken for deprecated library components in the 98/03 -standards. This is probably a matter best left to the Editor though. -

- - -

Proposed resolution:

-

-In X [iterator.syn] strike: -

- -
-template<class T> struct iterator_traits<T*>;
-
- - - - - - -
-

1132. JP-30: nested exceptions

-

Section: 18.8.6 [except.nested] Status: NAD - Submitter: Seiji Hayashida Opened: 2009-06-01 Last modified: 2015-04-08

-

View other active issues in [except.nested].

-

View all other issues in [except.nested].

-

View all issues with NAD status.

-

Discussion:

-

Addresses JP 30

- -

-C++0x nested_exception cannot handle a structured exception well. The -following codes show two types of tree structured exception handling. -

-

-The first one is based on nested_exception in C++0x, -while the second one is based on my library trickerr.h (in Japanese). -http://tricklib.com/cxx/dagger/trickerr.h -

-

-Assume that Function A() calls two sub functions A_a() and A_b(), both might -throw tree structured exceptions, and A_b() must be called even if A_a() -throws an exception. -

-

-List A (code of tree structured exception handling based on nested_exception -in C++0x) -

- -
-void A()
-{
-    try
-    {
-        std::vector<exception_ptr> exception_list;
-        try
-        {
-            // A_a() does a similar processing as A().
-            A_a();
-        }
-        catch(...)
-        {
-            exception_list.push_back(current_exception());
-        }
-
-        // ***The processing A() has to do even when A_a() fails. ***
-        try
-        {
-            // A_b() does a similar processing as A().
-            A_b();
-        }
-        catch(...)
-        {
-            exception_list.push_back(current_exception());
-        }
-        if (!exception_list.empty())
-        {
-            throw exception_list;
-        }
-    }
-    catch(...)
-    {
-        throw_with_nested(A_exception("someone error"));
-    }
-}
-void print_tree_exception(exception_ptr e, const std::string & indent ="")
-{
-    const char * indent_unit = " ";
-    const char * mark = "- ";
-    try
-    {
-        rethow_exception(e);
-    }
-    catch(const std::vector<exception_ptr> e)
-    {
-        for(std::vector<exception_ptr>::const_iterator i = e.begin(); i!=e.end(); ++i)
-        {
-            print_tree_exception(i, indent);
-        }
-    }
-    catch(const std::nested_exception  e)
-    {
-        print_tree_exception(evil_i(e), indent +indent_unit);
-    }
-    catch(const std::exception e)
-    {
-        std::cout << indent << mark << e.what() << std::endl;
-    }
-    catch(...)
-    {
-        std::cout << indent << mark << "unknown exception" << std::endl;
-    }
-}
-int main(int, char * [])
-{
-    try
-    {
-        A();
-    }
-    catch()
-    {
-        print_tree_exception(current_exception());
-    }
-    return EXIT_SUCCESS;
-}
-
- -

-List B ( code of tree structured exception handling based on trickerr.h. ) -"trickerr.h" (in Japanese), refer to: -http://tricklib.com/cxx/dagger/trickerr.h. -

- -
-void A()
-{
-    tricklib::error_listener_type error_listener;
-    // A_a() is like A(). A_a() can throw tree structured exception.
-    A_a();
-
-    // *** It must do process so that A_a() throws exception in A(). ***
-    // A_b() is like A(). A_b() can throw tree structured exception.
-    A_b();
-
-    if (error_listener.has_error()) // You can write this "if block" in destructor
-                                    //  of class derived from error_listener_type.
-    {
-        throw_error(new A_error("someone error",error_listener.listener_off().extract_pending_error()));
-    }
-}
-void print_tree_error(const tricklib::error_type &a_error, const std::string & indent = "")
-{
-    const char * indent_unit = " ";
-    const char * mark = "- ";
-
-    tricklib::error_type error = a_error;
-    while(error)
-    {
-        std::cout << indent << mark << error->message << std::endl;
-        if (error->children)
-        {
-            print_tree_error(error->children, indent +indent_unit);
-        }
-        error = error->next;
-    }
-}
-int main(int, char * [])
-{
-    tricklib::error_thread_power error_thread_power_on; // This object is necessary per thread.
-
-    try
-    {
-        A();
-    }
-    catch(error_type error)
-    {
-        print_tree_error(error);
-    }
-    catch(...)
-    {
-        std::cout << "- unknown exception" << std::endl;
-    }
-    return EXIT_SUCCESS;
-}
-
- -

-Prospect -

-

-We will focus on the method A() since the other methods, also main(), occur -only once respectively. -

- -
    -
  • - In the List A above (of the nested exception handling), it is hard to - find out an active reason to use the nested exception handling at this - scene. Rather, we can take a simpler description by throwing the entire - exception_list directly to the top level. -
    • -
  • - The code in the same example gives us a kind of redundant impression, - which might have come from the fact that the try-throw-catch framework does - not assume a tree structured exception handling. -
    • -
- -

-According to the above observation, we cannot help concluding that it is not -so easy to use the nested_exception handling as a tree structured exception -handling mechanism in a practical sense. -

-

-This text is based on the web page below (in Japanese). -http://d.hatena.ne.jp/wraith13/20081231/1230715424 -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. The committee agrees that nested_exception is not a good -match for this usage model. The committee did not see a way of improving -this within the timeframe allowed. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

1139. Thread support library not concept enabled

-

Section: 30 [thread] Status: NAD Concepts - Submitter: LWG Opened: 2009-06-15 Last modified: 2015-04-08

-

View all other issues in [thread].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses US 93, JP 79, UK 333, JP 81

- -

-The thread chapter is not concept enabled. -

- - - -

Proposed resolution:

- - - - - -
-

1140. Numerics library not concept enabled

-

Section: 26 [numerics] Status: NAD Concepts - Submitter: LWG Opened: 2009-06-15 Last modified: 2015-04-08

-

View all other issues in [numerics].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses US 84

- -

-The numerics chapter is not concept enabled. -

- -

-The portion of this comment dealing with random numbers was resolved by -N2836, -which was accepted in Summit. -

- - - -

Proposed resolution:

- - - - - -
-

1141. Input/Output library not concept enabled

-

Section: 27 [input.output] Status: NAD Concepts - Submitter: LWG Opened: 2009-06-15 Last modified: 2015-04-08

-

View all other issues in [input.output].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses US 85, JP 67, JP 68, JP 69, JP 72, UK 308

- -

-The input/output chapter is not concept enabled. -

- - - -

Proposed resolution:

- - - - - -
-

1142. Regular expressions library not concept enabled

-

Section: 28 [re] Status: NAD Concepts - Submitter: LWG Opened: 2009-06-15 Last modified: 2015-04-08

-

View other active issues in [re].

-

View all other issues in [re].

-

View all issues with NAD Concepts status.

-

Discussion:

- -

Addresses US 86, UK 309, UK 310

- -

-The regular expressions chapter is not concept enabled. -

- - - -

Proposed resolution:

- - - - - -
-

1148. Wrong argument type of I/O stream manipulators setprecision() -and setw()

-

Section: 27.7 [iostream.format] Status: NAD - Submitter: Marc Steinbach Opened: 2009-06-20 Last modified: 2015-04-08

-

View all other issues in [iostream.format].

-

View all issues with NAD status.

-

Discussion:

-

-The header <iomanip> synopsis in 27.7 [iostream.format] specifies -

-
-T5 setprecision(int n);
-T6 setw(int n);
-
- -

-The argument types should be streamsize, as in class ios_base -(see 27.5.3 [ios.base]): -

-
-streamsize precision() const;
-streamsize precision(streamsize prec);
-streamsize width() const;
-streamsize width(streamsize wide);
-
- -

-(Editorial: 'wide' should probably be renamed as 'width', or maybe just 'w'.) -

- -

[ -2009-07-29 Daniel clarified wording. -]

- - -

[ -2009 Santa Cruz: -]

- - -
-

-No concensus for this change. There was some interest in doing the opposite -fix: Change the streamsize in <ios> to int. -But ultimately there was no concensus for that change either. -

-
- - - -

Proposed resolution:

-
    -
  1. -

    -In 27.7 [iostream.format], header <iomanip> synopsis change as indicated: -

    - -
    -T5 setprecision(intstreamsize n);
-T6 setw(intstreamsize n);
-
    -
    2. - -
  2. -

    -In 27.7.4 [std.manip], just before p. 6 change as indicated: -

    - -
    -unspecified setprecision(intstreamsize n);
-
    -
    3. - -
  3. -

    -In 27.7.4 [std.manip], just before p. 7 change as indicated: -

    - -
    -unspecified setw(intstreamsize n);
-
    -
    4. -
- - - - - - - - -
-

1149. Reformulating NonemptyRange axiom

-

Section: X [rand.concept.urng] Status: NAD Concepts - Submitter: Walter Brown Opened: 2009-06-25 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

-In X [rand.concept.urng], we have the following: -

-
-concept UniformRandomNumberGenerator<typename G> : Callable<G> {
-  ...
-  axiom NonemptyRange(G& g) {
-    G::min() < G::max();
-  }
-  ...
-}
-
- -

-Since the parameter G is in scope throughout the concept, there is no -need for the axiom to be further parameterized, and so the axiom can be -slightly simplified as: -

- -
-axiom NonemptyRange()  {
-  G::min() < G::max();
-}
-
- -

-We can further reformulate so as to avoid any axiom machinery as: -

- -
-requires True< G::min() < G::max() >;
-
- -

-This is not only a simpler statement of the same requirement, but also -forces the requirement to be checked. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - -

Proposed resolution:

-

-In X [rand.concept.urng], replace the NonemptyRange axiom by: -

- -
-axiom NonemptyRange(G& g) { 
-   G::min() < G::max(); 
-}
-requires True< G::min() < G::max() >;
-
- - - - - - -
-

1153. Standard library needs review for constructors to be -explicit to avoid treatment as initializer-list constructor

-

Section: 17 [library], 30 [thread], D [depr] Status: NAD - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD status.

-

Discussion:

- -

Addresses DE 2

- -

Description

-

Marking a constructor with explicit has semantics - even for a constructor with zero or several parameters: - Such a constructor cannot be used with list-initialization - in a copy-initialization context, see 13.3.1.7 [over.match.list]. The - standard library apparently has not been reviewed for - marking non-single-parameter constructors as explicit.

-

Suggestion

-

Consider marking zero-parameter and multi-parameter - constructors explicit in classes that have at least one - constructor marked explicit and that do not have an - initializer-list constructor.

- -

Notes

-

Robert Klarer to address this one.

- -

[ -2009 Santa Cruz: -]

- - -

-Move to "Open". Robert Klarer has promised to provide wording. -

- -

[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]

- - - - -

Rationale:

-

-We are unaware of any cases where initializer lists cause problem in this -context, but if problems arise in the future the issue can be reopened. -

- - -

Proposed resolution:

- - - - - -
-

1155. Reference should be to C99

-

Section: C.5 [diff.library] Status: NAD Editorial - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [diff.library].

-

View all issues with NAD Editorial status.

-

Discussion:

- -

Addresses FR 38

- -

Description

-

What is ISO/IEC 1990:9899/DAM - 1? My guess is that's a typo for ISO/IEC - 9899/Amd.1:1995 which I'd - have expected to be referenced here (the tables - make reference to things - which were introduced by Amd.1).

-

Suggestion

-

One need probably a reference - to the document which introduce char16_t and - char32_t in C (ISO/IEC TR 19769:2004?).

-

Notes

-

Create issue. Document in question should be C99, not C90+amendment1. The - rest of the section requires careful review for completeness. Example <cstdint> - 18.4.1 [cstdint.syn]. Assign to C liasons.

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD Editorial. Already fixed. -

- - - -

Proposed resolution:

- - - - - -
-

1156. Constraints on bitmask and enumeration types to be tightened

-

Section: 17.5.2.1.2 [enumerated.types], 17.5.2.1.3 [bitmask.types] Status: NAD - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

- -

Addresses UK 165

- -

Description

-

Constraints on - bitmask and enumeration types were supposed to be tightened - up as part of the motivation for the constexpr feature - - see paper - N2235 - for details

-

Suggestion

-

Adopt wording in line with the motivation - described in - N2235

-

Notes

-

Robert Klarer to review

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Open. Ping Robert Klarer to provide wording, using N2235 as guidance. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD. Rationale added. -

- - - -

Rationale:

-

-UK NB did not sufficiently describe how to resolve their comment, and -therefore we cannot make a change for the FCD. If a resolution were -provided in the future, we would be happy to apply it. -

- - -

Proposed resolution:

- - - - - -
-

1164. promise::swap should pass by rvalue reference

-

Section: 30.6.5 [futures.promise] Status: NAD - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

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-

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-

Discussion:

- -

Addresses UK 341

- -

Description

-

promise::swap accepts its parameter by lvalue reference. This is -inconsistent with other types that provide a swap member function, -where those swap functions accept an rvalue reference

- -

Suggestion

-

Change promise::swap to take an rvalue reference.

- -

Notes

-

Create an issue. Detlef will look into it. Probably ready as it.

- -

[ -2009-07 Frankfurt -]

- - -

-NAD, by virtue of the changed rvalue rules and swap signatures from Summit. -

- - - -

Proposed resolution:

- - - - - -
-

1167. pair<T,U> doesn't model LessThanComparable in unconstrained code even if - T and U do.

-

Section: 20.3 [pairs] Status: NAD Concepts - Submitter: Dave Abrahams Opened: 2009-07-01 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Discussion:

-

-LessThanComparable requires (and provides default - implementations for) <=,>, and >=. However, the defaults - don't take effect in unconstrained code. -

-

-Still, it's a problem to have types acting one way in -constrained code and another in unconstrained code, except in cases of -syntax adaptation. It's also inconsistent with the containers, which -supply all those operators. -

-

-Totally Unbiased -Suggested Resolution: -

-

-accept the exported concept maps proposal and - change the way this stuff is handled to use an - explicit exported concept map rather than nested - function templates -

-

-e.g., remove from the body of std::list -

-
-template <LessThanComparable T, class Allocator> 
-bool operator< (const list<T,Allocator>& x, const list<T,Allocator>& y); 
-template <LessThanComparable T, class Allocator> 
-bool operator> (const list<T,Allocator>& x, const list<T,Allocator>& y); 
-template <LessThanComparable T, class Allocator> 
-bool operator>=(const list<T,Allocator>& x, const list<T,Allocator>& y); 
-template <LessThanComparable T, class Allocator> 
-bool operator<=(const list<T,Allocator>& x, const list<T,Allocator>& y); 
-
-

-and add this concept_map afterwards: -

-
-template <LessThanComparable T, class Allocator> 
-export concept_map LessThanComparable<list<T,Allocator> >
-{
-    bool operator<(const list<T,Allocator>& x, const list<T,Allocator>& y);
-}
-
-

-do similarly for std::pair. While you're at it, do the same for -operator== and != everywhere, and seek out other such opportunities. -

-

-Alternative Resolution: keep the ugly, complex specification and add the - missing operators to std::pair. -

- - -

Proposed resolution:

- - - - - -
-

1168. Odd wording for bitset equality operators

-

Section: 20.6.2 [bitset.members] Status: NAD Editorial - Submitter: Alisdair Meredith Opened: 2009-07-02 Last modified: 2015-04-08

-

View all other issues in [bitset.members].

-

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-

Discussion:

-

-The following wording seems a little unusual to me: -

-

-p42/43 20.6.2 [bitset.members] -

- -
-
-bool operator==(const bitset<N>& rhs) const;
-
-

--42- Returns: A nonzero value if the value of each bit in -*this equals the value of the corresponding bit in -rhs. -

-
-bool operator!=(const bitset<N>& rhs) const;
-
-

--43- Returns: A nonzero value if !(*this == rhs). -

-
- -

-"A nonzero value" may be well defined as equivalent to the literal 'true' -for Booleans, but the wording is clumsy. I suggest replacing "A nonzero value" -with the literal 'true' (in appropriate font) in each case. -

- -

[ -2009-07-24 Alisdair recommends NAD Editorial. -]

- - -

[ -2009-07-27 Pete adds: -]

- - -

-It's obviously editorial. There's no need for further discussion. -

- -

[ -2009-07-27 Howard sets to NAD Editorial. -]

- - - - -

Proposed resolution:

-

-Change 20.6.2 [bitset.members] p42-43: -

- -
-
-bool operator==(const bitset<N>& rhs) const;
-
-

--42- Returns: A nonzero value true if the value of each bit in -*this equals the value of the corresponding bit in -rhs. -

-
-bool operator!=(const bitset<N>& rhs) const;
-
-

--43- Returns: A nonzero value true if !(*this == rhs). -

-
- - - - - - -
-

1176. Make thread constructor non-variadic

-

Section: 30.3.1.2 [thread.thread.constr] Status: NAD - Submitter: Howard Hinnant Opened: 2009-07-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The variadic thread constructor is causing controversy, e.g. -N2901. -This issue has been created as a placeholder for this course of action. -

- -
-template <class F, class ...Args> thread(F&& f, Args&&... args);
-
- -

-See 929 for wording which specifies an rvalue-ref signature but -with "decay behavior", but using variadics. -

- -

[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Proposed resolution:

-

-

- - -

Rationale:

-

-The (tentative) concensus of the LWG is to keep the variadic thread constructor. -

- - - - - -
-

1179. Probably editorial in [structure.specifications]

-

Section: 17.5.1.4 [structure.specifications] Status: NAD Editorial - Submitter: Robert Klarer Opened: 2009-07-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-While reviewing 971 I noted that 17.5.1.4 [structure.specifications]/7 says: -

- -

--7- Error conditions specify conditions where a function may fail. The -conditions are listed, together with a suitable explanation, as the enum -class errc constants (19.5) that could be used as an argument to -function make_error_condition (19.5.3.6). -

- -

-This paragraph should mention make_error_code or the text "that -could be used as an argument to function make_error_condition -(19.5.3.6)" should be deleted. I believe this is editorial. -

- -

[ -2009-07-21 Chris adds: -]

- - -
-

-I'm not convinced there's a problem there, because as far as the "Error -conditions" clauses are concerned, make_error_condition() is used by a -user to test for the condition, whereas make_error_code is not. For -example: -

- -
-void foobar(error_code& ec = throws());
-
- -

- Error conditions: -

-

-permission_denied - Insufficient privilege to perform operation. -

- -

-When a user writes: -

- -
-error_code ec;
-foobar(ec);
-if (ec == errc::permission_denied)
-   ...
-
- -

-the implicit conversion errc->error_condition makes the if-test -equivalent to: -

- -
-if (ec == make_error_condition(errc::permission_denied))
-
- -

-On the other hand, if the user had written: -

- -
-if (ec == make_error_code(errc::permission_denied))
-
- -

-the test is now checking for a specific error code. The test may -evaluate to false even though foobar() failed due to the documented -error condition "Insufficient privilege". -

-
- -

[ -2009 Santa Cruz: -]

- - -
-

-NAD Editorial. -

-

-What the WP says right now is literally true: these codes can be used as -an argument to make_error_condition. (It is also true that they can be -used as an argument to make_error_code, which the WP doesn't say.) Maybe -it would be clearer to just delete "that could be used as an argument to -function make_error_condition", since that fact is already implied by -other things that we say. We believe that this is editorial. -

-
- - - -

Proposed resolution:

-

-

- - - - - -
-

1186. Forward list could model a stack

-

Section: 23.6.5 [stack] Status: NAD Concepts - Submitter: Alisdair Meredith Opened: 2009-07-31 Last modified: 2015-04-08

-

View all issues with NAD Concepts status.

-

Discussion:

-

-The library template forward_list could easily model the idea of a -stack, where the operations work on the front of the list rather than -the back. However, the standard library stack adaptor cannot support -this. -

- -

-It would be relatively easy to write a partial specialization for stack -to support forward_list, but that opens the question of which header to -place it in. A much better solution would be to add a concept_map for -the StackLikeContainer concept to the <forward_list> header and then -everything just works, including a user's own further uses in a -stack-like context. -

- -

-Therefore while I am submitting the issue now so that it is on record, I -strongly recommend we resolve as "NAD Concepts" as any non-concepts -based solution will be inferior to the final goal, and the feature is -not so compelling it must be supported ahead of the concepts-based -library. -

- -

[ -2009-11-02 Howard adds: -]

- - -

-Moved to Tentatively NAD Concepts after 5 positive votes on c++std-lib. -

- - -

Rationale:

-

-Any non-concepts based solution will be inferior to the final goal, and the -feature is not so compelling it must be supported ahead of the concepts-based -library. -

- - - -

Proposed resolution:

- - - - - -
-

1190. Setting the maximum load factor should return the previous value

-

Section: 23.2.5 [unord.req], 23.5 [unord] Status: NAD - Submitter: Matt Austern Opened: 2009-08-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The unordered associative container requirements table specifies that -a.set_max_load_factor(z) has return type void. However, there is a -useful piece of information to return: the previous value. Users who -don't need it can always ignore it. -

- - -

[ -2010 Rapperswil: -]

- - -

-The benefit seems minor, while breaking with the getter/setter idiom these overloads support. - -Move to Tentatively NAD. -

- -

[ -Moved to NAD at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-In the unordered associative container requirements table, change: -

- -
- - - - - - - - - - - - - - -
Table 87 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
a.max_load_factor(z)void floatPre: z shall be positive. Changes the container's maximum -load load factor, using z as a hint. -Returns: the previous value of -a.max_load_factor(). - -constant -
-
- -

-Change the return type of set_max_load_factor -in the class synopses in 23.5.4 [unord.map], 23.5.5 [unord.multimap], 23.5.6 [unord.set], -and 23.5.7 [unord.multiset]. -

- -

-If issue 1188 is also accepted, make the same changes for -min_load_factor. -

- - - - - -
-

1200. "surprising" char_traits<T>::int_type requirements

-

Section: 21.2.2 [char.traits.typedefs] Status: NAD - Submitter: Sean Hunt Opened: 2009-09-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The footnote for int_type in 21.2.2 [char.traits.typedefs] says that -

- -

-If eof() can be held in char_type then some iostreams implementations -may give surprising results. -

- -

-This implies that int_type should be a superset of -char_type. However, the requirements for char16_t and char32_t define -int_type to be equal to int_least16_t and int_least32_t respectively. -int_least16_t is likely to be the same size as char_16_t, which may lead -to surprising behavior, even if eof() is not a valid UTF-16 code unit. -The standard should not prescribe surprising behavior, especially -without saying what it is (it's apparently not undefined, just -surprising). The same applies for 32-bit types. -

- -

-I personally recommend that behavior be undefined if eof() is a member -of char_type, and another type be chosen for int_type (my personal -favorite has always been a struct {bool eof; char_type c;}). -Alternatively, the exact results of such a situation should be defined, -at least so far that I/O could be conducted on these types as long as -the code units remain valid. Note that the argument that no one streams -char16_t or char32_t is not really valid as it would be perfectly -reasonable to use a basic_stringstream in conjunction with UTF character -types. -

- -

[ -2009-10-28 Ganesh provides two possible resolutions and expresses a preference -for the second: -]

- - -
-
    -
  1. -

    -Replace 21.2.3.2 [char.traits.specializations.char16_t] para 3 with: -

    - -

    -The member eof() shall return an implementation-defined -constant that cannot appear as a valid UTF-16 code unit -UINT_LEAST16_MAX [Note: this value is guaranteed to -be a permanently reserved UCS-2 code position if UINT_LEAST16_MAX == -0xFFFF and it's not a UCS-2 code position otherwise — end -note]. -

    - -

    -Replace 21.2.3.3 [char.traits.specializations.char32_t] para 3 with: -

    - -

    -The member eof() shall return an implementation-defined constant that -cannot appear as a Unicode code point - -UINT_LEAST32_MAX [Note: this value is guaranteed to be a -permanently reserved UCS-4 code position if UINT_LEAST32_MAX == -0xFFFFFFFF and it's not a UCS-4 code position otherwise — end -note]. -

    -
    2. -
  2. -

    -In 21.2.3.2 [char.traits.specializations.char16_t], in the -definition of char_traits<char16_t> replace the definition of nested -typedef int_type with: -

    - -
    -namespace std {
-  template<> struct char_traits<char16_t> {
-    typedef char16_t         char_type;
-    typedef uint_least16_t uint_fast16_t int_type;
-     ...
-
    - -

    -Replace 21.2.3.2 [char.traits.specializations.char16_t] para 3 with: -

    - -

    -The member eof() shall return an implementation-defined -constant that cannot appear as a valid UTF-16 code unit -UINT_FAST16_MAX [Note: this value is guaranteed to -be a permanently reserved UCS-2 code position if UINT_FAST16_MAX == -0xFFFF and it's not a UCS-2 code position otherwise — end -note]. -

    - -

    -In 21.2.3.3 [char.traits.specializations.char32_t], in the -definition of char_traits<char32_t> replace the definition of nested -typedef int_type with: -

    - -
    -namespace std {
-  template<> struct char_traits<char32_t> {
-    typedef char32_t         char_type;
-    typedef uint_least32_t uint_fast32_t int_type;
-     ...
-
    - -

    -Replace 21.2.3.3 [char.traits.specializations.char32_t] para 3 with: -

    - -

    -The member eof() shall return an implementation-defined constant that -cannot appear as a Unicode code point - -UINT_FAST32_MAX [Note: this value is guaranteed to be a -permanently reserved UCS-4 code position if UINT_FAST32_MAX == -0xFFFFFFFF and it's not a UCS-4 code position otherwise — end -note]. -

    -
    3. -
-
- - -

[ -2010 Rapperswil: -]

- - -

-This seems an overspecification, and it is not clear what problem is being solved - -these values can be used portably by using the named functions; there is no need -for the value itself to be portable. - -Move to Tentatively NAD. -

- -

[ -Moved to NAD at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-

- - - - - -
-

1202. integral_constant needs a spring clean

-

Section: 20.10.3 [meta.help] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-09-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The specification of integral_constant has been inherited -essentially unchanged from TR1: -

- -
-template <class T, T v>
-struct integral_constant {
-  static const T value = v;
-  typedef T value_type;
-  typedef integral_constant<T,v> type;
-};
-
- -

-In light of 0x language changes there are several things we might -consider changing, notably the form of specification for value. -

- -

-The current form requires a static data member have storage allocated -for it, where we could now implement without this using the new enum -syntax: -

- -
-template <class T, T v>
-struct integral_constant {
-  enum : T { value = v };
-  typedef T value_type;
-  typedef integral_constant type;
-};
-
- -

-The effective difference between these two implementation is: -

- -
    -
  1. -No requirement to allocate storage for data member (which we hope but do -not guarantee compilers strip today) -
    2. - -
  2. -You can no longer take the address of the constant as -&integral_constant<T,v>::value; -
    3. -
- -

-Also note the editorial change to drop the explicit qualification of -integral_constant in the typedef type. This makes it quite clear we -mean the current instantiation, and cannot be mistaken for a recursive -metaprogram. -

- -

-Even if we don't mandate this implementation, it would be nice to give -vendors freedom under QoI to choose their preferred representation. -

- -

-The other side of this issue is if we choose to retain the static -constant form. In that case we should go further and insist on -constexpr, much like we did throughout numeric_limits: -

- -
-template <class T, T v>
-struct integral_constant {
-  static constexpr T value = v;
-  typedef T value_type;
-  typedef integral_constant type;
-};
-
- -

-[Footnote] It turns out constexpr is part of the Tentatively Ready -resolution for 1019. I don't want to interfere with that issue, but -would like a new issue to consider if the fixed-base enum implementation -should be allowed. -

- -

[ -2009-09-05 Daniel adds: -]

- - -
-

-I think that the suggested resolution is incomplete and -may have some possible unwanted side-effects. To understand -why, note that integral_constant is completely specified -by code in 20.10.3 [meta.help]. While this is usually considered -as a good thing, let me give a possible user-defined -specialization that would break given the suggested changes: -

- -
-enum NodeColor { Red, Black };
-
-std::integral_constant<NodeColor, Red> red;
-
- -

-The reason why that breaks is due to the fact that -current core language rules does only allow integral -types as enum-bases, see 7.2 [dcl.enum]/2. -

- -

-So, I think that we cannot leave the implementation the -freedom to decide which way they would like to provide -the implementation, because that is easily user-visible -(I don't speak of addresses, but of instantiation errors), -therefore if applied, this should be either specified or -wording must be added that gives a note about this -freedom of implementation. -

- -

-Another possible disadvantage seems to me that user-expectations -are easy to disappoint if they see a failure -of the test -

- -
-assert(typeid(std::integral_constant<int, 0>::value) == typeid(int));
-
- -

-or of -

- -
-static_assert(std::is_same<decltype(std::integral_constant<int, 0>::value), const int>::value, "Bad library");
-
- -
- -

[ -2010-01-14 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -]

- - - - -

Rationale:

-

-We think that the suggested resolution is incomplete and may have some possible -unwanted side-effects. (see Daniel's 2009-09-05 comment for details). -

- - -

Proposed resolution:

- - - - - -
-

1219. unique_lock::lock and resource_deadlock_would_occur

-

Section: 30.4.2.2.2 [thread.lock.unique.locking] Status: Dup - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1159

-

Discussion:

- - - -

-unique_lock::lock and friends raise -"resource_deadlock_would_occur -- if the current thread already -owns the mutex (i.e., on entry, owns is true)." 1) -The current thread owning a mutex is not the same as any particular -unique_lock::owns being true. 2) There's no need to -raise this exception for a recursive_mutex if owns is -false. 3) If owns is true, we need to raise some -exception or the unique_lock will lose track of whether to unlock itself -on destruction, but "deadlock" isn't it. For (3), s/bool owns/int -ownership_level/ would fix it. -

- -

[ -2009-11-11 Alisdair notes that this issue is very closely related to 1159, -if not a dup. -]

- - -

[ -2009-11-14 Moved to Tentatively Dup after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- - - - - -
-

1223. condition_variable_any lock matching?

-

Section: 30.5.2 [thread.condition.condvarany] Status: NAD - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-For condition_variable_any, must all lock arguments to concurrent wait calls -"match" in some way, similar to the requirement in -30.5.1 [thread.condition.condvar] that lock.mutex() returns the same -value for each of the lock arguments supplied by all concurrently -waiting threads (via wait or timed_wait)? -

- -

[ -2010-02-12 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - - -

Rationale:

-

-The rationale is that it doesn't matter, and you can't check: the lock types may -be different, or the same and user-defined, so the implementation must provide -internal synchronization anyway. -

- - -

Proposed resolution:

- - - - - -
-

1224. condition_variable_any support for recursive mutexes?

-

Section: 30.5.2 [thread.condition.condvarany] Status: NAD - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-For condition_variable_any, are recursive mutexes allowed? (I think "no") -

- -

[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Proposed resolution:

- - -

Rationale:

-

-condition_variable_any::wait accepts any type of mutex. It calls -unlock precisely once on entry and lock precisely once on -exit. It is up to the user to ensure that this provides the required -synchronization. Use of a recursive mutex is safe if either its lock count is 1, -so after the single unlock it can be acquired by another thread, or another -mechanism is used to synchronize the data. -

- - - - - -
-

1228. User-specialized nothrow type traits

-

Section: 20.10.4.3 [meta.unary.prop] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-10-07 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

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-

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-

Discussion:

-

-According to p1 20.10.2 [meta.type.synop]: -

- -

-The behavior of a program that adds specializations for any of the class -templates defined in this subclause is undefined unless otherwise -specified. -

- -

-I believe we should 'otherwise specify' for the nothrow traits, are -these are exactly the use cases where the end user actually has more -information than the compiler. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Open. Definitely need to give the users the ability to ensure -that the traits give the right answers. Unsure we want to give them the -ability to say this in more than one way. Believes the noexcept proposal -already gives this. -

- -

[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]

- - - - -

Rationale:

-

-We believe the solution offered by -N3050 -is superior. -

- - -

Proposed resolution:

-

-Add the following comment: -

- -

-user specialization permitted to derive from std::true_type when the -operation is known not to throw. -

- -

-to the following traits in 20.10.4.3 [meta.unary.prop] Table 43 Type -property predicates. -

- -

[ -This may require a new Comments column -]

- - -
-has_nothrow_default_constructor
-has_nothrow_copy_constructor
-has_nothrow_assign
-
- - - - - -
-

1230. mem_fn and variadic templates

-

Section: 20.9.11 [func.memfn] Status: Dup - Submitter: Alisdair Meredith Opened: 2009-10-09 Last modified: 2015-04-08

-

View all other issues in [func.memfn].

-

View all issues with Dup status.

-

Duplicate of: 920

-

Discussion:

- - - -

-Since we have removed the entry in B [implimits] for the -library-specific limit for number of arguments passed to -function/tuple/etc. I believe we need to update the -spec for mem_fn to reflect this. -

- -

-The "Remarks: Implementations may implement mem_fn as a set of -overloaded function templates." no longer holds, as we cannot create an -arbitrary number of such overloads. I believe we should strike the -remark and add a second signature: -

- -
-template<class R, class T, typename ... ArgTypes>
-  unspecified mem_fn(R (T::*pm)(ArgTypes...));
-
- -

-I believe we need two signatures as pointer-to-data-member and -pointer-to-member-function-taking-no-args appear to use subtly different -syntax. -

- -

[ -920 as a similar proposed resolution. -]

- - - -

Proposed resolution:

-

-Add to 20.9 [function.objects] and 20.9.11 [func.memfn]: -

-
-template<class R, class T> unspecified mem_fn(R T::* pm)
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...));
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...)&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile&);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...)&&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const&&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile&&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile&&);
-
- -

-Strike 20.9.11 [func.memfn], p5: -

- -

-Remarks: Implementations may implement mem_fn as a set -of overloaded function templates. -

- - - - - - -
-

1232. Still swap's with rvalue-references

-

Section: 17 [library] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2009-10-11 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-The current library contains still rvalue reference-swaps that seem to be -overlooked in the process of switching back to lvalue-ref swaps. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Editor accepts as NAD Editorial. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 20.3 [pairs]/1 as indicated: -

    - -
    -template <class T1, class T2>
-struct pair {
-  ...
-  void swap(pair&& p);
-};
-
    -
    2. - -
  2. -

    -Change 20.3 [pairs] before p. 17 as indicated: -

    - -
    -void swap(pair&& p);
-
    - -
    3. - -
  3. - -

    -Change 20.3 [pairs] before p. 21 as indicated: -

    - -
    -template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>& y);
-template<class T1, class T2> void swap(pair<T1, T2>&& x, pair<T1, T2>& y);
-template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>&& y);
-
    - -
    4. - -
  4. -

    -Change 20.4.1 [tuple.general]/2, header <tuple> synopsis, as indicated: -

    - -
    -// 20.5.2.9, specialized algorithms:
-template <class... Types>
-void swap(tuple<Types...>& x, tuple<Types...>& y);
-template <class... Types>
-void swap(tuple<Types...>&& x, tuple<Types...>& y);
-template <class... Types>
-void swap(tuple<Types...>& x, tuple<Types...>&& y);
-
    - -
    5. - -
  5. -

    -Change 20.4.2 [tuple.tuple] as indicated: -

    - -
    -// 20.5.2.3, tuple swap
-void swap(tuple&&)
-
    - -
    6. - -
  6. -

    -Change 20.4.2.3 [tuple.swap] before 1 as indicated: -

    - -
    -void swap(tuple&& rhs);
-
    - -
    7. - -
  7. -

    -Change 20.9 [function.objects]/2, header <functional> synopsis, as indicated: -

    - -
    -template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
-template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
-template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)&&);
-
    - -
    8. - -
  8. -

    -Change 20.9.12.2 [func.wrap.func], as indicated: -

    - -
    -// 20.7.15.2.2, function modifiers:
-void swap(function&&);
-template<class F, class A> void assign(F, const A&);
-
-[..]
-
-// 20.7.15.2.7, specialized algorithms:
-template <class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
-template <class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
-template <class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);
-
    - -
    9. - -
  9. -

    -Change 20.9.12.2.7 [func.wrap.func.alg] before 1 as indicated: -

    - -
    -template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>& f2);
-template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>&& f1, function<R(ArgTypes...)>& f2);
-template<class R, class... ArgTypes>
-void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>&& f2);
-
    - -
    10. - -
  10. -

    -Change 20.8.2.2 [util.smartptr.shared]/1 as indicated: -

    - -
    -// 20.8.12.2.4, modifiers:
-void swap(shared_ptr&& r);
-
-[..]
-
-// 20.8.12.2.9, shared_ptr specialized algorithms:
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);
-
    - -
    11. - -
  11. -

    -Change 21.3 [string.classes]/1, header <string> synopsis, as indicated: -

    - -
    -// 21.4.8.8: swap
-template<class charT, class traits, class Allocator>
-void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>& rhs);
-template<class charT, class traits, class Allocator>
-void swap(basic_string<charT,traits,Allocator>&& lhs, basic_string<charT,traits,Allocator>& rhs);
-template<class charT, class traits, class Allocator>
-void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>&& rhs);
-
    - -
    12. - -
  12. -

    -Change 23.3 [sequences]/1, header <deque> synopsis, as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);
-
    - -
    13. - -
  13. -

    -Change 23.3 [sequences]/1, header <list> synopsis, as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>&& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>&& y);
-
    - -
    14. - -
  14. -

    -Change 23.3 [sequences]/1, header <queue> synopsis, as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(queue<T, Container>& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>&& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>& x, queue<T, Container>&& y);
-
-template <class T, class Container = vector<T>, class Compare = less<typename Container::value_type> >
-class priority_queue;
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);
-
    - -
    15. - -
  15. -

    -Change 23.3 [sequences]/1, header <stack> synopsis, as indicated: -

    - -
    -template <class T, class Container>
-void swap(stack<T, Container>& x, stack<T, Container>& y);
-template <class T, class Container>
-void swap(stack<T, Container>&& x, stack<T, Container>& y);
-template <class T, class Container>
-void swap(stack<T, Container>& x, stack<T, Container>&& y);
-
    - -
    16. - -
  16. -

    -Change 23.3 [sequences]/1, header <vector> synopsis, as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);
-
    - -
    17. - -
  17. -

    -Change 23.3.3 [deque]/2 as indicated: -

    - -
    -iterator erase(const_iterator position);
-iterator erase(const_iterator first, const_iterator last);
-void swap(deque<T,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);
-
    - -
    18. - -
  18. -

    -Change 23.3.3.5 [deque.special] as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);
-
    - -
    19. - -
  19. -

    -Change 23.3.4 [forwardlist]/2 as indicated: -

    - -
    -iterator erase_after(const_iterator position);
-iterator erase_after(const_iterator position, iterator last);
-void swap(forward_list<T,Allocator>&&);
-
-[..]
-
-// 23.3.3.6 specialized algorithms:
-template <class T, class Allocator>
-void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(forward_list<T,Allocator>&& x, forward_list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>&& y);
-
    - -
    20. - -
  20. -

    -Change 23.3.4.7 [forwardlist.spec] as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(forward_list<T,Allocator>&& x, forward_list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>&& y);
-
    - -
    21. - -
  21. -

    -Change 23.3.5 [list]/2 as indicated: -

    - -
    -iterator erase(const_iterator position);
-iterator erase(const_iterator position, const_iterator last);
-void swap(list<T,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>&& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>&& y);
-
    - -
    22. - -
  22. -

    -Change 23.3.5.6 [list.special] as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>&& x, list<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(list<T,Allocator>& x, list<T,Allocator>&& y);
-
    - -
    23. - -
  23. -

    -Change 23.6.3.1 [queue.defn] as indicated: -

    - -
    -void swap(queue&& q) { c.swap(q.c); }
-
-[..]
-
-template <class T, class Container>
-void swap(queue<T, Container>& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>&& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>& x, queue<T, Container>&& y);
-
    - -
    24. - -
  24. -

    -Change 23.6.3.5 [queue.special] as indicated: -

    - -
    -template <class T, class Container>
-void swap(queue<T, Container>& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>&& x, queue<T, Container>& y);
-template <class T, class Container>
-void swap(queue<T, Container>& x, queue<T, Container>&& y);
-
    - -
    25. - -
  25. -

    -Change 23.6.4 [priority.queue]/1 as indicated: -

    - -
    -void swap(priority_queue&&);
-
-// no equality is provided
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, class Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);
-
    - -
    26. - -
  26. -

    -Change 23.6.4.4 [priqueue.special] as indicated: -

    - -
    -template <class T, class Container, Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, Compare>
-void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y);
-template <class T, class Container, Compare>
-void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);
-
    - -
    27. - -
  27. -

    -Change 23.6.5.2 [stack.defn] as indicated: -

    - -
    -void swap(stack&& s) { c.swap(s.c); }
-
-[..]
-
-template <class T, class Allocator>
-void swap(stack<T,Allocator>& x, stack<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(stack<T,Allocator>&& x, stack<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(stack<T,Allocator>& x, stack<T,Allocator>&& y);
-
    - - -
    28. - -
  28. -

    -Change 23.6.5.6 [stack.special] as indicated: -

    - -
    -template <class T, class Container>
-void swap(stack<T, Container>& x, stack<T, Container>& y);
-template <class T, class Container>
-void swap(stack<T, Container>&& x, stack<T, Container>& y);
-template <class T, class Container>
-void swap(stack<T, Container>& x, stack<T, Container>&& y);
-
    - -
    29. - -
  29. -

    -Change 23.3.6 [vector]/2 as indicated: -

    - -
    -void swap(vector<T,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);
-
    - -
    30. - -
  30. -

    -Change 23.3.6.3 [vector.capacity] before p. 8 as indicated: -

    - -
    -void swap(vector<T,Allocator>&& x);
-
    - -
    31. - -
  31. -

    -Change 23.3.6.6 [vector.special] as indicated: -

    - -
    -template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y);
-template <class T, class Allocator>
-void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);
-
    - -
    32. - -
  32. -

    -Change 23.3.7 [vector.bool]/1 as indicated: -

    - -
    -iterator erase(const_iterator first, const_iterator last);
-void swap(vector<bool,Allocator>&&);
-static void swap(reference x, reference y);
-
    - -
    33. - -
  33. -

    -Change 23.4 [associative]/1, header <map> synopsis as indicated: -

    - -
    -template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator&& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator& x, map<Key,T,Compare,Allocator>&& y);
-
-[..]
-
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator&& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator& x, multimap<Key,T,Compare,Allocator>&& y);
-
    - -
    34. - -
  34. -

    -Change 23.4 [associative]/1, header <set> synopsis as indicated: -

    - -
    -template <class Key, class Compare, class Allocator>
-void swap(set<Key,Compare,Allocator>& x, set<Key,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(set<Key,T,Compare,Allocator&& x, set<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(set<Key,T,Compare,Allocator& x, set<Key,T,Compare,Allocator>&& y);
-
-[..]
-
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multiset<Key,T,Compare,Allocator&& x, multiset<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multiset<Key,T,Compare,Allocator& x, multiset<Key,T,Compare,Allocator>&& y);
-
    - -
    35. - -
  35. -

    -Change 23.4.4 [map]/2 as indicated: -

    - -
    -iterator erase(const_iterator first, const_iterator last);
-void swap(map<Key,T,Compare,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator&& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator& x, map<Key,T,Compare,Allocator>&& y);
-
    - -
    36. - -
  36. -

    -Change 23.4.4.5 [map.special] as indicated: -

    - -
    -template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator>&& x, map<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>&& y);
-
    - -
    37. - -
  37. -

    -Change 23.4.5 [multimap]/2 as indicated: -

    - -
    -iterator erase(const_iterator first, const_iterator last);
-void swap(multimap<Key,T,Compare,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator&& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator& x, multimap<Key,T,Compare,Allocator>&& y);
-
    - -
    38. - -
  38. -

    -Change 23.4.5.4 [multimap.special] as indicated: -

    - -
    -template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator>&& x, multimap<Key,T,Compare,Allocator>& y);
-template <class Key, class T, class Compare, class Allocator>
-void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>&& y);
-
    - -
    39. - -
  39. -

    -Change 23.4.6 [set]/2 and 23.4.6.3 [set.special] as indicated: (twice!) -

    - -
    -// specialized algorithms:
-template <class Key, class Compare, class Allocator>
-void swap(set<Key,Compare,Allocator>& x, set<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(set<Key,Compare,Allocator&& x, set<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(set<Key,Compare,Allocator& x, set<Key,Compare,Allocator>&& y);
-
    - -
    40. - -
  40. -

    -Change 23.4.7 [multiset]/2 as indicated: -

    - -
    -iterator erase(const_iterator first, const_iterator last);
-void swap(multiset<Key,Compare,Allocator>&&);
-void clear();
-
-[..]
-
-// specialized algorithms:
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator&& x, multiset<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator& x, multiset<Key,Compare,Allocator>&& y);
-
    - -
    41. - -
  41. -

    -Change 23.4.7.3 [multiset.special] as indicated: -

    - -
    -template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator>&& x, multiset<Key,Compare,Allocator>& y);
-template <class Key, class Compare, class Allocator>
-void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>&& y);
-
    - -
    42. -
- - - - - -
-

1233. Missing unique_ptr signatures in synopsis

-

Section: 20.7 [memory] Status: NAD Editorial - Submitter: Daniel Krügler Opened: 2009-10-11 Last modified: 2015-04-08

-

View all other issues in [memory].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-Related to 296. Some unique_ptr signatures are missing -from the synopsis in 20.7 [memory]. -

- -

[ -2009-11-04 Howard adds: -]

- - -

-Moved to Tentatively NAD Editorial. The editor has adopted the fix. -

- - -

Proposed resolution:

-

-Add in 20.7 [memory], Header <memory> synopsis -missing declarations as shown below: -

- -
-// 20.8.11 Class unique_ptr:
-template <class X> class default_delete;
-template<class T> struct default_delete<T[]>;
-template <class X, class D = default_delete<T>> class unique_ptr;
-template<class T, class D> class unique_ptr<T[], D>;
-
-template<class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y);
-
-template<class T1, class D1, class T2, class D2>
-bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-template<class T1, class D1, class T2, class D2>
-bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-template<class T1, class D1, class T2, class D2>
-bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-template<class T1, class D1, class T2, class D2>
-bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-template<class T1, class D1, class T2, class D2>
-bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-template<class T1, class D1, class T2, class D2>
-bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
- - - - - -
-

1236. reserved identifiers in programs not using the library

-

Section: 17 [library] Status: NAD - Submitter: Sean Hunt Opened: 2009-10-13 Last modified: 2015-04-08

-

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-

View all other issues in [library].

-

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-

Discussion:

-

-I wasn't sure whether to consider this a library or a language issue, -because the issue is I think it's incorrectly categorized as being part -of the library, so I thought I'd send a message to both of you and let -you sort it out. -

- -

-Most reserved identifiers are treated as unilaterally available to the -implementation, such as to implement language extensions, or provide -macros documenting its functionality. However, the requirements for -reserved identifers are in 17.6.4.3 [reserved.names], which are a -subsection of 17.6.4 [constraints]. 17.6.4.1 [constraints.overview] appears only to apply to "C++ programs -that use the facilities of the C++ standard library", meaning that, in -theory, all implementations are erroneous in having any non-standard -identifiers predefined for programs that do not, at some point, include -a standard library header. -

- -

-Furthermore, it's unclear whether the use of certain identifiers is UB -or results in an ill-formed program. In particular, 17.6.4.3.1 [macro.names] uses a "shall not", where [global.names] says that names are "reserved to the -implementation". 17.6.4.3 [reserved.names] seems only to cover the -instance of a name being described as "reserved", so are implementations -required to diagnose a program that performs, as an example, "#undef -get"? -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to NAD. There may in theory be multiple interpretations possible, -but there's no evidence that this causes any genuine problems or -uncertainty about what implementations are allowed to do. We do not -believe this rises to the level of a defect. -

- - - -

Proposed resolution:

- - - - - -
-

1239. Defect report

-

Section: 20.10.4.3 [meta.unary.prop] Status: NAD Editorial - Submitter: David Abrahams Opened: 2009-10-16 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

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-

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-

Discussion:

-

-Table 43 defines a number of traits that yield true for arrays of class -types with the trait's property, but not arrays of other types with that -property. For example, has_trivial_default_constructor: -

- -

-T is a trivial type (3.9) or a class type with a trivial default -constructor (12.1) or an array of such a class type. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -
-

-An array of a trivial type is a trivial type. -

-

-Mark as Tentatively NAD Editorial. The wording is OK as is, -since an array of a trivial type is a trivial type, but the wording as -proposed might be clearer. -

-
- - - -

Rationale:

-

-The wording is OK as is, since an array of a trivial type is a trivial type. -Project editor may wish to accept the suggested wording as editorial. -

- - -

Proposed resolution:

-

-Change all the traits in question following this pattern: -

- -

-T is a trivial type (3.9) or a class type with a trivial default - constructor (12.1), or an array of such a class type. -

- -

-i.e., add a comma and delete a "class." -

- - - - - -
-

1243. Missing operator+= (initializer_list<T>) for valarray

-

Section: 26.6.2.7 [valarray.cassign] Status: NAD - Submitter: Daniel Krügler Opened: 2009-10-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses JP 64

- -

-During the additions of initializer_list overloads -basic_string added: -

- -
-basic_string& operator+=(initializer_list<charT>);
-
- -

-but -

- -
-valarray<T>& operator+= (initializer_list<T>);
-
- -

-was not defined. -

- -

[ -Daniel adds on opening: -]

- - -

-Recommend NAD. The operator+= overload of basic_string -behaves as-if calling append, which is completely different in -meaning as the existing operator+= overloads in -valarray which just sum the value or values to the existing -elements. The suggestion to add a corresponding append function to -valarray was not considered as appropriate and the request was -withdrawn (c++std-lib-24968). -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD. Request has been withdrawn by NB. -

- - - -

Proposed resolution:

-

-Add to 26.6.2.7 [valarray.cassign]: -

- -
-valarray<T>& operator+= (initializer_list<T>);
-
- - - - - -
-

1246. vector::resize() missing efficiency guarantee

-

Section: 23.3.6.3 [vector.capacity] Status: NAD - Submitter: David Abrahams Opened: 2009-10-24 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-If v is a vector, I think repeated calls to -v.resize( v.size() + 1 ) should be amortized O(1), but it's not -clear that's true from the text of the standard: -

- -
-void resize(size_type sz);
-
-

-Effects: If sz < size(), equivalent to erase(begin() + sz, end());. If -size() < sz, appends sz - size() default constructed elements to the -sequence. -

-
- -

-Seems to me if we used push_back instead of appends, we might be giving -the guarantee I'd like. Thoughts? -

- -

[ -2009-11-10 Howard adds: -]

- - -

-Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale added -below. -

- - - -

Proposed resolution:

-

-In 23.3.6.3 [vector.capacity]/10, change -

- -
-void resize(size_type sz);
-
-

-Effects: If sz < size(), equivalent to erase(begin() + sz, end());. If -size() < sz, appends sz - size() default constructed elements to the -sequence -equivalent to sz - size() consecutive evaluations of push_back(T()). -

-
- - - -

Rationale:

-

-The description in terms of push_back led some to believe that -one could expect the exact same growth pattern from both resize and -push_back (e.g.) which could lead to sub-optimal implementations. -Additionally, 23.3.6 [vector], p1 includes a statement that this container -"supports (amortized) constant time insert and erase operations at the end;", -therefore addressing the concern of this issue. -

- - - - - -
-

1251. move constructing basic_stringbuf

-

Section: 27.8.2.1 [stringbuf.cons] Status: NAD - Submitter: Martin Sebor Opened: 2009-10-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I just came across issue 1204 -- Global permission to move, which -seems to address the concern raised by the example in c++std-lib-25030. -

-

-IIUC, the example violates the permission to assume that arguments -bound to rvalue references are unnamed temporaries granted to -implementations by the resolution of issue 1204 - Global permission -to move. -

- -

-I.e., the ostringstream(ostringstream &&rhs) ctor can leave the rhs -pointers pointing to the newly constructed object's buffer just as -long as the dtor doesn't change or invalidate the buffer. The caller -may not make any assumptions about rhs after the move beyond it being -safe to destroy or reassign. -

- -

-So unless I misunderstood something, I still think the basic_stringbuf -move ctor is overspecified. Specifically, I think the third sentence -in the Effects clause and the last 6 bullets in the Postconditions -clause can, and IMO should, be stricken. -

- -

[ -2010-01-31 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Rationale:

-

-The sense of 1251 appears to be that the basic_stringbuf move -constructor offers more guarantees than the minimum. This is true, and quite -correct. The additional words guarantee that the internal buffer has genuinely -transferred from one object to another, and further operations on the original -will not affect the buffer of the newly created object. This is a very -important guarantee, much as we see that a moved-from unique_ptr is -guaranteed to be empty. -

- - -

Proposed resolution:

-

-Strike from 27.8.2.1 [stringbuf.cons]: -

- -
-basic_stringbuf(basic_stringbuf&& rhs);
-
-
-

-Effects: Move constructs from the rvalue rhs. It is -implementation-defined whether the sequence pointers in *this -(eback(), gptr(), egptr(), pbase(), -pptr(), epptr()) obtain the values which rhs -had. Whether they do or not, *this and rhs reference -separate buffers (if any at all) after the construction. The openmode, -locale and any other state of rhs is also copied. -

- -

-Postconditions: Let rhs_p refer to the state of -rhs just prior to this construction and let rhs_a -referto the state of rhs just after this construction. -

-
    -
  • -str() == rhs_p.str() -
    • -
  • -gptr() - eback() == rhs_p.gptr() - rhs_p.eback() -
    • -
  • -egptr() - eback() == rhs_p.egptr() - rhs_p.eback() -
    • -
  • -pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase() -
    • -
  • -epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase() -
    • -
  • -if (eback()) eback() != rhs_a.eback() -
    • -
  • -if (gptr()) gptr() != rhs_a.gptr() -
    • -
  • -if (egptr()) egptr() != rhs_a.egptr() -
    • -
  • -if (pbase()) pbase() != rhs_a.pbase() -
    • -
  • -if (pptr()) pptr() != rhs_a.pptr() -
    • -
  • -if (epptr()) epptr() != rhs_a.epptr() -
    • -
-
-
- - - - - - -
-

1259. Should initializer-list constructors move elements?

-

Section: 23.2.3 [sequence.reqmts] Status: NAD - Submitter: Sean Hunt Opened: 2009-11-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-According to 23.2.3 [sequence.reqmts], X(il) is -equivalent to X(il.begin(), il.end()). Should it instead be -equivalent to X(move_iterator(il.begin()), -move_iterator(il.end())) so that needless copies are not made? This -doesn't seem ideal either - it may make more sense to provide two -overloads for the constructor, one for move and one for copy. -

- -

[ -2009-11-10 Howard adds: -]

- - -

-I've moved this issue to Tentatively NAD after 5 positive votes on c++std-lib, -and added a rationale below. -

- - -

Proposed resolution:

-

-

- - -

Rationale:

-

-There is no consensus at this time within EWG or CWG to make the -required language changes. Therefore this is not something that the LWG -can even consider. Should such language changes be made for a future -standard, no doubt there would need to be an accompanying library impact -survey. -

- - - - - -
-

1263. missing swap overloads for regex

-

Section: 28.4 [re.syn] Status: NAD - Submitter: Howard Hinnant Opened: 2009-11-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses: UK 314

- -

-In Message c++std-lib-25529, Alisdair writes: -

- -
-

-UK comment 314 -requests rvalue swap overloads in a couple of places they -were missed. -

- -

-We have in general reverted to the single swap signature taking lvalue -references, which could be seen as the alternative solution to -UK 314, -bringing consistency to the standard <g> -

- -

-Either way, I no longer expect to see any work to resolve this comment - -the work is complete and it should be either marked Rejected, or -Accepted with Modifications (namely, removing all other rvalue swaps!) -

-
- -

[ -Moved to Tentatively NAD after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

- - -

Rationale:

-

-We have in general reverted to the single swap signature taking -lvalue references, which could be seen as the alternative solution to -UK 314, bringing consistency to the standard. -

- - - - - -
-

1265. longjmp and destructors

-

Section: 18.10 [support.runtime] Status: NAD - Submitter: Sean Hunt Opened: 2009-11-16 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-18.10 [support.runtime]/4 says that longjmp is undefined if -unwinding by the mechanism used by catch and throw would invoke any nontrivial -destructors. However, the text as written is rather vague, in particular when -dealing with catch(...): -

- -
-void foo() {
-  jump_buf buf;
-  non_trivial_dtor n1; // 1
-  if (!setjmp(buf)) {
-    non_trivial_dtor n2; // 2
-    try {
-      longjmp(buf, 1);
-    } catch (...) {
-    }
-  }
-}
-
- -

-My interpretation of the meaning of 18.10 [support.runtime]/4 is that -declaration 2, but not 1, would cause the longjmp to be undefined -behavior. However, it's not entirely clear from the text. Arguably, replacing -the setjmp and longjmp with catch would still cause -the destructor for n1 to be called after the unwinding, which would -lead to undefined behavior. This is clearly not an intended consequence of the -wording. However, it is probably still UB, as n1 now has -"indeterminate" value, and running its destructor on foo's exit will -cause Bad Things. -

- -

-Declarations 2 has a more interesting issue. The catch(...) muddles up -the definition that uses throw and catch - if -longjmp() were indeed a throw, control would never return to -the setjmp. As such, n2's destructor wouldn't be called -(except by the argument for n1, which is that the destructor would be -called later as the frame was left in the normal control flow). -

- -

-I suggest that paragraph 4 of 18.10 [support.runtime] should be replaced -with the following, or something that reads better but has the same effect: -

- -

-The function signature longjmp(jmp_buf jbuf, int val) has more -restricted behavior in this International Standard. A call to longjmp -has undefined behavior if any non-trivial destructors would be called were the -longjmp call replaced with a throw-expression whose nearest matching -handler were a (possibly imaginary) function-try-block on the function -containing the corresponding setjmp call. -

- -

[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - -

Proposed resolution:

-

-Change 18.10 [support.runtime]/4: -

- -

-The function signature longjmp(jmp_buf jbuf, int val) has more -restricted behavior in this International Standard. A -setjmp/longjmp call pair has undefined behavior if replacing -the setjmp and longjmp by catch and throw -would invoke any non-trivial destructors for any automatic objects. -A call to longjmp has undefined behavior if any non-trivial -destructors would be called were the longjmp call replaced with a -throw-expression whose nearest matching handler were a (possibly imaginary) -function-try-block on the function containing the corresponding setjmp -call. -

- - -

Rationale:

-

-In the given example, it is clear that it is only n2 and not -n1 that is destroyed by the longjmp. -

-

-At this late stage in the standards process, we are focusing on issues that -impact users or implementers. Trying to rewrite complex wording just for the -sake of improved clarity is likely to do more harm than good. -

- - - - - -
-

1296. map and multimap value_compare overspecified

-

Section: 23.4.4 [map] Status: NAD - Submitter: Alisdair Meredith Opened: 2009-12-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The container class templates map and multimap both contain a -nested type called value_compare, that is used to compare the -value_type pair elements, an adaptor of the user-supplied comparison -function-like object. -

- -

-I believe these types are over-specified, as we require a distinct type for each -template, even though the allocator plays no part in the comparator, and -map and multimap value_compare classes could easily be shared. - The benefits are similar to the SCARY iterator proposal (although on a much -smaller scale!) but unlike SCARY, this is not a QoI issue today but actively -prohibited. -

- -

-If the value_compare classes were marked 'exposition only', a vendor -would be free to experiment with implementations that do not produce so many -template instantiations with negligible impact on conforming programs. (There -is a minor risk that programs could no longer portably overload functions taking -value_compare types. This scenario is extremely unlikely outside -conformance suites.) -

- -

-(Note that there are no similar problems for unordered maps, nor any of the set -variants) -

- -

[ -2010-01-31 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]

- - -

Rationale:

-

-The value_compare specification is an unfortunate bit from the past -that we have to live with. Fortunately vendors can work around the problems -mentioned in this issue. -

- - - - -

Proposed resolution:

-

-p2 23.4.4 [map]: -Above the declaration of class value_compare in the map synopsis, add: -

- -
-template <class Key, class T, class Compare = less<Key>,
-          class Allocator = allocator<pair<const Key, T> > >
-class map {
-public:
-  // types:
-  ...
-  // exposition only.
-  class value_compare
-    : public binary_function<value_type,value_type,bool> {
-    ...
-
- - - -

-p2 23.4.5 [multimap]: -Above the declaration of class value_compare in the map synopsis, add: -

- -
-template <class Key, class T, class Compare = less<Key>,
-          class Allocator = allocator<pair<const Key, T> > >
-class multimap {
-public:
-  // types:
-  ...
-  // exposition only.
-  class value_compare
-    : public binary_function<value_type,value_type,bool> {
-    ...
-
- - - - - -
-

1301. clear() and assignment

-

Section: 23.2.3 [sequence.reqmts] Status: NAD Editorial - Submitter: Nicolai Josuttis Opened: 2010-01-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I propose that clear() be defined to be equivalent to -erase(begin(),end()) except not using copy or move of elements. -

- -
-

-To: C++ libraries mailing list
-Message c++std-lib-26465 -

- -

-and specifiying as post: size()==0 might also not be appropriate -because forward-Lists provide no size(), this it should be: -post: empty()==true -

- -

-Bjarne Stroustrup schrieb/wrote: -

- -
-

-To: C++ libraries mailing list
-Message c++std-lib-26458 -

- -

-in table 94 we define clear() as: -

- -
-a.clear() void erase(begin(), end())
-post: size() == 0
-
- -

-Now erase requires assignment (MoveAssignable) which makes -sense if we have to move an element, but why should that be required from -clear() where all elements are destroyed? -

-
-
- -

[ -2010-01-23 Alisdiar provides wording. -]

- - -

[ -2010-01-30 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-01-30 Daniel opens: -]

- - -
-

-First, I read the newly proposed spec for clear() that it does in -general not invalidate a previous past-the-end iterator value, but -deque says in 23.3.3.4 [deque.modifiers] for the semantics of -erase that erasures at the end will invalidate the past-the-end -iterator. With removal of a direct binding between clear() and -erase() there seem to be some fixes necessary. One way to fix that -would be to mention in Table 94 that this "may also invalidate the past-the-end -iterator" and then to mention for all specific containers where this does not -happen, the exception, [1] e.g. in std::vector. std::vector -has no own specification of clear() and one aspect of the closed issue -1102 was to realize just that (indirectly via erase). IMO -we should now add an extra specification for clear(). Btw.: -std::vector::erase reads to me that it would invalidate previous -past-the-end values (and that seems correct in general). -

-

-Before I will provide explicit wording, I would like to -discuss these points. -

- -

-[1] std::list does fortunately specify that clear does not invalidate -the past-the-end iterator. -

-
- -

[ -2010-02-08 Moved to Tentatively NAD Editorial after 5 positive votes on c++std-lib. -Rationale added below. -]

- - - - -

Rationale:

-

-Solved as proposed by LWG 704. -

- - -

Proposed resolution:

- -

-Change 23.2.1 [container.requirements.general]/10: -

- -
-

-Unless otherwise specified (see 23.2.4.1, 23.2.5.1, 23.3.2.3, and 23.3.6.4) all -container types defined in this Clause meet the following additional -requirements: -

- -
    -
  • -.. -
    • - -
  • -no erase(), clear(), pop_back() or -pop_front() function throws an exception. -
    • - -
  • -... -
    • -
- -
- -

-Replace the following words from Table 94 — Sequence container -requirements (in addition to container) in 23.2.3 [sequence.reqmts]: -

- -
- - - - - - - - - - - - - -
Table 94 — Sequence container requirements (in addition to -container)
ExpressionReturn typeAssertion/note
pre-/post-condition
a.clear()voiderase(begin(), end())
-Destroys all elements in the container a. Invalidates all references, -pointers, and iterators referring to the elements of a and may -invalidate the past-the-end iterator.
-post: size() == 0 a.empty() == true.
-
- -

-Add a new paragraph after 23.3.4.5 [forwardlist.modifiers]/23: -

- -
-void clear();
-
- -
-

-23 Effects: Erases all elements in the range [begin(),end()). -

-

-Remarks: Does not invalidate past-the-end iterators. -

-
-
- - - - - - -
-

1302. different emplace semantics for sequence and associated containers

-

Section: 23.2.4 [associative.reqmts], 23.2.5 [unord.req] Status: NAD - Submitter: Nicolai Josuttis Opened: 2010-01-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-According to the new naming scheme introduced with -N2680 -

- -
-vector<T> v;
-v.emplace(v.begin(),x,y,z)
-
- -

-now has a different semantics than -

- -
-set<T> s;
-s.emplace(s.begin(),x,y,z);
-
- -

-While the version for vectors takes the first argument as position and -the remaining for construction, the version for sets takes all -arguments for construction. -

- -

-IMO, this is a serious design mistake for a couple of reasons: -

- -
    -
  • -

    -First, in principle, all STL member functions should have the same behavior with -the same member function to avoid confusion and allow to write proper generic -code. -

    -

    -In fact, when I write the following simple function template: -

    -
    -template <typename T>
-void doEmplace (T& cont)
-{
-   cont.emplace(cont.begin(),"nico","josuttis",42);
-}
-
    -

    -the semantics depends on the type of the container. -

    -
    • -
  • -

    -In addition, I also guess using the name emplace_hint() instead of -emplace() for associative containers is a design mistake. According to -my knowledge, it was a design goal of the original STL to provide ONE -insert function, which works for ALL containers. This was -insert(pos,val). -

    -

    -The trick to declare pos as a hint, allowed that we could implement a -generic insert for all containers. Now, with the new emplace -naming scheme, this trick is gone for the new kind of insertion. -

    -
    • -
- -

-I consider this to be a serious design penalty because once this -is specified we can't fix that without breaking backward compatibility. -

- -

-However, we have two choices for a fix: -

- -
    -
  • -rename emplace_hint(pos,val) for associative containers back to -emplace(pos,val). However to avoid the overloading problems, we also -have to rename the existing emplace(val) functions to something else (I -don't have a good name here at hand). -
    • -
  • -Keep emplace(val) for associative containers as it is, but rename -emplace(pos,val) for sequence containers and -emplace_hint(pos,val) to something like emplace_at(pos,val), -declaring that pos is a hint for associative containers. -
    • -
- -

[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]

- - - - -

Rationale:

-

-There was no consensus to make this change. -

- - -

Proposed resolution:

-

In 23.2.5 [unord.req], change:

-
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 96 — Associative container requirements (in addition to - container)
expressionReturn typeAssertion/note pre-/post-conditionPost-condition
...
a_uniq.emplace_value(args)pair<iterator, bool>inserts a T object t constructed with std::forward<Args>(args)...
- if and only if there is no element in the container with key equivalent - to the key of t.
- The bool component of the returned pair is true if and only if the insertion - takes place, and the iterator component of the pair points to the element - with key equivalent to the key of t.		logarithmic
a_eq.emplace_value(args)iteratorinserts a T object t constructed with std::forward<Args>(args)... - and returns the iterator pointing to the newly inserted element.logarithmic
a.emplace_hint(p,args)iteratorequivalent to - a.emplace_value(std::forward<Args>(args)...). - Return value is an iterator pointing to the element with the key - equivalent to the newly inserted element. The const_iterator p is a hint - pointing to where the search should start. Implementations are permitted - to ignore the hint. logarithmic in general, but amortized - constant if the element is inserted right after p
...
- -
-

In 23.2.5 [unord.req], change:

-
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 98 — Unordered associative container requirements (in - addition to container)
expressionReturn typeAssertion/note pre-/post-conditionPost-condition
...
a_uniq.emplace_value(args)pair<iterator, bool>inserts a T object t constructed with std::forward<Args>(args)... if - and only if there is no element in the container with key equivalent to - the key of t. The bool component of the returned pair is true if and only - if the insertion takes place, and the iterator component of the pair points - to the element with key equivalent to the key of t.Average case O(1), worst case O(a_uniq.size()).
a_eq.emplace_value(args)iteratorinserts a T object t constructed with std::forward<Args>(args)... - and returns the iterator pointing to the newly inserted element.Average case O(1), worst case O(a_eq.size()).
a.emplace_hint(p,args)iteratorequivalent to - a.emplace_value(std::forward<Args>(args)...). - Return value is an iterator pointing to the element with the key - equivalent to the newly inserted element. The const_iterator p is a hint - pointing to where the search should start. Implementations are permitted - to ignore the hint. Average case O(1), worst case - O(a.size()).
...
-
- -

-In 23.4.4 [map], 23.4.6 [set], 23.5.4 [unord.map], 23.5.6 [unord.set], change: -

-
-

// modifiers:
- template <class... Args> pair<iterator, bool> emplace_value(Args&&... - args);
- template <class... Args> iterator emplace_hint(const_iterator - position, Args&&... args);

-
- -

-In 23.4.5 [multimap], 23.4.7 [multiset], 23.5.5 [unord.multimap], 23.5.7 [unord.multiset], change: -

-
-

// modifiers:
template <class... Args> iterator emplace_value(Args&&... - args);
- template <class... Args> iterator emplace_hint(const_iterator position, - Args&&... args);
-

-
- - - - - -
-

1308. Concerns about initializer_list overloads of min, -max, and minmax

-

Section: 25.4.7 [alg.min.max] Status: NAD - Submitter: Niels Dekker Opened: 2010-02-02 Last modified: 2015-04-08

-

View all other issues in [alg.min.max].

-

View all issues with NAD status.

-

Discussion:

-

-In San Francisco, June 2008, -N2722 -was adopted, replacing the variadic templates min, max, and -minmax by overloads that have an initializer_list<T> -parameter. The paper showed benchmark results wherein initializer_list -versions of min appeared to outperform the corresponding variadic -template. Unfortunately, in October 2009 a very serious error was detected in -the benchmark. (c++std-lib-25210). -In fact, an initializer_list<T> version of min often -appears to perform worse than the corresponding variadic template, -especially when T has an expensive copy constructor -(c++std-lib-25253, -http://www.xs4all.nl/~nd/dekkerware/issues/n2772_fix). -

-

-IMO, the biggest problem of the initializer_list overloads is that they -pass and return T objects by value. Which has the following -consequences: -

- -
    -
  1. -They require that T is CopyConstructible. IMO that is too much of a -constraint for a generic, general purpose function like -std::min<T>. -
    2. -
  2. -They potentially throw an exception, even if T's less-than-operator -throws nothing. (And of course, less-than typically throws nothing.) -
    3. -
  3. -They are inconsistent with C++03 std::min and std::max. -Consider the subtle difference between const T& c1 = min(a,b); and -const T& c2 = min({a,b}); -(c++std-lib-25265) -
    4. -
  4. -They do not conveniently support use cases that need to have a reference to the -minimum or maximum object itself, rather than just a copy. -
    5. -
  5. -They potentially perform badly: possibly O(n), when the arguments -themselves have a size of n. -
    6. -
- -

-In the future, this problem might be solvable by using an -initializer_list of const references, instead: -

-
-const T& min(initializer_list<const T&>);
-const T& max(initializer_list<const T&>);
-pair<const T&, const T&> minmax(initializer_list<const T&>);
-
- -

-It is unlikely that C++0x will support initializer_list<const T&>, -but technically it seems possible to add such a language -feature after C++0x -(c++std-core-15428). -

-

-Variadic templates of min, max, and minmax, as -proposed by -N2551 -(Sylvain Pion), do have some other advantages over initializer_list -overloads: -

-
    -
  1. -It is likely that those variadic templates can be declared constexpr, -now that - -CWG issue #991 is in drafting status. -
    2. -
  2. -They provide complete compile-time protection against accidentally passing zero -arguments. -
    3. -
- -

-Unfortunately, the variadic templates of min, max, and -minmax may still need further improvement, before having them in the -Standard Library. Especially the optional Compare parameter appears to -be a concern. So for this moment I recommend to keep both versions out of C++0x, -and postpone further discussion until after C++0x. -

- -

[ -2010 Pittsburgh: Discussed and the LWG still prefers the initializer list -solution of -N2772. -]

- - - - -

Rationale:

-We prefer the solution of -N2772 -which will be reapplied. -

- -

Proposed resolution:

-

-Remove both variadic templates and initializer_list overloads of -min, max, and minmax from the synopsis in -25.1 [algorithms.general] and from 25.4.7 [alg.min.max]. -

- -
-

[ -Note: This proposed resolution will resolve LWG 915 as NAD. -]

- -
- - - - - -
-

1313. Seed sequence's param function not useful for pure output iterator

-

Section: 26.5.7.1 [rand.util.seedseq] Status: NAD - Submitter: Daniel Krügler Opened: 2010-02-07 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with NAD status.

-

Discussion:

-

-The Seed sequence requirements (26.5.1.2 [rand.req.seedseq]) require the -existence of a member function -

- -
-template<typename OutputIterator>
-void param(OutputIterator ob);
-
- -

-The fact that this function returns void instead of the value of -ob after accepting the sequence data leads to the same problem as in -issue 865 - In case of pure output iterators there is no way to -serialize further data into that data sink. -

- -

[ -2010-02-07 Howard adds: -]

- - -

-At the time this issue was opened, the suggested changes are with respect to an -anticipated draft which does not yet exist. -

- -

[ -2010 Pittsburgh: -]

- - -

-No technical counterarguments, but it is simply too late in the process -to make this change at this point. -

- - -

Proposed resolution:

-
    -
  1. -

    -In Table 109 — Seed sequence requirements, expression "r.param(ob)" -change the
    -Return type entry: -

    - -
    -voidOutputIterator
-
    -
    2. - -
  2. -

    -In 26.5.7.1 [rand.util.seedseq], class seed_seq synopsis change -

    - -
    -template<class OutputIterator>
-voidOutputIterator param(OutputIterator dest) const;
-
    -
    3. - -
- - - - - - -
-

1314. NULL and nullptr

-

Section: 18.2 [support.types] Status: NAD - Submitter: Sean Hunt Opened: 2010-02-07 Last modified: 2015-04-08

-

View all other issues in [support.types].

-

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-

Discussion:

-

-Currently, the 18.2 [support.types]/3 allows NULL to be any -null pointer constant. The footnote marks that 0 or 0L might be appropriate. -However, this definition also allows the implementation to define NULL -to be nullptr. This may lead to overload and conversion issues more -serious than with the C++98 version: -

- -
-void f(void*);
-void f(int);
-
-void g()
-{
- // calls f(int) if NULL is integral
- // calls f(void*) if NULL is nullptr
- f(NULL);
-}
-
- -

-Possible resolutions: -

-
    -
  • -Forbid NULL from being nullptr -
    • -
  • -Require NULL to be nullptr -
    • -
  • -Leave it as is -
    • -
- -

-Making NULL nullptr would improve code correctness, and -breaking backwards compatibility shouldn't be a huge concern as NULL -shouldn't be used except as a null pointer constant anyways. -

- -

[ -2010-02-10 Chris provided wording. -]

- - -

[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]

- - - - -

Rationale:

-

-The LWG discussed the proposed resolution and several other options. There was -no concensus to make this or any other changes. -

- - -

Proposed resolution:

-

-18.2 [support.types] -

- -
-

-3 The macro NULL is defined to be nullptr. is -an implementation-defined C++ null pointer constant in this International -Standard (4.10).196 -

- -

-196) Possible definitions include 0 and 0L, but not -(void*)0. -

-
- -

-20.7.13 [c.malloc] -

- -

-7 The contents are the same as the Standard C library header -<string.h>, with the change to memchr() specified in -21.6 and the macro NULL defined to be nullptr. -

- - -

-20.12.8 [date.time] -

- -

-2 The contents are the same as the Standard C library header -<time.h>.232 except the macro -NULL, which is defined to be nullptr. The functions -asctime, ctime, gmtime, and localtime are -not required to avoid data races (17.6.4.8). -

- - -

-22.6 [c.locales] -

- -

-2 The contents are the same as the Standard C library header -<locale.h> except the macro NULL, which is defined -to be nullptr. -

- -

-C.5.2.4 [diff.null] -

- -

-1 The macro NULL, defined in any of <clocale>, -<cstddef>, <cstdio>, <cstdlib>, -<cstring>, <ctime>, or <cwchar>, is -nullptr an implementation-defined C++ null pointer constant in -this International Standard (18.2). -

- - - - - - -
-

1315. return type of async

-

Section: 30.6.8 [futures.async] Status: NAD Editorial - Submitter: Jonathan Wakely Opened: 2009-02-09 Last modified: 2015-04-08

-

View all other issues in [futures.async].

-

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-

Discussion:

-

-Both overloads of async return future<typename -F::result_type> which requires that F has a nested type. This -prevents async being used with function pointers and makes the example -in 30.6.8 [futures.async] invalid. I believe this is unintentional. -

- -

-The proposed resolution also addresses editorial issues with the -launch_policy function parameter. -

- -

-For the first overload it is not sufficient to return future<typename -result_of<F(ArgTypes...)>::type>. Calling async(launch::xxx, -foo, bar) performs argument deduction on both async overloads, -which for the first overload attempts to instantiate result_of<launch(F, -ArgTypes...)>, which is invalid. SFINAE must be used to prevent that. -

- -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-12 Daniel opens: -]

- - -
-

-[..] if decay<F>::type is of type std::launch. -

-

-or -

-

-[..] if remove_cv<remove_reference<F>::type>::type is of -type std::launch. -

- -

-The latter is the more specific form, but the former is equivalent to -the latter for all cases that can occur here. I suggest to use the -former for simplicity, but expect that implementations can effectively -use the latter. - -

-
- -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Editorial. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-

-In 30.6.1 [futures.overview] paragraph 1: -

- -
-template <class F, class... Args>
-  future<typename F::result_type>
-  future<typename result_of<F(Args...)>::type>
-  async(F&& f, Args&&... args);
-template <class F, class... Args>
-  future<typename F::result_type>
-  future<typename result_of<F(Args...)>::type>
-  async(launch policy, F&& f, Args&&... args);
-
- -

-In 30.6.8 [futures.async] before paragraph 1 -

- -
-template <class F, class... Args>
-  future<typename F::result_type>
-  future<typename result_of<F(Args...)>::type>
-  async(F&& f, Args&&... args);
-template <class F, class... Args>
-  future<typename F::result_type>
-  future<typename result_of<F(Args...)>::type>
-  async(launch policy, F&& f, Args&&... args);
-
-
-

...

-

-Remarks: The first signature shall not participate in overload resolution -if decay<F>::type is std::launch. -

-
-
- - - - - - -
-

1318. N2982 removes previous allocator capabilities

-

Section: 20.7.8.1 [allocator.traits.types] Status: NAD - Submitter: Pete Becker Opened: 2010-02-11 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Duplicate of: 1375

-

Discussion:

-

Addresses US-87

-

-N2982 -says that containers should have a nested typedef that defines their -reference_type as value_type&; the previous -standard deferred to the allocator to define its -reference_type, and containers simply passed the allocator's -typedef on. This change is a mistake. Allocators should define both a -pointer type and a reference type. That's essential -for their original purpose, which was to make different memory models -transparent. If an allocator defines a pointer type that isn't -compatible with a normal pointer it also has to define a corresponding -reference type. For example (and please forgive a Windows-ism), -if an allocator's pointer is T __far*, then it's -reference has to be T __far&. Otherwise everything -crashes (under the hood, references are pointers and have to have the -same memory access mechanics). Extensions such as this for more general -memory models were explicitly encouraged by C++03, and the allocator's -pointer and reference typedefs were the hooks for such -extensions. Removing the allocator's reference and -const_reference typedefs makes those extensions unimplementable -and breaks existing implementations that rely on those hooks. -

- -

[ -2010-02-25 Alisdair adds: -]

- - -
-

-vector<bool>::reference is a nested class, and not a typedef. It -should be removed from the list of containers when this change is made. -

- -

-In general, I am uncomfortable placing this reference requirement on each -container, as I would prefer to require: -

- -
-is_same<Container::reference, Container::iterator::reference>
-
- -

-This distinction is important, if we intend to support proxy iterators. The -iterator paper in the pre-Pittsburgh mailing -(N3046) -does not make this proposal, but organises clause 24 in such a way this -will be much easier to specify. -

- -

-The changes to clause 20 remain important for all the reasons Pete highlights. -

-
- -

[ -2010 Batavia -]

- - -

-Removed vector from list of templates that should be adjusted as of meeting outcome. -

- -

[ -2010 post-Batavia -]

- - -

-Replaced vector<bool> reference by vector reference because of misinterpreting meeting typo. -Additional corrected numbering in P/R to N3225 wording. -

- -

[ -2010-12-06 Daniel reopens -]

- - -

-Unfortunately, the current P/R is defective for several reasons: -

-
    -
  1. Table 43 — Descriptive variable definitions still contains three -references to T&, namely in: -
    - - - - - - - - - - - - - -
    -t -a value of type const T&
    -r -a value of type T& obtained by the expression *p
    -s -a value of type const T& obtained by the expression *q -or by conversion from a value r
    -
    -Especially the second and third items are misses in the 1318 P/R, -e.g. in N2723 or in C++03 these were referring -to X::reference and X::const_reference, resp. -None of them is referenced anywhere in the allocator requirements -table: r and s where historically needed to -define the expressions a.address(r) and a.address(s) which are gone now, -and t was needed to define the expression a.construct(p, t) which has been -replaced by a.construct(p,args). -

    -The easiest fix seems to be to remove all three rows from Table 43. -

    2. -
  2. -Further-on, the current P/R suggests to replace the the current -definitions of the adaptor classes -
    -stack
-priority_queue
-queue
-
    -similar to the other container types, i.e. to define reference and -const_reference now as -
    -typedef typename allocator_traits<Allocator>::reference reference;
-typedef typename allocator_traits<Allocator>::const_reference const_reference;
-
    -This would not only be an ill-formed definition (because there is no name -Allocator in scope), but it would also introduce a breakage compared to C++03, -where these definitions where already referring to the definition of the wrapped -containers. So, the adaptor class templates should be removed from the current list. -
    3. -
  3. -Then the current P/R wording leads to one further unexpected and unwanted change due to -the general formular used: match_result::reference is currently defined as -
    -typedef const_reference reference;
-
    -because it is an immutable container (And we had this definition -already in N2723). The application of the rule would change this silently. -
    4. -
  4. -Finally the suggested wording for the unordered_ containers is incomplete. -The reason is a current inconsistency between these containers and the rest: While -normally the definition of the pointer types is -
    -typedef typename allocator_traits<Allocator>::pointer pointer;
-typedef typename allocator_traits<Allocator>::const_pointer const_pointer;
-
    -for the unordered containers they are -
    -typedef typename allocator_type::pointer pointer;
-typedef typename allocator_type::const_pointer const_pointer;
-
    -These definitions are not equivalent, because allocators are no longer -required to define typedefs pointer and const_pointer, the -allocator_traits were invented as a further indirection to cope -with that. I.e. for the unordered containers we need to bring both the definition -of references and pointers in sync. -
    5. -
- -

[ -2011-02-23 Daniel updates the proposed wording with support from Pablo -]

- - -

The update attempts to fix the backward-compatibility problem that we have -introduced by ignoring the C++03 member function overloads address -of allocator types in C++0x completely. The resolution attempts to fix that -by adding these functions as optional members of allocators that are considered -first before falling back to pointer_traits::pointer_to. This still -allows us to remove the unused symbol t from the table, but we adapt -the symbols r and s to purely refer to the typenames -reference and const_reference.

- -

[2011-03-06 Daniel adapts numbering to N3242]

- - -

[2011-03-11 Daniel removes noexcept specifiers from address functions]

- - -

[2011-03-12 Further wording improvements by Daniel and Pablo]

- - -

[2011-03-22 Madrid]

- - -

Closed as NAD, no consensus to make a change

- - - -

Rationale:

No consensus to make a change

- -

Proposed resolution:

- - - - - -
-

1330. Move container requirements into requirements tables

-

Section: 23.2 [container.requirements] Status: NAD - Submitter: Nicolai Josuttis Opened: 2010-03-10 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

View all other issues in [container.requirements].

-

View all issues with NAD status.

-

Discussion:

-

-Abstract: -

-

-In general, it seems that in a couple of places container behavior is -not described in requirement tables although it is a general behavior. -

- -

-History: -

- -

-Issue 676 added move semantics to unordered containers. -For the added insert functions the Editor requested to put their -semantic description into a requirements table rather than describing -them for each container individually. The text however was taken from -the associative containers, where we also have the semantics for each -container described. Also, 1034 is to some extend -requesting a clarification of the requirement tables and it turned out -that in other places we have the same problem (e.g. we have no general -requirement for type pointer and const_pointer although each container -has them with issue 1306). -

- -

-From my personal list of functions in requirement tables -and containers, the following types/functions are missing in -requirement tables: -

- -
    -
  • -pointer, const_pointer in Table 91 (container requirements) -
    • -
  • -

    -all copy constructors, copy constructors with allocator, - assignment operators, and insert operators - with move semantics for associative and unordered containers -

    -
    -ContType c1(c2&&)
-ContType c1(c2&&,alloc)
-c1 = c2&&
-c.insert(val&&)
-c.insert(pos,val&&)
-
    -
    • -
- -

-As a special case, we lack the following requirements for all sequence -containers BUT array (so special wording or a new container category is -required): -

- -
    -
  • -

    -constructor with only a size argument -

    -
    -ContType c(num)
-
    -
    • -
  • -

    -copy constructor with allocator and move semantics -

    -
    -ContType c1(c2&&,alloc)
-
    -
    • -
  • -

    -all constructors that insert multiple elements with additional allocator -

    -
    -ContType c(num, val,alloc)
-ContType c(beg, end,alloc)
-ContType c(initlist,alloc)
-
    -
    • -
  • -

    -all resize functiuons: -

    -
    -c.resize(num)
-c.resize(num,val)
-
    -
    • -
- -

-Note that we also might have to add additional requirements on other -places for sequence containers because having an allocator requires -additional statements for the treatment of the allocators. E.g. swap for -containers with allocators is not specified in any requirement table. -

- -

-And finally, if we have the requirements in the requirements tables, we -can remove the corresponding descriptions for the individual container. -However, note that sequence container requirements have NO complexity -column, so that we still need container specific descriptions for the -functions listed there. -

- -

[ -2010 Batavia -]

- -

-While there is consensus that further cleaning up the container requirement -tables would be a good thing, there is no feeling that this must -be done in time for 0x. The issue remains open, but Deferred. -

- -

[ -2011 Bloomington -]

- - -

-Closes as NAD. There are a number of deficiencies in the way the container -requirements tables are presented, and the LWG welcomes further papers that -will help clear up this presentation. -

- - - - -

Proposed resolution:

- - - - - -
-

1331. incorporate move special member functions into library

-

Section: 17 [library] Status: NAD - Submitter: Martin Sebor Opened: 2010-03-10 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD status.

-

Discussion:

-

-Review the library portion of the spec and incorporate the newly added -core feature Move Special Member Functions (N3044). -

- -

Rationale:

-2010 Batavia: This has now been done to a large extent. -

- - - -

Proposed resolution:

- - - - - -
-

1348. Exception safety of unspecified types

-

Section: 17 [library] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with NAD status.

-

Discussion:

-

Addresses GB-64

-

-There are a number of unspecified types used throughout -the library, such as the container iterators. Many of these -unspecified types have restrictions or expectations on -their behaviour in terms of exceptions. Are they permitted -or required to use exception specifications, more -specifically the new noexcept specification? For example, -if vector<T>::iterator is implemented as a native pointer, -all its operations will have an (effective) noexcept -specification. If the implementation uses a class type to -implement this iterator, is it permitted or required to -support that same guarantee? -

- -

[ -Resolution proposed by ballot comment -]

- -

-Clearly state the requirements for exception -specifications on all unspecified library types. For -example, all container iterator operations should -be conditionally noexcept, with the condition -matching the same operation applied to the -allocator's pointer_type, a certain subset of which -are already required not to throw. -

- -

[2011-03-24 Madrid meeting]

- - -

Discussion:

-

Alisdair: Probably an NAD Future at least but could be NAD. -

-Daniel K: Approach is not consistent with what we've decided with noexcept. -

-Alisdair: Any objection to marking 1348 as NAD? -

-No objections. -

- - - -

Rationale:

Standard is correct as written

-

Proposed resolution:

- - - - - -
-

1350. Implicit contructors accidentally made some library types move-only

-

Section: 17 [library] Status: Dup - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

View all other issues in [library].

-

View all issues with Dup status.

-

Duplicate of: 1421

-

Discussion:

-

Addresses CH-15

-

-Due to the new rules about implicit copy and move -constructors some library facilities are now move-only. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Make them copyable again. -

- - -

Proposed resolution:

- - - - - -
-

1351. Replace dynamic exception specifications with noexcept

-

Section: 17 [library] Status: Dup - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

View all other issues in [library].

-

View all issues with Dup status.

-

Duplicate of: 1344

-

Discussion:

- -

Addresses CH-16

-

-Dynamic exception specifications are deprecated. -Deprecated features shouldn't be used in the Standard. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Replace dynamic exception specifications with noexcept. -

- - -

Proposed resolution:

- - - - - -
-

1352. Apply noexcept where library specification says "Throws: Nothing"

-

Section: 17 [library] Status: Dup - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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Duplicate of: 1346

-

Discussion:

- -

Addresses CH-17

-

-The introduction of noexcept makes "Throws: Nothing" clauses looking strange. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Consider replacing "Throws: Nothing." clause by -the respective noexcept specification. -

- - - -

Proposed resolution:

- - - - - -
-

1358. Add <chrono> and <ratio> to -freestanding implementations

-

Section: 17.6.1.3 [compliance] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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View all issues with NAD status.

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Discussion:

-

Addresses GB-55

-

-The <thread> header uses duration types, found in the -<chrono> header, and which rely on the ratio types -declared in the <ratio> header. -

- -

[ -Extracts from lengthy Rapperswil discussion: -]

- -

-There is a concern that this issue is a misunderstanding of the actual -requirements of a free-standing implementation to support the <thread> -header. In general, a free-standanding implementation will provide an empty -header, specifically so that a user can test for the absence of the -_ _ STDCPP_THREADS _ _ macro. This idiom as used as there is no portable -way to test for the lack of a header. -

-

-At this point, it was suggested the NB comment is trying to solve the wrong problem, -and that _ _ STDCPP_THREADS _ _ should be a pre-defined macro in clause 16 -that can be tested before including <thread>. That would remove the -need to add additional headers to the free-standanding requirements. -

-

-It is worth noting that Japan requested <ratio> as a free-standing header -in their CD1 comments. No-one seemed keen to require clocks of a free-standing -implementation though. -

- -

Detlef volunteers to look at a way to redraft 17.6.1.3 p3.

- -

[ -Original resolution proposed by NB comment: -]

- - -
-

-Add the <chrono> and <ratio> headers to the -freestanding requirements. -

-

-It might be necessary to address scaled-down -expectations of clock support in a freestanding -environment, much like <thread>. -

-
- -

[2011-02-25: Alberto drafts wording]

- - -

[2011-03-06: Daniel observes:]

- - -

Accepting the proposal n3256 -would solve this issue.

- -

[2011-03-24 Madrid meeting]

- - -

Freestanding no longer requires <thread> header

- - -

Rationale:

We are not adding new headers to freestanding at this point.

- -

Proposed resolution:

- -
    -

  1. Add a new entry in Table 14 — C++ library headers:

    - -
    - - - - - - - - - - - - - - - - - -
    Table 14 — C++ library headers
    …
    <iterator>
    <library_support>
    <limits>
    …
    -
    -
    2. - -

  2. Remove the last row 30.3 [thread.threads] <threads> -from Table 16 — C++ headers for freestanding implementations and insert -a new one instead (To the editor: For the actual target Clause please see the comment -in bullet 5 of this proposed resolution):

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 16 — C++ headers for freestanding implementations
    SubclauseHeader(s)
    …
    30.3 [thread.threads] Threads<thread>
    ?? Library support<library_support>
    - -
    -
    3. - -

  3. Modify paragraph 17.6.1.3 [compliance] p. 3:

    -

    - 3 The supplied version of the header <cstdlib> shall declare at least the functions - abort, atexit, at_quick_exit, exit, and quick_exit - (18.5). The supplied version of the header <thread> shall meet the -same requirements as for a hosted implementation or including it shall have no effect. The -other headers listed in this table shall meet the same requirements as for a hosted -implementation. A program can detect the presence of standard headers not listed in Table -16 using the facilities provided by the <library_support> header. -

    -
    4. - -

  4. Remove the following line from the header <thread> synopsis in -30.3 [thread.threads] p. 1:

    -
    -namespace std {
-  #define __STDCPP_THREADS__ __cplusplus
-
-  class thread;
-  [...]
-}
-
    -
    5. - -

  5. Add a new section in Clause 18 or 20 (or any other suitable place at -the editor's discretion):

    - -
    -

    ?? Library support [library.support]

    -

    -The header <library_support> defines an implementation-defined set -of macros to allow a program detect the presence of standard headers in freestanding -implementations. [Note: Hosted implementations shall provide all -standard headers, thus shall provide all macros. — end note] -

    -

    -For each standard header listed in Tables 14 (C++ library headers) and 15 (C++ headers for C library facilities) -that is provided by the implementation, <library_support> shall define a macro with name -_ _HAS_XXX_HEADER_ _ where XXX is replaced by the uppercase version of the -name of the header. Each such macro shall expand to the value _ _cplusplus. -[Example:

    -
    -#include <library_support>
-
-#ifdef _ _HAS_THREADS_HEADER_ _
-  #include <threads>
-  // code that exploit the presence of threads
-#else
-  // fallback code that doesn't rely on threads
-#endif
-
    -

    — end example]

    -
    -

    -No other standard header shall define macros with a name beginning with _ _HAS_ -and ending with _HEADER_ _. -

    - -
    -
    6. -
- - - - - -
-

1359. Add <tuple> and <utility> to freestanding implementations

-

Section: 17.6.1.3 [compliance] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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Discussion:

-

Addresses GB-56

-

-The <utility> header provides support for several -important C++ idioms with move, forward and swap. -Likewise, declval will be frequently used like a type trait. -In order to complete cycles introduced by std::pair, the -<tuple> header should also be made available. This is a -similarly primitive set of functionality, with no dependency -of a hosted environment, but does go beyond the minimal -set of functionality otherwise suggested by the -freestanding libraries. -

-

-Alternatively, split the move/forward/swap/declval -functions out of <utility> and into a new primitive header, -requiring only that of freestanding implementation. -

- -

[ -Summary of Rapperswil discusions -]

- -

-The preference of the meeting was to extract the rvalue-reference related utilities -and swap into a freestanding header, but there was no clear preference for a name. -Howard suggested simply dropping them into <type_traits> as both -these utilities and type traits are used pretty much everywhere in the library -implementation, it is the most convenient place to keep them (from an implementer's -perspective). -

- -

-Poll: Two-way: New header for forward, move, swap, move_with_noexcept and declval vs. -calling out forward, move, swap, move_with_noexcept and declval as freestanding explicitly? - -SF new header: 4 WF new header: 3 WF call out as freestanding: 1 SF call out as freestanding: 2 - -Alisdair: Willing to write up both solutions, give us some time to think on it. - -Action: Need an issue and proposed wording for GB 56 - Alisdair to draft both options as in the last poll. -

- -

[ -Resolution proposed by ballot comment -]

- -
-

-Add <utility> and <tuple> to table 15, headers -required for a free-standing implementation. -

-
- -

[ -2010-Batavia: -]

- -

-Closed as NAD, reversing the decision at Rapperswil. -

-

-The consensus was that -any freestanding implementation is going to feel compelled to offer the important -features of <utility> even if we do not make them a freestanding -requirement; breaking out additional small headers may have additional costs at -compile time, and while the critical move-related functions could migrate -to <type_traits>, the header name is far from appealing; adding the -whole of <utility> starts to drag in dependencies on <tuple> -and <memory>, so we prefer to place the burden of slicing or supporting -this whole header on free-standing vendors. -

- - - -

Proposed resolution:

- - -

Rationale:

No consensus for a change at this time.

- - - - -
-

1361. Does use of std::size_t in a header imply that typedef name is available to users?

-

Section: 17.6.2 [using] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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Discussion:

-

Addresses GB-58

-

-It is not clear whether a library header specified in terms -of a typedef name makes that same typedef name -available for use, or if it simply requires that the specified -type is an alias of the same type, and so the typedef name -cannot be used without including the specific header that -defines it. For example, is the following code required to -be accepted: -

-
-#include <vector>
-std::size_t x = 0;
-
-

-Most often, this question concerns the typedefs defined in -header <cstddef> -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add a paragraph under 17.6.2 [using] clarifying whether -or not headers specified in terms of std::size_t can -be used to access the typedef size_t, or whether -the header <cstddef> must be included to reliably -use this name. -

-

[Batavia: NAD - see rationale below]

- - - - -

Proposed resolution:

- -

Rationale:

The standard is correct as written.

- - - - -
-

1369. rethrow_exception may introduce data races

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Section: 18.8.5 [propagation] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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Discussion:

-

Addresses GB-74

-

-One idea for the exception_ptr type was that a reference-counted -implementation could simply 'reactivate' the same -exception object in the context of a call to -rethrow_exception. Such an implementation would allow -the same exception object to be active in multiple threads -(such as when multiple threads join on a shared_future) -and introduce potential data races in any exception -handler that catches exceptions by reference - notably -existing library code written before this capability was -added. rethrow_exception should always make a copy -of the target exception object. -

- -

[Resolution suggested by NB comment]

- - -

-Add the following to 18.8.5, [propogation] -

-

-Throws: a copy of the exception object to which p refers. -

- -

[2011-03-15: Anthony drafts wording]

- - -

[2011-03-23 Madrid meeting]

- - -

No consensus for a change

- - - -

Rationale:

It would break too many existing implementations

- -

Proposed resolution:

- -
    -

  1. Alter 15.1 [except.throw] p. 5 as follows:

    - -

    -5 When the thrown object is a class object, the copy/move constructor and the destructor shall be accessible, -even if the copy/move operation is elided (12.8 [class.copy]). The copy constructor shall be -accessible, and is odr-used (3.2 [basic.def.odr]), even if the copy operation is elided, -or a move constructor used to construct the exception object. -

    -
    2. - -

  2. Alter 18.8.5 [propagation] p. 7 as follows:

    - -
    -exception_ptr current_exception() noexcept;
-
    -

    -7 Returns: An exception_ptr object that refers to the currently handled exception -(15.3 [except.handle]) or a copy of the currently handled exception, or a null exception_ptr -object if no exception is being handled. The referenced object shall remain valid at least as long as there -is an exception_ptr object that refers to it. If the function needs to allocate memory and the -attempt fails, it returns an exception_ptr object that refers to an instance of bad_alloc. -It is unspecified whether the return values of two successive calls to current_exception refer to -the same exception object. [ Note: That is, it is unspecified whether current_exception -creates a new copy each time it is called. — end note ] If the attempt to copy the current -exception object throws an exception, or is otherwise not possible, the function returns an -exception_ptr object that refers to the thrown exception if any or, if this is not possible, -to an instance of bad_exception. [ Note: The copy constructor of the thrown exception -may also fail, so the implementation is allowed to substitute a bad_exception object to avoid -infinite recursion. — end note ] -

    -
    -
    3. - -

  3. Alter 18.8.5 [propagation] p. 9 and add a new paragraph after p. 9 as follows:

    - -
    -[[noreturn]] void rethrow_exception(exception_ptr p);
-
    -

    -8 Requires: p shall not be a null pointer. -

    -9 Throws: a copy of the exception object to which p refers, or any exception -thrown by the attempt to copy the exception object to which p refers. -

    -? Synchronization: Calls to rethrow_exception on exception_ptr objects -that refer to the same exception object shall appear to occur in a single total order. The completion -of each call shall synchronize with (1.10 [intro.multithread]) the next call in that total order. -

    -
    -
    4. -
- - - - - - -
-

1371. Standard exceptions require stronger no-throw guarantees

-

Section: 19 [diagnostics] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses GB-75

-

-None of the exception types defined in clause 19 are -allowed to throw an exception on copy or move -operations, but there is no clear specification that the -operations have an exception specification to prove it. -Note that the implicitly declared constructors, taking the -exception specification from their base class (ultimately -std::exception) will implicitly generate a noexcept -exception specification if all of their data members -similarly declare noexcept operations. As the -representation is unspecified, we cannot assume nonthrowing -operations unless we explicitly state this as a -constraint on the implementation. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add a global guarantee that all exception types -defined in clause 19 that rely on implicitly declared -operations have a non-throwing exception -specification on those operations. -

- -

[ -2010 Batavia: -]

- -

-This is addressed by the current words in 18.8.1 [exception], p2 -

-

-Each standard library class T that derives from class exception -shall have a publicly accessible copy constructor and a publicly accessible copy -assignment operator that do not exit with an exception. -

- - - -

Proposed resolution:

- - - - - -
-

1373. Customizable traits should have their own headers

-

Section: 20.2 [utility] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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Discussion:

-

Addresses GB-79

-

-The library provides several traits mechanisms intended a -customization points for users. Typically, they are -declared in headers that are growing quite large. This is -not a problem for standard library vendors, who can -manage their internal file structure to avoid large -dependencies, but can be a problem for end users who -have no option but to include these large headers. -

- -

[ -2010 Rapperswil -]

- -

-There was no enthusiasm for touching char_traits or regex_traits. -Consensus to move iterator_traits, allocator_traits -and pointer_traits to their own respective headers once wording supplied. -

- -

[ -2010 Rapperswil -]

- -

-After some discussion, consensus is that moving these features into separate -headers does not buy much in practice, as the larger headers will inevitably -be included anyway. Resolve as NAD. -

- -

[ -Resolution proposed in ballot comment -]

- -

-Move the following traits classes into their own -headers, and require the existing header to -#include the traits header to support backwards -compatibility: -

-
-iterator_traits (plus the iterator tag-types)
-allocator_traits
-pointer_traits
-char_traits
-regex_traits
-
- -

[ -2010 Batavia: -]

- -

-Closed as NAD with the rationale below. -

- - - -

Rationale:

-This suggest is not a defect, as the likely benefit is small, if any, -compared to the cost of not just implementating the feature, but also -explaining/teaching it. -

- -

Proposed resolution:

- - - - - -
-

1374. Clarify moved-from objects are "toxic"

-

Section: 17.6.3.1 [utility.arg.requirements] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses US-85

-

-20.2.1 Table 34 "MoveConstructible requirements" says -"Note: rv remains a valid object. Its state is unspecified". -Some components give stronger guarantees. For -example, moved-from shared_ptrs are guaranteed empty -(20.9.11.2.1/25). -In general, what the standard really should say (preferably -as a global blanket statement) is that moved-from objects -can be destroyed and can be the destination of an -assignment. Anything else is radioactive. For example, -containers can be "emptier than empty". This needs to be -explicit and required generally. -

-

-Note: The last time that one of us mentioned "emptier -than empty" (i.e. containers missing sentinel nodes, etc.) -the objection was that containers can store sentinel nodes -inside themselves in order to avoid dynamically allocating -them. This is unacceptable because -

-

-(a) it forces existing implementations (i.e. Dinkumware's, Microsoft's, -IBM's, etc.) to change for no good reason (i.e. permitting more -operations on moved-from objects), and -

-

-(b) it invalidates end-iterators when swapping containers. (The Working -Paper currently permits end-iterator invalidation, which we -consider to be wrong, but that's a separate argument. In -any event, mandating end-iterator invalidation is very -different from permitting it.) -

- -

[ -Resolution proposed in ballot comment -]

- -

-State as a general requirement that moved-from -objects can be destroyed and can be the -destination of an assignment. Any other use is -undefined behavior. -

- - -

Proposed resolution:

-

Resolved by N3241

- - - - - -
-

1375. reference_type should not have been removed from the -allocator requirements

-

Section: 17.6.3.5 [allocator.requirements] Status: Dup - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

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Duplicate of: 1318

-

Discussion:

- -

Addresses US-87

-

-reference_type should not have been removed from the -allocator requirements. Even if it is always the same as -value_type&, it is an important customization point for -extensions and future features. -

- - -

Proposed resolution:

-

-In [allocator.requirements] Table 42 - Allocotor Requirements, -Add a row (after value_type) with columns: -

-

-Expression: X::reference_type
-Return type: T&
-Assertion/note...: (empty)
-Default: T&
-

-

-[allocator.traits]: -

-
-namespace std {
-  template <class Alloc> struct allocator_traits {
-    typedef Alloc allocator_type;
-    
-    typedef typename Alloc::value_type value_type;
-
-    typedef see below   pointer;
-    typedef see below   const_pointer;
-    typedef see below   void_pointer;
-    typedef see below   const_void_pointer;
-    typedef value_type& reference_type;
-
-

-Add reference_type to -allocator_traits template, defaulted to -value_type&. -

- - - - - -
-

1376. Allocator interface is not backward compatible

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

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Discussion:

-

Addresses US-88

-

-Allocator interface is not backward compatible. -

- -

[ -Resolution proposed by ballot comment -]

- -

-See Appendix 1 - Additional Details -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-n3165 provides an alternative resolution. -

- -

[ -2910 Batavia: -]

- -

-Closed as NAD - withdrawn by the submitter. -

- - -

Proposed resolution:

-See n3165 -

- -

Rationale:

Withdrawn by the submitter.

- - - - -
-

1395. Inconsistent reference links should be unified

-

Section: 20.10.6 [meta.rel] Status: NAD Editorial - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses JP-32

-

-Representations of reference link are not unified. -Most reference links to clause (table) number, say X, are -in the form "Clause X" ("Table X") capitalized, and -subsection Y.Y.Y is referenced with its number only in the -form "Y.Y.Y". Whether they are parenthesized or not -depends on the context. -However there are some notations "(Z)" consisting of only -a number Z in parentheses to confer Clause or Table -number Z. -

- - -

Proposed resolution:

-

-Change "(10)" to "(Clause 10)". -

- - - - - -
-

1398. Users should be able to specialize functors without depending on whole <functional> header

-

Section: 20.9 [function.objects] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses GB-96

-

-The function templates hash, less and equal_to -are important customization points for user-defined types to -be supported by several standard containers. These are -accessed through the <functional> header which has -grown significantly larger in C++0x, exposing many more -facilities than a user is likely to need through there own -header, simply to declare the necessary specialization. -There should be a smaller header available for users to -make the necessary customization. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Provide a tiny forwarding header for important -functor types in the <functional> header that a -user may want to specialize. This should contain -the template declaration for equal_to, hash and -less. -

- -

[ -Rapperswill summary -]

- -

Alisdair: Would recommend NAD unless someone takes the issue.

- -

Daniel: Volunteers to write a paper for this.

- -

[ -2010-11-07 Daniel provides a paper available on the Batavia document list -]

- - -

[ -2010 Batavia: -]

- -

-Closed as NAD - the consensus was that forwarding headers such as -<iosfwd> do not bring the expected benefits, and are -not widely used (to the surprise of some active users in the room!). -Without real experience reporting a benefit, there is no further interest -in pursuing this issue as an extension - hence NAD rather than NAD Future. -

- - - -

Rationale:

No consensus to make a change

- -

Proposed resolution:

-

-See paper "Forwarding <functional> functor templates" -on the Batavia LWG document list -

- - - - - -
-

1411. Add a compile-time flag to detect monotonic_clock

-

Section: X [time.clock.monotonic] Status: Dup - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Duplicate of: 1410

-

Discussion:

- -

Addresses DE-20

-

-The library component monotonic_clock is conditionally -supported, but no compile-time flag exists that allows -user-code to query its existence. Further-on there exist no -portable means to simulate such a query. (To do so, user -code would be required to add types to namespace -std::chrono.) -

- - -

Proposed resolution:

-

-Provide a compile-time flag (preferably a macro) -that can be used to query the existence of -monotonic_clock. -

- - - - - -
-

1413. Specify whether high_resolution_clock is a distinct type or a typedef

-

Section: 20.12.7.3 [time.clock.hires] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses US-112

-

-What it means for high_resolution_clock to be a synonym -is undefined. If it may or may not be a typedef, then -certain classes of programs become unportable. -

- -

[ -Resolution proposed in ballot comment -]

- -

-Require that it be a distinct class type. -

- -

[ -2010 Batavia -]

- -

-This is not a defect. Threre are a number of places in the standard where -we allow implentations to choose their preferred technique, the most obvious -example being the iterator/const_iterator types of set. -

-

-Typically, this means it is not portable to declare function overloads that differ -only in their use of these types. -

- - - -

Proposed resolution:

- - - - - -
-

1415. Iterator stability bans the short-string optimization

-

Section: 23.2.1 [container.requirements.general] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Requirements on iterators swapping allegiance would -disallow the small-string optimization. -

-

[ -Resolved in Rapperswil by paper N3108. -]

- - - - -

Proposed resolution:

-

-Add an exclusion for basic_string to the sentence -beginning “Every iterator referring to an -element...”. Add a sentence to 21.4.6.8/2 saying -that iterators and references to string elements -remain valid, but it is not specified whether they -refer to the same string or the other string. -

- - - - - -
-

1419. forward_list::erase_after should return an iterator

-

Section: 23.3.4 [forwardlist] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

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-

Discussion:

-

Addresses US-117

-

-forward_list::erase_after should return an iterator. -

-

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-See Appendix 1 - Additional Details -

- - - - - -
-

1433. random_shuffle and shuffle should have consistent signatures

-

Section: 25.3.12 [alg.random.shuffle] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

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-

Duplicate of: 1432

-

Discussion:

-

Addresses GB-119

-

-The functions random_shuffle and shuffle both take -arguments providing a source of randomness, but one -take its argument by rvalue reference, and the other -requires an lvalue reference. The technical merits of which -form of argument passing should be settled for this -specific case, and a single preferred form used -consistently. -

- - -

Proposed resolution:

-

-[DEPENDS ON WHETHER RVALUE OR -LVALUE REFERENCE IS THE PREFERRED -FORM] -

- - - - - -
-

1434. For min/max functions replace variadic arguments by initializer_list argument

-

Section: 25.4.7 [alg.min.max] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-122

-

-It was the LWG's intent in Pittsburgh that N2772 be applied to the WP. -

-

[ -Resolved in Rapperswil by paper N3106. -]

- - - - -

Proposed resolution:

-

Apply N2772 to the WP.

- - - - - -
-

1442. "happens-before" should be "synchronizes-with"

-

Section: 30 [thread] Status: NAD Editorial - Submitter: Canada Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1443

-

Discussion:

-

Addresses CA-9, GB-122

- -

[CA-9:]

- -

-Imposed happens-before edges should be in -synchronizes-with
-Each use of the words "happens-before" should be -replaced with the words "synchronizes-with" in the -following sentences:
-27.2.3p2
-30.3.1.2p6
-30.3.1.5p7
-30.6.4p7
-30.6.9p5
-30.6.10.1p23
-Rationale: Happens-before is defined in 1.10p11 in a way -that (deliberately) does not make it explicitly transitively -closed. Adding edges to happens-before directly, as in -27.2.3p2 etc., does not provide transitivity with -sequenced-before or any other existing happens-before -edge. This lack of transitivity seems to be unintentional. -

- -

[GB-122]

- - -

At various points in the standard new edges are added to -happens-before, for example 27.2.3:2 adds happens-before edges between -writes and reads from a stream:

- -

If one thread makes a library call a that writes a value to a -stream and, as a result, another thread reads this value from the -stream through a library call b such that this does not result in a -data race, then a happens before b.

- -

Happens-before is defined in 1.10:11 in a deliberate way that makes it -not explicitly transitively closed. Adding edges to happens-before -directly, as in 27.2.3:2, does not provide transitivity with -sequenced-before or any other existing happens-before edge. This lack -of transitivity seems to be unintentional. In order to achieve -transitivity we suggest each edge be added to -inter-thread-happens-before as a synchronises-with edge (as per -conversation with Hans Boehm). In the standard, each use of the words -"happens-before" should be replaced with the words "synchronizes-with" -in the following sentences:

- -

27.2.3:2, -30.3.1.2:6, -30.3.1.5:7, -30.6.4:7, -30.6.9:5, -30.6.10.1:23

- -

Proposed resolution:

- -

[Beman provided specific wording for the proposed resolution.]

- - -

Change 27.2.3 Thread Safety [iostreams.threadsafety] paragraph 2:

- -

If one thread makes a library call a that writes a value to a stream -and, as a result, another thread reads this value from the stream through a library -call b such that this does not result in a data race, then a -happens before synchronizes with b.

- -

Change 30.3.1.2 thread constructors [thread.thread.constr] paragraph 6:

- -

Synchronization: The invocation of the constructor happens -before synchronizes with the invocation of the copy of f.

- -

Change 30.3.1.5 thread members [thread.thread.member] paragraph 7:

- -

Synchronization: The completion of the thread represented by *this -happens before synchronizes with (1.10) join() -returns returning. [ Note: Operations on *this -are not synchronized. --end note ]

- -

Change 30.6.4 Associated asynchronous state [futures.state] paragraph 7:

- -

Calls to functions that successfully set the stored result of an associated -asynchronous state synchronize with (1.10) calls to functions successfully detecting -the ready state resulting from that setting. The storage of the result (whether normal -or exceptional) into the associated asynchronous state happens before -synchronizes with (1.10) that state is being set to ready.

- -

Change 30.6.9 Function template async [futures.async] paragraph 5:

- -

Synchronization: the invocation of async happens before -synchronizes with (1.10) the invocation of f. [ Note: this -statement applies even when the corresponding future object is moved to another thread. — end -note ] If the invocation is not deferred, a call to a waiting function on an asynchronous return object -that shares the associated asynchronous state created by this async call shall block until the associated -thread has completed. If the invocation is not deferred, the join() on the created thread -happens before synchronizes with (1.10) the first function that successfully -detects the ready status of the associated asynchronous state returns or before the function that -gives up the last reference to the associated asynchronous state returns, whichever happens first. -If the invocation is deferred, the completion of the invocation of the deferred function happens -before synchronizes with the calls to the waiting functions return.

- -

Change 30.6.10.1 packaged_task member functions [futures.task.members] paragraph 23:

- -

Synchronization: a successful call to operator() synchronizes with (1.10) a call -to any member function of a future, shared_future, or atomic_future object -that shares the associated asynchronous state of *this. The completion of the invocation -of the stored task and the storage of the result (whether normal or exceptional) into the associated -asynchronous state happens before synchronizes with (1.10) the state is -being set to ready. [ Note: operator() synchronizes and serializes with other -functions through the associated asynchronous state. —end note ]

- - - - - - -
-

1443. Imposed happens-before edges are not made transitive

-

Section: 30 [thread] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1442

-

Discussion:

- - -

Addresses GB-122

- -

At various points in the standard new edges are added to -happens-before, for example 27.2.3:2 adds happens-before edges between -writes and reads from a stream:

- -

If one thread makes a library call a that writes a value to a -stream and, as a result, another thread reads this value from the -stream through a library call b such that this does not result in a -data race, then a happens before b.

- -

Happens-before is defined in 1.10:11 in a deliberate way that makes it -not explicitly transitively closed. Adding edges to happens-before -directly, as in 27.2.3:2, does not provide transitivity with -sequenced-before or any other existing happens-before edge. This lack -of transitivity seems to be unintentional. In order to achieve -transitivity we suggest each edge be added to -inter-thread-happens-before as a synchronises-with edge (as per -conversation with Hans Boehm). In the standard, each use of the words -"happens-before" should be replaced with the words "synchronizes-with" -in the following sentences:

- -

27.2.3:2, -30.3.1.2:6, -30.3.1.5:7, -30.6.4:7, -30.6.9:5, -30.6.10.1:23

- - -

Proposed resolution:

-

-Request the concurrency working group to -determine if changes are needed -

- - - - - -
-

1444. OFF_T is not defined

-

Section: 27.5.4.2 [fpos.operations] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1414

-

Discussion:

- -

Addresses GB-123

-

-Several rows in table 124 specify a Return type of -'OFF_T', which does not appear to be a type defined in -this standard. -

- - -

Proposed resolution:

-

-Resolve outstanding references to the removed type 'OFF_T'. -

- - - - - -
-

1446. Move and swap for I/O streams

-

Section: 27.7 [iostream.format] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-138

- -

-For istreams and ostreams, the move-constructor does -not move-construct, the move-assignment operator does -not move-assign, and the swap function does not swap -because these operations do not manage the rdbuf() -pointer. Useful applications of these operations are -prevented both by their incorrect semantics and because -they are protected. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-In short: reverse the resolution of issue 900, then -change the semantics to move and swap the -rdbuf() pointer. Add a new protected constructor -that takes an rvalue reference to a stream and a -pointer to a streambuf, a new protected assign() -operator that takes the same arguments, and a -new protected partial_swap() function that doesn't -swap rdbuf(). -See Appendix 1 - Additional Details -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3179 would solve this issue. -

- -

[ -2010-11 Batavia -]

- -

-Closed as NAD. -

-

-The Library Working Group reviewed n3179 and -concluded that this change alone was not sufficient, as it would require changes to some of the derived stream types in the library. -The preference is to not make such a broad fix, and retain the current semantics. This is closed as NAD rather than NAD future as it -will be difficult to rename the new functions introduced in the C++0x revision of the standard at a later date. -

- - - -

Proposed resolution:

- - - - - -
-

1451. regex should support allocators

-

Section: 28.8 [re.regex] Status: Dup - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1396

-

Discussion:

- -

Addresses US-141

- -

-std::basic_regex should have an allocator for all the -reasons that a std::string does. For example, I can use -boost::interprocess to put a string or vector -in shared memory, but not a regex. -

- - -

Proposed resolution:

-

-Add allocators to regexes; see paper N3171 -in the pre-Batavia mailing. -

- - - - - -
-

1452. "target sequence" is not defined

-

Section: 28.10.4 [re.results.acc] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-125

- -

The term "target sequence" is not defined (28.10.4 [re.results.acc] p. 2).

- -

[ -Resolution proposed by ballot comment: -]

- -

-Replace "target sequence" with "string being searched/matched" -

- -

[ -2010-11-01 Daniel comments: -]

- -

-The proposed resolution looks incomplete to me, there are more normative -usages of the term target sequence in clause 28, e.g. -28.12.2 [re.tokiter] p. 7. -

- -

[2011-03-22 Madrid meeting: Moved to NAD]

- - - - -

Rationale:

Standard is correct as written

- -

Proposed resolution:

-

-Wording changes are against N3126. They are intended not to conflict with the wording changes -suggested by n3158. -

-

-Change 28.10.4 [re.results.acc] p. 2 as indicated: -

-
-difference_type position(size_type sub = 0) const;
-

-2 Returns: The distance from the start of the target sequencestring being matched to (*this)[sub].first. -

- - - - - -
-

1454. Ensure C compatibility for atomics

-

Section: 29 [atomics] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

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-

Duplicate of: 1455

-

Discussion:

- -

Addresses GB-128

-

-WG14 has made some late changes to their specification -of atomics, and care should be taken to ensure that we -retain a common subset of language/library syntax to -declare headers that are portable to both languages. -Ideally, such headers would not require users to define -their own macros, especially not macros that map to -keywords (which remains undefined behaviour) -

- - -

[ -Resolution proposed by ballot comment -]

- -

-Depends on result of the review of WG14 work, -which is expected to be out to ballot during the -time wg21 is resolving its own ballot comments. -Liaison may also want to file comments in WG14 -to ensure compatibity from both sides. -

- - -

Proposed resolution:

- - - - - -
-

1456. Missing fixed-size atomic_ typedefs

-

Section: 29 [atomics] Status: NAD - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-129

-

-Table 143 lists the typedefs for various atomic types -corresponding to the various standard integer typedefs, -such as atomic_int_least8_t for int_least8_t, and -atomic_uint_fast64_t for uint_fast64_t. However, there are -no atomic typedefs corresponding to the fixed-size -standard typedefs int8_t, int16_t, and so forth. -

-

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3164 would solve this issue. -

- -

[ -2011-02-15 Anthony corrects numbering/naming for N3225, Howard suggests improvement for the position -of '(optional)', Daniel reorders rows in harmony to remaining entries and suggests specific optionality -comments: -]

- - -

[2011-02-16 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- -

[2011-03-16: Hans reopenes and comments]

- - -

WG14 briefly discussed LWG 1456. It turns out that they had previously made a conscious decision not to make a -similar change. If C++ would deviate, this would introduce a C divergence. -

-We should reopen the issue and, in my opinion, probably resolve it as NAD instead. This is in a part of the standard -that is there mostly for C compatibility, so introducing divergence here seems to make no sense. -

- -

[2011-03-24 Madrid]

- -

Rationale:

-WG14 does not require these typedefs, and we see no reason to be gratuitously different. -

- - - -

Proposed resolution:

-

-Add the following entries to table 143: -

-
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 146 — atomic <inttypes.h> typedefs
Atomic typedef<inttypes.h> type
......
atomic_intmax_tintmax_t
atomic_uintmax_tuintmax_t
atomic_int8_t // iff int8_t is providedint8_t
atomic_uint8_t // iff uint8_t is provideduint8_t
atomic_int16_t // iff int16_t is providedint16_t
atomic_uint16_t // iff uint16_t is provideduint16_t
atomic_int32_t // iff int32_t is providedint32_t
atomic_uint32_t // iff uint32_t is provideduint32_t
atomic_int64_t // iff int64_t is providedint64_t
atomic_uint64_t // iff uint64_t is provideduint64_t
-
- - - - - -
-

1458. Overlapping evaluations are allowed

-

Section: 29.3 [atomics.order] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [atomics.order].

-

View all other issues in [atomics.order].

-

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-

Duplicate of: 1459

-

Discussion:

- -

Addresses GB-131

- -

-29.4 [atomics.lockfree] p.8 states: -

-

-An atomic store shall only store a value that has been computed -from constants and program input values by a finite sequence of -program evaluations, such that each evaluation observes the values -of variables as computed by the last prior assignment in the -sequence. -

-

-... but 1.9 [intro.execution] p.13 states: -

-

-If A is not sequenced before B and B is not sequenced before A, -then A and B are unsequenced. [ Note: The execution of unsequenced -evaluations can overlap. — end note ] -

-

-Overlapping executions can make it impossible to construct the sequence -described in 29.4 [atomics.lockfree] p.8. We are not sure of the intention here and do not -offer a suggestion for change, but note that 29.4 [atomics.lockfree] p.8 is the condition -that prevents out-of-thin-air reads. -

- - -

Proposed resolution:

-

-Request the concurrency working group to -determine if changes are needed. Consider -changing the use of "sequence" in 29.4 [atomics.lockfree] -

- - - - - -
-

1461. Rename all ATOMIC_* macros as STD_ATOMIC_*

-

Section: 29 [atomics] Status: NAD - Submitter: Canada Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

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-

Discussion:

-

Addresses CA-1

-

-All ATOMIC_... macros should be prefixed with STD_ as -in STD_ATOMIC_... to indicate they are STD macros as -other standard macros. The rationale that they all seem too long seems weak. -

- -

[2011-03-06: Daniel adapts suggested wording to N3242 and comments]

- - -

I suggest to declare this issue as NAD. Reason for this suggestion is, that -C1x is currently going to suggest exactly the same macros as additions to -header <stdatomic.h>, therefore C++0x should not define a -whole new set. I'm making this suggestion with the understanding that -C1x is intending to keep in sync in this regard. For example, the most -recent -draft of C1x does contain the macro ATOMIC_ADDRESS_LOCK_FREE -which has recently been removed from the C++ working draft.

- -

[2011-03-24]

- -

Rationale:

-C is not going to change the name of these macros, and it is -important they have the same name for compatibility -

- - - -

Proposed resolution:

-
    -

  1. Change sub-clause 29.2 [atomics.syn] as indicated:

    -
    -[..]
-// [atomics.lockfree], lock-free property
-#define STD_ATOMIC_CHAR_LOCK_FREE unspecified
-#define STD_ATOMIC_CHAR16_T_LOCK_FREE unspecified
-#define STD_ATOMIC_CHAR32_T_LOCK_FREE unspecified
-#define STD_ATOMIC_WCHAR_T_LOCK_FREE unspecified
-#define STD_ATOMIC_SHORT_LOCK_FREE unspecified
-#define STD_ATOMIC_INT_LOCK_FREE unspecified
-#define STD_ATOMIC_LONG_LOCK_FREE unspecified
-#define STD_ATOMIC_LLONG_LOCK_FREE unspecified
-
-// [atomics.types.operations.req], operations on atomic types
-#define STD_ATOMIC_VAR_INIT(value) see below
-[..]
-
    -
    2. -
  2. -

    Change 29.4 [atomics.lockfree] p. 1 as indicated:

    -
    -#define STD_ATOMIC_CHAR_LOCK_FREE implementation-defined
-#define STD_ATOMIC_CHAR16_T_LOCK_FREE implementation-defined
-#define STD_ATOMIC_CHAR32_T_LOCK_FREE implementation-defined
-#define STD_ATOMIC_WCHAR_T_LOCK_FREE implementation-defined
-#define STD_ATOMIC_SHORT_LOCK_FREE implementation-defined
-#define STD_ATOMIC_INT_LOCK_FREE implementation-defined
-#define STD_ATOMIC_LONG_LOCK_FREE implementation-defined
-#define STD_ATOMIC_LLONG_LOCK_FREE implementation-defined
-
    -

    -1 The STD_ATOMIC_..._LOCK_FREE macros indicate the lock-free property of the corresponding atomic types, [..] -

    -
    3. -
  3. -

    Change 29.6.5 [atomics.types.operations.req] p. 6 as indicated:

    -
    -#define STD_ATOMIC_VAR_INIT(value) see below
-

    -5 Remarks: The macro expands to a token sequence suitable for constant initialization -an atomic variable of static storage duration of a type that is initialization-compatible -with value. [ Note: This operation may need to initialize locks. — end note ] -Concurrent access to the variable being initialized, even via an atomic operation, constitutes -a data race. [ Example: -

    -atomic<int> v = STD_ATOMIC_VAR_INIT(5);
-
    -

    — end example ]

    -
    -
    4. -
  4. -

    Change 29.7 [atomics.flag] p. 1+4 as indicated:

    -
    -namespace std {
-  [..]
-  #define STD_ATOMIC_FLAG_INIT see below
-}
-

    -[..] -4 The macro STD_ATOMIC_FLAG_INIT shall be defined in such a way that it can be used to initialize an object of -type atomic_flag to the clear state. For a static-duration object, that initialization shall be static. It is -unspecified whether an unitialized atomic_flag object has an initial state of set or clear. [ Example: -

    -atomic_flag guard = STD_ATOMIC_FLAG_INIT;
-
    -

    — end example ]

    -
    -
    5. -
- - - - - -
-

1463. Inconsistent value assignment for atomic_bool

-

Section: X [atomics.types.integral] Status: Dup - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1462

-

Discussion:

- -

Addresses US-157

- -

-atomic_bool has a volatile assignment operator but not a -non-volatile operator. The other integral types have both. -

- - -

Proposed resolution:

-

-Add a non-volatile assignment operator to atomic_bool. -

- - - - - -
-

1470. "Same-ness" curiosities

-

Section: 29.6 [atomics.types.operations] Status: Dup - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

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-

Duplicate of: 1474

-

Discussion:

-

Addresses US-165

- -

-According to 29.6 [atomics.types.operations] p. 23: -

-

-“is the same that same as that of” is not grammatical (and is not clear) -

- - - -

Proposed resolution:

- - - - - -
-

1471. Default constructor of atomics needs specification

-

Section: 29.6 [atomics.types.operations] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-168

- -

-29.6 [atomics.types.operations] around p. 4: The definition of the default constructor needs exposition. -

- - -

Proposed resolution:

-

-Insert a new general prototype description following the current 29.6 [atomics.types.operations] p. 3 as indicated: -

-

-3 [Note: Many operations are volatile-qualified. The “volatile as device register” semantics have not changed -in the standard. This qualification means that volatility is preserved when applying these operations to -volatile objects. It does not mean that operations on non-volatile objects become volatile. Thus, volatile -qualified operations on non-volatile objects may be merged under some conditions. -- end note] -

-
-A::A() = default;
-

-? Effects: Leaves the atomic object in an uninitialized state. -[Note: These semantics ensure compatiblity with C. -- end note] -

-
-constexpr A::A(C desired);
-[..]
-
- - - - - -
-

1472. Incorrect semantics of atomic_init

-

Section: 29.6 [atomics.types.operations] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-171

- -

-As of 29.6 [atomics.types.operations] p. 7: -

-The atomic_init definition "Non-atomically assigns the -value" is not quite correct, as the atomic_init purpose is -initialization. -

- - -

Proposed resolution:

-

-Change 29.6 [atomics.types.operations] p. 7 as indicated: -

-
-void atomic_init(volatile A *object, C desired);
-void atomic_init(A *object, C desired);
-

-7 Effects: Non-atomically assigns the value desired to *objectInitializes *object with value -desired. Concurrent access from another thread, even via an atomic operation, constitutes a data race. -[Note: This function should only be applied to objects that have been default constructed. These semantics ensure -compatibility with C. — end note] -

- - - - - -
-

1473. Incomplete memory order specifications

-

Section: 29.6 [atomics.types.operations] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

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-

Discussion:

-

Addresses US-172

- -

-As of 29.6 [atomics.types.operations] p. 9, 13, 17, 20: -

-The order specifications are incomplete because the non-_explicit -functions do not have such parameters. -

-Add a new sentence: "If the program does not specify an order, it shall be -memory_order_seq_cst." Or perhaps: "The non-_explicit -non-member functions shall affect memory as though they were _explicit with -memory_order_seq_cst." -

- -

[ -2010 Batavia -]

- -

-The Concurrency subgroup reviewed this, and deemed it NAD according to -29.6 [atomics.types.operations] paragraph 2, bullet 4. -

- -

Rationale:

The working paper is correct as written.

- - - -

Proposed resolution:

-
    -
  1. Change 29.6 [atomics.types.operations] p. 9 as indicated: -
    -void atomic_store(volatile A* object, C desired);
-void atomic_store(A* object, C desired);
-void atomic_store_explicit(volatile A *object, C desired, memory_order order);
-void atomic_store_explicit(A* object, C desired, memory_order order);
-void A::store(C desired, memory_order order = memory_order_seq_cst) volatile;
-void A::store(C desired, memory_order order = memory_order_seq_cst);
-

    -8 Requires: The order argument shall not be memory_order_consume, memory_order_acquire, nor -memory_order_acq_rel. -

    -9 Effects: Atomically replaces the value pointed to by object or by this with the value of desired. -Memory is affected according to the value of order. If the program does not specify an order, it shall be -memory_order_seq_cst. -

    -
    -
    2. -
  2. Change 29.6 [atomics.types.operations] p. 13 as indicated: -
    -C atomic_load(const volatile A* object);
-C atomic_load(const A* object);
-C atomic_load_explicit(const volatile A* object, memory_order);
-C atomic_load_explicit(const A* object, memory_order);
-C A::load(memory_order order = memory_order_seq_cst) const volatile;
-C A::load(memory_order order = memory_order_seq_cst) const;
-

    -12 Requires: The order argument shall not be memory_order_release nor memory_order_acq_rel. -

    -13 Effects: Memory is affected according to the value of order. If the program does not specify an order, it shall be -memory_order_seq_cst. -

    -14 Returns: Atomically returns the value pointed to by object or by this. -

    -
    -
    3. -
  3. Change 29.6 [atomics.types.operations] p. 17 as indicated: -
    -C atomic_exchange(volatile A* object, C desired);
-C atomic_exchange(A* object, C desired);
-C atomic_exchange_explicit(volatile A* object, C desired, memory_order);
-C atomic_exchange_explicit(A* object, C desired, memory_order);
-C A::exchange(C desired, memory_order order = memory_order_seq_cst) volatile;
-C A::exchange(C desired, memory_order order = memory_order_seq_cst);
-

    -17 Effects: Atomically replaces the value pointed to by object or by this with desired. Memory -is affected according to the value of order. These operations are atomic read-modify-write operations -(1.10). If the program does not specify an order, it shall be memory_order_seq_cst. -

    -18 Returns: Atomically returns the value pointed to by object or by this immediately before the effects. -

    -
    -
    4. -
  4. Change 29.6 [atomics.types.operations] p. 20 as indicated: -
    -bool atomic_compare_exchange_weak(volatile A* object, C * expected, C desired);
-bool atomic_compare_exchange_weak(A* object, C * expected, C desired);
-bool atomic_compare_exchange_strong(volatile A* object, C * expected, C desired);
-bool atomic_compare_exchange_strong(A* object, C * expected, C desired);
-bool atomic_compare_exchange_weak_explicit(volatile A* object, C * expected, C desired,
-  memory_order success, memory_order failure);
-bool atomic_compare_exchange_weak_explicit(A* object, C * expected, C desired,
-  memory_order success, memory_order failure);
-bool atomic_compare_exchange_strong_explicit(volatile A* object, C * expected, C desired,
-  memory_order success, memory_order failure);
-bool atomic_compare_exchange_strong_explicit(A* object, C * expected, C desired,
-  memory_order success, memory_order failure);
-bool A::compare_exchange_weak(C & expected, C desired,
-  memory_order success, memory_order failure) volatile;
-bool A::compare_exchange_weak(C & expected, C desired,
-  memory_order success, memory_order failure);
-bool A::compare_exchange_strong(C & expected, C desired,
-  memory_order success, memory_order failure) volatile;
-bool A::compare_exchange_strong(C & expected, C desired,
-  memory_order success, memory_order failure);
-bool A::compare_exchange_weak(C & expected, C desired,
-  memory_order order = memory_order_seq_cst) volatile;
-bool A::compare_exchange_weak(C & expected, C desired,
-  memory_order order = memory_order_seq_cst);
-bool A::compare_exchange_strong(C & expected, C desired,
-  memory_order order = memory_order_seq_cst) volatile;
-bool A::compare_exchange_strong(C & expected, C desired,
-  memory_order order = memory_order_seq_cst);
-

    -19 Requires: The failure argument shall not be memory_order_release nor memory_order_acq_rel. -The failure argument shall be no stronger than the success argument. -

    -20 Effects: Atomically, compares the contents of the memory pointed to by object or by this for equality -with that in expected, and if true, replaces the contents of the memory pointed to by object or by -this with that in desired, and if false, updates the contents of the memory in expected with the -contents of the memory pointed to by object or by this. Further, if the comparison is true, memory -is affected according to the value of success, and if the comparison is false, memory is affected -according to the value of failure. When only one memory_order argument is supplied, the value of -success is order, and the value of failure is order except that a value of -memory_order_acq_rel shall be replaced by the value memory_order_acquire and a value of -memory_order_release shall be replaced by the value memory_order_relaxed. If -the program does not specify an order, it shall be memory_order_seq_cst. If the operation returns true, -these operations are atomic read-modify-write operations (1.10). Otherwise, these operations are atomic load operations. -

    -[..] -

    -
    -
    5. -
- - - - - -
-

1475. weak compare-and-exchange confusion II

-

Section: 29.6 [atomics.types.operations] Status: Dup - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

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-

Duplicate of: 1474

-

Discussion:

-

Addresses CH-23

- -

-29.6 [atomics.types.operations] p. 23: The first sentence has non-English syntax. -

- -

[ -Resolution proposed in ballot comment: -]

- - -

-Change to "The weak compare-and-exchange -operations may fail spuriously, that is, return false -while leaving the contents of memory pointed to -by expected unchanged." -

- -

[ -Daniel translates NB comment in a proposed resolution -]

- - -

Change 29.6 [atomics.types.operations] p. 23 as indicated:

- -

-23 Remark: The weak compare-and-exchange operations may fail spuriously, that is, return false while -leaving the contents of memory pointed to by expected before the operation is the same that same -as that of the object and the same as that of expected after the operationThe weak -compare-and-exchange operations may fail spuriously, that is, return false while leaving the contents of memory -pointed to by expected unchanged.. [ Note: This spurious failure enables implementation of -compare-and-exchange on a broader class of machines, e.g., loadlocked store-conditional machines. A consequence of -spurious failure is that nearly all uses of weak compare-and-exchange will be in a loop. -

-When a compare-and-exchange is in a loop, the weak version will yield better performance on some -platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the -strong one is preferable. — end note ] -

- -

[ -See 1474 for the proposed resolution -]

- - - -

Proposed resolution:

- - - - - -
-

1476. Meaningless specification of spurious failure

-

Section: 29.6 [atomics.types.operations] Status: Dup - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

View all issues with Dup status.

-

Duplicate of: 1474

-

Discussion:

- -

Addresses US-177

- -

-The first sentence of this paragraph doesn't make sense. -

- -

[ -Resolution proposed in ballot comment -]

- -

-Figure out what it's supposed to say, and say it. -

- - -

Proposed resolution:

- - - - - -
-

1477. weak compare-and-exchange confusion III

-

Section: 29.6 [atomics.types.operations] Status: Dup - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 1474

-

Discussion:

-

Addresses GB-135

- -

-The first sentence of 29.6 [atomics.types.operations] p.23 was changed by n2992 but -now makes no sense: "that is, return false while leaving -the contents of memory pointed to by expected before the -operation is the same that same as that of the object and -the same as that of expected after the operation." -There's a minor editorial difference between n2992 ("is -that same as that" vs "is the same that same as that") but -neither version makes sense. -Also, the remark talks about "object" which should -probably be "object or this" to cover the member functions -which have no object parameter. -

- -

[ -Resolution proposed in ballot comment: -]

- -

-Fix the Remark to say whatever was intended. -

- - - -

Proposed resolution:

- - - - - -
-

1483. __STDCPP_THREADS spelling

-

Section: 30.3 [thread.threads] Status: NAD Editorial - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with NAD Editorial status.

-

Discussion:

-

Addresses DE-23

- -

-Predefined macros usually start and end with two -underscores, see 16.8 and FDIS 29124 = WG21 N3060 -clause 7. __STDCPP_THREADS should blend in. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-Change the macro name to __STDCPP_THREADS__. -

- - - - - -
-

1485. Unclear thread::id specification

-

Section: 30.3.1.1 [thread.thread.id] Status: NAD - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-184

-

-It is unclear when a thread::id ceases to be meaningful. -The sentence "The library may reuse the value of a -thread::id of a terminated thread that can no longer be -joined." implies that some terminated threads can be -joined. It says nothing about detached threads. -

-

[ -Resolution proposed by ballot comment: -]

- -

-Require a unique thread::id for every thread that is -(1) detached and not terminated or (2) has an associated std::thread -object. -

- -

[ -2010-11-22 Howard Hinnant observes -]

- - -

-A thread can either be running or terminated. Additionally a thread can be joined, detached, or neither. -These combine into the five possible states shown in this table: -

- - - - - - - - - - - - - - -
RunningTerminated
Neither joined nor detachedshall not reuse idshall not reuse id
detachedshall not reuse idmay reuse id
joinedimpossible statemay reuse id
-

-Only if a thread is neither joined nor detached can it be joined. Or said differently, if a -thread has already been joined or detached, then it can not be joined. The sentence: -

-

-The library may reuse the value of a thread::id of a terminated thread that can no longer be joined. -

-

-precisely defines the two states shown in the above table where a thread::id may be reused. -

-

-The following program illustrates all of the possibilities: -

-
-#include <mutex>
-#include <thread>
-#include <iostream>
-#include <chrono>
-
-std::mutex mut;
-
-void f()
-{
-   std::lock_guard<std::mutex> _(mut);
-   std::cout << "f id = " << std::this_thread::get_id() << " terminating\n";
-}
-
-void g()
-{
-   std::lock_guard<std::mutex> _(mut);
-   std::cout << "g id = " << std::this_thread::get_id() << " terminating\n";
-}
-
-int main()
-{
-   std::cout << "main id = " << std::this_thread::get_id() << "\n";
-   std::thread t1(f);
-   std::thread(g).detach();
-   std::this_thread::sleep_for(std::chrono::seconds(1));
-   std::cout << "g's thread::id can be reused here because g has terminated and is detached.\n";
-   std::cout << "f's thread::id can't be reused here because f has terminated but is still joinable.\n";
-   std::cout << "f id = " << t1.get_id() << "\n";
-   t1.join();
-   std::cout << "f's thread::id can be reused here because f has terminated and is joined.\n";
-   std::cout << "f id = " << t1.get_id() << "\n";
-}
-
-main id = 0x7fff71197ca0
-f id = 0x100381000 terminating
-g id = 0x100581000 terminating
-g's thread::id can be reused here because g has terminated and is detached.
-f's thread::id can't be reused here because f has terminated but is still joinable.
-f id = 0x100381000
-f's thread::id can be reused here because f has terminated and is joined.
-f id = 0x0
-
- -

[2011-02-11 Reflector discussion]

- -

-Moved to Tentatively NAD after 5 votes. -

- - - - -

Proposed resolution:

- - - - - -
-

1486. Value of this_thread::get_id() underspecified for detached thread

-

Section: 30.3.2 [thread.thread.this] Status: NAD - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.thread.this].

-

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-

Discussion:

-

Addresses CH-24

-

-What would be the value this_thread::get_id() when called from a detached thread? -

-

[ -Resolution proposed by ballot comment: -]

- -

-Add some text to clarify that get_id() still returns the same value even after detaching. -

- -

[ -2010-11-22 Howard Hinnant observes -]

- - -

-30.3.2 [thread.thread.this]/1 contains the following sentence describing this_thread::get_id(): -

- -

-... No other thread of execution shall have this id and this thread of execution shall always have this id. -

- -

I don't object to adding "even if detached" to this sentence, but it seems unnecessary to me. "Always" means always.

- -

[2011-02-11 Reflector discussion]

- -

-Moved to Tentatively NAD after 5 votes. -

- - - -

Proposed resolution:

- - - - - -
-

1489. unlock functions and unlock mutex requirements are inconsistent

-

Section: 30.4 [thread.mutex] Status: NAD Editorial - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses CH-26

- -

-Specifications of unlock member functions and unlock -mutex requirements are inconsistent wrt to exceptions and -pre- and postconditions. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-unlock should specifiy the precondition that the -current thread "owns the lock", this will make calls -without holding the locks "undefined behavior". -unlock in [mutex.requirements] should either be -noexcept(true) or be allowed to throw -system_error like unique_lock::unlock, or the latter -should be nothrow(true) and have the precondition -owns == true. -Furthermore unique_lock's postcondition is wrong -in the case of a recursive mutex where owns -might stay true, when it is not the last unlock -needed to be called. -

- - - -

Proposed resolution:

- - - - - -
-

1495. Condition variable wait_for return value insufficient

-

Section: 30.5 [thread.condition] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-191

- -

-The condition variable wait_for returning cv_status is insufficient. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Return a duration of timeout remaining instead. -See Appendix 1 of n3141 - Additional Details, p. 211 -

- - - -

Proposed resolution:

- - - - - -
-

1496. condition_variable not implementable

-

Section: 30.5.1 [thread.condition.condvar] Status: NAD Editorial - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

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-

Discussion:

-

Addresses CH-28

- -

-Requiring wait_until makes it impossible to implement -condition_variable correctly using respective objects -provided by the operating system (i.e. implementing the -native_handle() function) on many platforms (e.g. POSIX, -Windows, MacOS X) or using the same object as for the -condition variable proposed for C. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Remove the wait_until functions or make them at least conditionally supported. -

- - -

Proposed resolution:

- - - - - -
-

1500. Consider removal of native_handle()

-

Section: 30.5.2 [thread.condition.condvarany] Status: NAD Editorial - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvarany].

-

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-

Discussion:

-

Addresses CH-32

- -

-Given that the lock type can be something the underlying -doesn't know 'native_handle()' is probably -unimplementable on essentially all platforms. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-Consider the removal of 'native_handle()'. -

- - - - - -
-

1503. "associated asynchronous state" must go

-

Section: 30.6.4 [futures.state] Status: NAD Editorial - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses CH-35

-

-The term "associated asynchronous state" is long, ugly and misleading terminology. When -introduced we agreed upon that we should come up with a better name. Here it is: -"liaison state". Since the state is hidden and provides synchronization of a -future with its corresponding promise, we believe "liaison state" is -a much better and shorter name (liaison ~ (typically hidden) relationship) -

-

[ -Resolution proposed by ballot comment: -]

- -

-Change all occurrences of "associated -asynchronous state" to "liaison state". -

- - -

Proposed resolution:

-

The project editor may supply a more appopriate term, or use "liaison state", -at his own discretion.

- - - - - -
-

1506. set_exception with a null pointer

-

Section: 30.6.5 [futures.promise] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

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-

Discussion:

-

Addresses US-198

-

-promise::set_exception can be called with a null pointer, -but none of the descriptions of the get() functions for the -three types of futures say what happens for this case. -

-

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-Add the following sentence to the end of -30.6.5/22: The behavior of a program that calls -set_exception with a null pointer is undefined. -

- - - - - -
-

1509. No restriction on calling future::get more than once

-

Section: X [futures.atomic_future] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-202

-

-The note in this paragraph says "unlike future, calling get -more than once on the same atomic_future object is well -defined and produces the result again." There is nothing -in future that says anything negative about calling get -more than once. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Remove this note, or add words to the -requirements for future that reflect what this note -says. -

- - -

Proposed resolution:

- - - - - -
-

1510. Should be undefined behaviour to call atomic_future operations unless valid()

-

Section: X [futures.atomic_future] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [futures.atomic_future].

-

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-

Discussion:

-

Addresses US-203

-

-Both future and shared_future specify that calling most -member functions on an object for which valid() == false -produces undefined behavior. There is no such statement -for atomic_future. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add a new paragraph after X [futures.atomic_future]/2 with the same words as -30.6.7 [futures.shared_future]/3. -

- -

[ -2010-11-02 Daniel translates proposed changes into specific deltas and comments: -]

- - -

-While applying the wording, I notice that 30.6.7 [futures.shared_future]/3 does -speak of the move-assignment operator, and not of the copy-assignment operator. -atomic_future obviously needs this to be true for the copy-assignment operator, -but I strongly assume that shared_future needs to mention both special member -assignment operators in this paragraph. To keep this consistent, the following P/R also -provides wording to fix the corresponding location for shared_future. -

- - - -

Proposed resolution:

-
    -
  1. Change 30.6.7 [futures.shared_future]/3 as indicated: -

    -3 The effect of calling any member function other than the destructor, the -copy-assignment operator, the move-assignment operator, or valid() -on a shared_future object for which valid() == false is undefined. -

    -
    2. -
  2. Following X [futures.atomic_future]/2, add a new paragraph: -

    -? The effect of calling any member function other than the destructor, the copy-assignment operator, or valid() -on a atomic_future object for which valid() == false is undefined. -

    -
    3. -
- - - - - -
-

1511. Synchronize the move-constructor for atomic_future

-

Section: X [futures.atomic_future] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-204

-

-According to the definition of atomic_future, all members -of atomic_future are synchronizing except constructors. -However, it would probably be appropriate for a move -constructor to be synchronizing on the source object. If -not, the postconditions on paragraphs 7-8, might not be -satisfied. This may be applicable if a collection of futures -are being doled out to a set of threads that process their -value. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Make the move constructor for atomic future lock -the source -

- - - -

Proposed resolution:

- - - - - -
-

1512. Conflict in specification: block or join?

-

Section: 30.6.8 [futures.async] Status: NAD Editorial - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-205

-

-30.6.8 [futures.async] p. 3: The third sentence says -"If the invocation is not deferred, a call to a waiting function -on an asynchronous return object that shares the associated asynchronous state -created by this async call shall block until the associated -thread has completed." The next sentence says "If the -invocation is not deferred, the join() on the created -thread..." Blocking until a thread completes is not -necessarily a join. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Decide whether the requirement is to block until -finished or to call join, and rewrite to match. -

- - - -

Proposed resolution:

- - - - - -
-

2006. emplace broken for associative containers

-

Section: 23.2.5 [unord.req] Status: NAD - Submitter: Pablo Halpern Opened: 2010-10-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The current definition of emplace(args) for associative containers as -described in Table 99 is: -

-
-

-Requires: T shall be constructible from args. -

-Effects: Inserts a T object t constructed with -std::forward<Args>(args)... if and only if there is no element -in the container with key equivalent to the key of t. The bool -component of the returned pair is true if and only if the -insertion takes place, and the iterator component of the pair -points to the element with key equivalent to the key of t. -

-
-

-There is similar language in Table 100 for unordered associative containers. -

-The first issue is editorial: T should be value_type throughout -both tables. -

-The major issue is that, if the container is map, multimap, -unordered_map, or unordered_multimap, then the only way to -construct an object of value_type is to supply exactly two arguments -for Key and Value, a pair<Key,Value>, or a -piecewise_construct_t followed by two tuples. The original -emplace() proposal would have allowed you to specify a Key -value followed by any number of constructor arguments for Value. -When we removed the variadic constructor to pair, this ability went -away. I don't think that was deliberate. -

-Fixing this is non-trivial, I think. I think that emplace() for map -and multimap need several overloads: one for each overloaded constructor in -pair<Key,Value>, and one for the emplace(Key, valueargs...) case. -And it probably needs some SFINAE meta-programming to ensure that the last case -doesn't override any of the other ones. Alternatively, one could say that -there are exactly two cases: emplace(args) where pair<Key,Value> -is constructible from args, and emplace(args) where Key is -constructible form the first arg and Value is constructible from the -rest. -

-Alternatively, the status quo is to use piecewise_construct_t if you want to -construct an object. -

- -

[ -2010 Batavia: -]

- - -

-N3178 was looked at in session and moved to NAD. -

- - -

Proposed resolution:

- - - - - -
-

2026. hash should be std qualified for unordered container

-

Section: 23.5 [unord] Status: NAD - Submitter: Pete Becker Opened: 2011-02-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Tom Plum pointed out to me that there's an apparent inconsistency in the std:: qualification of template names in the unordered containers: -

- -
- template <class Key,
-           class T,
-           class Hash = hash<Key>,
-           class Pred = std::equal_to<Key>,
-           class Alloc = std::allocator<std::pair<const Key, T> > >
-   class unordered_map;
-
- -

-Is there a reason that hash is not qualified with std::? TR1 also -does not use std:: here. -

- -

[ -2011-02-07 Chris Jefferson adds: -]

- -

-I assumed (I might be wrong) it is because hash is designed to be a -customisation point, like swap. -

- -

[ -2011-02-07 Howard Hinnant adds: -]

- -

I think this is incorrect. We mean std::hash, though clients -are free to specialize std::hash on user-defined types. With the -possible exception of begin/end (which I'm not sure if -we've settled that), swap is the only intended customization point (look up a function by ADL) in the std:: lib. -

- -

[ -2011-02-24 Chris Jefferson adds: -]

- -

I recommend NAD, due to 17.6.1.1 [contents] p3:

-

-Whenever a name x defined in the standard library is mentioned, the name x is assumed to be fully qualified -as ::std::x, unless explicitly described otherwise. For example, if the Effects section for library function F -is described as calling library function G, the function ::std::G is meant. -

- -

[2011-02-25 Reflector discussion]

- -

-Moved to Tentatively NAD after 5 votes. -

- - -

Proposed resolution:

-

-

- - - - - -
-

2036. istream >> char and eofbit

-

Section: 27.7.2.1 [istream] Status: NAD - Submitter: Howard Hinnant Opened: 2011-02-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The question is: When a single character is extracted from an istream using operator>>, -does eofbit get set if this is the last character extracted from the stream? The current standard is at -best ambiguous on the subject. 27.7.2.1 [istream]/p3 describes all extraction operations with:

- -

-3 If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits::eof(), then the input -function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may -throw ios_base::failure (27.5.5.4 [iostate.flags]), before returning. -

- -

And 27.7.2.2.3 [istream::extractors]/p12 in describing operator>>(basic_istream<charT,traits>& in, charT& c); -offers no further clarification: -

- -

-12 Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in. -After a sentry object is constructed a character is extracted from in, if one is available, and -stored in c. Otherwise, the function calls in.setstate(failbit). -

- -

I coded it one way in libc++, and g++ coded it another way. Chris Jefferson noted that some boost code was -sensitive to the difference and fails for libc++. Therefore I believe that it is very important that we specify -this extraction operator in enough detail that both vendors and clients know what behavior is required and expected. -

- -

Here is a brief code example demonstrating the issue:

- -
-#include <sstream>
-#include <cassert>
-
-int main()
-{
-  std::istringstream ss("1");
-  char t;
-  ss >> t;
-  assert(!ss.eof());
-};
-
- -

For every type capable of reading this istringstream but char, ss.eof() will be true after the -extraction (bool, int, double, etc.). So for consistency's sake we might want to have -char behave the same way as other built-in types.

- -

However Jean-Marc Bourguet offers this counter example code using an interactive stream. He argues that -setting eof inhibits reading the next line:

- -
-#include <iostream>
-
-int main()
-{
- char c;
- std::cin >> std::noskipws;
- std::cout << "First line: ";
- while (std::cin >> c) {
-    if (c == '\n') {
-       std::cout << "Next line: ";
-    }
- }
-}
-
- -

As these two code examples demonstrate, whether or not eofbit gets set is an observable difference and it -is impacting real-world code. I feel it is critical that we clearly and unambiguously choose one behavior or the other. -I am proposing wording for both behaviors and ask the LWG to choose one (and only one!).

- -

Wording for setting eof bit:

- -

Modify 27.7.2.2.3 [istream::extractors]/p12 as follows:

- -

-12 Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in. -After a sentry object is constructed a character is extracted from in, if one is available, and -stored in c. Otherwise, the function calls in.setstate(failbit). If a character is -extracted and it is the last character in the pending sequence, the function calls in.setstate(eofbit). -If a character is not extracted the function calls in.setstate(failbit | eofbit). -

- -

Wording for not setting eof bit:

- -

-12 Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in. -After a sentry object is constructed a character is extracted from in, if one is available, -and stored in c. Otherwise, the function calls in.setstate(failbit). with -in.rdbuf()->sbumpc(). If traits::eof() is returned, the function calls -in.setstate(failbit | eofbit). Otherwise the return value is converted to type charT and stored -in c. -

- -

[2011-02-27: Jean-Marc Bourguet comments]

- - -

Just for completeness: it [the counter example] doesn't inhibit to read the next line, it inhibits the prompt -to be put at the appropriate time.

- -

More information to take into account when deciding:

- -
    -

  • if I'm reading correctly the section to get boolean values when boolalpha is set, there we mandate -that eof isn't set if trying to read past the end of the pending sequence wasn't needed to determine the result. -

    • - -

  • -see also the behaviour of getline (which isn't a formatted input function but won't set eof -if it occurs just after the delimiter) -

    • - -

  • -if I'm reading the C standard correctly scanf("%c") wouldn't set feof either in that situation. -

    • -
- -

[2011-02-28: Martin Sebor comments]

- - -

[Responds to bullet 1 of Jean-Marc's list]

- -

-Yes, this matches the stdcxx test suite for num_get and time_get -but not money_get when the currency symbol is last. I don't see -where in the locale.money.get.virtuals section we specify whether -eofbit is or isn't set and when. -

-IMO, if we try to fix the char extractor to be consistent we -should also fix all the others extractors and manipulators that -aren't consistent (including std::get_money and std::get_time). -

- -

[2011-03-24 Madrid meeting]

- - -

Dietmar convinced Howard, that the standard does already say the right words

- - - -

Rationale:

Reading the last character does not set eofbit and the standard says so already

- -

Proposed resolution:

-

- - - - - -
-

2043. std{in,out,err} should be usable as field names

-

Section: 27.9.2 [c.files] Status: NAD - Submitter: Jeffrey Yasskin Opened: 2011-03-23 Last modified: 2015-04-08

-

View all other issues in [c.files].

-

View all issues with NAD status.

-

Discussion:

-

-People often define structs and classes with fields named stdin, -stdout, or stderr. According to 27.9.2 [c.files], -though, these are macros. -

-glibc defines them to themselves, allowing their non-portable use as -field names, while the Mac OS X libc defines them to either __stdoutp -or (&__sF[1]), etc depending on __DARWIN_UNIX03. It's possible to -allow their use while, as far as I can see, only requiring minor -changes to various libc's, so C++1x should allow it. -

- -

[ -2011 Bloomington -]

- - -

-Closed as NAD. This is an extension request that has been an issue for over 20 years. -Supporting the extension would place a burden on the underlying C library that we may -not be in a position to influence. -

- - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  1. In 27.9.2 [c.files] add "stderr", "stdin", and "stdout" to a new Values section in Table -134 — Header <cstdio> synopsis:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    134 — Header <cstdio> synopsis
    Type Name(s)
    Macros:
    BUFSIZFOPEN_MAXSEEK_CURTMP_MAX_IONBFstdout
    EOFL_tmpnamSEEK_END_IOFBFstderr 
    FILENAME_MAXNULL <cstdio>SEEK_SET_IOLBFstdin 
    Types:FILEfpos_tsize_t <cstdio>  
    Functions:
    …
    Values:
    stderrstdinstdout   
    -
    - -
    2. - -

  2. Add a new paragraph after paragraph 2 as indicated:

    - -

    -2 Calls to the function tmpnam with an argument of NULL may -introduce a data race (17.6.5.9) with other calls to tmpnam with an -argument of NULL.
    -See also: ISO C 7.9, Amendment 1 4.6.2. -

    -? The macros stderr, stdin, and stdout shall -expand to stderr, stdin, and stdout, respectively. -[Note: This allows uses of #ifdef to detect their presence, -while allowing code in other scopes to use them as identifiers. — end note] -

    -
    3. - -

  3. In C.5 [diff.library] add "stderr", "stdin", and "stdout" to -Table 150 — Standard values:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 150 — Standard values
    CHAR_BITFLT_DIGINT_MINMB_LEN_MAX
    …
    ………SHRT_MIN
    ………stderr
    ………stdin
    ………stdout
    ………UCHAR_MAX
    …
    -
    - -
    4. - -
- - - - - - -
-

2046. shared_future(future<R>&&) should be allowed to throw

-

Section: 30.6.7 [futures.shared_future] Status: NAD - Submitter: Peter Sommerlad Opened: 2011-04-04 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

View all issues with NAD status.

-

Discussion:

- -

-Requiring the constructor shared_future(future<R>&& rhs) not to throw -is a pessimisation of the case where a future is returned from a call to -async(function,launch::deferred) and possible other cases. -

-Such a future not dealing with multiple threads only needs to keep (a copy of) the function -to be called it later. However, creating a shared_future from that future will require more -infrastructure, like space for the value of type R, an exception_ptr, and a synchronized -reference counter for the shared_future's instances. -

-Enforcing the constructor shared_future(future<R>&& rhs) not to throw, -implies that any implementation of future will need to pre-allocate space for shared_future's -infrastructure, that also requires an operating system resource for synchronization, regardless -if is ever needed. -

-All this came up when discussing D/N3267 and Concurrency Working Group decided that the constructor -shared_future(future<R>&& rhs) should be allowed to throw. -

- -

[ -2011 Bloomington -]

- - -

-Closed as NAD. Rationale to follow by email... -

- - -

Proposed resolution:

- -

Apply the proposed resolution of n3269

- - - - - - -
-

2060. unique_ptr<T[]>(nullptr_t) missing noexcept

-

Section: 20.8.1.3 [unique.ptr.runtime] Status: NAD Editorial - Submitter: Howard Hinnant, Paolo Carlini Opened: 2011-05-27 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.runtime].

-

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-

Discussion:

-

-The synopsis in 20.8.1.2 [unique.ptr.single] specifies: -

-constexpr unique_ptr(nullptr_t) noexcept
-

-which looks correct to me. However the corresponding constructor in 20.8.1.3 [unique.ptr.runtime] is missing noexcept: -

-constexpr unique_ptr(nullptr_t) : unique_ptr() { }
-
- -

[Bloomington, 2011]

- -

-Closed as NAD Editorial. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Modify the synopsis in 20.8.1.3 [unique.ptr.runtime]:

    -
    -namespace std {
-  template <class T, class D> class unique_ptr<T[], D> {
-  public:
-    typedef see below pointer;
-    typedef T element_type;
-    typedef D deleter_type;
-
-    // 20.7.1.3.1, constructors
-    constexpr unique_ptr() noexcept;
-    […]
-    constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
-	
-    […]
-  };
-}
-
    -
    2. -
- - - - - -
-

2068. std::pair not C++03-compatible with defaulted copy c'tor

-

Section: 20.3.2 [pairs.pair] Status: NAD - Submitter: Daniel Krügler Opened: 2011-06-18 Last modified: 2015-04-08

-

View all other issues in [pairs.pair].

-

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-

Discussion:

-

-The specification of the copy semantics of the C++03 version of std::pair -is defined by the class synopsis in [lib.pairs]: -

-
-template <class T1, class T2>
-struct pair {
-  typedef T1 first_type;
-  typedef T2 second_type;
-
-  T1 first;
-  T2 second;
-  pair();
-  pair(const T1& x, const T2& y);
-  template<class U, class V> pair(const pair<U, V> &p);
-};
-
-

-The effect of this specification is, that the copy constructor is compiler-declared -with the proper form depending on the contained member types. In particular, the -instantiation of pair is well-formed with an element type that has a -copy constructor with non-const first parameter type like specialzations of auto_ptr -or any user-defined type like the following one: -

-
-struct A {
-  A(A&){}
-};
-
-

-In contrast to container types which require CopyConstructible value types, the C++03 pair -does support these, albeit unusual, element types. -

-The FDIS version of the std::pair specification does specify the same semantics by -defaulting the copy and move constructor in 20.3.2 [pairs.pair]: -

-
-template <class T1, class T2>
-struct pair {
-  typedef T1 first_type;
-  typedef T2 second_type;
-
-  T1 first;
-  T2 second;
-  pair(const pair&) = default;
-  pair(pair&&) = default;
-  pair();
-  […]
-};
-
-

-But according to the current core rules this makes the instantiation of e.g. std::pair<A, int> -ill-formed, because of the const mismatch of the compiler-declared form of the copy constructor -with that of the defaulted declaration. -

-Unfortunately there seems to be no simple library solution for this problem. If the defaulted declarations -were removed, both copy c'tor and move c'tor would be deleted, because there exist user-declared -copy assignment and move assignment operators in the FDIS. But these operations need to be user-defined -to realize the wanted semantics of these operations for element types that are reference types. If core -rules would not be changed to fix that, I see the following options: -

-
    -
  1. Intentionally decide to break the support for element types with non-const copy c'tors in pair.
    2. -
  2. User-declare both copy and move ctor to at least support the instantiation of the pair specializations, -but this would still not allow to copy them by the copy constructor.
    3. -
  3. User-declare both the const and non-const copy ctors, the move ctor, and additionally the non-const copy assignment -operator to support the instantiation of the pair specializations and of these members. This would -support all element types as it did in C++03, but all copy/move members would be non-trivial.
    4. -
  4. Intentionally decide to give up support for element types that are references for pair, but -still keep the allocator support with the effect of removing all declarations of the special -copy/move members. User code that needs to use tuple instead. But this would be a rather -drastic step requiring further corrections of the draft, e.g. a change of the signature of the algorithm -minmax (not the overload with the initializer_list) with a different return type.
    5. -
-

-This problem does not extend as backward-compatibility problem to tuple, because the TR1 -specification did explicitly declare copy constructor and copy assignment operator via the "normal" -form: -

-
-tuple(const tuple&);
-tuple& operator=(const tuple&);
-
-

-

- -

[Bloomington, 2011]

- -

-Closed as NAD. -

- -

-This is an unfortunate change of behavior between C++03 and C++11, but is consistent with tuple. There is no desire to go to lengths supporting types like auto_ptr now that rvalue references are in the language. -

- -

-There may be an issue for Core/EWG to look at, so that some simple =default syntax could be used that would do the right thing. If such a facility became availabile, LWG might revisit this issue. -

- - - -

Proposed resolution:

- - - - - -
-

2073. Library exceptions that take string arguments

-

Section: 19.2 [std.exceptions], 19.5.6 [syserr.syserr], 27.5.3.1.1 [ios::failure] Status: NAD - Submitter: Eelis van der Weegen Opened: 2011-08-16 Last modified: 2015-04-08

-

View all other issues in [std.exceptions].

-

View all issues with NAD status.

-

Discussion:

- -

-This is an extension issue for LWG to add constructor overloads that take a -string by an rvalue reference in order to move the string into the -exception. -

- - -

[2012, Kona]

- -

-Move to NAD. -

-

-This was discussed during C++11 standardization, and deemed (at the time) to be a conforming -extension that vendors are free to add, but there seemed no need to call it out in the standard. -Since then it has been noted that the rvalue-reference overloads do not give you the move-semantic -guarantee the proposer is thought to be looking for, as in order to meet the requirements that -copy constructors do not throw (for standard exceptions) the exceptions that store strings must -actually store a reference-counted immutable string, rather than an std::string internally. -Therefore, an rvalue-reference overload is going to have to allocate memory in exactly the same -way as copying from a const string& argument. -

- - - -

Proposed resolution:

- - - - - -
-

2079. Required pow() overloads

-

Section: 26.8 [c.math] Status: NAD - Submitter: Steve Clamage Opened: 2011-08-29 Last modified: 2015-05-22

-

View other active issues in [c.math].

-

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-

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-

Discussion:

- -

-LWG issue 550 removed the functions: -

-
-float       pow(float, int);
-double      pow(double, int);
-long double pow(long double, int);
-
-

-from header <cmath>. This change does not seem to be mentioned in Annex C, C.2.14. -

-Howard: -

-

-N3290 26.8 [c.math]/p11 says: -

-

-Moreover, there shall be additional overloads sufficient to ensure: -

-
    -
  1. If any argument corresponding to a double parameter has type long double, -then all arguments corresponding to double parameters are effectively cast to -long double. -
    2. -
  2. Otherwise, if any argument corresponding to a double parameter has type double -or an integer type, then all arguments corresponding to double parameters are effectively -cast to double. -
    3. -
  3. Otherwise, all arguments corresponding to double parameters are effectively cast to -float. -
    4. -
-
-

-From C99 7.12.7.4 we have: -

-
-double pow(double, double);
-
-

-26.8 [c.math]/p11/b2 says that if the client calls pow(2.0f, 2), then the -int for second argument causes the following effective call to be made: -

-
-pow(static_cast<double>(2.0f), static_cast<double>(2)) -> double
-
-

-The first sentence of p11 implies that this is done by supplying the following additional overload: -

-
-double pow(float, int);
-
-

-If the client calls pow(2.0, 2), then the same reasoning (b2 again) implies the following -additional overload: -

-
-double pow(double, int);
-
-

-If the client calls pow(2.0l, 2), then b1 implies the following additional overload: -

-
-long double pow(long double, int);
-
-

-In all, p11 implies hundreds (perhaps thousands?) of extra overloads. All but one of which is a superset -of the overloads required by C++98/03 (that one being pow(float, int) which had its return -type changed from float to double). -

-In practice, at least some vendors implement p11 by using templated overloads as opposed to ordinary overloads. -

- -

-Steve Clamage: -

-

-Thanks. I didn't see that those extra overloads were actually implied by p11, despite the first sentence. -Without examples, the point is a bit subtle (at least for me). -

- -

[2015-05-05 Lenexa: Move to NAD]

- -

Billy: I believe this is NAD.

-

STL: Oh, Steve himself agrees.

-

Wakely: The issue marked as NAD will be sufficient.

-

STL: Yes, we should get rid of this.

-

Billy: I don't see any minutes from Issaquah.

-

Marshall: Since Steve agrees, does anyone object to marking as NAD?

-

Nope.

- - - -

Proposed resolution:

- - - - - -
-

2082. Misleading complexity requirements in <algorithm>

-

Section: 25 [algorithms] Status: NAD - Submitter: Nicolai Josuttis Opened: 2011-09-02 Last modified: 2015-04-08

-

View other active issues in [algorithms].

-

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-

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-

Discussion:

- -

-The partition_point() algorithm is specified with: -

-

-Complexity: O(log(last - first)) applications of pred. -

-

-While this is correct, it gives the impression that this is a logarithmic algorithm. -But unless random access iterators are used it is not logarithmic because for advancing -the iterator we have last-first steps, which means that the complexity becomes linear here. -

-Shouldn't we clarify the complexity here to something like: -

-

-Complexity: logarithmic for random-access iterators and linear otherwise - (in any case O(log(last - first)) applications of pred). -

-

-Or should we even require O(log(last - first) for random-access iterators only because -for other iterators just iterating over all elements, while calling pred for each element, -might often be faster. -

- -

-Daniel Krügler: -

-

-I agree that especially this description is a bit misleading. I'm not -convinced that this is a real defect, because the whole bunch of -templates within <algorithm> document the complexity solely of -applications* of predicates, assignment, or swaps, but never the -complexity of traversal operations (e.g. increment or iterator -equality tests). This means, the standard is consistent for this -function template, even though it could say a bit more. -

-I would like to see a wording improvement, but I would rather think that -the complexity of the predicate should be mentioned first (as in other -algorithms) and that a non-normative note could be added for -specifically this algorithm to point out that this does not imply -a logarithmic traversal complexity. The note could give more details, -by explicity pointing out the linear traversal complexity for -non-random-Access iterators. -

-

-Howard Hinnant: -

-

-If we are going to make such improvements, they should be made across the -board in <algorithm>, not to just partition_point. -For example all 4 algorithms in 25.4.3 [alg.binary.search] have the -same issue, and have since C++98. -

-stable_partition and inplace_merge should be inspected as well. -

-Perhaps a new paragraph in 25.1 [algorithms.general], similar to -p12 would be a better place to address this issue. -

- -

[2012, Kona]

- -

-Move to NAD. -

-

-There was some concern that the issue, if it were to be addressed, is much larger than -the couple of algorithms called out here, and applies across the whole library. There -is no interest in looking at this or similar issues without a paper addressing the whole -library. In fairness to anyone considering writing such a paper, it should be noted -that there was not much interest in such a paper in the group, although no strong opposition -either. -

- - - -

Proposed resolution:

- - - - - -
-

2084. basic_string use of charT*

-

Section: 21.4 [basic.string] Status: NAD - Submitter: Howard Hinnant Opened: 2011-09-11 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

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-

Discussion:

- -

-For C++11 we gave all of the containers, including basic_string new generalized pointer types: -

- -
-typedef typename allocator_traits<Allocator>::pointer       pointer:
-typedef typename allocator_traits<Allocator>::const_pointer const_pointer;
-
- -

-However, the constructors, assignment, and member functions still traffic exclusively in terms -of const charT*, for example: -

- -
-basic_string(const charT* s, const Allocator& a = Allocator());
-
- -

-Was this an oversight? Did we mean instead: -

- -
-basic_string(const_pointer s, const Allocator& a = Allocator());
-
- -

Rationale:

-It's intentional. char_traits assumes that all elements of -a string can be accessed indirect on plain pointers. So basic_string -doesn't support allocators with fancy pointers or references. And we meant -to do that. -

-Let's take the constructor example you called out: -

- -
-basic_string(const charT* s, const Allocator& a = Allocator());
-
- -

-This constructor allows us to create a basic_string object from a string literal. -If we were to change the pointer type, that would no longer be possible. -

-There is no issue here, as the implementation of the constructor must make a -copy of the string pointed-to by the pointer 's' rather than adopt ownership of -that buffer. It is that internal copy that must make use of the allocator::pointer type. -

-Now what about the return value of 'c_str()', should that return an allocator::pointer? -

-Again, the answer (I believe) is 'no' because this is the function that allows us -to pass the string's contents to a legacy/OS 'C' API. It is deliberately returning -a raw pointer for a reason. -

-There was an issue where vector::data was changed to return an allocator::pointer -to the internal buffer, and this was changed back exactly because this was intended -to support passing to external APIs. -

-Do we have a use-case where the pointer type of internal data structures of our -containers (notably basic_string and vector) need to be exposed through a public API? -All my current use-cases for allocator::pointer are specific to the implementation -of containers themselves. -

- - - -

Proposed resolution:

- - - - - -
-

2090. Minor Overconstraint in Mutex Types

-

Section: 30.4.1.2 [thread.mutex.requirements.mutex] Status: NAD - Submitter: Pete Becker Opened: 2011-10-17 Last modified: 2015-04-08

-

View all other issues in [thread.mutex.requirements.mutex].

-

View all issues with NAD status.

-

Discussion:

- -

-30.4.1.2 [thread.mutex.requirements.mutex]/6, fourth bullet requires the -return type of m.lock() to be void. -

-This is over-constrained. The true requirement is that the standard library -ignores any value that the function returns. Yes, allowing non-void return -types means that users can't store a pointer to this member function. No, -that's not the least bit important. -

-[See also the discussion following c++std-lib-31318] -

- -

[2012, Kona]

- -

-This does not specify a concept; it specifies requirements on the concrete mutex types. -

- - - -

Proposed resolution:

- - - - - -
-

2107. Some iterator category should guarantee the lifetime of references

-

Section: 24.2 [iterator.requirements] Status: NAD - Submitter: Jeffrey Yasskin Opened: 2011-11-21 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

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-

Discussion:

- -

-Many iterators guarantee that references and pointers returned from -their methods will outlive the iterator itself. Other useful iterators -can't guarantee this, leading to the rule in 24.2 [iterator.requirements] -p9 that "Destruction of an iterator may invalidate pointers and references -previously obtained from that iterator." -

-Some algorithms can take advantage of long-lived references by -returning them, while they can adapt to short-lived references by -returning by value instead. However, there doesn't seem to be a way in -the standard to distinguish between these two types of iterators. -

-The ForwardIterator requirements come close by saying "If a and b are -both dereferenceable, then a == b if and only if *a and *b are bound -to the same object." (24.2.5 [forward.iterators] p6) However, there are some -subtle ways to satisfy this rule and still return a short-lived reference, meaning -algorithms can't be guaranteed that forward_iterator_tag will imply -long-lived references. -

-On the other hand, defect 198, which added the invalidation wording -to iterator.requirements.general, refers to iterators with short-lived references -being used as arguments to reverse_iterator, which requires BidirectionalIterators. -If ForwardIterator required long-lived references, this would be impossible. -

-Either ForwardIterator should be clarified to require long-lived -references, or a new category should be added that does. -

-See also the discussion around c++std-lib-31477. -

-Daniel: Related to this issue is that when applying N3066 -we unintentionally lost some forward iterator requirements from C++03, where we -had the post-conditions a == X(a) of X(a), and u == a -of any copy operation from a to u. This wording must be restored as well. -

- -

[2012, Kona]

- -

-Move to NAD. -

-

-This issue affects only Input Iterators, as all other categories are required to return -a native reference, and are not (currently) allowed to return proxies. The issue with -Input Iterators is known, and has been present since the original standard. Any change -in this regard would be an extension requiring a more substantial paper than treatment -as a simple issue. -

- - - -

Proposed resolution:

- - - - - -
-

2113. Do library implementers have the freedom to add final to non-polymorphic components?

-

Section: 17.6.5 [conforming] Status: NAD - Submitter: Daniel Krügler Opened: 2011-11-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-Related to LWG 2112 the question has been raised whether a library implementation may declare -non-polymorphic library components, such as class template std::vector or std::basic_string, -as final class types. -

-This issue is not suggesting to enforce that libraries are required to do that, it is asking -whether libraries should have the freedom to do so. -

-The existing wording in 17.6.5.11 [derivation] does not give a clear permission to do so. In my opinion -this position should be clarified in either direction. -

-Giving implementations this freedom would have both advantages and disadvantages. Several opponents where -worried about breakage of code of existing user implementations. On the other hand such types where not -designed to be used as base classes. Allowing implementations to mark these components as final -could allow them to provide compile-modes that are intentionally restrictive to the advantage of user code -that want to be alterted about that. Any implementation that would be concerned about user complaints would -not take advantage of this feature anyway. -

-If agreement exists that such implementation freedom would be useful, wording like -

-

-An implementation may declare additional non-virtual member function signatures within a class as final. -

-

-or -

-

-An implementation may declare additional class without virtual member function signatures as final. -

-

-should be added to 17.6.5 [conforming] with corresponding exceptions of these rules (e.g. iterator, -unary_function, or pair). -

-If such freedom should not exist, it seems better to clarify this as well, e.g. by adding around 17.6.5.11 [derivation]: -

-

-An implementation shall not declare any class or any member function signature as final. -

- - -

[2012, Kona]

- -

-Move to NAD. -

-

-Unless the library uses the keyword final in a specification, the user clearly has -freedom to derive from such a class, and so equally clearly, the library vendor does not have -freedom to add a final overrider or class attribute. Howard observed there may be -some wiggle-room with 'unspecified types' such as those returned from bind expressions, -or iterators, but we did not see a need to further clarify the issue. Note that, for example, -a vector::iterator may be implemented as a raw pointer, so users cannot generally -assume the ability to derive from unspecified library types. -

- - - -

Proposed resolution:

- - - - - -
-

2124. Seed sequence over-specified

-

Section: 26.5.1.2 [rand.req.seedseq] Status: NAD - Submitter: Alberto Ganesh Barbati Opened: 2012-01-16 Last modified: 2015-04-08

-

View all other issues in [rand.req.seedseq].

-

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-

Discussion:

- -

-The seed sequence requirements described in 26.5.1.2 [rand.req.seedseq] appear to be over-specified. -All seed sequence types are required to have a result_type nested type, a specific set of -constructors, function members size() and param(), which are never used by the library. -In fact, the only library components that actively use seed sequences are the random engines and all the -engines need is the generate() member function. In particular, library components never attempts -to construct seed sequence objects. These extraneous requirements are clearly written to describe the -library provided type seed_seq type; while it's good that seed_seq has all those constructors and -members, it's not a compelling reason to require a user-provided seed sequence type to implement all of -them. -

-Suppose I want to write my own seed sequence class, this should do fine (and actually works as expected with libc++): -

-
-class my_seed_seq
-{
-  /* internals */
-public:
-  my_seed_seq(/* my own parameters */);
-
-  template <class It>
-  void generate(It first, It last);
-};
-
-my_seed_seq s(/* params */);
-std::default_random_engine e(s);
-
-

-The only reason to have these extra members would be to provide some support for generic serializability/persistence -of seed sequence objects. I believe that would be out of the scope of the random library, so I doubt we will ever need -those requirements in the future. -

-I therefore propose to remove all requirements from 26.5.1.2 [rand.req.seedseq] except for the presence of the -generate() function. -

- -

[2012, Kona]

- -

-Move to Tenatively NAD. (Tentative as issue was not in pre-meeting mailing) -

-

-The 'overspecification', as such, was a deliberate intent to provide guarantees consumers of the whole -random number framework may rely upon, especially in generic code. While the standard engines may be -built without relying on these guarantees, this specification is part of a commitment to a broader -framework, and Walter indicated future proposals in preparation for parallel generation of random -numbers that may depend more inimately on these existing requirements. -

-

-Alisdair noted that the result_type typedef was a call-back to how we used to specify -adaptable functors before TR1 result_of and the addition of std::bind and is -probably not something we should be actively promoting in future libraries. However, it is too -late to remove this requirement from seed sequences unless we are doing further surgery, as -recommended by this issue. -

-

-Walter notes that the result_type protocol has not been formally deprecated by the -standard. Alisdair replies that was the intent of deprecating the bind_1st/ -unary_function set of templates in C++11, although we did not say anything about -result_type in general. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -
  1. -

    Edit 26.5.1.2 [rand.req.seedseq] p2 as indicated:

    - -

    -A class S satisfies the requirements of a seed sequence if the expressions shown in Table 115 are valid and -have the indicated semantics, and if S also satisfies all other requirements of this section 26.5.1.2 [rand.req.seedseq]. -In that Table and throughout this section: -

    -
      -
    1. -T is the type named by S's associated result_type; -
      2. -
    2. -q is a value of S and r is a possibly const value of S; and -
      3. -
    3. -ib and ie are input iterators with an unsigned integer value_type of at least 32 bits; -
      4. -
    4. rb and re are mutable random access iterators with an unsigned integer value_type of at least 32 bits;
      5. -
    5. -ob is an output iterator; and -
      6. -
    6. -il is a value of initializer_list<T>. -
      7. -
    -
    -
    2. - -
  2. -

    Ditto, in Table 115, remove all rows except the one describing q.generate(rb, re):

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 115 — Seed sequence requirements
    ExpressionReturn typePre/Post-conditionComplexity
    -S::result_type - -T - -T is an unsigned integer
    -type (3.9.1 [basic.fundamental]) of at least 32 bits.     -    		 -compile-time -
    -S() - -  - -Creates a seed sequence with
    -the same initial state as all
    -other default-constructed seed
    -sequences of type S.     -    		 -constant -
    -S(ib,ie) - -  - -Creates a seed sequence having
    -internal state that depends on
    -some or all of the bits of the
    -supplied sequence [ib, ie).     -    		 -𝒪(ie - ib) -
    -S(il) - -  - -Same as S(il.begin(),
    -il.end())    .     -    		 -same as
    -S(il.begin(),
    -il.end())     -
    -q.generate(rb,re) - -void - -Does nothing if rb == re.
    -Otherwise, fills the supplied
    -sequence [rb, re) with 32-bit
    -quantities that depend on the
    -sequence supplied to the
    -constructor and possibly also
    -depend on the history of
    -generate's previous
    -invocations. -    		 -𝒪(re - rb) -
    -r.size() - -size_t - -The number of 32-bit units that
    -would be copied by a call to
    -r.param.     -    		 -constant -
    -r.param(ob) - -void - -Copies to the given destination -a sequence of 32-bit units that
    -can be provided to the
    -constructor of a second object
    -of type S, and that would
    -reproduce in that second object
    -a state indistinguishable from
    -the state of the first object.     -    		 -𝒪(r.size()) -
    -
    3. - -
- - - - - - -
-

2125. TimedMutex specification problem

-

Section: 30.4.1.3 [thread.timedmutex.requirements], 30.4.1.3.1 [thread.timedmutex.class] Status: Pending NAD Editorial - Submitter: Vicente J. Botet Escriba Opened: 2012-01-01 Last modified: 2015-04-08

-

View all other issues in [thread.timedmutex.requirements].

-

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-

Discussion:

- -

-30.4.1.3.1 [thread.timedmutex.class] says: -

-

-The class timed_mutex shall satisfy all of the TimedMutex requirements (30.4.1.3 [thread.timedmutex.requirements]). -It shall be a standardlayout class (Clause 9 [class]). -

-

-Problem here is that 30.4.1.3 [thread.timedmutex.requirements] does not define a requirement set named "TimedMutex", -it only refers to "timed mutex types" -

- -

[See also issue 2126]

- - -

[2012, Portland: move to Tentatively NAD Editorial]

- -

-We have timed mutex type, but it is labeled timed mutex requirements -

-

-We can make a suggestion, but will send to the editor as it seems purely editorial. -There is a typo, and we don't have the timed mutex but 30.4.1.3 [thread.timedmutex.requirements] already -says timed mutex type, and we need to reuse that term down in the class to fulfil the mutex requirement. -

-

[To Editor:]

- -

-Replace this one with timed mutex type. -

- - - -

Proposed resolution:

- - - - - -
-

2126. Several specification problems in regard to mutex requirements

-

Section: 30.4.1 [thread.mutex.requirements], 30.4.1.2.1 [thread.mutex.class], 30.4.1.2 [thread.mutex.requirements.mutex], 30.4.1.2.2 [thread.mutex.recursive], 30.4.1.3 [thread.timedmutex.requirements], 30.4.1.3.1 [thread.timedmutex.class], 30.4.1.3.2 [thread.timedmutex.recursive] Status: Pending NAD Editorial - Submitter: Pete Becker Opened: 2012-01-16 Last modified: 2015-04-08

-

View other active issues in [thread.mutex.requirements].

-

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-

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-

Discussion:

- -

- 30.4.1.2.1 [thread.mutex.class]/3 says that the class mutex "shall satisfy all the Mutex requirements (30.4.1 [thread.mutex.requirements])". - 30.4.1.2.1 [thread.mutex.class] is part of 30.4.1 [thread.mutex.requirements], so at the very least, this - requirement is recursive. But worse, there is nothing that says what "the Mutex requirements" refers to. For example, - the "Lockable requirements" section starts with "A type L meets the Lockable requirements if …". There is no such - statement for "the Mutex requirements". -

-Organizationally, paragraphs 1-26 in 30.4.1.2 [thread.mutex.requirements.mutex] should probably be in a subclause with a name. -(This is actually an ISO requirement, to avoid exactly this kind of ambiguous referencing) Then the first sentence of -30.4.1.2.1 [thread.mutex.class]/3 can become a note: "The class mutex meets the requirements of (whatever)", since that -subclause already says that the mutex types "shall meet the requirements set out in this section." -

-And similarly for 30.4.1.2.2 [thread.mutex.recursive]/2 (recursive_mutex). -

-30.4.1.3 [thread.timedmutex.requirements], Timed mutex types, also needs the same rearrangement: its introductory -requirements should be moved into a subclause, and the first sentences of 30.4.1.3.1 [thread.timedmutex.class]/2 -and 30.4.1.3.2 [thread.timedmutex.recursive]/2 should be turned into notes that refer to this new subclause and -to the new subclause in 30.4.1.2 [thread.mutex.requirements.mutex]. -

- -

[See also issue 2125]

- - -

[2012, Portland: move to Tentatively NAD Editorial]

- -

-Seems no real ambiguity. May need some reorg of text rather then changing the wording. -

-

-Is there much that needs to be changed? But Pete's suggestion of putting requirement in separate sub section is good. -Should be the direction to editor. -

-

-Suggest this is an editorial change. Happy with Pete's comments. -

- - - -

Proposed resolution:

- - - - - -
-

2131. Member function getline taking a string as parameter

-

Section: 27.7.2.3 [istream.unformatted] Status: NAD - Submitter: Loïc Joly Opened: 2012-03-05 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

-

-I think the following code should be legal: -

-
-void f(std::istream& is)
-{
-  std::string s;
-  is.getline(s); // Would be equivalent to std::getline(is, s)
-}
-
- -

[2013-04-20, Bristol]

- - -

-Unanimous that this is a new feature request and not a issue. -

-Resolution: Tentatively NAD -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change the class template basic_istream synopsis, 27.7.2.1 [istream], as indicated

    -
    -namespace std {
-  template <class charT, class traits = char_traits<charT> >
-  class basic_istream : virtual public basic_ios<charT,traits> {
-  public:
-    […]
-    // 27.7.2.3 Unformatted input:
-    […]
-    basic_istream<charT,traits>& getline(char_type* s, streamsize n);
-    basic_istream<charT,traits>& getline(char_type* s, streamsize n,
-      char_type delim);
-    template<class Allocator>
-    basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str);
-    template<class Allocator>
-    basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str,
-      char_type delim);
-    […]
-  };
-}
-
    -
    2. - -

  2. Insert the following two new prototype descriptions after 27.7.2.3 [istream.unformatted] paragraph 24:

    - -
    -
    -basic_istream<charT,traits>& getline(char_type* s, streamsize n);
-
    -

    --24- Returns: getline(s,n,widen('\n')) -

    -
    - -
    -template<class Allocator>
-basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str);
-
    -

    --??- Returns: std::getline(*this, str) -

    -
    - -
    -template<class Allocator>
-basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str, char_type delim);
-
    -

    --??- Returns: std::getline(*this, str, delim) -

    -
    - -
    -
    3. -
- - - - - - -
-

2134. Redundant Mutex requirement?

-

Section: 30.4.1.2 [thread.mutex.requirements.mutex] Status: Pending NAD Editorial - Submitter: Pete Becker Opened: 2012-03-05 Last modified: 2015-04-08

-

View all other issues in [thread.mutex.requirements.mutex].

-

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-

Discussion:

- -

-30.4.1.2 [thread.mutex.requirements.mutex]/11 says that prior unlock operations synchronize with m.lock(). -

-30.4.1.2 [thread.mutex.requirements.mutex]/19 says that if m.try_lock() succeeds, prior unlock operations -synchronize with the operation. -

-30.4.1.2 [thread.mutex.requirements.mutex]/25 says that m.unlock() synchronizes with subsequent -successful lock operations. -

-Does the third requirement add anything to the first two? If not, it should probably be a non-normative note. -

- -

[2012, Portland: move to Tentatively NAD Editorial]

- -

-Agree that third note should be non-normative and adds nothing. -

-

-Seems An Editorial change, but does changing a normative to non-normative wording makes it a non-editorial change? -

-

-Ask the editor. If not editorial, then we will agree on the fix as removal of the third point, -then we will put it in ready state for Bristol. -

- - - -

Proposed resolution:

- - - - - -
-

2167. Copy assignment requirements of Containers

-

Section: 23.2.1 [container.requirements.general] Status: NAD - Submitter: Dean Michael Berris Opened: 2012-07-13 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

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-

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-

Discussion:

- -

-Table 96 defines the general requirement for copy assignment (row 23, page 704) as: -

- - - - - - - - - - - - - - - - - - - - -
Table 96 — Container requirements
ExpressionReturn typeOperational semanticsAssertion/note pre-/post-conditionComplexity
-r = a - -X& - - - -post: r == a. - -linear -
- -

-However there is no requirement that T is CopyInsertable into X. -

- -

[2012, Portland: Move to Tentatively NAD]

- -

-Howard notes that this may be a difficult requirement for std::array -

- -

-We already have this requirement for allocator aware containers, and -std::array already adds the appropriate extra requirement. -

- -

-We say the necessary things in the necessary places, but the container requirements -continue to cause confusion in where we sometimes say things. Consensus is that -this issue remains NAD though. -

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change Table 96 — "Container requirements" in 23.2.1 [container.requirements.general]:

    - - - - - - - - - - - - - - - - - - - - -
    Table 96 — Container requirements
    ExpressionReturn typeOperational semanticsAssertion/note pre-/post-conditionComplexity
    -r = a - -X& - - - -Requires: T is CopyInsertable into X.
    -post: r == a. -    		 -linear -
    - -
    2. -
- - - - - - - -
-

2171. "swappable" undefined for swapping lvalue and rvalue

-

Section: 17.6.3.2 [swappable.requirements] Status: NAD - Submitter: Robert Shearer Opened: 2012-07-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-Paragraph 17.6.3.2 [swappable.requirements] p4 states: -

-

-An rvalue or lvalue t is swappable if and only if t is swappable with any rvalue or lvalue, -respectively, of type T. -

-

-This paragraph seems to establish two disjoint definitions of "swappable" — one for lvalues and one -for rvalues — with neither definition including the case of swapping an rvalue with an lvalue. -

-Resolution proposal: -

-Delete the word "respectively". -

- -

[ -2012-10 Portland: Close as NAD -]

- - -

-The current wording does intentionally specify two families of 'swappable' behaviors, for lvalues -and for rvalues, and not for mixed behavior. The need to support rvalues is for types like -vector<bool>::reference. Likewise, library types like string provide a -swap for values, but not a mixed-mode swap between lvalues and rvalues, which -were deliberately removed from C++11 after initally being part of the standard. -

- -

-Accepting this resolution would break the library specification, as no current library type would -meet the new requirements. -

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -

Change 17.6.3.2 [swappable.requirements] p4 as indicated:

- -

-An rvalue or lvalue t is swappable if and only if t is swappable with any rvalue or -lvalue , respectively, of type T. -

- - - - - - -
-

2204. reverse_iterator should not require a second copy of the base iterator

-

Section: 24.5.1.3.4 [reverse.iter.op.star] Status: NAD - Submitter: David Abrahams Opened: 2012-10-30 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

- -

-This note in 24.5.1.3.4 [reverse.iter.op.star]/2: -

-
- [ Note: This operation must use an auxiliary member variable rather than a - temporary variable to avoid returning a reference that persists beyond the - lifetime of its associated iterator. (See 24.2.) —end note ] -
-

-is incorrect because such iterator implementations are ruled out by -24.2.5 [forward.iterators]/6, where it says: -

-
- If a and b are both dereferenceable, then a == b if and only if *a and - *b are bound to the same object. -
- -

[2013-04-20, Bristol]

- - -

-Alisdair: sugested to strike the "exposition only" member. -

-Daniel: we must check that it wouldn't conflict with a previous solution to another issue. -

-Dietmar: This is an issue but the proposing word is not correct. When we have proxies inside the sequence. -

-Solution: NAD thanks to a contrieved example by Dietmar. -

- - -

Proposed resolution:

-

-Strike the note, 24.5.1.3.4 [reverse.iter.op.star]/2: -

- -
- [ Note: This operation must use an auxiliary member variable rather than a - temporary variable to avoid returning a reference that persists beyond the - lifetime of its associated iterator. (See 24.2.) —end note ] -
- - - - - - -
-

2251. C++ library should define ssize_t

-

Section: 18.2 [support.types] Status: NAD - Submitter: Matt Austern Opened: 2013-04-19 Last modified: 2015-05-22

-

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-

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-

Discussion:

- -

-The C++ standard library defines size_t, a typedef for an implementation defined unsigned integer type -that can represent the sizes of objects. The POSIX standard augments this with ssize_t, a typedef for a -signed integer type that corresponds to size_t. -

-The ssize_t typedef is useful — useful enough that the C++ standard even refers to it. (In a -non-normative footnote in 27.5.2 [stream.types].) Also, lots of OS vendors add it to their headers anyway, -even though it isn't part of the C or C++ standards, because those vendors are trying to define headers that -conform to multiple standards at once. We should make users' and implementers' lives easier by adding -ssize_t to 18.2 [support.types]. -

- -

[2013-09-29, Suggested wording from Jayson Oldfather]

- -

-I decided to use the phrase to describe ssize_t below because of the text describing it in the -POSIX standard. -In it, it describes ssize_t with the value range of [-1,{SSIZE_MAX}]. -SSIZE_MAX is specified in the POSIX -standard as a minimum value of _POSIX_SSIZE_MAX. This macro is referenced in the wording below. -

- -

[Lenexa 2015-05-05: NAD - no consensus for a change]

- -

Billy : ssize_t that was promised to be signed, was based on rsize_t from safe secure C

-

NM : ssize_t s ptrdif_t

-

Z : ptrdiff_t is full range, ssize_t has only -1 as negative value

-

Billy : motivations for ptrdiff_T, ssize_t and rsize_T all fuzzy. - Reads rsize max -

-

NM : ptrdiff_T not big enough to rep difference of pointers anymore

-

STL : description incorporates posixisms

-

Billy : Don't need it

-

NM : rather remove it from footnote

-

Z : Name has precise meaning

-

STL : everyone understands ptrdiff_t is signed counterpart to size_t

-

Billy : Not in all implementations anymore

-

DK : footnote says something different from ...

-

Z/NM : off_t historically tainted

-

STL : we have a type trait to make signed version of size_t. we should just use that

-

MC : NAD; is feature request

-

TP : It's not cstdsef

- - - -

Proposed resolution:

-
    -
  1. -

    -Ammend 18.2 [support.types], Table 30 as indicated: -

    - -
    - - - - - - - - - - - - - - - - -
    Table 30 — Header <cstddef> synopsis
    TypeName(s)
    -Macros: - -NULL offset_t -
    -Types: - -ptrdiff_t ssize_t size_t max_align_t nullptr_t -
    -
    - -

    Add the following paragraph to describe ssize_t

    -

    --?- The type ssize_t is an implementation-defined signed integer type that shall contain the minimum range -[-1, {SSIZE_MAX}] where SSIZE_MAX is specified at a minimum of _POSIX_SSIZE_MAX. -

    -

    Ammend p7 as follows:

    -

    --7- [Note: It is recommended that implementations choose types for ptrdiff_t, ssize_t, and size_t whose integer conversion ranks …

    -
    2. -
- - - - - -
-

2270. Inconsistent to_string overloads

-

Section: 21.5 [string.conversions] Status: NAD - Submitter: Raf Schietekat Opened: 2013-07-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-For internal consistency, to_string() should either list all relevant types (including bool, char, etc.), -or only those that are the destination types of integral or floating-point promotion (float not being among them). -

-A defensible reason for having (or rather keeping) the float overloads anyway could be to exactly mirror the adjacent -sets of stoX() function overloads (even without round-trip fidelity for floating-point numbers). -

-Unfortunately, that reveals a bigger issue than redundant overloads: the glaring and indefensible omission of an overloaded -function stoui(). Adding that is not as trivial as removing redundant overloads, of course, because it requires -everybody to take action. Still, it is the preferable remedy for the present situation. -

-As far as I can tell from easily accessible information, C++ has already created the precedent with stoi(), which -is not the equivalent of a pair of functions strtoi()/wcstoi() in C, but it would be if such functions -existed. The function atoi() may look similar, but it does not qualify because it is as different from a -hypothetical strtoi() as atol() currently is from strtol(), with the latter two both Standard C. -It is only logical to act on this one-sided precedent by completing the set. Whether or not Standard C leads the way -(or follows suit) is immaterial, but an invitation could be extended. -

- -

[2013-09 Chicago]

- -

-These overloads were very carefully and experimentally determined to be the minimal set, when all (known) promotion and -conversion scenarios were considered. Removing superfluous-looking overloads is likely to result in ambiguities. -

- - - -

Proposed resolution:

- -

This wording is relative to N3691.

- -
    -

  1. Modify 21.3 [string.classes], header <string> synopsis, as indicated:

    - -
    -#include <initializer_list>
-
-namespace std {
-  […]
-  string to_string(int val);
-  string to_string(unsigned val);
-  string to_string(long val);
-  string to_string(unsigned long val);
-  string to_string(long long val);
-  string to_string(unsigned long long val);
-  string to_string(float val);
-  string to_string(double val);
-  string to_string(long double val);
-  […]
-
-  […]
-  wstring to_wstring(int val);
-  wstring to_wstring(unsigned val);
-  wstring to_wstring(long val);
-  wstring to_wstring(unsigned long val);
-  wstring to_wstring(long long val);
-  wstring to_wstring(unsigned long long val);
-  wstring to_wstring(float val);
-  wstring to_wstring(double val);
-  wstring to_wstring(long double val);
-  […]
-}
-
    -
    2. - -

  2. Modify 21.5 [string.conversions] p7+14 as indicated:

    - -
    -
    -string to_string(int val);
-string to_string(unsigned val);
-string to_string(long val);
-string to_string(unsigned long val);
-string to_string(long long val);
-string to_string(unsigned long long val);
-string to_string(float val);
-string to_string(double val);
-string to_string(long double val);
-
    -
    -

    --7- Returns: Each function returns a string object holding the character representation of the value of -its argument that would be generated by calling sprintf(buf, fmt, val) with a format specifier of -"%d", "%u", "%ld", "%lu", "%lld", "%llu", "%f", -"%f", or "%Lf", respectively, where buf designates an internal character buffer of sufficient size. -

    -[…] -

    -
    -
    -wstring to_wstring(int val);
-wstring to_wstring(unsigned val);
-wstring to_wstring(long val);
-wstring to_wstring(unsigned long val);
-wstring to_wstring(long long val);
-wstring to_wstring(unsigned long long val);
-wstring to_wstring(float val);
-wstring to_wstring(double val);
-wstring to_wstring(long double val);
-
    -
    -

    --14- Returns: Each function returns a wstring object holding the character representation of the value of -its argument that would be generated by calling swprintf(buf, buffsz, fmt, val) with a format specifier of -L"%d", L"%u", L"%ld", L"%lu", L"%lld", L"%llu", L"%f", -L"%f", or L"%Lf", respectively, where buf designates an internal character buffer of sufficient -size buffsz. -

    -
    -
    -
    3. -
- - - - - - -
-

2279. Carefully state effects of list::splice function

-

Section: 23.3.5.5 [list.ops], 23.3.4.6 [forwardlist.ops] Status: NAD - Submitter: Arseny Klimovsky Opened: 2013-08-15 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with NAD status.

-

Discussion:

-

-I think that the effects of list::splice function should be stated more carefully. -

-Function transferring a single element is described now in the following way (23.3.5.5 [list.ops] p7): -

- -
-
-void splice(const_iterator position, list& x, const_iterator i);
-void splice(const_iterator position, list&& x, const_iterator i);
-
-
-

-Effects: Inserts an element pointed to by i from list x before position and removes the element from -x. The result is unchanged if position == i or position == ++i. Pointers and references to *i -continue to refer to this same element but as a member of *this. Iterators to *i (including i itself) -continue to refer to the same element, but now behave as iterators into *this, not into x. -

-
-
- -

-But it is incorrect to talk about operator== for iterators that are not from the same container (after acceptance of -N3066, 24.2.5 [forward.iterators] p2). -So, the text operates with an undefined behaviour. -

- -

-One is formally allowed to have list implementation where two iterators from different lists return true to operator==. -For example, this can only happen to non-dereferenceable iterators, and position and ++i can be -non-dereferenceable. So, literally according to the standard, it is not allowed in this implementation to transfer -such elements with splice function. -

- -

[2013-09 Chicago (late night issues)]

- -

-Moved to NAD. -

-

-The condition under which the list is unchanged is not program code, so there is no undefined behavior to protect against. -Rather, the precondition that the evaluation can be performed is implicit if determining when the condition applies. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Modify 23.3.4.6 [forwardlist.ops] p6 as indicated:

    - -
    -
    -void splice_after(const_iterator position, forward_list& x, const_iterator i);
-void splice_after(const_iterator position, forward_list&& x, const_iterator i);
-
    -
    -

    -[…] -

    --6- Effects: Inserts the element following i into *this, following position, -and removes it from x. The result is unchanged if &x == this and the following -condition is satisfied: position == i or position == ++i. Pointers and references to -*++i continue to refer to the same element but as a member of *this. Iterators to *++i -continue to refer to the same element, but now behave as iterators into *this, not into x. -

    -
    -
    -
    2. - -

  2. Modify 23.3.5.5 [list.ops] p7 as indicated:

    - -
    -
    -void splice(const_iterator position, list& x, const_iterator i);
-void splice(const_iterator position, list&& x, const_iterator i);
-
    -
    -

    --7- Effects: Inserts an element pointed to by i from list x before position and removes -the element from x. The result is unchanged if &x == this and the following -condition is satisfied: position == i or position == ++i. Pointers and references to -*i continue to refer to this same element but as a member of *this. Iterators to *i -(including i itself) continue to refer to the same element, but now behave as iterators into *this, -not into x. -

    -
    -
    -
    3. - -
- - - - - -
-

2281. C99 cross-reference typo in [using.linkage]

-

Section: 17.6.2.3 [using.linkage] Status: NAD Editorial - Submitter: Chris Sharpe Opened: 2013-08-23 Last modified: 2015-04-08

-

View all other issues in [using.linkage].

-

View all issues with NAD Editorial status.

-

Discussion:

-

-There is a footnote at section 17.6.2.3 [using.linkage]/2 that reads: -

-

-"The only reliable way to declare an object or function signature from the Standard C library is by including -the header that declares it, notwithstanding the latitude granted in 7.1.7 of the C Standard." -

-

-There is no section 7.1.7 in the C99 Standard (or C11 final draft). I think the relevant section is: -

-

-"Provided that a library function can be declared without reference to any type defined in a header, it is also -permissible to declare the function and use it without including its associated header." -

-

-at 7.1.4/2 from C99. -

- -

[2013-09 Chicago]

- -

-Moved to NAD Editorial. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit footnote 182, 17.6.2.3 [using.linkage] as indicated:

    - -
    -

    -The only reliable way to declare an object or function signature from the Standard C library is by including the header -that declares it, notwithstanding the latitude granted in 7.1.77.1.4 of the C Standard. -

    -
    -
    2. - -
- - - - - -
-

2297. [CD] Missing type requirements for std::exchange

-

Section: 20.2.3 [utility.exchange] Status: NAD - Submitter: Alisdair Meredith Opened: 2013-09-22 Last modified: 2015-04-08

-

View all other issues in [utility.exchange].

-

View all issues with NAD status.

-

Discussion:

-

Addresses GB 5

- -

-The wording describes example code including the call of a move constructor, but there is no requirement -stated that T be move constructible. -

-We would like to add a new Para 1 before existing paragraph: -

-

-Requires: Type T shall be MoveConstructible (Table 20) and MoveAssignable (Table 22). -

- -

-However the MoveAssignable concept currently does not cover cases where the source and destination types may differ. -

- -

[2013-09 Chicago]

- -

-The requirements are implicit according to 17.5.1.4 [structure.specifications]p4. There is no desire to redundantly -repeat a set of requirements. -

- - - -

Proposed resolution:

- - - - - -
-

2302. Passing null pointer to placement new

-

Section: 18.6.1.3 [new.delete.placement] Status: Pending NAD - Submitter: Marc Glisse Opened: 2013-09-12 Last modified: 2015-04-08

-

View all other issues in [new.delete.placement].

-

View all issues with Pending NAD status.

-

Discussion:

-

-Based on this discussion -and as discussed in c++std-core-23998 and -c++std-lib-34442, calling placement new currently forces the -compiler to check if the pointer is null before initializing the object (a non-negligible cost). It seems many people were not -aware of this and they consider it a user error to pass a null pointer to it. -

-Proposed resolution: for operator new and operator new[], add: -

-

-Requires: ptr shall not be a null pointer. -

- -

[2014-02-15 post-Issaquah session : move to Tentatively NAD]

- -

-AJM to supply the rationale... -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 18.6.1.3 [new.delete.placement] as indicated:

    - -
    -
    -void* operator new(std::size_t size, void* ptr) noexcept;
-
    -
    -

    --?- Requires: ptr shall not be a null pointer. -

    --2- Returns: ptr. -

    --3- Remarks: Intentionally performs no other action. -

    --4- [Example: This can be useful for constructing an object at a known address: -

    -void* place = operator new(sizeof(Something));
-Something* p = new (place) Something();
-
    -

    -— end example] -

    -
    -
    -
    -
    -void* operator new[](std::size_t size, void* ptr) noexcept;
-
    -
    -

    --?- Requires: ptr shall not be a null pointer. -

    --5- Returns: ptr. -

    --6- Remarks: Intentionally performs no other action. -

    -
    -
    -
    2. - -
- - - - - -
-

2305. [fund.ts] optional forwarding construction/assignment

-

Section: X [optional.object.ctor] Status: NAD - Submitter: Cassio Neri Opened: 2013-09-23 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

Addresses: fund.ts

- -

-Consider: -

-
-struct foo {
-  foo(std::initializer_list<int>&);        // 1
-  foo(const std::initializer_list<int>&);  // 2
-  foo(std::initializer_list<int>&&);       // 3
-  foo(const std::initializer_list<int>&&); // 4
-};
-
-std::initializer_list<int> il{0, 1, 2};
-
-foo foo_0{1, 2, 3};                                 // calls 3
-foo foo_1{il};                                      // calls 1
-foo foo_2((const std::initializer_list<int>&) il);  // calls 2
-foo foo_3{(std::initializer_list<int>&&) il};       // calls 3
-foo foo_4((const std::initializer_list<int>&&) il); // calls 4
-
-

-Although the constructors of foo are unusual (initializer_lists are normally passed by -value) users of optional could naturally expect perfect forwarding of initializer_lists. However, -all lines below end up calling 1. -

-
-optional<foo> opt0{in_place, {1, 2, 3}};
-optional<foo> opt1{in_place, il};                    
-optional<foo> opt3{in_place, (const std::initializer_list<int>&) il};
-optional<foo> opt2{in_place, (std::initializer_list<int>&&) il};
-optional<foo> opt4{in_place, (const std::initializer_list<int>&&) il};
-
-opt0.emplace({1, 2, 3});
-opt0.emplace(il);
-opt0.emplace((const std::initializer_list<int>&) il);
-opt0.emplace((std::initializer_list<int>&&) il);
-opt0.emplace((const std::initializer_list<int>&&) il);
-
-

-The constructor -

-
-template <class... Args> constexpr explicit optional(in_place_t, Args&&... args);
-
-

-can handle all constructor calls above, except the one taking {1, 2, 3}. Hence, a simple -modification of -

-
-template <class U, class... Args>
-constexpr explicit optional(in_place_t, initializer_list<U>&& il, Args&&... args);
-
-

-allows perfect forwarding of std::initializer_list<U>s to be complete. -

- -

[2014-06-06 pre-Rapperswil]

- -

-This issue has been reopened as fundamentals-ts. -

- -

[2014-06-17, Rapperswil]

- -

-Move to NAD -

- - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change X [optional.object.ctor] as indicated:

    - -
    -template <class U, class... Args> 
-constexpr explicit optional(in_place_t, initializer_list<U>&& il, Args&&... args);
-
    -

    --27- Requires: is_constructible<T, initializer_list<U>&&, Args&&...>::value is true. -

    --28- Effects: Initializes the contained value as if constructing an object of type T with the arguments -ilstd::move(il), std::forward<Args>(args).... -

    -[…] -

    --31- Remarks: The function shall not participate in overload resolution unless -is_constructible<T, initializer_list<U>&, Args&&...>::value is true. -

    -
    -
    -
    2. -

  2. Change X [optional.object.assign] as indicated:

    - -
    -template <class U, class... Args>
-void optional<T>::emplace(initializer_list<U>&& il, Args&&... args);
-
    -

    --27- Requires: is_constructible<T, initializer_list<U>&&, Args&&...>::value is true. -

    --28- Effects: Calls *this = nullopt. Then initializes the contained value as if constructing an object of -type T with the arguments ilstd::move(il), std::forward<Args>(args).... -

    -[…] -

    --32- Remarks: This function shall not participate in overload resolution unless -is_constructible<T, initializer_list<U>&, Args&&...>::value is true. -

    -
    -
    -
    3. -
- - - - - -
-

2311. Allocator requirements should be further minimized

-

Section: 17.6.3.5 [allocator.requirements] Status: NAD - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with NAD status.

-

Discussion:

-

-C++11's minimized allocator requirements are great, but they're still requiring more things from users than absolutely necessary. -

-
    -

  • -They require X::value_type, but that can be deduced from SomeAllocator<T, Args>. -

    • -

  • -They require a1 == a2, but that could default to true as most allocators are stateless. -

    • -

  • -They require a1 != a2, but if we start requiring STL implementations to go through allocator_traits -to provide an op== default, we won't need to require op!= from users at all. (std::allocator, -of course, would continue to provide op!=. Note that this is analogous to reference/const_reference — -std::allocator still provides them, but we don't require them from users, and in fact we don't require them to be -consistent or meaningful if present.) -

    • -

  • -They require a == b and a != b. This requirement was not present in C++98/03, it is not necessary -(a == b is always required to be equivalent to rebind-then-compare), and STL implementations don't even need -to compare allocators of different types directly. -

    • -
- -

[2014-02-14 Issaquah: Close as NAD]

- -

-Different vendors rely on each of the different elements suggested to be removed. -

-

-While value_type my be deduced as suggested, far too much wording relies on it being available, -and the standard churn is likely to be much harder than presented here. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change in 17.6.3.5 [allocator.requirements], Table 28 — "Allocator requirements" as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements (continued)
    ExpressionReturn typeAssertion/note pre-/post-conditionDefault
    -… -
    -X::value_type - -Identical to T - -  - -See Note B, below. -
    -… -
    -a1 == a2 - -bool - -returns true only if storage
    -allocated from each can be
    -deallocated via the other.
    -operator== shall be reflexive,
    -symmetric, and transitive, and
    -shall not exit via an exception.
    -    		 -true -
    -a1 != a2 - -bool - -same as !(a1 == a2) - -  -
    -a == b - -bool - -same as a ==
    -Y::rebind<T>::other(b)     -    		 -  -
    -a != b - -bool - -same as !(a == b) - -  -
    -… -
    -X a(b); - -  - -Shall not exit via an exception.
    -post: Y(a) == b, a == X(b) -    		 -  -
    -… -
    -X a(move(b)); - -  - -Shall not exit via an exception.
    -post: a equals the prior value of X(b). -    		 -  -
    -… -
    -
    - -
    2. - -

  2. After 17.6.3.5 [allocator.requirements] p3, add a new paragraph:

    - -
    -

    -Note B: If Allocator is a class template instantiation of the form SomeAllocator<T, Args>, -where Args is zero or more type arguments, and Allocator does not supply a nested type named value_type, -the standard allocator_traits template uses T in place of Allocator::value_type by default. -For allocator types that are not template instantiations of the above form, no default is provided. -

    -
    -
    3. - -

  3. In the example provided in 17.6.3.5 [allocator.requirements]/5, delete as indicated:

    - -
    -
    -template <class Tp>
-struct SimpleAllocator {
-  typedef Tp value_type;
-  SimpleAllocator(ctor args);
-  template <class T> SimpleAllocator(const SimpleAllocator<T>& other);
-  Tp *allocate(std::size_t n);
-  void deallocate(Tp *p, std::size_t n);
-};
-
-template <class T, class U>
-bool operator==(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
-template <class T, class U>
-bool operator!=(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
-
    -
    - -
    4. - -

  4. Edit 20.7.8 [allocator.traits]p1, class template allocator_traits synopsis, as indicated:

    - -
    -namespace std {
-  template <class Alloc> struct allocator_traits {
-    typedef Alloc allocator_type;
-
-    typedef typename Alloc::value_typesee below value_type;
-
-    […]
-
-    static Alloc select_on_container_copy_construction(const Alloc& rhs);
-
-    static bool equal(const Alloc& a1, const Alloc& a2) noexcept;
-  };
-}
-
    -
    5. - -

  5. At the beginning of 20.7.8.1 [allocator.traits.types], add a new paragraph:

    - -
    -typedef see below value_type;
-
    -

    -Type: Alloc::value_type if such a type exists; otherwise, T if Alloc is a class template -instantiation of the form Alloc<T, Args>, where Args is zero or more type arguments; otherwise, the program -is ill-formed. -

    -
    -
    6. - -

  6. At the end of 20.7.8.2 [allocator.traits.members], add a new paragraph:

    - -
    -static bool equal(const Alloc& a1, const Alloc& a2) noexcept;
-
    -

    --?- Returns: a1 == a2 if that expression is well-formed; otherwise, true. -

    -
    -
    7. -
- - - - - -
-

2327. Non-power-of-two URNGs should be forbidden

-

Section: 26.5.1.3 [rand.req.urng] Status: NAD - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [rand.req.urng].

-

View all issues with NAD status.

-

Discussion:

-

-26.5.1.3 [rand.req.urng] allows URNGs with non-power-of-two (NPOT) ranges, like [0, 1729]. This is unnecessarily permissive -(I cannot imagine a realistic source of randomness that would generate such a range) and has real costs for implementers, as -uniform_int_distribution must be prepared to accept such URNGs. The most efficient way to accumulate randomness is to -concatenate random bits, so NPOT randomness is not just useless, it is actively harmful (to avoid bias, if a URNG generates a -random number outside of a power-of-two range, the number must be discarded). -

-Forbidding NPOT URNGs wouldn't affect users, and would simplify Standard Library implementations. It would be nice to require -min() to be 0, but this is not necessary; it is simple for implementations to say g() - G::min() and -this will optimize away if min() is 0. (It is vaguely plausible for a URNG to have a nonzero minimum; I can -imagine something that simply masks off low-order bits without shifting the rest downwards.) What is important is for the entire -range to have a power-of-two width; [1729, 1984] is acceptable as its size is 256. -

- -

[2013-10-12: Howard presents a counterexample]

- - -

-Consider: -

-
-#include <random>
-#include <string>
-#include <iostream>
-
-template <class Int>
-bool is_power_2m1(Int i)
-{
-  return (i & (i + 1)) == 0;
-}
-
-template <class URNG>
-void test(const std::string& urng)
-{
-  using namespace std;
-  typename URNG::result_type rng = URNG::max() - URNG::min();
-  if (!is_power_2m1(rng))
-  {
-    cout << hex;
-    cout << urng << " : min = " << URNG::min() << ", max = " << URNG::max()
-         << ", max-min = " << rng << '\n';
-  }
-};
-
-int main()
-{
-    using namespace std;
-    test<minstd_rand0>("minstd_rand0");
-    test<minstd_rand>("minstd_rand");
-    test<mt19937>("mt19937");
-    test<mt19937_64>("mt19937_64");
-    test<ranlux24_base>("ranlux24_base");
-    test<ranlux48_base>("ranlux48_base");
-    test<ranlux24>("ranlux24");
-    test<ranlux48>("ranlux48");
-    test<knuth_b>("knuth_b");
-}
-
- -

-Which for me outputs: -

- -
-minstd_rand0 : min = 1, max = 7ffffffe, max-min = 7ffffffd
-minstd_rand : min = 1, max = 7ffffffe, max-min = 7ffffffd
-knuth_b : min = 1, max = 7ffffffe, max-min = 7ffffffd
-
- -

-We do not want to outlaw these three URNG's, and the proposed wording would do that. -

- -

[Issaquah 2014-02-10: Moved to NAD]

- -

-STL withdraws the issue, non-power-of-2 URNGs are used in the field, it is too late to consider removing them. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Add a new paragraph at the end of 26.5.1.3 [rand.req.urng] as indicated:

    - -
    -

    --3- The following relation shall hold: G::min() < G::max(). -

    --?- G::max() - G::min() shall be 2n - 1 for some n > 0. -

    -
    -
    2. -
- - - - - -
-

2345. integer_sequence should have a self-typedef ::type

-

Section: 20.5.2 [intseq.intseq] Status: NAD - Submitter: Stephan T. Lavavej Opened: 2013-11-01 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-20.10.3 [meta.help] says that integral_constant<T, v> provides ::value_type (for T) -and ::type (for itself). -

-20.5.2 [intseq.intseq] says that integer_sequence<T, I...> provides ::value_type (for T), -but nothing for itself. -

-Self-typedefs can be useful when users create chains of derived classes, then want to get the Standard base type. -This is especially relevant to integer_sequence, as variadic templates encourage recursive inheritance. -

- -

[2014-02-13 Issaquah: Close as NAD]

- -

-AJM: My own implementation used a different alias for types representing parameter packs, and specifically -did not define type. I tried it both ways, and found bugs more quickly when type was -not defined. -

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Edit 20.5.2 [intseq.intseq] as indicated:

    - -
    -namespace std {
-  template<class T, T... I>
-  struct integer_sequence {
-    typedef T value_type;
-    typedef integer_sequence<T, I...> type;
-    static constexpr size_t size() noexcept { return sizeof...(I); }
-  };
-}
-
    -
    2. - -
- - - - - - -
-

2347. reverse_iterator::operator[] calls const version of current[]

-

Section: 24.5.1.3.12 [reverse.iter.opindex] Status: NAD - Submitter: Timo Bingmann Opened: 2013-11-11 Last modified: 2015-04-08

-

View all other issues in [reverse.iter.opindex].

-

View all issues with NAD status.

-

Discussion:

-

-Currently reverse_iterator::operator[]() returns "current[-n-1]" and has -an "unspecified" return type. -

-When Iterator is a mutable random access iterator, the expression -"current[-n-1]" calls "Iterator::operator[] const", which returns a -const reference. This const reference cannot be converted back to a -mutable reference. -

-This issue is related to the "unspecified" return value of -reverse_iterator::operator[], see defect 386. -

-The -1 is due to "current" pointing one item beyond the -reverse_iterator's real current value. -

-The current libstdc++ implementation reads "*(current + n)" for -reverse_iterator::operator[]. -

-This copied current, advances (backwards) via operator+ and -dereferences. It bypasses the issues due to reverse_iterator::operator[] -being const by copying the iterator. -

- -

[2014-02-13 Issaquah : close as NAD]

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Edit 24.5.1.1 [reverse.iterator], class template reverse_iterator synopsis, as indicated:

    - -
    -namespace std {
-  template <class Iterator>
-  class reverse_iterator : public
-  iterator<typename iterator_traits<Iterator>::iterator_category,
-    typename iterator_traits<Iterator>::value_type,
-    typename iterator_traits<Iterator>::difference_type,
-    typename iterator_traits<Iterator>::pointer,
-    typename iterator_traits<Iterator>::reference> {
-  public:
-    […]
-    unspecifiedreference operator[](difference_type n) const;
-    […]
-  };
-  […]
-}
-
    -
    2. - -

  2. Edit 24.5.1.3.12 [reverse.iter.opindex] as indicated:

    - -
    -unspecifiedreference operator[](
-  typename reverse_iterator<Iterator>::difference_type n) const;
-
    -

    --1- Returns: current[-n-1]*(current + n). -

    -
    -
    3. - -
- - - - - - -
-

2351. Does .seed() completely reset state of engine?

-

Section: 26.5.3 [rand.eng] Status: NAD - Submitter: Thomas Plum Opened: 2013-12-02 Last modified: 2015-05-22

-

View all other issues in [rand.eng].

-

View all issues with NAD status.

-

Discussion:

-

-With regard to Random number engine class templates 26.5.3 [rand.eng], -the Standard can be read in two different ways: when the member function -

-
-.seed(result_type s = default_seed)
-
-

-is invoked, is all associated state (such as carry) reset to the same -state that would have been created by the constructor -

-
-explicit engine-type(result_type s = default_seed)
-
-

-or is the exact state unspecified? -

-Implementations differ. -

- -

[2014-02-13, Issaquah]

- -

-Walter Brown says that Table 117 makes this very clear, and that the answer is "Yes" -

-Suggested resolution: NAD -

- -

[2015-05-05 Lenexa: Move to NAD]

- - - -

Proposed resolution:

-

-Suggested resolution: NAD -

- - - - - -
-

2355. "s" UDL suffix should be reserved for a compile-time string library type

-

Section: 21.7 [basic.string.literals] Status: NAD - Submitter: Michael Price Opened: 2014-01-18 Last modified: 2015-04-08

-

View all issues with NAD status.

-

Discussion:

-

-The current draft uses the "s" UDL suffix as a UDL for basic_string<charT> (21.7 [basic.string.literals]). -In light of EWG active issue 66 (concerning N3599), -the "s" suffix (when applied to character string literals) should be reserved for a compile-time string library type. -

- -

[Issaquah 2014-10-12: Move to NAD]

- - -

We discussed leaving the s UDL suffix for string_view in Portland, and voted strongly in favor of using it for std::string. -string is also an extremely widely used type, and the difference is observable in type deduction cases. -In addition, a compile-time string is likely to cost significant compile time, which we don't want to make the default with s.

- - - - -
Mark 2355 as NAD?
SFFNASA
8 4020
- - -

Proposed resolution:

- - - - - -
-

2373. Make new entities and names in namespace std conforming extensions

-

Section: 17.6.5 [conforming] Status: NAD - Submitter: Chandler Carruth Opened: 2014-03-22 Last modified: 2015-05-22

-

View all other issues in [conforming].

-

View all issues with NAD status.

-

Discussion:

-

-Technically, right now, it is not a conforming extension to add a new function to namespace std. Doing so could cause -unqualified lookup on the name of that function in the presence of a using directive to find a different function. This seems -an unreasonable restriction on library vendors providing conforming extensions, as such a using directive seems inherently risky -in unqualified name lookup. -

-

-17.6.5.5 [member.functions] implies that adding overloads to a method is a conforming extension, and within some -limits the same is true for global functions due to 17.6.5.4 [global.functions]. -

-It would likely be useful to specify that other new entities are valid conforming extensions, or preclude them where they pose -serious compatibility problems. -

- -

[Lenexa 2015-05-06: Move to NAD]

- -

JY: It's a design question, move to LEWG?

-

AM: NAD: extensions led to us being unable to use the names hash_map, leading to unordered_map etc. Will result in collisions between members.

-

MC: Agrees, implementations that extend std:: must use __ugly_names for this reason.

-

JY: I would not oppose NAD.

-

Move to NAD, consensus.

- - - -

Proposed resolution:

- - - - - -
-

2382. Unclear order of container update versus object destruction on removing an object

-

Section: 17.6.5.8 [reentrancy] Status: Pending NAD - Submitter: Peter Kasting Opened: 2014-05-06 Last modified: 2015-04-08

-

View all other issues in [reentrancy].

-

View all issues with Pending NAD status.

-

Discussion:

-

-The standard does not seem to discuss reentrant access to a container during removal of an element, -leaving it unclear whether a removed object is destroyed before or after it is removed from the container. -For example, the behavior of the following code seems to be unspecified: -

-
-#include <iostream>
-#include <map>
-#include <memory>
-
-struct T;
-typedef std::map<int, std::shared_ptr<T>> TMap;
-
-struct T {
-  T(TMap* t_map, int index) : t_map(t_map), index(index) {}
-  ~T() {
-    std::cout << "Object " << index << " is ";
-    if (t_map->count(index))
-      std::cout << "destroyed before being removed from the map" << std::endl;
-    else
-      std::cout << "removed from the map before being destroyed" << std::endl;
-  }
-
-  static void AddToMap(TMap* map, int index) {
-    (*map)[index] = std::make_shared<T>(map, index);
-  }
-
-  TMap* t_map;
-  int index;
-};
-
-int main()
-{
-  TMap t_map;
-  T::AddToMap(&t_map, 0);
-  T::AddToMap(&t_map, 1);
-  t_map.erase(1);
-  t_map.erase(0);
-}
-
-

-The output of this program in Visual Studio 2013 is: -

-
-Object 1 is removed from the map before being destroyed
-Object 0 is destroyed before being removed from the map
-
-

-The core issue here is whether an object removed from a container should be destroyed before or after -it is removed from the container. The current standard seems to be silent on this issue. -The above output demonstrates that the behavior is actually inconsistent. (It's difficult to fully -describe Visual Studio's behavior; for example, changing main() in the above example to the following:) -

-
-int main()
-{
-  TMap t_map;
-  T::AddToMap(&t_map, 0);
-  T::AddToMap(&t_map, 1);
-  T::AddToMap(&t_map, 2);
-  T::AddToMap(&t_map, 3);
-  t_map.erase(3);
-  t_map.clear();
-}
-
-

-(...gives this output:) -

-
-Object 3 is removed from the map before being destroyed
-Object 2 is destroyed before being removed from the map
-Object 1 is destroyed before being removed from the map
-Object 0 is removed from the map before being destroyed
-
-

-In my opinion, the standard should explicitly describe when objects are destroyed as part of removal from a container. -To me, it makes the most sense to say that objects should be removed from the container before they are destroyed. -

-

[2014-05-07, Jeffrey Yasskin comments]

- -

-I think there are two main points here beyond this writeup: -

-
    -

  1. We can't make recursive use of a standard library container valid -in all cases.

    2. -

  2. If recursion through especially erase() is undefined behavior, -that's pretty scary for existing large applications with code in -destructors. Of course, "scary" doesn't mean we have to define the -behavior.

    3. -
-

-I'll add a third: The language in 17.6.5.8 [reentrancy] nearly makes this -undefined behavior already. I think any fix is probably going to live -there, and extend the current "implementation-defined" on recursive -reentrancy for individual functions to recursive reentrancy on class -instances. I'm not sure exactly how to word that. -

- -

[2014-06 Rapperswil]

- -

-STL: We need more wording about how container methods can be reentrency. -

-Jeffrey: The title for this issue is confusing, what we really want is "reentrancy for objects". -

-Alisdair: Should we then close 2382 as NAD with a link to the new issue? -

- - -

Proposed resolution:

- - - - - -
-

2386. function::operator= handles allocators incorrectly

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: NAD - Submitter: Pablo Halpern Opened: 2014-05-23 Last modified: 2015-05-05

-

View all other issues in [func.wrap.func.con].

-

View all issues with NAD status.

-

Discussion:

-

-The Effects clauses for the assignment operator for class template function are -written as code that constructs a temporary function and then swaps it with *this. -The intention appears to be that assignment should have the strong exception -guarantee, i.e., *this is not modified if an exception is thrown. However, the current -description is incorrect when *this was constructed using an allocator. -

-Part of the problem is the under-specification of swap, which does not state the -allocator requirements or allocator postconditions. If swap behaves like the rest of the -standard library, swapping function objects constructed with different allocators -would be undefined behavior. Alternatively swap could exchange the allocators, -though I would argue against this specification. -

-For either specification of swap, the current Effects clauses for operator= are -incorrect. If swap does not exchange the allocators, then operator= would have -undefined behavior, which is clearly not desired. If swap does exchange the allocators, -then operator= would always leave the left-hand side (lhs) of the assignment with a -default allocator. The latter would be surprising behavior, as the allocator instance is -normally unchanged for the lifetime of an object (for good reason), and is certainly not -reset to default arbitrarily. -

-The desired behavior is that assignment would leave the allocator of the lhs -unchanged. The way to achieve this behavior is to construct the temporary function -using the original allocator. Unfortunately, we cannot describe the desired behavior in -pure code, because there is no way to name the type-erased value of the allocator. -(N3916 would improve this situation for the Library Fundamentals TS, but even with -those changes, there is no way to recover the original type of the allocator.) The PR -below, therefore, uses pseudo-code, inventing a fictitious ALLOCATOR_OF(f) -expression that evaluates to the actual allocator type, even if that allocator was type -erased. I have implemented this PR successfully. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3936.

- -
    -

  1. Change 20.9.12.2.1 [func.wrap.func.con] as indicated:

    - -
    -

    -In the following descriptions, ALLOCATOR_OF(f) is a copy of the allocator specified in the -construction of function f, or allocator<char>() if no allocator was specified. -

    -
    -function& operator=(const function& f);
-
    -
    -

    --12- Effects: function(allocator_arg, ALLOCATOR_OF(*this), f).swap(*this); -

    --13- Returns: *this -

    -
    -
    -function& operator=(function&& f);
-
    -
    -

    --14- Effects: Replaces the target of *this with the target of f.function(allocator_arg, -ALLOCATOR_OF(*this), std::move(f)).swap(*this); -

    --15- Returns: *this -

    -
    -
    -function& operator=(nullptr_t);
-
    -
    -

    --16- Effects: If *this != nullptr, destroys the target of this. -

    --17- Postconditions: !(*this). The allocator is unchanged. -

    --18- Returns: *this -

    --?- Throws: Nothing. -

    -
    -
    -template<class F> function& operator=(F&& f);
-
    -
    -

    --19- Effects: function(allocator_arg, ALLOCATOR_OF(*this), std::forward<F>(f)).swap(*this); -

    --20- Returns: *this -

    --21- Remarks: This assignment operator shall not participate in overload resolution unless -declval<typename decay<F>::type&>() is Callable (20.9.11.2) for argument types -ArgTypes... and return type R. -

    -
    -
    -template<class F> function& operator=(reference_wrapper<F> f);
-
    -
    -

    --22- Effects: function(allocator_arg, ALLOCATOR_OF(*this), f).swap(*this); -

    --23- Returns: *this -

    -
    - -
    -
    2. - -
- -
- -

[2015-05, Lenexa]

- -

-STL: think this is NAD, don't think this is implementable or even should be.
-STL: think this issue should be dealt with the same as 2370, don't think this should be done ever.
-STL: NAD because there is nothing broken here.
-STL: already fixed operator= noexcept so Throws nothing is not needed
-STL: nothing to salvage here
-MC: consensus for NAD -

- - -

Proposed resolution:

-

-There was consensus by the committee that the issue does not constitute as defect. -

- - - - - -
-

2388. Handling self-assignment in the proposed library function std::exchange

-

Section: 20.2.3 [utility.exchange] Status: NAD - Submitter: Nick Calus Opened: 2014-05-09 Last modified: 2015-05-06

-

View all other issues in [utility.exchange].

-

View all issues with NAD status.

-

Discussion:

-

-In paper N3668, the addition of a template function -std::exchange had been proposed. In the rationale provided by the paper, we find the following: -

-
-

-I chose the name for symmetry with atomic_exchange, since they behave the same except for this function not being atomic. -

-
-

-and: -

-
-

-Atomic objects provide an atomic_exchange function ([atomics.types.operations.req]p18) that assigns a new value to the object -and returns the old value. This operation is also useful on non-atomic objects, and this paper proposes adding it to the library. -

-But the specified semantics of std::exchange is defined as follows: -

-
-
-template <class T, class U=T> T exchange(T& obj, U&& new_val);
-
-
-

-Effects: Equivalent to: -

-
-T old_val = std::move(obj);
-obj = std::forward<U>(new_val);
-return old_val;
-
-
-
-
-

-When looking at the post-condition of the std::exchange function, one would expect the return value to be the old value -of obj and also that obj now contains the value of new_value. -This post-condition is violated when obj is a reference to the same object as new_value and type T -has move semantics. -

-Given it's specification, it is clear that std::exchange is meant to be used with types that have move semantics. -Therefore, the post-condition is violated for self-assignments. -

-Suppose the following situation: -

-You have a vector of objects. The objects implement move semantics and are emptied when moved from. -You provide a function that allows you to replace an object at a specific index by a new object (provided by reference as -an argument to your function). When replacing an object, your function calls a member-function do_something_fancy -on the old object. -

-
-void your_function(int i, X& new_val) {
-  std::exchange(vec[i], new_val).do_something_fancy();
-}
-
-

-Your function gets called with a given index and the corresponding element of said vector. (by coincidence or by purpose, it -doesn't really matter) -

-
-your_function(5, vec[5]);
-
-

-This will cause the object at vec[5] to be in an empty state. -If this object would not implement move semantics, assignment performance is potentially worse, but at least it -is not in an empty (to my business logic, invalid) state. -

-So to me, the current reference implementation of std::exchange does not have the behavior it is expected to have. -

- -

[2014-12-18 Telecon]

- -

-MC: does this resolution solve the problem? -

-JW: and is the cost of the extra construction and move acceptable? -

-AM: not all moves are cheap -

-VV: seems like a design change -

-JW: maybe this should be rolled into my unwritten paper on self-swap, so we deal with them consistently -

-VV: we should update the issue saying something like that and maybe NAD Future -

-MC: instead, add Requires clause saying the arguments are not the same. -

-JW: interesting, that can even be checked in a debug mode assertion -

-MC: ACTION: send alternative P/R that we can consider -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3936.

- -
    -

  1. Change 20.2.3 [utility.exchange] as indicated:

    -
    -template <class T, class U=T> T exchange(T& obj, U&& new_val);
-
    -
    -

    --1- Effects: Equivalent to: -

    -
    -T tmp = std::forward<U>(new_val);
-T old_val = std::move(obj);
-obj = std::forward<U>(new_val)std::move(tmp);
-return old_val;
-
    -
    -
    -
    -
    2. -
-
- -

-Previous resolution from Marshall [SUPERSEDED]: -

-
-

This wording is relative to N4296.

- -
    -

  1. Change 20.2.3 [utility.exchange] as indicated:

    -
    -template <class T, class U=T> T exchange(T& obj, U&& new_val);
-
    -
    -

    --?- Requires: obj and new_val shall not refer to the same object. -

    --1- Effects: Equivalent to: -

    -
    -T old_val = std::move(obj);
-obj = std::forward<U>(new_val);
-return old_val;
-
    -
    -
    -
    -
    2. -
-
- -

[2015-03-30, Marshall provides alternative wording]

- - -

[2015-05, Lenexa]

- -

-MC: self exchange does not work
-MC: PR is just to add requires
-STL: what if the new thing is a subobject, isn't that just as bad, any aliasing
-STL: don't know that we need to do anything here if we aren't changing the implementation
-NM: should remove the requires
-MC: so NAD
-STL: could add note
-NM: remove requires
-DK: requires isn't already there
-RL: no note?
-STL: no note, NAD, burden for next person that asks about aliasing
-DK: what do we do for swap?
-STL: self swap has always been noop, exchange could do something bad because it clears out
-MC: alright, NAD it is
-

- - - -

Proposed resolution:

-The current specification is clear about the implications described by the issue example and is as intended. - - - - - -
-

2405. rotate()'s return value is incorrect when middle == first

-

Section: 25.3.11 [alg.rotate] Status: NAD - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-04-08

-

View all other issues in [alg.rotate].

-

View all issues with NAD status.

-

Discussion:

-

-When LWG 488 was resolved, the intention was to return "where the subrange [first, middle) starts after -the rotate is performed". However, this wasn't achieved in one case. -

-When middle == last, rotate() does nothing and returns first. This is good. -

-When middle == first, rotate() does nothing and returns last. This is bad. In addition to being -inconsistent with the other do-nothing case, it prevents rotate() from providing the useful guarantee that LWG -488 wanted: when [first, last) is non-empty, rotate()'s return value should always be -dereferenceable to get the originally-first element. -

-Howard Hinnant: -

-As the author of LWG 488 I can assure everyone that the edge cases the proposed resolution specifies were -not specified by accident. rotate(i, i, j) should return j and rotate(i, j, j) should return i. -Doing otherwise will break working code. These return values were motivated by the uses of rotate in the implementation -of algorithms such as stable_partition and inplace_merge. The results of these edge cases were not chosen lightly. -

-Also a good read: -

-notes-on-programming-2006-10-13 -

-Summary: NAD. -

- -

[2014-06-16 Rapperswill]

- -

-Closed as NAD. -

- - - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 25.3.11 [alg.rotate] p2 as indicated:

    - -
    -

    --2- Returns: If middle == first, returns first. Otherwise, returns first + (last - middle). -

    -
    -
    2. - -
- - - - - -
-

2429. std::basic_ostringstream is missing an allocator-extended constructor

-

Section: 27.8.4 [ostringstream] Status: NAD - Submitter: Markus Kemp Opened: 2014-09-03 Last modified: 2015-04-08

-

View all other issues in [ostringstream].

-

View all issues with NAD status.

-

Discussion:

-

-I initially brought this issue up on Stack Overflow, -where I was then told to make a topic about this problem on std-discussion, -where I was then in turn asked to report the issue. -

-The problem: The std::basic_ostringstream class template can be instantiated with an allocator type, but none of the -constructors provided accept an allocator argument, which means it's impossible to use std::basic_ostringstream with -stateful allocators. The C++ Standard Library Defect Report List seems to already mention a similar issue (2210). -

- - -

[2014-11 Urbana]

- -

Closed as NAD

-

-This is not a rejection of the suggestion, but an observation that simply adding an allocator-aware -constructor is only part of the problem. stringstream returns the string assembled -in its buffer by value, as the result of a call to str, and typically this will not use the -same allocator as would be supplied at construction. -

-

-The appropriate way to make progress on this issue, if motivated, is to submit a paper to LEWG -addressing the larger design concerns in addition to 'just' adding an (optional) allocator to -the constructors. -

- -

Proposed resolution:

- - - - - - - diff --git a/libstdc++-v3/doc/html/ext/lwg-defects.html b/libstdc++-v3/doc/html/ext/lwg-defects.html deleted file mode 100644 index 1e78c35249ed..000000000000 --- a/libstdc++-v3/doc/html/ext/lwg-defects.html +++ /dev/null @@ -1,129794 +0,0 @@ - - - -C++ Standard Library Defect Report List - - - - - - - - - - - - - - - - - - - - -
Doc. no.N4485
Date:2015-05-23
Project:Programming Language C++
Reply to:Marshall Clow <lwgchair@gmail.com>
-

C++ Standard Library Defect Report List (Revision R93)

-

Revised 2015-05-23 at 15:05:40 UTC

-

-

Reference ISO/IEC IS 14882:2014(E)

-

Also see:

- -

This document contains only library issues which have been closed - by the Library Working Group (LWG) after being found to be defects - in the standard. That is, issues which have a status of DR, - TC1, C++11, - C++14, or Resolved. See - the Library Closed Issues List for issues closed as non-defects. See - the Library Active Issues List for active issues and more information. - The introductory material in that document also applies to this document.

- -

Revision History

- - -

Defect Reports

-
-

1. C library linkage editing oversight

-

Section: 17.6.2.3 [using.linkage] Status: TC1 - Submitter: Beman Dawes Opened: 1997-11-16 Last modified: 2015-04-08

-

View all other issues in [using.linkage].

-

View all issues with TC1 status.

-

Discussion:

-

The change specified in the proposed resolution below did not make -it into the Standard. This change was accepted in principle at the -London meeting, and the exact wording below was accepted at the -Morristown meeting.

- - -

Proposed resolution:

-

Change 17.6.2.3 [using.linkage] paragraph 2 -from:

- -
-

It is unspecified whether a name from the Standard C library - declared with external linkage has either extern "C" or - extern "C++" linkage.

-
- -

to:

- -
-

Whether a name from the Standard C library declared with external - linkage has extern "C" or extern "C++" linkage - is implementation defined. It is recommended that an implementation - use extern "C++" linkage for this purpose.

-
- - - - - -
-

3. Atexit registration during atexit() call is not described

-

Section: 18.5 [support.start.term] Status: TC1 - Submitter: Steve Clamage Opened: 1997-12-12 Last modified: 2015-04-08

-

View all other issues in [support.start.term].

-

View all issues with TC1 status.

-

Discussion:

-

We appear not to have covered all the possibilities of - exit processing with respect to -atexit registration.
-
-Example 1: (C and C++)

- -
    #include <stdlib.h>
-    void f1() { }
-    void f2() { atexit(f1); }
-    
-    int main()
-    {
-        atexit(f2); // the only use of f2
-        return 0; // for C compatibility
-    }
- -

At program exit, f2 gets called due to its registration in -main. Running f2 causes f1 to be newly registered during the exit -processing. Is this a valid program? If so, what are its -semantics?

- -

-Interestingly, neither the C standard, nor the C++ draft standard nor -the forthcoming C9X Committee Draft says directly whether you can -register a function with atexit during exit processing.

- -

-All 3 standards say that functions are run in reverse order of their -registration. Since f1 is registered last, it ought to be run first, -but by the time it is registered, it is too late to be first.

- -

If the program is valid, the standards are self-contradictory about -its semantics.

- -

Example 2: (C++ only)

- -
    
-    void F() { static T t; } // type T has a destructor
-
-    int main()
-    {
-        atexit(F); // the only use of F
-    }
-
- -

Function F registered with atexit has a local static variable t, -and F is called for the first time during exit processing. A local -static object is initialized the first time control flow passes -through its definition, and all static objects are destroyed during -exit processing. Is the code valid? If so, what are its semantics?

- -

-Section 18.3 "Start and termination" says that if a function -F is registered with atexit before a static object t is initialized, F -will not be called until after t's destructor completes.

- -

-In example 2, function F is registered with atexit before its local -static object O could possibly be initialized. On that basis, it must -not be called by exit processing until after O's destructor -completes. But the destructor cannot be run until after F is called, -since otherwise the object could not be constructed in the first -place.

- -

If the program is valid, the standard is self-contradictory about -its semantics.

- -

I plan to submit Example 1 as a public comment on the C9X CD, with -a recommendation that the results be undefined. (Alternative: make it -unspecified. I don't think it is worthwhile to specify the case where -f1 itself registers additional functions, each of which registers -still more functions.)

- -

I think we should resolve the situation in the whatever way the C -committee decides.

- -

For Example 2, I recommend we declare the results undefined.

- -

[See reflector message lib-6500 for further discussion.]

- - - - -

Proposed resolution:

-

Change section 18.3/8 from:

-

- First, objects with static storage duration are destroyed and - functions registered by calling atexit are called. Objects with - static storage duration are destroyed in the reverse order of the - completion of their constructor. (Automatic objects are not - destroyed as a result of calling exit().) Functions registered with - atexit are called in the reverse order of their registration. A - function registered with atexit before an object obj1 of static - storage duration is initialized will not be called until obj1's - destruction has completed. A function registered with atexit after - an object obj2 of static storage duration is initialized will be - called before obj2's destruction starts. -

-

to:

-

- First, objects with static storage duration are destroyed and - functions registered by calling atexit are called. Non-local objects - with static storage duration are destroyed in the reverse order of - the completion of their constructor. (Automatic objects are not - destroyed as a result of calling exit().) Functions registered with - atexit are called in the reverse order of their registration, except - that a function is called after any previously registered functions - that had already been called at the time it was registered. A - function registered with atexit before a non-local object obj1 of - static storage duration is initialized will not be called until - obj1's destruction has completed. A function registered with atexit - after a non-local object obj2 of static storage duration is - initialized will be called before obj2's destruction starts. A local - static object obj3 is destroyed at the same time it would be if a - function calling the obj3 destructor were registered with atexit at - the completion of the obj3 constructor. -

- - -

Rationale:

-

See 99-0039/N1215, October 22, 1999, by Stephen D. Clamage for the analysis -supporting to the proposed resolution.

- - - - - -
-

5. String::compare specification questionable

-

Section: 21.4.6.8 [string::swap] Status: TC1 - Submitter: Jack Reeves Opened: 1997-12-11 Last modified: 2015-04-08

-

View all other issues in [string::swap].

-

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-

Duplicate of: 87

-

Discussion:

-

At the very end of the basic_string class definition is the signature: int -compare(size_type pos1, size_type n1, const charT* s, size_type n2 = npos) const; In the -following text this is defined as: returns -basic_string<charT,traits,Allocator>(*this,pos1,n1).compare( -basic_string<charT,traits,Allocator>(s,n2);

- -

Since the constructor basic_string(const charT* s, size_type n, const Allocator& a -= Allocator()) clearly requires that s != NULL and n < npos and further states that it -throws length_error if n == npos, it appears the compare() signature above should always -throw length error if invoked like so: str.compare(1, str.size()-1, s); where 's' is some -null terminated character array.

- -

This appears to be a typo since the obvious intent is to allow either the call above or -something like: str.compare(1, str.size()-1, s, strlen(s)-1);

- -

This would imply that what was really intended was two signatures int compare(size_type -pos1, size_type n1, const charT* s) const int compare(size_type pos1, size_type n1, const -charT* s, size_type n2) const; each defined in terms of the corresponding constructor.

- - -

Proposed resolution:

-

Replace the compare signature in 21.4 [basic.string] -(at the very end of the basic_string synopsis) which reads:

- -
-

int compare(size_type pos1, size_type n1,
-             const charT* s, - size_type n2 = npos) const;

-
- -

with:

- -
-

int compare(size_type pos1, size_type n1,
-             const charT* s) const;
- int compare(size_type pos1, size_type n1,
-             const charT* s, - size_type n2) const;

-
- -

Replace the portion of 21.4.6.8 [string::swap] -paragraphs 5 and 6 which read:

- -
-

int compare(size_type pos, size_type n1,
-             charT * s, size_type n2 - = npos) const;
- Returns:
- basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
-              - basic_string<charT,traits,Allocator>( s, n2))

-
- -

with:

- -
-

int compare(size_type pos, size_type n1,
-             const charT * s) const;
- Returns:
- basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
-              - basic_string<charT,traits,Allocator>( s ))
-
- int compare(size_type pos, size_type n1,
-             const charT * s, - size_type n2) const;
- Returns:
- basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
-              - basic_string<charT,traits,Allocator>( s, n2))

-
- -

Editors please note that in addition to splitting the signature, the third argument -becomes const, matching the existing synopsis.

- - -

Rationale:

-

While the LWG dislikes adding signatures, this is a clear defect in -the Standard which must be fixed.  The same problem was also -identified in issues 7 (item 5) and 87.

- - - - - -
-

7. String clause minor problems

-

Section: 21 [strings] Status: TC1 - Submitter: Matt Austern Opened: 1997-12-15 Last modified: 2015-04-08

-

View all other issues in [strings].

-

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-

Discussion:

-

(1) In 21.4.6.4 [string::insert], the description of template -<class InputIterator> insert(iterator, InputIterator, -InputIterator) makes no sense. It refers to a member function that -doesn't exist. It also talks about the return value of a void -function.

- -

(2) Several versions of basic_string::replace don't appear in the -class synopsis.

- -

(3) basic_string::push_back appears in the synopsis, but is never -described elsewhere. In the synopsis its argument is const charT, -which doesn't makes much sense; it should probably be charT, or -possible const charT&.

- -

(4) basic_string::pop_back is missing.

- -

(5) int compare(size_type pos, size_type n1, charT* s, size_type n2 -= npos) make no sense. First, it's const charT* in the synopsis and -charT* in the description. Second, given what it says in RETURNS, -leaving out the final argument will always result in an exception -getting thrown. This is paragraphs 5 and 6 of -21.4.6.8 [string::swap]

- -

(6) In table 37, in section 21.2.1 [char.traits.require], -there's a note for X::move(s, p, n). It says "Copies correctly -even where p is in [s, s+n)". This is correct as far as it goes, -but it doesn't go far enough; it should also guarantee that the copy -is correct even where s in in [p, p+n). These are two orthogonal -guarantees, and neither one follows from the other. Both guarantees -are necessary if X::move is supposed to have the same sort of -semantics as memmove (which was clearly the intent), and both -guarantees are necessary if X::move is actually supposed to be -useful.

- - -

Proposed resolution:

-

ITEM 1: In 21.3.5.4 [lib.string::insert], change paragraph 16 to
-
-    EFFECTS: Equivalent to insert(p - begin(), basic_string(first, last)).
-
-ITEM 2:  Not a defect; the Standard is clear.. There are ten versions of replace() in -the synopsis, and ten versions in 21.3.5.6 [lib.string::replace].
-
-ITEM 3: Change the declaration of push_back in the string synopsis (21.3, -[lib.basic.string]) from:

- -

     void push_back(const charT)
-
-to
-
-     void push_back(charT)
-
-Add the following text immediately after 21.3.5.2 [lib.string::append], paragraph 10.
-
-    void basic_string::push_back(charT c);
-    EFFECTS: Equivalent to append(static_cast<size_type>(1), c);
-
-ITEM 4: Not a defect. The omission appears to have been deliberate.
-
-ITEM 5: Duplicate; see issue 5 (and 87).
-
-ITEM 6: In table 37, Replace:
-
-    "Copies correctly even where p is in [s, s+n)."
-
-with:
-
-     "Copies correctly even where the ranges [p, p+n) and [s, -s+n) overlap."

- - - - - -
-

8. Locale::global lacks guarantee

-

Section: 22.3.1.5 [locale.statics] Status: TC1 - Submitter: Matt Austern Opened: 1997-12-24 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

-

It appears there's an important guarantee missing from clause -22. We're told that invoking locale::global(L) sets the C locale if L -has a name. However, we're not told whether or not invoking -setlocale(s) sets the global C++ locale.

- -

The intent, I think, is that it should not, but I can't find any -such words anywhere.

- - -

Proposed resolution:

-

Add a sentence at the end of 22.3.1.5 [locale.statics], -paragraph 2: 

- -
-

No library function other than locale::global() shall affect - the value returned by locale().

- -
- - - - - -
-

9. Operator new(0) calls should not yield the same pointer

-

Section: 18.6.1 [new.delete] Status: TC1 - Submitter: Steve Clamage Opened: 1998-01-04 Last modified: 2015-04-08

-

View all other issues in [new.delete].

-

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-

Discussion:

-

Scott Meyers, in a comp.std.c++ posting: I just noticed that -section 3.7.3.1 of CD2 seems to allow for the possibility that all -calls to operator new(0) yield the same pointer, an implementation -technique specifically prohibited by ARM 5.3.3.Was this prohibition -really lifted? Does the FDIS agree with CD2 in the regard? [Issues -list maintainer's note: the IS is the same.]

- - -

Proposed resolution:

-

Change the last paragraph of 3.7.3 from:

-
-

Any allocation and/or deallocation functions defined in a C++ program shall - conform to the semantics specified in 3.7.3.1 and 3.7.3.2.

-
-

to:

-
-

Any allocation and/or deallocation functions defined in a C++ program, - including the default versions in the library, shall conform to the semantics - specified in 3.7.3.1 and 3.7.3.2.

-
-

Change 3.7.3.1/2, next-to-last sentence, from :

-
-

If the size of the space requested is zero, the value returned shall not be - a null pointer value (4.10).

-
-

to:

-
-

Even if the size of the space requested is zero, the request can fail. If - the request succeeds, the value returned shall be a non-null pointer value - (4.10) p0 different from any previously returned value p1, unless that value - p1 was since passed to an operator delete.

-
-

5.3.4/7 currently reads:

-
-

When the value of the expression in a direct-new-declarator is zero, the - allocation function is called to allocate an array with no elements. The - pointer returned by the new-expression is non-null. [Note: If the library - allocation function is called, the pointer returned is distinct from the - pointer to any other object.]

-
-

Retain the first sentence, and delete the remainder.

-

18.5.1 currently has no text. Add the following:

-
-

Except where otherwise specified, the provisions of 3.7.3 apply to the - library versions of operator new and operator delete.

-
-

To 18.5.1.3, add the following text:

-
-

The provisions of 3.7.3 do not apply to these reserved placement forms of - operator new and operator delete.

-
- - -

Rationale:

-

See 99-0040/N1216, October 22, 1999, by Stephen D. Clamage for the analysis -supporting to the proposed resolution.

- - - - - -
-

11. Bitset minor problems

-

Section: 20.6 [template.bitset] Status: TC1 - Submitter: Matt Austern Opened: 1998-01-22 Last modified: 2015-04-08

-

View other active issues in [template.bitset].

-

View all other issues in [template.bitset].

-

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-

Discussion:

-

(1) bitset<>::operator[] is mentioned in the class synopsis (23.3.5), but it is -not documented in 23.3.5.2.

- -

(2) The class synopsis only gives a single signature for bitset<>::operator[], -reference operator[](size_t pos). This doesn't make much sense. It ought to be overloaded -on const. reference operator[](size_t pos); bool operator[](size_t pos) const.

- -

(3) Bitset's stream input function (23.3.5.3) ought to skip all whitespace before -trying to extract 0s and 1s. The standard doesn't explicitly say that, though. This should -go in the Effects clause.

- - -

Proposed resolution:

-

ITEMS 1 AND 2:
-
-In the bitset synopsis (20.6 [template.bitset]), -replace the member function
-
-    reference operator[](size_t pos);
-
-with the two member functions
-
-    bool operator[](size_t pos) const;
-    reference operator[](size_t pos);
-
-Add the following text at the end of 20.6.2 [bitset.members], -immediately after paragraph 45:

- -
-

bool operator[](size_t pos) const;
- Requires: pos is valid
- Throws: nothing
- Returns: test(pos)
-
- bitset<N>::reference operator[](size_t pos);
- Requires: pos is valid
- Throws: nothing
- Returns: An object of type bitset<N>::reference such that (*this)[pos] - == this->test(pos), and such that (*this)[pos] = val is equivalent to this->set(pos, - val);

-
- - -

Rationale:

-

The LWG believes Item 3 is not a defect. "Formatted -input" implies the desired semantics. See 27.7.2.2 [istream.formatted]. -

- - - - - -
-

13. Eos refuses to die

-

Section: 27.7.2.2.3 [istream::extractors] Status: TC1 - Submitter: William M. Miller Opened: 1998-03-03 Last modified: 2015-04-08

-

View all other issues in [istream::extractors].

-

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-

Discussion:

-

In 27.6.1.2.3, there is a reference to "eos", which is -the only one in the whole draft (at least using Acrobat search), so -it's undefined.

- - -

Proposed resolution:

-

In 27.7.2.2.3 [istream::extractors], replace "eos" with -"charT()"

- - - - - -
-

14. Locale::combine should be const

-

Section: 22.3.1.3 [locale.members] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.members].

-

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-

Discussion:

-

locale::combine is the only member function of locale (other than constructors and -destructor) that is not const. There is no reason for it not to be const, and good reasons -why it should have been const. Furthermore, leaving it non-const conflicts with 22.1.1 -paragraph 6: "An instance of a locale is immutable."

- -

History: this member function originally was a constructor. it happened that the -interface it specified had no corresponding language syntax, so it was changed to a member -function. As constructors are never const, there was no "const" in the interface -which was transformed into member "combine". It should have been added at that -time, but the omission was not noticed.

- - -

Proposed resolution:

-

In 22.3.1 [locale] and also in 22.3.1.3 [locale.members], add -"const" to the declaration of member combine:

-
- 
template <class Facet> locale combine(const locale& other) const;
-
- - - - - -
-

15. Locale::name requirement inconsistent

-

Section: 22.3.1.3 [locale.members] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.members].

-

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-

Discussion:

-

locale::name() is described as returning a string that can be passed to a locale -constructor, but there is no matching constructor.

- - -

Proposed resolution:

-

In 22.3.1.3 [locale.members], paragraph 5, replace -"locale(name())" with -"locale(name().c_str())". -

- - - - - -
-

16. Bad ctype_byname<char> decl

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

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-

Discussion:

-

The new virtual members ctype_byname<char>::do_widen and do_narrow did not get -edited in properly. Instead, the member do_widen appears four times, with wrong argument -lists.

- - -

Proposed resolution:

-

The correct declarations for the overloaded members -do_narrow and do_widen should be copied -from 22.4.1.3 [facet.ctype.special].

- - - - - -
-

17. Bad bool parsing

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

View all other issues in [facet.num.get.virtuals].

-

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-

Discussion:

-

This section describes the process of parsing a text boolean value from the input -stream. It does not say it recognizes either of the sequences "true" or -"false" and returns the corresponding bool value; instead, it says it recognizes -only one of those sequences, and chooses which according to the received value of a -reference argument intended for returning the result, and reports an error if the other -sequence is found. (!) Furthermore, it claims to get the names from the ctype<> -facet rather than the numpunct<> facet, and it examines the "boolalpha" -flag wrongly; it doesn't define the value "loc"; and finally, it computes -wrongly whether to use numeric or "alpha" parsing.
-
-I believe the correct algorithm is "as if":

- -
  // in, err, val, and str are arguments.
-  err = 0;
-  const numpunct<charT>& np = use_facet<numpunct<charT> >(str.getloc());
-  const string_type t = np.truename(), f = np.falsename();
-  bool tm = true, fm = true;
-  size_t pos = 0;
-  while (tm && pos < t.size() || fm && pos < f.size()) {
-    if (in == end) { err = str.eofbit; }
-    bool matched = false;
-    if (tm && pos < t.size()) {
-      if (!err && t[pos] == *in) matched = true;
-      else tm = false;
-    }
-    if (fm && pos < f.size()) {
-      if (!err && f[pos] == *in) matched = true;
-      else fm = false;
-    }
-    if (matched) { ++in; ++pos; }
-    if (pos > t.size()) tm = false;
-    if (pos > f.size()) fm = false;
-  }
-  if (tm == fm || pos == 0) { err |= str.failbit; }
-  else                      { val = tm; }
-  return in;
- -

Notice this works reasonably when the candidate strings are both empty, or equal, or -when one is a substring of the other. The proposed text below captures the logic of the -code above.

- - -

Proposed resolution:

-

In 22.4.2.1.2 [facet.num.get.virtuals], in the first line of paragraph 14, -change "&&" to "&".

- -

Then, replace paragraphs 15 and 16 as follows:

- -
- -

Otherwise target sequences are determined "as if" by - calling the members falsename() and - truename() of the facet obtained by - use_facet<numpunct<charT> >(str.getloc()). - Successive characters in the range [in,end) (see - [lib.sequence.reqmts]) are obtained and matched against - corresponding positions in the target sequences only as necessary to - identify a unique match. The input iterator in is - compared to end only when necessary to obtain a - character. If and only if a target sequence is uniquely matched, - val is set to the corresponding value.

- -
- -
-

The in iterator is always left pointing one position beyond the last character - successfully matched. If val is set, then err is set to str.goodbit; or to - str.eofbit if, when seeking another character to match, it is found that - (in==end). If val is not set, then err is set to str.failbit; or to - (str.failbit|str.eofbit)if - the reason for the failure was that (in==end). [Example: for targets - true:"a" and false:"abb", the input sequence "a" yields - val==true and err==str.eofbit; the input sequence "abc" yields - err=str.failbit, with in ending at the 'c' element. For targets - true:"1" - and false:"0", the input sequence "1" yields val==true - and err=str.goodbit. For empty targets (""), any input sequence yields - err==str.failbit. --end example]

-
- - - - - -
-

18. Get(...bool&) omitted

-

Section: 22.4.2.1.1 [facet.num.get.members] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [facet.num.get.members].

-

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-

Discussion:

-

In the list of num_get<> non-virtual members on page 22-23, the member -that parses bool values was omitted from the list of definitions of non-virtual -members, though it is listed in the class definition and the corresponding -virtual is listed everywhere appropriate.

- - -

Proposed resolution:

-

Add at the beginning of 22.4.2.1.1 [facet.num.get.members] -another get member for bool&, copied from the entry in -22.4.2.1 [locale.num.get].

- - - - - -
-

19. "Noconv" definition too vague

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

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-

Duplicate of: 10

-

Discussion:

-

-In the definitions of codecvt<>::do_out and do_in, they are -specified to return noconv if "no conversion is -needed". This definition is too vague, and does not say -normatively what is done with the buffers. -

- - -

Proposed resolution:

-

-Change the entry for noconv in the table under paragraph 4 in section -22.4.1.4.2 [locale.codecvt.virtuals] to read: -

-
-

noconv: internT and externT are the same type, - and input sequence is identical to converted sequence.

-
-

Change the Note in paragraph 2 to normative text as follows:

-
-

If returns noconv, internT and externT are the - same type and the converted sequence is identical to the input sequence [from,from_next). - to_next is set equal to to, the value of state is - unchanged, and there are no changes to the values in [to, to_limit).

-
- - - - - -
-

20. Thousands_sep returns wrong type

-

Section: 22.4.3.1.2 [facet.numpunct.virtuals] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

-

The synopsis for numpunct<>::do_thousands_sep, and the -definition of numpunct<>::thousands_sep which calls it, specify -that it returns a value of type char_type. Here it is erroneously -described as returning a "string_type".

- - -

Proposed resolution:

-

In 22.4.3.1.2 [facet.numpunct.virtuals], above paragraph 2, change -"string_type" to "char_type".

- - - - - -
-

21. Codecvt_byname<> instantiations

-

Section: 22.3.1.1.1 [locale.category] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.category].

-

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-

Discussion:

-

In the second table in the section, captioned "Required -instantiations", the instantiations for codecvt_byname<> -have been omitted. These are necessary to allow users to construct a -locale by name from facets.

- - -

Proposed resolution:

-

Add in 22.3.1.1.1 [locale.category] to the table captioned -"Required instantiations", in the category "ctype" -the lines

- -
- 
codecvt_byname<char,char,mbstate_t>,
-codecvt_byname<wchar_t,char,mbstate_t>
-
- - - - - -
-

22. Member open vs. flags

-

Section: 27.9.1.9 [ifstream.members] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The description of basic_istream<>::open leaves unanswered questions about how it -responds to or changes flags in the error status for the stream. A strict reading -indicates that it ignores the bits and does not change them, which confuses users who do -not expect eofbit and failbit to remain set after a successful open. There are three -reasonable resolutions: 1) status quo 2) fail if fail(), ignore eofbit 3) clear failbit -and eofbit on call to open().

- - -

Proposed resolution:

-

In 27.9.1.9 [ifstream.members] paragraph 3, and in 27.9.1.13 [ofstream.members] paragraph 3, under open() effects, add a footnote: -

- -
-

A successful open does not change the error state.

-
- - -

Rationale:

-

This may seem surprising to some users, but it's just an instance -of a general rule: error flags are never cleared by the -implementation. The only way error flags are are ever cleared is if -the user explicitly clears them by hand.

- -

The LWG believed that preserving this general rule was -important enough so that an exception shouldn't be made just for this -one case. The resolution of this issue clarifies what the LWG -believes to have been the original intent.

- - - - - - -
-

23. Num_get overflow result

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

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-

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-

Discussion:

-

The current description of numeric input does not account for the -possibility of overflow. This is an implicit result of changing the -description to rely on the definition of scanf() (which fails to -report overflow), and conflicts with the documented behavior of -traditional and current implementations.

- -

Users expect, when reading a character sequence that results in a -value unrepresentable in the specified type, to have an error -reported. The standard as written does not permit this.

- -

Further comments from Dietmar:

- -

-I don't feel comfortable with the proposed resolution to issue 23: It -kind of simplifies the issue to much. Here is what is going on: -

- -

-Currently, the behavior of numeric overflow is rather counter intuitive -and hard to trace, so I will describe it briefly: -

- -
    -
  • - According to 22.4.2.1.2 [facet.num.get.virtuals] - paragraph 11 failbit is set if scanf() would - return an input error; otherwise a value is converted to the rules - of scanf. -
    • -
  • - scanf() is defined in terms of fscanf(). -
    • -
  • - fscanf() returns an input failure if during conversion no - character matching the conversion specification could be extracted - before reaching EOF. This is the only reason for fscanf() - to fail due to an input error and clearly does not apply to the case - of overflow. -
    • -
  • - Thus, the conversion is performed according to the rules of - fscanf() which basically says that strtod, - strtol(), etc. are to be used for the conversion. -
    • -
  • - The strtod(), strtol(), etc. functions consume as - many matching characters as there are and on overflow continue to - consume matching characters but also return a value identical to - the maximum (or minimum for signed types if there was a leading minus) - value of the corresponding type and set errno to ERANGE. -
    • -
  • - Thus, according to the current wording in the standard, overflows - can be detected! All what is to be done is to check errno - after reading an element and, of course, clearing errno - before trying a conversion. With the current wording, it can be - detected whether the overflow was due to a positive or negative - number for signed types. -
    • -
- -

Further discussion from Redmond:

- -

The basic problem is that we've defined our behavior, -including our error-reporting behavior, in terms of C90. However, -C90's method of reporting overflow in scanf is not technically an -"input error". The strto_* functions are more precise.

- -

There was general consensus that failbit should be set -upon overflow. We considered three options based on this:

-
    -
  1. Set failbit upon conversion error (including overflow), and - don't store any value.
    2. -
  2. Set failbit upon conversion error, and also set errno to - indicated the precise nature of the error.
    3. -
  3. Set failbit upon conversion error. If the error was due to - overflow, store +-numeric_limits<T>::max() as an - overflow indication.
    4. -
- -

Straw poll: (1) 5; (2) 0; (3) 8.

- - -

Discussed at Lillehammer. General outline of what we want the - solution to look like: we want to say that overflow is an error, and - provide a way to distinguish overflow from other kinds of errors. - Choose candidate field the same way scanf does, but don't describe - the rest of the process in terms of format. If a finite input field - is too large (positive or negative) to be represented as a finite - value, then set failbit and assign the nearest representable value. - Bill will provide wording.

- -

-Discussed at Toronto: -N2327 -is in alignment with the direction we wanted to go with in Lillehammer. Bill -to work on. -

- - - -

Proposed resolution:

- -

-Change 22.4.2.1.2 [facet.num.get.virtuals], end of p3: -

- -
-

-Stage 3: The result of stage 2 processing can be one of -The sequence of chars accumulated in stage 2 (the field) is -converted to a numeric value by the rules of one of the functions declared -in the header <cstdlib>: -

-
    -
  • -A sequence of chars has been accumulated in stage 2 that is -converted (according to the rules of scanf) to a value of the -type of val. This value is stored in val and ios_base::goodbit is -stored in err. -For a signed integer value, the function strtoll. -
    • -
  • -The sequence of chars accumulated in stage 2 would have caused -scanf to report an input failure. ios_base::failbit is -assigned to err. -For an unsigned integer value, the function strtoull. -
    • -
  • -For a floating-point value, the function strtold. -
    • -
-

-The numeric value to be stored can be one of: -

-
    -
  • zero, if the conversion function fails to convert the entire field. -ios_base::failbit is assigned to err.
    • -
  • the most positive representable value, if the field represents a value -too large positive to be represented in val. ios_base::failbit is assigned -to err.
    • -
  • the most negative representable value (zero for unsigned integer), if -the field represents a value too large negative to be represented in val. -ios_base::failbit is assigned to err.
    • -
  • the converted value, otherwise.
    • -
- -

-The resultant numeric value is stored in val. -

-
- -

-Change 22.4.2.1.2 [facet.num.get.virtuals], p6-p7: -

- -
-
-iter_type do_get(iter_type in, iter_type end, ios_base& str, 
-                 ios_base::iostate& err, bool& val) const;
-
-
-

--6- Effects: If -(str.flags()&ios_base::boolalpha)==0 then input -proceeds as it would for a long except that if a value is being -stored into val, the value is determined according to the -following: If the value to be stored is 0 then false is stored. -If the value is 1 then true is stored. Otherwise -err|=ios_base::failbit is performed and no value true is -stored. and ios_base::failbit is assigned to err. -

-

--7- Otherwise target sequences are determined "as if" by calling the -members falsename() and truename() of the facet -obtained by use_facet<numpunct<charT> ->(str.getloc()). Successive characters in the range -[in,end) (see 23.1.1) are obtained and matched -against corresponding positions in the target sequences only as -necessary to identify a unique match. The input iterator in is -compared to end only when necessary to obtain a character. If and -only if a target sequence is uniquely matched, val is set to the -corresponding value. Otherwise false is stored and ios_base::failbit -is assigned to err. -

-
-
- - - - - -
-

24. "do_convert" doesn't exist

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

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-

Duplicate of: 72

-

Discussion:

-

The description of codecvt<>::do_out and do_in mentions a -symbol "do_convert" which is not defined in the -standard. This is a leftover from an edit, and should be "do_in -and do_out".

- - -

Proposed resolution:

-

In 22.4.1.4 [locale.codecvt], paragraph 3, change -"do_convert" to "do_in or do_out". Also, in 22.4.1.4.2 [locale.codecvt.virtuals], change "do_convert()" to "do_in -or do_out".

- - - - - -
-

25. String operator<< uses width() value wrong

-

Section: 21.4.8.9 [string.io] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [string.io].

-

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-

Duplicate of: 67

-

Discussion:

-

In the description of operator<< applied to strings, the standard says that uses -the smaller of os.width() and str.size(), to pad "as described in stage 3" -elsewhere; but this is inconsistent, as this allows no possibility of space for padding.

- - -

Proposed resolution:

-

Change 21.4.8.9 [string.io] paragraph 4 from:
-
-    "... where n is the smaller of os.width() and str.size(); -..."
-
-to:
-
-    "... where n is the larger of os.width() and str.size(); -..."

- - - - - -
-

26. Bad sentry example

-

Section: 27.7.2.1.3 [istream::sentry] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [istream::sentry].

-

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-

Discussion:

-

In paragraph 6, the code in the example:

- -
  template <class charT, class traits = char_traits<charT> >
-  basic_istream<charT,traits>::sentry(
-           basic_istream<charT,traits>& is, bool noskipws = false) {
-      ...
-      int_type c;
-      typedef ctype<charT> ctype_type;
-      const ctype_type& ctype = use_facet<ctype_type>(is.getloc());
-      while ((c = is.rdbuf()->snextc()) != traits::eof()) {
-        if (ctype.is(ctype.space,c)==0) {
-          is.rdbuf()->sputbackc (c);
-          break;
-        }
-      }
-      ...
-   }
- -

fails to demonstrate correct use of the facilities described. In -particular, it fails to use traits operators, and specifies incorrect -semantics. (E.g. it specifies skipping over the first character in the -sequence without examining it.)

- - -

Proposed resolution:

-

Remove the example above from 27.7.2.1.3 [istream::sentry] -paragraph 6.

- - -

Rationale:

-

The originally proposed replacement code for the example was not -correct. The LWG tried in Kona and again in Tokyo to correct it -without success. In Tokyo, an implementor reported that actual working -code ran over one page in length and was quite complicated. The LWG -decided that it would be counter-productive to include such a lengthy -example, which might well still contain errors.

- - - - - -
-

27. String::erase(range) yields wrong iterator

-

Section: 21.4.6.5 [string::erase] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [string::erase].

-

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-

Discussion:

-

The string::erase(iterator first, iterator last) is specified to return an element one -place beyond the next element after the last one erased. E.g. for the string -"abcde", erasing the range ['b'..'d') would yield an iterator for element 'e', -while 'd' has not been erased.

- - -

Proposed resolution:

-

In 21.4.6.5 [string::erase], paragraph 10, change:

- -
-

Returns: an iterator which points to the element immediately following _last_ prior to - the element being erased.

-
- -

to read

- -
-

Returns: an iterator which points to the element pointed to by _last_ prior to the - other elements being erased.

-
- - - - - -
-

28. Ctype<char>is ambiguous

-

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [facet.ctype.char.members].

-

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-

Duplicate of: 236

-

Discussion:

-

The description of the vector form of ctype<char>::is can be interpreted to mean -something very different from what was intended. Paragraph 4 says

- -
-

Effects: The second form, for all *p in the range [low, high), assigns vec[p-low] to - table()[(unsigned char)*p].

-
- -

This is intended to copy the value indexed from table()[] into the place identified in -vec[].

- - -

Proposed resolution:

-

Change 22.4.1.3.2 [facet.ctype.char.members], paragraph 4, to read

- -
-

Effects: The second form, for all *p in the range [low, high), assigns into vec[p-low] - the value table()[(unsigned char)*p].

-
- - - - - -
-

29. Ios_base::init doesn't exist

-

Section: 27.4.2 [narrow.stream.objects] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [narrow.stream.objects].

-

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-

Discussion:

-

Sections 27.4.2 [narrow.stream.objects] and 27.4.3 [wide.stream.objects] mention -a function ios_base::init, which is not defined. Probably they mean -basic_ios<>::init, defined in 27.5.5.2 [basic.ios.cons], -paragraph 3.

- - -

Proposed resolution:

-

[R12: modified to include paragraph 5.]

- -

In 27.4.2 [narrow.stream.objects] paragraph 2 and 5, change

- -
-

ios_base::init

-
- -

to

- -
-

basic_ios<char>::init

-
- -

Also, make a similar change in 27.4.3 [wide.stream.objects] except it -should read

- -
-

basic_ios<wchar_t>::init

-
- - - - - -
-

30. Wrong header for LC_*

-

Section: 22.3.1.1.1 [locale.category] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.category].

-

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-

Discussion:

-

Paragraph 2 implies that the C macros LC_CTYPE etc. are defined in <cctype>, -where they are in fact defined elsewhere to appear in <clocale>.

- - -

Proposed resolution:

-

In 22.3.1.1.1 [locale.category], paragraph 2, change -"<cctype>" to read "<clocale>".

- - - - - -
-

31. Immutable locale values

-

Section: 22.3.1 [locale] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale].

-

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-

Duplicate of: 378

-

Discussion:

-

Paragraph 6, says "An instance of locale is -immutable; once a facet reference is obtained from it, -...". This has caused some confusion, because locale variables -are manifestly assignable.

- - -

Proposed resolution:

-

In 22.3.1 [locale] replace paragraph 6

- -
-

An instance of locale is immutable; once a facet - reference is obtained from it, that reference remains usable as long - as the locale value itself exists.

-
- -

with

- -
-

Once a facet reference is obtained from a locale object by - calling use_facet<>, that reference remains usable, and the - results from member functions of it may be cached and re-used, as - long as some locale object refers to that facet.

-
- - - - - -
-

32. Pbackfail description inconsistent

-

Section: 27.6.3.4.4 [streambuf.virt.pback] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

-

The description of the required state before calling virtual member -basic_streambuf<>::pbackfail requirements is inconsistent with the conditions -described in 27.5.2.2.4 [lib.streambuf.pub.pback] where member sputbackc calls it. -Specifically, the latter says it calls pbackfail if:

- -

    traits::eq(c,gptr()[-1]) is false

- -

where pbackfail claims to require:

- -

    traits::eq(*gptr(),traits::to_char_type(c)) returns false

- -

It appears that the pbackfail description is wrong.

- - -

Proposed resolution:

-

In 27.6.3.4.4 [streambuf.virt.pback], paragraph 1, change:

- -
-

"traits::eq(*gptr(),traits::to_char_type( c))"

-
- -

to

- -
-

"traits::eq(traits::to_char_type(c),gptr()[-1])" -

-
- - -

Rationale:

-

Note deliberate reordering of arguments for clarity in addition to the correction of -the argument value.

- - - - - -
-

33. Codecvt<> mentions from_type

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt].

-

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-

Duplicate of: 43

-

Discussion:

-

In the table defining the results from do_out and do_in, the specification for the -result error says

- -
-

encountered a from_type character it could not convert

-
- -

but from_type is not defined. This clearly is intended to be an externT for do_in, or -an internT for do_out.

- - -

Proposed resolution:

-

In 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 4, replace the definition -in the table for the case of _error_ with

- -
-

encountered a character in [from,from_end) that it could not convert.

-
- - - - - -
-

34. True/falsename() not in ctype<>

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [facet.num.put.virtuals].

-

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-

Discussion:

-

In paragraph 19, Effects:, members truename() and falsename are used from facet -ctype<charT>, but it has no such members. Note that this is also a problem in -22.2.2.1.2, addressed in (4).

- - -

Proposed resolution:

-

In 22.4.2.2.2 [facet.num.put.virtuals], paragraph 19, in the Effects: -clause for member put(...., bool), replace the initialization of the -string_type value s as follows:

- -
- 
const numpunct& np = use_facet<numpunct<charT> >(loc);
-string_type s = val ? np.truename() : np.falsename();
-
- - - - - -
-

35. No manipulator unitbuf in synopsis

-

Section: 27.5 [iostreams.base] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [iostreams.base].

-

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-

Discussion:

-

In 27.5.6.1 [fmtflags.manip], we have a definition for a manipulator -named "unitbuf". Unlike other manipulators, it's not listed -in synopsis. Similarly for "nounitbuf".

- - -

Proposed resolution:

-

Add to the synopsis for <ios> in 27.5 [iostreams.base], after -the entry for "nouppercase", the prototypes:

- -
- 
ios_base& unitbuf(ios_base& str);
-ios_base& nounitbuf(ios_base& str);
-
- - - - - -
-

36. Iword & pword storage lifetime omitted

-

Section: 27.5.3.5 [ios.base.storage] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [ios.base.storage].

-

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-

Discussion:

-

In the definitions for ios_base::iword and pword, the lifetime of the storage is -specified badly, so that an implementation which only keeps the last value stored appears -to conform. In particular, it says:

- -

The reference returned may become invalid after another call to the object's iword -member with a different index ...

- -

This is not idle speculation; at least one implementation was done this way.

- - -

Proposed resolution:

-

Add in 27.5.3.5 [ios.base.storage], in both paragraph 2 and also in -paragraph 4, replace the sentence:

- -
-

The reference returned may become invalid after another call to the object's iword - [pword] member with a different index, after a call to its copyfmt member, or when the - object is destroyed.

-
- -

with:

- -
-

The reference returned is invalid after any other operations on the object. However, - the value of the storage referred to is retained, so that until the next call to copyfmt, - calling iword [pword] with the same index yields another reference to the same value.

-
- -

substituting "iword" or "pword" as appropriate.

- - - - - -
-

37. Leftover "global" reference

-

Section: 22.3.1 [locale] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [locale].

-

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-

Discussion:

-

In the overview of locale semantics, paragraph 4, is the sentence

- -
-

If Facet is not present in a locale (or, failing that, in the global locale), it throws - the standard exception bad_cast.

-
- -

This is not supported by the definition of use_facet<>, and represents semantics -from an old draft.

- - -

Proposed resolution:

-

In 22.3.1 [locale], paragraph 4, delete the parenthesized -expression

- -
-

(or, failing that, in the global locale)

-
- - - - - -
-

38. Facet definition incomplete

-

Section: 22.3.2 [locale.global.templates] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

-

It has been noticed by Esa Pulkkinen that the definition of -"facet" is incomplete. In particular, a class derived from -another facet, but which does not define a member id, cannot -safely serve as the argument F to use_facet<F>(loc), -because there is no guarantee that a reference to the facet instance -stored in loc is safely convertible to F.

- - -

Proposed resolution:

-

In the definition of std::use_facet<>(), replace the text in paragraph 1 which -reads:

- -
-

Get a reference to a facet of a locale.

-
- -

with:

- -
-

Requires: Facet is a facet class whose definition - contains the public static member id as defined in 22.3.1.1.2 [locale.facet].

-
- -

[ -Kona: strike as overspecification the text "(not inherits)" -from the original resolution, which read "... whose definition -contains (not inherits) the public static member -id..." -]

- - - - - - - -
-

39. istreambuf_iterator<>::operator++(int) definition garbled

-

Section: 24.6.3.4 [istreambuf.iterator::op++] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

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-

Discussion:

-

Following the definition of istreambuf_iterator<>::operator++(int) in paragraph -3, the standard contains three lines of garbage text left over from a previous edit.

- -
- 
istreambuf_iterator<charT,traits> tmp = *this;
-sbuf_->sbumpc();
-return(tmp);
-
- - -

Proposed resolution:

-

In 24.6.3.4 [istreambuf.iterator::op++], delete the three lines of code at the -end of paragraph 3.

- - - - - -
-

40. Meaningless normative paragraph in examples

-

Section: 22.4.8 [facets.examples] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [facets.examples].

-

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-

Discussion:

-

Paragraph 3 of the locale examples is a description of part of an -implementation technique that has lost its referent, and doesn't mean -anything.

- - -

Proposed resolution:

-

Delete 22.4.8 [facets.examples] paragraph 3 which begins "This -initialization/identification system depends...", or (at the -editor's option) replace it with a place-holder to keep the paragraph -numbering the same.

- - - - - -
-

41. Ios_base needs clear(), exceptions()

-

Section: 27.5.3 [ios.base] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [ios.base].

-

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-

Duplicate of: 157

-

Discussion:

-

The description of ios_base::iword() and pword() in 27.5.3.4 [ios.members.static], say that if they fail, they "set badbit, -which may throw an exception". However, ios_base offers no -interface to set or to test badbit; those interfaces are defined in -basic_ios<>.

- - -

Proposed resolution:

-

Change the description in 27.5.3.5 [ios.base.storage] in -paragraph 2, and also in paragraph 4, as follows. Replace

- -
-

If the function fails it sets badbit, which may throw an exception.

-
- -

with

- -
-

If the function fails, and *this is a base sub-object of - a basic_ios<> object or sub-object, the effect is - equivalent to calling basic_ios<>::setstate(badbit) - on the derived object (which may throw failure).

-
- -

[Kona: LWG reviewed wording; setstate(failbit) changed to -setstate(badbit).]

- - - - - - - -
-

42. String ctors specify wrong default allocator

-

Section: 21.4 [basic.string] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

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-

Discussion:

-

The basic_string<> copy constructor:

- -
basic_string(const basic_string& str, size_type pos = 0,
-             size_type n = npos, const Allocator& a = Allocator());
- -

specifies an Allocator argument default value that is -counter-intuitive. The natural choice for a the allocator to copy from -is str.get_allocator(). Though this cannot be expressed in -default-argument notation, overloading suffices.

- -

Alternatively, the other containers in Clause 23 (deque, list, -vector) do not have this form of constructor, so it is inconsistent, -and an evident source of confusion, for basic_string<> to have -it, so it might better be removed.

- - -

Proposed resolution:

-

In 21.4 [basic.string], replace the declaration of the copy -constructor as follows:

- -
- 
basic_string(const basic_string& str);
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-             const Allocator& a = Allocator());
-
- -

In 21.4.1 [string.require], replace the copy constructor declaration -as above. Add to paragraph 5, Effects:

- -
-

In the first form, the Allocator value used is copied from - str.get_allocator().

-
- - -

Rationale:

-

The LWG believes the constructor is actually broken, rather than -just an unfortunate design choice.

- -

The LWG considered two other possible resolutions:

- -

A. In 21.4 [basic.string], replace the declaration of the copy -constructor as follows:

- -
- 
basic_string(const basic_string& str, size_type pos = 0,
-             size_type n = npos);
-basic_string(const basic_string& str, size_type pos,
-             size_type n, const Allocator& a);
-
- -

In 21.4.1 [string.require], replace the copy constructor declaration -as above. Add to paragraph 5, Effects:

- -
-

When no Allocator argument is provided, the string is constructed using the - value str.get_allocator().

-
- -

B. In 21.4 [basic.string], and also in 21.4.1 [string.require], replace -the declaration of the copy constructor as follows:

- -
- 
basic_string(const basic_string& str, size_type pos = 0,
-             size_type n = npos);
-
- -

The proposed resolution reflects the original intent of the LWG. It -was also noted by Pete Becker that this fix "will cause -a small amount of existing code to now work correctly."

- -

[ -Kona: issue editing snafu fixed - the proposed resolution now correctly -reflects the LWG consensus. -]

- - - - - - -
-

44. Iostreams use operator== on int_type values

-

Section: 27 [input.output] Status: CD1 - Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2015-04-08

-

View all other issues in [input.output].

-

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-

Discussion:

-

Many of the specifications for iostreams specify that character -values or their int_type equivalents are compared using operators == -or !=, though in other places traits::eq() or traits::eq_int_type is -specified to be used throughout. This is an inconsistency; we should -change uses of == and != to use the traits members instead.

- - -

Proposed resolution:

- -

[Pre-Kona: Dietmar supplied wording]

- - -

List of changes to clause 27:

-
    -
  1. - In lib.basic.ios.members paragraph 13 (postcondition clause for - 'fill(cT)') change - -
    -     fillch == fill()
-
    - - to - -
    -     traits::eq(fillch, fill())
-
    - - -
    2. -
  2. - In lib.istream.unformatted paragraph 7 (effects clause for - 'get(cT,streamsize,cT)'), third bullet, change - -
    -     c == delim for the next available input character c
-
    - - to - -
    -     traits::eq(c, delim) for the next available input character c
-
    - -
    3. -
  3. - In lib.istream.unformatted paragraph 12 (effects clause for - 'get(basic_streambuf<cT,Tr>&,cT)'), third bullet, change - -
    -     c == delim for the next available input character c
-
    - - to - -
    -     traits::eq(c, delim) for the next available input character c
-
    - -
    4. -
  4. - In lib.istream.unformatted paragraph 17 (effects clause for - 'getline(cT,streamsize,cT)'), second bullet, change - -
    -     c == delim for the next available input character c
-
    - - to - -
    -     traits::eq(c, delim) for the next available input character c
-
    - -
    5. -
  5. - In lib.istream.unformatted paragraph 24 (effects clause for - 'ignore(int,int_type)'), second bullet, change - -
    -     c == delim for the next available input character c
-
    - - to - -
    -     traits::eq_int_type(c, delim) for the next available input
-     character c
-
    - -
    6. -
  6. - In lib.istream.unformatted paragraph 25 (notes clause for - 'ignore(int,int_type)'), second bullet, change - -
    -     The last condition will never occur if delim == traits::eof()
-
    - - to - -
    -     The last condition will never occur if
-     traits::eq_int_type(delim, traits::eof()).
-
    - -
    7. -
  7. - In lib.istream.sentry paragraph 6 (example implementation for the - sentry constructor) change - -
    -     while ((c = is.rdbuf()->snextc()) != traits::eof()) {
-
    - - to - -
    -     while (!traits::eq_int_type(c = is.rdbuf()->snextc(), traits::eof())) {
-
    - -
    8. -
- -

List of changes to Chapter 21:

- -
    -
  1. - In lib.string::find paragraph 1 (effects clause for find()), - second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    - -
    2. -
  2. - In lib.string::rfind paragraph 1 (effects clause for rfind()), - second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    - -
    3. -
  3. - In lib.string::find.first.of paragraph 1 (effects clause for - find_first_of()), second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    - -
    4. -
  4. - In lib.string::find.last.of paragraph 1 (effects clause for - find_last_of()), second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    - -
    5. -
  5. - In lib.string::find.first.not.of paragraph 1 (effects clause for - find_first_not_of()), second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    -
    6. - -
  6. - In lib.string::find.last.not.of paragraph 1 (effects clause for - find_last_not_of()), second bullet, change - -
    -     at(xpos+I) == str.at(I) for all elements ...
-
    - - to - -
    -     traits::eq(at(xpos+I), str.at(I)) for all elements ...
-
    -
    7. - -
  7. - In lib.string.ios paragraph 5 (effects clause for getline()), - second bullet, change - -
    -     c == delim for the next available input character c 
-
    - - to - -
    -     traits::eq(c, delim) for the next available input character c 
-
    -
    8. - -
- -

Notes:

-
    -
  • - Fixing this issue highlights another sloppyness in - lib.istream.unformatted paragraph 24: this clause mentions a "character" - which is then compared to an 'int_type' (see item 5. in the list - below). It is not clear whether this requires explicit words and - if so what these words are supposed to be. A similar issue exists, - BTW, for operator*() of istreambuf_iterator which returns the result - of sgetc() as a character type (see lib.istreambuf.iterator::op* - paragraph 1), and for operator++() of istreambuf_iterator which - passes the result of sbumpc() to a constructor taking a char_type - (see lib.istreambuf.iterator::operator++ paragraph 3). Similarily, the - assignment operator ostreambuf_iterator passes a char_type to a function - taking an int_type (see lib.ostreambuf.iter.ops paragraph 1). -
    • -
  • - It is inconsistent to use comparisons using the traits functions in - Chapter 27 while not using them in Chapter 21, especially as some - of the inconsistent uses actually involve streams (eg. getline() on - streams). To avoid leaving this issue open still longer due to this - inconsistency (it is open since 1998), a list of changes to Chapter - 21 is below. -
    • -
  • - In Chapter 24 there are several places with statements like "the end - of stream is reached (streambuf_type::sgetc() returns traits::eof())" - (lib.istreambuf.iterator paragraph 1, lib.ostreambuf.iter.ops - paragraph 5). It is unclear whether these should be clarified to use - traits::eq_int_type() for detecting traits::eof(). -
    • -
- - - - - - -
-

46. Minor Annex D errors

-

Section: D.7 [depr.str.strstreams] Status: TC1 - Submitter: Brendan Kehoe Opened: 1998-06-01 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

See lib-6522 and edit-814.

- -

Proposed resolution:

-

Change D.7.1 [depr.strstreambuf] (since streambuf is a typedef of -basic_streambuf<char>) from:

- -
         virtual streambuf<char>* setbuf(char* s, streamsize n);
- -

to:

- -
         virtual streambuf* setbuf(char* s, streamsize n);
- -

In D.7.4 [depr.strstream] insert the semicolon now missing after -int_type:

- -
     namespace std {
-       class strstream
-         : public basic_iostream<char> {
-       public:
-         // Types
-         typedef char                                char_type;
-         typedef typename char_traits<char>::int_type int_type
-         typedef typename char_traits<char>::pos_type pos_type;
- - - - - -
-

47. Imbue() and getloc() Returns clauses swapped

-

Section: 27.5.3.3 [ios.base.locales] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Section 27.4.2.3 specifies how imbue() and getloc() work. That -section has two RETURNS clauses, and they make no sense as -stated. They make perfect sense, though, if you swap them. Am I -correct in thinking that paragraphs 2 and 4 just got mixed up by -accident?

- - -

Proposed resolution:

-

In 27.5.3.3 [ios.base.locales] swap paragraphs 2 and 4.

- - - - - -
-

48. Use of non-existent exception constructor

-

Section: 27.5.3.1.1 [ios::failure] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

27.4.2.1.1, paragraph 2, says that class failure initializes the -base class, exception, with exception(msg). Class exception (see -18.6.1) has no such constructor.

- - -

Proposed resolution:

-

Replace 27.5.3.1.1 [ios::failure], paragraph 2, with

- -
-

EFFECTS: Constructs an object of class failure.

-
- - - - - -
-

49. Underspecification of ios_base::sync_with_stdio

-

Section: 27.5.3.4 [ios.members.static] Status: CD1 - Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2015-04-08

-

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-

Discussion:

-

Two problems

- -

(1) 27.4.2.4 doesn't say what ios_base::sync_with_stdio(f) -returns. Does it return f, or does it return the previous -synchronization state? My guess is the latter, but the standard -doesn't say so.

- -

(2) 27.4.2.4 doesn't say what it means for streams to be -synchronized with stdio. Again, of course, I can make some -guesses. (And I'm unhappy about the performance implications of those -guesses, but that's another matter.)

- - -

Proposed resolution:

-

Change the following sentence in 27.5.3.4 [ios.members.static] -returns clause from:

- -
-

true if the standard iostream objects (27.3) are - synchronized and otherwise returns false.

-
- -

to:

- -
-

true if the previous state of the standard iostream - objects (27.3) was synchronized and otherwise returns - false.

-
- -

Add the following immediately after 27.5.3.4 [ios.members.static], -paragraph 2:

- -
-

When a standard iostream object str is synchronized with a -standard stdio stream f, the effect of inserting a character c by

-
-  fputc(f, c);
-
- -

is the same as the effect of

-
-  str.rdbuf()->sputc(c);
-
- -

for any sequence of characters; the effect of extracting a -character c by

-
-  c = fgetc(f);
-
- -

is the same as the effect of:

-
-  c = str.rdbuf()->sbumpc(c);
-
- -

for any sequences of characters; and the effect of pushing -back a character c by

-
-  ungetc(c, f);
-
- -

is the same as the effect of

-
-  str.rdbuf()->sputbackc(c);
-
- -

for any sequence of characters. [Footnote: This implies -that operations on a standard iostream object can be mixed arbitrarily -with operations on the corresponding stdio stream. In practical -terms, synchronization usually means that a standard iostream object -and a standard stdio object share a buffer. --End Footnote]

-
- -

[pre-Copenhagen: PJP and Matt contributed the definition -of "synchronization"]

- - -

[post-Copenhagen: proposed resolution was revised slightly: -text was added in the non-normative footnote to say that operations -on the two streams can be mixed arbitrarily.]

- - - - - - -
-

50. Copy constructor and assignment operator of ios_base

-

Section: 27.5.3 [ios.base] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

As written, ios_base has a copy constructor and an assignment -operator. (Nothing in the standard says it doesn't have one, and all -classes have copy constructors and assignment operators unless you -take specific steps to avoid them.) However, nothing in 27.4.2 says -what the copy constructor and assignment operator do.

- -

My guess is that this was an oversight, that ios_base is, like -basic_ios, not supposed to have a copy constructor or an assignment -operator.

- -

-Jerry Schwarz comments: Yes, its an oversight, but in the opposite -sense to what you're suggesting. At one point there was a definite -intention that you could copy ios_base. It's an easy way to save the -entire state of a stream for future use. As you note, to carry out -that intention would have required a explicit description of the -semantics (e.g. what happens to the iarray and parray stuff). -

- - -

Proposed resolution:

-

In 27.5.3 [ios.base], class ios_base, specify the copy -constructor and operator= members as being private.

- - -

Rationale:

-

The LWG believes the difficulty of specifying correct semantics -outweighs any benefit of allowing ios_base objects to be copyable.

- - - - - -
-

51. Requirement to not invalidate iterators missing

-

Section: 23.2 [container.requirements] Status: TC1 - Submitter: David Vandevoorde Opened: 1998-06-23 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

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-

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-

Discussion:

-

The std::sort algorithm can in general only sort a given sequence -by moving around values. The list<>::sort() member on the other -hand could move around values or just update internal pointers. Either -method can leave iterators into the list<> dereferencable, but -they would point to different things.

- -

Does the FDIS mandate anywhere which method should be used for -list<>::sort()?

- -

Matt Austern comments:

- -

I think you've found an omission in the standard.

- -

The library working group discussed this point, and there was -supposed to be a general requirement saying that list, set, map, -multiset, and multimap may not invalidate iterators, or change the -values that iterators point to, except when an operation does it -explicitly. So, for example, insert() doesn't invalidate any iterators -and erase() and remove() only invalidate iterators pointing to the -elements that are being erased.

- -

I looked for that general requirement in the FDIS, and, while I -found a limited form of it for the sorted associative containers, I -didn't find it for list. It looks like it just got omitted.

- -

The intention, though, is that list<>::sort does not -invalidate any iterators and does not change the values that any -iterator points to. There would be no reason to have the member -function otherwise.

- - -

Proposed resolution:

-

Add a new paragraph at the end of 23.1:

- -
-

Unless otherwise specified (either explicitly or by defining a function in terms of - other functions), invoking a container member function or passing a container as an - argument to a library function shall not invalidate iterators to, or change the values of, - objects within that container.

-
- - -

Rationale:

-

This was US issue CD2-23-011; it was accepted in London but the -change was not made due to an editing oversight. The wording in the -proposed resolution below is somewhat updated from CD2-23-011, -particularly the addition of the phrase "or change the values -of"

- - - - - -
-

52. Small I/O problems

-

Section: 27.5.4.2 [fpos.operations] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-23 Last modified: 2015-04-08

-

View all other issues in [fpos.operations].

-

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-

Discussion:

-

First, 27.5.5.2 [basic.ios.cons], table 89. This is pretty obvious: -it should be titled "basic_ios<>() effects", not -"ios_base() effects".

- -

[The second item is a duplicate; see issue 6 for -resolution.]

- -

Second, 27.5.4.2 [fpos.operations] table 88 . There are a couple -different things wrong with it, some of which I've already discussed -with Jerry, but the most obvious mechanical sort of error is that it -uses expressions like P(i) and p(i), without ever defining what sort -of thing "i" is. -

- -

(The other problem is that it requires support for streampos -arithmetic. This is impossible on some systems, i.e. ones where file -position is a complicated structure rather than just a number. Jerry -tells me that the intention was to require syntactic support for -streampos arithmetic, but that it wasn't actually supposed to do -anything meaningful except on platforms, like Unix, where genuine -arithmetic is possible.)

- - -

Proposed resolution:

-

Change 27.5.5.2 [basic.ios.cons] table 89 title from -"ios_base() effects" to "basic_ios<>() -effects".

- - - - - -
-

53. Basic_ios destructor unspecified

-

Section: 27.5.5.2 [basic.ios.cons] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-23 Last modified: 2015-04-08

-

View all other issues in [basic.ios.cons].

-

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-

Discussion:

-

There's nothing in 27.4.4 saying what basic_ios's destructor does. -The important question is whether basic_ios::~basic_ios() destroys -rdbuf().

- - -

Proposed resolution:

-

Add after 27.5.5.2 [basic.ios.cons] paragraph 2:

- -
-

virtual ~basic_ios();

-

Notes: The destructor does not destroy rdbuf().

-
- - -

Rationale:

-

The LWG reviewed the additional question of whether or not -rdbuf(0) may set badbit. The answer is -clearly yes; it may be set via clear(). See 27.5.5.3 [basic.ios.members], paragraph 6. This issue was reviewed at length -by the LWG, which removed from the original proposed resolution a -footnote which incorrectly said "rdbuf(0) does not set -badbit".

- - - - - -
-

54. Basic_streambuf's destructor

-

Section: 27.6.3.1 [streambuf.cons] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The class synopsis for basic_streambuf shows a (virtual) -destructor, but the standard doesn't say what that destructor does. My -assumption is that it does nothing, but the standard should say so -explicitly.

- - -

Proposed resolution:

-

Add after 27.6.3.1 [streambuf.cons] paragraph 2:

- -
-

virtual  ~basic_streambuf();

-

Effects: None.

-
- - - - - -
-

55. Invalid stream position is undefined

-

Section: 27 [input.output] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-26 Last modified: 2015-04-08

-

View all other issues in [input.output].

-

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-

Discussion:

-

Several member functions in clause 27 are defined in certain -circumstances to return an "invalid stream position", a term -that is defined nowhere in the standard. Two places (27.5.2.4.2, -paragraph 4, and 27.8.1.4, paragraph 15) contain a cross-reference to -a definition in _lib.iostreams.definitions_, a nonexistent -section.

- -

I suspect that the invalid stream position is just supposed to be -pos_type(-1). Probably best to say explicitly in (for example) -27.5.2.4.2 that the return value is pos_type(-1), rather than to use -the term "invalid stream position", define that term -somewhere, and then put in a cross-reference.

- -

The phrase "invalid stream position" appears ten times in -the C++ Standard. In seven places it refers to a return value, and it -should be changed. In three places it refers to an argument, and it -should not be changed. Here are the three places where "invalid -stream position" should not be changed:

- -
-

27.8.2.4 [stringbuf.virtuals], paragraph 14
- 27.9.1.5 [filebuf.virtuals], paragraph 14
- D.7.1.3 [depr.strstreambuf.virtuals], paragraph 17 -

-
- - -

Proposed resolution:

-

In 27.6.3.4.2 [streambuf.virt.buffer], paragraph 4, change "Returns an -object of class pos_type that stores an invalid stream position -(_lib.iostreams.definitions_)" to "Returns -pos_type(off_type(-1))". -

- -

In 27.6.3.4.2 [streambuf.virt.buffer], paragraph 6, change "Returns -an object of class pos_type that stores an invalid stream -position" to "Returns pos_type(off_type(-1))".

- -

In 27.8.2.4 [stringbuf.virtuals], paragraph 13, change "the object -stores an invalid stream position" to "the return value is -pos_type(off_type(-1))".

- -

In 27.9.1.5 [filebuf.virtuals], paragraph 13, change "returns an -invalid stream position (27.4.3)" to "returns -pos_type(off_type(-1))"

- -

In 27.9.1.5 [filebuf.virtuals], paragraph 15, change "Otherwise -returns an invalid stream position (_lib.iostreams.definitions_)" -to "Otherwise returns pos_type(off_type(-1))" -

- -

In D.7.1.3 [depr.strstreambuf.virtuals], paragraph 15, change "the object -stores an invalid stream position" to "the return value is -pos_type(off_type(-1))"

- -

In D.7.1.3 [depr.strstreambuf.virtuals], paragraph 18, change "the object -stores an invalid stream position" to "the return value is -pos_type(off_type(-1))"

- - - - - -
-

56. Showmanyc's return type

-

Section: 27.6.3 [streambuf] Status: TC1 - Submitter: Matt Austern Opened: 1998-06-29 Last modified: 2015-04-08

-

View all other issues in [streambuf].

-

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-

Discussion:

-

The class summary for basic_streambuf<>, in 27.5.2, says that -showmanyc has return type int. However, 27.5.2.4.3 says that its -return type is streamsize.

- - -

Proposed resolution:

-

Change showmanyc's return type in the -27.6.3 [streambuf] class summary to streamsize.

- - - - - -
-

57. Mistake in char_traits

-

Section: 21.2.3.4 [char.traits.specializations.wchar.t] Status: TC1 - Submitter: Matt Austern Opened: 1998-07-01 Last modified: 2015-04-08

-

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-

Discussion:

-

21.1.3.2, paragraph 3, says "The types streampos and -wstreampos may be different if the implementation supports no shift -encoding in narrow-oriented iostreams but supports one or more shift -encodings in wide-oriented streams".

- -

That's wrong: the two are the same type. The <iosfwd> summary -in 27.2 says that streampos and wstreampos are, respectively, synonyms -for fpos<char_traits<char>::state_type> and -fpos<char_traits<wchar_t>::state_type>, and, flipping back -to clause 21, we see in 21.1.3.1 and 21.1.3.2 that -char_traits<char>::state_type and -char_traits<wchar_t>::state_type must both be mbstate_t.

- - -

Proposed resolution:

-

Remove the sentence in 21.2.3.4 [char.traits.specializations.wchar.t] paragraph 3 which -begins "The types streampos and wstreampos may be -different..." .

- - - - - -
-

59. Ambiguity in specification of gbump

-

Section: 27.6.3.3.2 [streambuf.get.area] Status: TC1 - Submitter: Matt Austern Opened: 1998-07-28 Last modified: 2015-04-08

-

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-

Discussion:

-

27.5.2.3.1 says that basic_streambuf::gbump() "Advances the -next pointer for the input sequence by n."

- -

The straightforward interpretation is that it is just gptr() += -n. An alternative interpretation, though, is that it behaves as if it -calls sbumpc n times. (The issue, of course, is whether it might ever -call underflow.) There is a similar ambiguity in the case of -pbump.

- -

(The "classic" AT&T implementation used the -former interpretation.)

- - -

Proposed resolution:

-

Change 27.6.3.3.2 [streambuf.get.area] paragraph 4 gbump effects from:

- -
-

Effects: Advances the next pointer for the input sequence by n.

-
- -

to:

- -
-

Effects: Adds n to the next pointer for the input sequence.

-
- -

Make the same change to 27.6.3.3.3 [streambuf.put.area] paragraph 4 pbump -effects.

- - - - - -
-

60. What is a formatted input function?

-

Section: 27.7.2.2.1 [istream.formatted.reqmts] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-03 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 162, 163, 166

-

Discussion:

-

Paragraph 1 of 27.6.1.2.1 contains general requirements for all -formatted input functions. Some of the functions defined in section -27.6.1.2 explicitly say that those requirements apply ("Behaves -like a formatted input member (as described in 27.6.1.2.1)"), but -others don't. The question: is 27.6.1.2.1 supposed to apply to -everything in 27.6.1.2, or only to those member functions that -explicitly say "behaves like a formatted input member"? Or -to put it differently: are we to assume that everything that appears -in a section called "Formatted input functions" really is a -formatted input function? I assume that 27.6.1.2.1 is intended to -apply to the arithmetic extractors (27.6.1.2.2), but I assume that it -is not intended to apply to extractors like

- -
    basic_istream& operator>>(basic_istream& (*pf)(basic_istream&));
- -

and

- -
    basic_istream& operator>>(basic_streammbuf*);
- -

There is a similar ambiguity for unformatted input, formatted output, and unformatted -output.

- -

Comments from Judy Ward: It seems like the problem is that the -basic_istream and basic_ostream operator <<()'s that are used -for the manipulators and streambuf* are in the wrong section and -should have their own separate section or be modified to make it clear -that the "Common requirements" listed in section 27.6.1.2.1 -(for basic_istream) and section 27.6.2.5.1 (for basic_ostream) do not -apply to them.

- -

Additional comments from Dietmar Kühl: It appears to be somewhat -nonsensical to consider the functions defined in 27.7.2.2.3 [istream::extractors] paragraphs 1 to 5 to be "Formatted input -function" but since these functions are defined in a section -labeled "Formatted input functions" it is unclear to me -whether these operators are considered formatted input functions which -have to conform to the "common requirements" from 27.7.2.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not -just ws, would skip whitespace unless noskipws is -set (... but setting noskipws using the manipulator syntax -would also skip whitespace :-)

It is not clear which functions -are to be considered unformatted input functions. As written, it seems -that all functions in 27.7.2.3 [istream.unformatted] are unformatted input -functions. However, it does not really make much sense to construct a -sentry object for gcount(), sync(), ... Also it is -unclear what happens to the gcount() if -eg. gcount(), putback(), unget(), or -sync() is called: These functions don't extract characters, -some of them even "unextract" a character. Should this still -be reflected in gcount()? Of course, it could be read as if -after a call to gcount() gcount() return 0 -(the last unformatted input function, gcount(), didn't -extract any character) and after a call to putback() -gcount() returns -1 (the last unformatted input -function putback() did "extract" back into the -stream). Correspondingly for unget(). Is this what is -intended? If so, this should be clarified. Otherwise, a corresponding -clarification should be used.

- - -

Proposed resolution:

-

-In 27.6.1.2.2 [lib.istream.formatted.arithmetic], paragraph 1. -Change the beginning of the second sentence from "The conversion -occurs" to "These extractors behave as formatted input functions (as -described in 27.6.1.2.1). After a sentry object is constructed, -the conversion occurs" -

- -

-In 27.6.1.2.3, [lib.istream::extractors], before paragraph 1. -Add an effects clause. "Effects: None. This extractor does -not behave as a formatted input function (as described in -27.6.1.2.1). -

- -

-In 27.6.1.2.3, [lib.istream::extractors], paragraph 2. Change the -effects clause to "Effects: Calls pf(*this). This extractor does not -behave as a formatted input function (as described in 27.6.1.2.1). -

- -

-In 27.6.1.2.3, [lib.istream::extractors], paragraph 4. Change the -effects clause to "Effects: Calls pf(*this). This extractor does not -behave as a formatted input function (as described in 27.6.1.2.1). -

- -

-In 27.6.1.2.3, [lib.istream::extractors], paragraph 12. Change the -first two sentences from "If sb is null, calls setstate(failbit), -which may throw ios_base::failure (27.4.4.3). Extracts characters -from *this..." to "Behaves as a formatted input function (as described -in 27.6.1.2.1). If sb is null, calls setstate(failbit), which may -throw ios_base::failure (27.4.4.3). After a sentry object is -constructed, extracts characters from *this...". -

- -

-In 27.6.1.3, [lib.istream.unformatted], before paragraph 2. Add an -effects clause. "Effects: none. This member function does not behave -as an unformatted input function (as described in 27.6.1.3, paragraph 1)." -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 3. Change the -beginning of the first sentence of the effects clause from "Extracts a -character" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts a -character" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 5. Change the -beginning of the first sentence of the effects clause from "Extracts a -character" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts a -character" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 7. Change the -beginning of the first sentence of the effects clause from "Extracts -characters" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts -characters" -

- -

-[No change needed in paragraph 10, because it refers to paragraph 7.] -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 12. Change the -beginning of the first sentence of the effects clause from "Extracts -characters" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts -characters" -

- -

-[No change needed in paragraph 15.] -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 17. Change the -beginning of the first sentence of the effects clause from "Extracts -characters" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts -characters" -

- -

-[No change needed in paragraph 23.] -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 24. Change the -beginning of the first sentence of the effects clause from "Extracts -characters" to "Behaves as an unformatted input function (as described -in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts -characters" -

- -

-In 27.6.1.3, [lib.istream.unformatted], before paragraph 27. Add an -Effects clause: "Effects: Behaves as an unformatted input function (as -described in 27.6.1.3, paragraph 1). After constructing a sentry -object, reads but does not extract the current input character." -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 28. Change the -first sentence of the Effects clause from "If !good() calls" to -Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1). After constructing a sentry object, if !good() calls" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 30. Change the -first sentence of the Effects clause from "If !good() calls" to -"Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1). After constructing a sentry object, if !good() calls" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 32. Change the -first sentence of the Effects clause from "If !good() calls..." to -"Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1). After constructing a sentry object, if !good() -calls..." Add a new sentence to the end of the Effects clause: -"[Note: this function extracts no characters, so the value returned -by the next call to gcount() is 0.]" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 34. Change the -first sentence of the Effects clause from "If !good() calls" to -"Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1). After constructing a sentry object, if !good() calls". -Add a new sentence to the end of the Effects clause: "[Note: this -function extracts no characters, so the value returned by the next -call to gcount() is 0.]" -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 36. Change the -first sentence of the Effects clause from "If !rdbuf() is" to "Behaves -as an unformatted input function (as described in 27.6.1.3, paragraph -1), except that it does not count the number of characters extracted -and does not affect the value returned by subsequent calls to -gcount(). After constructing a sentry object, if rdbuf() is" -

- -

-In 27.6.1.3, [lib.istream.unformatted], before paragraph 37. Add an -Effects clause: "Effects: Behaves as an unformatted input function (as -described in 27.6.1.3, paragraph 1), except that it does not count the -number of characters extracted and does not affect the value returned -by subsequent calls to gcount()." Change the first sentence of -paragraph 37 from "if fail()" to "after constructing a sentry object, -if fail()". -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 38. Change the -first sentence of the Effects clause from "If fail()" to "Behaves -as an unformatted input function (as described in 27.6.1.3, paragraph -1), except that it does not count the number of characters extracted -and does not affect the value returned by subsequent calls to -gcount(). After constructing a sentry object, if fail() -

- -

-In 27.6.1.3, [lib.istream.unformatted], paragraph 40. Change the -first sentence of the Effects clause from "If fail()" to "Behaves -as an unformatted input function (as described in 27.6.1.3, paragraph -1), except that it does not count the number of characters extracted -and does not affect the value returned by subsequent calls to -gcount(). After constructing a sentry object, if fail() -

- -

-In 27.6.2.5.2 [lib.ostream.inserters.arithmetic], paragraph 1. Change -the beginning of the third sentence from "The formatting conversion" -to "These extractors behave as formatted output functions (as -described in 27.6.2.5.1). After the sentry object is constructed, the -conversion occurs". -

- -

-In 27.6.2.5.3 [lib.ostream.inserters], before paragraph 1. Add an -effects clause: "Effects: None. Does not behave as a formatted output -function (as described in 27.6.2.5.1).". -

- -

-In 27.6.2.5.3 [lib.ostream.inserters], paragraph 2. Change the -effects clause to "Effects: calls pf(*this). This extractor does not -behave as a formatted output function (as described in 27.6.2.5.1).". -

- -

-In 27.6.2.5.3 [lib.ostream.inserters], paragraph 4. Change the -effects clause to "Effects: calls pf(*this). This extractor does not -behave as a formatted output function (as described in 27.6.2.5.1).". -

- -

-In 27.6.2.5.3 [lib.ostream.inserters], paragraph 6. Change the first -sentence from "If sb" to "Behaves as a formatted output function (as -described in 27.6.2.5.1). After the sentry object is constructed, if -sb". -

- -

-In 27.6.2.6 [lib.ostream.unformatted], paragraph 2. Change the first -sentence from "Inserts the character" to "Behaves as an unformatted -output function (as described in 27.6.2.6, paragraph 1). After -constructing a sentry object, inserts the character". -

- -

-In 27.6.2.6 [lib.ostream.unformatted], paragraph 5. Change the first -sentence from "Obtains characters" to "Behaves as an unformatted -output function (as described in 27.6.2.6, paragraph 1). After -constructing a sentry object, obtains characters". -

- -

-In 27.6.2.6 [lib.ostream.unformatted], paragraph 7. Add a new -sentence at the end of the paragraph: "Does not behave as an -unformatted output function (as described in 27.6.2.6, paragraph 1)." -

- - -

Rationale:

-

See J16/99-0043==WG21/N1219, Proposed Resolution to Library Issue 60, -by Judy Ward and Matt Austern. This proposed resolution is section -VI of that paper.

- - - - - -
-

61. Ambiguity in iostreams exception policy

-

Section: 27.7.2.3 [istream.unformatted] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-06 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

The introduction to the section on unformatted input (27.6.1.3) -says that every unformatted input function catches all exceptions that -were thrown during input, sets badbit, and then conditionally rethrows -the exception. That seems clear enough. Several of the specific -functions, however, such as get() and read(), are documented in some -circumstances as setting eofbit and/or failbit. (The standard notes, -correctly, that setting eofbit or failbit can sometimes result in an -exception being thrown.) The question: if one of these functions -throws an exception triggered by setting failbit, is this an exception -"thrown during input" and hence covered by 27.6.1.3, or does -27.6.1.3 only refer to a limited class of exceptions? Just to make -this concrete, suppose you have the following snippet.

- -
  
-  char buffer[N];
-  istream is;
-  ...
-  is.exceptions(istream::failbit); // Throw on failbit but not on badbit.
-  is.read(buffer, N);
- -

Now suppose we reach EOF before we've read N characters. What -iostate bits can we expect to be set, and what exception (if any) will -be thrown?

- - -

Proposed resolution:

-

-In 27.6.1.3, paragraph 1, after the sentence that begins -"If an exception is thrown...", add the following -parenthetical comment: "(Exceptions thrown from -basic_ios<>::clear() are not caught or rethrown.)" -

- - -

Rationale:

-

The LWG looked to two alternative wordings, and choose the proposed -resolution as better standardese.

- - - - - -
-

62. Sync's return value

-

Section: 27.7.2.3 [istream.unformatted] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-06 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

The Effects clause for sync() (27.6.1.3, paragraph 36) says that it -"calls rdbuf()->pubsync() and, if that function returns -1 -... returns traits::eof()."

- -

That looks suspicious, because traits::eof() is of type -traits::int_type while the return type of sync() is int.

- - -

Proposed resolution:

-

In 27.7.2.3 [istream.unformatted], paragraph 36, change "returns -traits::eof()" to "returns -1". -

- - - - - -
-

63. Exception-handling policy for unformatted output

-

Section: 27.7.3.7 [ostream.unformatted] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Clause 27 details an exception-handling policy for formatted input, -unformatted input, and formatted output. It says nothing for -unformatted output (27.6.2.6). 27.6.2.6 should either include the same -kind of exception-handling policy as in the other three places, or -else it should have a footnote saying that the omission is -deliberate.

- - -

Proposed resolution:

-

-In 27.6.2.6, paragraph 1, replace the last sentence ("In any -case, the unformatted output function ends by destroying the sentry -object, then returning the value specified for the formatted output -function.") with the following text: -

-

-If an exception is thrown during output, then ios::badbit is -turned on [Footnote: without causing an ios::failure to be -thrown.] in *this's error state. If (exceptions() & -badbit) != 0 then the exception is rethrown. In any case, the -unformatted output function ends by destroying the sentry object, -then, if no exception was thrown, returning the value specified for -the formatted output function. -

- - -

Rationale:

-

-This exception-handling policy is consistent with that of formatted -input, unformatted input, and formatted output. -

- - - - - -
-

64. Exception handling in basic_istream::operator>>(basic_streambuf*)

-

Section: 27.7.2.2.3 [istream::extractors] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

27.6.1.2.3, paragraph 13, is ambiguous. It can be interpreted two -different ways, depending on whether the second sentence is read as an -elaboration of the first.

- - -

Proposed resolution:

-

Replace 27.7.2.2.3 [istream::extractors], paragraph 13, which begins -"If the function inserts no characters ..." with:

- -
-

If the function inserts no characters, it calls - setstate(failbit), which may throw - ios_base::failure (27.4.4.3). If it inserted no characters - because it caught an exception thrown while extracting characters - from sb and failbit is on in exceptions() - (27.4.4.3), then the caught exception is rethrown.

-
- - - - - -
-

66. Strstreambuf::setbuf

-

Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: TC1 - Submitter: Matt Austern Opened: 1998-08-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

D.7.1.3, paragraph 19, says that strstreambuf::setbuf -"Performs an operation that is defined separately for each class -derived from strstreambuf". This is obviously an incorrect -cut-and-paste from basic_streambuf. There are no classes derived from -strstreambuf.

- - -

Proposed resolution:

-

D.7.1.3 [depr.strstreambuf.virtuals], paragraph 19, replace the setbuf effects -clause which currently says "Performs an operation that is -defined separately for each class derived from strstreambuf" -with:

- -
-

Effects: implementation defined, except that - setbuf(0,0) has no effect.

-
- - - - - -
-

68. Extractors for char* should store null at end

-

Section: 27.7.2.2.3 [istream::extractors] Status: TC1 - Submitter: Angelika Langer Opened: 1998-07-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Extractors for char* (27.6.1.2.3) do not store a null character -after the extracted character sequence whereas the unformatted -functions like get() do. Why is this?

- -

Comment from Jerry Schwarz: There is apparently an editing -glitch. You'll notice that the last item of the list of what stops -extraction doesn't make any sense. It was supposed to be the line that -said a null is stored.

- - -

Proposed resolution:

-

27.7.2.2.3 [istream::extractors], paragraph 7, change the last list -item from:

- -

- A null byte (charT()) in the next position, which may be - the first position if no characters were extracted. -

- -

to become a new paragraph which reads:

- -

- Operator>> then stores a null byte (charT()) in the - next position, which may be the first position if no characters were - extracted. -

- - - - - -
-

69. Must elements of a vector be contiguous?

-

Section: 23.3.6 [vector] Status: TC1 - Submitter: Andrew Koenig Opened: 1998-07-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The issue is this: Must the elements of a vector be in contiguous memory?

- -

(Please note that this is entirely separate from the question of -whether a vector iterator is required to be a pointer; the answer to -that question is clearly "no," as it would rule out -debugging implementations)

- - -

Proposed resolution:

-

Add the following text to the end of 23.3.6 [vector], -paragraph 1.

- -
-

The elements of a vector are stored contiguously, meaning that if - v is a vector<T, Allocator> where T is some type - other than bool, then it obeys the identity &v[n] - == &v[0] + n for all 0 <= n < v.size().

-
- - -

Rationale:

-

The LWG feels that as a practical matter the answer is clearly -"yes". There was considerable discussion as to the best way -to express the concept of "contiguous", which is not -directly defined in the standard. Discussion included:

- -
    -
  • An operational definition similar to the above proposed resolution is - already used for valarray (26.6.2.4 [valarray.access]).
    • -
  • There is no need to explicitly consider a user-defined operator& - because elements must be copyconstructible (23.2 [container.requirements] para 3) - and copyconstructible (17.6.3.1 [utility.arg.requirements]) specifies - requirements for operator&.
    • -
  • There is no issue of one-past-the-end because of language rules.
    • -
- - - - - -
-

70. Uncaught_exception() missing throw() specification

-

Section: 18.8 [support.exception], X [uncaught] Status: TC1 - Submitter: Steve Clamage Opened: 1998-08-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In article 3E04@pratique.fr, Valentin Bonnard writes:

- -

uncaught_exception() doesn't have a throw specification.

- -

It is intentional ? Does it means that one should be prepared to -handle exceptions thrown from uncaught_exception() ?

- -

uncaught_exception() is called in exception handling contexts where -exception safety is very important.

- - -

Proposed resolution:

-

In 15.5.3 [except.uncaught], paragraph 1, 18.8 [support.exception], and X [uncaught], add "throw()" to uncaught_exception().

- - - - -
-

71. Do_get_monthname synopsis missing argument

-

Section: 22.4.5.1 [locale.time.get] Status: TC1 - Submitter: Nathan Myers Opened: 1998-08-13 Last modified: 2015-04-08

-

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-

Discussion:

-

The locale facet member time_get<>::do_get_monthname -is described in 22.4.5.1.2 [locale.time.get.virtuals] with five arguments, -consistent with do_get_weekday and with its specified use by member -get_monthname. However, in the synopsis, it is specified instead with -four arguments. The missing argument is the "end" iterator -value.

- - -

Proposed resolution:

-

In 22.4.5.1 [locale.time.get], add an "end" argument to -the declaration of member do_monthname as follows:

- -
  virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_base&,
-                                     ios_base::iostate& err, tm* t) const;
- - - - -
-

74. Garbled text for codecvt::do_max_length

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Matt Austern Opened: 1998-09-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The text of codecvt::do_max_length's "Returns" -clause (22.2.1.5.2, paragraph 11) is garbled. It has unbalanced -parentheses and a spurious n.

- - -

Proposed resolution:

-

Replace 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 11 with the -following:

- -

- Returns: The maximum value that - do_length(state, from, from_end, 1) can return for any - valid range [from, from_end) and stateT value - state. The specialization codecvt<char, char, - mbstate_t>::do_max_length() returns 1. -

- - - - -
-

75. Contradiction in codecvt::length's argument types

-

Section: 22.4.1.4 [locale.codecvt] Status: TC1 - Submitter: Matt -Austern Opened: 1998-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The class synopses for classes codecvt<> (22.2.1.5) -and codecvt_byname<> (22.2.1.6) say that the first -parameter of the member functions length and -do_length is of type const stateT&. The member -function descriptions, however (22.2.1.5.1, paragraph 6; 22.2.1.5.2, -paragraph 9) say that the type is stateT&. Either the -synopsis or the summary must be changed.

- -

If (as I believe) the member function descriptions are correct, -then we must also add text saying how do_length changes its -stateT argument.

- - -

Proposed resolution:

-

In 22.4.1.4 [locale.codecvt], and also in 22.4.1.5 [locale.codecvt.byname], -change the stateT argument type on both member -length() and member do_length() from

- -
-

const stateT&

-
- -

to

- -
-

stateT&

-
- -

In 22.4.1.4.2 [locale.codecvt.virtuals], add to the definition for member -do_length a paragraph:

- -
-

Effects: The effect on the state argument is ``as if'' - it called do_in(state, from, from_end, from, to, to+max, - to) for to pointing to a buffer of at least - max elements.

-
- - - - -
-

76. Can a codecvt facet always convert one internal character at a time?

-

Section: 22.4.1.4 [locale.codecvt] Status: CD1 - Submitter: Matt Austern Opened: 1998-09-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

This issue concerns the requirements on classes derived from -codecvt, including user-defined classes. What are the -restrictions on the conversion from external characters -(e.g. char) to internal characters (e.g. wchar_t)? -Or, alternatively, what assumptions about codecvt facets can -the I/O library make?

- -

The question is whether it's possible to convert from internal -characters to external characters one internal character at a time, -and whether, given a valid sequence of external characters, it's -possible to pick off internal characters one at a time. Or, to put it -differently: given a sequence of external characters and the -corresponding sequence of internal characters, does a position in the -internal sequence correspond to some position in the external -sequence?

- -

To make this concrete, suppose that [first, last) is a -sequence of M external characters and that [ifirst, -ilast) is the corresponding sequence of N internal -characters, where N > 1. That is, my_encoding.in(), -applied to [first, last), yields [ifirst, -ilast). Now the question: does there necessarily exist a -subsequence of external characters, [first, last_1), such -that the corresponding sequence of internal characters is the single -character *ifirst? -

- -

(What a "no" answer would mean is that -my_encoding translates sequences only as blocks. There's a -sequence of M external characters that maps to a sequence of -N internal characters, but that external sequence has no -subsequence that maps to N-1 internal characters.)

- -

Some of the wording in the standard, such as the description of -codecvt::do_max_length (22.4.1.4.2 [locale.codecvt.virtuals], -paragraph 11) and basic_filebuf::underflow (27.9.1.5 [filebuf.virtuals], paragraph 3) suggests that it must always be -possible to pick off internal characters one at a time from a sequence -of external characters. However, this is never explicitly stated one -way or the other.

- -

This issue seems (and is) quite technical, but it is important if -we expect users to provide their own encoding facets. This is an area -where the standard library calls user-supplied code, so a well-defined -set of requirements for the user-supplied code is crucial. Users must -be aware of the assumptions that the library makes. This issue affects -positioning operations on basic_filebuf, unbuffered input, -and several of codecvt's member functions.

- - -

Proposed resolution:

-

Add the following text as a new paragraph, following 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 2:

- -
-

A codecvt facet that is used by basic_filebuf -(27.9 [file.streams]) must have the property that if

-
-    do_out(state, from, from_end, from_next, to, to_lim, to_next)
-
-

would return ok, where from != from_end, then

-
-    do_out(state, from, from + 1, from_next, to, to_end, to_next)
-
-

must also return ok, and that if

-
-    do_in(state, from, from_end, from_next, to, to_lim, to_next)
-
-

would return ok, where to != to_lim, then

-
-    do_in(state, from, from_end, from_next, to, to + 1, to_next)
-
-

must also return ok. [Footnote: Informally, this -means that basic_filebuf assumes that the mapping from -internal to external characters is 1 to N: a codecvt that is -used by basic_filebuf must be able to translate characters -one internal character at a time. --End Footnote]

-
- -

[Redmond: Minor change in proposed resolution. Original -proposed resolution talked about "success", with a parenthetical -comment that success meant returning ok. New wording -removes all talk about "success", and just talks about the -return value.]

- - - - -

Rationale:

- -

The proposed resoluion says that conversions can be performed one - internal character at a time. This rules out some encodings that - would otherwise be legal. The alternative answer would mean there - would be some internal positions that do not correspond to any - external file position.

-

- An example of an encoding that this rules out is one where the - internT and externT are of the same type, and - where the internal sequence c1 c2 corresponds to the - external sequence c2 c1. -

-

It was generally agreed that basic_filebuf relies - on this property: it was designed under the assumption that - the external-to-internal mapping is N-to-1, and it is not clear - that basic_filebuf is implementable without that - restriction. -

-

- The proposed resolution is expressed as a restriction on - codecvt when used by basic_filebuf, rather - than a blanket restriction on all codecvt facets, - because basic_filebuf is the only other part of the - library that uses codecvt. If a user wants to define - a codecvt facet that implements a more general N-to-M - mapping, there is no reason to prohibit it, so long as the user - does not expect basic_filebuf to be able to use it. -

- - - - - -
-

78. Typo: event_call_back

-

Section: 27.5.3 [ios.base] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

typo: event_call_back should be event_callback  

- - -

Proposed resolution:

-

In the 27.5.3 [ios.base] synopsis change -"event_call_back" to "event_callback".

- - - - -
-

79. Inconsistent declaration of polar()

-

Section: 26.4.1 [complex.syn], 26.4.7 [complex.value.ops] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In 26.4.1 [complex.syn] polar is declared as follows:

-
   template<class T> complex<T> polar(const T&, const T&);
- -

In 26.4.7 [complex.value.ops] it is declared as follows:

-
   template<class T> complex<T> polar(const T& rho, const T& theta = 0);
- -

Thus whether the second parameter is optional is not clear.

- - -

Proposed resolution:

-

In 26.4.1 [complex.syn] change:

-
   template<class T> complex<T> polar(const T&, const T&);
- -

to:

-
   template<class T> complex<T> polar(const T& rho, const T& theta = 0);
- - - - - -
-

80. Global Operators of complex declared twice

-

Section: 26.4.1 [complex.syn], 26.4.2 [complex] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Both 26.2.1 and 26.2.2 contain declarations of global operators for -class complex. This redundancy should be removed.

- - -

Proposed resolution:

-

Reduce redundancy according to the general style of the standard.

- - - - -
-

83. String::npos vs. string::max_size()

-

Section: 21.4 [basic.string] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 89

-

Discussion:

-

Many string member functions throw if size is getting or exceeding -npos. However, I wonder why they don't throw if size is getting or -exceeding max_size() instead of npos. May be npos is known at compile -time, while max_size() is known at runtime. However, what happens if -size exceeds max_size() but not npos, then? It seems the standard -lacks some clarifications here.

- - -

Proposed resolution:

-

After 21.4 [basic.string] paragraph 4 ("The functions -described in this clause...") add a new paragraph:

- -
-

For any string operation, if as a result of the operation, size() would exceed - max_size() then - the operation throws length_error.

-
- - -

Rationale:

-

The LWG believes length_error is the correct exception to throw.

- - - - -
-

86. String constructors don't describe exceptions

-

Section: 21.4.1 [string.require] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The constructor from a range:

- -
template<class InputIterator> 
-         basic_string(InputIterator begin, InputIterator end, 
-                      const Allocator& a = Allocator());
- -

lacks a throws clause. However, I would expect that it throws -according to the other constructors if the numbers of characters in -the range equals npos (or exceeds max_size(), see above).

- - -

Proposed resolution:

-

In 21.4.1 [string.require], Strike throws paragraphs for -constructors which say "Throws: length_error if n == -npos."

- - -

Rationale:

-

Throws clauses for length_error if n == npos are no longer needed -because they are subsumed by the general wording added by the -resolution for issue 83.

- - - - -
-

90. Incorrect description of operator >> for strings

-

Section: 21.4.8.9 [string.io] Status: TC1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The effect of operator >> for strings contain the following item:

- -

    isspace(c,getloc()) is true for the next available input -character c.

- -

Here getloc() has to be replaced by is.getloc().

- - -

Proposed resolution:

-

In 21.4.8.9 [string.io] paragraph 1 Effects clause replace:

- -
-

isspace(c,getloc()) is true for the next available input character c.

-
- -

with:

- -
-

isspace(c,is.getloc()) is true for the next available input character c.

-
- - - - - -
-

91. Description of operator>> and getline() for string<> might cause endless loop

-

Section: 21.4.8.9 [string.io] Status: CD1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Operator >> and getline() for strings read until eof() -in the input stream is true. However, this might never happen, if the -stream can't read anymore without reaching EOF. So shouldn't it be -changed into that it reads until !good() ?

- - -

Proposed resolution:

-

In 21.4.8.9 [string.io], paragraph 1, replace:

-

-Effects: Begins by constructing a sentry object k as if k were -constructed by typename basic_istream<charT,traits>::sentry k( is). If -bool( k) is true, it calls str.erase() and then extracts characters -from is and appends them to str as if by calling str.append(1, c). If -is.width() is greater than zero, the maximum number n of characters -appended is is.width(); otherwise n is str.max_size(). Characters are -extracted and appended until any of the following occurs: -

-

with:

-

-Effects: Behaves as a formatted input function (27.7.2.2.1 [istream.formatted.reqmts]). After constructing a sentry object, if the -sentry converts to true, calls str.erase() and then extracts -characters from is and appends them to str as if by calling -str.append(1,c). If is.width() is greater than zero, the maximum -number n of characters appended is is.width(); otherwise n is -str.max_size(). Characters are extracted and appended until any of the -following occurs: -

- -

In 21.4.8.9 [string.io], paragraph 6, replace

-

-Effects: Begins by constructing a sentry object k as if by typename -basic_istream<charT,traits>::sentry k( is, true). If bool( k) is true, -it calls str.erase() and then extracts characters from is and appends -them to str as if by calling str.append(1, c) until any of the -following occurs: -

-

with:

-

-Effects: Behaves as an unformatted input function (27.7.2.3 [istream.unformatted]), except that it does not affect the value returned -by subsequent calls to basic_istream<>::gcount(). After -constructing a sentry object, if the sentry converts to true, calls -str.erase() and then extracts characters from is and appends them to -str as if by calling str.append(1,c) until any of the following -occurs: -

- -

[Redmond: Made changes in proposed resolution. operator>> -should be a formatted input function, not an unformatted input function. -getline should not be required to set gcount, since -there is no mechanism for gcount to be set except by one of -basic_istream's member functions.]

- - -

[Curaçao: Nico agrees with proposed resolution.]

- - - - -

Rationale:

-

The real issue here is whether or not these string input functions -get their characters from a streambuf, rather than by calling an -istream's member functions, a streambuf signals failure either by -returning eof or by throwing an exception; there are no other -possibilities. The proposed resolution makes it clear that these two -functions do get characters from a streambuf.

- - - - - -
-

92. Incomplete Algorithm Requirements

-

Section: 25 [algorithms] Status: CD1 - Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

The standard does not state, how often a function object is copied, -called, or the order of calls inside an algorithm. This may lead to -surprising/buggy behavior. Consider the following example:

- -
class Nth {    // function object that returns true for the nth element 
-  private: 
-    int nth;     // element to return true for 
-    int count;   // element counter 
-  public: 
-    Nth (int n) : nth(n), count(0) { 
-    } 
-    bool operator() (int) { 
-        return ++count == nth; 
-    } 
-}; 
-.... 
-// remove third element 
-    list<int>::iterator pos; 
-    pos = remove_if(coll.begin(),coll.end(),  // range 
-                    Nth(3)),                  // remove criterion 
-    coll.erase(pos,coll.end());
- -

This call, in fact removes the 3rd AND the 6th element. This -happens because the usual implementation of the algorithm copies the -function object internally:

- -
template <class ForwIter, class Predicate> 
-ForwIter std::remove_if(ForwIter beg, ForwIter end, Predicate op) 
-{ 
-    beg = find_if(beg, end, op); 
-    if (beg == end) { 
-        return beg; 
-    } 
-    else { 
-        ForwIter next = beg; 
-        return remove_copy_if(++next, end, beg, op); 
-    } 
-}
- -

The algorithm uses find_if() to find the first element that should -be removed. However, it then uses a copy of the passed function object -to process the resulting elements (if any). Here, Nth is used again -and removes also the sixth element. This behavior compromises the -advantage of function objects being able to have a state. Without any -cost it could be avoided (just implement it directly instead of -calling find_if()).

- - -

Proposed resolution:

- -

Add a new paragraph following 25 [algorithms] paragraph 8:

-

-[Note: Unless otherwise specified, algorithms that take function -objects as arguments are permitted to copy those function objects -freely. Programmers for whom object identity is important should -consider using a wrapper class that points to a noncopied -implementation object, or some equivalent solution.] -

- -

[Dublin: Pete Becker felt that this may not be a defect, -but rather something that programmers need to be educated about. -There was discussion of adding wording to the effect that the number -and order of calls to function objects, including predicates, not -affect the behavior of the function object.]

- - -

[Pre-Kona: Nico comments: It seems the problem is that we don't -have a clear statement of "predicate" in the -standard. People including me seemed to think "a function -returning a Boolean value and being able to be called by an STL -algorithm or be used as sorting criterion or ... is a -predicate". But a predicate has more requirements: It should -never change its behavior due to a call or being copied. IMHO we have -to state this in the standard. If you like, see section 8.1.4 of my -library book for a detailed discussion.]

- - -

[Kona: Nico will provide wording to the effect that "unless -otherwise specified, the number of copies of and calls to function -objects by algorithms is unspecified".  Consider placing in -25 [algorithms] after paragraph 9.]

- - -

[Santa Cruz: The standard doesn't currently guarantee that - functions object won't be copied, and what isn't forbidden is - allowed. It is believed (especially since implementations that were - written in concert with the standard do make copies of function - objects) that this was intentional. Thus, no normative change is - needed. What we should put in is a non-normative note suggesting to - programmers that if they want to guarantee the lack of copying they - should use something like the ref wrapper.]

- - -

[Oxford: Matt provided wording.]

- - - - - - - - -
-

98. Input iterator requirements are badly written

-

Section: 24.2.3 [input.iterators] Status: CD1 - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Table 72 in 24.2.3 [input.iterators] specifies semantics for -*r++ of:

- -

   { T tmp = *r; ++r; return tmp; }

- -

There are two problems with this. First, the return type is -specified to be "T", as opposed to something like "convertible to T". -This is too specific: we want to allow *r++ to return an lvalue.

- -

Second, writing the semantics in terms of code misleadingly -suggests that the effects *r++ should precisely replicate the behavior -of this code, including side effects. (Does this mean that *r++ -should invoke the copy constructor exactly as many times as the sample -code above would?) See issue 334 for a similar -problem.

- - - -

Proposed resolution:

-

In Table 72 in 24.2.3 [input.iterators], change the return type -for *r++ from T to "convertible to T".

- - -

Rationale:

-

This issue has two parts: the return type, and the number of times - the copy constructor is invoked.

- -

The LWG believes the the first part is a real issue. It's - inappropriate for the return type to be specified so much more - precisely for *r++ than it is for *r. In particular, if r is of - (say) type int*, then *r++ isn't int, - but int&.

- -

The LWG does not believe that the number of times the copy - constructor is invoked is a real issue. This can vary in any case, - because of language rules on copy constructor elision. That's too - much to read into these semantics clauses.

- -

Additionally, as Dave Abrahams pointed out (c++std-lib-13703): since - we're told (24.1/3) that forward iterators satisfy all the requirements - of input iterators, we can't impose any requirements in the Input - Iterator requirements table that forward iterators don't satisfy.

- - - - - -
-

103. set::iterator is required to be modifiable, but this allows modification of keys

-

Section: 23.2.4 [associative.reqmts] Status: CD1 - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Set::iterator is described as implementation-defined with a -reference to the container requirement; the container requirement says -that const_iterator is an iterator pointing to const T and iterator an -iterator pointing to T.

- -

23.1.2 paragraph 2 implies that the keys should not be modified to -break the ordering of elements. But that is not clearly -specified. Especially considering that the current standard requires -that iterator for associative containers be different from -const_iterator. Set, for example, has the following:

- -

typedef implementation defined iterator;
-       // See _lib.container.requirements_

- -

23.2 [container.requirements] actually requires that iterator type pointing -to T (table 65). Disallowing user modification of keys by changing the -standard to require an iterator for associative container to be the -same as const_iterator would be overkill since that will unnecessarily -significantly restrict the usage of associative container. A class to -be used as elements of set, for example, can no longer be modified -easily without either redesigning the class (using mutable on fields -that have nothing to do with ordering), or using const_cast, which -defeats requiring iterator to be const_iterator. The proposed solution -goes in line with trusting user knows what he is doing.

- -

Other Options Evaluated:

- -

Option A.   In 23.2.4 [associative.reqmts], paragraph 2, after -first sentence, and before "In addition,...", add one line: -

- -
-

Modification of keys shall not change their strict weak ordering.

-
- -

Option B. Add three new sentences to 23.2.4 [associative.reqmts]:

- -
-

At the end of paragraph 5: "Keys in an associative container - are immutable." At the end of paragraph 6: "For - associative containers where the value type is the same as the key - type, both iterator and const_iterator are - constant iterators. It is unspecified whether or not - iterator and const_iterator are the same - type."

-
- -

Option C. To 23.2.4 [associative.reqmts], paragraph 3, which -currently reads:

- -
-

The phrase ``equivalence of keys'' means the equivalence relation imposed by the - comparison and not the operator== on keys. That is, two keys k1 and k2 in the same - container are considered to be equivalent if for the comparison object comp, comp(k1, k2) - == false && comp(k2, k1) == false.

-
- -

  add the following:

- -
-

For any two keys k1 and k2 in the same container, comp(k1, k2) shall return the same - value whenever it is evaluated. [Note: If k2 is removed from the container and later - reinserted, comp(k1, k2) must still return a consistent value but this value may be - different than it was the first time k1 and k2 were in the same container. This is - intended to allow usage like a string key that contains a filename, where comp compares - file contents; if k2 is removed, the file is changed, and the same k2 (filename) is - reinserted, comp(k1, k2) must again return a consistent value but this value may be - different than it was the previous time k2 was in the container.]

-
- - - -

Proposed resolution:

-

Add the following to 23.2.4 [associative.reqmts] at -the indicated location:

- -
-

At the end of paragraph 3: "For any two keys k1 and k2 in the same container, - calling comp(k1, k2) shall always return the same - value."

-

At the end of paragraph 5: "Keys in an associative container are immutable."

-

At the end of paragraph 6: "For associative containers where the value type is the - same as the key type, both iterator and const_iterator are constant - iterators. It is unspecified whether or not iterator and const_iterator - are the same type."

-
- - -

Rationale:

-

Several arguments were advanced for and against allowing set elements to be -mutable as long as the ordering was not effected. The argument which swayed the -LWG was one of safety; if elements were mutable, there would be no compile-time -way to detect of a simple user oversight which caused ordering to be -modified. There was a report that this had actually happened in practice, -and had been painful to diagnose. If users need to modify elements, -it is possible to use mutable members or const_cast.

- -

Simply requiring that keys be immutable is not sufficient, because the comparison -object may indirectly (via pointers) operate on values outside of the keys.

- -

-The types iterator and const_iterator are permitted -to be different types to allow for potential future work in which some -member functions might be overloaded between the two types. No such -member functions exist now, and the LWG believes that user functionality -will not be impaired by permitting the two types to be the same. A -function that operates on both iterator types can be defined for -const_iterator alone, and can rely on the automatic -conversion from iterator to const_iterator. -

- -

[Tokyo: The LWG crafted the proposed resolution and rationale.]

- - - - - - -
-

106. Numeric library private members are implementation defined

-

Section: 26.6.5 [template.slice.array] Status: TC1 - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

This is the only place in the whole standard where the implementation has to document -something private.

- - -

Proposed resolution:

-

-Remove the comment which says "// remainder implementation defined" from: -

- -
    -
  • 26.6.5 [template.slice.array]
    • -
  • 26.6.7 [template.gslice.array]
    • -
  • 26.6.8 [template.mask.array]
    • -
  • 26.6.9 [template.indirect.array]
    • -
- - - - - -
-

108. Lifetime of exception::what() return unspecified

-

Section: 18.7.1 [type.info] Status: TC1 - Submitter: AFNOR Opened: 1998-10-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In 18.6.1, paragraphs 8-9, the lifetime of the return value of -exception::what() is left unspecified. This issue has implications -with exception safety of exception handling: some exceptions should -not throw bad_alloc.

- - -

Proposed resolution:

-

Add to 18.7.1 [type.info] paragraph 9 (exception::what notes -clause) the sentence:

- -
-

The return value remains valid until the exception object from which it is obtained is - destroyed or a non-const member function of the exception object is called.

-
- - -

Rationale:

-

If an exception object has non-const members, they may be used -to set internal state that should affect the contents of the string -returned by what(). -

- - - - - -
-

109. Missing binders for non-const sequence elements

-

Section: X [depr.lib.binders] Status: CD1 - Submitter: Bjarne Stroustrup Opened: 1998-10-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

There are no versions of binders that apply to non-const elements -of a sequence. This makes examples like for_each() using bind2nd() on -page 521 of "The C++ Programming Language (3rd)" -non-conforming. Suitable versions of the binders need to be added.

- -

Further discussion from Nico:

- -

What is probably meant here is shown in the following example:

- -
class Elem { 
-  public: 
-    void print (int i) const { } 
-    void modify (int i) { } 
-};
-
int main() 
-{ 
-    vector<Elem> coll(2); 
-    for_each (coll.begin(), coll.end(), bind2nd(mem_fun_ref(&Elem::print),42));    // OK 
-    for_each (coll.begin(), coll.end(), bind2nd(mem_fun_ref(&Elem::modify),42));   // ERROR 
-}
- -

The error results from the fact that bind2nd() passes its first -argument (the argument of the sequence) as constant reference. See the -following typical implementation:

- -
- 
template <class Operation> 
-class binder2nd 
-  : public unary_function<typename Operation::first_argument_type, 
-                          typename Operation::result_type> { 
-protected: 
-  Operation op; 
-  typename Operation::second_argument_type value; 
-public: 
-  binder2nd(const Operation& o, 
-            const typename Operation::second_argument_type& v) 
-      : op(o), value(v) {}
- 
 typename Operation::result_type 
-  operator()(const typename Operation::first_argument_type& x) const { 
-    return op(x, value); 
-  } 
-};
-
- -

The solution is to overload operator () of bind2nd for non-constant arguments:

- -
- 
template <class Operation> 
-class binder2nd 
-  : public unary_function<typename Operation::first_argument_type, 
-                          typename Operation::result_type> { 
-protected: 
-  Operation op; 
-  typename Operation::second_argument_type value; 
-public: 
-  binder2nd(const Operation& o, 
-            const typename Operation::second_argument_type& v) 
-      : op(o), value(v) {}
- 
 typename Operation::result_type 
-  operator()(const typename Operation::first_argument_type& x) const { 
-    return op(x, value); 
-  } 
-  typename Operation::result_type 
-  operator()(typename Operation::first_argument_type& x) const { 
-    return op(x, value); 
-  } 
-};
-
- - -

Proposed resolution:

- -

Howard believes there is a flaw in this resolution. -See c++std-lib-9127. We may need to reopen this issue.

- -

In X [depr.lib.binders] in the declaration of binder1st after:

-
-

typename Operation::result_type
-  operator()(const typename Operation::second_argument_type& x) const;

-
-

insert:

-
-

typename Operation::result_type
-  operator()(typename Operation::second_argument_type& x) const;

-
-

In X [depr.lib.binders] in the declaration of binder2nd after:

-
-

typename Operation::result_type
-  operator()(const typename Operation::first_argument_type& x) const;

-
-

insert:

-
-

typename Operation::result_type
-  operator()(typename Operation::first_argument_type& x) const;

-
- -

[Kona: The LWG discussed this at some length.It was agreed that -this is a mistake in the design, but there was no consensus on whether -it was a defect in the Standard. Straw vote: NAD - 5. Accept -proposed resolution - 3. Leave open - 6.]

- - -

[Copenhagen: It was generally agreed that this was a defect. -Strap poll: NAD - 0. Accept proposed resolution - 10. -Leave open - 1.]

- - - - - - - -
-

110. istreambuf_iterator::equal not const

-

Section: 24.6.3 [istreambuf.iterator], 24.6.3.5 [istreambuf.iterator::equal] Status: TC1 - Submitter: Nathan Myers Opened: 1998-10-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Member istreambuf_iterator<>::equal is not declared -"const", yet 24.6.3.6 [istreambuf.iterator::op==] says that operator==, -which is const, calls it. This is contradictory.

- - -

Proposed resolution:

-

In 24.6.3 [istreambuf.iterator] and also in 24.6.3.5 [istreambuf.iterator::equal], -replace:

- -
- 
bool equal(istreambuf_iterator& b);
-
- -

with:

- -
- 
bool equal(const istreambuf_iterator& b) const;
-
- - - - - -
-

112. Minor typo in ostreambuf_iterator constructor

-

Section: 24.6.4.1 [ostreambuf.iter.cons] Status: TC1 - Submitter: Matt Austern Opened: 1998-10-20 Last modified: 2015-04-08

-

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-

Discussion:

-

The requires clause for ostreambuf_iterator's -constructor from an ostream_type (24.5.4.1, paragraph 1) -reads "s is not null". However, s is a -reference, and references can't be null.

- - -

Proposed resolution:

-

In 24.6.4.1 [ostreambuf.iter.cons]:

- -

Move the current paragraph 1, which reads "Requires: s is not -null.", from the first constructor to the second constructor.

- -

Insert a new paragraph 1 Requires clause for the first constructor -reading:

- -
-

Requires: s.rdbuf() is not null.

-
- - - - - -
-

114. Placement forms example in error twice

-

Section: 18.6.1.3 [new.delete.placement] Status: TC1 - Submitter: Steve Clamage Opened: 1998-10-28 Last modified: 2015-04-08

-

View all other issues in [new.delete.placement].

-

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-

Duplicate of: 196

-

Discussion:

-

Section 18.5.1.3 contains the following example:

- -
[Example: This can be useful for constructing an object at a known address:
-        char place[sizeof(Something)];
-        Something* p = new (place) Something();
- -end example]
- -

First code line: "place" need not have any special alignment, and the -following constructor could fail due to misaligned data.

- -

Second code line: Aren't the parens on Something() incorrect?  [Dublin: the LWG -believes the () are correct.]

- -

Examples are not normative, but nevertheless should not show code that is invalid or -likely to fail.

- - -

Proposed resolution:

-

Replace the first line of code in the example in -18.6.1.3 [new.delete.placement] with: -

- -
- 
void* place = operator new(sizeof(Something));
-
- - - - - -
-

115. Typo in strstream constructors

-

Section: D.7.4.1 [depr.strstream.cons] Status: TC1 - Submitter: Steve Clamage Opened: 1998-11-02 Last modified: 2015-04-08

-

View all issues with TC1 status.

-

Discussion:

-

D.7.4.1 strstream constructors paragraph 2 says:

- -
-

Effects: Constructs an object of class strstream, initializing the base class with - iostream(& sb) and initializing sb with one of the two constructors:

-

- If mode&app==0, then s shall designate the first element of an array of n - elements. The constructor is strstreambuf(s, n, s).

-

- If mode&app==0, then s shall designate the first element of an array of n - elements that contains an NTBS whose first element is designated by s. The constructor is - strstreambuf(s, n, s+std::strlen(s)).

-
- -

Notice the second condition is the same as the first. I think the second condition -should be "If mode&app==app", or "mode&app!=0", meaning that -the append bit is set.

- - -

Proposed resolution:

-

In D.7.3.1 [depr.ostrstream.cons] paragraph 2 and D.7.4.1 [depr.strstream.cons] -paragraph 2, change the first condition to (mode&app)==0 -and the second condition to (mode&app)!=0.

- - - - - -
-

117. basic_ostream uses nonexistent num_put member functions

-

Section: 27.7.3.6.2 [ostream.inserters.arithmetic] Status: CD1 - Submitter: Matt Austern Opened: 1998-11-20 Last modified: 2015-04-08

-

View all other issues in [ostream.inserters.arithmetic].

-

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-

Discussion:

-

The effects clause for numeric inserters says that -insertion of a value x, whose type is either bool, -short, unsigned short, int, unsigned -int, long, unsigned long, float, -double, long double, or const void*, is -delegated to num_put, and that insertion is performed as if -through the following code fragment:

- -
bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> > 
-   >(getloc()).put(*this, *this, fill(), val). failed();
- -

This doesn't work, because num_put<>::put is only -overloaded for the types bool, long, unsigned -long, double, long double, and const -void*. That is, the code fragment in the standard is incorrect -(it is diagnosed as ambiguous at compile time) for the types -short, unsigned short, int, unsigned -int, and float.

- -

We must either add new member functions to num_put, or -else change the description in ostream so that it only calls -functions that are actually there. I prefer the latter.

- - -

Proposed resolution:

-

Replace 27.6.2.5.2, paragraph 1 with the following:

- -
-

-The classes num_get<> and num_put<> handle locale-dependent numeric -formatting and parsing. These inserter functions use the imbued -locale value to perform numeric formatting. When val is of type bool, -long, unsigned long, double, long double, or const void*, the -formatting conversion occurs as if it performed the following code -fragment: -

- -
-bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> >
-   >(getloc()).put(*this, *this, fill(), val). failed();
-
- -

-When val is of type short the formatting conversion occurs as if it -performed the following code fragment: -

- -
-ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
-bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> >
-   >(getloc()).put(*this, *this, fill(),
-      baseflags == ios_base::oct || baseflags == ios_base::hex
-         ? static_cast<long>(static_cast<unsigned short>(val))
-         : static_cast<long>(val)). failed();
-
- -

-When val is of type int the formatting conversion occurs as if it performed -the following code fragment: -

- -
-ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
-bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> >
-   >(getloc()).put(*this, *this, fill(),
-      baseflags == ios_base::oct || baseflags == ios_base::hex
-         ? static_cast<long>(static_cast<unsigned int>(val))
-         : static_cast<long>(val)). failed();
-
- -

-When val is of type unsigned short or unsigned int the formatting conversion -occurs as if it performed the following code fragment: -

- -
-bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> >
-   >(getloc()).put(*this, *this, fill(), static_cast<unsigned long>(val)).
-failed();
-
- -

-When val is of type float the formatting conversion occurs as if it -performed the following code fragment: -

- -
-bool failed = use_facet<
-   num_put<charT,ostreambuf_iterator<charT,traits> >
-   >(getloc()).put(*this, *this, fill(), static_cast<double>(val)).
-failed();
-
- -
- -

[post-Toronto: This differs from the previous proposed -resolution; PJP provided the new wording. The differences are in -signed short and int output.]

- - - -

Rationale:

-

The original proposed resolution was to cast int and short to long, -unsigned int and unsigned short to unsigned long, and float to double, -thus ensuring that we don't try to use nonexistent num_put<> -member functions. The current proposed resolution is more -complicated, but gives more expected results for hex and octal output -of signed short and signed int. (On a system with 16-bit short, for -example, printing short(-1) in hex format should yield 0xffff.)

- - - - - -
-

118. basic_istream uses nonexistent num_get member functions

-

Section: 27.7.2.2.2 [istream.formatted.arithmetic] Status: CD1 - Submitter: Matt Austern Opened: 1998-11-20 Last modified: 2015-04-08

-

View all other issues in [istream.formatted.arithmetic].

-

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-

Discussion:

-

Formatted input is defined for the types short, unsigned short, int, -unsigned int, long, unsigned long, float, double, -long double, bool, and void*. According to section 27.6.1.2.2, -formatted input of a value x is done as if by the following code fragment:

- -
typedef num_get< charT,istreambuf_iterator<charT,traits> > numget; 
-iostate err = 0; 
-use_facet< numget >(loc).get(*this, 0, *this, err, val); 
-setstate(err);
- -

According to section 22.4.2.1.1 [facet.num.get.members], however, -num_get<>::get() is only overloaded for the types -bool, long, unsigned short, unsigned -int, unsigned long, unsigned long, -float, double, long double, and -void*. Comparing the lists from the two sections, we find -that 27.6.1.2.2 is using a nonexistent function for types -short and int.

- - -

Proposed resolution:

-

In 27.7.2.2.2 [istream.formatted.arithmetic] Arithmetic Extractors, remove the -two lines (1st and 3rd) which read:

-
- 
operator>>(short& val);
-...
-operator>>(int& val);
-
- -

And add the following at the end of that section (27.6.1.2.2) :

- -
- 
operator>>(short& val);
-

The conversion occurs as if performed by the following code fragment (using - the same notation as for the preceding code fragment):

- 
  typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
-  iostate err = 0;
-  long lval;
-  use_facet< numget >(loc).get(*this, 0, *this, err, lval);
-        if (err == 0
-                && (lval < numeric_limits<short>::min() || numeric_limits<short>::max() < lval))
-                err = ios_base::failbit;
-  setstate(err);
- 
operator>>(int& val);
-

The conversion occurs as if performed by the following code fragment (using - the same notation as for the preceding code fragment):

- 
  typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
-  iostate err = 0;
-  long lval;
-  use_facet< numget >(loc).get(*this, 0, *this, err, lval);
-        if (err == 0
-                && (lval < numeric_limits<int>::min() || numeric_limits<int>::max() < lval))
-                err = ios_base::failbit;
-  setstate(err);
-
- -

[Post-Tokyo: PJP provided the above wording.]

- - - - - - -
-

119. Should virtual functions be allowed to strengthen the exception specification?

-

Section: 17.6.5.12 [res.on.exception.handling] Status: TC1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [res.on.exception.handling].

-

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-

Discussion:

-

Section 17.6.5.12 [res.on.exception.handling] states:

- -

"An implementation may strengthen the exception-specification -for a function by removing listed exceptions."

- -

The problem is that if an implementation is allowed to do this for -virtual functions, then a library user cannot write a class that -portably derives from that class.

- -

For example, this would not compile if ios_base::failure::~failure -had an empty exception specification:

- -
#include <ios>
-#include <string>
-
-class D : public std::ios_base::failure {
-public:
-        D(const std::string&);
-        ~D(); // error - exception specification must be compatible with 
-              // overridden virtual function ios_base::failure::~failure()
-};
- - -

Proposed resolution:

-

Change Section 17.6.5.12 [res.on.exception.handling] from:

- -

     "may strengthen the -exception-specification for a function"

- -

to:

- -

     "may strengthen the -exception-specification for a non-virtual function".

- - - - - -
-

120. Can an implementor add specializations?

-

Section: 17.6.4.3 [reserved.names] Status: CD1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [reserved.names].

-

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-

Discussion:

- -

The original issue asked whether a library implementor could -specialize standard library templates for built-in types. (This was -an issue because users are permitted to explicitly instantiate -standard library templates.)

- -

Specializations are no longer a problem, because of the resolution -to core issue 259. Under the proposed resolution, it will be legal -for a translation unit to contain both a specialization and an -explicit instantiation of the same template, provided that the -specialization comes first. In such a case, the explicit -instantiation will be ignored. Further discussion of library issue -120 assumes that the core 259 resolution will be adopted.

- -

However, as noted in lib-7047, one piece of this issue still -remains: what happens if a standard library implementor explicitly -instantiates a standard library templates? It's illegal for a program -to contain two different explicit instantiations of the same template -for the same type in two different translation units (ODR violation), -and the core working group doesn't believe it is practical to relax -that restriction.

- -

The issue, then, is: are users allowed to explicitly instantiate -standard library templates for non-user defined types? The status quo -answer is 'yes'. Changing it to 'no' would give library implementors -more freedom.

- -

This is an issue because, for performance reasons, library -implementors often need to explicitly instantiate standard library -templates. (for example, std::basic_string<char>) Does giving -users freedom to explicitly instantiate standard library templates for -non-user defined types make it impossible or painfully difficult for -library implementors to do this?

- -

John Spicer suggests, in lib-8957, that library implementors have a -mechanism they can use for explicit instantiations that doesn't -prevent users from performing their own explicit instantiations: put -each explicit instantiation in its own object file. (Different -solutions might be necessary for Unix DSOs or MS-Windows DLLs.) On -some platforms, library implementors might not need to do anything -special: the "undefined behavior" that results from having two -different explicit instantiations might be harmless.

- - - -

Proposed resolution:

-

Append to 17.6.4.3 [reserved.names] paragraph 1:

-

- A program may explicitly instantiate any templates in the standard - library only if the declaration depends on the name of a user-defined - type of external linkage and the instantiation meets the standard library - requirements for the original template. -

- -

[Kona: changed the wording from "a user-defined name" to "the name of - a user-defined type"]

- - - - -

Rationale:

-

The LWG considered another possible resolution:

-
-

In light of the resolution to core issue 259, no normative changes - in the library clauses are necessary. Add the following non-normative - note to the end of 17.6.4.3 [reserved.names] paragraph 1:

-

- [Note: A program may explicitly instantiate standard library - templates, even when an explicit instantiation does not depend on - a user-defined name. --end note] -

-
- -

The LWG rejected this because it was believed that it would make - it unnecessarily difficult for library implementors to write - high-quality implementations. A program may not include an - explicit instantiation of the same template, for the same template - arguments, in two different translation units. If users are - allowed to provide explicit instantiations of Standard Library - templates for built-in types, then library implementors aren't, - at least not without nonportable tricks.

- -

The most serious problem is a class template that has writeable - static member variables. Unfortunately, such class templates are - important and, in existing Standard Library implementations, are - often explicitly specialized by library implementors: locale facets, - which have a writeable static member variable id. If a - user's explicit instantiation collided with the implementations - explicit instantiation, iostream initialization could cause locales - to be constructed in an inconsistent state.

- -

One proposed implementation technique was for Standard Library - implementors to provide explicit instantiations in separate object - files, so that they would not be picked up by the linker when the - user also provides an explicit instantiation. However, this - technique only applies for Standard Library implementations that - are packaged as static archives. Most Standard Library - implementations nowadays are packaged as dynamic libraries, so this - technique would not apply.

- -

The Committee is now considering standardization of dynamic - linking. If there are such changes in the future, it may be - appropriate to revisit this issue later.

- - - - - -
-

122. streambuf/wstreambuf description should not say they are specializations

-

Section: 27.6.3 [streambuf] Status: TC1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [streambuf].

-

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-

Discussion:

-

Section 27.5.2 describes the streambuf classes this way:

- -
- -

The class streambuf is a specialization of the template class basic_streambuf -specialized for the type char.

- -

The class wstreambuf is a specialization of the template class basic_streambuf -specialized for the type wchar_t.

- -
- -

This implies that these classes must be template specializations, not typedefs.

- -

It doesn't seem this was intended, since Section 27.5 has them declared as typedefs.

- - -

Proposed resolution:

-

Remove 27.6.3 [streambuf] paragraphs 2 and 3 (the above two -sentences).

- - -

Rationale:

-

The streambuf synopsis already has a declaration for the -typedefs and that is sufficient.

- - - - - -
-

123. Should valarray helper arrays fill functions be const?

-

Section: 26.6.5.4 [slice.arr.fill], 26.6.7.4 [gslice.array.fill], 26.6.8.4 [mask.array.fill], 26.6.9.4 [indirect.array.fill] Status: CD1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

One of the operator= in the valarray helper arrays is const and one -is not. For example, look at slice_array. This operator= in Section -26.6.5.2 [slice.arr.assign] is const:

- -

    void operator=(const valarray<T>&) const;

- -

but this one in Section 26.6.5.4 [slice.arr.fill] is not:

- -

    void operator=(const T&);

- -

The description of the semantics for these two functions is similar.

- - -

Proposed resolution:

- -

26.6.5 [template.slice.array] Template class slice_array

-
- -

In the class template definition for slice_array, replace the member - function declaration

- 
-      void operator=(const T&);
-
-

with

- 
-      void operator=(const T&) const;
-
-
- -

26.6.5.4 [slice.arr.fill] slice_array fill function

-
- -

Change the function declaration

- 
-      void operator=(const T&);
-
-

to

- 
-      void operator=(const T&) const;
-
-
- -

26.6.7 [template.gslice.array] Template class gslice_array

-
- -

In the class template definition for gslice_array, replace the member - function declaration

- 
-      void operator=(const T&);
-
-

with

- 
-      void operator=(const T&) const;
-
-
- -

26.6.7.4 [gslice.array.fill] gslice_array fill function

-
- -

Change the function declaration

- 
-      void operator=(const T&);
-
-

to

- 
-      void operator=(const T&) const;
-
-
- -

26.6.8 [template.mask.array] Template class mask_array

-
- -

In the class template definition for mask_array, replace the member - function declaration

- 
-      void operator=(const T&);
-
-

with

- 
-      void operator=(const T&) const;
-
-
- -

26.6.8.4 [mask.array.fill] mask_array fill function

-
- -

Change the function declaration

- 
-      void operator=(const T&);
-
-

to

- 
-      void operator=(const T&) const;
-
-
- -

26.6.9 [template.indirect.array] Template class indirect_array

-
- -

In the class template definition for indirect_array, replace the member - function declaration

- 
-      void operator=(const T&);
-
-

with

- 
-      void operator=(const T&) const;
-
-
- -

26.6.9.4 [indirect.array.fill] indirect_array fill function

-
- -

Change the function declaration

- 
-      void operator=(const T&);
-
-

to

- 
-      void operator=(const T&) const;
-
-
- - -

[Redmond: Robert provided wording.]

- - - - -

Rationale:

-

There's no good reason for one version of operator= being const and -another one not. Because of issue 253, this now -matters: these functions are now callable in more circumstances. In -many existing implementations, both versions are already const.

- - - - - -
-

124. ctype_byname<charT>::do_scan_is & do_scan_not return type should be const charT*

-

Section: 22.4.1.2 [locale.ctype.byname] Status: TC1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [locale.ctype.byname].

-

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-

Discussion:

-

In Section 22.4.1.2 [locale.ctype.byname] -ctype_byname<charT>::do_scan_is() and do_scan_not() are declared -to return a const char* not a const charT*.

- - -

Proposed resolution:

-

Change Section 22.4.1.2 [locale.ctype.byname] do_scan_is() and -do_scan_not() to return a const -charT*.

- - - - - -
-

125. valarray<T>::operator!() return type is inconsistent

-

Section: 26.6.2 [template.valarray] Status: TC1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [template.valarray].

-

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-

Discussion:

-

In Section 26.6.2 [template.valarray] valarray<T>::operator!() is -declared to return a valarray<T>, but in Section 26.6.2.6 [valarray.unary] it is declared to return a valarray<bool>. The -latter appears to be correct.

- - -

Proposed resolution:

-

Change in Section 26.6.2 [template.valarray] the declaration of -operator!() so that the return type is -valarray<bool>.

- - - - -
-

126. typos in Effects clause of ctype::do_narrow()

-

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: TC1 - Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2015-04-08

-

View all other issues in [locale.ctype.virtuals].

-

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-

Discussion:

Typos in 22.2.1.1.2 need to be fixed.

- -

Proposed resolution:

-

In Section 22.4.1.1.2 [locale.ctype.virtuals] change:

- -
   do_widen(do_narrow(c),0) == c
- -

to:

- -
   do_widen(do_narrow(c,0)) == c
- -

and change:

- -
   (is(M,c) || !ctc.is(M, do_narrow(c),dfault) )
- -

to:

- -
   (is(M,c) || !ctc.is(M, do_narrow(c,dfault)) )
- - - - - -
-

127. auto_ptr<> conversion issues

-

Section: X [auto.ptr] Status: TC1 - Submitter: Greg Colvin Opened: 1999-02-17 Last modified: 2015-04-08

-

View all other issues in [auto.ptr].

-

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-

Discussion:

-

There are two problems with the current auto_ptr wording -in the standard:

- -

First, the auto_ptr_ref definition cannot be nested -because auto_ptr<Derived>::auto_ptr_ref is unrelated to -auto_ptr<Base>::auto_ptr_ref. Also submitted by -Nathan Myers, with the same proposed resolution.

- -

Second, there is no auto_ptr assignment operator taking an -auto_ptr_ref argument.

- -

I have discussed these problems with my proposal coauthor, Bill -Gibbons, and with some compiler and library implementors, and we -believe that these problems are not desired or desirable implications -of the standard.

- -

25 Aug 1999: The proposed resolution now reflects changes suggested -by Dave Abrahams, with Greg Colvin's concurrence; 1) changed -"assignment operator" to "public assignment -operator", 2) changed effects to specify use of release(), 3) -made the conversion to auto_ptr_ref const.

- -

2 Feb 2000: Lisa Lippincott comments: [The resolution of] this issue -states that the conversion from auto_ptr to auto_ptr_ref should -be const. This is not acceptable, because it would allow -initialization and assignment from _any_ const auto_ptr! It also -introduces an implementation difficulty in writing this conversion -function -- namely, somewhere along the line, a const_cast will be -necessary to remove that const so that release() may be called. This -may result in undefined behavior [7.1.5.1/4]. The conversion -operator does not have to be const, because a non-const implicit -object parameter may be bound to an rvalue [13.3.3.1.4/3] -[13.3.1/5].

- -

Tokyo: The LWG removed the following from the proposed resolution:

- -

In 20.10.4 [meta.unary], paragraph 2, and 20.10.4.3 [meta.unary.prop], - paragraph 2, make the conversion to auto_ptr_ref const:

-
- 
template<class Y> operator auto_ptr_ref<Y>() const throw();
-
- - -

Proposed resolution:

-

In 20.10.4 [meta.unary], paragraph 2, move -the auto_ptr_ref definition to namespace scope.

- -

In 20.10.4 [meta.unary], paragraph 2, add -a public assignment operator to the auto_ptr definition:

- -
- 
auto_ptr& operator=(auto_ptr_ref<X> r) throw();
-
- -

Also add the assignment operator to 20.10.4.3 [meta.unary.prop]:

- -
- 
auto_ptr& operator=(auto_ptr_ref<X> r) throw()
- -

Effects: Calls reset(p.release()) for the auto_ptr - p that r holds a reference to.
- Returns: *this.

- -
- - - - - -
-

129. Need error indication from seekp() and seekg()

-

Section: 27.7.2.3 [istream.unformatted], 27.7.3.5 [ostream.seeks] Status: TC1 - Submitter: Angelika Langer Opened: 1999-02-22 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

-

Currently, the standard does not specify how seekg() and seekp() -indicate failure. They are not required to set failbit, and they can't -return an error indication because they must return *this, i.e. the -stream. Hence, it is undefined what happens if they fail. And they -can fail, for instance, when a file stream is disconnected from the -underlying file (is_open()==false) or when a wide character file -stream must perform a state-dependent code conversion, etc.

- -

The stream functions seekg() and seekp() should set failbit in the -stream state in case of failure.

- - -

Proposed resolution:

-

Add to the Effects: clause of  seekg() in -27.7.2.3 [istream.unformatted] and to the Effects: clause of seekp() in -27.7.3.5 [ostream.seeks]:

- -
-

In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure). -

-
- - -

Rationale:

-

Setting failbit is the usual error reporting mechanism for streams

- - - - -
-

130. Return type of container::erase(iterator) differs for associative containers

-

Section: 23.2.4 [associative.reqmts], 23.2.3 [sequence.reqmts] Status: CD1 - Submitter: Andrew Koenig Opened: 1999-03-02 Last modified: 2015-04-08

-

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Duplicate of: 451

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Discussion:

-

Table 67 (23.1.1) says that container::erase(iterator) returns an -iterator. Table 69 (23.1.2) says that in addition to this requirement, -associative containers also say that container::erase(iterator) -returns void. That's not an addition; it's a change to the -requirements, which has the effect of making associative containers -fail to meet the requirements for containers.

- - -

Proposed resolution:

- -

-In 23.2.4 [associative.reqmts], in Table 69 Associative container -requirements, change the return type of a.erase(q) from -void to iterator. Change the -assertion/not/pre/post-condition from "erases the element pointed to -by q" to "erases the element pointed to by q. -Returns an iterator pointing to the element immediately following q -prior to the element being erased. If no such element exists, a.end() -is returned." -

- -

-In 23.2.4 [associative.reqmts], in Table 69 Associative container -requirements, change the return type of a.erase(q1, q2) -from void to iterator. Change the -assertion/not/pre/post-condition from "erases the elements in the -range [q1, q2)" to "erases the elements in the range [q1, -q2). Returns q2." -

- -

-In 23.4.4 [map], in the map class synopsis; and -in 23.4.5 [multimap], in the multimap class synopsis; and -in 23.4.6 [set], in the set class synopsis; and -in 23.4.7 [multiset], in the multiset class synopsis: -change the signature of the first erase overload to -

-
-   iterator erase(iterator position);
-
-

and change the signature of the third erase overload to

-
-  iterator erase(iterator first, iterator last); 
-
- - -

[Pre-Kona: reopened at the request of Howard Hinnant]

- - -

[Post-Kona: the LWG agrees the return type should be -iterator, not void. (Alex Stepanov agrees too.) -Matt provided wording.]

- - -

[ - Sydney: the proposed wording went in the right direction, but it - wasn't good enough. We want to return an iterator from the range form - of erase as well as the single-iterator form. Also, the wording is - slightly different from the wording we have for sequences; there's no - good reason for having a difference. Matt provided new wording, -(reflected above) which we will review at the next meeting. -]

- - -

[ -Redmond: formally voted into WP. -]

- - - - - - - -
-

132. list::resize description uses random access iterators

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Section: 23.3.5.3 [list.capacity] Status: TC1 - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

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Discussion:

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The description reads:

- -

-1- Effects:

- -
         if (sz > size())
-           insert(end(), sz-size(), c);
-         else if (sz < size())
-           erase(begin()+sz, end());
-         else
-           ;                           //  do nothing
- -

Obviously list::resize should not be specified in terms of random access iterators.

- - -

Proposed resolution:

-

Change 23.3.5.3 [list.capacity] paragraph 1 to:

- -

Effects:

- -
         if (sz > size())
-           insert(end(), sz-size(), c);
-         else if (sz < size())
-         {
-           iterator i = begin();
-           advance(i, sz);
-           erase(i, end());
-         }
- -

[Dublin: The LWG asked Howard to discuss exception safety offline -with David Abrahams. They had a discussion and believe there is -no issue of exception safety with the proposed resolution.]

- - - - - - -
-

133. map missing get_allocator()

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Section: 23.4.4 [map] Status: TC1 - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

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Discussion:

The title says it all.

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Proposed resolution:

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Insert in 23.4.4 [map], paragraph 2, -after operator= in the map declaration:

- -
    allocator_type get_allocator() const;
- - - - -
-

134. vector constructors over specified

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Section: 23.3.6.2 [vector.cons] Status: TC1 - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

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Discussion:

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The complexity description says: "It does at most 2N calls to the copy constructor -of T and logN reallocations if they are just input iterators ...".

- -

This appears to be overly restrictive, dictating the precise memory/performance -tradeoff for the implementor.

- - -

Proposed resolution:

-

Change 23.3.6.2 [vector.cons], paragraph 1 to:

- -

-1- Complexity: The constructor template <class -InputIterator> vector(InputIterator first, InputIterator last) -makes only N calls to the copy constructor of T (where N is the -distance between first and last) and no reallocations if iterators -first and last are of forward, bidirectional, or random access -categories. It makes order N calls to the copy constructor of T and -order logN reallocations if they are just input iterators. -

- - -

Rationale:

-

"at most 2N calls" is correct only if the growth factor -is greater than or equal to 2. -

- - - - -
-

136. seekp, seekg setting wrong streams?

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Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2015-04-08

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Discussion:

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I may be misunderstanding the intent, but should not seekg set only -the input stream and seekp set only the output stream? The description -seems to say that each should set both input and output streams. If -that's really the intent, I withdraw this proposal.

- - -

Proposed resolution:

-

In section 27.6.1.3 change:

- -
basic_istream<charT,traits>& seekg(pos_type pos);
-Effects: If fail() != true, executes rdbuf()->pubseekpos(pos).
- -

To:

- -
basic_istream<charT,traits>& seekg(pos_type pos);
-Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::in).
- -

In section 27.6.1.3 change:

- -
basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);
-Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir).
- -

To:

- -
basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);
-Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::in).
- -

In section 27.6.2.4, paragraph 2 change:

- -
-2- Effects: If fail() != true, executes rdbuf()->pubseekpos(pos).
- -

To:

- -
-2- Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out).
- -

In section 27.6.2.4, paragraph 4 change:

- -
-4- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir).
- -

To:

- -
-4- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out).
- -

[Dublin: Dietmar Kühl thinks this is probably correct, but would -like the opinion of more iostream experts before taking action.]

- - -

[Tokyo: Reviewed by the LWG. PJP noted that although his docs are -incorrect, his implementation already implements the Proposed -Resolution.]

- - -

[Post-Tokyo: Matt Austern comments:
-Is it a problem with basic_istream and basic_ostream, or is it a problem -with basic_stringbuf? -We could resolve the issue either by changing basic_istream and -basic_ostream, or by changing basic_stringbuf. I prefer the latter -change (or maybe both changes): I don't see any reason for the standard to -require that std::stringbuf s(std::string("foo"), std::ios_base::in); -s.pubseekoff(0, std::ios_base::beg); must fail.
-This requirement is a bit weird. There's no similar requirement -for basic_streambuf<>::seekpos, or for basic_filebuf<>::seekoff or -basic_filebuf<>::seekpos.]

- - - - - - -
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137. Do use_facet and has_facet look in the global locale?

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Section: 22.3.1 [locale] Status: TC1 - Submitter: Angelika Langer Opened: 1999-03-17 Last modified: 2015-04-08

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Discussion:

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Section 22.3.1 [locale] says:

- -

-4- In the call to use_facet<Facet>(loc), the type argument -chooses a facet, making available all members of the named type. If -Facet is not present in a locale (or, failing that, in the global -locale), it throws the standard exception bad_cast. A C++ program can -check if a locale implements a particular facet with the template -function has_facet<Facet>().

- -

This contradicts the specification given in section -22.3.2 [locale.global.templates]: -

-template <class  Facet> const  Facet& use_facet(const -locale&  loc);
-
--1- Get a reference to a facet of a locale.
--2- Returns: a reference to the corresponding facet of loc, if present.
--3- Throws: bad_cast if has_facet<Facet>(loc) is false.
--4- Notes: The reference returned remains valid at least as long as any copy of loc exists -

- - -

Proposed resolution:

-

Remove the phrase "(or, failing that, in the global locale)" -from section 22.1.1.

- - -

Rationale:

-

Needed for consistency with the way locales are handled elsewhere -in the standard.

- - - - -
-

139. Optional sequence operation table description unclear

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Section: 23.2.3 [sequence.reqmts] Status: TC1 - Submitter: Andrew Koenig Opened: 1999-03-30 Last modified: 2015-04-08

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Discussion:

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The sentence introducing the Optional sequence operation table -(23.1.1 paragraph 12) has two problems:

- -

A. It says ``The operations in table 68 are provided only for the containers for which -they take constant time.''
-
-That could be interpreted in two ways, one of them being ``Even though table 68 shows -particular operations as being provided, implementations are free to omit them if they -cannot implement them in constant time.''
-
-B. That paragraph says nothing about amortized constant time, and it should. 

- - -

Proposed resolution:

-

Replace the wording in 23.1.1 paragraph 12  which begins ``The operations in table 68 are provided only..." -with:

- -
-

Table 68 lists sequence operations that are provided for some types of sequential - containers but not others. An implementation shall provide these operations for all - container types shown in the ``container'' column, and shall implement them so as to take - amortized constant time.

-
- - - - -
-

141. basic_string::find_last_of, find_last_not_of say pos instead of xpos

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Section: 21.4.6.4 [string::insert], 21.4.6.6 [string::replace] Status: TC1 - Submitter: Arch Robison Opened: 1999-04-28 Last modified: 2015-04-08

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Discussion:

-

Sections 21.3.6.4 paragraph 1 and 21.3.6.6 paragraph 1 surely have misprints where they -say:
-
-— xpos <= pos and pos < size();

- -

Surely the document meant to say ``xpos < size()'' in both places.

- -

[Judy Ward also sent in this issue for 21.3.6.4 with the same -proposed resolution.]

- - - -

Proposed resolution:

-

Change Sections 21.3.6.4 paragraph 1 and 21.3.6.6 paragraph 1, the line which says:
-
-— xpos <= pos and pos < size();
-
-to:
-
-— xpos <= pos and xpos < size();

- - - - -
-

142. lexicographical_compare complexity wrong

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Section: 25.4.8 [alg.lex.comparison] Status: TC1 - Submitter: Howard Hinnant Opened: 1999-06-20 Last modified: 2015-04-08

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Discussion:

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The lexicographical_compare complexity is specified as:
-
-     "At most min((last1 - first1), (last2 - first2)) -applications of the corresponding comparison."
-
-The best I can do is twice that expensive.

- -

Nicolai Josuttis comments in lib-6862: You mean, to check for -equality you have to check both < and >? Yes, IMO you are -right! (and Matt states this complexity in his book)

- - - -

Proposed resolution:

-

Change 25.4.8 [alg.lex.comparison] complexity to:

-

- At most 2*min((last1 - first1), (last2 - first2)) - applications of the corresponding comparison. -

- -

Change the example at the end of paragraph 3 to read:

-

- [Example:
-
-     for ( ; first1 != last1 && first2 != last2 ; - ++first1, ++first2) {
-       if (*first1 < *first2) return true;
-       if (*first2 < *first1) return false;
-     }
-     return first1 == last1 && first2 != last2;
-    
- --end example] -

- - - - -
-

144. Deque constructor complexity wrong

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Section: 23.3.3.2 [deque.cons] Status: TC1 - Submitter: Herb Sutter Opened: 1999-05-09 Last modified: 2015-04-08

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Discussion:

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In 23.3.3.2 [deque.cons] paragraph 6, the deque ctor that takes an iterator range appears -to have complexity requirements which are incorrect, and which contradict the -complexity requirements for insert(). I suspect that the text in question, -below, was taken from vector:

-
-

Complexity: If the iterators first and last are forward iterators, - bidirectional iterators, or random access iterators the constructor makes only - N calls to the copy constructor, and performs no reallocations, where N is - last - first.

-
-

The word "reallocations" does not really apply to deque. Further, -all of the following appears to be spurious:

-
-

It makes at most 2N calls to the copy constructor of T and log N - reallocations if they are input iterators.1)

-

1) The complexity is greater in the case of input iterators because each - element must be added individually: it is impossible to determine the distance - between first abd last before doing the copying.

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-

This makes perfect sense for vector, but not for deque. Why should deque gain -an efficiency advantage from knowing in advance the number of elements to -insert?

- - -

Proposed resolution:

-

In 23.3.3.2 [deque.cons] paragraph 6, replace the Complexity description, including the -footnote, with the following text (which also corrects the "abd" -typo):

-
-

Complexity: Makes last - first calls to the copy constructor of T.

-
- - - - -
-

146. complex<T> Inserter and Extractor need sentries

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Section: 26.4.6 [complex.ops] Status: TC1 - Submitter: Angelika Langer Opened: 1999-05-12 Last modified: 2015-04-08

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Discussion:

-

The extractor for complex numbers is specified as: 

- -
- -

template<class T, class charT, class traits> 
- basic_istream<charT, traits>& 
- operator>>(basic_istream<charT, traits>& is, complex<T>& x);
- 
-Effects: Extracts a complex number x of the form: u, (u), or (u,v), -where u is the real part and v is the imaginary part -(lib.istream.formatted). 
-Requires: The input values be convertible to T. If bad input is -encountered, calls is.setstate(ios::failbit) (which may throw -ios::failure (lib.iostate.flags). 
-Returns: is .

- -
-

Is it intended that the extractor for complex numbers does not skip -whitespace, unlike all other extractors in the standard library do? -Shouldn't a sentry be used? 
-
-The inserter for complex numbers is specified as:

- -
- -

template<class T, class charT, class traits> 
- basic_ostream<charT, traits>& 
- operator<<(basic_ostream<charT, traits>& o, const complex<T>& x);
-
-Effects: inserts the complex number x onto the stream o as if it were implemented as follows:
-
- template<class T, class charT, class traits> 
- basic_ostream<charT, traits>& 
- operator<<(basic_ostream<charT, traits>& o, const complex<T>& x) 
- { 
- basic_ostringstream<charT, traits> s; 
- s.flags(o.flags()); 
- s.imbue(o.getloc()); 
- s.precision(o.precision()); 
- s << '(' << x.real() << "," << x.imag() << ')'; 
- return o << s.str(); 
- }

- -
- -

Is it intended that the inserter for complex numbers ignores the -field width and does not do any padding? If, with the suggested -implementation above, the field width were set in the stream then the -opening parentheses would be adjusted, but the rest not, because the -field width is reset to zero after each insertion.

- -

I think that both operations should use sentries, for sake of -consistency with the other inserters and extractors in the -library. Regarding the issue of padding in the inserter, I don't know -what the intent was. 

- - -

Proposed resolution:

-

After 26.4.6 [complex.ops] paragraph 14 (operator>>), add a -Notes clause:

- -
- -

Notes: This extraction is performed as a series of simpler -extractions. Therefore, the skipping of whitespace is specified to be the -same for each of the simpler extractions.

- -
- - -

Rationale:

-

For extractors, the note is added to make it clear that skipping whitespace -follows an "all-or-none" rule.

- -

For inserters, the LWG believes there is no defect; the standard is correct -as written.

- - - - -
-

147. Library Intro refers to global functions that aren't global

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Section: 17.6.5.4 [global.functions] Status: TC1 - Submitter: Lois Goldthwaite Opened: 1999-06-04 Last modified: 2015-04-08

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Discussion:

-

The library had many global functions until 17.4.1.1 [lib.contents] -paragraph 2 was added:

- -
- -

All library entities except macros, operator new and operator -delete are defined within the namespace std or namespaces nested -within namespace std.

- -
- -

It appears "global function" was never updated in the following:

- -
- -

17.4.4.3 - Global functions [lib.global.functions]
-
--1- It is unspecified whether any global functions in the C++ Standard -Library are defined as inline (dcl.fct.spec).
-
--2- A call to a global function signature described in Clauses -lib.language.support through lib.input.output behaves the same as if -the implementation declares no additional global function -signatures.*
-
- [Footnote: A valid C++ program always calls the expected library - global function. An implementation may also define additional - global functions that would otherwise not be called by a valid C++ - program. --- end footnote]
-
--3- A global function cannot be declared by the implementation as -taking additional default arguments. 
-
-17.4.4.4 - Member functions [lib.member.functions]
-
--2- An implementation can declare additional non-virtual member -function signatures within a class:

- -
- -

-- by adding arguments with default values to a member function -signature; The same latitude does not extend to the implementation of -virtual or global functions, however.

- -
-
- - -

Proposed resolution:

-

Change "global" to "global or non-member" in:

-
-

17.4.4.3 [lib.global.functions] section title,
- 17.4.4.3 [lib.global.functions] para 1,
- 17.4.4.3 [lib.global.functions] para 2 in 2 places plus 2 - places in the footnote,
- 17.4.4.3 [lib.global.functions] para 3,
- 17.4.4.4 [lib.member.functions] para 2

-
- - -

Rationale:

-

-Because operator new and delete are global, the proposed resolution -was changed from "non-member" to "global or non-member. -

- - - - -
-

148. Functions in the example facet BoolNames should be const

-

Section: 22.4.8 [facets.examples] Status: TC1 - Submitter: Jeremy Siek Opened: 1999-06-03 Last modified: 2015-04-08

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Discussion:

-

In 22.4.8 [facets.examples] paragraph 13, the do_truename() and -do_falsename() functions in the example facet BoolNames should be -const. The functions they are overriding in -numpunct_byname<char> are const.

- - -

Proposed resolution:

-

In 22.4.8 [facets.examples] paragraph 13, insert "const" in -two places:

-
-

string do_truename() const { return "Oui Oui!"; }
- string do_falsename() const { return "Mais Non!"; }

-
- - - - -
-

149. Insert should return iterator to first element inserted

-

Section: 23.2.3 [sequence.reqmts] Status: C++11 - Submitter: Andrew Koenig Opened: 1999-06-28 Last modified: 2015-04-08

-

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-

Discussion:

-

Suppose that c and c1 are sequential containers and i is an -iterator that refers to an element of c. Then I can insert a copy of -c1's elements into c ahead of element i by executing

- -
- -
c.insert(i, c1.begin(), c1.end());
- -
- -

If c is a vector, it is fairly easy for me to find out where the -newly inserted elements are, even though i is now invalid:

- -
- -
size_t i_loc = i - c.begin();
-c.insert(i, c1.begin(), c1.end());
- -
- -

and now the first inserted element is at c.begin()+i_loc and one -past the last is at c.begin()+i_loc+c1.size().
-
-But what if c is a list? I can still find the location of one -past the last inserted element, because i is still valid. -To find the location of the first inserted element, though, -I must execute something like

- -
- -
for (size_t n = c1.size(); n; --n)
-   --i;
- -
- -

because i is now no longer a random-access iterator.
-
-Alternatively, I might write something like

- -
- -
bool first = i == c.begin();
-list<T>::iterator j = i;
-if (!first) --j;
-c.insert(i, c1.begin(), c1.end());
-if (first)
-   j = c.begin();
-else
-   ++j;
- -
- -

which, although wretched, requires less overhead.
-
-But I think the right solution is to change the definition of insert -so that instead of returning void, it returns an iterator that refers -to the first element inserted, if any, and otherwise is a copy of its -first argument. 

- -

[ -Summit: -]

- - -

-Reopened by Alisdair. -

- -

[ -Post Summit Alisdair adds: -]

- - -
-

-In addition to the original rationale for C++03, this change also gives a -consistent interface for all container insert operations i.e. they all -return an iterator to the (first) inserted item. -

- -

-Proposed wording provided. -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-Q: why isn't this change also proposed for associative containers? -

- -

-A: The returned iterator wouldn't necessarily point to a contiguous range. -

- -

-Moved to Ready. -

-
- - - -

Proposed resolution:

-

-23.2.3 [sequence.reqmts] Table 83 -change return type from void to iterator for the following rows: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - -
Table 83 — Sequence container requirements (in addition to container)
ExpressionReturn typeAssertion/note pre-/post-condition
-a.insert(p,n,t) - -void iterator - -Inserts n copies of t before p. -
-a.insert(p,i,j) - -void iterator - -Each iterator in the range [i,j) shall be -dereferenced exactly once. -pre: i and j are not iterators into a. -Inserts copies of elements in [i, j) before p -
-a.insert(p,il) - -void iterator - -a.insert(p, il.begin(), il.end()). -
-
- -

-Add after p6 23.2.3 [sequence.reqmts]: -

- -
-

-6- ...

- -

-The iterator returned from a.insert(p,n,t) points to the copy of the -first element inserted into a, or p if n == 0. -

- -

-The iterator returned from a.insert(p,i,j) points to the copy of the -first element inserted into a, or p if i == j. -

- -

-The iterator returned from a.insert(p,il) points to the copy of the -first element inserted into a, or p if il is empty. -

- -
- -

-p2 23.3.3 [deque] Update class definition, change return type -from void to iterator: -

- -
-void iterator insert(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-  void iterator insert(const_iterator position, initializer_list<T>);
-
- -

-23.3.3.4 [deque.modifiers] change return type from void to iterator on following declarations: -

- -
-  void iterator insert(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
- -

-Add the following (missing) declaration -

- -
-iterator insert(const_iterator position, initializer_list<T>);
-
- -

-23.3.4 [forwardlist] Update class definition, change return type -from void to iterator: -

- -
-void iterator insert_after(const_iterator position, initializer_list<T> il);
-void iterator insert_after(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-  void iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
-
- -

-p8 23.3.4.5 [forwardlist.modifiers] change return type from void to iterator: -

- -
-void iterator insert_after(const_iterator position, size_type n, const T& x);
-
- -

-Add paragraph: -

- -

-Returns: position. -

- -

-p10 23.3.4.5 [forwardlist.modifiers] change return type from void to iterator: -

- -
-template <class InputIterator>
-  void iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
-
- -

-Add paragraph: -

- -

-Returns: position. -

- -

-p12 23.3.4.5 [forwardlist.modifiers] change return type from void to iterator on following declarations: -

- -
-void iterator insert_after(const_iterator position, initializer_list<T> il);
-
- -

-change return type from void to iterator on following declarations: -

- -

-p2 23.3.5 [list] Update class definition, change return type from void to iterator: -

- -
-void iterator insert(const_iterator position, size_type n, const T& x);
-
-template <class InputIterator>
-void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
-void iterator insert(const_iterator position, initializer_list<T>);
-
- -

-23.3.5.4 [list.modifiers] change return type from void to iterator on following declarations: -

- -
-void iterator insert(const_iterator position, size_type n, const T& x);
-
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
- -

-Add the following (missing) declaration -

- -
-iterator insert(const_iterator position, initializer_list<T>);
-
- -

-p2 23.3.6 [vector] -

- -

-Update class definition, change return type from void to iterator: -

- -
-void iterator insert(const_iterator position, T&& x);
-
-void iterator insert(const_iterator position, size_type n, const T& x);
-
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
-void iterator insert(const_iterator position, initializer_list<T>);
-
- -

-23.3.6.5 [vector.modifiers] change return type from void to iterator on following declarations: -

- -
-void iterator insert(const_iterator position, size_type n, const T& x);
-
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
- -

-Add the following (missing) declaration -

- -
-iterator insert(const_iterator position, initializer_list<T>);
-
- - -

-p1 23.3.7 [vector.bool] Update class definition, change return type from void to iterator: -

- -
-void iterator insert (const_iterator position, size_type n, const bool& x);
-
-template <class InputIterator>
-  void iterator insert(const_iterator position, InputIterator first, InputIterator last);
-
-  void iterator insert(const_iterator position, initializer_list<bool> il);
-
- -

-p5 21.4 [basic.string] Update class definition, change return type from void to iterator: -

- -
-void iterator insert(const_iterator p, size_type n, charT c);
-
-template<class InputIterator>
-  void iterator insert(const_iterator p, InputIterator first, InputIterator last);
-
-void iterator insert(const_iterator p, initializer_list<charT>);
-
- -

-p13 21.4.6.4 [string::insert] change return type from void to iterator: -

- -
-void iterator insert(const_iterator p, size_type n, charT c);
-
- -

-Add paragraph: -

- -

-Returns: an iterator which refers to the copy of the first inserted -character, or p if n == 0. -

- -

-p15 21.4.6.4 [string::insert] change return type from void to iterator: -

- -
-template<class InputIterator>
-  void iterator insert(const_iterator p, InputIterator first, InputIterator last);
-
- -

-Add paragraph: -

- -

-Returns: an iterator which refers to the copy of the first inserted -character, or p if first == last. -

- -

-p17 21.4.6.4 [string::insert] change return type from void to iterator: -

- -
-void iterator insert(const_iterator p, initializer_list<charT> il);
-
- -

-Add paragraph: -

- -

-Returns: an iterator which refers to the copy of the first inserted -character, or p if il is empty. -

- - - -

Rationale:

- -

[ -The following was the C++98/03 rationale and does not necessarily apply to the -proposed resolution in the C++0X time frame: -]

- - -
-

The LWG believes this was an intentional design decision and so is -not a defect. It may be worth revisiting for the next standard.

-
- - - - -
-

150. Find_first_of says integer instead of iterator

-

Section: 25.2.7 [alg.find.first.of] Status: TC1 - Submitter: Matt McClure Opened: 1999-06-30 Last modified: 2015-04-08

-

View all other issues in [alg.find.first.of].

-

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-

Discussion:

- - -

Proposed resolution:

-

Change 25.2.7 [alg.find.first.of] paragraph 2 from:

- -
-

Returns: The first iterator i in the range [first1, last1) such -that for some integer j in the range [first2, last2) ...

-
- -

to:

- -
-

Returns: The first iterator i in the range [first1, last1) such -that for some iterator j in the range [first2, last2) ...

-
- - - - -
-

151. Can't currently clear() empty container

-

Section: 23.2.3 [sequence.reqmts] Status: TC1 - Submitter: Ed Brey Opened: 1999-06-21 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

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-

Discussion:

-

For both sequences and associative containers, a.clear() has the -semantics of erase(a.begin(),a.end()), which is undefined for an empty -container since erase(q1,q2) requires that q1 be dereferenceable -(23.1.1,3 and 23.1.2,7). When the container is empty, a.begin() is -not dereferenceable.
-
-The requirement that q1 be unconditionally dereferenceable causes many -operations to be intuitively undefined, of which clearing an empty -container is probably the most dire.
-
-Since q1 and q2 are only referenced in the range [q1, q2), and [q1, -q2) is required to be a valid range, stating that q1 and q2 must be -iterators or certain kinds of iterators is unnecessary. -

- - -

Proposed resolution:

-

In 23.1.1, paragraph 3, change:

-
-

p and q2 denote valid iterators to a, q and q1 denote valid dereferenceable iterators to a, [q1, q2) denotes a valid range

-
-

to:

-
-

p denotes a valid iterator to a, q denotes a valid dereferenceable iterator to a, [q1, q2) denotes a valid range - in a

-
-

In 23.1.2, paragraph 7, change:

-
-

p and q2 are valid iterators to a, q and q1 are valid dereferenceable - iterators to a, [q1, q2) is a valid range

-
-

to

-
-

p is a valid iterator to a, q is a valid dereferenceable iterator to a, [q1, q2) is a valid range - into a

-
- - - - -
-

152. Typo in scan_is() semantics

-

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The semantics of scan_is() (paragraphs 4 and 6) is not exactly described -because there is no function is() which only takes a character as -argument. Also, in the effects clause (paragraph 3), the semantic is also kept -vague.

- - -

Proposed resolution:

-

In 22.4.1.1.2 [locale.ctype.virtuals] paragraphs 4 and 6, change the returns -clause from:

-
-

"... such that is(*p) -would..."

-
-

to:  "... such that is(m, *p) - would...."

- - - - - -
-

153. Typo in narrow() semantics

-

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: CD1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 207

-

Discussion:

-

The description of the array version of narrow() (in -paragraph 11) is flawed: There is no member do_narrow() which -takes only three arguments because in addition to the range a default -character is needed.

- -

Additionally, for both widen and narrow we have -two signatures followed by a Returns clause that only addresses -one of them.

- - - -

Proposed resolution:

-

Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] -paragraph 10 from:

-

    Returns: do_widen(low, high, to).

- -

to:

-

    Returns: do_widen(c) or do_widen(low, high, to), -respectively.

- -

Change 22.4.1.3.2 [facet.ctype.char.members] paragraph 10 and 11 from:

-
        char        narrow(char c, char /*dfault*/) const;
-        const char* narrow(const char* low, const char* high,
-                           char /*dfault*/, char* to) const;
-
        Returns: do_narrow(low, high, to).
-

to:

-
        char        narrow(char c, char dfault) const;
-        const char* narrow(const char* low, const char* high,
-                           char dfault, char* to) const;
-
        Returns: do_narrow(c, dfault) or
-                 do_narrow(low, high, dfault, to), respectively.
- -

[Kona: 1) the problem occurs in additional places, 2) a user -defined version could be different.]

- - -

[Post-Tokyo: Dietmar provided the above wording at the request of -the LWG. He could find no other places the problem occurred. He -asks for clarification of the Kona "a user defined -version..." comment above. Perhaps it was a circuitous way of -saying "dfault" needed to be uncommented?]

- - -

[Post-Toronto: the issues list maintainer has merged in the -proposed resolution from issue 207, which addresses the -same paragraphs.]

- - - - - - -
-

154. Missing double specifier for do_get()

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

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-

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-

Discussion:

-

The table in paragraph 7 for the length modifier does not list the length -modifier l to be applied if the type is double. Thus, the -standard asks the implementation to do undefined things when using scanf() -(the missing length modifier for scanf() when scanning doubles -is actually a problem I found quite often in production code, too).

- - -

Proposed resolution:

-

In 22.4.2.1.2 [facet.num.get.virtuals], paragraph 7, add a row in the Length -Modifier table to say that for double a length modifier -l is to be used.

- - -

Rationale:

-

The standard makes an embarrassing beginner's mistake.

- - - - -
-

155. Typo in naming the class defining the class Init

-

Section: 27.4 [iostream.objects] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

There are conflicting statements about where the class -Init is defined. According to 27.4 [iostream.objects] paragraph 2 -it is defined as basic_ios::Init, according to 27.5.3 [ios.base] it is defined as ios_base::Init.

- - -

Proposed resolution:

-

Change 27.4 [iostream.objects] paragraph 2 from -"basic_ios::Init" to -"ios_base::Init".

- - -

Rationale:

-

Although not strictly wrong, the standard was misleading enough to warrant -the change.

- - - - -
-

156. Typo in imbue() description

-

Section: 27.5.3.3 [ios.base.locales] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View all other issues in [ios.base.locales].

-

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-

Discussion:

-

There is a small discrepancy between the declarations of -imbue(): in 27.5.3 [ios.base] the argument is passed as -locale const& (correct), in 27.5.3.3 [ios.base.locales] it -is passed as locale const (wrong).

- - -

Proposed resolution:

-

In 27.5.3.3 [ios.base.locales] change the imbue argument -from "locale const" to "locale -const&".

- - - - -
-

158. Underspecified semantics for setbuf()

-

Section: 27.6.3.4.2 [streambuf.virt.buffer] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View all other issues in [streambuf.virt.buffer].

-

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-

Discussion:

-

The default behavior of setbuf() is described only for the -situation that gptr() != 0 && gptr() != egptr(): -namely to do nothing. What has to be done in other situations  -is not described although there is actually only one reasonable -approach, namely to do nothing, too.

- -

Since changing the buffer would almost certainly mess up most -buffer management of derived classes unless these classes do it -themselves, the default behavior of setbuf() should always be -to do nothing.

- - -

Proposed resolution:

-

Change 27.6.3.4.2 [streambuf.virt.buffer], paragraph 3, Default behavior, -to: "Default behavior: Does nothing. Returns this."

- - - - -
-

159. Strange use of underflow()

-

Section: 27.6.3.4.3 [streambuf.virt.get] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

Discussion:

-

The description of the meaning of the result of -showmanyc() seems to be rather strange: It uses calls to -underflow(). Using underflow() is strange because -this function only reads the current character but does not extract -it, uflow() would extract the current character. This should -be fixed to use sbumpc() instead.

- - -

Proposed resolution:

-

Change 27.6.3.4.3 [streambuf.virt.get] paragraph 1, -showmanyc()returns clause, by replacing the word -"supplied" with the words "extracted from the -stream".

- - - - -
-

160. Typo: Use of non-existing function exception()

-

Section: 27.7.2.1 [istream] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View all other issues in [istream].

-

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-

Discussion:

-

The paragraph 4 refers to the function exception() which -is not defined. Probably, the referred function is -basic_ios<>::exceptions().

- - -

Proposed resolution:

-

In 27.7.2.1 [istream], 27.7.2.3 [istream.unformatted], paragraph 1, -27.7.3.1 [ostream], paragraph 3, and 27.7.3.6.1 [ostream.formatted.reqmts], -paragraph 1, change "exception()" to -"exceptions()".

- -

[Note to Editor: "exceptions" with an "s" -is the correct spelling.]

- - - - - - -
-

161. Typo: istream_iterator vs. istreambuf_iterator

-

Section: 27.7.2.2.2 [istream.formatted.arithmetic] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The note in the second paragraph pretends that the first argument -is an object of type istream_iterator. This is wrong: It is -an object of type istreambuf_iterator.

- - -

Proposed resolution:

-

Change 27.7.2.2.2 [istream.formatted.arithmetic] from:

-
-

The first argument provides an object of the istream_iterator class...

-
-

to

-
-

The first argument provides an object of the istreambuf_iterator class...

-
- - - - - -
-

164. do_put() has apparently unused fill argument

-

Section: 22.4.5.3.2 [locale.time.put.virtuals] Status: TC1 - Submitter: Angelika Langer Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

Discussion:

-

In 22.4.5.3.2 [locale.time.put.virtuals] the do_put() function is specified -as taking a fill character as an argument, but the description of the -function does not say whether the character is used at all and, if so, -in which way. The same holds for any format control parameters that -are accessible through the ios_base& argument, such as the -adjustment or the field width. Is strftime() supposed to use the fill -character in any way? In any case, the specification of -time_put.do_put() looks inconsistent to me.

Is the -signature of do_put() wrong, or is the effects clause incomplete?

- - -

Proposed resolution:

-

Add the following note after 22.4.5.3.2 [locale.time.put.virtuals] -paragraph 2:

-
-

[Note: the fill argument may be used in the implementation-defined formats, or by derivations. A space character is a reasonable default - for this argument. --end Note]

-
- - -

Rationale:

-

The LWG felt that while the normative text was correct, -users need some guidance on what to pass for the fill -argument since the standard doesn't say how it's used.

- - - - -
-

165. xsputn(), pubsync() never called by basic_ostream members?

-

Section: 27.7.3.1 [ostream] Status: CD1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Paragraph 2 explicitly states that none of the basic_ostream -functions falling into one of the groups "formatted output functions" -and "unformatted output functions" calls any stream buffer function -which might call a virtual function other than overflow(). Basically -this is fine but this implies that sputn() (this function would call -the virtual function xsputn()) is never called by any of the standard -output functions. Is this really intended? At minimum it would be convenient to -call xsputn() for strings... Also, the statement that overflow() -is the only virtual member of basic_streambuf called is in conflict -with the definition of flush() which calls rdbuf()->pubsync() -and thereby the virtual function sync() (flush() is listed -under "unformatted output functions").

-

In addition, I guess that the sentence starting with "They may use other -public members of basic_ostream ..." probably was intended to -start with "They may use other public members of basic_streamuf..." -although the problem with the virtual members exists in both cases.

-

I see two obvious resolutions:

-
    -
  1. state in a footnote that this means that xsputn() will never be - called by any ostream member and that this is intended.
    2. -
  2. relax the restriction and allow calling overflow() and xsputn(). - Of course, the problem with flush() has to be resolved in some way.
    3. -
- - -

Proposed resolution:

-

Change the last sentence of 27.6.2.1 (lib.ostream) paragraph 2 from:

-
-

They may use other public members of basic_ostream except that they do not - invoke any virtual members of rdbuf() except overflow().

-
-

to:

-
-

They may use other public members of basic_ostream except that they shall - not invoke any virtual members of rdbuf() except overflow(), xsputn(), and - sync().

-
- -

[Kona: the LWG believes this is a problem. Wish to ask Jerry or -PJP why the standard is written this way.]

- - -

[Post-Tokyo: Dietmar supplied wording at the request of the -LWG. He comments: The rules can be made a little bit more specific if -necessary be explicitly spelling out what virtuals are allowed to be -called from what functions and eg to state specifically that flush() -is allowed to call sync() while other functions are not.]

- - - - - - -
-

167. Improper use of traits_type::length()

-

Section: 27.7.3.6.4 [ostream.inserters.character] Status: CD1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Paragraph 4 states that the length is determined using -traits::length(s). Unfortunately, this function is not -defined for example if the character type is wchar_t and the -type of s is char const*. Similar problems exist if -the character type is char and the type of s is -either signed char const* or unsigned char -const*.

- - -

Proposed resolution:

-

Change 27.7.3.6.4 [ostream.inserters.character] paragraph 4 from:

-
-

Effects: Behaves like an formatted inserter (as described in - lib.ostream.formatted.reqmts) of out. After a sentry object is - constructed it inserts characters. The number of characters starting - at s to be inserted is traits::length(s). Padding is determined as - described in lib.facet.num.put.virtuals. The traits::length(s) - characters starting at s are widened using out.widen - (lib.basic.ios.members). The widened characters and any required - padding are inserted into out. Calls width(0).

-
-

to:

-
-

Effects: Behaves like a formatted inserter (as described in - lib.ostream.formatted.reqmts) of out. After a sentry object is - constructed it inserts n characters starting at s, - where n is the number that would be computed as if by:

-
    -
  • traits::length(s) for the overload where the first argument is of - type basic_ostream<charT, traits>& and the second is - of type const charT*, and also for the overload where the first - argument is of type basic_ostream<char, traits>& and - the second is of type const char*.
    • -
  • std::char_traits<char>::length(s) - for the overload where the first argument is of type - basic_ostream<charT, traits>& and the second is of type - const char*.
    • -
  • traits::length(reinterpret_cast<const char*>(s)) - for the other two overloads.
    • -
-

Padding is determined as described in - lib.facet.num.put.virtuals. The n characters starting at - s are widened using out.widen (lib.basic.ios.members). The - widened characters and any required padding are inserted into - out. Calls width(0).

-
- -

[Santa Cruz: Matt supplied new wording]

- - -

[Kona: changed "where n is" to " where n is the - number that would be computed as if by"]

- - - - -

Rationale:

-

We have five separate cases. In two of them we can use the -user-supplied traits class without any fuss. In the other three we -try to use something as close to that user-supplied class as possible. -In two cases we've got a traits class that's appropriate for -char and what we've got is a const signed char* or a const -unsigned char*; that's close enough so we can just use a reinterpret -cast, and continue to use the user-supplied traits class. Finally, -there's one case where we just have to give up: where we've got a -traits class for some arbitrary charT type, and we somehow have to -deal with a const char*. There's nothing better to do but fall back -to char_traits<char>

- - - - - -
-

168. Typo: formatted vs. unformatted

-

Section: 27.7.3.7 [ostream.unformatted] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The first paragraph begins with a descriptions what has to be done -in formatted output functions. Probably this is a typo and the -paragraph really want to describe unformatted output functions...

- - -

Proposed resolution:

-

In 27.7.3.7 [ostream.unformatted] paragraph 1, the first and last -sentences, change the word "formatted" to -"unformatted":

-
-

"Each unformatted output function begins ..."
- "... value specified for the unformatted output - function."

-
- - - - -
-

169. Bad efficiency of overflow() mandated

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Paragraph 8, Notes, of this section seems to mandate an extremely -inefficient way of buffer handling for basic_stringbuf, -especially in view of the restriction that basic_ostream -member functions are not allowed to use xsputn() (see 27.7.3.1 [ostream]): For each character to be inserted, a new buffer -is to be created.

-

Of course, the resolution below requires some handling of -simultaneous input and output since it is no longer possible to update -egptr() whenever epptr() is changed. A possible -solution is to handle this in underflow().

- - -

Proposed resolution:

-

In 27.8.2.4 [stringbuf.virtuals] paragraph 8, Notes, insert the words -"at least" as in the following:

-
-

To make a write position available, the function reallocates (or initially - allocates) an array object with a sufficient number of elements to hold the - current array object (if any), plus at least one additional write - position.

-
- - - - -
-

170. Inconsistent definition of traits_type

-

Section: 27.8.5 [stringstream] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

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-

Discussion:

-

The classes basic_stringstream (27.8.5 [stringstream]), -basic_istringstream (27.8.3 [istringstream]), and -basic_ostringstream (27.8.4 [ostringstream]) are inconsistent -in their definition of the type traits_type: For -istringstream, this type is defined, for the other two it is -not. This should be consistent.

- - -

Proposed resolution:

-

Proposed resolution:

To the declarations of -basic_ostringstream (27.8.4 [ostringstream]) and -basic_stringstream (27.8.5 [stringstream]) add:

-
-
typedef traits traits_type;
-
- - - - -
-

171. Strange seekpos() semantics due to joint position

-

Section: 27.9.1.5 [filebuf.virtuals] Status: CD1 - Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2015-04-08

-

View all other issues in [filebuf.virtuals].

-

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-

Discussion:

-

Overridden virtual functions, seekpos()

In 27.9.1.1 [filebuf] paragraph 3, it is stated that a joint input and -output position is maintained by basic_filebuf. Still, the -description of seekpos() seems to talk about different file -positions. In particular, it is unclear (at least to me) what is -supposed to happen to the output buffer (if there is one) if only the -input position is changed. The standard seems to mandate that the -output buffer is kept and processed as if there was no positioning of -the output position (by changing the input position). Of course, this -can be exactly what you want if the flag ios_base::ate is -set. However, I think, the standard should say something like -this:

-
    -
  • If (which & mode) == 0 neither read nor write position is - changed and the call fails. Otherwise, the joint read and write position is - altered to correspond to sp.
    • -
  • If there is an output buffer, the output sequences is updated and any - unshift sequence is written before the position is altered.
    • -
  • If there is an input buffer, the input sequence is updated after the - position is altered.
    • -
-

Plus the appropriate error handling, that is...

- - -

Proposed resolution:

-

Change the unnumbered paragraph in 27.8.1.4 (lib.filebuf.virtuals) before -paragraph 14 from:

-
-

pos_type seekpos(pos_type sp, ios_base::openmode = ios_base::in | - ios_base::out);

-

Alters the file position, if possible, to correspond to the position stored - in sp (as described below).

-

- if (which&ios_base::in)!=0, set the file position to sp, then update - the input sequence

-

- if (which&ios_base::out)!=0, then update the output sequence, write - any unshift sequence, and set the file position to sp.

-
-

to:

-
-

pos_type seekpos(pos_type sp, ios_base::openmode = ios_base::in | - ios_base::out);

-

Alters the file position, if possible, to correspond to the position stored - in sp (as described below). Altering the file position performs as follows:

-

1. if (om & ios_base::out)!=0, then update the output sequence and - write any unshift sequence;

-

2. set the file position to sp;

-

3. if (om & ios_base::in)!=0, then update the input sequence;

-

where om is the open mode passed to the last call to open(). The operation - fails if is_open() returns false.

-
- -

[Kona: Dietmar is working on a proposed resolution.]

- -

[Post-Tokyo: Dietmar supplied the above wording.]

- - - - - - -
-

172. Inconsistent types for basic_istream::ignore()

-

Section: 27.7.2.3 [istream.unformatted] Status: TC1 - Submitter: Greg Comeau, Dietmar Kühl Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

In 27.7.2.1 [istream] the function -ignore() gets an object of type streamsize as first -argument. However, in 27.7.2.3 [istream.unformatted] -paragraph 23 the first argument is of type int.

- -

As far as I can see this is not really a contradiction because -everything is consistent if streamsize is typedef to be -int. However, this is almost certainly not what was -intended. The same thing happened to basic_filebuf::setbuf(), -as described in issue 173.

- -

Darin Adler also -submitted this issue, commenting: Either 27.6.1.1 should be modified -to show a first parameter of type int, or 27.6.1.3 should be modified -to show a first parameter of type streamsize and use -numeric_limits<streamsize>::max.

- - -

Proposed resolution:

-

In 27.7.2.3 [istream.unformatted] paragraph 23 and 24, change both uses -of int in the description of ignore() to -streamsize.

- - - - -
-

173. Inconsistent types for basic_filebuf::setbuf()

-

Section: 27.9.1.5 [filebuf.virtuals] Status: TC1 - Submitter: Greg Comeau, Dietmar Kühl Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-In 27.9.1.1 [filebuf] the function setbuf() gets an -object of type streamsize as second argument. However, in -27.9.1.5 [filebuf.virtuals] paragraph 9 the second argument is of type -int. -

- -

-As far as I can see this is not really a contradiction because -everything is consistent if streamsize is typedef to be -int. However, this is almost certainly not what was -intended. The same thing happened to basic_istream::ignore(), -as described in issue 172. -

- - - -

Proposed resolution:

-

In 27.9.1.5 [filebuf.virtuals] paragraph 9, change all uses of -int in the description of setbuf() to -streamsize.

- - - - -
-

174. Typo: OFF_T vs. POS_T

-

Section: D.6 [depr.ios.members] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

According to paragraph 1 of this section, streampos is the -type OFF_T, the same type as streamoff. However, in -paragraph 6 the streampos gets the type POS_T

- - -

Proposed resolution:

-

Change D.6 [depr.ios.members] paragraph 1 from "typedef -OFF_T streampos;" to "typedef POS_T -streampos;"

- - - - -
-

175. Ambiguity for basic_streambuf::pubseekpos() and a few other functions.

-

Section: D.6 [depr.ios.members] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

According to paragraph 8 of this section, the methods -basic_streambuf::pubseekpos(), -basic_ifstream::open(), and basic_ofstream::open -"may" be overloaded by a version of this function taking the -type ios_base::open_mode as last argument argument instead of -ios_base::openmode (ios_base::open_mode is defined -in this section to be an alias for one of the integral types). The -clause specifies, that the last argument has a default argument in -three cases. However, this generates an ambiguity with the overloaded -version because now the arguments are absolutely identical if the last -argument is not specified.

- - -

Proposed resolution:

-

In D.6 [depr.ios.members] paragraph 8, remove the default arguments for -basic_streambuf::pubseekpos(), -basic_ifstream::open(), and -basic_ofstream::open().

- - - - -
-

176. exceptions() in ios_base...?

-

Section: D.6 [depr.ios.members] Status: TC1 - Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The "overload" for the function exceptions() in -paragraph 8 gives the impression that there is another function of -this function defined in class ios_base. However, this is not -the case. Thus, it is hard to tell how the semantics (paragraph 9) can -be implemented: "Call the corresponding member function specified -in clause 27 [input.output]."

- - -

Proposed resolution:

-

In D.6 [depr.ios.members] paragraph 8, move the declaration of the -function exceptions()into class basic_ios.

- - - - -
-

179. Comparison of const_iterators to iterators doesn't work

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Judy Ward Opened: 1998-07-02 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Currently the following will not compile on two well-known standard -library implementations:

- -
- 
#include <set>
-using namespace std;
-
-void f(const set<int> &s)
-{
-  set<int>::iterator i;
-  if (i==s.end()); // s.end() returns a const_iterator
-}
-
- -

-The reason this doesn't compile is because operator== was implemented -as a member function of the nested classes set:iterator and -set::const_iterator, and there is no conversion from const_iterator to -iterator. Surprisingly, (s.end() == i) does work, though, because of -the conversion from iterator to const_iterator. -

- -

-I don't see a requirement anywhere in the standard that this must -work. Should there be one? If so, I think the requirement would need -to be added to the tables in section 24.1.1. I'm not sure about the -wording. If this requirement existed in the standard, I would think -that implementors would have to make the comparison operators -non-member functions.

- -

This issues was also raised on comp.std.c++ by Darin -Adler.  The example given was:

- -
- 
bool check_equal(std::deque<int>::iterator i,
-std::deque<int>::const_iterator ci)
-{
-return i == ci;
-}
-
- -

Comment from John Potter:

-
-

- In case nobody has noticed, accepting it will break reverse_iterator. -

- -

- The fix is to make the comparison operators templated on two types. -

- - 
-    template <class Iterator1, class Iterator2>
-    bool operator== (reverse_iterator<Iterator1> const& x,
-                     reverse_iterator<Iterator2> const& y);
-
- -

- Obviously: return x.base() == y.base(); -

- -

- Currently, no reverse_iterator to const_reverse_iterator compares are - valid. -

- -

- BTW, I think the issue is in support of bad code. Compares should be - between two iterators of the same type. All std::algorithms require - the begin and end iterators to be of the same type. -

-
- - -

Proposed resolution:

-

Insert this paragraph after 23.2 [container.requirements] paragraph 7:

-
-

In the expressions

- 
-    i == j
-    i != j
-    i < j
-    i <= j
-    i >= j
-    i > j
-    i - j
-
-

Where i and j denote objects of a container's iterator type, - either or both may be replaced by an object of the container's - const_iterator type referring to the same element with no - change in semantics.

-
- -

[post-Toronto: Judy supplied a proposed resolution saying that -iterator and const_iterator could be freely mixed in -iterator comparison and difference operations.]

- - -

[Redmond: Dave and Howard supplied a new proposed resolution which -explicitly listed expressions; there was concern that the previous -proposed resolution was too informal.]

- - - -

Rationale:

-

-The LWG believes it is clear that the above wording applies only to -the nested types X::iterator and X::const_iterator, -where X is a container. There is no requirement that -X::reverse_iterator and X::const_reverse_iterator -can be mixed. If mixing them is considered important, that's a -separate issue. (Issue 280.) -

- - - - -
-

180. Container member iterator arguments constness has unintended consequences

-

Section: 21.4 [basic.string] Status: CD1 - Submitter: Dave Abrahams Opened: 1999-07-01 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

It is the constness of the container which should control whether -it can be modified through a member function such as erase(), not the -constness of the iterators. The iterators only serve to give -positioning information.

- -

Here's a simple and typical example problem which is currently very -difficult or impossible to solve without the change proposed -below.

- -

Wrap a standard container C in a class W which allows clients to -find and read (but not modify) a subrange of (C.begin(), C.end()]. The -only modification clients are allowed to make to elements in this -subrange is to erase them from C through the use of a member function -of W.

- -

[ -post Bellevue, Alisdair adds: -]

- - -
-

-This issue was implemented by -N2350 -for everything but basic_string. -

- -

-Note that the specific example in this issue (basic_string) is the one place -we forgot to amend in -N2350, -so we might open this issue for that -single container? -

-
- -

[ -Sophia Antipolis: -]

- - -
-

-This was a fix that was intended for all standard library containers, -and has been done for other containers, but string was missed. -

-

-The wording updated. -

-

-We did not make the change in replace, because this change would affect -the implementation because the string may be written into. This is an -issue that should be taken up by concepts. -

-

-We note that the supplied wording addresses the initializer list provided in -N2679. -

-
- - - -

Proposed resolution:

-

-Update the following signature in the basic_string class template definition in -21.4 [basic.string], p5: -

-
-namespace std {
-  template<class charT, class traits = char_traits<charT>,
-    class Allocator = allocator<charT> >
-  class basic_string {
-
-    ...
-
-    iterator insert(const_iterator p, charT c);
-    void insert(const_iterator p, size_type n, charT c);
-    template<class InputIterator>
-      void insert(const_iterator p, InputIterator first, InputIterator last);
-    void insert(const_iterator p, initializer_list<charT>);
-
-    ...
-
-    iterator erase(const_iterator const_position);
-    iterator erase(const_iterator first, const_iterator last);
-
-    ...
-
-  };
-}
-
- -

-Update the following signatures in 21.4.6.4 [string::insert]: -

- -
-iterator insert(const_iterator p, charT c);
-void insert(const_iterator p, size_type n, charT c);
-template<class InputIterator>
-  void insert(const_iterator p, InputIterator first, InputIterator last);
-void insert(const_iterator p, initializer_list<charT>);
-
- -

-Update the following signatures in 21.4.6.5 [string::erase]: -

- -
-iterator erase(const_iterator const_position);
-iterator erase(const_iterator first, const_iterator last);
-
- - - -

Rationale:

-

The issue was discussed at length. It was generally agreed that 1) -There is no major technical argument against the change (although -there is a minor argument that some obscure programs may break), and -2) Such a change would not break const correctness. The concerns about -making the change were 1) it is user detectable (although only in -boundary cases), 2) it changes a large number of signatures, and 3) it -seems more of a design issue that an out-and-out defect.

- -

The LWG believes that this issue should be considered as part of a -general review of const issues for the next revision of the -standard. Also see issue 200.

- - - - -
-

181. make_pair() unintended behavior

-

Section: 20.3 [pairs] Status: TC1 - Submitter: Andrew Koenig Opened: 1999-08-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The claim has surfaced in Usenet that expressions such as
-
-       make_pair("abc", 3)
-
-are illegal, notwithstanding their use in examples, because template instantiation tries to bind the first template -parameter to const char (&)[4], which type is uncopyable.
-
-I doubt anyone intended that behavior... -

- - -

Proposed resolution:

-

In 20.2 [utility], paragraph 1 change the following -declaration of make_pair():

-
- 
template <class T1, class T2> pair<T1,T2> make_pair(const T1&, const T2&);
-
-

to:

-
- 
template <class T1, class T2> pair<T1,T2> make_pair(T1, T2);
-
-

In 20.3 [pairs] paragraph 7 and the line before, change:

-
-
template <class T1, class T2>
-pair<T1, T2> make_pair(const T1& x, const T2& y);
-
-

to:

-
-
template <class T1, class T2>
-pair<T1, T2> make_pair(T1 x, T2 y);
-
-

and add the following footnote to the effects clause:

-
-

According to 12.8 [class.copy], an implementation is permitted - to not perform a copy of an argument, thus avoiding unnecessary - copies.

-
- - -

Rationale:

-

Two potential fixes were suggested by Matt Austern and Dietmar -Kühl, respectively, 1) overloading with array arguments, and 2) use of -a reference_traits class with a specialization for arrays. Andy -Koenig suggested changing to pass by value. In discussion, it appeared -that this was a much smaller change to the standard that the other two -suggestions, and any efficiency concerns were more than offset by the -advantages of the solution. Two implementors reported that the -proposed resolution passed their test suites.

- - - - -
-

182. Ambiguous references to size_t

-

Section: 17 [library] Status: CD1 - Submitter: Al Stevens Opened: 1999-08-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Many references to size_t throughout the document -omit the std:: namespace qualification.

For -example, 17.6.4.6 [replacement.functions] paragraph 2:

-
-
 operator new(size_t)
- operator new(size_t, const std::nothrow_t&)
- operator new[](size_t)
- operator new[](size_t, const std::nothrow_t&)
-
- - -

Proposed resolution:

-

In 17.6.4.6 [replacement.functions] paragraph 2: replace:

-
-

- operator new(size_t)
- - operator new(size_t, const std::nothrow_t&)
- - operator new[](size_t)
- - operator new[](size_t, const std::nothrow_t&)

-
-

by:

-
-
- operator new(std::size_t)
-- operator new(std::size_t, const std::nothrow_t&)
-- operator new[](std::size_t)
-- operator new[](std::size_t, const std::nothrow_t&)
-
-

In [lib.allocator.requirements] 20.1.5, paragraph 4: replace:

-
-

The typedef members pointer, const_pointer, size_type, and difference_type - are required to be T*, T const*, size_t, and ptrdiff_t, respectively.

-
-

 by:

-
-

The typedef members pointer, const_pointer, size_type, and difference_type - are required to be T*, T const*, std::size_t, and std::ptrdiff_t, - respectively.

-
-

In [lib.allocator.members] 20.4.1.1, paragraphs 3 and 6: replace:

-
-

3 Notes: Uses ::operator new(size_t) (18.4.1).

-

6 Note: the storage is obtained by calling ::operator new(size_t), but it - is unspecified when or how often this function is called. The use of hint is - unspecified, but intended as an aid to locality if an implementation so - desires.

-
-

by:

-
-

3 Notes: Uses ::operator new(std::size_t) (18.4.1).

-

6 Note: the storage is obtained by calling ::operator new(std::size_t), but - it is unspecified when or how often this function is called. The use of hint - is unspecified, but intended as an aid to locality if an implementation so - desires.

-
-

In [lib.char.traits.require] 21.1.1, paragraph 1: replace:

-
-

In Table 37, X denotes a Traits class defining types and functions for the - character container type CharT; c and d denote values of type CharT; p and q - denote values of type const CharT*; s denotes a value of type CharT*; n, i and - j denote values of type size_t; e and f denote values of type X::int_type; pos - denotes a value of type X::pos_type; and state denotes a value of type X::state_type.

-
-

by:

-
-

In Table 37, X denotes a Traits class defining types and functions for the - character container type CharT; c and d denote values of type CharT; p and q - denote values of type const CharT*; s denotes a value of type CharT*; n, i and - j denote values of type std::size_t; e and f denote values of type X::int_type; - pos denotes a value of type X::pos_type; and state denotes a value of type X::state_type.

-
-

In [lib.char.traits.require] 21.1.1, table 37: replace the return type of -X::length(p): "size_t" by "std::size_t".

-

In [lib.std.iterator.tags] 24.3.3, paragraph 2: replace:
-    typedef ptrdiff_t difference_type;
- by:
-    typedef std::ptrdiff_t difference_type;

-

In [lib.locale.ctype] 22.2.1.1 put namespace std { ...} around the declaration of template <class charT> class ctype.
-
- In [lib.iterator.traits] 24.3.1, paragraph 2 put namespace std { ...} around the declaration of:
-
-    template<class Iterator> struct iterator_traits
-    template<class T> struct iterator_traits<T*>
-    template<class T> struct iterator_traits<const T*>

- - -

Rationale:

-

The LWG believes correcting names like size_t and -ptrdiff_t to std::size_t and std::ptrdiff_t -to be essentially editorial. There there can't be another size_t or -ptrdiff_t meant anyway because, according to 17.6.4.3.3 [extern.types],

- -

-For each type T from the Standard C library, the types ::T and std::T -are reserved to the implementation and, when defined, ::T shall be -identical to std::T. -

- -

The issue is treated as a Defect Report to make explicit the Project -Editor's authority to make this change.

- -

[Post-Tokyo: Nico Josuttis provided the above wording at the -request of the LWG.]

- - -

[Toronto: This is tangentially related to issue 229, but only tangentially: the intent of this issue is to -address use of the name size_t in contexts outside of -namespace std, such as in the description of ::operator new. -The proposed changes should be reviewed to make sure they are -correct.]

- - -

[pre-Copenhagen: Nico has reviewed the changes and believes -them to be correct.]

- - - - - - - -
-

183. I/O stream manipulators don't work for wide character streams

-

Section: 27.7.4 [std.manip] Status: CD1 - Submitter: Andy Sawyer Opened: 1999-07-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

27.7.4 [std.manip] paragraph 3 says (clause numbering added for -exposition):

-
-

Returns: An object s of unspecified type such that if [1] out is an (instance -of) basic_ostream then the expression out<<s behaves as if f(s) were -called, and if [2] in is an (instance of) basic_istream then the expression -in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& -f(ios_base& str, ios_base::fmtflags mask) { // reset specified flags -str.setf(ios_base::fmtflags(0), mask); return str; } [3] The expression -out<<s has type ostream& and value out. [4] The expression in>>s -has type istream& and value in.

-
-

Given the definitions [1] and [2] for out and in, surely [3] should read: -"The expression out << s has type basic_ostream& ..." and -[4] should read: "The expression in >> s has type basic_istream& -..."

-

If the wording in the standard is correct, I can see no way of implementing -any of the manipulators so that they will work with wide character streams.

-

e.g. wcout << setbase( 16 );

-

Must have value 'wcout' (which makes sense) and type 'ostream&' (which -doesn't).

-

The same "cut'n'paste" type also seems to occur in Paras 4,5,7 and -8. In addition, Para 6 [setfill] has a similar error, but relates only to -ostreams.

-

I'd be happier if there was a better way of saying this, to make it clear -that the value of the expression is "the same specialization of -basic_ostream as out"&

- - -

Proposed resolution:

-

Replace section 27.7.4 [std.manip] except paragraph 1 with the -following:

-
-

2- The type designated smanip in each of the following function descriptions is implementation-specified and may be different for each -function.
-
-smanip resetiosflags(ios_base::fmtflags mask);
-
--3- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves -as if f(s, mask) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if -f(s, mask) were called. The function f can be defined as:*
-
-[Footnote: The expression cin >> resetiosflags(ios_base::skipws) clears ios_base::skipws in the format flags stored in the -basic_istream<charT,traits> object cin (the same as cin >> noskipws), and the expression cout << resetiosflags(ios_base::showbase) clears -ios_base::showbase in the format flags stored in the basic_ostream<charT,traits> object cout (the same as cout << -noshowbase). --- end footnote]
-
-     ios_base& f(ios_base& str, ios_base::fmtflags mask)
-   {
-   // reset specified flags
-   str.setf(ios_base::fmtflags(0), mask);
-   return str;
-   }
-
-The expression out<<s has type basic_ostream<charT,traits>& and value out. -The expression in>>s has type basic_istream<charT,traits>& and value in.
-
- smanip setiosflags(ios_base::fmtflags mask);
-
--4- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves -as if f(s, mask) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, -mask) were called. The function f can be defined as:
-
-     ios_base& f(ios_base& str, ios_base::fmtflags mask)
-   {
-   // set specified flags
-   str.setf(mask);
-   return str;
-   }
-
-The expression out<<s has type basic_ostream<charT,traits>& and value out. -The expression in>>s has type basic_istream<charT,traits>& and value in.
-
-smanip setbase(int base);
-
--5- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves -as if f(s, base) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, -base) were called. The function f can be defined as:
-
-     ios_base& f(ios_base& str, int base)
-   {
-   // set basefield
-   str.setf(base == 8 ? ios_base::oct :
-   base == 10 ? ios_base::dec :
-   base == 16 ? ios_base::hex :
-   ios_base::fmtflags(0), ios_base::basefield);
-   return str;
-   }
-
-The expression out<<s has type basic_ostream<charT,traits>& and value out. -The expression in>>s has type basic_istream<charT,traits>& and value in.
-
-smanip setfill(char_type c);
-
--6- Returns: An object s of unspecified type such that if out is (or is derived from) basic_ostream<charT,traits> and c has type charT then the -expression out<<s behaves as if f(s, c) were called. The function f can be -defined as:
-
-      template<class charT, class traits>
-   basic_ios<charT,traits>& f(basic_ios<charT,traits>& str, charT c)
-   {
-   // set fill character
-   str.fill(c);
-   return str;
-   }
-
-The expression out<<s has type basic_ostream<charT,traits>& and value out.
-
-smanip setprecision(int n);
-
--7- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves -as if f(s, n) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, n) -were called. The function f can be defined as:
-
-      ios_base& f(ios_base& str, int n)
-   {
-   // set precision
-   str.precision(n);
-   return str;
-   }
-
-The expression out<<s has type basic_ostream<charT,traits>& and value out. -The expression in>>s has type basic_istream<charT,traits>& and value in
-.
-smanip setw(int n);
-
--8- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves -as if f(s, n) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, n) -were called. The function f can be defined as:
-
-      ios_base& f(ios_base& str, int n)
-   {
-   // set width
-   str.width(n);
-   return str;
-   }
-
-The expression out<<s has type -basic_ostream<charT,traits>& and value out. The expression -in>>s has type basic_istream<charT,traits>& and value -in. -

-
- -

[Kona: Andy Sawyer and Beman Dawes will work to improve the wording of -the proposed resolution.]

- - -

[Tokyo - The LWG noted that issue 216 involves -the same paragraphs.]

- - -

[Post-Tokyo: The issues list maintainer combined the proposed -resolution of this issue with the proposed resolution for issue 216 as they both involved the same paragraphs, and were so -intertwined that dealing with them separately appear fraught with -error. The full text was supplied by Bill Plauger; it was cross -checked against changes supplied by Andy Sawyer. It should be further -checked by the LWG.]

- - - - - - -
-

184. numeric_limits<bool> wording problems

-

Section: 18.3.2.7 [numeric.special] Status: CD1 - Submitter: Gabriel Dos Reis Opened: 1999-07-21 Last modified: 2015-04-08

-

View all other issues in [numeric.special].

-

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-

Discussion:

-

bools are defined by the standard to be of integer types, as per -3.9.1 [basic.fundamental] paragraph 7. However "integer types" -seems to have a special meaning for the author of 18.2. The net effect -is an unclear and confusing specification for -numeric_limits<bool> as evidenced below.

- -

18.2.1.2/7 says numeric_limits<>::digits is, for built-in integer -types, the number of non-sign bits in the representation.

- -

4.5/4 states that a bool promotes to int ; whereas 4.12/1 says any non zero -arithmetical value converts to true.

- -

I don't think it makes sense at all to require -numeric_limits<bool>::digits and numeric_limits<bool>::digits10 to -be meaningful.

- -

The standard defines what constitutes a signed (resp. unsigned) integer -types. It doesn't categorize bool as being signed or unsigned. And the set of -values of bool type has only two elements.

- -

I don't think it makes sense to require numeric_limits<bool>::is_signed -to be meaningful.

- -

18.2.1.2/18 for numeric_limits<integer_type>::radix  says:

-
-

For integer types, specifies the base of the representation.186)

-
- -

This disposition is at best misleading and confusing for the standard -requires a "pure binary numeration system" for integer types as per -3.9.1/7

- -

The footnote 186) says: "Distinguishes types with base other than 2 (e.g -BCD)."  This also erroneous as the standard never defines any integer -types with base representation other than 2.

- -

Furthermore, numeric_limits<bool>::is_modulo and -numeric_limits<bool>::is_signed have similar problems.

- - -

Proposed resolution:

-

Append to the end of 18.3.2.7 [numeric.special]:

-
-

The specialization for bool shall be provided as follows:

- 
    namespace std {
-       template<> class numeric_limits<bool> {
-       public:
-         static const bool is_specialized = true;
-         static bool min() throw() { return false; }
-         static bool max() throw() { return true; }
-
-         static const int  digits = 1;
-         static const int  digits10 = 0;
-         static const bool is_signed = false;
-         static const bool is_integer = true;
-         static const bool is_exact = true;
-         static const int  radix = 2;
-         static bool epsilon() throw() { return 0; }
-         static bool round_error() throw() { return 0; }
-
-         static const int  min_exponent = 0;
-         static const int  min_exponent10 = 0;
-         static const int  max_exponent = 0;
-         static const int  max_exponent10 = 0;
-
-         static const bool has_infinity = false;
-         static const bool has_quiet_NaN = false;
-         static const bool has_signaling_NaN = false;
-         static const float_denorm_style has_denorm = denorm_absent;
-         static const bool has_denorm_loss = false;
-         static bool infinity() throw() { return 0; }
-         static bool quiet_NaN() throw() { return 0; }
-         static bool signaling_NaN() throw() { return 0; }
-         static bool denorm_min() throw() { return 0; }
-
-         static const bool is_iec559 = false;
-         static const bool is_bounded = true;
-         static const bool is_modulo = false;
-
-         static const bool traps = false;
-         static const bool tinyness_before = false;
-         static const float_round_style round_style = round_toward_zero;
-       };
-     }
-
- -

[Tokyo:  The LWG desires wording that specifies exact values -rather than more general wording in the original proposed -resolution.]

- - -

[Post-Tokyo:  At the request of the LWG in Tokyo, Nico -Josuttis provided the above wording.]

- - - - - - -
-

185. Questionable use of term "inline"

-

Section: 20.9 [function.objects] Status: CD1 - Submitter: UK Panel Opened: 1999-07-26 Last modified: 2015-04-08

-

View all other issues in [function.objects].

-

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-

Discussion:

-

Paragraph 4 of 20.9 [function.objects] says:

-
-

 [Example: To negate every element of a: transform(a.begin(), a.end(), - a.begin(), negate<double>()); The corresponding functions will inline - the addition and the negation. end example]

-
-

(Note: The "addition" referred to in the above is in para 3) we can -find no other wording, except this (non-normative) example which suggests that -any "inlining" will take place in this case.

-

Indeed both:

-
-

17.4.4.3 Global Functions [lib.global.functions] 1 It is - unspecified whether any global functions in the C++ Standard Library - are defined as inline (7.1.2).

-
-

and

-
-

17.4.4.4 Member Functions [lib.member.functions] 1 It is - unspecified whether any member functions in the C++ Standard Library - are defined as inline (7.1.2).

-
-

take care to state that this may indeed NOT be the case.

-

Thus the example "mandates" behavior that is explicitly -not required elsewhere.

- - -

Proposed resolution:

-

In 20.9 [function.objects] paragraph 1, remove the sentence:

-
-

They are important for the effective use of the library.

-
-

Remove 20.9 [function.objects] paragraph 2, which reads:

-
-

Using function objects together with function templates - increases the expressive power of the library as well as making the - resulting code much more efficient.

-
-

In 20.9 [function.objects] paragraph 4, remove the sentence:

-
-

The corresponding functions will inline the addition and the - negation.

-
- -

[Kona: The LWG agreed there was a defect.]

- -

[Tokyo: The LWG crafted the proposed resolution.]

- - - - - - -
-

186. bitset::set() second parameter should be bool

-

Section: 20.6.2 [bitset.members] Status: CD1 - Submitter: Darin Adler Opened: 1999-08-13 Last modified: 2015-04-08

-

View all other issues in [bitset.members].

-

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-

Discussion:

-

In section 20.6.2 [bitset.members], paragraph 13 defines the -bitset::set operation to take a second parameter of type int. The -function tests whether this value is non-zero to determine whether to -set the bit to true or false. The type of this second parameter should -be bool. For one thing, the intent is to specify a Boolean value. For -another, the result type from test() is bool. In addition, it's -possible to slice an integer that's larger than an int. This can't -happen with bool, since conversion to bool has the semantic of -translating 0 to false and any non-zero value to true.

- - -

Proposed resolution:

-

In 20.6 [template.bitset] Para 1 Replace:

-
-
bitset<N>& set(size_t pos, int val = true );
-
-

With:

-
- 
bitset<N>& set(size_t pos, bool val = true );
-
-

In 20.6.2 [bitset.members] Para 12(.5) Replace:

-
- 
bitset<N>& set(size_t pos, int val = 1 );
-
-

With:

-
- 
bitset<N>& set(size_t pos, bool val = true );
-
- -

[Kona: The LWG agrees with the description.  Andy Sawyer will work -on better P/R wording.]

- -

[Post-Tokyo: Andy provided the above wording.]

- - - -

Rationale:

-

bool is a better choice. It is believed that binary -compatibility is not an issue, because this member function is -usually implemented as inline, and because it is already -the case that users cannot rely on the type of a pointer to a -nonvirtual member of a standard library class.

- - - - - -
-

187. iter_swap underspecified

-

Section: 25.3.3 [alg.swap] Status: CD1 - Submitter: Andrew Koenig Opened: 1999-08-14 Last modified: 2015-04-08

-

View all other issues in [alg.swap].

-

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-

Discussion:

-

The description of iter_swap in 25.2.2 paragraph 7,says that it -``exchanges the values'' of the objects to which two iterators -refer.

What it doesn't say is whether it does so using swap -or using the assignment operator and copy constructor.

This -question is an important one to answer, because swap is specialized to -work efficiently for standard containers.
For example:

-
-
vector<int> v1, v2;
-iter_swap(&v1, &v2);
-
-

Is this call to iter_swap equivalent to calling swap(v1, v2)?  -Or is it equivalent to

-
-
{
-vector<int> temp = v1;
-v1 = v2;
-v2 = temp;
-}
-
-

The first alternative is O(1); the second is O(n).

-

A LWG member, Dave Abrahams, comments:

-
-

Not an objection necessarily, but I want to point out the cost of -that requirement:

-
-

iter_swap(list<T>::iterator, list<T>::iterator)

-
-

can currently be specialized to be more efficient than -iter_swap(T*,T*) for many T (by using splicing). Your proposal would -make that optimization illegal. 

-
- -

[Kona: The LWG notes the original need for iter_swap was proxy iterators -which are no longer permitted.]

- - - -

Proposed resolution:

-

Change the effect clause of iter_swap in 25.2.2 paragraph 7 from:

-
-

Exchanges the values pointed to by the two iterators a and b.

-
-

to

-
-

swap(*a, *b).

-
- - - -

Rationale:

-

It's useful to say just what iter_swap does. There may be - some iterators for which we want to specialize iter_swap, - but the fully general version should have a general specification.

- -

Note that in the specific case of list<T>::iterator, -iter_swap should not be specialized as suggested above. That would do -much more than exchanging the two iterators' values: it would change -predecessor/successor relationships, possibly moving the iterator from -one list to another. That would surely be inappropriate.

- - - - - -
-

189. setprecision() not specified correctly

-

Section: 27.5.3.2 [fmtflags.state] Status: TC1 - Submitter: Andrew Koenig Opened: 1999-08-25 Last modified: 2015-04-08

-

View all other issues in [fmtflags.state].

-

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-

Discussion:

-

27.4.2.2 paragraph 9 claims that setprecision() sets the precision, -and includes a parenthetical note saying that it is the number of -digits after the decimal point.
-
-This claim is not strictly correct. For example, in the default -floating-point output format, setprecision sets the number of -significant digits printed, not the number of digits after the decimal -point.
-
-I would like the committee to look at the definition carefully and -correct the statement in 27.4.2.2

- - -

Proposed resolution:

-

Remove from 27.5.3.2 [fmtflags.state], paragraph 9, the text -"(number of digits after the decimal point)".

- - - - -
-

193. Heap operations description incorrect

-

Section: 25.4.6 [alg.heap.operations] Status: TC1 - Submitter: Markus Mauhart Opened: 1999-09-24 Last modified: 2015-04-08

-

View all other issues in [alg.heap.operations].

-

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-

Duplicate of: 216

-

Discussion:

-

25.3.6 [lib.alg.heap.operations] states two key properties of a heap [a,b), the first of them -is
-
-    `"(1) *a is the largest element"
-
-I think this is incorrect and should be changed to the wording in the proposed -resolution.

-

Actually there are two independent changes:

-
-

A-"part of largest equivalence class" instead of "largest", cause 25.3 - [lib.alg.sorting] asserts "strict weak ordering" for all its sub clauses.

-

B-Take 'an oldest' from that equivalence class, otherwise the heap functions could not be used for a - priority queue as explained in 23.2.3.2.2 [lib.priqueue.members] (where I assume that a "priority queue" respects priority AND time).

-
- - -

Proposed resolution:

-

Change 25.4.6 [alg.heap.operations] property (1) from:

-
-

(1) *a is the largest element

-
-

to:

-
-

(1) There is no element greater than *a

-
- - - - - -
-

195. Should basic_istream::sentry's constructor ever set eofbit?

-

Section: 27.7.2.1.3 [istream::sentry] Status: TC1 - Submitter: Matt Austern Opened: 1999-10-13 Last modified: 2015-04-08

-

View all other issues in [istream::sentry].

-

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-

Discussion:

-

Suppose that is.flags() & ios_base::skipws is nonzero. -What should basic_istream<>::sentry's constructor do if it -reaches eof while skipping whitespace? 27.6.1.1.2/5 suggests it -should set failbit. Should it set eofbit as well? The standard -doesn't seem to answer that question.

- -

On the one hand, nothing in 27.7.2.1.3 [istream::sentry] says that -basic_istream<>::sentry should ever set eofbit. On the -other hand, 27.7.2.1 [istream] paragraph 4 says that if -extraction from a streambuf "returns -traits::eof(), then the input function, except as explicitly -noted otherwise, completes its actions and does -setstate(eofbit)". So the question comes down to -whether basic_istream<>::sentry's constructor is an -input function.

- -

Comments from Jerry Schwarz:

-
-

It was always my intention that eofbit should be set any time that a -virtual returned something to indicate eof, no matter what reason -iostream code had for calling the virtual.

-

-The motivation for this is that I did not want to require streambufs -to behave consistently if their virtuals are called after they have -signaled eof.

-

-The classic case is a streambuf reading from a UNIX file. EOF isn't -really a state for UNIX file descriptors. The convention is that a -read on UNIX returns 0 bytes to indicate "EOF", but the file -descriptor isn't shut down in any way and future reads do not -necessarily also return 0 bytes. In particular, you can read from -tty's on UNIX even after they have signaled "EOF". (It -isn't always understood that a ^D on UNIX is not an EOF indicator, but -an EOL indicator. By typing a "line" consisting solely of -^D you cause a read to return 0 bytes, and by convention this is -interpreted as end of file.)

-
- - -

Proposed resolution:

-

Add a sentence to the end of 27.6.1.1.2 paragraph 2:

-
-

If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() -returns traits::eof(), the function calls -setstate(failbit | eofbit) (which may throw -ios_base::failure). -

-
- - - - -
-

198. Validity of pointers and references unspecified after iterator destruction

-

Section: X [iterator.concepts] Status: CD1 - Submitter: Beman Dawes Opened: 1999-11-03 Last modified: 2015-04-08

-

View all other issues in [iterator.concepts].

-

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-

Discussion:

-

-Is a pointer or reference obtained from an iterator still valid after -destruction of the iterator? -

-

-Is a pointer or reference obtained from an iterator still valid after the value -of the iterator changes? -

-
-
-#include <iostream>
-#include <vector>
-#include <iterator>
-
-int main()
-{
-    typedef std::vector<int> vec_t;
-    vec_t v;
-    v.push_back( 1 );
-
-    // Is a pointer or reference obtained from an iterator still
-    // valid after destruction of the iterator?
-    int * p = &*v.begin();
-    std::cout << *p << '\n';  // OK?
-
-    // Is a pointer or reference obtained from an iterator still
-    // valid after the value of the iterator changes?
-    vec_t::iterator iter( v.begin() );
-    p = &*iter++;
-    std::cout << *p << '\n';  // OK?
-
-    return 0;
-}
-
-
- -

The standard doesn't appear to directly address these -questions. The standard needs to be clarified. At least two real-world -cases have been reported where library implementors wasted -considerable effort because of the lack of clarity in the -standard. The question is important because requiring pointers and -references to remain valid has the effect for practical purposes of -prohibiting iterators from pointing to cached rather than actual -elements of containers.

- -

The standard itself assumes that pointers and references obtained -from an iterator are still valid after iterator destruction or -change. The definition of reverse_iterator::operator*(), 24.5.1.3.3 [reverse.iter.conv], which returns a reference, defines -effects:

- -
- 
Iterator tmp = current;
-return *--tmp;
-
-

The definition of reverse_iterator::operator->(), 24.5.1.3.4 [reverse.iter.op.star], which returns a pointer, defines effects:

-
- 
return &(operator*());
-
- -

Because the standard itself assumes pointers and references remain -valid after iterator destruction or change, the standard should say so -explicitly. This will also reduce the chance of user code breaking -unexpectedly when porting to a different standard library -implementation.

- - -

Proposed resolution:

-

Add a new paragraph to X [iterator.concepts]:

-

-Destruction of an iterator may invalidate pointers and references -previously obtained from that iterator. -

- -

Replace paragraph 1 of 24.5.1.3.3 [reverse.iter.conv] with:

- -
-

Effects:

-
-  this->tmp = current;
-  --this->tmp;
-  return *this->tmp;
-
- -

-[Note: This operation must use an auxiliary member variable, -rather than a temporary variable, to avoid returning a reference that -persists beyond the lifetime of its associated iterator. (See -X [iterator.concepts].) The name of this member variable is shown for -exposition only. --end note] -

-
- -

[Post-Tokyo: The issue has been reformulated purely -in terms of iterators.]

- - -

[Pre-Toronto: Steve Cleary pointed out the no-invalidation -assumption by reverse_iterator. The issue and proposed resolution was -reformulated yet again to reflect this reality.]

- - -

[Copenhagen: Steve Cleary pointed out that reverse_iterator -assumes its underlying iterator has persistent pointers and -references. Andy Koenig pointed out that it is possible to rewrite -reverse_iterator so that it no longer makes such an assupmption. -However, this issue is related to issue 299. If we -decide it is intentional that p[n] may return by value -instead of reference when p is a Random Access Iterator, -other changes in reverse_iterator will be necessary.]

- - - -

Rationale:

-

This issue has been discussed extensively. Note that it is -not an issue about the behavior of predefined iterators. It is -asking whether or not user-defined iterators are permitted to have -transient pointers and references. Several people presented examples -of useful user-defined iterators that have such a property; examples -include a B-tree iterator, and an "iota iterator" that doesn't point -to memory. Library implementors already seem to be able to cope with -such iterators: they take pains to avoid forming references to memory -that gets iterated past. The only place where this is a problem is -reverse_iterator, so this issue changes -reverse_iterator to make it work.

- -

This resolution does not weaken any guarantees provided by -predefined iterators like list<int>::iterator. -Clause 23 should be reviewed to make sure that guarantees for -predefined iterators are as strong as users expect.

- - - - - - -
-

199. What does allocate(0) return?

-

Section: 17.6.3.5 [allocator.requirements] Status: TC1 - Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

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-

Discussion:

-

-Suppose that A is a class that conforms to the -Allocator requirements of Table 32, and a is an -object of class A What should be the return -value of a.allocate(0)? Three reasonable -possibilities: forbid the argument 0, return -a null pointer, or require that the return value be a -unique non-null pointer. -

- - -

Proposed resolution:

-

-Add a note to the allocate row of Table 32: -"[Note: If n == 0, the return value is unspecified. --end note]"

- - -

Rationale:

-

A key to understanding this issue is that the ultimate use of -allocate() is to construct an iterator, and that iterator for zero -length sequences must be the container's past-the-end -representation. Since this already implies special case code, it -would be over-specification to mandate the return value. -

- - - - -
-

200. Forward iterator requirements don't allow constant iterators

-

Section: 24.2.5 [forward.iterators] Status: CD1 - Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

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-

Discussion:

-

-In table 74, the return type of the expression *a is given -as T&, where T is the iterator's value type. -For constant iterators, however, this is wrong. ("Value type" -is never defined very precisely, but it is clear that the value type -of, say, std::list<int>::const_iterator is supposed to be -int, not const int.) -

- - -

Proposed resolution:

-

-In table 74, in the *a and *r++ rows, change the -return type from "T&" to "T& -if X is mutable, otherwise const T&". -In the a->m row, change the return type from -"U&" to "U& if X is mutable, -otherwise const U&". -

- -

[Tokyo: The LWG believes this is the tip of a larger iceberg; -there are multiple const problems with the STL portion of the library -and that these should be addressed as a single package.  Note -that issue 180 has already been declared NAD Future for -that very reason.]

- - -

[Redmond: the LWG thinks this is separable from other constness -issues. This issue is just cleanup; it clarifies language that was -written before we had iterator_traits. Proposed resolution was -modified: the original version only discussed *a. It was pointed out -that we also need to worry about *r++ and a->m.]

- - - - - - - -
-

201. Numeric limits terminology wrong

-

Section: 18.3.2 [limits] Status: CD1 - Submitter: Stephen Cleary Opened: 1999-12-21 Last modified: 2015-04-08

-

View all other issues in [limits].

-

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-

Discussion:

-

-In some places in this section, the terms "fundamental types" and -"scalar types" are used when the term "arithmetic types" is intended. -The current usage is incorrect because void is a fundamental type and -pointers are scalar types, neither of which should have -specializations of numeric_limits. -

-

[Lillehammer: it remains true that numeric_limits is using - imprecise language. However, none of the proposals for changed - wording are clearer. A redesign of numeric_limits is needed, but this - is more a task than an open issue.]

- - - -

Proposed resolution:

- -

-Change 18.3 [support.limits] to: -

- -
-

--1- The headers <limits>, <climits>, -<cfloat>, and <cinttypes> supply -characteristics of implementation-dependent fundamental -arithmetic types (3.9.1). -

-
- -

-Change 18.3.2 [limits] to: -

- -
-

--1- The numeric_limits component provides a C++ program with -information about various properties of the implementation's -representation of the fundamental arithmetic -types. -

-

--2- Specializations shall be provided for each fundamental -arithmetic type, both floating point and integer, including -bool. The member is_specialized shall be true -for all such specializations of numeric_limits. -

-

--4- Non-fundamentalarithmetic standard types, such -as complex<T> (26.3.2), shall not have specializations. -

-
- -

-Change 18.3.2.3 [numeric.limits] to: -

- -
-

--1- The member is_specialized makes it possible to distinguish -between fundamental types, which have specializations, and non-scalar types, -which do not. -

-
- - - - - - -
-

202. unique() effects unclear when predicate not an equivalence relation

-

Section: 25.3.9 [alg.unique] Status: CD1 - Submitter: Andrew Koenig Opened: 2000-01-13 Last modified: 2015-04-08

-

View all other issues in [alg.unique].

-

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-

Discussion:

-

-What should unique() do if you give it a predicate that is not an -equivalence relation? There are at least two plausible answers: -

- -
- -

- 1. You can't, because 25.2.8 says that it it "eliminates all but - the first element from every consecutive group of equal - elements..." and it wouldn't make sense to interpret "equal" as - meaning anything but an equivalence relation. [It also doesn't - make sense to interpret "equal" as meaning ==, because then there - would never be any sense in giving a predicate as an argument at - all.] -

- -

- 2. The word "equal" should be interpreted to mean whatever the - predicate says, even if it is not an equivalence relation - (and in particular, even if it is not transitive). -

- -
- -

-The example that raised this question is from Usenet: -

- -
- -
int f[] = { 1, 3, 7, 1, 2 };
-int* z = unique(f, f+5, greater<int>());
- -
- -

-If one blindly applies the definition using the predicate -greater<int>, and ignore the word "equal", you get: -

- -
- -

- Eliminates all but the first element from every consecutive group - of elements referred to by the iterator i in the range [first, last) - for which *i > *(i - 1). -

- -
- -

-The first surprise is the order of the comparison. If we wanted to -allow for the predicate not being an equivalence relation, then we -should surely compare elements the other way: pred(*(i - 1), *i). If -we do that, then the description would seem to say: "Break the -sequence into subsequences whose elements are in strictly increasing -order, and keep only the first element of each subsequence". So the -result would be 1, 1, 2. If we take the description at its word, it -would seem to call for strictly DEcreasing order, in which case the -result should be 1, 3, 7, 2.
-
-In fact, the SGI implementation of unique() does neither: It yields 1, -3, 7. -

- - -

Proposed resolution:

-

Change 25.3.9 [alg.unique] paragraph 1 to:

-

-For a nonempty range, eliminates all but the first element from every -consecutive group of equivalent elements referred to by the iterator -i in the range [first+1, last) for which the following -conditions hold: *(i-1) == *i or pred(*(i-1), *i) != -false. -

- -

-Also insert a new paragraph, paragraph 2a, that reads: "Requires: The -comparison function must be an equivalence relation." -

- -

[Redmond: discussed arguments for and against requiring the -comparison function to be an equivalence relation. Straw poll: -14-2-5. First number is to require that it be an equivalence -relation, second number is to explicitly not require that it be an -equivalence relation, third number is people who believe they need -more time to consider the issue. A separate issue: Andy Sawyer -pointed out that "i-1" is incorrect, since "i" can refer to the first -iterator in the range. Matt provided wording to address this -problem.]

- - -

[Curaçao: The LWG changed "... the range (first, -last)..." to "... the range [first+1, last)..." for -clarity. They considered this change close enough to editorial to not -require another round of review.]

- - - - -

Rationale:

-

The LWG also considered an alternative resolution: change -25.3.9 [alg.unique] paragraph 1 to:

- -

-For a nonempty range, eliminates all but the first element from every -consecutive group of elements referred to by the iterator -i in the range (first, last) for which the following -conditions hold: *(i-1) == *i or pred(*(i-1), *i) != -false. -

- -

-Also insert a new paragraph, paragraph 1a, that reads: "Notes: The -comparison function need not be an equivalence relation." -

- - -

Informally: the proposed resolution imposes an explicit requirement -that the comparison function be an equivalence relation. The -alternative resolution does not, and it gives enough information so -that the behavior of unique() for a non-equivalence relation is -specified. Both resolutions are consistent with the behavior of -existing implementations.

- - - - - -
-

206. operator new(size_t, nothrow) may become unlinked to ordinary operator new if ordinary version replaced

-

Section: 18.6.1.1 [new.delete.single] Status: CD1 - Submitter: Howard Hinnant Opened: 1999-08-29 Last modified: 2015-04-08

-

View all other issues in [new.delete.single].

-

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-

Discussion:

-

As specified, the implementation of the nothrow version of operator -new does not necessarily call the ordinary operator new, but may -instead simply call the same underlying allocator and return a null -pointer instead of throwing an exception in case of failure.

- -

Such an implementation breaks code that replaces the ordinary -version of new, but not the nothrow version. If the ordinary version -of new/delete is replaced, and if the replaced delete is not -compatible with pointers returned from the library versions of new, -then when the replaced delete receives a pointer allocated by the -library new(nothrow), crash follows.

- -

The fix appears to be that the lib version of new(nothrow) must -call the ordinary new. Thus when the ordinary new gets replaced, the -lib version will call the replaced ordinary new and things will -continue to work.

- -

An alternative would be to have the ordinary new call -new(nothrow). This seems sub-optimal to me as the ordinary version of -new is the version most commonly replaced in practice. So one would -still need to replace both ordinary and nothrow versions if one wanted -to replace the ordinary version.

- -

Another alternative is to put in clear text that if one version is -replaced, then the other must also be replaced to maintain -compatibility. Then the proposed resolution below would just be a -quality of implementation issue. There is already such text in -paragraph 7 (under the new(nothrow) version). But this nuance is -easily missed if one reads only the paragraphs relating to the -ordinary new.

- -

-N2158 -has been written explaining the rationale for the proposed resolution below. -

- - - -

Proposed resolution:

-

-Change 18.5.1.1 [new.delete.single]: -

- -
-
-void* operator new(std::size_t size, const std::nothrow_t&) throw();
-
-
-

--5- Effects: Same as above, except that it is called by a placement -version of a new-expression when a C++ program prefers a null pointer result as -an error indication, instead of a bad_alloc exception. -

- -

--6- Replaceable: a C++ program may define a function with this function -signature that displaces the default version defined by the C++ Standard -library. -

- -

--7- Required behavior: Return a non-null pointer to suitably aligned -storage (3.7.4), or else return a null pointer. This nothrow version of operator -new returns a pointer obtained as if acquired from the (possibly -replaced) ordinary version. This requirement is binding on a replacement -version of this function. -

- -

--8- Default behavior: -

-
    -
  • -Calls operator new(size). -
    • -
  • -If the call to operator new(size) returns normally, returns -the result of that call, else -
    • -
  • -if the call to operator new(size) throws an exception, returns -a null pointer. -
    • -
  • -Executes a loop: Within the loop, the function first attempts to allocate the -requested storage. Whether the attempt involves a call to the Standard C library -function malloc is unspecified. -
    • -
  • -Returns a pointer to the allocated storage if the attempt is successful. -Otherwise, if the last argument to set_new_handler() was a null -pointer, return a null pointer. -
    • -
  • -Otherwise, the function calls the current new_handler (18.5.2.2). If the -called function returns, the loop repeats. -
    • -
  • -The loop terminates when an attempt to allocate the requested storage is -successful or when a called new_handler function does not return. If the -called new_handler function terminates by throwing a bad_alloc -exception, the function returns a null pointer. -
    • -
-

--9- [Example: -

-
-T* p1 = new T;                 // throws bad_alloc if it fails
-T* p2 = new(nothrow) T;        // returns 0 if it fails
-
-

---end example] -

-
- -
-void operator delete(void* ptr) throw();
-void operator delete(void* ptr, const std::nothrow_t&) throw();
-
- -
-

--10- Effects: The deallocation function (3.7.4.2) called by a -delete-expression to render the value of ptr invalid. -

-

--11- Replaceable: a C++ program may define a function with this function -signature that displaces the default version defined by the C++ Standard -library. -

-

--12- Requires: the value of ptr is null or the value -returned by an earlier call to the default (possibly -replaced) operator new(std::size_t) or operator -new(std::size_t, const std::nothrow_t&). -

-

--13- Default behavior: -

-
    -
  • -For a null value of ptr, do nothing. -
    • -
  • -Any other value of ptr shall be a value returned earlier by a -call to the default operator new, which was not invalidated by an -intervening call to operator delete(void*) (17.4.3.7). For such a -non-null value of ptr, reclaims storage allocated by the earlier -call to the default operator new. -
    • -
-

--14- Remarks: It is unspecified under what conditions part or all of -such reclaimed storage is allocated by a subsequent call to operator -new or any of calloc, malloc, or realloc, -declared in <cstdlib>. -

-
- -
-void operator delete(void* ptr, const std::nothrow_t&) throw();
-
- -
-

--15- Effects: Same as above, except that it is called by the -implementation when an exception propagates from a nothrow placement version -of the new-expression (i.e. when the constructor throws an exception). -

-

--16- Replaceable: a C++ program may define a function with this function -signature that displaces the default version defined by the C++ Standard -library. -

-

--17- Requires: the value of ptr is null or the -value returned by an earlier call to the (possibly replaced) operator -new(std::size_t) or operator new(std::size_t, const -std::nothrow_t&).

-

--18- Default behavior: Calls operator delete(ptr). -

-
- -
- -

-Change 18.5.1.2 [new.delete.array] -

- -
-
-void* operator new[](std::size_t size, const std::nothrow_t&) throw();
-
- -
-

--5- Effects: Same as above, except that it is called by a placement -version of a new-expression when a C++ program prefers a null pointer result as -an error indication, instead of a bad_alloc exception. -

- -

--6- Replaceable: a C++ program can define a function with this function -signature that displaces the default version defined by the C++ Standard -library. -

- -

--7- Required behavior: Same as for operator new(std::size_t, -const std::nothrow_t&). This nothrow version of operator new[] -returns a pointer obtained as if acquired from the ordinary version. -Return a non-null pointer to suitably aligned storage (3.7.4), or else -return a null pointer. This nothrow version of operator new returns a pointer -obtained as if acquired from the (possibly replaced) operator -new[](std::size_t size). This requirement is binding on a -replacement version of this function. -

- -

--8- Default behavior: Returns operator new(size, -nothrow). -

- -
    -
  • -Calls operator new[](size). -
    • -
  • -If the call to operator new[](size) returns normally, returns -the result of that call, else -
    • -
  • -if the call to operator new[](size) throws an exception, returns -a null pointer. -
    • -
-
- -
-void operator delete[](void* ptr) throw(); 
-void operator delete[](void* ptr, const std::nothrow_t&) throw();
-
- -
-

--9- Effects: The deallocation function (3.7.4.2) called by the -array form of a delete-expression to render the value of -ptr invalid. -

- -

--10- Replaceable: a C++ program can define a function with this function -signature that displaces the default version defined by the C++ Standard -library. -

- -

--11- Requires: the value of -ptr is null or the value returned by an earlier call to -operator new[](std::size_t) or operator new[](std::size_t, const -std::nothrow_t&). -

- -

--12- Default behavior: Calls operator delete(ptr) or -operator delete[](ptr, std::nothrow) respectively. -

-
- -
- - - -

Rationale:

-

Yes, they may become unlinked, and that is by design. If a user -replaces one, the user should also replace the other.

- -

[ -Reopened due to a gcc conversation between Howard, Martin and Gaby. Forwarding -or not is visible behavior to the client and it would be useful for the client -to know which behavior it could depend on. -]

- - -

[ -Batavia: Robert voiced serious reservations about backwards compatibility for -his customers. -]

- - - - - - -
-

208. Unnecessary restriction on past-the-end iterators

-

Section: X [iterator.concepts] Status: TC1 - Submitter: Stephen Cleary Opened: 2000-02-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In 24.1 paragraph 5, it is stated ". . . Dereferenceable and -past-the-end values are always non-singular."

-

This places an unnecessary restriction on past-the-end iterators for -containers with forward iterators (for example, a singly-linked list). If the -past-the-end value on such a container was a well-known singular value, it would -still satisfy all forward iterator requirements.

-

Removing this restriction would allow, for example, a singly-linked list -without a "footer" node.

-

This would have an impact on existing code that expects past-the-end -iterators obtained from different (generic) containers being not equal.

- - -

Proposed resolution:

-

Change X [iterator.concepts] paragraph 5, the last sentence, from:

-
-

Dereferenceable and past-the-end values are always non-singular.

-
-

to:

-
-

Dereferenceable values are always non-singular. 

-
- - -

Rationale:

-

For some kinds of containers, including singly linked lists and -zero-length vectors, null pointers are perfectly reasonable past-the-end -iterators. Null pointers are singular. -

- - - - -
-

209. basic_string declarations inconsistent

-

Section: 21.4 [basic.string] Status: TC1 - Submitter: Igor Stauder Opened: 2000-02-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

In Section 21.4 [basic.string] the basic_string member function -declarations use a consistent style except for the following functions:

-
- 
void push_back(const charT);
-basic_string& assign(const basic_string&);
-void swap(basic_string<charT,traits,Allocator>&);
-
-

- push_back, assign, swap: missing argument name 
-- push_back: use of const with charT (i.e. POD type passed by value -not by reference - should be charT or const charT& )
-- swap: redundant use of template parameters in argument -basic_string<charT,traits,Allocator>&

- - -

Proposed resolution:

-

In Section 21.4 [basic.string] change the basic_string member -function declarations push_back, assign, and swap to:

-
- 
void push_back(charT c); 
-
-basic_string& assign(const basic_string& str);
-void swap(basic_string& str);
-
- - -

Rationale:

-

Although the standard is in general not consistent in declaration -style, the basic_string declarations are consistent other than the -above. The LWG felt that this was sufficient reason to merit the -change. -

- - - - -
-

210. distance first and last confused

-

Section: 25 [algorithms] Status: TC1 - Submitter: Lisa Lippincott Opened: 2000-02-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

In paragraph 9 of section 25 [algorithms], it is written:

-
-

In the description of the algorithms operators + and - are used - for some of the iterator categories for which they do not have to - be defined. In these cases the semantics of [...] a-b is the same - as of
-
-      return distance(a, b);

-
- - -

Proposed resolution:

-

On the last line of paragraph 9 of section 25 [algorithms] change -"a-b" to "b-a".

- - -

Rationale:

-

There are two ways to fix the defect; change the description to b-a -or change the return to distance(b,a). The LWG preferred the -former for consistency.

- - - - -
-

211. operator>>(istream&, string&) doesn't set failbit

-

Section: 21.4.8.9 [string.io] Status: TC1 - Submitter: Scott Snyder Opened: 2000-02-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The description of the stream extraction operator for std::string (section -21.3.7.9 [lib.string.io]) does not contain a requirement that failbit be set in -the case that the operator fails to extract any characters from the input -stream.

-

This implies that the typical construction

-
- 
std::istream is;
-std::string str;
-...
-while (is >> str) ... ;
-
-

(which tests failbit) is not required to terminate at EOF.

-

Furthermore, this is inconsistent with other extraction operators, -which do include this requirement. (See sections 27.7.2.2 [istream.formatted] and 27.7.2.3 [istream.unformatted]), where this -requirement is present, either explicitly or implicitly, for the -extraction operators. It is also present explicitly in the description -of getline (istream&, string&, charT) in section 21.4.8.9 [string.io] paragraph 8.)

- - -

Proposed resolution:

-

Insert new paragraph after paragraph 2 in section 21.4.8.9 [string.io]:

-
- -

If the function extracts no characters, it calls -is.setstate(ios::failbit) which may throw ios_base::failure -(27.4.4.3).

-
- - - - -
-

212. Empty range behavior unclear for several algorithms

-

Section: 25.4.7 [alg.min.max] Status: TC1 - Submitter: Nico Josuttis Opened: 2000-02-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The standard doesn't specify what min_element() and max_element() shall -return if the range is empty (first equals last). The usual implementations -return last. This problem seems also apply to partition(), stable_partition(), -next_permutation(), and prev_permutation().

- - -

Proposed resolution:

-

In 25.4.7 [alg.min.max] - Minimum and maximum, paragraphs 7 and -9, append: Returns last if first==last.

- - -

Rationale:

-

The LWG looked in some detail at all of the above mentioned -algorithms, but believes that except for min_element() and -max_element() it is already clear that last is returned if first == -last.

- - - - -
-

214. set::find() missing const overload

-

Section: 23.4.6 [set], 23.4.7 [multiset] Status: CD1 - Submitter: Judy Ward Opened: 2000-02-28 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 450

-

Discussion:

-

The specification for the associative container requirements in -Table 69 state that the find member function should "return -iterator; const_iterator for constant a". The map and multimap -container descriptions have two overloaded versions of find, but set -and multiset do not, all they have is:

-
- 
iterator find(const key_type & x) const;
-
- - -

Proposed resolution:

-

Change the prototypes for find(), lower_bound(), upper_bound(), and -equal_range() in section 23.4.6 [set] and section 23.4.7 [multiset] to each have two overloads:

-
- 
iterator find(const key_type & x);
-const_iterator find(const key_type & x) const;
- 
iterator lower_bound(const key_type & x);
-const_iterator lower_bound(const key_type & x) const;
- 
iterator upper_bound(const key_type & x);
-const_iterator upper_bound(const key_type & x) const;
- 
pair<iterator, iterator> equal_range(const key_type & x);
-pair<const_iterator, const_iterator> equal_range(const key_type & x) const;
-
- -

[Tokyo: At the request of the LWG, Judy Ward provided wording -extending the proposed resolution to lower_bound, upper_bound, and -equal_range.]

- - - - - - -
-

217. Facets example (Classifying Japanese characters) contains errors

-

Section: 22.4.8 [facets.examples] Status: TC1 - Submitter: Martin Sebor Opened: 2000-02-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The example in 22.2.8, paragraph 11 contains the following errors:

-

1) The member function `My::JCtype::is_kanji()' is non-const; the function -must be const in order for it to be callable on a const object (a reference to -which which is what std::use_facet<>() returns).

-

2) In file filt.C, the definition of `JCtype::id' must be qualified with the -name of the namespace `My'.

-

3) In the definition of `loc' and subsequently in the call to use_facet<>() -in main(), the name of the facet is misspelled: it should read `My::JCtype' -rather than `My::JCType'.

- - -

Proposed resolution:

-

Replace the "Classifying Japanese characters" example in 22.2.8, -paragraph 11 with the following:

-
#include <locale>
-
namespace My {
-    using namespace std;
-    class JCtype : public locale::facet {
-    public:
-        static locale::id id;     //  required for use as a new locale facet
-        bool is_kanji (wchar_t c) const;
-        JCtype() {}
-    protected:
-        ~JCtype() {}
-    };
-}
-
//  file:  filt.C
-#include <iostream>
-#include <locale>
-#include "jctype"                 //  above
-std::locale::id My::JCtype::id;   //  the static  JCtype  member
-declared above.
-
int main()
-{
-    using namespace std;
-    typedef ctype<wchar_t> wctype;
-    locale loc(locale(""),              //  the user's preferred locale...
-               new My::JCtype);         //  and a new feature ...
-    wchar_t c = use_facet<wctype>(loc).widen('!');
-    if (!use_facet<My::JCtype>(loc).is_kanji(c))
-        cout << "no it isn't!" << endl;
-    return 0;
-}
- - - - -
-

220. ~ios_base() usage valid?

-

Section: 27.5.3.7 [ios.base.cons] Status: TC1 - Submitter: Jonathan Schilling, Howard Hinnant Opened: 2000-03-13 Last modified: 2015-04-08

-

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-

Discussion:

-

The pre-conditions for the ios_base destructor are described in 27.4.2.7 -paragraph 2:

-
-

Effects: Destroys an object of class ios_base. Calls each registered - callback pair (fn,index) (27.4.2.6) as (*fn)(erase_event,*this,index) at such - time that any ios_base member function called from within fn has well defined - results.

-
-

But what is not clear is: If no callback functions were ever registered, does -it matter whether the ios_base members were ever initialized?

-

For instance, does this program have defined behavior:

-
- 
#include <ios>
- 
class D : public std::ios_base { };
- 
int main() { D d; }
-
-

It seems that registration of a callback function would surely affect the -state of an ios_base. That is, when you register a callback function with an -ios_base, the ios_base must record that fact somehow.

-

But if after construction the ios_base is in an indeterminate state, and that -state is not made determinate before the destructor is called, then how would -the destructor know if any callbacks had indeed been registered? And if the -number of callbacks that had been registered is indeterminate, then is not the -behavior of the destructor undefined?

-

By comparison, the basic_ios class description in 27.4.4.1 paragraph 2 makes -it explicit that destruction before initialization results in undefined -behavior.

- - -

Proposed resolution:

-

Modify 27.4.2.7 paragraph 1 from

-
-

Effects: Each ios_base member has an indeterminate value after - construction.

-
-

to

-
-

Effects: Each ios_base member has an indeterminate value after - construction. These members must be initialized by calling basic_ios::init. If an ios_base object is destroyed before these initializations - have taken place, the behavior is undefined.

-
- - - - -
-

221. num_get<>::do_get stage 2 processing broken

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 - Submitter: Matt Austern Opened: 2000-03-14 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Stage 2 processing of numeric conversion is broken.

- -

Table 55 in 22.2.2.1.2 says that when basefield is 0 the integral -conversion specifier is %i. A %i specifier determines a number's base -by its prefix (0 for octal, 0x for hex), so the intention is clearly -that a 0x prefix is allowed. Paragraph 8 in the same section, -however, describes very precisely how characters are processed. (It -must be done "as if" by a specified code fragment.) That -description does not allow a 0x prefix to be recognized.

- -

Very roughly, stage 2 processing reads a char_type ct. It converts -ct to a char, not by using narrow but by looking it up in a -translation table that was created by widening the string literal -"0123456789abcdefABCDEF+-". The character "x" is -not found in that table, so it can't be recognized by stage 2 -processing.

- - -

Proposed resolution:

-

In 22.2.2.1.2 paragraph 8, replace the line:

-
- 
static const char src[] = "0123456789abcdefABCDEF+-";
-
-

with the line:

-
- 
static const char src[] = "0123456789abcdefxABCDEFX+-";
-
- - -

Rationale:

-

If we're using the technique of widening a string literal, the -string literal must contain every character we wish to recognize. -This technique has the consequence that alternate representations -of digits will not be recognized. This design decision was made -deliberately, with full knowledge of that limitation.

- - - - - -
-

222. Are throw clauses necessary if a throw is already implied by the effects clause?

-

Section: 17.5.1.4 [structure.specifications] Status: TC1 - Submitter: Judy Ward Opened: 2000-03-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Section 21.3.6.8 describes the basic_string::compare function this way:

-
- 
21.3.6.8 - basic_string::compare [lib.string::compare]
-
-int compare(size_type pos1, size_type n1,
-                const basic_string<charT,traits,Allocator>&  str ,
-                size_type  pos2 , size_type  n2 ) const;
-
--4- Returns: 
-
-    basic_string<charT,traits,Allocator>(*this,pos1,n1).compare(
-                 basic_string<charT,traits,Allocator>(str,pos2,n2)) .
-
-

and the constructor that's implicitly called by the above is -defined to throw an out-of-range exception if pos > str.size(). See -section 21.4.1 [string.require] paragraph 4.

- -

On the other hand, the compare function descriptions themselves don't have -"Throws: " clauses and according to 17.3.1.3, paragraph 3, elements -that do not apply to a function are omitted.

-

So it seems there is an inconsistency in the standard -- are the -"Effects" clauses correct, or are the "Throws" clauses -missing?

- - -

Proposed resolution:

-

In 17.5.1.4 [structure.specifications] paragraph 3, the footnote 148 attached to -the sentence "Descriptions of function semantics contain the -following elements (as appropriate):", insert the word -"further" so that the foot note reads:

-
-

To save space, items that do not apply to a function are - omitted. For example, if a function does not specify any further - preconditions, there will be no "Requires" paragraph.

-
- - -

Rationale:

-

The standard is somewhat inconsistent, but a failure to note a -throw condition in a throws clause does not grant permission not to -throw. The inconsistent wording is in a footnote, and thus -non-normative. The proposed resolution from the LWG clarifies the -footnote.

- - - - -
-

223. reverse algorithm should use iter_swap rather than swap

-

Section: 25.3.10 [alg.reverse] Status: TC1 - Submitter: Dave Abrahams Opened: 2000-03-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Shouldn't the effects say "applies iter_swap to all pairs..."?

- - -

Proposed resolution:

-

In 25.3.10 [alg.reverse], replace:

-

- Effects: For each non-negative integer i <= (last - first)/2, - applies swap to all pairs of iterators first + i, (last - i) - 1. -

-

with:

-

- Effects: For each non-negative integer i <= (last - first)/2, - applies iter_swap to all pairs of iterators first + i, (last - i) - 1. -

- - - - -
-

224. clear() complexity for associative containers refers to undefined N

-

Section: 23.2.4 [associative.reqmts] Status: TC1 - Submitter: Ed Brey Opened: 2000-03-23 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

In the associative container requirements table in 23.1.2 paragraph 7, -a.clear() has complexity "log(size()) + N". However, the meaning of N -is not defined.

- - -

Proposed resolution:

-

In the associative container requirements table in 23.1.2 paragraph -7, the complexity of a.clear(), change "log(size()) + N" to -"linear in size()".

- - -

Rationale:

-

It's the "log(size())", not the "N", that is in -error: there's no difference between O(N) and O(N + -log(N)). The text in the standard is probably an incorrect -cut-and-paste from the range version of erase.

- - - - -
-

225. std:: algorithms use of other unqualified algorithms

-

Section: 17.6.5.4 [global.functions] Status: CD1 - Submitter: Dave Abrahams Opened: 2000-04-01 Last modified: 2015-04-08

-

View all other issues in [global.functions].

-

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-

Discussion:

-

Are algorithms in std:: allowed to use other algorithms without qualification, so functions in -user namespaces might be found through Koenig lookup?

-

For example, a popular standard library implementation includes this -implementation of std::unique:

-
-
namespace std {
-    template <class _ForwardIter>
-    _ForwardIter unique(_ForwardIter __first, _ForwardIter __last) {
-      __first = adjacent_find(__first, __last);
-      return unique_copy(__first, __last, __first);
-    }
-    }
-
-

Imagine two users on opposite sides of town, each using unique on his own -sequences bounded by my_iterators . User1 looks at his standard library -implementation and says, "I know how to implement a more efficient -unique_copy for my_iterators", and writes:

-
-
namespace user1 {
-    class my_iterator;
-    // faster version for my_iterator
-    my_iterator unique_copy(my_iterator, my_iterator, my_iterator);
-    }
-
-

user1::unique_copy() is selected by Koenig lookup, as he intended.

-

User2 has other needs, and writes:

-
-
namespace user2 {
-    class my_iterator;
-    // Returns true iff *c is a unique copy of *a and *b.
-    bool unique_copy(my_iterator a, my_iterator b, my_iterator c);
-    }
-
-

User2 is shocked to find later that his fully-qualified use of -std::unique(user2::my_iterator, user2::my_iterator, user2::my_iterator) fails to -compile (if he's lucky). Looking in the standard, he sees the following Effects -clause for unique():

-
-

Effects: Eliminates all but the first element from every consecutive group - of equal elements referred to by the iterator i in the range [first, last) for - which the following corresponding conditions hold: *i == *(i - 1) or pred(*i, - *(i - 1)) != false

-
-

The standard gives user2 absolutely no reason to think he can interfere with -std::unique by defining names in namespace user2. His standard library has been -built with the template export feature, so he is unable to inspect the -implementation. User1 eventually compiles his code with another compiler, and -his version of unique_copy silently stops being called. Eventually, he realizes -that he was depending on an implementation detail of his library and had no -right to expect his unique_copy() to be called portably.

-

On the face of it, and given above scenario, it may seem obvious that the -implementation of unique() shown is non-conforming because it uses unique_copy() -rather than ::std::unique_copy(). Most standard library implementations, -however, seem to disagree with this notion.

-

[Tokyo:  Steve Adamczyk from -the core working group indicates that "std::" is sufficient;  -leading "::" qualification is not required because any namespace -qualification is sufficient to suppress Koenig lookup.]

- - -

Proposed resolution:

-

Add a paragraph and a note at the end of -17.6.5.4 [global.functions]:

-
- -

Unless otherwise specified, no global or non-member function in the -standard library shall use a function from another namespace which is -found through argument-dependent name lookup (3.4.2 [basic.lookup.argdep]).

- -

[Note: the phrase "unless otherwise specified" is intended to -allow Koenig lookup in cases like that of ostream_iterators:
- -
- Effects:

-
-

*out_stream << value;
- if(delim != 0) *out_stream << delim;
- return (*this);

-

--end note]

-
-
- -

[Tokyo: The LWG agrees that this is a defect in the standard, but -is as yet unsure if the proposed resolution is the best -solution. Furthermore, the LWG believes that the same problem of -unqualified library names applies to wording in the standard itself, -and has opened issue 229 accordingly. Any resolution of -issue 225 should be coordinated with the resolution of -issue 229.]

- - -

[Toronto: The LWG is not sure if this is a defect in the -standard. Most LWG members believe that an implementation of -std::unique like the one quoted in this issue is already -illegal, since, under certain circumstances, its semantics are not -those specified in the standard. The standard's description of -unique does not say that overloading adjacent_find -should have any effect.]

- - -

[Curaçao: An LWG-subgroup spent an afternoon working on issues -225, 226, and 229. Their conclusion was that the issues should be -separated into an LWG portion (Howard's paper, N1387=02-0045), and a -EWG portion (Dave will write a proposal). The LWG and EWG had -(separate) discussions of this plan the next day. The proposed -resolution for this issue is in accordance with Howard's paper.]

- - - - -

Rationale:

-

It could be argued that this proposed isn't strictly necessary, - that the Standard doesn't grant implementors license to write a - standard function that behaves differently than specified in the - Standard just because of an unrelated user-defined name in some - other namespace. However, this is at worst a clarification. It is - surely right that algorithsm shouldn't pick up random names, that - user-defined names should have no effect unless otherwise specified. - Issue 226 deals with the question of when it is - appropriate for the standard to explicitly specify otherwise.

- - - - - -
-

226. User supplied specializations or overloads of namespace std function templates

-

Section: 17.6.4.3 [reserved.names] Status: CD1 - Submitter: Dave Abrahams Opened: 2000-04-01 Last modified: 2015-04-08

-

View all other issues in [reserved.names].

-

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-

Discussion:

-

The issues are: 

-

1. How can a 3rd party library implementor (lib1) write a version of a standard -algorithm which is specialized to work with his own class template? 

-

2. How can another library implementor (lib2) write a generic algorithm which -will take advantage of the specialized algorithm in lib1?

-

This appears to be the only viable answer under current language rules:

-
- 
namespace lib1
-{
-    // arbitrary-precision numbers using T as a basic unit
-    template <class T>
-    class big_num { //...
-    };
-
- 
    // defining this in namespace std is illegal (it would be an
-    // overload), so we hope users will rely on Koenig lookup
-    template <class T>
-    void swap(big_int<T>&, big_int<T>&);
-}
- 
#include <algorithm>
-namespace lib2
-{
-    template <class T>
-    void generic_sort(T* start, T* end)
-    {
-            ...
-        // using-declaration required so we can work on built-in types
-        using std::swap;
-        // use Koenig lookup to find specialized algorithm if available
-        swap(*x, *y);
-    }
-}
-
-

This answer has some drawbacks. First of all, it makes writing lib2 difficult -and somewhat slippery. The implementor needs to remember to write the -using-declaration, or generic_sort will fail to compile when T is a built-in -type. The second drawback is that the use of this style in lib2 effectively -"reserves" names in any namespace which defines types which may -eventually be used with lib2. This may seem innocuous at first when applied to -names like swap, but consider more ambiguous names like unique_copy() instead. -It is easy to imagine the user wanting to define these names differently in his -own namespace. A definition with semantics incompatible with the standard -library could cause serious problems (see issue 225).

-

Why, you may ask, can't we just partially specialize std::swap()? It's -because the language doesn't allow for partial specialization of function -templates. If you write:

-
- 
namespace std
-{
-    template <class T>
-    void swap(lib1::big_int<T>&, lib1::big_int<T>&);
-}
-
-

You have just overloaded std::swap, which is illegal under the current -language rules. On the other hand, the following full specialization is legal:

-
- 
namespace std
-{
-    template <>
-    void swap(lib1::other_type&, lib1::other_type&);
-}
-
- -

This issue reflects concerns raised by the "Namespace issue -with specialized swap" thread on comp.lang.c++.moderated. A -similar set of concerns was earlier raised on the boost.org mailing -list and the ACCU-general mailing list. Also see library reflector -message c++std-lib-7354.

- -

-J. C. van Winkel points out (in c++std-lib-9565) another unexpected -fact: it's impossible to output a container of std::pair's using copy -and an ostream_iterator, as long as both pair-members are built-in or -std:: types. That's because a user-defined operator<< for (for -example) std::pair<const std::string, int> will not be found: -lookup for operator<< will be performed only in namespace std. -Opinions differed on whether or not this was a defect, and, if so, -whether the defect is that something is wrong with user-defined -functionality and std, or whether it's that the standard library does -not provide an operator<< for std::pair<>. -

- - - -

Proposed resolution:

- -

Adopt the wording proposed in Howard Hinnant's paper - N1523=03-0106, "Proposed Resolution To LWG issues 225, 226, 229".

- - -

[Tokyo: Summary, "There is no conforming way to extend -std::swap for user defined templates."  The LWG agrees that -there is a problem. Would like more information before -proceeding. This may be a core issue. Core issue 229 has been opened -to discuss the core aspects of this problem. It was also noted that -submissions regarding this issue have been received from several -sources, but too late to be integrated into the issues list. -]

- - -

[Post-Tokyo: A paper with several proposed resolutions, -J16/00-0029==WG21/N1252, "Shades of namespace std functions -" by Alan Griffiths, is in the Post-Tokyo mailing. It -should be considered a part of this issue.]

- - -

[Toronto: Dave Abrahams and Peter Dimov have proposed a -resolution that involves core changes: it would add partial -specialization of function template. The Core Working Group is -reluctant to add partial specialization of function templates. It is -viewed as a large change, CWG believes that proposal presented leaves -some syntactic issues unanswered; if the CWG does add partial -specialization of function templates, it wishes to develop its own -proposal. The LWG continues to believe that there is a serious -problem: there is no good way for users to force the library to use -user specializations of generic standard library functions, and in -certain cases (e.g. transcendental functions called by -valarray and complex) this is important. Koenig -lookup isn't adequate, since names within the library must be -qualified with std (see issue 225), specialization doesn't -work (we don't have partial specialization of function templates), and -users aren't permitted to add overloads within namespace std. -]

- - -

[Copenhagen: Discussed at length, with no consensus. Relevant -papers in the pre-Copenhagen mailing: N1289, N1295, N1296. Discussion -focused on four options. (1) Relax restrictions on overloads within -namespace std. (2) Mandate that the standard library use unqualified -calls for swap and possibly other functions. (3) Introduce -helper class templates for swap and possibly other functions. -(4) Introduce partial specialization of function templates. Every -option had both support and opposition. Straw poll (first number is -support, second is strongly opposed): (1) 6, 4; (2) 6, 7; (3) 3, 8; -(4) 4, 4.]

- - -

[Redmond: Discussed, again no consensus. Herb presented an -argument that a user who is defining a type T with an -associated swap should not be expected to put that -swap in namespace std, either by overloading or by partial -specialization. The argument is that swap is part of -T's interface, and thus should to in the same namespace as -T and only in that namespace. If we accept this argument, -the consequence is that standard library functions should use -unqualified call of swap. (And which other functions? Any?) -A small group (Nathan, Howard, Jeremy, Dave, Matt, Walter, Marc) will -try to put together a proposal before the next meeting.]

- - -

[Curaçao: An LWG-subgroup spent an afternoon working on issues -225, 226, and 229. Their conclusion was that the issues should be -separated into an LWG portion (Howard's paper, N1387=02-0045), and a -EWG portion (Dave will write a proposal). The LWG and EWG had -(separate) discussions of this plan the next day. The proposed -resolution is the one proposed by Howard.]

- - -

[Santa Cruz: the LWG agreed with the general direction of - Howard's paper, N1387. (Roughly: Koenig lookup is disabled unless - we say otherwise; this issue is about when we do say otherwise.) - However, there were concerns about wording. Howard will provide new - wording. Bill and Jeremy will review it.]

- - -

[Kona: Howard proposed the new wording. The LWG accepted his - proposed resolution.]

- - - - -

Rationale:

-

Informally: introduce a Swappable concept, and specify that the - value types of the iterators passed to certain standard algorithms - (such as iter_swap, swap_ranges, reverse, rotate, and sort) conform - to that concept. The Swappable concept will make it clear that - these algorithms use unqualified lookup for the calls - to swap. Also, in 26.6.3.3 [valarray.transcend] paragraph 1, - state that the valarray transcendentals use unqualified lookup.

- - - - - -
-

227. std::swap() should require CopyConstructible or DefaultConstructible arguments

-

Section: 25.3.3 [alg.swap] Status: TC1 - Submitter: Dave Abrahams Opened: 2000-04-09 Last modified: 2015-04-08

-

View all other issues in [alg.swap].

-

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-

Discussion:

-

25.2.2 reads:

-
-

template<class T> void swap(T& a, T& b);
-
- Requires: Type T is Assignable (_lib.container.requirements_).
- Effects: Exchanges values stored in two locations.

-
-

The only reasonable** generic implementation of swap requires construction of a - new temporary copy of one of its arguments:

-
-
template<class T> void swap(T& a, T& b);
-  {
-      T tmp(a);
-      a = b;
-      b = tmp;
-  }
-
-

But a type which is only Assignable cannot be swapped by this implementation.

-

**Yes, there's also an unreasonable implementation which would require T to be - DefaultConstructible instead of CopyConstructible. I don't think this is worthy - of consideration:

-
-
template<class T> void swap(T& a, T& b);
-{
-    T tmp;
-    tmp = a;
-    a = b;
-    b = tmp;
-}
-
- - -

Proposed resolution:

-

Change 25.2.2 paragraph 1 from:

-
-

Requires: Type T is Assignable (23.1).

-
-

to:

-
-

Requires: Type T is CopyConstructible (20.1.3) and Assignable (23.1)

-
- - - - - -
-

228. Incorrect specification of "..._byname" facets

-

Section: 22.4 [locale.categories] Status: CD1 - Submitter: Dietmar Kühl Opened: 2000-04-20 Last modified: 2015-04-08

-

View all other issues in [locale.categories].

-

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-

Discussion:

-

The sections 22.4.1.2 [locale.ctype.byname], 22.4.1.5 [locale.codecvt.byname], -sref ref="22.2.1.6", 22.4.3.2 [locale.numpunct.byname], 22.4.4.2 [locale.collate.byname], 22.4.5.4 [locale.time.put.byname], 22.4.6.4 [locale.moneypunct.byname], and 22.4.7.2 [locale.messages.byname] overspecify the -definitions of the "..._byname" classes by listing a bunch -of virtual functions. At the same time, no semantics of these -functions are defined. Real implementations do not define these -functions because the functional part of the facets is actually -implemented in the corresponding base classes and the constructor of -the "..._byname" version just provides suitable date used by -these implementations. For example, the 'numpunct' methods just return -values from a struct. The base class uses a statically initialized -struct while the derived version reads the contents of this struct -from a table. However, no virtual function is defined in -'numpunct_byname'.

- -

For most classes this does not impose a problem but specifically -for 'ctype' it does: The specialization for 'ctype_byname<char>' -is required because otherwise the semantics would change due to the -virtual functions defined in the general version for 'ctype_byname': -In 'ctype<char>' the method 'do_is()' is not virtual but it is -made virtual in both 'ctype<cT>' and 'ctype_byname<cT>'. -Thus, a class derived from 'ctype_byname<char>' can tell whether -this class is specialized or not under the current specification: -Without the specialization, 'do_is()' is virtual while with -specialization it is not virtual.

- - -

Proposed resolution:

-

  Change section 22.2.1.2 (lib.locale.ctype.byname) to become:

-
     namespace std {
-       template <class charT>
-       class ctype_byname : public ctype<charT> {
-       public:
-         typedef ctype<charT>::mask mask;
-         explicit ctype_byname(const char*, size_t refs = 0);
-       protected:
-        ~ctype_byname();             //  virtual
-       };
-     }
-

  Change section 22.2.1.6 (lib.locale.codecvt.byname) to become:

-
    namespace std {
-      template <class internT, class externT, class stateT>
-      class codecvt_byname : public codecvt<internT, externT, stateT> {
-      public:
-       explicit codecvt_byname(const char*, size_t refs = 0);
-      protected:
-      ~codecvt_byname();             //  virtual
-       };
-     }
-
-

  Change section 22.2.3.2 (lib.locale.numpunct.byname) to become:

-
     namespace std {
-       template <class charT>
-       class numpunct_byname : public numpunct<charT> {
-     //  this class is specialized for  char  and  wchar_t.
-       public:
-         typedef charT                char_type;
-         typedef basic_string<charT>  string_type;
-         explicit numpunct_byname(const char*, size_t refs = 0);
-       protected:
-        ~numpunct_byname();          //  virtual
-       };
-     }
-

  Change section 22.2.4.2 (lib.locale.collate.byname) to become:

-
     namespace std {
-       template <class charT>
-       class collate_byname : public collate<charT> {
-       public:
-         typedef basic_string<charT> string_type;
-         explicit collate_byname(const char*, size_t refs = 0);
-       protected:
-        ~collate_byname();           //  virtual
-       };
-     }
-

  Change section 22.2.5.2 (lib.locale.time.get.byname) to become:

-
     namespace std {
-       template <class charT, class InputIterator = istreambuf_iterator<charT> >
-       class time_get_byname : public time_get<charT, InputIterator> {
-       public:
-         typedef time_base::dateorder dateorder;
-         typedef InputIterator        iter_type
-
         explicit time_get_byname(const char*, size_t refs = 0);
-       protected:
-        ~time_get_byname();          //  virtual
-       };
-     }
-

  Change section 22.2.5.4 (lib.locale.time.put.byname) to become:

-
     namespace std {
-       template <class charT, class OutputIterator = ostreambuf_iterator<charT> >
-       class time_put_byname : public time_put<charT, OutputIterator>
-       {
-       public:
-         typedef charT          char_type;
-         typedef OutputIterator iter_type;
-
         explicit time_put_byname(const char*, size_t refs = 0);
-       protected:
-        ~time_put_byname();          //  virtual
-       };
-     }"
-

  Change section 22.2.6.4 (lib.locale.moneypunct.byname) to become:

-
     namespace std {
-       template <class charT, bool Intl = false>
-       class moneypunct_byname : public moneypunct<charT, Intl> {
-       public:
-         typedef money_base::pattern pattern;
-         typedef basic_string<charT> string_type;
-
         explicit moneypunct_byname(const char*, size_t refs = 0);
-       protected:
-        ~moneypunct_byname();        //  virtual
-       };
-     }
-

  Change section 22.2.7.2 (lib.locale.messages.byname) to become:

-
     namespace std {
-       template <class charT>
-       class messages_byname : public messages<charT> {
-       public:
-         typedef messages_base::catalog catalog;
-         typedef basic_string<charT>    string_type;
-
         explicit messages_byname(const char*, size_t refs = 0);
-       protected:
-        ~messages_byname();          //  virtual
-       };
-     }
-

Remove section 22.4.1.4 [locale.codecvt] completely (because in -this case only those members are defined to be virtual which are -defined to be virtual in 'ctype<cT>'.)

- -

[Post-Tokyo: Dietmar Kühl submitted this issue at the request of -the LWG to solve the underlying problems raised by issue 138.]

- - -

[Copenhagen: proposed resolution was revised slightly, to remove -three last virtual functions from messages_byname.]

- - - - - - - -
-

229. Unqualified references of other library entities

-

Section: 17.6.1.1 [contents] Status: CD1 - Submitter: Steve Clamage Opened: 2000-04-19 Last modified: 2015-04-08

-

View all other issues in [contents].

-

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-

Discussion:

-

Throughout the library chapters, the descriptions of library entities refer -to other library entities without necessarily qualifying the names.

- -

For example, section 25.2.2 "Swap" describes the effect of -swap_ranges in terms of the unqualified name "swap". This section -could reasonably be interpreted to mean that the library must be implemented so -as to do a lookup of the unqualified name "swap", allowing users to -override any ::std::swap function when Koenig lookup applies.

- -

Although it would have been best to use explicit qualification with -"::std::" throughout, too many lines in the standard would have to be -adjusted to make that change in a Technical Corrigendum.

- -

Issue 182, which addresses qualification of -size_t, is a special case of this. -

- - -

Proposed resolution:

-

To section 17.4.1.1 "Library contents" Add the following paragraph:

-
-

Whenever a name x defined in the standard library is mentioned, the name x - is assumed to be fully qualified as ::std::x, unless explicitly described - otherwise. For example, if the Effects section for library function F is - described as calling library function G, the function ::std::G is meant.

-
- -

[Post-Tokyo: Steve Clamage submitted this issue at the request of -the LWG to solve a problem in the standard itself similar to the -problem within implementations of library identified by issue 225. Any resolution of issue 225 should be -coordinated with the resolution of this issue.]

- - -

[post-Toronto: Howard is undecided about whether it is -appropriate for all standard library function names referred to in -other standard library functions to be explicitly qualified by -std: it is common advice that users should define global -functions that operate on their class in the same namespace as the -class, and this requires argument-dependent lookup if those functions -are intended to be called by library code. Several LWG members are -concerned that valarray appears to require argument-dependent lookup, -but that the wording may not be clear enough to fall under -"unless explicitly described otherwise".]

- - -

[Curaçao: An LWG-subgroup spent an afternoon working on issues -225, 226, and 229. Their conclusion was that the issues should be -separated into an LWG portion (Howard's paper, N1387=02-0045), and a -EWG portion (Dave will write a proposal). The LWG and EWG had -(separate) discussions of this plan the next day. This paper resolves -issues 225 and 226. In light of that resolution, the proposed -resolution for the current issue makes sense.]

- - - - - - - -
-

230. Assignable specified without also specifying CopyConstructible

-

Section: 17 [library] Status: CD1 - Submitter: Beman Dawes Opened: 2000-04-26 Last modified: 2015-04-08

-

View other active issues in [library].

-

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-

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-

Discussion:

-

Issue 227 identified an instance (std::swap) where -Assignable was specified without also specifying -CopyConstructible. The LWG asked that the standard be searched to -determine if the same defect existed elsewhere.

- -

There are a number of places (see proposed resolution below) where -Assignable is specified without also specifying -CopyConstructible. There are also several cases where both are -specified. For example, 26.5.1 [rand.req].

- - -

Proposed resolution:

-

In 23.2 [container.requirements] table 65 for value_type: -change "T is Assignable" to "T is CopyConstructible and -Assignable" -

- -

In 23.2.4 [associative.reqmts] table 69 X::key_type; change -"Key is Assignable" to "Key is -CopyConstructible and Assignable"
-

- -

In 24.2.4 [output.iterators] paragraph 1, change: -

-
-

A class or a built-in type X satisfies the requirements of an -output iterator if X is an Assignable type (23.1) and also the -following expressions are valid, as shown in Table 73: -

-
-

to: -

-
-

A class or a built-in type X satisfies the requirements of an -output iterator if X is a CopyConstructible (20.1.3) and Assignable -type (23.1) and also the following expressions are valid, as shown in -Table 73: -

-
- -

[Post-Tokyo: Beman Dawes submitted this issue at the request of -the LWG. He asks that the 25.3.5 [alg.replace] and 25.3.6 [alg.fill] changes be studied carefully, as it is not clear that -CopyConstructible is really a requirement and may be -overspecification.]

- - -

[Portions of the resolution for issue 230 have been superceded by -the resolution of issue 276.]

- - - - -

Rationale:

-

The original proposed resolution also included changes to input -iterator, fill, and replace. The LWG believes that those changes are -not necessary. The LWG considered some blanket statement, where an -Assignable type was also required to be Copy Constructible, but -decided against this because fill and replace really don't require the -Copy Constructible property.

- - - - -
-

231. Precision in iostream?

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 - Submitter: James Kanze, Stephen Clamage Opened: 2000-04-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

What is the following program supposed to output?

-
#include <iostream>
-
-    int
-    main()
-    {
-        std::cout.setf( std::ios::scientific , std::ios::floatfield ) ;
-        std::cout.precision( 0 ) ;
-        std::cout << 1.00 << '\n' ;
-        return 0 ;
-    }
-

From my C experience, I would expect "1e+00"; this is what -printf("%.0e" , 1.00 ); does. G++ outputs -"1.000000e+00".

- -

The only indication I can find in the standard is 22.2.2.2.2/11, -where it says "For conversion from a floating-point type, if -(flags & fixed) != 0 or if str.precision() > 0, then -str.precision() is specified in the conversion specification." -This is an obvious error, however, fixed is not a mask for a field, -but a value that a multi-bit field may take -- the results of and'ing -fmtflags with ios::fixed are not defined, at least not if -ios::scientific has been set. G++'s behavior corresponds to what might -happen if you do use (flags & fixed) != 0 with a typical -implementation (floatfield == 3 << something, fixed == 1 -<< something, and scientific == 2 << something).

- -

Presumably, the intent is either (flags & floatfield) != 0, or -(flags & floatfield) == fixed; the first gives something more or -less like the effect of precision in a printf floating point -conversion. Only more or less, of course. In order to implement printf -formatting correctly, you must know whether the precision was -explicitly set or not. Say by initializing it to -1, instead of 6, and -stating that for floating point conversions, if precision < -1, 6 -will be used, for fixed point, if precision < -1, 1 will be used, -etc. Plus, of course, if precision == 0 and flags & floatfield == -0, 1 should be = used. But it probably isn't necessary to emulate all -of the anomalies of printf:-).

- - -

Proposed resolution:

-

-Replace 22.4.2.2.2 [facet.num.put.virtuals], paragraph 11, with the following -sentence: -

-

-For conversion from a floating-point type, -str.precision() is specified in the conversion -specification. -

- - -

Rationale:

-

The floatfield determines whether numbers are formatted as if -with %f, %e, or %g. If the fixed bit is set, it's %f, -if scientific it's %e, and if both bits are set, or -neither, it's %g.

-

Turning to the C standard, a precision of 0 is meaningful -for %f and %e. For %g, precision 0 is taken to be the same as -precision 1.

-

The proposed resolution has the effect that if neither -fixed nor scientific is set we'll be -specifying a precision of 0, which will be internally -turned into 1. There's no need to call it out as a special -case.

-

The output of the above program will be "1e+00".

- -

[Post-Curaçao: Howard provided improved wording covering the case -where precision is 0 and mode is %g.]

- - - - - - - -
-

232. "depends" poorly defined in 17.4.3.1

-

Section: 17.6.4.3 [reserved.names] Status: CD1 - Submitter: Peter Dimov Opened: 2000-04-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

17.4.3.1/1 uses the term "depends" to limit the set of allowed -specializations of standard templates to those that "depend on a -user-defined name of external linkage."

-

This term, however, is not adequately defined, making it possible to -construct a specialization that is, I believe, technically legal according to -17.4.3.1/1, but that specializes a standard template for a built-in type such as -'int'.

-

The following code demonstrates the problem:

-
- 
#include <algorithm>
- 
template<class T> struct X
-{
- typedef T type;
-};
- 
namespace std
-{
- template<> void swap(::X<int>::type& i, ::X<int>::type& j);
-}
-
- - -

Proposed resolution:

-

Change "user-defined name" to "user-defined -type".

- - -

Rationale:

-

This terminology is used in section 2.5.2 and 4.1.1 of The C++ -Programming Language. It disallows the example in the issue, -since the underlying type itself is not user-defined. The only -possible problem I can see is for non-type templates, but there's no -possible way for a user to come up with a specialization for bitset, -for example, that might not have already been specialized by the -implementor?

- -

[Toronto: this may be related to issue 120.]

- - -

[post-Toronto: Judy provided the above proposed resolution and -rationale.]

- - - - - - -
-

233. Insertion hints in associative containers

-

Section: 23.2.4 [associative.reqmts] Status: CD1 - Submitter: Andrew Koenig Opened: 2000-04-30 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 192, 246

-

Discussion:

-

-If mm is a multimap and p is an iterator -into the multimap, then mm.insert(p, x) inserts -x into mm with p as a hint as -to where it should go. Table 69 claims that the execution time is -amortized constant if the insert winds up taking place adjacent to -p, but does not say when, if ever, this is guaranteed to -happen. All it says it that p is a hint as to where to -insert. -

-

-The question is whether there is any guarantee about the relationship -between p and the insertion point, and, if so, what it -is. -

-

-I believe the present state is that there is no guarantee: The user -can supply p, and the implementation is allowed to -disregard it entirely. -

- -

Additional comments from Nathan:
- -The vote [in Redmond] was on whether to elaborately specify the use of -the hint, or to require behavior only if the value could be inserted -adjacent to the hint. I would like to ensure that we have a chance to -vote for a deterministic treatment: "before, if possible, otherwise -after, otherwise anywhere appropriate", as an alternative to the -proposed "before or after, if possible, otherwise [...]". -

- -

[Toronto: there was general agreement that this is a real defect: -when inserting an element x into a multiset that already contains -several copies of x, there is no way to know whether the hint will be -used. The proposed resolution was that the new element should always -be inserted as close to the hint as possible. So, for example, if -there is a subsequence of equivalent values, then providing a.begin() -as the hint means that the new element should be inserted before the -subsequence even if a.begin() is far away. JC van Winkel supplied -precise wording for this proposed resolution, and also for an -alternative resolution in which hints are only used when they are -adjacent to the insertion point.]

- - -

[Copenhagen: the LWG agreed to the original proposed resolution, -in which an insertion hint would be used even when it is far from the -insertion point. This was contingent on seeing a example -implementation showing that it is possible to implement this -requirement without loss of efficiency. John Potter provided such a -example implementation.]

- - -

[Redmond: The LWG was reluctant to adopt the proposal that -emerged from Copenhagen: it seemed excessively complicated, and went -beyond fixing the defect that we identified in Toronto. PJP provided -the new wording described in this issue. Nathan agrees that we -shouldn't adopt the more detailed semantics, and notes: "we know that -you can do it efficiently enough with a red-black tree, but there are -other (perhaps better) balanced tree techniques that might differ -enough to make the detailed semantics hard to satisfy."]

- - -

[Curaçao: Nathan should give us the alternative wording he -suggests so the LWG can decide between the two options.]

- - -

[Lillehammer: The LWG previously rejected the more detailed - semantics, because it seemed more loike a new feature than like - defect fixing. We're now more sympathetic to it, but we (especially - Bill) are still worried about performance. N1780 describes a naive - algorithm, but it's not clear whether there is a non-naive - implementation. Is it possible to implement this as efficently as - the current version of insert?]

- - -

[Post Lillehammer: -N1780 -updated in post meeting mailing with -feedback from Lillehammer with more information regarding performance. -]

- - -

[ -Batavia: -1780 -accepted with minor wording changes in the proposed wording (reflected in the -proposed resolution below). Concerns about the performance of the algorithm -were satisfactorily met by -1780. -371 already handles the stability of equal ranges -and so that part of the resolution from -1780 -is no longer needed (or reflected in the proposed wording below). -]

- - - - -

Proposed resolution:

- -

-Change the indicated rows of the "Associative container requirements" Table in -23.2.4 [associative.reqmts] to: -

- - - - - - - - - - - - - - -
Associative container requirements
expression return typeassertion/note
pre/post-condition		complexity
a_eq.insert(t)iterator -inserts t and returns the iterator pointing to the newly inserted -element. If a range containing elements equivalent to t exists in -a_eq, t is inserted at the end of that range. - -logarithmic -
a.insert(p,t)iterator -inserts t if and only if there is no element with key equivalent to the -key of t in containers with unique keys; always inserts t in containers -with equivalent keys. always returns the iterator pointing to the element with key -equivalent to the key of t. iterator p is a hint pointing to where -the insert should start to search. t is inserted as close as possible -to the position just prior to p. - -logarithmic in general, but amortized constant if t is inserted right after - before p. -
- - - - - - -
-

234. Typos in allocator definition

-

Section: 20.7.9.1 [allocator.members] Status: CD1 - Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In paragraphs 12 and 13 the effects of construct() and -destruct() are described as returns but the functions actually -return void.

- - -

Proposed resolution:

-

Substitute "Returns" by "Effect".

- - - - -
-

235. No specification of default ctor for reverse_iterator

-

Section: 24.5.1.1 [reverse.iterator] Status: CD1 - Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The declaration of reverse_iterator lists a default -constructor. However, no specification is given what this constructor -should do.

- - -

Proposed resolution:

-

In section 24.5.1.3.1 [reverse.iter.cons] add the following - paragraph:

-
-

reverse_iterator()

- -

Default initializes current. Iterator operations - applied to the resulting iterator have defined behavior if and - only if the corresponding operations are defined on a default - constructed iterator of type Iterator.

-
-

[pre-Copenhagen: Dietmar provide wording for proposed - resolution.]

- - - - - - -
-

237. Undefined expression in complexity specification

-

Section: 23.3.3.2 [deque.cons] Status: CD1 - Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The complexity specification in paragraph 6 says that the complexity -is linear in first - last. Even if operator-() is -defined on iterators this term is in general undefined because it -would have to be last - first.

- - -

Proposed resolution:

-

Change paragraph 6 from

-

Linear in first - last.

-

to become

-

Linear in distance(first, last).

- - - - -
-

238. Contradictory results of stringbuf initialization.

-

Section: 27.8.2.1 [stringbuf.cons] Status: CD1 - Submitter: Dietmar Kühl Opened: 2000-05-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In 27.7.1.1 paragraph 4 the results of calling the constructor of -'basic_stringbuf' are said to be str() == str. This is fine -that far but consider this code:

- -
-  std::basic_stringbuf<char> sbuf("hello, world", std::ios_base::openmode(0));
-  std::cout << "'" << sbuf.str() << "'\n";
-
- -

Paragraph 3 of 27.7.1.1 basically says that in this case neither -the output sequence nor the input sequence is initialized and -paragraph 2 of 27.7.1.2 basically says that str() either -returns the input or the output sequence. None of them is initialized, -ie. both are empty, in which case the return from str() is -defined to be basic_string<cT>().

- -

However, probably only test cases in some testsuites will detect this -"problem"...

- - -

Proposed resolution:

-

Remove 27.7.1.1 paragraph 4.

- - -

Rationale:

-

We could fix 27.7.1.1 paragraph 4, but there would be no point. If -we fixed it, it would say just the same thing as text that's already -in the standard.

- - - - -
-

239. Complexity of unique() and/or unique_copy incorrect

-

Section: 25.3.9 [alg.unique] Status: CD1 - Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The complexity of unique and unique_copy are inconsistent with each -other and inconsistent with the implementations.  The standard -specifies:

- -

for unique():

- -

-3- Complexity: If the range (last - first) is not empty, exactly -(last - first) - 1 applications of the corresponding predicate, otherwise -no applications of the predicate.

- -

for unique_copy():

- -

-7- Complexity: Exactly last - first applications of the corresponding -predicate.

- -

-The implementations do it the other way round: unique() applies the -predicate last-first times and unique_copy() applies it last-first-1 -times.

- -

As both algorithms use the predicate for pair-wise comparison of -sequence elements I don't see a justification for unique_copy() -applying the predicate last-first times, especially since it is not -specified to which pair in the sequence the predicate is applied -twice.

- - -

Proposed resolution:

-

Change both complexity sections in 25.3.9 [alg.unique] to:

- -

Complexity: For nonempty ranges, exactly last - first - 1 -applications of the corresponding predicate.

- - - - - - -
-

240. Complexity of adjacent_find() is meaningless

-

Section: 25.2.8 [alg.adjacent.find] Status: CD1 - Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The complexity section of adjacent_find is defective:

- -
-
-template <class ForwardIterator>
-ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last
-                              BinaryPredicate pred);
-
- -

-1- Returns: The first iterator i such that both i and i + 1 are in -the range [first, last) for which the following corresponding -conditions hold: *i == *(i + 1), pred(*i, *(i + 1)) != false. Returns -last if no such iterator is found.

- -

-2- Complexity: Exactly find(first, last, value) - first applications -of the corresponding predicate. -

-
- -

In the Complexity section, it is not defined what "value" -is supposed to mean. My best guess is that "value" means an -object for which one of the conditions pred(*i,value) or -pred(value,*i) is true, where i is the iterator defined in the Returns -section. However, the value type of the input sequence need not be -equality-comparable and for this reason the term find(first, last, -value) - first is meaningless.

- -

A term such as find_if(first, last, bind2nd(pred,*i)) - first or -find_if(first, last, bind1st(pred,*i)) - first might come closer to -the intended specification. Binders can only be applied to function -objects that have the function call operator declared const, which is -not required of predicates because they can have non-const data -members. For this reason, a specification using a binder could only be -an "as-if" specification.

- - -

Proposed resolution:

-

Change the complexity section in 25.2.8 [alg.adjacent.find] to:

-

-For a nonempty range, exactly min((i - first) + 1, -(last - first) - 1) applications of the -corresponding predicate, where i is adjacent_find's -return value. -

- -

[Copenhagen: the original resolution specified an upper -bound. The LWG preferred an exact count.]

- - - - - - - -
-

241. Does unique_copy() require CopyConstructible and Assignable?

-

Section: 25.3.9 [alg.unique] Status: CD1 - Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Some popular implementations of unique_copy() create temporary -copies of values in the input sequence, at least if the input iterator -is a pointer. Such an implementation is built on the assumption that -the value type is CopyConstructible and Assignable.

- -

It is common practice in the standard that algorithms explicitly -specify any additional requirements that they impose on any of the -types used by the algorithm. An example of an algorithm that creates -temporary copies and correctly specifies the additional requirements -is accumulate(), 26.5.1 [rand.req].

- -

Since the specifications of unique() and unique_copy() do not -require CopyConstructible and Assignable of the InputIterator's value -type the above mentioned implementations are not standard-compliant. I -cannot judge whether this is a defect in the standard or a defect in -the implementations.

- - -

Proposed resolution:

-

In 25.2.8 change:

- -

--4- Requires: The ranges [first, last) and [result, result+(last-first)) -shall not overlap. -

- -

to:

- -
-

-4- Requires: The ranges [first, last) and [result, - result+(last-first)) shall not overlap. The expression *result = - *first must be valid. If neither InputIterator nor OutputIterator - meets the requirements of forward iterator then the value type of - InputIterator must be copy constructible. Otherwise copy - constructible is not required.

-
- -

[Redmond: the original proposed resolution didn't impose an -explicit requirement that the iterator's value type must be copy -constructible, on the grounds that an input iterator's value type must -always be copy constructible. Not everyone in the LWG thought that -this requirement was clear from table 72. It has been suggested that -it might be possible to implement unique_copy without -requiring assignability, although current implementations do impose -that requirement. Howard provided new wording.]

- - -

[ -Curaçao: The LWG changed the PR editorially to specify -"neither...nor...meet..." as clearer than -"both...and...do not meet...". Change believed to be so -minor as not to require re-review. -]

- - - - - - - - -
-

242. Side effects of function objects

-

Section: 25.3.4 [alg.transform], 26.5 [rand] Status: CD1 - Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The algorithms transform(), accumulate(), inner_product(), -partial_sum(), and adjacent_difference() require that the function -object supplied to them shall not have any side effects.

- -

The standard defines a side effect in 1.9 [intro.execution] as:

-

-7- Accessing an object designated by a volatile lvalue (basic.lval), -modifying an object, calling a library I/O function, or calling a function -that does any of those operations are all side effects, which are changes -in the state of the execution environment.

- -

As a consequence, the function call operator of a function object supplied -to any of the algorithms listed above cannot modify data members, cannot -invoke any function that has a side effect, and cannot even create and -modify temporary objects.  It is difficult to imagine a function object -that is still useful under these severe limitations. For instance, any -non-trivial transformator supplied to transform() might involve creation -and modification of temporaries, which is prohibited according to the current -wording of the standard.

- -

On the other hand, popular implementations of these algorithms exhibit -uniform and predictable behavior when invoked with a side-effect-producing -function objects. It looks like the strong requirement is not needed for -efficient implementation of these algorithms.

- -

The requirement of  side-effect-free function objects could be -replaced by a more relaxed basic requirement (which would hold for all -function objects supplied to any algorithm in the standard library):

-

A function objects supplied to an algorithm shall not invalidate -any iterator or sequence that is used by the algorithm. Invalidation of -the sequence includes destruction of the sorting order if the algorithm -relies on the sorting order (see section 25.3 - Sorting and related operations -[lib.alg.sorting]).

- -

I can't judge whether it is intended that the function objects supplied -to transform(), accumulate(), inner_product(), partial_sum(), or adjacent_difference() -shall not modify sequence elements through dereferenced iterators.

- -

It is debatable whether this issue is a defect or a change request. -Since the consequences for user-supplied function objects are drastic and -limit the usefulness of the algorithms significantly I would consider it -a defect.

- - -

Proposed resolution:

- -

Things to notice about these changes:

- -
    -
  1. The fully-closed ("[]" as opposed to half-closed "[)" ranges - are intentional. we want to prevent side-effects from - invalidating the end iterators.
    2. - -
  2. That has the unintentional side-effect of prohibiting - modification of the end element as a side-effect. This could - conceivably be significant in some cases.
    3. - -
  3. The wording also prevents side-effects from modifying elements - of the output sequence. I can't imagine why anyone would want - to do this, but it is arguably a restriction that implementors - don't need to place on users.
    4. - -
  4. Lifting the restrictions imposed in #2 and #3 above is possible - and simple, but would require more verbiage.
    5. -
- -

Change 25.2.3/2 from:

- -

- -2- Requires: op and binary_op shall not have any side effects. -

- -

to:

- -

- -2- Requires: in the ranges [first1, last1], [first2, first2 + - (last1 - first1)] and [result, result + (last1- first1)], op and - binary_op shall neither modify elements nor invalidate iterators or - subranges. - [Footnote: The use of fully closed ranges is intentional --end footnote] -

- - -

Change 25.2.3/2 from:

- -

- -2- Requires: op and binary_op shall not have any side effects. -

- -

to:

- -

- -2- Requires: op and binary_op shall not invalidate iterators or - subranges, or modify elements in the ranges [first1, last1], - [first2, first2 + (last1 - first1)], and [result, result + (last1 - - first1)]. - [Footnote: The use of fully closed ranges is intentional --end footnote] -

- - -

Change 26.4.1/2 from:

- -

- -2- Requires: T must meet the requirements of CopyConstructible - (lib.copyconstructible) and Assignable (lib.container.requirements) - types. binary_op shall not cause side effects. -

- -

to:

- -

- -2- Requires: T must meet the requirements of CopyConstructible - (lib.copyconstructible) and Assignable - (lib.container.requirements) types. In the range [first, last], - binary_op shall neither modify elements nor invalidate iterators - or subranges. - [Footnote: The use of a fully closed range is intentional --end footnote] -

- -

Change 26.4.2/2 from:

- -

- -2- Requires: T must meet the requirements of CopyConstructible - (lib.copyconstructible) and Assignable (lib.container.requirements) - types. binary_op1 and binary_op2 shall not cause side effects. -

- -

to:

- -

- -2- Requires: T must meet the requirements of CopyConstructible - (lib.copyconstructible) and Assignable (lib.container.requirements) - types. In the ranges [first, last] and [first2, first2 + (last - - first)], binary_op1 and binary_op2 shall neither modify elements - nor invalidate iterators or subranges. - [Footnote: The use of fully closed ranges is intentional --end footnote] -

- - -

Change 26.4.3/4 from:

- -

- -4- Requires: binary_op is expected not to have any side effects. -

- -

to:

- -

- -4- Requires: In the ranges [first, last] and [result, result + - (last - first)], binary_op shall neither modify elements nor - invalidate iterators or subranges. - [Footnote: The use of fully closed ranges is intentional --end footnote] -

- -

Change 26.4.4/2 from:

- -

- -2- Requires: binary_op shall not have any side effects. -

- -

to:

- -

- -2- Requires: In the ranges [first, last] and [result, result + - (last - first)], binary_op shall neither modify elements nor - invalidate iterators or subranges. - [Footnote: The use of fully closed ranges is intentional --end footnote] -

- -

[Toronto: Dave Abrahams supplied wording.]

- - -

[Copenhagen: Proposed resolution was modified slightly. Matt -added footnotes pointing out that the use of closed ranges was -intentional.]

- - - - - - - -
-

243. get and getline when sentry reports failure

-

Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Martin Sebor Opened: 2000-05-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

basic_istream<>::get(), and basic_istream<>::getline(), -are unclear with respect to the behavior and side-effects of the named -functions in case of an error.

- -

27.6.1.3, p1 states that "... If the sentry object returns -true, when converted to a value of type bool, the function endeavors -to obtain the requested input..." It is not clear from this (or -the rest of the paragraph) what precisely the behavior should be when -the sentry ctor exits by throwing an exception or when the sentry -object returns false. In particular, what is the number of characters -extracted that gcount() returns supposed to be?

- -

27.6.1.3 p8 and p19 say about the effects of get() and getline(): -"... In any case, it then stores a null character (using -charT()) into the next successive location of the array." Is not -clear whether this sentence applies if either of the conditions above -holds (i.e., when sentry fails).

- - -

Proposed resolution:

-

Add to 27.6.1.3, p1 after the sentence

- -

-"... If the sentry object returns true, when converted to a value of -type bool, the function endeavors to obtain the requested input." -

- -

the following

- - -

-"Otherwise, if the sentry constructor exits by throwing an exception or -if the sentry object returns false, when converted to a value of type -bool, the function returns without attempting to obtain any input. In -either case the number of extracted characters is set to 0; unformatted -input functions taking a character array of non-zero size as an argument -shall also store a null character (using charT()) in the first location -of the array." -

- - -

Rationale:

-

Although the general philosophy of the input functions is that the -argument should not be modified upon failure, getline -historically added a terminating null unconditionally. Most -implementations still do that. Earlier versions of the draft standard -had language that made this an unambiguous requirement; those words -were moved to a place where their context made them less clear. See -Jerry Schwarz's message c++std-lib-7618.

- - - - -
-

247. vector, deque::insert complexity

-

Section: 23.3.6.5 [vector.modifiers] Status: CD1 - Submitter: Lisa Lippincott Opened: 2000-06-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Paragraph 2 of 23.3.6.5 [vector.modifiers] describes the complexity -of vector::insert:

- -

- Complexity: If first and last are forward iterators, bidirectional - iterators, or random access iterators, the complexity is linear in - the number of elements in the range [first, last) plus the distance - to the end of the vector. If they are input iterators, the complexity - is proportional to the number of elements in the range [first, last) - times the distance to the end of the vector. -

- -

First, this fails to address the non-iterator forms of -insert.

- -

Second, the complexity for input iterators misses an edge case -- -it requires that an arbitrary number of elements can be added at -the end of a vector in constant time.

- -

I looked to see if deque had a similar problem, and was -surprised to find that deque places no requirement on the -complexity of inserting multiple elements (23.3.3.4 [deque.modifiers], -paragraph 3):

- -

- Complexity: In the worst case, inserting a single element into a - deque takes time linear in the minimum of the distance from the - insertion point to the beginning of the deque and the distance - from the insertion point to the end of the deque. Inserting a - single element either at the beginning or end of a deque always - takes constant time and causes a single call to the copy constructor - of T. -

- - -

Proposed resolution:

- -

Change Paragraph 2 of 23.3.6.5 [vector.modifiers] to

-

- Complexity: The complexity is linear in the number of elements - inserted plus the distance to the end of the vector. -

- -

[For input iterators, one may achieve this complexity by first - inserting at the end of the vector, and then using - rotate.]

- - -

Change 23.3.3.4 [deque.modifiers], paragraph 3, to:

- -

- Complexity: The complexity is linear in the number of elements - inserted plus the shorter of the distances to the beginning and - end of the deque. Inserting a single element at either the - beginning or the end of a deque causes a single call to the copy - constructor of T. -

- - - -

Rationale:

-

This is a real defect, and proposed resolution fixes it: some - complexities aren't specified that should be. This proposed - resolution does constrain deque implementations (it rules out the - most naive possible implementations), but the LWG doesn't see a - reason to permit that implementation.

- - - - - -
-

248. time_get fails to set eofbit

-

Section: 22.4.5 [category.time] Status: CD1 - Submitter: Martin Sebor Opened: 2000-06-22 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

There is no requirement that any of time_get member functions set -ios::eofbit when they reach the end iterator while parsing their input. -Since members of both the num_get and money_get facets are required to -do so (22.2.2.1.2, and 22.2.6.1.2, respectively), time_get members -should follow the same requirement for consistency.

- - -

Proposed resolution:

-

Add paragraph 2 to section 22.2.5.1 with the following text:

- -

-If the end iterator is reached during parsing by any of the get() -member functions, the member sets ios_base::eofbit in err. -

- - -

Rationale:

-

Two alternative resolutions were proposed. The LWG chose this one -because it was more consistent with the way eof is described for other -input facets.

- - - - -
-

250. splicing invalidates iterators

-

Section: 23.3.5.5 [list.ops] Status: CD1 - Submitter: Brian Parker Opened: 2000-07-14 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with CD1 status.

-

Discussion:

-

-Section 23.3.5.5 [list.ops] states that -

-
-  void splice(iterator position, list<T, Allocator>& x);
-
-

-invalidates all iterators and references to list x. -

- -

-This is unnecessary and defeats an important feature of splice. In -fact, the SGI STL guarantees that iterators to x remain valid -after splice. -

- - -

Proposed resolution:

- -

Add a footnote to 23.3.5.5 [list.ops], paragraph 1:

-

-[Footnote: As specified in [default.con.req], paragraphs -4-5, the semantics described in this clause applies only to the case -where allocators compare equal. --end footnote] -

- -

In 23.3.5.5 [list.ops], replace paragraph 4 with:

-

-Effects: Inserts the contents of x before position and x becomes -empty. Pointers and references to the moved elements of x now refer to -those same elements but as members of *this. Iterators referring to the -moved elements will continue to refer to their elements, but they now -behave as iterators into *this, not into x. -

- -

In 23.3.5.5 [list.ops], replace paragraph 7 with:

-

-Effects: Inserts an element pointed to by i from list x before -position and removes the element from x. The result is unchanged if -position == i or position == ++i. Pointers and references to *i continue -to refer to this same element but as a member of *this. Iterators to *i -(including i itself) continue to refer to the same element, but now -behave as iterators into *this, not into x. -

- -

In 23.3.5.5 [list.ops], replace paragraph 12 with:

-

-Requires: [first, last) is a valid range in x. The result is -undefined if position is an iterator in the range [first, last). -Pointers and references to the moved elements of x now refer to those -same elements but as members of *this. Iterators referring to the moved -elements will continue to refer to their elements, but they now behave as -iterators into *this, not into x. -

- -

[pre-Copenhagen: Howard provided wording.]

- - - -

Rationale:

-

The original proposed resolution said that iterators and references -would remain "valid". The new proposed resolution clarifies what that -means. Note that this only applies to the case of equal allocators. -From [default.con.req] paragraph 4, the behavior of list when -allocators compare nonequal is outside the scope of the standard.

- - - - -
-

251. basic_stringbuf missing allocator_type

-

Section: 27.8.2 [stringbuf] Status: CD1 - Submitter: Martin Sebor Opened: 2000-07-28 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

The synopsis for the template class basic_stringbuf -doesn't list a typedef for the template parameter -Allocator. This makes it impossible to determine the type of -the allocator at compile time. It's also inconsistent with all other -template classes in the library that do provide a typedef for the -Allocator parameter.

- - -

Proposed resolution:

-

Add to the synopses of the class templates basic_stringbuf (27.7.1), -basic_istringstream (27.7.2), basic_ostringstream (27.7.3), and -basic_stringstream (27.7.4) the typedef:

-
-  typedef Allocator allocator_type;
-
- - - - -
-

252. missing casts/C-style casts used in iostreams

-

Section: 27.8 [string.streams] Status: CD1 - Submitter: Martin Sebor Opened: 2000-07-28 Last modified: 2015-04-08

-

View all other issues in [string.streams].

-

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-

Discussion:

-

27.7.2.2, p1 uses a C-style cast rather than the more appropriate -const_cast<> in the Returns clause for basic_istringstream<>::rdbuf(). -The same C-style cast is being used in 27.7.3.2, p1, D.7.2.2, p1, and -D.7.3.2, p1, and perhaps elsewhere. 27.7.6, p1 and D.7.2.2, p1 are missing -the cast altogether.

- -

C-style casts have not been deprecated, so the first part of this -issue is stylistic rather than a matter of correctness.

- - -

Proposed resolution:

-

In 27.7.2.2, p1 replace

-
  -1- Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb.
- -

with

-
  -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).
- - -

In 27.7.3.2, p1 replace

-
  -1- Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb.
- -

with

-
  -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).
- -

In 27.7.6, p1, replace

-
  -1- Returns: &sb
- -

with

-
  -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).
- -

In D.7.2.2, p1 replace

-
  -2- Returns: &sb.
- -

with

-
  -2- Returns: const_cast<strstreambuf*>(&sb).
- - - - -
-

253. valarray helper functions are almost entirely useless

-

Section: 26.6.2.2 [valarray.cons], 26.6.2.3 [valarray.assign] Status: CD1 - Submitter: Robert Klarer Opened: 2000-07-31 Last modified: 2015-04-08

-

View all other issues in [valarray.cons].

-

View all issues with CD1 status.

-

Discussion:

-

This discussion is adapted from message c++std-lib-7056 posted -November 11, 1999. I don't think that anyone can reasonably claim -that the problem described below is NAD.

- -

These valarray constructors can never be called:

- -
-   template <class T>
-         valarray<T>::valarray(const slice_array<T> &);
-   template <class T>
-         valarray<T>::valarray(const gslice_array<T> &);
-   template <class T>
-         valarray<T>::valarray(const mask_array<T> &);
-   template <class T>
-         valarray<T>::valarray(const indirect_array<T> &);
-
- -

Similarly, these valarray assignment operators cannot be -called:

- -
-     template <class T>
-     valarray<T> valarray<T>::operator=(const slice_array<T> &);
-     template <class T>
-     valarray<T> valarray<T>::operator=(const gslice_array<T> &);
-     template <class T>
-     valarray<T> valarray<T>::operator=(const mask_array<T> &);
-     template <class T>
-     valarray<T> valarray<T>::operator=(const indirect_array<T> &);
-
- -

Please consider the following example:

- -
-   #include <valarray>
-   using namespace std;
-
-   int main()
-   {
-       valarray<double> va1(12);
-       valarray<double> va2(va1[slice(1,4,3)]); // line 1
-   }
-
- - -

Since the valarray va1 is non-const, the result of the sub-expression -va1[slice(1,4,3)] at line 1 is an rvalue of type const -std::slice_array<double>. This slice_array rvalue is then used to -construct va2. The constructor that is used to construct va2 is -declared like this:

- -
-     template <class T>
-     valarray<T>::valarray(const slice_array<T> &);
-
- -

Notice the constructor's const reference parameter. When the -constructor is called, a slice_array must be bound to this reference. -The rules for binding an rvalue to a const reference are in 8.5.3, -paragraph 5 (see also 13.3.3.1.4). Specifically, paragraph 5 -indicates that a second slice_array rvalue is constructed (in this -case copy-constructed) from the first one; it is this second rvalue -that is bound to the reference parameter. Paragraph 5 also requires -that the constructor that is used for this purpose be callable, -regardless of whether the second rvalue is elided. The -copy-constructor in this case is not callable, however, because it is -private. Therefore, the compiler should report an error.

- -

Since slice_arrays are always rvalues, the valarray constructor that has a -parameter of type const slice_array<T> & can never be called. The -same reasoning applies to the three other constructors and the four -assignment operators that are listed at the beginning of this post. -Furthermore, since these functions cannot be called, the valarray helper -classes are almost entirely useless.

- - -

Proposed resolution:

-

slice_array:

-
    -
  • Make the copy constructor and copy-assignment operator declarations - public in the slice_array class template definition in 26.6.5 [template.slice.array]
    • -
  • remove paragraph 3 of 26.6.5 [template.slice.array]
    • -
  • remove the copy constructor declaration from [cons.slice.arr]
    • -
  • change paragraph 1 of [cons.slice.arr] to read "This constructor is declared - to be private. This constructor need not be defined."
    • -
  • remove the first sentence of paragraph 1 of 26.6.5.2 [slice.arr.assign]
    • -
  • Change the first three words of the second sentence of paragraph 1 of - 26.6.5.2 [slice.arr.assign] to "These assignment operators have"
    • -
- -

gslice_array:

-
    -
  • Make the copy constructor and copy-assignment operator declarations - public in the gslice_array class template definition in 26.6.7 [template.gslice.array]
    • -
  • remove the note in paragraph 3 of 26.6.7 [template.gslice.array]
    • -
  • remove the copy constructor declaration from [gslice.array.cons]
    • -
  • change paragraph 1 of [gslice.array.cons] to read "This constructor is declared - to be private. This constructor need not be defined."
    • -
  • remove the first sentence of paragraph 1 of 26.6.7.2 [gslice.array.assign]
    • -
  • Change the first three words of the second sentence of paragraph 1 of - 26.6.7.2 [gslice.array.assign] to "These assignment operators have"
    • -
- -

mask_array:

-
    -
  • Make the copy constructor and copy-assignment operator declarations - public in the mask_array class template definition in 26.6.8 [template.mask.array]
    • -
  • remove the note in paragraph 2 of 26.6.8 [template.mask.array]
    • -
  • remove the copy constructor declaration from [mask.array.cons]
    • -
  • change paragraph 1 of [mask.array.cons] to read "This constructor is declared - to be private. This constructor need not be defined."
    • -
  • remove the first sentence of paragraph 1 of 26.6.8.2 [mask.array.assign]
    • -
  • Change the first three words of the second sentence of paragraph 1 of - 26.6.8.2 [mask.array.assign] to "These assignment operators have"
    • -
- -

indirect_array:

-
    -
  • Make the copy constructor and copy-assignment operator declarations - public in the indirect_array class definition in 26.6.9 [template.indirect.array]
    • -
  • remove the note in paragraph 2 of 26.6.9 [template.indirect.array]
    • -
  • remove the copy constructor declaration from [indirect.array.cons]
    • -
  • change the descriptive text in [indirect.array.cons] to read "This constructor is - declared to be private. This constructor need not be defined."
    • -
  • remove the first sentence of paragraph 1 of 26.6.9.2 [indirect.array.assign]
    • -
  • Change the first three words of the second sentence of paragraph 1 of - 26.6.9.2 [indirect.array.assign] to "These assignment operators have"
    • -
-

[Proposed resolution was modified in Santa Cruz: explicitly make -copy constructor and copy assignment operators public, instead of -removing them.]

- - - -

Rationale:

-

Keeping the valarray constructors private is untenable. Merely -making valarray a friend of the helper classes isn't good enough, -because access to the copy constructor is checked in the user's -environment.

- -

Making the assignment operator public is not strictly necessary to -solve this problem. A majority of the LWG (straw poll: 13-4) -believed we should make the assignment operators public, in addition -to the copy constructors, for reasons of symmetry and user -expectation.

- - - - - -
-

254. Exception types in clause 19 are constructed from std::string

-

Section: 19.2 [std.exceptions], 27.5.3.1.1 [ios::failure] Status: CD1 - Submitter: Dave Abrahams Opened: 2000-08-01 Last modified: 2015-04-08

-

View all other issues in [std.exceptions].

-

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-

Discussion:

-

-Many of the standard exception types which implementations are -required to throw are constructed with a const std::string& -parameter. For example: -

- -
-     19.1.5  Class out_of_range                          [lib.out.of.range]
-     namespace std {
-       class out_of_range : public logic_error {
-       public:
-         explicit out_of_range(const string& what_arg);
-       };
-     }
-
-   1 The class out_of_range defines the type of objects  thrown  as  excep-
-     tions to report an argument value not in its expected range.
-
-     out_of_range(const string& what_arg);
-
-     Effects:
-       Constructs an object of class out_of_range.
-     Postcondition:
-       strcmp(what(), what_arg.c_str()) == 0.
-
- -

-There are at least two problems with this: -

-
    -
  1. A program which is low on memory may end up throwing -std::bad_alloc instead of out_of_range because memory runs out while -constructing the exception object.
    2. -
  2. An obvious implementation which stores a std::string data member -may end up invoking terminate() during exception unwinding because the -exception object allocates memory (or rather fails to) as it is being -copied.
    3. -
- -

-There may be no cure for (1) other than changing the interface to -out_of_range, though one could reasonably argue that (1) is not a -defect. Personally I don't care that much if out-of-memory is reported -when I only have 20 bytes left, in the case when out_of_range would -have been reported. People who use exception-specifications might care -a lot, though. -

- -

-There is a cure for (2), but it isn't completely obvious. I think a -note for implementors should be made in the standard. Avoiding -possible termination in this case shouldn't be left up to chance. The -cure is to use a reference-counted "string" implementation -in the exception object. I am not necessarily referring to a -std::string here; any simple reference-counting scheme for a NTBS -would do. -

- -

Further discussion, in email:

- -

-...I'm not so concerned about (1). After all, a library implementation -can add const char* constructors as an extension, and users don't -need to avail themselves of the standard exceptions, though this is -a lame position to be forced into. FWIW, std::exception and -std::bad_alloc don't require a temporary basic_string. -

- -

-...I don't think the fixed-size buffer is a solution to the problem, -strictly speaking, because you can't satisfy the postcondition -
-   strcmp(what(), what_arg.c_str()) == 0 -
-For all values of what_arg (i.e. very long values). That means that -the only truly conforming solution requires a dynamic allocation. -

- -

Further discussion, from Redmond:

- -

The most important progress we made at the Redmond meeting was -realizing that there are two separable issues here: the const -string& constructor, and the copy constructor. If a user writes -something like throw std::out_of_range("foo"), the const -string& constructor is invoked before anything gets thrown. The -copy constructor is potentially invoked during stack unwinding.

- -

The copy constructor is a more serious problem, becuase failure -during stack unwinding invokes terminate. The copy -constructor must be nothrow. Curaçao: Howard thinks this -requirement may already be present.

- -

The fundamental problem is that it's difficult to get the nothrow -requirement to work well with the requirement that the exception -objects store a string of unbounded size, particularly if you also try -to make the const string& constructor nothrow. Options discussed -include:

- -
    -
  • Limit the size of a string that exception objects are required to -throw: change the postconditions of 19.2.2 [domain.error] paragraph 3 -and 19.2.6 [runtime.error] paragraph 3 to something like this: -"strncmp(what(), what_arg._str(), N) == 0, where N is an -implementation defined constant no smaller than 256".
    • -
  • Allow the const string& constructor to throw, but not the -copy constructor. It's the implementor's responsibility to get it -right. (An implementor might use a simple refcount class.)
    • -
  • Compromise between the two: an implementation is not allowed to -throw if the string's length is less than some N, but, if it doesn't -throw, the string must compare equal to the argument.
    • -
  • Add a new constructor that takes a const char*
    • -
- -

(Not all of these options are mutually exclusive.)

- - - -

Proposed resolution:

- -

-Change 19.2.1 [logic.error] -

- -
-
-namespace std {
-  class logic_error : public exception {
-  public:
-    explicit logic_error(const string& what_arg);
-    explicit logic_error(const char* what_arg);
-  };
-}
-
-

...

-

-logic_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class logic_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.2 [domain.error] -

- -
-
-namespace std {
-  class domain_error : public logic_error {
-  public:
-    explicit domain_error(const string& what_arg);
-    explicit domain_error(const char* what_arg);
-  };
-}
-
-

...

-

-domain_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class domain_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

- -
-
- -

-Change 19.2.3 [invalid.argument] -

- -
-
-namespace std {
-  class invalid_argument : public logic_error {
-  public:
-    explicit invalid_argument(const string& what_arg);
-    explicit invalid_argument(const char* what_arg);
-  };
-}
-
-

...

-

-invalid_argument(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class invalid_argument. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.4 [length.error] -

- -
-
-namespace std {
-  class length_error : public logic_error {
-  public:
-    explicit length_error(const string& what_arg);
-    explicit length_error(const char* what_arg);
-  };
-}
-
-

...

-

-length_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class length_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.5 [out.of.range] -

- -
-
-namespace std {
-  class out_of_range : public logic_error {
-  public:
-    explicit out_of_range(const string& what_arg);
-    explicit out_of_range(const char* what_arg);
-  };
-}
-
-

...

-

-out_of_range(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class out_of_range. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.6 [runtime.error] -

- -
-
-namespace std {
-  class runtime_error : public exception {
-  public:
-    explicit runtime_error(const string& what_arg);
-    explicit runtime_error(const char* what_arg);
-  };
-}
-
-

...

-

-runtime_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class runtime_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.7 [range.error] -

- -
-
-namespace std {
-  class range_error : public runtime_error {
-  public:
-    explicit range_error(const string& what_arg);
-    explicit range_error(const char* what_arg);
-  };
-}
-
-

...

-

-range_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class range_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.8 [overflow.error] -

- -
-
-namespace std {
-  class overflow_error : public runtime_error {
-  public:
-    explicit overflow_error(const string& what_arg);
-    explicit overflow_error(const char* what_arg);
-  };
-}
-
-

...

-

-overflow_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class overflow_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 19.2.9 [underflow.error] -

- -
-
-namespace std {
-  class underflow_error : public runtime_error {
-  public:
-    explicit underflow_error(const string& what_arg);
-    explicit underflow_error(const char* what_arg);
-  };
-}
-
-

...

-

-underflow_error(const char* what_arg); -

-
-

--4- Effects: Constructs an object of class underflow_error. -

-

--5- Postcondition: strcmp(what(), what_arg) == 0. -

-
- -
- -

-Change 27.5.3.1.1 [ios::failure] -

- -
-
-namespace std {
-  class ios_base::failure : public exception {
-  public:
-    explicit failure(const string& msg);
-    explicit failure(const char* msg);
-    virtual const char* what() const throw();
-};
-}
-
-

...

-

-failure(const char* msg); -

-
-

--4- Effects: Constructs an object of class failure. -

-

--5- Postcondition: strcmp(what(), msg) == 0. -

-
- -
- - - -

Rationale:

- -

Throwing a bad_alloc while trying to construct a message for another -exception-derived class is not necessarily a bad thing. And the -bad_alloc constructor already has a no throw spec on it (18.4.2.1).

- -

Future:

- -

All involved would like to see const char* constructors added, but -this should probably be done for C++0X as opposed to a DR.

- -

I believe the no throw specs currently decorating these functions -could be improved by some kind of static no throw spec checking -mechanism (in a future C++ language). As they stand, the copy -constructors might fail via a call to unexpected. I think what is -intended here is that the copy constructors can't fail.

- -

[Pre-Sydney: reopened at the request of Howard Hinnant. - Post-Redmond: James Kanze noticed that the copy constructors of - exception-derived classes do not have nothrow clauses. Those - classes have no copy constructors declared, meaning the - compiler-generated implicit copy constructors are used, and those - compiler-generated constructors might in principle throw anything.]

- - -

[ -Batavia: Merged copy constructor and assignment operator spec into exception -and added ios::failure into the proposed resolution. -]

- - -

[ -Oxford: The proposed resolution simply addresses the issue of constructing -the exception objects with const char* and string literals without -the need to explicit include or construct a std::string. -]

- - - - - - - -
-

256. typo in 27.4.4.2, p17: copy_event does not exist

-

Section: 27.5.5.3 [basic.ios.members] Status: CD1 - Submitter: Martin Sebor Opened: 2000-08-21 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

View all issues with CD1 status.

-

Discussion:

-

-27.4.4.2, p17 says -

- -

--17- Before copying any parts of rhs, calls each registered callback -pair (fn,index) as (*fn)(erase_event,*this,index). After all parts but -exceptions() have been replaced, calls each callback pair that was -copied from rhs as (*fn)(copy_event,*this,index). -

- -

-The name copy_event isn't defined anywhere. The intended name was -copyfmt_event. -

- - -

Proposed resolution:

-

Replace copy_event with copyfmt_event in the named paragraph.

- - - - -
-

258. Missing allocator requirement

-

Section: 17.6.3.5 [allocator.requirements] Status: CD1 - Submitter: Matt Austern Opened: 2000-08-22 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

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-

Discussion:

-

-From lib-7752: -

- -

-I've been assuming (and probably everyone else has been assuming) that -allocator instances have a particular property, and I don't think that -property can be deduced from anything in Table 32. -

- -

-I think we have to assume that allocator type conversion is a -homomorphism. That is, if x1 and x2 are of type X, where -X::value_type is T, and if type Y is X::template -rebind<U>::other, then Y(x1) == Y(x2) if and only if x1 == x2. -

- -

-Further discussion: Howard Hinnant writes, in lib-7757: -

- -

-I think I can prove that this is not provable by Table 32. And I agree -it needs to be true except for the "and only if". If x1 != x2, I see no -reason why it can't be true that Y(x1) == Y(x2). Admittedly I can't -think of a practical instance where this would happen, or be valuable. -But I also don't see a need to add that extra restriction. I think we -only need: -

- -

- if (x1 == x2) then Y(x1) == Y(x2) -

- -

-If we decide that == on allocators is transitive, then I think I can -prove the above. But I don't think == is necessarily transitive on -allocators. That is: -

- -

-Given x1 == x2 and x2 == x3, this does not mean x1 == x3. -

- -

Example:

- -
-

-x1 can deallocate pointers from: x1, x2, x3
-x2 can deallocate pointers from: x1, x2, x4
-x3 can deallocate pointers from: x1, x3
-x4 can deallocate pointers from: x2, x4 -

- -

-x1 == x2, and x2 == x4, but x1 != x4 -

-
-

[Toronto: LWG members offered multiple opinions. One -opinion is that it should not be required that x1 == x2 -implies Y(x1) == Y(x2), and that it should not even be -required that X(x1) == x1. Another opinion is that -the second line from the bottom in table 32 already implies the -desired property. This issue should be considered in light of -other issues related to allocator instances.]

- - - -

Proposed resolution:

-

-Accept proposed wording from -N2436 part 3. -

- - -

[Lillehammer: Same conclusion as before: this should be - considered as part of an allocator redesign, not solved on its own.]

- - -

[ -Batavia: An allocator redesign is not forthcoming and thus we fixed this one issue. -]

- - -

[ -Toronto: Reopened at the request of the project editor (Pete) because the proposed -wording did not fit within the indicated table. The intent of the resolution remains -unchanged. Pablo to work with Pete on improved wording. -]

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which -was subsequently split out into a separate paper N2436 for the purposes of voting. -The resolution in N2436 addresses this issue. The LWG voted to accelerate this -issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

259. basic_string::operator[] and const correctness

-

Section: 21.4.4 [string.capacity] Status: CD1 - Submitter: Chris Newton Opened: 2000-08-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paraphrased from a message that Chris Newton posted to comp.std.c++: -

- -

-The standard's description of basic_string<>::operator[] -seems to violate const correctness. -

- -

-The standard (21.3.4/1) says that "If pos < size(), -returns data()[pos]." The types don't work. The -return value of data() is const charT*, but -operator[] has a non-const version whose return type is reference. -

- - -

Proposed resolution:

-

-In section 21.3.4, paragraph 1, change -"data()[pos]" to "*(begin() + -pos)". -

- - - - -
-

260. Inconsistent return type of istream_iterator::operator++(int)

-

Section: 24.6.1.2 [istream.iterator.ops] Status: CD1 - Submitter: Martin Sebor Opened: 2000-08-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The synopsis of istream_iterator::operator++(int) in 24.5.1 shows -it as returning the iterator by value. 24.5.1.2, p5 shows the same -operator as returning the iterator by reference. That's incorrect -given the Effects clause below (since a temporary is returned). The -`&' is probably just a typo.

- - -

Proposed resolution:

-

Change the declaration in 24.5.1.2, p5 from

- 
- istream_iterator<T,charT,traits,Distance>& operator++(int);
-
-

to

- 
- istream_iterator<T,charT,traits,Distance> operator++(int);
-
-

(that is, remove the `&').

- - - - -
-

261. Missing description of istream_iterator::operator!=

-

Section: 24.6.1.2 [istream.iterator.ops] Status: CD1 - Submitter: Martin Sebor Opened: 2000-08-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-24.5.1, p3 lists the synopsis for -

- -
-   template <class T, class charT, class traits, class Distance>
-        bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
-                        const istream_iterator<T,charT,traits,Distance>& y);
-
- -

-but there is no description of what the operator does (i.e., no Effects -or Returns clause) in 24.5.1.2. -

- - -

Proposed resolution:

-

-Add paragraph 7 to the end of section 24.5.1.2 with the following text: -

- -
-   template <class T, class charT, class traits, class Distance>
-        bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
-                        const istream_iterator<T,charT,traits,Distance>& y);
-
- -

-7- Returns: !(x == y).

- - - - -
-

262. Bitmask operator ~ specified incorrectly

-

Section: 17.5.2.1.3 [bitmask.types] Status: CD1 - Submitter: Beman Dawes Opened: 2000-09-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The ~ operation should be applied after the cast to int_type. -

- - -

Proposed resolution:

-

-Change 17.3.2.1.2 [lib.bitmask.types] operator~ from: -

- -
-   bitmask operator~ ( bitmask X )
-     { return static_cast< bitmask>(static_cast<int_type>(~ X)); }
-
- -

-to: -

- -
-   bitmask operator~ ( bitmask X )
-     { return static_cast< bitmask>(~static_cast<int_type>(X)); }
-
- - - - -
-

263. Severe restriction on basic_string reference counting

-

Section: 21.4 [basic.string] Status: CD1 - Submitter: Kevlin Henney Opened: 2000-09-04 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The note in paragraph 6 suggests that the invalidation rules for -references, pointers, and iterators in paragraph 5 permit a reference- -counted implementation (actually, according to paragraph 6, they permit -a "reference counted implementation", but this is a minor editorial fix). -

- -

-However, the last sub-bullet is so worded as to make a reference-counted -implementation unviable. In the following example none of the -conditions for iterator invalidation are satisfied: -

- -
-    // first example: "*******************" should be printed twice
-    string original = "some arbitrary text", copy = original;
-    const string & alias = original;
-
-    string::const_iterator i = alias.begin(), e = alias.end();
-    for(string::iterator j = original.begin(); j != original.end(); ++j)
-        *j = '*';
-    while(i != e)
-        cout << *i++;
-    cout << endl;
-    cout << original << endl;
-
- -

-Similarly, in the following example: -

- -
-    // second example: "some arbitrary text" should be printed out
-    string original = "some arbitrary text", copy = original;
-    const string & alias = original;
-
-    string::const_iterator i = alias.begin();
-    original.begin();
-    while(i != alias.end())
-        cout << *i++;
-
- -

-I have tested this on three string implementations, two of which were -reference counted. The reference-counted implementations gave -"surprising behavior" because they invalidated iterators on -the first call to non-const begin since construction. The current -wording does not permit such invalidation because it does not take -into account the first call since construction, only the first call -since various member and non-member function calls. -

- - -

Proposed resolution:

-

-Change the following sentence in 21.3 paragraph 5 from -

- -

- Subsequent to any of the above uses except the forms of insert() and - erase() which return iterators, the first call to non-const member - functions operator[](), at(), begin(), rbegin(), end(), or rend(). -

- -

to

- -

- Following construction or any of the above uses, except the forms of - insert() and erase() that return iterators, the first call to non- - const member functions operator[](), at(), begin(), rbegin(), end(), - or rend(). -

- - - - -
-

264. Associative container insert(i, j) complexity requirements are not feasible.

-

Section: 23.2.4 [associative.reqmts] Status: CD1 - Submitter: John Potter Opened: 2000-09-07 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 102

-

Discussion:

-

-Table 69 requires linear time if [i, j) is sorted. Sorted is necessary but not sufficient. -Consider inserting a sorted range of even integers into a set<int> containing the odd -integers in the same range. -

- -

Related issue: 102

- - -

Proposed resolution:

-

-In Table 69, in section 23.1.2, change the complexity clause for -insertion of a range from "N log(size() + N) (N is the distance -from i to j) in general; linear if [i, j) is sorted according to -value_comp()" to "N log(size() + N), where N is the distance -from i to j". -

- -

[Copenhagen: Minor fix in proposed resolution: fixed unbalanced -parens in the revised wording.]

- - - - -

Rationale:

-

-Testing for valid insertions could be less efficient than simply -inserting the elements when the range is not both sorted and between -two adjacent existing elements; this could be a QOI issue. -

- -

-The LWG considered two other options: (a) specifying that the -complexity was linear if [i, j) is sorted according to value_comp() -and between two adjacent existing elements; or (b) changing to -Klog(size() + N) + (N - K) (N is the distance from i to j and K is the -number of elements which do not insert immediately after the previous -element from [i, j) including the first). The LWG felt that, since -we can't guarantee linear time complexity whenever the range to be -inserted is sorted, it's more trouble than it's worth to say that it's -linear in some special cases. -

- - - - -
-

265. std::pair::pair() effects overly restrictive

-

Section: 20.3 [pairs] Status: CD1 - Submitter: Martin Sebor Opened: 2000-09-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I don't see any requirements on the types of the elements of the -std::pair container in 20.2.2. From the descriptions of the member -functions it appears that they must at least satisfy the requirements of -20.1.3 [lib.copyconstructible] and 20.1.4 [lib.default.con.req], and in -the case of the [in]equality operators also the requirements of 20.1.1 -[lib.equalitycomparable] and 20.1.2 [lib.lessthancomparable]. -

- -

-I believe that the the CopyConstructible requirement is unnecessary in -the case of 20.2.2, p2. -

- - -

Proposed resolution:

-

Change the Effects clause in 20.2.2, p2 from

- -

--2- Effects: Initializes its members as if implemented: pair() : -first(T1()), second(T2()) {} -

- -

to

- -

--2- Effects: Initializes its members as if implemented: pair() : -first(), second() {} -

- - -

Rationale:

-

The existing specification of pair's constructor appears to be a -historical artifact: there was concern that pair's members be properly -zero-initialized when they are built-in types. At one time there was -uncertainty about whether they would be zero-initialized if the -default constructor was written the obvious way. This has been -clarified by core issue 178, and there is no longer any doubt that -the straightforward implementation is correct.

- - - - -
-

266. bad_exception::~bad_exception() missing Effects clause

-

Section: 18.8.2 [bad.exception] Status: CD1 - Submitter: Martin Sebor Opened: 2000-09-24 Last modified: 2015-04-08

-

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-

Discussion:

-

-The synopsis for std::bad_exception lists the function ~bad_exception() -but there is no description of what the function does (the Effects -clause is missing). -

- - -

Proposed resolution:

-

-Remove the destructor from the class synopses of -bad_alloc (18.6.2.1 [bad.alloc]), -bad_cast (18.7.2 [bad.cast]), -bad_typeid (18.7.3 [bad.typeid]), -and bad_exception (18.8.2 [bad.exception]). -

- - -

Rationale:

-

-This is a general problem with the exception classes in clause 18. -The proposed resolution is to remove the destructors from the class -synopses, rather than to document the destructors' behavior, because -removing them is more consistent with how exception classes are -described in clause 19. -

- - - - -
-

268. Typo in locale synopsis

-

Section: 22.3.1 [locale] Status: CD1 - Submitter: Martin Sebor Opened: 2000-10-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The synopsis of the class std::locale in 22.1.1 contains two typos: -the semicolons after the declarations of the default ctor -locale::locale() and the copy ctor locale::locale(const locale&) -are missing.

- - -

Proposed resolution:

-

Add the missing semicolons, i.e., change

- -
-    //  construct/copy/destroy:
-        locale() throw()
-        locale(const locale& other) throw()
-
- -

in the synopsis in 22.1.1 to

- -
-    //  construct/copy/destroy:
-        locale() throw();
-        locale(const locale& other) throw();
-
- - - - -
-

270. Binary search requirements overly strict

-

Section: 25.4.3 [alg.binary.search] Status: CD1 - Submitter: Matt Austern Opened: 2000-10-18 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 472

-

Discussion:

-

-Each of the four binary search algorithms (lower_bound, upper_bound, -equal_range, binary_search) has a form that allows the user to pass a -comparison function object. According to 25.3, paragraph 2, that -comparison function object has to be a strict weak ordering. -

- -

-This requirement is slightly too strict. Suppose we are searching -through a sequence containing objects of type X, where X is some -large record with an integer key. We might reasonably want to look -up a record by key, in which case we would want to write something -like this: -

-
-    struct key_comp {
-      bool operator()(const X& x, int n) const {
-        return x.key() < n;
-      }
-    }
-
-    std::lower_bound(first, last, 47, key_comp());
-
- -

-key_comp is not a strict weak ordering, but there is no reason to -prohibit its use in lower_bound. -

- -

-There's no difficulty in implementing lower_bound so that it allows -the use of something like key_comp. (It will probably work unless an -implementor takes special pains to forbid it.) What's difficult is -formulating language in the standard to specify what kind of -comparison function is acceptable. We need a notion that's slightly -more general than that of a strict weak ordering, one that can encompass -a comparison function that involves different types. Expressing that -notion may be complicated. -

- -

Additional questions raised at the Toronto meeting:

-
    -
  • Do we really want to specify what ordering the implementor must - use when calling the function object? The standard gives - specific expressions when describing these algorithms, but it also - says that other expressions (with different argument order) are - equivalent.
    • -
  • If we are specifying ordering, note that the standard uses both - orderings when describing equal_range.
    • -
  • Are we talking about requiring these algorithms to work properly - when passed a binary function object whose two argument types - are not the same, or are we talking about requirements when - they are passed a binary function object with several overloaded - versions of operator()?
    • -
  • The definition of a strict weak ordering does not appear to give - any guidance on issues of overloading; it only discusses expressions, - and all of the values in these expressions are of the same type. - Some clarification would seem to be in order.
    • -
- -

Additional discussion from Copenhagen:

-
    -
  • It was generally agreed that there is a real defect here: if -the predicate is merely required to be a Strict Weak Ordering, then -it's possible to pass in a function object with an overloaded -operator(), where the version that's actually called does something -completely inappropriate. (Such as returning a random value.)
    • - -
  • An alternative formulation was presented in a paper distributed by -David Abrahams at the meeting, "Binary Search with Heterogeneous -Comparison", J16-01/0027 = WG21 N1313: Instead of viewing the -predicate as a Strict Weak Ordering acting on a sorted sequence, view -the predicate/value pair as something that partitions a sequence. -This is almost equivalent to saying that we should view binary search -as if we are given a unary predicate and a sequence, such that f(*p) -is true for all p below a specific point and false for all p above it. -The proposed resolution is based on that alternative formulation.
    • -
- - -

Proposed resolution:

- -

Change 25.3 [lib.alg.sorting] paragraph 3 from:

- -

- 3 For all algorithms that take Compare, there is a version that uses - operator< instead. That is, comp(*i, *j) != false defaults to *i < - *j != false. For the algorithms to work correctly, comp has to - induce a strict weak ordering on the values. -

- -

to:

- -

- 3 For all algorithms that take Compare, there is a version that uses - operator< instead. That is, comp(*i, *j) != false defaults to *i - < *j != false. For algorithms other than those described in - lib.alg.binary.search (25.3.3) to work correctly, comp has to induce - a strict weak ordering on the values. -

- -

Add the following paragraph after 25.3 [lib.alg.sorting] paragraph 5:

- -

- -6- A sequence [start, finish) is partitioned with respect to an - expression f(e) if there exists an integer n such that - for all 0 <= i < distance(start, finish), f(*(begin+i)) is true if - and only if i < n. -

- -

Change 25.3.3 [lib.alg.binary.search] paragraph 1 from:

- -

- -1- All of the algorithms in this section are versions of binary - search and assume that the sequence being searched is in order - according to the implied or explicit comparison function. They work - on non-random access iterators minimizing the number of - comparisons, which will be logarithmic for all types of - iterators. They are especially appropriate for random access - iterators, because these algorithms do a logarithmic number of - steps through the data structure. For non-random access iterators - they execute a linear number of steps. -

- -

to:

- -

- -1- All of the algorithms in this section are versions of binary - search and assume that the sequence being searched is partitioned - with respect to an expression formed by binding the search key to - an argument of the implied or explicit comparison function. They - work on non-random access iterators minimizing the number of - comparisons, which will be logarithmic for all types of - iterators. They are especially appropriate for random access - iterators, because these algorithms do a logarithmic number of - steps through the data structure. For non-random access iterators - they execute a linear number of steps. -

- -

Change 25.3.3.1 [lib.lower.bound] paragraph 1 from:

- -

- -1- Requires: Type T is LessThanComparable - (lib.lessthancomparable). -

- -

to:

- -

- -1- Requires: The elements e of [first, last) are partitioned with - respect to the expression e < value or comp(e, value) -

- - -

Remove 25.3.3.1 [lib.lower.bound] paragraph 2:

- -

- -2- Effects: Finds the first position into which value can be - inserted without violating the ordering. -

- -

Change 25.3.3.2 [lib.upper.bound] paragraph 1 from:

- -

- -1- Requires: Type T is LessThanComparable (lib.lessthancomparable). -

- -

to:

- -

- -1- Requires: The elements e of [first, last) are partitioned with - respect to the expression !(value < e) or !comp(value, e) -

- -

Remove 25.3.3.2 [lib.upper.bound] paragraph 2:

- -

- -2- Effects: Finds the furthermost position into which value can be - inserted without violating the ordering. -

- -

Change 25.3.3.3 [lib.equal.range] paragraph 1 from:

- -

- -1- Requires: Type T is LessThanComparable - (lib.lessthancomparable). -

- -

to:

- -

- -1- Requires: The elements e of [first, last) are partitioned with - respect to the expressions e < value and !(value < e) or - comp(e, value) and !comp(value, e). Also, for all elements e of - [first, last), e < value implies !(value < e) or comp(e, - value) implies !comp(value, e) -

- -

Change 25.3.3.3 [lib.equal.range] paragraph 2 from:

- -

- -2- Effects: Finds the largest subrange [i, j) such that the value - can be inserted at any iterator k in it without violating the - ordering. k satisfies the corresponding conditions: !(*k < value) - && !(value < *k) or comp(*k, value) == false && comp(value, *k) == - false. -

- -

to:

- -
-   -2- Returns: 
-         make_pair(lower_bound(first, last, value),
-                   upper_bound(first, last, value))
-       or
-         make_pair(lower_bound(first, last, value, comp),
-                   upper_bound(first, last, value, comp))
-
- -

Change 25.3.3.3 [lib.binary.search] paragraph 1 from:

- -

- -1- Requires: Type T is LessThanComparable - (lib.lessthancomparable). -

- -

to:

- -

- -1- Requires: The elements e of [first, last) are partitioned with - respect to the expressions e < value and !(value < e) or comp(e, - value) and !comp(value, e). Also, for all elements e of [first, - last), e < value implies !(value < e) or comp(e, value) implies - !comp(value, e) -

- -

[Copenhagen: Dave Abrahams provided this wording]

- - -

[Redmond: Minor changes in wording. (Removed "non-negative", and -changed the "other than those described in" wording.) Also, the LWG -decided to accept the "optional" part.]

- - - - -

Rationale:

-

The proposed resolution reinterprets binary search. Instead of -thinking about searching for a value in a sorted range, we view that -as an important special case of a more general algorithm: searching -for the partition point in a partitioned range.

- -

We also add a guarantee that the old wording did not: we ensure -that the upper bound is no earlier than the lower bound, that -the pair returned by equal_range is a valid range, and that the first -part of that pair is the lower bound.

- - - - - -
-

271. basic_iostream missing typedefs

-

Section: 27.7.2.5 [iostreamclass] Status: CD1 - Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2015-04-08

-

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-

Discussion:

-

-Class template basic_iostream has no typedefs. The typedefs it -inherits from its base classes can't be used, since (for example) -basic_iostream<T>::traits_type is ambiguous. -

- - -

Proposed resolution:

- -

Add the following to basic_iostream's class synopsis in -27.7.2.5 [iostreamclass], immediately after public:

- -
-  // types:
-  typedef charT                     char_type;
-  typedef typename traits::int_type int_type;
-  typedef typename traits::pos_type pos_type;
-  typedef typename traits::off_type off_type;
-  typedef traits                    traits_type;
-
- - - - -
-

272. Missing parentheses around subexpression

-

Section: 27.5.5.4 [iostate.flags] Status: CD1 - Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 569

-

Discussion:

-

-27.4.4.3, p4 says about the postcondition of the function: If -rdbuf()!=0 then state == rdstate(); otherwise -rdstate()==state|ios_base::badbit. -

- -

-The expression on the right-hand-side of the operator==() needs to be -parenthesized in order for the whole expression to ever evaluate to -anything but non-zero. -

- - -

Proposed resolution:

-

-Add parentheses like so: rdstate()==(state|ios_base::badbit). -

- - - - -
-

273. Missing ios_base qualification on members of a dependent class

-

Section: 27 [input.output] Status: CD1 - Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

27.5.2.4.2, p4, and 27.8.1.6, p2, 27.8.1.7, p3, 27.8.1.9, p2, -27.8.1.10, p3 refer to in and/or out w/o ios_base:: qualification. -That's incorrect since the names are members of a dependent base -class (14.6.2 [temp.dep]) and thus not visible.

- - -

Proposed resolution:

-

Qualify the names with the name of the class of which they are -members, i.e., ios_base.

- - - - -
-

274. a missing/impossible allocator requirement

-

Section: 17.6.3.5 [allocator.requirements] Status: CD1 - Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

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-

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-

Discussion:

-

-I see that table 31 in 20.1.5, p3 allows T in std::allocator<T> to be of -any type. But the synopsis in 20.4.1 calls for allocator<>::address() to -be overloaded on reference and const_reference, which is ill-formed for -all T = const U. In other words, this won't work: -

- -

-template class std::allocator<const int>; -

- -

-The obvious solution is to disallow specializations of allocators on -const types. However, while containers' elements are required to be -assignable (which rules out specializations on const T's), I think that -allocators might perhaps be potentially useful for const values in other -contexts. So if allocators are to allow const types a partial -specialization of std::allocator<const T> would probably have to be -provided. -

- - -

Proposed resolution:

-

Change the text in row 1, column 2 of table 32 in 20.1.5, p3 from

- -

- any type -

- -

to

-

- any non-const, non-reference type -

- -

[Redmond: previous proposed resolution was "any non-const, -non-volatile, non-reference type". Got rid of the "non-volatile".]

- - - - -

Rationale:

-

-Two resolutions were originally proposed: one that partially -specialized std::allocator for const types, and one that said an -allocator's value type may not be const. The LWG chose the second. -The first wouldn't be appropriate, because allocators are intended for -use by containers, and const value types don't work in containers. -Encouraging the use of allocators with const value types would only -lead to unsafe code. -

-

-The original text for proposed resolution 2 was modified so that it -also forbids volatile types and reference types. -

- -

[Curaçao: LWG double checked and believes volatile is correctly -excluded from the PR.]

- - - - - - - -
-

275. Wrong type in num_get::get() overloads

-

Section: 22.4.2.1.1 [facet.num.get.members] Status: CD1 - Submitter: Matt Austern Opened: 2000-11-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In 22.2.2.1.1, we have a list of overloads for num_get<>::get(). -There are eight overloads, all of which are identical except for the -last parameter. The overloads are: -

-
    -
  • long&
    • -
  • unsigned short&
    • -
  • unsigned int&
    • -
  • unsigned long&
    • -
  • short&
    • -
  • double&
    • -
  • long double&
    • -
  • void*&
    • -
- -

-There is a similar list, in 22.2.2.1.2, of overloads for -num_get<>::do_get(). In this list, the last parameter has -the types: -

-
    -
  • long&
    • -
  • unsigned short&
    • -
  • unsigned int&
    • -
  • unsigned long&
    • -
  • float&
    • -
  • double&
    • -
  • long double&
    • -
  • void*&
    • -
- -

-These two lists are not identical. They should be, since -get is supposed to call do_get with exactly -the arguments it was given. -

- - -

Proposed resolution:

-

In 22.4.2.1.1 [facet.num.get.members], change

-
-  iter_type get(iter_type in, iter_type end, ios_base& str,
-                ios_base::iostate& err, short& val) const;
-
-

to

-
-  iter_type get(iter_type in, iter_type end, ios_base& str,
-                ios_base::iostate& err, float& val) const;
-
- - - - -
-

276. Assignable requirement for container value type overly strict

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Peter Dimov Opened: 2000-11-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-23.1/3 states that the objects stored in a container must be -Assignable. 23.4.4 [map], paragraph 2, -states that map satisfies all requirements for a container, while in -the same time defining value_type as pair<const Key, T> - a type -that is not Assignable. -

- -

-It should be noted that there exists a valid and non-contradictory -interpretation of the current text. The wording in 23.1/3 avoids -mentioning value_type, referring instead to "objects stored in a -container." One might argue that map does not store objects of -type map::value_type, but of map::mapped_type instead, and that the -Assignable requirement applies to map::mapped_type, not -map::value_type. -

- -

-However, this makes map a special case (other containers store objects of -type value_type) and the Assignable requirement is needlessly restrictive in -general. -

- -

-For example, the proposed resolution of active library issue -103 is to make set::iterator a constant iterator; this -means that no set operations can exploit the fact that the stored -objects are Assignable. -

- -

-This is related to, but slightly broader than, closed issue -140. -

- - -

Proposed resolution:

-

23.1/3: Strike the trailing part of the sentence:

-

- , and the additional requirements of Assignable types from 23.1/3 -

-

so that it reads:

-

- -3- The type of objects stored in these components must meet the - requirements of CopyConstructible types (lib.copyconstructible). -

- -

23.1/4: Modify to make clear that this requirement is not for all -containers. Change to:

- -

--4- Table 64 defines the Assignable requirement. Some containers -require this property of the types to be stored in the container. T is -the type used to instantiate the container. t is a value of T, and u is -a value of (possibly const) T. -

- -

23.1, Table 65: in the first row, change "T is Assignable" to "T is -CopyConstructible".

- -

23.2.1/2: Add sentence for Assignable requirement. Change to:

- -

--2- A deque satisfies all of the requirements of a container and of a -reversible container (given in tables in lib.container.requirements) and -of a sequence, including the optional sequence requirements -(lib.sequence.reqmts). In addition to the requirements on the stored -object described in 23.1[lib.container.requirements], the stored object -must also meet the requirements of Assignable. Descriptions are -provided here only for operations on deque that are not described in one -of these tables or for operations where there is additional semantic -information. -

- -

23.2.2/2: Add Assignable requirement to specific methods of list. -Change to:

- -
-

-2- A list satisfies all of the requirements of a container and of a -reversible container (given in two tables in lib.container.requirements) -and of a sequence, including most of the the optional sequence -requirements (lib.sequence.reqmts). The exceptions are the operator[] -and at member functions, which are not provided. - -[Footnote: These member functions are only provided by containers whose -iterators are random access iterators. --- end foonote] -

- -

list does not require the stored type T to be Assignable unless the -following methods are instantiated: - -[Footnote: Implementors are permitted but not required to take advantage -of T's Assignable properties for these methods. -- end foonote] -

-
-     list<T,Allocator>& operator=(const list<T,Allocator>&  x );
-     template <class InputIterator>
-       void assign(InputIterator first, InputIterator last);
-     void assign(size_type n, const T& t);
-
- - -

Descriptions are provided here only for operations on list that are not -described in one of these tables or for operations where there is -additional semantic information.

-
- -

23.2.4/2: Add sentence for Assignable requirement. Change to:

- -

--2- A vector satisfies all of the requirements of a container and of a -reversible container (given in two tables in lib.container.requirements) -and of a sequence, including most of the optional sequence requirements -(lib.sequence.reqmts). The exceptions are the push_front and pop_front -member functions, which are not provided. In addition to the -requirements on the stored object described in -23.1[lib.container.requirements], the stored object must also meet the -requirements of Assignable. Descriptions are provided here only for -operations on vector that are not described in one of these tables or -for operations where there is additional semantic information. -

- - -

Rationale:

-

list, set, multiset, map, multimap are able to store non-Assignables. -However, there is some concern about list<T>: -although in general there's no reason for T to be Assignable, some -implementations of the member functions operator= and -assign do rely on that requirement. The LWG does not want -to forbid such implementations.

- -

Note that the type stored in a standard container must still satisfy -the requirements of the container's allocator; this rules out, for -example, such types as "const int". See issue 274 -for more details. -

- -

In principle we could also relax the "Assignable" requirement for -individual vector member functions, such as -push_back. However, the LWG did not see great value in such -selective relaxation. Doing so would remove implementors' freedom to -implement vector::push_back in terms of -vector::insert.

- - - - - -
-

278. What does iterator validity mean?

-

Section: 23.3.5.5 [list.ops] Status: CD1 - Submitter: P.J. Plauger Opened: 2000-11-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 23.3.5.5 [list.ops] states that -

-
-  void splice(iterator position, list<T, Allocator>& x);
-
-

-invalidates all iterators and references to list x. -

- -

-But what does the C++ Standard mean by "invalidate"? You -can still dereference the iterator to a spliced list element, but -you'd better not use it to delimit a range within the original -list. For the latter operation, it has definitely lost some of its -validity. -

- -

-If we accept the proposed resolution to issue 250, -then we'd better clarify that a "valid" iterator need no -longer designate an element within the same container as it once did. -We then have to clarify what we mean by invalidating a past-the-end -iterator, as when a vector or string grows by reallocation. Clearly, -such an iterator has a different kind of validity. Perhaps we should -introduce separate terms for the two kinds of "validity." -

- - -

Proposed resolution:

-

Add the following text to the end of section X [iterator.concepts], -after paragraph 5:

-

-An invalid iterator is an iterator that may be -singular. [Footnote: This definition applies to pointers, since -pointers are iterators. The effect of dereferencing an iterator that -has been invalidated is undefined.] -

- -

[post-Copenhagen: Matt provided wording.]

- - -

[Redmond: General agreement with the intent, some objections to -the wording. Dave provided new wording.]

- - - -

Rationale:

-

This resolution simply defines a term that the Standard uses but - never defines, "invalid", in terms of a term that is defined, - "singular".

- -

Why do we say "may be singular", instead of "is singular"? That's - becuase a valid iterator is one that is known to be nonsingular. - Invalidating an iterator means changing it in such a way that it's - no longer known to be nonsingular. An example: inserting an - element into the middle of a vector is correctly said to invalidate - all iterators pointing into the vector. That doesn't necessarily - mean they all become singular.

- - - - - -
-

280. Comparison of reverse_iterator to const reverse_iterator

-

Section: 24.5.1 [reverse.iterators] Status: CD1 - Submitter: Steve Cleary Opened: 2000-11-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-This came from an email from Steve Cleary to Fergus in reference to -issue 179. The library working group briefly discussed -this in Toronto and believed it should be a separate issue. There was -also some reservations about whether this was a worthwhile problem to -fix. -

- -

-Steve said: "Fixing reverse_iterator. std::reverse_iterator can -(and should) be changed to preserve these additional -requirements." He also said in email that it can be done without -breaking user's code: "If you take a look at my suggested -solution, reverse_iterator doesn't have to take two parameters; there -is no danger of breaking existing code, except someone taking the -address of one of the reverse_iterator global operator functions, and -I have to doubt if anyone has ever done that. . . But, just in -case they have, you can leave the old global functions in as well -- -they won't interfere with the two-template-argument functions. With -that, I don't see how any user code could break." -

- - -

Proposed resolution:

-

-Section: 24.5.1.1 [reverse.iterator] -add/change the following declarations:

-
-  A) Add a templated assignment operator, after the same manner
-        as the templated copy constructor, i.e.:
-
-  template < class U >
-  reverse_iterator < Iterator >& operator=(const reverse_iterator< U >& u);
-
-  B) Make all global functions (except the operator+) have
-  two template parameters instead of one, that is, for
-  operator ==, !=, <, >, <=, >=, - replace:
-
-       template < class Iterator >
-       typename reverse_iterator< Iterator >::difference_type operator-(
-                 const reverse_iterator< Iterator >& x,
-                 const reverse_iterator< Iterator >& y);
-
-  with:
-
-      template < class Iterator1, class Iterator2 >
-      typename reverse_iterator < Iterator1 >::difference_type operator-(
-                 const reverse_iterator < Iterator1 > & x,
-                 const reverse_iterator < Iterator2 > & y);
-
-

-Also make the addition/changes for these signatures in -24.5.1.3 [reverse.iter.ops]. -

- -

[ -Copenhagen: The LWG is concerned that the proposed resolution -introduces new overloads. Experience shows that introducing -overloads is always risky, and that it would be inappropriate to -make this change without implementation experience. It may be -desirable to provide this feature in a different way. -]

- - -

[ -Lillehammer: We now have implementation experience, and agree that -this solution is safe and correct. -]

- - - - - - - -
-

281. std::min() and max() requirements overly restrictive

-

Section: 25.4.7 [alg.min.max] Status: CD1 - Submitter: Martin Sebor Opened: 2000-12-02 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 486

-

Discussion:

-

The requirements in 25.3.7, p1 and 4 call for T to satisfy the -requirements of LessThanComparable ( [lessthancomparable]) -and CopyConstructible (17.6.3.1 [utility.arg.requirements]). -Since the functions take and return their arguments and result by -const reference, I believe the CopyConstructible requirement -is unnecessary. -

- - -

Proposed resolution:

-

Remove the CopyConstructible requirement. Specifically, replace -25.3.7, p1 with

-

-1- Requires: Type T is LessThanComparable -( [lessthancomparable]). -

-

and replace 25.3.7, p4 with

-

-4- Requires: Type T is LessThanComparable -( [lessthancomparable]). -

- - - - -
-

282. What types does numpunct grouping refer to?

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 - Submitter: Howard Hinnant Opened: 2000-12-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 16 mistakenly singles out integral types for inserting -thousands_sep() characters. This conflicts with the syntax for floating -point numbers described under 22.2.3.1/2. -

- - -

Proposed resolution:

-

Change paragraph 16 from:

- -

-For integral types, punct.thousands_sep() characters are inserted into -the sequence as determined by the value returned by punct.do_grouping() -using the method described in 22.4.3.1.2 [facet.numpunct.virtuals]. -

- -

To:

- -

-For arithmetic types, punct.thousands_sep() characters are inserted into -the sequence as determined by the value returned by punct.do_grouping() -using the method described in 22.4.3.1.2 [facet.numpunct.virtuals]. -

- -

[ -Copenhagen: Opinions were divided about whether this is actually an -inconsistency, but at best it seems to have been unintentional. This -is only an issue for floating-point output: The standard is -unambiguous that implementations must parse thousands_sep characters -when performing floating-point. The standard is also unambiguous that -this requirement does not apply to the "C" locale. -]

- - -

[ -A survey of existing practice is needed; it is believed that some -implementations do insert thousands_sep characters for floating-point -output and others fail to insert thousands_sep characters for -floating-point input even though this is unambiguously required by the -standard. -]

- - -

[Post-Curaçao: the above proposed resolution is the consensus of -Howard, Bill, Pete, Benjamin, Nathan, Dietmar, Boris, and Martin.]

- - - - - - -
-

283. std::replace() requirement incorrect/insufficient

-

Section: 25.3.5 [alg.replace] Status: CD1 - Submitter: Martin Sebor Opened: 2000-12-15 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 483

-

Discussion:

-

-(revision of the further discussion) -There are a number of problems with the requires clauses for the -algorithms in 25.1 and 25.2. The requires clause of each algorithm -should describe the necessary and sufficient requirements on the inputs -to the algorithm such that the algorithm compiles and runs properly. -Many of the requires clauses fail to do this. Here is a summary of the kinds -of mistakes: -

- -
    -
  1. -Use of EqualityComparable, which only puts requirements on a single -type, when in fact an equality operator is required between two -different types, typically either T and the iterator's value type -or between the value types of two different iterators. -
    2. -
  2. -Use of Assignable for T when in fact what was needed is Assignable -for the value_type of the iterator, and convertability from T to the -value_type of the iterator. Or for output iterators, the requirement -should be that T is writable to the iterator (output iterators do -not have value types). -
    3. -
- -

-Here is the list of algorithms that contain mistakes: -

- -
    -
  • 25.1.2 std::find
    • -
  • 25.1.6 std::count
    • -
  • 25.1.8 std::equal
    • -
  • 25.1.9 std::search, std::search_n
    • -
  • 25.2.4 std::replace, std::replace_copy
    • -
  • 25.2.5 std::fill
    • -
  • 25.2.7 std::remove, std::remove_copy
    • -
- -

-Also, in the requirements for EqualityComparable, the requirement that -the operator be defined for const objects is lacking. -

- - - -

Proposed resolution:

- -

20.1.1 Change p1 from

- -

In Table 28, T is a type to be supplied by a C++ program -instantiating a template, a, b, and c are -values of type T. -

- -

to

- -

-In Table 28, T is a type to be supplied by a C++ program -instantiating a template, a, b, and c are -values of type const T. -

- -

25 Between p8 and p9

- -

Add the following sentence:

- -

When the description of an algorithm gives an expression such as -*first == value for a condition, it is required that the expression -evaluate to either true or false in boolean contexts.

- -

25.1.2 Change p1 by deleting the requires clause.

- -

25.1.6 Change p1 by deleting the requires clause.

- -

25.1.9

- -

Change p4 from

- -

-4- Requires: Type T is EqualityComparable -(20.1.1), type Size is convertible to integral type (4.7.12.3). -

- -

to

- -

-4- Requires: The type Size is convertible to integral -type (4.7.12.3).

- -

25.2.4 Change p1 from

- -

-1- Requires: Type T is Assignable (23.1 ) (and, for replace(), EqualityComparable (20.1.1 )).

- -

to

- -

-1- Requires: The expression *first = new_value must be valid.

- -

and change p4 from

- -

-4- Requires: Type T is Assignable (23.1) (and, -for replace_copy(), EqualityComparable -(20.1.1)). The ranges [first, last) and [result, result + -(last - first)) shall not overlap.

- -

to

- -

-4- Requires: The results of the expressions *first and -new_value must be writable to the result output iterator. The -ranges [first, last) and [result, result + (last - -first)) shall not overlap.

- - -

25.2.5 Change p1 from

- -

-1- Requires: Type T is Assignable (23.1). The -type Size is convertible to an integral type (4.7.12.3).

- -

to

- -

-1- Requires: The expression value must be is writable to -the output iterator. The type Size is convertible to an -integral type (4.7.12.3).

- -

25.2.7 Change p1 from

- -

-1- Requires: Type T is EqualityComparable (20.1.1).

- -

to

- -

--1- Requires: The value type of the iterator must be -Assignable (23.1). -

- - - -

Rationale:

-

-The general idea of the proposed solution is to remove the faulty -requires clauses and let the returns and effects clauses speak for -themselves. That is, the returns clauses contain expressions that must -be valid, and therefore already imply the correct requirements. In -addition, a sentence is added at the beginning of chapter 25 saying -that expressions given as conditions must evaluate to true or false in -a boolean context. An alternative would be to say that the type of -these condition expressions must be literally bool, but that would be -imposing a greater restriction that what the standard currently says -(which is convertible to bool). -

- - - - - -
-

284. unportable example in 20.3.7, p6

-

Section: 20.9.6 [comparisons] Status: CD1 - Submitter: Martin Sebor Opened: 2000-12-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

The example in 20.9.6 [comparisons], p6 shows how to use the C -library function strcmp() with the function pointer adapter -ptr_fun(). But since it's unspecified whether the C library -functions have extern "C" or extern -"C++" linkage [17.6.2.3 [using.linkage]], and since -function pointers with different the language linkage specifications -(7.5 [dcl.link]) are incompatible, whether this example is -well-formed is unspecified. -

- - -

Proposed resolution:

-

Change 20.9.6 [comparisons] paragraph 6 from:

-
-

[Example:

- 
-    replace_if(v.begin(), v.end(), not1(bind2nd(ptr_fun(strcmp), "C")), "C++");
-
-

replaces each C with C++ in sequence v.

-
- - -

to:

-
-

[Example:

- 
-    int compare(const char*, const char*);
-    replace_if(v.begin(), v.end(),
-               not1(bind2nd(ptr_fun(compare), "abc")), "def");
-
-

replaces each abc with def in sequence v.

-
- -

Also, remove footnote 215 in that same paragraph.

- -

[Copenhagen: Minor change in the proposed resolution. Since this -issue deals in part with C and C++ linkage, it was believed to be too -confusing for the strings in the example to be "C" and "C++". -]

- - -

[Redmond: More minor changes. Got rid of the footnote (which -seems to make a sweeping normative requirement, even though footnotes -aren't normative), and changed the sentence after the footnote so that -it corresponds to the new code fragment.]

- - - - - - -
-

285. minor editorial errors in fstream ctors

-

Section: 27.9.1.7 [ifstream.cons] Status: CD1 - Submitter: Martin Sebor Opened: 2000-12-31 Last modified: 2015-04-08

-

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-

Discussion:

-

27.9.1.7 [ifstream.cons], p2, 27.9.1.11 [ofstream.cons], p2, and -27.9.1.15 [fstream.cons], p2 say about the effects of each constructor: -

- -

... If that function returns a null pointer, calls -setstate(failbit) (which may throw ios_base::failure). -

- -

The parenthetical note doesn't apply since the ctors cannot throw an -exception due to the requirement in 27.5.5.2 [basic.ios.cons], p3 -that exceptions() be initialized to ios_base::goodbit. -

- - -

Proposed resolution:

-

-Strike the parenthetical note from the Effects clause in each of the -paragraphs mentioned above. -

- - - - -
-

286. <cstdlib> requirements missing size_t typedef

-

Section: 25.5 [alg.c.library] Status: CD1 - Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The <cstdlib> header file contains prototypes for bsearch and -qsort (C++ Standard section 25.4 paragraphs 3 and 4) and other -prototypes (C++ Standard section 21.4 paragraph 1 table 49) that -require the typedef size_t. Yet size_t is not listed in the -<cstdlib> synopsis table 78 in section 25.4. -

- - -

Proposed resolution:

-

-Add the type size_t to Table 78 (section 25.4) and add -the type size_t <cstdlib> to Table 97 (section C.2). -

- - -

Rationale:

-

Since size_t is in <stdlib.h>, it must also be in <cstdlib>.

- - - - - -
-

288. <cerrno> requirements missing macro EILSEQ

-

Section: 19.4 [errno] Status: CD1 - Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2015-04-08

-

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-

Discussion:

-

-ISO/IEC 9899:1990/Amendment1:1994 Section 4.3 States: "The list -of macros defined in <errno.h> is adjusted to include a new -macro, EILSEQ" -

- -

-ISO/IEC 14882:1998(E) section 19.3 does not refer -to the above amendment. -

- - - -

Proposed resolution:

-

-Update Table 26 (section 19.3) "Header <cerrno> synopsis" -and Table 95 (section C.2) "Standard Macros" to include EILSEQ. -

- - - - - -
-

291. Underspecification of set algorithms

-

Section: 25.4.5 [alg.set.operations] Status: CD1 - Submitter: Matt Austern Opened: 2001-01-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The standard library contains four algorithms that compute set -operations on sorted ranges: set_union, set_intersection, -set_difference, and set_symmetric_difference. Each -of these algorithms takes two sorted ranges as inputs, and writes the -output of the appropriate set operation to an output range. The elements -in the output range are sorted. -

- -

-The ordinary mathematical definitions are generalized so that they -apply to ranges containing multiple copies of a given element. Two -elements are considered to be "the same" if, according to an -ordering relation provided by the user, neither one is less than the -other. So, for example, if one input range contains five copies of an -element and another contains three, the output range of set_union -will contain five copies, the output range of -set_intersection will contain three, the output range of -set_difference will contain two, and the output range of -set_symmetric_difference will contain two. -

- -

-Because two elements can be "the same" for the purposes -of these set algorithms, without being identical in other respects -(consider, for example, strings under case-insensitive comparison), -this raises a number of unanswered questions: -

- -
    -
  • If we're copying an element that's present in both of the -input ranges, which one do we copy it from?
    • -
  • If there are n copies of an element in the relevant -input range, and the output range will contain fewer copies (say -m) which ones do we choose? The first m, or the last -m, or something else?
    • -
  • Are these operations stable? That is, does a run of equivalent -elements appear in the output range in the same order as as it -appeared in the input range(s)?
    • -
- -

-The standard should either answer these questions, or explicitly -say that the answers are unspecified. I prefer the former option, -since, as far as I know, all existing implementations behave the -same way. -

- - - -

Proposed resolution:

- -

Add the following to the end of 25.4.5.2 [set.union] paragraph 5:

-

-If [first1, last1) contains m elements that are equivalent to -each other and [first2, last2) contains n elements that are -equivalent to them, then max(m, n) of these elements -will be copied to the output range: all m of these elements -from [first1, last1), and the last max(n-m, 0) of them from -[first2, last2), in that order. -

- -

Add the following to the end of 25.4.5.3 [set.intersection] paragraph 5:

-

-If [first1, last1) contains m elements that are equivalent to each -other and [first2, last2) contains n elements that are -equivalent to them, the first min(m, n) of those -elements from [first1, last1) are copied to the output range. -

- -

Add a new paragraph, Notes, after 25.4.5.4 [set.difference] -paragraph 4:

-

-If [first1, last1) contains m elements that are equivalent to each -other and [first2, last2) contains n elements that are -equivalent to them, the last max(m-n, 0) elements from -[first1, last1) are copied to the output range. -

- -

Add a new paragraph, Notes, after 25.4.5.5 [set.symmetric.difference] -paragraph 4:

-

-If [first1, last1) contains m elements that are equivalent to -each other and [first2, last2) contains n elements that are -equivalent to them, then |m - n| of those elements will be -copied to the output range: the last m - n of these elements -from [first1, last1) if m > n, and the last n - -m of these elements from [first2, last2) if m < n. -

- -

[Santa Cruz: it's believed that this language is clearer than - what's in the Standard. However, it's also believed that the - Standard may already make these guarantees (although not quite in - these words). Bill and Howard will check and see whether they think - that some or all of these changes may be redundant. If so, we may - close this issue as NAD.]

- - - - -

Rationale:

-

For simple cases, these descriptions are equivalent to what's - already in the Standard. For more complicated cases, they describe - the behavior of existing implementations.

- - - - - -
-

292. effects of a.copyfmt (a)

-

Section: 27.5.5.3 [basic.ios.members] Status: CD1 - Submitter: Martin Sebor Opened: 2001-01-05 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

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-

Discussion:

-

The Effects clause of the member function copyfmt() in -27.4.4.2, p15 doesn't consider the case where the left-hand side -argument is identical to the argument on the right-hand side, that is -(this == &rhs). If the two arguments are identical there -is no need to copy any of the data members or call any callbacks -registered with register_callback(). Also, as Howard Hinnant -points out in message c++std-lib-8149 it appears to be incorrect to -allow the object to fire erase_event followed by -copyfmt_event since the callback handling the latter event -may inadvertently attempt to access memory freed by the former. -

- - -

Proposed resolution:

-

Change the Effects clause in 27.4.4.2, p15 from

- -

--15- Effects:Assigns to the member objects of *this -the corresponding member objects of rhs, except that... -

- -

to

- -

--15- Effects:If (this == &rhs) does nothing. Otherwise -assigns to the member objects of *this the corresponding member -objects of rhs, except that... -

- - - - -
-

294. User defined macros and standard headers

-

Section: 17.6.4.3.1 [macro.names] Status: CD1 - Submitter: James Kanze Opened: 2001-01-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Paragraph 2 of 17.6.4.3.1 [macro.names] reads: "A -translation unit that includes a header shall not contain any macros -that define names declared in that header." As I read this, it -would mean that the following program is legal:

- -
-  #define npos 3.14
-  #include <sstream>
-
- -

since npos is not defined in <sstream>. It is, however, defined -in <string>, and it is hard to imagine an implementation in -which <sstream> didn't include <string>.

- -

I think that this phrase was probably formulated before it was -decided that a standard header may freely include other standard -headers. The phrase would be perfectly appropriate for C, for -example. In light of 17.6.5.2 [res.on.headers] paragraph 1, however, -it isn't stringent enough.

- - -

Proposed resolution:

-

For 17.6.4.3.1 [macro.names], replace the current wording, which reads:

-
-

Each name defined as a macro in a header is reserved to the - implementation for any use if the translation unit includes - the header.168)

- -

A translation unit that includes a header shall not contain any - macros that define names declared or defined in that header. Nor shall - such a translation unit define macros for names lexically - identical to keywords.

- -

168) It is not permissible to remove a library macro definition by - using the #undef directive.

-
- -

with the wording:

- -
-

A translation unit that includes a standard library header shall not - #define or #undef names declared in any standard library header.

- -

A translation unit shall not #define or #undef names lexically - identical to keywords.

-
- -

[Lillehammer: Beman provided new wording]

- - - - - - -
-

295. Is abs defined in <cmath>?

-

Section: 26.8 [c.math] Status: CD1 - Submitter: Jens Maurer Opened: 2001-01-12 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

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-

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-

Discussion:

-

-Table 80 lists the contents of the <cmath> header. It does not -list abs(). However, 26.5, paragraph 6, which lists added -signatures present in <cmath>, does say that several overloads -of abs() should be defined in <cmath>. -

- - -

Proposed resolution:

-

-Add abs to Table 80. Also, remove the parenthetical list -of functions "(abs(), div(), rand(), srand())" from 26.6 [numarray], -paragraph 1. -

- -

[Copenhagen: Modified proposed resolution so that it also gets -rid of that vestigial list of functions in paragraph 1.]

- - - - -

Rationale:

-

All this DR does is fix a typo; it's uncontroversial. A -separate question is whether we're doing the right thing in -putting some overloads in <cmath> that we aren't also -putting in <cstdlib>. That's issue 323.

- - - - - -
-

296. Missing descriptions and requirements of pair operators

-

Section: 20.3 [pairs] Status: C++11 - Submitter: Martin Sebor Opened: 2001-01-14 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Discussion:

-

The synopsis of the header <utility> in 20.2 [utility] -lists the complete set of equality and relational operators for pair -but the section describing the template and the operators only describes -operator==() and operator<(), and it fails to mention -any requirements on the template arguments. The remaining operators are -not mentioned at all. -

- -

[ -2009-09-27 Alisdair reopens. -]

- - -
-

-The issue is a lack of wording specifying the semantics of std::pair -relational operators. The rationale is that this is covered by -catch-all wording in the relops component, and that as relops directly -precedes pair in the document this is an easy connection to make. -

- -

-Reading the current working paper I make two observations: -

- -
    -
  1. -relops no longer immediately precedes pair in the order of -specification. However, even if it did, there is a lot of pair -specification itself between the (apparently) unrelated relops and the -relational operators for pair. (The catch-all still requires -operator== and operator< to be specified -explicitly) -
    2. - -
  2. -No other library component relies on the catch-all clause. The following -all explicitly document all six relational operators, usually in a -manner that could have deferred to the relops clause. -
    3. -
- -
-tuple
-unique_ptr
-duration
-time_point
-basic_string
-queue
-stack
-move_iterator
-reverse_iterator 
-regex submatch
-thread::id
-
- -

-The container components provide their own (equivalent) definition in -23.2.1 [container.requirements.general] Table 90 -- Container -requirements and do so do not defer to relops. -

- -

-Shared_ptr explicitly documents operator!= and does -not supply the other 3 missing operators -(>,>=,<=) so does not meet the -reqirements of the relops clause. -

- -

-Weak_ptr only supports operator< so would not be -covered by relops. -

- -

-At the very least I would request a note pointing to the relops clause -we rely on to provide this definition. If this route is taken, I would -recommend reducing many of the above listed clauses to a similar note -rather than providing redundant specification. -

- -

-My preference would be to supply the 4 missing specifications consistent -with the rest of the library. -

- -
- -

[ -2009-10-11 Daniel opens 1233 which deals with the same issue as -it pertains to unique_ptr. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready -

- - - -

Proposed resolution:

-

-After p20 20.3 [pairs] add: -

- -
-template <class T1, class T2>
-bool operator!=(const pair<T1,T2>& x, const pair<T1,T2>& y);
-
- -

-Returns: !(x==y) -

- -
-template <class T1, class T2>
-bool operator> (const pair<T1,T2>& x, const pair<T1,T2>& y);
-
- -

-Returns: y < x -

- -
-template <class T1, class T2>
-bool operator>=(const pair<T1,T2>& x, const pair<T1,T2>& y);
-
- -

-Returns: !(x < y) -

- -
-template <class T1, class T2>
-bool operator<=(const pair<T1,T2>& x, const pair<T1,T2>& y);
-
- -

-Returns: !(y < x) -

-
- - -

Rationale:

-

20.2.1 [operators] paragraph 10 already specifies the semantics. -That paragraph says that, if declarations of operator!=, operator>, -operator<=, and operator>= appear without definitions, they are -defined as specified in 20.2.1 [operators]. There should be no user -confusion, since that paragraph happens to immediately precede the -specification of pair.

- - - - - -
-

297. const_mem_fun_t<>::argument_type should be const T*

-

Section: 20.9.7 [logical.operations] Status: CD1 - Submitter: Martin Sebor Opened: 2001-01-06 Last modified: 2015-04-08

-

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-

Discussion:

-

The class templates const_mem_fun_t in 20.5.8, p8 and -const_mem_fun1_t -in 20.5.8, p9 derive from unary_function<T*, S>, and -binary_function<T*, -A, S>, respectively. Consequently, their argument_type, and -first_argument_type -members, respectively, are both defined to be T* (non-const). -However, their function call member operator takes a const T* -argument. It is my opinion that argument_type should be const -T* instead, so that one can easily refer to it in generic code. The -example below derived from existing code fails to compile due to the -discrepancy: -

- -

template <class T> -
void foo (typename T::argument_type arg)   // #1 -
{ -
    typename T::result_type (T::*pf) (typename -T::argument_type) -const =   // #2 -
        &T::operator(); -
} -

- -

struct X { /* ... */ };

- -

int main () -
{ -
    const X x; -
    foo<std::const_mem_fun_t<void, X> ->(&x);   -// #3 -
} -

- -

#1 foo() takes a plain unqualified X* as an argument -
#2 the type of the pointer is incompatible with the type of the member -function -
#3 the address of a constant being passed to a function taking a non-const -X* -

- - -

Proposed resolution:

-

Replace the top portion of the definition of the class template -const_mem_fun_t in 20.5.8, p8 -

-

template <class S, class T> class const_mem_fun_t -
          : public -unary_function<T*, S> { -

-

with

-

template <class S, class T> class const_mem_fun_t -
          : public -unary_function<const T*, S> { -

-

Also replace the top portion of the definition of the class template -const_mem_fun1_t in 20.5.8, p9

-

template <class S, class T, class A> class const_mem_fun1_t -
          : public -binary_function<T*, A, S> { -

-

with

-

template <class S, class T, class A> class const_mem_fun1_t -
          : public -binary_function<const T*, A, S> { -

- - -

Rationale:

-

This is simply a contradiction: the argument_type typedef, -and the argument type itself, are not the same.

- - - - - -
-

298. ::operator delete[] requirement incorrect/insufficient

-

Section: 18.6.1.2 [new.delete.array] Status: CD1 - Submitter: John A. Pedretti Opened: 2001-01-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-The default behavior of operator delete[] described in 18.5.1.2, p12 - -namely that for non-null value of ptr, the operator reclaims storage -allocated by the earlier call to the default operator new[] - is not -correct in all cases. Since the specified operator new[] default -behavior is to call operator new (18.5.1.2, p4, p8), which can be -replaced, along with operator delete, by the user, to implement their -own memory management, the specified default behavior of operator -delete[] must be to call operator delete. -

- - -

Proposed resolution:

-

Change 18.5.1.2, p12 from

-

--12- Default behavior:

-
    -
  • -For a null value of ptr , does nothing. -
    • -
  • -Any other value of ptr shall be a value returned -earlier by a call to the default operator new[](std::size_t). -[Footnote: The value must not have been invalidated by an intervening -call to operator delete[](void*) (17.6.4.9 [res.on.arguments]). ---- end footnote] -For such a non-null value of ptr , reclaims storage -allocated by the earlier call to the default operator new[]. -
    • -
-
- -

to

- -

--12- Default behavior: Calls operator -delete(ptr) -or operator delete(ptr, std::nothrow) respectively. -

-

and expunge paragraph 13.

- - - - -
-

300. list::merge() specification incomplete

-

Section: 23.3.5.5 [list.ops] Status: CD1 - Submitter: John Pedretti Opened: 2001-01-23 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

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-

Discussion:

-

-The "Effects" clause for list::merge() (23.3.5.5 [list.ops], p23) -appears to be incomplete: it doesn't cover the case where the argument -list is identical to *this (i.e., this == &x). The requirement in the -note in p24 (below) is that x be empty after the merge which is surely -unintended in this case. -

- - -

Proposed resolution:

-

In 23.3.5.5 [list.ops], replace paragraps 23-25 with:

-
-

-23 Effects: if (&x == this) does nothing; otherwise, merges the two -sorted ranges [begin(), end()) and [x.begin(), x.end()). The result -is a range in which the elements will be sorted in non-decreasing -order according to the ordering defined by comp; that is, for every -iterator i in the range other than the first, the condition comp(*i, -*(i - 1)) will be false. -

- -

-24 Notes: Stable: if (&x != this), then for equivalent elements in the -two original ranges, the elements from the original range [begin(), -end()) always precede the elements from the original range [x.begin(), -x.end()). If (&x != this) the range [x.begin(), x.end()) is empty -after the merge. -

- -

-25 Complexity: At most size() + x.size() - 1 applications of comp if -(&x ! = this); otherwise, no applications of comp are performed. If -an exception is thrown other than by a comparison there are no -effects. -

- -
- -

[Copenhagen: The original proposed resolution did not fix all of -the problems in 23.3.5.5 [list.ops], p22-25. Three different -paragraphs (23, 24, 25) describe the effects of merge. -Changing p23, without changing the other two, appears to introduce -contradictions. Additionally, "merges the argument list into the -list" is excessively vague.]

- - -

[Post-Curaçao: Robert Klarer provided new wording.]

- - - - - - - -
-

301. basic_string template ctor effects clause omits allocator argument

-

Section: 21.4.1 [string.require] Status: CD1 - Submitter: Martin Sebor Opened: 2001-01-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The effects clause for the basic_string template ctor in 21.3.1, p15 -leaves out the third argument of type Allocator. I believe this to be -a mistake. -

- - -

Proposed resolution:

-

Replace

- -
-

-15- Effects: If InputIterator is an integral - type, equivalent to

- -

basic_string(static_cast<size_type>(begin), - static_cast<value_type>(end))

-
- -

with

- -
-

-15- Effects: If InputIterator is an integral - type, equivalent to

- -

basic_string(static_cast<size_type>(begin), - static_cast<value_type>(end), a)

-
- - - - -
-

303. Bitset input operator underspecified

-

Section: 20.6.4 [bitset.operators] Status: CD1 - Submitter: Matt Austern Opened: 2001-02-05 Last modified: 2015-04-08

-

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-

Discussion:

-

-In 23.3.5.3, we are told that bitset's input operator -"Extracts up to N (single-byte) characters from -is.", where is is a stream of type -basic_istream<charT, traits>. -

- -

-The standard does not say what it means to extract single byte -characters from a stream whose character type, charT, is in -general not a single-byte character type. Existing implementations -differ. -

- -

-A reasonable solution will probably involve widen() and/or -narrow(), since they are the supplied mechanism for -converting a single character between char and -arbitrary charT. -

- -

Narrowing the input characters is not the same as widening the -literals '0' and '1', because there may be some -locales in which more than one wide character maps to the narrow -character '0'. Narrowing means that alternate -representations may be used for bitset input, widening means that -they may not be.

- -

Note that for numeric input, num_get<> -(22.2.2.1.2/8) compares input characters to widened version of narrow -character literals.

- -

From Pete Becker, in c++std-lib-8224:

-
-

-Different writing systems can have different representations for the -digits that represent 0 and 1. For example, in the Unicode representation -of the Devanagari script (used in many of the Indic languages) the digit 0 -is 0x0966, and the digit 1 is 0x0967. Calling narrow would translate those -into '0' and '1'. But Unicode also provides the ASCII values 0x0030 and -0x0031 for for the Latin representations of '0' and '1', as well as code -points for the same numeric values in several other scripts (Tamil has no -character for 0, but does have the digits 1-9), and any of these values -would also be narrowed to '0' and '1'. -

- -

...

- -

-It's fairly common to intermix both native and Latin -representations of numbers in a document. So I think the rule has to be -that if a wide character represents a digit whose value is 0 then the bit -should be cleared; if it represents a digit whose value is 1 then the bit -should be set; otherwise throw an exception. So in a Devanagari locale, -both 0x0966 and 0x0030 would clear the bit, and both 0x0967 and 0x0031 -would set it. Widen can't do that. It would pick one of those two values, -and exclude the other one. -

- -
- -

From Jens Maurer, in c++std-lib-8233:

- -
-

-Whatever we decide, I would find it most surprising if -bitset conversion worked differently from int conversion -with regard to alternate local representations of -numbers. -

- -

Thus, I think the options are:

-
    -
  • Have a new defect issue for 22.2.2.1.2/8 so that it will -require the use of narrow().
    • - -
  • Have a defect issue for bitset() which describes clearly -that widen() is to be used.
    • -
-
- - - -

Proposed resolution:

- -

Replace the first two sentences of paragraph 5 with:

- -

- Extracts up to N characters from is. Stores these - characters in a temporary object str of type - basic_string<charT, traits>, then evaluates the - expression x = bitset<N>(str). -

- -

Replace the third bullet item in paragraph 5 with:

-
  • - the next input character is neither is.widen(0) - nor is.widen(1) (in which case the input character - is not extracted). -
- - - -

Rationale:

-

Input for bitset should work the same way as numeric -input. Using widen does mean that alternative digit -representations will not be recognized, but this was a known -consequence of the design choice.

- - - - - -
-

305. Default behavior of codecvt<wchar_t, char, mbstate_t>::length()

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 - Submitter: Howard Hinnant Opened: 2001-01-24 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.byname].

-

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-

Discussion:

-

22.2.1.5/3 introduces codecvt in part with:

- -

- codecvt<wchar_t,char,mbstate_t> converts between the native - character sets for tiny and wide characters. Instantiations on - mbstate_t perform conversion between encodings known to the library - implementor. -

- -

But 22.2.1.5.2/10 describes do_length in part with:

- -

- ... codecvt<wchar_t, char, mbstate_t> ... return(s) the lesser of max and - (from_end-from). -

- -

-The semantics of do_in and do_length are linked. What one does must -be consistent with what the other does. 22.2.1.5/3 leads me to -believe that the vendor is allowed to choose the algorithm that -codecvt<wchar_t,char,mbstate_t>::do_in performs so that it makes -his customers happy on a given platform. But 22.2.1.5.2/10 explicitly -says what codecvt<wchar_t,char,mbstate_t>::do_length must -return. And thus indirectly specifies the algorithm that -codecvt<wchar_t,char,mbstate_t>::do_in must perform. I believe -that this is not what was intended and is a defect. -

- -

Discussion from the -lib reflector: - -
This proposal would have the effect of making the semantics of -all of the virtual functions in codecvt<wchar_t, char, -mbstate_t> implementation specified. Is that what we want, or -do we want to mandate specific behavior for the base class virtuals -and leave the implementation specified behavior for the codecvt_byname -derived class? The tradeoff is that former allows implementors to -write a base class that actually does something useful, while the -latter gives users a way to get known and specified---albeit -useless---behavior, and is consistent with the way the standard -handles other facets. It is not clear what the original intention -was.

- -

-Nathan has suggest a compromise: a character that is a widened version -of the characters in the basic execution character set must be -converted to a one-byte sequence, but there is no such requirement -for characters that are not part of the basic execution character set. -

- - -

Proposed resolution:

-

-Change 22.2.1.5.2/5 from: -

-

-The instantiations required in Table 51 (lib.locale.category), namely -codecvt<wchar_t,char,mbstate_t> and -codecvt<char,char,mbstate_t>, store no characters. Stores no more -than (to_limit-to) destination elements. It always leaves the to_next -pointer pointing one beyond the last element successfully stored. -

-

-to: -

-

-Stores no more than (to_limit-to) destination elements, and leaves the -to_next pointer pointing one beyond the last element successfully -stored. codecvt<char,char,mbstate_t> stores no characters. -

- -

Change 22.2.1.5.2/10 from:

- -

--10- Returns: (from_next-from) where from_next is the largest value in -the range [from,from_end] such that the sequence of values in the -range [from,from_next) represents max or fewer valid complete -characters of type internT. The instantiations required in Table 51 -(21.1.1.1.1), namely codecvt<wchar_t, char, mbstate_t> and -codecvt<char, char, mbstate_t>, return the lesser of max and -(from_end-from). -

- -

to:

- -

--10- Returns: (from_next-from) where from_next is the largest value in -the range [from,from_end] such that the sequence of values in the range -[from,from_next) represents max or fewer valid complete characters of -type internT. The instantiation codecvt<char, char, mbstate_t> returns -the lesser of max and (from_end-from). -

- -

[Redmond: Nathan suggested an alternative resolution: same as -above, but require that, in the default encoding, a character from the -basic execution character set would map to a single external -character. The straw poll was 8-1 in favor of the proposed -resolution.]

- - - - -

Rationale:

-

The default encoding should be whatever users of a given platform -would expect to be the most natural. This varies from platform to -platform. In many cases there is a preexisting C library, and users -would expect the default encoding to be whatever C uses in the default -"C" locale. We could impose a guarantee like the one Nathan suggested -(a character from the basic execution character set must map to a -single external character), but this would rule out important -encodings that are in common use: it would rule out JIS, for -example, and it would rule out a fixed-width encoding of UCS-4.

- -

[Curaçao: fixed rationale typo at the request of Ichiro Koshida; -"shift-JIS" changed to "JIS".]

- - - - - - - -
-

306. offsetof macro and non-POD types

-

Section: 18.2 [support.types] Status: CD1 - Submitter: Steve Clamage Opened: 2001-02-21 Last modified: 2015-04-08

-

View all other issues in [support.types].

-

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-

Discussion:

-

Spliced together from reflector messages c++std-lib-8294 and -8295:

- -

18.1, paragraph 5, reads: "The macro offsetof -accepts a restricted set of type arguments in this -International Standard. type shall be a POD structure or a POD -union (clause 9). The result of applying the offsetof macro to a field -that is a static data member or a function member is -undefined."

- -

For the POD requirement, it doesn't say "no diagnostic -required" or "undefined behavior". I read 1.4 [intro.compliance], paragraph 1, to mean that a diagnostic is required. -It's not clear whether this requirement was intended. While it's -possible to provide such a diagnostic, the extra complication doesn't -seem to add any value. -

- - -

Proposed resolution:

-

Change 18.1, paragraph 5, to "If type is not a POD -structure or a POD union the results are undefined."

- -

[Copenhagen: straw poll was 7-4 in favor. It was generally -agreed that requiring a diagnostic was inadvertent, but some LWG -members thought that diagnostics should be required whenever -possible.]

- - - - - - -
-

307. Lack of reference typedefs in container adaptors

-

Section: 23.3.5 [list] Status: CD1 - Submitter: Howard Hinnant Opened: 2001-03-13 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

- -

From reflector message c++std-lib-8330. See also lib-8317.

- -

-The standard is currently inconsistent in 23.3.5.3 [list.capacity] -paragraph 1 and 23.3.5.4 [list.modifiers] paragraph 1. -23.2.3.3/1, for example, says: -

- -

--1- Any sequence supporting operations back(), push_back() and pop_back() -can be used to instantiate stack. In particular, vector (lib.vector), list -(lib.list) and deque (lib.deque) can be used. -

- -

But this is false: vector<bool> can not be used, because the -container adaptors return a T& rather than using the underlying -container's reference type.

- -

This is a contradiction that can be fixed by:

- -
    -
  1. Modifying these paragraphs to say that vector<bool> - is an exception.
    2. -
  2. Removing the vector<bool> specialization.
    3. -
  3. Changing the return types of stack and priority_queue to use - reference typedef's.
    4. -
- -

-I propose 3. This does not preclude option 2 if we choose to do it -later (see issue 96); the issues are independent. Option -3 offers a small step towards support for proxied containers. This -small step fixes a current contradiction, is easy for vendors to -implement, is already implemented in at least one popular lib, and -does not break any code. -

- - - -

Proposed resolution:

-

Summary: Add reference and const_reference typedefs to queue, -priority_queue and stack. Change return types of "value_type&" to -"reference". Change return types of "const value_type&" to -"const_reference". Details:

- -

Change 23.2.3.1/1 from:

- -
-  namespace std {
-    template <class T, class Container = deque<T> >
-    class queue {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-
-    public:
-      explicit queue(const Container& = Container());
-
-      bool      empty() const             { return c.empty(); }
-      size_type size()  const             { return c.size(); }
-      value_type&       front()           { return c.front(); }
-      const value_type& front() const     { return c.front(); }
-      value_type&       back()            { return c.back(); }
-      const value_type& back() const      { return c.back(); }
-      void push(const value_type& x)      { c.push_back(x); }
-      void pop()                          { c.pop_front(); }
-    };
-
- -

to:

- -
-  namespace std {
-    template <class T, class Container = deque<T> >
-    class queue {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::reference             reference;
-      typedef typename Container::const_reference       const_reference;
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-
-    public:
-      explicit queue(const Container& = Container());
-
-      bool      empty() const             { return c.empty(); }
-      size_type size()  const             { return c.size(); }
-      reference         front()           { return c.front(); }
-      const_reference   front() const     { return c.front(); }
-      reference         back()            { return c.back(); }
-      const_reference   back() const      { return c.back(); }
-      void push(const value_type& x)      { c.push_back(x); }
-      void pop()                          { c.pop_front(); }
-    };
-
- -

Change 23.2.3.2/1 from:

- -
-  namespace std {
-    template <class T, class Container = vector<T>,
-              class Compare = less<typename Container::value_type> >
-    class priority_queue {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-      Compare comp;
-
-    public:
-      explicit priority_queue(const Compare& x = Compare(),
-                              const Container& = Container());
-      template <class InputIterator>
-        priority_queue(InputIterator first, InputIterator last,
-                       const Compare& x = Compare(),
-                       const Container& = Container());
-
-      bool      empty() const       { return c.empty(); }
-      size_type size()  const       { return c.size(); }
-      const value_type& top() const { return c.front(); }
-      void push(const value_type& x);
-      void pop();
-    };
-                                  //  no equality is provided
-  }
-
- -

to:

- -
-  namespace std {
-    template <class T, class Container = vector<T>,
-              class Compare = less<typename Container::value_type> >
-    class priority_queue {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::reference             reference;
-      typedef typename Container::const_reference       const_reference;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-      Compare comp;
-
-    public:
-      explicit priority_queue(const Compare& x = Compare(),
-                              const Container& = Container());
-      template <class InputIterator>
-        priority_queue(InputIterator first, InputIterator last,
-                       const Compare& x = Compare(),
-                       const Container& = Container());
-
-      bool      empty() const       { return c.empty(); }
-      size_type size()  const       { return c.size(); }
-      const_reference   top() const { return c.front(); }
-      void push(const value_type& x);
-      void pop();
-    };
-                                  //  no equality is provided
-  }
-
- -

And change 23.2.3.3/1 from:

- -
-  namespace std {
-    template <class T, class Container = deque<T> >
-    class stack {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-
-    public:
-      explicit stack(const Container& = Container());
-
-      bool      empty() const             { return c.empty(); }
-      size_type size()  const             { return c.size(); }
-      value_type&       top()             { return c.back(); }
-      const value_type& top() const       { return c.back(); }
-      void push(const value_type& x)      { c.push_back(x); }
-      void pop()                          { c.pop_back(); }
-    };
-
-    template <class T, class Container>
-      bool operator==(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator< (const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator!=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator> (const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator>=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator<=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-  }
-
- -

to:

- -
-  namespace std {
-    template <class T, class Container = deque<T> >
-    class stack {
-    public:
-      typedef typename Container::value_type            value_type;
-      typedef typename Container::reference             reference;
-      typedef typename Container::const_reference       const_reference;
-      typedef typename Container::size_type             size_type;
-      typedef          Container                        container_type;
-    protected:
-      Container c;
-
-    public:
-      explicit stack(const Container& = Container());
-
-      bool      empty() const             { return c.empty(); }
-      size_type size()  const             { return c.size(); }
-      reference         top()             { return c.back(); }
-      const_reference   top() const       { return c.back(); }
-      void push(const value_type& x)      { c.push_back(x); }
-      void pop()                          { c.pop_back(); }
-    };
-
-    template <class T, class Container>
-      bool operator==(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator< (const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator!=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator> (const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator>=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-    template <class T, class Container>
-      bool operator<=(const stack<T, Container>& x,
-                      const stack<T, Container>& y);
-  }
-
- -

[Copenhagen: This change was discussed before the IS was released -and it was deliberately not adopted. Nevertheless, the LWG believes -(straw poll: 10-2) that it is a genuine defect.]

- - - - - - -
-

308. Table 82 mentions unrelated headers

-

Section: 27 [input.output] Status: CD1 - Submitter: Martin Sebor Opened: 2001-03-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Table 82 in section 27 mentions the header <cstdlib> for String -streams (27.8 [string.streams]) and the headers <cstdio> and -<cwchar> for File streams (27.9 [file.streams]). It's not clear -why these headers are mentioned in this context since they do not -define any of the library entities described by the -subclauses. According to 17.6.1.1 [contents], only such headers -are to be listed in the summary. -

- - -

Proposed resolution:

-

Remove <cstdlib> and <cwchar> from -Table 82.

- -

[Copenhagen: changed the proposed resolution slightly. The -original proposed resolution also said to remove <cstdio> from -Table 82. However, <cstdio> is mentioned several times within -section 27.9 [file.streams], including 27.9.2 [c.files].]

- - - - - - -
-

310. Is errno a macro?

-

Section: 17.6.1.2 [headers], 19.4 [errno] Status: CD1 - Submitter: Steve Clamage Opened: 2001-03-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- Exactly how should errno be declared in a conforming C++ header? -

- -

- The C standard says in 7.1.4 that it is unspecified whether errno is a - macro or an identifier with external linkage. In some implementations - it can be either, depending on compile-time options. (E.g., on - Solaris in multi-threading mode, errno is a macro that expands to a - function call, but is an extern int otherwise. "Unspecified" allows - such variability.) -

- -

The C++ standard:

-
    -
  • 17.4.1.2 says in a note that errno must be macro in C. (false)
    • -
  • 17.4.3.1.3 footnote 166 says errno is reserved as an external - name (true), and implies that it is an identifier.
    • -
  • 19.3 simply lists errno as a macro (by what reasoning?) and goes - on to say that the contents of of C++ <errno.h> are the - same as in C, begging the question.
    • -
  • C.2, table 95 lists errno as a macro, without comment.
    • -
- -

I find no other references to errno.

- -

We should either explicitly say that errno must be a macro, even - though it need not be a macro in C, or else explicitly leave it - unspecified. We also need to say something about namespace std. - A user who includes <cerrno> needs to know whether to write - errno, or ::errno, or std::errno, or - else <cerrno> is useless.

- -

Two acceptable fixes:

-
    -

  • errno must be a macro. This is trivially satisfied by adding
    -   #define errno (::std::errno)
    - to the headers if errno is not already a macro. You then always - write errno without any scope qualification, and it always expands - to a correct reference. Since it is always a macro, you know to - avoid using errno as a local identifer.

    • -

  • errno is in the global namespace. This fix is inferior, because - ::errno is not guaranteed to be well-formed.

    • -
- -

[ - This issue was first raised in 1999, but it slipped through - the cracks. - ]

- - - -

Proposed resolution:

-

Change the Note in section 17.4.1.2p5 from

- -

- Note: the names defined as macros in C include the following: - assert, errno, offsetof, setjmp, va_arg, va_end, and va_start. -

- -

to

- -

- Note: the names defined as macros in C include the following: - assert, offsetof, setjmp, va_arg, va_end, and va_start. -

- -

In section 19.3, change paragraph 2 from

- -

- The contents are the same as the Standard C library header - <errno.h>. -

- -

to

- -

- The contents are the same as the Standard C library header - <errno.h>, except that errno shall be defined as a macro. -

- - -

Rationale:

-

C++ must not leave it up to the implementation to decide whether or -not a name is a macro; it must explicitly specify exactly which names -are required to be macros. The only one that really works is for it -to be a macro.

- -

[Curaçao: additional rationale added.]

- - - - - - - -
-

311. Incorrect wording in basic_ostream class synopsis

-

Section: 27.7.3.1 [ostream] Status: CD1 - Submitter: Andy Sawyer Opened: 2001-03-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

In 27.7.3.1 [ostream], the synopsis of class basic_ostream says:

- -
-  // partial specializationss
-  template<class traits>
-    basic_ostream<char,traits>& operator<<( basic_ostream<char,traits>&,
-                                            const char * );
-
- -

Problems:

-
    -
  • Too many 's's at the end of "specializationss"
    • -
  • This is an overload, not a partial specialization
    • -
- - - -

Proposed resolution:

-

In the synopsis in 27.7.3.1 [ostream], remove the -// partial specializationss comment. Also remove the same -comment (correctly spelled, but still incorrect) from the synopsis in -27.7.3.6.4 [ostream.inserters.character]. -

- -

[ -Pre-Redmond: added 27.7.3.6.4 [ostream.inserters.character] because of Martin's -comment in c++std-lib-8939. -]

- - - - - - - -
-

312. Table 27 is missing headers

-

Section: 20 [utilities] Status: CD1 - Submitter: Martin Sebor Opened: 2001-03-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Table 27 in section 20 lists the header <memory> (only) for -Memory (lib.memory) but neglects to mention the headers -<cstdlib> and <cstring> that are discussed in 20.10.6 [meta.rel].

- - -

Proposed resolution:

-

Add <cstdlib> and <cstring> to Table 27, in the same row -as <memory>.

- - - - - -
-

315. Bad "range" in list::unique complexity

-

Section: 23.3.5.5 [list.ops] Status: CD1 - Submitter: Andy Sawyer Opened: 2001-05-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-23.3.5.5 [list.ops], Para 21 describes the complexity of -list::unique as: "If the range (last - first) is not empty, exactly -(last - first) -1 applications of the corresponding predicate, -otherwise no applications of the predicate)". -

- -

-"(last - first)" is not a range. -

- - -

Proposed resolution:

-

-Change the "range" from (last - first) to [first, last). -

- - - - -
-

316. Vague text in Table 69

-

Section: 23.2.4 [associative.reqmts] Status: CD1 - Submitter: Martin Sebor Opened: 2001-05-04 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Table 69 says this about a_uniq.insert(t):

- -

-inserts t if and only if there is no element in the container with key -equivalent to the key of t. The bool component of the returned pair -indicates whether the insertion takes place and the iterator component of the -pair points to the element with key equivalent to the key of t. -

- -

The description should be more specific about exactly how the bool component -indicates whether the insertion takes place.

- - -

Proposed resolution:

-

Change the text in question to

- -

-...The bool component of the returned pair is true if and only if the insertion -takes place... -

- - - - - -
-

317. Instantiation vs. specialization of facets

-

Section: 22 [localization] Status: CD1 - Submitter: Martin Sebor Opened: 2001-05-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The localization section of the standard refers to specializations of -the facet templates as instantiations even though the required facets -are typically specialized rather than explicitly (or implicitly) -instantiated. In the case of ctype<char> and -ctype_byname<char> (and the wchar_t versions), these facets are -actually required to be specialized. The terminology should be -corrected to make it clear that the standard doesn't mandate explicit -instantiation (the term specialization encompasses both explicit -instantiations and specializations). -

- - -

Proposed resolution:

-

-In the following paragraphs, replace all occurrences of the word -instantiation or instantiations with specialization or specializations, -respectively: -

- -

-22.1.1.1.1, p4, Table 52, 22.2.1.1, p2, 22.2.1.5, p3, 22.2.1.5.1, p5, -22.2.1.5.2, p10, 22.2.2, p2, 22.2.3.1, p1, 22.2.3.1.2, p1, p2 and p3, -22.2.4.1, p1, 22.2.4.1.2, p1, 22,2,5, p1, 22,2,6, p2, 22.2.6.3.2, p7, and -Footnote 242. -

- -

And change the text in 22.1.1.1.1, p4 from

- -

- An implementation is required to provide those instantiations - for facet templates identified as members of a category, and - for those shown in Table 52: -

- -

to

- -

- An implementation is required to provide those specializations... -

- -

[Nathan will review these changes, and will look for places where -explicit specialization is necessary.]

- - - - -

Rationale:

-

This is a simple matter of outdated language. The language to -describe templates was clarified during the standardization process, -but the wording in clause 22 was never updated to reflect that -change.

- - - - - - - -
-

318. Misleading comment in definition of numpunct_byname

-

Section: 22.4.3.2 [locale.numpunct.byname] Status: CD1 - Submitter: Martin Sebor Opened: 2001-05-12 Last modified: 2015-04-08

-

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-

Discussion:

-

The definition of the numpunct_byname template contains the following -comment:

- -
-    namespace std {
-        template <class charT>
-        class numpunct_byname : public numpunct<charT> {
-    // this class is specialized for char and wchar_t.
-        ...
-
- -

There is no documentation of the specializations and it seems -conceivable that an implementation will not explicitly specialize the -template at all, but simply provide the primary template.

- - -

Proposed resolution:

-

Remove the comment from the text in 22.2.3.2 and from the proposed -resolution of library issue 228.

- - - - -
-

319. Storage allocation wording confuses "Required behavior", "Requires"

-

Section: 18.6.1.1 [new.delete.single], 18.6.1.2 [new.delete.array] Status: CD1 - Submitter: Beman Dawes Opened: 2001-05-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The standard specifies 17.5.1.4 [structure.specifications] that "Required -behavior" elements describe "the semantics of a function definition -provided by either the implementation or a C++ program."

- -

The standard specifies 17.5.1.4 [structure.specifications] that "Requires" -elements describe "the preconditions for calling the function."

- -

In the sections noted below, the current wording specifies -"Required Behavior" for what are actually preconditions, and thus -should be specified as "Requires".

- - - -

Proposed resolution:

- -

In 18.6.1.1 [new.delete.single] Para 12 Change:

-
-

Required behavior: accept a value of ptr that is null or that was - returned by an earlier call ...

-
-

to:

-
-

Requires: the value of ptr is null or the value returned by an - earlier call ...

-
- -

In 18.6.1.2 [new.delete.array] Para 11 Change:

-
-

Required behavior: accept a value of ptr that is null or that was - returned by an earlier call ...

-
-

to:

-
-

Requires: the value of ptr is null or the value returned by an - earlier call ...

-
- - - - - -
-

320. list::assign overspecified

-

Section: 23.3.5.2 [list.cons] Status: CD1 - Submitter: Howard Hinnant Opened: 2001-05-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 23.3.5.2 [list.cons], paragraphs 6-8 specify that list assign (both forms) have -the "effects" of a call to erase followed by a call to insert. -

- -

-I would like to document that implementers have the freedom to implement -assign by other methods, as long as the end result is the same and the -exception guarantee is as good or better than the basic guarantee. -

- -

-The motivation for this is to use T's assignment operator to recycle -existing nodes in the list instead of erasing them and reallocating -them with new values. It is also worth noting that, with careful -coding, most common cases of assign (everything but assignment with -true input iterators) can elevate the exception safety to strong if -T's assignment has a nothrow guarantee (with no extra memory cost). -Metrowerks does this. However I do not propose that this subtlety be -standardized. It is a QoI issue.

- -

Existing practise: -Metrowerks and SGI recycle nodes, Dinkumware and Rogue Wave don't. -

- - -

Proposed resolution:

-

Change 23.3.5.2 [list.cons]/7 from:

- -
-

Effects:

- -
-   erase(begin(), end());
-   insert(begin(), first, last);
-
-
- -

to:

- -
-

Effects: Replaces the contents of the list with the range [first, last).

-
- -

In 23.2.3 [sequence.reqmts], in Table 67 (sequence requirements), -add two new rows:

-
-      a.assign(i,j)     void      pre: i,j are not iterators into a.
-                                  Replaces elements in a with a copy
-                                  of [i, j).
-
-      a.assign(n,t)     void      pre: t is not a reference into a.
-                                  Replaces elements in a with n copies
-                                  of t.
-
- -

Change 23.3.5.2 [list.cons]/8 from:

- -
-

Effects:

-
-   erase(begin(), end());
-   insert(begin(), n, t);
-
-
-

to:

- -
-

Effects: Replaces the contents of the list with n copies of t.

-
- -

[Redmond: Proposed resolution was changed slightly. Previous -version made explicit statement about exception safety, which wasn't -consistent with the way exception safety is expressed elsewhere. -Also, the change in the sequence requirements is new. Without that -change, the proposed resolution would have required that assignment of -a subrange would have to work. That too would have been -overspecification; it would effectively mandate that assignment use a -temporary. Howard provided wording. -]

- - -

[Curaçao: Made editorial improvement in wording; changed -"Replaces elements in a with copies of elements in [i, j)." -with "Replaces the elements of a with a copy of [i, j)." -Changes not deemed serious enough to requre rereview.]

- - - - - - - -
-

321. Typo in num_get

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 - Submitter: Kevin Djang Opened: 2001-05-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Section 22.2.2.1.2 at p7 states that "A length specifier is added to -the conversion function, if needed, as indicated in Table 56." -However, Table 56 uses the term "length modifier", not "length -specifier". -

- - -

Proposed resolution:

-

-In 22.2.2.1.2 at p7, change the text "A length specifier is added ..." -to be "A length modifier is added ..." -

- - -

Rationale:

-

C uses the term "length modifier". We should be consistent.

- - - - - - -
-

322. iterator and const_iterator should have the same value type

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Matt Austern Opened: 2001-05-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-It's widely assumed that, if X is a container, -iterator_traits<X::iterator>::value_type and -iterator_traits<X::const_iterator>::value_type should both be -X::value_type. However, this is nowhere stated. The language in -Table 65 is not precise about the iterators' value types (it predates -iterator_traits), and could even be interpreted as saying that -iterator_traits<X::const_iterator>::value_type should be "const -X::value_type". -

- -

Related issue: 279.

- - -

Proposed resolution:

-

In Table 65 ("Container Requirements"), change the return type for -X::iterator to "iterator type whose value type is T". Change the -return type for X::const_iterator to "constant iterator type whose -value type is T".

- - -

Rationale:

-

-This belongs as a container requirement, rather than an iterator -requirement, because the whole notion of iterator/const_iterator -pairs is specific to containers' iterator. -

-

-It is existing practice that (for example) -iterator_traits<list<int>::const_iterator>::value_type -is "int", rather than "const int". This is consistent with -the way that const pointers are handled: the standard already -requires that iterator_traits<const int*>::value_type is int. -

- - - - - -
-

324. Do output iterators have value types?

-

Section: 24.2.4 [output.iterators] Status: CD1 - Submitter: Dave Abrahams Opened: 2001-06-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Table 73 suggests that output iterators have value types. It -requires the expression "*a = t". Additionally, although Table 73 -never lists "a = t" or "X(a) = t" in the "expressions" column, it -contains a note saying that "a = t" and "X(a) = t" have equivalent -(but nowhere specified!) semantics.

- -

According to 24.1/9, t is supposed to be "a value of value type -T":

- -

- In the following sections, a and b denote values of X, n denotes a - value of the difference type Distance, u, tmp, and m denote - identifiers, r denotes a value of X&, t denotes a value of - value type T. -

- -

Two other parts of the standard that are relevant to whether -output iterators have value types:

- -
    -
  • 24.1/1 says "All iterators i support the expression *i, - resulting in a value of some class, enumeration, or built-in type - T, called the value type of the iterator".
    • - -
  • - 24.3.1/1, which says "In the case of an output iterator, the types - iterator_traits<Iterator>::difference_type - iterator_traits<Iterator>::value_type are both defined as void." -
    • -
- -

The first of these passages suggests that "*i" is supposed to -return a useful value, which contradicts the note in 24.1.2/2 saying -that the only valid use of "*i" for output iterators is in an -expression of the form "*i = t". The second of these passages appears -to contradict Table 73, because it suggests that "*i"'s return value -should be void. The second passage is also broken in the case of a an -iterator type, like non-const pointers, that satisfies both the output -iterator requirements and the forward iterator requirements.

- -

What should the standard say about *i's return value when -i is an output iterator, and what should it say about that t is in the -expression "*i = t"? Finally, should the standard say anything about -output iterators' pointer and reference types?

- - - -

Proposed resolution:

-

24.1 p1, change

- -
-

All iterators i support the expression *i, resulting -in a value of some class, enumeration, or built-in type T, -called the value type of the iterator.

-
- -

to

- -
-

All input iterators i support the expression *i, -resulting in a value of some class, enumeration, or built-in type -T, called the value type of the iterator. All output -iterators support the expression *i = o where o is a -value of some type that is in the set of types that are writable to -the particular iterator type of i. -

-
- -

24.1 p9, add

- -
-

o denotes a value of some type that is writable to the -output iterator. -

-
- -

Table 73, change

- -
-
-*a = t
-
-
- -

to

- -
-
-*r = o
-
-
- -

and change

- -
-
-*r++ = t
-
-
- -

to

- -
-
-*r++ = o
-
-
- -

[post-Redmond: Jeremy provided wording]

- - - - -

Rationale:

-

The LWG considered two options: change all of the language that -seems to imply that output iterators have value types, thus making it -clear that output iterators have no value types, or else define value -types for output iterator consistently. The LWG chose the former -option, because it seems clear that output iterators were never -intended to have value types. This was a deliberate design decision, -and any language suggesting otherwise is simply a mistake.

- -

A future revision of the standard may wish to revisit this design -decision.

- - - - - -
-

325. Misleading text in moneypunct<>::do_grouping

-

Section: 22.4.6.3.2 [locale.moneypunct.virtuals] Status: CD1 - Submitter: Martin Sebor Opened: 2001-07-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

The Returns clause in 22.2.6.3.2, p3 says about -moneypunct<charT>::do_grouping() -

- -

- Returns: A pattern defined identically as the result of - numpunct<charT>::do_grouping().241) -

- -

Footnote 241 then reads

- -

- This is most commonly the value "\003" (not "3"). -

- -

-The returns clause seems to imply that the two member functions must -return an identical value which in reality may or may not be true, -since the facets are usually implemented in terms of struct std::lconv -and return the value of the grouping and mon_grouping, respectively. -The footnote also implies that the member function of the moneypunct -facet (rather than the overridden virtual functions in moneypunct_byname) -most commonly return "\003", which contradicts the C standard which -specifies the value of "" for the (most common) C locale. -

- - - -

Proposed resolution:

-

Replace the text in Returns clause in 22.2.6.3.2, p3 with the following:

- -

- Returns: A pattern defined identically as, but not necessarily - equal to, the result of numpunct<charT>::do_grouping().241) -

- -

and replace the text in Footnote 241 with the following:

- -

- To specify grouping by 3s the value is "\003", not "3". -

- - -

Rationale:

-

-The fundamental problem is that the description of the locale facet -virtuals serves two purposes: describing the behavior of the base -class, and describing the meaning of and constraints on the behavior -in arbitrary derived classes. The new wording makes that separation a -little bit clearer. The footnote (which is nonnormative) is not -supposed to say what the grouping is in the "C" locale or in any other -locale. It is just a reminder that the values are interpreted as small -integers, not ASCII characters. -

- - - - -
-

327. Typo in time_get facet in table 52

-

Section: 22.3.1.1.1 [locale.category] Status: CD1 - Submitter: Tiki Wan Opened: 2001-07-06 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 447

-

Discussion:

-

The wchar_t versions of time_get and -time_get_byname are listed incorrectly in table 52, -required instantiations. In both cases the second template -parameter is given as OutputIterator. It should instead be -InputIterator, since these are input facets.

- - -

Proposed resolution:

-

-In table 52, required instantiations, in -22.3.1.1.1 [locale.category], change

-
-    time_get<wchar_t, OutputIterator>
-    time_get_byname<wchar_t, OutputIterator>
-
-

to

-
-    time_get<wchar_t, InputIterator>
-    time_get_byname<wchar_t, InputIterator>
-
- -

[Redmond: Very minor change in proposed resolution. Original had -a typo, wchart instead of wchar_t.]

- - - - - - -
-

328. Bad sprintf format modifier in money_put<>::do_put()

-

Section: 22.4.6.2.2 [locale.money.put.virtuals] Status: CD1 - Submitter: Martin Sebor Opened: 2001-07-07 Last modified: 2015-04-08

-

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-

Discussion:

-

The sprintf format string , "%.01f" (that's the digit one), in the -description of the do_put() member functions of the money_put facet in -22.2.6.2.2, p1 is incorrect. First, the f format specifier is wrong -for values of type long double, and second, the precision of 01 -doesn't seem to make sense. What was most likely intended was -"%.0Lf"., that is a precision of zero followed by the L length -modifier.

- - -

Proposed resolution:

-

Change the format string to "%.0Lf".

- - -

Rationale:

Fixes an obvious typo

- - - - -
-

329. vector capacity, reserve and reallocation

-

Section: 23.3.6.3 [vector.capacity], 23.3.6.5 [vector.modifiers] Status: CD1 - Submitter: Anthony Williams Opened: 2001-07-13 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-There is an apparent contradiction about which circumstances can cause -a reallocation of a vector in Section 23.3.6.3 [vector.capacity] and -section 23.3.6.5 [vector.modifiers]. -

- -

23.3.6.3 [vector.capacity],p5 says:

-

-Notes: Reallocation invalidates all the references, pointers, and iterators -referring to the elements in the sequence. It is guaranteed that no -reallocation takes place during insertions that happen after a call to -reserve() until the time when an insertion would make the size of the vector -greater than the size specified in the most recent call to reserve(). -

- -

Which implies if I do

- -
-  std::vector<int> vec;
-  vec.reserve(23);
-  vec.reserve(0);
-  vec.insert(vec.end(),1);
-
- -

then the implementation may reallocate the vector for the insert, -as the size specified in the previous call to reserve was zero.

- -

However, the previous paragraphs (23.3.6.3 [vector.capacity], p1-2) state:

-
-

-(capacity) Returns: The total number of elements the vector -can hold without requiring reallocation -

-

-...After reserve(), capacity() is greater or equal to the -argument of reserve if reallocation happens; and equal to the previous value -of capacity() otherwise... -

-
- -

-This implies that vec.capacity() is still 23, and so the insert() -should not require a reallocation, as vec.size() is 0. This is backed -up by 23.3.6.5 [vector.modifiers], p1: -

-

-(insert) Notes: Causes reallocation if the new size is greater than the old -capacity. -

- -

-Though this doesn't rule out reallocation if the new size is less -than the old capacity, I think the intent is clear. -

- - - -

Proposed resolution:

-

Change the wording of 23.3.6.3 [vector.capacity] paragraph 5 to:

- -

-Notes: Reallocation invalidates all the references, pointers, and -iterators referring to the elements in the sequence. It is guaranteed -that no reallocation takes place during insertions that happen after a -call to reserve() until the time when an insertion would make the size -of the vector greater than the value of capacity(). -

- -

[Redmond: original proposed resolution was modified slightly. In -the original, the guarantee was that there would be no reallocation -until the size would be greater than the value of capacity() after the -most recent call to reserve(). The LWG did not believe that the -"after the most recent call to reserve()" added any useful -information.]

- - - - -

Rationale:

-

There was general agreement that, when reserve() is called twice in -succession and the argument to the second invocation is smaller than -the argument to the first, the intent was for the second invocation to -have no effect. Wording implying that such cases have an effect on -reallocation guarantees was inadvertant.

- - - - - -
-

331. bad declaration of destructor for ios_base::failure

-

Section: 27.5.3.1.1 [ios::failure] Status: CD1 - Submitter: PremAnand M. Rao Opened: 2001-08-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-With the change in 17.6.5.12 [res.on.exception.handling] to state - "An implementation may strengthen the exception-specification for a - non-virtual function by removing listed exceptions." -(issue 119) -and the following declaration of ~failure() in ios_base::failure -

-
-    namespace std {
-       class ios_base::failure : public exception {
-       public:
-           ...
-           virtual ~failure();
-           ...
-       };
-     }
-
-

the class failure cannot be implemented since in 18.7.1 [type.info] the destructor of class exception has an empty -exception specification:

-
-    namespace std {
-       class exception {
-       public:
-         ...
-         virtual ~exception() throw();
-         ...
-       };
-     }
-
- - -

Proposed resolution:

-

Remove the declaration of ~failure().

- - -

Rationale:

-

The proposed resolution is consistent with the way that destructors -of other classes derived from exception are handled.

- - - - - - - -
-

333. does endl imply synchronization with the device?

-

Section: 27.7.3.8 [ostream.manip] Status: CD1 - Submitter: PremAnand M. Rao Opened: 2001-08-27 Last modified: 2015-04-08

-

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-

Discussion:

-

A footnote in 27.7.3.8 [ostream.manip] states:

-

- [Footnote: The effect of executing cout << endl is to insert a - newline character in the output sequence controlled by cout, then - synchronize it with any external file with which it might be - associated. --- end foonote] -

- -

-Does the term "file" here refer to the external device? -This leads to some implementation ambiguity on systems with fully -buffered files where a newline does not cause a flush to the device. -

- -

-Choosing to sync with the device leads to significant performance -penalties for each call to endl, while not sync-ing leads to -errors under special circumstances. -

- -

-I could not find any other statement that explicitly defined -the behavior one way or the other. -

- - -

Proposed resolution:

-

Remove footnote 300 from section 27.7.3.8 [ostream.manip].

- - -

Rationale:

-

We already have normative text saying what endl does: it -inserts a newline character and calls flush. This footnote -is at best redundant, at worst (as this issue says) misleading, -because it appears to make promises about what flush -does.

- - - - - - - -
-

334. map::operator[] specification forces inefficient implementation

-

Section: 23.4.4.3 [map.access] Status: CD1 - Submitter: Andrea Griffini Opened: 2001-09-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current standard describes map::operator[] using a -code example. That code example is however quite -inefficient because it requires several useless copies -of both the passed key_type value and of default -constructed mapped_type instances. -My opinion is that was not meant by the comitee to -require all those temporary copies. -

- -

Currently map::operator[] behaviour is specified as:

-
-  Returns:
-    (*((insert(make_pair(x, T()))).first)).second.
-
- -

-This specification however uses make_pair that is a -template function of which parameters in this case -will be deduced being of type const key_type& and -const T&. This will create a pair<key_type,T> that -isn't the correct type expected by map::insert so -another copy will be required using the template -conversion constructor available in pair to build -the required pair<const key_type,T> instance. -

- -

If we consider calling of key_type copy constructor -and mapped_type default constructor and copy -constructor as observable behaviour (as I think we -should) then the standard is in this place requiring -two copies of a key_type element plus a default -construction and two copy construction of a mapped_type -(supposing the addressed element is already present -in the map; otherwise at least another copy -construction for each type). -

- -

A simple (half) solution would be replacing the description with:

-
-  Returns:
-    (*((insert(value_type(x, T()))).first)).second.
-
- -

This will remove the wrong typed pair construction that -requires one extra copy of both key and value.

- -

However still the using of map::insert requires temporary -objects while the operation, from a logical point of view, -doesn't require any.

- -

I think that a better solution would be leaving free an -implementer to use a different approach than map::insert -that, because of its interface, forces default constructed -temporaries and copies in this case. -The best solution in my opinion would be just requiring -map::operator[] to return a reference to the mapped_type -part of the contained element creating a default element -with the specified key if no such an element is already -present in the container. Also a logarithmic complexity -requirement should be specified for the operation. -

- -

-This would allow library implementers to write alternative -implementations not using map::insert and reaching optimal -performance in both cases of the addressed element being -present or absent from the map (no temporaries at all and -just the creation of a new pair inside the container if -the element isn't present). -Some implementer has already taken this option but I think -that the current wording of the standard rules that as -non-conforming. -

- - - -

Proposed resolution:

- -

-Replace 23.4.4.3 [map.access] paragraph 1 with -

-
-

--1- Effects: If there is no key equivalent to x in the map, inserts -value_type(x, T()) into the map. -

-

--2- Returns: A reference to the mapped_type corresponding to x in *this. -

-

--3- Complexity: logarithmic. -

-
- -

[This is the second option mentioned above. Howard provided -wording. We may also wish to have a blanket statement somewhere in -clause 17 saying that we do not intend the semantics of sample code -fragments to be interpreted as specifing exactly how many copies are -made. See issue 98 for a similar problem.]

- - - - -

Rationale:

-

-This is the second solution described above; as noted, it is -consistent with existing practice. -

- -

Note that we now need to specify the complexity explicitly, because -we are no longer defining operator[] in terms of -insert.

- - - - - -
-

335. minor issue with char_traits, table 37

-

Section: 21.2.1 [char.traits.require] Status: CD1 - Submitter: Andy Sawyer Opened: 2001-09-06 Last modified: 2015-04-08

-

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-

Discussion:

-

-Table 37, in 21.2.1 [char.traits.require], descibes char_traits::assign -as: -

-
-  X::assign(c,d)   assigns c = d.
-
- -

And para 1 says:

- -

- [...] c and d denote values of type CharT [...] -

- -

-Naturally, if c and d are values, then the assignment is -(effectively) meaningless. It's clearly intended that (in the case of -assign, at least), 'c' is intended to be a reference type. -

- -

I did a quick survey of the four implementations I happened to have -lying around, and sure enough they all have signatures:

-
-    assign( charT&, const charT& );
-
- -

(or the equivalent). It's also described this way in Nico's book. -(Not to mention the synopses of char_traits<char> in 21.1.3.1 -and char_traits<wchar_t> in 21.1.3.2...) -

- - -

Proposed resolution:

-

Add the following to 21.1.1 para 1:

-

- r denotes an lvalue of CharT -

- -

and change the description of assign in the table to:

-
-  X::assign(r,d)   assigns r = d
-
- - - - - -
-

336. Clause 17 lack of references to deprecated headers

-

Section: 17 [library] Status: CD1 - Submitter: Detlef Vollmann Opened: 2001-09-05 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

From c++std-edit-873:

- -

17.6.1.2 [headers], Table 11. In this table, the header -<strstream> is missing.

- -

This shows a general problem: The whole clause 17 refers quite -often to clauses 18 through 27, but D.7 is also a part of the standard -library (though a deprecated one).

- - - -

Proposed resolution:

- -

To 17.6.1.2 [headers] Table 11, C++ Library Headers, add -"<strstream>".

- -

In the following places, change "clauses 17 through 27" to "clauses -17 through 27 and Annex D":

- -
    -
  • 1.2 [intro.refs] Normative references/1/footnote 1
    • -
  • 1.3 [intro.defs] Definitions/1
    • -
  • 7 [dcl.dcl] Library introduction/9
    • -
  • 17.5 [description] Method of description (Informative)/1
    • -
  • 17.5.2.1.4 [character.seq] Character sequences/1/bullet 2
    • -
  • 17.5.2.2 [functions.within.classes] Functions within classes/1
    • -
  • 17.5.2.3 [objects.within.classes] Private members/1/(2 places)
    • -
  • 17.6 [requirements] Library-wide requirements/1
    • -
  • 17.6.1.2 [headers] Headers/4
    • -
  • 17.6.4.6 [replacement.functions] Replacement functions/1
    • -
  • 17.6.5.4 [global.functions] Global or non-member functions/2
    • -
  • 17.6.5.10 [protection.within.classes] Protection within classes/1
    • -
- - - - - - - -
-

337. replace_copy_if's template parameter should be InputIterator

-

Section: 25.3.5 [alg.replace] Status: CD1 - Submitter: Detlef Vollmann Opened: 2001-09-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

From c++std-edit-876:

- -

-In section 25.3.5 [alg.replace] before p4: The name of the first -parameter of template replace_copy_if should be "InputIterator" -instead of "Iterator". According to 17.5.2.1 [type.descriptions] p1 the -parameter name conveys real normative meaning. -

- - -

Proposed resolution:

-

Change Iterator to InputIterator.

- - - - - -
-

338. is whitespace allowed between `-' and a digit?

-

Section: 22.4 [locale.categories] Status: CD1 - Submitter: Martin Sebor Opened: 2001-09-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-From Stage 2 processing in 22.4.2.1.2 [facet.num.get.virtuals], p8 and 9 (the -original text or the text corrected by the proposed resolution of -issue 221) it seems clear that no whitespace is allowed -within a number, but 22.4.3.1 [locale.numpunct], p2, which gives the -format for integer and floating point values, says that whitespace is -optional between a plusminus and a sign. -

- -

-The text needs to be clarified to either consistently allow or -disallow whitespace between a plusminus and a sign. It might be -worthwhile to consider the fact that the C library stdio facility does -not permit whitespace embedded in numbers and neither does the C or -C++ core language (the syntax of integer-literals is given in 2.13.2 [lex.icon], that of floating-point-literals in 2.13.4 [lex.fcon] of the C++ standard). -

- - -

Proposed resolution:

-

Change the first part of 22.4.3.1 [locale.numpunct] paragraph 2 from:

-
-

-The syntax for number formats is as follows, where digit -represents the radix set specified by the fmtflags argument -value, whitespace is as determined by the facet -ctype<charT> (22.2.1.1), and thousands-sep and -decimal-point are the results of corresponding -numpunct<charT> members. Integer values have the -format: -

-
-  integer   ::= [sign] units
-  sign      ::= plusminus [whitespace]
-  plusminus ::= '+' | '-'
-  units     ::= digits [thousands-sep units]
-  digits    ::= digit [digits]
-
-
-

to:

-
-

-The syntax for number formats is as follows, where digit -represents the radix set specified by the fmtflags argument -value, and thousands-sep and decimal-point are the -results of corresponding numpunct<charT> members. -Integer values have the format: -

-
-  integer   ::= [sign] units
-  sign      ::= plusminus
-  plusminus ::= '+' | '-'
-  units     ::= digits [thousands-sep units]
-  digits    ::= digit [digits]
-
-
- - -

Rationale:

-

It's not clear whether the format described in 22.4.3.1 [locale.numpunct] paragraph 2 has any normative weight: nothing in the -standard says how, or whether, it's used. However, there's no reason -for it to differ gratuitously from the very specific description of -numeric processing in 22.4.2.1.2 [facet.num.get.virtuals]. The proposed -resolution removes all mention of "whitespace" from that format.

- - - - - -
-

339. definition of bitmask type restricted to clause 27

-

Section: 22.4.1 [category.ctype], 17.5.2.1.3 [bitmask.types] Status: CD1 - Submitter: Martin Sebor Opened: 2001-09-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The ctype_category::mask type is declared to be an enum in 22.4.1 [category.ctype] with p1 then stating that it is a bitmask type, most -likely referring to the definition of bitmask type in 17.5.2.1.3 [bitmask.types], p1. However, the said definition only applies to -clause 27, making the reference in 22.2.1 somewhat dubious. -

- - -

Proposed resolution:

-

Clarify 17.3.2.1.2, p1 by changing the current text from

-

- Several types defined in clause 27 are bitmask types. Each bitmask type - can be implemented as an enumerated type that overloads certain operators, - as an integer type, or as a bitset (20.6 [template.bitset]). -

-

to read

-

- Several types defined in clauses lib.language.support through - lib.input.output and Annex D are bitmask types. Each bitmask type can - be implemented as an enumerated type that overloads certain operators, - as an integer type, or as a bitset (lib.template.bitset). -

- -

-Additionally, change the definition in 22.2.1 to adopt the same -convention as in clause 27 by replacing the existing text with the -following (note, in particluar, the cross-reference to 17.3.2.1.2 in -22.2.1, p1): -

- -
-

22.2.1 The ctype category [lib.category.ctype]

-
-namespace std {
-    class ctype_base {
-    public:
-        typedef T mask;
-
-        // numeric values are for exposition only.
-        static const mask space = 1 << 0;
-        static const mask print = 1 << 1;
-        static const mask cntrl = 1 << 2;
-        static const mask upper = 1 << 3;
-        static const mask lower = 1 << 4;
-        static const mask alpha = 1 << 5;
-        static const mask digit = 1 << 6;
-        static const mask punct = 1 << 7;
-        static const mask xdigit = 1 << 8;
-        static const mask alnum = alpha | digit;
-        static const mask graph = alnum | punct;
-    };
-}
-
- -

The type mask is a bitmask type (17.5.2.1.3 [bitmask.types]).

-
- -

[Curaçao: The LWG notes that T above should be bold-italics to be -consistent with the rest of the standard.]

- - - - - - - - - -
-

340. interpretation of has_facet<Facet>(loc)

-

Section: 22.3.1.1.1 [locale.category] Status: CD1 - Submitter: Martin Sebor Opened: 2001-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It's unclear whether 22.1.1.1.1, p3 says that -has_facet<Facet>(loc) returns true for any Facet -from Table 51 or whether it includes Table 52 as well: -

- -

-For any locale loc either constructed, or returned by -locale::classic(), and any facet Facet that is a member of a -standard category, has_facet<Facet>(loc) is true. Each -locale member function which takes a locale::category -argument operates on the corresponding set of facets. -

- -

-It seems that it comes down to which facets are considered to be members of a -standard category. Intuitively, I would classify all the facets in Table 52 as -members of their respective standard categories, but there are an unbounded set -of them... -

- -

-The paragraph implies that, for instance, has_facet<num_put<C, -OutputIterator> >(loc) must always return true. I don't think that's -possible. If it were, then use_facet<num_put<C, OutputIterator> ->(loc) would have to return a reference to a distinct object for each -valid specialization of num_put<C, OutputIteratory>, which is -clearly impossible. -

- -

-On the other hand, if none of the facets in Table 52 is a member of a standard -category then none of the locale member functions that operate on entire -categories of facets will work properly. -

- -

-It seems that what p3 should mention that it's required (permitted?) -to hold only for specializations of Facet from Table 52 on -C from the set { char, wchar_t }, and -InputIterator and OutputIterator from the set of -{ -{i,o}streambuf_iterator<{char,wchar_t}> -}. -

- - -

Proposed resolution:

-

In 22.3.1.1.1 [locale.category], paragraph 3, change -"that is a member of a standard category" to "shown in Table 51".

- - -

Rationale:

-

The facets in Table 52 are an unbounded set. Locales should not be -required to contain an infinite number of facets.

- -

It's not necessary to talk about which values of InputIterator and -OutputIterator must be supported. Table 51 already contains a -complete list of the ones we need.

- - - - - - -
-

341. Vector reallocation and swap

-

Section: 23.3.6.3 [vector.capacity] Status: CD1 - Submitter: Anthony Williams Opened: 2001-09-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

It is a common idiom to reduce the capacity of a vector by swapping it with -an empty one:

-
-  std::vector<SomeType> vec;
-  // fill vec with data
-  std::vector<SomeType>().swap(vec);
-  // vec is now empty, with minimal capacity
-
- -

However, the wording of 23.3.6.3 [vector.capacity]paragraph 5 prevents -the capacity of a vector being reduced, following a call to -reserve(). This invalidates the idiom, as swap() is thus prevented -from reducing the capacity. The proposed wording for issue 329 does not affect this. Consequently, the example above -requires the temporary to be expanded to cater for the contents of -vec, and the contents be copied across. This is a linear-time -operation.

- -

However, the container requirements state that swap must have constant -complexity (23.2 [container.requirements] note to table 65).

- -

This is an important issue, as reallocation affects the validity of -references and iterators.

- -

If the wording of 23.2.4.2p5 is taken to be the desired intent, then -references and iterators remain valid after a call to swap, if they refer to -an element before the new end() of the vector into which they originally -pointed, in which case they refer to the element at the same index position. -Iterators and references that referred to an element whose index position -was beyond the new end of the vector are invalidated.

- -

If the note to table 65 is taken as the desired intent, then there are two -possibilities with regard to iterators and references:

- -
    -
  1. All Iterators and references into both vectors are invalidated.
    2. -
  2. Iterators and references into either vector remain valid, and remain -pointing to the same element. Consequently iterators and references that -referred to one vector now refer to the other, and vice-versa.
    3. -
- - -

Proposed resolution:

-

Add a new paragraph after 23.3.6.3 [vector.capacity] paragraph 5:

-
-
-  void swap(vector<T,Allocator>& x);
-
-

Effects: Exchanges the contents and capacity() of *this -with that of x.

-

Complexity: Constant time.

-
- -

[This solves the problem reported for this issue. We may also -have a problem with a circular definition of swap() for other -containers.]

- - - - -

Rationale:

-

-swap should be constant time. The clear intent is that it should just -do pointer twiddling, and that it should exchange all properties of -the two vectors, including their reallocation guarantees. -

- - - - - -
-

343. Unspecified library header dependencies

-

Section: 17 [library] Status: Resolved - Submitter: Martin Sebor Opened: 2001-10-09 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The synopses of the C++ library headers clearly show which names are -required to be defined in each header. Since in order to implement the -classes and templates defined in these headers declarations of other -templates (but not necessarily their definitions) are typically -necessary the standard in 17.4.4, p1 permits library implementers to -include any headers needed to implement the definitions in each header. -

- -

-For instance, although it is not explicitly specified in the synopsis of -<string>, at the point of definition of the std::basic_string template -the declaration of the std::allocator template must be in scope. All -current implementations simply include <memory> from within <string>, -either directly or indirectly, to bring the declaration of -std::allocator into scope. -

- -

-Additionally, however, some implementation also include <istream> and -<ostream> at the top of <string> to bring the declarations of -std::basic_istream and std::basic_ostream into scope (which are needed -in order to implement the string inserter and extractor operators -(21.3.7.9 [lib.string.io])). Other implementations only include -<iosfwd>, since strictly speaking, only the declarations and not the -full definitions are necessary. -

- -

-Obviously, it is possible to implement <string> without actually -providing the full definitions of all the templates std::basic_string -uses (std::allocator, std::basic_istream, and std::basic_ostream). -Furthermore, not only is it possible, doing so is likely to have a -positive effect on compile-time efficiency. -

- -

-But while it may seem perfectly reasonable to expect a program that uses -the std::basic_string insertion and extraction operators to also -explicitly include <istream> or <ostream>, respectively, it doesn't seem -reasonable to also expect it to explicitly include <memory>. Since -what's reasonable and what isn't is highly subjective one would expect -the standard to specify what can and what cannot be assumed. -Unfortunately, that isn't the case. -

- -

The examples below demonstrate the issue.

- -

Example 1:

- -

It is not clear whether the following program is complete:

- -
-#include <string>
-
-extern std::basic_ostream<char> &strm;
-
-int main () {
-    strm << std::string ("Hello, World!\n");
-}
-
- -

or whether one must explicitly include <memory> or -<ostream> (or both) in addition to <string> in order for -the program to compile.

- - -

Example 2:

- -

Similarly, it is unclear whether the following program is complete:

- -
-#include <istream>
-
-extern std::basic_iostream<char> &strm;
-
-int main () {
-    strm << "Hello, World!\n";
-}
-
- -

-or whether one needs to explicitly include <ostream>, and -perhaps even other headers containing the definitions of other -required templates:

- -
-#include <ios>
-#include <istream>
-#include <ostream>
-#include <streambuf>
-
-extern std::basic_iostream<char> &strm;
-
-int main () {
-    strm << "Hello, World!\n";
-}
-
- -

Example 3:

- -

Likewise, it seems unclear whether the program below is complete:

-
-#include <iterator>
-
-bool foo (std::istream_iterator<int> a, std::istream_iterator<int> b)
-{
-    return a == b;
-}
-
-int main () { }
-
- -

or whether one should be required to include <istream>.

- -

There are many more examples that demonstrate this lack of a -requirement. I believe that in a good number of cases it would be -unreasonable to require that a program explicitly include all the -headers necessary for a particular template to be specialized, but I -think that there are cases such as some of those above where it would -be desirable to allow implementations to include only as much as -necessary and not more.

- -

[ -post Bellevue: -]

- - -

-Position taken in prior reviews is that the idea of a table of header -dependencies is a good one. Our view is that a full paper is needed to -do justice to this, and we've made that recommendation to the issue -author. -

- -

[ -2009-07 Frankfurt -]

- - -

-Resolved. Handled by LWG 1178. -

- - - -

Proposed resolution:

-

-For every C++ library header, supply a minimum set of other C++ library -headers that are required to be included by that header. The proposed -list is below (C++ headers for C Library Facilities, table 12 in -17.4.1.2, p3, are omitted): -

- -
-+------------+--------------------+
-| C++ header |required to include |
-+============+====================+
-|<algorithm> |                    |
-+------------+--------------------+
-|<bitset>    |                    |
-+------------+--------------------+
-|<complex>   |                    |
-+------------+--------------------+
-|<deque>     |<memory>            |
-+------------+--------------------+
-|<exception> |                    |
-+------------+--------------------+
-|<fstream>   |<ios>               |
-+------------+--------------------+
-|<functional>|                    |
-+------------+--------------------+
-|<iomanip>   |<ios>               |
-+------------+--------------------+
-|<ios>       |<streambuf>         |
-+------------+--------------------+
-|<iosfwd>    |                    |
-+------------+--------------------+
-|<iostream>  |<istream>, <ostream>|
-+------------+--------------------+
-|<istream>   |<ios>               |
-+------------+--------------------+
-|<iterator>  |                    |
-+------------+--------------------+
-|<limits>    |                    |
-+------------+--------------------+
-|<list>      |<memory>            |
-+------------+--------------------+
-|<locale>    |                    |
-+------------+--------------------+
-|<map>       |<memory>            |
-+------------+--------------------+
-|<memory>    |                    |
-+------------+--------------------+
-|<new>       |<exception>         |
-+------------+--------------------+
-|<numeric>   |                    |
-+------------+--------------------+
-|<ostream>   |<ios>               |
-+------------+--------------------+
-|<queue>     |<deque>             |
-+------------+--------------------+
-|<set>       |<memory>            |
-+------------+--------------------+
-|<sstream>   |<ios>, <string>     |
-+------------+--------------------+
-|<stack>     |<deque>             |
-+------------+--------------------+
-|<stdexcept> |                    |
-+------------+--------------------+
-|<streambuf> |<ios>               |
-+------------+--------------------+
-|<string>    |<memory>            |
-+------------+--------------------+
-|<strstream> |                    |
-+------------+--------------------+
-|<typeinfo>  |<exception>         |
-+------------+--------------------+
-|<utility>   |                    |
-+------------+--------------------+
-|<valarray>  |                    |
-+------------+--------------------+
-|<vector>    |<memory>            |
-+------------+--------------------+
-
- - -

Rationale:

-

The portability problem is real. A program that works correctly on -one implementation might fail on another, because of different header -dependencies. This problem was understood before the standard was -completed, and it was a conscious design choice.

-

One possible way to deal with this, as a library extension, would -be an <all> header.

- -

-Hinnant: It's time we dealt with this issue for C++0X. Reopened. -

- - - - - - - -
-

345. type tm in <cwchar>

-

Section: 21.8 [c.strings] Status: CD1 - Submitter: Clark Nelson Opened: 2001-10-19 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-C99, and presumably amendment 1 to C90, specify that <wchar.h> -declares struct tm as an incomplete type. However, table 48 in 21.8 [c.strings] does not mention the type tm as being declared in -<cwchar>. Is this omission intentional or accidental? -

- - -

Proposed resolution:

-

In section 21.8 [c.strings], add "tm" to table 48.

- - - - - -
-

346. Some iterator member functions should be const

-

Section: X [iterator.concepts] Status: CD1 - Submitter: Jeremy Siek Opened: 2001-10-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Iterator member functions and operators that do not change the state -of the iterator should be defined as const member functions or as -functions that take iterators either by const reference or by -value. The standard does not explicitly state which functions should -be const. Since this a fairly common mistake, the following changes -are suggested to make this explicit.

- -

The tables almost indicate constness properly through naming: r -for non-const and a,b for const iterators. The following changes -make this more explicit and also fix a couple problems.

- - -

Proposed resolution:

-

In X [iterator.concepts] Change the first section of p9 from -"In the following sections, a and b denote values of X..." to -"In the following sections, a and b denote values of type const X...".

- -

In Table 73, change

-
-    a->m   U&         ...
-
- -

to

- -
-    a->m   const U&   ...
-    r->m   U&         ...
-
- -

In Table 73 expression column, change

- -
-    *a = t
-
- -

to

- -
-    *r = t
-
- -

[Redmond: The container requirements should be reviewed to see if -the same problem appears there.]

- - - - - - - -
-

347. locale::category and bitmask requirements

-

Section: 22.3.1.1.1 [locale.category] Status: CD1 - Submitter: P.J. Plauger, Nathan Myers Opened: 2001-10-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In 22.3.1.1.1 [locale.category] paragraph 1, the category members -are described as bitmask elements. In fact, the bitmask requirements -in 17.5.2.1.3 [bitmask.types] don't seem quite right: none -and all are bitmask constants, not bitmask elements.

- -

In particular, the requirements for none interact poorly -with the requirement that the LC_* constants from the C library must -be recognizable as C++ locale category constants. LC_* values should -not be mixed with these values to make category values.

- -

We have two options for the proposed resolution. Informally: -option 1 removes the requirement that LC_* values be recognized as -category arguments. Option 2 changes the category type so that this -requirement is implementable, by allowing none to be some -value such as 0x1000 instead of 0.

- -

Nathan writes: "I believe my proposed resolution [Option 2] merely -re-expresses the status quo more clearly, without introducing any -changes beyond resolving the DR.

- - - -

Proposed resolution:

-

Replace the first two paragraphs of 22.3.1.1 [locale.types] with:

-
-
-    typedef int category;
-
- -

Valid category values include the locale member bitmask -elements collate, ctype, monetary, -numeric, time, and messages, each of which -represents a single locale category. In addition, locale member -bitmask constant none is defined as zero and represents no -category. And locale member bitmask constant all is defined such that -the expression

-
-    (collate | ctype | monetary | numeric | time | messages | all) == all
-
-

-is true, and represents the union of all categories. Further -the expression (X | Y), where X and Y each -represent a single category, represents the union of the two -categories. -

- -

-locale member functions expecting a category -argument require one of the category values defined above, or -the union of two or more such values. Such a category -argument identifies a set of locale categories. Each locale category, -in turn, identifies a set of locale facets, including at least those -shown in Table 51: -

-
-

[Curaçao: need input from locale experts.]

- - - - -

Rationale:

- -

The LWG considered, and rejected, an alternate proposal (described - as "Option 2" in the discussion). The main reason for rejecting it - was that library implementors were concerened about implementation - difficult, given that getting a C++ library to work smoothly with a - separately written C library is already a delicate business. Some - library implementers were also concerned about the issue of adding - extra locale categories.

- -
-

Option 2:
-Replace the first paragraph of 22.3.1.1 [locale.types] with:

-
-

-Valid category values include the enumerated values. In addition, the -result of applying commutative operators | and & to any two valid -values is valid, and results in the setwise union and intersection, -respectively, of the argument categories. The values all and -none are defined such that for any valid value cat, the -expressions (cat | all == all), (cat & all == cat), -(cat | none == cat) and (cat & none == none) are -true. For non-equal values cat1 and cat2 of the -remaining enumerated values, (cat1 & cat2 == none) is true. -For any valid categories cat1 and cat2, the result -of (cat1 & ~cat2) is valid, and equals the setwise union of -those categories found in cat1 but not found in cat2. -[Footnote: it is not required that all equal the setwise union -of the other enumerated values; implementations may add extra categories.] -

-
-
- - - - - -
-

349. Minor typographical error in ostream_iterator

-

Section: 24.6.2 [ostream.iterator] Status: CD1 - Submitter: Andy Sawyer Opened: 2001-10-24 Last modified: 2015-04-08

-

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-

Discussion:

-

24.5.2 [lib.ostream.iterator] states:

-
-    [...]
-
-    private:
-    // basic_ostream<charT,traits>* out_stream; exposition only
-    // const char* delim; exposition only
-
- -

Whilst it's clearly marked "exposition only", I suspect 'delim' -should be of type 'const charT*'.

- - -

Proposed resolution:

-

-In 24.6.2 [ostream.iterator], replace const char* delim with -const charT* delim. -

- - - - - -
-

352. missing fpos requirements

-

Section: 21.2.2 [char.traits.typedefs] Status: CD1 - Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-(1) -There are no requirements on the stateT template parameter of -fpos listed in 27.4.3. The interface appears to require that -the type be at least Assignable and CopyConstructible (27.4.3.1, p1), -and I think also DefaultConstructible (to implement the operations in -Table 88). -

-

-21.1.2, p3, however, only requires that -char_traits<charT>::state_type meet the requirements of -CopyConstructible types. -

-

-(2) -Additionally, the stateT template argument has no -corresponding typedef in fpos which might make it difficult to use in -generic code. -

- - -

Proposed resolution:

-

-Modify 21.1.2, p4 from -

-

- Requires: state_type shall meet the requirements of - CopyConstructible types (20.1.3). -

-

- Requires: state_type shall meet the requirements of Assignable - (23.1, p4), CopyConstructible (20.1.3), and - DefaultConstructible (20.1.4) types. -

- - - -

Rationale:

-

The LWG feels this is two issues, as indicated above. The first is -a defect---std::basic_fstream is unimplementable without these -additional requirements---and the proposed resolution fixes it. The -second is questionable; who would use that typedef? The class -template fpos is used only in a very few places, all of which know the -state type already. Unless motivation is provided, the second should -be considered NAD.

- - - - - -
-

353. std::pair missing template assignment

-

Section: 20.3 [pairs] Status: Resolved - Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The class template std::pair defines a template ctor (20.2.2, p4) but -no template assignment operator. This may lead to inefficient code since -assigning an object of pair<C, D> to pair<A, B> -where the types C and D are distinct from but convertible to -A and B, respectively, results in a call to the template copy -ctor to construct an unnamed temporary of type pair<A, B> -followed by an ordinary (perhaps implicitly defined) assignment operator, -instead of just a straight assignment. -

- - -

Proposed resolution:

-

-Add the following declaration to the definition of std::pair: -

-
-    template<class U, class V>
-    pair& operator=(const pair<U, V> &p);
-
-

-And also add a paragraph describing the effects of the function template to the -end of 20.2.2: -

-
-    template<class U, class V>
-    pair& operator=(const pair<U, V> &p);
-
-

- Effects: first = p.first; - second = p.second; - Returns: *this -

- -

[Curaçao: There is no indication this is was anything other than -a design decision, and thus NAD.  May be appropriate for a future -standard.]

- - -

[ -Pre Bellevue: It was recognized that this was taken care of by -N1856, -and thus moved from NAD Future to NAD EditorialResolved. -]

- - - - - - -
-

354. Associative container lower/upper bound requirements

-

Section: 23.2.4 [associative.reqmts] Status: CD1 - Submitter: Hans Aberg Opened: 2001-12-17 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Discussions in the thread "Associative container lower/upper bound -requirements" on comp.std.c++ suggests that there is a defect in the -C++ standard, Table 69 of section 23.1.2, "Associative containers", -[lib.associative.reqmts]. It currently says:

- -
-

-a.find(k): returns an iterator pointing to an element with the key equivalent to -k, or a.end() if such an element is not found. -

- -

-a.lower_bound(k): returns an iterator pointing to the first element with -key not less than k. -

- -

-a.upper_bound(k): returns an iterator pointing to the first element with -key greater than k. -

-
- -

-We have "or a.end() if such an element is not found" for -find, but not for upper_bound or -lower_bound. As the text stands, one would be forced to -insert a new element into the container and return an iterator to that -in case the sought iterator does not exist, which does not seem to be -the intention (and not possible with the "const" versions). -

- - -

Proposed resolution:

- -

Change Table 69 of section 23.2.4 [associative.reqmts] indicated entries -to:

- -
-

-a.lower_bound(k): returns an iterator pointing to the first element with -key not less than k, or a.end() if such an element is not found. -

- -

-a.upper_bound(k): returns an iterator pointing to the first element with -key greater than k, or a.end() if such an element is not found. -

-
- -

[Curaçao: LWG reviewed PR.]

- - - - - - - - -
-

355. Operational semantics for a.back()

-

Section: 23.2.3 [sequence.reqmts] Status: CD1 - Submitter: Yaroslav Mironov Opened: 2002-01-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Table 68 "Optional Sequence Operations" in 23.1.1/12 -specifies operational semantics for "a.back()" as -"*--a.end()", which may be ill-formed [because calling -operator-- on a temporary (the return) of a built-in type is -ill-formed], provided a.end() returns a simple pointer rvalue -(this is almost always the case for std::vector::end(), for -example). Thus, the specification is not only incorrect, it -demonstrates a dangerous construct: "--a.end()" may -successfully compile and run as intended, but after changing the type -of the container or the mode of compilation it may produce -compile-time error.

- - - -

Proposed resolution:

-

Change the specification in table 68 "Optional Sequence -Operations" in 23.1.1/12 for "a.back()" from

- - -
-*--a.end()
-
- -

to

- -
-  { iterator tmp = a.end(); --tmp; return *tmp; }
-
- -

and the specification for "a.pop_back()" from

- -
-a.erase(--a.end())
-
- -

to

- -
-  { iterator tmp = a.end(); --tmp; a.erase(tmp); }
-
- -

[Curaçao: LWG changed PR from "{ X::iterator tmp = -a.end(); return *--tmp; }" to "*a.rbegin()", and from -"{ X::iterator tmp = a.end(); a.erase(--tmp); }" to -"a.erase(rbegin())".]

- - -

[There is a second possible defect; table 68 "Optional -Sequence Operations" in the "Operational Semantics" -column uses operations present only in the "Reversible -Container" requirements, yet there is no stated dependency -between these separate requirements tables. Ask in Santa Cruz if the -LWG would like a new issue opened.]

- - -

[Santa Cruz: the proposed resolution is even worse than what's in - the current standard: erase is undefined for reverse iterator. If - we're going to make the change, we need to define a temporary and - use operator--. Additionally, we don't know how prevalent this is: - do we need to make this change in more than one place? Martin has - volunteered to review the standard and see if this problem occurs - elsewhere.]

- - -

[Oxford: Matt provided new wording to address the concerns raised - in Santa Cruz. It does not appear that this problem appears - anywhere else in clauses 23 or 24.]

- - -

[Kona: In definition of operational semantics of back(), change -"*tmp" to "return *tmp;"]

- - - - - - - -
-

358. interpreting thousands_sep after a decimal_point

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 - Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-I don't think thousands_sep is being treated correctly after -decimal_point has been seen. Since grouping applies only to the -integral part of the number, the first such occurrence should, IMO, -terminate Stage 2. (If it does not terminate it, then 22.2.2.1.2, p12 -and 22.2.3.1.2, p3 need to explain how thousands_sep is to be -interpreted in the fractional part of a number.) -

- -

-The easiest change I can think of that resolves this issue would be -something like below. -

- - -

Proposed resolution:

-

-Change the first sentence of 22.2.2.1.2, p9 from -

- -

- If discard is true then the position of the character is - remembered, but the character is otherwise ignored. If it is not - discarded, then a check is made to determine if c is allowed as - the next character of an input field of the conversion specifier - returned by stage 1. If so it is accumulated. -

- -

to

- -

- If discard is true, then if '.' has not yet been - accumulated, then the position of the character is remembered, but - the character is otherwise ignored. Otherwise, if '.' has - already been accumulated, the character is discarded and Stage 2 - terminates. ... -

- - - -

Rationale:

-

We believe this reflects the intent of the Standard. Thousands sep - characters after the decimal point are not useful in any locale. - Some formatting conventions do group digits that follow the decimal - point, but they usually introduce a different grouping character - instead of reusing the thousand sep character. If we want to add - support for such conventions, we need to do so explicitly.

- - - - - - -
-

359. num_put<>::do_put (..., bool) undocumented

-

Section: 22.4.2.2.1 [facet.num.put.members] Status: CD1 - Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2015-04-08

-

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-

Discussion:

-

22.2.2.2.1, p1:

- - 
-    iter_type put (iter_type out, ios_base& str, char_type fill,
-                   bool val) const;
-    ...
-
-    1   Returns: do_put (out, str, fill, val).
-
- -

AFAICS, the behavior of do_put (..., bool) is not documented anywhere, -however, 22.2.2.2.2, p23:

- -
-
-iter_type put (iter_type out, ios_base& str, char_type fill,
-               bool val) const;
-
- - -

Effects: If (str.flags() & ios_base::boolalpha) == 0 then do - out = do_put(out, str, fill, (int)val) - Otherwise do

-
-             string_type s =
-                 val ? use_facet<ctype<charT> >(loc).truename()
-                     : use_facet<ctype<charT> >(loc).falsename();
-
-

and then insert the characters of s into out. out.

-
- -

-This means that the bool overload of do_put() will never be called, -which contradicts the first paragraph. Perhaps the declaration -should read do_put(), and not put()? -

- -

-Note also that there is no Returns clause for this function, which -should probably be corrected, just as should the second occurrence -of "out." in the text. -

- -

-I think the least invasive change to fix it would be something like -the following: -

- - -

Proposed resolution:

-

In 22.4.2.2.2 [facet.num.put.virtuals], just above paragraph 1, remove - the bool overload.

- -

-In 22.4.2.2.2 [facet.num.put.virtuals], p23, make the following changes -

- -

- Replace put() with do_put() in the declaration - of the member function. -

- -

- Change the Effects clause to a Returns clause (to - avoid the requirement to call do_put(..., int) from - do_put (..., bool)) - like so: -

- -

- 23 Returns: If (str.flags() & - ios_base::boolalpha) == 0 then - do_put (out, str, fill, (long)val) - Otherwise the function obtains a string s as if by

-
-             string_type s =
-                val ? use_facet<ctype<charT> >(loc).truename()
-                    : use_facet<ctype<charT> >(loc).falsename();
-
-

and then inserts each character c of s into out via - *out++ = c - and returns out.

-
- - - -

Rationale:

-This fixes a couple of obvious typos, and also fixes what appears to -be a requirement of gratuitous inefficiency. -

- - - - -
-

360. locale mandates inefficient implementation

-

Section: 22.3.1 [locale] Status: CD1 - Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2015-04-08

-

View all other issues in [locale].

-

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-

Discussion:

-

-22.1.1, p7 (copied below) allows iostream formatters and extractors -to make assumptions about the values returned from facet members. -However, such assumptions are apparently not guaranteed to hold -in other cases (e.g., when the facet members are being called directly -rather than as a result of iostream calls, or between successive -calls to the same iostream functions with no interevening calls to -imbue(), or even when the facet member functions are called -from other member functions of other facets). This restriction -prevents locale from being implemented efficiently. -

- - -

Proposed resolution:

-

Change the first sentence in 22.1.1, p7 from

-

- In successive calls to a locale facet member function during - a call to an iostream inserter or extractor or a streambuf member - function, the returned result shall be identical. [Note: This - implies that such results may safely be reused without calling - the locale facet member function again, and that member functions - of iostream classes cannot safely call imbue() - themselves, except as specified elsewhere. --end note] -

- -

to

- -

- In successive calls to a locale facet member function on a facet - object installed in the same locale, the returned result shall be - identical. ... -

- - - -

Rationale:

-

This change is reasonable becuase it clarifies the intent of this - part of the standard.

- - - - - -
-

362. bind1st/bind2nd type safety

-

Section: X [depr.lib.binders] Status: CD1 - Submitter: Andrew Demkin Opened: 2002-04-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The definition of bind1st() (X [depr.lib.binders]) can result in -the construction of an unsafe binding between incompatible pointer -types. For example, given a function whose first parameter type is -'pointer to T', it's possible without error to bind an argument of -type 'pointer to U' when U does not derive from T: -

-
-   foo(T*, int);
-
-   struct T {};
-   struct U {};
-
-   U u;
-
-   int* p;
-   int* q;
-
-   for_each(p, q, bind1st(ptr_fun(foo), &u));    // unsafe binding
-
- -

-The definition of bind1st() includes a functional-style conversion to -map its argument to the expected argument type of the bound function -(see below): -

-
-  typename Operation::first_argument_type(x)
-
- -

-A functional-style conversion (X [depr.lib.binders]) is defined to be -semantically equivalent to an explicit cast expression (X [depr.lib.binders]), which may (according to 5.4, paragraph 5) be interpreted -as a reinterpret_cast, thus masking the error. -

- -

The problem and proposed change also apply to X [depr.lib.binders].

- - -

Proposed resolution:

-

Add this sentence to the end of X [depr.lib.binders]/1: - "Binders bind1st and bind2nd are deprecated in - favor of std::tr1::bind."

- -

(Notes to editor: (1) when and if tr1::bind is incorporated into - the standard, "std::tr1::bind" should be changed to "std::bind". (2) - 20.5.6 should probably be moved to Annex D.

- - -

Rationale:

-

There is no point in fixing bind1st and bind2nd. tr1::bind is a - superior solution. It solves this problem and others.

- - - - - -
-

363. Missing exception specification in 27.4.2.1.1

-

Section: 27.5.3.1.1 [ios::failure] Status: CD1 - Submitter: Walter Brown and Marc Paterno Opened: 2002-05-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The destructor of ios_base::failure should have an empty throw -specification, because the destructor of its base class, exception, is -declared in this way. -

- - -

Proposed resolution:

-

Change the destructor to

-
-  virtual ~failure() throw();
-
- - -

Rationale:

-

Fixes an obvious glitch. This is almost editorial.

- - - - - -
-

364. Inconsistent wording in 27.5.2.4.2

-

Section: 27.6.3.4.2 [streambuf.virt.buffer] Status: CD1 - Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-27.6.3.4.2 [streambuf.virt.buffer] paragraph 1 is inconsistent with the Effects -clause for seekoff. -

- - -

Proposed resolution:

-

-Make this paragraph, the Effects clause for setbuf, consistent in wording -with the Effects clause for seekoff in paragraph 3 by amending paragraph 1 -to indicate the purpose of setbuf: -

- -

Original text:

- -

-1 Effects: Performs an operation that is defined separately for each -class derived from basic_streambuf in this clause (27.7.1.3, 27.8.1.4). -

- -

Proposed text:

- -

-1 Effects: Influences stream buffering in a way that is defined separately -for each class derived from basic_streambuf in this clause -(27.7.1.3, 27.8.1.4). -

- - - -

Rationale:

-

The LWG doesn't believe there is any normative difference between - the existing wording and what's in the proposed resolution, but the - change may make the intent clearer.

- - - - - -
-

365. Lack of const-qualification in clause 27

-

Section: 27 [input.output] Status: CD1 - Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Some stream and streambuf member functions are declared non-const, -even thought they appear only to report information rather than to -change an object's logical state. They should be declared const. See -document N1360 for details and rationale. -

- -

The list of member functions under discussion: in_avail, -showmanyc, tellg, tellp, is_open.

- -

Related issue: 73

- - - -

Proposed resolution:

-

In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13

-

Replace

-
-  bool is_open();
-
-

with

-
-  bool is_open() const;
-
- - -

Rationale:

-

Of the changes proposed in N1360, the only one that is safe is -changing the filestreams' is_open to const. The LWG believed that -this was NAD the first time it considered this issue (issue 73), but now thinks otherwise. The corresponding streambuf -member function, after all,is already const.

- -

The other proposed changes are less safe, because some streambuf -functions that appear merely to report a value do actually perform -mutating operations. It's not even clear that they should be -considered "logically const", because streambuf has two interfaces, a -public one and a protected one. These functions may, and often do, -change the state as exposed by the protected interface, even if the -state exposed by the public interface is unchanged.

- -

Note that implementers can make this change in a binary compatible -way by providing both overloads; this would be a conforming extension.

- - - - - - -
-

369. io stream objects and static ctors

-

Section: 27.4 [iostream.objects] Status: CD1 - Submitter: Ruslan Abdikeev Opened: 2002-07-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Is it safe to use standard iostream objects from constructors of -static objects? Are standard iostream objects constructed and are -their associations established at that time? -

- -

Surpisingly enough, Standard does NOT require that.

- -

-27.3/2 [lib.iostream.objects] guarantees that standard iostream -objects are constructed and their associations are established before -the body of main() begins execution. It also refers to ios_base::Init -class as the panacea for constructors of static objects. -

- -

-However, there's nothing in 27.3 [lib.iostream.objects], -in 27.4.2 [lib.ios.base], and in 27.4.2.1.6 [lib.ios::Init], -that would require implementations to allow access to standard -iostream objects from constructors of static objects. -

- -

Details:

- -

Core text refers to some magic object ios_base::Init, which will -be discussed below:

- -

- "The [standard iostream] objects are constructed, and their - associations are established at some time prior to or during - first time an object of class basic_ios<charT,traits>::Init - is constructed, and in any case before the body of main - begins execution." (27.3/2 [lib.iostream.objects]) -

- -

-The first non-normative footnote encourages implementations -to initialize standard iostream objects earlier than required. -

- -

However, the second non-normative footnote makes an explicit -and unsupported claim:

- -

- "Constructors and destructors for static objects can access these - [standard iostream] objects to read input from stdin or write output - to stdout or stderr." (27.3/2 footnote 265 [lib.iostream.objects]) -

- -

-The only bit of magic is related to that ios_base::Init class. AFAIK, -the rationale behind ios_base::Init was to bring an instance of this -class to each translation unit which #included <iostream> or -related header. Such an inclusion would support the claim of footnote -quoted above, because in order to use some standard iostream object it -is necessary to #include <iostream>. -

- -

-However, while Standard explicitly describes ios_base::Init as -an appropriate class for doing the trick, I failed to found a -mention of an _instance_ of ios_base::Init in Standard. -

- - -

Proposed resolution:

- -

Add to 27.4 [iostream.objects], p2, immediately before the last sentence -of the paragraph, the following two sentences:

- -

-If a translation unit includes <iostream>, or explicitly -constructs an ios_base::Init object, these stream objects shall -be constructed before dynamic initialization of non-local -objects defined later in that translation unit, and these stream -objects shall be destroyed after the destruction of dynamically -initialized non-local objects defined later in that translation unit. -

- -

[Lillehammer: Matt provided wording.]

- -

[Mont Tremblant: Matt provided revised wording.]

- - - -

Rationale:

-

-The original proposed resolution unconditionally required -implementations to define an ios_base::Init object of some -implementation-defined name in the header <iostream>. That's an -overspecification. First, defining the object may be unnecessary -and even detrimental to performance if an implementation can -guarantee that the 8 standard iostream objects will be initialized -before any other user-defined object in a program. Second, there -is no need to require implementations to document the name of the -object.

- -

-The new proposed resolution gives users guidance on what they need to -do to ensure that stream objects are constructed during startup.

- - - - - -
-

370. Minor error in basic_istream::get

-

Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Ray Lischner Opened: 2002-07-15 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Defect report for description of basic_istream::get (section 27.7.2.3 [istream.unformatted]), paragraph 15. The description for the get function -with the following signature:

- -
-  basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>&
-  sb);
-
- -

is incorrect. It reads

- -

- Effects: Calls get(s,n,widen('\n')) -

- -

which I believe should be:

- -

- Effects: Calls get(sb,widen('\n')) -

- - -

Proposed resolution:

-

Change the Effects paragraph to:

-

- Effects: Calls get(sb,this->widen('\n')) -

- -

[Pre-Oxford: Minor correction from Howard: replaced 'widen' - with 'this->widen'.]

- - - - -

Rationale:

Fixes an obvious typo.

- - - - -
-

371. Stability of multiset and multimap member functions

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Frank Compagner Opened: 2002-07-20 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The requirements for multiset and multimap containers (23.1 -[lib.containers.requirements], 23.1.2 [lib.associative.reqmnts], -23.3.2 [lib.multimap] and 23.3.4 [lib.multiset]) make no mention of -the stability of the required (mutating) member functions. It appears -the standard allows these functions to reorder equivalent elements of -the container at will, yet the pervasive red-black tree implementation -appears to provide stable behaviour. -

- -

This is of most concern when considering the behaviour of erase(). -A stability requirement would guarantee the correct working of the -following 'idiom' that removes elements based on a certain predicate -function. -

- -
-  multimap<int, int> m;
-  multimap<int, int>::iterator i = m.begin();
-  while (i != m.end()) {
-      if (pred(i))
-          m.erase (i++);
-      else
-          ++i;
-  }
-
- -

-Although clause 23.1.2/8 guarantees that i remains a valid iterator -througout this loop, absence of the stability requirement could -potentially result in elements being skipped. This would make -this code incorrect, and, furthermore, means that there is no way -of erasing these elements without iterating first over the entire -container, and second over the elements to be erased. This would -be unfortunate, and have a negative impact on both performance and -code simplicity. -

- -

-If the stability requirement is intended, it should be made explicit -(probably through an extra paragraph in clause 23.1.2). -

-

-If it turns out stability cannot be guaranteed, i'd argue that a -remark or footnote is called for (also somewhere in clause 23.1.2) to -warn against relying on stable behaviour (as demonstrated by the code -above). If most implementations will display stable behaviour, any -problems emerging on an implementation without stable behaviour will -be hard to track down by users. This would also make the need for an -erase_if() member function that much greater. -

- -

This issue is somewhat related to LWG issue 130.

- - - -

Proposed resolution:

- -

Add the following to the end of 23.2.4 [associative.reqmts] paragraph 4: -"For multiset and multimap, insertand erase - are stable: they preserve the relative ordering of equivalent - elements.

- -

[Lillehammer: Matt provided wording]

- -

[Joe Gottman points out that the provided wording does not address -multimap and multiset. N1780 also addresses this issue and suggests -wording.]

- - -

[Mont Tremblant: Changed set and map to multiset and multimap.]

- - - - -

Rationale:

-

The LWG agrees that this guarantee is necessary for common user - idioms to work, and that all existing implementations provide this - property. Note that this resolution guarantees stability for - multimap and multiset, not for all associative containers in - general.

- - - - - - -
-

373. Are basic_istream and basic_ostream to use (exceptions()&badbit) != 0 ?

-

Section: 27.7.2.2.1 [istream.formatted.reqmts], 27.7.3.6.1 [ostream.formatted.reqmts] Status: CD1 - Submitter: Keith Baker Opened: 2002-07-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-In 27.7.2.2.1 [istream.formatted.reqmts] and 27.7.3.6.1 [ostream.formatted.reqmts] -(exception()&badbit) != 0 is used in testing for rethrow, yet -exception() is the constructor to class std::exception in 18.7.1 [type.info] that has no return type. Should member function -exceptions() found in 27.5.5 [ios] be used instead? -

- - - -

Proposed resolution:

-

-In 27.7.2.2.1 [istream.formatted.reqmts] and 27.7.3.6.1 [ostream.formatted.reqmts], change -"(exception()&badbit) != 0" to "(exceptions()&badbit) != 0". -

- - -

Rationale:

-

Fixes an obvious typo.

- - - - - -
-

375. basic_ios should be ios_base in 27.7.1.3

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: CD1 - Submitter: Ray Lischner Opened: 2002-08-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In Section 27.8.2.4 [stringbuf.virtuals]: Table 90, Table 91, and paragraph -14 all contain references to "basic_ios::" which should be -"ios_base::". -

- - -

Proposed resolution:

-

-Change all references to "basic_ios" in Table 90, Table 91, and -paragraph 14 to "ios_base". -

- - -

Rationale:

Fixes an obvious typo.

- - - - -
-

376. basic_streambuf semantics

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: CD1 - Submitter: Ray Lischner Opened: 2002-08-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In Section 27.8.2.4 [stringbuf.virtuals], Table 90, the implication is that -the four conditions should be mutually exclusive, but they are not. -The first two cases, as written, are subcases of the third.

- -

-As written, it is unclear what should be the result if cases 1 and 2 -are both true, but case 3 is false. -

- - - -

Proposed resolution:

- -

Rewrite these conditions as:

-
-

- (which & (ios_base::in|ios_base::out)) == ios_base::in -

- -

- (which & (ios_base::in|ios_base::out)) == ios_base::out -

- -

- (which & (ios_base::in|ios_base::out)) == -(ios_base::in|ios_base::out) - and way == either ios_base::beg or ios_base::end -

- -

Otherwise

-
- - - -

Rationale:

-

It's clear what we wanted to say, we just failed to say it. This - fixes it.

- - - - - -
-

379. nonsensical ctype::do_widen() requirement

-

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: CD1 - Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The last sentence in 22.2.1.1.2, p11 below doesn't seem to make sense. -

-
-  charT do_widen (char c) const;
-
-  -11- Effects: Applies the simplest reasonable transformation from
-       a char value or sequence of char values to the corresponding
-       charT value or values. The only characters for which unique
-       transformations are required are those in the basic source
-       character set (2.2). For any named ctype category with a
-       ctype<charT> facet ctw and valid ctype_base::mask value
-       M (is(M, c) || !ctw.is(M, do_widen(c))) is true.
-
-

-Shouldn't the last sentence instead read -

-
-       For any named ctype category with a ctype<char> facet ctc
-       and valid ctype_base::mask value M
-       (ctc.is(M, c) || !is(M, do_widen(c))) is true.
-
-

-I.e., if the narrow character c is not a member of a class of -characters then neither is the widened form of c. (To paraphrase -footnote 224.) -

- - -

Proposed resolution:

-

-Replace the last sentence of 22.4.1.1.2 [locale.ctype.virtuals], p11 with the -following text: -

-
-       For any named ctype category with a ctype<char> facet ctc
-       and valid ctype_base::mask value M,
-       (ctc.is(M, c) || !is(M, do_widen(c))) is true.
-
- -

[Kona: Minor edit. Added a comma after the M for clarity.]

- - - - -

Rationale:

-

The LWG believes this is just a typo, and that this is the correct fix.

- - - - - -
-

380. typos in codecvt tables 53 and 54

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 - Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Tables 53 and 54 in 22.4.1.5 [locale.codecvt.byname] are both titled "convert -result values," when surely "do_in/do_out result values" must have -been intended for Table 53 and "do_unshift result values" for Table -54. -

-

-Table 54, row 3 says that the meaning of partial is "more characters -needed to be supplied to complete termination." The function is not -supplied any characters, it is given a buffer which it fills with -characters or, more precisely, destination elements (i.e., an escape -sequence). So partial means that space for more than (to_limit - to) -destination elements was needed to terminate a sequence given the -value of state. -

- - -

Proposed resolution:

-

-Change the title of Table 53 to "do_in/do_out result values" and -the title of Table 54 to "do_unshift result values." -

-

-Change the text in Table 54, row 3 (the partial row), under the -heading Meaning, to "space for more than (to_limit - to) destination -elements was needed to terminate a sequence given the value of state." -

- - - - -
-

381. detection of invalid mbstate_t in codecvt

-

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 - Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-All but one codecvt member functions that take a state_type argument -list as one of their preconditions that the state_type argument have -a valid value. However, according to 22.2.1.5.2, p6, -codecvt::do_unshift() is the only codecvt member that is supposed to -return error if the state_type object is invalid. -

- -

-It seems to me that the treatment of state_type by all codecvt member -functions should be the same and the current requirements should be -changed. Since the detection of invalid state_type values may be -difficult in general or computationally expensive in some specific -cases, I propose the following: -

- - -

Proposed resolution:

-

-Add a new paragraph before 22.2.1.5.2, p5, and after the function -declaration below -

-
-    result do_unshift(stateT& state,
-    externT* to, externT* to_limit, externT*& to_next) const;
-
-

-as follows: -

-
-    Requires: (to <= to_end) well defined and true; state initialized,
-    if at the beginning of a sequence, or else equal to the result of
-    converting the preceding characters in the sequence.
-
-

-and change the text in Table 54, row 4, the error row, under -the heading Meaning, from -

-
-    state has invalid value
-
-

-to -

-
-    an unspecified error has occurred
-
- - -

Rationale:

-

The intent is that implementations should not be required to detect -invalid state values; such a requirement appears nowhere else. An -invalid state value is a precondition violation, i.e. undefined -behavior. Implementations that do choose to detect invalid state -values, or that choose to detect any other kind of error, may return -error as an indication.

- - - - - -
-

383. Bidirectional iterator assertion typo

-

Section: 24.2.6 [bidirectional.iterators] Status: CD1 - Submitter: ysapir (submitted via comp.std.c++) Opened: 2002-10-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Following a discussion on the boost list regarding end iterators and -the possibility of performing operator--() on them, it seems to me -that there is a typo in the standard. This typo has nothing to do -with that discussion. -

- -

-I have checked this newsgroup, as well as attempted a search of the -Active/Defect/Closed Issues List on the site for the words "s is -derefer" so I believe this has not been proposed before. Furthermore, -the "Lists by Index" mentions only DR 299 on section -24.1.4, and DR 299 is not related to this issue. -

- -

-The standard makes the following assertion on bidirectional iterators, -in section 24.1.4 [lib.bidirectional.iterators], Table 75: -

- -
-                         operational  assertion/note
-expression  return type   semantics    pre/post-condition
-
---r          X&                        pre: there exists s such
-                                       that r == ++s.
-                                       post: s is dereferenceable.
-                                       --(++r) == r.
-                                       --r == --s implies r == s.
-                                       &r == &--r.
-
- -

-(See http://lists.boost.org/Archives/boost/2002/10/37636.php.) -

- -

-In particular, "s is dereferenceable" seems to be in error. It seems -that the intention was to say "r is dereferenceable". -

- -

-If it were to say "r is dereferenceable" it would -make perfect sense. Since s must be dereferenceable prior to -operator++, then the natural result of operator-- (to undo operator++) -would be to make r dereferenceable. Furthermore, without other -assertions, and basing only on precondition and postconditions, we -could not otherwise know this. So it is also interesting information. -

- - - -

Proposed resolution:

-

-Change the guarantee to "postcondition: r is dereferenceable." -

- - -

Rationale:

Fixes an obvious typo

- - - - -
-

384. equal_range has unimplementable runtime complexity

-

Section: 25.4.3.3 [equal.range] Status: CD1 - Submitter: Hans Bos Opened: 2002-10-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 25.4.3.3 [equal.range] -states that at most 2 * log(last - first) + 1 -comparisons are allowed for equal_range. -

- -

It is not possible to implement equal_range with these constraints.

- -

In a range of one element as in:

-
-    int x = 1;
-    equal_range(&x, &x + 1, 1)
-
- -

it is easy to see that at least 2 comparison operations are needed.

- -

For this case at most 2 * log(1) + 1 = 1 comparison is allowed.

- -

I have checked a few libraries and they all use the same (nonconforming) -algorithm for equal_range that has a complexity of

-
-     2* log(distance(first, last)) + 2.
-
-

I guess this is the algorithm that the standard assumes for equal_range.

- -

-It is easy to see that 2 * log(distance) + 2 comparisons are enough -since equal range can be implemented with lower_bound and upper_bound -(both log(distance) + 1). -

- -

-I think it is better to require something like 2log(distance) + O(1) (or -even logarithmic as multiset::equal_range). -Then an implementation has more room to optimize for certain cases (e.g. -have log(distance) characteristics when at most match is found in the range -but 2log(distance) + 4 for the worst case). -

- - - -

Proposed resolution:

-

In 25.4.3.1 [lower.bound]/4, change log(last - first) + 1 -to log2(last - first) + O(1).

- -

In 25.4.3.2 [upper.bound]/4, change log(last - first) + 1 -to log2(last - first) + O(1).

- -

In 25.4.3.3 [equal.range]/4, change 2*log(last - first) + 1 -to 2*log2(last - first) + O(1).

- -

[Matt provided wording]

- - - -

Rationale:

-

The LWG considered just saying O(log n) for all three, but - decided that threw away too much valuable information. The fact - that lower_bound is twice as fast as equal_range is important. - However, it's better to allow an arbitrary additive constant than to - specify an exact count. An exact count would have to - involve floor or ceil. It would be too easy to - get this wrong, and don't provide any substantial value for users.

- - - - -
-

386. Reverse iterator's operator[] has impossible return type

-

Section: 24.5.1.3.11 [reverse.iter.op-=] Status: CD1 - Submitter: Matt Austern Opened: 2002-10-23 Last modified: 2015-04-08

-

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-

Discussion:

-

In 24.5.1.3.11 [reverse.iter.op-=], reverse_iterator<>::operator[] -is specified as having a return type of reverse_iterator::reference, -which is the same as iterator_traits<Iterator>::reference. -(Where Iterator is the underlying iterator type.)

- -

The trouble is that Iterator's own operator[] doesn't - necessarily have a return type - of iterator_traits<Iterator>::reference. Its - return type is merely required to be convertible - to Iterator's value type. The return type specified for - reverse_iterator's operator[] would thus appear to be impossible.

- -

With the resolution of issue 299, the type of - a[n] will continue to be required (for random access - iterators) to be convertible to the value type, and also a[n] = - t will be a valid expression. Implementations of - reverse_iterator will likely need to return a proxy from - operator[] to meet these requirements. As mentioned in the - comment from Dave Abrahams, the simplest way to specify that - reverse_iterator meet this requirement to just mandate - it and leave the return type of operator[] unspecified.

- - - -

Proposed resolution:

- -

In 24.5.1.2 [reverse.iter.requirements] change:

- -
-
-reference operator[](difference_type n) const;
-
-
- -

to:

- -
-
-unspecified operator[](difference_type n) const; // see 24.2.7 [random.access.iterators]
-
-
- - - - -

[ -Comments from Dave Abrahams: IMO we should resolve 386 by just saying - that the return type of reverse_iterator's operator[] is - unspecified, allowing the random access iterator requirements to - impose an appropriate return type. If we accept 299's proposed - resolution (and I think we should), the return type will be - readable and writable, which is about as good as we can do. -]

- - - - - - -
-

387. std::complex over-encapsulated

-

Section: 26.4 [complex.numbers] Status: CD1 - Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The absence of explicit description of std::complex<T> layout -makes it imposible to reuse existing software developed in traditional -languages like Fortran or C with unambigous and commonly accepted -layout assumptions. There ought to be a way for practitioners to -predict with confidence the layout of std::complex<T> whenever T -is a numerical datatype. The absence of ways to access individual -parts of a std::complex<T> object as lvalues unduly promotes -severe pessimizations. For example, the only way to change, -independently, the real and imaginary parts is to write something like -

- -
-complex<T> z;
-// ...
-// set the real part to r
-z = complex<T>(r, z.imag());
-// ...
-// set the imaginary part to i
-z = complex<T>(z.real(), i);
-
- -

-At this point, it seems appropriate to recall that a complex number -is, in effect, just a pair of numbers with no particular invariant to -maintain. Existing practice in numerical computations has it that a -complex number datatype is usually represented by Cartesian -coordinates. Therefore the over-encapsulation put in the specification -of std::complex<> is not justified. -

- - - -

Proposed resolution:

-

Add the following requirements to 26.4 [complex.numbers] as 26.3/4:

-
-

If z is an lvalue expression of type cv std::complex<T> then

- -
    -
  • the expression reinterpret_cast<cv T(&)[2]>(z) -is well-formed; and
    • -
  • reinterpret_cast<cv T(&)[2]>(z)[0] designates the -real part of z; and
    • -
  • reinterpret_cast<cv T(&)[2]>(z)[1] designates the -imaginary part of z.
    • -
- -

-Moreover, if a is an expression of pointer type cv complex<T>* -and the expression a[i] is well-defined for an integer expression -i then: -

- -
    -
  • reinterpret_cast<cv T*>(a)[2*i] designates the real -part of a[i]; and
    • -
  • reinterpret_cast<cv T*>(a)[2*i+1] designates the -imaginary part of a[i].
    • -
-
- -

-In 26.4.2 [complex] and 26.4.3 [complex.special] add the following member functions -(changing T to concrete types as appropriate for the specializations). -

- -
-void real(T);
-void imag(T);
-
- -

-Add to 26.4.4 [complex.members] -

- -
-
-T real() const;
-
-

-Returns: the value of the real component -

-
-void real(T val);
-
-

-Assigns val to the real component. -

-
-T imag() const;
-
-

-Returns: the value of the imaginary component -

-
-void imag(T val);
-
-

-Assigns val to the imaginary component. -

-
- -

[Kona: The layout guarantee is absolutely necessary for C - compatibility. However, there was disagreement about the other part - of this proposal: retrieving elements of the complex number as - lvalues. An alternative: continue to have real() and imag() return - rvalues, but add set_real() and set_imag(). Straw poll: return - lvalues - 2, add setter functions - 5. Related issue: do we want - reinterpret_cast as the interface for converting a complex to an - array of two reals, or do we want to provide a more explicit way of - doing it? Howard will try to resolve this issue for the next - meeting.]

- - -

[pre-Sydney: Howard summarized the options in n1589.]

- - -

[ -Bellevue: -]

- - -

-Second half of proposed wording replaced and moved to Ready. -

- -

[ -Pre-Sophia Antipolis, Howard adds: -]

- - -

-Added the members to 26.4.3 [complex.special] and changed from Ready to Review. -

- -

[ -Post-Sophia Antipolis: -]

- - -

-Moved from WP back to Ready so that the "and 26.4.3 [complex.special]" in the proposed -resolution can be officially applied. -

- - - -

Rationale:

-

The LWG believes that C99 compatibility would be enough -justification for this change even without other considerations. All -existing implementations already have the layout proposed here.

- - - - - -
-

389. Const overload of valarray::operator[] returns by value

-

Section: 26.6.2.4 [valarray.access] Status: CD1 - Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2015-04-08

-

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-

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-

Duplicate of: 77

-

Discussion:

-

Consider the following program:

-
-    #include <iostream>
-    #include <ostream>
-    #include <vector>
-    #include <valarray>
-    #include <algorithm>
-    #include <iterator>
-    template<typename Array>
-    void print(const Array& a)
-    {
-    using namespace std;
-    typedef typename Array::value_type T;
-    copy(&a[0], &a[0] + a.size(),
-    ostream_iterator<T>(std::cout, " "));
-    }
-    template<typename T, unsigned N>
-    unsigned size(T(&)[N]) { return N; }
-    int main()
-    {
-    double array[] = { 0.89, 9.3, 7, 6.23 };
-    std::vector<double> v(array, array + size(array));
-    std::valarray<double> w(array, size(array));
-    print(v); // #1
-    std::cout << std::endl;
-    print(w); // #2
-    std::cout << std::endl;
-    }
-
- -

While the call numbered #1 succeeds, the call numbered #2 fails -because the const version of the member function -valarray<T>::operator[](size_t) returns a value instead of a -const-reference. That seems to be so for no apparent reason, no -benefit. Not only does that defeats users' expectation but it also -does hinder existing software (written either in C or Fortran) -integration within programs written in C++. There is no reason why -subscripting an expression of type valarray<T> that is const-qualified -should not return a const T&.

- - -

Proposed resolution:

-

In the class synopsis in 26.6.2 [template.valarray], and in -26.6.2.4 [valarray.access] just above paragraph 1, change

-
-  T operator[](size_t const);
-
-

to

-
-  const T& operator[](size_t const);
-
- -

[Kona: fixed a minor typo: put semicolon at the end of the line - wehre it belongs.]

- - - - -

Rationale:

-

Return by value seems to serve no purpose. Valaray was explicitly -designed to have a specified layout so that it could easily be -integrated with libraries in other languages, and return by value -defeats that purpose. It is believed that this change will have no -impact on allowable optimizations.

- - - - - -
-

391. non-member functions specified as const

-

Section: 22.3.3.2 [conversions] Status: CD1 - Submitter: James Kanze Opened: 2002-12-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-The specifications of toupper and tolower both specify the functions as -const, althought they are not member functions, and are not specified as -const in the header file synopsis in section 22.3 [locales]. -

- - -

Proposed resolution:

-

In 22.3.3.2 [conversions], remove const from the function - declarations of std::toupper and std::tolower

- - -

Rationale:

Fixes an obvious typo

- - - - -
-

395. inconsistencies in the definitions of rand() and random_shuffle()

-

Section: 26.8 [c.math] Status: CD1 - Submitter: James Kanze Opened: 2003-01-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In 26.8 [c.math], the C++ standard refers to the C standard for the -definition of rand(); in the C standard, it is written that "The -implementation shall behave as if no library function calls the rand -function." -

- -

-In 25.3.12 [alg.random.shuffle], there is no specification as to -how the two parameter version of the function generates its random -value. I believe that all current implementations in fact call rand() -(in contradiction with the requirement avove); if an implementation does -not call rand(), there is the question of how whatever random generator -it does use is seeded. Something is missing. -

- - - -

Proposed resolution:

-

-In [lib.c.math], add a paragraph specifying that the C definition of -rand shal be modified to say that "Unless otherwise specified, the -implementation shall behave as if no library function calls the rand -function." -

- -

-In [lib.alg.random.shuffle], add a sentence to the effect that "In -the two argument form of the function, the underlying source of -random numbers is implementation defined. [Note: in particular, an -implementation is permitted to use rand.] -

- - -

Rationale:

-

The original proposed resolution proposed requiring the - two-argument from of random_shuffle to - use rand. We don't want to do that, because some existing - implementations already use something else: gcc - uses lrand48, for example. Using rand presents a - problem if the number of elements in the sequence is greater than - RAND_MAX.

- - - - - -
-

396. what are characters zero and one

-

Section: 20.6.1 [bitset.cons] Status: CD1 - Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-23.3.5.1, p6 [lib.bitset.cons] talks about a generic character -having the value of 0 or 1 but there is no definition of what -that means for charT other than char and wchar_t. And even for -those two types, the values 0 and 1 are not actually what is -intended -- the values '0' and '1' are. This, along with the -converse problem in the description of to_string() in 23.3.5.2, -p33, looks like a defect remotely related to DR 303. -

-

-http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#303 -

- 
-23.3.5.1:
-  -6-  An element of the constructed string has value zero if the
-       corresponding character in str, beginning at position pos,
-       is 0. Otherwise, the element has the value one.
-
- 
-23.3.5.2:
-  -33-  Effects: Constructs a string object of the appropriate
-        type and initializes it to a string of length N characters.
-        Each character is determined by the value of its
-        corresponding bit position in *this. Character position N
-        ?- 1 corresponds to bit position zero. Subsequent decreasing
-        character positions correspond to increasing bit positions.
-        Bit value zero becomes the character 0, bit value one becomes
-        the character 1.
-
-

-Also note the typo in 23.3.5.1, p6: the object under construction -is a bitset, not a string. -

- -

[ -Sophia Antipolis: -]

- - -
-

-We note that bitset has been moved from section 23 to section 20, by -another issue (842) previously resolved at this meeting. -

-

-Disposition: move to ready. -

-

-We request that Howard submit a separate issue regarding the three to_string overloads. -

-
- - - -

Proposed resolution:

-

Change the constructor's function declaration immediately before -20.6.1 [bitset.cons] p3 to:

-
-    template <class charT, class traits, class Allocator>
-    explicit
-    bitset(const basic_string<charT, traits, Allocator>& str,
-           typename basic_string<charT, traits, Allocator>::size_type pos = 0,
-           typename basic_string<charT, traits, Allocator>::size_type n =
-             basic_string<charT, traits, Allocator>::npos,
-           charT zero = charT('0'), charT one = charT('1'))
-
-

Change the first two sentences of 20.6.1 [bitset.cons] p6 to: "An -element of the constructed string has value 0 if the corresponding -character in str, beginning at position pos, -is zero. Otherwise, the element has the value 1.

- -

Change the text of the second sentence in 23.3.5.1, p5 to read: - "The function then throws invalid_argument if any of the rlen - characters in str beginning at position pos is other than zero - or one. The function uses traits::eq() to compare the character - values." -

- -

Change the declaration of the to_string member function - immediately before 20.6.2 [bitset.members] p33 to:

-
-    template <class charT, class traits, class Allocator>
-    basic_string<charT, traits, Allocator> 
-    to_string(charT zero = charT('0'), charT one = charT('1')) const;
-
-

Change the last sentence of 20.6.2 [bitset.members] p33 to: "Bit - value 0 becomes the character zero, bit value 1 becomes the - character one.

-

Change 20.6.4 [bitset.operators] p8 to:

-

Returns:

-
-  os << x.template to_string<charT,traits,allocator<charT> >(
-      use_facet<ctype<charT> >(os.getloc()).widen('0'),
-      use_facet<ctype<charT> >(os.getloc()).widen('1'));
-
- - -

Rationale:

-

There is a real problem here: we need the character values of '0' - and '1', and we have no way to get them since strings don't have - imbued locales. In principle the "right" solution would be to - provide an extra object, either a ctype facet or a full locale, - which would be used to widen '0' and '1'. However, there was some - discomfort about using such a heavyweight mechanism. The proposed - resolution allows those users who care about this issue to get it - right.

-

We fix the inserter to use the new arguments. Note that we already - fixed the analogous problem with the extractor in issue 303.

- - - -

[ -post Bellevue: -]

- - -

-We are happy with the resolution as proposed, and we move this to Ready. -

- -

[ -Howard adds: -]

- - -

-The proposed wording neglects the 3 newer to_string overloads. -

- - - - -
-

400. redundant type cast in lib.allocator.members

-

Section: 20.7.9.1 [allocator.members] Status: CD1 - Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-20.7.9.1 [allocator.members] allocator members, contains -the following 3 lines: -

- -
-  12 Returns: new((void *) p) T( val)
-     void destroy(pointer p);
-  13 Returns: ((T*) p)->~T()
-
- -

-The type cast "(T*) p" in the last line is redundant cause -we know that std::allocator<T>::pointer is a typedef for T*. -

- - -

Proposed resolution:

-

-Replace "((T*) p)" with "p". -

- - -

Rationale:

Just a typo, this is really editorial.

- - - - -
-

401. incorrect type casts in table 32 in lib.allocator.requirements

-

Section: 17.6.3.5 [allocator.requirements] Status: CD1 - Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-I think that in par2 of [default.con.req] the last two -lines of table 32 contain two incorrect type casts. The lines are ... -

- -
-  a.construct(p,t)   Effect: new((void*)p) T(t)
-  a.destroy(p)       Effect: ((T*)p)?->~T()
-
- -

-.... with the prerequisits coming from the preceding two paragraphs, especially -from table 31: -

- -
-  alloc<T>             a     ;// an allocator for T
-  alloc<T>::pointer    p     ;// random access iterator
-                              // (may be different from T*)
-  alloc<T>::reference  r = *p;// T&
-  T const&             t     ;
-
- -

-For that two type casts ("(void*)p" and "(T*)p") to be well-formed -this would require then conversions to T* and void* for all -alloc<T>::pointer, so it would implicitely introduce extra -requirements for alloc<T>::pointer, additionally to the only -current requirement (being a random access iterator). -

- - -

Proposed resolution:

- -

-Accept proposed wording from -N2436 part 1. -

- -

-Note: Actually I would prefer to replace "((T*)p)?->dtor_name" with -"p?->dtor_name", but AFAICS this is not possible cause of an omission -in 13.5.6 [over.ref] (for which I have filed another DR on 29.11.2002). -

- -

[Kona: The LWG thinks this is somewhere on the border between - Open and NAD. The intend is clear: construct constructs an - object at the location p. It's reading too much into the - description to think that literally calling new is - required. Tweaking this description is low priority until we can do - a thorough review of allocators, and, in particular, allocators with - non-default pointer types.]

- - -

[ -Batavia: Proposed resolution changed to less code and more description. -]

- - -

[ -post Oxford: This would be rendered NAD Editorial by acceptance of -N2257. -]

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which -was subsequently split out into a separate paper N2436 for the purposes of voting. -The resolution in N2436 addresses this issue. The LWG voted to accelerate this -issue to Ready status to be voted into the WP at Kona. -]

- - - - - - - -
-

402. wrong new expression in [some_]allocator::construct

-

Section: 17.6.3.5 [allocator.requirements], 20.7.9.1 [allocator.members] Status: CD1 - Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-This applies to the new expression that is contained in both par12 of -20.7.9.1 [allocator.members] and in par2 (table 32) of [default.con.req]. -I think this new expression is wrong, involving unintended side -effects. -

- - -

20.7.9.1 [allocator.members] contains the following 3 lines:

- -
-  11 Returns: the largest value N for which the call allocate(N,0) might succeed.
-     void construct(pointer p, const_reference val);
-  12 Returns: new((void *) p) T( val)
-
- - -

[default.con.req] in table 32 has the following line:

-
-  a.construct(p,t)   Effect: new((void*)p) T(t)
-
- -

-.... with the prerequisits coming from the preceding two paragraphs, -especially from table 31: -

- -
-  alloc<T>             a     ;// an allocator for T
-  alloc<T>::pointer    p     ;// random access iterator
-                              // (may be different from T*)
-  alloc<T>::reference  r = *p;// T&
-  T const&             t     ;
-
- -

-Cause of using "new" but not "::new", any existing "T::operator new" -function will hide the global placement new function. When there is no -"T::operator new" with adequate signature, -every_alloc<T>::construct(..) is ill-formed, and most -std::container<T,every_alloc<T>> use it; a workaround -would be adding placement new and delete functions with adequate -signature and semantic to class T, but class T might come from another -party. Maybe even worse is the case when T has placement new and -delete functions with adequate signature but with "unknown" semantic: -I dont like to speculate about it, but whoever implements -any_container<T,any_alloc> and wants to use construct(..) -probably must think about it. -

- - -

Proposed resolution:

-

-Replace "new" with "::new" in both cases. -

- - - - - - - -
-

403. basic_string::swap should not throw exceptions

-

Section: 21.4.6.8 [string::swap] Status: CD1 - Submitter: Beman Dawes Opened: 2003-03-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-std::basic_string, 21.4 [basic.string] paragraph 2 says that -basic_string "conforms to the requirements of a Sequence, as specified -in (23.1.1)." The sequence requirements specified in (23.1.1) to not -include any prohibition on swap members throwing exceptions. -

- -

-Section 23.2 [container.requirements] paragraph 10 does limit conditions under -which exceptions may be thrown, but applies only to "all container -types defined in this clause" and so excludes basic_string::swap -because it is defined elsewhere. -

- -

-Eric Niebler points out that 21.4 [basic.string] paragraph 5 explicitly -permits basic_string::swap to invalidates iterators, which is -disallowed by 23.2 [container.requirements] paragraph 10. Thus the standard would -be contradictory if it were read or extended to read as having -basic_string meet 23.2 [container.requirements] paragraph 10 requirements. -

- -

-Yet several LWG members have expressed the belief that the original -intent was that basic_string::swap should not throw exceptions as -specified by 23.2 [container.requirements] paragraph 10, and that the standard is -unclear on this issue. The complexity of basic_string::swap is -specified as "constant time", indicating the intent was to avoid -copying (which could cause a bad_alloc or other exception). An -important use of swap is to ensure that exceptions are not thrown in -exception-safe code. -

- -

-Note: There remains long standing concern over whether or not it is -possible to reasonably meet the 23.2 [container.requirements] paragraph 10 swap -requirements when allocators are unequal. The specification of -basic_string::swap exception requirements is in no way intended to -address, prejudice, or otherwise impact that concern. -

- - - - - - - -

Proposed resolution:

-

-In 21.4.6.8 [string::swap], add a throws clause: -

- -

-Throws: Shall not throw exceptions. -

- - - - - -
-

404. May a replacement allocation function be declared inline?

-

Section: 17.6.4.6 [replacement.functions], 18.6.1 [new.delete] Status: CD1 - Submitter: Matt Austern Opened: 2003-04-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The eight basic dynamic memory allocation functions (single-object -and array versions of ::operator new and ::operator delete, in the -ordinary and nothrow forms) are replaceable. A C++ program may -provide an alternative definition for any of them, which will be used -in preference to the implementation's definition. -

- -

-Three different parts of the standard mention requirements on -replacement functions: 17.6.4.6 [replacement.functions], 18.6.1.1 [new.delete.single] -and 18.6.1.2 [new.delete.array], and 3.7.3 [basic.stc.auto]. -

- -

None of these three places say whether a replacement function may - be declared inline. 18.6.1.1 [new.delete.single] paragraph 2 specifies a - signature for the replacement function, but that's not enough: - the inline specifier is not part of a function's signature. - One might also reason from 7.1.2 [dcl.fct.spec] paragraph 2, which - requires that "an inline function shall be defined in every - translation unit in which it is used," but this may not be quite - specific enough either. We should either explicitly allow or - explicitly forbid inline replacement memory allocation - functions.

- - -

Proposed resolution:

-

-Add a new sentence to the end of 17.6.4.6 [replacement.functions] paragraph 3: -"The program's definitions shall not be specified as inline. -No diagnostic is required." -

- -

[Kona: added "no diagnostic is required"]

- - - - -

Rationale:

-

-The fact that inline isn't mentioned appears to have been -nothing more than an oversight. Existing implementations do not -permit inline functions as replacement memory allocation functions. -Providing this functionality would be difficult in some cases, and is -believed to be of limited value. -

- - - - - -
-

405. qsort and POD

-

Section: 25.5 [alg.c.library] Status: CD1 - Submitter: Ray Lischner Opened: 2003-04-08 Last modified: 2015-04-08

-

View all other issues in [alg.c.library].

-

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-

Discussion:

-

-Section 25.5 [alg.c.library] describes bsearch and qsort, from the C -standard library. Paragraph 4 does not list any restrictions on qsort, -but it should limit the base parameter to point to POD. Presumably, -qsort sorts the array by copying bytes, which requires POD. -

- - -

Proposed resolution:

-

-In 25.5 [alg.c.library] paragraph 4, just after the declarations and -before the nonnormative note, add these words: "both of which have the -same behavior as the original declaration. The behavior is undefined -unless the objects in the array pointed to by base are of POD -type." -

- -

[Something along these lines is clearly necessary. Matt - provided wording.]

- - - - - - -
-

406. vector::insert(s) exception safety

-

Section: 23.3.6.5 [vector.modifiers] Status: CD1 - Submitter: Dave Abrahams Opened: 2003-04-27 Last modified: 2015-04-08

-

View other active issues in [vector.modifiers].

-

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-

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-

Discussion:

-

-There is a possible defect in the standard: the standard text was -never intended to prevent arbitrary ForwardIterators, whose operations -may throw exceptions, from being passed, and it also wasn't intended -to require a temporary buffer in the case where ForwardIterators were -passed (and I think most implementations don't use one). As is, the -standard appears to impose requirements that aren't met by any -existing implementation. -

- - -

Proposed resolution:

-

Replace 23.3.6.5 [vector.modifiers] paragraph 1 with:

-

- 1- Notes: Causes reallocation if the new size is greater than the - old capacity. If no reallocation happens, all the iterators and - references before the insertion point remain valid. If an exception - is thrown other than by the copy constructor or assignment operator - of T or by any InputIterator operation there are no effects. -

- -

[We probably need to say something similar for deque.]

- - - - - - - -
-

407. Can singular iterators be destroyed?

-

Section: X [iterator.concepts] Status: CD1 - Submitter: Nathan Myers Opened: 2003-06-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Clause X [iterator.concepts], paragraph 5, says that the only expression -that is defined for a singular iterator is "an assignment of a -non-singular value to an iterator that holds a singular value". This -means that destroying a singular iterator (e.g. letting an automatic -variable go out of scope) is technically undefined behavior. This -seems overly strict, and probably unintentional. -

- - -

Proposed resolution:

-

-Change the sentence in question to "... the only exceptions are -destroying an iterator that holds a singular value, or the assignment -of a non-singular value to an iterator that holds a singular value." -

- - - - - -
-

409. Closing an fstream should clear error state

-

Section: 27.9.1.9 [ifstream.members], 27.9.1.13 [ofstream.members] Status: CD1 - Submitter: Nathan Myers Opened: 2003-06-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-A strict reading of 27.9.1 [fstreams] shows that opening or -closing a basic_[io]fstream does not affect the error bits. This -means, for example, that if you read through a file up to EOF, and -then close the stream and reopen it at the beginning of the file, -the EOF bit in the stream's error state is still set. This is -counterintuitive. -

-

-The LWG considered this issue once before, as issue 22, -and put in a footnote to clarify that the strict reading was indeed -correct. We did that because we believed the standard was -unambiguous and consistent, and that we should not make architectural -changes in a TC. Now that we're working on a new revision of the -language, those considerations no longer apply. -

- - -

Proposed resolution:

- -

Change 27.9.1.9 [ifstream.members], para. 3 from:

- -

-Calls rdbuf()->open(s,mode|in). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)]. -

- -

to:

- -

-Calls rdbuf()->open(s,mode|in). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)), else calls clear(). -

- -

Change 27.9.1.13 [ofstream.members], para. 3 from:

- -

-Calls rdbuf()->open(s,mode|out). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)). -

- -

to:

- -

-Calls rdbuf()->open(s,mode|out). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)), else calls clear(). -

- -

Change 27.9.1.17 [fstream.members], para. 3 from:

- -

-Calls rdbuf()->open(s,mode), If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::failure). (lib.iostate.flags) ) -

- -

to:

- -

-Calls rdbuf()->open(s,mode), If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::failure). (lib.iostate.flags) ), else calls clear(). -

- - - -

[Kona: the LWG agrees this is a good idea. Post-Kona: Bill -provided wording. He suggests having open, not close, clear the error -flags.]

- - -

[Post-Sydney: Howard provided a new proposed resolution. The - old one didn't make sense because it proposed to fix this at the - level of basic_filebuf, which doesn't have access to the stream's - error state. Howard's proposed resolution fixes this at the level - of the three fstream class template instead.]

- - - - - - - - -
-

410. Missing semantics for stack and queue comparison operators

-

Section: 23.3.5.2 [list.cons], 23.3.5.4 [list.modifiers] Status: CD1 - Submitter: Hans Bos Opened: 2003-06-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Sections 23.3.5.2 [list.cons] and 23.3.5.4 [list.modifiers] list -comparison operators (==, !=, <, <=, >, =>) for queue and -stack. Only the semantics for queue::operator== (23.3.5.2 [list.cons] par2) and queue::operator< (23.3.5.2 [list.cons] -par3) are defined. -

- - -

Proposed resolution:

- -

Add the following new paragraphs after 23.3.5.2 [list.cons] - paragraph 3:

- -
- -
-  operator!=
-
-

Returns: x.c != y.c

- -
-  operator>
-
-

Returns: x.c > y.c

- -
-  operator<=
-
-

Returns: x.c <= y.c

- -
-  operator>=
-
-

Returns: x.c >= y.c

- -
- -

Add the following paragraphs at the end of 23.3.5.4 [list.modifiers]:

- -
- -
-  operator==
-
-

Returns: x.c == y.c

- -
-  operator<
-
-

Returns: x.c < y.c

- -
-  operator!=
-
-

Returns: x.c != y.c

- -
-  operator>
-
-

Returns: x.c > y.c

- -
-  operator<=
-
-

Returns: x.c <= y.c

- -
-  operator>=
-
-

Returns: x.c >= y.c

- -
- - -

[Kona: Matt provided wording.]

- - - - -

Rationale:

-

There isn't any real doubt about what these operators are -supposed to do, but we ought to spell it out.

- - - - - -
-

411. Wrong names of set member functions

-

Section: 25.4.5 [alg.set.operations] Status: CD1 - Submitter: Daniel Frey Opened: 2003-07-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-25.4.5 [alg.set.operations] paragraph 1 reads: -"The semantics of the set operations are generalized to multisets in a -standard way by defining union() to contain the maximum number of -occurrences of every element, intersection() to contain the minimum, and -so on." -

- -

-This is wrong. The name of the functions are set_union() and -set_intersection(), not union() and intersection(). -

- - -

Proposed resolution:

-

Change that sentence to use the correct names.

- - - - - -
-

412. Typo in 27.4.4.3

-

Section: 27.5.5.4 [iostate.flags] Status: CD1 - Submitter: Martin Sebor Opened: 2003-07-10 Last modified: 2015-04-08

-

View all other issues in [iostate.flags].

-

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-

Duplicate of: 429

-

Discussion:

-

-The Effects clause in 27.5.5.4 [iostate.flags] paragraph 5 says that the -function only throws if the respective bits are already set prior to -the function call. That's obviously not the intent. The typo ought to -be corrected and the text reworded as: "If (state & -exceptions()) == 0, returns. ..." -

- - -

Proposed resolution:

-

-In 27.5.5.4 [iostate.flags] paragraph 5, replace "If (rdstate() & -exceptions()) == 0" with "If ((state | (rdbuf() ? goodbit : badbit)) -& exceptions()) == 0". -

- -

[Kona: the original proposed resolution wasn't quite right. We - really do mean rdstate(); the ambiguity is that the wording in the - standard doesn't make it clear whether we mean rdstate() before - setting the new state, or rdsate() after setting it. We intend the - latter, of course. Post-Kona: Martin provided wording.]

- - - - - - - -
-

413. Proposed resolution to LDR#64 still wrong

-

Section: 27.7.2.2.3 [istream::extractors] Status: CD1 - Submitter: Bo Persson Opened: 2003-07-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The second sentence of the proposed resolution says: -

- -

-"If it inserted no characters because it caught an exception thrown -while extracting characters from sb and ..." -

- -

-However, we are not extracting from sb, but extracting from the -basic_istream (*this) and inserting into sb. I can't really tell if -"extracting" or "sb" is a typo. -

- -

[ -Sydney: Definitely a real issue. We are, indeed, extracting characters -from an istream and not from sb. The problem was there in the FDIS and -wasn't fixed by issue 64. Probably what was intended was -to have *this instead of sb. We're talking about the exception flag -state of a basic_istream object, and there's only one basic_istream -object in this discussion, so that would be a consistent -interpretation. (But we need to be careful: the exception policy of -this member function must be consistent with that of other -extractors.) PJP will provide wording. -]

- - - - -

Proposed resolution:

-

Change the sentence from:

- -

-If it inserted no characters because it caught an exception thrown -while extracting characters from sb and failbit is on in exceptions(), -then the caught exception is rethrown. -

- -

to:

- -

-If it inserted no characters because it caught an exception thrown -while extracting characters from *this and failbit is on in exceptions(), -then the caught exception is rethrown. -

- - - - - -
-

414. Which iterators are invalidated by v.erase()?

-

Section: 23.3.6.5 [vector.modifiers] Status: CD1 - Submitter: Matt Austern Opened: 2003-08-19 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Consider the following code fragment: -

-
-
-int A[8] = { 1,3,5,7,9,8,4,2 };
-std::vector<int> v(A, A+8);
-
-std::vector<int>::iterator i1 = v.begin() + 3;
-std::vector<int>::iterator i2 = v.begin() + 4;
-v.erase(i1);
-
-
- -

-Which iterators are invalidated by v.erase(i1): i1, i2, -both, or neither? -

- -

-On all existing implementations that I know of, the status of i1 and -i2 is the same: both of them will be iterators that point to some -elements of the vector (albeit not the same elements they did -before). You won't get a crash if you use them. Depending on -exactly what you mean by "invalidate", you might say that neither one -has been invalidated because they still point to something, -or you might say that both have been invalidated because in both -cases the elements they point to have been changed out from under the -iterator. -

- -

-The standard doesn't say either of those things. It says that erase -invalidates all iterators and references "after the point of the -erase". This doesn't include i1, since it's at the point of the -erase instead of after it. I can't think of any sensible definition -of invalidation by which one can say that i2 is invalidated but i1 -isn't. -

- -

-(This issue is important if you try to reason about iterator validity -based only on the guarantees in the standard, rather than reasoning -from typical implementation techniques. Strict debugging modes, -which some programmers find useful, do not use typical implementation -techniques.) -

- - -

Proposed resolution:

-

-In 23.3.6.5 [vector.modifiers] paragraph 3, change "Invalidates all the -iterators and references after the point of the erase" to -"Invalidates iterators and references at or after the point of the -erase". -

- - -

Rationale:

-

I believe this was essentially a typographical error, and that it - was taken for granted that erasing an element invalidates iterators - that point to it. The effects clause in question treats iterators - and references in parallel, and it would seem counterintuitive to - say that a reference to an erased value remains valid.

- - - - - -
-

415. behavior of std::ws

-

Section: 27.7.2.4 [istream.manip] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-According to 27.6.1.4, the ws() manipulator is not required to construct -the sentry object. The manipulator is also not a member function so the -text in 27.6.1, p1 through 4 that describes the exception policy for -istream member functions does not apply. That seems inconsistent with -the rest of extractors and all the other input functions (i.e., ws will -not cause a tied stream to be flushed before extraction, it doesn't check -the stream's exceptions or catch exceptions thrown during input, and it -doesn't affect the stream's gcount). -

- - -

Proposed resolution:

-

-Add to 27.7.2.4 [istream.manip], immediately before the first sentence -of paragraph 1, the following text: -

- -

- Behaves as an unformatted input function (as described in - 27.6.1.3, paragraph 1), except that it does not count the number - of characters extracted and does not affect the value returned by - subsequent calls to is.gcount(). After constructing a sentry - object... -

- -

[Post-Kona: Martin provided wording]

- - - - - - -
-

416. definitions of XXX_MIN and XXX_MAX macros in climits

-

Section: 18.3.3 [c.limits] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

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-

Discussion:

-

- -Given two overloads of the function foo(), one taking an argument of type -int and the other taking a long, which one will the call foo(LONG_MAX) -resolve to? The expected answer should be foo(long), but whether that -is true depends on the #defintion of the LONG_MAX macro, specifically -its type. This issue is about the fact that the type of these macros -is not actually required to be the same as the the type each respective -limit. -
- -Section 18.2.2 of the C++ Standard does not specify the exact types of -the XXX_MIN and XXX_MAX macros #defined in the <climits> and <limits.h> -headers such as INT_MAX and LONG_MAX and instead defers to the C standard. -
- -Section 5.2.4.2.1, p1 of the C standard specifies that "The values [of -these constants] shall be replaced by constant expressions suitable for use -in #if preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, -the following shall be replaced by expressions that have the same type as -would an expression that is an object of the corresponding type converted -according to the integer promotions." -
- -The "corresponding type converted according to the integer promotions" for -LONG_MAX is, according to 6.4.4.1, p5 of the C standard, the type of long -converted to the first of the following set of types that can represent it: -int, long int, long long int. So on an implementation where (sizeof(long) -== sizeof(int)) this type is actually int, while on an implementation where -(sizeof(long) > sizeof(int)) holds this type will be long. -
- -This is not an issue in C since the type of the macro cannot be detected -by any conforming C program, but it presents a portability problem in C++ -where the actual type is easily detectable by overload resolution. - -

-

[Kona: the LWG does not believe this is a defect. The C macro - definitions are what they are; we've got a better - mechanism, std::numeric_limits, that is specified more - precisely than the C limit macros. At most we should add a - nonnormative note recommending that users who care about the exact - types of limit quantities should use <limits> instead of - <climits>.]

- - - - -

Proposed resolution:

- -

-Change 18.3.3 [c.limits], paragraph 2: -

- -

--2- The contents are the same as the Standard C library header <limits.h>. -[Note: The types of the macros in <climits> are not guaranteed -to match the type to which they refer.--end note] -

- - - - - -
-

419. istream extractors not setting failbit if eofbit is already set

-

Section: 27.7.2.1.3 [istream::sentry] Status: C++11 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -27.7.2.1.3 [istream::sentry], p2 says that istream::sentry ctor prepares for input if is.good() -is true. p4 then goes on to say that the ctor sets the sentry::ok_ member to -true if the stream state is good after any preparation. 27.7.2.2.1 [istream.formatted.reqmts], p1 then -says that a formatted input function endeavors to obtain the requested input -if the sentry's operator bool() returns true. - -Given these requirements, no formatted extractor should ever set failbit if -the initial stream rdstate() == eofbit. That is contrary to the behavior of -all implementations I tested. The program below prints out -

-
-eof = 1, fail = 0
-eof = 1, fail = 1
-
-

-on all of them. -

-
-
-#include <sstream>
-#include <cstdio>
-
-int main()
-{
-    std::istringstream strm ("1");
-
-    int i = 0;
-
-    strm >> i;
-
-    std::printf ("eof = %d, fail = %d\n",
-                 !!strm.eof (), !!strm.fail ());
-
-    strm >> i;
-
-    std::printf ("eof = %d, fail = %d\n",
-                 !!strm.eof (), !!strm.fail ());
-}
-
-
-

-
- -Comments from Jerry Schwarz (c++std-lib-11373): -
- -Jerry Schwarz wrote: -
- -I don't know where (if anywhere) it says it in the standard, but the -formatted extractors are supposed to set failbit if they don't extract -any characters. If they didn't then simple loops like -
- -while (cin >> x); -
- -would loop forever. -
- -Further comments from Martin Sebor: -
- -The question is which part of the extraction should prevent this from happening -by setting failbit when eofbit is already set. It could either be the sentry -object or the extractor. It seems that most implementations have chosen to -set failbit in the sentry [...] so that's the text that will need to be -corrected. - -

-

-Pre Berlin: This issue is related to 342. If the sentry -sets failbit when it finds eofbit already set, then -you can never seek away from the end of stream. -

-

Kona: Possibly NAD. If eofbit is set then good() will return false. We - then set ok to false. We believe that the sentry's - constructor should always set failbit when ok is false, and - we also think the standard already says that. Possibly it could be - clearer.

- - -

[ -2009-07 Frankfurt -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-Change 27.7.2.1.3 [istream::sentry], p2 to: -

- -
-
explicit sentry(basic_istream<charT,traits>& is , bool noskipws = false);
-

--2- Effects: If is.good() is true -false, calls is.setstate(failbit). -Otherwise prepares for formatted or unformatted input. ... -

-
- - - - - - -
-

420. is std::FILE a complete type?

-

Section: 27.9.1 [fstreams] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-7.19.1, p2, of C99 requires that the FILE type only be declared in -<stdio.h>. None of the (implementation-defined) members of the -struct is mentioned anywhere for obvious reasons. -

- -

-C++ says in 27.8.1, p2 that FILE is a type that's defined in <cstdio>. Is -it really the intent that FILE be a complete type or is an implementation -allowed to just declare it without providing a full definition? -

- - -

Proposed resolution:

-

In the first sentence of 27.9.1 [fstreams] paragraph 2, change - "defined" to "declared".

- - -

Rationale:

-

We don't want to impose any restrictions beyond what the C standard - already says. We don't want to make anything implementation defined, - because that imposes new requirements in implementations.

- - - - - -
-

422. explicit specializations of member functions of class templates

-

Section: 17.6.4.3 [reserved.names] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It has been suggested that 17.4.3.1, p1 may or may not allow programs to -explicitly specialize members of standard templates on user-defined types. -The answer to the question might have an impact where library requirements -are given using the "as if" rule. I.e., if programs are allowed to specialize -member functions they will be able to detect an implementation's strict -conformance to Effects clauses that describe the behavior of the function -in terms of the other member function (the one explicitly specialized by -the program) by relying on the "as if" rule. -

- - -

Proposed resolution:

- -

- Add the following sentence to 17.6.4.3 [reserved.names], p1: -

- -

-It is undefined for a C++ program to add declarations or definitions to -namespace std or namespaces within namespace std unless otherwise specified. A -program may add template specializations for any standard library template to -namespace std. Such a specialization (complete or partial) of a standard library -template results in undefined behavior unless the declaration depends on a -user-defined type of external linkage and unless the specialization meets the -standard library requirements for the original template.168) -A program has undefined behavior if it declares -

-
    -
  • an explicit specialization of any member function of a standard - library class template, or
    • -
  • an explicit specialization of any member function template of a - standard library class or class template, or
    • -
  • an explicit or partial specialization of any member class - template of a standard library class or class template.
    • -
-

-A program may explicitly instantiate any templates in the standard library only -if the declaration depends on the name of a user-defined type of external -linkage and the instantiation meets the standard library requirements for the -original template. -

- -

[Kona: straw poll was 6-1 that user programs should not be - allowed to specialize individual member functions of standard - library class templates, and that doing so invokes undefined - behavior. Post-Kona: Martin provided wording.]

- - -

[Sydney: The LWG agrees that the standard shouldn't permit users -to specialize individual member functions unless they specialize the -whole class, but we're not sure these words say what we want them to; -they could be read as prohibiting the specialization of any standard -library class templates. We need to consult with CWG to make sure we -use the right wording.]

- - - - - - -
-

425. return value of std::get_temporary_buffer

-

Section: 20.7.11 [temporary.buffer] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The standard is not clear about the requirements on the value returned from -a call to get_temporary_buffer(0). In particular, it fails to specify whether -the call should return a distinct pointer each time it is called (like -operator new), or whether the value is unspecified (as if returned by -malloc). The standard also fails to mention what the required behavior -is when the argument is less than 0. -

- - -

Proposed resolution:

-

Change 20.10.3 [meta.help] paragraph 2 from "...or a pair of 0 -values if no storage can be obtained" to "...or a pair of 0 values if -no storage can be obtained or if n <= 0."

-

[Kona: Matt provided wording]

- - - - - -
-

426. search_n(), fill_n(), and generate_n() with negative n

-

Section: 25.2.13 [alg.search], 25.3.6 [alg.fill], 25.3.7 [alg.generate] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [alg.search].

-

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-

Discussion:

-

-The complexity requirements for these function templates are incorrect -(or don't even make sense) for negative n:

- -

25.1.9, p7 (search_n): -
-Complexity: At most (last1 - first1) * count applications -of the corresponding predicate.

- -

25.2.5, p3 (fill_n): -
-Complexity: Exactly last - first (or n) assignments.

- -

25.2.6, p3 (generate_n): -
-Complexity: Exactly last - first (or n) assignments.

- -

-In addition, the Requirements or the Effects clauses for the latter two -templates don't say anything about the behavior when n is negative. -

- - -

Proposed resolution:

-

Change 25.1.9, p7 to

- -

-Complexity: At most (last1 - first1) * count applications -of the corresponding predicate if count is positive, -or 0 otherwise. -

- -

Change 25.2.5, p2 to

-

-Effects: Assigns value through all the iterators in the range [first, -last), or [first, first + n) if n is positive, none otherwise. -

- -

Change 25.2.5, p3 to:

-

-Complexity: Exactly last - first (or n if n is positive, -or 0 otherwise) assignments. -

- -

-Change 25.2.6, p1 -to (notice the correction for the misspelled "through"): -

-

-Effects: Invokes the function object genand assigns the return -value of gen through all the iterators in the range [first, last), -or [first, first + n) if n is positive, or [first, first) -otherwise. -

- -

Change 25.2.6, p3 to:

-

-Complexity: Exactly last - first (or n if n is positive, -or 0 otherwise) assignments. -

- - -

Rationale:

-

Informally, we want to say that whenever we see a negative number - we treat it the same as if it were zero. We believe the above - changes do that (although they may not be the minimal way of saying - so). The LWG considered and rejected the alternative of saying that - negative numbers are undefined behavior.

- - - - - -
-

427. Stage 2 and rationale of DR 221

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: C++11 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

View all other issues in [facet.num.get.virtuals].

-

View all issues with C++11 status.

-

Discussion:

-

-The requirements specified in Stage 2 and reiterated in the rationale -of DR 221 (and echoed again in DR 303) specify that num_get<charT>:: -do_get() compares characters on the stream against the widened elements -of "012...abc...ABCX+-" -

- -

-An implementation is required to allow programs to instantiate the num_get -template on any charT that satisfies the requirements on a user-defined -character type. These requirements do not include the ability of the -character type to be equality comparable (the char_traits template must -be used to perform tests for equality). Hence, the num_get template cannot -be implemented to support any arbitrary character type. The num_get template -must either make the assumption that the character type is equality-comparable -(as some popular implementations do), or it may use char_traits<charT> to do -the comparisons (some other popular implementations do that). This diversity -of approaches makes it difficult to write portable programs that attempt to -instantiate the num_get template on user-defined types. -

- -

[Kona: the heart of the problem is that we're theoretically - supposed to use traits classes for all fundamental character - operations like assignment and comparison, but facets don't have - traits parameters. This is a fundamental design flaw and it - appears all over the place, not just in this one place. It's not - clear what the correct solution is, but a thorough review of facets - and traits is in order. The LWG considered and rejected the - possibility of changing numeric facets to use narrowing instead of - widening. This may be a good idea for other reasons (see issue - 459), but it doesn't solve the problem raised by this - issue. Whether we use widen or narrow the num_get facet - still has no idea which traits class the user wants to use for - the comparison, because only streams, not facets, are passed traits - classes. The standard does not require that two different - traits classes with the same char_type must necessarily - have the same behavior.]

- - -

Informally, one possibility: require that some of the basic -character operations, such as eq, lt, -and assign, must behave the same way for all traits classes -with the same char_type. If we accept that limitation on -traits classes, then the facet could reasonably be required to -use char_traits<charT>.

- -

[ -2009-07 Frankfurt -]

- - -
-

-There was general agreement that the standard only needs to specify the -behavior when the character type is char or wchar_t. -

-

-Beman: we don't need to worry about C++1x because there is a non-zero -possibility that we would have a replacement facility for iostreams that -would solve these problems. -

-

-We need to change the following sentence in [locale.category], paragraph -6 to specify that C is char and wchar_t: -

-

-"A template formal parameter with name C represents the set of all -possible specializations on a parameter that satisfies the requirements -for a character on which any member of the iostream components can be -instantiated." -

-

-We also need to specify in 27 that the basic character operations, such -as eq, lt, and assign use std::char_traits. -

-

-Daniel volunteered to provide wording. -

-
- -

[ -2009-09-19 Daniel provided wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as Open. Alisdair and/or Tom will provide wording based on discussions. -We want to clearly state that streams and locales work just on char -and wchar_t (except where otherwise specified). -

- -

[ -2010-02-06 Tom updated the proposed wording. -]

- - -
-

[ -The original proposed wording is preserved here: -]

- - -
-
    -
  1. -

    -Change 22.3.1.1.1 [locale.category]/6: -

    - -

    -[..] A template formal parameter with name C represents the set of all possible -specializations on a char or wchar_t parameter that satisfies -the requirements for a character on which any of the iostream components -can be instantiated. [..] -

    -
    2. - -
  2. -

    -Add the following sentence to the end of 22.4.2 [category.numeric]/2: -

    - -

    -[..] These specializations refer to [..], and also for the ctype<> facet to -perform character classification. Implementations are encouraged -but not required to use the char_traits<charT> functions for all -comparisons and assignments of characters of type charT that do -not belong to the set of required specializations. -

    -
    3. - -
  3. -

    -Change 22.4.2.1.2 [facet.num.get.virtuals]/3: -

    - -
    -

    -Stage 2: If in==end then stage 2 terminates. Otherwise a charT is taken -from in and local variables are initialized as if by -

    - -
    -char_type ct = *in;
-using tr = char_traits<char_type>;
-const char_type* pos = tr::find(atoms, sizeof(src) - 1, ct);
-char c = src[find(atoms, atoms + sizeof(src) - 1, ct) - atoms
-             pos ? pos - atoms : sizeof(src) - 1];
-if (tr::eq(ct, ct == use_facet<numpunct<charT>(loc).decimal_point()))
-    c = '.';
-bool discard =
-    tr::eq(ct, ct == use_facet<numpunct<charT>(loc).thousands_sep())
-    && use_facet<numpunct<charT> >(loc).grouping().length() != 0;
-
    - -

    -where the values src and atoms are defined as if by: [..] -

    -
    - -

    -[Remark of the author: I considered to replace the initialization -"char_type ct = *in;" -by the sequence "char_type ct; tr::assign(ct, *in);", but decided -against it, because -it is a copy-initialization context, not an assignment] -

    -
    4. - -
  4. -

    -Add the following sentence to the end of 22.4.5 [category.time]/1: -

    - -

    -[..] Their members use [..] , to determine formatting details. -Implementations are encouraged but not required to use the -char_traits<charT> functions for all comparisons and assignments -of characters of type charT that do -not belong to the set of required specializations. -

    -
    5. - -
  5. -

    -Change 22.4.5.1.1 [locale.time.get.members]/8 bullet 4: -

    - -
      -
    • -The next element of fmt is equal to '%' For the next element c -of fmt char_traits<char_type>::eq(c, use_facet<ctype<char_type>>(f.getloc()).widen('%')) == true, -[..] -
      • -
    -
    6. - -
  6. -

    -Add the following sentence to the end of 22.4.6 [category.monetary]/2: -

    - -

    -Their members use [..] to determine formatting details. -Implementations are encouraged but not required to use the -char_traits<charT> functions for all comparisons and assignments -of characters of type charT that do -not belong to the set of required specializations. -

    -
    7. - -
  7. -

    -Change 22.4.6.1.2 [locale.money.get.virtuals]/4: -

    - -
    -

    -[..] The value units is produced as if by: -

    - -
    -for (int i = 0; i < n; ++i)
-  buf2[i] = src[char_traits<charT>::find(atoms, atoms+sizeof(src), buf1[i]) - atoms];
-buf2[n] = 0;
-sscanf(buf2, "%Lf", &units);
-
    -
    -
    8. - -
  8. -

    -Change 22.4.6.2.2 [locale.money.put.virtuals]/1: -

    - -

    -[..] for character buffers buf1 and buf2. If for the first -character c -in digits or buf2 is equal to -ct.widen('-')char_traits<charT>::eq(c, -ct.widen('-')) == true, [..] -

    -
    9. - -
  9. -

    -Add a footnote to the first sentence of 27.7.2.2.2 [istream.formatted.arithmetic]/1: -

    - -
    -

    -As in the case of the inserters, these extractors depend on the locale's -num_get<> (22.4.2.1) object to perform parsing the input stream -data.(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    10. - -
  10. -

    -Add a footnote to the second sentence of 27.7.3.6.2 [ostream.inserters.arithmetic]/1: -

    - -
    -

    -Effects: The classes num_get<> and -num_put<> handle locale-dependent numeric formatting and -parsing. These inserter functions use the imbued locale value to perform -numeric formatting.(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    11. - -
  11. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/4: -

    - -
    -

    -Returns: An object of unspecified type such that if in is an object of type -basic_istream<charT, traits> then the expression in >> get_money(mon, intl) -behaves as if it called f(in, mon, intl), where the function f is defined -as:(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    12. - -
  12. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/5: -

    - -
    -

    -Returns: An object of unspecified type such that if out is an object of type -basic_ostream<charT, traits> then the expression out << put_money(mon, intl) -behaves as a formatted input function that calls f(out, mon, intl), where the -function f is defined as:(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    13. - -
  13. -

    -13) Add a footnote after the first sentence of 27.7.5 [ext.manip]/8: -

    - -
    -

    -Returns: An object of unspecified type such that if in is an -object of type basic_istream<charT, traits> then the expression -in >>get_time(tmb, fmt) behaves as if it called f(in, tmb, fmt), -where the function f is defined as:(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    14. - -
  14. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/10: -

    - -
    -

    -Returns: An object of unspecified type such that if out is an object of type -basic_ostream<charT, traits> then the expression out <<put_time(tmb, fmt) -behaves as if it called f(out, tmb, fmt), where the function f is defined -as:(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    15. -
- -
-
- -

[ -2010 Pittsburgh: -]

- - -
-

-Moved to Ready with only two of the bullets. The original wording is preserved -here: -

- -
-
    -
  1. -

    -Change 22.3.1.1.1 [locale.category]/6: -

    - -

    -[..] A template formal parameter with name C represents -the set -of all possible specializations on a -of types containing char, wchar_t, -and any other implementation-defined character type - - parameter -that satisfies -the requirements for a character on which any of the iostream components -can be instantiated. [..] -

    -
    2. - -
  2. -

    -Add the following sentence to the end of 22.4.2 [category.numeric]/2: -

    - -

    -[..] These specializations refer to [..], and also for the ctype<> facet to -perform character classification. [Note: Implementations are encouraged -but not required to use the char_traits<charT> functions for all -comparisons and assignments of characters of type charT that do -not belong to the set of required specializations - end note]. -

    -
    3. - -
  3. -

    -Change 22.4.2.1.2 [facet.num.get.virtuals]/3: -

    - -
    -

    -Stage 2: If in==end then stage 2 terminates. Otherwise a charT is taken -from in and local variables are initialized as if by -

    - -
    -char_type ct = *in;
-using tr = char_traits<char_type>;
-const char_type* pos = tr::find(atoms, sizeof(src) - 1, ct);
-char c = src[find(atoms, atoms + sizeof(src) - 1, ct) - atoms
-             pos ? pos - atoms : sizeof(src) - 1];
-if (tr::eq(ct, ct == use_facet<numpunct<charT>(loc).decimal_point()))
-    c = '.';
-bool discard =
-    tr::eq(ct, ct == use_facet<numpunct<charT>(loc).thousands_sep())
-    && use_facet<numpunct<charT> >(loc).grouping().length() != 0;
-
    - -

    -where the values src and atoms are defined as if by: [..] -

    -
    - -

    -[Remark of the author: I considered to replace the initialization -"char_type ct = *in;" -by the sequence "char_type ct; tr::assign(ct, *in);", but decided -against it, because -it is a copy-initialization context, not an assignment] -

    -
    4. - -
  4. -

    -Add the following sentence to the end of 22.4.5 [category.time]/1: -

    - -

    -[..] Their members use [..] , to determine formatting details. -[Note: Implementations are encouraged but not required to use the -char_traits<charT> functions for all comparisons and assignments -of characters of type charT that do -not belong to the set of required specializations - end note]. -

    -
    5. - -
  5. -

    -Change 22.4.5.1.1 [locale.time.get.members]/8 bullet 4: -

    - -
      -
    • -The next element of fmt is equal to '%' For the next element c -of fmt char_traits<char_type>::eq(c, use_facet<ctype<char_type>>(f.getloc()).widen('%')) == true, -[..] -
      • -
    -
    6. - -
  6. -

    -Add the following sentence to the end of 22.4.6 [category.monetary]/2: -

    - -

    -Their members use [..] to determine formatting details. -[Note: Implementations are encouraged but not required to use the -char_traits<charT> functions for all comparisons and assignments -of characters of type charT that do -not belong to the set of required specializations - end note]. -

    -
    7. - -
  7. -

    -Change 22.4.6.1.2 [locale.money.get.virtuals]/4: -

    - -
    -

    -[..] The value units is produced as if by: -

    - -
    -for (int i = 0; i < n; ++i)
-  buf2[i] = src[char_traits<charT>::find(atoms, atoms+sizeof(src), buf1[i]) - atoms];
-buf2[n] = 0;
-sscanf(buf2, "%Lf", &units);
-
    -
    -
    8. - -
  8. -

    -Change 22.4.6.2.2 [locale.money.put.virtuals]/1: -

    - -

    -[..] for character buffers buf1 and buf2. If for the first -character c -in digits or buf2 is equal to -ct.widen('-')char_traits<charT>::eq(c, -ct.widen('-')) == true, [..] -

    -
    9. - -
  9. -

    -Add a new paragraph after the -first paragraph of 27.2.2 [iostreams.limits.pos]/1: -

    -

    -In the classes of clause 27, -a template formal parameter with name charT represents -one of -the set of types -containing char, wchar_t, -and any other implementation-defined character type -that satisfies -the requirements for a character on which any of the iostream components -can be instantiated. -

    -
    10. - -
  10. -

    -Add a footnote to the first sentence of 27.7.2.2.2 [istream.formatted.arithmetic]/1: -

    - -
    -

    -As in the case of the inserters, these extractors depend on the locale's -num_get<> (22.4.2.1) object to perform parsing the input stream -data.(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    11. - -
  11. -

    -Add a footnote to the second sentence of 27.7.3.6.2 [ostream.inserters.arithmetic]/1: -

    - -
    -

    -Effects: The classes num_get<> and -num_put<> handle locale-dependent numeric formatting and -parsing. These inserter functions use the imbued locale value to perform -numeric formatting.(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    12. - - -
  12. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/4: -

    - -
    -

    -Returns: An object of unspecified type such that if in is an object of type -basic_istream<charT, traits> then the expression in >> get_money(mon, intl) -behaves as if it called f(in, mon, intl), where the function f is defined -as:(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    13. - -
  13. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/5: -

    - -
    -

    -Returns: An object of unspecified type such that if out is an object of type -basic_ostream<charT, traits> then the expression out << put_money(mon, intl) -behaves as a formatted input function that calls f(out, mon, intl), where the -function f is defined as:(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    14. - -
  14. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/8: -

    - -
    -

    -Returns: An object of unspecified type such that if in is an -object of type basic_istream<charT, traits> then the expression -in >>get_time(tmb, fmt) behaves as if it called f(in, tmb, fmt), -where the function f is defined as:(footnote) [..] -

    - -

    - -footnote) If the traits of the input stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    15. - -
  15. -

    -Add a footnote after the first sentence of 27.7.5 [ext.manip]/10: -

    - -
    -

    -Returns: An object of unspecified type such that if out is an object of type -basic_ostream<charT, traits> then the expression out <<put_time(tmb, fmt) -behaves as if it called f(out, tmb, fmt), where the function f is defined -as:(footnote) [..] -

    - -

    - -footnote) If the traits of the output stream has different semantics for lt(), -eq(), and assign() than char_traits<char_type>, this may give surprising -results. - -

    -
    -
    16. -
-
-
- - - -

Proposed resolution:

-
    -
  1. -

    -Change 22.3.1.1.1 [locale.category]/6: -

    - -

    -[..] A template formal parameter with name C represents -the set -of all possible specializations on a -of types containing char, wchar_t, -and any other implementation-defined character type - - parameter -that satisfies -the requirements for a character on which any of the iostream components -can be instantiated. [..] -

    -
    2. - -
  2. -

    -Add a new paragraph after the -first paragraph of 27.2.2 [iostreams.limits.pos]/1: -

    -

    -In the classes of clause 27, -a template formal parameter with name charT represents -one of -the set of types -containing char, wchar_t, -and any other implementation-defined character type -that satisfies -the requirements for a character on which any of the iostream components -can be instantiated. -

    -
    3. - -
- - - - -
-

428. string::erase(iterator) validity

-

Section: 21.4.6.5 [string::erase] Status: CD1 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all other issues in [string::erase].

-

View all issues with CD1 status.

-

Discussion:

-

-23.1.1, p3 along with Table 67 specify as a prerequisite for a.erase(q) -that q must be a valid dereferenceable iterator into the sequence a. -

- -

-However, 21.3.5.5, p5 describing string::erase(p) only requires that -p be a valid iterator. -

- -

-This may be interepreted as a relaxation of the general requirement, -which is most likely not the intent. -

- - -

Proposed resolution:

-

Remove 21.4.6.5 [string::erase] paragraph 5.

- - -

Rationale:

-

The LWG considered two options: changing the string requirements to - match the general container requirements, or just removing the - erroneous string requirements altogether. The LWG chose the latter - option, on the grounds that duplicating text always risks the - possibility that it might be duplicated incorrectly.

- - - - - -
-

430. valarray subset operations

-

Section: 26.6.2.5 [valarray.sub] Status: C++11 - Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-The standard fails to specify the behavior of valarray::operator[](slice) -and other valarray subset operations when they are passed an "invalid" -slice object, i.e., either a slice that doesn't make sense at all (e.g., -slice (0, 1, 0) or one that doesn't specify a valid subset of the valarray -object (e.g., slice (2, 1, 1) for a valarray of size 1). -

-

[Kona: the LWG believes that invalid slices should invoke - undefined behavior. Valarrays are supposed to be designed for high - performance, so we don't want to require specific checking. We - need wording to express this decision.]

- - -

[ -Bellevue: -]

- - -

-Please note that the standard also fails to specify the behavior of -slice_array and gslice_array in the valid case. Bill Plauger will -endeavor to provide revised wording for slice_array and gslice_array. -

- -

[ -post-Bellevue: Bill provided wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-Move to Ready. -

-
- -

[ -2009-11-04 Pete opens: -]

- - -

-The resolution to LWG issue 430 has not been applied — there have been -changes to the underlying text, and the resolution needs to be reworked. -

- -

[ -2010-03-09 Matt updated wording. -]

- - -

[ -2010 Pittsburgh: Moved to Ready for Pittsburgh. -]

- - - - -

Proposed resolution:

-

-Replace 26.6.2.5 [valarray.sub], with the following: -

- -
-

-The member operator is overloaded to provide several ways to select -sequences of elements from among those controlled by *this. -Each of these operations returns a subset of the array. The -const-qualified versions return this subset as a new valarray. The -non-const versions return a class template object which has reference -semantics to the original array, working in conjunction with various -overloads of operator= (and other assigning operators) to allow -selective replacement (slicing) of the controlled sequence. In each case -the selected element(s) must exist. -

- -
-valarray<T> operator[](slice slicearr) const; 
-
- -
-

-This function returns an object of class valarray<T> -containing those elements of the controlled sequence designated by -slicearr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-valarray<char> v1("ABCDE", 5); 
-v0[slice(2, 5, 3)] = v1; 
-// v0 == valarray<char>("abAdeBghCjkDmnEp", 16)
-
-

-end example] -

-
- -
-valarray<T> operator[](slice slicearr); 
-
- -
-

-This function selects those elements of the controlled sequence -designated by slicearr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-valarray<char> v1("ABCDE", 5); 
-v0[slice(2, 5, 3)] = v1; 
-// v0 == valarray<char>("abAdeBghCjkDmnEp", 16)
-
-

-end example] -

-
- -
-valarray<T> operator[](const gslice& gslicearr) const; 
-
- -
-

-This function returns an object of class valarray<T> -containing those elements of the controlled sequence designated by -gslicearr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-const size_t lv[] = {2, 3}; 
-const size_t dv[] = {7, 2}; 
-const valarray<size_t> len(lv, 2), str(dv, 2); 
-// v0[gslice(3, len, str)] returns 
-// valarray<char>("dfhkmo", 6)
-
-

-end example] -

-
- -
-gslice_array<T> operator[](const gslice& gslicearr); 
-
- -
-

-This function selects those elements of the controlled sequence -designated by gslicearr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-valarray<char> v1("ABCDEF", 6); 
-const size_t lv[] = {2, 3}; 
-const size_t dv[] = {7, 2}; 
-const valarray<size_t> len(lv, 2), str(dv, 2); 
-v0[gslice(3, len, str)] = v1; 
-// v0 == valarray<char>("abcAeBgCijDlEnFp", 16)
-
-

-end example] -

-
- -
-valarray<T> operator[](const valarray<bool>& boolarr) const; 
-
- -
-

-This function returns an object of class valarray<T> -containing those elements of the controlled sequence designated by -boolarr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-const bool vb[] = {false, false, true, true, false, true}; 
-// v0[valarray<bool>(vb, 6)] returns 
-// valarray<char>("cdf", 3)
-
-

-end example] -

-
- -
-mask_array<T> operator[](const valarray<bool>& boolarr); 
-
- -
-

-This function selects those elements of the controlled sequence -designated by boolarr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-valarray<char> v1("ABC", 3); 
-const bool vb[] = {false, false, true, true, false, true}; 
-v0[valarray<bool>(vb, 6)] = v1; 
-// v0 == valarray<char>("abABeCghijklmnop", 16)
-
-

-end example] -

-
- -
-valarray<T> operator[](const valarray<size_t>& indarr) const; 
-
- -
-

-This function returns an object of class valarray<T> -containing those elements of the controlled sequence designated by -indarr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-const size_t vi[] = {7, 5, 2, 3, 8}; 
-// v0[valarray<size_t>(vi, 5)] returns 
-// valarray<char>("hfcdi", 5)
-
-

-end example] -

-
- -
-indirect_array<T> operator[](const valarray<size_t>& indarr);
-
- -
-

-This function selects those elements of the controlled sequence -designated by indarr. [Example: -

- -
-valarray<char> v0("abcdefghijklmnop", 16); 
-valarray<char> v1("ABCDE", 5); 
-const size_t vi[] = {7, 5, 2, 3, 8}; 
-v0[valarray<size_t>(vi, 5)] = v1; 
-// v0 == valarray<char>("abCDeBgAEjklmnop", 16)
-
-

-end example] -

-
- -
- - - - - -
-

431. Swapping containers with unequal allocators

-

Section: 17.6.3.5 [allocator.requirements], 25 [algorithms] Status: Resolved - Submitter: Matt Austern Opened: 2003-09-20 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Resolved status.

-

Discussion:

-

Clause 17.6.3.5 [allocator.requirements] paragraph 4 says that implementations - are permitted to supply containers that are unable to cope with - allocator instances and that container implementations may assume - that all instances of an allocator type compare equal. We gave - implementers this latitude as a temporary hack, and eventually we - want to get rid of it. What happens when we're dealing with - allocators that don't compare equal? -

- -

In particular: suppose that v1 and v2 are both - objects of type vector<int, my_alloc> and that - v1.get_allocator() != v2.get_allocator(). What happens if - we write v1.swap(v2)? Informally, three possibilities:

- -

1. This operation is illegal. Perhaps we could say that an - implementation is required to check and to throw an exception, or - perhaps we could say it's undefined behavior.

-

2. The operation performs a slow swap (i.e. using three - invocations of operator=, leaving each allocator with its - original container. This would be an O(N) operation.

-

3. The operation swaps both the vectors' contents and their - allocators. This would be an O(1) operation. That is:

-
- 
-    my_alloc a1(...);
-    my_alloc a2(...);
-    assert(a1 != a2);
-
-    vector<int, my_alloc> v1(a1);
-    vector<int, my_alloc> v2(a2);
-    assert(a1 == v1.get_allocator());
-    assert(a2 == v2.get_allocator());
-
-    v1.swap(v2);
-    assert(a1 == v2.get_allocator());
-    assert(a2 == v1.get_allocator());
-
-
- -

[Kona: This is part of a general problem. We need a paper - saying how to deal with unequal allocators in general.]

- - -

[pre-Sydney: Howard argues for option 3 in -N1599. -]

- - -

[ -2007-01-12, Howard: This issue will now tend to come up more often with move constructors -and move assignment operators. For containers, these members transfer resources (i.e. -the allocated memory) just like swap. -]

- - -

[ -Batavia: There is agreement to overload the container swap on the allocator's Swappable -requirement using concepts. If the allocator supports Swappable, then container's swap will -swap allocators, else it will perform a "slow swap" using copy construction and copy assignment. -]

- - -

[ -2009-04-28 Pablo adds: -]

- -

-Fixed in -N2525. -I argued for marking this Tentatively-Ready right after Bellevue, -but there was a concern that -N2525 -would break in the presence of the RVO. (That breakage had nothing to do with -swap, but never-the-less). I addressed that breakage in in -N2840 -(Summit) by means of a non-normative reference: -

-

-[Note: in situations where the copy constructor for a container is elided, -this function is not called. The behavior in these cases is as if -select_on_container_copy_construction returned x — end note] -

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2982. -

- - - -

Proposed resolution:

- - - - - -
-

432. stringbuf::overflow() makes only one write position available

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: CD1 - Submitter: Christian W Brock Opened: 2003-09-24 Last modified: 2015-04-08

-

View all other issues in [stringbuf.virtuals].

-

View all issues with CD1 status.

-

Discussion:

-

27.7.1.3 par 8 says:

-

-Notes: The function can make a write position available only if - ( mode & ios_base::out) != 0. To make a write position - available, the function reallocates (or initially allocates) an - array object with a sufficient number of elements to hold the - current array object (if any), plus one additional write position. - If ( mode & ios_base::in) != 0, the function alters the read end - pointer egptr() to point just past the new write position (as - does the write end pointer epptr()). -

- -

-The sentences "plus one additional write position." and especially - "(as does the write end pointer epptr())" COULD by interpreted - (and is interpreted by at least my library vendor) as: -

- -

- post-condition: epptr() == pptr()+1 -

- -

-This WOULD force sputc() to call the virtual overflow() each time. -

- -

The proposed change also affects Defect Report 169.

- - - -

Proposed resolution:

-

27.7.1.1/2 Change:

- -

-2- Notes: The function allocates no array object. -

- -

-to: -

- -

-2- Postcondition: str() == "". -

- -

-27.7.1.1/3 Change: -

- -
-

--3- Effects: Constructs an object of class basic_stringbuf, -initializing the base class with basic_streambuf() -(lib.streambuf.cons), and initializing mode with which . Then copies -the content of str into the basic_stringbuf underlying character -sequence and initializes the input and output sequences according to -which. If which & ios_base::out is true, initializes the output -sequence with the underlying sequence. If which & ios_base::in is -true, initializes the input sequence with the underlying sequence. -

-
- -

to:

- -
-

--3- Effects: Constructs an object of class basic_stringbuf, -initializing the base class with basic_streambuf() -(lib.streambuf.cons), and initializing mode with which. Then copies -the content of str into the basic_stringbuf underlying character -sequence. If which & ios_base::out is true, initializes the output -sequence such that pbase() points to the first underlying character, -epptr() points one past the last underlying character, and if (which & -ios_base::ate) is true, pptr() is set equal to -epptr() else pptr() is set equal to pbase(). If which & ios_base::in -is true, initializes the input sequence such that eback() and gptr() -point to the first underlying character and egptr() points one past -the last underlying character. -

-
- -

27.7.1.2/1 Change:

- -
-

--1- Returns: A basic_string object whose content is equal to the -basic_stringbuf underlying character sequence. If the buffer is only -created in input mode, the underlying character sequence is equal to -the input sequence; otherwise, it is equal to the output sequence. In -case of an empty underlying character sequence, the function returns -basic_string<charT,traits,Allocator>(). -

-
- -

to:

- -
-

--1- Returns: A basic_string object whose content is equal to the -basic_stringbuf underlying character sequence. If the basic_stringbuf -was created only in input mode, the resultant basic_string contains -the character sequence in the range [eback(), egptr()). If the -basic_stringbuf was created with (which & ios_base::out) being true -then the resultant basic_string contains the character sequence in the -range [pbase(), high_mark) where high_mark represents the position one -past the highest initialized character in the buffer. Characters can -be initialized either through writing to the stream, or by -constructing the basic_stringbuf with a basic_string, or by calling -the str(basic_string) member function. In the case of calling the -str(basic_string) member function, all characters initialized prior to -the call are now considered uninitialized (except for those -characters re-initialized by the new basic_string). Otherwise the -basic_stringbuf has been created in neither input nor output mode and -a zero length basic_string is returned. -

-
- -

-27.7.1.2/2 Change: -

- -
-

--2- Effects: If the basic_stringbuf's underlying character sequence is -not empty, deallocates it. Then copies the content of s into the -basic_stringbuf underlying character sequence and initializes the -input and output sequences according to the mode stored when creating -the basic_stringbuf object. If (mode&ios_base::out) is true, then -initializes the output sequence with the underlying sequence. If -(mode&ios_base::in) is true, then initializes the input sequence with -the underlying sequence. -

-
- -

to:

- -
-

--2- Effects: Copies the content of s into the basic_stringbuf -underlying character sequence. If mode & ios_base::out is true, -initializes the output sequence such that pbase() points to the first -underlying character, epptr() points one past the last underlying -character, and if (mode & ios_base::ate) is true, -pptr() is set equal to epptr() else pptr() is set equal to pbase(). If -mode & ios_base::in is true, initializes the input sequence such that -eback() and gptr() point to the first underlying character and egptr() -points one past the last underlying character. -

-
- -

Remove 27.2.1.2/3. (Same rationale as issue 238: incorrect and unnecessary.)

- -

27.7.1.3/1 Change:

- -
-

-1- Returns: If the input sequence has a read position available, -returns traits::to_int_type(*gptr()). Otherwise, returns -traits::eof(). -

-
- -

to:

- -
-

-1- Returns: If the input sequence has a read position available, -returns traits::to_int_type(*gptr()). Otherwise, returns -traits::eof(). Any character in the underlying buffer which has been -initialized is considered to be part of the input sequence. -

-
- -

27.7.1.3/9 Change:

- -
-

--9- Notes: The function can make a write position available only if ( -mode & ios_base::out) != 0. To make a write position available, the -function reallocates (or initially allocates) an array object with a -sufficient number of elements to hold the current array object (if -any), plus one additional write position. If ( mode & ios_base::in) != -0, the function alters the read end pointer egptr() to point just past -the new write position (as does the write end pointer epptr()). -

-
- -

to:

- -
-

--9- The function can make a write position available only if ( mode & -ios_base::out) != 0. To make a write position available, the function -reallocates (or initially allocates) an array object with a sufficient -number of elements to hold the current array object (if any), plus one -additional write position. If ( mode & ios_base::in) != 0, the -function alters the read end pointer egptr() to point just past the -new write position. -

-
- -

27.7.1.3/12 Change:

- -
-

--12- _ If (newoff + off) < 0, or (xend - xbeg) < (newoff + off), the -positioning operation fails. Otherwise, the function assigns xbeg + -newoff + off to the next pointer xnext . -

-
- -

to:

- -
-

--12- _ If (newoff + off) < 0, or if (newoff + off) refers to an -uninitialized character (as defined in 27.8.2.3 [stringbuf.members] -paragraph 1), the positioning operation fails. Otherwise, the function -assigns xbeg + newoff + off to the next pointer xnext . -

-
- -

[post-Kona: Howard provided wording. At Kona the LWG agreed that - something along these lines was a good idea, but the original - proposed resolution didn't say enough about the effect of various - member functions on the underlying character sequences.]

- - - - -

Rationale:

-

The current basic_stringbuf description is over-constrained in such -a way as to prohibit vendors from making this the high-performance -in-memory stream it was meant to be. The fundamental problem is that -the pointers: eback(), gptr(), egptr(), pbase(), pptr(), epptr() are -observable from a derived client, and the current description -restricts the range [pbase(), epptr()) from being grown geometrically. -This change allows, but does not require, geometric growth of this -range.

- -

Backwards compatibility issues: These changes will break code that -derives from basic_stringbuf, observes epptr(), and depends upon -[pbase(), epptr()) growing by one character on each call to overflow() -(i.e. test suites). Otherwise there are no backwards compatibility -issues.

- -

27.7.1.1/2: The non-normative note is non-binding, and if it were -binding, would be over specification. The recommended change focuses -on the important observable fact.

- -

27.7.1.1/3: This change does two things: 1. It describes exactly -what must happen in terms of the sequences. The terms "input -sequence" and "output sequence" are not well defined. 2. It -introduces a common extension: open with app or ate mode. I concur -with issue 238 that paragraph 4 is both wrong and unnecessary.

- -

27.7.1.2/1: This change is the crux of the efficiency issue. The -resultant basic_string is not dependent upon epptr(), and thus -implementors are free to grow the underlying buffer geometrically -during overflow() *and* place epptr() at the end of that buffer.

- -

27.7.1.2/2: Made consistent with the proposed 27.7.1.1/3.

- -

27.7.1.3/1: Clarifies that characters written to the stream beyond -the initially specified string are available for reading in an i/o -basic_streambuf.

- -

27.7.1.3/9: Made normative by removing "Notes:", and removed the -trailing parenthetical comment concerning epptr().

- -

27.7.1.3/12: Restricting the positioning to [xbeg, xend) is no -longer allowable since [pbase(), epptr()) may now contain -uninitialized characters. Positioning is only allowable over the -initialized range.

- - - - - -
-

434. bitset::to_string() hard to use

-

Section: 20.6.2 [bitset.members] Status: CD1 - Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2015-04-08

-

View all other issues in [bitset.members].

-

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-

Discussion:

-

-It has been pointed out a number of times that the bitset to_string() member -function template is tedious to use since callers must explicitly specify the -entire template argument list (3 arguments). At least two implementations -provide a number of overloads of this template to make it easier to use. -

- - - -

Proposed resolution:

-

In order to allow callers to specify no template arguments at all, just the -first one (charT), or the first 2 (charT and traits), in addition to all -three template arguments, add the following three overloads to both the -interface (declarations only) of the class template bitset as well as to -section 23.3.5.2, immediately after p34, the Returns clause of the existing -to_string() member function template:

- -
-    template <class charT, class traits>
-    basic_string<charT, traits, allocator<charT> >
-    to_string () const;
-
-    -34.1- Returns: to_string<charT, traits, allocator<charT> >().
-
-    template <class charT>
-    basic_string<charT, char_traits<charT>, allocator<charT> >
-    to_string () const;
-
-    -34.2- Returns: to_string<charT, char_traits<charT>, allocator<charT> >().
-
-    basic_string<char, char_traits<char>, allocator<char> >
-    to_string () const;
-
-    -34.3- Returns: to_string<char, char_traits<char>, allocator<char> >().
-
- -

[Kona: the LWG agrees that this is an improvement over the - status quo. Dietmar thought about an alternative using a proxy - object but now believes that the proposed resolution above is the - right choice. -]

- - - - - - - - -
-

435. bug in DR 25

-

Section: 21.4.8.9 [string.io] Status: CD1 - Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2015-04-08

-

View all other issues in [string.io].

-

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-

Discussion:

- -

-It has been pointed out that the proposed resolution in DR 25 may not be -quite up to snuff:
-http://gcc.gnu.org/ml/libstdc++/2003-09/msg00147.html -http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#25
-

- -

-It looks like Petur is right. The complete corrected text is copied below. -I think we may have have been confused by the reference to 22.2.2.2.2 and -the subsequent description of `n' which actually talks about the second -argument to sputn(), not about the number of fill characters to pad with. -

- -

-So the question is: was the original text correct? If the intent was to -follow classic iostreams then it most likely wasn't, since setting width() -to less than the length of the string doesn't truncate it on output. This -is also the behavior of most implementations (except for SGI's standard -iostreams where the operator does truncate). -

- - - -

Proposed resolution:

-

Change the text in 21.3.7.9, p4 from

-

- If bool(k) is true, inserts characters as if by calling - os.rdbuf()->sputn(str.data(), n), padding as described in stage 3 - of lib.facet.num.put.virtuals, where n is the larger of os.width() - and str.size(); -

-

to

-

- If bool(k) is true, determines padding as described in - lib.facet.num.put.virtuals, and then inserts the resulting - sequence of characters seq as if by calling - os.rdbuf()->sputn(seq, n), where n is the larger of - os.width() and str.size(); -

- -

[Kona: it appears that neither the original wording, DR25, nor the - proposed resolution, is quite what we want. We want to say that - the string will be output, padded to os.width() if necessary. We - don't want to duplicate the padding rules in clause 22, because - they're complicated, but we need to be careful because they weren't - quite written with quite this case in mind. We need to say what - the character sequence is, and then defer to clause 22. Post-Kona: - Benjamin provided wording.]

- - - - - - - -
-

436. are cv-qualified facet types valid facets?

-

Section: 22.3.1.1.2 [locale.facet] Status: CD1 - Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-Is "const std::ctype<char>" a valid template argument to has_facet, use_facet, -and the locale template ctor? And if so, does it designate the same Facet as -the non-const "std::ctype<char>?" What about "volatile std::ctype<char>?" -Different implementations behave differently: some fail to compile, others -accept such types but behave inconsistently. -

- - -

Proposed resolution:

-

Change 22.1.1.1.2, p1 to read:

- -

Template parameters in this clause which are required to be facets -are those named Facet in declarations. A program that passes a type -that is not a facet, or a type that refers to volatile-qualified -facet, as an (explicit or deduced) template parameter to a locale -function expecting a facet, is ill-formed. A const-qualified facet is -a valid template argument to any locale function that expects a Facet -template parameter.

- -

[Kona: changed the last sentence from a footnote to normative -text.]

- - - - - - -
-

438. Ambiguity in the "do the right thing" clause

-

Section: 23.2.3 [sequence.reqmts] Status: CD1 - Submitter: Howard Hinnant Opened: 2003-10-20 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with CD1 status.

-

Discussion:

- -

Section 23.2.3 [sequence.reqmts], paragraphs 9-11, fixed up the problem -noticed with statements like:

-
-vector<int> v(10, 1);
-
- -

The intent of the above statement was to construct with:

-
-vector(size_type, const value_type&);
-
- -

but early implementations failed to compile as they bound to:

-
-template <class InputIterator>
-vector(InputIterator f, InputIterator l);
-
-

instead.

- -

Paragraphs 9-11 say that if InputIterator is an integral type, then the -member template constructor will have the same effect as:

-
-vector<static_cast<size_type>(f), static_cast<value_type>(l));
-
-

(and similarly for the other member template functions of sequences).

- -

There is also a note that describes one implementation technique:

-

- One way that sequence implementors can satisfy this requirement is to - specialize the member template for every integral type. -

- -

This might look something like:

-
-
-template <class T>
-struct vector
-{
-     typedef unsigned size_type;
-
-     explicit vector(size_type) {}
-     vector(size_type, const T&) {}
-
-     template <class I>
-     vector(I, I);
-
-     // ...
-};
-
-template <class T>
-template <class I>
-vector<T>::vector(I, I) { ... }
-
-template <>
-template <>
-vector<int>::vector(int, int) { ... }
-
-template <>
-template <>
-vector<int>::vector(unsigned, unsigned) { ... }
-
-//  ...
-
-
- -

Label this solution 'A'.

- -

The standard also says:

-

- Less cumbersome implementation techniques also exist. -

-

-A popular technique is to not specialize as above, but instead catch -every call with the member template, detect the type of InputIterator, -and then redirect to the correct logic. Something like: -

-
-
-template <class T>
-template <class I>
-vector<T>::vector(I f, I l)
-{
-     choose_init(f, l, int2type<is_integral<I>::value>());
-}
-
-template <class T>
-template <class I>
-vector<T>::choose_init(I f, I l, int2type<false>)
-{
-    // construct with iterators
-}
-
-template <class T>
-template <class I>
-vector<T>::choose_init(I f, I l, int2type<true>)
-{
-    size_type sz = static_cast<size_type>(f);
-    value_type v = static_cast<value_type>(l);
-    // construct with sz,v
-}
-
-
- -

Label this solution 'B'.

- -

Both of these solutions solve the case the standard specifically -mentions:

-
-vector<int> v(10, 1);  // ok, vector size 10, initialized to 1
-
- -

-However, (and here is the problem), the two solutions have different -behavior in some cases where the value_type of the sequence is not an -integral type. For example consider: -

-
-     pair<char, char>                     p('a', 'b');
-     vector<vector<pair<char, char> > >   d('a', 'b');
-
-

-The second line of this snippet is likely an error. Solution A catches -the error and refuses to compile. The reason is that there is no -specialization of the member template constructor that looks like: -

-
-template <>
-template <>
-vector<vector<pair<char, char> > >::vector(char, char) { ... }
-
- -

-So the expression binds to the unspecialized member template -constructor, and then fails (compile time) because char is not an -InputIterator. -

- -

-Solution B compiles the above example though. 'a' is casted to an -unsigned integral type and used to size the outer vector. 'b' is -static casted to the inner vector using it's explicit constructor: -

- -
-explicit vector(size_type n);
-
- -

-and so you end up with a static_cast<size_type>('a') by -static_cast<size_type>('b') matrix. -

- -

-It is certainly possible that this is what the coder intended. But the -explicit qualifier on the inner vector has been thwarted at any rate. -

- -

-The standard is not clear whether the expression: -

- -
-     vector<vector<pair<char, char> > >   d('a', 'b');
-
- -

-(and similar expressions) are: -

- -
    -
  1. undefined behavior.
    2. -
  2. illegal and must be rejected.
    3. -
  3. legal and must be accepted.
    4. -
- -

My preference is listed in the order presented.

- -

There are still other techniques for implementing the requirements of -paragraphs 9-11, namely the "restricted template technique" (e.g. -enable_if). This technique is the most compact and easy way of coding -the requirements, and has the behavior of #2 (rejects the above -expression). -

- -

-Choosing 1 would allow all implementation techniques I'm aware of. -Choosing 2 would allow only solution 'A' and the enable_if technique. -Choosing 3 would allow only solution 'B'. -

- -

-Possible wording for a future standard if we wanted to actively reject -the expression above would be to change "static_cast" in paragraphs -9-11 to "implicit_cast" where that is defined by: -

- -
-
-template <class T, class U>
-inline
-T implicit_cast(const U& u)
-{
-     return u;
-}
-
-
- - - -

Proposed resolution:

- -

Replace 23.2.3 [sequence.reqmts] paragraphs 9 - 11 with:

- -

For every sequence defined in this clause and in clause lib.strings:

- -
    -
  • -

    If the constructor

    - 
    -       template <class InputIterator>
-       X(InputIterator f, InputIterator l,
-         const allocator_type& a = allocator_type())
-
    -

    is called with a type InputIterator that does not qualify as - an input iterator, then the constructor will behave as if the - overloaded constructor:

    - 
    -       X(size_type, const value_type& = value_type(),
-         const allocator_type& = allocator_type())
-
    -

    were called instead, with the arguments static_cast<size_type>(f), l and a, respectively.

    -
    • - -
  • -

    If the member functions of the forms:

    - 
    -       template <class InputIterator>          //  such as  insert()
-       rt fx1(iterator p, InputIterator f, InputIterator l);
-
-       template <class InputIterator>          //  such as  append(), assign()
-       rt fx2(InputIterator f, InputIterator l);
-
-       template <class InputIterator>          //  such as  replace()
-       rt fx3(iterator i1, iterator i2, InputIterator f, InputIterator l);
-
    -

    are called with a type InputIterator that does not qualify as - an input iterator, then these functions will behave as if the - overloaded member functions:

    - 
    -       rt fx1(iterator, size_type, const value_type&);
-
-       rt fx2(size_type, const value_type&);
-
-       rt fx3(iterator, iterator, size_type, const value_type&);
-
    -

    were called instead, with the same arguments.

    -
    • -
- -

In the previous paragraph the alternative binding will fail if f -is not implicitly convertible to X::size_type or if l is not implicitly -convertible to X::value_type.

- -

-The extent to which an implementation determines that a type cannot be -an input iterator is unspecified, except that as a minimum integral -types shall not qualify as input iterators. -

- - - -

[ -Kona: agreed that the current standard requires v('a', 'b') -to be accepted, and also agreed that this is surprising behavior. The -LWG considered several options, including something like -implicit_cast, which doesn't appear to be quite what we want. We -considered Howards three options: allow acceptance or rejection, -require rejection as a compile time error, and require acceptance. By -straw poll (1-6-1), we chose to require a compile time error. -Post-Kona: Howard provided wording. -]

- - -

[ -Sydney: The LWG agreed with this general direction, but there was some -discomfort with the wording in the original proposed resolution. -Howard submitted new wording, and we will review this again in -Redmond. -]

- - -

[Redmond: one very small change in wording: the first argument - is cast to size_t. This fixes the problem of something like - vector<vector<int> >(5, 5), where int is not - implicitly convertible to the value type.]

- - - - -

Rationale:

-

The proposed resolution fixes:

- -
-  vector<int> v(10, 1);
-
- -

-since as integral types 10 and 1 must be disqualified as input -iterators and therefore the (size,value) constructor is called (as -if).

- -

The proposed resolution breaks:

- -
-  vector<vector<T> > v(10, 1);
-
- -

-because the integral type 1 is not *implicitly* convertible to -vector<T>. The wording above requires a diagnostic.

- -

-The proposed resolution leaves the behavior of the following code -unspecified. -

- -
-  struct A
-  {
-    operator int () const {return 10;}
-  };
-
-  struct B
-  {
-    B(A) {}
-  };
-
-  vector<B> v(A(), A());
-
- -

-The implementation may or may not detect that A is not an input -iterator and employee the (size,value) constructor. Note though that -in the above example if the B(A) constructor is qualified explicit, -then the implementation must reject the constructor as A is no longer -implicitly convertible to B. -

- - - - - -
-

441. Is fpos::state const?

-

Section: 27.5.4 [fpos] Status: CD1 - Submitter: Vincent Leloup Opened: 2003-11-17 Last modified: 2015-04-08

-

View all other issues in [fpos].

-

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-

Discussion:

-

-In section 27.5.4.1 [fpos.members] fpos<stateT>::state() is declared -non const, but in section 27.5.4 [fpos] it is declared const. -

- - -

Proposed resolution:

-

-In section 27.5.4.1 [fpos.members], change the declaration of -fpos<stateT>::state() to const. -

- - - - - -
-

442. sentry::operator bool() inconsistent signature

-

Section: 27.7.3.4 [ostream::sentry] Status: CD1 - Submitter: Vincent Leloup Opened: 2003-11-18 Last modified: 2015-04-08

-

View all other issues in [ostream::sentry].

-

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-

Discussion:

-

-In section 27.7.3.4 [ostream::sentry] paragraph 4, in description part -basic_ostream<charT, traits>::sentry::operator bool() is declared -as non const, but in section 27.6.2.3, in synopsis it is declared -const. -

- - -

Proposed resolution:

-

-In section 27.7.3.4 [ostream::sentry] paragraph 4, change the declaration -of sentry::operator bool() to const. -

- - - - - -
-

443. filebuf::close() inconsistent use of EOF

-

Section: 27.9.1.4 [filebuf.members] Status: CD1 - Submitter: Vincent Leloup Opened: 2003-11-20 Last modified: 2015-04-08

-

View all other issues in [filebuf.members].

-

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-

Discussion:

-

-In section 27.9.1.4 [filebuf.members] par6, in effects description of -basic_filebuf<charT, traits>::close(), overflow(EOF) is used twice; -should be overflow(traits::eof()). -

- - -

Proposed resolution:

-

-Change overflow(EOF) to overflow(traits::eof()). -

- - - - - -
-

444. Bad use of casts in fstream

-

Section: 27.9.1 [fstreams] Status: CD1 - Submitter: Vincent Leloup Opened: 2003-11-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-27.9.1.9 [ifstream.members] p1, 27.9.1.13 [ofstream.members] p1, 27.9.1.17 [fstream.members] p1 seems have same problem as exposed in LWG issue -252. -

- - -

Proposed resolution:

- -

[Sydney: Genuine defect. 27.8.1.13 needs a cast to cast away - constness. The other two places are stylistic: we could change the - C-style casts to const_cast. Post-Sydney: Howard provided wording. -]

- - -

Change 27.8.1.7/1 from:

-

- Returns: (basic_filebuf<charT,traits>*)&sb. -

- -

to:

-

- Returns: const_cast<basic_filebuf<charT,traits>*>(&sb). -

- -

Change 27.8.1.10/1 from:

-

- Returns: (basic_filebuf<charT,traits>*)&sb. -

- -

to:

-

- Returns: const_cast<basic_filebuf<charT,traits>*>(&sb). -

- -

Change 27.8.1.13/1 from:

-

- Returns: &sb. -

- -

to:

-

- Returns: const_cast<basic_filebuf<charT,traits>*>(&sb). -

- - - - - - - - -
-

445. iterator_traits::reference unspecified for some iterator categories

-

Section: 24.4.1 [iterator.traits] Status: CD1 - Submitter: Dave Abrahams Opened: 2003-12-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The standard places no restrictions at all on the reference type -of input, output, or forward iterators (for forward iterators it -only specifies that *x must be value_type& and doesn't mention -the reference type). Bidirectional iterators' reference type is -restricted only by implication, since the base iterator's -reference type is used as the return type of reverse_iterator's -operator*, which must be T& in order to be a conforming forward -iterator. -

- -

-Here's what I think we ought to be able to expect from an input -or forward iterator's reference type R, where a is an iterator -and V is its value_type -

- -
    -
  • - *a is convertible to R -
    • - -
  • - R is convertible to V -
    • - -
  • - static_cast<V>(static_cast<R>(*a)) is equivalent to - static_cast<V>(*a) -
    • -
- -

A mutable forward iterator ought to satisfy, for x of type V:

- 
-      { R r = *a; r = x; } is equivalent to *a = x;
-
- -

-I think these requirements capture existing container iterators -(including vector<bool>'s), but render istream_iterator invalid; -its reference type would have to be changed to a constant -reference. -

- - -

-(Jeremy Siek) During the discussion in Sydney, it was felt that a -simpler long term solution for this was needed. The solution proposed -was to require reference to be the same type as *a -and pointer to be the same type as a->. Most -iterators in the Standard Library already meet this requirement. Some -iterators are output iterators, and do not need to meet the -requirement, and others are only specified through the general -iterator requirements (which will change with this resolution). The -sole case where there is an explicit definition of the reference type -that will need to change is istreambuf_iterator which returns -charT from operator* but has a reference type of -charT&. We propose changing the reference type of -istreambuf_iterator to charT. -

- -

The other option for resolving the issue with pointer, - mentioned in the note below, is to remove pointer - altogether. I prefer placing requirements on pointer to - removing it for two reasons. First, pointer will become - useful for implementing iterator adaptors and in particular, - reverse_iterator will become more well defined. Second, - removing pointer is a rather drastic and publicly-visible - action to take.

- -

The proposed resolution technically enlarges the requirements for -iterators, which means there are existing iterators (such as -istreambuf_iterator, and potentially some programmer-defined -iterators) that will no longer meet the requirements. Will this break -existing code? The scenario in which it would is if an algorithm -implementation (say in the Standard Library) is changed to rely on -iterator_traits::reference, and then is used with one of the -iterators that do not have an appropriately defined -iterator_traits::reference. -

- - -

The proposed resolution makes one other subtle change. Previously, -it was required that output iterators have a difference_type -and value_type of void, which means that a forward -iterator could not be an output iterator. This is clearly a mistake, -so I've changed the wording to say that those types may be -void. -

- - - -

Proposed resolution:

- -

In 24.4.1 [iterator.traits], after:

- -

-be defined as the iterator's difference type, value type and iterator -category, respectively. -

- -

add

- -

-In addition, the types

-
-iterator_traits<Iterator>::reference
-iterator_traits<Iterator>::pointer
-
-

must be defined as the iterator's reference and pointer types, that -is, the same type as the type of *a and a->, -respectively.

-
- -

In 24.4.1 [iterator.traits], change:

- -

-In the case of an output iterator, the types

-
-iterator_traits<Iterator>::difference_type
-iterator_traits<Iterator>::value_type
-
-

are both defined as void.

-
- -

to:

-

-In the case of an output iterator, the types

-
-iterator_traits<Iterator>::difference_type
-iterator_traits<Iterator>::value_type
-iterator_traits<Iterator>::reference
-iterator_traits<Iterator>::pointer
-
-

may be defined as void.

-
- -

In 24.6.3 [istreambuf.iterator], change:

-
-
-typename traits::off_type, charT*, charT&>
-
-
-

to:

-
-
-typename traits::off_type, charT*, charT>
-
-
- -

[ -Redmond: there was concern in Sydney that this might not be the only place -where things were underspecified and needed to be changed. Jeremy -reviewed iterators in the standard and confirmed that nothing else -needed to be changed. -]

- - - - - - - - - -
-

448. Random Access Iterators over abstract classes

-

Section: 24.2.7 [random.access.iterators] Status: CD1 - Submitter: Dave Abrahams Opened: 2004-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Table 76, the random access iterator requirement table, says that the -return type of a[n] must be "convertible to T". When an iterator's -value_type T is an abstract class, nothing is convertible to T. -Surely this isn't an intended restriction? -

- - -

Proposed resolution:

-

-Change the return type to "convertible to T const&". -

- - - - - -
-

449. Library Issue 306 Goes Too Far

-

Section: 18.2 [support.types] Status: CD1 - Submitter: Pete Becker Opened: 2004-01-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Original text:

-

-The macro offsetof accepts a restricted set of type arguments in this -International Standard. type shall be a POD structure or a POD union -(clause 9). The result of applying the offsetof macro to a field that -is a static data member or a function member is undefined." -

- -

Revised text:

-

-"If type is not a POD structure or a POD union the results are undefined." -

- -

-Looks to me like the revised text should have replaced only the second -sentence. It doesn't make sense standing alone. -

- - - -

Proposed resolution:

-

Change 18.1, paragraph 5, to:

- -

-The macro offsetof accepts a restricted set of type arguments in this -International Standard. If type is not a POD structure or a POD union -the results are undefined. The result of applying the offsetof macro -to a field that is a static data member or a function member is -undefined." -

- - - - - -
-

453. basic_stringbuf::seekoff need not always fail for an empty stream

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: CD1 - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
-  pos_type basic_stringbuf::seekoff(off_type, ios_base::seekdir,
-                                    ios_base::openmode);
-
-

-is obliged to fail if nothing has been inserted into the stream. This -is unnecessary and undesirable. It should be permissible to seek to -an effective offset of zero.

- -

[ - Sydney: Agreed that this is an annoying problem: seeking to zero should be - legal. Bill will provide wording. -]

- - - - -

Proposed resolution:

-

Change the sentence from:

-

-For a sequence to be positioned, if its next pointer (either -gptr() or pptr()) is a null pointer, the positioning operation -fails. -

- -

to:

- -

-For a sequence to be positioned, if its next pointer (either -gptr() or pptr()) is a null pointer and the new offset newoff -is nonzero, the positioning operation fails. -

- - - - - -
-

455. cerr::tie() and wcerr::tie() are overspecified

-

Section: 27.4 [iostream.objects] Status: CD1 - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Both cerr::tie() and wcerr::tie() are obliged to be null at program -startup. This is overspecification and overkill. It is both traditional -and useful to tie cerr to cout, to ensure that standard output is drained -whenever an error message is written. This behavior should at least be -permitted if not required. Same for wcerr::tie(). -

- - -

Proposed resolution:

- -

Add to the description of cerr:

-

-After the object cerr is initialized, cerr.tie() returns &cout. -Its state is otherwise the same as required for basic_ios<char>::init -(lib.basic.ios.cons). -

- -

Add to the description of wcerr:

- -

-After the object wcerr is initialized, wcerr.tie() returns &wcout. -Its state is otherwise the same as required for basic_ios<wchar_t>::init -(lib.basic.ios.cons). -

- -

[Sydney: straw poll (3-1): we should require, not just - permit, cout and cerr to be tied on startup. Pre-Redmond: Bill will - provide wording.]

- - - - - - -
-

456. Traditional C header files are overspecified

-

Section: 17.6.1.2 [headers] Status: CD1 - Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2015-04-08

-

View all other issues in [headers].

-

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-

Discussion:

- -

The C++ Standard effectively requires that the traditional C headers -(of the form <xxx.h>) be defined in terms of the newer C++ -headers (of the form <cxxx>). Clauses 17.4.1.2/4 and D.5 combine -to require that:

- -
    -
  • Including the header <cxxx> declares a C name in namespace std.
    • - -
  • Including the header <xxx.h> declares a C name in namespace std - (effectively by including <cxxx>), then imports it into the global - namespace with an individual using declaration.
    • -
- -

-The rules were left in this form despited repeated and heated objections -from several compiler vendors. The C headers are often beyond the direct -control of C++ implementors. In some organizations, it's all they can do -to get a few #ifdef __cplusplus tests added. Third-party library vendors -can perhaps wrap the C headers. But neither of these approaches supports -the drastic restructuring required by the C++ Standard. As a result, it is -still widespread practice to ignore this conformance requirement, nearly -seven years after the committee last debated this topic. Instead, what is -often implemented is: -

- -
    -
  • Including the header <xxx.h> declares a C name in the - global namespace.
    • - -
  • Including the header <cxxx> declares a C name in the - global namespace (effectively by including <xxx.h>), then - imports it into namespace std with an individual using declaration.
    • -
- -

-The practical benefit for implementors with the second approach is that -they can use existing C library headers, as they are pretty much obliged -to do. The practical cost for programmers facing a mix of implementations -is that they have to assume weaker rules:

- -
    -
  • If you want to assuredly declare a C name in the global - namespace, include <xxx.h>. You may or may not also get the - declaration in namespace std.
    • - -
  • If you want to assuredly declare a C name in namespace std, - include <cxxx>. You may or may not also get the declaration in - the global namespace.
    • -
- -

-There also exists the possibility of subtle differences due to -Koenig lookup, but there are so few non-builtin types defined in the C -headers that I've yet to see an example of any real problems in this -area. -

- -

-It is worth observing that the rate at which programmers fall afoul of -these differences has remained small, at least as measured by newsgroup -postings and our own bug reports. (By an overwhelming margin, the -commonest problem is still that programmers include <string> and can't -understand why the typename string isn't defined -- this a decade after -the committee invented namespace std, nominally for the benefit of all -programmers.) -

- -

-We should accept the fact that we made a serious mistake and rectify it, -however belatedly, by explicitly allowing either of the two schemes for -declaring C names in headers. -

- -

[Sydney: This issue has been debated many times, and will - certainly have to be discussed in full committee before any action - can be taken. However, the preliminary sentiment of the LWG was in - favor of the change. (6 yes, 0 no, 2 abstain) Robert Klarer - suggests that we might also want to undeprecate the - C-style .h headers.]

- - - - -

Proposed resolution:

-

-Add to 17.6.1.2 [headers], para. 4: -

- -

-Except as noted in clauses 18 through 27 and Annex D, the contents of each -header cname shall be the same as that of the corresponding header -name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause -7), or ISO/IEC:1990 Programming Languages-C AMENDMENT 1: C Integrity, (Clause -7), as appropriate, as if by inclusion. In the C++ Standard Library, however, -the declarations and definitions (except for names which are defined -as macros in C) are within namespace scope (3.3.5) of the namespace std. -It is unspecified whether these names are first declared within the global -namespace scope and are then injected into namespace std by explicit -using-declarations (7.3.3 [namespace.udecl]). -

- -

-Change D.5 [depr.c.headers], para. 2-3: -

- -
-

--2- Every C header, each of which has a name of the form name.h, behaves -as if each name placed in the Standard library namespace by the corresponding -cname header is also placed within the global -namespace scope. of the namespace std and is followed -by an explicit using-declaration (7.3.3 [namespace.udecl]). -It is unspecified whether these names are first declared or defined within -namespace scope (3.3.6 [basic.scope.namespace]) of the namespace -std and are then injected into the global namespace scope by explicit -using-declarations (7.3.3 [namespace.udecl]). -

-

--3- [Example: The header <cstdlib> assuredly -provides its declarations and definitions within the namespace std. -It may also provide these names within the global namespace. The -header <stdlib.h> makes these available also in -assuredly provides the same declarations and definitions within the -global namespace, much as in the C Standard. It may also provide these -names within the namespace std. -- end example] -

-
- - - - - -
-

457. bitset constructor: incorrect number of initialized bits

-

Section: 20.6.1 [bitset.cons] Status: CD1 - Submitter: Dag Henriksson Opened: 2004-01-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The constructor from unsigned long says it initializes "the first M -bit positions to the corresponding bit values in val. M is the smaller -of N and the value CHAR_BIT * sizeof(unsigned long)." -

- -

-Object-representation vs. value-representation strikes again. CHAR_BIT * -sizeof (unsigned long) does not give us the number of bits an unsigned long -uses to hold the value. Thus, the first M bit position above is not -guaranteed to have any corresponding bit values in val. -

- - -

Proposed resolution:

-

In 20.6.1 [bitset.cons] paragraph 2, change "M is the smaller of - N and the value CHAR_BIT * sizeof (unsigned long). (249)" to - "M is the smaller of N and the number of bits in - the value representation (section 3.9 [basic.types]) of unsigned - long." -

- - - - - -
-

460. Default modes missing from basic_fstream member specifications

-

Section: 27.9.1 [fstreams] Status: CD1 - Submitter: Ben Hutchings Opened: 2004-04-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The second parameters of the non-default constructor and of the open -member function for basic_fstream, named "mode", are optional -according to the class declaration in 27.8.1.11 [lib.fstream]. The -specifications of these members in 27.8.1.12 [lib.fstream.cons] and -27.8.1.13 lib.fstream.members] disagree with this, though the -constructor declaration has the "explicit" function-specifier implying -that it is intended to be callable with one argument. -

- - -

Proposed resolution:

-

In 27.9.1.15 [fstream.cons], change

-
-  explicit basic_fstream(const char* s, ios_base::openmode mode); 
-
-

to

-
-  explicit basic_fstream(const char* s,
-                         ios_base::openmode mode = ios_base::in|ios_base::out);
-
-

In 27.9.1.17 [fstream.members], change

-
-  void open(const char*s, ios_base::openmode mode); 
-
-

to

-
-  void open(const char*s,
-            ios_base::openmode mode = ios_base::in|ios_base::out);
-
- - - - - -
-

461. time_get hard or impossible to implement

-

Section: 22.4.5.1.2 [locale.time.get.virtuals] Status: CD1 - Submitter: Bill Plauger Opened: 2004-03-23 Last modified: 2015-04-08

-

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-

Discussion:

-

-Template time_get currently contains difficult, if not impossible, -requirements for do_date_order, do_get_time, and do_get_date. All require -the implementation to scan a field generated by the %x or %X conversion -specifier in strftime. Yes, do_date_order can always return no_order, but -that doesn't help the other functions. The problem is that %x can be -nearly anything, and it can vary widely with locales. It's horribly -onerous to have to parse "third sunday after Michaelmas in the year of -our Lord two thousand and three," but that's what we currently ask of -do_get_date. More practically, it leads some people to think that if -%x produces 10.2.04, we should know to look for dots as separators. Still -not easy. -

- -

-Note that this is the opposite effect from the intent stated in the -footnote earlier in this subclause: -

- -

-"In other words, user confirmation is required for reliable parsing of -user-entered dates and times, but machine-generated formats can be -parsed reliably. This allows parsers to be aggressive about interpreting -user variations on standard formats." -

- -

-We should give both implementers and users an easier and more reliable -alternative: provide a (short) list of alternative delimiters and say -what the default date order is for no_order. For backward compatibility, -and maximum latitude, we can permit an implementation to parse whatever -%x or %X generates, but we shouldn't require it. -

- - -

Proposed resolution:

- -

In the description:

-
-iter_type do_get_time(iter_type s, iter_type end, ios_base& str,
-        ios_base::iostate& err, tm* t) const;
-
- -

-2 Effects: Reads characters starting at suntil it has extracted those -struct tm members, and remaining format characters, used by -time_put<>::put to produce the format specified by 'X', or until it -encounters an error or end of sequence. -

- -

change: 'X'

- -

to: "%H:%M:%S"

- - -

Change

-
-iter_type do_get_date(iter_type s, iter_type end, ios_base& str,
-        ios_base::iostate& err, tm* t) const;
-
-4 Effects: Reads characters starting at s until it has extracted those
-struct tm members, and remaining format characters, used by
-time_put<>::put to produce the format specified by 'x', or until it
-encounters an error.
-
- -

to

-
-iter_type do_get_date(iter_type s, iter_type end, ios_base& str,
-        ios_base::iostate& err, tm* t) const;
-
- -

-4 Effects: Reads characters starting at s until it has extracted those -struct tm members, and remaining format characters, used by -time_put<>::put to produce one of the following formats, or until it -encounters an error. The format depends on the value returned by -date_order() as follows: -

- -
-        date_order()  format
-
-        no_order      "%m/%d/%y"
-        dmy           "%d/%m/%y"
-        mdy           "%m/%d/%y"
-        ymd           "%y/%m/%d"
-        ydm           "%y/%d/%m"
-
-

-An implementation may also accept additional implementation-defined formats. -

- -

[Redmond: agreed that this is a real problem. The solution is - probably to match C99's parsing rules. Bill provided wording. -]

- - - - - - - -
-

464. Suggestion for new member functions in standard containers

-

Section: 23.3.6 [vector], 23.4.4 [map] Status: CD1 - Submitter: Thorsten Ottosen Opened: 2004-05-12 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

To add slightly more convenience to vector<T> and map<Key,T> we should consider to add

-
    -
  1. add vector<T>::data() member (const and non-const version) -semantics: if( empty() ) return 0; else return buffer_;
    2. -
  2. add map<Key,T>::at( const Key& k ) member (const and non-const version) -semantics: iterator i = find( k ); if( i != end() ) return *i; else throw range_error();
    3. -
- -

Rationale:

- -
    -
  • To obtain a pointer to the vector's buffer, one must use either operator[]() (which can give undefined behavior for empty vectors) or at() (which will then throw if the vector is empty).
    • -
  • tr1::array<T,sz> already has a data() member
    • -
  • e cannot use operator[]() when T is not DefaultDonstructible
    • -
  • Neither when the map is const.
    • -
  • when we want to make sure we don't add an element accidently
    • -
  • when it should be considered an error if a key is not in the map
    • -
- - - -

Proposed resolution:

-

In 23.3.6 [vector], add the following to the vector - synopsis after "element access" and before "modifiers":

-
-  // [lib.vector.data] data access
-  pointer       data();
-  const_pointer data() const;
-
- -

Add a new subsection of 23.3.6 [vector]:

-
-

23.2.4.x vector data access

-
-   pointer       data();
-   const_pointer data() const;
-
-

Returns: A pointer such that [data(), data() + size()) is a valid - range. For a non-empty vector, data() == &front().

-

Complexity: Constant time.

-

Throws: Nothing.

-
- -

In 23.4.4 [map], add the following to the map -synopsis immediately after the line for operator[]:

-
-  T&       at(const key_type& x);
-  const T& at(const key_type& x) const;
-
- -

Add the following to 23.4.4.3 [map.access]:

-
-
-  T&       at(const key_type& x);
-  const T& at(const key_type& x) const;
-
- -

Returns: A reference to the element whose key is equivalent - to x, if such an element is present in the map.

-

Throws: out_of_range if no such element is present.

- -
- - - -

Rationale:

-

Neither of these additions provides any new functionality but the - LWG agreed that they are convenient, especially for novices. The - exception type chosen for at, std::out_of_range, - was chosen to match vector::at.

- - - - - -
-

465. Contents of <ciso646>

-

Section: 17.6.1.2 [headers] Status: CD1 - Submitter: Steve Clamage Opened: 2004-06-03 Last modified: 2015-04-08

-

View all other issues in [headers].

-

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-

Discussion:

-

C header <iso646.h> defines macros for some operators, such as -not_eq for !=.

- -

Section 17.6.1.2 [headers] "Headers" says that except as noted in -clauses 18 through 27, the <cname> C++ header contents are the same -as the C header <name.h>. In particular, table 12 lists -<ciso646> as a C++ header.

- -

I don't find any other mention of <ciso646>, or any mention of -<iso646.h>, in clauses 17 thorough 27. That implies that the -contents of <ciso646> are the same as C header <iso646.h>.

- -

Annex C (informative, not normative) in [diff.header.iso646.h] C.2.2.2 -"Header <iso646.h>" says that the alternative tokens are not -defined as macros in <ciso646>, but does not mention the contents -of <iso646.h>.

- -

I don't find any normative text to support C.2.2.2.

- - - -

Proposed resolution:

-

Add to section 17.4.1.2 Headers [lib.headers] a new paragraph after - paragraph 6 (the one about functions must be functions):

- -
-

Identifiers that are keywords or operators in C++ shall not be defined -as macros in C++ standard library headers. -[Footnote:In particular, including the standard header <iso646.h> -or <ciso646> has no effect.

-
- -

[post-Redmond: Steve provided wording.]

- - - - - - - -
-

467. char_traits::lt(), compare(), and memcmp()

-

Section: 21.2.3.1 [char.traits.specializations.char] Status: CD1 - Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

- -

-Table 37 describes the requirements on Traits::compare() in terms of -those on Traits::lt(). 21.1.3.1, p6 requires char_traits<char>::lt() -to yield the same result as operator<(char, char). -

- -

-Most, if not all, implementations of char_traits<char>::compare() -call memcmp() for efficiency. However, the C standard requires both -memcmp() and strcmp() to interpret characters under comparison as -unsigned, regardless of the signedness of char. As a result, all -these char_traits implementations fail to meet the requirement -imposed by Table 37 on compare() when char is signed. -

- - -

Read email thread starting with c++std-lib-13499 for more.

- - -

Proposed resolution:

- - -

Change 21.1.3.1, p6 from

-

- The two-argument members assign, eq, and lt are defined identically - to the built-in operators =, ==, and < respectively. -

-

to

-

- The two-argument member assign is defined identically to - the built-in operator =. The two - argument members eq and lt are defined identically to - the built-in operators == and < for type unsigned char. -

- -

[Redmond: The LWG agreed with this general direction, but we - also need to change eq to be consistent with this change. - Post-Redmond: Martin provided wording.]

- - - - - - -
-

468. unexpected consequences of ios_base::operator void*()

-

Section: 27.5.5.4 [iostate.flags] Status: CD1 - Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2015-04-08

-

View all other issues in [iostate.flags].

-

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-

Discussion:

- -

The program below is required to compile but when run it typically -produces unexpected results due to the user-defined conversion from -std::cout or any object derived from basic_ios to void*. -

- -
-    #include <cassert>
-    #include <iostream>
-
-    int main ()
-    {
-        assert (std::cin.tie () == std::cout);
-        // calls std::cout.ios::operator void*()
-    }
-
- - -

Proposed resolution:

- -

-Replace std::basic_ios<charT, traits>::operator void*() with another -conversion operator to some unspecified type that is guaranteed not -to be convertible to any other type except for bool (a pointer-to-member -might be one such suitable type). In addition, make it clear that the -pointer type need not be a pointer to a complete type and when non-null, -the value need not be valid. -

- -

Specifically, change in [lib.ios] the signature of

-
-    operator void*() const;
-
-

to

-
-    operator unspecified-bool-type() const;
-
-

and change [lib.iostate.flags], p1 from

-
-    operator void*() const;
-
-

to

-
-operator unspecified-bool-type() const;
-
-     -1- Returns: if fail() then a value that will evaluate false in a
-      boolean context; otherwise a value that will evaluate true in a
-      boolean context. The value type returned shall not be
-      convertible to int.
-
-     -2- [Note: This conversion can be used in contexts where a bool
-      is expected (e.g., an if condition); however, implicit
-      conversions (e.g., to int) that can occur with bool are not
-      allowed, eliminating some sources of user error. One possible
-      implementation choice for this type is pointer-to-member.  - end
-      note]
-
- -

[Redmond: 5-4 straw poll in favor of doing this.]

- -

[Lillehammer: Doug provided revised wording for - "unspecified-bool-type".]

- - - - - - - - -
-

469. vector<bool> ill-formed relational operators

-

Section: 23.3.6 [vector] Status: CD1 - Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2015-04-08

-

View all other issues in [vector].

-

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-

Discussion:

- -

-The overloads of relational operators for vector<bool> specified -in [lib.vector.bool] are redundant (they are semantically identical -to those provided for the vector primary template) and may even be -diagnosed as ill-formed (refer to Daveed Vandevoorde's explanation -in c++std-lib-13647). -

- - - -

Proposed resolution:

-

-Remove all overloads of overloads of relational operators for -vector<bool> from [lib.vector.bool]. -

- - - - -
-

471. result of what() implementation-defined

-

Section: 18.8.1 [exception] Status: C++11 - Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

- -

[lib.exception] specifies the following:

-
-    exception (const exception&) throw();
-    exception& operator= (const exception&) throw();
-
-    -4- Effects: Copies an exception object.
-    -5- Notes: The effects of calling what() after assignment
-        are implementation-defined.
-
- -

-First, does the Note only apply to the assignment operator? If so, -what are the effects of calling what() on a copy of an object? Is -the returned pointer supposed to point to an identical copy of -the NTBS returned by what() called on the original object or not? -

- -

-Second, is this Note intended to extend to all the derived classes -in section 19? I.e., does the standard provide any guarantee for -the effects of what() called on a copy of any of the derived class -described in section 19? -

- -

-Finally, if the answer to the first question is no, I believe it -constitutes a defect since throwing an exception object typically -implies invoking the copy ctor on the object. If the answer is yes, -then I believe the standard ought to be clarified to spell out -exactly what the effects are on the copy (i.e., after the copy -ctor was called). -

- -

[Redmond: Yes, this is fuzzy. The issue of derived classes is - fuzzy too.]

- - -

[ -Batavia: Howard provided wording. -]

- - -

[ -Bellevue: -]

- - -
-

-Eric concerned this is unimplementable, due to nothrow guarantees. -Suggested implementation would involve reference counting. -

-

-Is the implied reference counting subtle enough to call out a note on -implementation? Probably not. -

-

-If reference counting required, could we tighten specification further -to require same pointer value? Probably an overspecification, especially -if exception classes defer evalutation of final string to calls to -what(). -

-

-Remember issue moved open and not resolved at Batavia, but cannot -remember who objected to canvas a disenting opinion - please speak up if -you disagree while reading these minutes! -

-

-Move to Ready as we are accepting words unmodified. -

-
- -

[ -Sophia Antipolis: -]

- - -

-The issue was pulled from Ready. It needs to make clear that only homogenous copying -is intended to be supported, not coping from a derived to a base. -

- -

[ -Batavia (2009-05): -]

- -
-

-Howard supplied the following replacement wording -for paragraph 7 of the proposed resolution: -

-

--7- Postcondition: what() shall return the same NTBS - as would be obtained by using static_cast - to cast the rhs to the same types as the lhs - and then calling what() on that possibly sliced object. -

-

-Pete asks what "the same NTBS" means. -

-
- -

[ -2009-07-30 Niels adds: -]

- - -

-Further discussion in the thread starting with c++std-lib-24512. -

- -

[ -2009-09-24 Niels provided updated wording: -]

- - -
-

-I think the resolution should at least guarantee -that the result of what() is independent of whether the compiler does -copy-elision. And for any class derived from std::excepion that has a -constructor that allows specifying a what_arg, it should make sure that -the text of a user-provided what_arg is preserved, when the object is -copied. Note that all the implementations I've tested already appear to -satisfy the proposed resolution, including MSVC 2008 SP1, Apache -stdcxx-4.2.1, GCC 4.1.2, GCC 4.3.2, and CodeGear C++ 6.13. -

-

-The proposed resolution was updated with help from Daniel Krügler; -the update aims to clarify that the proposed postcondition only -applies to homogeneous copying. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready after inserting "publicly accessible" in two places. -

- - - -

Proposed resolution:

- -

-Change 18.8.1 [exception] to: -

- -
-

--1- The class exception defines the base class for the types of -objects thrown as exceptions by C++ standard library components, and -certain expressions, to report errors detected during program execution. -

-

-Each standard library class T that derives from class -exception shall have a publicly accessible copy constructor and a publicly accessible copy assignment -operator that do not exit with an exception. These member functions -shall preserve the following postcondition: If two objects lhs -and rhs both have dynamic type T, and lhs is a -copy of rhs, then strcmp(lhs.what(), -rhs.what()) == 0. -

-

- ... -

- -
exception(const exception& rhs) throw();
-exception& operator=(const exception& rhs) throw();
- -
-

--4- Effects: Copies an exception object. -

-

- -5- Remarks: The effects of calling what() after assignment -are implementation-defined. -

-

--5- Postcondition: - If *this - and rhs both have dynamic type exception - then strcmp(what(), rhs.what()) == 0. -

- -
- -
- - - - - -
-

473. underspecified ctype calls

-

Section: 22.4.1.1 [locale.ctype] Status: C++11 - Submitter: Martin Sebor Opened: 2004-07-01 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Most ctype member functions come in two forms: one that operates -on a single character at a time and another form that operates -on a range of characters. Both forms are typically described by -a single Effects and/or Returns clause. -

-

-The Returns clause of each of the single-character non-virtual forms -suggests that the function calls the corresponding single character -virtual function, and that the array form calls the corresponding -virtual array form. Neither of the two forms of each virtual member -function is required to be implemented in terms of the other. -

-

-There are three problems: -

-

-1. One is that while the standard does suggest that each non-virtual -member function calls the corresponding form of the virtual function, -it doesn't actually explicitly require it. -

-

-Implementations that cache results from some of the virtual member -functions for some or all values of their arguments might want to -call the array form from the non-array form the first time to fill -the cache and avoid any or most subsequent virtual calls. Programs -that rely on each form of the virtual function being called from -the corresponding non-virtual function will see unexpected behavior -when using such implementations. -

-

-2. The second problem is that either form of each of the virtual -functions can be overridden by a user-defined function in a derived -class to return a value that is different from the one produced by -the virtual function of the alternate form that has not been -overriden. -

-

-Thus, it might be possible for, say, ctype::widen(c) to return one -value, while for ctype::widen(&c, &c + 1, &wc) to set -wc to another value. This is almost certainly not intended. Both -forms of every function should be required to return the same result -for the same character, otherwise the same program using an -implementation that calls one form of the functions will behave -differently than when using another implementation that calls the -other form of the function "under the hood." -

-

-3. The last problem is that the standard text fails to specify whether -one form of any of the virtual functions is permitted to be implemented -in terms of the other form or not, and if so, whether it is required -or permitted to call the overridden virtual function or not. -

-

-Thus, a program that overrides one of the virtual functions so that -it calls the other form which then calls the base member might end -up in an infinite loop if the called form of the base implementation -of the function in turn calls the other form. -

-

-Lillehammer: Part of this isn't a real problem. We already talk about -caching. 22.1.1/6 But part is a real problem. ctype virtuals may call -each other, so users don't know which ones to override to avoid avoid -infinite loops.

- -

This is a problem for all facet virtuals, not just ctype virtuals, -so we probably want a blanket statement in clause 22 for all -facets. The LWG is leaning toward a blanket prohibition, that a -facet's virtuals may never call each other. We might want to do that -in clause 27 too, for that matter. A review is necessary. Bill will -provide wording.

- -

[ -2009-07 Frankfurt, Howard provided wording directed by consensus. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add paragraph 3 to 22.4 [locale.categories]: -

- -

--3- Within this clause it is unspecified if one virtual function calls another -virtual function. -

- - - -

Rationale:

-

-We are explicitly not addressing bullet -item #2, thus giving implementors more latitude. Users will have to -override both virtual functions, not just one. -

- - - - -
-

474. confusing Footnote 297

-

Section: 27.7.3.6.4 [ostream.inserters.character] Status: CD1 - Submitter: Martin Sebor Opened: 2004-07-01 Last modified: 2015-04-08

-

View all other issues in [ostream.inserters.character].

-

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-

Discussion:

- -

-I think Footnote 297 is confused. The paragraph it applies to seems -quite clear in that widen() is only called if the object is not a char -stream (i.e., not basic_ostream<char>), so it's irrelevant what the -value of widen(c) is otherwise. -

- - -

Proposed resolution:

-

-I propose to strike the Footnote. -

- - - - -
-

475. May the function object passed to for_each modify the elements of the iterated sequence?

-

Section: 25.2.4 [alg.foreach] Status: CD1 - Submitter: Stephan T. Lavavej, Jaakko Jarvi Opened: 2004-07-09 Last modified: 2015-04-08

-

View all other issues in [alg.foreach].

-

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-

Discussion:

-

-It is not clear whether the function object passed to for_each is allowed to -modify the elements of the sequence being iterated over. -

- -

-for_each is classified without explanation in [lib.alg.nonmodifying], "25.1 -Non-modifying sequence operations". 'Non-modifying sequence operation' is -never defined. -

- -

-25(5) says: "If an algorithm's Effects section says that a value pointed to -by any iterator passed as an argument is modified, then that algorithm has -an additional type requirement: The type of that argument shall satisfy the -requirements of a mutable iterator (24.1)." -

- -

for_each's Effects section does not mention whether arguments can be -modified:

- -

- "Effects: Applies f to the result of dereferencing every iterator in the - range [first, last), starting from first and proceeding to last - 1." -

- -

-Every other algorithm in [lib.alg.nonmodifying] is "really" non-modifying in -the sense that neither the algorithms themselves nor the function objects -passed to the algorithms may modify the sequences or elements in any way. -This DR affects only for_each. -

- -

-We suspect that for_each's classification in "non-modifying sequence -operations" means that the algorithm itself does not inherently modify the -sequence or the elements in the sequence, but that the function object -passed to it may modify the elements it operates on. -

- -

-The original STL document by Stepanov and Lee explicitly prohibited the -function object from modifying its argument. -The "obvious" implementation of for_each found in several standard library -implementations, however, does not impose this restriction. -As a result, we suspect that the use of for_each with function objects that modify -their arguments is wide-spread. -If the restriction was reinstated, all such code would become non-conforming. -Further, none of the other algorithms in the Standard -could serve the purpose of for_each (transform does not guarantee the order in -which its function object is called). -

- -

-We suggest that the standard be clarified to explicitly allow the function object -passed to for_each modify its argument.

- - - -

Proposed resolution:

-

Add a nonnormative note to the Effects in 25.2.4 [alg.foreach]: If -the type of 'first' satisfies the requirements of a mutable iterator, -'f' may apply nonconstant functions through the dereferenced iterators -passed to it. -

- - - -

Rationale:

-

The LWG believes that nothing in the standard prohibits function - objects that modify the sequence elements. The problem is that - for_each is in a secion entitled "nonmutating algorithms", and the - title may be confusing. A nonnormative note should clarify that.

- - - - - -
-

478. Should forward iterator requirements table have a line for r->m?

-

Section: 24.2.5 [forward.iterators] Status: CD1 - Submitter: Dave Abrahams Opened: 2004-07-11 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

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-

Duplicate of: 477

-

Discussion:

-

-The Forward Iterator requirements table contains the following: -

-
- expression  return type         operational  precondition
-                                  semantics
-  ==========  ==================  ===========  ==========================
-  a->m        U& if X is mutable, (*a).m       pre: (*a).m is well-defined.
-              otherwise const U&
-
-  r->m        U&                  (*r).m       pre: (*r).m is well-defined.
-
- -

The second line may be unnecessary. Paragraph 11 of - [lib.iterator.requirements] says: -

- -

- In the following sections, a and b denote values of type const X, n - denotes a value of the difference type Distance, u, tmp, and m - denote identifiers, r denotes a value of X&, t denotes a value of - value type T, o denotes a value of some type that is writable to - the output iterator. -

- -

-Because operators can be overloaded on an iterator's const-ness, the -current requirements allow iterators to make many of the operations -specified using the identifiers a and b invalid for non-const -iterators.

- -

Related issue: 477

- - -

Proposed resolution:

- -

Remove the "r->m" line from the Forward Iterator requirements -table. Change

-

- "const X" -

- -

to

- -

- "X or const X" -

- -

in paragraph 11 of [lib.iterator.requirements].

- - - - -

Rationale:

-

-This is a defect because it constrains an lvalue to returning a modifiable lvalue. -

- - - - - -
-

482. Swapping pairs

-

Section: 20.3 [pairs], 20.4 [tuple] Status: Resolved - Submitter: Andrew Koenig Opened: 2004-09-14 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Discussion:

-

(Based on recent comp.std.c++ discussion)

- -

Pair (and tuple) should specialize std::swap to work in terms of -std::swap on their components. For example, there's no obvious reason -why swapping two objects of type pair<vector<int>, -list<double> > should not take O(1).

- -

[Lillehammer: We agree it should be swappable. Howard will - provide wording.]

- - -

[ -Post Oxford: We got swap for pair but accidently -missed tuple. tuple::swap is being tracked by 522. -]

- - - - -

Proposed resolution:

-

-Wording provided in -N1856. -

- -

Rationale:

-

-Recommend NADResolved, fixed by -N1856. -

- - - - - -
-

485. output iterator insufficiently constrained

-

Section: 24.2.4 [output.iterators] Status: Resolved - Submitter: Chris Jefferson Opened: 2004-10-13 Last modified: 2015-04-08

-

View other active issues in [output.iterators].

-

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-

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-

Discussion:

-

-The note on 24.1.2 Output iterators insufficiently limits what can be -performed on output iterators. While it requires that each iterator is -progressed through only once and that each iterator is written to only -once, it does not require the following things:

- -

Note: Here it is assumed that x is an output iterator of type X which -has not yet been assigned to.

- -

a) That each value of the output iterator is written to: -The standard allows: -++x; ++x; ++x; -

- -

-b) That assignments to the output iterator are made in order -X a(x); ++a; *a=1; *x=2; is allowed -

- -

-c) Chains of output iterators cannot be constructed: -X a(x); ++a; X b(a); ++b; X c(b); ++c; is allowed, and under the current -wording (I believe) x,a,b,c could be written to in any order. -

- -

I do not believe this was the intension of the standard?

-

[Lillehammer: Real issue. There are lots of constraints we - intended but didn't specify. Should be solved as part of iterator - redesign.]

- - -

[ -2009-07 Frankfurt -]

- - -

-Bill provided wording according to consensus. -

- -

[ -2009-07-21 Alisdair requests change from Review to Open. See thread starting -with c++std-lib-24459 for discussion. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Modified wording. Set to Review. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready after looking at again in a larger group in Santa Cruz. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3066. -

- - -

Proposed resolution:

-

-Change Table 101 — Output iterator requirements in 24.2.4 [output.iterators]: -

-
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 101 — Output iterator requirements
ExpressionReturn typeOperational semanticsAssertion/note pre-/post-condition
-X(a) - -  - -  - -a = t is equivalent to X(a) = t. note: a destructor is assumed. -
-X u(a);
-X u = a; -		 -  - -  - -  -
-*r = o - -result is not used - -  - - -Post: r is not required to be dereferenceable. r is incrementable. - -
-++r - -X& - -  - -&r == &++r - -Post: r is dereferenceable, unless otherwise specified. r is not required to be incrementable. - -
-r++ - -convertible to const X& - -{X tmp = r;
++r;
return tmp;} -		 - -Post: r is dereferenceable, unless otherwise specified. r is not required to be incrementable. - -
-*r++ = o; - -result is not used - -  - - -
-
- - - - - -
-

488. rotate throws away useful information

-

Section: 25.3.11 [alg.rotate] Status: CD1 - Submitter: Howard Hinnant Opened: 2004-11-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-rotate takes 3 iterators: first, middle and last which point into a -sequence, and rearranges the sequence such that the subrange [middle, -last) is now at the beginning of the sequence and the subrange [first, -middle) follows. The return type is void. -

- -

-In many use cases of rotate, the client needs to know where the -subrange [first, middle) starts after the rotate is performed. This -might look like: -

-
-  rotate(first, middle, last);
-  Iterator i = advance(first, distance(middle, last));
-
- -

-Unless the iterators are random access, the computation to find the -start of the subrange [first, middle) has linear complexity. However, -it is not difficult for rotate to return this information with -negligible additional computation expense. So the client could code: -

-
-  Iterator i = rotate(first, middle, last);
-
- -

-and the resulting program becomes significantly more efficient. -

- -

-While the backwards compatibility hit with this change is not zero, it -is very small (similar to that of lwg 130), and there is -a significant benefit to the change. -

- - - -

Proposed resolution:

-

In 25 [algorithms] p2, change:

- -
-  template<class ForwardIterator>
-    void ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
-                ForwardIterator last);
-
- -

In 25.3.11 [alg.rotate], change:

- -
-  template<class ForwardIterator>
-    void ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
-                ForwardIterator last);
-
- -

In 25.3.11 [alg.rotate] insert a new paragraph after p1:

- -
-

Returns: first + (last - middle).

-
- -

[ -The LWG agrees with this idea, but has one quibble: we want to make -sure not to give the impression that the function "advance" is -actually called, just that the nth iterator is returned. (Calling -advance is observable behavior, since users can specialize it for -their own iterators.) Howard will provide wording. -]

- - -

[Howard provided wording for mid-meeting-mailing Jun. 2005.]

- - -

[ -Toronto: moved to Ready. -]

- - - - - - - -
-

495. Clause 22 template parameter requirements

-

Section: 22 [localization] Status: CD1 - Submitter: Beman Dawes Opened: 2005-01-10 Last modified: 2015-04-08

-

View all other issues in [localization].

-

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-

Discussion:

-

It appears that there are no requirements specified for many of the -template parameters in clause 22. It looks like this issue has never -come up, except perhaps for Facet.

- -

Clause 22 isn't even listed in 17.3.2.1 [lib.type.descriptions], -either, which is the wording that allows requirements on template -parameters to be identified by name.

- -

So one issue is that 17.3.2.1 [lib.type.descriptions] Should be -changed to cover clause 22. A better change, which will cover us in -the future, would be to say that it applies to all the library -clauses. Then if a template gets added to any library clause we are -covered.

- -

charT, InputIterator, and other names with requirements defined -elsewhere are fine, assuming the 17.3.2.1 [lib.type.descriptions] fix. -But there are a few template arguments names which I don't think have -requirements given elsewhere:

- -
    -
  • internT and externT. The fix is to add wording saying that internT -and externT must meet the same requirements as template arguments -named charT.
    • - -
  • stateT. I'm not sure about this one. There already is some wording, -but it seems a bit vague.
    • - -
  • Intl. [lib.locale.moneypunct.byname] The fix for this one is to -rename "Intl" to "International". The name is important because other -text identifies the requirements for the name International but not -for Intl.
    • -
- -

Proposed resolution:

-

Change 17.5.2.1 [type.descriptions], paragraph 1, from:

-

-The Requirements subclauses may describe names that are used to -specify constraints on template arguments.153) These names are used in -clauses 20, 23, 25, and 26 to describe the types that may be supplied -as arguments by a C++ program when instantiating template components -from the library. -

-

to:

-

-The Requirements subclauses may describe names that are used to -specify constraints on template arguments.153) These names are used in -library clauses to describe the types that may be supplied as -arguments by a C++ program when instantiating template components from -the library. -

- -

In the front matter of class 22, locales, add:

-

-Template parameter types internT and externT shall meet the -requirements of charT (described in 21 [strings]). -

- - -

Rationale:

-

- Again, a blanket clause isn't blanket enough. Also, we've got a - couple of names that we don't have blanket requirement statements - for. The only issue is what to do about stateT. This wording is - thin, but probably adequate.

- - - - - -
-

496. Illegal use of "T" in vector<bool>

-

Section: 23.3.6 [vector] Status: CD1 - Submitter: richard@ex-parrot.com Opened: 2005-02-10 Last modified: 2015-04-08

-

View all other issues in [vector].

-

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-

Discussion:

-

-In the synopsis of the std::vector<bool> specialisation in 23.3.6 [vector], -the non-template assign() function has the signature

- -
-  void assign( size_type n, const T& t );
-
- -

The type, T, is not defined in this context.

- - -

Proposed resolution:

-

Replace "T" with "value_type".

- - - - - -
-

497. meaning of numeric_limits::traps for floating point types

-

Section: 18.3.2.4 [numeric.limits.members] Status: CD1 - Submitter: Martin Sebor Opened: 2005-03-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

18.2.1.2, p59 says this much about the traps member of numeric_limits:

- -
-

static const bool traps;
--59- true if trapping is implemented for the type.204) -
-Footnote 204: Required by LIA-1. -

-
- -

It's not clear what is meant by "is implemented" here.

- -

-In the context of floating point numbers it seems reasonable to expect -to be able to use traps to determine whether a program can "safely" use -infinity(), quiet_NaN(), etc., in arithmetic expressions, that is -without causing a trap (i.e., on UNIX without having to worry about -getting a signal). When traps is true, I would expect any of the -operations in section 7 of IEEE 754 to cause a trap (and my program -to get a SIGFPE). So, for example, on Alpha, I would expect traps -to be true by default (unless I compiled my program with the -ieee -option), false by default on most other popular architectures, -including IA64, MIPS, PA-RISC, PPC, SPARC, and x86 which require -traps to be explicitly enabled by the program. -

- -

-Another possible interpretation of p59 is that traps should be true -on any implementation that supports traps regardless of whether they -are enabled by default or not. I don't think such an interpretation -makes the traps member very useful, even though that is how traps is -implemented on several platforms. It is also the only way to implement -traps on platforms that allow programs to enable and disable trapping -at runtime. -

- - -

Proposed resolution:

-

Change p59 to read:

-

True if, at program startup, there exists a value of the type that - would cause an arithmetic operation using that value to trap.

- - -

Rationale:

-

- Real issue, since trapping can be turned on and off. Unclear what a - static query can say about a dynamic issue. The real advice we should - give users is to use cfenv for these sorts of queries. But this new - proposed resolution is at least consistent and slightly better than - nothing.

- - - - - -
-

498. Requirements for partition() and stable_partition() too strong

-

Section: 25.3.13 [alg.partitions] Status: C++11 - Submitter: Sean Parent, Joe Gottman Opened: 2005-05-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Problem: -The iterator requirements for partition() and stable_partition() [25.2.12] -are listed as BidirectionalIterator, however, there are efficient algorithms -for these functions that only require ForwardIterator that have been known -since before the standard existed. The SGI implementation includes these (see -http://www.sgi.com/tech/stl/partition.html -and -http://www.sgi.com/tech/stl/stable_partition.html). -

- -

[ -2009-04-30 Alisdair adds: -]

- - -
-

-Now we have concepts this is easier to express! -

-

-Proposed resolution: -

-

-Add the following signature to: -

-

-Header <algorithm> synopsis [algorithms.syn]
-p3 Partitions 25.3.13 [alg.partitions] -

-
- template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred>
-   requires ShuffleIterator<Iter>
-         && CopyConstructible<Pred>
-   Iter partition(Iter first, Iter last, Pred pred);
-
- -

-Update p3 Partitions 25.3.13 [alg.partitions]: -

- -
-

-Complexity: At most (last - first)/2 swaps. Exactly last - first -applications of the predicate -are done. - -If Iter satisfies BidirectionalIterator, at most (last - -first)/2 swaps. Exactly last - first applications of the predicate -are done. - -

-

-If Iter merely satisfied ForwardIterator at most (last - first) swaps -are done. Exactly (last - first) applications of the predicate are done. -

-
- -

-[Editorial note: I looked for existing precedent in how we might call out -distinct overloads overloads from a set of constrained templates, but there -is not much existing practice to lean on. advance/distance were the only -algorithms I could find, and that wording is no clearer.] -

- -
- -

[ -2009-07 Frankfurt -]

- - -
-

-Hinnant: if you want to partition your std::forward_list, you'll need -partition() to accept ForwardIterators. -

-

-No objection to Ready. -

-

-Move to Ready. -

-
- - - -

Proposed resolution:

-

-Change 25.2.12 from

-
-template<class BidirectionalIterator, class Predicate> 
-BidirectionalIterator partition(BidirectionalIterato r first, 
-                                BidirectionalIterator last, 
-                                Predicate pred); 
-
-

to

-
-template<class ForwardIterator, class Predicate> 
-ForwardIterator partition(ForwardIterator first, 
-                          ForwardIterator last, 
-                          Predicate pred); 
-
-

Change the complexity from

- -

-At most (last - first)/2 swaps are done. Exactly (last - first) -applications of the predicate are done. -

- -

to

- -

-If ForwardIterator is a bidirectional_iterator, at most (last - first)/2 -swaps are done; otherwise at most (last - first) swaps are done. Exactly -(last - first) applications of the predicate are done. -

- - - -

Rationale:

-

-Partition is a "foundation" algorithm useful in many contexts (like sorting -as just one example) - my motivation for extending it to include forward -iterators is foward_list - without this extension you can't partition an foward_list -(without writing your own partition). Holes like this in the standard -library weaken the argument for generic programming (ideally I'd be able -to provide a library that would refine std::partition() to other concepts -without fear of conflicting with other libraries doing the same - but -that is a digression). I consider the fact that partition isn't defined -to work for ForwardIterator a minor embarrassment. -

- -

[Mont Tremblant: Moved to Open, request motivation and use cases by next meeting. Sean provided further rationale by post-meeting mailing.]

- - - - - - - -
-

505. Result_type in random distribution requirements

-

Section: 26.5.1 [rand.req], TR1 5.1.1 [tr.rand.req] Status: CD1 - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Table 17: Random distribution requirements -

-

-Row 1 requires that each random distribution provide a nested type "input_type"; -this type denotes the type of the values that the distribution consumes. -

-

-Inspection of all distributions in [tr.rand.dist] reveals that each distribution -provides a second typedef ("result_type") that denotes the type of the values the -distribution produces when called. -

- - -

Proposed resolution:

-

-It seems to me that this is also a requirement -for all distributions and should therefore be indicated as such via a new second -row to this table 17: -

- - -
X::result_typeT---compile-time
- -

[ -Berlin: Voted to WP. N1932 adopts the proposed resolution: see Table 5 row 1. -]

- - - - - - - -
-

507. Missing requirement for variate_generator::operator()

-

Section: 26.5 [rand], TR1 5.1.3 [tr.rand.var] Status: CD1 - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Paragraph 11 of [tr.rand.var] equires that the member template -

-
-template<class T> result_type operator() (T value);
-
-

-return -

-
-distribution()(e, value)
-
-

-However, not all distributions have an operator() with a corresponding signature. -

- -

[ -Berlin: As a working group we voted in favor of N1932 which makes this moot: -variate_generator has been eliminated. Then in full committee we voted to give -this issue WP status (mistakenly). -]

- - - - -

Proposed resolution:

-

-We therefore recommend that we insert the following precondition before paragraph 11: -

-

-Precondition: distribution().operator()(e,value) is well-formed. -

- - - - - -
-

508. Bad parameters for ranlux64_base_01

-

Section: 26.5.5 [rand.predef], TR1 5.1.5 [tr.rand.predef] Status: CD1 - Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The fifth of these engines with predefined parameters, ranlux64_base_01, -appears to have an unintentional error for which there is a simple correction. -The two pre-defined subtract_with_carry_01 engines are given as: -

-
-typedef subtract_with_carry_01<float,  24, 10, 24> ranlux_base_01;
-typedef subtract_with_carry_01<double, 48, 10, 24> ranlux64_base_01;
-
-

-We demonstrate below that ranlux64_base_01 fails to meet the intent of the -random number generation proposal, but that the simple correction to -

-
-typedef subtract_with_carry_01<double, 48,  5, 12> ranlux64_base_01;
-
-

-does meet the intent of defining well-known good parameterizations. -

-

-The ranlux64_base_01 engine as presented fails to meet the intent for -predefined engines, stated in proposal N1398 (section E): -

-

-In order to make good random numbers available to a large number of library -users, this proposal not only defines generic random-number engines, but also -provides a number of predefined well-known good parameterizations for those. -

-

-The predefined ranlux_base_01 engine has been proven [1,2,3] to have a very -long period and so meets this criterion. This property makes it suitable for -use in the excellent discard_block engines defined subsequently. The proof -of long period relies on the fact (proven in [1]) that 2**(w*r) - 2**(w*s) -+ 1 is prime (w, r, and s are template parameters to subtract_with_carry_01, -as defined in [tr.rand.eng.sub1]). -

-

-The ranlux64_base_01 engine as presented in [tr.rand.predef] uses w=48, r=24, s=10. -For these numbers, the combination 2**(w*r)-2**(w*s)+1 is non-prime (though -explicit factorization would be a challenge). In consequence, while it is -certainly possible for some seeding states that this engine would have a very -long period, it is not at all "well-known" that this is the case. The intent -in the N1398 proposal involved the base of the ranlux64 engine, which finds heavy -use in the physics community. This is isomorphic to the predefined ranlux_base_01, -but exploits the ability of double variables to hold (at least) 48 bits of mantissa, -to deliver 48 random bits at a time rather than 24. -

- - -

Proposed resolution:

-

-To achieve this intended behavior, the correct template parameteriztion would be: -

-
-typedef subtract_with_carry_01<double, 48, 5, 12> ranlux64_base_01;
-
-

-The sequence of mantissa bits delivered by this is isomorphic (treating each -double as having the bits of two floats) to that delivered by ranlux_base_01. -

-

-References: -

-
    -
  1. F. James, Comput. Phys. Commun. 60(1990) 329
    2. -
  2. G. Marsaglia and A. Zaman, Ann. Appl. Prob 1(1991) 462
    3. -
  3. M. Luscher, Comput. Phys. Commun. 79(1994) 100-110
    4. -
- -

[ -Berlin: Voted to WP. N1932 adopts the proposed resolution in 26.3.5, -just above paragraph 5. -]

- - - - - - - -
-

518. Are insert and erase stable for unordered_multiset and unordered_multimap?

-

Section: 23.2.5 [unord.req], TR1 6.3.1 [tr.unord.req] Status: CD1 - Submitter: Matt Austern Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Issue 371 deals with stability of multiset/multimap under insert and erase -(i.e. do they preserve the relative order in ranges of equal elements). -The same issue applies to unordered_multiset and unordered_multimap. -

-

[ -Moved to open (from review): There is no resolution. -]

- - -

[ -Toronto: We have a resolution now. Moved to Review. Some concern was noted -as to whether this conflicted with existing practice or not. An additional -concern was in specifying (partial) ordering for an unordered container. -]

- - - - -

Proposed resolution:

-

-Wording for the proposed resolution is taken from the equivalent text for associative containers. -

- -

-Change 23.2.5 [unord.req], Unordered associative containers, paragraph 6 to: -

- -

-An unordered associative container supports unique keys if it may -contain at most one element for each key. Otherwise, it supports equivalent -keys. unordered_set and unordered_map support -unique keys. unordered_multiset and unordered_multimap -support equivalent keys. In containers that support equivalent keys, elements -with equivalent keys are adjacent to each other. For -unordered_multiset -and unordered_multimap, insert and erase -preserve the relative ordering of equivalent elements. -

- -

-Change 23.2.5 [unord.req], Unordered associative containers, paragraph 8 to: -

- -
-

The elements of an unordered associative container are organized into -buckets. Keys with the same hash code appear in the same bucket. The number -of buckets is automatically increased as elements are added to an unordered -associative container, so that the average number of elements per bucket is kept -below a bound. Rehashing invalidates iterators, changes ordering between -elements, and changes which buckets elements appear in, but does not invalidate -pointers or references to elements. For unordered_multiset -and unordered_multimap, rehashing -preserves the relative ordering of equivalent elements.

-
- - - - - - -
-

519. Data() undocumented

-

Section: 23.3.2 [array], TR1 6.2.2 [tr.array.array] Status: CD1 - Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-array<>::data() is present in the class synopsis, but not documented. -

- - -

Proposed resolution:

-

-Add a new section, after 6.2.2.3: -

-
-T*       data()
-const T* data() const;
-
-

-Returns: elems. -

-

-Change 6.2.2.4/2 to: -

-

-In the case where N == 0, begin() == end(). The return value -of data() is unspecified. -

- - - - - -
-

520. Result_of and pointers to data members

-

Section: 20.9.10 [func.bind], TR1 3.6 [tr.func.bind] Status: CD1 - Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

Discussion:

-

-In the original proposal for binders, the return type of bind() when -called with a pointer to member data as it's callable object was -defined to be mem_fn(ptr); when Peter Dimov and I unified the -descriptions of the TR1 function objects we hoisted the descriptions -of return types into the INVOKE pseudo-function and into result_of. -Unfortunately, we left pointer to member data out of result_of, so -bind doesn't have any specified behavior when called with a pointer -to member data. -

- - -

Proposed resolution:

-

[ -Pete and Peter will provide wording. -]

- - -

-In 20.5.4 [lib.func.ret] ([tr.func.ret]) p3 add the following bullet after bullet 2: -

-
    -
  1. […]
    2. -
  2. […]
    3. -
  3. If F is a member data pointer type R T::*, type -shall be cv R& when T1 is cv U1&, -R otherwise.
    4. -
- -

[ -Peter provided wording. -]

- - - - - - - -
-

521. Garbled requirements for argument_type in reference_wrapper

-

Section: 20.9.4 [refwrap], TR1 2.1.2 [tr.util.refwrp.refwrp] Status: CD1 - Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-2.1.2/3, second bullet item currently says that reference_wrapper<T> is -derived from unary_function<T, R> if T is: -

-

-a pointer to member function type with cv-qualifier cv and no arguments; -the type T1 is cv T* and R is the return type of the pointer to member function; -

-

-The type of T1 can't be cv T*, 'cause that's a pointer to a pointer to member -function. It should be a pointer to the class that T is a pointer to member of. -Like this: -

-

-a pointer to a member function R T0::f() cv (where cv represents the member -function's cv-qualifiers); the type T1 is cv T0* -

-

-Similarly, bullet item 2 in 2.1.2/4 should be: -

-

-a pointer to a member function R T0::f(T2) cv (where cv represents the member -function's cv-qualifiers); the type T1 is cv T0* -

- - -

Proposed resolution:

- -

-Change bullet item 2 in 2.1.2/3: -

- -
-
    -
  • -a pointer to member function type with cv-qualifier cv and no arguments; -the type T1 is cv T* and R is the return -type of the pointer to member function R T0::f() cv -(where cv represents the member function's cv-qualifiers); -the type T1 is cv T0* -
    • -
-
- -

-Change bullet item 2 in 2.1.2/4: -

- -
-
    -
  • -a pointer to member function with cv-qualifier cv and taking one argument -of type T2; the type T1 is cv T* and -R is the return type of the pointer to member function -R T0::f(T2) cv (where cv represents the member -function's cv-qualifiers); the type T1 is cv T0* -
    • -
-
- - - - - - -
-

522. Tuple doesn't define swap

-

Section: 20.4 [tuple], TR1 6.1 [tr.tuple] Status: CD1 - Submitter: Andy Koenig Opened: 2005-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Tuple doesn't define swap(). It should. -

-

[ -Berlin: Doug to provide wording. -]

- -

[ -Batavia: Howard to provide wording. -]

- -

[ -Toronto: Howard to provide wording (really this time). -]

- - -

[ -Bellevue: Alisdair provided wording. -]

- - - - -

Proposed resolution:

- -

-Add these signatures to 20.4 [tuple] -

- -
-template <class... Types>
-  void swap(tuple<Types...>& x, tuple<Types...>& y);
-template <class... Types>
-  void swap(tuple<Types...>&& x, tuple<Types...>& y);
-template <class... Types>
-  void swap(tuple<Types...>& x, tuple<Types...>&& y); 
-
- -

-Add this signature to 20.4.2 [tuple.tuple] -

- -
-void swap(tuple&&);
-
- -

-Add the following two sections to the end of the tuple clauses -

- -
-

-20.3.1.7 tuple swap [tuple.swap] -

- -
-void swap(tuple&& rhs); 
-
- -
-

-Requires: Each type in Types shall be Swappable. -

-

-Effects: Calls swap for each element in *this and its corresponding element -in rhs. -

-

-Throws: Nothing, unless one of the element-wise swap calls throw an -exception. -

-
- -

-20.3.1.8 tuple specialized algorithms [tuple.special] -

- -
-template <class... Types>
-  void swap(tuple<Types...>& x, tuple<Types...>& y);
-template <class... Types>
-  void swap(tuple<Types...>&& x, tuple<Types...>& y);
-template <class... Types>
-  void swap(tuple<Types...>& x, tuple<Types...>&& y); 
-
- -
-

-Effects: x.swap(y) -

-
-
- - - - - - -
-

524. regex named character classes and case-insensitivity don't mix

-

Section: 28 [re] Status: CD1 - Submitter: Eric Niebler Opened: 2005-07-01 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-This defect is also being discussed on the Boost developers list. The -full discussion can be found here: -http://lists.boost.org/boost/2005/07/29546.php -

-

--- Begin original message -- -

-

-Also, I may have found another issue, closely related to the one under -discussion. It regards case-insensitive matching of named character -classes. The regex_traits<> provides two functions for working with -named char classes: lookup_classname and isctype. To match a char class -such as [[:alpha:]], you pass "alpha" to lookup_classname and get a -bitmask. Later, you pass a char and the bitmask to isctype and get a -bool yes/no answer. -

-

-But how does case-insensitivity work in this scenario? Suppose we're -doing a case-insensitive match on [[:lower:]]. It should behave as if it -were [[:lower:][:upper:]], right? But there doesn't seem to be enough -smarts in the regex_traits interface to do this. -

-

-Imagine I write a traits class which recognizes [[:fubar:]], and the -"fubar" char class happens to be case-sensitive. How is the regex engine -to know that? And how should it do a case-insensitive match of a -character against the [[:fubar:]] char class? John, can you confirm this -is a legitimate problem? -

-

-I see two options: -

-

-1) Add a bool icase parameter to lookup_classname. Then, -lookup_classname( "upper", true ) will know to return lower|upper -instead of just upper. -

-

-2) Add a isctype_nocase function -

-

-I prefer (1) because the extra computation happens at the time the -pattern is compiled rather than when it is executed. -

-

--- End original message -- -

- -

-For what it's worth, John has also expressed his preference for option -(1) above. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2409. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

525. type traits definitions not clear

-

Section: 20.10.4 [meta.unary], TR1 4.5 [tr.meta.unary] Status: Resolved - Submitter: Robert Klarer Opened: 2005-07-11 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-It is not completely clear how the primary type traits deal with -cv-qualified types. And several of the secondary type traits -seem to be lacking a definition. -

- -

[ -Berlin: Howard to provide wording. -]

- - - -

Proposed resolution:

-

-Wording provided in N2028. -A revision (N2157) -provides more detail for motivation. -

- - -

Rationale:

-Solved by revision (N2157) -in the WP. -

- - - - -
-

527. tr1::bind has lost its Throws clause

-

Section: 20.9.10.3 [func.bind.bind], TR1 3.6.3 [tr.func.bind.bind] Status: CD1 - Submitter: Peter Dimov Opened: 2005-10-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The original bind proposal gives the guarantee that tr1::bind(f, t1, ..., tN) -does not throw when the copy constructors of f, t1, ..., tN don't. -

- -

-This guarantee is not present in the final version of TR1. -

- -

-I'm pretty certain that we never removed it on purpose. Editorial omission? :-) -

- -

[ -Berlin: not quite editorial, needs proposed wording. -]

- -

[ -Batavia: Doug to translate wording to variadic templates. -]

- - -

[ -Toronto: We agree but aren't quite happy with the wording. The "t"'s no -longer refer to anything. Alan to provide improved wording. -]

- - - -

[ -Pre-Bellevue: Alisdair provided wording. -]

- - -

-TR1 proposed resolution: -

- -
-

-In TR1 3.6.3 [tr.func.bind.bind], add a new paragraph after p2: -

-

-Throws: Nothing unless one of the copy constructors of f, t1, t2, ..., tN -throws an exception. -

- -

-Add a new paragraph after p4: -

-

-Throws: nothing unless one of the copy constructors of f, t1, t2, ..., tN -throws an exception. -

- -
- - - -

Proposed resolution:

-

-In 20.9.10.3 [func.bind.bind], add a new paragraph after p2: -

- -

-Throws: Nothing unless the copy constructor of F or of one of the types -in the BoundArgs... pack expansion throws an exception. -

- -

-In 20.9.10.3 [func.bind.bind], add a new paragraph after p4: -

- -

-Throws: Nothing unless the copy constructor of F or of one of the types -in the BoundArgs... pack expansion throws an exception. -

- - - - - - -
-

530. Must elements of a string be contiguous?

-

Section: 21.4 [basic.string] Status: CD1 - Submitter: Matt Austern Opened: 2005-11-15 Last modified: 2015-04-08

-

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-

Discussion:

-

Issue 69, which was incorporated into C++03, mandated - that the elements of a vector must be stored in contiguous memory. - Should the same also apply to basic_string?

- -

We almost require contiguity already. Clause 23.4.7 [multiset] - defines operator[] as data()[pos]. What's missing - is a similar guarantee if we access the string's elements via the - iterator interface.

- -

Given the existence of data(), and the definition of - operator[] and at in terms of data, - I don't believe it's possible to write a useful and standard- - conforming basic_string that isn't contiguous. I'm not - aware of any non-contiguous implementation. We should just require - it. -

- - -

Proposed resolution:

-

Add the following text to the end of 21.4 [basic.string], -paragraph 2.

- -
-

The characters in a string are stored contiguously, meaning that if - s is a basic_string<charT, Allocator>, then - it obeys the identity - &*(s.begin() + n) == &*s.begin() + n - for all 0 <= n < s.size(). -

-
- - -

Rationale:

-

-Not standardizing this existing practice does not give implementors more -freedom. We thought it might a decade ago. But the vendors have spoken -both with their implementations, and with their voice at the LWG -meetings. The implementations are going to be contiguous no matter what -the standard says. So the standard might as well give string clients -more design choices. -

- - - - - -
-

531. array forms of unformatted input functions

-

Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Martin Sebor Opened: 2005-11-23 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The array forms of unformatted input functions don't seem to have well-defined -semantics for zero-element arrays in a couple of cases. The affected ones -(istream::get() and istream::getline()) are supposed to -terminate when (n - 1) characters are stored, which obviously can -never be true when (n == 0) holds to start with. See -c++std-lib-16071. -

- - -

Proposed resolution:

-

-I suggest changing 27.6.1.3, p7 (istream::get()), bullet 1 to read: -

-
    -
  • - (n < 1) is true or (n - 1) characters - are stored; -
    • -
-

-Change 27.6.1.3, p9: -

- -

-If the function stores no characters, it calls setstate(failbit) (which -may throw ios_base::failure (27.4.4.3)). In any case, if (n -> 0) is true it then stores a null character into the next -successive location of the array. -

- -

- -and similarly p17 (istream::getline()), bullet 3 to: - -

-
    -
  • - (n < 1) is true or (n - 1) characters - are stored (in which case the function calls - setstate(failbit)). -
    • -
- -

- -In addition, to clarify that istream::getline() must not store the -terminating NUL character unless the the array has non-zero size, Robert -Klarer suggests in c++std-lib-16082 to change 27.6.1.3, p20 to read: - -

-

- -In any case, provided (n > 0) is true, it then stores a null character -(using charT()) into the next successive location of the array. - -

- -

[ -post-Redmond: Pete noticed that the current resolution for get requires -writing to out of bounds memory when n == 0. Martin provided fix. -]

- - - - - - - -
-

533. typo in 2.2.3.10/1

-

Section: 20.8.2.2.10 [util.smartptr.getdeleter], TR1 2.2.3.10 [tr.util.smartptr.getdeleter] Status: CD1 - Submitter: Paolo Carlini Opened: 2005-11-09 Last modified: 2015-04-08

-

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-

Discussion:

-

-I'm seeing something that looks like a typo. The Return of get_deleter -says: -

-

-If *this owns a deleter d... -

-

-but get_deleter is a free function! -

- - -

Proposed resolution:

-

-Therefore, I think should be: -

-

-If *this p owns a deleter d... -

- - - - - -
-

534. Missing basic_string members

-

Section: 21.4 [basic.string] Status: CD1 - Submitter: Alisdair Meredith Opened: 2005-11-16 Last modified: 2015-04-08

-

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-

Discussion:

-

-OK, we all know std::basic_string is bloated and already has way too -many members. However, I propose it is missing 3 useful members that -are often expected by users believing it is a close approximation of the -container concept. All 3 are listed in table 71 as 'optional' -

- -

-i/ pop_back. -

- -

-This is the one I feel most strongly about, as I only just discovered it -was missing as we are switching to a more conforming standard library -<g> -

- -

-I find it particularly inconsistent to support push_back, but not -pop_back. -

- -

-ii/ back. -

- -

-There are certainly cases where I want to examine the last character of -a string before deciding to append, or to trim trailing path separators -from directory names etc. *rbegin() somehow feels inelegant. -

- -

-iii/ front -

- -

-This one I don't feel strongly about, but if I can get the first two, -this one feels that it should be added as a 'me too' for consistency. -

- -

-I believe this would be similarly useful to the data() member recently -added to vector, or at() member added to the maps. -

- - -

Proposed resolution:

-

-Add the following members to definition of class template basic_string, 21.3p7 -

-
-void pop_back ()
-
-const charT & front() const
-charT & front()
-
-const charT & back() const
-charT & back()
-
-

-Add the following paragraphs to basic_string description -

- -

-21.3.4p5 -

-
-
-const charT & front() const
-charT & front()
-
-

-Precondition: !empty() -

-

-Effects: Equivalent to operator[](0). -

-
- -

-21.3.4p6 -

-
-
-const charT & back() const
-charT & back()
-
-

-Precondition: !empty() -

-

-Effects: Equivalent to operator[]( size() - 1). -

-
- -

-21.3.5.5p10 -

-
-
-void pop_back ()
-
-

-Precondition: !empty() -

-

-Effects: Equivalent to erase( size() - 1, 1 ). -

-
- -

-Update Table 71: (optional sequence operations) -Add basic_string to the list of containers for the following operations. -

-
-a.front()
-a.back()
-a.push_back()
-a.pop_back()
-a[n]
-
- -

[ -Berlin: Has support. Alisdair provided wording. -]

- - - - - - -
-

535. std::string::swap specification poorly worded

-

Section: 21.4.6.8 [string::swap] Status: CD1 - Submitter: Beman Dawes Opened: 2005-12-14 Last modified: 2015-04-08

-

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-

Discussion:

-

-std::string::swap currently says for effects and postcondition: -

- -
-

-Effects: Swaps the contents of the two strings. -

- -

-Postcondition: *this contains the characters that were in s, -s contains the characters that were in *this. -

-
- -

-Specifying both Effects and Postcondition seems redundant, and the postcondition -needs to be made stronger. Users would be unhappy if the characters were not in -the same order after the swap. -

- - -

Proposed resolution:

-
-

-Effects: Swaps the contents of the two strings. -

- -

-Postcondition: *this contains the same sequence of -characters that were was in s, -s contains the same sequence of characters that -were was in *this. -

-
- - - - - -
-

537. Typos in the signatures in 27.6.1.3/42-43 and 27.6.2.4

-

Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Paolo Carlini Opened: 2006-02-12 Last modified: 2015-04-08

-

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-

Discussion:

-

-In the most recent working draft, I'm still seeing: -

- -
-seekg(off_type& off, ios_base::seekdir dir)
-
- -

-and -

- -
-seekp(pos_type& pos)
-
-seekp(off_type& off, ios_base::seekdir dir)
-
- -

-that is, by reference off and pos arguments. -

- - -

Proposed resolution:

-

-After 27.6.1.3p42 change: -

- -
-basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);
-
- -

-After 27.6.2.4p1 change: -

- -
-basic_ostream<charT,traits>& seekp(pos_type& pos);
-
- -

-After 27.6.2.4p3 change: -

- -
-basic_ostream<charT,traits>& seekp(off_type& off, ios_base::seekdir dir);
-
- - - - - -
-

538. 241 again: Does unique_copy() require CopyConstructible and Assignable?

-

Section: 25.3.9 [alg.unique] Status: CD1 - Submitter: Howard Hinnant Opened: 2006-02-09 Last modified: 2015-04-08

-

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-

Discussion:

-

-I believe I botched the resolution of - -241 "Does unique_copy() require CopyConstructible and Assignable?" which now -has WP status. -

- -

-This talks about unique_copy requirements and currently reads: -

- -

--5- Requires: The ranges [first, last) and -[result, result+(last-first)) -shall not overlap. The expression *result = *first shall -be valid. If neither InputIterator nor OutputIterator meets the -requirements of forward iterator then the value type of InputIterator -must be CopyConstructible (20.1.3). Otherwise CopyConstructible is not required. -

- -

-The problem (which Paolo discovered) is that when the iterators are at their -most restrictive (InputIterator, OutputIterator), then we want -InputIterator::value_type to be both CopyConstructible and -CopyAssignable (for the most efficient implementation). However this -proposed resolution only makes it clear that it is CopyConstructible, -and that one can assign from *first to *result. -This latter requirement does not necessarily imply that you can: -

- -
-*first = *first;
-
- - -

Proposed resolution:

-

--5- Requires: The ranges [first, last) and -[result, result+(last-first)) -shall not overlap. The expression *result = *first -shall -be valid. If neither InputIterator nor OutputIterator meets the -requirements of forward iterator then the value type -value_type of InputIterator -must be CopyConstructible (20.1.3) and Assignable. -Otherwise CopyConstructible is not required. -

- - - - - -
-

539. partial_sum and adjacent_difference should mention requirements

-

Section: 26.7.4 [partial.sum] Status: C++11 - Submitter: Marc Schoolderman Opened: 2006-02-06 Last modified: 2015-04-08

-

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-

Discussion:

-

-There are some problems in the definition of partial_sum and -adjacent_difference in 26.4 [lib.numeric.ops] -

- -

-Unlike accumulate and inner_product, these functions are not -parametrized on a "type T", instead, 26.4.3 [lib.partial.sum] simply -specifies the effects clause as; -

- -

-Assigns to every element referred to by iterator i in the range -[result,result + (last - first)) a value correspondingly equal to -

-
-((...(* first + *( first + 1)) + ...) + *( first + ( i - result )))
-
-
- -

-And similarly for BinaryOperation. Using just this definition, it seems -logical to expect that: -

- - -
-char i_array[4] = { 100, 100, 100, 100 };
-int  o_array[4];
-
-std::partial_sum(i_array, i_array+4, o_array);
-
- -

-Is equivalent to -

- -
-int o_array[4] = { 100, 100+100, 100+100+100, 100+100+100+100 };
-
- -

-i.e. 100, 200, 300, 400, with addition happening in the result type, -int. -

- -

-Yet all implementations I have tested produce 100, -56, 44, -112, -because they are using an accumulator of the InputIterator's -value_type, which in this case is char, not int. -

- -

-The issue becomes more noticeable when the result of the expression *i + -*(i+1) or binary_op(*i, *i-1) can't be converted to the -value_type. In a contrived example: -

- -
-enum not_int { x = 1, y = 2 };
-...
-not_int e_array[4] = { x, x, y, y };
-std::partial_sum(e_array, e_array+4, o_array);
-
- -

-Is it the intent that the operations happen in the input type, or in -the result type? -

- -

-If the intent is that operations happen in the result type, something -like this should be added to the "Requires" clause of 26.4.3/4 -[lib.partial.sum]: -

- -

-The type of *i + *(i+1) or binary_op(*i, *(i+1)) shall meet the -requirements of CopyConstructible (20.1.3) and Assignable -(23.1) types. -

- -

-(As also required for T in 26.4.1 [lib.accumulate] and 26.4.2 -[lib.inner.product].) -

- -

-The "auto initializer" feature proposed in -N1894 -is not required to -implement partial_sum this way. The 'narrowing' behaviour can still be -obtained by using the std::plus<> function object. -

- -

-If the intent is that operations happen in the input type, then -something like this should be added instead; -

- -

-The type of *first shall meet the requirements of -CopyConstructible (20.1.3) and Assignable (23.1) types. -The result of *i + *(i+1) or binary_op(*i, *(i+1)) shall be -convertible to this type. -

- -

-The 'widening' behaviour can then be obtained by writing a custom proxy -iterator, which is somewhat involved. -

- -

-In both cases, the semantics should probably be clarified. -

- -

-26.4.4 [lib.adjacent.difference] is similarly underspecified, although -all implementations seem to perform operations in the 'result' type: -

- -
-unsigned char i_array[4] = { 4, 3, 2, 1 };
-int o_array[4];
-
-std::adjacent_difference(i_array, i_array+4, o_array);
-
- -

-o_array is 4, -1, -1, -1 as expected, not 4, 255, 255, 255. -

- -

-In any case, adjacent_difference doesn't mention the requirements on the -value_type; it can be brought in line with the rest of 26.4 -[lib.numeric.ops] by adding the following to 26.4.4/2 -[lib.adjacent.difference]: -

- -

-The type of *first shall meet the requirements of -CopyConstructible (20.1.3) and Assignable (23.1) types." -

-

[ -Berlin: Giving output iterator's value_types very controversial. Suggestion of -adding signatures to allow user to specify "accumulator". -]

- - -

[ -Bellevue: -]

- - -

-The intent of the algorithms is to perform their calculations using the type of the input iterator. -Proposed wording provided. -

- -

[ -Sophia Antipolis: -]

- - -

-We did not agree that the proposed resolution was correct. For example, -when the arguments are types (float*, float*, double*), the -highest-quality solution would use double as the type of the -accumulator. If the intent of the wording is to require that the type of -the accumulator must be the input_iterator's value_type, the wording -should specify it. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -
-

-Now that we have the facility, the 'best' accumulator type could probably be -deduced as: -

-
-std::common_type<InIter::value_type, OutIter::reference>::type
-
-

-This type would then have additional requirements of constructability and -incrementability/assignability. -

-

-If this extracting an accumulator type from a pair/set of iterators (with -additional requirements on that type) is a problem for multiple functions, -it might be worth extracting into a SharedAccumulator concept or similar. -

-

-I'll go no further in writing up wording now, until the group gives a -clearer indication of preferred direction. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-The proposed resolution isn't quite right. For example, "the type of -*first" should be changed to "iterator::value_type" or similar. Daniel -volunteered to correct the wording. -

- -

[ -2009-07-29 Daniel corrected wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- - - -
    -
  1. -

    -Change 26.7.4 [partial.sum]/1 as indicated: -

    - -
    -

    -Effects: Let VT be InputIterator's value type. For a nonempty range, -initializes an accumulator acc of type VT with *first and performs -*result = acc. For every iterator i in [first + 1, last) in order, acc is then -modified by acc = acc + *i or acc = binary_op(acc, *i) and is assigned -to *(result + (i - first)). Assigns to every element referred to by -iterator i in the range [result,result + (last - first)) a value -correspondingly -equal to -

    - -
    
-((...(*first + *(first + 1)) + ...) + *(first + (i - result)))
-
    - -

    -or -

    - -
    
-binary_op(binary_op(...,
-   binary_op(*first, *(first + 1)),...), *(first + (i - result)))
-
    -
    -
    2. - -
  2. -

    -Change 26.7.4 [partial.sum]/3 as indicated: -

    - -

    -Complexity: Exactly max((last - first) - 1, 0) -applications -of binary_opthe binary operation. -

    -
    3. - -
  3. -

    -Change 26.7.4 [partial.sum]/4 as indicated: -

    - -

    -Requires: VT shall be constructible from the type of *first, the result of -acc + *i or binary_op(acc, *i) shall be implicitly convertible to VT, and -the result of the expression acc shall be writable to the result -output iterator. In the ranges [first,last] and -[result,result + (last - first)] [..] -

    -
    4. - -
  4. -

    -Change 26.7.5 [adjacent.difference]/1 as indicated: -

    - -
    -

    -Effects: Let VT be InputIterator's value type. For a nonempty range, -initializes an accumulator acc of type VT with *first and performs -*result = acc. For every iterator i in [first + 1, last) in order, -initializes a -value val of type VT with *i, assigns the result of val - acc or -binary_op(val, acc) -to *(result + (i - first)) and modifies acc = std::move(val). -Assigns to every element referred to by iterator i in the range -[result + 1, -result + (last - first)) a value correspondingly equal to -

    - -
    
-*(first + (i - result)) - *(first + (i - result) - 1)
-
    - -

    -or -

    - -
    
-binary_op(*(first + (i - result)), *(first + (i - result) - 1)).
-
    - -

    -result gets the value of *first. -

    -
    -
    5. - -
  5. -

    -Change 26.7.5 [adjacent.difference]/2 as indicated: -

    - -

    -Requires: VT shall be MoveAssignable ([moveassignable]) -and shall be -constructible from the type of *first. The result -of the expression acc and the result of the expression val - acc or -binary_op(val, acc) -shall be writable to the result output iterator. In the ranges -[first,last] [..] -

    -
    6. - -
  6. -

    -Change 26.7.5 [adjacent.difference]/5 as indicated: -

    - -

    -Complexity: Exactly max((last - first) - 1, 0) -applications -of binary_opthe binary operation. -

    -
    7. -
- - - - - - - - -
-

540. shared_ptr<void>::operator*()

-

Section: 20.8.2.2.5 [util.smartptr.shared.obs], TR1 2.2.3.5 [tr.util.smartptr.shared.obs] Status: CD1 - Submitter: Martin Sebor Opened: 2005-10-15 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I'm trying to reconcile the note in tr.util.smartptr.shared.obs, p6 -that talks about the operator*() member function of shared_ptr: -

- -

- Notes: When T is void, attempting to instantiate this member function - renders the program ill-formed. [Note: Instantiating shared_ptr<void> - does not necessarily result in instantiating this member function. - --end note] -

- -

-with the requirement in temp.inst, p1: -

- -

- The implicit instantiation of a class template specialization causes - the implicit instantiation of the declarations, but not of the - definitions... -

- -

-I assume that what the note is really trying to say is that -"instantiating shared_ptr<void> *must not* result in instantiating -this member function." That is, that this function must not be -declared a member of shared_ptr<void>. Is my interpretation -correct? -

- - -

Proposed resolution:

-

-Change 2.2.3.5p6 -

- -

--6- Notes: When T is void, attempting to instantiate -this member function renders the program ill-formed. [Note: -Instantiating shared_ptr<void> does not necessarily result in -instantiating this member function. --end note] it is -unspecified whether this member function is declared or not, and if so, what its -return type is, except that the declaration (although not necessarily the -definition) of the function shall be well-formed. -

- - - - - - -
-

541. shared_ptr template assignment and void

-

Section: 20.8.2.2 [util.smartptr.shared], TR1 2.2.3 [tr.util.smartptr.shared] Status: CD1 - Submitter: Martin Sebor Opened: 2005-10-16 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Is the void specialization of the template assignment operator taking -a shared_ptr<void> as an argument supposed be well-formed? -

-

-I.e., is this snippet well-formed: -

-
-shared_ptr<void> p;
-p.operator=<void>(p);
-
- -

-Gcc complains about auto_ptr<void>::operator*() returning a reference -to void. I suspect it's because shared_ptr has two template assignment -operators, one of which takes auto_ptr, and the auto_ptr template gets -implicitly instantiated in the process of overload resolution. -

- -

-The only way I see around it is to do the same trick with auto_ptr<void> -operator*() as with the same operator in shared_ptr<void>. -

- -

-PS Strangely enough, the EDG front end doesn't mind the code, even -though in a small test case (below) I can reproduce the error with -it as well. -

- -
-template <class T>
-struct A { T& operator*() { return *(T*)0; } };
-
-template <class T>
-struct B {
-    void operator= (const B&) { }
-    template <class U>
-    void operator= (const B<U>&) { }
-    template <class U>
-    void operator= (const A<U>&) { }
-};
-
-int main ()
-{
-    B<void> b;
-    b.operator=<void>(b);
-}
-
- - -

Proposed resolution:

-

-In [lib.memory] change: -

-
-template<class X> class auto_ptr;
-template<> class auto_ptr<void>;
-
- -

-In [lib.auto.ptr]/2 add the following before the last closing brace: -

- -
-template<> class auto_ptr<void>
-{
-public:
-    typedef void element_type;
-};
-
- - - - - - -
-

542. shared_ptr observers

-

Section: 20.8.2.2.5 [util.smartptr.shared.obs], TR1 2.2.3.5 [tr.util.smartptr.shared.obs] Status: CD1 - Submitter: Martin Sebor Opened: 2005-10-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Peter Dimov wrote: -To: C++ libraries mailing list -Message c++std-lib-15614 -[...] -The intent is for both use_count() and unique() to work in a threaded environment. -They are intrinsically prone to race conditions, but they never return garbage. -

- -

-This is a crucial piece of information that I really wish were -captured in the text. Having this in a non-normative note would -have made everything crystal clear to me and probably stopped -me from ever starting this discussion :) Instead, the sentence -in p12 "use only for debugging and testing purposes, not for -production code" very strongly suggests that implementations -can and even are encouraged to return garbage (when threads -are involved) for performance reasons. -

-

-How about adding an informative note along these lines: -

-

- Note: Implementations are encouraged to provide well-defined - behavior for use_count() and unique() even in the presence of - multiple threads. -

-

-I don't necessarily insist on the exact wording, just that we -capture the intent. -

- - -

Proposed resolution:

-

-Change 20.8.2.2.5 [util.smartptr.shared.obs] p12: -

-

-[Note: use_count() is not necessarily efficient. Use only for -debugging and testing purposes, not for production code. --end note] -

- -

-Change 20.8.2.3.5 [util.smartptr.weak.obs] p3: -

-

-[Note: use_count() is not necessarily efficient. Use only for -debugging and testing purposes, not for production code. --end note] -

- - - - - -
-

543. valarray slice default constructor

-

Section: 26.6.4 [class.slice] Status: CD1 - Submitter: Howard Hinnant Opened: 2005-11-03 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-If one explicitly constructs a slice or glice with the default -constructor, does the standard require this slice to have any usable -state? It says "creates a slice which specifies no elements", which -could be interpreted two ways: -

-
    -
  1. There are no elements to which the slice refers (i.e. undefined).
    2. -
  2. The slice specifies an array with no elements in it (i.e. defined).
    3. -
-

-Here is a bit of code to illustrate: -

-
-#include <iostream>
-#include <valarray>
-
-int main()
-{
-    std::valarray<int> v(10);
-    std::valarray<int> v2 = v[std::slice()];
-    std::cout << "v[slice()].size() = " << v2.size() << '\n';
-}
-
- -

-Is the behavior undefined? Or should the output be: -

- -
-v[slice()].size() = 0
-
- -

-There is a similar question and wording for gslice at 26.3.6.1p1. -

- - -

Proposed resolution:

- -

[Martin suggests removing the second sentence in 26.6.4.2 [cons.slice] as well.]

- - -

-Change 26.6.4.2 [cons.slice]: -

- -

-1 - The default constructor for slice creates a slice -which specifies no elements. The default constructor is equivalent to -slice(0, 0, 0). A default constructor is provided only to permit -the declaration of arrays of slices. The constructor with arguments for a slice -takes a start, length, and stride parameter. -

- -

-Change 26.6.6.2 [gslice.cons]: -

- -

-1 - The default constructor creates a gslice which specifies no -elements. The default constructor is equivalent to gslice(0, -valarray<size_t>(), valarray<size_t>()). The constructor -with arguments builds a gslice based on a specification of start, -lengths, and strides, as explained in the previous section. -

- - - - - - -
-

545. When is a deleter deleted?

-

Section: 20.8.2.2.10 [util.smartptr.getdeleter], TR1 2.2.3.2 [tr.util.smartptr.shared.dest] Status: CD1 - Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.getdeleter].

-

View all issues with CD1 status.

-

Discussion:

-

-The description of ~shared_ptr doesn't say when the shared_ptr's deleter, if -any, is destroyed. In principle there are two possibilities: it is destroyed -unconditionally whenever ~shared_ptr is executed (which, from an implementation -standpoint, means that the deleter is copied whenever the shared_ptr is copied), -or it is destroyed immediately after the owned pointer is destroyed (which, from -an implementation standpoint, means that the deleter object is shared between -instances). We should say which it is. -

- - -

Proposed resolution:

-

-Add after the first sentence of 20.8.2.2.10 [util.smartptr.getdeleter]/1: -

-
-

-The returned pointer remains valid as long as there exists a shared_ptr instance -that owns d. -

-

-[Note: it is unspecified whether the pointer remains valid longer than that. -This can happen if the implementation doesn't destroy the deleter until all -weak_ptr instances in the ownership group are destroyed. -- end note] -

-
- - - - - -
-

550. What should the return type of pow(float,int) be?

-

Section: 26.8 [c.math] Status: CD1 - Submitter: Howard Hinnant Opened: 2006-01-12 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

View all other issues in [c.math].

-

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-

Discussion:

-

-Assuming we adopt the -C -compatibility package from C99 what should be the return type of the -following signature be: -

-
-?  pow(float, int);
-
-

-C++03 says that the return type should be float. - -TR1 and C90/99 say the return type should be double. This can put -clients into a situation where C++03 provides answers that are not as high -quality as C90/C99/TR1. For example: -

-
-#include <math.h>
-
-int main()
-{
-    float x = 2080703.375F;
-    double y = pow(x, 2);
-}
-
-

-Assuming an IEEE 32 bit float and IEEE 64 bit double, C90/C99/TR1 all suggest: -

- -
-y = 4329326534736.390625
-
- -

-which is exactly right. While C++98/C++03 demands: -

- -
-y = 4329326510080.
-
- -

-which is only approximately right. -

- -

-I recommend that C++0X adopt the mixed mode arithmetic already adopted by -Fortran, C and TR1 and make the return type of pow(float,int) be -double. -

- -

[ -Kona (2007): Other functions that are affected by this issue include -ldexp, scalbln, and scalbn. We also believe that there is a typo in -26.7/10: float nexttoward(float, long double); [sic] should be float -nexttoward(float, float); Proposed Disposition: Review (the proposed -resolution appears above, rather than below, the heading "Proposed -resolution") -]

- - -

[Howard, post Kona:]

- -
-

-Unfortunately I strongly disagree with a part of the resolution -from Kona. I am moving from New to Open instead of to Review because I do not believe -we have consensus on the intent of the resolution. -

-

-This issue does not include ldexp, scalbln, and scalbn because -the second integral parameter in each of these signatures (from C99) is not a -generic parameter according to C99 7.22p2. The corresponding C++ overloads are -intended (as far as I know) to correspond directly to C99's definition of generic parameter. -

-

-For similar reasons, I do not believe that the second long double parameter of -nexttoward, nor the return type of this function, is in error. I believe the -correct signature is: -

-
-
-float nexttoward(float, long double);
-
-
-

-which is what both the C++0X working paper and C99 state (as far as I currently understand). -

-

-This is really only about pow(float, int). And this is because C++98 took one -route (with pow only) and C99 took another (with many math functions in <tgmath.h>. -The proposed resolution basically says: C++98 got it wrong and C99 got it right; let's go with C99. -

-
- -

[ -Bellevue: -]

- - -

-This signature was not picked up from C99. Instead, if one types -pow(2.0f,2), the promotion rules will invoke "double pow(double, -double)", which generally gives special treatment for integral -exponents, preserving full accuracy of the result. New proposed -wording provided. -

- - -

Proposed resolution:

-

-Change 26.8 [c.math] p10: -

- -
-

-The added signatures are: -

-
-...
-float pow(float, int);
-...
-double pow(double, int);
-...
-long double pow(long double, int);
-
-
- - - - - - -
-

551. <ccomplex>

-

Section: X [cmplxh], TR1 8.3 [tr.c99.cmplxh] Status: CD1 - Submitter: Howard Hinnant Opened: 2006-01-23 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-Previously xxx.h was parsable by C++. But in the case of C99's <complex.h> -it isn't. Otherwise we could model it just like <string.h>, <cstring>, <string>: -

- -
    -
  • <string> : C++ API in namespace std
    • -
  • <cstring> : C API in namespace std
    • -
  • <string.h> : C API in global namespace
    • -
- -

-In the case of C's complex, the C API won't compile in C++. So we have: -

- -
    -
  • <complex> : C++ API in namespace std
    • -
  • <ccomplex> : ?
    • -
  • <complex.h> : ?
    • -
- -

-The ? can't refer to the C API. TR1 currently says: -

- -
    -
  • <complex> : C++ API in namespace std
    • -
  • <ccomplex> : C++ API in namespace std
    • -
  • <complex.h> : C++ API in global namespace
    • -
- - - -

Proposed resolution:

-

-Change 26.3.11 [cmplxh]: -

- -
-

-The header behaves as if it includes the header -<ccomplex>., and provides sufficient using -declarations to declare in the global namespace all function and type names -declared or defined in the neader <complex>. -[Note: <complex.h> does not promote any interface -into the global namespace as there is no C interface to promote. --end -note] -

-
- - - - - - -
-

552. random_shuffle and its generator

-

Section: 25.3.12 [alg.random.shuffle] Status: CD1 - Submitter: Martin Sebor Opened: 2006-01-25 Last modified: 2015-04-08

-

View all other issues in [alg.random.shuffle].

-

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-

Discussion:

-

-...is specified to shuffle its range by calling swap but not how -(or even that) it's supposed to use the RandomNumberGenerator -argument passed to it. -

-

-Shouldn't we require that the generator object actually be used -by the algorithm to obtain a series of random numbers and specify -how many times its operator() should be invoked by the algorithm? -

- -

-See N2391 and -N2423 -for some further discussion. -

- - - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

556. Is Compare a BinaryPredicate?

-

Section: 25.4 [alg.sorting] Status: C++11 - Submitter: Martin Sebor Opened: 2006-02-05 Last modified: 2015-04-08

-

View all other issues in [alg.sorting].

-

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-

Discussion:

-

-In 25, p8 we allow BinaryPredicates to return a type that's convertible -to bool but need not actually be bool. That allows predicates to return -things like proxies and requires that implementations be careful about -what kinds of expressions they use the result of the predicate in (e.g., -the expression in if (!pred(a, b)) need not be well-formed since the -negation operator may be inaccessible or return a type that's not -convertible to bool). -

-

-Here's the text for reference: -

-

- ...if an algorithm takes BinaryPredicate binary_pred as its argument - and first1 and first2 as its iterator arguments, it should work - correctly in the construct if (binary_pred(*first1, first2)){...}. -

- -

-In 25.3, p2 we require that the Compare function object return true -of false, which would seem to preclude such proxies. The relevant text -is here: -

-

- Compare is used as a function object which returns true if the first - argument is less than the second, and false otherwise... -

- -

[ -Portland: Jack to define "convertible to bool" such that short circuiting isn't -destroyed. -]

- - -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Review once wording received. Stefanus to send proposed wording. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Review once wording received. Stefanus to send proposed wording. -

- -

[ -2009-10-24 Stefanus supplied wording. -]

- - -

-Move to Review once wording received. Stefanus to send proposed wording. -Old proposed wording here: -

-

-I think we could fix this by rewording 25.3, p2 to read somthing like: -

-

--2- Compare is used as a function object which returns -true if the first argument a BinaryPredicate. The -return value of the function call operator applied to an object of type -Compare, when converted to type bool, yields true -if the first argument of the call is less than the second, and -false otherwise. Compare comp is used throughout for -algorithms assuming an ordering relation. It is assumed that comp -will not apply any non-constant function through the dereferenced iterator. -

-
-
- -

[ -2010-01-17: -]

- - -
-

-Howard expresses concern that the current direction of the proposed -wording outlaws expressions such as: -

- -
-if (!comp(x, y))
-
- -

-Daniel provides wording which addresses that concern. -

- -

-The previous wording is saved here: -

- -
- -

-Change 25.4 [alg.sorting] p2: -

-

-Compare is used as a function object. The return value of -the function call operator applied to an object of type Compare, when -converted to type bool, yields true if the first argument of the -call which returns true if the first argument -is less than the second, and false otherwise. Compare -comp is used throughout for algorithms assuming an ordering -relation. It is assumed that comp will not apply any -non-constant function through the dereferenced iterator. -

- -
- -
- -

[ -2010-01-22 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

- -
    -
  1. -

    -Change 25.1 [algorithms.general]/7+8 as indicated. [This change is -recommended to bring the return value requirements of BinaryPredicate -and Compare in sync.] -

    - -
    -

    -7 The Predicate parameter is used whenever an algorithm expects a -function object that when applied to the result of dereferencing the -corresponding iterator returns a value testable as true. In other -words, if an algorithm takes Predicate pred as its argument and -first as its iterator argument, it should work correctly in the -construct if (pred(*first)){...} pred(*first) -contextually converted to bool (4 [conv]). The -function object pred shall not apply any nonconstant function through -the dereferenced iterator. This function object may be a pointer to function, or -an object of a type with an appropriate function call operator. -

    - -

    -8 The BinaryPredicate parameter is used whenever an algorithm expects a -function object that when applied to the result of dereferencing two -corresponding iterators or to dereferencing an iterator and type T when -T is part of the signature returns a value testable as true. -In other words, if an algorithm takes BinaryPredicate -binary_pred as its argument and first1 and first2 as -its iterator arguments, it should work correctly in the construct if -(binary_pred(*first1, *first2)){...} binary_pred(*first1, -*first2) contextually converted to bool (4 [conv]). BinaryPredicate always takes the first iterator -type as its first argument, that is, in those cases when T value is -part of the signature, it should work correctly in the context of if -(binary_pred(*first1, value)){...} construct -binary_pred(*first1, value) contextually converted to bool -(4 [conv]). binary_pred shall not apply any -non-constant function through the dereferenced iterators. -

    -
    -
    2. - -
  2. -

    -Change 25.4 [alg.sorting]/2 as indicated: -

    - -

    -2 Compare is used as a function object type (20.9 [function.objects]). The return value of the function call operation -applied to an object of type Compare, when contextually converted to -type bool (4 [conv]), yields true if the first -argument of the call which returns true if the first -argument is less than the second, and false otherwise. -Compare comp is used throughout for algorithms assuming an ordering -relation. It is assumed that comp will not apply any non-constant -function through the dereferenced iterator. -

    -
    3. - -
- - - - - - -
-

559. numeric_limits<const T>

-

Section: 18.3.2 [limits] Status: CD1 - Submitter: Martin Sebor Opened: 2006-02-19 Last modified: 2015-04-08

-

View all other issues in [limits].

-

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-

Discussion:

-

- -18.3.2 [limits], p2 requires implementations to provide specializations of the -numeric_limits template for each scalar type. While this -could be interepreted to include cv-qualified forms of such types such -an interepretation is not reflected in the synopsis of the -<limits> header. - -

-

- -The absence of specializations of the template on cv-qualified forms -of fundamental types makes numeric_limits difficult to -use in generic code where the constness (or volatility) of a type is -not always immediately apparent. In such contexts, the primary -template ends up being instantiated instead of the provided -specialization, typically yielding unexpected behavior. - -

-

- -Require that specializations of numeric_limits on -cv-qualified fundamental types have the same semantics as those on the -unqualifed forms of the same types. - -

- - -

Proposed resolution:

-

- -Add to the synopsis of the <limits> header, -immediately below the declaration of the primary template, the -following: -

- -
-
-template <class T> class numeric_limits<const T>;
-template <class T> class numeric_limits<volatile T>;
-template <class T> class numeric_limits<const volatile T>;
-
-
- -

- -Add a new paragraph to the end of 18.3.2.3 [numeric.limits], with the following -text: - -

-

- --new-para- The value of each member of a numeric_limits -specialization on a cv-qualified T is equal to the value of the same -member of numeric_limits<T>. - -

- -

[ -Portland: Martin will clarify that user-defined types get cv-specializations -automatically. -]

- - - - - - - -
-

561. inserter overly generic

-

Section: 24.5.2.6.5 [inserter] Status: CD1 - Submitter: Howard Hinnant Opened: 2006-02-21 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-The declaration of std::inserter is: -

- -
-template <class Container, class Iterator>
-insert_iterator<Container>
-inserter(Container& x, Iterator i);
-
- -

-The template parameter Iterator in this function is completely unrelated -to the template parameter Container when it doesn't need to be. This -causes the code to be overly generic. That is, any type at all can be deduced -as Iterator, whether or not it makes sense. Now the same is true of -Container. However, for every free (unconstrained) template parameter -one has in a signature, the opportunity for a mistaken binding grows geometrically. -

- -

-It would be much better if inserter had the following signature instead: -

- -
-template <class Container>
-insert_iterator<Container>
-inserter(Container& x, typename Container::iterator i);
-
- -

-Now there is only one free template parameter. And the second argument to -inserter must be implicitly convertible to the container's iterator, -else the call will not be a viable overload (allowing other functions in the -overload set to take precedence). Furthermore, the first parameter must have a -nested type named iterator, or again the binding to std::inserter -is not viable. Contrast this with the current situation -where any type can bind to Container or Iterator and those -types need not be anything closely related to containers or iterators. -

- -

-This can adversely impact well written code. Consider: -

- -
-#include <iterator>
-#include <string>
-
-namespace my
-{
-
-template <class String>
-struct my_type {};
-
-struct my_container
-{
-template <class String>
-void push_back(const my_type<String>&);
-};
-
-template <class String>
-void inserter(const my_type<String>& m, my_container& c) {c.push_back(m);}
-
-}  // my
-
-int main()
-{
-    my::my_container c;
-    my::my_type<std::string> m;
-    inserter(m, c);
-}
-
- -

-Today this code fails because the call to inserter binds to -std::inserter instead of to my::inserter. However with the -proposed change std::inserter will no longer be a viable function which -leaves only my::inserter in the overload resolution set. Everything -works as the client intends. -

- -

-To make matters a little more insidious, the above example works today if you -simply change the first argument to an rvalue: -

- -
-    inserter(my::my_type(), c);
-
- -

-It will also work if instantiated with some string type other than -std::string (or any other std type). It will also work if -<iterator> happens to not get included. -

- -

-And it will fail again for such inocuous reaons as my_type or -my_container privately deriving from any std type. -

- -

-It seems unfortunate that such simple changes in the client's code can result -in such radically differing behavior. -

- - - -

Proposed resolution:

-

-Change 24.2: -

- -

-24.2 Header <iterator> synopsis -

-
-...
-template <class Container, class Iterator>
-   insert_iterator<Container> inserter(Container& x, Iterator typename Container::iterator i);
-...
-
-
- -

-Change 24.4.2.5: -

- -

-24.4.2.5 Class template insert_iterator

-
-...
-template <class Container, class Iterator>
-   insert_iterator<Container> inserter(Container& x, Iterator typename Container::iterator i);
-...
-
-
- -

-Change 24.4.2.6.5: -

- -
-

-24.4.2.6.5 inserter -

-
-template <class Container, class Inserter>
-   insert_iterator<Container> inserter(Container& x, Inserter typename Container::iterator i);
-
-

--1- Returns: insert_iterator<Container>(x,typename Container::iterator(i)). -

-
- - - -

[ -Kona (2007): This issue will probably be addressed as a part of the concepts overhaul of the library anyway, but the proposed resolution is correct in the absence of concepts. -Proposed Disposition: Ready -]

- - - - - -
-

562. stringbuf ctor inefficient

-

Section: 27.8 [string.streams] Status: CD1 - Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2015-04-08

-

View all other issues in [string.streams].

-

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-

Discussion:

-

- -For better efficiency, the requirement on the stringbuf ctor that -takes a string argument should be loosened up to let it set -epptr() beyond just one past the last initialized -character just like overflow() has been changed to be -allowed to do (see issue 432). That way the first call to -sputc() on an object won't necessarily cause a call to -overflow. The corresponding change should be made to the -string overload of the str() member function. - -

- - -

Proposed resolution:

-

- -Change 27.7.1.1, p3 of the Working Draft, N1804, as follows: - -

- -
-explicit basic_stringbuf(const basic_string<charT,traits,Allocator>& str,
-               ios_base::openmode which = ios_base::in | ios_base::out);
-
- -

--3- Effects: Constructs an object of class basic_stringbuf, -initializing the base class with basic_streambuf() -(27.5.2.1), and initializing mode with which. -Then calls str(s). copies the content of -str into the basic_stringbuf underlying character -sequence. If which & ios_base::out is true, initializes the -output sequence such that pbase() points to the first underlying -character, epptr() points one past the last underlying character, and -pptr() is equal to epptr() if which & ios_base::ate -is true, otherwise pptr() is equal to pbase(). If -which & ios_base::in is true, initializes the input sequence such -that eback() and gptr() point to the first underlying -character and egptr() points one past the last underlying character. -

-
- -

- -Change the Effects clause of the str() in 27.7.1.2, p2 to -read: - -

-
-

--2- Effects: Copies the contents of s into the -basic_stringbuf underlying character sequence and -initializes the input and output sequences according to mode. -If -mode & ios_base::out is true, initializes the output -sequence such that pbase() points to the first underlying character, -epptr() points one past the last underlying character, and pptr() -is equal to epptr() if mode & ios_base::in -is true, otherwise pptr() is equal to pbase(). If -mode & ios_base::in is true, initializes the input sequence -such that eback() and gptr() point to the first underlying -character and egptr() points one past the last underlying character. -

- -

- --3- Postconditions: If mode & ios_base::out is true, -pbase() points to the first underlying character and -(epptr() >= pbase() + s.size()) holds; in addition, if -mode & ios_base::in is true, (pptr() == pbase() -+ s.data()) holds, otherwise (pptr() == pbase()) -is true. If mode & ios_base::in is true, -eback() points to the first underlying character, and -(gptr() == eback()) and (egptr() == eback() + -s.size()) hold. - -

-
- - -

[ -Kona (2007) Moved to Ready. -]

- - - - - -
-

563. stringbuf seeking from end

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: CD1 - Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2015-04-08

-

View all other issues in [stringbuf.virtuals].

-

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-

Discussion:

-

-According to Table 92 (unchanged by issue 432), when (way == -end) the newoff value in out mode is computed as -the difference between epptr() and pbase(). -

-

- -This value isn't meaningful unless the value of epptr() -can be precisely controlled by a program. That used to be possible -until we accepted the resolution of issue 432, but since then the -requirements on overflow() have been relaxed to allow it -to make more than 1 write position available (i.e., by setting -epptr() to some unspecified value past -pptr()). So after the first call to -overflow() positioning the output sequence relative to -end will have unspecified results. - -

-

- -In addition, in in|out mode, since (egptr() == -epptr()) need not hold, there are two different possible values -for newoff: epptr() - pbase() and -egptr() - eback(). - -

- - -

Proposed resolution:

-

- -Change the newoff column in the last row of Table 94 to -read: - -

-

- -the end high mark pointer minus the beginning -pointer (xend high_mark - xbeg). - -

- - -

[ -Kona (2007) Moved to Ready. -]

- - - - - -
-

564. stringbuf seekpos underspecified

-

Section: 27.8.2.4 [stringbuf.virtuals] Status: C++11 - Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2015-04-08

-

View all other issues in [stringbuf.virtuals].

-

View all issues with C++11 status.

-

Discussion:

-

-The effects of the seekpos() member function of -basic_stringbuf simply say that the function positions -the input and/or output sequences but fail to spell out exactly -how. This is in contrast to the detail in which seekoff() -is described. -

- -

[ -2009-07 Frankfurt -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

- -Change 27.7.1.3, p13 to read: - -

-
-

--13- Effects: Equivalent to seekoff(off_type(sp), ios_base::beg, -which). Alters the stream position within the controlled sequences, -if possible, to correspond to the stream position stored in sp -(as described below). -

-
    -
  • If (which & ios_base::in) != 0, positions the input sequence.
    • -
  • If (which & ios_base::out) != 0, positions the output sequence.
    • -
  • If sp is an invalid stream position, or if the function -positions neither sequence, the positioning operation fails. If sp -has not been obtained by a previous successful call to one of the positioning -functions (seekoff, seekpos, tellg, tellp) -the effect is undefined.
    • -
-
- - -

[ -Kona (2007): A pos_type is a position in a stream by -definition, so there is no ambiguity as to what it means. Proposed -Disposition: NAD -]

- - -

[ -Post-Kona Martin adds: -I'm afraid I disagree -with the Kona '07 rationale for marking it NAD. The only text -that describes precisely what it means to position the input -or output sequence is in seekoff(). The seekpos() Effects -clause is inadequate in comparison and the proposed resolution -plugs the hole by specifying seekpos() in terms of seekoff(). -]

- - - - - -
-

565. xsputn inefficient

-

Section: 27.6.3.4.5 [streambuf.virt.put] Status: C++11 - Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

- -streambuf::xsputn() is specified to have the effect of -"writing up to n characters to the output sequence as if by -repeated calls to sputc(c)." - -

-

- -Since sputc() is required to call overflow() when -(pptr() == epptr()) is true, strictly speaking -xsputn() should do the same. However, doing so would be -suboptimal in some interesting cases, such as in unbuffered mode or -when the buffer is basic_stringbuf. - -

-

- -Assuming calling overflow() is not really intended to be -required and the wording is simply meant to describe the general -effect of appending to the end of the sequence it would be worthwhile -to mention in xsputn() that the function is not actually -required to cause a call to overflow(). - -

- -

[ -2009-07 Frankfurt -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

- -Add the following sentence to the xsputn() Effects clause in -27.5.2.4.5, p1 (N1804): - -

-
-

--1- Effects: Writes up to n characters to the output -sequence as if by repeated calls to sputc(c). The characters -written are obtained from successive elements of the array whose first element -is designated by s. Writing stops when either n -characters have been written or a call to sputc(c) would return -traits::eof(). It is uspecified whether the function calls -overflow() when (pptr() == epptr()) becomes true or whether -it achieves the same effects by other means. -

-
-

- -In addition, I suggest to add a footnote to this function with the -same text as Footnote 292 to make it extra clear that derived classes -are permitted to override xsputn() for efficiency. - -

- - -

[ -Kona (2007): We want to permit a streambuf that streams output directly -to a device without making calls to sputc or overflow. We believe that -has always been the intention of the committee. We believe that the -proposed wording doesn't accomplish that. Proposed Disposition: Open -]

- - - - - -
-

566. array forms of unformatted input function undefined for zero-element arrays

-

Section: 27.7.2.3 [istream.unformatted] Status: CD1 - Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

-

- -The array forms of unformatted input functions don't have well-defined -semantics for zero-element arrays in a couple of cases. The affected -ones (istream::get() and getline()) are supposed to -terminate when (n - 1) characters are stored, which obviously -can never be true when (n == 0) to start with. - -

- - -

Proposed resolution:

-

- -I propose the following changes (references are relative to the -Working Draft (document N1804). - -

-

- -Change 27.6.1.3, p8 (istream::get()), bullet 1 as follows: - -

-
-

- -if (n < 1) is true or (n - 1) -characters are stored; - -

-
-

- -Similarly, change 27.6.1.3, p18 (istream::getline()), bullet -3 as follows: - -

-
-

- -(n < 1) is true or (n - 1) characters -are stored (in which case the function calls -setstate(failbit)). - -

-
-

- -Finally, change p21 as follows: - -

-
-

- -In any case, provided (n > 0) is true, it then -stores a null character (using charT()) into the next successive -location of the array. - -

-
- - - - - -
-

567. streambuf inserter and extractor should be unformatted

-

Section: 27.7 [iostream.format] Status: CD1 - Submitter: Martin Sebor Opened: 2006-02-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -Issue 60 explicitly made the extractor and inserter operators that -take a basic_streambuf* argument formatted input and output -functions, respectively. I believe that's wrong, certainly in the -case of the extractor, since formatted functions begin by extracting -and discarding whitespace. The extractor should not discard any -characters. - -

- - -

Proposed resolution:

-

- -I propose to change each operator to behave as unformatted input and -output function, respectively. The changes below are relative to the -working draft document number N1804. - -

-

- -Specifically, change 27.6.1.2.3, p14 as follows: - -

- -
-

- -Effects: Behaves as an unformatted input function -(as described in 27.6.1.2.127.6.1.3, paragraph -1). - -

-
-

- -And change 27.6.2.5.3, p7 as follows: - -

- -
-

- -Effects: Behaves as an unformatted output function -(as described in 27.6.2.5.127.6.2.6, paragraph -1). - -

-
- - -

[ -Kona (2007): Proposed Disposition: Ready -]

- - - - - -
-

574. DR 369 Contradicts Text

-

Section: 27.4 [iostream.objects] Status: CD1 - Submitter: Pete Becker Opened: 2006-04-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-lib.iostream.objects requires that the standard stream objects are never -destroyed, and it requires that they be destroyed. -

-

-DR 369 adds words to say that we really mean for ios_base::Init objects to force -construction of standard stream objects. It ends, though, with the phrase "these -stream objects shall be destroyed after the destruction of dynamically ...". -However, the rule for destruction is stated in the standard: "The objects are -not destroyed during program execution." -

- - -

Proposed resolution:

-

-Change 27.4 [iostream.objects]/1: -

- -
-

--2- The objects are constructed and the associations are established at -some time prior to or during the first time an object of class -ios_base::Init is constructed, and in any case before the body of main -begins execution.290) The objects are not destroyed during program -execution.291) If a translation unit includes <iostream> or explicitly -constructs an ios_base::Init object, these stream objects shall be -constructed before dynamic initialization of non-local objects defined -later in that translation unit, and these stream objects shall be -destroyed after the destruction of dynamically initialized non-local -objects defined later in that translation unit. -

-
- - -

[ -Kona (2007): From 27.4 [iostream.objects]/2, strike the words "...and these stream objects -shall be destroyed after the destruction of dynamically initialized -non-local objects defined later in that translation unit." Proposed -Disposition: Review -]

- - - - - -
-

575. the specification of ~shared_ptr is MT-unfriendly, makes implementation assumptions

-

Section: 20.8.2.2.2 [util.smartptr.shared.dest], TR1 2.2.3.2 [tr.util.smartptr.shared.dest] Status: CD1 - Submitter: Peter Dimov Opened: 2006-04-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-[tr.util.smartptr.shared.dest] says in its second bullet: -

- -

-"If *this shares ownership with another shared_ptr instance (use_count() > 1), -decrements that instance's use count." -

- -

-The problem with this formulation is that it presupposes the existence of an -"use count" variable that can be decremented and that is part of the state of a -shared_ptr instance (because of the "that instance's use count".) -

- -

-This is contrary to the spirit of the rest of the specification that carefully -avoids to require an use count variable. Instead, use_count() is specified to -return a value, a number of instances. -

- -

-In multithreaded code, the usual implicit assumption is that a shared variable -should not be accessed by more than one thread without explicit synchronization, -and by introducing the concept of an "use count" variable, the current wording -implies that two shared_ptr instances that share ownership cannot be destroyed -simultaneously. -

- -

-In addition, if we allow the interpretation that an use count variable is part -of shared_ptr's state, this would lead to other undesirable consequences WRT -multiple threads. For example, -

- -
-p1 = p2;
-
- -

-would now visibly modify the state of p2, a "write" operation, requiring a lock. -

- - -

Proposed resolution:

-

-Change the first two bullets of [lib.util.smartptr.shared.dest]/1 to: -

- -
-
    -
  • If *this is empty or shares ownership with another -shared_ptr instance (use_count() > 1), there are no side effects.
    • -
  • If *this shares ownership with another shared_ptr instance -(use_count() > 1), decrements that instance's use count.
    • -
-
- -

-Add the following paragraph after [lib.util.smartptr.shared.dest]/1: -

- -

-[Note: since the destruction of *this decreases the number of instances in -*this's ownership group by one, all shared_ptr instances that share ownership -with *this will report an use_count() that is one lower than its previous value -after *this is destroyed. --end note] -

- - - - - -
-

576. find_first_of is overconstrained

-

Section: 25.2.7 [alg.find.first.of] Status: CD1 - Submitter: Doug Gregor Opened: 2006-04-25 Last modified: 2015-04-08

-

View all other issues in [alg.find.first.of].

-

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-

Discussion:

-

-In 25.1.4 Find First [lib.alg.find.first], the two iterator type parameters to -find_first_of are specified to require Forward Iterators, as follows: -

- -
-template<class ForwardIterator1, class ForwardIterator2>
-  ForwardIterator1
-  find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
-                        ForwardIterator2 first2, ForwardIterator2 last2);
-template<class ForwardIterator1, class ForwardIterator2,
-                  class BinaryPredicate>
-ForwardIterator1
-  find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
-                         ForwardIterator2 first2, ForwardIterator2 last2,
-                        BinaryPredicate pred);
-
- -

-However, ForwardIterator1 need not actually be a Forward Iterator; an Input -Iterator suffices, because we do not need the multi-pass property of the Forward -Iterator or a true reference. -

- - -

Proposed resolution:

-

-Change the declarations of find_first_of to: -

- -
-template<class ForwardIterator1InputIterator1, class ForwardIterator2>
-  ForwardIterator1InputIterator1
-  find_first_of(ForwardIterator1InputIterator1 first1, ForwardIterator1InputIterator1 last1,
-                        ForwardIterator2 first2, ForwardIterator2 last2);
-template<class ForwardIterator1InputIterator1, class ForwardIterator2,
-                  class BinaryPredicate>
-ForwardIterator1InputIterator1
-  find_first_of(ForwardIterator1InputIterator1 first1, ForwardIterator1InputIterator1 last1,
-                         ForwardIterator2 first2, ForwardIterator2 last2,
-                        BinaryPredicate pred);
-
- - - - - - -
-

577. upper_bound(first, last, ...) cannot return last

-

Section: 25.4.3.2 [upper.bound] Status: CD1 - Submitter: Seungbeom Kim Opened: 2006-05-03 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-ISO/IEC 14882:2003 says: -

- -
-

-25.3.3.2 upper_bound -

-

-Returns: The furthermost iterator i in the range -[first, last) such that -for any iterator j in the range [first, i) the following corresponding -conditions hold: !(value < *j) or comp(value, *j) == false. -

-
- -

-From the description above, upper_bound cannot return last, since it's -not in the interval [first, last). This seems to be a typo, because if -value is greater than or equal to any other values in the range, or if -the range is empty, returning last seems to be the intended behaviour. -The corresponding interval for lower_bound is also [first, last]. -

- - -

Proposed resolution:

-

-Change [lib.upper.bound]: -

- -
-

-Returns: The furthermost iterator i in the range -[first, last)] such that -for any iterator j in the range [first, i) the following corresponding -conditions hold: !(value < *j) or comp(value, *j) == false. -

-
- - - - - - -
-

578. purpose of hint to allocator::allocate()

-

Section: 20.7.9.1 [allocator.members] Status: CD1 - Submitter: Martin Sebor Opened: 2006-05-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -The description of the allocator member function -allocate() requires that the hint argument be -either 0 or a value previously returned from allocate(). -Footnote 227 further suggests that containers may pass the address of -an adjacent element as this argument. - -

-

- -I believe that either the footnote is wrong or the normative -requirement that the argument be a value previously returned from a -call to allocate() is wrong. The latter is supported by -the resolution to issue 20-004 proposed in c++std-lib-3736 by Nathan -Myers. In addition, the hint is an ordinary void* and not the -pointer type returned by allocate(), with -the two types potentially being incompatible and the requirement -impossible to satisfy. - -

-

- -See also c++std-lib-14323 for some more context on where this came up -(again). - -

- - -

Proposed resolution:

-

- -Remove the requirement in 20.6.1.1, p4 that the hint be a value -previously returned from allocate(). Specifically, change -the paragraph as follows: - -

-

-Requires: hint either 0 or previously obtained from member -allocate and not yet passed to member deallocate. -The value hint may be used by an implementation to help improve performance -223). [Note: The value hint may be used by an -implementation to help improve performance. -- end note] -

-

-[Footnote: 223)In a container member function, the address of an -adjacent element is often a good choice to pass for this argument. -

- - - - -
-

581. flush() not unformatted function

-

Section: 27.7.3.7 [ostream.unformatted] Status: CD1 - Submitter: Martin Sebor Opened: 2006-06-14 Last modified: 2015-04-08

-

View all other issues in [ostream.unformatted].

-

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-

Discussion:

-

- -The resolution of issue 60 changed basic_ostream::flush() -so as not to require it to behave as an unformatted output function. -That has at least two in my opinion problematic consequences: - -

-

- -First, flush() now calls rdbuf()->pubsync() -unconditionally, without regard to the state of the stream. I can't -think of any reason why flush() should behave differently -from the vast majority of stream functions in this respect. - -

-

- -Second, flush() is not required to catch exceptions from -pubsync() or set badbit in response to such -events. That doesn't seem right either, as most other stream functions -do so. - -

- - -

Proposed resolution:

-

- -I propose to revert the resolution of issue 60 with respect to -flush(). Specifically, I propose to change 27.6.2.6, p7 -as follows: - -

- -

-Effects: Behaves as an unformatted output function (as described -in 27.6.2.6, paragraph 1). If rdbuf() is not a null -pointer, constructs a sentry object. If this object returns -true when converted to a value of type bool the function -calls rdbuf()->pubsync(). If that function returns --1 calls setstate(badbit) (which may throw -ios_base::failure (27.4.4.3)). Otherwise, if the -sentry object returns false, does nothing.Does -not behave as an unformatted output function (as described in -27.6.2.6, paragraph 1). -

- - - -

[ -Kona (2007): Proposed Disposition: Ready -]

- - - - - -
-

586. string inserter not a formatted function

-

Section: 21.4.8.9 [string.io] Status: CD1 - Submitter: Martin Sebor Opened: 2006-06-22 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

- -Section and paragraph numbers in this paper are relative to the -working draft document number N2009 from 4/21/2006. - -

- -

- -The basic_string extractor in 21.3.7.9, p1 is clearly -required to behave as a formatted input function, as is the -std::getline() overload for string described in p7. - -

-

- -However, the basic_string inserter described in p5 of the -same section has no such requirement. This has implications on how the -operator responds to exceptions thrown from xsputn() -(formatted output functions are required to set badbit -and swallow the exception unless badbit is also set in -exceptions(); the string inserter doesn't have any such -requirement). - -

-

- -I don't see anything in the spec for the string inserter that would -justify requiring it to treat exceptions differently from all other -similar operators. (If it did, I think it should be made this explicit -by saying that the operator "does not behave as a formatted output -function" as has been made customary by the adoption of the resolution -of issue 60). - -

- - -

Proposed resolution:

-

- -I propose to change the Effects clause in 21.3.7.9, p5, as follows: - -

-
-

- -Effects: Begins by constructing a sentry object k as if k -were constructed by typename basic_ostream<charT, -traits>::sentry k (os). If bool(k) is -true, Behaves as a formatted output function -(27.6.2.5.1). After constructing a sentry object, if -this object returns true when converted to a value of -type bool, determines padding as described in -22.2.2.2.2, then inserts the resulting sequence of characters -seq as if by calling os.rdbuf()->sputn(seq , -n), where n is the larger of -os.width() and str.size(); then calls -os.width(0). If the call to sputn fails, calls -os.setstate(ios_base::failbit). - -

-
-

- -This proposed resilution assumes the resolution of issue 394 (i.e., -that all formatted output functions are required to set -ios_base::badbit in response to any kind of streambuf -failure), and implicitly assumes that a return value of -sputn(seq, n) other than n -indicates a failure. - -

- - - - -
-

589. Requirements on iterators of member template functions of containers

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Peter Dimov Opened: 2006-08-02 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 536

-

Discussion:

-

-There appears to be no requirements on the InputIterators used in sequences in 23.1.1 in -terms of their value_type, and the requirements in 23.1.2 appear to be overly strict -(requires InputIterator::value_type be the same type as the container's value_type). -

- - -

Proposed resolution:

-

-Change 23.1.1 p3: -

- -

-In Tables 82 and 83, X denotes a sequence class, a denotes a -value of X, i and j denote iterators satisfying input -iterator requirements and refer to elements implicitly -convertible to value_type, [i, j) denotes a valid -range, n denotes a value of X::size_type, p denotes a -valid iterator to a, q denotes a valid dereferenceable -iterator to a, [q1, q2) denotes a valid range in a, -and t denotes a value of X::value_type. -

- -

-Change 23.1.2 p7: -

- -

-In Table 84, X is an associative container class, a is a value -of X, a_uniq is a value of X when X supports -unique keys, and a_eq is a value of X when X supports -multiple keys, i and j satisfy input iterator requirements and -refer to elements of implicitly convertible to -value_type, [i, j) is a valid range, p is a valid -iterator to a, q is a valid dereferenceable iterator to -a, [q1, q2) is a valid range in a, t is a -value of X::value_type, k is a value of X::key_type -and c is a value of type X::key_compare. -

- - - -

Rationale:

-

-Concepts will probably come in and rewrite this section anyway. But just in case it is -easy to fix this up as a safety net and as a clear statement of intent. -

- - - - - -
-

593. __STDC_CONSTANT_MACROS

-

Section: 18.4 [cstdint], TR1 8.22 [tr.c99.cstdint] Status: CD1 - Submitter: Walter Brown Opened: 2006-08-28 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Clause 18.3 of the current Working Paper (N2009) deals with the new C++ headers -<cstdint> and <stdint.h>. These are of course based on the C99 header -<stdint.h>, and were part of TR1. -

- -

-Per 18.3.1/1, these headers define a number of macros and function macros. -While the WP does not mention __STDC_CONSTANT_MACROS in this context, C99 -footnotes do mention __STDC_CONSTANT_MACROS. Further, 18.3.1/2 states that "The -header defines all ... macros the same as C99 subclause 7.18." -

- -

-Therefore, if I wish to have the above-referenced macros and function macros -defined, must I #define __STDC_CONSTANT_MACROS before I #include <cstdint>, or -does the C++ header define these macros/function macros unconditionally? -

- - -

Proposed resolution:

-

-To put this issue to rest for C++0X, I propose the following addition to -18.3.1/2 of the Working Paper N2009: -

- -

-[Note: The macros defined by <cstdint> are provided unconditionally: in -particular, the symbols __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS -(mentioned in C99 footnotes 219, 220, and 222) play no role in C++. --end note] -

- - - - - -
-

594. Disadvantages of defining Swappable in terms of CopyConstructible and Assignable

-

Section: 17.6.3.1 [utility.arg.requirements] Status: Resolved - Submitter: Niels Dekker Opened: 2006-11-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-It seems undesirable to define the Swappable requirement in terms of -CopyConstructible and Assignable requirements. And likewise, once the -MoveConstructible and MoveAssignable requirements (N1860) have made it -into the Working Draft, it seems undesirable to define the Swappable -requirement in terms of those requirements. Instead, it appears -preferable to have the Swappable requirement defined exclusively in -terms of the existence of an appropriate swap function. -

- -

-Section 20.1.4 [lib.swappable] of the current Working Draft (N2009) -says: -

- -

-The Swappable requirement is met by satisfying one or more of the -following conditions:

-
    -
  • -T is Swappable if T satisfies the CopyConstructible requirements -(20.1.3) and the Assignable requirements (23.1); -
    • -
  • -T is Swappable if a namespace scope function named swap exists in the -same namespace as the definition of T, such that the expression -swap(t,u) is valid and has the semantics described in Table 33. -
    • -
-
- -

-I can think of three disadvantages of this definition: -

- -
    -
  1. -

    -If a client's type T satisfies the first condition (T is both -CopyConstructible and Assignable), the client cannot stop T from -satisfying the Swappable requirement without stopping T from -satisfying the first condition. -

    -

    -A client might want to stop T from satisfying the Swappable -requirement, because swapping by means of copy construction and -assignment might throw an exception, and she might find a throwing -swap unacceptable for her type. On the other hand, she might not feel -the need to fully implement her own swap function for this type. In -this case she would want to be able to simply prevent algorithms that -would swap objects of type T from being used, e.g., by declaring a -swap function for T, and leaving this function purposely undefined. -This would trigger a link error, if an attempt would be made to use -such an algorithm for this type. For most standard library -implementations, this practice would indeed have the effect of -stopping T from satisfying the Swappable requirement. -

    -
    2. -
  2. -

    -A client's type T that does not satisfy the first condition can not be -made Swappable by providing a specialization of std::swap for T. -

    -

    -While I'm aware about the fact that people have mixed feelings about -providing a specialization of std::swap, it is well-defined to do so. -It sounds rather counter-intuitive to say that T is not Swappable, if -it has a valid and semantically correct specialization of std::swap. -Also in practice, providing such a specialization will have the same -effect as satisfying the Swappable requirement. -

    -
    3. -
  3. -

    -For a client's type T that satisfies both conditions of the Swappable -requirement, it is not specified which of the two conditions prevails. -After reading section 20.1.4 [lib.swappable], one might wonder whether -objects of T will be swapped by doing copy construction and -assignments, or by calling the swap function of T. -

    -

    -I'm aware that the intention of the Draft is to prefer calling the -swap function of T over doing copy construction and assignments. Still -in my opinion, it would be better to make this clear in the wording of -the definition of Swappable. -

    -
    4. -
- -

-I would like to have the Swappable requirement defined in such a way -that the following code fragment will correctly swap two objects of a -type T, if and only if T is Swappable: -

- -
-   using std::swap;
-   swap(t, u);  // t and u are of type T.
-
- -

-This is also the way Scott Meyers recommends calling a swap function, -in Effective C++, Third Edition, item 25. -

- -

-Most aspects of this issue have been dealt with in a discussion on -comp.std.c++ about the Swappable requirement, from 13 September to 4 -October 2006, including valuable input by David Abrahams, Pete Becker, -Greg Herlihy, Howard Hinnant and others. -

- -

[ -San Francisco: -]

- - -

-Recommend NADResolved. Solved by -N2774. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved to Open. Waiting for non-concepts draft. -

- -

[ -2009-11-08 Howard adds: -]

- - -

-This issue is very closely related to 742. -

- -

[ -2010-02-03 Sean Hunt adds: -]

- - -
-

-While reading N3000, I independently came across Issue 594. Having seen that -it's an issue under discussion, I think the proposed wording needs fixing to -something more like "...function call swap(t,u) that includes std::swap in its -overload set is valid...", because "...is valid within the namespace std..." -does not allow other libraries to simply use the Swappable requirement by -referring to the standard's definition, since they cannot actually perform any -calls within std. -

- -

-This wording I suggested would also make overloads visible in the same scope as -the `using std::swap` valid for Swappable requirements; a more complex wording -limiting the non-ADL overload set to std::swap might be required. -

-
- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Editorial. Rationale added. -

- - - -

Rationale:

-

-Solved by N3048. -

- - -

Proposed resolution:

-

-Change section 20.1.4 [lib.swappable] as follows: -

-

-The Swappable requirement is met by satisfying -one or more of the following conditions: -the following condition:

-
    - -
  • -T is Swappable if T satisfies the CopyConstructible requirements -(20.1.3) and the Assignable requirements (23.1); -
    • -
  • - -T is Swappable if a namespace scope function named swap exists in the -same namespace as the definition of T, such that the expression -swap(t,u) is valid and has the semantics described in Table 33. - -T is Swappable if an unqualified function call swap(t,u) is valid -within the namespace std, and has the semantics described in Table 33. -
    • -
-
- - - - - -
-

595. TR1/C++0x: fabs(complex<T>) redundant / wrongly specified

-

Section: 26.4.7 [complex.value.ops] Status: CD1 - Submitter: Stefan Große Pawig Opened: 2006-09-24 Last modified: 2015-04-08

-

View all other issues in [complex.value.ops].

-

View all issues with CD1 status.

-

Discussion:

-

-TR1 introduced, in the C compatibility chapter, the function -fabs(complex<T>): -

-
------ SNIP -----
-8.1.1 Synopsis                                [tr.c99.cmplx.syn]
-
-  namespace std {
-  namespace tr1 {
-[...]
-  template<class T> complex<T> fabs(const complex<T>& x);
-  } // namespace tr1
-  } // namespace std
-
-[...]
-
-8.1.8 Function fabs                          [tr.c99.cmplx.fabs]
-
-1 Effects: Behaves the same as C99 function cabs, defined in
-  subclause 7.3.8.1.
------ SNIP -----
-
- -

-The current C++0X draft document (n2009.pdf) adopted this -definition in chapter 26.3.1 (under the comment // 26.3.7 values) -and 26.3.7/7. -

-

-But in C99 (ISO/IEC 9899:1999 as well as the 9899:TC2 draft document -n1124), the referenced subclause reads -

- -
------ SNIP -----
-7.3.8.1 The cabs functions
-
-  Synopsis
-
-1 #include <complex.h>
-  double cabs(double complex z);
-  float cabsf(float complex z);
-  long double cabsl(long double z);
-
-  Description
-
-2 The cabs functions compute the complex absolute value (also called
-  norm, modulus, or magnitude) of z.
-
-  Returns
-
-3 The cabs functions return the complex absolute value.
------ SNIP -----
-
- -

-Note that the return type of the cabs*() functions is not a complex -type. Thus, they are equivalent to the already well established - template<class T> T abs(const complex<T>& x); -(26.2.7/2 in ISO/IEC 14882:1998, 26.3.7/2 in the current draft -document n2009.pdf). -

-

-So either the return value of fabs() is specified wrongly, or fabs() -does not behave the same as C99's cabs*(). -

-

-Possible Resolutions -

-

-This depends on the intention behind the introduction of fabs(). -

-

-If the intention was to provide a /complex/ valued function that -calculates the magnitude of its argument, this should be -explicitly specified. In TR1, the categorization under "C -compatibility" is definitely wrong, since C99 does not provide -such a complex valued function. -

-

-Also, it remains questionable if such a complex valued function -is really needed, since complex<T> supports construction and -assignment from real valued arguments. There is no difference -in observable behaviour between -

-
-  complex<double> x, y;
-  y = fabs(x);
-  complex<double> z(fabs(x));
-
-

-and -

-
-  complex<double> x, y;
-  y = abs(x);
-  complex<double> z(abs(x));
-
-

-If on the other hand the intention was to provide the intended -functionality of C99, fabs() should be either declared deprecated -or (for C++0X) removed from the standard, since the functionality -is already provided by the corresponding overloads of abs(). -

- -

[ -Bellevue: -]

- - -

-Bill believes that abs() is a suitable overload. We should remove fabs(). -

- - -

Proposed resolution:

- -

-Change the synopsis in 26.4.1 [complex.syn]: -

- -
-template<class T> complex<T> fabs(const complex<T>&);
-
- -

-Remove 26.4.7 [complex.value.ops], p7: -

- -
-
-template<class T> complex<T> fabs(const complex<T>& x);
-
-
-

--7- Effects: Behaves the same as C99 function cabs, defined in subclause 7.3.8.1. -

-
-
- - - -

[ -Kona (2007): Change the return type of fabs(complex) to T. -Proposed Disposition: Ready -]

- - - - - -
-

596. 27.8.1.3 Table 112 omits "a+" and "a+b" modes

-

Section: 27.9.1.4 [filebuf.members] Status: CD1 - Submitter: Thomas Plum Opened: 2006-09-26 Last modified: 2015-04-08

-

View all other issues in [filebuf.members].

-

View all issues with CD1 status.

-

Discussion:

-

-In testing 27.9.1.4 [filebuf.members], Table 112 (in the latest N2009 draft), we invoke -

-
-   ostr.open("somename", ios_base::out | ios_base::in | ios_base::app)
-
-

-and we expect the open to fail, because out|in|app is not listed in -Table 92, and just before the table we see very specific words: -

-

- If mode is not some combination of flags shown in the table - then the open fails. -

-

-But the corresponding table in the C standard, 7.19.5.3, provides two -modes "a+" and "a+b", to which the C++ modes out|in|app and -out|in|app|binary would presumably apply. -

-

-We would like to argue that the intent of Table 112 was to match the -semantics of 7.19.5.3 and that the omission of "a+" and "a+b" was -unintentional. (Otherwise there would be valid and useful behaviors -available in C file I/O which are unavailable using C++, for no -valid functional reason.) -

-

-We further request that the missing modes be explicitly restored to -the WP, for inclusion in C++0x. -

- -

[ -Martin adds: -]

- - -

-...besides "a+" and "a+b" the C++ table is also missing a row -for a lone app bit which in at least two current implementation -as well as in Classic Iostreams corresponds to the C stdio "a" -mode and has been traditionally documented as implying ios::out. -Which means the table should also have a row for in|app meaning -the same thing as "a+" already proposed in the issue. -

- - -

Proposed resolution:

-

-Add to the table "File open modes" in 27.9.1.4 [filebuf.members]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
File open modes
ios_base Flag combinationstdio equivalent
binaryinouttruncapp 
    +     "w"
    +   + "a"
        + "a"
    + +   "w"
  +       "r"
  + +     "r+"
  + + +   "w+"
  + +   + "a+"
  +     + "a+"
+   +     "wb"
+   +   + "ab"
+       + "ab"
+   + +   "wb"
+ +       "rb"
+ + +     "r+b"
+ + + +   "w+b"
+ + +   + "a+b"
+ +     + "a+b"
-
- - - -

[ -Kona (2007) Added proposed wording and moved to Review. -]

- - - - - -
-

598. Decimal: Conversion to integral should truncate, not round.

-

Section: TRDecimal 3.2 [trdec.types.types] Status: TRDec - Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2015-04-08

-

View all other issues in [trdec.types.types].

-

View all issues with TRDec status.

-

Discussion:

- -

-In a private email, Daniel writes: -

-
-

-I would like to -ask, what where the reason for the decision to -define the semantics of the integral conversion of the decimal types, namely -

-
-"operator long long() const;
-
-     Returns: Returns the result of the 
-conversion of *this to the type long long, as if 
-performed by the expression llrounddXX(*this)."
-
-

-where XX stands for either 32, 64, or 128, -corresponding to the proper decimal type. The -exact meaning of llrounddXX is not given in that -paper, so I compared it to the corresponding -definition given in C99, 2nd edition (ISO 9899), which says in 7.12.9.7 p. 2: -

-

-"The lround and llround functions round their -argument to the nearest integer value, -rounding halfway cases away from zero, regardless -of the current rounding direction. [..]" -

-

-Now considering the fact that integral conversion -of the usual floating-point types ("4.9 -Floating-integral conversions") has truncation -semantic I wonder why this conversion behaviour -has not been transferred for the decimal types. -

-
-

-Robert comments: -

-

-Also, there is a further error in the Returns: clause for converting decimal::decimal128 to long long. It currently calls llroundd64, not llroundd128. -

- - - -

Proposed resolution:

-

-Change the Returns: clause in 3.2.2.4 to: -

-

-Returns: Returns the result of the conversion of *this to the type long long, as if performed by the expression llroundd32(*this) while the decimal rounding direction mode [3.5.2] FE_DEC_TOWARD_ZERO is in effect. -

-

-Change the Returns: clause in 3.2.3.4 to: -

-

-Returns: Returns the result of the conversion of *this to the type long long, as if performed by the expression llroundd64(*this) while the decimal rounding direction mode [3.5.2] FE_DEC_TOWARD_ZERO is in effect. -

-

-Change the Returns: clause in 3.2.4.4 to: -

-

-Returns: Returns the result of the conversion of *this to the type long long, as if performed by the expression llroundd64(*this) llroundd128(*this) while the decimal rounding direction mode [3.5.2] FE_DEC_TOWARD_ZERO is in effect. -

- - - - - - -
-

599. Decimal: Say "octets" instead of "bytes."

-

Section: TRDecimal 3.1 [trdec.types.encodings] Status: TRDec - Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2015-04-08

-

View all issues with TRDec status.

-

Discussion:

-

-Daniel writes in a private email: -

- -
-

-- 3.1 'Decimal type encodings' says in its note: -

-
-"this implies that 
-sizeof(std::decimal::decimal32) == 4, 
-sizeof(std::decimal::decimal64) == 8, and 
-sizeof(std::decimal::decimal128) == 16."
-
-

-This is a wrong assertion, because the definition -of 'byte' in 1.7 'The C+ + memory model' of ISO -14882 (2nd edition) does not specify that a byte -must be necessarily 8 bits large, which would be -necessary to compare with the specified bit sizes -of the types decimal32, decimal64, and decimal128. -

-
- - -

Proposed resolution:

-

-Change 3.1 as follows: -

-
-

-The three decimal encoding formats defined in IEEE-754R correspond to the three decimal floating types as follows: -

-
    -
  • -decimal32 is a decimal32 number, which is encoded in four consecutive bytes octets (32 bits) -
    • -
  • -decimal64 is a decimal64 number, which is encoded in eight consecutive bytes octets (64 bits) - -
    • -
  • -decimal128 is a decimal128 number, which is encoded in 16 consecutive bytes octets (128 bits) -
    • -
-

-[Note: this implies that sizeof(std::decimal::decimal32) == 4, sizeof(std::decimal::decimal64) == 8, and sizeof(std::decimal::decimal128) == 16. --end note] -

-
- - - - -
-

600. Decimal: Wrong parameters for wcstod* functions

-

Section: TRDecimal 3.9 [trdec.types.cwchar] Status: TRDec - Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2015-04-08

-

View all issues with TRDec status.

-

Discussion:

-

-Daniel writes: -

-

-- 3.9.1 'Additions to <cwchar>' provides wrong -signatures to the wcstod32, wcstod64, and -wcstod128 functions ([the parameters have type pointer-to-] char instead of wchar_t). -

- - -

Proposed resolution:

-

-Change "3.9.1 Additions to <cwchar> synopsis" to: -

-
-       namespace std {
-       namespace decimal {
-         // 3.9.2 wcstod functions:
-         decimal32  wcstod32  (const char wchar_t * nptr, char wchar_t ** endptr);
-         decimal64  wcstod64  (const char wchar_t * nptr, char wchar_t ** endptr);
-         decimal128 wcstod128 (const char wchar_t * nptr, char wchar_t ** endptr);
-       }
-       }
-
- - - - -
-

601. Decimal: numeric_limits typos

-

Section: TRDecimal 3.3 [trdec.types.limits] Status: TRDec - Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2015-04-08

-

View all issues with TRDec status.

-

Discussion:

-

-Daniel writes in a private email: -

- -
-

-- 3.3 'Additions to header <limits>' contains two -errors in the specialisation of numeric_limits<decimal::decimal128>: -

-
    -
  1. The static member max() returns DEC128_MIN, this should be DEC128_MAX.
    2. -
  2. The static member digits is assigned to 384, -this should be 34 (Probably mixed up with the -max. exponent for decimal::decimal64).
    3. -
-
- - -

Proposed resolution:

-

-In "3.3 Additions to header <limits>" change numeric_limits<decimal::decimal128> as follows: -

-
-        template<> class numeric_limits<decimal::decimal128> {
-          public:
-            static const bool is_specialized = true;
-
-            static decimal::decimal128 min() throw() { return DEC128_MIN; }
-            static decimal::decimal128 max() throw() { return DEC128_MIN; DEC128_MAX; }
-
-            static const int digits       = 384 34;
-            /* ... */
-
- - - - -
-

602. Decimal: "generic floating type" not defined.

-

Section: TRDecimal 3 [trdec.types] Status: TRDec - Submitter: Daniel Krügler Opened: 2006-05-28 Last modified: 2015-04-08

-

View all other issues in [trdec.types].

-

View all issues with TRDec status.

-

Discussion:

-

-The document uses the term "generic floating types," but defines it nowhere. -

- - -

Proposed resolution:

-

-Change the first paragraph of "3 Decimal floating-point types" as follows: -

-

-This Technical Report introduces three decimal floating-point types, named -decimal32, decimal64, and decimal128. The set of values of type decimal32 is a -subset of the set of values of type decimal64; the set of values of the type -decimal64 is a subset of the set of values of the type decimal128. Support for -decimal128 is optional. These types supplement the Standard C++ types -float, double, and long double, which are -collectively described as the basic floating types. -

- - - - -
-

603. Decimal: Trivially simplifying decimal classes.

-

Section: TRDecimal 3 [trdec.types] Status: TRDec - Submitter: Martin Sebor Opened: 2006-05-28 Last modified: 2015-04-08

-

View all other issues in [trdec.types].

-

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-

Discussion:

-

In c++std-lib-17198, Martin writes:

- -

-Each of the three classes proposed in the paper (decimal32, decimal64, -and decimal128) explicitly declares and specifies the semantics of its -copy constructor, copy assignment operator, and destructor. Since the -semantics of all three functions are identical to the trivial versions -implicitly generated by the compiler in the absence of any declarations -it is safe to drop them from the spec. This change would make the -proposed classes consistent with other similar classes already in the -standard (e.g., std::complex). -

- - -

Proposed resolution:

-

-Change "3.2.2 Class decimal32" as follows: -

-
-      namespace std {
-      namespace decimal {
-        class decimal32 {
-          public:
-            // 3.2.2.1 construct/copy/destroy:
-            decimal32();
-            decimal32(const decimal32 & d32);
-            decimal32 & operator=(const decimal32 & d32);
-            ~decimal32();
-            /* ... */
-
-

-Change "3.2.2.1 construct/copy/destroy" as follows: -

-
-        decimal32();
-
-    Effects: Constructs an object of type decimal32 with the value 0;
-
-        decimal32(const decimal32 & d32);
-        decimal32 & operator=(const decimal32 & d32);
-
-    Effects: Copies an object of type decimal32.
-
-        ~decimal32();
-
-    Effects: Destroys an object of type decimal32.
-
-
-

-Change "3.2.3 Class decimal64" as follows: -

-
-      namespace std {
-      namespace decimal {
-        class decimal64 {
-          public:
-            // 3.2.3.1 construct/copy/destroy:
-            decimal64();
-            decimal64(const decimal64 & d64);
-            decimal64 & operator=(const decimal64 & d64);
-            ~decimal64();
-            /* ... */
-
-

-Change "3.2.3.1 construct/copy/destroy" as follows: -

-
-        decimal64();
-
-    Effects: Constructs an object of type decimal64 with the value 0;
-
-        decimal64(const decimal64 & d64);
-        decimal64 & operator=(const decimal64 & d64);
-
-    Effects: Copies an object of type decimal64.
-
-        ~decimal64();
-
-    Effects: Destroys an object of type decimal64.
-
-
-

-Change "3.2.4 Class decimal128" as follows: -

-
-      namespace std {
-      namespace decimal {
-        class decimal128 {
-          public:
-            // 3.2.4.1 construct/copy/destroy:
-            decimal128();
-            decimal128(const decimal128 & d128);
-            decimal128 & operator=(const decimal128 & d128);
-            ~decimal128();
-            /* ... */
-
-

-Change "3.2.4.1 construct/copy/destroy" as follows: -

-
-        decimal128();
-
-    Effects: Constructs an object of type decimal128 with the value 0;
-
-        decimal128(const decimal128 & d128);
-        decimal128 & operator=(const decimal128 & d128);
-
-    Effects: Copies an object of type decimal128.
-
-        ~decimal128();
-
-    Effects: Destroys an object of type decimal128.
-
-
- - - - -
-

604. Decimal: Storing a reference to a facet unsafe.

-

Section: TRDecimal 3 [trdec.types] Status: TRDec - Submitter: Martin Sebor Opened: 2006-05-28 Last modified: 2015-04-08

-

View all other issues in [trdec.types].

-

View all issues with TRDec status.

-

Discussion:

-

-In c++std-lib-17197, Martin writes: -

-

-The extended_num_get and extended_num_put facets are designed -to store a reference to a num_get or num_put facet which the -extended facets delegate the parsing and formatting of types -other than decimal. One form of the extended facet's ctor (the -default ctor and the size_t overload) obtains the reference -from the global C++ locale while the other form takes this -reference as an argument. -

-

-The problem with storing a reference to a facet in another -object (as opposed to storing the locale object in which the -facet is installed) is that doing so bypasses the reference -counting mechanism designed to prevent a facet that is still -being referenced (i.e., one that is still installed in some -locale) from being destroyed when another locale that contains -it is destroyed. Separating a facet reference from the locale -it comes from van make it cumbersome (and in some cases might -even make it impossible) for programs to prevent invalidating -the reference. (The danger of this design is highlighted in -the paper.) -

-

-This problem could be easily avoided by having the extended -facets store a copy of the locale from which they would extract -the base facet either at construction time or when needed. To -make it possible, the forms of ctors of the extended facets that -take a reference to the base facet would need to be changed to -take a locale argument instead. -

- - -

Proposed resolution:

-

-1. Change the extended_num_get synopsis in 3.10.2 as follows: -

-
-            extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0);
-
-            /* ... */
-
-            // const std::num_get<charT, InputIterator> & base;        exposition only
-            // std::locale baseloc;                                    exposition only
-
-

-2. Change the description of the above constructor in 3.10.2.1: -

-
-            extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0);
-
-
-
-

-Effects: Constructs an extended_num_get facet as if by: -

-
-       extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0)
-                : facet(refs), baseloc(b)
-                { /* ... */ }
-
-
-

-Notes: Care must be taken by the implementation to ensure that the lifetime of the facet referenced by base exceeds that of the resulting extended_num_get facet. -

-
-

-3. Change the Returns: clause for do_get(iter_type, iter_type, ios_base &, ios_base::iostate &, bool &) const, et al to -

-

-Returns: base std::use_facet<std::num_get<charT, InputIterator> >(baseloc).get(in, end, str, err, val). -

-

-4. Change the extended_num_put synopsis in 3.10.3 as follows: -

-
-            extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0);
-
-            /* ... */
-
-            // const std::num_put<charT, OutputIterator> & base;       exposition only
-            // std::locale baseloc;                                    exposition only
-
-

-5. Change the description of the above constructor in 3.10.3.1: -

-
-            extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0);
-
-
-

-Effects: Constructs an extended_num_put facet as if by: -

-
-       extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0)
-                : facet(refs), baseloc(b)
-                { /* ... */ }
-
-
-

-Notes: Care must be taken by the implementation to ensure that the lifetime of the facet referenced by base exceeds that of the resulting extended_num_put facet. -

-
-

-6. Change the Returns: clause for do_put(iter_type, ios_base &, char_type, bool &) const, et al to -

-

-Returns: base std::use_facet<std::num_put<charT, OutputIterator> >(baseloc).put(s, f, fill, val). -

- -

[ -Redmond: We would prefer to rename "extended" to "decimal". -]

- - - - - - -
-

605. Decimal: <decfloat.h> doesn't live here anymore.

-

Section: TRDecimal 3.4 [trdec.types.cdecfloat] Status: TRDec - Submitter: Robert Klarer Opened: 2006-10-17 Last modified: 2015-04-08

-

View all issues with TRDec status.

-

Discussion:

-

-In Berlin, WG14 decided to drop the <decfloat.h> header. The contents of that header have been moved into <float.h>. For the sake of C compatibility, we should make corresponding changes. -

- - -

Proposed resolution:

-

-1. Change the heading of subclause 3.4, "Headers <cdecfloat> and <decfloat.h>" to "Additions to headers <cfloat> and <float.h>." -

-

-2. Change the text of subclause 3.4 as follows: -

-
-

-The standard C++ headers <cfloat> and <float.h> define characteristics of the floating-point types float, double, and long double. Their contents remain unchanged by this Technical Report. -

-

-Headers <cdecfloat> and <decfloat.h> define characteristics of the decimal floating-point types decimal32, decimal64, and decimal128. As well, <decfloat.h> defines the convenience typedefs _Decimal32, _Decimal64, and _Decimal128, for compatibilty with the C programming language. -

-

-The header <cfloat> is described in [tr.c99.cfloat]. The header <float.h> is described in [tr.c99.floath]. These headers are extended by this Technical Report to define characteristics of the decimal floating-point types decimal32, decimal64, and decimal128. As well, <float.h> is extended to define the convenience typedefs _Decimal32, _Decimal64, and _Decimal128 for compatibility with the C programming language. -

-
-

-3. Change the heading of subclause 3.4.1, "Header <cdecfloat> synopsis" to "Additions to header <cfloat> synopsis." -

-

-4. Change the heading of subclause 3.4.2, "Header <decfloat.h> synopsis" to "Additions to header <float.h> synopsis." -

-

-5. Change the contents of 3.4.2 as follows: -

-
-      #include <cdecfloat>
-
-      // C-compatibility convenience typedefs:
-
-      typedef std::decimal::decimal32  _Decimal32;
-      typedef std::decimal::decimal64  _Decimal64;
-      typedef std::decimal::decimal128 _Decimal128;
-
- - - - - -
-

607. Concern about short seed vectors

-

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 - Submitter: Charles Karney Opened: 2006-10-26 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with CD1 status.

-

Discussion:

-

-Short seed vectors of 32-bit quantities all result in different states. However -this is not true of seed vectors of 16-bit (or smaller) quantities. For example -these two seeds -

- -
-unsigned short seed = {1, 2, 3};
-unsigned short seed = {1, 2, 3, 0};
-
- -

-both pack to -

- -
-unsigned seed = {0x20001, 0x3};
-
- -

-yielding the same state. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

608. Unclear seed_seq construction details

-

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 - Submitter: Charles Karney Opened: 2006-10-26 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

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-

Discussion:

-

-In 26.4.7.1 [rand.util.seedseq] /6, the order of packing the inputs into b and the -treatment of signed quantities is unclear. Better to spell it out. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

609. missing static const

-

Section: 26.5.4.3 [rand.adapt.ibits], TR1 5.1 [tr.rand] Status: CD1 - Submitter: Walter E. Brown Opened: 2006-11-02 Last modified: 2015-04-08

-

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-

Discussion:

-

-In preparing N2111, an error on my part resulted in the omission of the -following line from the template synopsis in the cited section: -

- -
-static const size_t word_size = w;
-
- -

-(This same constant is found, for example, in 26.4.3.3 [rand.eng.sub].) -

- - -

Proposed resolution:

-

-Add the above declaration as the first line after the comment in [rand.adapt.ibits] p4: -

- -
-// engine characteristics
-static const size_t word_size = w;
-
- -

-and accept my apologies for the oversight. -

- - - - - -
-

610. Suggested non-normative note for C++0x

-

Section: 20.9.12.2.1 [func.wrap.func.con], TR1 3.7.2.1 [tr.func.wrap.func.con] Status: CD1 - Submitter: Scott Meyers Opened: 2006-11-02 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.con].

-

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-

Discussion:

-

-My suggestion is that implementers of both tr1::function and its -official C++0x successor be explicitly encouraged (but not required) to -optimize for the cases mentioned above, i.e., function pointers and -small function objects. They could do this by using a small internal -buffer akin to the buffer used by implementations of the small string -optimization. (That would make this the small functor optimization -- -SFO :-}) The form of this encouragement could be a note in the standard -akin to footnote 214 of the current standard. -

- -

-Dave Abrahams notes: -

- -

-"shall not throw exceptions" should really be "nothing," both to be more -grammatical and to be consistent with existing wording in the standard. -

- -

-Doug Gregor comments: I think this is a good idea. Currently, implementations of -tr1::function are required to have non-throwing constructors and assignment -operators when the target function object is a function pointer or a -reference_wrapper. The common case, however, is for a tr1::function to store -either an empty function object or a member pointer + an object pointer. -

-

-The function implementation in the upcoming Boost 1.34.0 uses the -"SFO", so that the function objects for typical bind expressions like -

-
-bind(&X::f, this, _1, _2, _3)
-
- -

-do not require heap allocation when stored in a boost::function. I -believe Dinkumware's implementation also performs this optimization. -

- - - -

Proposed resolution:

-

-Revise 20.5.14.2.1 p6 [func.wrap.func.con] to add a note as follows: -

- -
-

-Throws: shall not throw exceptions if f's target is a function -pointer or a function object passed via reference_wrapper. Otherwise, -may throw bad_alloc or any exception thrown by the copy constructor of -the stored function object. -

-

-Note: Implementations are encouraged to avoid the use of dynamically -allocated memory for "small" function objects, e.g., where f's target -is an object holding only a pointer or reference to an object and a member -function pointer (a "bound member function"). -

-
- - - - - -
-

611. Standard library templates and incomplete types

-

Section: 17.6.4.8 [res.on.functions] Status: CD1 - Submitter: Nicola Musatti Opened: 2006-11-13 Last modified: 2015-04-08

-

View all other issues in [res.on.functions].

-

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-

Discussion:

-

-In the latest available draft standard -(N2134) -§ 17.4.3.6 [res.on.functions] states: -

- -
-

--1- In certain cases (replacement functions, handler functions, operations on -types used to instantiate standard library template components), the C++ -Standard Library depends on components supplied by a C++ program. If these -components do not meet their requirements, the Standard places no requirements -on the implementation. -

- -

--2- In particular, the effects are undefined in the following cases: -

-

-[...] -

-
    -
  • if an incomplete type (3.9) is used as a template argument when -instantiating a template component.
    • -
-
- -

-This is contradicted by § 20.6.6.2/2 [util.smartptr.shared] which -states: -

- -
-

-[...] -

- -

-The template parameter T of shared_ptr may be an incomplete type. -

-
- - -

Proposed resolution:

-

-Modify the last bullet of § 17.4.3.6/2 [res.on.functions] to allow for -exceptions: -

- -
-
    -
  • if an incomplete type (3.9) is used as a template argument when -instantiating a template component, unless specifically allowed for the -component.
    • -
-
- - - - - - -
-

612. numeric_limits::is_modulo insufficiently defined

-

Section: 18.3.2.4 [numeric.limits.members] Status: CD1 - Submitter: Chris Jefferson Opened: 2006-11-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-18.2.1.2 55 states that "A type is modulo if it is possible to add two -positive numbers together and have a result that wraps around to a -third number that is less". -This seems insufficient for the following reasons: -

- -
    -
  1. Doesn't define what that value received is.
    2. -
  2. Doesn't state the result is repeatable
    3. -
  3. Doesn't require that doing addition, subtraction and other -operations on all values is defined behaviour.
    4. -
- -

[ -Batavia: Related to -N2144. -Pete: is there an ISO definition of modulo? Underflow on signed behavior is undefined. -]

- - -

[ -Bellevue: accept resolution, move to ready status. -Does this mandate that is_modulo be true on platforms for which int -happens to b modulo? A: the standard already seems to require that. -]

- - - -

Proposed resolution:

-

-Suggest 18.3.2.4 [numeric.limits.members], paragraph 57 is amended to: -

- -

-A type is modulo if, it is possible to add two positive numbers -and have a result that wraps around to a third number that is less. -given any operation involving +,- or * on values of that type whose value -would fall outside the range [min(), max()], then the value returned -differs from the true value by an integer multiple of (max() - min() + -1). -

- - - - - - -
-

613. max_digits10 missing from numeric_limits

-

Section: 18.3.2.7 [numeric.special] Status: CD1 - Submitter: Bo Persson Opened: 2006-11-20 Last modified: 2015-04-08

-

View all other issues in [numeric.special].

-

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-

Discussion:

-

-Section 18.3.2.7 [numeric.special] starts out by saying that "All members shall be provided -for all specializations." -

-

-Then it goes on to show specializations for float and bool, where one member -is missing (max_digits10). -

- -

-Maarten Kronenburg adds: -

- -

-I agree, just adding the comment that the exact number of decimal digits -is digits * ln(radix) / ln(10), where probably this real number is -rounded downward for digits10, and rounded upward for max_digits10 -(when radix=10, then digits10=max_digits10). -Why not add this exact definition also to the standard, so the user -knows what these numbers exactly mean. -

- -

-Howard adds: -

- -

-For reference, here are the correct formulas from -N1822: -

- -
-digits10 = floor((digits-1) * log10(2))
-max_digits10 = ceil((1 + digits) * log10(2))
-
- -

-We are also missing a statement regarding for what specializations this member has meaning. -

- - - -

Proposed resolution:

-

-Change and add after 18.3.2.4 [numeric.limits.members], p11: -

- -
-
static const int max_digits10;
-
-

--11- Number of base 10 digits required to ensure that values which -differ by only one epsilon are always differentiated. -

-

--12- Meaningful for all floating point types. -

-
-
- -

-Change 18.3.2.7 [numeric.special], p2: -

- -
-template<> class numeric_limits<float> { 
-public: 
-  static const bool is_specialized = true; 
-  ...
-  static const int digits10 = 6;
-  static const int max_digits10 = 9;
-  ...
-
- -

-Change 18.3.2.7 [numeric.special], p3: -

- -
-template<> class numeric_limits<bool> { 
-public: 
-  static const bool is_specialized = true; 
-  ...
-  static const int digits10 = 0;
-  static const int max_digits10 = 0;
-  ...
-
- - - - - - - -
-

616. missing 'typename' in ctype_byname

-

Section: 22.4.1.2 [locale.ctype.byname] Status: CD1 - Submitter: Bo Persson Opened: 2006-12-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Section 22.2.1.2 defines the ctype_byname class template. It contains the -line -

- -
-typedef ctype<charT>::mask   mask;
-
- - - -

Proposed resolution:

-

-as this is a dependent type, it should obviously be -

- -
-typedef typename ctype<charT>::mask   mask;
-
- - - - - -
-

618. valarray::cshift() effects on empty array

-

Section: 26.6.2.8 [valarray.members] Status: CD1 - Submitter: Gabriel Dos Reis Opened: 2007-01-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-I would respectfully request an issue be opened with the intention to -clarify the wording for size() == 0 for cshift. -

- - -

Proposed resolution:

-

-Change 26.6.2.8 [valarray.members], paragraph 10: -

- -
- -
-valarray<T> cshift(int n) const;
-
- -
-

-This function returns an object of class valarray<T>, of -length size(), each of whose elements I is -(*this)[(I + n ) % size()]. Thus, if element zero is taken as -the leftmost element, a positive value of n shifts the elements -circularly left n places. that is a circular shift of *this. If -element zero is taken as the leftmost element, a non-negative value of -n shifts the elements circularly left n places and a -negative value of n shifts the elements circularly right --n places. -

-
-
- - - -

Rationale:

-

-We do not believe that there is any real ambiguity about what happens -when size() == 0, but we do believe that spelling this out as a C++ -expression causes more trouble that it solves. The expression is -certainly wrong when n < 0, since the sign of % with negative arguments -is implementation defined. -

- - -

[ -Kona (2007) Changed proposed wording, added rationale and set to Review. -]

- - - - - -
-

619. Longjmp wording problem

-

Section: 18.10 [support.runtime] Status: CD1 - Submitter: Lawrence Crowl Opened: 2007-01-12 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The wording for longjmp is confusing. -

-

-18.10 [support.runtime] -4- Other runtime support -

-

-The function signature longjmp(jmp_buf jbuf, int val) has more restricted -behavior in this International Standard. If any automatic objects would -be destroyed by a thrown exception transferring control to another -(destination) point in the program, then a call to longjmp(jbuf, val) that -the throw point that transfers control to the same (destination) point has -undefined behavior. -

-

-Someone at Google thinks that should say "then a call to longjmp(jbuf, val) -*at* the throw point that transfers control". -

-

-Bill Gibbons thinks it should say something like "If any automatic objects -would be destroyed by an exception thrown at the point of the longjmp and -caught only at the point of the setjmp, the behavior is undefined." -

- - -

Proposed resolution:

-

-In general, accept Bill Gibbons' recommendation, -but add "call" to indicate that the undefined behavior -comes from the dynamic call, not from its presence in the code. -In 18.10 [support.runtime] paragraph 4, change -

- -

-The function signature longjmp(jmp_buf jbuf, int val) has more -restricted behavior in this International Standard. If any automatic -objects would be destroyed by a thrown exception transferring control to another -(destination) point in the program, then a call to longjmp(jbuf, val) -that the throw point that transfers control to the same (destination) point has -undefined behavior. A setjmp/longjmp call pair has -undefined behavior if replacing the setjmp and longjmp by -catch and throw would destroy any automatic objects. -

- - - - - -
-

620. valid uses of empty valarrays

-

Section: 26.6.2.2 [valarray.cons] Status: CD1 - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

View all other issues in [valarray.cons].

-

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-

Discussion:

-

- -The Effects clause for the default valarray ctor -suggests that it is possible to increase the size of an empty -valarray object by calling other non-const member -functions of the class besides resize(). However, such an -interpretation would be contradicted by the requirement on the copy -assignment operator (and apparently also that on the computed -assignments) that the assigned arrays be the same size. See the -reflector discussion starting with c++std-lib-17871. - -

-

- -In addition, Footnote 280 uses some questionable normative -language. - -

- - -

Proposed resolution:

-

- -Reword the Effects clause and Footnote 280 as follows (26.6.2.2 [valarray.cons]): - -

-
-

- -valarray(); - -

-

- -Effects: Constructs an object of class -valarray<T>,279) which has zero -length until it is passed into a library function as a modifiable -lvalue or through a non-constant this pointer.280) - -

-

- -Postcondition: size() == 0. - -

-

- -Footnote 280: This default constructor is essential, since -arrays of valarray are likely to prove useful. -There shall also be a way to change the size of an array after -initialization; this is supplied by the semantics may be -useful. The length of an empty array can be increased after -initialization by means of the resize() member -function. - -

-
- - - - - -
-

621. non-const copy assignment operators of helper arrays

-

Section: 26.6 [numarray] Status: CD1 - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

View all other issues in [numarray].

-

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-

Discussion:

-

- -The computed and "fill" assignment operators of valarray -helper array class templates (slice_array, -gslice_array, mask_array, and -indirect_array) are const member functions of each class -template (the latter by the resolution of 123 -since they have reference semantics and thus do not affect -the state of the object on which they are called. However, the copy -assignment operators of these class templates, which also have -reference semantics, are non-const. The absence of constness opens -the door to speculation about whether they really are intended to have -reference semantics (existing implementations vary widely). - -

- -

-Pre-Kona, Martin adds: -

- -

-I realized that adding the const qualifier to the -functions as I suggested would break the const correctness of the -classes. A few possible solutions come to mind: -

- -
    -
  1. Add the const qualifier to the return types of these functions.
    2. -
  2. Change the return type of all the functions to void to match -the signatures of all the other assignment operators these classes -define.
    3. -
  3. Prohibit the copy assignment of these classes by declaring the -copy assignment operators private (as is done and documented by -some implementations).
    4. -
- - - -

Proposed resolution:

-

- -Declare the copy assignment operators of all four helper array -class templates const. - -

-

- -Specifically, make the following edits: - -

-

- -Change the signature in 26.6.5 [template.slice.array] and -26.6.5.2 [slice.arr.assign] as follows: - -

- 
-
-const slice_array& operator= (const slice_array&) const;
-
-
-

- -Change the signature in 26.6.7 [template.gslice.array] and -26.6.7.2 [gslice.array.assign] as follows: - -

- 
-
-const gslice_array& operator= (const gslice_array&) const;
-
-
-

- -Change the signature in 26.6.8 [template.mask.array] and 26.6.8.2 [mask.array.assign] as -follows: - -

- 
-
-const mask_array& operator= (const mask_array&) const;
-
-
-

- -Change the signature in 26.6.9 [template.indirect.array] and -26.6.9.2 [indirect.array.assign] as follows: - -

- 
-
-const indirect_array& operator= (const indirect_array&) const;
-
-
- - -

[ -Kona (2007) Added const qualification to the return types and set to Ready. -]

- - - - - -
-

622. behavior of filebuf dtor and close on error

-

Section: 27.9.1.17 [fstream.members] Status: CD1 - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

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-

Discussion:

-

- -basic_filebuf dtor is specified to have the following -straightforward effects: - -

-

- -Effects: Destroys an object of class -basic_filebuf. Calls close(). - -

-

- -close() does a lot of potentially complicated processing, -including calling overflow() to write out the termination -sequence (to bring the output sequence to its initial shift -state). Since any of the functions called during the processing can -throw an exception, what should the effects of an exception be on the -dtor? Should the dtor catch and swallow it or should it propagate it -to the caller? The text doesn't seem to provide any guidance in this -regard other than the general restriction on throwing (but not -propagating) exceptions from destructors of library classes in -17.6.5.12 [res.on.exception.handling]. - -

-

- -Further, the last thing close() is specified to do is -call fclose() to close the FILE pointer. The -last sentence of the Effects clause reads: - -

-

- -... If any of the calls to overflow or -std::fclose fails then close fails. - -

-

- -This suggests that close() might be required to call -fclose() if and only if none of the calls to -overflow() fails, and avoid closing the FILE -otherwise. This way, if overflow() failed to flush out -the data, the caller would have the opportunity to try to flush it -again (perhaps after trying to deal with whatever problem may have -caused the failure), rather than losing it outright. - -

-

- -On the other hand, the function's Postcondition specifies that -is_open() == false, which suggests that it should call -fclose() unconditionally. However, since -Postcondition clauses are specified for many functions in the -standard, including constructors where they obviously cannot apply -after an exception, it's not clear whether this Postcondition -clause is intended to apply even after an exception. - -

-

- -It might be worth noting that the traditional behavior (Classic -Iostreams fstream::close() and C fclose()) -is to close the FILE unconditionally, regardless of -errors. - -

- -

[ -See 397 and 418 for related issues. -]

- - - - -

Proposed resolution:

-

- -After discussing this on the reflector (see the thread starting with -c++std-lib-17650) we propose that close() be clarified to -match the traditional behavior, that is to close the FILE -unconditionally, even after errors or exceptions. In addition, we -propose the dtor description be amended so as to explicitly require it -to catch and swallow any exceptions thrown by close(). - -

-

- -Specifically, we propose to make the following edits in -27.9.1.4 [filebuf.members]: - -

-
- 
-
-basic_filebuf<charT,traits>* close();
-
-
-

- -Effects: If is_open() == false, returns a null -pointer. If a put area exists, calls -overflow(traits::eof()) to flush characters. If the last -virtual member function called on *this (between -underflow, overflow, seekoff, -and seekpos) was overflow then calls -a_codecvt.unshift (possibly several times) to determine a -termination sequence, inserts those characters and calls -overflow(traits::eof()) again. Finally, regardless -of whether any of the preceding calls fails or throws an exception, -the function it closes the file ("as if" by calling -std::fclose(file)).334) If any of the calls -made by the functionto overflow -or, including std::fclose, -fails then close fails by returning a null pointer. -If one of these calls throws an exception, the exception is caught and -rethrown after closing the file. - -

-
-

- -And to make the following edits in 27.9.1.2 [filebuf.cons]. - -

-
- 
-
-virtual ~basic_filebuf();
-
-
-

- -Effects: Destroys an object of class -basic_filebuf<charT,traits>. Calls -close(). If an exception occurs during the -destruction of the object, including the call to close(), -the exception is caught but not rethrown (see -17.6.5.12 [res.on.exception.handling]). - -

-
- - - - - -
-

623. pubimbue forbidden to call imbue

-

Section: 27.2.1 [iostream.limits.imbue] Status: CD1 - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

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-

Discussion:

-

- -27.2.1 [iostream.limits.imbue] specifies that "no function described in -clause 27 except for ios_base::imbue causes any instance -of basic_ios::imbue or -basic_streambuf::imbue to be called." - -

-

- -That contradicts the Effects clause for -basic_streambuf::pubimbue() which requires the function -to do just that: call basic_streambuf::imbue(). - -

- - -

Proposed resolution:

-

- -To fix this, rephrase the sentence above to allow -pubimbue to do what it was designed to do. Specifically. -change 27.2.1 [iostream.limits.imbue], p1 to read: - -

-

- -No function described in clause 27 except for -ios_base::imbue and basic_filebuf::pubimbue -causes any instance of basic_ios::imbue or -basic_streambuf::imbue to be called. ... - -

- - - - - -
-

624. valarray assignment and arrays of unequal length

-

Section: 26.6.2.3 [valarray.assign] Status: CD1 - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

View all other issues in [valarray.assign].

-

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-

Discussion:

-

- -The behavior of the valarray copy assignment operator is -defined only when both sides have the same number of elements and the -spec is explicit about assignments of arrays of unequal lengths having -undefined behavior. - -

-

- -However, the generalized subscripting assignment operators overloaded -on slice_array et al (26.6.2.3 [valarray.assign]) don't have any -such restriction, leading the reader to believe that the behavior of -these overloads is well defined regardless of the lengths of the -arguments. - -

-

- -For example, based on the reading of the spec the behavior of the -snippet below can be expected to be well-defined: - -

- 
-    const std::slice from_0_to_3 (0, 3, 1);   // refers to elements 0, 1, 2
-    const std::valarray<int> a (1, 3);        // a = { 1, 1, 1 }
-    std::valarray<int>       b (2, 4);        // b = { 2, 2, 2, 2 }
-
-    b = a [from_0_to_3];
-
-

- -In practice, b may end up being { 1, 1, 1 }, -{ 1, 1, 1, 2 }, or anything else, indicating that -existing implementations vary. - -

- -

-Quoting from Section 3.4, Assignment operators, of Al Vermeulen's -Proposal for Standard C++ Array Classes (see c++std-lib-704; -N0308): -

-

- ...if the size of the array on the right hand side of the equal - sign differs from the size of the array on the left, a run time - error occurs. How this error is handled is implementation - dependent; for compilers which support it, throwing an exception - would be reasonable. -

- -

-And see more history in -N0280. -

- -

- -It has been argued in discussions on the committee's reflector that -the semantics of all valarray assignment operators should -be permitted to be undefined unless the length of the arrays being -assigned is the same as the length of the one being assigned from. See -the thread starting at c++std-lib-17786. - -

-

- -In order to reflect such views, the standard must specify that the -size of the array referred to by the argument of the assignment must -match the size of the array under assignment, for example by adding a -Requires clause to 26.6.2.3 [valarray.assign] as follows: - -

-

- -Requires: The length of the array to which the argument refers -equals size(). - -

- -

- -Note that it's far from clear that such leeway is necessary in order -to implement valarray efficiently. - -

- - -

Proposed resolution:

-

-Insert new paragraph into 26.6.2.3 [valarray.assign]: -

- -
-
-valarray<T>& operator=(const slice_array<T>&); 
-valarray<T>& operator=(const gslice_array<T>&); 
-valarray<T>& operator=(const mask_array<T>&); 
-valarray<T>& operator=(const indirect_array<T>&);
-
-
-

-Requires: The length of the array to which the argument refers -equals size(). -

-

-These operators allow the results of a generalized subscripting operation to be assigned directly to a valarray. -

-
-
- - - - - -
-

625. Mixed up Effects and Returns clauses

-

Section: 17 [library] Status: Resolved - Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2015-04-08

-

View other active issues in [library].

-

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-

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-

Duplicate of: 895

-

Discussion:

-

- -Many member functions of basic_string are overloaded, -with some of the overloads taking a string argument, -others value_type*, others size_type, and -others still iterators. Often, the requirements on one of -the overloads are expressed in the form of Effects, -Throws, and in the Working Paper -(N2134) -also Remark clauses, while those on the rest of the overloads -via a reference to this overload and using a Returns clause. -

- -

-The difference between the two forms of specification is that per -17.5.1.4 [structure.specifications], p3, an Effects clause specifies -"actions performed by the functions," i.e., its observable -effects, while a Returns clause is "a description of the -return value(s) of a function" that does not impose any -requirements on the function's observable effects. -

- -

-Since only Notes are explicitly defined to be informative and -all other paragraphs are explicitly defined to be normative, like -Effects and Returns, the new Remark clauses also -impose normative requirements. -

- -

-So by this strict reading of the standard there are some member -functions of basic_string that are required to throw an -exception under some conditions or use specific traits members while -many other otherwise equivalent overloads, while obliged to return the -same values, aren't required to follow the exact same requirements -with regards to the observable effects. -

- -

-Here's an example of this problem that was precipitated by the change -from informative Notes to normative Remarks (presumably made to -address 424): -

- -

-In the Working Paper, find(string, size_type) contains a -Remark clause (which is just a Note in the current -standard) requiring it to use traits::eq(). -

- -

-find(const charT *s, size_type pos) is specified to -return find(string(s), pos) by a Returns clause -and so it is not required to use traits::eq(). However, -the Working Paper has replaced the original informative Note -about the function using traits::length() with a -normative requirement in the form of a Remark. Calling -traits::length() may be suboptimal, for example when the -argument is a very long array whose initial substring doesn't appear -anywhere in *this. -

- -

-Here's another similar example, one that existed even prior to the -introduction of Remarks: -

- -

- insert(size_type pos, string, size_type, size_type) is -required to throw out_of_range if pos > -size(). -

- -

-insert(size_type pos, string str) is specified to return -insert(pos, str, 0, npos) by a Returns clause and -so its effects when pos > size() are strictly speaking -unspecified. -

- -

-I believe a careful review of the current Effects and -Returns clauses is needed in order to identify all such -problematic cases. In addition, a review of the Working Paper should -be done to make sure that the newly introduced normative Remark -clauses do not impose any undesirable normative requirements in place -of the original informative Notes. -

- -

[ -Batavia: Alan and Pete to work. -]

- - -

[ -Bellevue: Marked as NAD Editorial. -]

- - -

[ -Post-Sophia Antipolis: -Martin indicates there is still work to be done on this issue. -Reopened. -]

- - -

[ -Batavia (2009-05): -]

- -

-Tom proposes we say that, unless specified otherwise, -it is always the caller's responsibility to verify that supplied arguments -meet the called function's requirements. -If further semantics are specified -(e.g., that the function throws under certain conditions), -then it is up to the implementer to check those conditions. -Alan feels strongly that our current use of Requires in this context -is confusing, especially now that requires is a new keyword. -

- -

[ -2009-07 Frankfurt -]

- - -

-Move to Tentatively NAD. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Open. Martin will work on proposed wording. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD Editorial, solved by revision to N3021. -

- - - - -

Rationale:

-

-Solved by revision to N3021. -

- - -

Proposed resolution:

-

-

- - - - - -
-

628. Inconsistent definition of basic_regex constructor

-

Section: 28.8 [re.regex] Status: CD1 - Submitter: Bo Persson Opened: 2007-01-23 Last modified: 2015-04-08

-

View all other issues in [re.regex].

-

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-

Discussion:

-

-Section 28.8 [re.regex] lists a constructor -

- -
-template<class InputIterator>
-basic_regex(InputIterator first, InputIterator last,
-                       flag_type f = regex_constants::ECMAScript);
-
- -

-However, in section 28.8.2 [re.regex.construct], this constructor takes a -pair of ForwardIterator. -

- - -

Proposed resolution:

-

-Change 28.8.2 [re.regex.construct]: -

- -
-template <class ForwardIterator InputIterator>
-  basic_regex(ForwardIterator InputIterator first, ForwardIterator InputIterator last, 
-              flag_type f = regex_constants::ECMAScript);
-
- - - - - - -
-

629. complex<T> insertion and locale dependence

-

Section: 26.4.6 [complex.ops] Status: CD1 - Submitter: Gabriel Dos Reis Opened: 2007-01-28 Last modified: 2015-04-08

-

View all other issues in [complex.ops].

-

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-

Discussion:

-

-is there an issue opened for (0,3) as complex number with -the French local? With the English local, the above parses as an -imaginery complex number. With the French locale it parses as a -real complex number. -

- -

-Further notes/ideas from the lib-reflector, messages 17982-17984: -

- -
-

-Add additional entries in num_punct to cover the complex separator (French would be ';'). -

-

-Insert a space before the comma, which should eliminate the ambiguity. -

-

-Solve the problem for ordered sequences in general, perhaps with a -dedicated facet. Then complex should use that solution. -

-
- -

[ -Bellevue: -]

- - -
-

-After much discussion, we agreed on the following: Add a footnote: -

-

-[In a locale in which comma is being used as a decimal point character, -inserting "showbase" into the output stream forces all outputs to show -an explicit decimal point character; then all inserted complex sequences -will extract unambiguously.] -

-

-And move this to READY status. -

-
- -

[ -Pre-Sophia Antipolis, Howard adds: -]

- - -

-Changed "showbase" to "showpoint" and changed from Ready to Review. -

- -

[ -Post-Sophia Antipolis: -]

- - -
-

-I neglected to pull this issue from the formal motions page after the "showbase" to "showpoint" change. -In Sophia Antipolis this change was reviewed by the LWG and the issue was set to Ready. We subsequently -voted the footnote into the WP with "showbase". -

-

-I'm changing from WP back to Ready to pick up the "showbase" to "showpoint" change. -

-
- - - -

Proposed resolution:

-

-Add a footnote to 26.4.6 [complex.ops] p16: -

- -

-[In a locale in which comma is being used as a decimal point character, -inserting showpoint into the output stream forces all outputs to show -an explicit decimal point character; then all inserted complex sequences -will extract unambiguously.] -

- - - - - -
-

630. arrays of valarray

-

Section: 26.6.2.2 [valarray.cons] Status: C++11 - Submitter: Martin Sebor Opened: 2007-01-28 Last modified: 2015-04-08

-

View all other issues in [valarray.cons].

-

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-

Discussion:

-

- -Section 26.2 [numeric.requirements], p1 suggests that a -valarray specialization on a type T that -satisfies the requirements enumerated in the paragraph is itself a -valid type on which valarray may be instantiated -(Footnote 269 makes this clear). I.e., -valarray<valarray<T> > is valid as long as -T is valid. However, since implementations of -valarray are permitted to initialize storage allocated by -the class by invoking the default ctor of T followed by -the copy assignment operator, such implementations of -valarray wouldn't work with (perhaps user-defined) -specializations of valarray whose assignment operator had -undefined behavior when the size of its argument didn't match the size -of *this. By "wouldn't work" I mean that it would -be impossible to resize such an array of arrays by calling the -resize() member function on it if the function used the -copy assignment operator after constructing all elements using the -default ctor (e.g., by invoking new value_type[N]) to -obtain default-initialized storage) as it's permitted to do. - -

-

- -Stated more generally, the problem is that -valarray<valarray<T> >::resize(size_t) isn't -required or guaranteed to have well-defined semantics for every type -T that satisfies all requirements in -26.2 [numeric.requirements]. - -

-

- -I believe this problem was introduced by the adoption of the -resolution outlined in N0857, -Assignment of valarrays, from 1996. The copy assignment -operator of the original numerical array classes proposed in N0280, -as well as the one proposed in N0308 -(both from 1993), had well-defined semantics for arrays of unequal -size (the latter explicitly only when *this was empty; -assignment of non empty arrays of unequal size was a runtime error). - -

-

- -The justification for the change given in N0857 was the "loss of -performance [deemed] only significant for very simple operations on -small arrays or for architectures with very few registers." - -

-

- -Since tiny arrays on a limited subset of hardware architectures are -likely to be an exceedingly rare case (despite the continued -popularity of x86) I propose to revert the resolution and make the -behavior of all valarray assignment operators -well-defined even for non-conformal arrays (i.e., arrays of unequal -size). I have implemented this change and measured no significant -degradation in performance in the common case (non-empty arrays of -equal size). I have measured a 50% (and in some cases even greater) -speedup in the case of assignments to empty arrays versus calling -resize() first followed by an invocation of the copy -assignment operator. - -

- -

[ -Bellevue: -]

- - -

-If no proposed wording by June meeting, this issue should be closed NAD. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Move resolution 1 to Ready. -

-

-Howard: second resolution has been commented out (made invisible). -Can be brought back on demand. -

-
- - - -

Proposed resolution:

-

- -Change 26.6.2.3 [valarray.assign], p1 as follows: - -

-
-

- - -valarray<T>& operator=(const valarray<T>& x); - - -

-

- --1- Each element of the *this array is assigned the value -of the corresponding element of the argument array. The -resulting behavior is undefined if When the length of -the argument array is not equal to the length of the *this -array. resizes *this to make the two -arrays the same length, as if by calling -resize(x.size()), before performing the assignment. - -

-
-

- -And add a new paragraph just below paragraph 1 with the following -text: - -

-
-

- --2- Postcondition: size() == x.size(). - -

-
-

- -Also add the following paragraph to 26.6.2.3 [valarray.assign], immediately after p4: - -

-
-

- --?- When the length, N of the array referred -to by the argument is not equal to the length of *this, -the operator resizes *this to make the two arrays the -same length, as if by calling resize(N), before -performing the assignment. - -

-
- -

[ -pre-Sophia Antipolis, Martin adds the following compromise wording, but -prefers the original proposed resolution: -]

- - - - - - -

[ -Kona (2007): Gaby to propose wording for an alternative resolution in -which you can assign to a valarray of size 0, but not to any other -valarray whose size is unequal to the right hand side of the assignment. -]

- - - - - -
-

634. allocator.address() doesn't work for types overloading operator&

-

Section: 20.7.9.1 [allocator.members] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-02-07 Last modified: 2015-04-08

-

View all other issues in [allocator.members].

-

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-

Duplicate of: 350

-

Discussion:

- -

-20.7.9.1 [allocator.members] says: -

-
-
pointer address(reference x) const;
-
-

--1- Returns: &x. -

-
-
- -

-20.7.9.1 [allocator.members] defines CopyConstructible which currently not -only defines the semantics of copy construction, but also restricts what an overloaded -operator& may do. I believe proposals are in the works (such as concepts -and rvalue reference) to decouple these two requirements. Indeed it is not evident -that we should disallow overloading operator& to return something other -than the address of *this. -

- -

-An example of when you want to overload operator& to return something -other than the object's address is proxy references such as vector<bool> -(or its replacement, currently code-named bit_vector). Taking the address of -such a proxy reference should logically yield a proxy pointer, which when dereferenced, -yields a copy of the original proxy reference again. -

- -

-On the other hand, some code truly needs the address of an object, and not a proxy -(typically for determining the identity of an object compared to a reference object). -boost has long recognized this dilemma and solved it with -boost::addressof. -It appears to me that this would be useful functionality for the default allocator. Adopting -this definition for allocator::address would free the standard of requiring -anything special from types which overload operator&. Issue 580 -is expected to make use of allocator::address mandatory for containers. -

- - - -

Proposed resolution:

-

-Change 20.7.9.1 [allocator.members]: -

- -
-
pointer address(reference x) const;
-
-

--1- Returns: &x. The actual address of object referenced by x, -even in the presence of an overloaded operator&. -

-
- -
const_pointer address(address(const_reference x) const;
-
-

--2- Returns: &x. The actual address of object referenced by x, -even in the presence of an overloaded operator&. -

-
-
- -

[ -post Oxford: This would be rendered NAD Editorial by acceptance of -N2257. -]

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which -was subsequently split out into a separate paper N2436 for the purposes of voting. -The resolution in N2436 addresses this issue. The LWG voted to accelerate this -issue to Ready status to be voted into the WP at Kona. -]

- - - - - - - -
-

635. domain of allocator::address

-

Section: 17.6.3.5 [allocator.requirements] Status: Resolved - Submitter: Howard Hinnant Opened: 2007-02-08 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

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-

Discussion:

-

-The table of allocator requirements in 17.6.3.5 [allocator.requirements] describes -allocator::address as: -

-
-a.address(r)
-a.address(s)
-
-

-where r and s are described as: -

-

-a value of type X::reference obtained by the expression *p. -

- -

-and p is -

- -

-a value of type X::pointer, obtained by calling a1.allocate, -where a1 == a -

- -

-This all implies that to get the address of some value of type T that -value must have been allocated by this allocator or a copy of it. -

- -

-However sometimes container code needs to compare the address of an external value of -type T with an internal value. For example list::remove(const T& t) -may want to compare the address of the external value t with that of a value -stored within the list. Similarly vector or deque insert may -want to make similar comparisons (to check for self-referencing calls). -

- -

-Mandating that allocator::address can only be called for values which the -allocator allocated seems overly restrictive. -

- -

[ -post San Francisco: -]

- - -

-Pablo recommends NAD Editorial, solved by -N2768. -

- -

[ -2009-04-28 Pablo adds: -]

- - -

-Tentatively-ready NAD Editorial as fixed by -N2768. -

- -

[ -2009-07 Frankfurt -]

- - -

-Fixed by N2768. -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2982. -

- - - -

Proposed resolution:

-

-Change 17.6.3.5 [allocator.requirements]: -

- -
-

-r : a value of type X::reference obtained by the expression *p. -

-

-s : a value of type X::const_reference obtained by the -expression *q or by conversion from a value r. -

-
- -

[ -post Oxford: This would be rendered NAD Editorial by acceptance of -N2257. -]

- - -

[ -Kona (2007): This issue is section 8 of N2387. There was some discussion of it but -no resolution to this issue was recorded. Moved to Open. -]

- - - - - - - -
-

638. deque end invalidation during erase

-

Section: 23.3.3.4 [deque.modifiers] Status: CD1 - Submitter: Steve LoBasso Opened: 2007-02-17 Last modified: 2015-04-08

-

View all other issues in [deque.modifiers].

-

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-

Discussion:

-

-The standard states at 23.3.3.4 [deque.modifiers]/4: -

-
-deque erase(...)
-
-

-Effects: ... An erase at either end of the deque invalidates only -the iterators and the references to the erased elements. -

-
-

-This does not state that iterators to end will be invalidated. -It needs to be amended in such a way as to account for end invalidation. -

-

-Something like: -

-

-Any time the last element is erased, iterators to end are invalidated. -

- -

-This would handle situations like: -

-
-erase(begin(), end())
-erase(end() - 1)
-pop_back()
-resize(n, ...) where n < size()
-pop_front() with size() == 1
-
-
- -

[ -Post Kona, Steve LoBasso notes: -]

- - -

-My only issue with the proposed resolution is that it might not be clear -that pop_front() [where size() == 1] can invalidate past-the-end -iterators. -

- - - -

Proposed resolution:

-

-Change 23.3.3.4 [deque.modifiers], p4: -

- -
-
-iterator erase(const_iterator position); 
-iterator erase(const_iterator first, const_iterator last);
-
- -
-

--4- Effects: An erase in the middle of the deque -invalidates all the iterators and references to elements of the -deque and the past-the-end iterator. An erase at -either end of the deque invalidates only the iterators and the -references to the erased elements, except that erasing at the end -also invalidates the past-the-end iterator. -

-
-
- - - -

[ -Kona (2007): Proposed wording added and moved to Review. -]

- - -

[ -Bellevue: -]

- - -

-Note that there is existing code that relies on iterators not being -invalidated, but there are also existing implementations that do -invalidate iterators. Thus, such code is not portable in any case. There -is a pop_front() note, which should possibly be a separate issue. Mike -Spertus to evaluate and, if need be, file an issue. -

- - - - -
-

640. 27.6.2.5.2 does not handle (unsigned) long long

-

Section: 27.7.3.6.2 [ostream.inserters.arithmetic] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-02-17 Last modified: 2015-04-08

-

View all other issues in [ostream.inserters.arithmetic].

-

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-

Discussion:

-

-The arithmetic inserters are described in 27.7.3.6.2 [ostream.inserters.arithmetic]. -Although the section starts with a listing of the inserters including -the new ones: -

- -
-operator<<(long long val );
-operator<<(unsigned long long val );
-
- -

-the text in paragraph 1, which describes the corresponding effects -of the inserters, depending on the actual type of val, does not -handle the types long long and unsigned long long. -

- -

[ -Alisdair: In addition to the (unsigned) long long problem, that whole paragraph -misses any reference to extended integral types supplied by the -implementation - one of the additions by core a couple of working papers -back. -]

- - - - -

Proposed resolution:

-

-In 27.7.3.6.2 [ostream.inserters.arithmetic]/1 change the third sentence -

- -

-When val is of type bool, long, unsigned -long, long long, unsigned long long, double, -long double, or const void*, the formatting conversion -occurs as if it performed the following code fragment: -

- - - - - -
-

643. Impossible "as if" clauses

-

Section: 27.9.1.1 [filebuf], 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-02-20 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-The current standard 14882:2003(E) as well as N2134 have the -following -defects: -

- -

-27.9.1.1 [filebuf]/5 says: -

- -
-

-In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a -facet, referred to as a_codecvt in following sections, obtained "as if" by -

-
-codecvt<charT,char,typename traits::state_type> a_codecvt =
-  use_facet<codecvt<charT,char,typename traits::state_type> >(getloc());
-
-
- -

-use_facet returns a const facet reference and no facet is -copyconstructible, so the codecvt construction should fail to compile. -

- -

-A similar issue arises in 22.4.2.2.2 [facet.num.put.virtuals]/15 for num_punct. -

- - -

Proposed resolution:

-

-In 27.9.1.1 [filebuf]/5 change the "as if" code -

- -
-const codecvt<charT,char,typename traits::state_type>& a_codecvt =
-  use_facet<codecvt<charT,char,typename traits::state_type> >(getloc());
-
- -

-In 22.4.2.2.2 [facet.num.put.virtuals]/15 (This is para 5 in N2134) change -

- -
-

-A local variable punct is initialized via -

-
-const numpunct<charT>& punct = use_facet< numpunct<charT> >(str.getloc() );
-
-
- -

-(Please note also the additional provided trailing semicolon) -

- - - - - - -
-

646. const incorrect match_result members

-

Section: 28.10.5 [re.results.form] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2015-04-08

-

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-

Discussion:

-

-28.10.5 [re.results.form] (root and para 3) in N2134 defines the two function template -members format as non-const functions, although they are declared -as const in 28.10 [re.results]/3. -

- - -

Proposed resolution:

-

-Add the missing const specifier to both format overloads described -in section 28.10.5 [re.results.form]. -

- - - - - -
-

650. regex_token_iterator and const correctness

-

Section: 28.12.2 [re.tokiter] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Both the class definition of regex_token_iterator (28.12.2 [re.tokiter]/6) and the latter member specifications (28.12.2.2 [re.tokiter.comp]/1+2) declare both comparison operators as -non-const functions. Furtheron, both dereference operators are -unexpectedly also declared as non-const in 28.12.2 [re.tokiter]/6 -as well as in (28.12.2.3 [re.tokiter.deref]/1+2). -

- - -

Proposed resolution:

-

-1) In (28.12.2 [re.tokiter]/6) change the current declarations -

- -
-bool operator==(const regex_token_iterator&) const;
-bool operator!=(const regex_token_iterator&) const;
-const value_type& operator*() const;
-const value_type* operator->() const;
-
- -

-2) In 28.12.2.2 [re.tokiter.comp] change the following declarations -

- -
-bool operator==(const regex_token_iterator& right) const;
-bool operator!=(const regex_token_iterator& right) const;
-
- -

-3) In 28.12.2.3 [re.tokiter.deref] change the following declarations -

- -
-const value_type& operator*() const;
-const value_type* operator->() const;
-
- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which -is to adopt the proposed wording in this issue). -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

651. Missing preconditions for regex_token_iterator c'tors

-

Section: 28.12.2.1 [re.tokiter.cnstr] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The text provided in 28.12.2.1 [re.tokiter.cnstr]/2+3 describes -the effects of the three non-default constructors of class -template regex_token_iterator but is does not clarify which values -are legal values for submatch/submatches. This becomes -an issue, if one takes 28.12.2 [re.tokiter]/9 into account, which explains -the notion of a "current match" by saying: -

- -

-The current match is (*position).prefix() if subs[N] -== -1, or (*position)[subs[N]] for any other value of -subs[N]. -

- -

-It's not clear to me, whether other negative values except -1 -are legal arguments or not - it seems they are not. -

- - -

Proposed resolution:

-

-Add the following precondition paragraph just before the current -28.12.2.1 [re.tokiter.cnstr]/2: -

- -

-Requires: Each of the initialization values of subs must be >= -1. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which -is to adopt the proposed wording in this issue). -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

652. regex_iterator and const correctness

-

Section: 28.12.1 [re.regiter] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2015-04-08

-

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-

Discussion:

-

-Both the class definition of regex_iterator (28.12.1 [re.regiter]/1) and the latter member specification (28.12.1.2 [re.regiter.comp]/1+2) declare both comparison operators as -non-const functions. Furtheron, both dereference operators are -unexpectedly also declared as non-const in 28.12.1 [re.regiter]/1 -as well as in (28.12.1.3 [re.regiter.deref]/1+2). -

- - -

Proposed resolution:

-

-1) In (28.12.1 [re.regiter]/1) change the current declarations -

- -
-bool operator==(const regex_iterator&) const;
-bool operator!=(const regex_iterator&) const;
-const value_type& operator*() const;
-const value_type* operator->() const;
-
- -

-2) In 28.12.1.3 [re.regiter.deref] change the following declarations -

- -
-const value_type& operator*() const;
-const value_type* operator->() const;
-
- -

-3) In 28.12.1.2 [re.regiter.comp] change the following declarations -

- -
-bool operator==(const regex_iterator& right) const;
-bool operator!=(const regex_iterator& right) const;
-
- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which -is to adopt the proposed wording in this issue). -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

654. Missing IO roundtrip for random number engines

-

Section: 26.5.1.4 [rand.req.eng] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2015-04-08

-

View all other issues in [rand.req.eng].

-

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-

Discussion:

-

-Table 98 and para 5 in 26.5.1.4 [rand.req.eng] specify -the IO insertion and extraction semantic of random -number engines. It can be shown, v.i., that the specification -of the extractor cannot guarantee to fulfill the requirement -from para 5: -

- -

-If a textual representation written via os << x was -subsequently read via is >> v, then x == v provided that -there have been no intervening invocations of x or of v. -

- -

-The problem is, that the extraction process described in -table 98 misses to specify that it will initially set the -if.fmtflags to ios_base::dec, see table 104: -

- -

-dec: converts integer input or generates integer output -in decimal base -

- -

-Proof: The following small program demonstrates the violation -of requirements (exception safety not fulfilled): -

- -
-#include <cassert>
-#include <ostream>
-#include <iostream>
-#include <iomanip>
-#include <sstream>
-
-class RanNumEngine {
-  int state;
-public:
-  RanNumEngine() : state(42) {}
-
-  bool operator==(RanNumEngine other) const {
-      return state == other.state;
-  }
-
-  template <typename Ch, typename Tr>
-  friend std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& os, RanNumEngine engine) {
-    Ch old = os.fill(os.widen(' ')); // Sets space character
-    std::ios_base::fmtflags f = os.flags();
-    os << std::dec << std::left << engine.state; // Adds ios_base::dec|ios_base::left
-    os.fill(old); // Undo
-    os.flags(f);
-    return os;
-  }
-
-  template <typename Ch, typename Tr>
-  friend std::basic_istream<Ch, Tr>& operator>>(std::basic_istream<Ch, Tr>& is, RanNumEngine& engine) {
-       // Uncomment only for the fix.
-
-    //std::ios_base::fmtflags f = is.flags();
-    //is >> std::dec;
-    is >> engine.state;
-    //is.flags(f);
-    return is;
-  }
-};
-
-int main() {
-    std::stringstream s;
-    s << std::setfill('#'); // No problem
-        s << std::oct; // Yikes!
-        // Here starts para 5 requirements:
-    RanNumEngine x;
-    s << x;
-    RanNumEngine v;
-    s >> v;
-    assert(x == v); // Fails: 42 == 34
-}
-
- -

-A second, minor issue seems to be, that the insertion -description from table 98 unnecessarily requires the -addition of ios_base::fixed (which only influences floating-point -numbers). Its not entirely clear to me whether the proposed -standard does require that the state of random number engines -is stored in integral types or not, but I have the impression -that this is the indent, see e.g. p. 3 -

- -

-The specification of each random number engine defines the -size of its state in multiples of the size of its result_type. -

- -

-If other types than integrals are supported, then I wonder why -no requirements are specified for the precision of the stream. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

655. Signature of generate_canonical not useful

-

Section: 26.5.7.2 [rand.util.canonical] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2015-04-08

-

View all other issues in [rand.util.canonical].

-

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-

Discussion:

-

-In 26.5.2 [rand.synopsis] we have the declaration -

- -
-template<class RealType, class UniformRandomNumberGenerator,
-  size_t bits>
-result_type generate_canonical(UniformRandomNumberGenerator& g);
-
- -

-Besides the "result_type" issue (already recognized by Bo Persson -at Sun, 11 Feb 2007 05:26:47 GMT in this group) it's clear, that -the template parameter order is not reasonably choosen: Obviously -one always needs to specify all three parameters, although usually -only two are required, namely the result type RealType and the -wanted bits, because UniformRandomNumberGenerator can usually -be deduced. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

658. Two unspecified function comparators in [function.objects]

-

Section: 20.9 [function.objects] Status: Resolved - Submitter: Daniel Krügler Opened: 2007-03-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The header <functional> synopsis in 20.9 [function.objects] -contains the following two free comparison operator templates -for the function class template -

- -
-template<class Function1, class Function2>
-void operator==(const function<Function1>&, const function<Function2>&);
-template<class Function1, class Function2>
-void operator!=(const function<Function1>&, const function<Function2>&);
-
- -

-which are nowhere described. I assume that they are relicts before the -corresponding two private and undefined member templates in the function -template (see 20.9.12.2 [func.wrap.func] and [func.wrap.func.undef]) have been introduced. The original free -function templates should be removed, because using an undefined entity -would lead to an ODR violation of the user. -

- - -

Proposed resolution:

-

-Remove the above mentioned two function templates from -the header <functional> synopsis (20.9 [function.objects]) -

- -
-template<class Function1, class Function2>
-void operator==(const function<Function1>&, const function<Function2>&);
-template<class Function1, class Function2>
-void operator!=(const function<Function1>&, const function<Function2>&);
-
- - - -

Rationale:

-Fixed by -N2292 -Standard Library Applications for Deleted Functions. -

- - - - -
-

659. istreambuf_iterator should have an operator->()

-

Section: 24.6.3 [istreambuf.iterator] Status: C++11 - Submitter: Niels Dekker Opened: 2007-03-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Greg Herlihy has clearly demonstrated that a user defined input -iterator should have an operator->(), even if its -value type is a built-in type (comp.std.c++, "Re: Should any iterator -have an operator->() in C++0x?", March 2007). And as Howard -Hinnant remarked in the same thread that the input iterator -istreambuf_iterator doesn't have one, this must be a -defect! -

-

-Based on Greg's example, the following code demonstrates the issue: -

- #include <iostream> 
- #include <fstream>
- #include <streambuf> 
-
- typedef char C;
- int main ()
- {
-   std::ifstream s("filename", std::ios::in);
-   std::istreambuf_iterator<char> i(s);
-
-   (*i).~C();  // This is well-formed...
-   i->~C();  // ... so this should be supported!
- }
-
-

-Of course, operator-> is also needed when the value_type of -istreambuf_iterator is a class. -

-

-The operator-> could be implemented in various ways. For instance, -by storing the current value inside the iterator, and returning its -address. Or by returning a proxy, like operator_arrow_proxy, from -http://www.boost.org/boost/iterator/iterator_facade.hpp -

-

-I hope that the resolution of this issue will contribute to getting a -clear and consistent definition of iterator concepts. -

- -

[ -Kona (2007): The proposed resolution is inconsistent because the return -type of istreambuf_iterator::operator->() is specified to be pointer, -but the proposed text also states that "operator-> may return a proxy." -]

- - -

[ -Niels Dekker (mailed to Howard Hinnant): -]

- -
-

-The proposed resolution does -not seem inconsistent to me. istreambuf_iterator::operator->() should -have istreambuf_iterator::pointer as return type, and this return type -may in fact be a proxy. -

-

-AFAIK, the resolution of 445 ("iterator_traits::reference -unspecified for some iterator categories") implies that for any iterator -class Iter, the return type of operator->() is Iter::pointer, by -definition. I don't think Iter::pointer needs to be a raw pointer. -

-

-Still I wouldn't mind if the text "operator-> may return a proxy" would -be removed from the resolution. I think it's up to the library -implementation, how to implement istreambuf_iterator::operator->(). As -longs as it behaves as expected: i->m should have the same effect as -(*i).m. Even for an explicit destructor call, i->~C(). The main issue -is just: istreambuf_iterator should have an operator->()! -

-
- -

[ -2009-04-30 Alisdair adds: -]

- - -

-Note that operator-> is now a requirement in the InputIterator concept, so -this issue cannot be ignored or existing valid programs will break when -compiled with an 0x library. -

- -

[ -2009-05-29 Alisdair adds: -]

- - -
-

-I agree with the observation that in principle the type 'pointer' may be a -proxy, and the words highlighting this are redundant. -

-

-However, in the current draught pointer is required to be exactly 'charT *' -by the derivation from std::iterator. At a minimum, the 4th parameter of -this base class template should become unspecified. That permits the -introduction of a proxy as a nested class in some further undocumented (not -even exposition-only) base. -

-

-It also permits the istream_iterator approach where the cached value is -stored in the iterator itself, and the iterator serves as its own proxy for -post-increment operator++ - removing the need for the existing -exposition-only nested class proxy. -

-

-Note that the current proxy class also has exactly the right properties to -serve as the pointer proxy too. This is likely to be a common case where an -InputIterator does not hold internal state but delegates to another class. -

-

-Proposed Resolution: -

-

-In addition to the current proposal: -

-

-24.6.3 [istreambuf.iterator] -

-
-template<class charT, class traits = char_traits<charT> >
-class istreambuf_iterator
-  : public iterator<input_iterator_tag, charT,
-                    typename traits::off_type, charT* unspecified, charT> {
-
-
- -

[ -2009-07 Frankfurt -]

- - -
-

-Move the additional part into the proposed resolution, and wrap the -descriptive text in a Note. -

-

[Howard: done.]

- -

-Move to Ready. -

-
- - - -

Proposed resolution:

-

-Add to the synopsis in 24.6.3 [istreambuf.iterator]: -

- -
-charT operator*() const;
-pointer operator->() const;
-istreambuf_iterator<charT,traits>& operator++();
-
- -

-24.6.3 [istreambuf.iterator] -

- -
-template<class charT, class traits = char_traits<charT> >
-class istreambuf_iterator
-  : public iterator<input_iterator_tag, charT,
-                    typename traits::off_type, charT* unspecified, charT> {
-
- -

-Change 24.6.3 [istreambuf.iterator], p1: -

- -

-The class template istreambuf_iterator reads successive -characters from the streambuf for which it was constructed. -operator* provides access to the current input character, if -any. [Note: operator-> may return a proxy. — -end note] Each time -operator++ is evaluated, the iterator advances to the next -input character. If the end of stream is reached -(streambuf_type::sgetc() returns traits::eof()), the -iterator becomes equal to the end of stream iterator value. The default -constructor istreambuf_iterator() and the constructor -istreambuf_iterator(0) both construct an end of stream iterator -object suitable for use as an end-of-range. -

- - - - - - - -
-

660. Missing Bitwise Operations

-

Section: 20.9 [function.objects] Status: CD1 - Submitter: Beman Dawes Opened: 2007-04-02 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Section 20.9 [function.objects] provides function objects for some unary and binary -operations, but others are missing. In a LWG reflector discussion, beginning -with c++std-lib-18078, pros and cons of adding some of the missing operations -were discussed. Bjarne Stroustrup commented "Why standardize what isn't used? -Yes, I see the chicken and egg problems here, but it would be nice to see a -couple of genuine uses before making additions."

-

A number of libraries, including Rogue Wave, GNU, Adobe ASL, and Boost, have -already added these functions, either publicly or for internal use. For example, -Doug Gregor commented: "Boost will also add ... (|, &, ^) in 1.35.0, because we -need those function objects to represent various parallel -collective operations (reductions, prefix reductions, etc.) in the new Message -Passing Interface (MPI) library."

-

Because the bitwise operators have the strongest use cases, the proposed -resolution is limited to them.

- - -

Proposed resolution:

-

To 20.9 [function.objects], Function objects, paragraph 2, add to the header -<functional> synopsis:

-
- 
template <class T> struct bit_and;
-template <class T> struct bit_or;
-template <class T> struct bit_xor;
-
-

At a location in clause 20 to be determined by the Project Editor, add:

-
-

The library provides basic function object classes for all of the bitwise - operators in the language ([expr.bit.and], [expr.or], [exp.xor]).

- 
template <class T> struct bit_and : binary_function<T,T,T> {
-  T operator()(const T& x , const T& y ) const;
-};
-
-

operator() returns x & y .

-
- 
template <class T> struct bit_or : binary_function<T,T,T> {
-  T operator()(const T& x , const T& y ) const;
-};
-
-

operator() returns x | y .

-
- 
template <class T> struct bit_xor : binary_function<T,T,T> {
-  T operator()(const T& x , const T& y ) const;
-};
-
-

operator() returns x ^ y .

-
-
- - - - - -
-

661. New 27.6.1.2.2 changes make special extractions useless

-

Section: 27.7.2.2.2 [istream.formatted.arithmetic] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-04-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-To the more drastic changes of 27.7.2.2.2 [istream.formatted.arithmetic] in the current draft N2134 belong -the explicit description of the extraction of the types short and int in -terms of as-if code fragments. -

- -
    -
  1. -The corresponding as-if extractions in paragraph 2 and 3 will never -result in a change of the operator>> argument val, because the -contents of the local variable lval is in no case written into val. -Furtheron both fragments need a currently missing parentheses in the -beginning of the if-statement to be valid C++. -
    2. -
  2. -I would like to ask whether the omission of a similar explicit -extraction of unsigned short and unsigned int in terms of long - -compared to their corresponding new insertions, as described in 27.7.3.6.2 [ostream.inserters.arithmetic], is a deliberate decision or an -oversight. -
    3. -
- - -

Proposed resolution:

-
    -
  1. -

    -In 27.7.2.2.2 [istream.formatted.arithmetic]/2 change the current as-if code fragment -

    -
    -typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
-iostate err = 0;
-long lval;
-use_facet<numget>(loc).get(*this, 0, *this, err, lval );
-if (err == 0) {
-  && if (lval < numeric_limits<short>::min() || numeric_limits<short>::max() < lval))
-      err = ios_base::failbit;
-  else
-    val = static_cast<short>(lval);
-}
-setstate(err);
-
    - -

    -Similarily in 27.7.2.2.2 [istream.formatted.arithmetic]/3 change the current as-if fragment -

    - -
    -typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
-iostate err = 0;
-long lval;
-use_facet<numget>(loc).get(*this, 0, *this, err, lval );
-if (err == 0) {
-  && if (lval < numeric_limits<int>::min() || numeric_limits<int>::max() < lval))
-      err = ios_base::failbit;
-  else
-    val = static_cast<int>(lval);
-}
-setstate(err);
-
    -
    2. -
  2. ---- -
    3. -
- - -

[ -Kona (2007): Note to the editor: the name lval in the call to use_facet -is incorrectly italicized in the code fragments corresponding to -operator>>(short &) and operator >>(int &). Also, val -- which appears -twice on the line with the static_cast in the proposed resolution -- -should be italicized. Also, in response to part two of the issue: this -is deliberate. -]

- - - - - -
-

664. do_unshift for codecvt<char, char, mbstate_t>

-

Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: CD1 - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.virtuals].

-

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-

Discussion:

-

-22.4.1.4.2 [locale.codecvt.virtuals], para 7 says (regarding do_unshift): -

- -

-Effects: Places characters starting at to that should be appended to -terminate a sequence when the current stateT is given by -state.237) Stores no more than (to_limit - -to) destination elements, and leaves the to_next -pointer pointing one beyond the last element successfully stored. -codecvt<char, char, mbstate_t> stores no characters. -

- -

-The following objection has been raised: -

- -

-Since the C++ Standard permits a nontrivial conversion for the required -instantiations of codecvt, it is overly restrictive to say that -do_unshift must store no characters and return noconv. -

- -

-[Plum ref _222152Y50] -

- - -

Proposed resolution:

-

-Change 22.4.1.4.2 [locale.codecvt.virtuals], p7: -

- -
-

-Effects: Places characters starting at to that should be -appended to terminate a sequence when the current stateT is -given by state.237) Stores no more than (to_limit -to) -destination elements, and leaves the to_next pointer pointing one -beyond the last element successfully stored. codecvt<char, char, -mbstate_t> stores no characters. -

-
- - - - - -
-

665. do_unshift return value

-

Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: CD1 - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

View all other issues in [locale.codecvt.virtuals].

-

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-

Discussion:

-

-22.4.1.4.2 [locale.codecvt.virtuals], para 8 says: -

- -

-codecvt<char,char,mbstate_t>, returns noconv. -

- -

-The following objection has been raised: -

- -

-Despite what the C++ Standard -says, unshift can't always return noconv for the default facets, since -they can be nontrivial. At least one implementation does whatever the -C functions do. -

- -

-[Plum ref _222152Y62] -

- - -

Proposed resolution:

-

-Change 22.4.1.4.2 [locale.codecvt.virtuals], p8: -

- -
-

Returns: An enumeration value, as summarized in Table 76:

-

...

-

-codecvt<char,char,mbstate_t>, returns noconv. -

-
- - - - - - -
-

666. moneypunct::do_curr_symbol()

-

Section: 22.4.6.3.2 [locale.moneypunct.virtuals] Status: CD1 - Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-22.4.6.3.2 [locale.moneypunct.virtuals], para 4 footnote 257 says -

- -

-257) For international -specializations (second template parameter true) this is always four -characters long, usually three letters and a space. -

- -

-The following objection has been raised: -

- -

-The international currency -symbol is whatever the underlying locale says it is, not necessarily -four characters long. -

- -

-[Plum ref _222632Y41] -

- - -

Proposed resolution:

-

-Change footnote 253 in 22.4.6.3.2 [locale.moneypunct.virtuals]: -

- -
-

-253) For international specializations (second template -parameter true) this is always typically -four characters long, usually three letters and a space. -

-
- - - - - -
-

671. precision of hexfloat

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: C++11 - Submitter: John Salmon Opened: 2007-04-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I am trying to understand how TR1 supports hex float (%a) output. -

-

-As far as I can tell, it does so via the following: -

-

-8.15 Additions to header <locale> [tr.c99.locale] -

-

-In subclause 22.4.2.2.2 [facet.num.put.virtuals], Table 58 Floating-point conversions, after -the line:
-floatfield == ios_base::scientific %E -

-

-add the two lines: -

-
-floatfield == ios_base::fixed | ios_base::scientific && !uppercase %a
-floatfield == ios_base::fixed | ios_base::scientific %A 2
-
-

-[Note: The additional requirements on print and scan functions, later -in this clause, ensure that the print functions generate hexadecimal -floating-point fields with a %a or %A conversion specifier, and that -the scan functions match hexadecimal floating-point fields with a %g -conversion specifier. end note] -

-

-Following the thread, in 22.4.2.2.2 [facet.num.put.virtuals], we find: -

-

-For conversion from a floating-point type, if (flags & fixed) != 0 or -if str.precision() > 0, then str.precision() is specified in the -conversion specification. -

-

-This would seem to imply that when floatfield == fixed|scientific, the -precision of the conversion specifier is to be taken from -str.precision(). Is this really what's intended? I sincerely hope -that I'm either missing something or this is an oversight. Please -tell me that the committee did not intend to mandate that hex floats -(and doubles) should by default be printed as if by %.6a. -

- -

[ -Howard: I think the fundamental issue we overlooked was that with %f, -%e, %g, the default precision was always 6. With %a the default -precision is not 6, it is infinity. So for the first time, we need to -distinguish between the default value of precision, and the precision -value 6. -]

- - -

[ -2009-07 Frankfurt -]

- - -
-

-Leave this open for Robert and Daniel to work on. -

-

-Straw poll: Disposition? -

-
    -
  • Default is %.6a (i.e. NAD): 2
    • -
  • Always %a (no precision): 6
    • -
  • precision(-1) == %a: 3
    • -
-

-Daniel and Robert have direction to write up wording for the "always %a" solution. -

- -

[ -2009-07-15 Robert provided wording. -]

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Change 22.4.2.2.2 [facet.num.put.virtuals], Stage 1, under p5 (near the end -of Stage 1): -

- -

-For conversion from a floating-point type, str.precision() is specified -as precision in the conversion specification -if floatfield != (ios_base::fixed | ios_base::scientific), else no -precision is specified. -

- - - -

[ -Kona (2007): Robert volunteers to propose wording. -]

- - - - - -
-

672. Swappable requirements need updating

-

Section: 17.6.3.1 [utility.arg.requirements] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-05-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current Swappable is: -

- -
- - - - - -
Table 37: Swappable requirements [swappable]
expressionreturn typepost-condition
swap(s,t)voidt has the value originally held by u, and u has the value originally -held by t
-

-The Swappable requirement is met by satisfying one or more of the following conditions: -

-
    -
  • -T is Swappable if T satisfies the CopyConstructible requirements (Table 34) -and the CopyAssignable requirements (Table 36); -
    • -
  • -T is Swappable if a namespace scope function named swap exists in the same -namespace as the definition of T, such that the expression swap(t,u) is valid -and has the semantics described in this table. -
    • -
-
-
- -

-With the passage of rvalue reference into the language, Swappable needs to be updated to -require only MoveConstructible and MoveAssignable. This is a minimum. -

- -

-Additionally we may want to support proxy references such that the following code is acceptable: -

- -
-namespace Mine {
-
-template <class T>
-struct proxy {...};
-
-template <class T>
-struct proxied_iterator
-{
-   typedef T value_type;
-   typedef proxy<T> reference;
-   reference operator*() const;
-   ...
-};
-
-struct A
-{
-   // heavy type, has an optimized swap, maybe isn't even copyable or movable, just swappable
-   void swap(A&);
-   ...
-};
-
-void swap(A&, A&);
-void swap(proxy<A>, A&);
-void swap(A&, proxy<A>);
-void swap(proxy<A>, proxy<A>);
-
-}  // Mine
-
-...
-
-Mine::proxied_iterator<Mine::A> i(...)
-Mine::A a;
-swap(*i1, a);
-
- -

-I.e. here is a call to swap which the user enables swapping between a proxy to a class and the class -itself. We do not need to anything in terms of implementation except not block their way with overly -constrained concepts. That is, the Swappable concept should be expanded to allow swapping -between two different types for the case that one is binding to a user-defined swap. -

- - - -

Proposed resolution:

- -

-Change 17.6.3.1 [utility.arg.requirements]: -

- -
- -

--1- The template definitions in the C++ Standard Library refer to various -named requirements whose details are set out in tables 31-38. In these -tables, T is a type to be supplied by a C++ program -instantiating a template; a, b, and c are -values of type const T; s and t are modifiable -lvalues of type T; u is a value of type (possibly -const) T; and rv is a non-const -rvalue of type T. -

- - - - - - - -
Table 37: Swappable requirements [swappable]
expressionreturn typepost-condition
swap(s,t)voidt has the value originally -held by u, and -u has the value originally held -by t
-

-The Swappable requirement is met by satisfying one or more of the following conditions: -

-
    -
  • -T is Swappable if T satisfies the -CopyConstructible MoveConstructible -requirements (Table 34 33) and the CopyAssignable MoveAssignable -requirements (Table 36 35); -
    • -
  • -T is Swappable if a namespace scope function named -swap exists in the same namespace as the definition of -T, such that the expression -swap(t,u) is valid and has the -semantics described in this table. -
    • -
-
-
- - - -

[ -Kona (2007): We like the change to the Swappable requirements to use -move semantics. The issue relating to the support of proxies is -separable from the one relating to move semantics, and it's bigger than -just swap. We'd like to address only the move semantics changes under -this issue, and open a separated issue (742) to handle proxies. Also, there -may be a third issue, in that the current definition of Swappable does -not permit rvalues to be operands to a swap operation, and Howard's -proposed resolution would allow the right-most operand to be an rvalue, -but it would not allow the left-most operand to be an rvalue (some swap -functions in the library have been overloaded to permit left operands to -swap to be rvalues). -]

- - - - - -
-

673. unique_ptr update

-

Section: 20.8.1 [unique.ptr] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-05-04 Last modified: 2015-04-08

-

View all other issues in [unique.ptr].

-

View all issues with CD1 status.

-

Discussion:

-

-Since the publication of -N1856 -there have been a few small but significant advances which should be included into -unique_ptr. There exists a -example implementation -for all of these changes. -

- -
    - -
  • -

    -Even though unique_ptr<void> is not a valid use case (unlike for shared_ptr<void>), -unexpected cases to crop up which require the instantiation of the interface of unique_ptr<void> -even if it is never used. For example see 541 for how this accidently happened to auto_ptr. -I believe the most robust way to protect unique_ptr against this -type of failure is to augment the return type of unique_ptr<T>:operator*() with -add_lvalue_reference<T>::type. This means that given an instantiated unique_ptr<void> -the act of dereferencing it will simply return void instead of causing a compile time failure. -This is simpler than creating a unique_ptr<void> specialization which isn't robust in the -face of cv-qualified void types. -

    - -

    -This resolution also supports instantiations such as unique_ptr<void, free_deleter> -which could be very useful to the client. -

    - -
    • - -
  • -

    -Efforts have been made to better support containers and smart pointers in shared -memory contexts. One of the key hurdles in such support is not assuming that a -pointer type is actually a T*. This can easily be accomplished -for unique_ptr by having the deleter define the pointer type: -D::pointer. Furthermore this type can easily be defaulted to -T* should the deleter D choose not to define a pointer -type (example implementation -here). -This change has no run time overhead. It has no interface overhead on -authors of custom delter types. It simply allows (but not requires) -authors of custom deleter types to define a smart pointer for the -storage type of unique_ptr if they find such functionality -useful. std::default_delete is an example of a deleter which -defaults pointer to T* by simply ignoring this issue -and not including a pointer typedef. -

    -
    • - -
  • -

    -When the deleter type is a function pointer then it is unsafe to construct -a unique_ptr without specifying the function pointer in the constructor. -This case is easy to check for with a static_assert assuring that the -deleter is not a pointer type in those constructors which do not accept deleters. -

    - -
    -unique_ptr<A, void(*)(void*)> p(new A);  // error, no function given to delete the pointer!
-
    - -
    • - -
- -

[ -Kona (2007): We don't like the solution given to the first bullet in -light of concepts. The second bullet solves the problem of supporting -fancy pointers for one library component only. The full LWG needs to -decide whether to solve the problem of supporting fancy pointers -piecemeal, or whether a paper addressing the whole library is needed. We -think that the third bullet is correct. -]

- - -

[ -Post Kona: Howard adds example user code related to the first bullet: -]

- - -
-
-void legacy_code(void*, std::size_t);
-
-void foo(std::size_t N)
-{
-    std::unique_ptr<void, void(*)(void*)> ptr(std::malloc(N), std::free);
-    legacy_code(ptr.get(), N);
-}   // unique_ptr used for exception safety purposes
-
-
- -

-I.e. unique_ptr<void> is a useful tool that we don't want -to disable with concepts. The only part of unique_ptr<void> we -want to disable (with concepts or by other means) are the two member functions: -

- -
-T& operator*() const;
-T* operator->() const;
-
- - - -

Proposed resolution:

- -

[ -I am grateful for the generous aid of Peter Dimov and Ion Gaztañaga in helping formulate and review -the proposed resolutions below. -]

- - -
    -
  • - -

    -Change 20.8.1.2 [unique.ptr.single]: -

    - -
    -template <class T, class D = default_delete<T>> class unique_ptr {
-   ...
-   T& typename add_lvalue_reference<T>::type operator*() const;
-   ...
-};
-
    - -

    -Change 20.8.1.2.4 [unique.ptr.single.observers]: -

    - -
    -T& typename add_lvalue_reference<T>::type operator*() const;
-
    - -
    • - -
  • -

    -Change 20.8.1.2 [unique.ptr.single]: -

    - -
    -template <class T, class D = default_delete<T>> class unique_ptr {
-public:
-  typedef implementation (see description below) pointer;
-   ...
-   explicit unique_ptr(T* pointer p);
-   ...
-   unique_ptr(T* pointer p, implementation defined (see description below) d);
-   unique_ptr(T* pointer p, implementation defined (see description below) d);
-   ...
-   T* pointer operator->() const;
-   T* pointer get() const;
-   ...
-   T* pointer release();
-   void reset(T* pointer p = 0 pointer());
-};
-
    - -

    - --3- If the type remove_reference<D>::type::pointer -exists, then unique_ptr<T, D>::pointer is a typedef to -remove_reference<D>::type::pointer. Otherwise -unique_ptr<T, D>::pointer is a typedef to T*. -The type unique_ptr<T, D>::pointer shall be CopyConstructible -and CopyAssignable. - -

    - -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor]: -

    - -
    -unique_ptr(T* pointer p);
-...
-unique_ptr(T* pointer p, implementation defined d); 
-unique_ptr(T* pointer p, implementation defined d); 
-...
-unique_ptr(T* pointer p, const A& d);
-unique_ptr(T* pointer p, A&& d);
-...
-unique_ptr(T* pointer p, A& d); 
-unique_ptr(T* pointer p, A&& d);
-...
-unique_ptr(T* pointer p, const A& d); 
-unique_ptr(T* pointer p, const A&& d);
-...
-
    - -

    --23- Requires: If D is not a reference type, -construction of the deleter D from an rvalue of type E -must shall be well formed and not throw an exception. If D is a -reference type, then E must shall be the same type as D -(diagnostic required). U* unique_ptr<U,E>::pointer -must shall be implicitly convertible to T* -pointer. -

    - -

    --25- Postconditions: get() == value u.get() had before -the construction, modulo any required offset adjustments resulting from -the cast from U* -unique_ptr<U,E>::pointer to T* -pointer. get_deleter() returns a reference to the -internally stored deleter which was constructed from -u.get_deleter(). -

    - -

    -Change 20.8.1.2.3 [unique.ptr.single.asgn]: -

    - -
    -

    --8- Requires: Assignment of the deleter D from an rvalue -D must shall not throw an exception. U* -unique_ptr<U,E>::pointer must shall be implicitly -convertible to T* pointer. -

    -
    - -

    -Change 20.8.1.2.4 [unique.ptr.single.observers]: -

    - -
    -
    T* pointer operator->() const;
    -

    ...

    -
    T* pointer get() const;
    -
    - -

    -Change 20.8.1.2.5 [unique.ptr.single.modifiers]: -

    - -
    -
    T* pointer release();
    -

    ...

    -
    void reset(T* pointer p = 0 pointer());
    -
    - -

    -Change 20.8.1.3 [unique.ptr.runtime]: -

    - -
    -template <class T, class D> class unique_ptr<T[], D> {
-public:
-  typedef implementation pointer;
-   ...
-   explicit unique_ptr(T* pointer p);
-   ...
-   unique_ptr(T* pointer p, implementation defined d);
-   unique_ptr(T* pointer p, implementation defined d);
-   ...
-   T* pointer get() const;
-   ...
-   T* pointer release();
-   void reset(T* pointer p = 0 pointer());
-};
-
    - -

    -Change 20.8.1.3.1 [unique.ptr.runtime.ctor]: -

    - -
    -
    -unique_ptr(T* pointer p);
-unique_ptr(T* pointer p, implementation defined d);
-unique_ptr(T* pointer p, implementation defined d);
-
    - -

    -These constructors behave the same as in the primary template except -that they do not accept pointer types which are convertible to -T* pointer. [Note: One -implementation technique is to create private templated overloads of -these members. -- end note] -

    -
    - -

    -Change 20.8.1.3.4 [unique.ptr.runtime.modifiers]: -

    - -
    -
    -void reset(T* pointer p = 0 pointer());
-
    - -

    --1- Requires: Does not accept pointer types which are convertible -to T* pointer (diagnostic -required). [Note: One implementation technique is to create a private -templated overload. -- end note] -

    -
    - -
    • - -
  • - -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor]: -

    - -
    -
    unique_ptr();
    -
    -

    -Requires: D must shall be default constructible, and that -construction must shall not throw an exception. D must shall not be a -reference type or pointer type (diagnostic required). -

    -
    -
    unique_ptr(T* pointer p);
    -
    -

    -Requires: The expression D()(p) must shall be well formed. -The default constructor of D must shall not throw an exception. -D must shall not be a reference type or pointer type (diagnostic -required). -

    -
    -
    - -
    • - -
- - - - - - -
-

674. shared_ptr interface changes for consistency with N1856

-

Section: 20.8.2.2 [util.smartptr.shared] Status: CD1 - Submitter: Peter Dimov Opened: 2007-05-05 Last modified: 2015-04-08

-

View other active issues in [util.smartptr.shared].

-

View all other issues in [util.smartptr.shared].

-

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-

Discussion:

-

-N1856 does not propose -any changes to shared_ptr. It needs to be updated to use a rvalue reference where appropriate -and to interoperate with unique_ptr as it does with auto_ptr. -

- - -

Proposed resolution:

- -

-Change 20.8.2.2 [util.smartptr.shared] as follows: -

- -
-
template<class Y> explicit shared_ptr(auto_ptr<Y>&&& r);
-template<class Y, class D> explicit shared_ptr(const unique_ptr<Y,D>& r) = delete;
-template<class Y, class D> explicit shared_ptr(unique_ptr<Y,D>&& r);
-...
-template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);
-template<class Y, class D> shared_ptr& operator=(const unique_ptr<Y,D>& r) = delete;
-template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);
-
- -

-Change 20.8.2.2.1 [util.smartptr.shared.const] as follows: -

- -
-
template<class Y> shared_ptr(auto_ptr<Y>&&& r);
-
- -

-Add to 20.8.2.2.1 [util.smartptr.shared.const]: -

- -
-
template<class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
-
- -

-Effects: Equivalent to shared_ptr( r.release(), r.get_deleter() ) when D is - not a reference type, shared_ptr( r.release(), ref( r.get_deleter() ) ) - otherwise. -

- -

-Exception safety: If an exception is thrown, the constructor has no effect. -

-
- -
- -

-Change 20.8.2.2.3 [util.smartptr.shared.assign] as follows: -

- -
-
template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);
-
- -

-Add to 20.8.2.2.3 [util.smartptr.shared.assign]: -

- -
-
template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);
- -
-

--4- Effects: Equivalent to shared_ptr(std::move(r)).swap(*this). -

-

--5- Returns: *this. -

-
- -
- - - -

[ -Kona (2007): We may need to open an issue (743) to deal with the question of -whether shared_ptr needs an rvalue swap. -]

- - - - - -
-

675. Move assignment of containers

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-05-05 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

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-

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-

Discussion:

-

-James Hopkin pointed out to me that if vector<T> move assignment is O(1) -(just a swap) then containers such as vector<shared_ptr<ostream>> might have -the wrong semantics under move assignment when the source is not truly an rvalue, but a -moved-from lvalue (destructors could run late). -

- -
-vector<shared_ptr<ostream>> v1;
-vector<shared_ptr<ostream>> v2;
-...
-v1 = v2;               // #1
-v1 = std::move(v2);    // #2
-
- -

-Move semantics means not caring what happens to the source (v2 in this example). -It doesn't mean not caring what happens to the target (v1). In the above example -both assignments should have the same effect on v1. Any non-shared ostream's -v1 owns before the assignment should be closed, whether v1 is undergoing -copy assignment or move assignment. -

- -

-This implies that the semantics of move assignment of a generic container should be -clear, swap instead of just swap. An alternative which could achieve the same -effect would be to move assign each element. In either case, the complexity of move -assignment needs to be relaxed to O(v1.size()). -

- -

-The performance hit of this change is not nearly as drastic as it sounds. -In practice, the target of a move assignment has always just been move constructed -or move assigned from. Therefore under clear, swap semantics (in -this common use case) we are still achieving O(1) complexity. -

- - - -

Proposed resolution:

-

-Change 23.2 [container.requirements]: -

- -
- - - - - - - - - - - - -
Table 89: Container requirements
expressionreturn typeoperational semanticsassertion/note pre/post-conditioncomplexity
a = rv;X&All existing elements of a are either move assigned or destructeda shall be equal to the -value that rv had -before this construction -(Note C) linear
- -

-Notes: the algorithms swap(), equal() and -lexicographical_compare() are defined in clause 25. Those -entries marked "(Note A)" should have constant complexity. Those entries -marked "(Note B)" have constant complexity unless -allocator_propagate_never<X::allocator_type>::value is -true, in which case they have linear complexity. -Those entries -marked "(Note C)" have constant complexity if a.get_allocator() == -rv.get_allocator() or if either -allocator_propagate_on_move_assignment<X::allocator_type>::value -is true or -allocator_propagate_on_copy_assignment<X::allocator_type>::value -is true and linear complexity otherwise. -

-
- - - -

[ -post Bellevue Howard adds: -]

- - -
-

-This issue was voted to WP in Bellevue, but accidently got stepped on by -N2525 -which was voted to WP simulataneously. Moving back to Open for the purpose of getting -the wording right. The intent of this issue and N2525 are not in conflict. -

-
- -

[ -post Sophia Antipolis Howard updated proposed wording: -]

- - - - - -
-

676. Moving the unordered containers

-

Section: 23.5 [unord] Status: C++11 - Submitter: Howard Hinnant Opened: 2007-05-05 Last modified: 2015-04-08

-

View all other issues in [unord].

-

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-

Discussion:

-

-Move semantics are missing from the unordered containers. The proposed -resolution below adds move-support consistent with -N1858 -and the current working draft. -

- -

-The current proposed resolution simply lists the requirements for each function. -These might better be hoisted into the requirements table for unordered associative containers. -Futhermore a mild reorganization of the container requirements could well be in order. -This defect report is purposefully ignoring these larger issues and just focusing -on getting the unordered containers "moved". -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10-17 Removed rvalue-swaps from wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Review. Alisdair will review proposed wording. -

- -

[ -2009-10-29 Daniel updates wording. -]

- - -

[ -2010-01-26 Alisdair updates wording. -]

- - -

[ -2010-02-10 Howard updates wording to reference the unordered container -requirements table (modified by 704) as much as possible. -]

- - -

[ -Voted to WP in Bellevue. -]

- - -

[ -post Bellevue, Pete notes: -]

- - -
-

-Please remind people who are reviewing issues to check that the text -modifications match the current draft. Issue 676, for example, adds two -overloads for unordered_map::insert taking a hint. One takes a -const_iterator and returns a const_iterator, and the other takes an -iterator and returns an iterator. This was correct at the time the issue -was written, but was changed in Toronto so there is only one hint -overload, taking a const_iterator and returning an iterator. -

-

-This issue is not ready. In addition to the relatively minor signature -problem I mentioned earlier, it puts requirements in the wrong places. -Instead of duplicating requirements throughout the template -specifications, it should put them in the front matter that talks about -requirements for unordered containers in general. This presentation -problem is editorial, but I'm not willing to do the extensive rewrite -that it requires. Please put it back into Open status. -

-
- -

[ -2010-02-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-24 Pete moved to Open: -]

- - -

-The descriptions of the semantics of the added insert functions belong -in the requirements table. That's where the rest of the insert -functions are. -

- -

[ -2010 Pittsburgh: -]

- - -

-Move issue 676 to Ready for Pittsburgh. Nico to send Howard an issue for -the broader problem. -

- - - -

Rationale:

-

[ -San Francisco: -]

- - -

-Solved by -N2776. -

- -

[ -Rationale is obsolete. -]

- - - - - -

Proposed resolution:

- -

unordered_map

- -

-Change 23.5.4 [unord.map]: -

- -
-class unordered_map
-{
-    ...
-    unordered_map(const unordered_map&);
-    unordered_map(unordered_map&&);
-    unordered_map(const Allocator&);
-    unordered_map(const unordered_map&, const Allocator&);
-    unordered_map(unordered_map&&, const Allocator&);
-    ...
-    unordered_map& operator=(const unordered_map&);
-    unordered_map& operator=(unordered_map&&);
-    ...
-    // modifiers
-    ...
-    std::pair<iterator, bool> insert(const value_type& obj); 
-    template <class P> pair<iterator, bool> insert(P&& obj);
-    iterator       insert(const_iterator hint, const value_type& obj);
-    template <class P> iterator       insert(const_iterator hint, P&& obj);
-    ...
-    mapped_type& operator[](const key_type& k);
-    mapped_type& operator[](key_type&& k);
-    ...
-};
-
-
- -

-Add to 23.5.4.3 [unord.map.elem]: -

- -
- -
mapped_type& operator[](const key_type& k);
- -
-

...

-

-Requires: key_type shall be CopyConstructible -and mapped_type shall be DefaultConstructible. -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -
- -
mapped_type& operator[](key_type&& k);
- -
-

-Requires: key_type shall be MoveConstructible and -mapped_type shall be DefaultConstructible. -

- -

-Effects: If the unordered_map does not already contain an -element whose key is equivalent to k , inserts the value -value_type(std::move(k), mapped_type()). -

- -

-Returns: A reference to x.second, where x is the -(unique) element whose key is equivalent to k. -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -
- -
- -

-Add new section [unord.map.modifiers]: -

- -
-
-template <class P>
-  pair<iterator, bool> insert(P&& x);
-
- -
- -

-Requires: value_type is constructible from -std::forward<P>(x). -

- -

-Effects: Inserts x converted to value_type if and only -if there is no element in the container with key equivalent to the key of -value_type(x). -

- -

-Returns: The bool component of the returned -pair indicates whether the insertion takes place, and the iterator -component points to the element with key equivalent to the key of -value_type(x). -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -

-Remarks: P shall be implicitly convertible to -value_type, else this signature shall not participate in overload -resolution. -

- -
- - -
-template <class P>
-  iterator insert(const_iterator hint, P&& x);
-
- -
- -

-Requires: value_type is constructible from -std::forward<P>(x). -

- -

-Effects: Inserts x converted to value_type if and only -if there is no element in the container with key equivalent to the key of -value_type(x). The iterator hint is a hint pointing to where -the search should start. Implementations are permitted to ignore the hint. -

- -

-Returns: An iterator pointing to the element with key equivalent to the -key of value_type(x). -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -

-Remarks: P shall be implicitly convertible to -value_type, else this signature shall not participate in overload -resolution. -

- -
- -
- -

unordered_multimap

- -

-Change 23.5.5 [unord.multimap]: -

- -
-class unordered_multimap
-{
-    ...
-    unordered_multimap(const unordered_multimap&);
-    unordered_multimap(unordered_multimap&&);
-    unordered_multimap(const Allocator&);
-    unordered_multimap(const unordered_multimap&, const Allocator&);
-    unordered_multimap(unordered_multimap&&, const Allocator&);
-    ...
-    unordered_multimap& operator=(const unordered_multimap&);
-    unordered_multimap& operator=(unordered_multimap&&);
-    ...
-    // modifiers
-    ...
-    iterator insert(const value_type& obj); 
-    template <class P> iterator insert(P&& obj);
-    iterator       insert(const_iterator hint, const value_type& obj);
-    template <class P> iterator       insert(const_iterator hint, P&& obj);
-    ...
-};
-
-
- -

-Add new section [unord.multimap.modifiers]: -

- -
-
-template <class P>
-  iterator insert(P&& x);
-
- -
- -

-Requires: value_type is constructible from -std::forward<P>(x). -

- -

-Effects: Inserts x converted to value_type. -

- -

-Returns: An iterator pointing to the element with key equivalent to the -key of value_type(x). -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -

-Remarks: P shall be implicitly convertible to -value_type, else this signature shall not participate in overload -resolution. -

- -
- -
-template <class P>
-  iterator insert(const_iterator hint, P&& x);
-
- -
- -

-Requires: value_type is constructible from -std::forward<P>(x). -

- -

-Effects: Inserts x converted to value_type if and only -if there is no element in the container with key equivalent to the key of -value_type(x). The iterator hint is a hint pointing to where -the search should start. Implementations are permitted to ignore the hint. -

- -

-Returns: An iterator pointing to the element with key equivalent to the -key of value_type(x). -

- -

-Complexity: Average case O(1), worst case O(size()). -

- -

-Remarks: P shall be implicitly convertible to -value_type, else this signature shall not participate in overload -resolution. -

- -
- -
- -

unordered_set

- -

-Change 23.5.6 [unord.set]: -

- -
-class unordered_set
-{
-    ...
-    unordered_set(const unordered_set&);
-    unordered_set(unordered_set&&);
-    unordered_set(const Allocator&);
-    unordered_set(const unordered_set&, const Allocator&);
-    unordered_set(unordered_set&&, const Allocator&);
-    ...
-    unordered_set& operator=(const unordered_set&);
-    unordered_set& operator=(unordered_set&&);
-    ...
-    // modifiers 
-    ...
-    std::pair<iterator, bool> insert(const value_type& obj); 
-    pair<iterator, bool> insert(value_type&& obj);
-    iterator       insert(const_iterator hint, const value_type& obj);
-    iterator       insert(const_iterator hint, value_type&& obj);
-    ...
-};
-
- -

unordered_multiset

- -

-Change 23.5.7 [unord.multiset]: -

- -
-class unordered_multiset
-{
-    ...
-    unordered_multiset(const unordered_multiset&);
-    unordered_multiset(unordered_multiset&&);
-    unordered_multiset(const Allocator&);
-    unordered_multiset(const unordered_multiset&, const Allocator&);
-    unordered_multiset(unordered_multiset&&, const Allocator&);
-    ...
-    unordered_multiset& operator=(const unordered_multiset&);
-    unordered_multiset& operator=(unordered_multiset&&);
-    ...
-    // modifiers
-    ...
-    iterator insert(const value_type& obj); 
-    iterator insert(value_type&& obj);
-    iterator       insert(const_iterator hint, const value_type& obj);
-    iterator       insert(const_iterator hint, value_type&& obj);
-    ...
-};
-
-
- - - - - - -
-

677. Weaknesses in seed_seq::randomize [rand.util.seedseq]

-

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 - Submitter: Charles Karney Opened: 2007-05-15 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

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-

Discussion:

-

-seed_seq::randomize provides a mechanism for initializing random number -engines which ideally would yield "distant" states when given "close" -seeds. The algorithm for seed_seq::randomize given in the current -Working Draft for C++, -N2284 -(2007-05-08), has 3 weaknesses -

- -
    -
  1. -

    Collisions in state. Because of the way the state is initialized, - seeds of different lengths may result in the same state. The - current version of seed_seq has the following properties:

    -
      -
    • For a given s <= n, each of the 2^(32s) seed vectors results in a - distinct state.
      • -
    -

    - The proposed algorithm (below) has the considerably stronger - properties:

    -
      -
    • All of the (2^(32n)-1)/(2^32-1) seed vectors of lengths s < n - result in distinct states. -
      • -
    • All of the 2^(32n) seed vectors of length s == n result in - distinct states. -
      • -
    -
    2. -
  2. -

    Poor mixing of v's entropy into the state. Consider v.size() == n - and hold v[n/2] thru v[n-1] fixed while varying v[0] thru v[n/2-1], - a total of 2^(16n) possibilities. Because of the simple recursion - used in seed_seq, begin[n/2] thru begin[n-1] can take on only 2^64 - possible states.

    - -

    The proposed algorithm uses a more complex recursion which results - in much better mixing.

    -
    3. -
  3. seed_seq::randomize is undefined for v.size() == 0. The proposed - algorithm remedies this. -
    4. -
-

-The current algorithm for seed_seq::randomize is adapted by me from the -initialization procedure for the Mersenne Twister by Makoto Matsumoto -and Takuji Nishimura. The weakness (2) given above was communicated to -me by Matsumoto last year. -

-

-The proposed replacement for seed_seq::randomize is due to Mutsuo Saito, -a student of Matsumoto, and is given in the implementation of the -SIMD-oriented Fast Mersenne Twister random number generator SFMT. -http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/index.html -http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/SFMT-src-1.2.tar.gz -

-

-See -Mutsuo Saito, -An Application of Finite Field: Design and Implementation of 128-bit -Instruction-Based Fast Pseudorandom Number Generator, -Master's Thesis, Dept. of Math., Hiroshima University (Feb. 2007) -http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/M062821.pdf -

-

-One change has been made here, namely to treat the case of small n -(setting t = (n-1)/2 for n < 7). -

-

-Since seed_seq was introduced relatively recently there is little cost -in making this incompatible improvement to it. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

678. Changes for [rand.req.eng]

-

Section: 26.5.1.4 [rand.req.eng] Status: CD1 - Submitter: Charles Karney Opened: 2007-05-15 Last modified: 2015-04-08

-

View all other issues in [rand.req.eng].

-

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-

Discussion:

-

-Section 26.5.1.4 [rand.req.eng] Random number engine requirements: -

- -

-This change follows naturally from the proposed change to -seed_seq::randomize in 677. -

- -

-In table 104 the description of X(q) contains a special treatment of -the case q.size() == 0. This is undesirable for 4 reasons: -

- -
    -
  1. It replicates the functionality provided by X().
    2. -
  2. It leads to the possibility of a collision in the state provided - by some other X(q) with q.size() > 0.
    3. -
  3. It is inconsistent with the description of the X(q) in -paragraphs 26.5.3.1 [rand.eng.lcong] p5, 26.5.3.2 [rand.eng.mers] p8, and 26.5.3.3 [rand.eng.sub] p10 where -there is no special treatment of q.size() == 0.
    4. -
  4. The proposed replacement for seed_seq::randomize given above - allows for the case q.size() == 0.
    5. -
- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

679. resize parameter by value

-

Section: 23.3 [sequences] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-06-11 Last modified: 2015-04-08

-

View all other issues in [sequences].

-

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-

Discussion:

-

-The C++98 standard specifies that one member function alone of the containers -passes its parameter (T) by value instead of by const reference: -

- -
-void resize(size_type sz, T c = T());
-
- -

-This fact has been discussed / debated repeatedly over the years, the first time -being even before C++98 was ratified. The rationale for passing this parameter by -value has been: -

- -
-

-So that self referencing statements are guaranteed to work, for example: -

-
-v.resize(v.size() + 1, v[0]);
-
-
- -

-However this rationale is not convincing as the signature for push_back is: -

- -
-void push_back(const T& x);
-
- -

-And push_back has similar semantics to resize (append). -And push_back must also work in the self referencing case: -

- -
-v.push_back(v[0]);  // must work
-
- -

-The problem with passing T by value is that it can be significantly more -expensive than passing by reference. The converse is also true, however when it is -true it is usually far less dramatic (e.g. for scalar types). -

- -

-Even with move semantics available, passing this parameter by value can be expensive. -Consider for example vector<vector<int>>: -

- -
-std::vector<int> x(1000);
-std::vector<std::vector<int>> v;
-...
-v.resize(v.size()+1, x);
-
- -

-In the pass-by-value case, x is copied once to the parameter of -resize. And then internally, since the code can not know at compile -time by how much resize is growing the vector, x is -usually copied (not moved) a second time from resize's parameter into its proper place -within the vector. -

- -

-With pass-by-const-reference, the x in the above example need be copied -only once. In this case, x has an expensive copy constructor and so any -copies that can be saved represents a significant savings. -

- -

-If we can be efficient for push_back, we should be efficient for resize -as well. The resize taking a reference parameter has been coded and shipped in the -CodeWarrior library with no reports of problems which I am aware of. -

- - - -

Proposed resolution:

-

-Change 23.3.3 [deque], p2: -

- -
-class deque {
-   ...
-   void resize(size_type sz, const T& c);
-
- -

-Change 23.3.3.3 [deque.capacity], p3: -

- -
-void resize(size_type sz, const T& c);
-
- -

-Change 23.3.5 [list], p2: -

- -
-class list {
-   ...
-   void resize(size_type sz, const T& c);
-
- -

-Change 23.3.5.3 [list.capacity], p3: -

- -
-void resize(size_type sz, const T& c);
-
- -

-Change 23.3.6 [vector], p2: -

- -
-class vector {
-   ...
-   void resize(size_type sz, const T& c);
-
- -

-Change 23.3.6.3 [vector.capacity], p11: -

- -
-void resize(size_type sz, const T& c);
-
- - - - - - -
-

680. move_iterator operator-> return

-

Section: 24.5.3.1 [move.iterator] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-06-11 Last modified: 2015-04-08

-

View all other issues in [move.iterator].

-

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-

Discussion:

-

-move_iterator's operator-> return type pointer -does not consistently match the type which is returned in the description -in 24.5.3.3.5 [move.iter.op.ref]. -

- -
-template <class Iterator>
-class move_iterator {
-public:
-    ...
-    typedef typename iterator_traits<Iterator>::pointer pointer;
-    ...
-    pointer operator->() const {return current;}
-    ...
-private: 
-    Iterator current; // exposition only
-};
-
- - -

-There are two possible fixes. -

- -
    -
  1. pointer operator->() const {return &*current;}
    2. -
  2. typedef Iterator pointer;
    3. -
- -

-The first solution is the one chosen by reverse_iterator. A potential -disadvantage of this is it may not work well with iterators which return a -proxy on dereference and that proxy has overloaded operator&(). Proxy -references often need to overloaad operator&() to return a proxy -pointer. That proxy pointer may or may not be the same type as the iterator's -pointer type. -

- -

-By simply returning the Iterator and taking advantage of the fact that -the language forwards calls to operator-> automatically until it -finds a non-class type, the second solution avoids the issue of an overloaded -operator&() entirely. -

- -

Proposed resolution:

-

-Change the synopsis in 24.5.3.1 [move.iterator]: -

- -
-typedef typename iterator_traits<Iterator>::pointer pointer;
-
- - - - - - -
-

681. Operator functions impossible to compare are defined in [re.submatch.op]

-

Section: 28.9.2 [re.submatch.op] Status: CD1 - Submitter: Nozomu Katoo Opened: 2007-05-27 Last modified: 2015-04-08

-

View all other issues in [re.submatch.op].

-

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-

Discussion:

-

-In 28.9.2 [re.submatch.op] of N2284, -operator functions numbered 31-42 seem impossible to compare. E.g.: -

- -
-
-template <class BiIter>
-   bool operator==(typename iterator_traits<BiIter>::value_type const& lhs,
-                    const sub_match<BiIter>& rhs);
-
-
-

--31- Returns: lhs == rhs.str(). -

-
-
- -

-When char* is used as BiIter, iterator_traits<BiIter>::value_type would be -char, so that lhs == rhs.str() ends up comparing a char value and an object -of std::basic_string<char>. However, the behaviour of comparison between -these two types is not defined in 21.4.8 [string.nonmembers] of N2284. - This applies when wchar_t* is used as BiIter. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2409. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

682. basic_regex ctor takes InputIterator or ForwardIterator?

-

Section: 28.8.2 [re.regex.construct] Status: CD1 - Submitter: Eric Niebler Opened: 2007-06-03 Last modified: 2015-04-08

-

View all other issues in [re.regex.construct].

-

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-

Discussion:

-

-Looking at N2284, 28.8 [re.regex], p3 basic_regex class template synopsis shows this -constructor: -

-
-template <class InputIterator>
-     basic_regex(InputIterator first, InputIterator last, 
-                 flag_type f = regex_constants::ECMAScript);
-
- -

-In 28.8.2 [re.regex.construct], p15, the constructor appears with this signature: -

- -
-template <class ForwardIterator>
-     basic_regex(ForwardIterator first, ForwardIterator last, 
-                 flag_type f = regex_constants::ECMAScript);
-
- -

-ForwardIterator is probably correct, so the synopsis is wrong. -

- -

[ -John adds: -]

- - -
-

-I think either could be implemented? Although an input iterator would -probably require an internal copy of the string being made. -

-

-I have no strong feelings either way, although I think my original intent -was InputIterator. -

-
- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2409. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

685. reverse_iterator/move_iterator difference has invalid signatures

-

Section: 24.5.1.3.19 [reverse.iter.opdiff], 24.5.3.3.14 [move.iter.nonmember] Status: CD1 - Submitter: Bo Persson Opened: 2007-06-10 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-In C++03 the difference between two reverse_iterators -

-
-ri1 - ri2
-
-

-is possible to compute only if both iterators have the same base -iterator. The result type is the difference_type of the base iterator. -

-

-In the current draft, the operator is defined as 24.5.1.3.19 [reverse.iter.opdiff] -

-
-template<class Iterator1, class Iterator2> 
-typename reverse_iterator<Iterator>::difference_type 
-   operator-(const reverse_iterator<Iterator1>& x, 
-                    const reverse_iterator<Iterator2>& y);
-
-

-The return type is the same as the C++03 one, based on the no longer -present Iterator template parameter. -

-

-Besides being slightly invalid, should this operator work only when -Iterator1 and Iterator2 has the same difference_type? Or should the -implementation choose one of them? Which one? -

-

-The same problem now also appears in operator-() for move_iterator -24.5.3.3.14 [move.iter.nonmember]. -

- - -

Proposed resolution:

-

-Change the synopsis in 24.5.1.1 [reverse.iterator]: -

- -
-
-template <class Iterator1, class Iterator2> 
-  typename reverse_iterator<Iterator>::difference_type auto operator-( 
-    const reverse_iterator<Iterator1>& x, 
-    const reverse_iterator<Iterator2>& y) -> decltype(y.current - x.current);
-
-
- -

-Change 24.5.1.3.19 [reverse.iter.opdiff]: -

- -
-
-template <class Iterator1, class Iterator2> 
-  typename reverse_iterator<Iterator>::difference_type auto operator-( 
-    const reverse_iterator<Iterator1>& x, 
-    const reverse_iterator<Iterator2>& y) -> decltype(y.current - x.current);
-
-
-

-Returns: y.current - x.current. -

-
-
- - -

-Change the synopsis in 24.5.3.1 [move.iterator]: -

- -
-
-template <class Iterator1, class Iterator2> 
-  typename move_iterator<Iterator>::difference_type auto operator-( 
-    const move_iterator<Iterator1>& x, 
-    const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());
-
-
- -

-Change 24.5.3.3.14 [move.iter.nonmember]: -

- -
-
-template <class Iterator1, class Iterator2> 
-  typename move_iterator<Iterator>::difference_type auto operator-( 
-    const move_iterator<Iterator1>& x, 
-    const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());
-
-
-

-Returns: x.base() - y.base(). -

-
-
- -

[ -Pre Bellevue: This issue needs to wait until the auto -> return language feature -goes in. -]

- - - - - - - -
-

687. shared_ptr conversion constructor not constrained

-

Section: 20.8.2.2.1 [util.smartptr.shared.const], 20.8.2.3.1 [util.smartptr.weak.const] Status: CD1 - Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

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-

Discussion:

-

-Since all conversions from shared_ptr<T> to shared_ptr<U> have the same -rank regardless of the relationship between T and U, reasonable user -code that works with raw pointers fails with shared_ptr: -

- -
-void f( shared_ptr<void> );
-void f( shared_ptr<int> );
-
-int main()
-{
-  f( shared_ptr<double>() ); // ambiguous
-}
-
- -

-Now that we officially have enable_if, we can constrain the constructor -and the corresponding assignment operator to only participate in the -overload resolution when the pointer types are compatible. -

- - -

Proposed resolution:

-

-In 20.8.2.2.1 [util.smartptr.shared.const], change: -

- -

--14- Requires: For the second constructor The -second constructor shall not participate in the overload resolution -unless Y* shall be is implicitly convertible -to T*. -

- -

-In 20.8.2.3.1 [util.smartptr.weak.const], change: -

- -
-
-template<class Y> weak_ptr(shared_ptr<Y> const& r);
-weak_ptr(weak_ptr const& r);
-template<class Y> weak_ptr(weak_ptr<Y> const& r);
-weak_ptr(weak_ptr const& r);
-template<class Y> weak_ptr(weak_ptr<Y> const& r);
-template<class Y> weak_ptr(shared_ptr<Y> const& r);
-
-

--4- Requires: For tThe second and -third constructors, shall not participate in the -overload resolution unless Y* shall be -is implicitly convertible to T*. -

-
- - - - - - -
-

688. reference_wrapper, cref unsafe, allow binding to rvalues

-

Section: 20.9.4.1 [refwrap.const] Status: C++11 - Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2015-04-08

-

View all other issues in [refwrap.const].

-

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-

Discussion:

-

-A reference_wrapper can be constructed from an rvalue, either by using -the constructor, or via cref (and ref in some corner cases). This leads -to a dangling reference being stored into the reference_wrapper object. -Now that we have a mechanism to detect an rvalue, we can fix them to -disallow this source of undefined behavior. -

- -

-Also please see the thread starting at c++std-lib-17398 for some good discussion on this subject. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -
-

-Now that ref/cref are constained that T must be an ObjectType, I do not -believe there is any risk of binding ref to a temporary (which would rely on -deducing T to be an rvalue reference type) -

-

-However, the problem for cref remains, so I recommend retaining that deleted -overload. -

-
- -

[ -2009-05-10 Howard adds: -]

- - -
-

-Without: -

- -
-template <class T> void ref(const T&& t) = delete;
-
-

-I believe this program will compile: -

- -
-#include <functional>
-
-struct A {};
-
-const A source() {return A();}
-
-int main()
-{
-   std::reference_wrapper<const A> r = std::ref(source());
-}
-
-

-I.e. in: -

-
-template <ObjectType T> reference_wrapper<T> ref(T& t);
-
- -

-this: -

- -
-ref(source())
-
-

-deduces T as const A, and so: -

- -
-ref(const A& t)
-
- -

-will bind to a temporary (tested with a pre-concepts rvalue-ref enabled compiler). -

-

-Therefore I think we still need the ref-protection. I respectfully disagree with Alisdair's -comment and am in favor of the proposed wording as it stands. Also, CWG 606 -(noted below) has now been "favorably" resolved. -

- -
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-In 20.9 [function.objects], add the following two signatures to the synopsis: -

- -
-template <class T> void ref(const T&& t) = delete;
-template <class T> void cref(const T&& t) = delete;
-
- - - -

[ -N2292 -addresses the first part of the resolution but not the second. -]

- - -

[ -Bellevue: Doug noticed problems with the current wording. -]

- - -

[ -post Bellevue: Howard and Peter provided revised wording. -]

- - -

[ -This resolution depends on a "favorable" resolution of CWG 606: that is, -the "special deduction rule" is disabled with the const T&& pattern. -]

- - - - - -
-

689. reference_wrapper constructor overly constrained

-

Section: 20.9.4.1 [refwrap.const] Status: CD1 - Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2015-04-08

-

View all other issues in [refwrap.const].

-

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-

Discussion:

-

-The constructor of reference_wrapper is currently explicit. The primary -motivation behind this is the safety problem with respect to rvalues, -which is addressed by the proposed resolution of the previous issue. -Therefore we should consider relaxing the requirements on the -constructor since requests for the implicit conversion keep resurfacing. -

-

-Also please see the thread starting at c++std-lib-17398 for some good discussion on this subject. -

- - -

Proposed resolution:

-

-Remove the explicit from the constructor of reference_wrapper. If the -proposed resolution of the previous issue is accepted, remove the -explicit from the T&& constructor as well to keep them in sync. -

- - - - - -
-

691. const_local_iterator cbegin, cend missing from TR1

-

Section: 23.5 [unord], TR1 6.3 [tr.hash] Status: CD1 - Submitter: Joaquín M López Muñoz Opened: 2007-06-14 Last modified: 2015-04-08

-

View all other issues in [unord].

-

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-

Discussion:

-

-The last version of TR1 does not include the following member -functions -for unordered containers: -

- -
-const_local_iterator cbegin(size_type n) const;
-const_local_iterator cend(size_type n) const;
-
- -

-which looks like an oversight to me. I've checked th TR1 issues lists -and the latest working draft of the C++0x std (N2284) and haven't -found any mention to these menfuns or to their absence. -

-

-Is this really an oversight, or am I missing something? -

- - - -

Proposed resolution:

-

-Add the following two rows to table 93 (unordered associative container -requirements) in section 23.2.5 [unord.req]: -

- -
- - - - - - - - - - - -
Unordered associative container requirements (in addition to container)
expression return type assertion/note pre/post-condition complexity
b.cbegin(n) const_local_iterator n shall be in the range [0, bucket_count()). Note: [b.cbegin(n), b.cend(n)) is a valid range containing all of the elements in the nth bucket. Constant
b.cend(n) const_local_iterator n shall be in the range [0, bucket_count()). Constant
-
- -

-Add to the synopsis in 23.5.4 [unord.map]: -

- -
-const_local_iterator cbegin(size_type n) const;
-const_local_iterator cend(size_type n) const;
-
- -

-Add to the synopsis in 23.5.5 [unord.multimap]: -

- -
-const_local_iterator cbegin(size_type n) const;
-const_local_iterator cend(size_type n) const;
-
- -

-Add to the synopsis in 23.5.6 [unord.set]: -

- -
-const_local_iterator cbegin(size_type n) const;
-const_local_iterator cend(size_type n) const;
-
- -

-Add to the synopsis in 23.5.7 [unord.multiset]: -

- -
-const_local_iterator cbegin(size_type n) const;
-const_local_iterator cend(size_type n) const;
-
- - - - - - -
-

692. get_money and put_money should be formatted I/O functions

-

Section: 27.7.5 [ext.manip] Status: CD1 - Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2015-04-08

-

View all other issues in [ext.manip].

-

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-

Discussion:

-

-In a private email Bill Plauger notes: -

-

-I believe that the function that implements get_money -[from N2072] -should behave as a formatted input function, and the function that -implements put_money should behave as a formatted output -function. This has implications regarding the skipping of whitespace -and the handling of errors, among other things. -

-

-The words don't say that right now and I'm far from convinced that -such a change is editorial. -

-

-Martin's response: -

-

-I agree that the manipulators should handle exceptions the same way as -formatted I/O functions do. The text in N2072 assumes so but the -Returns clause explicitly omits exception handling for the sake -of brevity. The spec should be clarified to that effect. -

-

-As for dealing with whitespace, I also agree it would make sense for -the extractors and inserters involving the new manipulators to treat -it the same way as formatted I/O. -

- - -

Proposed resolution:

-

-Add a new paragraph immediately above p4 of 27.7.5 [ext.manip] with the -following text: -

-

-Effects: The expression in >> get_money(mon, intl) -described below behaves as a formatted input function (as -described in 27.7.2.2.1 [istream.formatted.reqmts]). -

-

-Also change p4 of 27.7.5 [ext.manip] as follows: -

-

-Returns: An object s of unspecified type such that -if in is an object of type basic_istream<charT, -traits> then the expression in >> -get_money(mon, intl) behaves as a formatted input function -that calls f(in, mon, intl) were -called. The function f can be defined as... -

- - -

[ -post Bellevue: -]

- - -

-We recommend moving immediately to Review. We've looked at the issue and -have a consensus that the proposed resolution is correct, but want an -iostream expert to sign off. Alisdair has taken the action item to putt -this up on the reflector for possible movement by Howard to Tenatively -Ready. -

- - - - -
-

693. std::bitset::all() missing

-

Section: 20.6 [template.bitset] Status: CD1 - Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2015-04-08

-

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-

View all other issues in [template.bitset].

-

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-

Discussion:

-

-The bitset class template provides the member function -any() to determine whether an object of the type has any -bits set, and the member function none() to determine -whether all of an object's bits are clear. However, the template does -not provide a corresponding function to discover whether a -bitset object has all its bits set. While it is -possible, even easy, to obtain this information by comparing the -result of count() with the result of size() -for equality (i.e., via b.count() == b.size()) the -operation is less efficient than a member function designed -specifically for that purpose could be. (count() must -count all non-zero bits in a bitset a word at a time -while all() could stop counting as soon as it encountered -the first word with a zero bit). -

- - -

Proposed resolution:

-

-Add a declaration of the new member function all() to the -defintion of the bitset template in 20.6 [template.bitset], p1, -right above the declaration of any() as shown below: -

- -
-bool operator!=(const bitset<N>& rhs) const;
-bool test(size_t pos) const;
-bool all() const;
-bool any() const;
-bool none() const;
-
- -

-Add a description of the new member function to the end of 20.6.2 [bitset.members] with the following text: -

-

-bool all() const; -

-

-Returns: count() == size(). -

-
- -

-In addition, change the description of any() and -none() for consistency with all() as -follows: -

-

-bool any() const; -

-
-

-Returns: true if any bit in *this -is onecount() != 0. -

-
-

-bool none() const; -

-
-

-Returns: true if no bit in *this -is onecount() == 0. -

-
-
- - - - - -
-

694. std::bitset and long long

-

Section: 20.6 [template.bitset] Status: CD1 - Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Objects of the bitset class template specializations can -be constructed from and explicitly converted to values of the widest -C++ integer type, unsigned long. With the introduction -of long long into the language the template should be -enhanced to make it possible to interoperate with values of this type -as well, or perhaps uintmax_t. See c++std-lib-18274 for -a brief discussion in support of this change. -

- - -

Proposed resolution:

-

-For simplicity, instead of adding overloads for unsigned long -long and dealing with possible ambiguities in the spec, replace -the bitset ctor that takes an unsigned long -argument with one taking unsigned long long in the -definition of the template as shown below. (The standard permits -implementations to add overloads on other integer types or employ -template tricks to achieve the same effect provided they don't cause -ambiguities or changes in behavior.) -

-
-
-// [bitset.cons] constructors:
-bitset();
-bitset(unsigned long long val);
-template<class charT, class traits, class Allocator>
-explicit bitset(
-                const basic_string<charT,traits,Allocator>& str,
-                typename basic_string<charT,traits,Allocator>::size_type pos = 0,
-                typename basic_string<charT,traits,Allocator>::size_type n =
-                    basic_string<charT,traits,Allocator>::npos);
-
-
-

-Make a corresponding change in 20.6.1 [bitset.cons], p2: -

-
-

-bitset(unsigned long long val); -

-

-Effects: Constructs an object of class bitset<N>, -initializing the first M bit positions to the -corresponding bit values in val. -M is the smaller of N and the -number of bits in the value representation (section [basic.types]) of -unsigned long long. If M < -N is true, the remaining bit -positions are initialized to zero. -

-
- -

-Additionally, introduce a new member function to_ullong() -to make it possible to convert bitset to values of the -new type. Add the following declaration to the definition of the -template, immediate after the declaration of to_ulong() -in 20.6 [template.bitset], p1, as shown below: -

-
-
-// element access:
-bool operator[](size_t pos) const; // for b[i];
-reference operator[](size_t pos); // for b[i];
-unsigned long to_ulong() const;
-unsigned long long to_ullong() const;
-template <class charT, class traits, class Allocator>
-basic_string<charT, traits, Allocator> to_string() const;
-
-
-

-And add a description of the new member function to 20.6.2 [bitset.members], -below the description of the existing to_ulong() (if -possible), with the following text: -

-
-

-unsigned long long to_ullong() const; -

-

-Throws: overflow_error if the integral value -x corresponding to the bits in *this -cannot be represented as type unsigned long long. -

-

-Returns: x. -

-
- - - - - -
-

695. ctype<char>::classic_table() not accessible

-

Section: 22.4.1.3 [facet.ctype.special] Status: CD1 - Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2015-04-08

-

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-

Discussion:

-

-The ctype<char>::classic_table() static member -function returns a pointer to an array of const -ctype_base::mask objects (enums) that contains -ctype<char>::table_size elements. The table -describes the properties of the character set in the "C" locale (i.e., -whether a character at an index given by its value is alpha, digit, -punct, etc.), and is typically used to initialize the -ctype<char> facet in the classic "C" locale (the -protected ctype<char> member function -table() then returns the same value as -classic_table()). -

-

-However, while ctype<char>::table_size (the size of -the table) is a public static const member of the -ctype<char> specialization, the -classic_table() static member function is protected. That -makes getting at the classic data less than convenient (i.e., one has -to create a whole derived class just to get at the masks array). It -makes little sense to expose the size of the table in the public -interface while making the table itself protected, especially when the -table is a constant object. -

-

-The same argument can be made for the non-static protected member -function table(). -

- - -

Proposed resolution:

-

-Make the ctype<char>::classic_table() and -ctype<char>::table() member functions public by -moving their declarations into the public section of the definition of -specialization in 22.4.1.3 [facet.ctype.special] as shown below: -

-
-
-  static locale::id id;
-  static const size_t table_size = IMPLEMENTATION_DEFINED;
-protected:
-  const mask* table() const throw();
-  static const mask* classic_table() throw();
-protected:
-
-~ctype(); // virtual
-virtual char do_toupper(char c) const;
-
-
- - - - - -
-

696. istream::operator>>(int&) broken

-

Section: 27.7.2.2.2 [istream.formatted.arithmetic] Status: C++11 - Submitter: Martin Sebor Opened: 2007-06-23 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-From message c++std-lib-17897: -

-

-The code shown in 27.7.2.2.2 [istream.formatted.arithmetic] as the "as if" -implementation of the two arithmetic extractors that don't have a -corresponding num_get interface (i.e., the -short and int overloads) is subtly buggy in -how it deals with EOF, overflow, and other similar -conditions (in addition to containing a few typos). -

-

-One problem is that if num_get::get() reaches the EOF -after reading in an otherwise valid value that exceeds the limits of -the narrower type (but not LONG_MIN or -LONG_MAX), it will set err to -eofbit. Because of the if condition testing for -(err == 0), the extractor won't set -failbit (and presumably, return a bogus value to the -caller). -

-

-Another problem with the code is that it never actually sets the -argument to the extracted value. It can't happen after the call to -setstate() since the function may throw, so we need to -show when and how it's done (we can't just punt as say: "it happens -afterwards"). However, it turns out that showing how it's done isn't -quite so easy since the argument is normally left unchanged by the -facet on error except when the error is due to a misplaced thousands -separator, which causes failbit to be set but doesn't -prevent the facet from storing the value. -

- -

[ -Batavia (2009-05): -]

- -
-

-We believe this part of the Standard has been recently adjusted -and that this issue was addressed during that rewrite. -

-

-Move to NAD. -

-
- -

[ -2009-05-28 Howard adds: -]

- - -
-

-I've moved this issue from Tentatively NAD to Open. -

- -

-The current wording of -N2857 -in 22.4.2.1.2 [facet.num.get.virtuals] p3, stage 3 appears to indicate that -in parsing arithmetic types, the value is always set, but sometimes in addition -to setting failbit. -

- -
    -
  • -If there is a range error, the value is set to min or max, else -
    • -
  • -if there is a conversion error, the value is set to 0, else -
    • -
  • -if there is a grouping error, the value is set to whatever it would be if grouping were ignored, else -
    • -
  • -the value is set to its error-free result. -
    • -
- -

-However there is a contradictory sentence in 22.4.2.1.2 [facet.num.get.virtuals] p1. -

- -

-27.7.2.2.2 [istream.formatted.arithmetic] should mimic the behavior of 22.4.2.1.2 [facet.num.get.virtuals] -(whatever we decide that behavior is) for -int and short, and currently does not. I believe that the -correct code fragment should look like: -

- -
-typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
-iostate err = ios_base::goodbit;
-long lval;
-use_facet<numget>(loc).get(*this, 0, *this, err, lval);
-if (lval < numeric_limits<int>::min())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<int>::min();
-}
-else if (lval > numeric_limits<int>::max())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<int>::max();
-}
-else
-  val = static_cast<int>(lval);
-setstate(err);
-
-
- -

[ -2009-07 Frankfurt -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Change 22.4.2.1.2 [facet.num.get.virtuals], p1: -

- -

--1- Effects: Reads characters from in, interpreting them -according to str.flags(), use_facet<ctype<charT> ->(loc), and use_facet< numpunct<charT> ->(loc), where loc is str.getloc(). If an error -occurs, val is unchanged; otherwise it is set to the resulting value. -

- -

-Change 27.7.2.2.2 [istream.formatted.arithmetic], p2 and p3: -

- -
-
-operator>>(short& val);
-
-
-

--2- The conversion occurs as if performed by the following code fragment (using the same notation as for -the preceding code fragment): -

- -
-typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
-iostate err = iostate_base::goodbit;
-long lval;
-use_facet<numget>(loc).get(*this, 0, *this, err, lval);
-if (err != 0)
-  ;
-else if (lval < numeric_limits<short>::min()
-  || numeric_limits<short>::max() < lval)
-     err = ios_base::failbit;
-if (lval < numeric_limits<short>::min())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<short>::min();
-}
-else if (lval > numeric_limits<short>::max())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<short>::max();
-}
-else
-  val = static_cast<short>(lval);
-setstate(err);
-
- -
- -
-operator>>(int& val);
-
-
-

--3- The conversion occurs as if performed by the following code fragment (using the same notation as for -the preceding code fragment): -

- -
-typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
-iostate err = iostate_base::goodbit;
-long lval;
-use_facet<numget>(loc).get(*this, 0, *this, err, lval);
-if (err != 0)
-  ;
-else if (lval < numeric_limits<int>::min()
-  || numeric_limits<int>::max() < lval)
-     err = ios_base::failbit;
-if (lval < numeric_limits<int>::min())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<int>::min();
-}
-else if (lval > numeric_limits<int>::max())
-{
-  err |= ios_base::failbit;
-  val = numeric_limits<int>::max();
-}
-else
-  val = static_cast<int>(lval);
-setstate(err);
-
- -
- -
- - - - - -
-

697. New <system_error> header leads to name clashes

-

Section: 19.5 [syserr] Status: Resolved - Submitter: Daniel Krügler Opened: 2007-06-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The most recent state of -N2241 -as well as the current draft -N2284 -(section 19.5 [syserr], p.2) proposes a -new -enumeration type posix_errno immediatly in the namespace std. One of -the enumerators has the name invalid_argument, or fully qualified: -std::invalid_argument. This name clashes with the exception type -std::invalid_argument, see 19.2 [std.exceptions]/p.3. This clash makes -e.g. the following snippet invalid: -

- -
-#include <system_error>
-#include <stdexcept>
-
-void foo() { throw std::invalid_argument("Don't call us - we call you!"); }
-
- -

-I propose that this enumeration type (and probably the remaining parts -of -<system_error> as well) should be moved into one additional inner -namespace, e.g. sys or system to reduce foreseeable future clashes -due -to the great number of members that std::posix_errno already contains -(Btw.: Why has the already proposed std::sys sub-namespace from -N2066 -been rejected?). A further clash candidate seems to be -std::protocol_error -(a reasonable name for an exception related to a std network library, -I guess). -

- -

-Another possible resolution would rely on the proposed strongly typed -enums, -as described in N2213. -But maybe the forbidden implicit conversion to integral types would -make -these enumerators less attractive in this special case? -

- - -

Proposed resolution:

-

-Fixed by issue 7 of N2422. -

- - - - - - -
-

698. system_error needs const char* constructors

-

Section: 19.5.6.1 [syserr.syserr.overview] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-06-24 Last modified: 2015-04-08

-

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-

Discussion:

-

-In 19.5.6.1 [syserr.syserr.overview] we have the class definition of -std::system_error. In contrast to all exception classes, which -are constructible with a what_arg string (see 19.2 [std.exceptions], -or ios_base::failure in 27.5.3.1.1 [ios::failure]), only overloads with with -const string& are possible. For consistency with the re-designed -remaining exception classes this class should also provide -c'tors which accept a const char* what_arg string. -

-

-Please note that this proposed addition makes sense even -considering the given implementation hint for what(), because -what_arg is required to be set as what_arg of the base class -runtime_error, which now has the additional c'tor overload -accepting a const char*. -

- - -

Proposed resolution:

-

-This proposed wording assumes issue 832 has been accepted and applied to the working paper. -

- -

-Change 19.5.6.1 [syserr.syserr.overview] Class system_error overview, as indicated: -

- -
-public:
-  system_error(error_code ec, const string& what_arg);
-  system_error(error_code ec, const char* what_arg);
-  system_error(error_code ec);
-  system_error(int ev, const error_category* ecat,
-      const string& what_arg);
-  system_error(int ev, const error_category* ecat,
-      const char* what_arg);
-  system_error(int ev, const error_category* ecat);
-
- -

-To 19.5.6.2 [syserr.syserr.members] Class system_error members add: -

- -
-
-system_error(error_code ec, const char* what_arg);
-
-
-

-Effects: Constructs an object of class system_error. -

-

-Postconditions: code() == ec and strcmp(runtime_error::what(), what_arg) == 0. -

-
- -
-system_error(int ev, const error_category* ecat, const char* what_arg);
-
- -
-

-Effects: Constructs an object of class system_error. -

-

-Postconditions: code() == error_code(ev, ecat) and strcmp(runtime_error::what(), what_arg) == 0. -

-
-
- - - - - - -
-

699. N2111 changes min/max

-

Section: 26.5 [rand] Status: CD1 - Submitter: P.J. Plauger Opened: 2007-07-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-N2111 -changes min/max in several places in random from member -functions to static data members. I believe this introduces -a needless backward compatibility problem between C++0X and -TR1. I'd like us to find new names for the static data members, -or perhaps change min/max to constexprs in C++0X. -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

700. N1856 defines struct identity

-

Section: 20.2.4 [forward] Status: CD1 - Submitter: P.J. Plauger Opened: 2007-07-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-N1856 -defines struct identity in <utility> which clashes with -the traditional definition of struct identity in <functional> -(not standard, but a common extension from old STL). Be nice -if we could avoid this name clash for backward compatibility. -

- - -

Proposed resolution:

-

-Change 20.2.4 [forward]: -

- -
-
-template <class T> struct identity
-{
-    typedef T type;
-    const T& operator()(const T& x) const;
-};
-
-
-
-const T& operator()(const T& x) const;
-
-
-

-Returns: x. -

-
-
- -
- - - - - - -
-

703. map::at() need a complexity specification

-

Section: 23.4.4.3 [map.access] Status: CD1 - Submitter: Joe Gottman Opened: 2007-07-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-map::at() need a complexity specification. -

- - -

Proposed resolution:

-

-Add the following to the specification of map::at(), 23.4.4.3 [map.access]: -

-
-

-Complexity: logarithmic. -

-
- - - - - -
-

704. MoveAssignable requirement for container value type overly strict

-

Section: 23.2 [container.requirements] Status: C++11 - Submitter: Howard Hinnant Opened: 2007-05-20 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

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-

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-

Discussion:

-

-The move-related changes inadvertently overwrote the intent of 276. -Issue 276 removed the requirement of CopyAssignable from -most of the member functions of node-based containers. But the move-related changes -unnecessarily introduced the MoveAssignable requirement for those members which used to -require CopyAssignable. -

- -

-We also discussed (c++std-lib-18722) the possibility of dropping MoveAssignable -from some of the sequence requirements. Additionally the in-place construction -work may further reduce requirements. For purposes of an easy reference, here are the -minimum sequence requirements as I currently understand them. Those items in requirements -table in the working draft which do not appear below have been purposefully omitted for -brevity as they do not have any requirements of this nature. Some items which do not -have any requirements of this nature are included below just to confirm that they were -not omitted by mistake. -

- - - - - - - - -
Container Requirements
X u(a)value_type must be CopyConstructible
X u(rv)array requires value_type to be CopyConstructible
a = uSequences require value_type to be CopyConstructible and CopyAssignable. - Associative containers require value_type to be CopyConstructible.
a = rvarray requires value_type to be CopyAssignable. - Sequences containers with propagate_on_container_move_assignment == false allocators require value_type to be MoveConstructible and MoveAssignable. - Associative containers with propagate_on_container_move_assignment == false allocators require value_type to be MoveConstructible.
swap(a,u)array requires value_type to be Swappable.
- -

-

- - - - - - - - - - - - - - - - - -
Sequence Requirements
X(n)value_type must be DefaultConstructible
X(n, t)value_type must be CopyConstructible
X(i, j)Sequences require value_type to be constructible from *i. Additionally if input_iterators - are used, vector and deque require MoveContructible and MoveAssignable.
a.insert(p, t)The value_type must be CopyConstructible. - The sequences vector and deque also require the value_type to be CopyAssignable.
a.insert(p, rv)The value_type must be MoveConstructible. - The sequences vector and deque also require the value_type to be MoveAssignable.
a.insert(p, n, t)The value_type must be CopyConstructible. - The sequences vector and deque also require the value_type to be CopyAssignable.
a.insert(p, i, j)If the iterators return an lvalue the value_type must be CopyConstructible. - The sequences vector and deque also require the value_type to be CopyAssignable when the iterators return an lvalue. - If the iterators return an rvalue the value_type must be MoveConstructible. - The sequences vector and deque also require the value_type to be MoveAssignable when the iterators return an rvalue.
a.erase(p)The sequences vector and deque require the value_type to be MoveAssignable.
a.erase(q1, q2)The sequences vector and deque require the value_type to be MoveAssignable.
a.clear()
a.assign(i, j)If the iterators return an lvalue the value_type must be CopyConstructible and CopyAssignable. - If the iterators return an rvalue the value_type must be MoveConstructible and MoveAssignable.
a.assign(n, t)The value_type must be CopyConstructible and CopyAssignable.
a.resize(n)The value_type must be DefaultConstructible. - The sequence vector also requires the value_type to be MoveConstructible.
a.resize(n, t)The value_type must be CopyConstructible.
- -

-

- - - - - - - - - - - - - -
Optional Sequence Requirements
a.front()
a.back()
a.push_front(t)The value_type must be CopyConstructible.
a.push_front(rv)The value_type must be MoveConstructible.
a.push_back(t)The value_type must be CopyConstructible.
a.push_back(rv)The value_type must be MoveConstructible.
a.pop_front()
a.pop_back()
a[n]
a.at[n]
- -

-

- - - - - - - - - - - -
Associative Container Requirements
X(i, j)If the iterators return an lvalue the value_type must be CopyConstructible. - If the iterators return an rvalue the value_type must be MoveConstructible.
a_uniq.insert(t)The value_type must be CopyConstructible.
a_uniq.insert(rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a_eq.insert(t)The value_type must be CopyConstructible.
a_eq.insert(rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a.insert(p, t)The value_type must be CopyConstructible.
a.insert(p, rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a.insert(i, j)If the iterators return an lvalue the value_type must be CopyConstructible. - If the iterators return an rvalue the key_type and the mapped_type (if it exists) must be MoveConstructible..
- -

-

- - - - - - - - - - - -
Unordered Associative Container Requirements
X(i, j, n, hf, eq)If the iterators return an lvalue the value_type must be CopyConstructible. - If the iterators return an rvalue the value_type must be MoveConstructible.
a_uniq.insert(t)The value_type must be CopyConstructible.
a_uniq.insert(rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a_eq.insert(t)The value_type must be CopyConstructible.
a_eq.insert(rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a.insert(p, t)The value_type must be CopyConstructible.
a.insert(p, rv)The key_type and the mapped_type (if it exists) must be MoveConstructible.
a.insert(i, j)If the iterators return an lvalue the value_type must be CopyConstructible. - If the iterators return an rvalue the key_type and the mapped_type (if it exists) must be MoveConstructible..
- -

-

- - - - - -
Miscellaneous Requirements
map[lvalue-key]The key_type must be CopyConstructible. - The mapped_type must be DefaultConstructible and MoveConstructible.
map[rvalue-key]The key_type must be MoveConstructible. - The mapped_type must be DefaultConstructible and MoveConstructible.
- -

[ -Kona (2007): Howard and Alan to update requirements table in issue with emplace signatures. -]

- - -

[ -Bellevue: This should be handled as part of the concepts work. -]

- - -

[ -2009-07-20 Reopened by Howard: -]

- - -
-

-This is one of the issues that was "solved by concepts" and is now no longer solved. -

- -

-In a nutshell, concepts adopted the "minimum requirements" philosophy outlined -in the discussion of this issue, and enforced it. My strong suggestion is that -we translate the concepts specification into documentation for the containers. -

- -

-What this means for vendors is that they will have to implement container members -being careful to only use those characteristics of a type that the concepts specification -formally allowed. Note that I am not talking about enable_if'ing -everything. I am simply suggesting that (for example) we tell the vendor he can't call T's -copy constructor or move constructor within the emplace member function, etc. -

- -

-What this means for customers is that they will be able to use types within C++03 -containers which are sometimes not CopyConstructible, and sometimes not even -MoveConstructible, etc. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave open. Howard to provide wording. -

- -

[ -2010-02-06 Howard provides wording. -]

- - -

[ -2010-02-08 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-10 Howard opened. I neglected to reduce the requirements on value_type -for the insert function of the ordered and unordered associative containers when -the argument is an rvalue. Fixed it. -]

- - -

[ -2010-02-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-03-08 Nico opens: -]

- - -
-

-I took the task to see whether 868 is covered by 704 -already. -However, by doing that I have the impression that -704 is a big mistake. -

- -

-Take e.g. the second change of 868: -

- -
-

-Change 23.3.3.2 [deque.cons] para 5: -

-

-Effects: Constructs a deque with n default constructed -elements. -

-

-where "default constructed" should be replaced by "value-initialized". -This is the constructor out of a number of elements: -

-
-ContType c(num)
-
- -

-704 says: -

- -
-

-Remove the entire section 23.3.3.2 [deque.cons]. -

-

-[ This section is already specified by the requirements tables. ] -

-
- -

-BUT, there is no requirement table that lists this constructor at all, -which means that we would lose the entire specification of this function -!!! -

- -

-In fact, I found with further investigation, if we follow -704 to remove 23.3.2.1 we -

-
    -
  • -have no semantics for - ContType c(num) -
    • -
  • -have no complexity and no allocator specification for - ContType c(num,val) -
    • -
  • -have no semantics for - ContType c(num,val,alloc) -
    • -
  • -- have no complexity and no allocator specification for - ContType c(beg,end) -
    • -
  • -- have no semantics for - ContType c(beg,end,alloc) -
    • -
  • -- have different wording (which might or might not give - the same guarantees) for the assign functions -
    • -
- -

-because all these guarantees are given in the removed -section but nowhere else (as far as I saw). -

-

-Looks to me that 704 need a significant review before we -take that change, because chances are high that there -are similar flaws in other proposed changes there -(provided I am not missing anything). -

-
-
- -

[ -2010 Pittsburgh: -]

- - -
-

-Removed the parts from the proposed wording that removed existing sections, -and set to Ready for Pittsburgh. -

-
- - - -

Rationale:

-

[ -post San Francisco: -]

- - -

-Solved by -N2776. -

- -

-This rationale is obsolete. -

- - - -

Proposed resolution:

- - - -

-Change 23.2.1 [container.requirements.general]/4: -

- -

-4 In Tables 91 and 92, X denotes a container class containing objects -of type T, a and b denote values of type X, -u denotes an identifier, r denotes an lvalue or a const -rvalue a non-const value of type X, and rv -denotes a non-const rvalue of type X. -

- -

-Change the following rows in Table 91 — Container requirements -23.2.1 [container.requirements.general]: -

- -
- - - - - - - - - - - - - - - - - -
Table 91 — Container requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
X::value_typeTRequires: T is Destructible.compile time
- -
- -

-Change 23.2.1 [container.requirements.general]/10: -

- -
-

-Unless otherwise specified (see 23.2.4.1, 23.2.5.1, 23.3.2.3, and 23.3.6.4) all -container types defined in this Clause meet the following additional -requirements: -

- -
    -
  • -

    …

    -
    • - -

  • -no erase(), clear(), pop_back() or -pop_front() function throws an exception. -

    • - -
  • -

    …

    -
    • -
- -
- -

-Insert a new paragraph prior to 23.2.1 [container.requirements.general]/14: -

- -
-

-The descriptions of the requirements of the type T in this section -use the terms CopyConstructible, MoveConstructible, constructible -from *i, and constructible from args. These terms -are equivalent to the following expression using the appropriate arguments: -

- -

-allocator_traits<allocator_type>::construct(x.get_allocator(), q, args...);
-
- -

-where x is a non-const lvalue of some container type X and -q has type X::value_type*. -

- -

-[Example: The container is going to move construct a T, so will -call: -

- -

-allocator_traits<allocator_type>::construct(get_allocator(), q, std::move(t));
-
- -

-The default implementation of construct will call: -

- -

-::new (q) T(std::forward<T>(t)); // where forward is the same as move here, cast to rvalue
-
- -

-But the allocator author may override the above definition of construct -and do the construction of T by some other means. — end -example] -

- -

-14 ... -

-
- -

-Add to 23.2.1 [container.requirements.general]/14: -

- -

-14 In Table 93, X denotes an allocator-aware container class with a -value_type of T using allocator of type A, u -denotes a variable, a and b denote non-const lvalues of -type X, t denotes an lvalue or a const rvalue of type -X, rv denotes a non-const rvalue of type X, -m is a value of type A, and Q is an allocator type. -

- -

-Change or add the following rows in Table 93 — Allocator-aware container -requirements in 23.2.1 [container.requirements.general]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 93 — Allocator-aware container requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
X(t, m)
X u(t, m);		Requires: T is CopyConstructible.
-post: u == t,
-get_allocator() == m		linear
X(rv, m)
X u(rv, m);		Requires: T is MoveConstructible.
-post: u shall have the same elements, or copies of the elements, that -rv had before this construction,
-get_allocator() == m		constant if m == rv.get_allocator(), otherwise linear
a = tX&Requires: T is CopyConstructible and -CopyAssignable
-post: a == t.		linear
a = rvX&Requires: If allocator_traits< allocator_type > -::propagate_on_container_move_assignment ::value is false, -T is MoveConstructible and MoveAssignable.
-All existing elements of a are either move assigned -to or destroyed.
-a shall be equal to the value that rv had before this -assignment		linear
a.swap(b);voidexchanges the contents of a and bconstant
- -
- -

-Change the following rows in Table 94 — Sequence container requirements -(in addition to container) in 23.2.3 [sequence.reqmts]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 94 — Sequence container requirements (in addition to -container)
ExpressionReturn typeAssertion/note
pre-/post-condition
X(i, j)
X a(i, j)		Requires: If the iterator's dereference operation returns an -lvalue or a const rvalue, T shall be CopyConstructible. -T shall be constructible from *i.
-If the iterator does not meet the forward iterator requirements (24.2.5 [forward.iterators]), then vector also requires T to -be MoveConstructible.
-Each iterator in the range [i,j) shall be dereferenced exactly -once.
-post: size() == distance between i and j
-Constructs a sequence container equal to the range [i, j)
a = il;X&Requires: T is CopyConstructible and -CopyAssignable.
-a = X(il);
-Assigns the range [il.begin(), il.end()) into a. All -existing elements of a are either assigned or destroyed.
-rReturns *this;
a.emplace(p, args);iteratorRequires: ConstructibleAsElement<A, T, -Args>. T is constructible from args. -vector and deque also require T to be -MoveConstructible and MoveAssignable. Inserts an object -of type T constructed with -std::forward<Args>(args)... before p.
a.insert(p, t);iteratorRequires: ConstructibleAsElement<A, T, Args> and -T shall be CopyAssignable. T shall be -CopyConstructible. vector and deque also require -T to be CopyAssignable. Inserts a copy t before -p.
a.insert(p, rv);iteratorRequires: ConstructibleAsElement<A, T, -T&&> and T shall be MoveAssignable. -T shall be MoveConstructible. vector and -deque also require T to be MoveAssignable. -Inserts a copy rv before p.
a.insert(p, i, j)iteratorRequires: If the iterator's dereference operation returns an -lvalue or a const rvalue, T shall be CopyConstructible. -T shall be constructible from *i.
If the -iterator does not meet the forward iterator requirements (24.2.5 [forward.iterators]), then vector also requires T to -be MoveConstructible and MoveAssignable.
Each -iterator in the range [i,j) shall be dereferenced exactly once.
-pre: i and j are not iterators into a.
Inserts -copies of elements in [i, j) before p
a.erase(q);iteratorRequires: T and T shall be -MoveAssignable. vector and deque require -T to be MoveAssignable. Erases the element pointed to by -q.
a.erase(q1, q2);iteratorRequires: T and T shall be -MoveAssignable. vector and deque require -T to be MoveAssignable. Erases the elements in the range -[q1, q2).
a.clear();voiderase(begin(), end())
-Destroys all elements in a. Invalidates all references, -pointers, and iterators referring to the elements of a and may -invalidate the past-the-end iterator.
 -post: size() == 0 a.empty() == true
a.assign(i, j)voidRequires: If the iterator's dereference operation returns an -lvalue or a const rvalue, T shall be CopyConstructible and -CopyAssignable. -T shall be constructible and assignable from *i. If the -iterator does not meet the forward iterator requirements (24.2.5 [forward.iterators]), then vector also requires T to -be MoveConstructible.
-Each iterator in the range [i,j) shall be dereferenced exactly -once.
-pre: i, j are not iterators into a.
-Replaces elements in a with a copy of [i, j).
- -
- -

-Change the following rows in Table 95 — Optional sequence container operations -in 23.2.3 [sequence.reqmts]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 95 — Optional sequence container operations
ExpressionReturn typeOperational semanticsContainer
a.emplace_front(args)voida.emplace(a.begin(), std::forward<Args>(args)...)
-Prepends an object of type T constructed with -std::forward<Args>(args)....
-Requires: ConstructibleAsElement<A, T, Args> -T shall be constructible from args.		list, deque, forward_list
a.emplace_back(args)voida.emplace(a.end(), std::forward<Args>(args)...)
-Appends an object of type T constructed with -std::forward<Args>(args)....
-Requires: ConstructibleAsElement<A, T, Args> -T shall be constructible from args. vector also -requires T to be MoveConstructible.		list, deque, vector
a.push_front(t)voida.insert(a.begin(), t)
-Prepends a copy of t.
-Requires: ConstructibleAsElement<A, T, T> and -T shall be CopyAssignable. -T shall be CopyConstructible.		list, deque, forward_list
a.push_front(rv)voida.insert(a.begin(), t)
-Prepends a copy of rv.
-Requires: ConstructibleAsElement<A, T, T&&> and -T shall be MoveAssignable. -T shall be MoveConstructible.		list, deque, forward_list
a.push_back(t)voida.insert(a.end(), t)
-Appends a copy of t.
-Requires: ConstructibleAsElement<A, T, T> and -T shall be CopyAssignable. -T shall be CopyConstructible.		vector, list, deque, basic_string
a.push_back(rv)voida.insert(a.end(), t)
-Appends a copy of rv.
-Requires: ConstructibleAsElement<A, T, T&&> and -T shall be MoveAssignable. -T shall be MoveConstructible.		vector, list, deque, basic_string
a.pop_front()voida.erase(a.begin())
-Destroys the first element.
-Requires: a.empty() shall be false.		list, deque, forward_list
a.pop_back()void{ iterator tmp = a.end();
--tmp;
a.erase(tmp); }
-Destroys the last element.
-Requires: a.empty() shall be false.		vector, list, deque, basic_string
- -
- -

-Insert a new paragraph prior to 23.2.4 [associative.reqmts]/7, and -edit paragraph 7: -

- -
-

-The associative containers meet all of the requirements of Allocator-aware -containers (23.2.1 [container.requirements.general]), except for the -containers map and multimap, the requirements placed on -value_type in Table 93 apply instead directly to key_type and -mapped_type. [Note: For example key_type and -mapped_type are sometimes required to be CopyAssignable even -though the value_type (pair<const key_type, -mapped_type>) is not CopyAssignable. — end note] -

- -

-7 In Table 96, X denotes an associative container class, a denotes a -value of X, a_uniq denotes a value of X when -X supports unique keys, a_eq denotes a value of X -when X supports multiple keys, u denotes an identifier, -r denotes an lvalue or a const rvalue of type X, -rv denotes a non-const rvalue of type X, i and -j satisfy input iterator requirements and refer to elements implicitly -convertible to value_type, [i,j) denotes a valid range, -p denotes a valid const iterator to a, q denotes a -valid dereferenceable const iterator to a, [q1, q2) denotes a -valid range of const iterators in a, il designates an object -of type initializer_list<value_type>, t denotes a value -of X::value_type, k denotes a value of X::key_type -and c denotes a value of type X::key_compare. A -denotes the storage allocator used by X, if any, or -std::allocator<X::value_type> otherwise, and m denotes -an allocator of a type convertible to A.

-
- -

-Change or add the following rows in Table 96 — Associative container -requirements (in addition to container) in 23.2.4 [associative.reqmts]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 96 — Associative container requirements (in addition to -container)
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
X::key_typeKeyRequires: Key is CopyConstructible and -CopyAssignable Destructiblecompile time
X::mapped_type (map and multimap only)TRequires: T is Destructiblecompile time
X(c)
X a(c);		Requires: ConstructibleAsElement<A, key_compare, -key_compare>.
-key_compare is CopyConstructible.
-Constructs an empty container.
-Uses a copy of c as a comparison object.		constant
X()
X a;		Requires: ConstructibleAsElement<A, key_compare, -key_compare>.
-key_compare is DefaultConstructible.
-Constructs an empty container.
-Uses Compare() as a comparison object.		constant
X(i, j, c)
X a(i, j, c);		Requires: ConstructibleAsElement<A, key_compare, -key_compare>.
-key_compare is CopyConstructible. value_type -shall be constructible from *i.
-Constructs an empty container ans inserts elements from the range [i, -j) into it; uses c as a comparison object.		N log N in general (N is the distance from -i to j); linear if [i, j) is sorted with -value_comp()
X(i, j)
X a(i, j);		Requires: ConstructibleAsElement<A, key_compare, -key_compare>.
value_type shall be constructible -from *i. key_compare is -DefaultConstructible.
Same as above, but uses -Compare() as a comparison object.		same as above
a = ilX&a = X(il);
-return *this;
-Requires: T is CopyConstructible and -CopyAssignable.
-Assigns the range [il.begin(), il.end()) into a. All -existing elements of a are either assigned or destroyed.		Same as a = X(il). -N log N in general (N is -il.size() added to the existing size of a); linear if -[il.begin(), il.end()) is sorted with value_comp()
a_uniq.emplace(args)pair<iterator, bool>Requires: T shall be constructible from -args
-inserts a T object t constructed with -std::forward<Args>(args)... if and only if there is no element in -the container with key equivalent to the key of t. The bool -component of the returned pair is true if and only if the insertion takes place, -and the iterator component of the pair points to the element with key equivalent -to the key of t.		logarithmic
a_eq.emplace(args)iteratorRequires: T shall be constructible from -args
-inserts a T object t constructed with -std::forward<Args>(args)... and returns the iterator pointing to -the newly inserted element.		logarithmic
a_uniq.insert(t)pair<iterator, bool>Requires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-inserts t if and only if there is no element in the container with key -equivalent to the key of t. The bool component of the returned -pair is true if and only if the insertion takes place, and the iterator -component of the pair points to the element with key equivalent to the key of -t.		logarithmic
a_eq.insert(t)iteratorRequires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-inserts t and returns the iterator pointing to the newly inserted -element. If a range containing elements equivalent to t exists in -a_eq, t is inserted at the end of that range.		logarithmic
a.insert(p, t)iteratorRequires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-inserts t if and only if there is no element with key equivalent to the -key of t in containers with unique keys; always inserts t in -containers with equivalent keys; always returns the iterator pointing to the -element with key equivalent to the key of t. t is inserted as -close as possible to the position just prior to p.		logarithmic in general, but amortized constant if t is inserted -right before p.
a.insert(i, j)voidRequires: T shall be -constructible from *i.
-pre: i, j are not iterators into a. inserts each -element from the range [i,j) if and only if there is no element with -key equivalent to the key of that element in containers with unique keys; always -inserts that element in containers with equivalent keys.		N log(size() + N ) (N is the distance from i to j)
- -
- -

-Insert a new paragraph prior to 23.2.5 [unord.req]/9: -

- -
-

-The unordered associative containers meet all of the requirements of -Allocator-aware containers (23.2.1 [container.requirements.general]), -except for the containers unordered_map and unordered_multimap, -the requirements placed on value_type in Table 93 apply instead -directly to key_type and mapped_type. [Note: For -example key_type and mapped_type are sometimes required to be -CopyAssignable even though the value_type (pair<const -key_type, mapped_type>) is not CopyAssignable. — end -note] -

- -

-9 ... -

-
- -

-Change or add the following rows in Table 98 — Unordered associative -container requirements (in addition to container) in 23.2.5 [unord.req]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 98 — Unordered associative -container requirements (in addition to container)
ExpressionReturn typeAssertion/note
pre-/post-condition		Complexity
X::key_typeKeyRequires: Key shall be CopyAssignable and -CopyConstructible Destructiblecompile time
X::mapped_type (unordered_map and -unordered_multimap only)TRequires:T is Destructiblecompile time
X(n, hf, eq)
X a(n, hf, eq)		XRequires: hasher and key_equal are -CopyConstructible. Constructs an empty container with at least -n buckets, using hf as the hash function and eq as -the key equality predicate. O(N)
X(n, hf)
X a(n, hf)		XRequires: hasher is CopyConstructible and -key_equal is DefaultConstructible. Constructs an empty -container with at least n buckets, using hf as the hash -function and key_equal() as the key equality predicate.O(N)
X(n)
X a(n)		XRequires: hasher and key_equal are -DefaultConstructible. Constructs an empty container with at least -n buckets, using hasher() as the hash function and key_equal() as -the key equality predicate. O(N)
X()
X a		XRequires: hasher and key_equal are -DefaultConstructible. Constructs an empty container an unspecified number of buckets, -using hasher() as the hash function and key_equal() as -the key equality predicate. constant
X(i, j, n, hf, eq)
X a(i, j, n, hf, eq)		XRequires: value_type is constructible from -*i. hasher and key_equal are -CopyConstructible.
-Constructs an empty container with at least n buckets, using -hf as the hash function and eq as the key equality predicate, -and inserts elements from [i, j) into it.		Average case O(N) (N is distance(i, j)), worst -case O(N2)
X(i, j, n, hf)
X a(i, j, n, hf)		XRequires: value_type is constructible from *i. -hasher is CopyConstructible and key_equal is -DefaultConstructible.
Constructs an empty container with at -least n buckets, using hf as the hash function and -key_equal() as the key equality predicate, and inserts elements from -[i, j) into it.		Average case O(N) (N is distance(i, j)), worst -case O(N2)
X(i, j, n)
X a(i, j, n)		XRequires: value_type is constructible from *i. -hasher and key_equal are -DefaultConstructible.
Constructs an empty container with at -least n buckets, using hasher() as the hash function and -key_equal() as the key equality predicate, and inserts elements from -[i, j) into it.		Average case O(N) (N is distance(i, j)), worst -case O(N2)
X(i, j)
X a(i, j)		XRequires: value_type is constructible from *i. -hasher and key_equal are -DefaultConstructible.
Constructs an empty container with an -unspecified number of buckets, using hasher() as the hash function and -key_equal() as the key equality predicate, and inserts elements from -[i, j) into it.		Average case O(N) (N is distance(i, j)), worst -case O(N2)
X(b)
X a(b)		XCopy constructor. In addition to the contained elements -requirements of Table 93 (23.2.1 [container.requirements.general]), copies the hash function, -predicate, and maximum load factor.Average case linear in b.size(), worst case quadratic.
a = bX&Copy assignment operator. In addition to the contained elements -requirements of Table 93 (23.2.1 [container.requirements.general]), copies the hash function, -predicate, and maximum load factor.Average case linear in b.size(), worst case quadratic.
a = ilX&a = X(il); return *this;
-Requires: T is CopyConstructible and -CopyAssignable.
-Assigns the range [il.begin(), il.end()) into a. All -existing elements of a are either assigned or destroyed.		Average case linear in il.size(), worst case quadratic.
a_uniq.emplace(args)pair<iterator, bool>Requires: T shall be constructible from -args
-inserts a T object t constructed with -std::forward<Args>(args)... if and only if there is no element in -the container with key equivalent to the key of t. The bool -component of the returned pair is true if and only if the insertion takes place, -and the iterator component of the pair points to the element with key equivalent -to the key of t.		Average case O(1), worst case O(a_uniq.size()).
a_eq.emplace(args)iteratorRequires: T shall be constructible from -args
-inserts a T object t constructed with -std::forward<Args>(args)... and returns the iterator pointing to -the newly inserted element.		Average case O(1), worst case O(a_eq.size()).
a.emplace_hint(p, args)iteratorRequires: T shall be constructible from -args
-equivalent to a.emplace( std::forward<Args>(args)...). Return -value is an iterator pointing to the element with the key equivalent to the -newly inserted element. The const_iterator p is a hint pointing to -where the search should start. Implementations are permitted to ignore the -hint.		Average case O(1), worst case O(a.size()).
a_uniq.insert(t)pair<iterator, bool>Requires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-Inserts t if and only if there is no element in the container with key -equivalent to the key of t. The bool component of the returned -pair indicates whether the insertion takes place, and the iterator component -points to the element with key equivalent to the key of t.		Average case O(1), worst case O(a_uniq.size()).
a_eq.insert(t)iteratorRequires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-Inserts t, and returns an iterator pointing to the newly inserted -element.		Average case O(1), worst case O(a_uniq.size()).
a.insert(q, t)iteratorRequires: T shall be MoveConstructible if -t is a non-const rvalue expression, else T shall be -CopyConstructible.
-Equivalent to a.insert(t). Return value is an iterator pointing to the -element with the key equivalent to that of t. The iterator q -is a hint pointing to where the search should start. Implementations are -permitted to ignore the hint.		Average case O(1), worst case O(a_uniq.size()).
a.insert(i, j)voidRequires: T shall be -constructible from *i.
-Pre: i and j are not iterators in a. Equivalent to -a.insert(t) for each element in [i,j).		Average case O(N), where N is distance(i, j). -Worst case O(N * a.size()).
- -
- -

-Change 23.3.4 [forwardlist]/2: -

- -

-2 A forward_list satisfies all of the requirements of a container -(table 91), except that the size() member function is not provided. -A forward_list also satisfies all of the requirements of an -allocator-aware container (table 93). And forward_list provides the -assign member functions as specified in Table 94, Sequence container -requirements, and several of the optional sequence container requirements (Table -95). -Descriptions are provided here only for operations on forward_list that -are not described in that table or for operations where there is additional -semantic information. -

- -

-Add a new paragraph after 23.3.4.5 [forwardlist.modifiers]/23: -

- -
-void clear();
-
- -
-

-23 Effects: Erases all elements in the range [begin(),end()). -

-

-Remarks: Does not invalidate past-the-end iterators. -

-
-
- -

-Change 23.3.6.3 [vector.capacity]/13: -

- -
-void resize(size_type sz, const T& c);
-
-

-13 Requires: T shall be CopyConstructible. -If value_type has a move constructor, that constructor shall not throw -any exceptions. -

-
- -

-In 23.5.6 [unord.set] and 23.5.7 [unord.multiset] substitute -"Key" for "Value". -

- -
-

[ -The above substitution is normative as it ties into the requirements table. -]

- -
- - - - - - -
-

705. type-trait decay incompletely specified

-

Section: 20.10.7.6 [meta.trans.other] Status: CD1 - Submitter: Thorsten Ottosen Opened: 2007-07-08 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The current working draft has a type-trait decay in 20.10.7.6 [meta.trans.other]. -

- -

-Its use is to turn C++03 pass-by-value parameters into efficient C++0x -pass-by-rvalue-reference parameters. However, the current definition -introduces an incompatible change where the cv-qualification of the -parameter type is retained. The deduced type should loose such -cv-qualification, as pass-by-value does. -

- - -

Proposed resolution:

-

-In 20.10.7.6 [meta.trans.other] change the last sentence: -

- -

-Otherwise the member typedef type equals remove_cv<U>::type. -

- -

-In 20.4.2.4 [tuple.creation]/1 change: -

- -

-where each Vi in VTypes is X& if, for the -corresponding type Ti in Types, -remove_cv<remove_reference<Ti>::type>::type equals -reference_wrapper<X>, otherwise Vi is -decay<Ti>::type. -Let Ui be decay<Ti>::type for each -Ti in Types. Then each Vi in VTypes -is X& if Ui equals -reference_wrapper<X>, otherwise Vi is -Ui. -

- - - - - - -
-

706. make_pair() should behave as make_tuple() wrt. reference_wrapper()

-

Section: 20.3 [pairs] Status: CD1 - Submitter: Thorsten Ottosen Opened: 2007-07-08 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current draft has make_pair() in 20.3 [pairs]/16 -and make_tuple() in 20.4.2.4 [tuple.creation]. -make_tuple() detects the presence of -reference_wrapper<X> arguments and "unwraps" the reference in -such cases. make_pair() would OTOH create a -reference_wrapper<X> member. I suggest that the two -functions are made to behave similar in this respect to minimize -confusion. -

- - -

Proposed resolution:

-

-In 20.2 [utility] change the synopsis for make_pair() to read -

- -
-template <class T1, class T2>
-  pair<typename decay<T1>::type V1, typename decay<T2>::type V2> make_pair(T1&&, T2&&);
-
- -

-In 20.3 [pairs]/16 change the declaration to match the above synopsis. -Then change the 20.3 [pairs]/17 to: -

- -
-

-Returns: pair<typename decay<T1>::type V1,typename decay<T2>::type V2>(forward<T1>(x),forward<T2>(y)) where V1 and -V2 are determined as follows: Let Ui be -decay<Ti>::type for each Ti. Then each -Vi is X& if Ui equals -reference_wrapper<X>, otherwise Vi is -Ui. -

-
- - - - - - -
-

709. char_traits::not_eof has wrong signature

-

Section: 21.2.3 [char.traits.specializations] Status: CD1 - Submitter: Bo Persson Opened: 2007-08-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The changes made for constexpr in 21.2.3 [char.traits.specializations] have -not only changed the not_eof function from pass by const reference to -pass by value, it has also changed the parameter type from int_type to -char_type. -

-

-This doesn't work for type char, and is inconsistent with the -requirements in Table 56, Traits requirements, 21.2.1 [char.traits.require]. -

- -

-Pete adds: -

- -

-For what it's worth, that may not have been an intentional change. -N2349, which detailed the changes for adding constant expressions to -the library, has strikeout bars through the const and the & that -surround the char_type argument, but none through char_type itself. -So the intention may have been just to change to pass by value, with -text incorrectly copied from the standard. -

- - - -

Proposed resolution:

-

-Change the signature in 21.2.3.1 [char.traits.specializations.char], -21.2.3.2 [char.traits.specializations.char16_t], 21.2.3.3 [char.traits.specializations.char32_t], -and 21.2.3.4 [char.traits.specializations.wchar.t] to -

- -
-static constexpr int_type not_eof(char_type int_type c);
-
- - - -

[ -Bellevue: -]

- - -

-Resolution: NAD editorial - up to Pete's judgment -

- -

[ -Post Sophia Antipolis -]

- - -

-Moved from Pending NAD Editorial to Review. The proposed wording appears to be correct but non-editorial. -

- - - - -
-

710. Missing postconditions

-

Section: 20.8.2.2 [util.smartptr.shared] Status: CD1 - Submitter: Peter Dimov Opened: 2007-08-24 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-A discussion on -comp.std.c++ -has identified a contradiction in the shared_ptr specification. -The shared_ptr move constructor and the cast functions are -missing postconditions for the get() accessor. -

- -

[ -Bellevue: -]

- - -
-

-Move to "ready", adopting the first (Peter's) proposed resolution. -

-

-Note to the project editor: there is an editorial issue here. The -wording for the postconditions of the casts is slightly awkward, and the -editor should consider rewording "If w is the return value...", e. g. as -"For a return value w...". -

-
- - -

Proposed resolution:

-

-Add to 20.8.2.2.1 [util.smartptr.shared.const]: -

- -
-
-shared_ptr(shared_ptr&& r);
-template<class Y> shared_ptr(shared_ptr<Y>&& r);
-
-
-

-Postconditions: *this shall contain the old value of r. r -shall be empty. r.get() == 0. -

-
-
- -

-Add to 20.8.2.2.9 [util.smartptr.shared.cast]: -

- -
-
-template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U> const& r);
-
-
-

-Postconditions: If w is the return value, -w.get() == static_cast<T*>(r.get()) && w.use_count() == r.use_count(). -

-
-
- -
-
-template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const& r);
-
-
-

-Postconditions: If w is the return value, w.get() == dynamic_cast<T*>(r.get()). -

-
-
- -
-
-template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U> const& r);
-
-
-

-Postconditions: If w is the return value, -w.get() == const_cast<T*>(r.get()) && w.use_count() == r.use_count(). -

-
-
- -

-Alberto Ganesh Barbati has written an -alternative proposal -where he suggests (among other things) that the casts be respecified in terms of -the aliasing constructor as follows: -

- -

-Change 20.8.2.2.9 [util.smartptr.shared.cast]: -

- -
-

--2- Returns: If r is empty, an empty -shared_ptr<T>; otherwise, a shared_ptr<T> -object that stores static_cast<T*>(r.get()) and shares ownership with -r. shared_ptr<T>(r, static_cast<T*>(r.get()). -

-
- -
-

--6- Returns: -

-
    -
  • When dynamic_cast<T*>(r.get()) returns a nonzero value, -a shared_ptr<T> object that stores a copy -of it and shares ownership with r;
    • -
  • Otherwise, an empty shared_ptr<T> object.
    • -
  • If p = dynamic_cast<T*>(r.get()) is a non-null pointer, shared_ptr<T>(r, p);
    • -
  • Otherwise, shared_ptr<T>().
    • -
-
- -
-

--10- Returns: If r is empty, an empty -shared_ptr<T>; otherwise, a shared_ptr<T> -object that stores const_cast<T*>(r.get()) and shares ownership with -r. shared_ptr<T>(r, const_cast<T*>(r.get()). -

-
- -

-This takes care of the missing postconditions for the casts by bringing -in the aliasing constructor postcondition "by reference". -

- - - - - - -
-

711. Contradiction in empty shared_ptr

-

Section: 20.8.2.2.5 [util.smartptr.shared.obs] Status: C++11 - Submitter: Peter Dimov Opened: 2007-08-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-A discussion on -comp.std.c++ -has identified a contradiction in the shared_ptr specification. -The note: -

- -

-[ Note: this constructor allows creation of an empty shared_ptr instance with a non-NULL stored pointer. --end note ] -

- -

-after the aliasing constructor -

- -
-template<class Y> shared_ptr(shared_ptr<Y> const& r, T *p);
-
- -

-reflects the intent of -N2351 -to, well, allow the creation of an empty shared_ptr -with a non-NULL stored pointer. -

- -

-This is contradicted by the second sentence in the Returns clause of 20.8.2.2.5 [util.smartptr.shared.obs]: -

- -
-
-T* get() const;
-
-

-Returns: the stored pointer. Returns a null pointer if *this is empty. -

-
- -

[ -Bellevue: -]

- - -
-

-Adopt option 1 and move to review, not ready. -

-

-There was a lot of confusion about what an empty shared_ptr is (the term -isn't defined anywhere), and whether we have a good mental model for how -one behaves. We think it might be possible to deduce what the definition -should be, but the words just aren't there. We need to open an issue on -the use of this undefined term. (The resolution of that issue might -affect the resolution of issue 711.) -

-

-The LWG is getting more uncomfortable with the aliasing proposal (N2351) -now that we realize some of its implications, and we need to keep an eye -on it, but there isn't support for removing this feature at this time. -

-
- -

[ -Sophia Antipolis: -]

- - -
-

-We heard from Peter Dimov, who explained his reason for preferring solution 1. -

-

-Because it doesn't seem to add anything. It simply makes the behavior -for p = 0 undefined. For programmers who don't create empty pointers -with p = 0, there is no difference. Those who do insist on creating them -presumably have a good reason, and it costs nothing for us to define the -behavior in this case. -

-

-The aliasing constructor is sharp enough as it is, so "protecting" users -doesn't make much sense in this particular case. -

-

-> Do you have a use case for r being empty and r being non-null? -

-

-I have received a few requests for it from "performance-conscious" -people (you should be familiar with this mindset) who don't like the -overhead of allocating and maintaining a control block when a null -deleter is used to approximate a raw pointer. It is obviously an "at -your own risk", low-level feature; essentially a raw pointer behind a -shared_ptr facade. -

-

-We could not agree upon a resolution to the issue; some of us thought -that Peter's description above is supporting an undesirable behavior. -

-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-We favor option 1, move to Ready. -

-

[ -Howard: Option 2 commented out for clarity, and can be brought back. -]

- -
- - - -

Proposed resolution:

-

-In keeping the N2351 spirit and obviously my preference, change 20.8.2.2.5 [util.smartptr.shared.obs]: -

- -
-
-T* get() const;
-
-

-Returns: the stored pointer. Returns a null pointer if *this is empty. -

-
- - - - - - - - -
-

712. seed_seq::size no longer useful

-

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 - Submitter: Marc Paterno Opened: 2007-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-One of the motivations for incorporating seed_seq::size() -was to simplify the wording -in other parts of 26.5 [rand]. -As a side effect of resolving related issues, -all such references -to seed_seq::size() will have been excised. -More importantly, -the present specification is contradictory, -as "The number of 32-bit units the object can deliver" -is not the same as "the result of v.size()." -

- -

-See N2391 and -N2423 -for some further discussion. -

- - -

Proposed resolution:

-

-Adopt the proposed resolution in -N2423. -

- - -

[ -Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. -The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. -]

- - - - - -
-

713. sort() complexity is too lax

-

Section: 25.4.1.1 [sort] Status: CD1 - Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2015-04-08

-

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-

Discussion:

-

-The complexity of sort() is specified as "Approximately N -log(N) (where N == last - first ) comparisons on the -average", with no worst case complicity specified. The intention was to -allow a median-of-three quicksort implementation, which is usually O(N -log N) but can be quadratic for pathological inputs. However, there is -no longer any reason to allow implementers the freedom to have a -worst-cast-quadratic sort algorithm. Implementers who want to use -quicksort can use a variant like David Musser's "Introsort" (Software -Practice and Experience 27:983-993, 1997), which is guaranteed to be O(N -log N) in the worst case without incurring additional overhead in the -average case. Most C++ library implementers already do this, and there -is no reason not to guarantee it in the standard. -

- - -

Proposed resolution:

-

-In 25.4.1.1 [sort], change the complexity to "O(N log N)", and remove footnote 266: -

- -
-

-Complexity: Approximately O(N log(N)) (where N == last - first ) -comparisons on the average.266) -

-

-266) -If the worst case behavior is important stable_sort() (25.3.1.2) or partial_sort() -(25.3.1.3) should be used. -

-
- - - - - - -
-

714. search_n complexity is too lax

-

Section: 25.2.13 [alg.search] Status: CD1 - Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The complexity for search_n (25.2.13 [alg.search] par 7) is specified as "At most -(last - first ) * count applications of the corresponding predicate if -count is positive, or 0 otherwise." This is unnecessarily pessimistic. -Regardless of the value of count, there is no reason to examine any -element in the range more than once. -

- - -

Proposed resolution:

-

-Change the complexity to "At most (last - first) applications of the corresponding predicate". -

- -
-
-template<class ForwardIterator, class Size, class T> 
-  ForwardIterator 
-    search_n(ForwardIterator first , ForwardIterator last , Size count , 
-             const T& value ); 
-
-template<class ForwardIterator, class Size, class T, 
-         class BinaryPredicate> 
-  ForwardIterator 
-    search_n(ForwardIterator first , ForwardIterator last , Size count , 
-             const T& value , BinaryPredicate pred );
-
-
-

-Complexity: At most (last - first ) * count applications of the corresponding predicate -if count is positive, or 0 otherwise. -

-
-
- - - - - - -
-

715. minmax_element complexity is too lax

-

Section: 25.4.7 [alg.min.max] Status: CD1 - Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The complexity for minmax_element (25.4.7 [alg.min.max] par 16) says "At most max(2 * -(last - first ) - 2, 0) applications of the corresponding comparisons", -i.e. the worst case complexity is no better than calling min_element and -max_element separately. This is gratuitously inefficient. There is a -well known technique that does better: see section 9.1 of CLRS -(Introduction to Algorithms, by Cormen, Leiserson, Rivest, and Stein). -

- - -

Proposed resolution:

-

-Change 25.4.7 [alg.min.max] to: -

- -
-
-template<class ForwardIterator> 
-  pair<ForwardIterator, ForwardIterator> 
-    minmax_element(ForwardIterator first , ForwardIterator last); 
-template<class ForwardIterator, class Compare> 
-  pair<ForwardIterator, ForwardIterator> 
-    minmax_element(ForwardIterator first , ForwardIterator last , Compare comp);
-
-
-

-Returns: make_pair(m, M), where m is -min_element(first, last) or min_element(first, last, -comp) the first iterator in [first, -last) such that no iterator in the range refers to a smaller element, and -where M is max_element(first, last) or -max_element(first, last, comp) the last iterator -in [first, last) such that no iterator in the range refers to a larger element. -

-

-Complexity: At most max(2 * (last - first ) - 2, 0) -max(⌊(3/2) (N-1)⌋, 0) applications of the -corresponding comparisons predicate, where N is distance(first, last). -

-
-
- - - - - - -
-

716. Production in [re.grammar] not actually modified

-

Section: 28.13 [re.grammar] Status: C++11 - Submitter: Stephan T. Lavavej Opened: 2007-08-31 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-TR1 7.13 [tr.re.grammar]/3 and C++0x WP 28.13 [re.grammar]/3 say: -

- -
-

-The following productions within the ECMAScript grammar are modified as follows: -

- -
-CharacterClass ::
-[ [lookahead ∉ {^}] ClassRanges ]
-[ ^ ClassRanges ]
-
- -
- -

-This definition for CharacterClass appears to be exactly identical to that in ECMA-262. -

- -

-Was an actual modification intended here and accidentally omitted, or was this production accidentally included? -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree that what is specified is identical to what ECMA-262 specifies. -Pete would like to take a bit of time to assess whether we had intended, -but failed, to make a change. -It would also be useful to hear from John Maddock on the issue. -

-

-Move to Open. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Remove this mention of the CharacterClass production. -

- -
-CharacterClass ::
-[ [lookahead ∉ {^}] ClassRanges ]
-[ ^ ClassRanges ]
-
- - - - - - -
-

719. std::is_literal type traits should be provided

-

Section: 20.10 [meta] Status: Resolved - Submitter: Daniel Krügler Opened: 2007-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 750

-

Discussion:

-

-Since the inclusion of constexpr in the standard draft N2369 we have -a new type category "literal", which is defined in 3.9 [basic.types]/p.11: -

- -
-

--11- A type is a literal type if it is: -

-
    -
  • a scalar type; or
    • -

  • a class type (clause 9) with

    -
      -
    • a trivial copy constructor,
      • -
    • a trivial destructor,
      • -
    • at least one constexpr constructor other than the copy constructor,
      • -
    • no virtual base classes, and
      • -
    • all non-static data members and base classes of literal types; or
      • -
    -
    • -
  • an array of literal type.
    • -
-
- -

-I strongly suggest that the standard provides a type traits for -literal types in 20.10.4.3 [meta.unary.prop] for several reasons: -

- -
    -
  1. To keep the traits in sync with existing types.
    2. -
  2. I see many reasons for programmers to use this trait in template - code to provide optimized template definitions for these types, - see below.
    3. -
  3. A user-provided definition of this trait is practically impossible -to write portably.
    4. -
- -

-The special problem of reason (c) is that I don't see currently a -way to portably test the condition for literal class types: -

- -
-
    -
  • at least one constexpr constructor other than the copy constructor,
    • -
-
- -

[ -Alisdair is considering preparing a paper listing a number of missing -type traits, and feels that it might be useful to handle them all -together rather than piecemeal. This would affect issue 719 and 750. -These two issues should move to OPEN pending AM paper on type traits. -]

- - -

[ -2009-07 Frankfurt: -]

- - -

-Beman, Daniel, and Alisdair will work on a paper proposing new type traits. -

- -

[ -Addressed in N2947. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2984. -

- - - -

Proposed resolution:

-

-In 20.10.2 [meta.type.synop] in the group "type properties", -just below the line -

- -
-template <class T> struct is_pod;
-
- -

-add a new one: -

- -
-template <class T> struct is_literal;
-
- -

-In 20.10.4.3 [meta.unary.prop], table Type Property Predicates, just -below the line for the is_pod property add a new line: -

- - - - - - - - - - -
TemplateConditionPreconditions
template <class T> struct is_literal;T is a literal type (3.9)T shall be a complete type, an -array of unknown bound, or -(possibly cv-qualified) void.
- - - - - - -
-

720. Omissions in constexpr usages

-

Section: 23.3.2 [array], 20.6 [template.bitset] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-
    -
  1. -The member function bool array<T,N>::empty() const should be a -constexpr because this is easily to proof and to implement following it's operational -semantics defined by Table 87 (Container requirements) which says: a.size() == 0. -
    2. -
  2. -The member function bool bitset<N>::test() const must be a -constexpr (otherwise it would violate the specification of constexpr -bitset<N>::operator[](size_t) const, because it's return clause delegates to test()). -
    3. -
  3. -I wonder how the constructor bitset<N>::bitset(unsigned long) can -be declared as a constexpr. Current implementations usually have no such bitset -c'tor which would fulfill the requirements of a constexpr c'tor because they have a -non-empty c'tor body that typically contains for-loops or memcpy to compute the -initialisation. What have I overlooked here? -
    4. -
- -

[ -Sophia Antipolis: -]

- - -
-

-We handle this as two parts -

-
    -
  1. -The proposed resolution is correct; move to ready. -
    2. -
  2. -The issue points out a real problem, but the issue is larger than just -this solution. We believe a paper is needed, applying the full new -features of C++ (including extensible literals) to update std::bitset. -We note that we do not consider this new work, and that is should be -handled by the Library Working Group. -
    3. -
-

-In order to have a consistent working paper, Alisdair and Daniel produced a new wording for the resolution. -

-
- - - -

Proposed resolution:

-
    -
  1. -

    In the class template definition of 23.3.2 [array]/p. 3 change

    -
    -constexpr bool empty() const;
-
    -
    2. - -
  2. -

    In the class template definition of 20.6 [template.bitset]/p. 1 change

    -
    -constexpr bool test(size_t pos ) const;
-
    - -

    -and in 20.6.2 [bitset.members] change -

    - -
    -constexpr bool test(size_t pos ) const;
-
    - -
    3. -
- - - - - -
-

722. Missing [c.math] functions nanf and nanl

-

Section: 26.8 [c.math] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-08-27 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In the listing of 26.8 [c.math], table 108: Header <cmath> synopsis I miss -the following C99 functions (from 7.12.11.2): -

- -
-float nanf(const char *tagp);
-long double nanl(const char *tagp);
-
- -

-(Note: These functions cannot be overloaded and they are also not -listed anywhere else) -

- - -

Proposed resolution:

-

-In 26.8 [c.math], table 108, section "Functions", add nanf and nanl -just after the existing entry nan. -

- - - - - -
-

723. basic_regex should be moveable

-

Section: 28.8 [re.regex] Status: C++11 - Submitter: Daniel Krügler Opened: 2007-08-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 316

- -

-According to the current state of the standard draft, the class -template basic_regex, as described in 28.8 [re.regex]/3, is -neither MoveConstructible nor MoveAssignable. -IMO it should be, because typical regex state machines tend -to have a rather large data quantum and I have seen several -use cases, where a factory function returns regex values, -which would take advantage of moveabilities. -

- -

[ -Sophia Antipolis: -]

- - -

-Needs wording for the semantics, the idea is agreed upon. -

- -

[ -Post Summit Daniel updated wording to reflect new "swap rules". -]

- - -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-In the class definition of basic_regex, just below 28.8 [re.regex]/3, -perform the following changes: -

- -
    -
  1. -

    -Just after basic_regex(const basic_regex&); insert: -

    - -
    -basic_regex(basic_regex&&);
-
    -
    2. -
  2. -

    -Just after basic_regex& operator=(const basic_regex&); insert: -

    -
    -basic_regex& operator=(basic_regex&&);
-
    -
    3. -
  3. -

    -Just after basic_regex& assign(const basic_regex& that); insert: -

    -
    -basic_regex& assign(basic_regex&& that);
-
    -
    4. -
  4. -

    -In 28.8.2 [re.regex.construct], just after p.11 add the following -new member definition: -

    -
    -basic_regex(basic_regex&& e);
-
    -
    -

    -Effects: Move-constructs a basic_regex instance from e. -

    -

    -Postconditions: flags() and mark_count() return e.flags() and -e.mark_count(), respectively, -that e had before construction, leaving -e in a valid state with an unspecified value. -

    -

    -Throws: nothing. -

    -
    -
    -
    5. -
  5. -

    -Also in 28.8.2 [re.regex.construct], just after p.18 add the -following new member definition: -

    - -
    -basic_regex& operator=(basic_regex&& e);
-
    -

    -Effects: Returns the result of assign(std::move(e)). -

    -
    -
    6. -
  6. -

    -In 28.8.3 [re.regex.assign], just after p. 2 add the following new -member definition: -

    -
    -basic_regex& assign(basic_regex&& rhs);
-
    -
    -

    -Effects: Move-assigns a basic_regex instance from rhs and returns *this. -

    -

    -Postconditions: flags() and mark_count() return rhs.flags() -and rhs.mark_count(), respectively, that -rhs had before assignment, leaving rhs -in a valid state with an unspecified value. -

    -

    -Throws: nothing. -

    -
    -
    -
    7. -
- - - - - -
-

724. DefaultConstructible is not defined

-

Section: 17.6.3.1 [utility.arg.requirements] Status: C++11 - Submitter: Pablo Halpern Opened: 2007-09-12 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with C++11 status.

-

Discussion:

-

-The DefaultConstructible requirement is referenced in -several places in the August 2007 working draft -N2369, -but is not defined anywhere. -

- -

[ -Bellevue: -]

- - -
-

-Walking into the default/value-initialization mess... -

-

-Why two lines? Because we need both expressions to be valid. -

-

-AJM not sure what the phrase "default constructed" means. This is -unfortunate, as the phrase is already used 24 times in the library! -

-

-Example: const int would not accept first line, but will accept the second. -

-

-This is an issue that must be solved by concepts, but we might need to solve it independantly first. -

-

-It seems that the requirements are the syntax in the proposed first -column is valid, but not clear what semantics we need. -

-

-A table where there is no post-condition seems odd, but appears to sum up our position best. -

-

-At a minimum an object is declared and is destructible. -

-

-Move to open, as no-one happy to produce wording on the fly. -

-
- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-08-17 Daniel adds "[defaultconstructible]" to table title. 408 -depends upon this issue. -]

- - -

[ -2009-08-18 Alisdair adds: -]

- - -
-

-Looking at the proposed table in this issue, it really needs two rows: -

- -
- - - - - - - - - - - - - -
Table 33: DefaultConstructible requirements [defaultconstructible]
expressionpost-condition
T t;t is default-initialized.
T{}Object of type T is value-initialized.
-
- -

-Note I am using the new brace-initialization syntax that is unambiguous -in all use cases (no most vexing parse.) -

-
- -

[ -2009-10-03 Daniel adds: -]

- - -
-

-The suggested definition T{} describing it as -value-initialization is wrong, because it belongs to list-initialization -which would - as the current rules are - always prefer a -initializer-list constructor over a default-constructor. I don't -consider this as an appropriate definition of -DefaultConstructible. My primary suggestion is to ask core, -whether the special case T{} (which also easily leads to -ambiguity situations for more than one initializer-list in a class) -would always prefer a default-constructor - if any - before considering -an initializer-list constructor or to provide another syntax form to -prefer value-initialization over list-initialization. If that fails I -would fall back to suggest to use the expression T() instead of -T{} with all it's disadvantages for the meaning of the -expression -

- -
-T t();
-
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave Open. Core is looking to make Alisdair's proposed -resolution correct. -

- -

[ -2010-01-24 At Alisdair's request, moved his proposal into the proposed wording -section. The old wording is preserved here: -]

- - -
-

-In section 17.6.3.1 [utility.arg.requirements], before table 33, add the -following table: -

- -

Table 33: DefaultConstructible -requirements [defaultconstructible]

- - - - - - - - - - -
-

expression

- 		-

post-condition

-
-

T t;
- T()

- 		-

T is default constructed.

-
- -
- -

[ -2010-02-04: Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Rationale:

-

[ -San Francisco: -]

- -

-We believe concepts will solve this problem -(N2774). -

- -

[ -Rationale is obsolete. -]

- - - -

Proposed resolution:

-

-In section 17.6.3.1 [utility.arg.requirements], before table 33, add the -following table: -

- -
- - - - - - - - - - - - - - - - - - -
Table 33: DefaultConstructible requirements [defaultconstructible]
expressionpost-condition
T t;Object t is default-initialized.
T u{};Object u is value-initialized.
T()
T{}		A temporary object of type T is value-initialized.
-
- - - - - - -
-

727. regex_replace() doesn't accept basic_strings with custom traits and allocators

-

Section: 28.11.4 [re.alg.replace] Status: C++11 - Submitter: Stephan T. Lavavej Opened: 2007-09-22 Last modified: 2015-04-08

-

View all other issues in [re.alg.replace].

-

View all issues with C++11 status.

-

Discussion:

-

-regex_match() and regex_search() take const basic_string<charT, ST, -SA>&. regex_replace() takes const basic_string<charT>&. This prevents -regex_replace() from accepting basic_strings with custom traits and -allocators. -

- -

-Overloads of regex_replace() taking basic_string should be additionally -templated on class ST, class SA and take const basic_string<charT, ST, -SA>&. Consistency with regex_match() and regex_search() would place -class ST, class SA as the first template arguments; compatibility with -existing code using TR1 and giving explicit template arguments to -regex_replace() would place class ST, class SA as the last template -arguments. -

- -

[ -Batavia (2009-05): -]

- -
-

-Bill comments, "We need to look at the depth of this change." -

-

-Pete remarks that we are here dealing with a convenience function -that saves a user from calling the iterato-based overload. -

-

-Move to Open. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Howard to ask Stephan Lavavej to provide wording. -

- -

[ -2009-07-17 Stephan provided wording. -]

- - -

[ -2009-07-25 Daniel tweaks both this issue and 726. -]

- - -
-

-One relevant part of the proposed resolution below suggests -to add a new overload of the format member function in the -match_results class template that accepts two character pointers -defining the begin and end of a format range. A more general -approach could have proposed a pair of iterators instead, but -the used pair of char pointers reflects existing practice. If the -committee strongly favors an iterator-based signature, this -could be simply changed. I think that the minimum requirement -should be a BidirectionalIterator, but current implementations -take advantage (at least partially) of the RandomAccessIterator -sub interface of the char pointers. -

- -

Suggested Resolution:

- -

[Moved into the proposed resloution]

- - - -
- -

[ -2009-07-30 Stephan agrees with Daniel's wording. Howard places Daniel's wording -in the Proposed Resolution. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Review. Chair is anxious to move this to Ready in Pittsburgh. -

- -

[ -2010-01-27 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -
    -
  1. -

    -Change 28.4 [re.syn] as indicated: -

    - -
    -// 28.11.4, function template regex_replace:
-template <class OutputIterator, class BidirectionalIterator,
-          class traits, class charT, class ST, class SA>
-  OutputIterator
-  regex_replace(OutputIterator out,
-                BidirectionalIterator first, BidirectionalIterator last,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, ST, SA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-template <class OutputIterator, class BidirectionalIterator,
-          class traits, class charT>
-  OutputIterator
-  regex_replace(OutputIterator out,
-                BidirectionalIterator first, BidirectionalIterator last,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-template <class traits, class charT, class ST, class SA,
-          class FST, class FSA>
-  basic_string<charT, ST, SA>
-  regex_replace(const basic_string<charT, ST, SA>& s,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, FST, FSA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-template <class traits, class charT, class ST, class SA>
-  basic_string<charT, ST, SA>
-  regex_replace(const basic_string<charT, ST, SA>& s,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-
-template <class traits, class charT, class ST, class SA>
-  basic_string<charT>
-  regex_replace(const charT* s,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, ST, SA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-
-template <class traits, class charT>
-  basic_string<charT>
-  regex_replace(const charT* s,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
    -
    2. - -
  2. -

    -Change 28.10 [re.results]/3, class template match_results as -indicated: -

    - -
    -
-template <class OutputIter>
-  OutputIter
-  format(OutputIter out,
-         const char_type* fmt_first, const char_type* fmt_last,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
-
-template <class OutputIter, class ST, class SA>
-  OutputIter
-  format(OutputIter out,
-         const string_typebasic_string<char_type, ST, SA>& fmt,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
-template <class ST, class SA>
-  string_typebasic_string<char_type, ST, SA>
-  format(const string_typebasic_string<char_type, ST, SA>& fmt,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
-
-string_type
-format(const char_type* fmt,
-       regex_constants::match_flag_type flags =
-         regex_constants::format_default) const;
-
-
    -
    3. - -
  3. -

    -Insert at the very beginning of 28.10.5 [re.results.form] the following: -

    - -
    -
-template <class OutputIter>
-  OutputIter
-  format(OutputIter out,
-         const char_type* fmt_first, const char_type* fmt_last,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
-
    -
    - -

    -1 Requires: The type OutputIter shall satisfy the requirements for an -Output Iterator (24.2.4 [output.iterators]). -

    - -

    -2 Effects: Copies the character sequence [fmt_first,fmt_last) to -OutputIter out. Replaces each format specifier or escape sequence in -the copied range with either the character(s) it represents or the sequence of -characters within *this to which it refers. The bitmasks specified in -flags determine which format specifiers and escape sequences are -recognized. -

    - -

    -3 Returns: out. -

    -
    -
    -
    4. - -
  4. -

    -Change 28.10.5 [re.results.form], before p. 1 until p. 3 as indicated: -

    - -
    -template <class OutputIter, class ST, class SA>
-  OutputIter
-  format(OutputIter out,
-         const string_typebasic_string<char_type, ST, SA>& fmt,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
    - -
    -

    -1 Requires: The type OutputIter shall satisfy the requirements for -an Output Iterator (24.2.3). -

    - -

    -2 Effects: Copies the character sequence -[fmt.begin(),fmt.end()) to OutputIter out. Replaces each -format specifier or escape sequence in fmt with either the character(s) -it represents or the sequence of characters within *this to which it -refers. The bitmasks specified in flags determines what format -specifiers and escape sequences are recognized Equivalent to -return format(out, fmt.data(), fmt.data() + fmt.size(), flags). -

    - -

    -3 Returns: out. -

    -
    -
    -
    5. - -
  5. -

    -Change 28.10.5 [re.results.form], before p. 4 until p. 4 as indicated: -

    - -
    -template <class ST, class SA>
-  string_typebasic_string<char_type, ST, SA>
-  format(const string_typebasic_string<char_type, ST, SA>& fmt,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
    - -
    -

    -Effects: Returns a copy of the string fmt. Replaces each format -specifier or escape sequence -in fmt with either the character(s) it represents or the sequence of -characters within *this to which -it refers. The bitmasks specified in flags determines what format -specifiers and escape sequences are -recognized. Constructs an empty string result of type -basic_string<char_type, ST, SA>, -and calls format(back_inserter(result), fmt, flags). -

    - -

    -Returns: result -

    -
    -
    -
    6. - -
  6. -

    -At the end of 28.10.5 [re.results.form] insert as indicated: -

    - -
    -
-string_type
-  format(const char_type* fmt,
-         regex_constants::match_flag_type flags =
-           regex_constants::format_default) const;
-
    - -
    -

    -Effects: Constructs an empty string result of type string_type, and calls -format(back_inserter(result), fmt, fmt + -char_traits<char_type>::length(fmt), flags). -

    -

    -Returns: result -

    -
    -
    - -
    7. - -
  7. -

    -Change 28.11.4 [re.alg.replace] before p. 1 as indicated: -

    - -
    -template <class OutputIterator, class BidirectionalIterator,
-          class traits, class charT, class ST, class SA>
-  OutputIterator
-  regex_replace(OutputIterator out,
-                BidirectionalIterator first, BidirectionalIterator last,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, ST, SA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-template <class OutputIterator, class BidirectionalIterator,
-          class traits, class charT>
-  OutputIterator
-  regex_replace(OutputIterator out,
-                BidirectionalIterator first, BidirectionalIterator last,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
    - -

    -Effects: [..]. If any matches are found then, for each such match, if !(flags & - regex_constants::format_no_copy) calls std::copy(m.prefix().first, -m.prefix().second, - out), and then calls m.format(out, fmt, flags) for the first -form of the function - and m.format(out, fmt, fmt + char_traits<charT>::length(fmt), flags) -for the second - form. [..]. -

    -
    -
    8. - -
  8. -

    -Change 28.11.4 [re.alg.replace] before p. 3 as indicated: -

    - -
    -template <class traits, class charT, class ST, class SA,
-          class FST, class FSA>
-  basic_string<charT, ST, SA>
-  regex_replace(const basic_string<charT, ST, SA>& s,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, FST, FSA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-template <class traits, class charT, class ST, class SA>
-  basic_string<charT, ST, SA>
-  regex_replace(const basic_string<charT, ST, SA>& s,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
    - -

    -Effects: Constructs an empty string result of type basic_string<charT, -ST, SA>, calls regex_replace(back_inserter(result), s.begin(), s.end(), -e, fmt, flags), and then returns result. -

    -
    -
    9. - -
  9. -

    -At the end of 28.11.4 [re.alg.replace] add the following new prototype description: -

    - -
    -
-template <class traits, class charT, class ST, class SA>
-  basic_string<charT>
-  regex_replace(const charT* s,
-                const basic_regex<charT, traits>& e,
-                const basic_string<charT, ST, SA>& fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
-
-
-template <class traits, class charT>
-  basic_string<charT>
-  regex_replace(const charT* s,
-                const basic_regex<charT, traits>& e,
-                const charT* fmt,
-                regex_constants::match_flag_type flags =
-                  regex_constants::match_default);
-
    - -

    - -Effects: Constructs an empty string result of type basic_string<charT>, -calls regex_replace(back_inserter(result), s, s + -char_traits<charT>::length(s), -e, fmt, flags), and then returns result. - -

    -
    -
    10. - -
- - - - - - - -
-

728. Problem in [rand.eng.mers]/6

-

Section: 26.5.3.2 [rand.eng.mers] Status: CD1 - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

View all other issues in [rand.eng.mers].

-

View all issues with CD1 status.

-

Discussion:

-

-The mersenne_twister_engine is required to use a seeding method that is given -as an algorithm parameterized over the number of bits W. I doubt whether the given generalization -of an algorithm that was originally developed only for unsigned 32-bit integers is appropriate -for other bit widths. For instance, W could be theoretically 16 and UIntType a 16-bit integer, in -which case the given multiplier would not fit into the UIntType. Moreover, T. Nishimura and M. -Matsumoto have chosen a dif ferent multiplier for their 64 bit Mersenne Twister -[reference]. -

- -

-I see two possible resolutions: -

- -
    -
  1. Restrict the parameter W of the mersenne_twister_template to values of 32 or 64 and use the -multiplier from [the above reference] for the 64-bit case (my preference)
    2. -
  2. Interpret the state array for any W as a 32-bit array of appropriate length (and a specified byte -order) and always employ the 32-bit algorithm for seeding -
    3. -
- -

-See N2424 -for further discussion. -

- -

[ -Bellevue: -]

- - -
-

-Stephan Tolksdorf has additional comments on N2424. He comments: "there -is a typo in the required behaviour for mt19937_64: It should be the -10000th (not 100000th) invocation whose value is given, and the value -should be 9981545732273789042 (not 14002232017267485025)." These values -need checking. -

-

-Take the proposed recommendation in N2424 and move to REVIEW. -

-
- - - - -

Proposed resolution:

- -

-See N2424 -for the proposed resolution. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -

-I support the proposed resolution in -N2424, -but there is a typo in the -required behaviour for mt19937_64: It should be the 10000th (not -100000th) invocation whose value is given, and the value should be -9981545732273789042 (not 14002232017267485025). The change to para. 8 -proposed by Charles Karney should also be included in the proposed -wording. -

- -

[ -Sophia Antipolis: -]

- - -

-Note the main part of the issue is resolved by -N2424. -

- - - - - - -
-

732. Defect in [rand.dist.samp.genpdf]

-

Section: X [rand.dist.samp.genpdf] Status: Resolved - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.genpdf].

-

View all issues with Resolved status.

-

Duplicate of: 795

-

Discussion:

-

-X [rand.dist.samp.genpdf] describes the interface for a distribution template that is -meant to simulate random numbers from any general distribution given only the density and the -support of the distribution. I'm not aware of any general purpose algorithm that would be capable -of correctly and efficiently implementing the described functionality. From what I know, this is -essentially an unsolved research problem. Existing algorithms either require more knowledge -about the distribution and the problem domain or work only under very limited circumstances. -Even the state of the art special purpose library UNU.RAN does not solve the problem in full -generality, and in any case, testing and customer support for such a library feature would be a -nightmare. -

- -

-Possible resolution: For these reasons, I propose to delete section X [rand.dist.samp.genpdf]. -

- -

[ -Bellevue: -]

- - -
-

-Disagreement persists. -

-

-Objection to this issue is that this function takes a general functor. -The general approach would be to normalize this function, integrate it, -and take the inverse of the integral, which is not possible in general. -An example function is sin(1+n*x) — for any spatial frequency that the -implementor chooses, there is a value of n that renders that choice -arbitrarily erroneous. -

-

-Correction: The formula above should instead read 1+sin(n*x). -

-

-Objector proposes the following possible compromise positions: -

-
    -
  • -rand.dist.samp.genpdf takes an number of points so that implementor need not guess. -
    • -
  • -replace rand.disk.samp.genpdf with an extension to either or both of the discrete -functions to take arguments that take a functor and number of points in place of -the list of probabilities. Reference issues 793 and 794. -
    • -
-
- - - -

Proposed resolution:

-

-See N2813 -for the proposed resolution. -

- - -

Rationale:

-Addressed by -N2836 -"Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - -
-

734. Unnecessary restriction in [rand.dist.norm.chisq]

-

Section: 26.5.8.5.3 [rand.dist.norm.chisq] Status: CD1 - Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-chi_squared_distribution, fisher_f_distribution and student_t_distribution -have parameters for the "degrees of freedom" n and m that are specified as integers. For the -following two reasons this is an unnecessary restriction: First, in many applications such as -Bayesian inference or Monte Carlo simulations it is more convenient to treat the respective param- -eters as continuous variables. Second, the standard non-naive algorithms (i.e. -O(1) algorithms) for simulating from these distributions work with floating-point parameters anyway (all -three distributions could be easily implemented using the Gamma distribution, for instance). -

- -

-Similar arguments could in principle be made for the parameters t and k of the discrete -binomial_distribution and negative_binomial_distribution, though in both cases continuous -parameters are less frequently used in practice and in case of the binomial_distribution -the implementation would be significantly complicated by a non-discrete parameter (in most -implementations one would need an approximation of the log-gamma function instead of just the -log-factorial function). -

- -

-Possible resolution: For these reasons, I propose to change the type of the respective parameters -to double. -

- -

[ -Bellevue: -]

- - -

-In N2424. Not wildly enthusiastic, not really felt necessary. Less -frequently used in practice. Not terribly bad either. Move to OPEN. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Marc Paterno: The generalizations were explicitly left out when designing the facility. It's harder to test. -

-

-Marc Paterno: Ask implementers whether floating-point is a significant burden. -

-

-Alisdair: It's neater to do it now, do ask Bill Plauger. -

-

-Disposition: move to review with the option for "NAD" if it's not straightforward to implement; unanimous consent. -

-
- - - -

Proposed resolution:

-

-See N2424 -for the proposed resolution. -

- -

[ -Stephan Tolksdorf adds pre-Bellevue: -]

- - -
-

-In 26.5.8.5.3 [rand.dist.norm.chisq]: -

- -
-

-Delete ", where n is a positive integer" in the first paragraph. -

- -

-Replace both occurrences of "explicit chi_squared_distribution(int n = 1);" -with "explicit chi_squared_distribution(RealType n = 1);". -

- -

-Replace both occurrences of "int n() const;" with "RealType n() const;". -

- -
- -

-In 26.5.8.5.5 [rand.dist.norm.f]: -

-
-

-Delete ", where m and n are positive integers" in the first paragraph. -

- -

-Replace both occurrences of -

-
-explicit fisher_f_distribution(int m = 1, int n = 1);
-
-

-with -

-
-explicit fisher_f_distribution(RealType m = 1, RealType n = 1);
-
- -

-Replace both occurrences of "int m() const;" with "RealType m() const;". -

- -

-Replace both occurrences of "int n() const;" with "RealType n() const;". -

-
- -

-In 26.5.8.5.6 [rand.dist.norm.t]: -

- -
-

-Delete ", where n is a positive integer" in the first paragraph. -

- -

-Replace both occurrences of "explicit student_t_distribution(int n = 1);" -with "explicit student_t_distribution(RealType n = 1);". -

- -

-Replace both occurrences of "int n() const;" with "RealType n() const;". -

-
- -
- - - - - -
-

740. Please remove *_ptr<T[N]>

-

Section: 20.8.1 [unique.ptr] Status: CD1 - Submitter: Herb Sutter Opened: 2007-10-04 Last modified: 2015-04-08

-

View all other issues in [unique.ptr].

-

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-

Discussion:

-

-Please don't provide *_ptr<T[N]>. It doesn't enable any useful -bounds-checking (e.g., you could imagine that doing op++ on a -shared_ptr<T[N]> yields a shared_ptr<T[N-1]>, but that promising path -immediately falters on op-- which can't reliably dereference because we -don't know the lower bound). Also, most buffers you'd want to point to -don't have a compile-time known size. -

- -

-To enable any bounds-checking would require run-time information, with -the usual triplet: base (lower bound), current offset, and max offset -(upper bound). And I can sympathize with the point of view that you -wouldn't want to require this on *_ptr itself. But please let's not -follow the <T[N]> path, especially not with additional functions to -query the bounds etc., because this sets wrong user expectations by -embarking on a path that doesn't go all the way to bounds checking as it -seems to imply. -

- -

-If bounds checking is desired, consider a checked_*_ptr instead (e.g., -checked_shared_ptr). And make the interfaces otherwise identical so that -user code could easily #define/typedef between prepending checked_ on -debug builds and not doing so on release builds (for example). -

- -

-Note that some may object that checked_*_ptr may seem to make the smart -pointer more like vector, and we don't want two ways to spell vector. I -don't agree, but if that were true that would be another reason to -remove *_ptr<T[N]> which equally makes the smart pointer more like -std::array. :-) -

- -

[ -Bellevue: -]

- - -
-

-Suggestion that fixed-size array instantiations are going to fail at compile time anyway (if we remove specialization) due to pointer decay, at least that appears to be result from available compilers. -

-

-So concerns about about requiring static_assert seem unfounded. -

-

-After a little more experimentation with compiler, it appears that fixed size arrays would only work at all if we supply these explicit specialization. So removing them appears less breaking than originally thought. -

-

-straw poll unanimous move to Ready. -

-
- - - -

Proposed resolution:

-

-Change the synopsis under 20.8.1 [unique.ptr] p2: -

- -
-...
-template<class T> struct default_delete; 
-template<class T> struct default_delete<T[]>; 
-template<class T, size_t N> struct default_delete<T[N]>;
-
-template<class T, class D = default_delete<T>> class unique_ptr; 
-template<class T, class D> class unique_ptr<T[], D>; 
-template<class T, class D, size_t N> class unique_ptr<T[N], D>;
-...
-
- -

-Remove the entire section [unique.ptr.dltr.dflt2] default_delete<T[N]>. -

- -

-Remove the entire section [unique.ptr.compiletime] unique_ptr for array objects with a compile time length -and its subsections: [unique.ptr.compiletime.dtor], [unique.ptr.compiletime.observers], - [unique.ptr.compiletime.modifiers]. -

- - - - - - -
-

742. Enabling swap for proxy iterators

-

Section: 17.6.3.1 [utility.arg.requirements] Status: Resolved - Submitter: Howard Hinnant Opened: 2007-10-10 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

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-

Discussion:

-

-This issue was split from 672. 672 now just -deals with changing the requirements of T in the Swappable -requirement from CopyConstructible and CopyAssignable to -MoveConstructible and MoveAssignable. -

- -

-This issue seeks to widen the Swappable requirement to support proxy iterators. Here -is example code: -

- -
-namespace Mine {
-
-template <class T>
-struct proxy {...};
-
-template <class T>
-struct proxied_iterator
-{
-   typedef T value_type;
-   typedef proxy<T> reference;
-   reference operator*() const;
-   ...
-};
-
-struct A
-{
-   // heavy type, has an optimized swap, maybe isn't even copyable or movable, just swappable
-   void swap(A&);
-   ...
-};
-
-void swap(A&, A&);
-void swap(proxy<A>, A&);
-void swap(A&, proxy<A>);
-void swap(proxy<A>, proxy<A>);
-
-}  // Mine
-
-...
-
-Mine::proxied_iterator<Mine::A> i(...)
-Mine::A a;
-swap(*i1, a);
-
- -

-The key point to note in the above code is that in the call to swap, *i1 -and a are different types (currently types can only be Swappable with the -same type). A secondary point is that to support proxies, one must be able to pass rvalues -to swap. But note that I am not stating that the general purpose std::swap -should accept rvalues! Only that overloaded swaps, as in the example above, be allowed -to take rvalues. -

- -

-That is, no standard library code needs to change. We simply need to have a more flexible -definition of Swappable. -

- -

[ -Bellevue: -]

- - -
-

-While we believe Concepts work will define a swappable concept, we -should still resolve this issue if possible to give guidance to the -Concepts work. -

-

-Would an ambiguous swap function in two namespaces found by ADL break -this wording? Suggest that the phrase "valid expression" means such a -pair of types would still not be swappable. -

-

-Motivation is proxy-iterators, but facility is considerably more -general. Are we happy going so far? -

-

-We think this wording is probably correct and probably an improvement on -what's there in the WP. On the other hand, what's already there in the -WP is awfully complicated. Why do we need the two bullet points? They're -too implementation-centric. They don't add anything to the semantics of -what swap() means, which is there in the post-condition. What's wrong -with saying that types are swappable if you can call swap() and it -satisfies the semantics of swapping? -

-
- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as Open. Dave to provide wording. -

- -

[ -2009-11-08 Howard adds: -]

- - -

-Updated wording to sync with -N3000. -Also this issue is very closely related to 594. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added. -

- - - -

Rationale:

-

-Solved by N3048. -

- - -

Proposed resolution:

-

-Change 17.6.3.1 [utility.arg.requirements]: -

- -
- -

--1- The template definitions in the C++ Standard Library refer to various -named requirements whose details are set out in tables 31-38. In these -tables, T and V are is a types to be supplied by a C++ program -instantiating a template; a, b, and c are -values of type const T; s and t are modifiable -lvalues of type T; u is a value of type (possibly -const) T; and rv is a non-const -rvalue of type T; w is a value of type T; and v is a value of type V. -

- - - - - - - -
Table 37: Swappable requirements [swappable]
expressionReturn typePost-condition
swap(sw,tv)voidtw has the value originally -held by uv, and -uv has the value originally held -by tw
-

-The Swappable requirement is met by satisfying one or more of the following conditions: -

-
    -
  • -T is Swappable if T and V are -the same type and T satisfies the -MoveConstructible requirements (Table -33) and the -MoveAssignable requirements (Table -35); -
    • -
  • -T is Swappable with V if a namespace scope function named -swap exists in the same namespace as the definition of -T or V, such that the expression -swap(sw,t v) is valid and has the -semantics described in this table. -
    • -
  • -T is Swappable if T is an array type whose -element type is Swappable. -
    • -
-
-
- - - -

Rationale:

-

[ -post San Francisco: -]

- - -

-Solved by -N2758. -

- - - - - - -
-

743. rvalue swap for shared_ptr

-

Section: 20.8.2.2.8 [util.smartptr.shared.spec] Status: CD1 - Submitter: Howard Hinnant Opened: 2007-10-10 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-When the LWG looked at 674 in Kona the following note was made: -

- -

-We may need to open an issue to deal with the question of -whether shared_ptr needs an rvalue swap. -

- -

-This issue was opened in response to that note. -

- -

-I believe allowing rvalue shared_ptrs to swap is both -appropriate, and consistent with how other library components are currently specified. -

- -

[ -Bellevue: -]

- - -
-

-Concern that the three signatures for swap is needlessly complicated, -but this issue merely brings shared_ptr into equal complexity with the -rest of the library. Will open a new issue for concern about triplicate -signatures. -

-

-Adopt issue as written. -

-
- - -

Proposed resolution:

-

-Change the synopsis in 20.8.2.2 [util.smartptr.shared]: -

- -
-void swap(shared_ptr&& r);
-...
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);
-
- -

-Change 20.8.2.2.4 [util.smartptr.shared.mod]: -

- -
-void swap(shared_ptr&& r);
-
- -

-Change 20.8.2.2.8 [util.smartptr.shared.spec]: -

- -
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
-template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);
-
- - - - - -
-

744. What is the lifetime of an exception pointed to by an exception_ptr?

-

Section: 18.8.5 [propagation] Status: CD1 - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Without some lifetime guarantee, it is hard to know how this type can be -used. Very specifically, I don't see how the current wording would -guarantee and exception_ptr caught at the end of one thread could be safely -stored and rethrown in another thread - the original motivation for this -API. -

-

-(Peter Dimov agreed it should be clearer, maybe a non-normative note to -explain?) -

- -

[ -Bellevue: -]

- - -
-

-Agree the issue is real. -

-

-Intent is lifetime is similar to a shared_ptr (and we might even want to -consider explicitly saying that it is a shared_ptr< unspecified type >). -

-

-We expect that most implementations will use shared_ptr, and the -standard should be clear that the exception_ptr type is intended to be -something whose semantics are smart-pointer-like so that the user does -not need to worry about lifetime management. We still need someone to -draught those words - suggest emailing Peter Dimov. -

-

-Move to Open. -

-
- - -

Proposed resolution:

-

-Change 18.8.5 [propagation]/7: -

- -

--7- Returns: An exception_ptr object that refers to the currently -handled exception or a copy of the currently handled exception, or a -null exception_ptr object if no exception is being handled. -The referenced object remains valid at least as long as there is an -exception_ptr that refers to it. -If the function needs to allocate memory and the attempt -fails, it returns an exception_ptr object that refers to an instance of -bad_alloc. It is unspecified whether the return values of two successive -calls to current_exception refer to the same exception object. [Note: -that is, it is unspecified whether current_exception creates a new copy -each time it is called. --end note] -

- - - - - -
-

746. current_exception may fail with bad_alloc

-

Section: 18.8.5 [propagation] Status: CD1 - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I understand that the attempt to copy an exception may run out of memory, -but I believe this is the only part of the standard that mandates failure -with specifically bad_alloc, as opposed to allowing an -implementation-defined type derived from bad_alloc. For instance, the Core -language for a failed new expression is: -

-
-

-Any other allocation function that fails to allocate storage shall indicate -failure only by throwing an exception of a type that would match a handler -(15.3) of type std::bad_alloc (18.5.2.1). -

-
-

-I think we should allow similar freedom here (or add a blanket -compatible-exception freedom paragraph in 17) -

-

-I prefer the clause 17 approach myself, and maybe clean up any outstanding -wording that could also rely on it. -

-

-Although filed against a specific case, this issue is a problem throughout -the library. -

- -

[ -Bellevue: -]

- - -
-

-Is issue bigger than library? -

-

-No - Core are already very clear about their wording, which is inspiration for the issue. -

-

-While not sold on the original 18.7.5 use case, the generalised 17.4.4.8 wording is the real issue. -

-

-Accept the broad view and move to ready -

-
- - -

Proposed resolution:

-

-Add the following exemption clause to 17.6.5.12 [res.on.exception.handling]: -

- -

-A function may throw a type not listed in its Throws clause so long as it is -derived from a class named in the Throws clause, and would be caught by an -exception handler for the base type. -

- - - - - -
-

749. Currently has_nothrow_copy_constructor<T>::value is true if T has 'a' nothrow copy constructor.

-

Section: 20.10.4.3 [meta.unary.prop] Status: CD1 - Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

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-

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-

Discussion:

-

-Unfortunately a class can have multiple copy constructors, and I believe to -be useful this trait should only return true is ALL copy constructors are -no-throw. -

-

-For instance: -

-
-
-struct awkward {
- awkward( const awkward & ) throw() {}
- awkward( awkward & ) { throw "oops"; } };
-
-
- - -

Proposed resolution:

-

-Change 20.10.4.3 [meta.unary.prop]: -

- -
-
has_trivial_copy_constructor
-

-T is a trivial type (3.9) or a reference type or a class type with a trivial copy constructor -where all copy constructors are trivial (12.8). -

-
- -
-
has_trivial_assign
-

-T is neither const nor a reference type, and T is a trivial type (3.9) -or a class type with a trivial copy assignment operator where all copy assignment operators are trivial (12.8). -

-
- -
-
has_nothrow_copy_constructor
-

-has_trivial_copy_constructor<T>::value is true or T is a class type with -a where all copy constructors that is are -known not to throw any exceptions or T is an -array of such a class type -

-
- -
-
has_nothrow_assign
-

-T is neither const nor a reference type, and -has_trivial_assign<T>::value is true or T is a class type with a -where all copy -assignment operators takeing an lvalue of type T that is known not to -throw any exceptions or T is an array of such a class type. -

-
- - - - - - -
-

752. Allocator complexity requirement

-

Section: 17.6.3.5 [allocator.requirements] Status: C++11 - Submitter: Hans Boehm Opened: 2007-10-11 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

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-

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-

Discussion:

-

-Did LWG recently discuss 17.6.3.5 [allocator.requirements]-2, which states that "All the operations -on the allocators are expected to be amortized constant time."? -

-

-As I think I pointed out earlier, this is currently fiction for -allocate() if it has to obtain memory from the OS, and it's unclear to -me how to interpret this for construct() and destroy() if they deal with -large objects. Would it be controversial to officially let these take -time linear in the size of the object, as they already do in real life? -

-

-Allocate() more blatantly takes time proportional to the size of the -object if you mix in GC. But it's not really a new problem, and I think -we'd be confusing things by leaving the bogus requirements there. The -current requirement on allocate() is generally not important anyway, -since it takes O(size) to construct objects in the resulting space. -There are real performance issues here, but they're all concerned with -the constants, not the asymptotic complexity. -

- - -

Proposed resolution:

-

-Change 17.6.3.5 [allocator.requirements]/2: -

- -
-

--2- Table 39 describes the requirements on types manipulated through -allocators. All the operations on the allocators are expected to be -amortized constant time. Table 40 describes the -requirements on allocator types. -

-
- - - - - -
-

753. Move constructor in draft

-

Section: 17.6.3.1 [utility.arg.requirements] Status: C++11 - Submitter: Yechezkel Mett Opened: 2007-10-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The draft standard n2369 uses the term move constructor in a few -places, but doesn't seem to define it. -

- -

-MoveConstructible requirements are defined in Table 33 in 17.6.3.1 [utility.arg.requirements] as -follows: -

- -
- - - - - - - - - - - -
MoveConstructible requirements
expression post-condition
T t = rv t is equivalent to the value of rv before the construction
[Note: There is no requirement on the value of rv after the -construction. -- end note]
-
- -

-(where rv is a non-const rvalue of type T). -

- -

-So I assume the move constructor is the constructor that would be used -in filling the above requirement. -

- -

-For vector::reserve, vector::resize and the vector modifiers given in -23.3.6.5 [vector.modifiers] we have -

- -

-Requires: If value_type has a move constructor, that constructor shall -not throw any exceptions. -

- -

-Firstly "If value_type has a move constructor" is superfluous; every -type which can be put into a vector has a move constructor (a copy -constructor is also a move constructor). Secondly it means that for -any value_type which has a throwing copy constructor and no other move -constructor these functions cannot be used -- which I think will come -as a shock to people who have been using such types in vector until -now! -

- -

-I can see two ways to correct this. The simpler, which is presumably -what was intended, is to say "If value_type has a move constructor and -no copy constructor, the move constructor shall not throw any -exceptions" or "If value_type has a move constructor which changes the -value of its parameter,". -

- -

-The other alternative is add to MoveConstructible the requirement that -the expression does not throw. This would mean that not every type -that satisfies the CopyConstructible requirements also satisfies the -MoveConstructible requirements. It would mean changing requirements in -various places in the draft to allow either MoveConstructible or -CopyConstructible, but I think the result would be clearer and -possibly more concise too. -

- - -

Proposed resolution:

-

-Add new defintions to 17.3 [definitions]: -

- -
-

-move constructor -

-

-a constructor which accepts only rvalue arguments of that type, and modifies the rvalue as a -side effect during the construction. -

-

-move assignment operator -

-

-an assignment operator which accepts only rvalue arguments of that type, and modifies the rvalue as a -side effect during the assignment. -

-

-move assignment -

-

-use of the move assignment operator. -

-
- -

[ -Howard adds post-Bellevue: -]

- - -
-

-Unfortunately I believe the wording recommended by the LWG in Bellevue is incorrect. reserve et. al. -will use a move constructor if one is available, else it will use a copy constructor. A type may have both. -If the move constructor is used, it must not throw. If the copy constructor is used, it can throw. The -sentence in the proposed wording is correct without the recommended insertion. The Bellevue LWG recommended -moving this issue to Ready. I am unfortunately pulling it back to Open. But I'm drafting wording to atone -for this egregious action. :-) -

-
- - - - - - -
-

755. std::vector and std:string lack explicit shrink-to-fit operations

-

Section: 23.3.6.3 [vector.capacity], 21.4.4 [string.capacity] Status: CD1 - Submitter: Beman Dawes Opened: 2007-10-31 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-A std::vector can be shrunk-to-fit via the swap idiom: -

- -
-vector<int> v;
-...
-v.swap(vector<int>(v));  // shrink to fit
-
-

-or: -

-
-vector<int>(v).swap(v);  // shrink to fit
-
-

-or: -

-
-swap(v, vector<int>(v));  // shrink to fit
-
-
- -

-A non-binding request for shrink-to-fit can be made to a std::string via: -

- -
-string s;
-...
-s.reserve(0);
-
- -

-Neither of these is at all obvious to beginners, and even some -experienced C++ programmers are not aware that shrink-to-fit is -trivially available. -

-

-Lack of explicit functions to perform these commonly requested -operations makes vector and string less usable for non-experts. Because -the idioms are somewhat obscure, code readability is impaired. It is -also unfortunate that two similar vector-like containers use different -syntax for the same operation. -

-

-The proposed resolution addresses these concerns. The proposed function -takes no arguments to keep the solution simple and focused. -

- - -

Proposed resolution:

-

-To Class template basic_string 21.4 [basic.string] synopsis, -Class template vector 23.3.6 [vector] synopsis, and Class -vector<bool> 23.3.7 [vector.bool] synopsis, add: -

- -
    
-void shrink_to_fit();
-
- -

-To basic_string capacity 21.4.4 [string.capacity] and vector -capacity 23.3.6.3 [vector.capacity], add: -

- -
-
-void shrink_to_fit();
-
-

-Remarks: shrink_to_fit is a non-binding request to reduce -capacity() to size(). [Note: The request is non-binding to -allow latitude for implementation-specific optimizations. -— end note] -

-
- -

[ -850 has been added to deal with this issue with respect to deque. -]

- - - - - - -
-

756. Container adaptors push

-

Section: 23.6 [container.adaptors] Status: Resolved - Submitter: Paolo Carlini Opened: 2007-10-31 Last modified: 2015-04-08

-

View all other issues in [container.adaptors].

-

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-

Discussion:

-

-After n2369 we have a single push_back overload in the sequence containers, -of the "emplace" type. At variance with that, still in n2461, we have -two separate overloads, the C++03 one + one taking an rvalue reference -in the container adaptors. Therefore, simply from a consistency point of -view, I was wondering whether the container adaptors should be aligned -with the specifications of the sequence container themselves: thus have -a single push along the lines: -

- -
-template<typename... _Args>
-void
-push(_Args&&... __args)
-  { c.push_back(std::forward<_Args>(__args)...); }
-
- -

[ -Related to 767 -]

- - - -

Proposed resolution:

-

-Change 23.6.3.1 [queue.defn]: -

- -
-void push(const value_type& x) { c.push_back(x); }
-void push(value_type&& x) { c.push_back(std::move(x)); }
-template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
-
- -

-Change 23.6.4 [priority.queue]: -

- -
-void push(const value_type& x) { c.push_back(x); }
-void push(value_type&& x) { c.push_back(std::move(x)); }
-template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
-
- -

-Change 23.6.4.3 [priqueue.members]: -

- -
-
-void push(const value_type& x);
-
-
-

-Effects: -

-
-c.push_back(x);
-push_heap(c.begin(), c.end(), comp);
-
-
- -
-template<class... Args> void push(value_type Args&&... x args);
-
-
-

-Effects: -

-
-c.push_back(std::moveforward<Args>(x args)...);
-push_heap(c.begin(), c.end(), comp);
-
-
-
- -

-Change 23.6.5.2 [stack.defn]: -

- -
-void push(const value_type& x) { c.push_back(x); }
-void push(value_type&& x) { c.push_back(std::move(x)); }
-template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
-
- - - -

Rationale:

-

-Addressed by -N2680 Proposed Wording for Placement Insert (Revision 1). -

- - - - - -
-

758. shared_ptr and nullptr

-

Section: 20.8.2.2 [util.smartptr.shared] Status: C++11 - Submitter: Joe Gottman Opened: 2007-10-31 Last modified: 2015-04-08

-

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Discussion:

-

-Consider the following program: -

- -
-int main() {
-   shared_ptr<int> p(nullptr); 
-   return 0;
-}
-
- -

-This program will fail to compile because shared_ptr uses the following -template constructor to construct itself from pointers: -

- -
-template <class Y> shared_ptr(Y *);
-
- -

-According -to N2431, -the conversion from nullptr_t to Y * is not -deducible, so the above constructor will not be found. There are similar problems with the -constructors that take a pointer and a deleter or a -pointer, a deleter and an allocator, as well as the -corresponding forms of reset(). Note that N2435 -will solve this problem for constructing from just nullptr, but not for constructors that use -deleters or allocators or for reset(). -

- -

-In the case of the functions that take deleters, there is the additional -question of what argument should be passed to the deleter when it is -eventually called. There are two reasonable possibilities: nullptr or -static_cast<T *>(0), where T is the template argument of the -shared_ptr. It is not immediately clear which of these is better. If -D::operator() is a template function similar to shared_ptr's -constructor, then d(static_cast<T*>(0)) will compile and d(nullptr) -will not. On the other hand, if D::operator()() takes a parameter that -is a pointer to some type other that T (for instance U* where U derives -from T) then d(nullptr) will compile and d(static_cast<T *>(0)) may not. -

- -

[ -Bellevue: -]

- - -
-

-The general idea is right, we need to be able to pass a nullptr to a -shared_ptr, but there are a few borderline editorial issues here. (For -example, the single-argument nullptr_t constructor in the class synopsis -isn't marked explicit, but it is marked explicit in the proposed wording -for 20.6.6.2.1. There is a missing empty parenthesis in the form that -takes a nullptr_t, a deleter, and an allocator.) -

-

-More seriously: this issue says that a shared_ptr constructed from a -nullptr is empty. Since "empty" is undefined, it's hard to know whether -that's right. This issue is pending on handling that term better. -

-

-Peter suggests definition of empty should be "does not own anything" -

-

-Is there an editorial issue that post-conditions should refer to get() = -nullptr, rather than get() = 0? -

-

-No strong feeling towards accept or NAD, but prefer to make a decision than leave it open. -

-

-Seems there are no technical merits between NAD and Ready, comes down to -"Do we intentially want to allow/disallow null pointers with these -functions". Staw Poll - support null pointers 5 - No null pointers 0 -

-

-Move to Ready, modulo editorial comments -

-
- -

[ -post Bellevue Peter adds: -]

- - -
-

-The following wording changes are less intrusive: -

- -

-In 20.8.2.2.1 [util.smartptr.shared.const], add: -

- -
-shared_ptr(nullptr_t);
-
- -

-after: -

- -
-shared_ptr();
-
- -

-(Absence of explicit intentional.) -

- -

-px.reset( nullptr ) seems a somewhat contrived way to write px.reset(), so -I'm not convinced of its utility. -

-

-It's similarly not clear to me whether the deleter constructors need to be -extended to take nullptr, but if they need to: -

-

-Add -

- -
-template<class D> shared_ptr(nullptr_t p, D d);
-template<class D, class A> shared_ptr(nullptr_t p, D d, A a);
-
- -

-after -

- -
-template<class Y, class D> shared_ptr(Y* p, D d);
-template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);
-
- -

-Note that this changes the semantics of the new constructors such that they -consistently call d(p) instead of d((T*)0) when p is nullptr. -

-

-The ability to be able to pass 0/NULL to a function that takes a shared_ptr -has repeatedly been requested by users, but the other additions that the -proposed resolution makes are not supported by real world demand or -motivating examples. -

-

-It might be useful to split the obvious and non-controversial nullptr_t -constructor into a separate issue. Waiting for "empty" to be clarified is -unnecessary; this is effectively an alias for the default constructor. -

-
- -

[ -Sophia Antipolis: -]

- - -
-

-We want to remove the reset functions from the proposed resolution. -

-

-The remaining proposed resolution text (addressing the constructors) are wanted. -

-

-Disposition: move to review. The review should check the wording in the then-current working draft. -

-
- - - -

Proposed resolution:

-

-In 20.8.2.2 [util.smartptr.shared] p4, add to the definition/synopsis -of shared_ptr: -

- -
-template<class D> shared_ptr(nullptr_t p, D d);
-template<class D, class A> shared_ptr(nullptr_t p, D d, A a);
-
- -

-after -

- -
-template<class Y, class D> shared_ptr(Y* p, D d);
-template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);
-
- -

-In 20.8.2.2.1 [util.smartptr.shared.const] add: -

- -
-template<class D> shared_ptr(nullptr_t p, D d);
-template<class D, class A> shared_ptr(nullptr_t p, D d, A a);
-
- -

-after -

- -
-template<class Y, class D> shared_ptr(Y* p, D d);
-template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);
-
- -

-(reusing the following paragraphs 20.8.2.2.1 [util.smartptr.shared.const]/9-13 that speak of p.) -

- -

-In 20.8.2.2.1 [util.smartptr.shared.const]/10, change -

- -

-Effects: Constructs a shared_ptr object that owns the -pointer object p and the deleter d. The second -constructor shall use a copy of a to allocate memory for internal use. -

- - -

Rationale:

-

[ -San Francisco: -]

- - -

-"pointer" is changed to "object" to handle the fact that nullptr_t isn't a pointer. -

- - - - - - -
-

759. A reference is not an object

-

Section: 23.2 [container.requirements] Status: CD1 - Submitter: Jens Maurer Opened: 2007-11-06 Last modified: 2015-04-08

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Discussion:

-

-23.2 [container.requirements] says: -

- -

--12- Objects passed to member functions of a container as rvalue references shall not be elements of that container. No -diagnostic required. -

- -

-A reference is not an object, but this sentence appears to claim so. -

- -

-What is probably meant here: -

-

-An object bound to an rvalue -reference parameter of a member function of a container shall not be -an element of that container; no diagnostic required. -

- - - -

Proposed resolution:

-

-Change 23.2 [container.requirements]: -

- -

--12- Objects passed to member functions of a container as rvalue references shall not be elements -An object bound to an rvalue -reference parameter of a member function of a container shall not be -an element -of that container.; Nno -diagnostic required. -

- - - - - - -
-

761. unordered_map needs an at() member function

-

Section: 23.5.4.3 [unord.map.elem] Status: CD1 - Submitter: Joe Gottman Opened: 2007-11-15 Last modified: 2015-04-08

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-

Discussion:

-

-The new member function at() was recently added to std::map(). It acts -like operator[](), except it throws an exception when the input key is -not found. It is useful when the map is const, the value_type of the -key doesn't have a default constructor, it is an error if the key is -not found, or the user wants to avoid accidentally adding an element to -the map. For exactly these same reasons, at() would be equally useful -in std::unordered_map. -

- - -

Proposed resolution:

-

-Add the following functions to the definition of unordered_map under "lookup" (23.5.4 [unord.map]): -

- -
-mapped_type& at(const key_type& k);
-const mapped_type &at(const key_type &k) const;
-
- -

-Add the following definitions to 23.5.4.3 [unord.map.elem]: -

- -
-
-mapped_type& at(const key_type& k);
-const mapped_type &at(const key_type &k) const;
-
-
-

-Returns: A reference to x.second, where x is the (unique) element -whose key is equivalent to k. -

-

-Throws: An exception object of type out_of_range if no such element -is present. -

-
-
- -

[ -Bellevue: Editorial note: the "(unique)" differs from map. -]

- - - - - - - -
-

762. std::unique_ptr requires complete type?

-

Section: 20.8.1 [unique.ptr] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-11-30 Last modified: 2015-04-08

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Discussion:

-

-In contrast to the proposed std::shared_ptr, std::unique_ptr -does currently not support incomplete types, because it -gives no explicit grant - thus instantiating unique_ptr with -an incomplete pointee type T automatically belongs to -undefined behaviour according to 17.6.4.8 [res.on.functions]/2, last -bullet. This is an unnecessary restriction and prevents -many well-established patterns - like the bridge pattern - for std::unique_ptr. -

- -

[ -Bellevue: -]

- - -

-Move to open. The LWG is comfortable with the intent of allowing -incomplete types and making unique_ptr more like shared_ptr, but we are -not comfortable with the wording. The specification for unique_ptr -should be more like that of shared_ptr. We need to know, for individual -member functions, which ones require their types to be complete. The -shared_ptr specification is careful to say that for each function, and -we need the same level of care here. We also aren't comfortable with the -"part of the operational semantic" language; it's not used elsewhere in -the standard, and it's not clear what it means. We need a volunteer to -produce new wording. -

- - -

Proposed resolution:

-

-The proposed changes in the following revision refers to the current state of -N2521 including the assumption that [unique.ptr.compiletime] will be removed -according to the current state of 740. -

-

-The specialization unique_ptr<T[]> has some more restrictive constraints on -type-completeness on T than unique_ptr<T>. The following proposed wordings -try to cope with that. If the committee sees less usefulness on relaxed -constraints on unique_ptr<T[]>, the alternative would be to stop this relaxation -e.g. by adding one further bullet to 20.8.1.3 [unique.ptr.runtime]/1: -"T shall be a complete type, if used as template argument of -unique_ptr<T[], D> -

-

-This issue has some overlap with 673, but it seems not to cause any -problems with this one, -because 673 adds only optional requirements on D that do not conflict -with the here discussed -ones, provided that D::pointer's operations (including default -construction, copy construction/assignment, -and pointer conversion) are specified not to throw, otherwise this -would have impact on the -current specification of unique_ptr. -

- -
    -
  1. -

    -In 20.8.1 [unique.ptr]/2 add as the last sentence to the existing para: -

    - -

    -The unique_ptr provides a semantics of strict ownership. A -unique_ptr owns the object it holds a pointer to. A -unique_ptr is not CopyConstructible, nor -CopyAssignable, however it is MoveConstructible and -MoveAssignable. The template parameter T of -unique_ptr may be an incomplete type. [ Note: The -uses of unique_ptr include providing exception safety for -dynamically allcoated memory, passing ownership of dynamically allocated -memory to a function, and returning dynamically allocated memory from a -function. -- end note ] -

    -
    2. - -
  2. -

    -20.8.1.2.1 [unique.ptr.single.ctor]/1: No changes necessary. -

    - -
    -

    [ -N.B.: We only need the requirement that D is DefaultConstructible. -The current wording says just this. -]

    - -
    -
    3. - -
  3. -

    -In 20.8.1.2.1 [unique.ptr.single.ctor]/5 change the requires clause to say: -

    - -
    -

    -Requires: The expression D()(p) shall be well formed. The default constructor -of D shall not throw an exception. -D must not be a reference type. - -D shall be default constructible, and that construction -shall not throw an exception. - -

    -

    [ -N.B.: There is no need that the expression D()(p) is well-formed at -this point. I assume that the current wording is based on the -corresponding shared_ptr wording. In case of shared_ptr this -requirement is necessary, because the corresponding c'tor *can* fail -and must invoke delete p/d(p) in this case. Unique_ptr is simpler in -this regard. The *only* functions that must insist on well-formedness -and well-definedness of the expression get_deleter()(get()) are (1) -the destructor and (2) reset. The reasoning for the wording change to -explicitly require DefaultConstructible of D is to guarantee that -invocation of -D's default c'tor is both well-formed and well-defined. Note also that -we do *not* need the -requirement that T must be complete, also in contrast to shared_ptr. -Shared_ptr needs this, because it's c'tor is a template c'tor which -potentially requires Convertible<Y*, X*>, which -again requires Completeness of Y, if !SameType<X, Y> -]

    - -
    -
    4. - -
  4. -

    -Merge 20.8.1.2.1 [unique.ptr.single.ctor]/12+13 thereby removing the sentence -of 12, but transferring the "requires" to 13: -

    - -
    -

    -Requires: If D is not an lvalue-reference type then[..] -

    -

    [ -N.B.: For the same reasons as for (3), there is no need that d(p) is -well-formed/well-defined at this point. The current wording guarantees -all what we need, namely that the initialization of both the T* -pointer and the D deleter are well-formed and well-defined. -]

    - -
    -
    5. - -
  5. -20.8.1.2.1 [unique.ptr.single.ctor]/17: No changes necessary. -
    6. -
  6. -

    20.8.1.2.1 [unique.ptr.single.ctor]/21:

    - -

    -Requires: If D is not a reference type, construction of -the deleter D from an rvalue of type E shall be well -formed and shall not throw an exception. If D is a reference -type, then E shall be the same type as D (diagnostic -required). U* shall be implicitly convertible to T*. -[Note: These requirements imply that T and U -be complete types. -- end note] -

    - -

    [ -N.B.: The current wording of 21 already implicitly guarantees that U -is completely defined, because it requires that Convertible<U*, T*> is -true. If the committee wishes this explicit requirement can be added, -e.g. "U shall be a complete type." -]

    - -
    7. - -
  7. -

    -20.8.1.2.2 [unique.ptr.single.dtor]: Just before p1 add a new paragraph: -

    -
    -

    -Requires: The expression get_deleter()(get()) shall be well-formed, -shall have well-defined behavior, and shall not throw exceptions. -[Note: The use of default_delete requires T to -be a complete type. -- end note] -

    -

    [ -N.B.: This requirement ensures that the whole responsibility on -type-completeness of T is delegated to this expression. -]

    - -
    -
    8. - -
  8. -

    -20.8.1.2.3 [unique.ptr.single.asgn]/1: No changes necessary, except the -current editorial issue, that "must shall" has to be changed to -"shall", but this change is not a special part of this resolution. -

    - -

    [ -N.B. The current wording is sufficient, because we can delegate all -further requirements on the requirements of the effects clause -]

    - -
    9. - -
  9. -

    -20.8.1.2.3 [unique.ptr.single.asgn]/6: -

    - -

    -Requires: Assignment of the deleter D from an rvalue -D shall not throw an exception. U* shall be implicitly -convertible to T*. -[Note: These requirements imply that T and U -be complete types. -- end note] -

    - -

    [ -N.B.: The current wording of p. 6 already implicitly guarantees that -U is completely defined, because it requires that Convertible<U*, T*> -is true, see (6)+(8). -]

    - -
    10. - -
  10. -

    -20.8.1.2.3 [unique.ptr.single.asgn]/11: No changes necessary. -

    -

    [ -N.B.: Delegation to requirements of effects clause is sufficient. -]

    - -
    11. - -
  11. -

    -20.8.1.2.4 [unique.ptr.single.observers]/1+4+7+9+11: -

    - -
    -
    T* operator->() const;
    -

    -Note: Use typically requires T shall be complete. — end note] -

    -
    -
    12. - -
  12. -20.8.1.2.5 [unique.ptr.single.modifiers]/1: No changes necessary. -
    13. - -
  13. -

    -20.8.1.2.5 [unique.ptr.single.modifiers]/4: Just before p. 4 add a new paragraph: -

    -

    -Requires: The expression get_deleter()(get()) shall be well-formed, -shall have well-defined behavior, and shall not throw exceptions. -

    -
    14. - -
  14. -20.8.1.2.5 [unique.ptr.single.modifiers]/7: No changes necessary. -
    15. - -
  15. -

    -20.8.1.3 [unique.ptr.runtime]: Add one additional bullet on paragraph 1: -

    - -
    -

    -A specialization for array types is provided with a slightly altered interface. -

    - -
      -
    • -... -
      • -
    • -T shall be a complete type. -
      • -
    -
    -
    16. -
- -

[ -post Bellevue: Daniel provided revised wording. -]

- - - - - - - -
-

765. More on iterator validity

-

Section: X [iterator.concepts] Status: C++11 - Submitter: Martin Sebor Opened: 2007-12-14 Last modified: 2015-04-08

-

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-

Discussion:

-

- -Issue 278 -defines the meaning of the term "invalid iterator" as one that may be -singular. - -

-

- -Consider the following code: - -

- 
-   std::deque<int> x, y;
-   std::deque<int>::iterator i = x.end(), j = y.end();
-   x.swap(y);
-
-

- -Given that swap() is required not to invalidate iterators -and using the definition above, what should be the expected result of -comparing i and j to x.end() -and y.end(), respectively, after the swap()? - -

-

- -I.e., is the expression below required to evaluate -to true? - -

- 
-   i == y.end() && j == x.end()
-
-

- -(There are at least two implementations where the expression -returns false.) - -

-

- -More generally, is the definition introduced in issue 278 meant to -make any guarantees about whether iterators actually point to the same -elements or be associated with the same containers after a -non-invalidating operation as they did before? - -

-

- -Here's a motivating example intended to demonstrate the importance of -the question: - -

- 
-   Container x, y ({ 1, 2});   // pseudocode to initialize y with { 1, 2 }
-   Container::iterator i = y.begin() + 1;
-   Container::iterator j = y.end();
-   std::swap(x, y);
-   std::find(i, j, 3);
-
-

- -swap() guarantees that i and j -continue to be valid. Unless the spec says that even though they are -valid they may no longer denote a valid range the code above must be -well-defined. Expert opinions on this differ as does the behavior of -popular implementations for some standard Containers. - -

-

[ -San Francisco: -]

- - -
-

-Pablo: add a note to the last bullet of paragraph 11 of 23.1.1 clarifying that -the end() iterator doesn't refer to an element and that it can therefore be invalidated. -

-

-Proposed wording: -

-

-[Note: The end() iterator does not refer to any element and can -therefore be invalidated. -- end note] -

-

-Howard will add this proposed wording to the issue and then move it to Review. -

-
- -

[ -Post Summit: -]

- - -
-

-Lawrence: suggestion: "Note: The end() iterator does not refer to any element" -

-

-Walter: "Note: The end() iterator can nevertheless be invalidated, -because it does not refer to any element." -

-

-Nick: "The end() iterator does not refer to any element. It is therefore -subject to being invalidated." -

-

-Consensus: go with Nick -

-

-With that update, Recommend Tentatively Ready. -

-
- - - -

Proposed resolution:

-

-Add to 23.2.1 [container.requirements.general], p11: -

- -
-

-Unless otherwise specified (see 23.1.4.1, 23.1.5.1, 23.2.2.3, and -23.2.6.4) all container types defined in this Clause meet the following -additional requirements: -

-
    -
  • ...
    • -
  • -no swap() function invalidates any references, pointers, or -iterators referring to the elements of the containers being swapped. -[Note: The end() iterator does not refer to any element. -It is therefore subject to being invalidated. — end note] -
    • -
-
- - - - - -
-

766. Inconsistent exception guarantees between ordered and unordered associative containers

-

Section: 23.2 [container.requirements], 23.2.5.1 [unord.req.except] Status: CD1 - Submitter: Ion Gaztañaga Opened: 2007-12-22 Last modified: 2015-04-08

-

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Discussion:

-

-23.2 [container.requirements]p10 states: -

- -
-

-Unless otherwise specified (see 23.2.2.3 and 23.2.5.4) all container types defined in this clause meet the following -additional requirements: -

-
    - -
  • [...]
    • - -
  • no erase(), pop_back() or pop_front() function throws an exception.
    • - -
-
- -

-23.3.3.4 [deque.modifiers] and 23.3.6.5 [vector.modifiers] offer -additional guarantees for deque/vector insert() and -erase() members. However, 23.2 [container.requirements] p10 -does not mention 23.2.5.1 [unord.req.except] that specifies exception -safety guarantees for unordered containers. In addition, -23.2.5.1 [unord.req.except] p1 offers the following guaratee for -erase(): -

- -

-No erase() function throws an exception unless that exception -is thrown by the container's Hash or Pred object (if any). -

- -

-Summary: -

- -

-According to 23.2 [container.requirements] p10 no -erase() function should throw an exception unless otherwise -specified. Although does not explicitly mention 23.2.5.1 [unord.req.except], this section offers additional guarantees -for unordered containers, allowing erase() to throw if -predicate or hash function throws. -

- -

-In contrast, associative containers have no exception safety guarantees -section so no erase() function should throw, including -erase(k) that needs to use the predicate function to -perform its work. This means that the predicate of an associative -container is not allowed to throw. -

- -

-So: -

- -
    -
  1. -erase(k) for associative containers is not allowed to throw. On -the other hand, erase(k) for unordered associative containers -is allowed to throw. -
    2. -
  2. -erase(q) for associative containers is not allowed to throw. On -the other hand, erase(q) for unordered associative containers -is allowed to throw if it uses the hash or predicate. -
    3. -
  3. -To fulfill 1), predicates of associative containers are not allowed to throw. -Predicates of unordered associative containers are allowed to throw. -
    4. -
  4. -2) breaks a widely used programming pattern (flyweight pattern) for -unordered containers, where objects are registered in a global map in -their constructors and unregistered in their destructors. If erase(q) is -allowed to throw, the destructor of the object would need to rethrow the -exception or swallow it, leaving the object registered. -
    5. -
- - -

Proposed resolution:

-

-Create a new sub-section of 23.2.4 [associative.reqmts] (perhaps -[associative.req.except]) titled "Exception safety guarantees". -

- -
-

-1 For associative containers, no clear() function throws an exception. -erase(k) does not throw an exception unless that exception is thrown by -the container's Pred object (if any). -

- -

-2 For associative containers, if an exception is thrown by any operation -from within an insert() function inserting a single element, the -insert() function has no effect. -

- -

-3 For associative containers, no swap function throws an exception -unless that exception is thrown by the copy constructor or copy -assignment operator of the container's Pred object (if any). -

-
- -

-Change 23.2.5.1 [unord.req.except]p1: -

- -

-For unordered associative containers, no clear() function -throws an exception. No erase(k) -function does not throws an exception -unless that exception is thrown by the container's Hash or Pred object -(if any). -

- -

-Change 23.2 [container.requirements] p10 to add references to new sections: -

- -

-Unless otherwise specified (see [deque.modifiers], -and [vector.modifiers], [associative.req.except], -[unord.req.except]) all container types defined in this clause meet -the following additional requirements: -

- -

-Change 23.2 [container.requirements] p10 referring to swap: -

- -
-
    -
  • -no swap() function throws an exception unless that exception is thrown -by the copy constructor or assignment operator of the container's -Compare object (if any; see [associative.reqmts]). -
    • -
-
- - - - - - -
-

767. Forwarding and backward compatibility

-

Section: 23 [containers] Status: Resolved - Submitter: Sylvain Pion Opened: 2007-12-28 Last modified: 2015-04-08

-

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-

Discussion:

-

-Playing with g++'s C++0X mode, I noticed that the following code, which used to compile: -

- -
-#include <vector>
-
-int main()
-{
-    std::vector<char *> v;
-    v.push_back(0);
-}
-
- -

-now fails with the following error message: -

- -

-.../include/c++/4.3.0/ext/new_allocator.h: In member function 'void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, _Args&& ...) [with _Args = int, _Tp = char*]': -.../include/c++/4.3.0/bits/stl_vector.h:707: instantiated from 'void std::vector<_Tp, _Alloc>::push_back(_Args&& ...) [with _Args = int, _Tp = char*, _Alloc = std::allocator<char*>]' -test.cpp:6: instantiated from here -.../include/c++/4.3.0/ext/new_allocator.h:114: error: invalid conversion from 'int' to 'char*' -

- -

-As far as I know, g++ follows the current draft here. -

-

-Does the committee really intend to break compatibility for such cases? -

- -

[ -Sylvain adds: -]

- - -
-

-I just noticed that std::pair has the same issue. -The following now fails with GCC's -std=c++0x mode: -

- -
-#include <utility>
-
-int main()
-{
-   std::pair<char *, char *> p (0,0);
-}
-
- -

-I have not made any general audit for such problems elsewhere. -

-
- -

[ -Related to 756 -]

- - -

[ -Bellevue: -]

- - -
-

-Motivation is to handle the old-style int-zero-valued NULL pointers. -Problem: this solution requires concepts in some cases, which some users -will be slow to adopt. Some discussion of alternatives involving -prohibiting variadic forms and additional library-implementation -complexity. -

-

-Discussion of "perfect world" solutions, the only such solution put -forward being to retroactively prohibit use of the integer zero for a -NULL pointer. This approach was deemed unacceptable given the large -bodies of pre-existing code that do use integer zero for a NULL pointer. -

-

-Another approach is to change the member names. Yet another approach is -to forbid the extension in absence of concepts. -

-

-Resolution: These issues (756, 767, 760, -763) will be subsumed into a paper to be produced by Alan Talbot -in time for review at the 2008 meeting in France. Once this paper is produced, -these issues will be moved to NADResolved. -

-
- - - -

Proposed resolution:

-

-Add the following rows to Table 90 "Optional sequence container operations", 23.2.3 [sequence.reqmts]: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
expression return type assertion/note
pre-/post-condition		 container
-a.push_front(t) - -void - -a.insert(a.begin(), t)
-Requires: T shall be CopyConstructible. -		 -list, deque -
-a.push_front(rv) - -void - -a.insert(a.begin(), rv)
-Requires: T shall be MoveConstructible. -		 -list, deque -
-a.push_back(t) - -void - -a.insert(a.end(), t)
-Requires: T shall be CopyConstructible. -		 -list, deque, vector, basic_string -
-a.push_back(rv) - -void - -a.insert(a.end(), rv)
-Requires: T shall be MoveConstructible. -		 -list, deque, vector, basic_string -
-
- -

-Change the synopsis in 23.3.3 [deque]: -

- -
-void push_front(const T& x);
-void push_front(T&& x);
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- -

-Change 23.3.3.4 [deque.modifiers]: -

- -
-void push_front(const T& x);
-void push_front(T&& x);
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- -

-Change the synopsis in 23.3.5 [list]: -

- -
-void push_front(const T& x);
-void push_front(T&& x);
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- -

-Change 23.3.5.4 [list.modifiers]: -

- -
-void push_front(const T& x);
-void push_front(T&& x);
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- -

-Change the synopsis in 23.3.6 [vector]: -

- -
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- -

-Change 23.3.6.5 [vector.modifiers]: -

- -
-void push_back(const T& x);
-void push_back(T&& x);
-template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
-
- - - - -

Rationale:

-

-Addressed by -N2680 Proposed Wording for Placement Insert (Revision 1). -

- -

-If there is still an issue with pair, Howard should submit another issue. -

- - - - - -
-

768. Typos in [atomics]?

-

Section: 29.5 [atomics.types.generic] Status: CD1 - Submitter: Alberto Ganesh Barbati Opened: 2007-12-28 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-in the latest publicly available draft, paper -N2641, -in section 29.5 [atomics.types.generic], the following specialization of the template -atomic<> is provided for pointers: -

- -
-template <class T> struct atomic<T*> : atomic_address { 
-  T* fetch_add(ptrdiff_t, memory_order = memory_order_seq_cst) volatile; 
-  T* fetch_sub(ptrdiff_t, memory_order = memory_order_seq_cst) volatile; 
-
-  atomic() = default; 
-  constexpr explicit atomic(T); 
-  atomic(const atomic&) = delete; 
-  atomic& operator=(const atomic&) = delete; 
-
-  T* operator=(T*) volatile; 
-  T* operator++(int) volatile; 
-  T* operator--(int) volatile; 
-  T* operator++() volatile; 
-  T* operator--() volatile; 
-  T* operator+=(ptrdiff_t) volatile;
-  T* operator-=(ptrdiff_t) volatile; 
-};
-
- -

-First of all, there is a typo in the non-default constructor which -should take a T* rather than a T. -

- -

-As you can see, the specialization redefine and therefore hide a few -methods from the base class atomic_address, namely fetch_add, fetch_sub, -operator=, operator+= and operator-=. That's good, but... what happened -to the other methods, in particular these ones: -

- -
-void store(T*, memory_order = memory_order_seq_cst) volatile;
-T* load( memory_order = memory_order_seq_cst ) volatile;
-T* swap( T*, memory_order = memory_order_seq_cst ) volatile;
-bool compare_swap( T*&, T*, memory_order, memory_order ) volatile;
-bool compare_swap( T*&, T*, memory_order = memory_order_seq_cst ) volatile;
-
- -

-By reading paper -N2427 "C++ Atomic Types and Operations", -I see that the -definition of the specialization atomic<T*> matches the one in the -draft, but in the example implementation the methods load(), swap() -and compare_swap() are indeed present. -

- -

-Strangely, the example implementation does not redefine the method -store(). It's true that a T* is always convertible to void*, but not -hiding the void* signature from the base class makes the class -error-prone to say the least: it lets you assign pointers of any type to -a T*, without any hint from the compiler. -

- -

-Is there a true intent to remove them from the specialization or are -they just missing from the definition because of a mistake? -

- -

[ -Bellevue: -]

- - -
-

-The proposed revisions are accepted. -

-

-Further discussion: why is the ctor labeled "constexpr"? Lawrence said -this permits the object to be statically initialized, and that's -important because otherwise there would be a race condition on -initialization. -

-
- - -

Proposed resolution:

-

-Change the synopsis in 29.5 [atomics.types.generic]: -

- -
-template <class T> struct atomic<T*> : atomic_address { 
-  void store(T*, memory_order = memory_order_seq_cst) volatile;
-  T* load( memory_order = memory_order_seq_cst ) volatile;
-  T* swap( T*, memory_order = memory_order_seq_cst ) volatile;
-  bool compare_swap( T*&, T*, memory_order, memory_order ) volatile;
-  bool compare_swap( T*&, T*, memory_order = memory_order_seq_cst ) volatile;
-
-  T* fetch_add(ptrdiff_t, memory_order = memory_order_seq_cst) volatile; 
-  T* fetch_sub(ptrdiff_t, memory_order = memory_order_seq_cst) volatile; 
-
-  atomic() = default; 
-  constexpr explicit atomic(T*); 
-  atomic(const atomic&) = delete; 
-  atomic& operator=(const atomic&) = delete; 
-
-  T* operator=(T*) volatile; 
-  T* operator++(int) volatile; 
-  T* operator--(int) volatile; 
-  T* operator++() volatile; 
-  T* operator--() volatile; 
-  T* operator+=(ptrdiff_t) volatile;
-  T* operator-=(ptrdiff_t) volatile; 
-};
-
- - - - - - -
-

769. std::function should use nullptr_t instead of "unspecified-null-pointer-type"

-

Section: 20.9.12.2 [func.wrap.func] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-10 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-N2461 already replaced in 20.9.12.2 [func.wrap.func] it's originally proposed -(implicit) conversion operator to "unspecified-bool-type" by the new -explicit bool conversion, but the inverse conversion should also -use the new std::nullptr_t type instead of "unspecified-null-pointer- -type". -

- - -

Proposed resolution:

- -

-In 20.9 [function.objects], header <functional> synopsis replace: -

- -
-template<class R, class... ArgTypes>
-  bool operator==(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
-template<class R, class... ArgTypes>
-  bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
-template<class R, class... ArgTypes>
-  bool operator!=(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
-template<class R, class... ArgTypes>
-  bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
-
- -

-In the class function synopsis of 20.9.12.2 [func.wrap.func] replace -

- -
-function(unspecified-null-pointer-type nullptr_t);
-...
-function& operator=(unspecified-null-pointer-type nullptr_t);
-
- -

-In 20.9.12.2 [func.wrap.func], "Null pointer comparisons" replace: -

- -
-template <class R, class... ArgTypes>
-  bool operator==(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
-template <class R, class... ArgTypes>
-  bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
-template <class R, class... ArgTypes>
-  bool operator!=(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
-template <class R, class... ArgTypes>
-  bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
-
- -

-In 20.9.12.2.1 [func.wrap.func.con], replace -

- -
-function(unspecified-null-pointer-type nullptr_t);
-...
-function& operator=(unspecified-null-pointer-type nullptr_t);
-
- -

-In 20.9.12.2.6 [func.wrap.func.nullptr], replace -

- -
-template <class R, class... ArgTypes>
-  bool operator==(const function<R(ArgTypes...)>& f, unspecified-null-pointer-type nullptr_t);
-template <class R, class... ArgTypes>
-  bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>& f);
-
- -

-and replace -

- -
-template <class R, class... ArgTypes>
-  bool operator!=(const function<R(ArgTypes...)>& f, unspecified-null-pointer-type nullptr_t);
-template <class R, class... ArgTypes>
-  bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>& f);
-
- - - - - - -
-

770. std::function should use rvalue swap

-

Section: 20.9.12 [func.wrap] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-It is expected that typical implementations of std::function will -use dynamic memory allocations at least under given conditions, -so it seems appropriate to change the current lvalue swappabilty of -this class to rvalue swappability. -

- - -

Proposed resolution:

-

-In 20.9 [function.objects], header <functional> synopsis, just below of -

- -
-template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
-template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
-template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);
-
- -

-In 20.9.12.2 [func.wrap.func] class function definition, change -

- -
-void swap(function&&);
-
- -

-In 20.9.12.2 [func.wrap.func], just below of -

- -
-template <class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
-template <class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
-template <class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);
-
- -

-In 20.9.12.2.2 [func.wrap.func.mod] change -

- -
-void swap(function&& other);
-
- -

-In 20.9.12.2.7 [func.wrap.func.alg] add the two overloads -

- -
-template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>&& f1, function<R(ArgTypes...)>& f2);
-template<class R, class... ArgTypes>
-  void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>&& f2);
-
- - - - - - -
-

771. Impossible throws clause in [string.conversions]

-

Section: 21.5 [string.conversions] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The new to_string and to_wstring functions described in 21.5 [string.conversions] -have throws clauses (paragraphs 8 and 16) which say: -

- -

-Throws: nothing -

- -

-Since all overloads return either a std::string or a std::wstring by value -this throws clause is impossible to realize in general, since the basic_string -constructors can fail due to out-of-memory conditions. Either these throws -clauses should be removed or should be more detailled like: -

- -

-Throws: Nothing if the string construction throws nothing -

- -

-Further there is an editorial issue in p. 14: All three to_wstring -overloads return a string, which should be wstring instead (The -header <string> synopsis of 21.3 [string.classes] is correct in this -regard). -

- - - -

Proposed resolution:

-

-In 21.5 [string.conversions], remove the paragraphs 8 and 16. -

- -
-
-string to_string(long long val); 
-string to_string(unsigned long long val); 
-string to_string(long double val); 
-
-

-Throws: nothing -

-
- -
-
-wstring to_wstring(long long val); 
-wstring to_wstring(unsigned long long val); 
-wstring to_wstring(long double val); 
-
-

-Throws: nothing -

-
- - - - - - -
-

772. Impossible return clause in [string.conversions]

-

Section: 21.5 [string.conversions] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The return clause 21.5 [string.conversions] paragraph 15 of the new to_wstring -overloads says: -

- -

-Returns: each function returns a wstring object holding the character -representation of the value of its argument that would be generated by -calling wsprintf(buf, fmt, val) with a format specifier of L"%lld", L"%ulld", -or L"%f", respectively. -

- -

-Problem is: There does not exist any wsprintf function in C99 (I checked -the 2nd edition of ISO 9899, and the first and the second corrigenda from -2001-09-01 and 2004-11-15). What probably meant here is the function -swprintf from <wchar.h>/<cwchar>, but this has the non-equivalent -declaration: -

- -
-int swprintf(wchar_t * restrict s, size_t n,
-const wchar_t * restrict format, ...);
-
- -

-therefore the paragraph needs to mention the size_t parameter n. -

- - - -

Proposed resolution:

-

-Change the current wording of 21.5 [string.conversions] p. 15 to: -

- -

-Returns: eEach function returns a -wstring object holding the character representation of the -value of its argument that would be generated by calling -wsswprintf(buf, bufsz, fmt, -val) with a format specifier fmt of L"%lld", -L"%ulld", or L"%f", respectively, where buf -designates an internal character buffer of sufficient size bufsz. -

- -

-[Hint to the editor: The resolution also adds to mention the name of -the format specifier "fmt"] -

- -

-I also would like to remark that the current wording of it's equivalent -paragraph 7 should also mention the meaning of buf and fmt. -

- -

-Change the current wording of 21.5 [string.conversions] p. 7 to: -

- -

-Returns: eEach function returns a string object holding the -character representation of the value of its argument that would be -generated by calling sprintf(buf, fmt, val) with a format specifier fmt of -"%lld", "%ulld", or "%f", respectively, where buf designates an internal -character buffer of sufficient size. -

- - - - - - -
-

774. Member swap undefined for most containers

-

Section: 23 [containers] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-01-14 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-It appears most containers declare but do not define a member-swap -function. -

- -

-This is unfortunate, as all overload the swap algorithm to call the -member-swap function! -(required for swappable guarantees [Table 37] and Container Requirements -[Table 87]) -

- -

-Note in particular that Table 87 gives semantics of a.swap(b) as swap(a,b), -yet for all containers we define swap(a,b) to call a.swap(b) - a circular -definition. -

- -

-A quick survey of clause 23 shows that the following containers provide a -definition for member-swap: -

- -
-array
-queue
-stack
-vector
-
- -

-Whereas the following declare it, but do not define the semantics: -

- -
-deque
-list
-map
-multimap
-multiset
-priority_queue
-set
-unordered_map
-unordered_multi_map
-unordered_multi_set
-unordered_set
-
- -

-Suggested resolution: -

-

-Provide a definition for each of the affected containers... -

- -

[ -Bellevue: -]

- - -

-Move to Open and ask Alisdair to provide wording. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Daniel to provide wording. -N2590 -is no longer applicable. -

- -

[ -2009-07-28 Daniel provided wording. -]

- - -
-
    -
  1. -It assumes that the proposed resolution for 883 is applied, -which breaks the circularity of definition between member -swap and free swap. -
    2. - -
  2. -It uses the notation of the pre-concept allocator trait -allocator_propagation_map, which might be renamed after the -next refactoring phase of generalized allocators. -
    3. - -
  3. -It requires that compare objects, key equal functions and -hash functions in containers are swapped via unqualified free -swap according to 594. -
    4. -
-
- -

[ -2009-09-30 Daniel adds: -]

- - -

-The outcome of this issue should be considered with the outcome of -1198 both in style and in content (e.g. bullet 9 suggests to -define the semantic of void priority_queue::swap(priority_queue&) -in terms of the member swap of the container). -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Looked at, but took no action on as it overlaps too much with -N2982. -Waiting for a new draft WP. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as open. Pablo to provide wording. -

- -

[ -2009-10-26 Pablo updated wording. Here is the wording he replaced: -]

- - -
-
    -
  1. -

    -Add a new Throws clause just after X [allocator.propagation.map]/5: -

    - -
    -static void swap(Alloc& a, Alloc& b);
-
    -
    -

    -Effects: [..] -

    - -

    -Throws: Nothing. -

    -
    -
    -

    [ -This exception requirement is added, such that it's combination with the -general container requirements of -N2723 -[container.requirements.general]/9 -make it unambiguously clear that the following descriptions of "swaps the -allocators" have the following meaning: (a) This swap is done by calling -allocator_propagation_map<allocator_type>::swap and (b) This allocator -swap does never propagate an exception -]

    - -
    2. - -
  2. -

    -Change 23.2.4.1 [associative.reqmts.except]/3 as indicated: -

    - -

    -For associative containers, no swap function throws an exception unless that -exception is thrown by the copy constructor or copy assignment -operator -swap of the container's Pred objects (if any). -

    -
    3. - -
  3. -

    -Change 23.2.5.1 [unord.req.except]/3 as indicated: -

    - -

    -For unordered associative containers, no swap function throws an -exception unless -that exception is thrown by the copy constructor or copy -assignment operator -swap of the container's Hash or Pred objects, -respectively (if any). -

    -
    4. - -
  4. -

    -Insert a new paragraph just after 23.3 [sequences]/1: -

    - -

    -In addition to being available via inclusion of the <algorithm> header, -the swap function templates in 25.3.3 [alg.swap] are also available when the -header <queue> is included. -

    - -

    [ -There is a new issue in process that will suggest a minimum header for swap -and move. If this one is provided, this text can be removed and the header -dependency should be added to <queue> -]

    - - -
    5. - -
  5. -

    -Add one further clause at the end of 23.3.2.3 [array.special]: -

    -

    [This part is added, because otherwise array::swap would otherwise -contradict the -general contract of 23.2.1 [container.requirements.general] p. 10 b. 5]

    - - -

    -Throws: Nothing, unless one of the element-wise swap calls throws -an exception. -

    -
    6. - -
  6. -
      -
    1. -

      -In 23.3.3 [deque], class template deque synopsis change as indicated: -

      -
      -void swap(deque<T,Alloc>&);
-
      -
      2. - -
    2. -

      -At the end of 23.3.3.4 [deque.modifiers] add as indicated: -

      - -
      -void swap(deque& x);
-
      -
      -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x. -

      -

      -Complexity: Constant time. -

      -
      -
      -
      3. -
    -
    7. - -
  7. -
      -
    1. -

      -In 23.3.4 [forwardlist], class template forward_list synopsis change as indicated: -

      - -
      -void swap(forward_list<T,Allocator>&);
-
      -
      2. - -
    2. -

      -At the end of 23.3.4.5 [forwardlist.modifiers] add as indicated: -

      - -
      -void swap(forward_list& x);
-
      -
      -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x. -

      -

      -Complexity: Constant time. -

      -
      -
      -
      3. -
    -
    8. - -
  8. -
      -
    1. -

      -In 23.3.5 [list], class template list synopsis change as indicated: -

      - -
      -void swap(list<T,Allocator>&);
-
      -
      2. - -
    2. -

      -At the end of 23.3.5.4 [list.modifiers] add as indicated: -

      - -
      -void swap(list& x);
-
      - -
      -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x. -

      - -

      -Complexity: Constant time. -

      -
      -
      -
      3. -
    -
    9. - -
  9. -

    -At the end of 23.6.4.3 [priqueue.members] add a new prototype description: -

    - -
    -void swap(priority_queue& q);
-
    -
    -

    -Requires: Compare shall satisfy the Swappable requirements -( [swappable]). -

    - -

    [ -This requirement is added to ensure that even a user defined swap -which is found by ADL for Compare satisfies the Swappable requirements -]

    - - -

    -Effects: this->c.swap(q.c); swap(this->comp, q.comp); -

    -

    -Throws: What and if c.swap(q.c) and swap(comp, q.comp) throws. -

    -
    -
    -

    [ -This part is added, because otherwise priority_queue::swap would otherwise -contradict the general contract of 23.2.1 [container.requirements.general] p. 10 b. 5 -]

    - -
    10. - -
  10. -
      -
    1. -

      -In 23.3.6 [vector], class template vector synopsis change as indicated: -

      - -
      -void swap(vector<T,Allocator>&);
-
      -
      2. - -
    2. -

      -Change 23.3.6.3 [vector.capacity] p. 8 as indicated: -

      - -
      -void swap(vector<T,Allocator>& x);
-
      - -

      -Effects: Exchanges the contents and capacity() and swaps the -allocators of *this with that of x. -

      -
      -
      3. -
    -
    11. - -
  11. -

    -Insert a new paragraph just before 23.4 [associative]/1: -

    - -

    -In addition to being available via inclusion of the <algorithm> header, -the swap function templates in 25.3.3 [alg.swap] are also available when any of the -headers <map> or <set> are included. -

    -
    12. - -
  12. -
      -
    1. -

      -In 23.4.4 [map], class template map synopsis change as indicated: -

      - -
      -void swap(map<Key,T,Compare,Allocator>&);
-
      -
      2. - -
    2. -

      -At the end of 23.4.4.4 [map.modifiers] add as indicated: -

      - -
      -void swap(map& x);
-
      - -
      -

      -Requires: Compare shall satisfy the Swappable requirements -( [swappable]). -

      - -

      [ -This requirement is added to ensure that even a user defined swap -which is found by ADL for Compare satisfies the Swappable -requirements -]

      - - -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x, followed by an unqualified swap of the comparison objects -of *this and x. -

      - -

      -Complexity: Constant time -

      -
      -
      -
      3. -
    -
    13. - -
  13. -
      -
    1. -

      -In 23.4.5 [multimap], class template multimap synopsis change as indicated: -

      - -
      -void swap(multimap<Key,T,Compare,Allocator>&);
-
      -
      2. - -
    2. -

      -At the end of 23.4.5.3 [multimap.modifiers] add as indicated: -

      - -
      -void swap(multimap& x);
-
      - -
      -

      -Requires: Compare shall satisfy the Swappable requirements -( [swappable]). -

      -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x, followed by an unqualified swap of the comparison objects -of *this and x. -

      -

      -Complexity: Constant time -

      -
      -
      -
      3. -
    -
    14. - -
  14. -
      -
    1. -

      -In 23.4.6 [set], class template set synopsis change as indicated: -

      - -
      -void swap(set<Key,Compare,Allocator>&);
-
      -
      2. - -
    2. -

      -After section 23.4.6.2 [set.cons] add a new section set modifiers - [set.modifiers] -and add the following paragraphs: -

      - -
      -void swap(set& x);
-
      - -
      -

      -Requires: Compare shall satisfy the Swappable requirements -( [swappable]). -

      - -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x, followed by an unqualified swap of the comparison objects -of *this and x. -

      - -

      -Complexity: Constant time -

      -
      -
      -
      3. -
    -
    15. - -
  15. -
      -
    1. -

      -In 23.4.7 [multiset], class template multiset synosis, change as indicated: -

      - -
      -void swap(multiset<Key,Compare,Allocator>&);
-
      -
      2. - -
    2. -

      -After section 23.4.7.2 [multiset.cons] add a new section multiset modifiers - [multiset.modifiers] and add the following paragraphs: -

      - -
      -void swap(multiset& x);
-
      - -
      -

      -Requires: Compare shall satisfy the Swappable requirements -( [swappable]). -

      - -

      -Effects: Exchanges the contents and swaps the allocators of *this -with that of x, followed by an unqualified swap of the comparison objects -of *this and x. -

      - -

      -Complexity: Constant time -

      -
      -
      -
      3. -
    -
    16. - -
  16. -

    -Insert a new paragraph just before 23.5 [unord] p. 1: -

    - -

    -In addition to being available via inclusion of the <algorithm> header, -the swap function templates in 25.3.3 [alg.swap] are also available when any of the -headers <unordered_map> or <unordered_set> are included. -

    - -
    17. - -
  17. -

    -After section 23.5.4.3 [unord.map.elem] add a new section unordered_map -modifiers 23.5.4.4 [unord.map.modifiers] and add the following paragraphs: -

    - -
    -void swap(unordered_map& x);
-
    - -
    -

    -Requires: Hash and Pred shall satisfy the Swappable requirements -( [swappable]). -

    - -

    [ -This requirement is added to ensure that even a user defined swap -which is found by ADL for Hash and Pred satisfies the Swappable -requirements -]

    - - -

    -Effects: Exchanges the contents and hash policy and swaps the allocators of *this -with that of x, followed by an unqualified swap of the Pred objects -and an unqualified swap of the Hash objects of *this and x. -

    - -

    -Complexity: Constant time -

    -
    -
    -
    18. - -
  18. -

    -After section 23.5.5.2 [unord.multimap.cnstr] add a new section -unordered_multimap -modifiers 23.5.5.3 [unord.multimap.modifiers] and add the following paragraphs: -

    - -
    -void swap(unordered_multimap& x);
-
    - -
    -

    -Requires: Hash and Pred shall satisfy the Swappable requirements -( [swappable]). -

    - -

    -Effects: Exchanges the contents and hash policy and swaps the -allocators of *this -with that of x, followed by an unqualified swap of the Pred objects -and an unqualified swap of the Hash objects of *this and x -

    -

    -Complexity: Constant time -

    -
    -
    -
    19. - -
  19. -

    -After section 23.5.6.2 [unord.set.cnstr] add a new section -unordered_set modifiers - [unord.set.modifiers] and add the following paragraphs: -

    - -
    -void swap(unordered_set& x);
-
    - -
    -

    -Requires: Hash and Pred shall satisfy the Swappable requirements -( [swappable]). -

    - -

    -Effects: Exchanges the contents and hash policy and swaps the -allocators of *this -with that of x, followed by an unqualified swap of the Pred objects -and an unqualified swap of the Hash objects of *this and x -

    - -

    -Complexity: Constant time -

    -
    -
    -
    20. - -
  20. -

    -After section 23.5.7.2 [unord.multiset.cnstr] add a new section -unordered_multiset -modifiers [unord.multiset.modifiers] and add the following paragraphs: -

    - -
    -void swap(unordered_multiset& x);
-
    - -
    -

    -Requires: Hash and Pred shall satisfy the Swappable requirements -( [swappable]). -

    - -

    -Effects: Exchanges the contents and hash policy and swaps the -allocators of *this -with that of x, followed by an unqualified swap of the Pred objects -and an unqualified swap of the Hash objects of *this and x -

    -

    -Complexity: Constant time -

    -
    -
    -
    21. - -
- -
- -

[ -2009-10-30 Pablo and Daniel updated wording. -]

- - -

[ -2010 Pittsburgh: Ready for Pittsburgh. -]

- - - - -

Proposed resolution:

- -

[ -This resolution is based on the September 2009 WP, -N2960, -except that it assumes that -N2982 -and issues 883 and 1232 have already been applied. Note in -particular that Table 91 in -N2960 -is refered to as Table 90 because -N2982 -removed the old Table 90. This resolution also addresses issue 431. -]

- -

-In 23.2.1 [container.requirements.general], replace the a.swap(b) row in table 90, -"container requirements" (was table 91 before the application of -N2982 -to the WP): -

-
- - - - - - - - - - - - - - - -
a.swap(b)void   swap(a,b)Exchange the contents of a and b.(Note A)
swap(a,b)void   a.swap(b)(Note A)
-
-

-Modify the notes immediately following Table 90 in -23.2.1 [container.requirements.general] as follows (The wording below is after the -application of N2982 -to N2960. The -editor might also want to combine Notes A and B into one.): -

-

-Notes: the algorithms swap(), equal() and lexicographical_compare() -are defined in Clause 25. Those entries marked "(Note A)" or "(Note B)" -should have linear complexity for array and constant -complexity for all other standard containers. -

-

-In 23.2.1 [container.requirements.general], before paragraph 8, add: -

-

-The expression a.swap(b), for containers a -and b of a standard container type other than array, -exchanges the values of a and b without invoking any -move, copy, or swap operations on the individual container elements. -Any Compare, Pred, or Hash function -objects belonging to a and b shall be -swappable and are exchanged by unqualified calls -to non-member swap. If -allocator_traits<allocator_type>::propagate_on_container_swap::value -== true, then the allocators of a and b are -also exchanged using an unqualified call to non-member swap. -Otherwise, the behavior is undefined unless a.get_allocator() == -b.get_allocator(). Each iterator refering to an element in one -container before the swap shall refer to the same element in the other -container after the swap. It is unspecified whether an iterator with -value a.end() before the swap will have -value b.end() after the swap. In addition to being available via -inclusion of the <utility> header, the swap -function template in 25.3.3 [alg.swap] is also available within the definition of -every standard container's swap function. -

-

[ -Note to the editor: Paragraph 2 starts with a sentence fragment, -clearly from an editing or source-control error. -]

- -

-Modify 23.2.4.1 [associative.reqmts.except] as follows: -

-
-

-23.2.4.1 Exception safety guarantees 23.2.4.1 [associative.reqmts.except] -

-

-For associative containers, no clear() function throws an -exception. erase(k) does not throw an exception unless that -exception is thrown by the -container's PredCompare object (if any). -

-

-For associative containers, if an exception is thrown by any operation from -within an insert() function inserting a single element, -the insert() function has no effect. -

-

-For associative containers, no swap function throws an exception -unless that exception is thrown by the copy constructor -or copy assignment operatorswap of the -container's PredCompare object (if any). -

-

-Modify 23.2.5.1 [unord.req.except], paragraph 3 as follows: -

-

-For unordered associative containers, no swap function throws an -exception unless that exception is thrown by the copy constructor or copy -assignment operatorswap of the container's Hash -or Pred object (if any). -

-

-Modify section 23.3.2.3 [array.special]: -

-
-

-array specialized algorithms 23.3.2.3 [array.special] -

-

-template <class T, size_t N> void swap(array<T,N>& x,array<T,N>& y); -

-
-

-Effects: swap_ranges(x.begin(), x.end(), y.begin() );x.swap(y); -

-
-
-

-Add a new section after 23.3.2.6 [array.fill] (Note to the editor: array::fill make use -of a concept requirement that must be removed or changed to text.): -

-
-

-array::swap [array.swap] -

-

-void swap(array& y); -

-
-

-Effects: swap_ranges(this->begin(), this->end(), y.begin() ); -

-

-Throws: Nothing unless one of the element-wise swap calls throws an -exception. -

-

-[Note: Unlike other containers' swap functions, -array::swap takes linear, not constant, time, may exit via an -exception, and does not cause iterators to become associated with the other -container. — end note] -

-
-
- -

-Insert a new paragraph just after 23.6 [container.adaptors]/1: -

-

-For container adaptors, no swap function throws an exception -unless that exception is thrown by the swap of the -adaptor's Container or Compare object (if any). -

- - - - - - - - - - - - -
-

775. Tuple indexing should be unsigned?

-

Section: 20.4.2.5 [tuple.helper] Status: CD1 - Submitter: Alisdair Meredith Opened: 2008-01-16 Last modified: 2015-04-08

-

View all other issues in [tuple.helper].

-

View all issues with CD1 status.

-

Discussion:

-

-The tuple element access API identifies the element in the sequence -using signed integers, and then goes on to enforce the requirement that -I be >= 0. There is a much easier way to do this - declare I as -unsigned. -

-

-In fact the proposal is to use std::size_t, matching the -type used in the tuple_size API. -

-

-A second suggestion is that it is hard to imagine an API that deduces -and index at compile time and returns a reference throwing an exception. -Add a specific Throws: Nothing paragraph to each element -access API. -

-

-In addition to tuple, update the API applies to -pair and array, and should be updated -accordingly. -

- -

-A third observation is that the return type of the get -functions for std::pair is pseudo-code, but it is not -clearly marked as such. There is actually no need for pseudo-code as -the return type can be specified precisely with a call to -tuple_element. This is already done for -std::tuple, and std::array does not have a -problem as all elements are of type T. -

- - -

Proposed resolution:

-

-Update header <utility> synopsis in 20.2 [utility] -

-
-// 20.2.3, tuple-like access to pair:
-template <class T> class tuple_size;
-template <intsize_t I, class T> class tuple_element;
-
-template <class T1, class T2> struct tuple_size<std::pair<T1, T2> >;
-template <class T1, class T2> struct tuple_element<0, std::pair<T1, T2> >;
-template <class T1, class T2> struct tuple_element<1, std::pair<T1, T2> >;
-
-template<intsize_t I, class T1, class T2>
-  Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(std::pair<T1, T2>&);
-template<intsize_t I, class T1, class T2>
-  const Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(const std::pair<T1, T2>&);
-
-

-Update 20.3 [pairs] Pairs -

-
-template<intsize_t I, class T1, class T2>
-  Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(pair<T1, T2>&);
-template<intsize_t I, class T1, class T2>
-  const Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(const pair<T1, T2>&);
-
-

-24 Return type: If I == 0 then P is T1, if I == 1 then P is T2, and otherwise the program is ill-formed. -

-

-25 Returns: If I == 0 returns p.first, otherwise if I == 1 returns p.second, and otherwise the program is ill-formed. -

-

-Throws: Nothing. -

- - -

-Update header <tuple> synopsis in 20.4 [tuple] with a APIs as below: -

-
-template <intsize_t I, class T> class tuple_element; // undefined
-template <intsize_t I, class... Types> class tuple_element<I, tuple<Types...> >;
-
-// 20.3.1.4, element access:
-template <intsize_t I, class... Types>
-  typename tuple_element<I, tuple<Types...> >::type& get(tuple<Types...>&);
-template <intsize_t I, class ... types>
-  typename tuple_element<I, tuple<Types...> >::type const& get(const tuple<Types...>&);
-
- -

-Update 20.4.2.5 [tuple.helper] Tuple helper classes -

-
template <intsize_t I, class... Types>
-class tuple_element<I, tuple<Types...> > {
-public:
-  typedef TI type;
-};
-

-1 Requires: 0 <= I and I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

-

-2 Type: TI is the type of the Ith element of Types, where indexing is zero-based. -

-

-Update 20.4.2.6 [tuple.elem] Element access -

-
-template <intsize_t I, class... types >
-typename tuple_element<I, tuple<Types...> >::type& get(tuple<Types...>& t);
-
-

-1 Requires: 0 <= I and I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

-2 Returns: A reference to the Ith element of t, where indexing is zero-based. -

-Throws: Nothing. -
-template <intsize_t I, class... types>
-typename tuple_element<I, tuple<Types...> >::type const& get(const tuple<Types...>& t);
-
-

-3 Requires: 0 <= I and I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

-

-4 Returns: A const reference to the Ith element of t, where indexing is zero-based. -

-

-Throws: Nothing. -

- - -

-Update header <array> synopsis in 20.2 [utility] -

-
-template <class T> class tuple_size; // forward declaration
-template <intsize_t I, class T> class tuple_element; // forward declaration
-template <class T, size_t N>
-  struct tuple_size<array<T, N> >;
-template <intsize_t I, class T, size_t N>
-  struct tuple_element<I, array<T, N> >;
-template <intsize_t I, class T, size_t N>
-  T& get(array<T, N>&);
-template <intsize_t I, class T, size_t N>
-  const T& get(const array<T, N>&);
-
- -

-Update 23.3.2.9 [array.tuple] Tuple interface to class template array -

-
-tuple_element<size_t I, array<T, N> >::type
-
-

-3 Requires: 0 <= I < N. The program is ill-formed if I is out of bounds. -

-

-4 Value: The type T. -

-
-template <intsize_t I, class T, size_t N> T& get(array<T, N>& a);
-
-

-5 Requires: 0 <= I < N. The program is ill-formed if I is out of bounds. -

-

-Returns: A reference to the Ith element of a, where indexing is zero-based. -

-

-Throws: Nothing. -

-
-template <intsize_t I, class T, size_t N> const T& get(const array<T, N>& a);
-
-

-6 Requires: 0 <= I < N. The program is ill-formed if I is out of bounds. -

-

-7 Returns: A const reference to the Ith element of a, where indexing is zero-based. -

-

-Throws: Nothing. -

- - -

[ -Bellevue: Note also that the phrase "The program is ill-formed if I is -out of bounds" in the requires clauses are probably unnecessary, and -could be removed at the editor's discretion. Also std:: qualification -for pair is also unnecessary. -]

- - - - -
-

776. Undescribed assign function of std::array

-

Section: 23.3.2 [array] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-20 Last modified: 2015-04-08

-

View other active issues in [array].

-

View all other issues in [array].

-

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-

Discussion:

-

-The class template array synopsis in 23.3.2 [array] p. 3 declares a member -function -

- -
-void assign(const T& u);
-
- -

-which's semantic is no-where described. Since this signature is -not part of the container requirements, such a semantic cannot -be derived by those. -

- -

-I found only one reference to this function in the issue list, -588 where the question is raised: -

- -

-what's the effect of calling assign(T&) on a zero-sized array? -

- -

-which does not answer the basic question of this issue. -

- -

-If this function shall be part of the std::array, it's probable -semantic should correspond to that of boost::array, but of -course such wording must be added. -

- - -

Proposed resolution:

-

-Just after the section 23.3.2.5 [array.data] add the following new section: -

- -

-23.2.1.5 array::fill [array.fill] -

- -
-
-void fill(const T& u);
-
- -

-1: Effects: fill_n(begin(), N, u) -

-
- -

-[N.B: I wonder, why class array does not have a "modifiers" -section. If it had, then assign would naturally belong to it] -

- -

-Change the synopsis in 23.3.2 [array]/3: -

- -
-template <class T, size_t N>
-struct array { 
-  ...
-  void assign fill(const T& u);
-  ...
-
- - -

[ -Bellevue: -]

- - -
-

-Suggest substituting "fill" instead of "assign". -

-

-Set state to Review given substitution of "fill" for "assign". -

-
- - - - -
-

777. Atomics Library Issue

-

Section: 29.6 [atomics.types.operations] Status: CD1 - Submitter: Lawrence Crowl Opened: 2008-01-21 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

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-

Discussion:

-

-The load functions are defined as -

- -
-C atomic_load(volatile A* object);
-C atomic_load_explicit(volatile A* object, memory_order);
-C A::load(memory_order order = memory_order_seq_cst) volatile;
-
- -

-which prevents their use in const contexts. -

- -

[ -post Bellevue Peter adds: -]

- - -
-

-Issue 777 suggests making atomic_load operate on const objects. There is a -subtle point here. Atomic loads do not generally write to the object, except -potentially for the memory_order_seq_cst constraint. Depending on the -architecture, a dummy write with the same value may be required to be issued -by the atomic load to maintain sequential consistency. This, in turn, may -make the following code: -

- -
-const atomic_int x{};
-
-int main()
-{
-  x.load();
-}
-
- -

-dump core under a straightforward implementation that puts const objects in -a read-only section. -

-

-There are ways to sidestep the problem, but it needs to be considered. -

-

-The tradeoff is between making the data member of the atomic types -mutable and requiring the user to explicitly mark atomic members as -mutable, as is already the case with mutexes. -

-
- - - -

Proposed resolution:

-

-Add the const qualifier to *object and *this. -

- -
-C atomic_load(const volatile A* object);
-C atomic_load_explicit(const volatile A* object, memory_order);
-C A::load(memory_order order = memory_order_seq_cst) const volatile;
-
- - - - - - -
-

778. std::bitset does not have any constructor taking a string literal

-

Section: 20.6.1 [bitset.cons] Status: CD1 - Submitter: Thorsten Ottosen Opened: 2008-01-24 Last modified: 2015-04-08

-

View all other issues in [bitset.cons].

-

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-

Duplicate of: 116

-

Discussion:

-

-A small issue with std::bitset: it does not have any constructor -taking a string literal, which is clumsy and looks like an oversigt when -we tried to enable uniform use of string and const char* in the library. -

- -

-Suggestion: Add -

- -
-explicit bitset( const char* str );
-
- -

-to std::bitset. -

- - -

Proposed resolution:

-

-Add to synopsis in 20.6 [template.bitset] -

- -
-explicit bitset( const char* str );
-
- -

-Add to synopsis in 20.6.1 [bitset.cons] -

- -
-explicit bitset( const char* str );
-
-

-Effects: Constructs a bitset as if bitset(string(str)). -

-
- - - - - - -
-

779. Resolution of #283 incomplete

-

Section: 25.3.8 [alg.remove] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-25 Last modified: 2015-04-08

-

View all other issues in [alg.remove].

-

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-

Discussion:

-

-The resolution of 283 did not resolve similar necessary changes for algorithm -remove_copy[_if], which seems to be an oversight. -

- - -

Proposed resolution:

-

-In 25.3.8 [alg.remove] p.6, replace the N2461 requires clause with: -

- -

-Requires: Type T is EqualityComparable (31). The ranges [first,last) -and [result,result + (last - first)) shall not overlap. The expression *result = *first shall be -valid. -

- - - - - - -
-

780. std::merge() specification incorrect/insufficient

-

Section: 25.4.4 [alg.merge] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-01-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Though issue 283 has fixed many open issues, it seems that some are still open: -

- -

-Both 25.3.4 [lib.alg.merge] in 14882:2003 and 25.4.4 [alg.merge] in N2461 -have no Requires element and the Effects element contains some requirements, -which is probably editorial. Worse is that: -

- -
    -
  • -no assignment requirements are specified (neither implicit nor explicit). -
    • - -
  • -the effects clause just speaks of "merges", which is badly worded -near to a circular definition. -
    • - -
  • -p. 2 mentions a range [first, last), which is not defined by the -function arguments or otherwise. -
    • - -
  • -p. 2 says "according to the ordering defined by comp" which is both -incomplete (because -this excludes the first variant with <) and redundant (because the -following subordinate -clause mentions comp again) -
    • -
- -

[ -Post Summit Alisdair adds: -]

- - -
-

-Suggest: -

-

-(where last is equal to next(result, distance(first1, last1) + -distance(first2, last2)), such that resulting range will be sorted in -non-decreasing order; that is, for every iterator i in [result,last) other -than result, the condition *i < *prev(i) or, respectively, comp(*i, -*prev(i)) will be false. -

- -

-Note that this might still not be technically accurate in the case of -InputIterators, depending on other resolutions working their way through the -system (1011). -

-
- -

[ -Post Summit Daniel adds: -]

- - -

-If we want to use prev and next here (Note: merge -is sufficiently satisfied with InputIterator) we should instead add more to -25 [algorithms] p. 6, but I can currently not propose any good wording for this. -

- -

[ -Batavia (2009-05): -]

- -
-

-Pete points out the existing wording in [algorithms] p. 4 -that permits the use of + in algorithm specifications. -

-

-Alisdair points out that that wording may not apply to input iterators. -

-

-Move to Review. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- -

[ -2009-08-23 Daniel reopens: -]

- - -
-

-The proposed wording must be rephrased, because the part -

- -

-for every iterator i in [result,last) other than result, the condition -*i < *(i - 1) or, respectively, comp(*i, *(i - 1)) will be false" -

- -

-isn't meaningful, because the range [result,last) is that of a pure -OutputIterator, which is not readable in general. -

- -

[Howard: Proposed wording updated by Daniel, status moved from Ready to Review.]

- -
- -

[ -2009-10 Santa Cruz: -]

- - -
-

-Matt has some different words to propose. Those words have been moved into -the proposed wording section, and the original proposed wording now appears -here: -

-
-

-In 25.4.4 [alg.merge] replace p.1+ 2: -

- -
-

-Effects: MergesCopies all the elements of the -two sorted ranges -[first1,last1) and [first2,last2) into the range [result,result + -(last1 - first1) + (last2 - first2)) -, such that resulting range will be sorted in non-decreasing -order; that is for every -pair of iterators i and j of either input ranges, where *i was copied -to the output range -before *j was copied to the output range, the condition *j < *i or, -respectively, comp(*j, *i) -will be false. -

- -

-Requires:The resulting range shall not overlap with either -of the original ranges. -The list will be sorted in non-decreasing order according to the -ordering defined by -comp; that is, for every iterator i in [first,last) other than first, -the condition *i < *(i - 1) or -comp(*i, *(i - 1)) will be false. -

-
-
-
- -

[ -2010-02-10 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -

-Change 25.4.4 [alg.merge] 1 and 2: -

- -
-

1 -Effects: Merges two sorted ranges [first1,last1) and -[first2,last2) into the range [result, result + (last1 - -first1) + (last2 - first2)). -

-

-Effects: Copies all the elements of the two ranges -[first1,last1) and [first2,last2) into the range -[result, result_last), where result_last is result -+ (last1 - first1) + (last2 - first2), such that the resulting -range satisfies is_sorted(result, result_last) or -is_sorted(result, result_last, comp), respectively. -

- -

-2 Requires: The ranges [first1,last1) and -[first2,last2) shall be sorted with respect to operator< or -comp. The resulting range shall not overlap with either of the -original ranges. The list will be sorted in non-decreasing order according -to the ordering defined by comp; that is, for every iterator i -in [first,last) other than first, the condition *i < -*(i - 1) or comp(*i, *(i - 1)) will be false. -

- -
- -

-Change 25.4.4 [alg.merge] p. 6+7 as indicated [This ensures harmonization -between inplace_merge and merge] -

- -
-

-6 Effects: Merges two sorted consecutive ranges -[first,middle) and [middle,last), putting the result of the -merge into the range [first,last). The resulting range will be in -non-decreasing order; that is, for every iterator i in -[first,last) other than first, the condition *i < *(i - -1) or, respectively, comp(*i, *(i - 1)) will be false. -

- -

-7 Requires: The ranges [first,middle) and -[middle,last) shall be sorted with respect to operator< or -comp. The type of *first shall satisfy the -Swappable requirements (37), the MoveConstructible -requirements (Table 33), and the the MoveAssignable requirements (Table -35). -

-
- - - - - - -
-

781. std::complex should add missing C99 functions

-

Section: 26.4.7 [complex.value.ops] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-A comparision of the N2461 header <complex> synopsis ([complex.syn]) -with the C99 standard (ISO 9899, 2nd edition and the two corrigenda) show -some complex functions that are missing in C++. These are: -

- -
    -
  1. -7.3.9.4: (required elements of the C99 library)
    -The cproj functions -
    2. -
  2. -7.26.1: (optional elements of the C99 library)
    -
    -cerf    cerfc    cexp2
-cexpm1  clog10   clog1p
-clog2   clgamma  ctgamma
-
    -
    3. -
- -

-I propose that at least the required cproj overloads are provided as equivalent -C++ functions. This addition is easy to do in one sentence (delegation to C99 -function). -

- -

-Please note also that the current entry polar -in 26.4.9 [cmplx.over] p. 1 -should be removed from the mentioned overload list. It does not make sense to require that a -function already expecting scalar arguments -should cast these arguments into corresponding -complex<T> arguments, which are not accepted by -this function. -

- - -

Proposed resolution:

-

-In 26.4.1 [complex.syn] add just between the declaration of conj and fabs: -

- -
-template<class T> complex<T> conj(const complex<T>&);
-template<class T> complex<T> proj(const complex<T>&);
-template<class T> complex<T> fabs(const complex<T>&);
-
- -

-In 26.4.7 [complex.value.ops] just after p.6 (return clause of conj) add: -

- -
-
-template<class T> complex<T> proj(const complex<T>& x);
-
-

-Effects: Behaves the same as C99 function cproj, defined in -subclause 7.3.9.4." -

-
- -

-In 26.4.9 [cmplx.over] p. 1, add one further entry proj to -the overload list. -

- -
-

-The following function templates shall have additional overloads: -

-
-arg           norm 
-conj          polar proj
-imag          real
-
-
- - - - - - -
-

782. Extended seed_seq constructor is useless

-

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-01-27 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Part of the resolution of n2423, issue 8 was the proposal to -extend the seed_seq constructor accepting an input range -as follows (which is now part of N2461): -

- -
-template<class InputIterator,
-size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
-seed_seq(InputIterator begin, InputIterator end);
-
- -

-First, the expression iterator_traits<InputIterator>::value_type -is invalid due to missing typename keyword, which is easy to -fix. -

- -

-Second (and worse), while the language now supports default -template arguments of function templates, this customization -point via the second size_t template parameter is of no advantage, -because u can never be deduced, and worse - because it is a -constructor function template - it can also never be explicitly -provided (14.8.1 [temp.arg.explicit]/7). -

- -

-The question arises, which advantages result from a compile-time -knowledge of u versus a run time knowledge? If run time knowledge -suffices, this parameter should be provided as normal function -default argument [Resolution marked (A)], if compile-time knowledge -is important, this could be done via a tagging template or more -user-friendly via a standardized helper generator function -(make_seed_seq), which allows this [Resolution marked (B)]. -

- -

[ -Bellevue: -]

- - -
-

-Fermilab does not have a strong opinion. Would prefer to go with -solution A. Bill agrees that solution A is a lot simpler and does the -job. -

-

-Proposed Resolution: Accept Solution A. -

-
- -

-Issue 803 claims to make this issue moot. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 26.5.7.1 [rand.util.seedseq]/2, class seed_seq synopsis replace: -

    - -
    -class seed_seq 
-{ 
-public:
-   ...
-   template<class InputIterator,
-      size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
-          seed_seq(InputIterator begin, InputIterator end,
-          size_t u = numeric_limits<typename iterator_traits<InputIterator>::value_type>::digits);
-   ...
-};
-
    - -

    -and do a similar replacement in the member description between -p.3 and p.4. -

    -
    2. - -
  2. -

    -In 26.5.7.1 [rand.util.seedseq]/2, class seed_seq synopsis and in the -member description between p.3 and p.4 replace: -

    - -
    -template<class InputIterator,
-  size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
-      seed_seq(InputIterator begin, InputIterator end);
-template<class InputIterator, size_t u>
-seed_seq(InputIterator begin, InputIterator end, implementation-defined s);
-
    - -

    -In 26.5.2 [rand.synopsis], header <random> synopsis, immediately after the -class seed_seq declaration and in 26.5.7.1 [rand.util.seedseq]/2, immediately -after the class seed_seq definition add: -

    - -
    -template<size_t u, class InputIterator>
-  seed_seq make_seed_seq(InputIterator begin, InputIterator end);
-
    - -

    -In 26.5.7.1 [rand.util.seedseq], just before p.5 insert two paragraphs: -

    - -
    -

    -The first constructor behaves as if it would provide an -integral constant expression u of type size_t of value -numeric_limits<typename iterator_traits<InputIterator>::value_type>::digits. -

    -

    -The second constructor uses an implementation-defined mechanism -to provide an integral constant expression u of type size_t and -is called by the function make_seed_seq. -

    -
    - -

    -In 26.5.7.1 [rand.util.seedseq], just after the last paragraph add: -

    - -
    -
    -template<size_t u, class InputIterator>
-   seed_seq make_seed_seq(InputIterator begin, InputIterator end);
-
    -
    -

    -where u is used to construct an object s of implementation-defined type. -

    -

    -Returns: seed_seq(begin, end, s); -

    -
    -
    - -
    3. -
- - - - - - -
-

783. thread::id reuse

-

Section: 30.3.1.1 [thread.thread.id] Status: CD1 - Submitter: Hans Boehm Opened: 2008-02-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current working paper -(N2497, -integrated just before Bellevue) is -not completely clear whether a given thread::id value may be reused once -a thread has exited and has been joined or detached. Posix allows -thread ids (pthread_t values) to be reused in this case. Although it is -not completely clear whether this originally was the right decision, it -is clearly the established practice, and we believe it was always the -intent of the C++ threads API to follow Posix and allow this. Howard -Hinnant's example implementation implicitly relies on allowing reuse -of ids, since it uses Posix thread ids directly. -

- -

-It is important to be clear on this point, since it the reuse of thread -ids often requires extra care in client code, which would not be -necessary if thread ids were unique across all time. For example, a -hash table indexed by thread id may have to be careful not to associate -data values from an old thread with a new one that happens to reuse the -id. Simply removing the old entry after joining a thread may not be -sufficient, if it creates a visible window between the join and removal -during which a new thread with the same id could have been created and -added to the table. -

- -

[ -post Bellevue Peter adds: -]

- - -
-

-There is a real issue with thread::id reuse, but I urge the LWG to -reconsider fixing this by disallowing reuse, rather than explicitly allowing -it. Dealing with thread id reuse is an incredibly painful exercise that -would just force the world to reimplement a non-conflicting thread::id over -and over. -

-

-In addition, it would be nice if a thread::id could be manipulated -atomically in a lock-free manner, as motivated by the recursive lock -example: -

- -

-http://www.decadent.org.uk/pipermail/cpp-threads/2006-August/001091.html -

-
- - - -

Proposed resolution:

-

-Add a sentence to 30.3.1.1 [thread.thread.id]/p1: -

- -
-

-An object of type thread::id provides -a unique identifier for each thread of execution -and a single distinct value for all thread objects -that do not represent a thread of execution ([thread.threads.class]). -Each thread of execution has a thread::id -that is not equal to the thread::id -of other threads of execution -and that is not equal to -the thread::id of std::thread objects -that do not represent threads of execution. -The library may reuse the value of a thread::id of a -terminated thread that can no longer be joined. -

-
- - - - - -
-

786. Thread library timed waits, UTC and monotonic clocks

-

Section: 20.12 [time] Status: Resolved - Submitter: Christopher Kohlhoff, Jeff Garland Opened: 2008-02-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The draft C++0x thread library requires that the time points of type -system_time and returned by get_system_time() represent Coordinated -Universal Time (UTC) (section [datetime.system]). This can lead to -surprising behavior when a library user performs a duration-based wait, -such as condition_variable::timed_wait(). A complete explanation of the -problem may be found in the -Rationale for the Monotonic Clock -section in POSIX, but in summary: -

- -
    -
  • -Operations such as condition_variable::timed_wait() (and its POSIX -equivalent, pthread_cond_timedwait()) are specified using absolute times -to address the problem of spurious wakeups. -
    • - -
  • -The typical use of the timed wait operations is to perform a relative -wait. This may be achieved by first calculating an absolute time as the -sum of the current time and the desired duration. In fact, the C++0x -thread library includes duration-based overloads of -condition_variable::timed_wait() that behave as if by calling the -corresponding absolute time overload with a time point value of -get_system_time() + rel_time. -
    • - -
  • -A UTC clock may be affected by changes to the system time, such as -synchronization with an external source, leap seconds, or manual changes -to the clock. -
    • - -
  • -Should the clock change during a timed wait operation, the actual -duration of the wait will not be the expected length. For example, a -user may intend a timed wait of one second duration but, due to an -adjustment of the system clock backwards by a minute, the wait instead -takes 61 seconds. -
    • -
- -

-POSIX solves the problem by introducing a new monotonic clock, which is -unaffected by changes to the system time. When a condition variable is -initialized, the user may specify whether the monotonic clock is to be -used. (It is worth noting that on POSIX systems it is not possible to -use condition_variable::native_handle() to access this facility, since -the desired clock type must be specified during construction of the -condition variable object.) -

- -

-In the context of the C++0x thread library, there are added dimensions -to the problem due to the need to support platforms other than POSIX: -

- -
    -
  • -Some environments (such as embedded systems) do not have a UTC clock, but do have a monotonic clock. -
    • - -
  • -Some environments do not have a monotonic clock, but do have a UTC clock. -
    • - -
  • -The Microsoft Windows API's synchronization functions use relative -timeouts based on an implied monotonic clock. A program that switches -from the Windows API to the C++0x thread library will now find itself -susceptible to clock changes. -
    • -
- -

-One possible minimal solution: -

- -
    -
  • -Strike normative references to UTC and an epoch based on 1970-01-01. -
    • - -
  • -Make the semantics of system_time and get_system_time() -implementation-defined (i.e standard library implementors may choose the -appropriate underlying clock based on the capabilities of the target -platform). -
    • - -
  • -Add a non-normative note encouraging use of a monotonic clock. -
    • - -
  • -Remove system_time::seconds_since_epoch(). -
    • - -
  • -Change the constructor explicit system_time(time_t secs, nanoseconds ns -= 0) to explicit system_time(nanoseconds ns). -
    • -
- - - -

Proposed resolution:

-

-

- - -

Rationale:

-Addressed by -N2661: A Foundation to Sleep On. -

- - - - -
-

787. complexity of binary_search

-

Section: 25.4.3.4 [binary.search] Status: CD1 - Submitter: Daniel Krügler Opened: 2007-09-08 Last modified: 2015-04-08

-

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-

Discussion:

-

-In 25.4.3.4 [binary.search] p. 3 the complexity of binary_search is described as -

- -

-At most log(last - first) + 2 comparisons. -

- -

-This should be precised and brought in line with the nomenclature used for -lower_bound, upper_bound, and equal_range. -

- -

-All existing libraries I'm aware of, delegate to -lower_bound (+ one further comparison). Since -issue 384 has now WP status, the resolution of #787 should -be brought in-line with 384 by changing the + 2 -to + O(1). -

- -

[ -Sophia Antipolis: -]

- - -

-Alisdair prefers to apply an upper bound instead of O(1), but that would -require fixing for lower_bound, upper_bound etc. as well. If he really -cares about it, he'll send an issue to Howard. -

- - - -

Proposed resolution:

-

-Change 25.4.3.4 [binary.search]/3 -

- -

-Complexity: At most log2(last - first) + 2 O(1) comparisons. -

- - - - - -
-

788. Ambiguity in [istream.iterator]

-

Section: 24.6.1 [istream.iterator] Status: C++11 - Submitter: Martin Sebor Opened: 2008-02-06 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

Addresses UK 287

- -
-

-It is not clear what the initial state of an istream_iterator should be. Is -_value_ initialized by reading the stream, or default/value initialized? If -it is initialized by reading the stream, what happens if the initialization -is deferred until first dereference, when ideally the iterator value should -have been that of an end-of-stream iterator which is not safely -dereferencable? -

- -

-Recommendation: Specify _value_ is initialized by reading the stream, or -the iterator takes on the end-of-stream value if the stream is empty. -

-
- -

-The description of how an istream_iterator object becomes an -end-of-stream iterator is a) ambiguous and b) out of date WRT -issue 468: -

- -

-istream_iterator reads (using operator>>) successive elements from the -input stream for which it was constructed. After it is constructed, and -every time ++ is used, the iterator reads and stores a value of T. If -the end of stream is reached (operator void*() on the stream returns -false), the iterator becomes equal to the end-of-stream iterator value. -The constructor with no arguments istream_iterator() always constructs -an end of stream input iterator object, which is the only legitimate -iterator to be used for the end condition. The result of operator* on an -end of stream is not defined. For any other iterator value a const T& is -returned. The result of operator-> on an end of stream is not defined. -For any other iterator value a const T* is returned. It is impossible to -store things into istream iterators. The main peculiarity of the istream -iterators is the fact that ++ operators are not equality preserving, -that is, i == j does not guarantee at all that ++i == ++j. Every time ++ -is used a new value is read. -

- -

-istream::operator void*() returns null if istream::fail() is true, -otherwise non-null. istream::fail() returns true if failbit or -badbit is set in rdstate(). Reaching the end of stream doesn't -necessarily imply that failbit or badbit is set (e.g., after -extracting an int from stringstream("123") the stream object will -have reached the end of stream but fail() is false and operator -void*() will return a non-null value). -

- -

-Also I would prefer to be explicit about calling fail() here -(there is no operator void*() anymore.) -

- -

[ -Summit: -]

- - -

-Moved from Ready to Open for the purposes of using this issue to address NB UK 287. -Martin to handle. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-This improves the wording. -

-

-Move to Ready. -

-
- - - -

Proposed resolution:

-

-Change 24.6.1 [istream.iterator]/1: -

- -

-istream_iterator reads (using operator>>) successive elements from the -input stream for which it was constructed. After it is constructed, and -every time ++ is used, the iterator reads and stores a value of T. If -the end of stream is reached the iterator fails to read and store a value of T -(operator void*() fail() on the stream returns -false true), the iterator becomes equal to the end-of-stream iterator value. -The constructor with no arguments istream_iterator() always constructs -an end of stream input iterator object, which is the only legitimate -iterator to be used for the end condition. The result of operator* on an -end of stream is not defined. For any other iterator value a const T& is -returned. The result of operator-> on an end of stream is not defined. -For any other iterator value a const T* is returned. It is impossible to -store things into istream iterators. The main peculiarity of the istream -iterators is the fact that ++ operators are not equality preserving, -that is, i == j does not guarantee at all that ++i == ++j. Every time ++ -is used a new value is read. -

- - - - - -
-

789. xor_combine_engine(result_type) should be explicit

-

Section: X [rand.adapt.xor] Status: CD1 - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-xor_combine_engine(result_type) should be explicit. (Obvious oversight.) -

- -

[ -Bellevue: -]

- - -

-Non-controversial. Bill is right, but Fermilab believes that this is -easy to use badly and hard to use right, and so it should be removed -entirely. Got into TR1 by well defined route, do we have permission to -remove stuff? Should probably check with Jens, as it is believed he is -the originator. Broad consensus that this is not a robust engine -adapter. -

- - -

Proposed resolution:

-

-Remove xor_combine_engine from synopsis of 26.5.2 [rand.synopsis]. -

-

-Remove X [rand.adapt.xor] xor_combine_engine. -

- - - - - -
-

792. piecewise_constant_distribution is undefined for a range with just one endpoint

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: CD1 - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-piecewise_constant_distribution is undefined for a range with just one -endpoint. (Probably should be the same as an empty range.) -

- - -

Proposed resolution:

-

-Change 26.5.8.6.2 [rand.dist.samp.pconst] paragraph 3b: -

- -

-b) If firstB == lastB or the sequence w has the length zero, -

- - - - - -
-

793. discrete_distribution missing constructor

-

Section: 26.5.8.6.1 [rand.dist.samp.discrete] Status: Resolved - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-discrete_distribution should have a constructor like: -

- -
-template<class _Fn>
-  discrete_distribution(result_type _Count, double _Low, double _High,
-                        _Fn& _Func);
-
- -

-(Makes it easier to fill a histogram with function values over a range.) -

- -

[ -Bellevue: -]

- - -

-How do you specify the function so that it does not return negative -values? If you do it is a bad construction. This requirement is already -there. Where in each bin does one evaluate the function? In the middle. -Need to revisit tomorrow. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Bill is not requesting this. -

-

-Marc Paterno: _Fn cannot return negative values at the points where the -function is sampled. It is sampled in the middle of each bin. _Fn cannot -return 0 everywhere it is sampled. -

-

-Jens: lambda expressions are rvalues -

-

-Add a library issue to provide an -initializer_list<double> constructor for -discrete_distribution. -

-

-Marc Paterno: dislikes reference for _Fn parameter. Make it pass-by-value (to use lambda), -use std::ref to wrap giant-state function objects. -

-

-Daniel: See random_shuffle, pass-by-rvalue-reference. -

-

-Daniel to draft wording. -

-
- -

[ -Pre San Francisco, Daniel provided wording: -]

- - -

-The here proposed changes of the WP refer to the current state of -N2691. -During the Sophia Antipolis meeting two different proposals came up -regarding the functor argument type, either by value or by rvalue-reference. -For consistence with existing conventions (state-free algorithms and the -general_pdf_distribution c'tor signature) the author decided to propose a -function argument that is provided by value. If severe concerns exists that -stateful functions would be of dominant relevance, it should be possible to -replace the two occurrences of Func by Func&& in this proposal as part -of an editorial process. -

- - - -

Proposed resolution:

- -

Non-concept version of the proposed resolution

- -
    -
  1. -

    -In 26.5.8.6.1 [rand.dist.samp.discrete]/1, class discrete_distribution, just -before the member declaration -

    - -
    -explicit discrete_distribution(const param_type& parm);
-
    - -

    -insert: -

    - - -
    -template<typename Func>
-discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 insert a series of new paragraphs as part of the -new member description:: -

    -
    -template<typename Func>
-discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
-
    - -

    -Complexity: Exactly nf invocations of fw. -

    -

    -Requires: -

    -
      -
    1. -fw shall be callable with one argument of type double, and shall -return values of a type convertible to double;
      2. - -
    2. If nf > 0, the relation xmin < xmax shall hold, and for all sample values -xk, fw(xk) shall return a weight value wk that is non-negative, non-NaN, -and non-infinity;
      3. - -
    3. The following relations shall hold: nf ≥ 0, and 0 < S = w0+. . .+wn-1.
      4. - -
    - -

    -Effects: -

    -
      -
    1. If nf == 0, sets n = 1 and lets the sequence w have length n = 1 and - consist of the single value w0 = 1.
      2. - -
    2. -

      Otherwise, sets n = nf, deltax = (xmax - xmin)/n -and xcent = xmin + 0.5 * deltax.

      -

      -For each k = 0, . . . ,n-1, calculates:

      -

      -xk = xcent + k * deltax -wk = fw(xk) -

      -
      3. -
    3. -

      Constructs a discrete_distribution object with probabilities:

      -

      -pk = wk/S for k = 0, . . . , n-1. -

      -
      4. -
    -
    -
    3. -
- -

Concept version of the proposed resolution

- - -
    -
  1. -

    -In 26.5.8.6.1 [rand.dist.samp.discrete]/1, class discrete_distribution, just -before the member declaration -

    - -
    -explicit discrete_distribution(const param_type& parm);
-
    - -

    -insert: -

    - - -
    -template<Callable<auto, double> Func>
- requires Convertible<Func::result_type, double>
-discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 insert a series of new paragraphs as part of the -new member description:: -

    -
    -template<Callable<auto, double> Func>
- requires Convertible<Func::result_type, double>
-discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
-
    - -

    -Complexity: Exactly nf invocations of fw. -

    -

    -Requires: -

    -
      -
    1. If nf > 0, the relation xmin < xmax shall hold, and for all sample values -xk, fw(xk) shall return a weight value wk that is non-negative, non-NaN, -and non-infinity;
      2. - -
    2. The following relations shall hold: nf ≥ 0, and 0 < S = w0+. . .+wn-1.
      3. - -
    - -

    -Effects: -

    -
      -
    1. If nf == 0, sets n = 1 and lets the sequence w have length n = 1 and - consist of the single value w0 = 1.
      2. - -
    2. -

      Otherwise, sets n = nf, deltax = (xmax - xmin)/n -and xcent = xmin + 0.5 * deltax. -

      -For each k = 0, . . . ,n-1, calculates: -

      -xk = xcent + k * deltax -wk = fw(xk) -

      -
      3. -
    3. -

      Constructs a discrete_distribution object with probabilities:

      -

      -pk = wk/S for k = 0, . . . , n-1. -

      -
      4. -
    -
    -
    3. -
- - - -

Rationale:

-Addressed by -N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - - -
-

794. piecewise_constant_distribution missing constructor

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: Resolved - Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.pconst].

-

View all issues with Resolved status.

-

Discussion:

-

-piecewise_constant_distribution should have a constructor like: -

- -
-template<class _Fn>
-   piecewise_constant_distribution(size_t _Count,
-            _Ty _Low, _Ty _High, _Fn& _Func);
-
- -

-(Makes it easier to fill a histogram with function values over a range. -The two (reference 793) make a sensible replacement for -general_pdf_distribution.) -

- -

[ -Sophia Antipolis: -]

- - -
-

-Marc: uses variable width of bins and weight for each bin. This is not -giving enough flexibility to control both variables. -

-

-Add a library issue to provide an constructor taking an -initializer_list<double> and _Fn for piecewise_constant_distribution. -

-

-Daniel to draft wording. -

-
- -

[ -Pre San Francisco, Daniel provided wording. -]

- - -

-The here proposed changes of the WP refer to the current state of -N2691. -For reasons explained in 793, the author decided to propose a function -argument that is provided by value. The issue proposes a c'tor signature, -that does not take advantage of the full flexibility of -piecewise_constant_distribution, -because it restricts on a constant bin width, but the use-case seems to -be popular enough to justify it's introduction. -

- - - -

Proposed resolution:

- -

Non-concept version of the proposed resolution

- -
    -
  1. -

    -In 26.5.8.6.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, -just before the member declaration -

    - -
    -explicit piecewise_constant_distribution(const param_type& parm);
-
    -

    -insert: -

    -
    -template<typename Func>
-piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 insert a new sequence of paragraphs nominated -below as [p5_1], [p5_2], -[p5_3], and [p5_4] as part of the new member description: -

    - -
    -template<typename Func>
-piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
-
    -
    -

    -[p5_1] Complexity: Exactly nf invocations of fw. -

    -

    -[p5_2] Requires: -

    -
      -
    1. fw shall be callable with one argument of type RealType, and shall -return values of a type convertible to double; -
      2. -
    2. -For all sample values xk defined below, fw(xk) shall return a weight -value wk that is non-negative, non-NaN, and non-infinity; -
      3. -
    3. -The following relations shall hold: xmin < xmax, and -0 < S = w0+. . .+wn-1. -
      4. -
    -

    -[p5_3] Effects: -

    -
      -
    1. -

      If nf == 0,

      -
        -
      1. -sets deltax = xmax - xmin, and
        2. -
      2. lets the sequence w have length n = 1 and consist of the single - value w0 = 1, and
        3. -
      3. lets the sequence b have length n+1 with b0 = xmin and - b1 = xmax -
        4. -
      -
      2. -
    2. -

      Otherwise,

      -
        -
      1. sets n = nf, deltax = (xmax - xmin)/n, - xcent = xmin + 0.5 * deltax, and -
        2. -

      2. lets the sequences w and b have length n and n+1, resp. and -

        -for each k = 0, . . . ,n-1, calculates: -

        - dxk = k * deltax - bk = xmin + dxk - xk = xcent + dxk - wk = fw(xk), -

        -

        and

        -
        3. -
      3. sets bn = xmax
        4. -
      -
      3. -
    3. -

      -Constructs a piecewise_constant_distribution object with -the above computed sequence b as the interval boundaries -and with the probability densities: -

      -

      -ρk = wk/(S * deltax) for k = 0, . . . , n-1. -

      -
      4. -
    -

    -[p5_4] [Note: In this context, the subintervals [bk, bk+1) are commonly - known as the bins of a histogram. -- end note] -

    -
    -
    -
    3. -
- -

Concept version of the proposed resolution

- -
    -
  1. -

    -In 26.5.8.6.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, -just before the member declaration -

    - -
    -explicit piecewise_constant_distribution(const param_type& parm);
-
    -

    -insert: -

    -
    -template<Callable<auto, RealType> Func>
- requires Convertible<Func::result_type, double>
-piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 insert a new sequence of paragraphs nominated -below as [p5_1], [p5_2], -[p5_3], and [p5_4] as part of the new member description: -

    - -
    -template<Callable<auto, RealType> Func>
- requires Convertible<Func::result_type, double>
-piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
-
    -
    -

    -[p5_1] Complexity: Exactly nf invocations of fw. -

    -

    -[p5_2] Requires: -

    -
      -
    1. -For all sample values xk defined below, fw(xk) shall return a weight -value wk that is non-negative, non-NaN, and non-infinity; -
      2. -
    2. -The following relations shall hold: xmin < xmax, and -0 < S = w0+. . .+wn-1. -
      3. -
    -

    -[p5_3] Effects: -

    -
      -
    1. -

      If nf == 0,

      -
        -
      1. -sets deltax = xmax - xmin, and
        2. -
      2. lets the sequence w have length n = 1 and consist of the single - value w0 = 1, and
        3. -
      3. lets the sequence b have length n+1 with b0 = xmin and - b1 = xmax -
        4. -
      -
      2. -
    2. -

      Otherwise,

      -
        -
      1. sets n = nf, deltax = (xmax - xmin)/n, - xcent = xmin + 0.5 * deltax, and -
        2. -

      2. lets the sequences w and b have length n and n+1, resp. and -

        -for each k = 0, . . . ,n-1, calculates: - dxk = k * deltax - bk = xmin + dxk - xk = xcent + dxk - wk = fw(xk), -

        -

        and

        -
        3. -
      3. sets bn = xmax
        4. -
      -
      3. -
    3. -

      -Constructs a piecewise_constant_distribution object with -the above computed sequence b as the interval boundaries -and with the probability densities: -

      -

      -ρk = wk/(S * deltax) for k = 0, . . . , n-1. -

      -
      4. -
    -

    -[p5_4] [Note: In this context, the subintervals [bk, bk+1) are commonly - known as the bins of a histogram. -- end note] -

    -
    -
    -
    3. -
- - - -

Rationale:

-

-Addressed by -N2836 -"Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - - -
-

798. Refactoring of binders lead to interface breakage

-

Section: X [depr.lib.binders] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-02-14 Last modified: 2015-04-08

-

View all other issues in [depr.lib.binders].

-

View all issues with CD1 status.

-

Discussion:

-

-N2521 -and its earlier predecessors have moved the old binders from -[lib.binders] to X [depr.lib.binders] thereby introducing some renaming -of the template parameter names (Operation -> Fn). During this -renaming process the protected data member op was also renamed to -fn, which seems as an unnecessary interface breakage to me - even if -this user access point is probably rarely used. -

- - -

Proposed resolution:

-

-Change [depr.lib.binder.1st]: -

- -
-
-template <class Fn> 
-class binder1st 
-  : public unary_function<typename Fn::second_argument_type, 
-                          typename Fn::result_type> { 
-protected: 
-  Fn fn op; 
-  typename Fn::first_argument_type value; 
-public: 
-  binder1st(const Fn& x, 
-            const typename Fn::first_argument_type& y); 
-  typename Fn::result_type 
-    operator()(const typename Fn::second_argument_type& x) const; 
-  typename Fn::result_type 
-    operator()(typename Fn::second_argument_type& x) const; 
-};
-
- -
-

--1- The constructor initializes fn op with x and value with y. -

-

--2- operator() returns fnop(value,x). -

-
-
- -

-Change [depr.lib.binder.2nd]: -

- -
-
-template <class Fn> 
-class binder2nd
-  : public unary_function<typename Fn::first_argument_type, 
-                          typename Fn::result_type> { 
-protected: 
-  Fn fn op; 
-  typename Fn::second_argument_type value; 
-public: 
-  binder2nd(const Fn& x, 
-            const typename Fn::second_argument_type& y); 
-  typename Fn::result_type 
-    operator()(const typename Fn::first_argument_type& x) const; 
-  typename Fn::result_type 
-    operator()(typename Fn::first_argument_type& x) const; 
-};
-
- -
-

--1- The constructor initializes fn op with x and value with y. -

-

--2- operator() returns fnop(value,x). -

-
-
- - - - - - -
-

800. Issues in 26.4.7.1 [rand.util.seedseq](6)

-

Section: 26.5.7.1 [rand.util.seedseq] Status: Resolved - Submitter: Stephan Tolksdorf Opened: 2008-02-18 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with Resolved status.

-

Discussion:

-

-The for-loop in the algorithm specification has n iterations, where n is -defined to be end - begin, i.e. the number of supplied w-bit quantities. -Previous versions of this algorithm and the general logic behind it -suggest that this is an oversight and that in the context of the -for-loop n should be the number of full 32-bit quantities in b (rounded -upwards). If w is 64, the current algorithm throws away half of all bits -in b. If w is 16, the current algorithm sets half of all elements in v -to 0. -

- -

-There are two more minor issues: -

- -
    -
  • -Strictly speaking end - begin is not defined since -InputIterator is not required to be a random access iterator. -
    • -
  • -Currently all integral types are allowed as input to the seed_seq -constructor, including bool. IMHO allowing bools unnecessarily -complicates the implementation without any real benefit to the user. -I'd suggest to exclude bools as input. -
    • -
- -

[ -Bellevue: -]

- - -

-Move to Open: Bill will try to propose a resolution by the next meeting. -

- -

[ -post Bellevue: Bill provided wording. -]

- - -

-This issue is made moot if 803 is accepted. -

- - - -

Proposed resolution:

-

-Replace 26.5.7.1 [rand.util.seedseq] paragraph 6 with: -

- -
-

-Effects: Constructs a seed_seq object by effectively concatenating the -low-order u bits of each of the elements of the supplied sequence [begin, -end) in ascending order of significance to make a (possibly very large) unsigned -binary number b having a total of n bits, and then carrying out the -following algorithm: -

- -

-for( v.clear(); n > 0; n -= 32 ) - v.push_back(b mod 232), b /= 232; -

-
- - -

Rationale:

-Addressed by -N2836 -"Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - -
-

801. tuple and pair trivial members

-

Section: 20.4 [tuple] Status: Resolved - Submitter: Lawrence Crowl Opened: 2008-02-18 Last modified: 2015-04-08

-

View all other issues in [tuple].

-

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-

Discussion:

-

-Classes with trivial special member functions are inherently more -efficient than classes without such functions. This efficiency is -particularly pronounced on modern ABIs that can pass small classes -in registers. Examples include value classes such as complex numbers -and floating-point intervals. Perhaps more important, though, are -classes that are simple collections, like pair and tuple. When the -parameter types of these classes are trivial, the pairs and tuples -themselves can be trivial, leading to substantial performance wins. -

-

-The current working draft make specification of trivial functions -(where possible) much easer through defaulted and deleted functions. -As long as the semantics of defaulted and deleted functions match -the intended semantics, specification of defaulted and deleted -functions will yield more efficient programs. -

-

-There are at least two cases where specification of an explicitly -defaulted function may be desirable. -

-

-First, the std::pair template has a non-trivial default constructor, -which prevents static initialization of the pair even when the -types are statically initializable. Changing the definition to -

- -
-pair() = default;
-
- -

-would enable such initialization. Unfortunately, the change is -not semantically neutral in that the current definition effectively -forces value initialization whereas the change would not value -initialize in some contexts. -

- -

-** Does the committee confirm that forced value initialization -was the intent? If not, does the committee wish to change the -behavior of std::pair in C++0x? -

-

-Second, the same default constructor issue applies to std::tuple. -Furthermore, the tuple copy constructor is current non-trivial, -which effectively prevents passing it in registers. To enable -passing tuples in registers, the copy constructor should be -make explicitly defaulted. The new declarations are: -

- -
-tuple() = default;
-tuple(const tuple&) = default;
-
- -

-This changes is not implementation neutral. In particular, it -prevents implementations based on pointers to the parameter -types. It does however, permit implementations using the -parameter types as bases. -

-

-** How does the committee wish to trade implementation -efficiency versus implementation flexibility? -

- -

[ -Bellevue: -]

- - -
-

-General agreement; the first half of the issue is NAD. -

-

-Before voting on the second half, it was agreed that a "Strongly Favor" -vote meant support for trivial tuples (assuming usual requirements met), -even at the expense of other desired qualities. A "Weakly Favor" vote -meant support only if not at the expense of other desired qualities. -

-

-Concensus: Go forward, but not at expense of other desired qualities. -

-

-It was agreed to Alisdair should fold this work in with his other -pair/tuple action items, above, and that issue 801 should be "open", but -tabled until Alisdair's proposals are disposed of. -

-
- -

[ -2009-05-27 Daniel adds: -]

- - -

-This is partly solved by 1117. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Wait for dust to settle from fixing exception safety problem -with rvalue refs. -

- -

[ -2009-07-20 Alisdair adds: -]

- - -
-

-Basically, this issue is what should we do with the default constructor -for pairs and tuples of trivial types. The motivation of the issue was -to force static initialization rather than dynamic initialization, and -was rejected in the case of pair as it would change the meaning of -existing programs. The advice was "do the best we can" for tuple -without changing existing meaning. -

- -

-Frankfurt seems to simply wait and see the resolution on no-throw move -constructors, which (I believe) is only tangentially related to this -issue, but as good as any to defer until Santa Cruz. -

- -

-Looking again now, I think constant (static) initialization for pair can -be salvaged by making the default construct constexpr. I have a -clarification from Core that this is intended to work, even if the -constructor is not trivial/constexpr, so long as no temporaries are -implied in the process (even if elided). -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as open. Alisdair to provide wording. -

- -

[ -2010 Pittsburgh: -]

- - -
-

-We believe this may be NAD Editorial since both pair and tuple now have -constexpr default constructors, but we're not sure. -

-
- - -

[ -2010 Rapperswil: -]

- - -

-Daniel believes his pair/tuple paper will resolve this issue. constexpr -will allow static initialization, and he is already changing the move and copy -constructors to be defaulted. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-The proposed resolution of -n3140 -should resolve this issue. -

- - - -

Proposed resolution:

-

-See n3140. -

- - - - - -
-

803. Simplification of seed_seq::seq_seq

-

Section: 26.5.7.1 [rand.util.seedseq] Status: Resolved - Submitter: Charles Karney Opened: 2008-02-22 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

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-

Discussion:

-

-seed_seq(InputIterator begin, InputIterator end); constructs a seed_seq -object repacking the bits of supplied sequence [begin, end) into a -32-bit vector. -

-

-This repacking triggers several problems: -

-
    -
  1. -Distinctness of the output of seed_seq::generate required the -introduction of the initial "if (w < 32) v.push_back(n);" (Otherwise -the unsigned short vectors [1, 0] and [1] generate the same sequence.) -
    2. -
  2. -Portability demanded the introduction of the template parameter u. -(Otherwise some sequences could not be obtained on computers where no -integer types are exactly 32-bits wide.) -
    3. -
  3. -The description and algorithm have become unduly complicated. -
    4. -
-

-I propose simplifying this seed_seq constructor to be "32-bit only". -Despite it's being simpler, there is NO loss of functionality (see -below). -

-

-Here's how the description would read -

-
-

-26.5.7.1 [rand.util.seedseq] Class seed_seq -

- -
-
-template<class InputIterator>
-  seed_seq(InputIterator begin, InputIterator end);
-
-
-

-5 Requires: NO CHANGE -

-

-6 Effects: Constructs a seed_seq object by -

-

-for (InputIterator s = begin; s != end; ++s) - v.push_back((*s) mod 232); -

-
-
-
- -

-Discussion: -

-

-The chief virtues here are simplicity, portability, and generality. -

-
    -
  • -Simplicity — compare the above specification with the -n2461 proposal. -
    • -
  • -Portability — with iterator_traits<InputIterator>::value_type = -uint_least32_t the user is guaranteed to get the same behavior across -platforms. -
    • -
  • -Generality — any behavior that the -n2461 -proposal can achieve can be -obtained with this simpler proposal (albeit with a shuffling of bits -in the input sequence). -
    • -
-

-Arguments (and counter-arguments) against making this change (and -retaining the -n2461 -behavior) are: -

-
    -
  • -

    -The user can pass an array of unsigned char and seed_seq will nicely - repack it. -

    -

    - Response: So what? Consider the seed string "ABC". The - n2461 - proposal results in -

    -
    -v = { 0x3, 0x434241 };
-
    -

    -while the simplified proposal yields -

    -
    -v = { 0x41, 0x42, 0x43 };
-
    -

    -The results produced by seed_seq::generate with the two inputs are -different but nevertheless equivalently "mixed up" and this remains -true even if the seed string is long. -

    -
    • -
  • -

    -With long strings (e.g., with bit-length comparable to the number of - bits in the state), v is longer (by a factor of 4) with the simplified - proposal and seed_seq::generate will be slower. -

    -

    -Response: It's unlikely that the efficiency of seed_seq::generate will - be a big issue. If it is, the user is free to repack the seed vector - before constructing seed_seq. -

    -
    • -
  • -

    -A user can pass an array of 64-bit integers and all the bits will be - used. -

    -

    - Response: Indeed. However, there are many instances in the - n2461 - where integers are silently coerced to a narrower width and this - should just be a case of the user needing to read the documentation. - The user can of course get equivalent behavior by repacking his seed - into 32-bit pieces. Furthermore, the unportability of the - n2461 - proposal with -

    -
    -unsigned long s[] = {1, 2, 3, 4};
-seed_seq q(s, s+4);
-
    -

    - which typically results in v = {1, 2, 3, 4} on 32-bit machines and in -v = {1, 0, 2, 0, 3, 0, 4, 0} on 64-bit machines is a major pitfall for - unsuspecting users. -

    -
    • -
- -

-Note: this proposal renders moot issues 782 and 800. -

- -

[ -Bellevue: -]

- - -

-Walter needs to ask Fermilab for guidance. Defer till tomorrow. Bill likes the proposed resolution. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Marc Paterno wants portable behavior between 32bit and 64bit machines; -we've gone to significant trouble to support portability of engines and -their values. -

-

-Jens: the new algorithm looks perfectly portable -

-

-Marc Paterno to review off-line. -

-

-Modify the proposed resolution to read "Constructs a seed_seq object by the following algorithm ..." -

-

-Disposition: move to review; unanimous consent. -

-

-(moots 782 and 800) -

-
- - - -

Proposed resolution:

-

-Change 26.5.7.1 [rand.util.seedseq]: -

- -
-
-template<class InputIterator, 
-  size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
-  seed_seq(InputIterator begin, InputIterator end);
-
-
-

--5- Requires: InputIterator shall satisfy the requirements of an input iterator (24.1.1) -such that iterator_traits<InputIterator>::value_type shall denote an integral type. -

-

--6- Constructs a seed_seq object by the following algorithm rearranging some or all of the bits of the supplied sequence -[begin,end) of w-bit quantities into 32-bit units, as if by the following: -

-

-First extract the rightmost u bits from each of the n = end -- begin elements of the supplied sequence and concatenate all the -extracted bits to initialize a single (possibly very large) unsigned -binary number, b = ∑n-1i=0 (begin[i] -mod 2u) · 2w·i (in which the bits of each begin[i] -are treated as denoting an unsigned quantity). Then carry out -the following algorithm: -

-

-v.clear(); -if ($w$ < 32) - v.push_back($n$); -for( ; $n$ > 0; --$n$) - v.push_back(b mod 232), b /= 232; -

-
-

-for (InputIterator s = begin; s != end; ++s) - v.push_back((*s) mod 232); -

-
-
-
- - -

Rationale:

-Addressed by -N2836 -"Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - -
-

804. Some problems with classes error_code/error_condition

-

Section: 19.5 [syserr] Status: CD1 - Submitter: Daniel Krügler Opened: 2008-02-24 Last modified: 2015-04-08

-

View all other issues in [syserr].

-

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-

Discussion:

-
    -
  1. -

    -19.5.2.1 [syserr.errcode.overview]/1, class error_code and -19.5.3.1 [syserr.errcondition.overview]/, class error_condition synopses -declare an expository data member cat_: -

    -
    -const error_category& cat_; // exposition only
-
    -

    -which is used to define the semantics of several members. The decision -to use a member of reference type lead to several problems: -

    -
      -
    1. -The classes are not (Copy)Assignable, which is probably not the intent. -
      2. -
    2. -The post conditions of all modifiers from -19.5.2.3 [syserr.errcode.modifiers] and 19.5.3.3 [syserr.errcondition.modifiers], resp., -cannot be fulfilled. -
      3. -
    -

    -The simple fix would be to replace the reference by a pointer member. -

    -
    2. - -
  2. -I would like to give the editorial remark that in both classes the -constrained operator= -overload (template with ErrorCodeEnum argument) makes in invalid -usage of std::enable_if: By using the default value for the second enable_if -parameter the return type would be defined to be void& even in otherwise -valid circumstances - this return type must be explicitly provided (In -error_condition the first declaration uses an explicit value, but of wrong -type). -
    3. - -
  3. -The member function message throws clauses ( -19.5.1.2 [syserr.errcat.virtuals]/10, 19.5.2.4 [syserr.errcode.observers]/8, and -19.5.3.4 [syserr.errcondition.observers]/6) guarantee "throws nothing", -although -they return a std::string by value, which might throw in out-of-memory -conditions (see related issue 771). -
    4. -
- -

[ -Sophia Antipolis: -]

- - -
-

-Part A: NAD (editorial), cleared by the resolution of issue 832. -

-

-Part B: Technically correct, save for typo. Rendered moot by the concept proposal -(N2620) NAD (editorial). -

-

-Part C: We agree; this is consistent with the resolution of issue 721. -

-

-Howard: please ping Beman, asking him to clear away parts A and B from -the wording in the proposed resolution, so it is clear to the editor -what needs to be applied to the working paper. -

-

-Beman provided updated wording. Since issue 832 is not going -forward, the provided wording includes resolution of part A. -

-
- - - -

Proposed resolution:

- -

-Resolution of part A: -

-
-

-Change 19.5.2.1 [syserr.errcode.overview] Class error_code overview synopsis as indicated: -

- -
-private:
-  int val_;                    // exposition only
-  const error_category&* cat_; // exposition only
-
- -

-Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors as indicated: -

- -
-
-error_code();
-
-
-

-Effects: Constructs an object of type error_code. -

-

-Postconditions: val_ == 0 and cat_ == &system_category. -

-

-Throws: Nothing. -

-
-
-error_code(int val, const error_category& cat);
-
-
-

-Effects: Constructs an object of type error_code. -

-

-Postconditions: val_ == val and cat_ == &cat. -

-

-Throws: Nothing. -

-
-
- -

-Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as indicated: -

- -
-
-void assign(int val, const error_category& cat);
-
-
-

-Postconditions: val_ == val and cat_ == &cat. -

-

-Throws: Nothing. -

-
-
- -

-Change 19.5.2.4 [syserr.errcode.observers] Class error_code observers as indicated: -

- -
-const error_category& category() const;
-
-

-Returns: *cat_. -

-

-Throws: Nothing. -

-
-
- -

-Change 19.5.3.1 [syserr.errcondition.overview] Class error_condition overview synopsis as indicated: -

- -
-private:
-  int val_;                    // exposition only
-  const error_category&* cat_; // exposition only
-
- -

-Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition constructors as indicated: -

-

[ -(If the proposed resolution of issue 805 has already been applied, the -name posix_category will have been changed to generic_category. That has -no effect on this resolution.) -]

- - -
-
-error_condition();
-
-
-

-Effects: Constructs an object of type error_condition. -

-

-Postconditions: val_ == 0 and cat_ == &posix_category. -

-

-Throws: Nothing. -

-
-
-error_condition(int val, const error_category& cat);
-
-
-

-Effects: Constructs an object of type error_condition. -

-

-Postconditions: val_ == val and cat_ == &cat. -

-

-Throws: Nothing. -

-
-
- -

-Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition modifiers as indicated: -

- -
-void assign(int val, const error_category& cat);
-
-

-Postconditions: val_ == val and cat_ == &cat. -

-

-Throws: Nothing. -

-
-
- -

-Change 19.5.3.4 [syserr.errcondition.observers] Class error_condition observers as indicated: -

- -
-const error_category& category() const;
-
-

-Returns: *cat_. -

-

-Throws: Nothing. -

-
-
-
- -

-Resolution of part C: -

- -
- -

-In 19.5.1.2 [syserr.errcat.virtuals], remove the throws clause p. 10. -

- -
-
-virtual string message(int ev) const = 0;
-
- -
-

-Returns: A string that describes the error condition denoted by ev. -

-

-Throws: Nothing. -

-
-
- -

-In 19.5.2.4 [syserr.errcode.observers], remove the throws clause p. 8. -

- -
-
-string message() const;
-
-
-

-Returns: category().message(value()). -

-

-Throws: Nothing. -

-
-
- -

-In 19.5.3.4 [syserr.errcondition.observers], remove the throws clause p. 6. -

- -
-
-string message() const;
-
-
-

-Returns: category().message(value()). -

-

-Throws: Nothing. -

-
-
- -
- - - - - - -
-

805. posix_error::posix_errno concerns

-

Section: 19.5 [syserr] Status: CD1 - Submitter: Jens Maurer Opened: 2008-02-24 Last modified: 2015-04-08

-

View all other issues in [syserr].

-

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-

Discussion:

-

-19.5 [syserr] -

- -
-namespace posix_error {
-  enum posix_errno {
-    address_family_not_supported, // EAFNOSUPPORT
-    ...
-
- -

-should rather use the new scoped-enum facility (7.2 [dcl.enum]), -which would avoid the necessity for a new posix_error -namespace, if I understand correctly. -

- -

[ -Further discussion: -]

- - -
-

-See N2347, -Strongly Typed Enums, since renamed Scoped Enums. -

-

-Alberto Ganesh Barbati also raised this issue in private email, and also proposed the scoped-enum solution. -

-

-Nick Stoughton asked in Bellevue that posix_error and posix_errno not be used as names. The LWG agreed. -

-

-The wording for the Proposed resolution was provided by Beman Dawes. -

-
- - -

Proposed resolution:

-

-Change System error support 19.5 [syserr] as indicated: -

- -
-namespace posix_error {
-  enum posix_errno class errc {
-    address_family_not_supported, // EAFNOSUPPORT
-    ...
-    wrong_protocol_type, // EPROTOTYPE
-  };
-} // namespace posix_error
-
-template <> struct is_error_condition_enum<posix_error::posix_errno errc>
-  : public true_type {}
-
-namespace posix_error {
-  error_code make_error_code(posix_errno errc e);
-  error_condition make_error_condition(posix_errno errc e);
-} // namespace posix_error
-
- -

-Change System error support 19.5 [syserr] : -

- -

-The is_error_code_enum and is_error_condition_enum templates may be -specialized for user-defined types to indicate that such a type is -eligible for class error_code and class error_condition automatic -conversions, respectively. -

- -

-Change System error support 19.5 [syserr] and its subsections: -

- -
-
    -
  • -remove all occurrences of posix_error:: -
    • -
  • -change all instances of posix_errno to errc -
    • -
  • -change all instances of posix_category to generic_category -
    • -
  • -change all instances of get_posix_category to get_generic_category -
    • -
-
- -

-Change Error category objects 19.5.1.5 [syserr.errcat.objects], paragraph 2: -

- -

-Remarks: The object's default_error_condition and equivalent virtual -functions shall behave as specified for the class error_category. The -object's name virtual function shall return a pointer to the string -"POSIX" "generic". -

- -

-Change 19.5.2.5 [syserr.errcode.nonmembers] Class error_code non-member functions as indicated: -

- -
-
-error_code make_error_code(posix_errno errc e);
-
- -

-Returns: error_code(static_cast<int>(e), posixgeneric_category). -

-
- -

-Change 19.5.3.5 [syserr.errcondition.nonmembers] Class error_condition non-member functions as indicated: -

- -
-
-error_condition make_error_condition(posix_errno errc e);
-
- -

-Returns: error_condition(static_cast<int>(e), posixgeneric_category). -

-
- - - -

Rationale:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Names Considered
portable -Too non-specific. Did not wish to reserve such a common word in -namespace std. Not quite the right meaning, either. -
portable_error -Too long. Explicit qualification is always required for scoped enums, so -a short name is desirable. Not quite the right meaning, either. May be -misleading because *_error in the std lib is usually an exception class -name. -
std_error -Fairly short, yet explicit. But in fully qualified names like -std::std_error::not_enough_memory, the std_ would be unfortunate. Not -quite the right meaning, either. May be misleading because *_error in -the std lib is usually an exception class name. -
generic -Short enough. The category could be generic_category. Fully qualified -names like std::generic::not_enough_memory read well. Reserving in -namespace std seems dicey. -
generic_error -Longish. The category could be generic_category. Fully qualified names -like std::generic_error::not_enough_memory read well. Misleading because -*_error in the std lib is usually an exception class name. -
generic_err -A bit less longish. The category could be generic_category. Fully -qualified names like std::generic_err::not_enough_memory read well. -
gen_err -Shorter still. The category could be generic_category. Fully qualified -names like std::gen_err::not_enough_memory read well. -
generr -Shorter still. The category could be generic_category. Fully qualified -names like std::generr::not_enough_memory read well. -
error -Shorter still. The category could be generic_category. Fully qualified -names like std::error::not_enough_memory read well. Do we want to use -this general a name? -
err -Shorter still. The category could be generic_category. Fully qualified -names like std::err::not_enough_memory read well. Although alone it -looks odd as a name, given the existing errno and namespace std names, -it seems fairly intuitive. -Problem: err is used throughout the standard library as an argument name -and in examples as a variable name; it seems too confusing to add yet -another use of the name. -
errc -Short enough. The "c" stands for "constant". The category could be -generic_category. Fully qualified names like -std::errc::not_enough_memory read well. Although alone it looks odd as a -name, given the existing errno and namespace std names, it seems fairly -intuitive. There are no uses of errc in the current C++ standard. -
- - - - - -
-

806. unique_ptr::reset effects incorrect, too permissive

-

Section: 20.8.1.2.5 [unique.ptr.single.modifiers] Status: CD1 - Submitter: Peter Dimov Opened: 2008-03-13 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-void unique_ptr::reset(T* p = 0) is currently specified as: -

- -

-Effects: If p == get() there are no effects. Otherwise get_deleter()(get()). -

- -

-There are two problems with this. One, if get() == 0 and p != 0, the -deleter is called with a NULL pointer, and this is probably not what's -intended (the destructor avoids calling the deleter with 0.) -

- -

-Two, the special check for get() == p is generally not needed and such a -situation usually indicates an error in the client code, which is being -masked. As a data point, boost::shared_ptr was changed to assert on such -self-resets in 2001 and there were no complaints. -

- -

-One might think that self-resets are necessary for operator= to work; it's specified to perform -

- -
-reset( u.release() );
-
- -

-and the self-assignment -

- -
-p = move(p);
-
- -

-might appear to result in a self-reset. But it doesn't; the release() is -performed first, zeroing the stored pointer. In other words, p.reset( -q.release() ) works even when p and q are the same unique_ptr, and there -is no need to special-case p.reset( q.get() ) to work in a similar -scenario, as it definitely doesn't when p and q are separate. -

- - - -

Proposed resolution:

- -

-Change 20.8.1.2.5 [unique.ptr.single.modifiers]: -

- -
-
-void reset(T* p = 0);
-
-

--4- Effects: If p == get() == 0 there are no effects. Otherwise get_deleter()(get()). -

-
- -

-Change 20.8.1.3.4 [unique.ptr.runtime.modifiers]: -

- -
-
-void reset(T* p = 0);
-
-
-

...

-

--2- Effects: If p == get() == 0 there are no effects. Otherwise get_deleter()(get()). -

-
-
- - - - - - -
-

807. tuple construction should not fail unless its element's construction fails

-

Section: 20.4.2.1 [tuple.cnstr] Status: CD1 - Submitter: Howard Hinnant Opened: 2008-03-13 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-527 Added a throws clause to bind constructors. I believe the same throws clause -should be added to tuple except it ought to take into account move constructors as well. -

- - -

Proposed resolution:

-

-Add to 20.4.2.1 [tuple.cnstr]: -

- -
-

-For each tuple constructor and assignment operator, an exception is thrown only if the construction -or assignment of one of the types in Types throws an exception. -

-
- - - - - -
-

808. [forward] incorrect redundant specification

-

Section: 20.2.4 [forward] Status: CD1 - Submitter: Jens Maurer Opened: 2008-03-13 Last modified: 2015-04-08

-

View all other issues in [forward].

-

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-

Discussion:

-

-p4 (forward) says: -

-

-Return type: If T is an lvalue-reference type, an lvalue; otherwise, an rvalue. -

- -

-First of all, lvalue-ness and rvalue-ness are properties of an expression, -not of a type (see 3.10 [basic.lval]). Thus, the phrasing "Return type" is wrong. -Second, the phrase says exactly what the core language wording says for -folding references in 14.3.1 [temp.arg.type]/p4 and for function return values -in 5.2.2 [expr.call]/p10. (If we feel the wording should be retained, it should -at most be a note with cross-references to those sections.) -

-

-The prose after the example talks about "forwarding as an int& (an lvalue)" etc. -In my opinion, this is a category error: "int&" is a type, "lvalue" is a -property of an expression, orthogonal to its type. (Btw, expressions cannot -have reference type, ever.) -

-

-Similar with move: -

-

-Return type: an rvalue. -

-

-is just wrong and also redundant. -

- - -

Proposed resolution:

-

-Change 20.2.4 [forward] as indicated: -

- -
-
-template <class T> T&& forward(typename identity<T>::type&& t);
-
- -
-

...

-

-Return type: If T is an lvalue-reference type, an lvalue; otherwise, an rvalue. -

-

...

-

--7- In the first call to factory, A1 is deduced as int, so 2 is forwarded to A's constructor -as an int&& (an rvalue). In the second call to factory, A1 is deduced -as int&, so i is forwarded to A's constructor as an int& (an lvalue). -In both cases, A2 is deduced as double, so 1.414 is forwarded to A's constructor as -double&& (an rvalue). -

-
- -
-template <class T> typename remove_reference<T>::type&& move(T&& t);
-
- -
-

...

-

-Return type: an rvalue. -

-
- -
- - - - - - -
-

809. std::swap should be overloaded for array types

-

Section: 25.3.3 [alg.swap] Status: CD1 - Submitter: Niels Dekker Opened: 2008-02-28 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-For the sake of generic programming, the header <algorithm> should provide an -overload of std::swap for array types: -

-template<class T, size_t N> void swap(T (&a)[N], T (&b)[N]);
-
- -

-It became apparent to me that this overload is missing, when I considered how to write a swap -function for a generic wrapper class template. -(Actually I was thinking of Boost's value_initialized.) -Please look at the following template, W, and suppose that is intended to be a very -generic wrapper: -

-
-template<class T> class W {
-public:
-  T data;
-};
-
-

-Clearly W<T> is CopyConstructible and CopyAssignable, and therefore -Swappable, whenever T is CopyConstructible and CopyAssignable. -Moreover, W<T> is also Swappable when T is an array type -whose element type is CopyConstructible and CopyAssignable. -Still it is recommended to add a custom swap function template to such a class template, -for the sake of efficiency and exception safety. -(E.g., Scott Meyers, Effective C++, Third Edition, item 25: Consider support for a non-throwing -swap.) -This function template is typically written as follows: -

-
-template<class T> void swap(W<T>& x, W<T>& y) {
-  using std::swap;
-  swap(x.data, y.data);
-}
-
-

-Unfortunately, this will introduce an undesirable inconsistency, when T is an array. -For instance, W<std::string[8]> is Swappable, but the current Standard does not -allow calling the custom swap function that was especially written for W! -

-
-W<std::string[8]> w1, w2;  // Two objects of a Swappable type.
-std::swap(w1, w2);  // Well-defined, but inefficient.
-using std::swap;
-swap(w1, w2);  // Ill-formed, just because ADL finds W's swap function!!!
-
-

-W's swap function would try to call std::swap for an array, -std::string[8], which is not supported by the Standard Library. -This issue is easily solved by providing an overload of std::swap for array types. -This swap function should be implemented in terms of swapping the elements of the arrays, so that -it would be non-throwing for arrays whose element types have a non-throwing swap. -

- -

-Note that such an overload of std::swap should also support multi-dimensional -arrays. Fortunately that isn't really an issue, because it would do so automatically, by -means of recursion. -

- -

-For your information, there was a discussion on this issue at comp.lang.c++.moderated: [Standard -Library] Shouldn't std::swap be overloaded for C-style arrays? -

- - -

Proposed resolution:

-

-Add an extra condition to the definition of Swappable requirements [swappable] in 17.6.3.1 [utility.arg.requirements]: -

-

-- T is Swappable if T is an array type whose element type is Swappable. -

-

-Add the following to 25.3.3 [alg.swap]: -

-
-
-template<class T, size_t N> void swap(T (&a)[N], T (&b)[N]);
-
-

-Requires: Type T shall be Swappable. -

-

-Effects: swap_ranges(a, a + N, b); -

-
- - - - - -
-

810. Missing traits dependencies in operational semantics of extended manipulators

-

Section: 27.7.5 [ext.manip] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-03-01 Last modified: 2015-04-08

-

View all other issues in [ext.manip].

-

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-

Discussion:

-

-The recent draft (as well as the original proposal n2072) uses an -operational semantic -for get_money ([ext.manip]/4) and put_money ([ext.manip]/6), which uses -

- -
-istreambuf_iterator<charT>
-
- -

-and -

- -
-ostreambuf_iterator<charT>
-
- -

-resp, instead of the iterator instances, with explicitly provided -traits argument (The operational semantic defined by f is also traits -dependent). This is an obvious oversight because both *stream_buf -c'tors expect a basic_streambuf<charT,traits> as argument. -

-

-The same problem occurs within the get_time and put_time semantic -where additional to the problem we -have an editorial issue in get_time (streambuf_iterator instead of -istreambuf_iterator). -

- -

[ -Batavia (2009-05): -]

- -
-

-This appears to be an issue of presentation. -

-

-We agree with the proposed resolution. -Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-In 27.7.5 [ext.manip]/4 within function f replace the first line -

- -
-template <class charT, class traits, class moneyT> 
-void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) { 
-   typedef istreambuf_iterator<charT, traits> Iter;
-   ...
-
- -

-In 27.7.5 [ext.manip]/5 remove the first template charT parameter: -

- -
-template <class charT, class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);
-
- -

-In 27.7.5 [ext.manip]/6 within function f replace the first line -

- -
-template <class charT, class traits, class moneyT> 
-void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) { 
-  typedef ostreambuf_iterator<charT, traits> Iter;
-  ...
-
- -

-In 27.7.5 [ext.manip]/8 within function f replace the first line -

- -
-template <class charT, class traits> 
-void f(basic_ios<charT, traits>& str, struct tm *tmb, const charT *fmt) { 
-  typedef istreambuf_iterator<charT, traits> Iter;
-  ...
-
- -

-In 27.7.5 [ext.manip]/10 within function f replace the first line -

- -
-template <class charT, class traits> 
-void f(basic_ios<charT, traits>& str, const struct tm *tmb, const charT *fmt) { 
-  typedef ostreambuf_iterator<charT, traits> Iter;
-  ...
-
- -

-In 27.7 [iostream.format], Header <iomanip> synopsis change: -

- -
-template <class charT, class moneyT> T8 put_money(const moneyT& mon, bool intl = false);
-
- - - - - -
-

811. pair of pointers no longer works with literal 0

-

Section: 20.3 [pairs] Status: C++11 - Submitter: Doug Gregor Opened: 2008-03-14 Last modified: 2015-04-08

-

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-

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-

Discussion:

-
-#include <utility>
-
-int main()
-{
-   std::pair<char *, char *> p (0,0);
-}
-
- -

-I just got a bug report about that, because it's valid C++03, but not -C++0x. The important realization, for me, is that the emplace -proposal---which made push_back variadic, causing the push_back(0) -issue---didn't cause this break in backward compatibility. The break -actually happened when we added this pair constructor as part of adding -rvalue references into the language, long before variadic templates or -emplace came along: -

- -
-template<class U, class V> pair(U&& x, V&& y);
-
- -

-Now, concepts will address this issue by constraining that pair -constructor to only U's and V's that can properly construct "first" and -"second", e.g. (from -N2322): -

- -
-template<class U , class V >
-requires Constructible<T1, U&&> && Constructible<T2, V&&>
-pair(U&& x , V&& y );
-
- -

[ -San Francisco: -]

- - -
-

-Suggested to resolve using pass-by-value for that case. -

-

-Side question: Should pair interoperate with tuples? Can construct a -tuple of a pair, but not a pair from a two-element tuple. -

-

-Related to 885. -

-
- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as open. Howard to provide wording. -

- -

[ -2010-02-06 Howard provided wording. -]

- - -

[ -2010-02-09 Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - - -

Rationale:

-

[ -San Francisco: -]

- - -

-Solved by -N2770. -

- -

[ -The rationale is obsolete. -]

- - - - -

Proposed resolution:

-

-Add a paragraph to 20.3 [pairs]: -

- -
-
-template<class U, class V> pair(U&& x, V&& y);
-
-
-

-6 Effects: The constructor initializes first with -std::forward<U>(x) and second with -std::forward<V>(y). -

- -

-Remarks: U shall be implicitly convertible to -first_type and V shall be implicitly convertible to -second_type, else this constructor shall not participate in overload -resolution. -

-
-
- - - - - - -
-

813. "empty" undefined for shared_ptr

-

Section: 20.8.2.2 [util.smartptr.shared] Status: CD1 - Submitter: Matt Austern Opened: 2008-02-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Several places in 20.8.2.2 [util.smartptr.shared] refer to an "empty" shared_ptr. -However, that term is nowhere defined. The closest thing we have to a -definition is that the default constructor creates an empty shared_ptr -and that a copy of a default-constructed shared_ptr is empty. Are any -other shared_ptrs empty? For example, is shared_ptr((T*) 0) empty? What -are the properties of an empty shared_ptr? We should either clarify this -term or stop using it. -

-

-One reason it's not good enough to leave this term up to the reader's -intuition is that, in light of -N2351 -and issue 711, most readers' -intuitive understanding is likely to be wrong. Intuitively one might -expect that an empty shared_ptr is one that doesn't store a pointer, -but, whatever the definition is, that isn't it. -

- -

[ -Peter adds: -]

- - -
-

-Or, what is an "empty" shared_ptr? -

- -
    -
  • -

    -Are any other shared_ptrs empty? -

    -

    -Yes. Whether a given shared_ptr instance is empty or not is (*) -completely specified by the last mutating operation on that instance. -Give me an example and I'll tell you whether the shared_ptr is empty or -not. -

    -

    -(*) If it isn't, this is a legitimate defect. -

    -
    • - -
  • -

    -For example, is shared_ptr((T*) 0) empty? -

    -

    -No. If it were empty, it would have a use_count() of 0, whereas it is -specified to have an use_count() of 1. -

    -
    • - -
  • -

    -What are the properties of an empty shared_ptr? -

    -

    -The properties of an empty shared_ptr can be derived from the -specification. One example is that its destructor is a no-op. Another is -that its use_count() returns 0. I can enumerate the full list if you -really like. -

    -
    • - -
  • -

    -We should either clarify this term or stop using it. -

    -

    -I don't agree with the imperative tone -

    -

    -A clarification would be either a no-op - if it doesn't contradict the -existing wording - or a big mistake if it does. -

    -

    -I agree that a clarification that is formally a no-op may add value. -

    -
    • - -
  • -

    -However, that term is nowhere defined. -

    -

    -Terms can be useful without a definition. Consider the following -simplistic example. We have a type X with the following operations -defined: -

    -
    -X x;
-X x2(x);
-X f(X x);
-X g(X x1, X x2);
-
    -

    -A default-constructed value is green.
    -A copy has the same color as the original.
    -f(x) returns a red value if the argument is green, a green value otherwise.
    -g(x1,x2) returns a green value if the arguments are of the same color, a red value otherwise. -

    - -

    -Given these definitions, you can determine the color of every instance -of type X, even if you have absolutely no idea what green and red mean. -

    - -

    -Green and red are "nowhere defined" and completely defined at the same time. -

    -
    • -
- -

-Alisdair's wording is fine. -

-
- - -

Proposed resolution:

-

-Append the following sentance to 20.8.2.2 [util.smartptr.shared] -

-

-The shared_ptr class template stores a pointer, usually obtained -via new. shared_ptr implements semantics of -shared ownership; the last remaining owner of the pointer is responsible for -destroying the object, or otherwise releasing the resources associated with -the stored pointer. A shared_ptr object that does not own -a pointer is said to be empty. -

- - - - - -
-

814. vector<bool>::swap(reference, reference) not defined

-

Section: 23.3.7 [vector.bool] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-03-17 Last modified: 2015-04-08

-

View all other issues in [vector.bool].

-

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-

Discussion:

-

-vector<bool>::swap(reference, reference) has no definition. -

- -

[ -San Francisco: -]

- - -

-Move to Open. Alisdair to provide a resolution. -

- -

[ -Post Summit Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Just after 23.3.7 [vector.bool]/5 add the following prototype and description: -

- -
-

-static void swap(reference x, reference y); -

-
-

--6- Effects: Exchanges the contents of x and y as-if by: -

-

-bool b = x;
-x = y;
-y = b;
-
-
-
- - - - - -
-

815. std::function and reference_closure do not use perfect forwarding

-

Section: 20.9.12.2.4 [func.wrap.func.inv] Status: Resolved - Submitter: Alisdair Meredith Opened: 2008-03-16 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.inv].

-

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-

Discussion:

-

-std::function and reference_closure should use "perfect forwarding" as -described in the rvalue core proposal. -

- -

[ -Sophia Antipolis: -]

- - -

-According to Doug Gregor, as far as std::function is concerned, perfect -forwarding can not be obtained because of type erasure. Not everyone -agreed with this diagnosis of forwarding. -

- -

[ -2009-05-01 Howard adds: -]

- - -
-

-Sebastian Gesemann brought to my attention that the CopyConstructible -requirement on function's ArgTypes... is an unnecessary -restriction. -

- -
-template<Returnable R, CopyConstructible... ArgTypes>
-class function<R(ArgTypes...)>
-...
-
- -

-On further investigation, this complaint seemed to be the same -issue as this one. I believe the reason CopyConstructible was put -on ArgTypes in the first place was because of the nature of the -invoke member: -

- -
-template<class R, class ...ArgTypes>
-R
-function<R(ArgTypes...)>::operator()(ArgTypes... arg) const
-{
-    if (f_ == 0)
-        throw bad_function_call();
-    return (*f_)(arg...);
-}
-
- -

-However now with rvalue-refs, "by value" no longer implies CopyConstructible -(as Sebastian correctly points out). If rvalue arguments are supplied, MoveConstructible -is sufficient. Furthermore, the constraint need not be applied in function -if I understand correctly. Rather the client must apply the proper constraints -at the call site. Therefore, at the very least, I recommend that CopyConstructible -be removed from the template class function. -

- -

-Furthermore we need to mandate that the invoker is coded as: -

- -
-template<class R, class ...ArgTypes>
-R
-function<R(ArgTypes...)>::operator()(ArgTypes... arg) const
-{
-    if (f_ == 0)
-        throw bad_function_call();
-    return (*f_)(std::forward<ArgTypes>(arg)...);
-}
-
- -

-Note that ArgTypes&& (the "perfect forwarding signature") is not -appropriate here as this is not a deduced context for ArgTypes. Instead -the client's arguments must implicitly convert to the non-deduced ArgType -type. Catching these arguments by value makes sense to enable decay. -

- -

-Next forward is used to move the ArgTypes as efficiently as -possible, and also with minimum requirements (not CopyConstructible) -to the type-erased functor. For object types, this will be a move. For -reference type ArgTypes, this will be a copy. The end result must be -that the following is a valid program: -

- -
-#include <functional>
-#include <memory>
-#include <cassert>
-
-std::unique_ptr<int>
-f(std::unique_ptr<int> p, int& i)
-{
-    ++i;
-    return std::move(p);
-}
-
-int main()
-{
-    int i = 2;
-    std::function<std::unique_ptr<int>(std::unique_ptr<int>,
-                                       int&> g(f);
-    std::unique_ptr<int> p = g(std::unique_ptr<int>(new int(1)), i);
-    assert(*p == 1);
-    assert(i == 3);
-}
-
- -

[ -Tested in pre-concepts rvalue-ref-enabled compiler. -]

- - -

-In the example above, the first ArgType is unique_ptr<int> -and the second ArgType is int&. Both must work! -

- -
- -

[ -2009-05-27 Daniel adds: -]

- - -
-

-in the 2009-05-01 comment of above mentioned issue Howard -

- -
    -
  1. -Recommends to replace the CopyConstructible requirement by a -MoveConstructible requirement -
    2. -
  2. -Says: "Furthermore, the constraint need not be applied in function if I -understand correctly. Rather the client must apply the proper constraints -at the call site" -
    3. -
-

-I'm fine with (a), but I think comment (b) is incorrect, at least in the -sense I read these sentences. Let's look at Howard's example code: -

- -
-function<R(ArgTypes...)>::operator()(ArgTypes... arg) const
-{
-   if (f_ == 0)
-       throw bad_function_call();
-   return (*f_)(std::forward<ArgTypes>(arg)...);
-}
-
- -

-In the constrained scope of this operator() overload the expression -"(*f_)(std::forward<ArgTypes>(arg)...)" must be valid. How can it -do so, if ArgTypes aren't at least MoveConstructible? -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Leave this open and wait until concepts are removed from the Working -Draft so that we know how to write the proposed resolution in terms of -diffs to otherwise stable text. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as open. Howard to provide wording. Howard welcomes any help. -

- -

[ -2009-12-12 Jonathan Wakely adds: -]

- - -
-

-20.9.12.2 [func.wrap.func] says -

- -

-2 A function object f of type F is Callable for argument -types T1, T2, ..., TN in ArgTypes and a return type -R, if, given lvalues t1, t2, ..., tN of types T1, T2, ..., -TN, respectively, INVOKE (f, t1, t2, ..., tN) is well formed -(20.7.2) and, if R is not void, convertible to R. -

- -

-N.B. lvalues, which means you can't use function<R(T&&)> -or function<R(unique_ptr<T>)> -

- -

-I recently implemented rvalue arguments in GCC's std::function, all -that was needed was to use std::forward<ArgTypes> in a few -places. The example in issue 815 works. -

- -

-I think 815 could be resolved by removing the requirement that the target -function be callable with lvalues. Saying ArgTypes need to be -CopyConstructible is wrong, and IMHO saying MoveConstructible -is unnecessary, since the by-value signature implies that already, but if it is -needed it should only be on operator(), not the whole class (you could -in theory instantiate std::function<R(noncopyable)> as long as -you don't invoke the call operator.) -

- -

-I think defining invocation in terms of INVOKE already implies perfect -forwarding, so we don't need to say explicitly that std::forward should -be used (N.B. the types that are forwarded are those in ArgTypes, which -can differ from the actual parameter types of the target function. The actual -parameter types have gone via type erasure, but that's not a problem - IMHO -forwarding the arguments as ArgTypes is the right thing to do anyway.) -

- -

-Is it sufficient to simply replace "lvalues" with "values"? or do we need to say -something like "lvalues when Ti is an lvalue-reference and rvalues -otherwise"? I prefer the former, so I propose the following resolution for 815: -

- -

-Edit 20.9.12.2 [func.wrap.func] paragraph 2: -

- -

-2 A function object f of type F is Callable for argument -types T1, T2, ..., TN in ArgTypes and a return type -R, if, given lvalues t1, t2, ..., tN of types -T1, T2, ..., TN, respectively, INVOKE (f, t1, t2, ..., tN) is -well formed (20.7.2) and, if R is not void, convertible to -R. -

-
- -

[ -2009-12-12 Daniel adds: -]

- - -

-I don't like the reduction to "values" and prefer the alternative solution -suggested using "lvalues when Ti is an lvalue-reference and rvalues otherwise". -The reason why I dislike the shorter version is based on different usages of -"values" as part of defining the semantics of requirement tables via -expressions. E.g. 17.6.3.1 [utility.arg.requirements]/1 says "a, -b, and c are values of type const T;" or similar in -23.2.1 [container.requirements.general]/4 or /14 etc. My current reading -of all these parts is that both rvalues and lvalues are required to be -supported, but this interpretation would violate the intention of the suggested -fix of #815, if I correctly understand Jonathan's rationale. -

- -

[ -2009-12-12 Howard adds: -]

- - -
-

-"lvalues when Ti is an lvalue-reference and rvalues otherwise" -

-

-doesn't quite work here because the Ti aren't deduced. They are -specified by the function type. Ti might be const -int& (an lvalue reference) and a valid ti might be 2 -(a non-const rvalue). I've taken another stab at the wording using -"expressions" and "bindable to". -

-
- -

[ -2010-02-09 Wording updated by Jonathan, Ganesh and Daniel. -]

- - -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-10 Daniel opens to improve wording. -]

- - -

[ -2010-02-11 This issue is now addressed by 870. -]

- - -

[ -2010-02-12 Moved to Tentatively NAD Editorial after 5 positive votes on -c++std-lib. Rationale added below. -]

- - - - -

Rationale:

-

-Addressed by 870. -

- - -

Proposed resolution:

-

-Edit 20.9.12.2 [func.wrap.func] paragraph 2: -

- -
-

-2 A function object f of type F is Callable for argument -types T1, T2, ..., TN in ArgTypes and a -return type R, if, given lvalues t1, t2, ..., -tN of types T1, T2, ..., TN, respectively, the -expression INVOKE(f, declval<ArgTypes>()..., -Rt1, t2, ..., tN), considered as an unevaluated -operand (5 [expr]), is well formed (20.7.2) and, if -R is not void, convertible to R. -

- -
- - - - - -
-

816. Should bind()'s returned functor have a nofail copy ctor when bind() is nofail?

-

Section: 20.9.10.3 [func.bind.bind] Status: Resolved - Submitter: Stephan T. Lavavej Opened: 2008-02-08 Last modified: 2015-04-08

-

View all other issues in [func.bind.bind].

-

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-

Discussion:

-

-Library Issue 527 notes that bind(f, t1, ..., tN) -should be nofail when f, t1, ..., tN have nofail copy ctors. -

-

-However, no guarantees are provided for the copy ctor of the functor -returned by bind(). (It's guaranteed to have a copy ctor, which can -throw implementation-defined exceptions: bind() returns a forwarding -call wrapper, TR1 3.6.3/2. A forwarding call wrapper is a call wrapper, -TR1 3.3/4. Every call wrapper shall be CopyConstructible, TR1 3.3/4. -Everything without an exception-specification may throw -implementation-defined exceptions unless otherwise specified, C++03 -17.4.4.8/3.) -

-

-Should the nofail guarantee requested by Library Issue 527 be extended -to cover both calling bind() and copying the returned functor? -

- -

[ -Howard adds: -]

- - -

-tuple construction should probably have a similar guarantee. -

- -

[ -San Francisco: -]

- - -

-Howard to provide wording. -

- -

[ -Post Summit, Anthony provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -

-Part of all of this issue appears to be rendered moot -by the proposed resolution to issue 817 (q.v.). -We recommend the issues be considered simultaneously -(or possibly even merged) -to ensure there is no overlap. -Move to Open, and likewise for issue 817. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Related to 817 (see below). Leave Open. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. Decoupling from issue 817. -

- -

[ -2010-02-11 Moved from Ready to Tentatively NAD Editorial, rationale added below. -]

- - - - -

Rationale:

-

-This issue is solved as proposed by 817. -

- - -

Proposed resolution:

-

-Add a new sentence to the end of paragraphs 2 and 4 of 20.9.10.3 [func.bind.bind]: -

- -
-

--2- Returns: A forwarding call wrapper g with a weak result type (20.6.2). The effect of g(u1, u2, -..., uM) shall be INVOKE(f, v1, v2, ..., vN, Callable<F cv,V1, V2, ..., VN>::result_type), where cv -represents the cv-qualifiers of g and the values and types of the bound arguments -v1, v2, ..., vN are determined as specified below. -The copy constructor and move constructor of the forwarding call wrapper shall throw an -exception if and only if the corresponding constructor of F or any of the types -in BoundArgs... throw an exception. -

-

...

-

--5- Returns: A forwarding call wrapper g with a nested type result_type defined as a synonym -for R. The effect of g(u1, u2, ..., uM) shall be INVOKE(f, v1, v2, ..., vN, R), where the -values and types of the bound arguments v1, v2, ..., vN are determined as specified below. -The copy constructor and move constructor of the forwarding call wrapper shall throw an -exception if and only if the corresponding constructor of F or any of the types -in BoundArgs... throw an exception. -

- -
- - - - - -
-

817. bind needs to be moved

-

Section: 20.9.10.3 [func.bind.bind] Status: C++11 - Submitter: Howard Hinnant Opened: 2008-03-17 Last modified: 2015-04-08

-

View all other issues in [func.bind.bind].

-

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-

Discussion:

-

Addresses US 72, JP 38 and DE 21

- -

-The functor returned by bind() should have a move constructor that -requires only move construction of its contained functor and bound arguments. -That way move-only functors can be passed to objects such as thread. -

-

-This issue is related to issue 816. -

- -

-US 72: -

- -

-bind should support move-only functors and bound arguments. -

- -

-JP 38: -

- -
-

-add the move requirement for bind's return type. -

-

-For example, assume following th1 and th2, -

- -
-void f(vector<int> v) { }
-
-vector<int> v{ ... };
-thread th1([v]{ f(v); });
-thread th2(bind(f, v));
-
- -

-When function object are set to thread, v is moved to th1's lambda -expression in a Move Constructor of lambda expression because th1's lambda -expression has a Move Constructor. But bind of th2's -return type doesn't have the requirement of Move, so it may not -moved but copied. -

-

-Add the requirement of move to get rid of this useless copy. -

-

-And also, add the MoveConstructible as well as CopyConstructible. -

-
- -

-DE 21 -

- -

-The specification for bind claims twice that "the values and types for -the bound arguments v1, v2, ..., vN are determined as specified below". -No such specification appears to exist. -

- -

[ -San Francisco: -]

- - -

-Howard to provide wording. -

- -

[ -Post Summit Alisdair and Howard provided wording. -]

- - -
-

-Several issues are being combined in this resolution. They are all touching the -same words so this is an attempt to keep one issue from stepping on another, and -a place to see the complete solution in one place. -

- -
    -
  1. -bind needs to be "moved". -
    2. -
  2. -20.9.10.3 [func.bind.bind]/p3, p6 and p7 were accidently removed from N2798. -
    3. -
  3. -Issue 929 argues for a way to pass by && for -efficiency but retain the decaying behavior of pass by value for the -thread constructor. That same solution is applicable here. -
    4. -
-
- -

[ -Batavia (2009-05): -]

- -
-

-We were going to recommend moving this issue to Tentatively Ready -until we noticed potential overlap with issue 816 (q.v.). -

-

-Move to Open, -and recommend both issues be considered together -(and possibly merged). -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-The proposed resolution uses concepts. Leave Open. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as Open. Howard to provide deconceptified wording. -

- -

[ -2009-11-07 Howard updates wording. -]

- - -

[ -2009-11-15 Further updates by Peter, Chris and Daniel. -]

- - -

[ -Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 20.9 [function.objects] p2: -

- -
-template<class Fn, class... Types BoundArgs>
-  unspecified bind(Fn&&, Types BoundArgs&&...);
-template<class R, class Fn, class... Types BoundArgs>
-  unspecified bind(Fn&&, Types BoundArgs&&...);
-
- -

-Change 20.9.2 [func.require]: -

- -
-

-4 Every call wrapper (20.9.1 [func.def]) shall be -CopyMoveConstructible. A simple call -wrapper is a call wrapper that is CopyConstructible and -CopyAssignable and whose copy constructor, move constructor and assignment operator do not -throw exceptions. A forwarding call wrapper is a call wrapper that can be -called with an argument list. [Note: in a typical implementation -forwarding call wrappers have an overloaded function call operator of the form -

-
-template<class... ArgTypesUnBoundsArgs>
-R operator()(ArgTypesUnBoundsArgs&&... unbound_args) cv-qual;
-
-

-— end note] -

-
- -

-Change 20.9.10.3 [func.bind.bind]: -

- -
-

-Within this clause: -

- -
    -
  • -Let FD be a synonym for the type decay<F>::type. -
    • -
  • -Let fd be an lvalue of type FD constructed from -std::forward<F>(f). -
    • -
  • -Let Ti be a synonym for the ith type in the -template parameter pack BoundArgs. -
    • -
  • -Let TiD be a synonym for the type decay<Ti>::type. -
    • -
  • -Let ti be the ith argument in the function parameter -pack bound_args. -
    • -
  • -Let tid be an lvalue of type TiD constructed from -std::forward<Ti>(ti). -
    • -
  • -Let Uj be the jth deduced type of the UnBoundArgs&&... -parameter of the operator() of the forwarding call wrapper. -
    • -
  • -Let uj be the jth argument associated with Uj. -
    • -
- -
-template<class F, class... BoundArgs>
-  unspecified bind(F&& f, BoundArgs&&... bound_args);
-
- -
-

--1- Requires: -is_constructible<FD, F>::value -shall be true. -For each Ti in BoundArgs, -is_constructible<TiD, Ti>::value shall be -true. -F and each Ti in -BoundArgs shall be CopyConstructible. -INVOKE(fd, w1, w2, ..., wN) (20.9.2 [func.require]) shall be a valid expression for some values -w1, w2, ..., wN, where N == sizeof...(bound_args). -

-

--2- Returns: A forwarding call wrapper g with a weak -result type (20.9.2 [func.require]). The effect of g(u1, u2, -..., uM) shall be INVOKE(fd, v1, v2, ..., vN, -result_of<FD cv (V1, V2, ..., VN)>::type), where -cv represents the cv-qualifiers of g and the -values and types of the bound arguments v1, v2, ..., vN are -determined as specified below. -The copy constructor and move constructor of the forwarding call wrapper shall throw an -exception if and only if the corresponding constructor of FD or of any of the types -TiD throws an exception. -

-

--3- Throws: Nothing unless the copy -constructionor of -Ffd or of one of the values -tid types in the BoundArgs... pack -expansion throws an exception. -

-

- -Remarks: The unspecified return type shall satisfy the -requirements of MoveConstructible. If all of FD and -TiD satisfy the requirements of CopyConstructible then -the unspecified return type shall satisfy the requirements of -CopyConstructible. [Note: This implies that all of -FD and TiD shall be MoveConstructible — -end note] - -

-
- -
-template<class R, class F, class... BoundArgs>
-  unspecified bind(F&& f, BoundArgs&&... bound_args);
-
- -
-

--4- Requires: -is_constructible<FD, F>::value -shall be true. -For each Ti in BoundArgs, -is_constructible<TiD, Ti>::value shall be -true. -F and each Ti in -BoundArgs shall be CopyConstructible. -INVOKE(fd, w1, -w2, ..., wN) shall be a valid expression for some values w1, w2, -..., wN, where N == sizeof...(bound_args). -

-

--5- Returns: A forwarding call wrapper g with a nested -type result_type defined as a synonym for R. The -effect of g(u1, u2, ..., uM) shall be INVOKE(fd, v1, -v2, ..., vN, R), where the values and types of the bound arguments -v1, v2, ..., vN are determined as specified below. -The copy constructor and move constructor of the forwarding call wrapper shall throw an -exception if and only if the corresponding constructor of FD or of any of the types -TiD throws an exception. -

-

--6- Throws: Nothing unless the copy -constructionor of -Ffd or of one of the values -tid types in the BoundArgs... pack -expansion throws an exception. -

-

- -Remarks: The unspecified return type shall satisfy the -requirements of MoveConstructible. If all of FD and -TiD satisfy the requirements of CopyConstructible then -the unspecified return type shall satisfy the requirements of -CopyConstructible. [Note: This implies that all of -FD and TiD shall be MoveConstructible — -end note] - -

-
- -

--7- The values of the bound arguments v1, v2, ..., vN and -their corresponding types V1, V2, ..., VN depend on the types -TiD derived from -of the corresponding argument ti in bound_args of type -Ti in BoundArgs in -the call to bind and the -cv-qualifiers cv of the call wrapper g as -follows: -

- -
    -
  • -if ti TiD is of type -reference_wrapper<T> the argument is -tid.get() and its type Vi is T&; -
    • -
  • -if the value of -std::is_bind_expression<TiD>::value is -true the argument is tid(std::forward<Uj>(uj)... u1, u2, ..., uM) -and its type Vi is result_of<TiD cv -(Uj... U1&, U2&, ..., UM&)>::type; -
    • -
  • -if the value j of -std::is_placeholder<TiD>::value is not zero -the argument is std::forward<Uj>(uj) and its type -Vi is Uj&&; -
    • -
  • -otherwise the value is tid and its type Vi -is TiD cv &. -
    • -
- -
- - - - - - -
-

818. wording for memory ordering

-

Section: 29.3 [atomics.order] Status: CD1 - Submitter: Jens Maurer Opened: 2008-03-22 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-29.3 [atomics.order] p1 says in the table that -

- -
- - - - - - - - -
ElementMeaning
memory_order_acq_relthe operation has both acquire and release semantics
-
- -

-To my naked eye, that seems to imply that even an atomic read has both -acquire and release semantics. -

- -

-Then, p1 says in the table: -

- -
- - - - - - - - -
ElementMeaning
memory_order_seq_cstthe operation has both acquire and release semantics, - and, in addition, has sequentially-consistent operation ordering
-
- -

-So that seems to be "the same thing" as memory_order_acq_rel, with additional -constraints. -

- -

-I'm then reading p2, where it says: -

- -

-The memory_order_seq_cst operations that load a value are acquire operations -on the affected locations. The memory_order_seq_cst operations that store a value -are release operations on the affected locations. -

- -

-That seems to imply that atomic reads only have acquire semantics. If that -is intended, does this also apply to memory_order_acq_rel and the individual -load/store operations as well? -

- -

-Also, the table in p1 contains phrases with "thus" that seem to indicate -consequences of normative wording in 1.10 [intro.multithread]. That shouldn't be in -normative text, for the fear of redundant or inconsistent specification with -the other normative text. -

- -

-Double-check 29.6 [atomics.types.operations] that each -operation clearly says whether it's a load or a store operation, or -both. (It could be clearer, IMO. Solution not in current proposed resolution.) -

- -

-29.3 [atomics.order] p2: What's a "consistent execution"? It's not defined in -1.10 [intro.multithread], it's just used in notes there. -

- -

-And why does 29.6 [atomics.types.operations] p9 for "load" say: -

- - -

-Requires: The order argument shall not be memory_order_acquire -nor memory_order_acq_rel. -

- -

-(Since this is exactly the same restriction as for "store", it seems to be a typo.) -

- -

-And then: 29.6 [atomics.types.operations] p12: -

- -

-These operations are read-modify-write operations in the sense of the -"synchronizes with" definition (1.10 [intro.multithread]), so both such an operation and the -evaluation that produced the input value synchronize with any evaluation -that reads the updated value. -

- -

-This is redundant with 1.10 [intro.multithread], see above for the reasoning. -

- -

[ -San Francisco: -]

- - -
-

-Boehm: "I don't think that this changes anything terribly substantive, -but it improves the text." -

-

-Note that "Rephrase the table in as [sic] follows..." should read -"Replace the table in [atomics.order] with the following...." -

-

-The proposed resolution needs more work. Crowl volunteered to address -all of the atomics issues in one paper. -

- -

-This issue is addressed in -N2783. -

-
- - -

Proposed resolution:

-

-edit 29.3 [atomics.order], paragraph 1 as follows. -

- -
-

-The enumeration memory_order -specifies the detailed regular (non-atomic) memory synchronization order -as defined in Clause 1.7 section 1.10 -and may provide for operation ordering. -Its enumerated values and their meanings are as follows: -

-
-
-
For memory_order_relaxed,
-
no operation orders memory.
-
For memory_order_release, -memory_order_acq_rel, -and memory_order_seq_cst,
-
a store operation performs a release operation -on the affected memory location.
-
For memory_order_consume,
-
a load operation performs a consume operation -on the affected memory location.
-
For memory_order_acquire, -memory_order_acq_rel, -and memory_order_seq_cst,
-
a load operation performs an acquire operation -on the affected memory location.
-
-
-
- -

-remove table 136 in 29.3 [atomics.order]. -

- -
- - - - - - - - - - - - - - - -
Table 136 — memory_order effects
ElementMeaning
memory_order_relaxedthe operation does not order memory
memory_order_releasethe operation -performs a release operation on the affected memory location, -thus making regular memory writes visible to other threads -through the atomic variable to which it is applied
memory_order_acquirethe operation -performs an acquire operation on the affected memory location, -thus making regular memory writes in other threads -released through the atomic variable to which it is applied -visible to the current thread
memory_order_consumethe operation -performs a consume operation on the affected memory location, -thus making regular memory writes in other threads -released through the atomic variable to which it is applied -visible to the regular memory reads -that are dependencies of this consume operation.
memory_order_acq_relthe operation has both acquire and release semantics
memory_order_seq_cstthe operation has both acquire and release semantics, -and, in addition, has sequentially-consistent operation ordering
-
- -

-edit 29.3 [atomics.order], paragraph 2 as follows. -

- -
-

-The memory_order_seq_cst operations that load a value -are acquire operations on the affected locations. -The memory_order_seq_cst operations that store a value -are release operations on the affected locations. -In addition, in a consistent execution, -there There must be is -a single total order S -on all memory_order_seq_cst operations, -consistent with the happens before order -and modification orders for all affected locations, -such that each memory_order_seq_cst operation -observes either the last preceding modification -according to this order S, -or the result of an operation that is not memory_order_seq_cst. -[Note: -Although it is not explicitly required that S include locks, -it can always be extended to an order -that does include lock and unlock operations, -since the ordering between those -is already included in the happens before ordering. -—end note] -

-
- - - - - - -
-

819. rethrow_if_nested

-

Section: 18.8.6 [except.nested] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-03-25 Last modified: 2015-04-08

-

View other active issues in [except.nested].

-

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-

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-

Discussion:

-

-Looking at the wording I submitted for rethrow_if_nested, I don't think I -got it quite right. -

- -

-The current wording says: -

- -
-
-template <class E> void rethrow_if_nested(const E& e);
-
-
-

-Effects: Calls e.rethrow_nested() only if e -is publicly derived from nested_exception. -

-
-
- -

-This is trying to be a bit subtle, by requiring e (not E) to be publicly -derived from nested_exception the idea is that a dynamic_cast would be -required to be sure. Unfortunately, if e is dynamically but not statically -derived from nested_exception, e.rethrow_nested() is ill-formed. -

- -

[ -San Francisco: -]

- - -

-Alisdair was volunteered to provide wording. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave as Open. Alisdair to provide wording. -

- -

[ -2009-11-09 Alisdair provided wording. -]

- - -

[ -2010-03-10 Dietmar updated wording. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

-

-Change 18.8.6 [except.nested], p8: -

- -
-template <class E> void rethrow_if_nested(const E& e);
-
-

--8- Effects: Calls e.rethrow_nested() -oOnly if the dynamic type of e is -publicly and unambiguously derived from -nested_exception this calls -dynamic_cast<const nested_exception&>(e).rethrow_nested(). -

-
- - - - - - -
-

820. current_exception()'s interaction with throwing copy ctors

-

Section: 18.8.5 [propagation] Status: CD1 - Submitter: Stephan T. Lavavej Opened: 2008-03-26 Last modified: 2015-04-08

-

View all other issues in [propagation].

-

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-

Discussion:

-

-As of N2521, the Working Paper appears to be silent about what -current_exception() should do if it tries to copy the currently handled -exception and its copy constructor throws. 18.8.5 [propagation]/7 says "If the -function needs to allocate memory and the attempt fails, it returns an -exception_ptr object that refers to an instance of bad_alloc.", but -doesn't say anything about what should happen if memory allocation -succeeds but the actual copying fails. -

- -

-I see three alternatives: (1) return an exception_ptr object that refers -to an instance of some fixed exception type, (2) return an exception_ptr -object that refers to an instance of the copy ctor's thrown exception -(but if that has a throwing copy ctor, an infinite loop can occur), or -(3) call terminate(). -

- -

-I believe that terminate() is the most reasonable course of action, but -before we go implement that, I wanted to raise this issue. -

- -

[ -Peter's summary: -]

- - -
-

-The current practice is to not have throwing copy constructors in -exception classes, because this can lead to terminate() as described in -15.5.1 [except.terminate]. Thus calling terminate() in this situation seems -consistent and does not introduce any new problems. -

- -

-However, the resolution of core issue 475 may relax this requirement: -

- -

-The CWG agreed with the position that std::uncaught_exception() should -return false during the copy to the exception object and that std::terminate() -should not be called if that constructor exits with an exception. -

- -

-Since throwing copy constructors will no longer call terminate(), option -(3) doesn't seem reasonable as it is deemed too drastic a response in a -recoverable situation. -

- -

-Option (2) cannot be adopted by itself, because a potential infinite -recursion will need to be terminated by one of the other options. -

- -
- - -

Proposed resolution:

-

-Add the following paragraph after 18.8.5 [propagation]/7: -

- -
-

-Returns (continued): If the attempt to copy the current exception -object throws an exception, the function returns an exception_ptr that -refers to the thrown exception or, if this is not possible, to an -instance of bad_exception. -

-

-[Note: The copy constructor of the thrown exception may also fail, so -the implementation is allowed to substitute a bad_exception to avoid -infinite recursion. -- end note.] -

-
- - - -

Rationale:

-

[ -San Francisco: -]

- - -
-

-Pete: there may be an implied assumption in the proposed wording that -current_exception() copies the existing exception object; the -implementation may not actually do that. -

-

-Pete will make the required editorial tweaks to rectify this. -

-
- - - - - -
-

821. Minor cleanup : unique_ptr

-

Section: 20.8.1.3.4 [unique.ptr.runtime.modifiers] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-03-30 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.runtime.modifiers].

-

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-

Discussion:

-

-Reading resolution of LWG issue 673 I noticed the following: -

- -
-
-void reset(T* pointer p = 0 pointer());
-
- -

--1- Requires: Does not accept pointer types which are convertible -to T* pointer (diagnostic -required). [Note: One implementation technique is to create a private -templated overload. -- end note] -

-
- -

-This could be cleaned up by mandating the overload as a public deleted -function. In addition, we should probably overload reset on nullptr_t -to be a stronger match than the deleted overload. Words... -

- - -

Proposed resolution:

-

-Add to class template definition in 20.8.1.3 [unique.ptr.runtime] -

- -
-
-// modifiers 
-pointer release(); 
-void reset(pointer p = pointer()); 
-void reset( nullptr_t );
-template< typename U > void reset( U ) = delete;
-void swap(unique_ptr&& u);
-
-
- -

-Update 20.8.1.3.4 [unique.ptr.runtime.modifiers] -

- -
-
-void reset(pointer p = pointer());
-void reset(nullptr_t);
-
- -

--1- Requires: Does not accept pointer types which are convertible -to pointer (diagnostic -required). [Note: One implementation technique is to create a private -templated overload. -- end note] -

-

-Effects: If get() == nullptr there are no effects. Otherwise get_deleter()(get()). -

-

...

-
- -

[ -Note this wording incorporates resolutions for 806 (New) and 673 (Ready). -]

- - - - - - -
-

823. identity<void> seems broken

-

Section: 20.2.4 [forward] Status: Resolved - Submitter: Walter Brown Opened: 2008-04-09 Last modified: 2015-04-08

-

View all other issues in [forward].

-

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-

Discussion:

-

-N2588 seems to have added an operator() member function to the -identity<> helper in 20.2.4 [forward]. I believe this change makes it no -longer possible to instantiate identity<void>, as it would require -forming a reference-to-void type as this operator()'s parameter type. -

- -

-Suggested resolution: Specialize identity<void> so as not to require -the member function's presence. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Jens: suggests to add a requires clause to avoid specializing on void. -

-

-Alisdair: also consider cv-qualified void. -

-

-Alberto provided proposed wording. -

-
- -

[ -2009-07-30 Daniel reopens: -]

- - -
-

-This issue became closed, because the ReferentType requirement -fixed the problem - this is no longer the case. In retrospective it seems -to be that the root of current issues around std::identity (823, 700, -939) -is that it was standardized as something very different (an unconditional -type mapper) than traditional usage indicated (a function object that should -derive from std::unary_function), as the SGI definition does. This issue could -be solved, if std::identity is removed (one proposal of 939), but until this -has been decided, this issue should remain open. An alternative for -removing it, would be, to do the following: -

- -
    -
  1. -

    -Let identity stay as a real function object, which would -now properly -derive from unary_function: -

    - -
    -template <class T> struct identity : unary_function<T, T> {
-  const T& operator()(const T&) const;
-};
-
    -
    2. - -
  2. -

    -Invent (if needed) a generic type wrapper (corresponding to concept -IdentityOf), -e.g. identity_of, and move it's prototype description back to 20.2.4 [forward]: -

    - -
    -template <class T> struct identity_of {
-  typedef T type;
-};
-
    - -

    -and adapt the std::forward signature to use identity_of -instead of identity. -

    -
    3. -
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD EditorialResolved, fixed by 939. -

- - - -

Proposed resolution:

-

-Change definition of identity in 20.2.4 [forward], paragraph 2, to: -

- -
-template <class T>  struct identity {
-    typedef T type;
-
-    requires ReferentType<T>
-      const T& operator()(const T& x) const;
-  };
-
-

...

-
-  requires ReferentType<T>
-    const T& operator()(const T& x) const;
-
- - -

Rationale:

-

-The point here is to able to write T& given T and ReferentType is -precisely the concept that guarantees so, according to N2677 -(Foundational concepts). Because of this, it seems preferable than an -explicit check for cv void using SameType/remove_cv as it was suggested -in Sophia. In particular, Daniel remarked that there may be types other -than cv void which aren't referent types (int[], perhaps?). -

- - - - - -
-

824. rvalue ref issue with basic_string inserter

-

Section: 21.4.8.9 [string.io] Status: CD1 - Submitter: Alisdair Meredith Opened: 2008-04-10 Last modified: 2015-04-08

-

View all other issues in [string.io].

-

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-

Discussion:

-

-In the current working paper, the <string> header synopsis at the end of -21.3 [string.classes] lists a single operator<< overload -for basic_string. -

- -
-template<class charT, class traits, class Allocator>
- basic_ostream<charT, traits>&
-   operator<<(basic_ostream<charT, traits>&& os,
-              const basic_string<charT,traits,Allocator>& str);
-
- -

-The definition in 21.4.8.9 [string.io] lists two: -

- -
-template<class charT, class traits, class Allocator>
- basic_ostream<charT, traits>&
-   operator<<(basic_ostream<charT, traits>& os,
-              const basic_string<charT,traits,Allocator>& str);
-
-template<class charT, class traits, class Allocator>
- basic_ostream<charT, traits>&
-   operator<<(basic_ostream<charT, traits>&& os,
-              const basic_string<charT,traits,Allocator>& str);
-
- -

-I believe the synopsis in 21.3 [string.classes] is correct, and the first of the two -signatures in 21.4.8.9 [string.io] should be deleted. -

- - -

Proposed resolution:

-

-Delete the first of the two signatures in 21.4.8.9 [string.io]: -

- -
-template<class charT, class traits, class Allocator>
- basic_ostream<charT, traits>&
-   operator<<(basic_ostream<charT, traits>& os,
-              const basic_string<charT,traits,Allocator>& str);
-
-template<class charT, class traits, class Allocator>
- basic_ostream<charT, traits>&
-   operator<<(basic_ostream<charT, traits>&& os,
-              const basic_string<charT,traits,Allocator>& str);
-
- - - - - -
-

825. Missing rvalues reference stream insert/extract operators?

-

Section: 19.5.2.1 [syserr.errcode.overview], 20.8.2.2.11 [util.smartptr.shared.io], 22.4.8 [facets.examples], 20.6.4 [bitset.operators], 26.4.6 [complex.ops], 27.6 [stream.buffers], 28.9 [re.submatch] Status: Resolved - Submitter: Alisdair Meredith Opened: 2008-04-10 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

Addresses UK 220

- -

-Should the following use rvalues references to stream in insert/extract operators? -

- -
    -
  • 19.5.2.1 [syserr.errcode.overview]
    • -
  • 20.8.2.2.11 [util.smartptr.shared.io]
    • -
  • 22.4.8 [facets.examples]
    • -
  • 20.6.4 [bitset.operators]
    • -
  • 26.4.6 [complex.ops]
    • -
  • Doubled signatures in 27.6 [stream.buffers] for character inserters -(ref 27.7.3.6.4 [ostream.inserters.character]) -+ definition 27.7.3.6.4 [ostream.inserters.character]
    • -
  • 28.9 [re.submatch]
    • -
- -

[ -Sophia Antipolis -]

- - -

-Agree with the idea in the issue, Alisdair to provide wording. -

- -

[ -Daniel adds 2009-02-14: -]

- - -

-The proposal given in the paper -N2831 -apparently resolves this issue. -

- -

[ -Batavia (2009-05): -]

- -
-

-The cited paper is an earlier version of -N2844, -which changed the rvalue reference binding rules. -That paper includes generic templates -operator<< and operator>> -that adapt rvalue streams. -

-

-We therefore agree with Daniel's observation. Move to NAD EditorialResolved. -

-
- - -

Proposed resolution:

-

-

- - - - - -
-

827. constexpr shared_ptr::shared_ptr()?

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: Resolved - Submitter: Peter Dimov Opened: 2008-04-11 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

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-

Discussion:

-

-Would anyone object to making the default constructor of shared_ptr (and -weak_ptr and enable_shared_from_this) constexpr? This would enable -static initialization for shared_ptr variables, eliminating another -unfair advantage of raw pointers. -

- -

[ -San Francisco: -]

- - -
-

-It's not clear to us that you can initialize a pointer with the literal -0 in a constant expression. We need to ask CWG to make sure this works. -Bjarne has been appointed to do this. -

-

-Core got back to us and assured as that nullptr would do the job -nicely here. -

-
- -

[ -2009-05-01 Alisdair adds: -]

- - -
-

-I don't believe that constexpr will buy anything in this case. -shared_ptr/weak_ptr/enable_shared_from_this cannot be literal types as they -have a non-trivial copy constructor. As they do not produce literal types, -then the constexpr default constructor will not guarantee constant -initialization, and so not buy the hoped for optimization. -

-

-I recommend referring this back to Core to see if we can get static -initialization for types with constexpr constructors, even if they are not -literal types. Otherwise this should be closed as NAD. -

-
- -

[ -2009-05-26 Daniel adds: -]

- - -

-If Alisdair's 2009-05-01 comment is correct, wouldn't that also make -constexpr mutex() useless, because this class has a non-trivial -destructor? (828) -

- -

[ -2009-07-21 Alisdair adds: -]

- - -
-

-The feedback from core is that this and similar uses of constexpr -constructors to force static initialization should be supported. If -there are any problems with this in the working draught, we should file -core issues. -

- -

-Recommend we declare the default constructor constexpr as the issue suggests -(proposed wording added). -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2994. -

- - -

Proposed resolution:

-

-Change 20.8.2.2 [util.smartptr.shared] and 20.8.2.2.1 [util.smartptr.shared.const]: -

- -
-constexpr shared_ptr();
-
- -

-Change 20.8.2.3 [util.smartptr.weak] and 20.8.2.3.1 [util.smartptr.weak.const]: -

- -
-constexpr weak_ptr();
-
- -

-Change 20.8.2.5 [util.smartptr.enab] (2 places): -

- -
-constexpr enable_shared_from_this();
-
- - - - - - -
-

828. Static initialization for std::mutex?

-

Section: 30.4.1.2.1 [thread.mutex.class] Status: Resolved - Submitter: Peter Dimov Opened: 2008-04-18 Last modified: 2015-04-08

-

View all other issues in [thread.mutex.class].

-

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-

Discussion:

-

-[Note: I'm assuming here that 3.6.2 [basic.start.init]/1 will be fixed.] -

-

-Currently std::mutex doesn't support static initialization. This is a -regression with respect to pthread_mutex_t, which does. I believe that -we should strive to eliminate such regressions in expressive power where -possible, both to ease migration and to not provide incentives to (or -force) people to forego the C++ primitives in favor of pthreads. -

- -

[ -Sophia Antipolis: -]

- - -
-

-We believe this is implementable on POSIX, because the initializer-list -feature and the constexpr feature make this work. Double-check core -language about static initialization for this case. Ask core for a core -issue about order of destruction of statically-initialized objects wrt. -dynamically-initialized objects (should come afterwards). Check -non-POSIX systems for implementability. -

-

-If ubiquitous implementability cannot be assured, plan B is to introduce -another constructor, make this constexpr, which is -conditionally-supported. To avoid ambiguities, this new constructor needs -to have an additional parameter. -

-
- -

[ -Post Summit: -]

- - -
-

-Jens: constant initialization seems to be ok core-language wise -

-

-Consensus: Defer to threading experts, in particular a Microsoft platform expert. -

-

-Lawrence to send e-mail to Herb Sutter, Jonathan Caves, Anthony Wiliams, -Paul McKenney, Martin Tasker, Hans Boehm, Bill Plauger, Pete Becker, -Peter Dimov to alert them of this issue. -

-

-Lawrence: What about header file shared with C? The initialization syntax is different in C and C++. -

-

-Recommend Keep in Review -

-
- -

[ -Batavia (2009-05): -]

- -

-Keep in Review status pending feedback from members of the Concurrency subgroup. -

- -

[ -See related comments from Alisdair and Daniel in 827. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2994. -

- - - -

Proposed resolution:

-

-Change 30.4.1.2.1 [thread.mutex.class]: -

- -
-class mutex {
-public:
-  constexpr mutex();
-  ...
-
- - - - - -
-

829. current_exception wording unclear about exception type

-

Section: 18.8.5 [propagation] Status: CD1 - Submitter: Beman Dawes Opened: 2008-04-20 Last modified: 2015-04-08

-

View all other issues in [propagation].

-

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-

Discussion:

-

Consider this code:

- -
-
exception_ptr xp;
-
try {do_something(); }
-
-catch (const runtime_error& ) {xp = current_exception();}
-
-...
-
-rethrow_exception(xp);
-
- -

-Say do_something() throws an exception object of type -range_error. What is the type of the exception object thrown by -rethrow_exception(xp) above? It must have a type of range_error; -if it were of type runtime_error it still isn't possible to -propagate an exception and the exception_ptr/current_exception/rethrow_exception -machinery serves no useful purpose. -

- -

-Unfortunately, the current wording does not explicitly say that. Different -people read the current wording and come to different conclusions. While it may -be possible to deduce the correct type from the current wording, it would be -much clearer to come right out and explicitly say what the type of the referred -to exception is. -

- -

[ -Peter adds: -]

- - -
-

-I don't like the proposed resolution of 829. The normative text is -unambiguous that the exception_ptr refers to the currently handled -exception. This term has a standard meaning, see 15.3 [except.handle]/8; this is the -exception that throw; would rethrow, see 15.1 [except.throw]/7. -

-

-A better way to address this is to simply add the non-normative example -in question as a clarification. The term currently handled exception -should be italicized and cross-referenced. A [Note: the currently -handled exception is the exception that a throw expression without an -operand (15.1 [except.throw]/7) would rethrow. --end note] is also an option. -

-
- - - -

Proposed resolution:

- -

-After 18.8.5 [propagation] , paragraph 7, add the indicated text: -

- -
-
exception_ptr current_exception();
- -
-

-Returns: exception_ptr object that refers -to the currently handled exception (15.3 [except.handle]) or a copy of the currently handled -exception, or a null exception_ptr object if no exception is being handled. If -the function needs to allocate memory and the attempt fails, it returns an -exception_ptr object that refers to an instance of bad_alloc. -It is unspecified whether the return values of two successive calls to -current_exception refer to the same exception object. -[Note: that is, it -is unspecified whether current_exception -creates a new copy each time it is called. --- end note] -

- -

-Throws: nothing. -

- -
-
- - - - - - -
-

834. unique_ptr::pointer requirements underspecified

-

Section: 20.8.1.2 [unique.ptr.single] Status: Resolved - Submitter: Daniel Krügler Opened: 2008-05-14 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single].

-

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-

Discussion:

-

-Issue 673 (including recent updates by 821) proposes a useful -extension point for unique_ptr by granting support for an optional -deleter_type::pointer to act as pointer-like replacement for element_type* -(In the following: pointer). -

-

-Unfortunately no requirements are specified for the type pointer which has -impact on at least two key features of unique_ptr: -

- -
    -
  1. Operational fail-safety.
    2. -
  2. (Well-)Definedness of expressions.
    3. -
- -

-The unique_ptr specification makes great efforts to require that essentially all -operations cannot throw and therefore adds proper wording to the affected -operations of the deleter as well. If user-provided pointer-emulating types -("smart pointers") will be allowed, either all throw-nothing clauses have to -be replaced by weaker "An exception is thrown only if pointer's {op} throws -an exception"-clauses or it has to be said explicitly that all used -operations of pointer are required not to throw. I understand the main -focus of unique_ptr to be as near as possible to the advantages of native pointers which cannot -fail and thus strongly favor the second choice. Also, the alternative position -would make it much harder to write safe and simple template code for -unique_ptr. Additionally, I assume that a general statement need to be given -that all of the expressions of pointer used to define semantics are required to -be well-formed and well-defined (also as back-end for 762). -

- -

[ -Sophia Antipolis: -]

- - -
-

-Howard: We maybe need a core concept PointerLike, but we don't need the -arithmetic (see shared_ptr vs. vector<T>::iterator. -

-

-Howard will go through and enumerate the individual requirements wrt. pointer for each member function. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- -

[ -2009-10-15 Alisdair pulls from Ready: -]

- - -
-

-I hate to pull an issue out of Ready status, but I don't think 834 is -fully baked yet. -

- -

-For reference the proposed resolution is to add the following words: -

- -

-unique_ptr<T, D>::pointer's operations shall be -well-formed, shall have well defined behavior, and shall not throw -exceptions. -

- -

-This leaves me with a big question : which operations? -

- -

-Are all pointer operations required to be nothrow, including operations -that have nothing to do with interactions with unique_ptr? This was -much simpler with concepts where we could point to operations within a -certain concept, and so nail down the interactions. -

-
- -

[ -2009-10-15 Daniel adds: -]

- - -

-I volunteer to prepare a more fine-grained solution, but I would like -to ask for feedback that helps me doing so. If this question is asked -early in the meeting I might be able to fix it within the week, but I -cannot promise that now. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave in open. Daniel to provide wording as already suggested. -

- -

[ -2009-12-22 Daniel provided wording and rationale. -]

- - -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-The here proposed resolution has considerable overlap with the requirements that -are used in the allocator requirements. -

- -

-This might be a convincing argument to isolate the common subset into one -requirement. The reason I did not do that is basically because we might find out -that they are either over-constraining or under-constraining at this late point -of specification. Note also that as a result of the idea of a general -requirement set I added the requirement: -

- -

-A default-initialized object may have a singular value -

- -

-even though this does not play a relevant role for unique_ptr. -

- -

-One further characteristics of the resolution is that availability of relational -operators of unique_ptr<T, D>::pointer is not part of the basic -requirements, which is in sync with the allocator requirements on pointer-like -(this means that unique_ptr can hold a void_pointer or -const_void_pointer). -

- -

-Solved by -N3073. -

- - - -

Proposed resolution:

- -
    - -
  1. -

    -Change 20.8.1.2 [unique.ptr.single] p. 1 as indicated: [The intent is to -replace the coupling between T* and the deleter's operator() -by a coupling between unique_ptr<T, D>::pointer and this -operator()] -

    - -

    -1 - The default type for the template parameter D is -default_delete. A client-supplied template argument D shall be -a function pointer or functor for which, given a value d of type -D and a pointer value ptr of type -T* unique_ptr<T, D>::pointer, the -expression d(ptr) is valid and has the effect of deallocating the -pointer as appropriate for that deleter. D may also be an -lvalue-reference to a deleter. -

    -
    2. - -
  2. -

    -Change 20.8.1.2 [unique.ptr.single] p. 3 as indicated: -

    - -
    -

    -3 - If the type remove_reference<D>::type::pointer exists, then -unique_ptr<T, D>::pointer shall be a synonym for -remove_reference<D>::type::pointer. Otherwise -unique_ptr<T, D>::pointer shall be a synonym for T*. The -type unique_ptr<T, D>::pointer shall be satisfy -the requirements of EqualityComparable, -DefaultConstructible, CopyConstructible (Table 34) -and, CopyAssignable (Table 36), -Swappable, and Destructible (17.6.3.1 [utility.arg.requirements]). A default-initialized object may have a -singular value. A value-initialized object produces the null value of the type. -The null value shall be equivalent only to itself. An object of this type can be -copy-initialized with a value of type nullptr_t, compared for equality -with a value of type nullptr_t, and assigned a value of type -nullptr_t. The effect shall be as if a value-initialized object had -been used in place of the null pointer constant. An object p of this -type can be contextually converted to bool. The effect shall be as if -p != nullptr had been evaluated in place of p. No operation on -this type which is part of the above mentioned requirements shall exit via an -exception. - -

    -

    -[Note: Given an allocator type X (17.6.3.5 [allocator.requirements]), the types X::pointer, -X::const_pointer, X::void_pointer, and -X::const_void_pointer may be used as unique_ptr<T, -D>::pointer — end note] -

    - -

    -In addition to being available via inclusion of the <utility> -header, the swap function template in 20.2.2 [utility.swap] is -also available within the definition of unique_ptr's swap -function. -

    -
    -
    3. - -
  3. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor] p. 2+3 as indicated: [The first -change ensures that we explicitly say, how the stored pointer is initialized. -This is important for a constexpr function, because this may make a -difference for user-defined pointer-like types] -

    - -
    -constexpr unique_ptr();
-
    -
    -

    ...

    -

    -2 - Effects: Constructs a unique_ptr which owns nothing, -value-initializing the stored pointer. -

    - -

    -3 - Postconditions: get() == 0 nullptr. -

    -
    -
    -
    4. - -
  4. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor] p. 6+7 as indicated: [This is a -step-by-fix to ensure consistency to the changes of -N2976] -

    - -
    -unique_ptr(pointer p);
-
    -
    -

    ...

    -

    -6 - Effects: Constructs a unique_ptr which owns p, -initializing the stored pointer with p. -

    - -

    -7 - Postconditions: get() == p. get_deleter() returns a -reference to a default constructed value-initialized -deleter D. -

    -
    -
    -
    5. - -
  5. -

    -Insert a new effects clause in 20.8.1.2.1 [unique.ptr.single.ctor] just -before p. 14: [The intent is to fix the current lack of specification in -which way the stored pointer is initialized] -

    - -
    -unique_ptr(pointer p, implementation-defined see below d1);
-unique_ptr(pointer p, implementation-defined see below d2);
-
    -
    -

    ...

    -

    -Effects: Constructs a unique_ptr which owns p, -initializing the stored pointer with p and the initializing the deleter -as described above. -

    - -

    -14 - Postconditions: get() == p. get_deleter() returns a -reference to the internally stored deleter. If D is a reference type -then get_deleter() returns a reference to the lvalue d. -

    -
    -
    -
    6. - -
  6. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor] p. 18+22 as indicated: [The intent -is to clarify that the moved-from source must contain a null pointer, there is -no other choice left] -

    - -
    -unique_ptr(unique_ptr&& u);
-
    -
    -

    -[..] -

    - -

    -18 - Postconditions: get() == value u.get() had before the -construction and u.get() == nullptr. get_deleter() -returns a reference to the internally stored deleter which was constructed from -u.get_deleter(). If D is a reference type then -get_deleter() and u.get_deleter() both reference the same -lvalue deleter. -

    - -
    - -
    -template <class U, class E> unique_ptr(unique_ptr<U, E>&& u);
-
    - -
    - -

    -[..] -

    - -

    -22 - Postconditions: get() == value u.get() had before the -construction, modulo any required offset adjustments resulting from the cast -from unique_ptr<U, E>::pointer to pointer and -u.get() == nullptr. get_deleter() returns a reference to -the internally stored deleter which was constructed from -u.get_deleter(). -

    -
    -
    -
    7. - -
  7. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor] p. 20 as indicated: [With the -possibility of user-defined pointer-like types the implication does only exist, -if those are built-in pointers. Note that this change should also be applied -with the acceptance of 950] -

    - -
    -template <class U, class E> unique_ptr(unique_ptr<U, E>&& u);
-
    -

    -20 - Requires: If D is not a reference type, construction of the -deleter D from an rvalue of type E shall be well formed and -shall not throw an exception. If D is a reference type, then E -shall be the same type as D (diagnostic required). unique_ptr<U, -E>::pointer shall be implicitly convertible to pointer. -[Note: These requirements imply that T and U are -complete types. — end note] -

    -
    -
    8. - -
  8. -

    -Change 20.8.1.2.2 [unique.ptr.single.dtor] p. 2 as indicated: -

    - -
    -~unique_ptr();
-
    -
    -

    ...

    -

    -2 - Effects: If get() == 0 nullptr there -are no effects. Otherwise get_deleter()(get()). -

    -
    -
    -
    9. - -
  9. -

    -Change 20.8.1.2.3 [unique.ptr.single.asgn] p. 3+8 as indicated: [The intent is to -clarify that the moved-from source must contain a null pointer, there -is no other choice left] -

    - -
    -unique_ptr& operator=(unique_ptr&& u);
-
    -
    -

    [..]

    -

    -3 - Postconditions: This unique_ptr now owns the pointer which u -owned, and u no longer owns it, u.get() == nullptr. -[Note: If D is a reference type, then the referenced lvalue deleters -are move assigned. — end note] -

    -
    - -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u);
-
    - -
    -

    [..]

    - -

    -8 - Postconditions: This unique_ptr now owns the pointer which -u owned, and u no longer owns it, u.get() == -nullptr. -

    -
    -
    -
    10. - -
  10. -

    -Change 20.8.1.2.3 [unique.ptr.single.asgn] p. 6 as indicated: [With the -possibility of user-defined pointer-like types the implication does only exist, -if those are built-in pointers. Note that this change should also be applied -with the acceptance of 950] -

    - -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u);
-
    -
    -

    [..]

    -

    -6 - Requires: Assignment of the deleter D from an rvalue -D shall not throw an exception. unique_ptr<U, -E>::pointer shall be implicitly convertible to pointer. -[Note: These requirements imply that T and U are -complete types. — end note] -

    -
    -
    -
    11. - -
  11. -

    -Change 20.8.1.2.3 [unique.ptr.single.asgn] before p. 11 and p. 12 as -indicated: [The first change is a simple typo fix] -

    - -
    -unique_ptr& operator=(nullptr_t});
-
    - -
    -

    -11 - Effects: reset(). -

    - -

    -12 - Postcondition: get() == 0 nullptr -

    -
    -
    -
    12. - -
  12. -

    -Change 20.8.1.2.4 [unique.ptr.single.observers] p. 1+4+12 as indicated: -

    - -
    -typename add_lvalue_reference<T>::type operator*() const;
-
    -
    -

    -1 - Requires: get() != 0 nullptr. The -variable definition add_lvalue_reference<T>::type t = *get() -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    -

    -[..] -

    - -
    - -
    -pointer operator->() const;
-
    - -
    -

    -4 - Requires: get() != 0 nullptr. -

    - -

    -[..] -

    - -
    - -
    -explicit operator bool() const;
-
    - -

    -12 - Returns: get() != 0nullptr. -

    -
    -
    13. - -
  13. -

    -Change 20.8.1.2.5 [unique.ptr.single.modifiers] p. 1 as indicated: -

    - -
    -pointer release();
-
    - -

    -1 - Postcondition: get() == 0 nullptr. -

    -
    -
    14. - -
  14. -

    -Change 20.8.1.2.5 [unique.ptr.single.modifiers] p. 9 as indicated: [The -intent is to ensure that potentially user-defined swaps are used. A side-step -fix and harmonization with the specification of the the deleter is realized. -Please note the additional requirement in bullet 2 of this proposed resolution -regarding the availability of the generic swap templates within the -member swap function.] -

    - -
    -void swap(unique_ptr& u);
-
    - -
    -

    -8 - Requires: The deleter D shall be Swappable and -shall not throw an exception under swap. -

    - -

    -9 - Effects: The stored pointers of *this and -u are exchanged by an unqualified call to non-member -swap. The stored deleters are swap'd -(unqualified) exchanged by an unqualified call to non-member -swap. -

    -
    -
    -
    15. - -
  15. -

    -Change 20.8.1.3.3 [unique.ptr.runtime.observers] p. 1 as indicated: -

    - -
    -T& operator[](size_t i) const;
-
    -

    -Requires: i < the size of the array to which the stored -pointer points. The variable definition T& t = get()[i] shall -be well formed, shall have well-defined behavior, and shall not exit via an -exception. -

    -
    -
    16. - -
  16. -

    -Change 20.8.1.3.4 [unique.ptr.runtime.modifiers] p. 1 as indicated: -

    - -
    -void reset(pointer p = pointer());
-void reset(nullptr_t p);
-
    - -

    -1 - Effects: If get() == 0 nullptr there -are no effects. Otherwise get_deleter()(get()). -

    -
    -
    17. - -
  17. -

    -Change 20.8.1.5 [unique.ptr.special] as indicated: [We don't add the -relational operators to the basic requirement set, therefore we need special -handling here] -

    - -
    -
    -template <class T1, class D1, class T2, class D2>
-  bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() == y.get(); shall be -well formed, shall have well-defined behavior, and shall not exit via an exception. -

    - -

    -2 - Returns: x.get() == y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() != y.get(); -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    - -

    -3 - Returns: x.get() != y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() < y.get(); -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    - -

    -4 - Returns: x.get() < y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() <= y.get(); -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    - -

    -5 - Returns: x.get() <= y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() > y.get(); -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    - -

    -6 - Returns: x.get() > y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -Requires: The variable definition bool b = x.get() >= y.get(); -shall be well formed, shall have well-defined behavior, and shall not exit via -an exception. -

    - -

    -7 - Returns: x.get() >= y.get(). -

    - -

    -Throws: nothing. -

    -
    - -
    -
    18. - -
- - - - - - - -
-

835. Tying two streams together (correction to DR 581)

-

Section: 27.5.5.3 [basic.ios.members] Status: C++11 - Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

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-

Discussion:

-

- -The fix for -issue 581, -now integrated into the working paper, overlooks a couple of minor -problems. - -

-

- -First, being an unformatted function once again, flush() -is required to create a sentry object whose constructor must, among -other things, flush the tied stream. When two streams are tied -together, either directly or through another intermediate stream -object, flushing one will also cause a call to flush() on -the other tied stream(s) and vice versa, ad infinitum. The program -below demonstrates the problem. - -

-

- -Second, as Bo Persson notes in his -comp.lang.c++.moderated post, -for streams with the unitbuf flag set such -as std::stderr, the destructor of the sentry object will -again call flush(). This seems to create an infinite -recursion for std::cerr << std::flush; - -

-
- 
-#include <iostream>
-
-int main ()
-{
-   std::cout.tie (&std::cerr);
-   std::cerr.tie (&std::cout);
-   std::cout << "cout\n";
-   std::cerr << "cerr\n";
-} 
-
-
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Review. -

- -

[ -2009-05-26 Daniel adds: -]

- - -
-

-I think that the most recently suggested change in -27.7.3.4 [ostream::sentry] need some further word-smithing. As -written, it would make the behavior undefined, if under -conditions when pubsync() should be called, but when -in this scenario os.rdbuf() returns 0. -

-

-This case is explicitly handled in flush() and needs to be -taken care of. My suggested fix is: -

- -

-If ((os.flags() & ios_base::unitbuf) && !uncaught_exception() -&& os.rdbuf() != 0) is true, calls os.flush() -os.rdbuf()->pubsync(). -

- -

-Two secondary questions are: -

- -
    -
  1. -Should pubsync() be invoked in any case or shouldn't a -base requirement for this trial be that os.good() == true -as required in the original flush() case? -
    2. -
  2. -Since uncaught_exception() is explicitly tested, shouldn't -a return value of -1 of pubsync() produce setstate(badbit) -(which may throw ios_base::failure)? -
    3. -
-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-Daniel volunteered to modify the proposed resolution to address his two questions. -

-

-Move back to Open. -

-
- -

[ -2009-07-26 Daniel provided wording. Moved to Review. -]

- - -

[ -2009-10-13 Daniel adds: -]

- - -

-This proposed wording is written to match the outcome -of 397. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Open. Martin to propose updated wording that will also resolve -issue 397 consistently. -

- -

[ -2010-02-15 Martin provided wording. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

- -
    -
  1. -

    -Just before 27.5.5.3 [basic.ios.members] p. 2 insert a new paragraph: -

    - -

    -Requires: If (tiestr != 0) is true, -tiestr must not be reachable by traversing the linked list of tied -stream objects starting from tiestr->tie(). -

    -
    2. - -
  2. -

    -Change 27.7.3.4 [ostream::sentry] p. 4 as indicated: -

    - -

    -If ((os.flags() & ios_base::unitbuf) && !uncaught_exception() -&& os.good()) is true, calls -os.flush() os.rdbuf()->pubsync(). If that -function returns -1 sets badbit in os.rdstate() without -propagating an exception. -

    -
    3. - -
  3. -

    -Add after 27.7.3.4 [ostream::sentry] p17, the following paragraph: -

    - -

    -Throws: Nothing. -

    - -
    4. - -
- - - - - - -
-

836. - Effects of money_base::space and - money_base::none on money_get -

-

Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: C++11 - Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2015-04-08

-

View all other issues in [locale.money.get.virtuals].

-

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-

Duplicate of: 670

-

Discussion:

- -

- -In paragraph 2, 22.4.6.1.2 [locale.money.get.virtuals] specifies the following: - -

-

- -Where space or none appears in the format -pattern, except at the end, optional white space (as recognized -by ct.is) is consumed after any required space. - -

-

- -This requirement can be (and has been) interpreted two mutually -exclusive ways by different readers. One possible interpretation -is that: - -

-
-
    -
  1. - -where money_base::space appears in the format, at least -one space is required, and - -
    2. -
  2. - -where money_base::none appears in the format, space is -allowed but not required. - -
    3. -
-
-

- -The other is that: - -

-

- -where either money_base::space or money_base::none appears in the format, white space is optional. - -

- -

[ -San Francisco: -]

- - -

-Martin will revise the proposed resolution. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-There is a noun missing from the proposed resolution. It's not clear -that the last sentence would be helpful, even if the word were not -missing: -

-

-In either case, any required MISSINGWORD followed by all optional whitespace -(as recognized by ct.is()) is consumed. -

-

-Strike this sentence and move to Review. -

- -

[ -Howard: done. -]

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

- -I propose to change the text to make it clear that the first -interpretation is intended, that is, to make following change to -22.4.6.1.2 [locale.money.get.virtuals], p. 2: - -

- -

- -When money_base::space -or money_base::none appears as the last -element in the format pattern, except at the end, optional -white space (as recognized by ct.is) is consumed after -any required space. no white space is consumed. Otherwise, -where money_base::space appears in any of the initial -elements of the format pattern, at least one white space character is -required. Where money_base::none appears in any of the -initial elements of the format pattern, white space is allowed but not -required. -If (str.flags() & str.showbase) is false, ... - -

- - - - -
-

838. - Can an end-of-stream iterator become a non-end-of-stream one? -

-

Section: 24.6.1 [istream.iterator] Status: C++11 - Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2015-04-08

-

View all other issues in [istream.iterator].

-

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-

Discussion:

-

- -From message c++std-lib-20003... - -

-

- -The description of istream_iterator in -24.6.1 [istream.iterator], p. 1 specifies that objects of the -class become the end-of-stream (EOS) iterators under the -following condition (see also issue 788 another problem -with this paragraph): - -

-

- -If the end of stream is reached (operator void*() on the -stream returns false), the iterator becomes equal to -the end-of-stream iterator value. - -

-

- -One possible implementation approach that has been used in practice is -for the iterator to set its in_stream pointer to 0 when -it reaches the end of the stream, just like the default ctor does on -initialization. The problem with this approach is that -the Effects clause for operator++() says the -iterator unconditionally extracts the next value from the stream by -evaluating *in_stream >> value, without checking -for (in_stream == 0). - -

-

- -Conformance to the requirement outlined in the Effects clause -can easily be verified in programs by setting eofbit -or failbit in exceptions() of the associated -stream and attempting to iterate past the end of the stream: each -past-the-end access should trigger an exception. This suggests that -some other, more elaborate technique might be intended. - -

-

- -Another approach, one that allows operator++() to attempt -to extract the value even for EOS iterators (just as long -as in_stream is non-0) is for the iterator to maintain a -flag indicating whether it has reached the end of the stream. This -technique would satisfy the presumed requirement implied by -the Effects clause mentioned above, but it isn't supported by -the exposition-only members of the class (no such flag is shown). This -approach is also found in existing practice. - -

-

- -The inconsistency between existing implementations raises the question -of whether the intent of the specification is that a non-EOS iterator -that has reached the EOS become a non-EOS one again after the -stream's eofbit flag has been cleared? That is, are the -assertions in the program below expected to pass? - -

-
- 
-   sstream strm ("1 ");
-   istream_iterator eos;
-   istream_iterator it (strm);
-   int i;
-   i = *it++
-   assert (it == eos);
-   strm.clear ();
-   strm << "2 3 ";
-   assert (it != eos);
-   i = *++it;
-   assert (3 == i);
-
-
-

- -Or is it intended that once an iterator becomes EOS it stays EOS until -the end of its lifetime? - -

- -

[ -San Francisco: -]

- - -
-

-We like the direction of the proposed resolution. We're not sure about -the wording, and we need more time to reflect on it, -

-

-Move to Open. Detlef to rewrite the proposed resolution in such a way -that no reference is made to exposition only members of -istream_iterator. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

- -The discussion of this issue on the reflector suggests that the intent -of the standard is for an istreambuf_iterator that has -reached the EOS to remain in the EOS state until the end of its -lifetime. Implementations that permit EOS iterators to return to a -non-EOS state may only do so as an extension, and only as a result of -calling istream_iterator member functions on EOS -iterators whose behavior is in this case undefined. - -

-

- -To this end we propose to change 24.6.1 [istream.iterator], p1, -as follows: - -

-

- -The result of operator-> on an end-of-stream -is not defined. For any other iterator value a const T* -is returned. Invoking operator++() on -an end-of-stream iterator is undefined. It is impossible -to store things into istream iterators... - -

-

- -Add pre/postconditions to the member function descriptions of istream_iterator like so: - -

-
- -
istream_iterator();
-

-Effects: Constructs the end-of-stream iterator.
-Postcondition: in_stream == 0. -

-
istream_iterator(istream_type &s);
-

-Effects: Initializes in_stream with &s. value -may be initialized during construction or the first time it is -referenced.
-Postcondition: in_stream == &s. -

-
istream_iterator(const istream_iterator &x);
-

-Effects: Constructs a copy of x.
-Postcondition: in_stream == x.in_stream. -

-
istream_iterator& operator++();
-

-Requires: in_stream != 0.
-Effects: *in_stream >> value. -

-
istream_iterator& operator++(int);
-

-Requires: in_stream != 0.
-Effects: -

-
-istream_iterator tmp (*this);
-*in_stream >> value;
-return tmp;
-
-
-
- - - - -
-

842. ConstructibleAsElement and bit containers

-

Section: 23.2 [container.requirements], 23.3.7 [vector.bool], 20.6 [template.bitset] Status: CD1 - Submitter: Howard Hinnant Opened: 2008-06-03 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

View all other issues in [container.requirements].

-

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-

Discussion:

-

-23.2 [container.requirements] p. 3 says: -

- -

-Objects stored in these components shall be constructed using -construct_element (20.6.9). For each operation that inserts an -element of type T into a container (insert, -push_back, push_front, emplace, etc.) with -arguments args... T shall be ConstructibleAsElement, -as described in table 88. [Note: If the component is instantiated -with a scoped allocator of type A (i.e., an allocator for which -is_scoped_allocator<A>::value is true), then -construct_element may pass an inner allocator argument to -T's constructor. -- end note] -

- -

-However vector<bool, A> (23.3.7 [vector.bool]) and bitset<N> -(20.6 [template.bitset]) store bits, not bools, and bitset<N> -does not even have an allocator. But these containers are governed by this clause. Clearly this -is not implementable. -

- - -

Proposed resolution:

-

-Change 23.2 [container.requirements] p. 3: -

- -

-Objects stored in these components shall be constructed using -construct_element (20.6.9), unless otherwise specified. -For each operation that inserts an -element of type T into a container (insert, -push_back, push_front, emplace, etc.) with -arguments args... T shall be ConstructibleAsElement, -as described in table 88. [Note: If the component is instantiated -with a scoped allocator of type A (i.e., an allocator for which -is_scoped_allocator<A>::value is true), then -construct_element may pass an inner allocator argument to -T's constructor. -- end note] -

- -

-Change 23.3.7 [vector.bool]/p2: -

- -

-Unless described below, all operations have the same requirements and semantics as the primary vector template, -except that operations dealing with the bool value type map to bit values in the container storage, -and construct_element (23.2 [container.requirements]) is not used to construct these values. -

- -

-Move 20.6 [template.bitset] to clause 20. -

- - - - - - -
-

843. Reference Closure

-

Section: X [func.referenceclosure.cons] Status: CD1 - Submitter: Lawrence Crowl Opened: 2008-06-02 Last modified: 2015-04-08

-

View all issues with CD1 status.

-

Discussion:

-

-The std::reference_closure type has a deleted copy assignment operator -under the theory that references cannot be assigned, and hence the -assignment of its reference member must necessarily be ill-formed. -

-

-However, other types, notably std::reference_wrapper and std::function -provide for the "copying of references", and thus the current definition -of std::reference_closure seems unnecessarily restrictive. In particular, -it should be possible to write generic functions using both std::function -and std::reference_closure, but this generality is much harder when -one such type does not support assignment. -

-

-The definition of reference_closure does not necessarily imply direct -implementation via reference types. Indeed, the reference_closure is -best implemented via a frame pointer, for which there is no standard -type. -

-

-The semantics of assignment are effectively obtained by use of the -default destructor and default copy assignment operator via -

- -
-x.~reference_closure(); new (x) reference_closure(y);
-
- -

-So the copy assignment operator generates no significant real burden -to the implementation. -

- - -

Proposed resolution:

-

-In [func.referenceclosure] Class template reference_closure, -replace the =delete in the copy assignment operator in the synopsis -with =default. -

- -
-template<class R , class... ArgTypes > 
-  class reference_closure<R (ArgTypes...)> { 
-  public:
-     ...
-     reference_closure& operator=(const reference_closure&) = delete default;
-     ...
-
- -

-In X [func.referenceclosure.cons] Construct, copy, destroy, -add the member function description -

- -
-
-reference_closure& operator=(const reference_closure& f)
-
-
-

-Postcondition: *this is a copy of f. -

-

-Returns: *this. -

-
-
- - - - - - - -
-

844. complex pow return type is ambiguous

-

Section: 26.4.9 [cmplx.over] Status: CD1 - Submitter: Howard Hinnant Opened: 2008-06-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current working draft is in an inconsistent state. -

- -

-26.4.8 [complex.transcendentals] says that: -

- -

-pow(complex<float>(), int()) returns a complex<float>. -

- -

-26.4.9 [cmplx.over] says that: -

- -

-pow(complex<float>(), int()) returns a complex<double>. -

- -

[ -Sophia Antipolis: -]

- - -
-

-Since int promotes to double, and C99 doesn't have an int-based -overload for pow, the C99 result is complex<double>, see also C99 -7.22, see also library issue 550. -

-

-Special note: ask P.J. Plauger. -

-

-Looks fine. -

-
- - -

Proposed resolution:

-

-Strike this pow overload in 26.4.1 [complex.syn] and in 26.4.8 [complex.transcendentals]: -

- -
-template<class T> complex<T> pow(const complex<T>& x, int y);
-
- - - - - -
-

845. atomics cannot support aggregate initialization

-

Section: 29.5 [atomics.types.generic] Status: CD1 - Submitter: Alisdair Meredith Opened: 2008-06-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The atomic classes (and class templates) are required to support aggregate -initialization (X [atomics.types.integral] p. 2 / X [atomics.types.address] p. 1) -yet also have user declared constructors, so cannot be aggregates. -

-

-This problem might be solved with the introduction of the proposed -initialization syntax at Antipolis, but the wording above should be altered. -Either strike the sentence as redundant with new syntax, or refer to 'brace -initialization'. -

- -

[ -Jens adds: -]

- - -
-

-Note that -

-
-atomic_itype a1 = { 5 };
-
-

-would be aggregate-initialization syntax (now coming under the disguise -of brace initialization), but would be ill-formed, because the corresponding -constructor for atomic_itype is explicit. This works, though: -

-
-atomic_itype a2 { 6 };
-
- -
- -

[ -San Francisco: -]

- - -
-

-The preferred approach to resolving this is to remove the explicit -specifiers from the atomic integral type constructors. -

-

-Lawrence will provide wording. -

-

-This issue is addressed in -N2783. -

-
- - - -

Proposed resolution:

-

-within the synopsis in X [atomics.types.integral] edit as follows. -

- -

-....
-typedef struct atomic_bool {
-....
-  constexpr explicit atomic_bool(bool);
-....
-typedef struct atomic_itype {
-....
-  constexpr explicit atomic_itype(integral);
-....
-
- -

-edit X [atomics.types.integral] paragraph 2 as follows. -

- -

-The atomic integral types shall have standard layout. -They shall each have a trivial default constructor, -a constexpr explicit value constructor, -a deleted copy constructor, -a deleted copy assignment operator, -and a trivial destructor. -They shall each support aggregate initialization syntax. -

- -

-within the synopsis of X [atomics.types.address] edit as follows. -

- -

-....
-typedef struct atomic_address {
-....
-  constexpr explicit atomic_address(void*);
-....
-
- -

-edit X [atomics.types.address] paragraph 1 as follows. -

- -

-The type atomic_address shall have standard layout. -It shall have a trivial default constructor, -a constexpr explicit value constructor, -a deleted copy constructor, -a deleted copy assignment operator, -and a trivial destructor. -It shall support aggregate initialization syntax. -

- -

-within the synopsis of 29.5 [atomics.types.generic] edit as follows. -

- -

-....
-template <class T> struct atomic {
-....
-  constexpr explicit atomic(T);
-....
-template <> struct atomic<integral> : atomic_itype {
-....
-  constexpr explicit atomic(integral);
-....
-template <> struct atomic<T*> : atomic_address {
-....
-  constexpr explicit atomic(T*);
-....
-
- -

-edit 29.5 [atomics.types.generic] paragraph 2 as follows. -

- -

-Specializations of the atomic template -shall have a deleted copy constructor, -a deleted copy assignment operator, -and a constexpr explicit value constructor. -

- - - - - - -
-

846. No definition for constructor

-

Section: 29.6 [atomics.types.operations] Status: CD1 - Submitter: Alisdair Meredith Opened: 2008-06-03 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The atomic classes and class templates (X [atomics.types.integral] / -X [atomics.types.address]) have a constexpr -constructor taking a value of the appropriate type for that atomic. -However, neither clause provides semantics or a definition for this -constructor. I'm not sure if the initialization is implied by use of -constexpr keyword (which restricts the form of a constructor) but even if -that is the case, I think it is worth spelling out explicitly as the -inference would be far too subtle in that case. -

- -

[ -San Francisco: -]

- - -
-

-Lawrence will provide wording. -

-

-This issue is addressed in -N2783. -

-
- - -

Proposed resolution:

- -

-before the description of ...is_lock_free, -that is before 29.6 [atomics.types.operations] paragraph 4, -add the following description. -

- -
-

-constexpr A::A(C desired);
-
-
-
Effects:
-
-Initializes the object with the value desired. -[Note: -Construction is not atomic. -—end note] -
-
-
- - - - - -
-

847. string exception safety guarantees

-

Section: 21.4.1 [string.require] Status: C++11 - Submitter: Hervé Brönnimann Opened: 2008-06-05 Last modified: 2015-04-08

-

View all other issues in [string.require].

-

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-

Discussion:

-

-In March, on comp.lang.c++.moderated, I asked what were the -string exception safety guarantees are, because I cannot see -*any* in the working paper, and any implementation I know offers -the strong exception safety guarantee (string unchanged if a -member throws exception). The closest the current draft comes to -offering any guarantees is 21.4 [basic.string], para 3: -

- -

-The class template basic_string conforms to the requirements -for a Sequence Container (23.1.1), for a Reversible Container (23.1), -and for an Allocator-aware container (91). The iterators supported by -basic_string are random access iterators (24.1.5). -

- -

-However, the chapter 23 only says, on the topic of exceptions: 23.2 [container.requirements], -para 10: -

- -
-

-Unless otherwise specified (see 23.2.2.3 and 23.2.6.4) all container types defined in this clause meet the following -additional requirements: -

- -
    -
  • if an exception is thrown by...
    • -
-
- -

-I take it as saying that this paragraph has *no* implication on -std::basic_string, as basic_string isn't defined in Clause 23 and -this paragraph does not define a *requirement* of Sequence -nor Reversible Container, just of the models defined in Clause 23. -In addition, LWG Issue 718 proposes to remove 23.2 [container.requirements], para 3. -

- -

-Finally, the fact that no operation on Traits should throw -exceptions has no bearing, except to suggest (since the only -other throws should be allocation, out_of_range, or length_error) -that the strong exception guarantee can be achieved. -

- -

-The reaction in that group by Niels Dekker, Martin Sebor, and -Bo Persson, was all that this would be worth an LWG issue. -

- -

-A related issue is that erase() does not throw. This should be -stated somewhere (and again, I don't think that the 23.2 [container.requirements], para 1 -applies here). -

- -

[ -San Francisco: -]

- - -

-Implementors will study this to confirm that it is actually possible. -

- -

[ -Daniel adds 2009-02-14: -]

- - -

-The proposed resolution of paper -N2815 -interacts with this issue (the paper does not refer to this issue). -

- -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add a blanket statement in 21.4.1 [string.require]: -

- -
-

-- if any member function or operator of basic_string<charT, traits, Allocator> -throws, that function or operator has no effect. -

-

-- no erase() or pop_back() function throws. -

-
- -

-As far as I can tell, this is achieved by any implementation. If I made a -mistake and it is not possible to offer this guarantee, then -either state all the functions for which this is possible -(certainly at least operator+=, append, assign, and insert), -or add paragraphs to Effects clauses wherever appropriate. -

- - - - - -
-

848. Missing std::hash specializations for std::bitset/std::vector<bool>

-

Section: 20.9.13 [unord.hash] Status: CD1 - Submitter: Thorsten Ottosen Opened: 2008-06-05 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

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-

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-

Discussion:

-

-In the current working draft, std::hash<T> is specialized for builtin -types and a few other types. Bitsets seems like one that is missing from -the list, not because it cannot not be done by the user, but because it -is hard or impossible to write an efficient implementation that works on -32bit/64bit chunks at a time. For example, std::bitset is too much -encapsulated in this respect. -

- - -

Proposed resolution:

-

-Add the following to the synopsis in 20.9 [function.objects]/2: -

- -
-template<class Allocator> struct hash<std::vector<bool,Allocator>>;
-template<size_t N> struct hash<std::bitset<N>>;
-
- -

-Modify the last sentence of 20.9.13 [unord.hash]/1 to end with: -

- -

-... and std::string, std::u16string, std::u32string, std::wstring, -std::error_code, std::thread::id, std::bitset, and std::vector<bool>. -

- - - - - - -
-

850. Should shrink_to_fit apply to std::deque?

-

Section: 23.3.3.3 [deque.capacity] Status: CD1 - Submitter: Niels Dekker Opened: 2008-06-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Issue 755 added a shrink_to_fit function to std::vector and std::string. -It did not yet deal with std::deque, because of the fundamental -difference between std::deque and the other two container types. The -need for std::deque may seem less evident, because one might think that -for this container, the overhead is a small map, and some number of -blocks that's bounded by a small constant. -

-

-The container overhead can in fact be arbitrarily large (i.e. is not -necessarily O(N) where N is the number of elements currently held by the -deque). As Bill Plauger noted in a reflector message, unless the map of -block pointers is shrunk, it must hold at least maxN⁄B pointers where -maxN is the maximum of N over the lifetime of the deque since its -creation. This is independent of how the map is implemented -(vector-like circular buffer and all), and maxN bears no relation to N, -the number of elements it currently holds. -

-

-Hervé Brönnimann reports a situation where a deque of requests grew very -large due to some temporary backup (the front request hanging), and the -map of the deque grew quite large before getting back to normal. Just -to put some color on it, assuming a deque with 1K pointer elements in -steady regime, that held, at some point in its lifetime, maxN=10M -pointers, with one block holding 128 elements, the spine must be at -least (maxN ⁄ 128), in that case 100K. In that case, shrink-to-fit -would allow to reuse about 100K which would otherwise never be reclaimed -in the lifetime of the deque. -

-

-An added bonus would be that it allows implementations to hang on to -empty blocks at the end (but does not care if they do or not). A -shrink_to_fit would take care of both shrinks, and guarantee that at -most O(B) space is used in addition to the storage to hold the N -elements and the N⁄B block pointers. -

- - -

Proposed resolution:

-

-To class template deque 23.3.3 [deque] synopsis, add: -

-
-void shrink_to_fit();
-
- -

-To deque capacity 23.3.3.3 [deque.capacity], add: -

-
-void shrink_to_fit();
-
- -

-Remarks: shrink_to_fit is a non-binding request to reduce memory -use. [Note: The request is non-binding to allow latitude for -implementation-specific optimizations. — end note] -

-
- - - - - -
-

852. unordered containers begin(n) mistakenly const

-

Section: 23.5 [unord] Status: CD1 - Submitter: Robert Klarer Opened: 2008-06-12 Last modified: 2015-04-08

-

View all other issues in [unord].

-

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-

Discussion:

-

-In 3 of the four unordered containers the local begin member is mistakenly declared const: -

- -
-local_iterator begin(size_type n) const;
-
- - -

Proposed resolution:

-

-Change the synopsis in 23.5.4 [unord.map], 23.5.5 [unord.multimap], and 23.5.7 [unord.multiset]: -

- -
-local_iterator begin(size_type n) const;
-
- - - - - -
-

853. to_string needs updating with zero and one

-

Section: 20.6 [template.bitset] Status: C++11 - Submitter: Howard Hinnant Opened: 2008-06-18 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Issue 396 adds defaulted arguments to the to_string member, but neglects to update -the three newer to_string overloads. -

- -

[ -post San Francisco: -]

- - -

-Daniel found problems with the wording and provided fixes. Moved from Ready -to Review. -

- -

[ -Post Summit: -]

- - -
-

-Alisdair: suggest to not repeat the default arguments in B, C, D -(definition of to_string members) -

-

-Walter: This is not really a definition. -

-

-Consensus: Add note to the editor: Please apply editor's judgement -whether default arguments should be repeated for B, C, D changes. -

-

-Recommend Tentatively Ready. -

-
- -

[ -2009-05-09: See alternative solution in issue 1113. -]

- - - - -

Proposed resolution:

-
    -
  1. -

    replace in 20.6 [template.bitset]/1 (class bitset) -

    -
    -template <class charT, class traits>
-  basic_string<charT, traits, allocator<charT> >
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-template <class charT>
-  basic_string<charT, char_traits<charT>, allocator<charT> >
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-basic_string<char, char_traits<char>, allocator<char> >
-  to_string(char zero = '0', char one = '1') const;
-
    -
    2. -
  2. -

    -replace in 20.6.2 [bitset.members]/37 -

    -
    -template <class charT, class traits>
-  basic_string<charT, traits, allocator<charT> >
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-
    -

    -37 Returns: to_string<charT, traits, allocator<charT> >(zero, one). -

    -
    -
    3. -
  3. -

    -replace in 20.6.2 [bitset.members]/38 -

    - -
    -template <class charT>
-  basic_string<charT, char_traits<charT>, allocator<charT> >
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-
    -

    -38 Returns: to_string<charT, char_traits<charT>, allocator<charT> >(zero, one). -

    -
    -
    4. - -
  4. -

    -replace in 20.6.2 [bitset.members]/39 -

    - -
    -basic_string<char, char_traits<char>, allocator<char> >
-  to_string(char zero = '0', char one = '1') const;
-
    -

    -39 Returns: to_string<char, char_traits<char>, allocator<char> >(zero, one). -

    -
    -
    5. - -
- - - - - - -
-

854. default_delete converting constructor underspecified

-

Section: 20.8.1.1.2 [unique.ptr.dltr.dflt] Status: C++11 - Submitter: Howard Hinnant Opened: 2008-06-18 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-No relationship between U and T in the converting constructor for default_delete template. -

-

-Requirements: U* is convertible to T* and has_virtual_destructor<T>; -the latter should also become a concept. -

-

-Rules out cross-casting. -

-

-The requirements for unique_ptr conversions should be the same as those on the deleter. -

- -

[ -Howard adds 2008-11-26: -]

- - -
-

-I believe we need to be careful to not outlaw the following use case, and -I believe the current proposed wording -(requires Convertible<U*, T*> && HasVirtualDestructor<T>) does so: -

- -
-#include <memory>
-
-int main()
-{
-    std::unique_ptr<int> p1(new int(1));
-    std::unique_ptr<const int> p2(move(p1));
-    int i = *p2;
-//    *p2 = i;  // should not compile
-}
-
- -

-I've removed "&& HasVirtualDestructor<T>" from the -requires clause in the proposed wording. -

- -
- -

[ -Post Summit: -]

- - -
-

-Alisdair: This issue has to stay in review pending a paper constraining -unique_ptr. -

-

-Consensus: We agree with the resolution, but unique_ptr needs -to be constrained, too. -

-

-Recommend Keep in Review. -

-
- -

[ -Batavia (2009-05): -]

- -

-Keep in Review status for the reasons cited. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-The proposed resolution uses concepts. Howard needs to rewrite the -proposed resolution. -

-

-Move back to Open. -

-
- -

[ -2009-07-26 Howard provided rewritten proposed wording and moved to Review. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add after 20.8.1.1.2 [unique.ptr.dltr.dflt], p1: -

- -
-template <class U> default_delete(const default_delete<U>& other);
-
-
-

--1- Effects: ... -

-

-Remarks: This constructor shall participate in overload resolution -if and only if U* is implicitly convertible to T*. -

-
-
- - - - - - -
-

856. Removal of aligned_union

-

Section: 20.10.7.6 [meta.trans.other] Status: CD1 - Submitter: Jens Maurer Opened: 2008-06-12 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with CD1 status.

-

Discussion:

-

-With the arrival of extended unions -(N2544), -there is no -known use of aligned_union that couldn't be handled by -the "extended unions" core-language facility. -

- - -

Proposed resolution:

-

-Remove the following signature from 20.10.2 [meta.type.synop]: -

-
-template <std::size_t Len, class... Types> struct aligned_union;
-
- -

-Remove the second row from table 51 in 20.10.7.6 [meta.trans.other], -starting with: -

- -
-template <std::size_t Len,
-class... Types>
-struct aligned_union;
-
- - - - - -
-

857. condition_variable::time_wait return bool error prone

-

Section: 30.5.1 [thread.condition.condvar] Status: C++11 - Submitter: Beman Dawes Opened: 2008-06-13 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

View all issues with C++11 status.

-

Discussion:

-

-The meaning of the bool returned by condition_variable::timed_wait is so -obscure that even the class' designer can't deduce it correctly. Several -people have independently stumbled on this issue. -

-

-It might be simpler to change the return type to a scoped enum: -

-
-enum class timeout { not_reached, reached };
-
- -

-That's the same cost as returning a bool, but not subject to mistakes. Your example below would be: -

- -
-if (cv.wait_until(lk, time_limit) == timeout::reached )
-  throw time_out();
-
- -

[ -Beman to supply exact wording. -]

- - -

[ -San Francisco: -]

- - -
-

-There is concern that the enumeration names are just as confusing, if -not more so, as the bool. You might have awoken because of a signal or a -spurious wakeup, for example. -

-

-Group feels that this is a defect that needs fixing. -

-

-Group prefers returning an enum over a void return. -

-

-Howard to provide wording. -

-
- -

[ -2009-06-14 Beman provided wording. -]

- - -

[ -2009-07 Frankfurt: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Change Condition variables 30.5 [thread.condition], Header -condition_variable synopsis, as indicated: -

- -
-namespace std {
-  class condition_variable;
-  class condition_variable_any;
-
-  enum class cv_status { no_timeout, timeout };
-}
-
- -

-Change class condition_variable 30.5.1 [thread.condition.condvar] as indicated: -

- -
-class condition_variable { 
-public:
-  ...
-  template <class Clock, class Duration>
-    bool cv_status wait_until(unique_lock<mutex>& lock,
-                    const chrono::time_point<Clock, Duration>& abs_time);
-  template <class Clock, class Duration, class Predicate>
-    bool wait_until(unique_lock<mutex>& lock,
-                    const chrono::time_point<Clock, Duration>& abs_time,
-                    Predicate pred);
-
-  template <class Rep, class Period>
-    bool cv_status wait_for(unique_lock<mutex>& lock,
-                  const chrono::duration<Rep, Period>& rel_time);
-  template <class Rep, class Period, class Predicate>
-    bool wait_for(unique_lock<mutex>& lock,
-                  const chrono::duration<Rep, Period>& rel_time,
-                  Predicate pred);
-  ...
-};
-
-...
-
-template <class Clock, class Duration>
-  bool cv_status wait_until(unique_lock<mutex>& lock,
-                  const chrono::time_point<Clock, Duration>& abs_time);
-
-
-

--15- Precondition: lock is locked by the calling thread, and either -

-
    -
  • -no other thread is waiting on this condition_variable object or -
    • -
  • -lock.mutex() returns the same value for each of the lock -arguments supplied by all concurrently waiting threads (via wait, -wait_for or wait_until.). -
    • -
- -

--16- Effects: -

- -
    -
  • -Atomically calls lock.unlock() and blocks on *this. -
    • -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock) and returns. -
    • -
  • -The function will unblock when signaled by a call to notify_one(), -a call to notify_all(), by -the current time exceeding abs_time if Clock::now() >= abs_time, -or spuriously. -
    • -
  • -If the function exits via an exception, lock.unlock() shall be called prior -to exiting the function scope. -
    • -
- -

--17- Postcondition: lock is locked by the calling thread. -

- -

--18- Returns: Clock::now() < abs_time -cv_status::timeout if the function unblocked because abs_time -was reached, otherwise cv_status::no_timeout. -

- -

--19- Throws: std::system_error when the effects or postcondition -cannot be achieved. -

- -

--20- Error conditions: -

- -
    -
  • -operation_not_permitted — if the thread does not own the lock. -
    • -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
-
- -
-template <class Rep, class Period>
-  bool cv_status wait_for(unique_lock<mutex>& lock,
-                const chrono::duration<Rep, Period>& rel_time);
-
-
-
-

--21- Effects Returns: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time)
-
-

--22- Returns: false if the call is returning because the time -duration specified by rel_time has elapsed, -otherwise true. -

- -

[ -This part of the wording may conflict with 859 in detail, but does -not do so in spirit. If both issues are accepted, there is a logical merge. -]

- -
- -
-template <class Clock, class Duration, class Predicate> 
-  bool wait_until(unique_lock<mutex>& lock, 
-                  const chrono::time_point<Clock, Duration>& abs_time, 
-                  Predicate pred);
-
- -
-

--23- Effects: -

-
-while (!pred()) 
-  if (!wait_until(lock, abs_time) == cv_status::timeout) 
-    return pred(); 
-return true;
-
- -

--24- Returns: pred(). -

- -

--25- [Note: -The returned value indicates whether the predicate evaluates to -true regardless of whether the timeout was triggered. -— end note]. -

-
-
- -

-Change Class condition_variable_any 30.5.2 [thread.condition.condvarany] as indicated: -

- -
-class condition_variable_any {
-public:
-  ...
-  template <class Lock, class Clock, class Duration>
-    bool cv_status wait_until(Lock& lock,
-                    const chrono::time_point<Clock, Duration>& abs_time);
-  template <class Lock, class Clock, class Duration, class Predicate>
-    bool wait_until(Lock& lock,
-                    const chrono::time_point<Clock, Duration>& abs_time,
-                    Predicate pred);
-
-  template <class Lock, class Rep, class Period>
-    bool cv_status wait_for(Lock& lock,
-                  const chrono::duration<Rep, Period>& rel_time);
-  template <class Lock, class Rep, class Period, class Predicate>
-    bool wait_for(Lock& lock,
-                  const chrono::duration<Rep, Period>& rel_time,
-                  Predicate pred);
-  ...
-};
-
-...
-
-template <class Lock, class Clock, class Duration>
-  bool cv_status wait_until(Lock& lock,
-                  const chrono::time_point<Clock, Duration>& abs_time);
-
- -
- -

--13- Effects: -

- -
    -
  • -Atomically calls lock.unlock() and blocks on *this. -
    • -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock) and returns. -
    • -
  • -The function will unblock when signaled by a call to notify_one(), -a call to notify_all(), by -the current time exceeding abs_time if Clock::now() >= abs_time, -or spuriously. -
    • -
  • -If the function exits via an exception, lock.unlock() shall be called prior -to exiting the function scope. -
    • -
- -

--14- Postcondition: lock is locked by the calling thread. -

- -

--15- Returns: Clock::now() < abs_time -cv_status::timeout if the function unblocked because abs_time -was reached, otherwise cv_status::no_timeout. -

- -

--16- Throws: std::system_error when the effects or postcondition -cannot be achieved. -

- -

--17- Error conditions: -

- -
    -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
-
- -
-template <class Lock, class Rep, class Period>
-  bool cv_status wait_for(Lock& lock,
-                const chrono::duration<Rep, Period>& rel_time);
-
-
- -
-

--18- Effects Returns: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time)
-
- -

--19- Returns: false if the call is returning because the time -duration specified by rel_time has elapsed, -otherwise true. -

- -

[ -This part of the wording may conflict with 859 in detail, but does -not do so in spirit. If both issues are accepted, there is a logical merge. -]

- - -
- -
-template <class Lock, class Clock, class Duration, class Predicate> 
-  bool wait_until(Lock& lock, 
-                  const chrono::time_point<Clock, Duration>& rel_time abs_time, 
-                  Predicate pred);
-
- -
-

--20- Effects: -

-
-while (!pred()) 
-  if (!wait_until(lock, abs_time) == cv_status::timeout) 
-    return pred(); 
-return true;
-
- -

--21- Returns: pred(). -

- -

--22- [Note: -The returned value indicates whether the predicate evaluates to -true regardless of whether the timeout was triggered. -— end note]. -

-
- -
- - - - - - -
-

858. Wording for Minimal Support for Garbage Collection

-

Section: 20.7.4 [util.dynamic.safety] Status: CD1 - Submitter: Pete Becker Opened: 2008-06-21 Last modified: 2015-04-08

-

View all other issues in [util.dynamic.safety].

-

View all issues with CD1 status.

-

Discussion:

-

-The first sentence of the Effects clause for undeclare_reachable seems -to be missing some words. I can't parse -

-

-... for all non-null p referencing the argument is no longer declared reachable... -

-

-I take it the intent is that undeclare_reachable should be called only -when there has been a corresponding call to declare_reachable. In -particular, although the wording seems to allow it, I assume that code -shouldn't call declare_reachable once then call undeclare_reachable -twice. -

-

-I don't know what "shall be live" in the Requires clause means. -

-

-In the final Note for undeclare_reachable, what does "cannot be -deallocated" mean? Is this different from "will not be able to collect"? -

- -

-For the wording on nesting of declare_reachable and -undeclare_reachable, the words for locking and unlocking recursive -mutexes probably are a good model. -

- -

[ -San Francisco: -]

- - -
-

-Nick: what does "shall be live" mean? -

-

-Hans: I can provide an appropriate cross-reference to the Project Editor -to clarify the intent. -

-
- - -

Proposed resolution:

-

-In 20.7.4 [util.dynamic.safety] -(N2670, -Minimal Support for Garbage Collection) -

-

-Add at the beginning, before paragraph 39 -

- -

-A complete object is declared reachable while the number of calls -to declare_reachable with an argument referencing the object exceeds the -number of undeclare_reachable calls with pointers to the same complete -object. -

- -

-Change paragraph 42 (Requires clause for undeclare_reachable) -

- -

-If p is not null, declare_reachable(p) was previously called -the complete object referenced by p shall have -been previously declared reachable, and shall -be live (3.8 [basic.life]) from the time of the call until the last undeclare_reachable(p) -call on the object. -

- -

-Change the first sentence in paragraph 44 (Effects clause for -undeclare_reachable): -

- -

-Effects: -Once the number of calls to -undeclare_reachable(p) equals the number of calls to -declare_reachable(p) -for all non-null p referencing -the argument is no longer declared reachable. When this happens, -pointers to the object referenced by p may not be subsequently -dereferenced. - -After a call to undeclare_reachable(p), if p is not null and the object q -referenced by p is no longer declared reachable, then -dereferencing any pointer to q that is not safely derived -results in undefined behavior. - ... -

- -

-Change the final note: -

-

-[Note: It is expected that calls to declare_reachable(p) -will consume a small amount of memory, in addition to that occupied -by the referenced object, until the matching call to -undeclare_reachable(p) is encountered. In addition, the -referenced object cannot be deallocated during this period, and garbage -collecting implementations will not be able to collect the object while -it is declared reachable. Long running programs should arrange -that calls for short-lived objects are matched. --end -note] -

- - - - - - -
-

859. Monotonic Clock is Conditionally Supported?

-

Section: 30.5 [thread.condition] Status: C++11 - Submitter: Pete Becker Opened: 2008-06-23 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

View all issues with C++11 status.

-

Discussion:

- -

Related to 958, 959.

- -

-N2661 -says that there is a class named monotonic_clock. It also says that this -name may be a synonym for system_clock, and that it's conditionally -supported. So the actual requirement is that it can be monotonic or not, -and you can tell by looking at is_monotonic, or it might not exist at -all (since it's conditionally supported). Okay, maybe too much -flexibility, but so be it. -

-

-A problem comes up in the threading specification, where several -variants of wait_for explicitly use monotonic_clock::now(). What is the -meaning of an effects clause that says -

- -
-wait_until(lock, chrono::monotonic_clock::now() + rel_time)
-
- -

-when monotonic_clock is not required to exist? -

- -

[ -San Francisco: -]

- - -
-

-Nick: maybe instead of saying that chrono::monotonic_clock is -conditionally supported, we could say that it's always there, but not -necessarily supported.. -

-

-Beman: I'd prefer a typedef that identifies the best clock to use for -wait_for locks. -

-

-Tom: combine the two concepts; create a duration clock type, but keep -the is_monotonic test. -

-

-Howard: if we create a duration_clock type, is it a typedef or an -entirely true type? -

-

-There was broad preference for a typedef. -

-

-Move to Open. Howard to provide wording to add a typedef for -duration_clock and to replace all uses of monotonic_clock in function -calls and signatures with duration_clock. -

-
- -

[ -Howard notes post-San Francisco: -]

- - -
-

-After further thought I do not believe that creating a duration_clock typedef -is the best way to proceed. An implementation may not need to use a -time_point to implement the wait_for functions. -

- -

-For example, on POSIX systems sleep_for can be implemented in terms of -nanosleep which takes only a duration in terms of nanoseconds. The current -working paper does not describe sleep_for in terms of sleep_until. -And paragraph 2 of 30.2.4 [thread.req.timing] has the words strongly encouraging -implementations to use monotonic clocks for sleep_for: -

- -

-2 The member functions whose names end in _for take an argument that -specifies a relative time. Implementations should use a monotonic clock to -measure time for these functions. -

- -

-I believe the approach taken in describing the effects of sleep_for -and try_lock_for is also appropriate for wait_for. I.e. these -are not described in terms of their _until variants. -

- -
- -

[ -2009-07 Frankfurt: -]

- - -
-

-Beman will send some suggested wording changes to Howard. -

-

-Move to Ready. -

-
- -

[ -2009-07-21 Beman added the requested wording changes to 962. -]

- - - - -

Proposed resolution:

-

-Change 30.5.1 [thread.condition.condvar], p21-22: -

- -
-
-template <class Rep, class Period> 
-  bool wait_for(unique_lock<mutex>& lock, 
-                const chrono::duration<Rep, Period>& rel_time);
-
-
-

-Precondition: lock is locked by the calling thread, and either -

-
    -
  • no other thread is waiting on this condition_variable object or
    • -
  • lock.mutex() returns the same value for each of the lock -arguments supplied by all concurrently waiting threads (via wait, -wait_for or wait_until).
    • -
-

-21 Effects: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time)
-
-
    -
  • -Atomically calls lock.unlock() and blocks on *this. -
    • - -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock) and returns. -
    • - -
  • -The function will unblock when signaled by a call to notify_one(), a call -to notify_all(), by -the elapsed time rel_time passing (30.2.4 [thread.req.timing]), -or spuriously. -
    • - -
  • -If the function exits via an exception, lock.unlock() shall be called -prior to exiting the function scope. -
    • -
- -

-Postcondition: lock is locked by the calling thread. -

- - -

-22 Returns: false if the call is returning because the time -duration specified by rel_time has elapsed, otherwise true. -

- -

[ -This part of the wording may conflict with 857 in detail, but does -not do so in spirit. If both issues are accepted, there is a logical merge. -]

- - -

-Throws: std::system_error when the effects or postcondition cannot be achieved. -

- -

-Error conditions: -

- -
    -
  • -operation_not_permitted -- if the thread does not own the lock. -
    • -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
- -
-
- -

-Change 30.5.1 [thread.condition.condvar], p26-p29: -

- -
-
-template <class Rep, class Period, class Predicate> 
-  bool wait_for(unique_lock<mutex>& lock, 
-                const chrono::duration<Rep, Period>& rel_time, 
-                Predicate pred);
-
-
-

-Precondition: lock is locked by the calling thread, and either -

-
    -
  • no other thread is waiting on this condition_variable object or
    • -
  • lock.mutex() returns the same value for each of the lock -arguments supplied by all concurrently waiting threads (via wait, -wait_for or wait_until).
    • -
-

-26 Effects: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time, std::move(pred))
-
-
    -
  • -Executes a loop: Within the loop the function first evaluates pred() -and exits the loop if the result of pred() is true. -
    • -
  • -Atomically calls lock.unlock() -and blocks on *this. -
    • -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock). -
    • -
  • -The function will unblock when signaled by a call to notify_one(), a -call to notify_all(), by the elapsed time rel_time passing (30.1.4 -[thread.req.timing]), or spuriously. -
    • -
  • -If the function exits via an exception, lock.unlock() shall be called -prior to exiting the function scope. -
    • -
  • -The loop terminates when pred() returns true or when the time -duration specified by rel_time has elapsed. -
    • -
-
- -

-27 [Note: There is no blocking if pred() is initially true, -even if the timeout has already expired. -- end note] -

- -

-Postcondition: lock is locked by the calling thread. -

- -

-28 Returns: pred() -

- -

-29 [Note: The returned value indicates whether the predicate evaluates to -true regardless of whether the timeout was triggered. -- end note] -

- -

-Throws: std::system_error when the effects or postcondition cannot be achieved. -

- -

-Error conditions: -

- -
    -
  • -operation_not_permitted -- if the thread does not own the lock. -
    • -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
- -
-
- -

-Change 30.5.2 [thread.condition.condvarany], p18-19: -

- -
-
-template <class Lock, class Rep, class Period> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
-
-

-18 Effects: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time)
-
- -
    -
  • -Atomically calls lock.unlock() and blocks on *this. -
    • - -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock) and returns. -
    • - -
  • -The function will unblock when signaled by a call to notify_one(), a call to -notify_all(), by -the elapsed time rel_time passing (30.2.4 [thread.req.timing]), -or spuriously. -
    • - -
  • -If the function exits via an exception, lock.unlock() shall be called -prior to exiting the function scope. -
    • -
- -

-Postcondition: lock is locked by the calling thread. -

- -

-19 Returns: false if the call is returning because the time duration -specified by rel_time has elapsed, otherwise true. -

- -

-Throws: std::system_error when the returned value, effects, -or postcondition cannot be achieved. -

- -

-Error conditions: -

- -
    -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
-
-
- -

-Change 30.5.2 [thread.condition.condvarany], p23-p26: -

- -
-
-template <class Lock, class Rep, class Period, class Predicate> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
-
-
-

-Precondition: lock is locked by the calling thread, and either -

-
    -
  • no other thread is waiting on this condition_variable object or
    • -
  • lock.mutex() returns the same value for each of the lock -arguments supplied by all concurrently waiting threads (via wait, -wait_for or wait_until).
    • -
-

-23 Effects: -

-
-wait_until(lock, chrono::monotonic_clock::now() + rel_time, std::move(pred))
-
-
    -
  • -Executes a loop: Within the loop the function first evaluates pred() -and exits the loop if the result of pred() is true. -
    • -
  • -Atomically calls lock.unlock() -and blocks on *this. -
    • -
  • -When unblocked, calls lock.lock() (possibly blocking on the lock). -
    • -
  • -The function will unblock when signaled by a call to notify_one(), a -call to notify_all(), by the elapsed time rel_time passing (30.1.4 -[thread.req.timing]), or spuriously. -
    • -
  • -If the function exits via an exception, lock.unlock() shall be called -prior to exiting the function scope. -
    • -
  • -The loop terminates when pred() returns true or when the time -duration specified by rel_time has elapsed. -
    • -
-
- -

-24 [Note: There is no blocking if pred() is initially true, -even if the timeout has already expired. -- end note] -

- -

-Postcondition: lock is locked by the calling thread. -

- -

-25 Returns: pred() -

- -

-26 [Note: The returned value indicates whether the predicate evaluates to -true regardless of whether the timeout was triggered. -- end note] -

- -

-Throws: std::system_error when the effects or postcondition cannot be achieved. -

- -

-Error conditions: -

- -
    -
  • -operation_not_permitted -- if the thread does not own the lock. -
    • -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
- -
-
- - - - - - - -
-

860. Floating-Point State

-

Section: 26 [numerics] Status: C++11 - Submitter: Lawrence Crowl Opened: 2008-06-23 Last modified: 2015-04-08

-

View all other issues in [numerics].

-

View all issues with C++11 status.

-

Discussion:

-

-There are a number of functions that affect the floating point state. -These function need to be thread-safe, but I'm unsure of the right -approach in the standard, as we inherit them from C. -

- -

[ -San Francisco: -]

- - -
-

-Nick: I think we already say that these functions do not introduce data -races; see 17.6.5.6/20 -

-

-Pete: there's more to it than not introducing data races; are these -states maintained per thread? -

-

-Howard: 21.5/14 says that strtok and strerror are not required to avoid -data races, and 20.9/2 says the same about asctime, gmtime, ctime, and -gmtime. -

-

-Nick: POSIX has a list of not-safe functions. All other functions are -implicitly thread safe. -

-

-Lawrence is to form a group between meetings to attack this issue. Nick -and Tom volunteered to work with Lawrence. -

-

-Move to Open. -

-
- -

[ -Post Summit: -]

- - -
-

-Hans: Sane oses seem ok. Sensible thing is implementable and makes sense. -

-

-Nick: Default wording seems to cover this? Hole in POSIX, these -functions need to be added to list of thread-unsafe functions. -

-

-Lawrence: Not sufficient, not "thread-safe" per our definition, but -think of state as a thread-local variable. Need something like "these -functions only affect state in the current thread." -

-

-Hans: Suggest the following wording: "The floating point environment is -maintained per-thread." -

-

-Walter: Any other examples of state being thread safe that are not -already covered elsewhere? -

-

-Have thread unsafe functions paper which needs to be updated. Should -just fold in 26.3 [cfenv] functions. -

-

-Recommend Open. Lawrence instead suggests leaving it open until we have -suitable wording that may or may not include the thread local -commentary. -

-
- -

[ -2009-09-23 Hans provided wording. -]

- - -

-If I understand the history correctly, Nick, as the Posix liaison, -should probably get a veto on this, since I think it came from Posix (?) -via WG14 and should probably really be addressed there (?). But I think -we are basically in agreement that there is no other sane way to do -this, and hence we don't have to worry too much about stepping on toes. -As far as I can tell, this same issue also exists in the latest Posix -standard (?). -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-Add at the end of 26.3.1 [cfenv.syn]: -

- -
-

-2 The header defines all functions, types, and macros the same as C99 7.6. -

- -

-A separate floating point environment shall be maintained for each -thread. Each function accesses the environment corresponding to its -calling thread. -

-
- - - - - -
-

861. Incomplete specification of EqualityComparable for std::forward_list

-

Section: 23.2 [container.requirements] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-06-24 Last modified: 2015-04-08

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Discussion:

-

-Table 89, Container requirements, defines operator== in terms of the container -member function size() and the algorithm std::equal: -

- -

-== is an equivalence relation. a.size() == b.size() && -equal(a.begin(), a.end(), b.begin() -

- -

-The new container forward_list does not provide a size member function -by design but does provide operator== and operator!= without specifying it's semantic. -

-

-Other parts of the (sequence) container requirements do also depend on -size(), e.g. empty() -or clear(), but this issue explicitly attempts to solve the missing -EqualityComparable specification, -because of the special design choices of forward_list. -

-

-I propose to apply one of the following resolutions, which are described as: -

- -
    -
  1. -Provide a definition, which is optimal for this special container without -previous size test. This choice prevents two O(N) calls of std::distance() -with the corresponding container ranges and instead uses a special -equals implementation which takes two container ranges instead of 1 1/2. -
    2. -
  2. -The simple fix where the usual test is adapted such that size() is replaced -by distance with corresponding performance disadvantages. -
    3. -
-

-Both proposal choices are discussed, the preferred choice of the author is -to apply (A). -

- -

[ -San Francisco: -]

- - -
-

-There's an Option C: change the requirements table to use distance(). -

-

-LWG found Option C acceptable. -

-

-Martin will draft the wording for Option C. -

-
- -

[ -post San Francisco: -]

- - -

-Martin provided wording for Option C. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Other operational semantics (see, for example, Tables 82 and 83) are -written in terms of a container's size() member. Daniel to update -proposed resolution C. -

-

[ -Howard: Commented out options A and B. -]

- -
- -

[ -2009-07-26 Daniel updated proposed resolution C. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Mark NAD Editorial. Addressed by -N2986. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Reopened. -N2986 -was rejected in full committee on procedural grounds. -

- -

[ -2010-01-30 Howard updated Table numbers. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

- - -

-Option (C): -

-
- -
    -
  1. -

    -In 23.2.1 [container.requirements.general] change Table 90 -- Container requirements as indicated: -

    - -
      -
    1. -

      -Change the text in the Assertion/note column in the row for "X u;" -as follows: -

      - -

      -post: u.size() == 0empty() == true -

      -
      2. - -
    2. -

      -Change the text in the Assertion/note column in the row for "X();" -as follows: -

      - -

      -X().size() == 0empty() == true -

      -
      3. - -
    3. -

      -Change the text in the Operational Semantics column in the row for -"a == b" as follows: -

      -

      -== is an equivalence relation. -a.size()distance(a.begin(), a.end()) == - b.size()distance(b.begin(), b.end()) && -equal(a.begin(), a.end(), b.begin()) -

      -
      4. - -
    4. -

      -Add text in the Ass./Note/pre-/post-condition column in the row for -"a == b" as follows: -

      -

      -Requires: T is EqualityComparable -

      -
      5. - -
    5. -

      -Change the text in the Operational Semantics column in the row for -"a.size()" as follows: -

      - -

      -a.end() - a.begin()distance(a.begin(), a.end()) -

      -
      6. - -
    6. -

      -Change the text in the Operational Semantics column in the row for -"a.max_size()" as follows: -

      - -

      -size()distance(begin(), end()) of the largest -possible container -

      -
      7. - -
    7. -

      -Change the text in the Operational Semantics column in the row for -"a.empty()" as follows: -

      - -

      -a.size() == 0a.begin() == a.end() -

      -
      8. -
    -
    2. - -
  2. -

    -In 23.2.1 [container.requirements.general] change Table 93 — Allocator-aware container requirements as indicated: -

    - -
      -
    1. -

      -Change the text in the Assertion/note column in the row for "X() / -X u;" as follows: -

      - -

      -Requires: A is DefaultConstructible post: u.size() == -0u.empty() == true, get_allocator() == A() -

      -
      2. - -
    2. -

      -Change the text in the Assertion/note column in the row for "X(m) / -X u(m);" as follows: -

      - -

      -post: u.size() == 0u.empty() == true, -get_allocator() == m -

      -
      3. -
    -
    3. - -
  3. -

    -In 23.2.3 [sequence.reqmts] change Table 94 — Sequence container requirements as indicated: -

    - -
      -
    1. -

      -Change the text in the Assertion/note column in the row for "X(n, -t) / X a(n, t)" as follows: -

      - -

      -post: size()distance(begin(), end()) == n [..] -

      -
      2. - -
    2. -

      -Change the text in the Assertion/note column in the row for "X(i, -j) / X a(i, j)" as follows: -

      - -

      -[..] post: size() == distance between i and -jdistance(begin(), end()) == distance(i, j) [..] -

      -
      3. - -
    3. -

      -Change the text in the Assertion/note column in the row for -"a.clear()" as follows: -

      -

      -a.erase(a.begin(), a.end()) post: -size() == 0a.empty() == true -

      -
      4. -
    -
    4. - -
  4. -

    -In 23.2.4 [associative.reqmts] change Table 96 — Associative container requirements as indicated: -

    - -

    [ -Not every occurrence of size() was replaced, because all current -associative containers -have a size. The following changes ensure consistency regarding the -semantics of "erase" -for all tables and adds some missing objects -]

    - - -
      - -
    1. -

      -Change the text in the Complexity column in the row for X(i,j,c)/Xa(i,j,c); -as follows: -

      - -

      -N log N in general (N == distance(i, -j)is the distance from i to j); ... -

      - -
      2. - -
    2. -

      -Change the text in the Complexity column in the row for -"a.insert(i, j)" as follows: -

      -

      -N log(a.size() + N) (N is the distance from i to -j) where N == distance(i, j) -

      -
      3. - -
    3. -

      -Change the text in the Complexity column in the row for -"a.erase(k)" as follows: -

      -

      -log(a.size()) + a.count(k) -

      -
      4. - -
    4. -

      -Change the text in the Complexity column in the row for -"a.erase(q1, q2)" as follows: -

      - -

      -log(a.size()) + N where N is the distance from q1 -to q2 - == distance(q1, q2). -

      -
      5. - -
    5. -

      -Change the text in the Assertion/note column in the row for -"a.clear()" as follows: -

      - -

      -a.erase(a.begin(),a.end()) post: size() == -0a.empty() == true -

      -
      6. - -
    6. -

      -Change the text in the Complexity column in the row for "a.clear()" -as follows: -

      - -

      -linear in a.size() -

      -
      7. - -
    7. -

      -Change the text in the Complexity column in the row for -"a.count(k)" as follows: -

      - -

      -log(a.size()) + a.count(k) -

      -
      8. -
    -
    5. - -
  5. -

    -In 23.2.5 [unord.req] change Table 98 — Unordered associative container requirements as indicated: -

    -

    [ -The same rational as for Table 96 applies here -]

    - - -
      -
    1. -

      -Change the text in the Assertion/note column in the row for -"a.clear()" as follows: -

      - -

      -[..] Post: a.size() == 0empty() == true -

      -
      2. -
    -
    6. -
- - -
- - - - - -
-

865. More algorithms that throw away information

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Section: 25.3.6 [alg.fill], 25.3.7 [alg.generate] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-07-13 Last modified: 2015-04-08

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Discussion:

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-In regard to library defect 488 I found some more algorithms which -unnecessarily throw away information. These are typically algorithms, -which sequentially write into an OutputIterator, but do not return the -final value of this output iterator. These cases are: -

- -
    -
  1. -
    template<class OutputIterator, class Size, class T>
-void fill_n(OutputIterator first, Size n, const T& value);
    2. - -
  2. -
    template<class OutputIterator, class Size, class Generator>
-void generate_n(OutputIterator first, Size n, Generator gen);
    3. -
-

-In both cases the minimum requirements on the iterator are -OutputIterator, which means according to the requirements of -24.2.4 [output.iterators] p. 2 that only single-pass iterations are guaranteed. -So, if users of fill_n and generate_n have only an OutputIterator -available, they have no chance to continue pushing further values -into it, which seems to be a severe limitation to me. -

- -

[ -Post Summit Daniel "conceptualized" the wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Alisdair likes the idea, but has concerns about the specific wording -about the returns clauses. -

-

-Alan notes this is a feature request. -

-

-Bill notes we have made similar changes to other algorithms. -

-

-Move to Open. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-We have a consensus for moving forward on this issue, but Daniel needs -to deconceptify it. -

- -

[ -2009-07-25 Daniel provided non-concepts wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

- -
    -
  1. -

    -Replace the current declaration of fill_n in 25 [algorithms]/2, header -<algorithm> synopsis and in 25.3.6 [alg.fill] by -

    - -
    -template<class OutputIterator, class Size, class T>
-  voidOutputIterator fill_n(OutputIterator first, Size n, const T& value);
-
    - -

    -Just after the effects clause add a new returns clause saying: -

    - -

    -Returns: For fill_n and positive n, returns first + n. Otherwise -returns first for fill_n. -

    -
    2. - -
  2. -

    -Replace the current declaration of generate_n in 25 [algorithms]/2, -header <algorithm> synopsis and in 25.3.7 [alg.generate] by -

    - -
    -template<class OutputIterator, class Size, class Generator>
-  voidOutputIterator generate_n(OutputIterator first, Size n, Generator gen);
-
    - -

    -Just after the effects clause add a new returns clause saying: -

    - -

    -For generate_n and positive n, returns first + n. Otherwise -returns first for generate_n. -

    -
    3. -
- - - - - - - -
-

866. Qualification of placement new-expressions

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Section: 20.7.12 [specialized.algorithms], 20.8.2.2.6 [util.smartptr.shared.create] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2008-07-14 Last modified: 2015-04-08

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-

Discussion:

-

-LWG issue 402 replaced "new" with "::new" in the placement -new-expression in 20.7.9.1 [allocator.members]. I believe the rationale -given in 402 applies also to the following other contexts: -

-
    -
  • -

    -in 20.7.12 [specialized.algorithms], all four algorithms unitialized_copy, -unitialized_copy_n, unitialized_fill and unitialized_fill_n use -the unqualified placement new-expression in some variation of the form: -

    -
    -new  (static_cast<void*>(&*result)) typename  iterator_traits<ForwardIterator>::value_type(*first);
-
    -
    • -
  • -

    -in 20.8.2.2.6 [util.smartptr.shared.create] there is a reference to the unqualified placement new-expression: -

    -
    -new  (pv)  T(std::forward<Args>(args)...),
-
    -
    • -
-

-I suggest to add qualification in all those places. As far as I know, -these are all the remaining places in the whole library that explicitly -use a placement new-expression. Should other uses come out, they should -be qualified as well. -

-

-As an aside, a qualified placement new-expression does not need -additional requirements to be compiled in a constrained context. By -adding qualification, the HasPlacementNew concept introduced recently in -N2677 (Foundational Concepts) -would no longer be needed by library and -should therefore be removed. -

- -

[ -San Francisco: -]

- - -

-Detlef: If we move this to Ready, it's likely that we'll forget about -the side comment about the HasPlacementNew concept. -

- -

[ -post San Francisco: -]

- - -

-Daniel: HasPlacementNew has been removed from -N2774 (Foundational Concepts). -

- - - -

Proposed resolution:

-

-Replace "new" with "::new" in: -

-
    -
  • -20.7.12.2 [uninitialized.copy], paragraphs 1 and 3 -
    • -
  • -20.7.12.3 [uninitialized.fill] paragraph 1 -
    • -
  • -20.7.12.4 [uninitialized.fill.n] paragraph 1 -
    • -
  • -20.8.2.2.6 [util.smartptr.shared.create] once in paragraph 1 and twice in paragraph 2. -
    • -
- - - - - - -
-

868. Default construction and value-initialization

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Section: 23 [containers] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2008-07-22 Last modified: 2015-04-08

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Discussion:

-

-The term "default constructed" is often used in wording that predates -the introduction of the concept of value-initialization. In a few such -places the concept of value-initialization is more correct than the -current wording (for example when the type involved can be a built-in) -so a replacement is in order. Two of such places are already covered by -issue 867. This issue deliberately addresses the hopefully -non-controversial changes in the attempt of being approved more quickly. -A few other occurrences (for example in std::tuple, -std::reverse_iterator and std::move_iterator) are left to separate -issues. For std::reverse_iterator, see also issue 408. This issue is -related with issue 724. -

- -

[ -San Francisco: -]

- - -
-

-The list provided in the proposed resolution is not complete. James -Dennett will review the library and provide a complete list and will -double-check the vocabulary. -

-

-This issue relates to Issue 886 tuple construction -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-The proposed resolution is incomplete. -

-

-Move to Tentatively NAD Future. Howard will contact Ganesh for wording. -If wording is forthcoming, Howard will move it back to Review. -

-
- -

[ -2009-07-18 Ganesh updated the proposed wording. -]

- - -
-

-Howard: Moved back to Review. Note that 17.6.3.1 [utility.arg.requirements] -refers to a section that is not in the current working paper, but does refer to -a section that we expect to reappear after the de-concepts merge. This was a -point of confusion we did not recognize when we reviewed this issue in Frankfurt. -

-

-Howard: Ganesh also includes a survey of places in the WP surveyed for changes -of this nature and purposefully not treated: -

- -
-

-Places where changes are not being -proposed -

-

-In the following paragraphs, we are not proposing changes because -it's not clear whether we actually prefer value-initialization over -default-initialization (now partially covered by 1012): -

-
    -

  • 20.8.1.2.1 [unique.ptr.single.ctor] para 3 e 7

    • -

  • 24.5.1.3.1 [reverse.iter.cons] para 1

    • -

  • 24.5.3.3.1 [move.iter.op.const] para 1

    • -
-

In the following paragraphs, the expression "default -constructed" need not be changed, because the relevant type does -not depend on a template parameter and has a user-provided -constructor:

-
    -

  • [func.referenceclosure.invoke] para 12, type: - reference_closure

    • -

  • 30.3.1.2 [thread.thread.constr] para 30, type: thread

    • -

  • 30.3.1.5 [thread.thread.member] para 52, type: thread_id

    • -

  • 30.3.2 [thread.thread.this], para 1, type: thread_id

    • -
-
- -
- -

[ -2009-08-18 Daniel adds: -]

- - -
-

-I have no objections against the currently suggested changes, but I -also cross-checked -with the list regarding intentionally excluded changes, and from this -I miss the discussion -of -

- -
    -
  1. -

    -21.4.1 [string.require] p. 2: -

    - -

    -"[..] The Allocator object used shall be a copy of the Allocator> -object passed to the basic_string object's -constructor or, if the constructor does not take an Allocator -argument, a copy of a default-constructed -Allocator object." -

    -
    2. - -
  2. -

    -N2723, -26.5.1.4 [rand.req.eng], Table 109, expression "T()": -

    -

    -Pre-/post-condition: "Creates an engine with the same initial state as -all other default-constructed engines of type X." -

    - -

    -as well as in 26.5.5 [rand.predef]/1-9 (N2914), -26.5.7.1 [rand.util.seedseq]/3, 27.7.2.1.1 [istream.cons]/3, -27.7.3.2 [ostream.cons]/9 (N2914), -28.13 [re.grammar]/2, 30.3.1.4 [thread.thread.assign]/1 -(N2914), -

    -

    [ -Candidates for the "the expression "default constructed" need not be -changed" list -]

    - - -

    -I'm fine, if these would be added to the intentionally exclusion list, -but mentioning them makes it -easier for other potential reviewers to decide on the relevance or -not-relevance of them for this issue. -

    -
    3. - -
  3. -

    -I suggest to remove the reference of [func.referenceclosure.invoke] -in the "it's not clear" list, because -this component does no longer exist. -

    -
    4. - -
  4. -

    -I also suggest to add a short comment that all paragraphs in the -resolution whether they refer to N2723 or to N2914 numbering, because e.g. "Change 23.3.3.2 [deque.cons] para 5" is an N2723 coordinate, while "Change 23.3.3.3 [deque.capacity] para 1" is an N2914 coordinate. Even better would be to use one default document -for the numbering (probably N2914) and mention special cases (e.g. "Change 17.6.3.1 [utility.arg.requirements] para 2" as referring to N2723 numbering). -

    -
    5. -
- -
- -

[ -2009-08-18 Alisdair adds: -]

- - -
-

-I strongly believe the term "default constructed" should not appear in -the library clauses unless we very clearly define a meaning for it, and -I am not sure what that would be. -

- -

-In those cases where we do not want to replace "default constructed" -with "vale initialized" we should be using "default initialized". If we -have a term that could mean either, we reduce portability of programs. -

- -

-I have not done an exhaustive review to clarify if that is a vendor -freedom we have reason to support (e.g. value-init in debug, -default-init in release) so I may yet be convinced that LWG has reason -to define this new term of art, but generally C++ initialization is -confusing enough without supporting further ill-defined terms. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to review in order to enable conflict resolution with 704. -

- -

[ -2010-03-26 Daniel harmonized the wording with the upcoming FCD. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-Move to Ready. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 17.6.3.1 [utility.arg.requirements] para 2: -

- -

-2 In general, a default constructor is -not required. Certain container class member function signatures -specify the default constructorT() -as a default argument. T() shall be a well-defined expression (8.5) -if one of those signatures is called using the default argument -(8.3.6). -

- -

-Change 23.3.3.2 [deque.cons] para 3: -

- -

-3 Effects: Constructs a deque with n -default constructedvalue-initialized -elements. -

- -

-Change 23.3.3.3 [deque.capacity] para 1: -

- -

-1 Effects: If sz < size(), equivalent -to erase(begin() + sz, end());. If size() < sz, -appends sz - size() default constructedvalue-initialized -elements to the sequence. -

- -

-Change 23.3.4.2 [forwardlist.cons] para 3: -

- -

-3 Effects: Constructs a forward_list object with n -default constructedvalue-initialized elements. -

- -

-Change 23.3.4.5 [forwardlist.modifiers] para 22: -

- -

-22 Effects: [...] For the first signature -the inserted elements are default -constructedvalue-initialized, -and for the second signature they are copies of c. -

- -

-Change 23.3.5.2 [list.cons] para 3: -

- -

-3 Effects: Constructs a list with n default -constructedvalue-initialized -elements. -

- -

-Change 23.3.5.3 [list.capacity] para 1: -

- -

-1 Effects: If sz < size(), equivalent -to list<T>::iterator it = begin(); advance(it, sz); erase(it, -end());. If size() < sz, appends sz - size() -default constructedvalue-initialized elements to -the sequence. -

- -

-Change 23.3.6.2 [vector.cons] para 3: -

- -

-3 Effects: Constructs a vector with n -default constructedvalue-initialized -elements. -

- -

-Change 23.3.6.3 [vector.capacity] para 9: -

- -

-9 Effects: If sz < size(), equivalent -to erase(begin() + sz, end());. If size() < sz, appends -sz - size() default constructedvalue-initialized -elements to the sequence. -

- - - - - - -
-

869. Bucket (local) iterators and iterating past end

-

Section: 23.2.5 [unord.req] Status: C++11 - Submitter: Sohail Somani Opened: 2008-07-22 Last modified: 2015-04-08

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-

Discussion:

-

-Is there any language in the current draft specifying the behaviour of the following snippet? -

- -
-unordered_set<int> s;
-unordered_set<int>::local_iterator it = s.end(0);
-
-// Iterate past end - the unspecified part
-it++;
-
- -

-I don't think there is anything about s.end(n) being considered an -iterator for the past-the-end value though (I think) it should be. -

- -

[ -San Francisco: -]

- - -

-We believe that this is not a substantive change, but the proposed -change to the wording is clearer than what we have now. -

- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change Table 97 "Unordered associative container requirements" in 23.2.5 [unord.req]: -

- -
- - - - - - - - - - - - - - - - - -
Table 97: Unordered associative container requirements
expressionreturn typeassertion/note pre/post-conditioncomplexity
b.begin(n)local_iterator
const_local_iterator for const b.		Pre: n shall be in the range [0,b.bucket_count()). Note: [b.begin(n), b.end(n)) is a -valid range containing all of the elements in the nth bucket. -b.begin(n) returns an iterator referring to the first element in the bucket. -If the bucket is empty, then b.begin(n) == b.end(n).Constant
b.end(n)local_iterator
const_local_iterator for const b.		Pre: n shall be in the range [0, b.bucket_count()). -b.end(n) returns an iterator which is the past-the-end value for the bucket.Constant
-
- - - - - - -
-

870. Do unordered containers not support function pointers for predicate/hasher?

-

Section: 23.2.5 [unord.req] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-08-17 Last modified: 2015-04-08

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Discussion:

-

-Good ol' associative containers allow both function pointers and -function objects as feasible comparators, as described in -23.2.4 [associative.reqmts]/2: -

- -

-Each associative container is parameterized on Key and an ordering -relation Compare that induces a strict weak ordering (25.3) on -elements of Key. [..]. The object of type Compare is called the -comparison object of a container. This comparison object may be a pointer to -function or an object of a type with an appropriate function call operator.[..] -

- -

-The corresponding wording for unordered containers is not so clear, -but I read it to disallow function pointers for the hasher and I miss -a clear statement for the equality predicate, see -23.2.5 [unord.req]/3+4+5: -

- -
-

-Each unordered associative container is parameterized by Key, by a -function object Hash that -acts as a hash function for values of type Key, and by a binary -predicate Pred that induces an -equivalence relation on values of type Key.[..] -

-

-A hash function is a function object that takes a single argument of -type Key and returns a value of type std::size_t. -

-

-Two values k1 and k2 of type Key are considered -equal if the container's equality function object returns true -when passed those values.[..] -

-
- -

-and table 97 says in the column "assertion...post-condition" for the -expression X::hasher: -

- -

-Hash shall be a unary function object type such that the expression -hf(k) has type std::size_t. -

- -

-Note that 20.9 [function.objects]/1 defines as "Function objects are -objects with an operator() defined.[..]" -

-

-Does this restriction exist by design or is it an oversight? If an -oversight, I suggest that to apply -the following -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Ask Daniel to provide proposed wording that: makes it explicit that -function pointers are function objects at the beginning of -20.9 [function.objects]; fixes the "requirements" for typedefs in -20.9.4 [refwrap] to instead state that the function objects -defined in that clause have these typedefs, but not that these typedefs -are requirements on function objects; remove the wording that explicitly -calls out that associative container comparators may be function -pointers. -

- -

[ -2009-12-19 Daniel updates wording and rationale. -]

- - -

[ -2010-02-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Rationale:

- -

-The below provided wording also affects some part of the library which is -involved with callable types (20.9.1 [func.def]/3). Reason for -this is that callable objects do have a lot in common with function -objects. A simple formula seems to be: -

- -

-callable objects = function objects + pointers to member -

- -

-The latter group is excluded from function objects because of the -expression-based usage of function objects in the algorithm clause, -which is incompatible with the notation to dereference pointers to member -without a concept map available in the language. -

- -

-This analysis showed some currently existing normative definition differences -between the above subset of callable objects and function objects which seem to -be unintended: Backed by the Santa Cruz outcome function objects should include -both function pointers and "object[s] with an operator() defined". This clearly -excludes class types with a conversion function to a function pointer or all -similar conversion function situations described in 13.3 [over.match]/2 -b. 2. In contrast to this, the wording for callable types seems to be less -constrained (20.9.1 [func.def]/3): -

- -

-A callable type is a [..] class type whose objects can appear immediately to the -left of a function call operator. -

- -

-The rationale given in N1673 -and a recent private communication with Peter Dimov revealed that the intention -of this wording was to cover the above mentioned class types with conversion -functions as well. To me the current wording of callable types can be read -either way and I suggest to make the intention more explicit by replacing -

- -

-[..] class type whose objects can appear immediately to the left of a function -call operator -

-

-by -

-

-[..] class type whose objects can appear as the leftmost subexpression of a -function call expression 5.2.2 [expr.call]. -

- -

-and to use the same definition for the class type part of function -objects, because there is no reason to exclude class types with a -conversion function to e.g. pointer to function from being used in algorithms. -

- -

-Now this last term "function objects" itself brings us to a third unsatisfactory -state: The term is used both for objects (e.g. "Function objects are -objects[..]" in 20.9 [function.objects]/1) and for types (e.g. "Each -unordered associative container is parameterized [..] by a function object Hash -that acts as a hash function [..]" in 23.2.5 [unord.req]/3). This -impreciseness should be fixed and I suggest to introduce the term function -object type as the counter part to callable type. This word seems -to be a quite natural choice, because the library already uses it here and there -(e.g. "Hash shall be a unary function object type such that the expression -hf(k) has type std::size_t." in Table 98, "X::hasher" -or "Requires: T shall be a function object type [..]" in -20.9.12.2.5 [func.wrap.func.targ]/3). -

- -

-Finally I would like to add that part of the issue 870 discussion related to the -requirements for typedefs in 20.9.4 [refwrap] during the Santa Cruz -meeting is now handled by the new issue 1290. -

- -

-Obsolete rationale: -

- -
-

[ -San Francisco: -]

- - -

-This is fixed by -N2776. -

- -
- - - -

Proposed resolution:

- -
    - -
  1. -

    -Change 20.9 [function.objects]/1 as indicated: -

    - -
    -

    -1 Function objects are objects with an operator() -defined. An object type (3.9 [basic.types]) that can be the -type of the postfix-expression in a function call (5.2.2 [expr.call], -13.3.1.1 [over.match.call]) is called a function -object type*. A function object is an object of a -function object type. In the places where one would expect to -pass a pointer to a function to an algorithmic template (Clause 25 [algorithms]), -the interface is specified to accept an object with -an operator() defineda function object. This not only -makes algorithmic templates work with pointers to functions, but also enables -them to work with arbitrary function objects. -

    -

    -* Such a type is either a function pointer or a class type which often has a -member operator(), but in some cases it can omit that member and -provide a conversion to a pointer to function. -

    -
    -
    2. - -
  2. -

    -Change 20.9.1 [func.def]/3 as indicated: [The intent is to make the -commonality of callable types and function object -types more explicit and to get rid of wording redundancies] -

    - -

    -3 A callable type is a pointer to function, a pointer to -member function, a pointer to member data, or a class type whose -objects can appear immediately to the left of a function call operator -function object type (20.9 [function.objects]). -

    -
    3. - -
  3. -

    -Change [bind]/1 as indicated: -

    - -

    -1 The function template bind returns an object that binds a -function callable object passed as an argument to -additional arguments. -

    -
    4. - -
  4. -

    -Change 20.9.10 [func.bind]/1 as indicated: -

    - -

    -1 This subclause describes a uniform mechanism for binding arguments of -function callable objects. -

    -
    5. - -
  5. -

    -Change 20.9.12 [func.wrap]/1 as indicated: -

    - -

    -1 This subclause describes a polymorphic wrapper class that encapsulates -arbitrary function callable objects. -

    -
    6. - -
  6. -

    -Change 20.9.12.2 [func.wrap.func]/2 as indicated [The reason for this -change is that 20.9.12.2 [func.wrap.func]/1 clearly says that all callable -types may be wrapped by std::function and current implementations -indeed do provide support for pointer to members as well. One further suggested -improvement is to set the below definition of Callable in italics]: -

    - -

    -2 A functioncallable object f of type F -is Callable Callable for argument types -T1, T2, ..., TN in ArgTypes and a return -type R, if, given lvalues t1, t2, ..., tN of -types T1, T2, ..., TN, respectively, the expression -INVOKE(f, declval<ArgTypes>()..., Rt1, t2, ..., -tN), considered as an unevaluated operand (5 [expr]), -is well formed (20.7.2) and, if R is not void, convertible -to R. -

    -
    7. - - - -
  7. -

    -Change 20.9.12.2.1 [func.wrap.func.con]/7 as indicated: -

    - -
    -function(const function& f);
-template <class A> function(allocator_arg_t, const A& a, const function& f);
-
    -
    -

    ...

    -

    -7 Throws: shall not throw exceptions if f's target is a function -pointer or a function callable object passed via -reference_wrapper. Otherwise, may throw bad_alloc or any -exception thrown by the copy constructor of the stored function -callable object. [Note: Implementations are encouraged to -avoid the use of dynamically allocated memory for small function -callable objects, e.g., where f's target is an object -holding only a pointer or reference to an object and a member function pointer. -— end note] -

    -
    -
    -
    8. - -
  8. -

    -Change 20.9.12.2.1 [func.wrap.func.con]/11 as indicated: -

    - -
    -template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
    -
    -

    ...

    -

    -11 [..] [Note: implementations are encouraged to avoid the use of dynamically -allocated memory for small function callable objects, for -example, where f's target is an object holding only a pointer or -reference to an object and a member function pointer. — end note] -

    -
    -
    -
    9. - -
  9. -

    -Change 20.9.12.2.4 [func.wrap.func.inv]/3 as indicated: -

    - -
    -R operator()(ArgTypes... args) const
-
    -
    -

    ...

    -

    -3 Throws: bad_function_call if !*this; otherwise, any -exception thrown by the wrapped function callable object. -

    -
    -
    -
    10. - -
  10. -

    -Change 20.9.12.2.5 [func.wrap.func.targ]/3 as indicated: -

    - -
    -template<typename T>       T* target();
-template<typename T> const T* target() const;
-
    -
    -

    ...

    -

    -3 Requires: T shall be a function object type that is -Callable (20.9.12.2 [func.wrap.func]) for parameter types ArgTypes -and return type R. -

    -
    -
    -
    11. - -
  11. -

    -Change 23.2.4 [associative.reqmts]/2 as indicated: [The suggested -removal seems harmless, because 25.4 [alg.sorting]1 already clarifies -that Compare is a function object type. Nevertheless it is recommended, -because the explicit naming of "pointer to function" is misleading] -

    - -

    -2 Each associative container is parameterized on Key and an ordering -relation Compare that induces a strict weak ordering (25.4 [alg.sorting]) -on elements of Key. In addition, map and multimap -associate an arbitrary type T with the Key. The object of type -Compare is called the comparison object of a container. This -comparison object may be a pointer to function or an object of a type with an -appropriate function call operator. -

    -
    12. - -
  12. -

    -Change 23.2.5 [unord.req]/3 as indicated: -

    - -

    -3 Each unordered associative container is parameterized by Key, by a -function object type Hash that acts as a hash function for -values of type Key, and by a binary predicate Pred that -induces an equivalence relation on values of type Key. [..] -

    -
    13. - -
  13. -

    -Change 25.1 [algorithms.general]/7 as indicated: [The intent is to -bring this part in sync with 20.9 [function.objects]] -

    - -

    -7 The Predicate parameter is used whenever an algorithm expects a -function object (20.9 [function.objects]) that when applied -to the result of dereferencing the corresponding iterator returns a value -testable as true. In other words, if an algorithm takes Predicate -pred as its argument and first as its iterator argument, it should -work correctly in the construct if (pred(*first)){...}. The function -object pred shall not apply any nonconstant function through the -dereferenced iterator. This function object may be a pointer to function, -or an object of a type with an appropriate function call operator. -

    -
    14. - -
  14. -

    -Change 20.8.1.2 [unique.ptr.single]/1 as indicated: -

    - -

    -1 The default type for the template parameter D is -default_delete. A client-supplied template argument D shall be -a function pointer or functor object type for which, given -a value d of type D and a pointer ptr of type -T*, the expression d(ptr) is valid and has the effect of -deallocating the pointer as appropriate for that deleter. D may also be -an lvalue-reference to a deleter. -

    -
    15. - -
- - - - - - - - -
-

871. Iota's requirements on T are too strong

-

Section: 26.7.6 [numeric.iota] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-08-20 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-According to the recent WP -N2691, -26.7.6 [numeric.iota]/1, the requires clause -of std::iota says: -

- -

-T shall meet the requirements of CopyConstructible and Assignable types, and -shall be convertible to ForwardIterator's value type.[..] -

- -

-Neither CopyConstructible nor Assignable is needed, instead MoveConstructible -seems to be the correct choice. I guess the current wording resulted as an -artifact from comparing it with similar numerical algorithms like accumulate. -

- -

-Note: If this function will be conceptualized, the here proposed -MoveConstructible requirement can be removed, because this -is an implied requirement of function arguments, see -N2710/[temp.req.impl]/3, last bullet. -

- -

[ -post San Francisco: -]

- - -

-Issue pulled by author prior to review. -

- -

[ -2009-07-30 Daniel reopened: -]

- - -

-with the absence of concepts, this issue (closed) is valid again and I -suggest to reopen it. -I also revised by proposed resolution based on N2723 wording: -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Change 'convertible' to 'assignable', Move To Ready. -

- - - -

Proposed resolution:

-

-Change the first sentence of 26.7.6 [numeric.iota]/1: -

- -

-Requires: T shall meet the requirements of CopyConstructible and -Assignable types, and shall be -assignable to ForwardIterator's value type. [..] -

- - - - - - - - -
-

872. move_iterator::operator[] has wrong return type

-

Section: 24.5.3.3.12 [move.iter.op.index] Status: C++11 - Submitter: Doug Gregor Opened: 2008-08-21 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-move_iterator's operator[] is declared as: -

- -
-reference operator[](difference_type n) const;
-
- -

-This has the same problem that reverse_iterator's operator[] used to -have: if the underlying iterator's operator[] returns a proxy, the -implicit conversion to value_type&& could end up referencing a temporary -that has already been destroyed. This is essentially the same issue that -we dealt with for reverse_iterator in DR 386. -

- -

[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]

- - -

[ -2009-08-15 Howard adds: -]

- - -

-I recommend closing this as a duplicate of 1051 which addresses -this issue for both move_iterator and reverse_iterator. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. Note that if 1051 is reopened, it may yield a -better resolution, but 1051 is currently marked NAD. -

- - - -

Proposed resolution:

-

-In 24.5.3.1 [move.iterator] and 24.5.3.3.12 [move.iter.op.index], change the declaration of -move_iterator's operator[] to: -

- -
-reference unspecified operator[](difference_type n) const;
-
- - - -

Rationale:

-

[ -San Francisco: -]

- - -

-NAD Editorial, see -N2777. -

- - - - -
-

874. Missing initializer_list constructor for discrete_distribution

-

Section: 26.5.8.6.1 [rand.dist.samp.discrete] Status: Resolved - Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.discrete].

-

View all issues with Resolved status.

-

Discussion:

-

-During the Sophia Antipolis meeting it was decided to separate from 793 a -subrequest that adds initializer list support to discrete_distribution, specifically, -the issue proposed to add a c'tor taking a initializer_list<double>. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 26.5.8.6.1 [rand.dist.samp.discrete] p. 1, class discrete_distribution, -just before the member declaration -

    - -
    -explicit discrete_distribution(const param_type& parm);
-
    - -

    -insert -

    - -
    -discrete_distribution(initializer_list<double> wl);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 of the same section insert a new -paragraph as part of the new member description: -

    - -
    -discrete_distribution(initializer_list<double> wl);
-
    - -

    -Effects: Same as discrete_distribution(wl.begin(), wl.end()). -

    -
    -
    3. -
- - -

Rationale:

-Addressed by -N2836 -"Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - -
-

875. Missing initializer_list constructor for piecewise_constant_distribution

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: Resolved - Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.pconst].

-

View all issues with Resolved status.

-

Discussion:

-

-During the Sophia Antipolis meeting it was decided to separate from -794 a subrequest that adds initializer list support to -piecewise_constant_distribution, specifically, the issue proposed -to add a c'tor taking a initializer_list<double> and a Callable to evaluate -weight values. For consistency with the remainder of this class and -the remainder of the initializer_list-aware library the author decided to -change the list argument type to the template parameter RealType -instead. For the reasoning to use Func instead of Func&& as c'tor -function argument see issue 793. -

- - -

Proposed resolution:

-

Non-concept version of the proposed resolution

- -
    -
  1. -

    -In 26.5.8.6.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, -just before the member declaration -

    - -
    -explicit piecewise_constant_distribution(const param_type& parm);
-
    - -

    -insert -

    - -
    -template<typename Func>
-piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 of the same section insert a series of -new paragraphs nominated below as [p5_1], [p5_2], and [p5_3] -as part of the new member description: -

    - -
    -template<typename Func>
-piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
-
    - -
    - -

    -[p5_1] Complexity: Exactly nf = max(bl.size(), 1) - 1 invocations of fw. -

    - -

    -[p5_2] Requires: -

    - -
      -
    1. -fw shall be callable with one argument of type RealType, and shall - return values of a type convertible to double; -
      2. -
    2. -The relation 0 < S = w0+. . .+wn-1 shall hold. -For all sampled values xk defined below, fw(xk) shall return a weight - value wk that is non-negative, non-NaN, and non-infinity; -
      3. -
    3. -If nf > 0 let bk = *(bl.begin() + k), k = 0, . . . , bl.size()-1 and the -following relations shall hold for k = 0, . . . , nf-1: bk < bk+1. -
      4. -
    - -

    -[p5_3] Effects: -

    - -
      -
    1. -

      If nf == 0,

      -
        -
      1. -lets the sequence w have length n = 1 and consist of the single - value w0 = 1, and -
        2. -
      2. -lets the sequence b have length n+1 with b0 = 0 and b1 = 1. -
        3. -
      -
      2. - -
    2. -

      Otherwise,

      -
        -
      1. -sets n = nf, and [bl.begin(), bl.end()) shall form the sequence b of -length n+1, and -
        2. -
      2. -

        lets the sequences w have length n and for each k = 0, . . . ,n-1, - calculates:

        -

        -xk = 0.5*(bk+1 + bk) -wk = fw(xk) -

        -
        3. -
      -
      3. - -
    3. -

      -Constructs a piecewise_constant_distribution object with -the above computed sequence b as the interval boundaries -and with the probability densities: -

      -

      -ρk = wk/(S * (bk+1 - bk)) for k = 0, . . . , n-1. -

      - -
      4. -
    - -
    -
    -
    3. -
- -

Concept version of the proposed resolution

- -
    -
  1. -

    -In 26.5.8.6.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, -just before the member declaration -

    - -
    -explicit piecewise_constant_distribution(const param_type& parm);
-
    - -

    -insert -

    - -
    -template<Callable<auto, RealType> Func>
- requires Convertible<Func::result_type, double>
-piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
-
    -
    2. - -
  2. -

    -Between p.4 and p.5 of the same section insert a series of -new paragraphs nominated below as [p5_1], [p5_2], and [p5_3] -as part of the new member description: -

    - -
    -template<Callable<auto, RealType> Func>
- requires Convertible<Func::result_type, double>
-piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
-
    - -
    - -

    -[p5_1] Complexity: Exactly nf = max(bl.size(), 1) - 1 invocations of fw. -

    - -

    -[p5_2] Requires: -

    - -
      -
    1. -The relation 0 < S = w0+. . .+wn-1 shall hold. -For all sampled values xk defined below, fw(xk) shall return a weight - value wk that is non-negative, non-NaN, and non-infinity; -
      2. -
    2. -If nf > 0 let bk = *(bl.begin() + k), k = 0, . . . , bl.size()-1 and the -following relations shall hold for k = 0, . . . , nf-1: bk < bk+1. -
      3. -
    - -

    -[p5_3] Effects: -

    - -
      -
    1. -

      If nf == 0,

      -
        -
      1. -lets the sequence w have length n = 1 and consist of the single - value w0 = 1, and -
        2. -
      2. -lets the sequence b have length n+1 with b0 = 0 and b1 = 1. -
        3. -
      -
      2. - -
    2. -

      Otherwise,

      -
        -
      1. -sets n = nf, and [bl.begin(), bl.end()) shall form the sequence b of -length n+1, and -
        2. -
      2. -

        lets the sequences w have length n and for each k = 0, . . . ,n-1, - calculates:

        -

        -xk = 0.5*(bk+1 + bk) -wk = fw(xk) -

        -
        3. -
      -
      3. - -
    3. -

      -Constructs a piecewise_constant_distribution object with -the above computed sequence b as the interval boundaries -and with the probability densities: -

      -

      -ρk = wk/(S * (bk+1 - bk)) for k = 0, . . . , n-1. -

      - -
      4. -
    - -
    -
    -
    3. -
- - - -

Rationale:

-

-Addressed by -N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X". -

- - - - - -
-

876. basic_string access operations should give stronger guarantees

-

Section: 21.4 [basic.string] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with C++11 status.

-

Discussion:

-

-During the Sophia Antipolis meeting it was decided to split-off some -parts of the -n2647 -("Concurrency modifications for basic_string") -proposal into a separate issue, because these weren't actually -concurrency-related. The here proposed changes refer to the recent -update document -n2668 -and attempt to take advantage of the -stricter structural requirements. -

-

-Indeed there exists some leeway for more guarantees that would be -very useful for programmers, especially if interaction with transactionary -or exception-unaware C API code is important. This would also allow -compilers to take advantage of more performance optimizations, because -more functions can have throw() specifications. This proposal uses the -form of "Throws: Nothing" clauses to reach the same effect, because -there already exists a different issue in progress to clean-up the current -existing "schizophrenia" of the standard in this regard. -

-

-Due to earlier support for copy-on-write, we find the following -unnecessary limitations for C++0x: -

- -
    -
  1. -Missing no-throw guarantees: data() and c_str() simply return -a pointer to their guts, which is a non-failure operation. This should -be spelled out. It is also noteworthy to mention that the same -guarantees should also be given by the size query functions, -because the combination of pointer to content and the length is -typically needed during interaction with low-level API. -
    2. -
  2. -Missing complexity guarantees: data() and c_str() simply return -a pointer to their guts, which is guaranteed O(1). This should be -spelled out. -
    3. -
  3. -Missing reading access to the terminating character: Only the -const overload of operator[] allows reading access to the terminator -char. For more intuitive usage of strings, reading access to this -position should be extended to the non-const case. In contrast -to C++03 this reading access should now be homogeneously -an lvalue access. -
    4. -
- -

-The proposed resolution is split into a main part (A) and a -secondary part (B) (earlier called "Adjunct Adjunct Proposal"). -(B) extends (A) by also making access to index position -size() of the at() overloads a no-throw operation. This was -separated, because this part is theoretically observable in -specifically designed test programs. -

- -

[ -San Francisco: -]

- - -
-

-We oppose part 1 of the issue but hope to address size() in -issue 877. -

-

-We do not support part B. 4 of the issue because of the breaking API change. -

-

-We support part A. 2 of the issue. -

-

-On support part A. 3 of the issue: -

-

-Pete's broader comment: now that we know that basic_string will be a -block of contiguous memory, we should just rewrite its specification -with that in mind. The expression of the specification will be simpler -and probably more correct as a result. -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-Move proposed resolution A to Ready. -

-

[ -Howard: Commented out part B. -]

- -
- - - -

Proposed resolution:

-
    -
  1. -
      -
    1. -

      In 21.4.4 [string.capacity], just after p. 1 add a new paragraph: -

      -

      -Throws: Nothing. -

      - -
      2. -
    2. -

      -In 21.4.5 [string.access] replace p. 1 by the following 4 paragraghs: -

      - -
      -

      -Requires: pos ≤ size(). -

      -

      -Returns: If pos < size(), returns *(begin() + pos). Otherwise, returns -a reference to a charT() that shall not be modified. -

      -

      -Throws: Nothing. -

      -

      -Complexity: Constant time. -

      -
      - -
      3. -
    3. -

      -In 21.4.7.1 [string.accessors] replace the now common returns -clause of c_str() and data() by the following three paragraphs: -

      -
      -

      -Returns: A pointer p such that p+i == &operator[](i) for each i -in [0, size()]. -

      -

      -Throws: Nothing. -

      -

      -Complexity: Constant time. -

      -
      -
      4. -
    -
    2. - -
- - - - - - -
-

878. forward_list preconditions

-

Section: 23.3.4 [forwardlist] Status: C++11 - Submitter: Martin Sebor Opened: 2008-08-23 Last modified: 2015-04-08

-

View all other issues in [forwardlist].

-

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-

Discussion:

-

- -forward_list member functions that take -a forward_list::iterator (denoted position in the -function signatures) argument have the following precondition: - -

-

- -Requires: position is dereferenceable or equal -to before_begin(). - -

-

- -I believe what's actually intended is this: - -

-

- -Requires: position is in the range -[before_begin(), end()). - -

-

- -That is, when it's dereferenceable, position must point -into *this, not just any forward_list object. - -

- -

[ -San Francisco: -]

- - -

-Robert suggested alternate proposed wording which had large support. -

- -

[ -Post Summit: -]

- - -
-

-Walter: "position is before_begin() or a dereferenceable": add "is" after the "or" -

-

-With that minor update, Recommend Tentatively Ready. -

-
- - - -

Proposed resolution:

-

- -Change the Requires clauses - [forwardlist] , p21, p24, p26, p29, and, -23.3.4.6 [forwardlist.ops], p39, p43, p47 -as follows: - -

-

- -Requires: position is before_begin() or is a -dereferenceable -iterator in the range [begin(), end()) -or equal to before_begin(). ... - -

- - - - -
-

880. Missing atomic exchange parameter

-

Section: 29 [atomics] Status: Resolved - Submitter: Lawrence Crowl Opened: 2008-08-24 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with Resolved status.

-

Duplicate of: 942

-

Discussion:

-

-The atomic_exchange and atomic_exchange_explicit functions seem to -be inconsistently missing parameters. -

- -

[ -Post Summit: -]

- - -
-

-Lawrence: Need to write up a list for Pete with details. -

-

-Detlef: Should not be New, we already talked about in Concurrency group. -

-

-Recommend Open. -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-Lawrence will handle all issues relating to atomics in a single paper. -

-

-LWG will defer discussion on atomics until that paper appears. -

-

-Move to Open. -

-
- -

[ -2009-08-17 Handled by -N2925. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2992. -

- - - -

Proposed resolution:

-

-Add the appropriate parameters. For example, -

- -
-bool atomic_exchange(volatile atomic_bool*, bool);
-bool atomic_exchange_explicit(volatile atomic_bool*, bool, memory_order);
-
- - - - - -
-

881. shared_ptr conversion issue

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: C++11 - Submitter: Peter Dimov Opened: 2008-08-30 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

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-

Discussion:

-

-We've changed shared_ptr<Y> to not convert to shared_ptr<T> when Y* -doesn't convert to T* by resolving issue 687. This only fixed the -converting copy constructor though. -N2351 -later added move support, and -the converting move constructor is not constrained. -

- -

[ -San Francisco: -]

- - -

-We might be able to move this to NAD, Editorial once shared_ptr is -conceptualized, but we want to revisit this issue to make sure. -

- -

[ -2009-07 Frankfurt -]

- - -
-

-Moved to Ready. -

-

-This issue now represents the favored format for specifying constrained templates. -

-
- - - -

Proposed resolution:

-

-We need to change the Requires clause of the move constructor: -

- -
-shared_ptr(shared_ptr&& r); 
-template<class Y> shared_ptr(shared_ptr<Y>&& r); 
-
-

-Requires Remarks: For the second constructor Y* shall be -convertible to T*. - -The second constructor shall not participate in overload resolution -unless Y* is convertible to T*. - -

-
- -

-in order to actually make the example in 687 compile -(it now resolves to the move constructor). -

- - - - - - -
-

882. duration non-member arithmetic requirements

-

Section: 20.12.5.5 [time.duration.nonmember] Status: CD1 - Submitter: Howard Hinnant Opened: 2008-09-08 Last modified: 2015-04-08

-

View all other issues in [time.duration.nonmember].

-

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-

Discussion:

-

-N2661 -specified the following requirements for the non-member duration -arithmetic: -

- -
- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator*(const duration<Rep1, Period>& d, const Rep2& s);
-
-

-Requires: Let CR represent the common_type of Rep1 and -Rep2. Both Rep1 and Rep2 shall be implicitly convertible -to CR, diagnostic required. -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator*(const Rep1& s, const duration<Rep2, Period>& d);
-
- -

-Requires: Let CR represent the common_type of -Rep1 and Rep2. Both Rep1 and Rep2 -shall be implicitly convertible to CR, diagnostic required. -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator/(const duration<Rep1, Period>& d, const Rep2& s);
-
- -

-Requires: Let CR represent the common_type of -Rep1 and Rep2. Both Rep1 and Rep2 shall be -implicitly convertible to CR, and Rep2 shall not be an -instantiation of duration, diagnostic required. -

- -
- -

-During transcription into the working paper, the requirements clauses on these -three functions was changed to: -

- -

-Requires: CR(Rep1, Rep2) shall exist. Diagnostic required. -

- -

-This is a non editorial change with respect to -N2661 -as user written representations which are used in duration need not be -implicitly convertible to or from arithmetic types in order to interoperate with -durations based on arithmetic types. An explicit conversion will do -fine for most expressions as long as there exists a common_type specialization -relating the user written representation and the arithmetic type. For example: -

- -
-class saturate
-{
-public:
-  explicit saturate(long long i);
-  ...
-};
-
-namespace std {
-
-template <>
-struct common_type<saturate, long long>
-{
-    typedef saturate type;
-};
-
-template <>
-struct common_type<long long, saturate>
-{
-    typedef saturate type;
-};
-
-}  // std
-
-millisecond ms(3);  // integral-based duration
-duration<saturate, milli> my_ms = ms;  // ok, even with explicit conversions
-my_ms = my_ms + ms;                    // ok, even with explicit conversions
-
- -

-However, when dealing with multiplication of a duration and its representation, -implicit convertibility is required between the rhs and the lhs's representation -for the member *= operator: -

- -
-template <class Rep, class Period = ratio<1>> 
-class duration { 
-public: 
-   ...
-   duration& operator*=(const rep& rhs);
-   ...
-};
-...
-ms *= 2;               // ok, 2 is implicitly convertible to long long
-my_ms *= saturate(2);  // ok, rhs is lhs's representation
-my_ms *= 2;            // error, 2 is not implicitly convertible to saturate
-
- -

-The last line does not (and should not) compile. And we want non-member multiplication -to have the same behavior as member arithmetic: -

- -
-my_ms = my_ms * saturate(2);  // ok, rhs is lhs's representation
-my_ms = my_ms * 2;            // should be error, 2 is not implicitly convertible to saturate
-
- -

-The requirements clauses of -N2661 -make the last line an error as expected. However the latest working draft at -this time -(N2723) -allows the last line to compile. -

- -

-All that being said, there does appear to be an error in these requirements clauses -as specified by -N2661. -

- -

-Requires: ... Both Rep1 and Rep2 shall be implicitly convertible -to CR, diagnostic required. -

- -

-It is not necessary for both Reps to be implicitly convertible to -the CR. It is only necessary for the rhs Rep to be implicitly -convertible to the CR. The Rep within the duration -should be allowed to only be explicitly convertible to the CR. The -explicit-conversion-requirement is covered under 20.12.5.7 [time.duration.cast]. -

- - - -

Proposed resolution:

-

-Change the requirements clauses under 20.12.5.5 [time.duration.nonmember]: -

- -
- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator*(const duration<Rep1, Period>& d, const Rep2& s);
-
- -

-Requires: CR(Rep1, Rep2) shall exist. -Rep2 shall be implicitly convertible to CR(Rep1, Rep2). -Diagnostic required. -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator*(const Rep1& s, const duration<Rep2, Period>& d);
-
- -

-Requiresd behavior: CR(Rep1, Rep2) shall exist. -Rep1 shall be implicitly convertible to CR(Rep1, Rep2). -Diagnostic required. -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator/(const duration<Rep1, Period>& d, const Rep2& s);
-
- -

-Requires: CR(Rep1, Rep2) shall exist -Rep2 shall be implicitly convertible to CR(Rep1, Rep2) -and Rep2 shall not -be an instantiation of duration. Diagnostic required. -

- -
- - - - - -
-

883. swap circular definition

-

Section: 23 [containers] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-09-10 Last modified: 2015-04-08

-

View other active issues in [containers].

-

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-

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-

Discussion:

- -

-Note in particular that Table 90 "Container Requirements" gives -semantics of a.swap(b) as swap(a,b), yet for all -containers we define swap(a,b) to call a.swap(b) - a -circular definition. -

- -

[ -San Francisco: -]

- - -

-Robert to propose a resolution along the lines of "Postcondition: "a = b, b = a" -This will be a little tricky for the hash containers, since they don't have -operator==. -

- -

[ -Post Summit Anthony Williams provided proposed wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-Moved to Ready with minor edits (which have been made). -

- - - -

Proposed resolution:

-

-In table 80 in section 23.2.1 [container.requirements.general], -replace the postcondition of a.swap(b) with the following: -

- -
- - - - - - - - - - - - - - - - - - - - - - - -
Table 80 -- Container requirements
ExpressionReturn typeOperational semanticsAssertion/note pre-/post-conidtionComplexity
...............
a.swap(b);void swap(a,b) -Exchange the contents of a and b.(Note A)
-
- -

-Remove the reference to swap from the paragraph following the table. -

- -

-Notes: the algorithms swap(), equal() and -lexicographical_compare() are defined in Clause 25. ... -

- - - - - -
-

884. shared_ptr swap

-

Section: 20.8.2.2.4 [util.smartptr.shared.mod] Status: Resolved - Submitter: Jonathan Wakely Opened: 2008-09-15 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-
-#include <memory>
-#include <cassert>
-
-struct A { };
-struct B : A { };
-
-int main()
-{
-    std::shared_ptr<A> pa(new A);
-    std::shared_ptr<B> pb(new B);
-    std::swap<A>(pa, pb);  // N.B. no argument deduction
-    assert( pa.get() == pb.get() );
-    return 0;
-}
-
- -

-Is this behaviour correct (I believe it is) and if so, is it -unavoidable, or not worth worrying about? -

- -

-This calls the lvalue/rvalue swap overload for shared_ptr: -

- -
-template<class T> void swap( shared_ptr<T> & a, shared_ptr<T> && b );
-
- -

-silently converting the second argument from shared_ptr<B> to -shared_ptr<A> and binding the rvalue ref to the produced temporary. -

- -

-This is not, in my opinion, a shared_ptr problem; it is a general issue -with the rvalue swap overloads. Do we want to prevent this code from -compiling? If so, how? -

- -

-Perhaps we should limit rvalue args to swap to those types that would -benefit from the "swap trick". Or, since we now have shrink_to_fit(), just -eliminate the rvalue swap overloads altogether. The original motivation -was: -

- -
-vector<A> v = ...;
-...
-swap(v, vector<A>(v));
-
-

-N1690. -

-

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to NAD EditorialResolved. -

- - -

Proposed resolution:

-

-Recommend NAD EditorialResolved, fixed by -N2844. -

- - - - - -
-

885. pair assignment

-

Section: 20.3 [pairs] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Discussion:

-
-20.2.3 pairs
-Missing assignemnt operator:
-template<class U , class V>
-  requires CopyAssignable<T1, U> && CopyAssignable<T2, V>
-    pair& operator=(pair<U , V> const & p );
-
- -

-Well, that's interesting. This assignment operator isn't in the -current working paper, either. Perhaps we deemed it acceptable to -build a temporary of type pair from pair<U, V>, then move-assign -from that temporary? -

-

-It sounds more like an issue waiting to be opened, unless you want to plug -it now. As written we risk moving from lvalues. -

- -

[ -San Francisco: -]

- - -
-

-Would be NAD if better ctors fixed it. -

-

-Related to 811. -

-
- -

[ -post San Francisco: -]

- - -

-Possibly NAD Editorial, solved by -N2770. -

- -

[ -2009-05-25 Alisdair adds: -]

- - -

-Issue 885 was something I reported while reviewing the library concepts -documents ahead of San Francisco. The missing operator was added as part of -the paper adopted at that meeting -(N2770) -and I can confirm this operator is -present in the current working paper. I recommend NAD. -

- -

[ -2009-07 Frankfurt -]

- - -

-We agree with the intent, but we need to wait for the dust to settle on concepts. -

- -

[ -2010-03-11 Stefanus provided wording. -]

- - -

[ -2010 Pittsburgh: Moved to Ready for Pittsburgh. -]

- - - - -

Proposed resolution:

-

-Add the following declaration 20.3.2 [pairs.pair], before the -declaration of pair& operator=(pair&& p);: -

- -
-template<class U, class V> pair& operator=(const pair<U, V>& p);
-
- -

-Add the following description to 20.3.2 [pairs.pair] after paragraph 11 (before -the description of pair& operator=(pair&& p);): -

- -
-template<class U, class V> pair& operator=(const pair<U, V>& p);
-
-
-

-Requires: T1 shall satisfy the requirements of -CopyAssignable from U. T2 shall -satisfy the requirements of CopyAssignable from V. -

-

-Effects: Assigns p.first to first and -p.second to second. -

-

-Returns: *this. -

-
-
- - - - - - -
-

886. tuple construction

-

Section: 20.4.2.1 [tuple.cnstr] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-09-15 Last modified: 2015-04-08

-

View other active issues in [tuple.cnstr].

-

View all other issues in [tuple.cnstr].

-

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-

Discussion:

-

-20.4.2.1 [tuple.cnstr]: -

-

-Effects: Default initializes each element. -

- -

-Could be clarified to state each "non-trivial" element. Otherwise -we have a conflict with Core deinfition of default initialization - -trivial types do not get initialized (rather than initialization -having no effect) -

- -

-I'm going to punt on this one, because it's not an issue that's -related to concepts. I suggest bringing it to Howard's attention on -the reflector. -

- -

[ -San Francisco: -]

- - -
-

-Text in draft doesn't mean anything, changing to "non-trivial" makes it -meaningful. -

-

-We prefer "value initializes". Present implementations use -value-initialization. Users who don't want value initialization have -alternatives. -

-

-Request resolution text from Alisdair. -

- -

-This issue relates to Issue 868 default construction and value-initialization. -

-
- -

[ -2009-05-04 Alisdair provided wording and adds: -]

- - -
-

-Note: This IS a change of semantic from TR1, although one the room agreed -with during the discussion. To preserve TR1 semantics, this would have been -worded: -

-
-requires DefaultConstructible<Types>... tuple();
-
-

--2- Effects: Default-initializes each non-trivial element. -

-
- - -
- -

[ -2009-07 Frankfurt -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Change p2 in Construction 20.4.2.1 [tuple.cnstr]: -

- -
-requires DefaultConstructible<Types>... tuple();
-
-
-

--2- Effects: Default Value-initializes each element. -

-
-
- - - - - - -
-

888. this_thread::yield too strong

-

Section: 30.3.2 [thread.thread.this] Status: C++11 - Submitter: Lawrence Crowl Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [thread.thread.this].

-

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-

Discussion:

-

-I never thought I'd say this, but this_thread::yield seems to be too -strong in specification. The issue is that some systems distinguish -between yielding to another thread in the same process and yielding -to another process. Given that the C++ standard only talks about -a single program, one can infer that the specification allows yielding -only to another thread within the same program. Posix has no -facility for that behavior. Can you please file an issue to weaken -the wording. Perhaps "Offers the operating system the opportunity -to reschedule." -

- -

[ -Post Summit: -]

- - -

-Recommend move to Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change 30.3.2 [thread.thread.this]/3: -

- -
-
-void this_thread::yield();
-
-

-Effects: Offers the operating system implementation -the opportunity to reschedule. -another thread. -

-
- - - - - -
-

889. thread::id comparisons

-

Section: 30.3.1.1 [thread.thread.id] Status: Resolved - Submitter: Lawrence Crowl Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [thread.thread.id].

-

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-

Discussion:

- -

Addresses UK 324

- -

-The thread::id type supports the full set of comparison operators. This -is substantially more than is required for the associative containers that -justified them. Please place an issue against the threads library. -

- -

[ -San Francisco: -]

- - -
-

-Would depend on proposed extension to POSIX, or non-standard extension. -What about hash? POSIX discussing op. POSIX not known to be considering -support needed for hash, op. -

-

-Group expresses support for putting ids in both unordered and ordered containers. -

-
- -

[ -post San Francisco: -]

- - -
-

-Howard: It turns out the current working paper -N2723 -already has hash<thread::id> -(20.9 [function.objects], 20.9.13 [unord.hash]). We simply -overlooked it in the meeting. It is a good thing we voted in favor of it -(again). :-) -

-

-Recommend NAD. -

- -
- -

[ -Post Summit: -]

- - -

-Recommend to close as NAD. For POSIX, see if we need to add a function to -convert pthread_t to integer. -

- -

[ -Post Summit, Alisdair adds: -]

- - -
-

-The recommendation for LWG-889/UK-324 is NAD, already specified. -

-

-It is not clear to me that the specification is complete. -

-

-In particular, the synopsis of <functional> in -20.9 [function.objects] does not mention hash< thread::id> -nor hash< error_code >, although their existence is -implied by 20.9.13 [unord.hash], p1. -

-

-I am fairly uncomfortable putting the declaration for the -thread_id specialization into <functional> as -id is a nested class inside std::thread, so it implies -that <functional> would require the definition of the -thread class template in order to forward declared -thread::id and form this specialization. -

-

-It seems better to me that the dependency goes the other way around -(<thread> will more typically make use of -<functional> than vice-versa) and the -hash<thread::id> specialization be declared in the -<thread> header. -

-

-I think hash<error_code> could go into either -<system_error> or <functional> and have no -immediate preference either way. However, it should clearly appear in -the synopsis of one of these two. -

-

-Recommend moving 889 back to open, and tying in a reference to UK-324. -

-
- -

[ -Batavia (2009-05): -]

- -

-Howard observes that thread::id need not be a nested class; -it could be a typedef for a more visible type. -

- -

[ -2009-05-24 Alisdair adds: -]

- -

-I do not believe this is correct. thread::id is explicitly documents as a -nested class, rather than as an unspecified typedef analogous to an -iterator. If the intent is that this is not implemented as a nested class -(under the as-if freedoms) then this is a novel form of standardese. -

- -

[ -2009-07 Frankfurt -]

- - -

-Decided we want to move hash specialization for thread_id to the thread -header. Alisdair to provide wording. -

- -

[ -2009-07-28 Alisdair provided wording, moved to Review. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Add a strike for hash<thread::id>. Move to Ready -

- -

[ -2009-11-13 The proposed wording of 1182 is a superset of the -wording in this issue. -]

- - -

[ -2010-02-09 Moved from Ready to Open: -]

- - -
-

-Issue 1182 is not quite a superset of this issue and it is controversial -whether or not the note: -

- -

-hash template specialization allows thread::id objects to be used as keys in -unordered containers. -

- -

-should be added to the WP. -

- - -
- -

[ -2010-02-09 Objections to moving this to NAD EditorialResolved, addressed by 1182 have been removed. Set to Tentatively NAD EditorialResolved. -]

- - - - -

Rationale:

-

-Solved by 1182. -

- - -

Proposed resolution:

- -

-Remove the following prototype from the synopsis in -20.9 [function.objects]: -

- -

-template <> struct hash<std::thread::id>;
-
- -

-Add to 30.3 [thread.threads], p1 Header <thread> synopsis: -

- -
-template <class T> struct hash;
-template <> struct hash<thread::id>;
-
- -

-Add template specialization below class definition in 30.3.1.1 [thread.thread.id] -

- -
-template <>
-struct hash<thread::id> : public unary_function<thread::id, size_t> {
-   size_t operator()(thread::id val) const;
-};
-
- -

-Extend note in p2 30.3.1.1 [thread.thread.id] with second sentence: -

- -

-[Note: Relational operators allow thread::id objects to be used -as keys in associative containers. -hash template specialization allows thread::id objects to be used as keys -in unordered containers. -— end note] -

- -

-Add new paragraph to end of 30.3.1.1 [thread.thread.id] -

- -
-template <> struct hash<thread::id>;
-
-

-An explicit specialization of the class template hash (20.9.13 [unord.hash]) -shall be provided for the type thread::id. -

-
- - - - - -
-

890. Improving <system_error> initialization

-

Section: 19.5.1 [syserr.errcat] Status: C++11 - Submitter: Beman Dawes Opened: 2008-09-14 Last modified: 2015-04-08

-

View all other issues in [syserr.errcat].

-

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-

Discussion:

-

-The static const error_category objects generic_category and -system_category in header <system_error> are currently declared: -

- -
-const error_category& get_generic_category();
-const error_category& get_system_category();
-
-static const error_category& generic_category = get_generic_category();
-static const error_category& system_category = get_system_category();
-
- -

-This formulation has several problems: -

- -
    -
  • -Implementation details are exposed, since initialization is specified in -the interface. This over-constrains implementations without offsetting -user benefits. The form of initialization specified may be less than -maximally efficient on some platforms. -
    • -
  • -Use of the objects is more expensive in terms of number of machine level -instructions. See Implementation experience below. -
    • -
  • -Depending on the compiler, some cost may be incurred by each translation unit -that includes the header, even if the objects are not used. This is a -common scenario in user code, since the header is included by other -standard library headers. It should be mentioned that at least one -compilers is able to optimize this cost away, however. -
    • -
- -

-IO streams uses a somewhat different formulation for iostream_category, but -still suffer much the same problems. -

- -

-The original plan was to eliminate these problems by applying the C++0x -constexpr feature. See LWG issue 832. However, that approach turned out -to be unimplementable, since it would require a constexpr object of a -class with virtual functions, and that is not allowed by the core -language. -

- -

-The proposed resolution was developed as an alternative. It mitigates the above -problems by removing initialization from the visible interface, allowing -implementations flexibility. -

- -

-Implementation experience: -

- -

-Prototype implementations of the current WP interface and proposed -resolution interface were tested with recent Codegear, GCC, Intel, and Microsoft -compilers on Windows. The code generated by the Microsoft compiler was studied -at length; the WP and proposal versions generated very similar code. For both versions -the compiler did make use of static -initialization; apparently the compiler applied an implicit constexpr -where useful, even in cases where constexpr would not be permitted by -the language! -

- -

-Acknowledgements: -

- -

-Martin Sebor, Chris Kohlhoff, and John Lakos provided useful ideas and comments on initialization issues. -

- -

[ -San Francisco: -]

- - -
-

-Martin: prefers not to create more file-scope static objects, and would -like to see get_* functions instead. -

-
- - -

[Pre-Summit:]

- -
- - -

-Beman: The proposed resolution has been reworked to remove the file-scope -static objects, per Martin's suggestions. The get_ prefix has been -eliminated from the function names as no longer necessary and to conform with -standard library naming practice. -

- -
- -

[ -Post Summit: -]

- - -

-Agreement that this is wise and essential, text provided works and has -been implemented. Seems to be widespread consensus. Move to Tentative Ready. -

- - - -

Proposed resolution:

- -

Change 17.6.5.14 [value.error.codes] Value of error codes as indicated:

-
-

Certain functions in the C++ standard library report errors via a - std::error_code (19.4.2.2) object. That object's category() member shall - return a reference to std::system_category() for errors originating from the - operating system, or a reference to an implementation-defined error_category - object for errors originating elsewhere. The implementation shall define the - possible values of value() for each of these error categories. [Example: For - operating systems that are based on POSIX, implementations are encouraged to - define the std::system_category() values as identical to the POSIX errno values, - with additional values as defined by the operating system's documentation. - Implementations for operating systems that are not based on POSIX are - encouraged to define values identical to the operating system's values. For - errors that do not originate from the operating system, the implementation may - provide enums for the associated values --end example]

-
- -

-Change 19.5.1.1 [syserr.errcat.overview] Class error_category overview -error_category synopsis as indicated: -

- -
-
-const error_category& get_generic_category();
-const error_category& get_system_category();
-
-static storage-class-specifier const error_category& generic_category = get_generic_category();
-static storage-class-specifier const error_category& system_category = get_system_category();
-
-
- -

-Change 19.5.1.5 [syserr.errcat.objects] Error category objects as indicated: -

- -
-
const error_category& get_generic_category();
-
- -
- -

-Returns: A reference to an object of a type derived from class error_category. -

- -

-Remarks: The object's default_error_condition and equivalent virtual -functions shall behave as specified for the class error_category. The -object's name virtual function shall return a pointer to the string -"GENERIC". -

-
- -
-const error_category& get_system_category();
-
- -
-

-Returns: A reference to an object of a type derived from class error_category. -

- -

-Remarks: The object's equivalent virtual functions shall behave as -specified for class error_category. The object's name virtual function -shall return a pointer to the string "system". The object's -default_error_condition virtual function shall behave as follows: -

-

-If the argument ev corresponds to a POSIX errno value posv, the function -shall return error_condition(posv, generic_category()). Otherwise, the -function shall return error_condition(ev, system_category()). What -constitutes correspondence for any given operating system is -unspecified. [Note: The number of potential system error codes is large -and unbounded, and some may not correspond to any POSIX errno value. -Thus implementations are given latitude in determining correspondence. -— end note] -

-
- -
- -

Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors -as indicated:

-
- 
error_code();
-
-

Effects: Constructs an object of type error_code.

-

Postconditions: val_ == 0 and cat_ == &system_category().

-
-
-

Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as -indicated:

-
- 
void clear();
-
-

Postconditions: value() == 0 and category() == - system_category().

-
-
-

Change 19.5.2.5 [syserr.errcode.nonmembers] Class error_code non-member -functions as indicated:

-
- 
error_code make_error_code(errc e);
-
-

Returns: error_code(static_cast<int>(e), generic_category()).

-
-
-

Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition -constructors as indicated:

-
- 
error_condition();
-
-

Effects: Constructs an object of type error_condition.

-

Postconditions: val_ == 0 and cat_ == &generic_category().

-
-
-

Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition -modifiers as indicated:

-
- 
void clear();
-
-

Postconditions: value() == 0 and category() == - generic_category().

-
-
-

Change 19.5.3.5 [syserr.errcondition.nonmembers] Class error_condition -non-member functions as indicated:

-
- 
error_condition make_error_condition(errc e);
-
-

Returns: error_condition(static_cast<int>(e), generic_category()).

-
-
-

Change 27.5 [iostreams.base] Iostreams base classes, Header <ios> - synopsis as indicated:

-
- 
concept_map ErrorCodeEnum<io_errc> { };
-error_code make_error_code(io_errc e);
-error_condition make_error_condition(io_errc e);
-storage-class-specifier const error_category& iostream_category();
-
-

Change 27.5.3.1.1 [ios::failure] Class ios_base::failure, paragraph 2 as -indicated:

-
-

When throwing ios_base::failure exceptions, implementations should provide -values of ec that identify the specific reason for the failure. [ Note: Errors -arising from the operating system would typically be reported as -system_category() errors with an error value of the -error number reported by the operating system. Errors arising from within the -stream library would typically be reported as error_code(io_errc::stream, -iostream_category()). — end note ]

-
-

Change 27.5.6.5 [error.reporting] Error reporting as indicated:

-
- 
error_code make_error_code(io_errc e);
-
-

Returns: error_code(static_cast<int>(e), iostream_category()).

-
- 
error_condition make_error_condition(io_errc e);
-
-

Returns: error_condition(static_cast<int>(e), - iostream_category()).

-
- 
storage-class-specifier const error_category& iostream_category();
-
-

The implementation shall initialize iostream_category. Its storage-class-specifier - may be static or extern. It is unspecified whether initialization is static - or dynamic (3.6.2). If initialization is dynamic, it shall occur before - completion of the dynamic initialization of the first translation unit - dynamically initialized that includes header <system_error>.

 -

-Returns: A reference to an object of a type derived from class error_category. -

-

Remarks: The object's default_error_condition and equivalent virtual functions shall -behave as specified for the class error_category. The object's name virtual -function shall return a pointer to the string "iostream".

-
-
- - - - - - - -
-

891. std::thread, std::call_once issue

-

Section: 30.3.1.2 [thread.thread.constr], 30.4.4.2 [thread.once.callonce] Status: C++11 - Submitter: Peter Dimov Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [thread.thread.constr].

-

View all issues with C++11 status.

-

Discussion:

-

-I notice that the vararg overloads of std::thread and std::call_once -(N2723 30.3.1.2 [thread.thread.constr] and 30.4.4.2 [thread.once.callonce]) are no longer specified in terms of -std::bind; instead, some of the std::bind wording has been inlined into -the specification. -

-

-There are two problems with this. -

-

-First, the specification (and implementation) in terms of std::bind allows, for example: -

- -
-std::thread th( f, 1, std::bind( g ) );
-
- -

-which executes f( 1, g() ) in a thread. This can be useful. The -"inlined" formulation changes it to execute f( 1, bind(g) ) in a thread. -

-

-Second, assuming that we don't want the above, the specification has copied the wording -

- -

-INVOKE(func, w1, w2, ..., wN) (20.6.2) shall be a valid -expression for some values w1, w2, ..., wN -

- -

-but this is not needed since we know that our argument list is args; it should simply be -

- -

-INVOKE(func, args...) (20.6.2) shall be a valid expression -

- -

[ -Summit: -]

- - -

-Move to open. -

- -

[ -Post Summit Anthony provided proposed wording. -]

- - -

[ -2009-07 Frankfurt -]

- - -

-Leave Open. Await decision for thread variadic constructor. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-See proposed wording for 929 for this, for the formulation -on how to solve this. 929 modifies the thread constructor to -have "pass by value" behavior with pass by reference efficiency through the use -of the decay trait. This same formula would be useful for call_once. -

- -

[ -2010-02-11 Anthony updates wording. -]

- - -

[ -2010-02-12 Moved to Tentatively Ready after 5 postive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Modify 30.4.4.2 [thread.once.callonce] p1-p2 with the following: -

- -
-template<class Callable, class ...Args>
-  void call_once(once_flag& flag, Callable&& func, Args&&... args);
-
- -

-Given a function as follows: -

- -

-template<typename T> typename decay<T>::type decay_copy(T&& v)
-   { return std::forward<T>(v); }
-
- -

-1 Requires: The template parameters Callable and each -Ti in Args shall be CopyConstructible if an -lvalue and otherwise satisfy the MoveConstructible -requirements. -INVOKE(decay_copy(std::forward<Callable>(func), -w1, w2, ..., wN -decay_copy(std::forward<Args>(args))...) (20.9.2 [func.require]) -shall be a valid expression for some values w1, w2, ..., wN, where -N == sizeof...(Args). -

- -

-2 Effects: Calls to call_once on the same once_flag -object are serialized. If there has been a prior effective call to -call_once on the same once_flag object, the call to -call_once returns without invoking func. If there has been no -prior effective call to call_once on the same once_flag -object, the argument func (or a copy thereof) is called as if by -invoking func(args) -INVOKE(decay_copy(std::forward<Callable>(func)), -decay_copy(std::forward<Args>(args))...) is executed. The call -to call_once is effective if and only if func(args) -INVOKE(decay_copy(std::forward<Callable>(func)), -decay_copy(std::forward<Args>(args))...) returns without -throwing an exception. If an exception is thrown it is propagated to the caller. -

- -
- -
- - - - - - - -
-

893. std::mutex issue

-

Section: 30.4.1.2.1 [thread.mutex.class] Status: C++11 - Submitter: Peter Dimov Opened: 2008-09-15 Last modified: 2015-04-08

-

View all other issues in [thread.mutex.class].

-

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-

Duplicate of: 905

-

Discussion:

-

-30.4.1.2.1 [thread.mutex.class]/27 (in -N2723) -says that the behavior is undefined if: -

-
    -
  • a thread that owns a mutex object calls lock() or -try_lock() on that object
    • -
-

-I don't believe that this is right. Calling lock() or try_lock() on a -locked mutex is well defined in the general case. try_lock() is required -to fail and return false. lock() is required to either throw an -exception (and is allowed to do so if it detects deadlock) or to block -until the mutex is free. These general requirements apply regardless of -the current owner of the mutex; they should apply even if it's owned by -the current thread. -

-

-Making double lock() undefined behavior probably can be justified (even -though I'd still disagree with the justification), but try_lock() on a -locked mutex must fail. -

- -

[ -Summit: -]

- -
-

-Move to open. Proposed resolution: -

-
    -
  • -In 30.4.1 [thread.mutex.requirements] paragraph 12, change the error -condition for resource_deadlock_would_occur to: "if the implementation -detects that a deadlock would occur" -
    • -
  • -Strike 30.4.1.2.1 [thread.mutex.class] paragraph 3 bullet 2 "a thread that owns a mutex object -calls lock() or try_lock() on that object, or" -
    • -
-
- -

[ -2009-07 Frankfurt -]

- - -

-Move to Review. Alisdair to provide note. -

- -

[ -2009-07-31 Alisdair provided note. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- -

[ -2009-11-18 Peter Opens: -]

- - -
-

-I don't believe that the proposed note: -

- -

-[Note: a program may deadlock if the thread that owns a mutex -object calls lock() or try_lock() on that object. If the program can -detect the deadlock, a resource_deadlock_would_occur error condition may -be observed. — end note] -

- -

-is entirely correct. "or try_lock()" should be removed, because -try_lock is non-blocking and doesn't deadlock; it just returns -false when it fails to lock the mutex. -

- -

[ -Howard: I've set to Open and updated the wording per Peter's suggestion. -]

- - -
- -

[ -2009-11-18 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-In 30.4.1 [thread.mutex.requirements] paragraph 12 change: -

- -
-
    -
  • ...
    • -
  • -resource_deadlock_would_occur -- if the current thread already owns the mutex and is able -to detect it implementation detects that a deadlock would occur. -
    • -
  • ...
    • -
-
- -

-Strike 30.4.1.2.1 [thread.mutex.class] paragraph 3 bullet 2: -

-
-

--3- The behavior of a program is undefined if: -

-
    -
  • ...
    • -
  • -a thread that owns a mutex object calls lock() or try_lock() on that object, or -
    • -
  • ...
    • -
-
- -

-Add the following note after p3 30.4.1.2.1 [thread.mutex.class] -

- -

-[Note: a program may deadlock if the thread that owns a mutex -object calls lock() on that object. If the implementation can detect the -deadlock, a resource_deadlock_would_occur error condition may be -observed. — end note] -

- - - - - - -
-

894. longjmp and destructors

-

Section: 18.10 [support.runtime] Status: C++11 - Submitter: Lawrence Crowl, Alisdair Meredith Opened: 2008-09-17 Last modified: 2015-04-08

-

View other active issues in [support.runtime].

-

View all other issues in [support.runtime].

-

View all issues with C++11 status.

-

Discussion:

-

-The interaction between longjmp and exceptions seems unnecessarily -restrictive and not in keeping with existing practice. -

- - -

Proposed resolution:

-

-Edit paragraph 4 of 18.10 [support.runtime] as follows: -

- -

-The function signature longjmp(jmp_buf jbuf, int val) has more -restricted behavior in this International Standard. A -setjmp/longjmp call pair has undefined behavior if replacing the -setjmp and longjmp by catch and -throw would destroy -invoke any non-trivial destructors for -any automatic objects. -

- - - - - -
-

896. Library thread safety issue

-

Section: 20.8.2.2 [util.smartptr.shared] Status: C++11 - Submitter: Hans Boehm Opened: 2008-09-16 Last modified: 2015-04-08

-

View other active issues in [util.smartptr.shared].

-

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-

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-

Discussion:

-

-It is unclear whether shared_ptr is thread-safe in the sense that -multiple threads may simultaneously copy a shared_ptr. However this -is a critical piece of information for the client, and it has significant -impact on usability for many applications. (Detlef Vollman thinks it -is currently clear that it is not thread-safe. Hans Boehm thinks -it currently requires thread safety, since the use_count is not an -explicit field, and constructors and assignment take a const reference -to an existing shared_ptr.) -

- -

-Pro thread-safety: -

-

-Many multi-threaded usages are impossible. A thread-safe version can -be used to destroy an object when the last thread drops it, something -that is often required, and for which we have no other easy mechanism. -

-

-Against thread-safety: -

-

-The thread-safe version is well-known to be far more expensive, even -if used by a single thread. Many applications, including all single-threaded -ones, do not care. -

- -

[ -San Francisco: -]

- - -
-

-Beman: this is a complicated issue, and would like to move this to Open -and await comment from Peter Dimov; we need very careful and complete -rationale for any decision we make; let's go slow -

-

-Detlef: I think that shared_ptr should not be thread-safe. -

-

-Hans: When you create a thread with a lambda, it in some cases makes it -very difficult for the lambda to reference anything in the heap. It's -currently ambiguous as to whether you can use a shared_ptr to get at an -object. -

-

-Leave in Open. Detlef will submit an alternative proposed resolution -that makes shared_ptr explicitly unsafe. -

-

-A third option is to support both threadsafe and non-safe share_ptrs, -and to let the programmer decide which behavior they want. -

- -

-Beman: Peter, do you support the PR? -

- -

-Peter: -

-
-

-Yes, I support the proposed resolution, and I certainly oppose any -attempts to make shared_ptr thread-unsafe. -

-

-I'd mildly prefer if -

-

-[Note: This is true in spite of that fact that such functions often -modify use_count() --end note] -

-

-is changed to -

-

-[Note: This is true in spite of that fact that such functions often -cause a change in use_count() --end note] -

-

-(or something along these lines) to emphasise that use_count() is not, -conceptually, a variable, but a return value. -

-
- -
- -

[ -2009-07 Frankfurt -]

- - -
-

-Vote: Do we want one thread-safe shared pointer or two? If two, one -would allow concurrent construction and destruction of shared pointers, -and one would not be thread-safe. If one, then it would be thread-safe. -

-

-No concensus on that vote. -

-

-Hans to improve wording in consultation with Pete. Leave Open. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. Ask Editor to clear up wording a little when integrating to -make it clear that the portion after the first comma only applies for -the presence of data races. -

- -

[ -2009-10-24 Hans adds: -]

- - -
-

-I think we need to pull 896 back from ready, unfortunately. My wording -doesn't say the right thing. -

- -

-I suspect we really want to say something along the lines of: -

- -

-For purposes of determining the presence of a data race, member -functions access and modify only the shared_ptr and -weak_ptr objects themselves and not objects they refer to. -Changes in use_count() do not reflect modifications that can -introduce data races. -

- -

-But I think this needs further discussion by experts to make sure this -is right. -

- -

-Detlef and I agree continue to disagree on the resolution, but I think -we agree that it would be good to try to expedite this so that it can be -in CD2, since it's likely to generate NB comments no matter what we do. -And lack of clarity of intent is probably the worst option. I think it -would be good to look at this between meetings. -

-
- -

[ -2010-01-20 Howard: -]

- - -
-

-I've moved Hans' suggested wording above into the proposed resolution section -and preserved the previous wording here: -

- -
-

-Make it explicitly thread-safe, in this weak sense, as I believe was intended: -

-

-Insert in 20.8.2.2 [util.smartptr.shared], before p5: -

-
-

-For purposes of determining the presence of a data race, -member functions do not modify const shared_ptr and -const weak_ptr arguments, nor any objects they -refer to. [Note: This is true in spite of that fact that such functions often -cause a change in use_count() --end note] -

-
-

-On looking at the text, I'm not sure we need a similar disclaimer -anywhere else, since nothing else has the problem with the modified -use_count(). I think Howard arrived at a similar conclusion. -

-
-
- -

[ -2010 Pittsburgh: Moved to Ready for Pittsburgh -]

- - - - -

Proposed resolution:

- -

-Insert a new paragraph at the end of 20.8.2.2 [util.smartptr.shared]: -

- -

-For purposes of determining the presence of a data race, member functions access -and modify only the shared_ptr and weak_ptr objects themselves -and not objects they refer to. Changes in use_count() do not reflect -modifications that can introduce data races. -

- - - - - -
-

897. Forward_list issues... Part 2

-

Section: 23.3.4.5 [forwardlist.modifiers] Status: Resolved - Submitter: Howard Hinnant Opened: 2008-09-22 Last modified: 2015-04-08

-

View all other issues in [forwardlist.modifiers].

-

View all issues with Resolved status.

-

Discussion:

-

-This issue was split off from 892 at the request of the LWG. -

- -

[ -San Francisco: -]

- - -
-

-This issue is more complicated than it looks. -

-

-paragraph 47: replace each (first, last) with (first, last] -

-

-add a statement after paragraph 48 that complexity is O(1) -

-

-remove the complexity statement from the first overload of splice_after -

-

-We may have the same problems with other modifiers, like erase_after. -Should it require that all iterators in the range (position, last] be -dereferenceable? -

-
- -

-There are actually 3 issues here: -

- -
    -
  1. -

    -What value should erase_after return? With list, code often -looks like: -

    -
    -for (auto i = l.begin(); i != l.end();)
-{
-    // inspect *i and decide if you want to erase it
-    // ...
-    if (I want to erase *i)
-        i = l.erase(i);
-    else
-        ++i;
-}
-
    -

    -I.e. the iterator returned from erase is useful for setting up the -logic for operating on the next element. For forward_list this might -look something like: -

    -
    -auto i = fl.before_begin();
-auto ip1 = i;
-for (++ip1; ip1 != fl.end(); ++ip1)
-{
-    // inspect *(i+1) and decide if you want to erase it
-    // ...
-    if (I want to erase *(i+1))
-        i = fl.erase_after(i);
-    else
-        ++i;
-    ip1 = i;
-}
-
    -

    -In the above example code, it is convenient if erase_after returns -the element prior to the erased element (range) instead of the element -after the erase element (range). -

    -

    -Existing practice: -

    -
      -
    • SGI slist returns an iterator referencing the element after the erased range.
      • -
    • CodeWarrior slist returns an iterator referencing the element before the erased range.
      • -
    -

    -There is not a strong technical argument for either solution over the other. -

    -
    2. - -
  2. -

    -With all other containers, operations always work on the range -[first, last) and/or prior to the given position. -

    -

    -With forward_list, operations sometimes work on the range -(first, last] and/or after the given position. -

    -

    -This is simply due to the fact that in order to operate on -*first (with forward_list) one needs access to -*(first-1). And that's not practical with -forward_list. So the operating range needs to start with (first, -not [first (as the current working paper says). -

    -

    -Additionally, if one is interested in splicing the range (first, last), -then (with forward_list), one needs practical (constant time) access to -*(last-1) so that one can set the next field in this node to -the proper value. As this is not possible with forward_list, one must -specify the last element of interest instead of one past the last element of -interest. The syntax for doing this is to pass (first, last] instead -of (first, last). -

    -

    -With erase_after we have a choice of either erasing the range -(first, last] or (first, last). Choosing the latter -enables: -

    -
    -x.erase_after(pos, x.end());
-
    - -

    -With the former, the above statement is inconvenient or expensive due to the lack -of constant time access to x.end()-1. However we could introduce: -

    - -
    -iterator erase_to_end(const_iterator position);
-
    - -

    -to compensate. -

    - -

    -The advantage of the former ((first, last]) for erase_after -is a consistency with splice_after which uses (first, last] -as the specified range. But this either requires the addition of erase_to_end -or giving up such functionality. -

    - -
    3. - -
  3. -As stated in the discussion of 892, and reienforced by point 2 above, -a splice_after should work on the source range (first, last] -if the operation is to be Ο(1). When splicing an entire list x the -algorithm needs (x.before_begin(), x.end()-1]. Unfortunately x.end()-1 -is not available in constant time unless we specify that it must be. In order to -make x.end()-1 available in constant time, the implementation would have -to dedicate a pointer to it. I believe the design of -N2543 -intended a nominal overhead of foward_list of 1 pointer. Thus splicing -one entire forward_list into another can not be Ο(1). -
    4. -
- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Review. -

-
- -

[ -2009-07 Frankfurt -]

- - -
-

-We may need a new issue to correct splice_after, because it may no -longer be correct to accept an rvalues as an argument. Merge may be -affected, too. This might be issue 1133. (Howard: confirmed) -

-

-Move this to Ready, but the Requires clause of the second form of -splice_after should say "(first, last)," not "(first, last]" (there are -three occurrences). There was considerable discussion on this. (Howard: fixed) -

-

-Alan suggested removing the "foward_last<T. Alloc>&& x" -parameter from the second form of splice_after, because it is redundant. -PJP wanted to keep it, because it allows him to check for bad ranges -(i.e. "Granny knots"). -

-

-We prefer to keep x. -

-

-Beman. Whenever we deviate from the customary half-open range in the -specification, we should add a non-normative comment to the standard -explaining the deviation. This clarifies the intention and spares the -committee much confusion in the future. -

-

-Alan to write a non-normative comment to explain the use of fully-closed ranges. -

-

-Move to Ready, with the changes described above. (Howard: awaiting note from Alan) -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved, addressed by -N2988. -

- - - -

Proposed resolution:

-

-Wording below assumes issue 878 is accepted, but this issue is -independent of that issue. -

- -

-Change 23.3.4.5 [forwardlist.modifiers]: -

- -
-
-iterator erase_after(const_iterator position);
-
-
-

-Requires: The iterator following position is dereferenceable. -

-

-Effects: Erases the element pointed to by the iterator following position. -

-

-Returns: An iterator pointing to the element following the one that was erased, or end() if no such -element exists -An iterator equal to position. -

-
- - -
-iterator erase_after(const_iterator position, const_iterator last);
-
-
-

-Requires: All iterators in the range -[(position,last) -are dereferenceable. -

-

-Effects: Erases the elements in the range -[(position,last). -

-

-Returns: An iterator equal to position last -

-
-
- -

-Change 23.3.4.6 [forwardlist.ops]: -

- -
-
-void splice_after(const_iterator position, forward_list<T,Allocator>&& x);
-
-
-

-Requires: position is before_begin() or a -dereferenceable iterator in the range [begin(), end)). &x != this. -

-

-Effects: Inserts the contents of x after position, and -x becomes empty. Pointers and references to -the moved elements of x now refer to those same elements but as members of *this. -Iterators referring to the moved elements will continue to refer to their elements, -but they now behave as iterators into *this, not into x. -

-

-Throws: Nothing. -

-

-Complexity: Ο(1) Ο(distance(x.begin(), x.end())) -

-
- -

...

- -
-void splice_after(const_iterator position, forward_list<T,Allocator>&& x, 
-                  const_iterator first, const_iterator last);
-
-
-

-Requires: position is before_begin() or a -dereferenceable iterator in the range [begin(), end)). -(first,last) is a valid range in -x, and all iterators in the range -(first,last) are dereferenceable. -position is not an iterator in the range (first,last). -

-

-Effects: Inserts elements in the range (first,last) -after position and removes the elements from x. -Pointers and references to the moved elements of x now refer to -those same elements but as members of *this. Iterators -referring to the moved elements will continue to refer to their -elements, but they now behave as iterators into *this, not into -x. -

-

-Complexity: Ο(1). -

-
- -
- - - - - - -
-

898. Small contradiction in n2723 to forward to committee

-

Section: 23.3.4.6 [forwardlist.ops] Status: C++11 - Submitter: Arch Robison Opened: 2008-09-08 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with C++11 status.

-

Discussion:

-

-I ran across a small contradiction in working draft n2723. -

-
-

-23.3.4 [forwardlist]p2: A forward_list satisfies all of the -requirements of a container (table 90), except that the size() member -function is not provided. -

-

-23.3.4.6 [forwardlist.ops]p57: Complexity: At most size() + x.size() - 1 -comparisons. -

-
-

-Presumably 23.3.4.6 [forwardlist.ops]p57 needs to be rephrased to not use -size(), or note that it is used there only for sake of notational convenience. -

- -

[ -2009-03-29 Beman provided proposed wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

Change 23.3.4.6 [forwardlist.ops], -forward_list operations, paragraph 19, merge complexity as indicated: -

-

-Complexity: At most size() + x.size() -distance(begin(), end()) + distance(x.begin(), x.end()) - 1 -comparisons. -

- - - - - -
-

899. Adjusting shared_ptr for nullptr_t

-

Section: 20.8.2.2.2 [util.smartptr.shared.dest] Status: C++11 - Submitter: Peter Dimov Opened: 2008-09-18 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.dest].

-

View all issues with C++11 status.

-

Discussion:

-

-James Dennett, message c++std-lib-22442: -

-

-The wording below addresses one case of this, but opening an -issue to address the need to sanity check uses of the term "pointer" -in 20.8.2.2 [util.smartptr.shared] would be a good thing. -

-

-There's one more reference, in ~shared_ptr; we can apply your suggested change to it, too. That is: -

-

-Change 20.8.2.2.2 [util.smartptr.shared.dest]/1 second bullet from: -

-

-Otherwise, if *this owns a pointer p and a deleter d, d(p) is called. -

-

-to: -

-

-Otherwise, if *this owns an object p and a deleter d, d(p) is called. -

- -

[ -Post Summit: -]

- - -

-Recommend Review. -

- -

[ -Batavia (2009-05): -]

- -
-

-Peter Dimov notes the analogous change has already been made -to "the new nullptr_t taking constructors -in 20.8.2.2.1 [util.smartptr.shared.const] p9-13." -

-

-We agree with the proposed resolution. -Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-Change 20.8.2.2.2 [util.smartptr.shared.dest] p1 second bullet: -

-
-
    -
  • ...
    • -
  • -Otherwise, if *this owns a pointer -an object p and a -deleter d, d(p) is called. -
    • -
-
- - - - - -
-

900. Stream move-assignment

-

Section: 27.9.1.8 [ifstream.assign] Status: C++11 - Submitter: Niels Dekker Opened: 2008-09-20 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-It appears that we have an issue similar to issue 675 regarding the move-assignment of -stream types. For example, when assigning to an std::ifstream, ifstream1, it -seems preferable to close the file originally held by ifstream1: -

- -
-ifstream1 = std::move(ifstream2); 
-
- -

-The current Draft -(N2723) -specifies that the move-assignment of stream types like ifstream has the -same effect as a swap: -

- -
-

-Assign and swap 27.9.1.8 [ifstream.assign] -

-
-basic_ifstream& operator=(basic_ifstream&& rhs); 
-
-

-Effects: swap(rhs). -

-
- -

[ -Batavia (2009-05): -]

- -
-

-Howard agrees with the analysis and the direction proposed. -

-

-Move to Open pending specific wording to be supplied by Howard. -

-
- -

[ -2009-07 Frankfurt: -]

- - -

-Howard is going to write wording. -

- -

[ -2009-07-26 Howard provided wording. -]

- - -

[ -2009-09-13 Niels adds: -]

- - -

-Note: The proposed change of 27.9.1.3 [filebuf.assign] p1 depends on the -resolution of LWG 1204, which allows implementations to assume that -*this and rhs refer to different objects. -

- -

[ -2009 Santa Cruz: -]

- - -

-Leave as Open. Too closely related to 911 to move on at this time. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

- -

-Change 27.8.2.2 [stringbuf.assign]/1: -

- -
-basic_stringbuf& operator=(basic_stringbuf&& rhs);
-
-

--1- Effects: swap(rhs). -After the move assignment *this reflects the same observable -state it would have if it had been move constructed from rhs -(27.8.2.1 [stringbuf.cons]). - -

-
- -

-Change 27.8.3.2 [istringstream.assign]/1: -

- -
-basic_istringstream& operator=(basic_istringstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. - -

-
- -

-Change 27.8.4.2 [ostringstream.assign]/1: -

- -
-basic_ostringstream& operator=(basic_ostringstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. - -

-
- -

-Change 27.8.5.2 [stringstream.assign]/1: -

- -
-basic_stringstream& operator=(basic_stringstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. - -

-
- -

-Change 27.9.1.3 [filebuf.assign]/1: -

- -
-basic_filebuf& operator=(basic_filebuf&& rhs);
-
-

--1- Effects: swap(rhs). -Begins by calling this->close(). -After the move assignment *this reflects the same observable -state it would have if it had been move constructed from rhs -(27.9.1.2 [filebuf.cons]). - -

-
- -

-Change 27.9.1.8 [ifstream.assign]/1: -

- -
-basic_ifstream& operator=(basic_ifstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. -

-
- -

-Change 27.9.1.12 [ofstream.assign]/1: -

- -
-basic_ofstream& operator=(basic_ofstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. -

-
- -

-Change 27.9.1.16 [fstream.assign]/1: -

- -
-basic_fstream& operator=(basic_fstream&& rhs);
-
-

--1- Effects: swap(rhs). -Move assigns the base and members of *this with the respective -base and members of rhs. -

-
- - - - - - -
-

904. result_of argument types

-

Section: X [func.ret] Status: C++11 - Submitter: Jonathan Wakely Opened: 2008-09-10 Last modified: 2015-04-08

-

View all other issues in [func.ret].

-

View all issues with C++11 status.

-

Discussion:

-

-The WP and TR1 have the same text regarding the argument types of a -result_of expression: -

-

-The values ti are lvalues when the corresponding type Ti is a -reference type, and rvalues otherwise. -

-

-I read this to mean that this compiles: -

-
-typedef int (*func)(int&);
-result_of<func(int&&)>::type i = 0;
-
-

-even though this doesn't: -

-
-int f(int&);
-f( std::move(0) );
-
-

-Should the text be updated to say "when Ti is an lvalue-reference -type" or am I missing something? -

-

-I later came up with this self-contained example which won't compile, -but I think it should: -

-
-struct X {
-  void operator()(int&);
-  int operator()(int&&);
-} x;
-
-std::result_of< X(int&&) >::type i = x(std::move(0));
-
- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change X [func.ret], p1: -

- -

-... The values ti are lvalues -when the corresponding type Ti is an lvalue-reference type, -and rvalues otherwise. -

- - - - - -
-

907. Bitset's immutable element retrieval is inconsistently defined

-

Section: 20.6.2 [bitset.members] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2015-04-08

-

View all other issues in [bitset.members].

-

View all issues with C++11 status.

-

Discussion:

-

-The current standard 14882::2003(E) as well as the current draft -N2723 -have in common a contradiction of the operational semantics of member function -test 20.6.2 [bitset.members] p.56-58 and the immutable -member operator[] overload 20.6.2 [bitset.members] p.64-66 (all references -are defined in terms of -N2723): -

- -
    -
  1. -bool test(size_t pos) const;
-
    -
    -

    -Requires: pos is valid -

    -

    -Throws: out_of_range if pos does not correspond -to a valid bit position. -

    -

    -Returns: true if the bit at position pos in *this -has the value one. -

    -
    -
    2. -
  2. -constexpr bool operator[](size_t pos) const;
-
    -
    -

    -Requires: pos shall be valid. -

    -

    -Throws: nothing. -

    -

    -Returns: test(pos). -

    -
    -
    3. -
- -

-Three interpretations: -

- -
    -
  1. -The operator[] overload is indeed allowed to throw an exception -(via test(), if pos corresponds to an invalid bit position) which does -not leave the call frame. In this case this function cannot be a -constexpr function, because test() is not, due to -5.20 [expr.const]/2, last bullet. -
    2. -
  2. -The intend was not to throw an exception in test in case of an -invalid bit position. There is only little evidence for this interpretation. -
    3. -
  3. -The intend was that operator[] should not throw any exception, -but that test has the contract to do so, if the provided bit position -is invalid. -
    4. -
- -

-The problem became worse, because issue 720 -recently voted into WP argued that member test logically must be -a constexpr function, because it was used to define the semantics -of another constexpr function (the operator[] overload). -

- -

-Three alternatives are proposed, corresponding to the three bullets -(A), (B), and (C), the author suggests to follow proposal (C). -

- -

-Proposed alternatives: -

- -
    -
  1. -

    -Remove the constexpr specifier in front of operator[] overload and -undo that of member test (assuming 720 is accepted) in both the -class declaration 20.6 [template.bitset]/1 and in the member description -before 20.6.2 [bitset.members]/56 and before /64 to read: -

    -
    -constexpr bool test(size_t pos) const;
-..
-constexpr bool operator[](size_t pos) const;
-
    - -

    -Change the throws clause of p. 65 to read: -

    - -

    -Throws: nothing -out_of_range if pos does not correspond to a valid bit -position. -

    -
    2. -
  2. -

    -Replace the throws clause p. 57 to read: -

    - -

    -Throws: out_of_range if pos does not correspond to a valid bit -position nothing. -

    -
    3. -
  3. -

    -Undo the addition of the constexpr specifier to the test member -function in both class declaration 20.6 [template.bitset]/1 and in the -member description before 20.6.2 [bitset.members]/56, assuming that 720 -was applied. -

    - -
    -constexpr bool test(size_t pos) const;
-
    - -

    -Change the returns clause p. 66 to read: -

    - -

    -Returns: test(pos) true if the bit at position pos in *this -has the value one, otherwise false. -

    -
    4. -
- -

[ -Post Summit: -]

- - -
-

-Lawrence: proposed resolutions A, B, C are mutually exclusive. -

-

-Recommend Review with option C. -

-
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

- -
    -
  1. […]
    2. -
  2. […]
    3. -
  3. -

    -Undo the addition of the constexpr specifier to the test member -function in both class declaration 20.6 [template.bitset] p.1 and in the -member description before 20.6.2 [bitset.members] p.56, assuming that 720 -was applied. -

    - -
    -constexpr bool test(size_t pos) const;
-
    - -

    -Change the returns clause p. 66 to read: -

    - -

    -Returns: test(pos) true if the bit at position pos in *this -has the value one, otherwise false. -

    -
    4. -
- - - - - - -
-

908. Deleted assignment operators for atomic types must be volatile

-

Section: X [atomics.types] Status: Resolved - Submitter: Anthony Williams Opened: 2008-09-26 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 90

- -

-The deleted copy-assignment operators for the atomic types are not -marked as volatile in N2723, whereas the assignment operators from the -associated non-atomic types are. e.g. -

-
-atomic_bool& operator=(atomic_bool const&) = delete;
-atomic_bool& operator=(bool) volatile;
-
- -

-This leads to ambiguity when assigning a non-atomic value to a -non-volatile instance of an atomic type: -

-
-atomic_bool b;
-b=false;
-
- -

-Both assignment operators require a standard conversions: the -copy-assignment operator can use the implicit atomic_bool(bool) -conversion constructor to convert false to an instance of -atomic_bool, or b can undergo a qualification conversion in order to -use the assignment from a plain bool. -

- -

-This is only a problem once issue 845 is applied. -

- -

[ -Summit: -]

- -

-Move to open. Assign to Lawrence. Related to US 90 comment. -

- -

[ -2009-08-17 Handled by -N2925. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

-

-Add volatile qualification to the deleted copy-assignment operator of -all the atomic types: -

- -
-atomic_bool& operator=(atomic_bool const&) volatile = delete;
-atomic_itype& operator=(atomic_itype const&) volatile = delete;
-
- -

-etc. -

-

-This will mean that the deleted copy-assignment operator will require -two conversions in the above example, and thus be a worse match than -the assignment from plain bool. -

- - - - - -
-

909. regex_token_iterator should use initializer_list

-

Section: 28.12.2 [re.tokiter] Status: C++11 - Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2015-04-08

-

View all other issues in [re.tokiter].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 319

-

-Construction of a regex_token_iterator (28.12.2 [re.tokiter]/6+) usually -requires the provision of a sequence of integer values, which -can currently be done via a std::vector<int> or -a C array of int. Since the introduction of initializer_list in the -standard it seems much more reasonable to provide a -corresponding constructor that accepts an initializer_list<int> -instead. This could be done as a pure addition or one could -even consider replacement. The author suggests the -replacement strategy (A), but provides an alternative additive -proposal (B) as a fall-back, because of the handiness of this -range type: -

- -

[ -Batavia (2009-05): -]

- -

-We strongly recommend alternative B of the proposed resolution -in order that existing code not be broken. -With that understanding, move to Tentatively Ready. -

- -

Original proposed wording:

- -
    -

  1. -
      -
    1. -

      -In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 change the -constructor declaration: -

      - -
      -template <std::size_t N>
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     const int (&submatches)[N] initializer_list<int> submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-
      -
      2. - -
    2. -

      -In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence -

      - -

      -The third constructor initializes the member subs to hold -a copy of the sequence of integer values pointed to by the -iterator range [&submatches.begin(), -&submatches.end() + N). -

      -
      3. -
    -
    2. - -

  2. -
      -
    1. -

      -In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 insert the -following constructor declaration between the already existing ones -accepting a std::vector and a C array of int, resp.: -

      - -
      -regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     initializer_list<int> submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-
      -
      2. -
    2. -

      -In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence -

      - -

      -The third and fourth constructor initializes the member subs -to hold a copy of the sequence of integer values pointed to -by the iterator range [&submatches,&submatches + N) -and [submatches.begin(),submatches.end()), respectively. -

      -
      3. -
    -
    3. - -
- - - -

Proposed resolution:

- -
    -
  1. […]
    2. -

  2. -
      -
    1. -

      -In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 insert the -following constructor declaration between the already existing ones -accepting a std::vector and a C array of int, resp.: -

      - -
      -regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     initializer_list<int> submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-
      -
      2. -
    2. -

      -In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence -

      - -

      -The third and fourth constructor initializes the member subs -to hold a copy of the sequence of integer values pointed to -by the iterator range [&submatches,&submatches + N) -and [submatches.begin(),submatches.end()), respectively. -

      -
      3. -
    -
    3. - -
- - - - - - -
-

911. I/O streams and move/swap semantic

-

Section: 27.7.2 [input.streams], 27.7.3 [output.streams] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2008-09-29 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Class template basic_istream, basic_ostream and basic_iostream -implements public move constructors, move assignment operators and swap -method and free functions. This might induce both the user and the -compiler to think that those types are MoveConstructible, MoveAssignable -and Swappable. However, those class templates fail to fulfill the user -expectations. For example: -

- -
-std::ostream os(std::ofstream("file.txt"));
-assert(os.rdbuf() == 0); // buffer object is not moved to os, file.txt has been closed
-
-std::vector<std::ostream> v;
-v.push_back(std::ofstream("file.txt"));
-v.reserve(100); // causes reallocation
-assert(v[0].rdbuf() == 0); // file.txt has been closed!
-
-std::ostream&& os1 = std::ofstream("file1.txt");
-os1 = std::ofstream("file2.txt");
-os1 << "hello, world"; // still writes to file1.txt, not to file2.txt!
-
-std::ostream&& os1 = std::ofstream("file1.txt");
-std::ostream&& os2 = std::ofstream("file2.txt");
-std::swap(os1, os2);
-os1 << "hello, world"; // writes to file1.txt, not to file2.txt!
-
- -

-This is because the move constructor, the move assignment operator and -swap are all implemented through calls to std::basic_ios member -functions move() and swap() that do not move nor swap the controlled -stream buffers. That can't happen because the stream buffers may have -different types. -

- -

-Notice that for basic_streambuf, the member function swap() is -protected. I believe that is correct and all of basic_istream, -basic_ostream, basic_iostream should do the same as the move ctor, move -assignment operator and swap member function are needed by the derived -fstreams and stringstreams template. The free swap functions for -basic_(i|o|io)stream templates should be removed for the same reason. -

- -

[ -Batavia (2009-05): -]

- -
-

-We note that the rvalue swap functions have already been removed. -

-

-Bill is unsure about making the affected functions protected; -he believes they may need to be public. -

-

-We are also unsure about removing the lvalue swap functions as proposed. -

-

-Move to Open. -

-
- -

[ -2009-07 Frankfurt: -]

- - -
-

-It's not clear that the use case is compelling. -

-

-Howard: This needs to be implemented and tested. -

-
- -

[ -2009-07-26 Howard adds: -]

- - -
-

-I started out thinking I would recommend NAD for this one. I've turned around -to agree with the proposed resolution (which I've updated to the current draft). -I did not fully understand Ganesh's rationale, and attempt to describe my -improved understanding below. -

- -

-The move constructor, move assignment operator, and swap function are different -for basic_istream, basic_ostream and basic_iostream -than other classes. A timely conversation with Daniel reminded me of this long -forgotten fact. These members are sufficiently different that they would be -extremely confusing to use in general, but they are very much needed for derived -clients. -

- -
    -
  • -The move constructor moves everything but the rdbuf pointer. -
    • -
  • -The move assignment operator moves everything but the rdbuf pointer. -
    • -
  • -The swap function swaps everything but the rdbuf pointer. -
    • -
- -

-The reason for this behavior is that for the std-derived classes (stringstreams, -filestreams), the rdbuf pointer points back into the class itself -(self referencing). It can't be swapped or moved. But this fact isn't born out -at the stream level. Rather it is born out at the fstream/sstream -level. And the lower levels just need to deal with that fact by not messing around -with the rdbuf pointer which is stored down at the lower levels. -

- -

-In a nutshell, it is very confusing for all of those who are not so intimately -related with streams that they've implemented them. And it is even fairly -confusing for some of those who have (including myself). I do not think it is -safe to swap or move istreams or ostreams because this will -(by necessary design) separate stream state from streambuffer state. Derived -classes (such as fstream and stringstream must be used to -keep the stream state and stream buffer consistently packaged as one unit during -a move or swap. -

- -

-I've implemented this proposal and am living with it day to day. -

- -
- -

[ -2009 Santa Cruz: -]

- - -

-Leave Open. Pablo expected to propose alternative wording which would rename -move construction, move assignment and swap, and may or may not make them -protected. This will impact issue 900. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

-

-27.7.2.1 [istream]: make the following member functions protected: -

- -
-basic_istream(basic_istream&&  rhs);
-basic_istream&  operator=(basic_istream&&  rhs);
-void  swap(basic_istream&  rhs);
-
- -

-Ditto: remove the swap free function signature -

- -
-// swap: 
-template <class charT, class traits> 
-  void swap(basic_istream<charT, traits>& x, basic_istream<charT, traits>& y);
-
- -

-27.7.2.1.2 [istream.assign]: remove paragraph 4 -

- -
-template <class charT, class traits> 
-  void swap(basic_istream<charT, traits>& x, basic_istream<charT, traits>& y);
-
-

-Effects: x.swap(y). -

-
- -

-27.7.2.5 [iostreamclass]: make the following member function protected: -

- -
-basic_iostream(basic_iostream&&  rhs);
-basic_iostream&  operator=(basic_iostream&&  rhs);
-void  swap(basic_iostream&  rhs);
-
- -

-Ditto: remove the swap free function signature -

- -
-template <class charT, class traits> 
-  void swap(basic_iostream<charT, traits>& x, basic_iostream<charT, traits>& y);
-
- -

-27.7.2.5.3 [iostream.assign]: remove paragraph 3 -

- -
-template <class charT, class traits> 
-  void swap(basic_iostream<charT, traits>& x, basic_iostream<charT, traits>& y);
-
-

-Effects: x.swap(y). -

-
- -

-27.7.3.1 [ostream]: make the following member function protected: -

- -
-basic_ostream(basic_ostream&&  rhs);
-basic_ostream&  operator=(basic_ostream&&  rhs);
-void  swap(basic_ostream&  rhs);
-
- -

-Ditto: remove the swap free function signature -

- -
-// swap: 
-template <class charT, class traits> 
-  void swap(basic_ostream<charT, traits>& x, basic_ostream<charT, traits>& y);
-
- -

-27.7.3.3 [ostream.assign]: remove paragraph 4 -

- -
-template <class charT, class traits> 
-  void swap(basic_ostream<charT, traits>& x, basic_ostream<charT, traits>& y);
-
-

-Effects: x.swap(y). -

-
- - - - - - -
-

920. Ref-qualification support in the library

-

Section: 20.9.11 [func.memfn] Status: C++11 - Submitter: Bronek Kozicki Opened: 2008-10-06 Last modified: 2015-04-08

-

View all other issues in [func.memfn].

-

View all issues with C++11 status.

-

Duplicate of: 1230

-

Discussion:

-

-Daniel Krügler wrote: -

- -
-

-Shouldn't above list be completed for &- and &&-qualified -member functions This would cause to add: -

-
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) &);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) const &);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) volatile &);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) const volatile &);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) &&);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) const &&);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) volatile &&);
-template<Returnable R, class T, CopyConstructible... Args>
-unspecified mem_fn(R (T::* pm)(Args...) const volatile &&);
-
- -
- -

-yes, absolutely. Thanks for spotting this. Without this change mem_fn -cannot be initialized from pointer to ref-qualified member function. I -believe semantics of such function pointer is well defined. -

- -

[ -Post Summit Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-We need to think about whether we really want to go down the proposed path -of combinatorial explosion. -Perhaps a Note would suffice. -

-

-We would really like to have an implementation before proceeding. -

-

-Move to Open, and recommend this be deferred until after the next -Committee Draft has been issued. -

-
- -

[ -2009-10-10 Daniel updated wording to post-concepts. -]

- - -

-1230 has a similar proposed resolution -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 20.9 [function.objects]/2, header -<functional> synopsis as follows: -

    - -
    -// 20.7.14, member function adaptors:
-template<class R, class T> unspecified mem_fn(R T::*);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...));
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile &);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile &&);
-
    -
    2. - -
  2. -

    -Change the prototype list of 20.9.11 [func.memfn] as follows [NB: The -following text, most notably p.2 and p.3 which -discuss influence of the cv-qualification on the definition of the -base class's first template parameter remains -unchanged. ]: -

    - -
    -template<class R, class T> unspecified mem_fn(R T::* pm);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...));
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile &);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile &);
-
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile &&);
-template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile &&);
-
    -
    3. - -
  3. -

    -Remove 20.9.11 [func.memfn]/5: -

    - -

    -Remarks: Implementations may implement mem_fn as a set of -overloaded function templates. -

    -
    4. -
- - - - - - -
-

921. Rational Arithmetic should use template aliases

-

Section: 20.11.3 [ratio.ratio] Status: C++11 - Submitter: Pablo Halpern Opened: 2008-10-07 Last modified: 2015-04-08

-

View all other issues in [ratio.ratio].

-

View all issues with C++11 status.

-

Discussion:

-

-The compile-time functions that operate on ratio<N,D> require the -cumbersome and error-prone "evaluation" of a type member using a -meta-programming style that predates the invention of template aliases. -Thus, multiplying three ratios a, b, and c requires the expression: -

- -
-ratio_multiply<a, ratio_multiply<b, c>::type>::type
-
- -

-The simpler expression: -

- -
-ratio_multiply<a, ratio_multiply<b, c>>
-
- -

-Could be used by if template aliases were employed in the definitions. -

- -

[ -Post Summit: -]

- - -
-

-Jens: not a complete proposed resolution: "would need to make similar change" -

-

-Consensus: We agree with the direction of the issue. -

-

-Recommend Open. -

-
- -

[ -2009-05-11 Daniel adds: -]

- - -
-

-Personally I'm not in favor for the addition of: -

-
-typedef ratio type;
-
-

-For a reader of the standard it's usage or purpose is unclear. I haven't -seen similar examples of attempts to satisfy non-feature complete compilers. -

-
- -

[ -2009-05-11 Pablo adds: -]

- - -
-

-The addition of type to the ratio template allows the previous style -(i.e., in the prototype implementations) to remain valid and permits the -use of transitional library implementations for C++03 compilers. I do -not feel strongly about its inclusion, however, and leave it up to the -reviewers to decide. -

-
- -

[ -Batavia (2009-05): -]

- -

-Bill asks for additional discussion in the issue -that spells out more details of the implementation. -Howard points us to issue 948 -which has at least most of the requested details. -Tom is strongly in favor of overflow-checking at compile time. -Pete points out that there is no change of functionality implied. -We agree with the proposed resolution, -but recommend moving the issue to Review -to allow time to improve the discussion if needed. -

- -

[ -2009-07-21 Alisdair adds: -]

- - -

-See 1121 for a potentially incompatible proposal. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- - -
    -
  1. -

    -In 20.11 [ratio] p.3 change as indicated: -

    - -
    -// ratio arithmetic
-template <class R1, class R2> structusing ratio_add = see below;
-template <class R1, class R2> structusing ratio_subtract = see below;
-template <class R1, class R2> structusing ratio_multiply = see below;
-template <class R1, class R2> structusing ratio_divide = see below;
-
    -
    2. -
  2. -

    -In 20.11.3 [ratio.ratio], change as indicated: -

    -
    -namespace std {
-  template <intmax_t N, intmax_t D = 1>
-  class ratio {
-  public:
-    typedef ratio type;
-    static const intmax_t num;
-    static const intmax_t den;
-  };
-}
-
    -
    3. -
  3. -

    -In 20.11.4 [ratio.arithmetic] change as indicated: -

    - -
    -template <class R1, class R2> structusing ratio_add = see below{
-  typedef see below type;
-};
-
    - -
    -

    -1 The nested typedef type ratio_add<R1, R2> -shall be a synonym for ratio<T1, T2> -where T1 has the value R1::num * R2::den + R2::num * R1::den and T2 -has the value R1::den * R2::den. -

    -
    -
    -
    -template <class R1, class R2> structusing ratio_subtract = see below{
-  typedef see below type;
-};
-
    -
    -

    -2 The nested typedef type ratio_subtract<R1, R2> -shall be a synonym for ratio<T1, T2> -where T1 has the value R1::num * R2::den - R2::num * R1::den and T2 -has the value R1::den * R2::den. -

    -
    -
    -
    -template <class R1, class R2> structusing ratio_multiply = see below{
-  typedef see below type;
-};
-
    -
    -

    -3 The nested typedef type ratio_multiply<R1, R2> -shall be a synonym for ratio<T1, T2> -where T1 has the value R1::num * R2::num and T2 has the value R1::den * R2::den. -

    -
    -
    -
    -template <class R1, class R2> structusing ratio_divide = see below{
-  typedef see below type;
-};
-
    -
    -

    -4 The nested typedef type ratio_divide<R1, R2> -shall be a synonym for ratio<T1, T2> -where T1 has the value R1::num * R2::den and T2 has the value R1::den * R2::num. -

    -
    -
    -
    4. -
  4. -

    -In 20.12.5.1 [time.duration.cons] p.4 change as indicated: -

    -
    -

    -Requires: treat_as_floating_point<rep>::value shall be true or -ratio_divide<Period2, period>::type::den shall be 1.[..] -

    -
    -
    5. -
  5. -

    -In 20.12.5.7 [time.duration.cast] p.2 change as indicated: -

    -
    -

    -Returns: Let CF be ratio_divide<Period, typename -ToDuration::period>::type, and [..] -

    -
    -
    6. -
- - - - - -
-

922. [func.bind.place] Number of placeholders

-

Section: B [implimits] Status: C++11 - Submitter: Sohail Somani Opened: 2008-10-11 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses DE 24

- -

-With respect to the section 20.9.10.4 [func.bind.place]: -

-

-TR1 dropped some suggested implementation quantities for the number of -placeholders. The purpose of this defect is to put these back for C++0x. -

- -

[ -Post Summit: -]

- - -
-

-see DE 24 -

-

-Recommend applying the proposed resolution from DE 24, with that -Tentatively Ready. -

-
-

-Original proposed resolution: -

-

-Add 20.9.10.4 [func.bind.place] p.2: -

- -

-While the exact number of placeholders (_M) is implementation defined, -this number shall be at least 10. -

- - - -

Proposed resolution:

- -

-Add to B [implimits]: -

- -
    -
  • -Number of placeholders (20.9.10.4 [func.bind.place]) [10]. -
    • -
- - - - - - -
-

923. atomics with floating-point

-

Section: 29 [atomics] Status: Resolved - Submitter: Herb Sutter Opened: 2008-10-17 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with Resolved status.

-

Discussion:

-

-Right now, C++0x doesn't have atomic<float>. We're thinking of adding -the words to support it for TR2 (note: that would be slightly post-C++0x). If we -need it, we could probably add the words. -

-

-Proposed resolutions: Using atomic<FP>::compare_exchange (weak or -strong) should be either: -

- -
    -
  1. -ill-formed, or -
    2. -
  2. -well-defined. -
    3. -
- -

-I propose Option 1 for C++0x for expediency. If someone wants to argue -for Option 2, they need to say what exactly they want compare_exchange -to mean in this case (IIRC, C++0x doesn't even assume IEEE 754). -

- -

[ -Summit: -]

- - -

-Move to open. Blocked until concepts for atomics are addressed. -

- -

[ -Post Summit Anthony adds: -]

- - -
-

-Recommend NAD. C++0x does have std::atomic<float>, and both -compare_exchange_weak and compare_exchange_strong are well-defined in -this case. Maybe change the note in 29.6 [atomics.types.operations] paragraph 20 to: -

- -
-

-[Note: The effect of the compare-and-exchange operations is -

-
-if (!memcmp(object,expected,sizeof(*object)))
-    *object = desired;
-else
-    *expected = *object;
-
- -

-This may result in failed comparisons for values that compare equal if -the underlying type has padding bits or alternate representations of -the same value. -- end note] -

-
- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

-

-Change the note in 29.6 [atomics.types.operations] paragraph 20 to: -

- -
-

-[Note: The effect of the compare-and-exchange operations is -

-
-if (*object == *expected !memcmp(object,expected,sizeof(*object)))
-    *object = desired;
-else
-    *expected = *object;
-
- -

-This may result in failed comparisons for values that compare equal if -the underlying type has padding bits or alternate representations of -the same value. -- end note] -

-
- - - - - - -
-

924. structs with internal padding

-

Section: 29 [atomics] Status: Resolved - Submitter: Herb Sutter Opened: 2008-10-17 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with Resolved status.

-

Discussion:

-

-Right now, the compare_exchange_weak loop should rapidly converge on the -padding contents. But compare_exchange_strong will require a bit more -compiler work to ignore padding for comparison purposes. -

-

-Note that this isn't a problem for structs with no padding, and we do -already have one portable way to ensure that there is no padding that -covers the key use cases: Have elements be the same type. I suspect that -the greatest need is for a structure of two pointers, which has no -padding problem. I suspect the second need is a structure of a pointer -and some form of an integer. If that integer is intptr_t, there will be -no padding. -

-

-Related but separable issue: For unused bitfields, or other unused -fields for that matter, we should probably say it's the programmer's -responsibility to set them to zero or otherwise ensure they'll be -ignored by memcmp. -

- -

-Proposed resolution: Using -atomic<struct-with-padding>::compare_exchange_strong should be either: -

- -
    -
  1. -ill-formed, or -
    2. -
  2. -well-defined. -
    3. -
- -

-I propose Option 1 for C++0x for expediency, though I'm not sure how to -say it. I would be happy with Option 2, which I believe would mean that -compare_exchange_strong would be implemented to avoid comparing padding -bytes, or something equivalent such as always zeroing out padding when -loading/storing/comparing. (Either implementation might require compiler -support.) -

- -

[ -Summit: -]

- - -

-Move to open. Blocked until concepts for atomics are addressed. -

- -

[ -Post Summit Anthony adds: -]

- - -

-The resolution of LWG 923 should resolve this issue as well. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

925. shared_ptr's explicit conversion from unique_ptr

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: C++11 - Submitter: Rodolfo Lima Opened: 2008-10-12 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

View all issues with C++11 status.

-

Discussion:

-

-The current working draft -(N2798), -section 20.8.2.2.1 [util.smartptr.shared.const] declares -shared_ptr's constructor that takes a rvalue reference to unique_ptr and -auto_ptr as being explicit, affecting several valid smart pointer use -cases that would take advantage of this conversion being implicit, for -example: -

- -
-class A;
-std::unique_ptr<A> create();
-void process(std::shared_ptr<A> obj);
-
-int main()
-{
-   process(create());                  // use case #1
-   std::unique_ptr<A> uobj = create();
-   process(std::move(uobj));           // use case #2
-   return 0;
-}
-
- -

-If unique_ptr to shared_ptr conversions are explicit, the above lines -should be written: -

- -
-process(std::shared_ptr<A>(create()));        // use case #1
-process(std::shared_ptr<A>(std::move(uobj))); // use case #2
-
- -

-The extra cast required doesn't seems to give any benefits to the user, -nor protects him of any unintended conversions, this being the raison -d'etre of explicit constructors. -

- -

-It seems that this constructor was made explicit to mimic the conversion -from auto_ptr in pre-rvalue reference days, which accepts both lvalue and -rvalue references. Although this decision was valid back then, C++0x -allows the user to express in a clear and non verbose manner when he wants -move semantics to be employed, be it implicitly (use case 1) or explicitly -(use case 2). -

- -

[ -Batavia (2009-05): -]

- -
-

-Howard and Alisdair like the motivating use cases -and the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-In both 20.8.2.2 [util.smartptr.shared] paragraph 1 and -20.8.2.2.1 [util.smartptr.shared.const] change: -

- -
-template <class Y> explicit shared_ptr(auto_ptr<Y> &&r);
-template <class Y, class D> explicit shared_ptr(unique_ptr<Y, D> &&r);
-
- - - - - - -
-

929. Thread constructor

-

Section: 30.3.1.2 [thread.thread.constr] Status: C++11 - Submitter: Anthony Williams Opened: 2008-10-23 Last modified: 2015-04-08

-

View all other issues in [thread.thread.constr].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 323

- -

-The thread constructor for starting a new thread with a function and -arguments is overly constrained by the signature requiring rvalue -references for func and args and the CopyConstructible requirements -for the elements of args. The use of an rvalue reference for the -function restricts the potential use of a plain function name, since -the type of the bound parameter will be deduced to be a function -reference and decay to pointer-to-function will not happen. This -therefore complicates the implementation in order to handle a simple -case. Furthermore, the use of rvalue references for args prevents the -array to pointer decay. Since arrays are not CopyConstructible or even -MoveConstructible, this essentially prevents the passing of arrays as -parameters. In particular it prevents the passing of string literals. -Consequently a simple case such as -

- -
-void f(const char*);
-std::thread t(f,"hello");
-
- -

-is ill-formed since the type of the string literal is const char[6]. -

- -

-By changing the signature to take all parameters by value we can -eliminate the CopyConstructible requirement and permit the use of -arrays, as the parameter passing semantics will cause the necessary -array-to-pointer decay. They will also cause the function name to -decay to a pointer to function and allow the implementation to handle -functions and function objects identically. -

- -

-The new signature of the thread constructor for a function and -arguments is thus: -

- -
-template<typename F,typename... Args>
-thread(F,Args... args);
-
- -

-Since the parameter pack Args can be empty, the single-parameter -constructor that takes just a function by value is now redundant. -

- -

[ -Howard adds: -]

- - -
-

-I agree with everything Anthony says in this issue. However I believe we -can optimize in such a way as to get the pass-by-value behavior with the -pass-by-rvalue-ref performance. The performance difference is that the latter -removes a move when passing in an lvalue. -

- -

-This circumstance is very analogous to make_pair (20.3 [pairs]) -where we started with passing by const reference, changed to pass by value to -get pointer decay, and then changed to pass by rvalue reference, but modified with -decay<T> to retain the pass-by-value behavior. If we were to -apply the same solution here it would look like: -

- -
-template <class F> explicit thread(F f);
-template <class F, class ...Args> thread(F&& f, Args&&... args);
-
-
-

--4- Requires: F and each Ti in Args shall be CopyConstructible -if an lvalue and otherwise MoveConstructible. -INVOKE(f, w1, w2, ..., wN) (20.9.2 [func.require]) shall be a valid expression for -some values w1, w2, ... , wN, where N == sizeof...(Args). -

-

--5- Effects: Constructs an object of type thread -and executes INVOKE(f, t1, t2, ..., tN) in a new -thread of execution, where t1, t2, ..., tN are the values in args.... -Constructs -the following objects in memory which is accessible to a new thread of execution -as if: -

-
-typename decay<F>::type g(std::forward<F>(f));
-tuple<typename decay<Args>::type...> w(std::forward<Args>(args)...);
-
-

-The new thread of -execution executes INVOKE(g, wi...) where the wi... refers -to the elements stored in the tuple w. -Any return value from g is ignored. -If f terminates with an uncaught exception, std::terminate() shall be called. -If the evaluation of INVOKE(g, wi...) terminates -with an uncaught exception, std::terminate() shall be called [Note: -std::terminate() could be called before entering g. -- end note]. Any -exception thrown before the evaluation of INVOKE has started shall be -catchable in the calling thread. -

-
-
- -

-Text referring to when terminate() is called was contributed by Ganesh. -

- -
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution, -but would like the final sentence to be reworded -since "catchable" is not a term of art (and is used nowhere else). -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-This is linked to -N2901. -

-

-Howard to open a separate issue to remove (1176). -

-

-In Frankfurt there is no consensus for removing the variadic constructor. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-We want to move forward with this issue. If we later take it out via 1176 -then that's ok too. Needs small group to improve wording. -

- -

[ -2009-10 Santa Cruz: -]

- - -
-

-Stefanus provided revised wording. Moved to Review Here is the original wording: -

-
-

-Modify the class definition of std::thread in 30.3.1 [thread.thread.class] to remove the -following signature: -

- -
-template<class F> explicit thread(F f);
-template<class F, class ... Args> explicit thread(F&& f, Args&& ... args);
-
- -

-Modify 30.3.1.2 [thread.thread.constr] to replace the constructors prior to paragraph 4 with -the single constructor as above. Replace paragraph 4 - 6 with the -following: -

- -
-

--4- Requires: F and each Ti in Args shall be CopyConstructible -if an lvalue and otherwise MoveConstructible. -INVOKE(f, w1, w2, ..., wN) (20.9.2 [func.require]) shall be a valid expression for -some values w1, w2, ... , wN, where N == sizeof...(Args). -

-

--5- Effects: Constructs an object of type thread -and executes INVOKE(f, t1, t2, ..., tN) in a new -thread of execution, where t1, t2, ..., tN are the values in args.... -Constructs -the following objects: -

-
-typename decay<F>::type g(std::forward<F>(f));
-tuple<typename decay<Args>::type...> w(std::forward<Args>(args)...);
-
-

-and executes INVOKE(g, wi...) in a new thread of execution. -These objects shall be destroyed when the new thread of execution completes. -Any return value from g is ignored. -If f terminates with an uncaught exception, std::terminate() shall be called. -If the evaluation of INVOKE(g, wi...) terminates -with an uncaught exception, std::terminate() shall be called [Note: -std::terminate() could be called before entering g. -- end note]. Any -exception thrown before the evaluation of INVOKE has started shall be -catchable in the calling thread. -

-

--6- Synchronization: The invocation of the constructor happens before the -invocation of f g. -

-
- -
-
- -

[ -2010-01-19 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Modify the class definition of std::thread in 30.3.1 [thread.thread.class] to remove the -following signature: -

- -
-template<class F> explicit thread(F f);
-template<class F, class ... Args> explicit thread(F&& f, Args&& ... args);
-
- -

-Modify 30.3.1.2 [thread.thread.constr] to replace the constructors prior to paragraph 4 with -the single constructor as above. Replace paragraph 4 - 6 with the -following: -

- -
-

-Given a function as follows: -

- -

-template<typename T> typename decay<T>::type decay_copy(T&& v)
-    { return std::forward<T>(v); }
-
- -

--4- Requires: F and each Ti in Args shall -be CopyConstructible if an lvalue and otherwise satisfy -the MoveConstructible requirements. -INVOKE(f, w1, w2, ..., wN) (20.9.2 [func.require]) -shall be a valid expression for some values w1, w2, ... , wN, where -N == sizeof...(Args). -INVOKE(decay_copy(std::forward<F>(f)), decay_copy(std::forward<Args>(args))...) (20.9.2 [func.require]) shall be a valid expression. -

- -

--5- Effects: Constructs an object of type thread and executes -INVOKE(f, t1, t2, ..., tN) in a new thread of execution, where -t1, t2, ..., tN are the values in args.... -Any return -value from f is ignored. If f terminates with an -uncaught exception, std::terminate() shall be called. -The new thread of execution executes INVOKE(decay_copy(std::forward<F>(f)), -decay_copy(std::forward<Args>(args))...) with the calls to decay_copy() being evaluated in -the constructing thread. Any return value from this invocation is -ignored. [Note: this implies any exceptions not thrown from the -invocation of the copy of f will be thrown in the constructing thread, -not the new thread. — end note]. -If the invocation of INVOKE(decay_copy(std::forward<F>(f)), -decay_copy(std::forward<Args>(args))...) terminates with an uncaught -exception, std::terminate shall be called. -

- -

--6- Synchronization: The invocation of the constructor happens before the -invocation of the copy of f. -

-
- - - - - - -
-

931. type trait extent<T, I>

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++11 - Submitter: Yechezkel Mett Opened: 2008-11-04 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

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-

Discussion:

-

-The draft (N2798) says in 20.10.4.3 [meta.unary.prop] Table 44: -

-
- - - - - - - -
Table 44 -- Type property queries
TemplateValue
-template <class T, unsigned I = 0> struct extent; - -If T is not an array type (8.3.4), or if it has rank less than -I, or if I is 0 -and T has type "array of unknown bound of U", then 0; otherwise, the -size of the I'th dimension of T -
-
- -

-Firstly it isn't clear from the wording if I is 0-based or 1-based -("the I'th dimension" sort of implies 1-based). From the following -example it is clear that the intent is 0-based, in which case it -should say "or if it has rank less than or equal to I". -

-

-Sanity check: -

-

-The example says assert((extent<int[2], 1>::value) == 0); -

-

-Here the rank is 1 and I is 1, but the desired result is 0. -

- -

[ -Post Summit: -]

- - -
-

-Do not use "size" or "value", use "bound". Also, move the -cross-reference to 8.3.4 to just after "bound". -

-

-Recommend Tentatively Ready. -

-
- - - -

Proposed resolution:

-

-In Table 44 of 20.10.4.3 [meta.unary.prop], third row, column "Value", -change the cell content: -

- -
- - - - - - - -
Table 44 -- Type property queries
TemplateValue
-template <class T, unsigned I = 0> struct extent; - -If T is not an array type (8.3.4), or if it has rank less than - or equal to I, or if I is 0 -and T has type "array of unknown bound of U", then 0; otherwise, the -size bound (8.3.4) of the I'th dimension of T, -where indexing of I is zero-based. -
-
- -

[ -Wording supplied by Daniel. -]

- - - - - - - -
-

932. unique_ptr(pointer p) for pointer deleter types

-

Section: 20.8.1.2.1 [unique.ptr.single.ctor] Status: Resolved - Submitter: Howard Hinnant Opened: 2008-11-26 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.ctor].

-

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-

Discussion:

- -

Addresses US 79

- -

-20.8.1.2.1 [unique.ptr.single.ctor]/5 no longer requires for D -not to be a pointer type. I believe this restriction was accidently removed -when we relaxed the completeness reuqirements on T. The restriction -needs to be put back in. Otherwise we have a run time failure that could -have been caught at compile time: -

- -
-{
-unique_ptr<int, void(*)(void*)> p1(malloc(sizeof(int)));  // should not compile
-}  // p1.~unique_ptr() dereferences a null function pointer
-unique_ptr<int, void(*)(void*)> p2(malloc(sizeof(int)), free);  // ok
-
- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -improved for enable_if type constraining, possibly following Robert's -formula. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-We need to consider whether some requirements in the Requires paragraphs -of [unique.ptr] should instead be Remarks. -

-

-Leave Open. Howard to provide wording, and possibly demonstrate how this -can be implemented using enable_if. -

-
- -

[ -2009-07-27 Howard adds: -]

- - -
-

-The two constructors to which this issue applies are not easily constrained -with enable_if as they are not templated: -

- -
-unique_ptr();
-explicit unique_ptr(pointer p);
-
- -

-To "SFINAE" these constructors away would take heroic effort such as specializing -the entire unique_ptr class template on pointer deleter types. There -is insufficient motivation for such heroics. Here is the expected and -reasonable implementation for these constructors: -

- -
-unique_ptr()
-    : ptr_(pointer())
-    {
-        static_assert(!is_pointer<deleter_type>::value,
-            "unique_ptr constructed with null function pointer deleter");
-    }
-explicit unique_ptr(pointer p)
-    : ptr_(p)
-    {
-        static_assert(!is_pointer<deleter_type>::value,
-            "unique_ptr constructed with null function pointer deleter");
-    }
-
- -

-I.e. just use static_assert to verify that the constructor is not -instantiated with a function pointer for a deleter. The compiler will automatically -take care of issuing a diagnostic if the deleter is a reference type (uninitialized -reference error). -

- -

-In keeping with our discussions in Frankfurt, I'm moving this requirement on -the implementation from the Requires paragraph to a Remarks paragraph. -

- -
- -

[ -2009-08-17 Daniel adds: -]

- - -
-

-It is insufficient to require a diagnostic. This doesn't imply an -ill-formed program -as of 1.3 [defns.diagnostic] (a typical alternative would be a compiler -warning), but -exactly that seems to be the intend. I suggest to use the following -remark instead: -

- -

-Remarks: The program shall be ill-formed if this constructor is -instantiated when D is a pointer type or reference type. -

- -

-Via the general standard rules of 1.4 [intro.compliance] the "diagnostic -required" is implied. -

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- -

[ -2010-03-14 Howard adds: -]

- - -

-We moved -N3073 -to the formal motions page in Pittsburgh which should obsolete this issue. I've -moved this issue to NAD Editorial, solved by N3073. -

- - - -

Rationale:

-

-Solved by N3073. -

- - -

Proposed resolution:

-

-Change the description of the default constructor in 20.8.1.2.1 [unique.ptr.single.ctor]: -

- -
-unique_ptr();
-
-
-

--1- Requires: D shall be default constructible, and that construction -shall not throw an exception. D shall -not be a reference type or pointer type (diagnostic required). -

-

...

-

-Remarks: The program shall be ill-formed if this constructor is -instantiated when D is a pointer type or reference type. -

-
-
- -

-Add after 20.8.1.2.1 [unique.ptr.single.ctor]/8: -

- -
-unique_ptr(pointer p);
-
-
-

...

-

-Remarks: The program shall be ill-formed if this constructor is -instantiated when D is a pointer type or reference type. -

-
-
- - - - - -
-

934. duration is missing operator%

-

Section: 20.12.5 [time.duration] Status: C++11 - Submitter: Terry Golubiewski Opened: 2008-11-30 Last modified: 2015-04-08

-

View all other issues in [time.duration].

-

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-

Discussion:

- -

Addresses US 81

- -

-duration is missing operator%. This operator is convenient -for computing where in a time frame a given duration lies. A -motivating example is converting a duration into a "broken-down" -time duration such as hours::minutes::seconds: -

- -
-class ClockTime
-{
-    typedef std::chrono::hours hours;
-    typedef std::chrono::minutes minutes;
-    typedef std::chrono::seconds seconds;
-public:
-    hours hours_;
-    minutes minutes_;
-    seconds seconds_;
-
-    template <class Rep, class Period>
-      explicit ClockTime(const std::chrono::duration<Rep, Period>& d)
-        : hours_  (std::chrono::duration_cast<hours>  (d)),
-          minutes_(std::chrono::duration_cast<minutes>(d % hours(1))),
-          seconds_(std::chrono::duration_cast<seconds>(d % minutes(1)))
-          {}
-};
-
- -

[ -Summit: -]

- - -

-Agree except that there is a typo in the proposed resolution. The member -operators should be operator%=. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -improved for enable_if type constraining, possibly following Robert's -formula. -

- -

[ -2009-07 Frankfurt: -]

- - -
-

-Howard to open a separate issue (1177) to handle the removal of member -functions from overload sets, provide wording, and possibly demonstrate -how this can be implemented using enable_if (see 947). -

-

-Move to Ready. -

-
- - - -

Proposed resolution:

-

-Add to the synopsis in 20.12 [time]: -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator%(const duration<Rep1, Period>& d, const Rep2& s);
-template <class Rep1, class Period1, class Rep2, class Period2>
-  typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
-  operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-
- -

-Add to the synopsis of duration in 20.12.5 [time.duration]: -

- -
-template <class Rep, class Period = ratio<1>>
-class duration {
-public:
-  ...
-  duration& operator%=(const rep& rhs);
-  duration& operator%=(const duration& d);
-  ...
-};
-
- -

-Add to 20.12.5.3 [time.duration.arithmetic]: -

- -
-
-duration& operator%=(const rep& rhs);
-
-
-

-Effects: rep_ %= rhs. -

-

-Returns: *this. -

-
- -
-duration& operator%=(const duration& d);
-
-
-

-Effects: rep_ %= d.count(). -

-

-Returns: *this. -

-
-
- -

-Add to 20.12.5.5 [time.duration.nonmember]: -

- -
- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator%(const duration<Rep1, Period>& d, const Rep2& s);
-
-
-

-Requires: Rep2 shall be implicitly convertible to CR(Rep1, Rep2) and -Rep2 shall not be an instantiation of duration. Diagnostic required. -

-

-Returns: duration<CR, Period>(d) %= s. -

-
- -
-template <class Rep1, class Period1, class Rep2, class Period2>
-  typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
-  operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-
-
-

-Returns: common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type(lhs) %= rhs. -

-
- -
- - - - - - -
-

938. default_delete<T[]>::operator() should only accept T*

-

Section: 20.8.1.1.3 [unique.ptr.dltr.dflt1] Status: C++11 - Submitter: Howard Hinnant Opened: 2008-12-07 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Consider: -

- -
-derived* p = new derived[3];
-std::default_delete<base[]> d;
-d(p);  // should fail
-
- -

-Currently the marked line is a run time failure. We can make it a compile -time failure by "poisoning" op(U*). -

- -

[ -Post Summit: -]

- - -

-Recommend Review. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Add to 20.8.1.1.3 [unique.ptr.dltr.dflt1]: -

- -
-namespace std {
-  template <class T> struct default_delete<T[]> {
-    void operator()(T*) const;
-  template <class U> void operator()(U*) const = delete;
-};
-}
-
- - - - - -
-

939. Problem with std::identity and reference-to-temporaries

-

Section: 20.2.4 [forward] Status: C++11 - Submitter: Alisdair Meredith Opened: 2008-12-11 Last modified: 2015-04-08

-

View all other issues in [forward].

-

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-

Discussion:

-

-std::identity takes an argument of type T const & -and returns a result of T const &. -

-

-Unfortunately, this signature will accept a value of type other than T that -is convertible-to-T, and then return a reference to the dead temporary. The -constraint in the concepts version simply protects against returning -reference-to-void. -

-

-Solutions: -

-
-

-i/ Return-by-value, potentially slicing bases and rejecting non-copyable -types -

-

-ii/ Provide an additional overload: -

-
-template< typename T >
-template operator( U & ) = delete;
-
-

-This seems closer on intent, but moves beyond the original motivation for -the operator, which is compatibility with existing (non-standard) -implementations. -

-

-iii/ Remove the operator() overload. This restores the original definition -of the identity, although now effectively a type_trait rather than part of -the perfect forwarding protocol. -

-

-iv/ Remove std::identity completely; its original reason to exist is -replaced with the IdentityOf concept. -

-
-

-My own preference is somewhere between (ii) and (iii) - although I stumbled -over the issue with a specific application hoping for resolution (i)! -

- -

[ -Batavia (2009-05): -]

- -
-

-We dislike options i and iii, and option ii seems like overkill. -If we remove it (option iv), implementers can still provide it under a -different name. -

-

-Move to Open pending wording (from Alisdair) for option iv. -

-
- -

[ -2009-05-23 Alisdair provided wording for option iv. -]

- - -

[ -2009-07-20 Alisdair adds: -]

- - -
-

-I'm not sure why this issue was not discussed at Frankfurt (or I missed -the discussion) but the rationale is now fundamentally flawed. With the -removal of concepts, std::identity again becomes an important library -type so we cannot simply remove it. -

-

-At that point, we need to pick one of the other suggested resolutions, -but have no guidance at the moment. -

-
- -

[ -2009-07-20 Howard adds: -]

- - -
-

-I believe the rationale for not addressing this issue in Frankfurt was that it did -not address a national body comment. -

-

-I also believe that removal of identity is still a practical option as -my latest reformulation of forward, which is due to comments suggested -at Summit, no longer uses identity. :-) -

- -
-template <class T, class U,
-    class = typename enable_if
-            <
-                !is_lvalue_reference<T>::value || 
-                 is_lvalue_reference<T>::value &&
-                 is_lvalue_reference<U>::value
-            >::type,
-    class = typename enable_if
-            <
-                is_same<typename remove_all<T>::type,
-                        typename remove_all<U>::type>::value
-            >::type>
-inline
-T&&
-forward(U&& t)
-{
-    return static_cast<T&&>(t);
-
-}
-
- -

[ -The above code assumes acceptance of 1120 for the definition of -remove_all. This is just to make the syntax a little more palatable. -Without this trait the above is still very implementable. -]

- - -
- -

-Paper with rationale is on the way ... really, I promise this time! ;-) -

-
- -

[ -2009-07-30 Daniel adds: See 823 for an alternative resolution. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. Howard will update proposed wording to reflect current draft. -

- - - -

Proposed resolution:

-

-Strike from 20.2 [utility]: -

- -
-template <class T> struct identity;
-
- -

-Remove from 20.2.4 [forward]: -

- -
-
-template <class T> struct identity {
-  typedef T type;
-
-  const T& operator()(const T& x) const;
-};
-
-const T& operator()(const T& x) const;
-
-

--2- Returns: x -

-
- - - - - - -
-

940. std::distance

-

Section: 24.4.4 [iterator.operations] Status: Resolved - Submitter: Thomas Opened: 2008-12-14 Last modified: 2015-04-08

-

View all other issues in [iterator.operations].

-

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-

Discussion:

- -

Addresses UK 270

- -

-Regarding the std::distance - function, 24.4.4 [iterator.operations] -p.4 says: -

-

-Returns the number of increments or decrements needed to get from first to last. -

-

-This sentence is completely silent about the sign of the return value. -24.4.4 [iterator.operations] p.1 gives more information about the -underlying operations, but again no inferences about the sign can be made. -Strictly speaking, that is taking that sentence literally, I think this -sentence even implies a positive return value in all cases, as the -number of increments or decrements is clearly a ratio scale variable, -with a natural zero bound. -

-

-Practically speaking, my implementations did what common sense and -knowledge based on pointer arithmetic forecasts, namely a positive sign -for increments (that is, going from first to last by operator++), and a -negative sign for decrements (going from first to last by operator--). -

-

-Here are my two questions: -

-

-First, is that paragraph supposed to be interpreted in the way what I -called 'common sense', that is negative sign for decrements ? I am -fairly sure that's the supposed behavior, but a double-check here in -this group can't hurt. -

-

-Second, is the present wording (2003 standard version - no idea about -the draft for the upcoming standard) worth an edit to make it a bit more -sensible, to mention the sign of the return value explicitly ? -

- -

[ -Daniel adds: -]

- - -
-

-My first thought was that resolution 204 would already cover the -issue report, but it seems that current normative wording is in -contradiction to that resolution: -

- -

-Referring to -N2798, -24.4.4 [iterator.operations]/ p.4 says: -

- -

-Effects: Returns the number of increments or decrements needed to get -from first to last. -

- -

-IMO the part " or decrements" is in contradiction to p. 5 which says -

- -

-Requires: last shall be reachable from first. -

- -

-because "reachable" is defined in X [iterator.concepts]/7 as -

- -

-An iterator j is called reachable from an iterator i if and only if -there is a finite sequence of applications of the expression ++i that makes -i == j.[..] -

- -

-Here is wording that would be consistent with this definition of "reachable": -

- -

-Change 24.4.4 [iterator.operations] p4 as follows: -

- -

-Effects: Returns the number of increments or decrements -needed to get from first to last. -

- -
- -

-Thomas adds more discussion and an alternative view point -here. -

- -

[ -Summit: -]

- - -

-The proposed wording below was verbally agreed to. Howard provided. -

- -

[ -Batavia (2009-05): -]

- -
-

-Pete reports that a recent similar change has been made -for the advance() function. -

-

-We agree with the proposed resolution. -Move to Tentatively Ready. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Leave Open pending arrival of a post-Concepts WD. -

- -

[ -2009-10-14 Daniel provided de-conceptified wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready, replacing the Effects clause in the proposed wording with -"If InputIterator meets the requirements of random access iterator then -returns (last - first), otherwise returns the number of increments -needed to get from first to list.". -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3066. -

- - -

Proposed resolution:

-
    -
  1. -

    -Change 24.2.7 [random.access.iterators], Table 105 as indicated [This change is not -essential but it simplifies the specification] for the row with expression "b - a" -and the column Operational semantics: -

    - -
    -(a < b) ? distance(a,b)
-: -distance(b,a)
-
    -
    2. - -
  2. -

    -Change 24.4.4 [iterator.operations]/4+5 as indicated: -

    - -
    -template<class InputIterator>
-  typename iterator_traits<InputIterator>::difference_type
-    distance(InputIterator first, InputIterator last);
-
    -
    -

    -4 Effects: If InputIterator meets the requirements -of random access iterator then returns (last - first), -otherwise Rreturns the number of increments -or decrements needed to get from first to -last. -

    - -

    -5 Requires: If InputIterator meets the requirements -of random access iterator then last shall be reachable from -first or first shall be reachable from last, -otherwise last shall be reachable from first. -

    -
    -
    -
    3. -
- - - - - - - - - -
-

943. ssize_t undefined

-

Section: X [atomics.types.address] Status: C++11 - Submitter: Holger Grund Opened: 2008-12-19 Last modified: 2015-04-08

-

View all other issues in [atomics.types.address].

-

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-

Discussion:

-

-There is a row in "Table 122 - Atomics for standard typedef types" -in X [atomics.types.integral] with atomic_ssize_t -and ssize_t. Unless, I'm missing something ssize_t -is not defined by the standard. -

- -

[ -Summit: -]

- - -

-Move to review. Proposed resolution: Remove the typedef. Note: ssize_t -is a POSIX type. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Remove the row containing ssize_t from Table 119 -"Atomics for standard typedef types" in X [atomics.types.address]. -

- - - - - -
-

944. atomic<bool> derive from atomic_bool?

-

Section: 29.5 [atomics.types.generic] Status: Resolved - Submitter: Holger Grund Opened: 2008-12-19 Last modified: 2015-04-08

-

View other active issues in [atomics.types.generic].

-

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-

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-

Discussion:

-

-I think it's fairly obvious that atomic<bool> is supposed to be derived -from atomic_bool (and otherwise follow the atomic<integral> interface), -though I think the current wording doesn't support this. I raised this -point along with atomic<floating-point> privately with Herb and I seem -to recall it came up in the resulting discussion on this list. However, -I don't see anything on the current libs issue list mentioning this -problem. -

- -

-29.5 [atomics.types.generic]/3 reads -

- -

-There are full specializations over the integral types on the atomic -class template. For each integral type integral in the second column of -table 121 or table 122, the specialization atomic<integral> shall be -publicly derived from the corresponding atomic integral type in the -first column of the table. These specializations shall have trivial -default constructors and trivial destructors. -

- -

-Table 121 does not include (atomic_bool, bool), -so that this should probably be mentioned explicitly in the quoted paragraph. -

- -

[ -Summit: -]

- - -

-Move to open. Lawrence will draft a proposed resolution. Also, ask -Howard to fix the title. -

- -

[ -Post Summit Anthony provided proposed wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

-

-Replace paragraph 3 in 29.5 [atomics.types.generic] with -

- -

--3- There are full specializations over the integral types on the atomic -class template. For each integral type integral in the second column of -table 121 or table 122, the specialization atomic<integral> shall be -publicly derived from the corresponding atomic integral type in the first -column of the table. -In addition, the specialization atomic<bool> -shall be publicly derived from atomic_bool. -These specializations shall have trivial default -constructors and trivial destructors. -

- - - - - -
-

947. duration arithmetic: contradictory requirements

-

Section: 20.12.5.5 [time.duration.nonmember] Status: Resolved - Submitter: Pete Becker Opened: 2008-12-20 Last modified: 2015-04-08

-

View all other issues in [time.duration.nonmember].

-

View all issues with Resolved status.

-

Discussion:

-

-In 20.12.5.5 [time.duration.nonmember], paragraph 8 says that calling -dur / rep when rep is an instantiation of duration -requires a diagnostic. That's followed by an operator/ that takes -two durations. So dur1 / dur2 is legal under the second version, -but requires a diagnostic under the first. -

- -

[ -Howard adds: -]

- - -

-Please see the thread starting with c++std-lib-22980 for more information. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, pending proposed wording (and preferably an implementation). -

- -

[ -2009-07-27 Howard adds: -]

- - -
-

-I've addressed this issue under the proposed wording for 1177 which -cleans up several places under 20.12.5 [time.duration] which used the -phrase "diagnostic required". -

-

-For clarity's sake, here is an example implementation of the constrained operator/: -

- -
-template <class _Duration, class _Rep, bool = __is_duration<_Rep>::value>
-struct __duration_divide_result
-{
-};
-
-template <class _Duration, class _Rep2,
-    bool = is_convertible<_Rep2,
-                          typename common_type<typename _Duration::rep, _Rep2>::type>::value>
-struct __duration_divide_imp
-{
-};
-
-template <class _Rep1, class _Period, class _Rep2>
-struct __duration_divide_imp<duration<_Rep1, _Period>, _Rep2, true>
-{
-    typedef duration<typename common_type<_Rep1, _Rep2>::type, _Period> type;
-};
-
-template <class _Rep1, class _Period, class _Rep2>
-struct __duration_divide_result<duration<_Rep1, _Period>, _Rep2, false>
-    : __duration_divide_imp<duration<_Rep1, _Period>, _Rep2>
-{
-};
-
-template <class _Rep1, class _Period, class _Rep2>
-inline
-typename __duration_divide_result<duration<_Rep1, _Period>, _Rep2>::type
-operator/(const duration<_Rep1, _Period>& __d, const _Rep2& __s)
-{
-    typedef typename common_type<_Rep1, _Rep2>::type _Cr;
-    duration<_Cr, _Period> __r = __d;
-    __r /= static_cast<_Cr>(__s);
-    return __r;
-}
-
- -

-__duration_divide_result is basically a custom-built enable_if -that will contain type only if Rep2 is not a duration -and if Rep2 is implicitly convertible to -common_type<typename Duration::rep, Rep2>::type. __is_duration -is simply a private trait that answers false, but is specialized for -duration to answer true. -

- -

-The constrained operator% works identically. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark NAD EditorialResolved, fixed by 1177. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

948. ratio arithmetic tweak

-

Section: 20.11.4 [ratio.arithmetic] Status: C++11 - Submitter: Howard Hinnant Opened: 2008-12-26 Last modified: 2015-04-08

-

View all other issues in [ratio.arithmetic].

-

View all issues with C++11 status.

-

Discussion:

-

-N2800, -20.11.4 [ratio.arithmetic] lacks a paragraph from the proposal -N2661: -

- -
-

ratio arithmetic [ratio.arithmetic]

- -

-... If the implementation is unable to form the indicated ratio due to -overflow, a diagnostic shall be issued. -

-
- -

-The lack of a diagnostic on compile-time overflow is a significant lack of -functionality. This paragraph could be put back into the WP simply editorially. -However in forming this issue I realized that we can do better than that. This -paragraph should also allow alternative formulations which go to extra lengths -to avoid overflow when possible. I.e. we should not mandate overflow when the -implementation can avoid it. -

- -

-For example: -

- -
-
-template <class R1, class R2> struct ratio_multiply {
-  typedef see below} type; 
-
- -

-The nested typedef type shall be a synonym for ratio<T1, T2> where -T1 has the value R1::num * R2::num and T2 has the -value R1::den * R2::den. -

- -
- -

-Consider the case where intmax_t is a 64 bit 2's complement signed integer, -and we have: -

- -
-typedef std::ratio<0x7FFFFFFFFFFFFFFF, 0x7FFFFFFFFFFFFFF0> R1;
-typedef std::ratio<8, 7> R2;
-typedef std::ratio_multiply<R1, R2>::type RT;
-
- -

-According to the present formulation the implementaiton will multiply -0x7FFFFFFFFFFFFFFF * 8 which will result in an overflow and subsequently -require a diagnostic. -

- -

-However if the implementation is first allowed to divde 0x7FFFFFFFFFFFFFFF -by 7 obtaining 0x1249249249249249 / 1 and divide -8 by 0x7FFFFFFFFFFFFFF0 obtaining 1 / 0x0FFFFFFFFFFFFFFE, -then the exact result can then be computed without overflow: -

- -
-[0x7FFFFFFFFFFFFFFF/0x7FFFFFFFFFFFFFF0] * [8/7] = [0x1249249249249249/0x0FFFFFFFFFFFFFFE]
-
- -

-Example implmentation which accomplishes this: -

- -
-template <class R1, class R2>
-struct ratio_multiply
-{
-private:
-    typedef ratio<R1::num, R2::den> _R3;
-    typedef ratio<R2::num, R1::den> _R4;
-public:
-    typedef ratio<__ll_mul<_R3::num, _R4::num>::value,
-                  __ll_mul<_R3::den, _R4::den>::value> type;
-};
-
- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- - - - -

Proposed resolution:

-

-Add a paragraph prior to p1 in 20.11.4 [ratio.arithmetic]: -

- -

-Implementations may use other algorithms to compute the indicated ratios to avoid overflow. -If overflow occurs, a diagnostic shall be issued. -

- - - - - -
-

949. owner_less

-

Section: 20.8.2.4 [util.smartptr.ownerless] Status: C++11 - Submitter: Thomas Plum Opened: 2008-12-30 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-20.8.2.4 [util.smartptr.ownerless] (class template owner_less) says that -operator()(x,y) shall return x.before(y). -

-

-However, shared_ptr and weak_ptr have an owner_before() but not a -before(), and there's no base class to provide a missing before(). -

-

-Being that the class is named owner_less , I'm guessing that -"before()" should be "owner_before()", right? -

- -

[ -Herve adds: -]

- - -

-Agreed with the typo, it should be "shall return x.owner_before(y)". -

- -

[ -Post Summit: -]

- - -

-Recommend Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change 20.8.2.4 [util.smartptr.ownerless] p2: -

- -

--2- operator()(x,y) shall return -x.owner_before(y). [Note: ... -

- - - - - -
-

950. unique_ptr converting ctor shouldn't accept array form

-

Section: 20.8.1.2.1 [unique.ptr.single.ctor] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.ctor].

-

View all issues with Resolved status.

-

Discussion:

-

-unique_ptr's of array type should not convert to -unique_ptr's which do not have an array type. -

- -
-struct Deleter
-{
-   void operator()(void*) {}
-};
-
-int main()
-{
-   unique_ptr<int[], Deleter> s;
-   unique_ptr<int, Deleter> s2(std::move(s));  // should not compile
-}
-
- -

[ -Post Summit: -]

- - -
-

-Walter: Does the "diagnostic required" apply to both arms of the "and"? -

-

-Tom Plum: suggest to break into several sentences -

-

-Walter: suggest "comma" before the "and" in both places -

-

-Recommend Review. -

-
- -

[ -Batavia (2009-05): -]

- -

-The post-Summit comments have been applied to the proposed resolution. -We now agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -improved for enable_if type constraining, possibly following Robert's -formula. -

- -

[ -2009-08-01 Howard updates wording and sets to Review. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2010-02-27 Pete Opens: -]

- - -
-

-The proposed replacement text doesn't make sense. -

- -

-If D is a reference type, then E shall be the same type as -D, else this constructor shall not participate in overload resolution. -

- -

-This imposes two requirements. 1. If D is a reference type, E -has to be D. 2. If D is not a reference type, the constructor -shall not participate in overload resolution. If the latter apples, the language -in the preceding paragraph that this constructor shall not throw an exception if -D is not a reference type is superfluous. I suspect that's not the -intention, but I can't parse this text any other way. -

- -

-U shall not be an array type, else this constructor shall not -participate in overload resolution. -

- -

-I don't know what this means. -

-
- -

[ -2010-02-27 Peter adds: -]

- - -
-

-I think that the intent is (proposed text): -

- -
-

-Remarks: this constructor shall only participate in overload resolution -if: -

- -
    -
  • -unique_ptr<U, E>::pointer is implicitly convertible to -pointer, -
    • - -
  • -U is not an array type, and -
    • - -
  • -if D is a reference type, E is the same type as D. -
    • -
- -
- -
- -

[ -2010-02-28 Howard adds: -]

- - -
-

-I like Peter's proposal. Here is a tweak of it made after looking at my -implementation. I believe this fixes a further defect not addressed by the -current proposed wording: -

- -
-

-Remarks: this constructor shall only participate in overload resolution -if: -

- -
    -
  • -unique_ptr<U, E>::pointer is implicitly convertible to -pointer, and -
    • - -
  • -U is not an array type, and -
    • - -
  • -if D is a reference type, E is the same type as D, -else E shall be implicitly convertible to D. -
    • -
- -
- -
- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3073. -

- - -

Proposed resolution:

-

-Change 20.8.1.2.1 [unique.ptr.single.ctor]: -

- -
-
-template <class U, class E> unique_ptr(unique_ptr<U, E>&& u);
-
-
-

--20- Requires: If D is not a reference type, -construction of the deleter D from an rvalue of type E -shall be well formed and shall not throw an exception. If D is -a reference type, then E shall be the same type as D -(diagnostic required). unique_ptr<U, E>::pointer shall be -implicitly convertible to pointer. [Note: These requirements -imply that T and U are complete types. — end note] -

- -

-Remarks: If D is -a reference type, then E shall be the same type as D, else this -constructor shall not participate in overload resolution. unique_ptr<U, E>::pointer shall be -implicitly convertible to pointer, else this -constructor shall not participate in overload resolution. U shall not be -an array type, else this -constructor shall not participate in overload resolution. [Note: These requirements -imply that T and U are complete types. — end note] -

- -
-
- -

-Change 20.8.1.2.3 [unique.ptr.single.asgn]: -

- -
-
-template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u);
-
-
-

--6- Requires: Assignment of the deleter D from an rvalue -D shall not throw an exception. unique_ptr<U, -E>::pointer shall be implicitly convertible to pointer. -[Note: These requirements imply that T and U -are complete types. — end note] -

- -

-Remarks: unique_ptr<U, -E>::pointer shall be implicitly convertible to pointer, else this -operator shall not participate in overload resolution. -U shall not be an array type, else this -operator shall not participate in overload resolution. -[Note: These requirements imply that T and U -are complete types. — end note] -

- -
-
- - - - - - -
-

951. Various threading bugs #1

-

Section: 20.12.4.1 [time.traits.is_fp] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

- -

-Related to 953. -

- -

-20.12.4.1 [time.traits.is_fp] says that the type Rep "is -assumed to be ... a class emulating an integral type." What are the -requirements for such a type? -

-

[ -2009-05-10 Howard adds: -]

- - -

-IntegralLike. -

- -

[ -Batavia (2009-05): -]

- -
-

-As with issue 953, -we recommend this issue be addressed in the context of providing concepts for the entire thread header. -

-

-We look forward to proposed wording. -

-

-Move to Open. -

-
- -

[ -2009-08-01 Howard adds: -]

- - -
-

-I have surveyed all clauses of 20.12.4.2 [time.traits.duration_values], -20.12.4.3 [time.traits.specializations] and 20.12.5 [time.duration]. -I can not find any clause which involves the use of a duration::rep type -where the requirements on the rep type are not clearly spelled out. -These requirements were carefully crafted to allow any arithmetic type, or -any user-defined type emulating an arithmetic type. -

- -

-Indeed, treat_as_floating_point -becomes completely superfluous if duration::rep can never be a class type. -

- -

-There will be some Rep types which will not meet the requirements of -every duration operation. This is no different than the fact -that vector<T> can easily be used for types T which are -not DefaultConstructible, even though some members of vector<T> -require T to be DefaultConstructible. This is why the requirements -on Rep are specified for each operation individually. -

- -

-In 20.12.4.1 [time.traits.is_fp] p1: -

- -
-template <class Rep> struct treat_as_floating_point 
-  : is_floating_point<Rep> { };
-
- -

-The duration template uses the treat_as_floating_point trait to help -determine if a duration object can be converted to another duration -with a different tick period. If treat_as_floating_point<Rep>::value is -true, then Rep is a floating-point type and implicit conversions are -allowed among durations. Otherwise, the implicit convertibility depends -on the tick periods of the durations. If Rep is -a class type which emulates a floating-point type, -the author of Rep can specialize treat_as_floating_point so that -duration will treat this Rep as if it were a floating-point type. -Otherwise Rep is assumed to be an integral type or -a class emulating an integral type. -

-
- -

-The phrases "a class type which emulates a floating-point type" and -"a class emulating an integral type" are clarifying phrases which refer to -the summation of all the requirements on the Rep type specified in -detail elsewhere (and should not be repeated here). -

- -

-This specification has been implemented, now multiple times, and the experience -has been favorable. The current specification clearly specifies the requirements -at each point of use (though I'd be happy to fix any place I may have missed, -but none has been pointed out). -

- -

-I am amenable to improved wording of this paragraph (and any others), but do not have any -suggestions for improved wording at this time. I am strongly opposed to -changes which would significantly alter the semantics of the -specification under 20.12 [time] without firmly grounded and -documented rationale, example implementation, testing, and user -experience which relates a positive experience. -

- -

-I recommend NAD unless someone wants to produce some clarifying wording. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Stefanus to provide wording to turn this into a note. -

- -

[ -2010-02-11 Stefanus provided wording. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-Move to Ready. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 20.12.4.1 [time.traits.is_fp]/1: -

- -

-1 The duration template uses the treat_as_floating_point trait -to help determine if a duration object can be converted to another -duration with a different tick period. If -treat_as_floating_point<Rep>::value is true, then -Rep is a floating-point type and implicit conversions are allowed among -durations. Otherwise, the implicit convertibility depends on the tick -periods of the durations. If Rep is a class type which -emulates a floating-point type, the author of Rep can specialize -treat_as_floating_point so that duration will treat this Rep -as if it were a floating-point type. Otherwise Rep is assumed to be an -integral type or a class emulating an integral type. -[Note: The intention of this trait is to indicate whether a given -class behaves like a floating point type, and thus allows division of one value -by another with acceptable loss of precision. If -treat_as_floating_point<Rep>::value is false, -Rep will be treated as if it behaved like an integral type for the -purpose of these conversions. — end note] -

- - - - - - -
-

953. Various threading bugs #3

-

Section: 20.12.3 [time.clock.req] Status: Resolved - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [time.clock.req].

-

View all issues with Resolved status.

-

Discussion:

- -

-Related to 951. -

- -

-20.12.3 [time.clock.req] says that a clock's rep member is "an -arithmetic type or a class emulating an arithmetic type." What are the -requirements for such a type? -

- -

[ -2009-05-10 Howard adds: -]

- - -

-This wording was aimed directly at the ArithmeticLike concept. -

- -

[ -Batavia (2009-05): -]

- -
-

-We recommend this issue be addressed in the context of providing concepts -for the entire thread header. -

-

-May resolve for now by specifying arithmetic types, -and in future change to ArithmeticLike. -However, Alisdair believes this is not feasible. -

-

-Bill disagrees. -

-

-We look forward to proposed wording. Move to Open. -

-
- -

[ -2009-08-01 Howard adds: -]

- - -

-See commented dated 2009-08-01 in 951. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Stefanus to provide wording to turn this into a note. -

- -

[ -2010-02-11 Stephanus provided wording for 951 which addresses -this issue as well. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-Move to NAD EditorialResolved, resolved by 951. -

- - - - -

Proposed resolution:

-

-

- - - - - -
-

954. Various threading bugs #4

-

Section: 20.12.3 [time.clock.req] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [time.clock.req].

-

View all issues with C++11 status.

-

Discussion:

-

-Table 55 — Clock Requirements (in 20.12.3 [time.clock.req]) -

- -
    -
  1. -the requirements for C1::time_point require C1 and C2 -to "refer to the same epoch", but "epoch" is not defined. -
    2. -
  2. -"Different clocks may share a time_point definition if it is -valid to compare their time_points by comparing their -respective durations." What does "valid" mean here? And, since -C1::rep is "THE representation type of the native -duration and time_point" (emphasis added), there -doesn't seem to be much room for some other representation. -
    3. -
  3. -C1::is_monotonic has type "const bool". The -"const" should be removed. -
    4. -
  4. -C1::period has type ratio. ratio isn't a type, -it's a template. What is the required type? -
    5. -
- -

[ -2009-05-10 Howard adds: -]

- - -
    -
  1. -

    -"epoch" is purposefully not defined beyond the common English -definition. The C standard -also chose not to define epoch, though POSIX did. I believe it is a strength -of the C standard that epoch is not defined. When it is known that two time_points -refer to the same epoch, then a definition of the epoch is not needed to compare -the two time_points, or subtract them. -

    -

    -A time_point and a Clock implicitly refer to an (unspecified) epoch. -The time_point represents an offset (duration) from an epoch. -

    -
    2. -
  2. -

    -The sentence: -

    -

    -Different clocks -may share a time_point -definition if it is valid to -compare their time_points by -comparing their respective -durations. -

    - -

    -is redundant and could be removed. I believe the sentence which follows the above: -

    - -

    -C1 and C2 shall refer to the same epoch. -

    - -

    -is sufficient. If two clocks share the same epoch, then by definition, comparing -their time_points is valid. -

    -
    3. -
  3. -is_monotonic is meant to never change (be const). It is also -desired that this value be usable in compile-time computation and branching. -
    4. -
  4. -

    -This should probably instead be worded: -

    -

    -An instantiation of ratio. -

    -
    5. -
- -

[ -Batavia (2009-05): -]

- -
-

-Re (a): It is not clear to us whether "epoch" is a term of art. -

-

-Re (b), (c), and (d): We agree with Howard's comments, -and would consider adding to (c) a static constexpr requirement. -

-

-Move to Open pending proposed wording. -

-
- -

[ -2009-05-25 Daniel adds: -]

- - -

-In regards to (d) I suggest to say "a specialization of ratio" instead of -"An instantiation of ratio". This seems to be the better matching standard -core language term for this kind of entity. -

- -

[ -2009-05-25 Ganesh adds: -]

- - -
-

-Regarding (a), I found this paper on the ISO website using the term "epoch" consistently with the current wording: -

- -

-http://standards.iso.org/ittf/PubliclyAvailableStandards/C030811e_FILES/MAIN_C030811e/text/ISOIEC_18026E_TEMPORAL_CS.HTM -

-

-which is part of ISO/IEC 18026 "Information technology -- Spatial Reference Model (SRM)". -

-
- -

[ -2009-08-01 Howard: Moved to Reivew as the wording requested in Batavia has been provided. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 20.12.3 [time.clock.req] p1: -

    -

    --1- A clock is a bundle consisting of a native duration, a native time_point, and a function now() to get the -current time_point. The origin of the clock's time_point is referred to as the clock's epoch as defined in -section 6.3 of ISO/IEC 18026. -A clock shall meet the requirements in Table 45. -

    -
    2. -
  2. -

    -Remove the sentence from the time_point row of the table "Clock Requirements": -

    - - - - - - - -
    Clock requirements
    -C1::time_point - -chrono::time_point<C1> or chrono::time_point<C2, C1::duration> - -The native time_point type of the clock. -Different clocks may share a time_point definition if it is valid to compare their time_points by comparing their respective durations. -C1 and C2 shall refer to the same epoch. -
    -
    3. -
  3. -

    -Change the row starting with C1::period of the table "Clock Requirements": -

    - - - - - - - -
    Clock requirements
    -C1::period - -a specialization of ratio - -The tick period of the clock in seconds. -
    - -
    4. -
- - - - - -
-

956. Various threading bugs #6

-

Section: 20.12.3 [time.clock.req] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [time.clock.req].

-

View all issues with C++11 status.

-

Discussion:

-

-20.12.3 [time.clock.req] uses the word "native" in several places, -but doesn't define it. What is a "native duration"? -

- -

[ -2009-05-10 Howard adds: -]

- - -

-The standard uses "native" in several places without defining it (e.g. -2.13.3 [lex.ccon]). It is meant to mean "that which is defined -by the facility", or something along those lines. In this case it refers -to the nested time_point and duration types of the clock. -Better wording is welcome. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open pending proposed wording from Pete. -

- -

[ -2009-10-23 Pete provides wording: -]

- - -

[ -2009-11-18 Daniel adds: -]

- - -
-

-I see that 30.4.1.3 [thread.timedmutex.requirements]/3 says: -

- -

-Precondition: If the tick period of rel_time is not -exactly convertible to the native tick period, the duration -shall be rounded up to the nearest native tick period. -

- -

-I would prefer to see that adapted as well. Following the same style as -the proposed resolution I come up with -

- -

-Precondition: If the tick period of rel_time is not -exactly convertible to the native tick period of the -execution environment, the duration shall be rounded up to the -nearest native tick period of the execution -environment. -

- -
- -

[ -2010-03-28 Daniel synced wording with N3092 -]

- - -

[ -Post-Rapperswil, Howard provides wording: -]

- - -

-Moved to Tentatively Ready with revised wording from Howard Hinnant after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

-Change 20.12.3 [time.clock.req]: -

- -
-

-1 A clock is a bundle consisting of a native duration, a -native time_point, and a function now() to get the -current time_point. The origin of the clock's time_point is -referred to as the clock's epoch. A clock shall meet the requirements in -Table 56. -

- -

-2 ... -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 56 — Clock requirements
Expression Return type Operational semantics
C1::repAn arithmetic type or a class emulating an arithmetic typeThe representation type of the native -C1::duration. and -time_point.
C1::period......
C1::durationchrono::duration<C1::rep, C1::period>The native duration type of the clock.
C1::time_pointchrono::time_point<C1> or chrono::time_point<C2, -C1::duration>The native time_point type of the clock. C1 and -C2 shall refer to the same epoch.
...
-
- - - - - - -
-

957. Various threading bugs #7

-

Section: 20.12.7.1 [time.clock.system] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [time.clock.system].

-

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-

Discussion:

-

-20.12.7.1 [time.clock.system]: to_time_t is overspecified. It -requires truncation, but should allow rounding. For example, suppose a -system has a clock that gives times in milliseconds, but time() rounds -those times to the nearest second. Then system_clock can't use any -resolution finer than one second, because if it did, truncating times -between half a second and a full second would produce the wrong time_t -value. -

- -

[ -Post Summit Anthony Williams provided proposed wording. -]

- - -

[ -Batavia (2009-05): -]

- -

-Move to Review pending input from Howard. and other stakeholders. -

- -

[ -2009-05-23 Howard adds: -]

- - -

-I am in favor of the wording provided by Anthony. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-In 20.12.7.1 [time.clock.system] replace paragraphs 3 and 4 with: -

- -
-
-time_t to_time_t(const time_point& t);
-
-

--3- Returns: A time_t object that represents the same -point in time as t when both values are truncated -restricted to the coarser of the precisions of -time_t and time_point. It is implementation -defined whether values are rounded or truncated to the required -precision. -

- -
-time_point from_time_t(time_t t);
-
-

--4- Returns: A time_point object that represents the -same point in time as t when both values are truncated -restricted to the -coarser of the precisions of time_t and time_point. -It is implementation defined whether values are -rounded or truncated to the required precision. -

-
- - - - - -
-

958. Various threading bugs #8

-

Section: 30.5.1 [thread.condition.condvar] Status: Resolved - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar]: the specification for wait_for -with no predicate has an effects clause that says it calls wait_until, -and a returns clause that sets out in words how to determine the return -value. Is this description of the return value subtly different from the -description of the value returned by wait_until? Or should the effects -clause and the returns clause be merged? -

- -

[ -Summit: -]

- - -

-Move to open. Associate with LWG 859 and any other monotonic-clock -related issues. -

- -

[ -2009-08-01 Howard adds: -]

- - -

-I believe that 859 (currently Ready) addresses this issue, and -that this issue should be marked NAD, solved by 859 (assuming -it moves to WP). -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as NAD EditorialResolved, addressed by resolution -of Issue 859. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

960. Various threading bugs #10

-

Section: 30.4.1 [thread.mutex.requirements] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-30.4.1 [thread.mutex.requirements]: paragraph 4 is entitled -"Error conditions", but according to 17.5.1.4 [structure.specifications], "Error -conditions:" specifies "the error conditions for error codes reported by -the function." It's not clear what this should mean when there is no -function in sight. -

- -

[ -Summit: -]

- - -

-Move to open. -

- -

[ -Beman provided proposed wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. Fix the proposed wording with "functions of type Mutex" --> "functions of Mutex type" -

- - - -

Proposed resolution:

-

-Change 30.4.1 [thread.mutex.requirements] Mutex requirements, -paragraph 4 as indicated: -

- -
-

--4- Error conditions: -The error conditions for error codes, if any, reported by member -functions of Mutex type shall be: -

-
    -
  • -not_enough_memory — if there is not enough memory to construct -the mutex object. -
    • -
  • -resource_unavailable_try_again — if any native handle type -manipulated is not available. -
    • -
  • -operation_not_permitted — if the thread does not have the -necessary permission to change the state of the mutex object. -
    • -
  • -device_or_resource_busy — if any native handle type -manipulated is already locked. -
    • -
  • -invalid_argument — if any native handle type manipulated as -part of mutex construction is incorrect. -
    • -
-
- - - - - -
-

962. Various threading bugs #12

-

Section: 30.4.2.2.2 [thread.lock.unique.locking] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [thread.lock.unique.locking].

-

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-

Discussion:

-

-30.4.2.2.2 [thread.lock.unique.locking]: unique_lock::lock is -required to throw an object of type std::system_error "when the -postcondition cannot be achieved." The postcondition is owns == true, -and this is trivial to achieve. Presumably, the requirement is intended -to mean something more than that. -

- -

[ -Summit: -]

- -

-Move to open. -

- -

[ -Beman has volunteered to provide proposed wording. -]

- - -

[ -2009-07-21 Beman added wording to address 30.2.2 [thread.req.exception] -in response to the Frankfurt notes in 859. -]

- - -

[ -2009-09-25 Beman: minor update to wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- -

Change Exceptions 30.2.2 [thread.req.exception] as indicated:

-
-

Some functions described in this Clause are specified to throw exceptions of -type system_error (19.5.5). Such exceptions shall be thrown if -any of the Error conditions are detected or a call to an operating -system or other underlying API results in an error that prevents the library -function from satisfying its postconditions or from returning a meaningful -value meeting its specifications. Failure to -allocate storage shall be reported as described in -17.6.5.12 [res.on.exception.handling].

-
- -

Change thread assignment 30.3.1.5 [thread.thread.member], join(), -paragraph 8 as indicated:

-
-

Throws: std::system_error when the postconditions cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

- -
- -

Change thread assignment 30.3.1.5 [thread.thread.member], detach(), paragraph -13 as indicated:

-
- -

Throws: std::system_error when the effects or -postconditions cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

- -
- -

Change Mutex requirements 30.4.1 [thread.mutex.requirements], paragraph -11, as indicated:

-
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change unique_lock locking 30.4.2.2.2 [thread.lock.unique.locking], -paragraph 3, as indicated:

-
- -

Throws: std::system_error when the postcondition cannot be -achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change unique_lock locking 30.4.2.2.2 [thread.lock.unique.locking], -paragraph 8, as indicated:

-
- -

Throws: std::system_error when the postcondition cannot be -achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change unique_lock locking 30.4.2.2.2 [thread.lock.unique.locking], -paragraph 13, as indicated:

-
- -

Throws: std::system_error when the postcondition cannot be -achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change unique_lock locking 30.4.2.2.2 [thread.lock.unique.locking], -paragraph 18, as indicated:

-
- -

Throws: std::system_error when the postcondition cannot be -achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change unique_lock locking 30.4.2.2.2 [thread.lock.unique.locking], -paragraph 22, as indicated:

-
- -

Throws: std::system_error when the postcondition cannot be -achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change Function call_once 30.4.4.2 [thread.once.callonce], paragraph 4, as -indicated

-
-

Throws: std::system_error when the effects cannot be - achieved an exception is required (30.2.2 [thread.req.exception]), - or any exception thrown by func.

-
-

Change Class condition_variable 30.5.1 [thread.condition.condvar], -paragraph 12, as indicated:

-
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change Class condition_variable 30.5.1 [thread.condition.condvar], -paragraph 19, as indicated:

-
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change Class condition_variable_any 30.5.2 [thread.condition.condvarany], -paragraph 10, as indicated:

-
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
-

Change Class condition_variable_any 30.5.2 [thread.condition.condvarany], -paragraph 16, as indicated:

-
- -

Throws: std::system_error when the returned value, effects, or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
- -

Assuming issue 859, Monotonic Clock is Conditionally Supported?, has been -applied to the working paper, change Change 30.5.1 [thread.condition.condvar] as -indicated:

-
-
template <class Rep, class Period> 
-bool wait_for(unique_lock<mutex>& lock, 
-              const chrono::duration<Rep, Period>& rel_time);
-
...
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required ([thread.req.exception]).

-
- -

Assuming issue 859, Monotonic Clock is Conditionally Supported?, has been -applied to the working paper, change Change 30.5.1 [thread.condition.condvar] as -indicated:

-
-
template <class Rep, class Period, class Predicate> 
-  bool wait_for(unique_lock<mutex>& lock, 
-                const chrono::duration<Rep, Period>& rel_time, 
-                Predicate pred);
- 
...
- -

Throws: std::system_error when the effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
- -

Assuming issue 859, Monotonic Clock is Conditionally Supported?, has been -applied to the working paper, change 30.5.2 [thread.condition.condvarany] as -indicated:

-
-
template <class Lock, class Rep, class Period> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
- 
...
- -

Throws: std::system_error when the returned value, effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
- -

Assuming issue 859, Monotonic Clock is Conditionally Supported?, has been -applied to the working paper, change 30.5.2 [thread.condition.condvarany] as -indicated:

-
-
template <class Lock, class Rep, class Period, class Predicate> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
- 
...
- -

Throws: std::system_error when the returned value, effects or -postcondition cannot be achieved an exception is required (30.2.2 [thread.req.exception]).

-
- - - - - - -
-

963. Various threading bugs #13

-

Section: 30.3.1.5 [thread.thread.member] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-30.3.1.5 [thread.thread.member]: thread::detach is required to -throw an exception if the thread is "not a detachable thread". -"Detachable" is never defined. -

- -

[ -Howard adds: -]

- - -

-Due to a mistake on my part, 3 proposed resolutions appeared at approximately -the same time. They are all three noted below in the discussion. -

- -

[ -Summit, proposed resolution: -]

- - -
-

-In 30.3.1.5 [thread.thread.member] change: -

- -
-void detach();
-
-
-

...

-

-14- Error conditions:

-
    -
  • no_such_process -- if the thread is not a valid thread.
    • -
  • invalid_argument -- if the thread is not a detachable joinable thread.
    • -
-
- -
- -
- -

[ -Post Summit, Jonathan Wakely adds: -]

- - -
-

-A thread is detachable if it is joinable. As we've defined joinable, -we can just use that. -

-

-This corresponds to the pthreads specification, where pthread_detach -fails if the thread is not joinable: -

-

-EINVAL: The implementation has detected that the value specified by -thread does not refer to a joinable thread. -

-

-Jonathan recommends this proposed wording: -

-
-

-In 30.3.1.5 [thread.thread.member] change: -

- -
-void detach();
-
-
-

...

-

-14- Error conditions:

-
    -
  • ...
    • -
  • invalid_argument -- not a detachable joinable thread.
    • -
-
- -
-
-
- -

[ -Post Summit, Anthony Williams adds: -]

- - -
-

-This is covered by the precondition that joinable() be true. -

-

-Anthony recommends this proposed wording: -

- -
-

-In 30.3.1.5 [thread.thread.member] change: -

- -
-void detach();
-
-
-

...

-

-14- Error conditions:

-
    -
  • ...
    • -
  • invalid_argument -- not a detachable thread.
    • -
-
- -
- -
- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark as Ready with proposed resolution from Summit. -

- - - -

Proposed resolution:

- -

-In 30.3.1.5 [thread.thread.member] change: -

- -
-void detach();
-
-
-

...

-

-14- Error conditions:

-
    -
  • no_such_process -- if the thread is not a valid thread.
    • -
  • invalid_argument -- if the thread is not a detachable joinable thread.
    • -
-
- -
- - - - - - -
-

964. Various threading bugs #14

-

Section: 30.5.2 [thread.condition.condvarany] Status: Resolved - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The requirements for the constructor for condition_variable has several -error conditions, but the requirements for the constructor for -condition_variable_any has none. Is this difference intentional? -

- -

[ -Summit: -]

- - -

-Move to open, pass to Howard. If this is intentional, a note may be -helpful. If the error conditions are to be copied from -condition_variable, this depends on LWG 965. -

- -

[ -Post Summit Howard adds: -]

- - -

-The original intention -(N2447) -was to let the OS return whatever errors it was going to return, and for -those to be translated into exceptions, for both -condition_variable and condition_variable_any. I have not -received any complaints about specific error conditions from vendors on -non-POSIX platforms, but such complaints would not surprise me if they surfaced. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave open. Benjamin to provide wording. -

- -

[ -2010 Pittsburgh: -]

- - -
-

-We don't have throw clauses for condition variables. -

-

-This issue may be dependent on LWG 1268. -

-

-Leave open. Detlef will coordinate with Benjamin. -

-

-Consider merging LWG 964, 966, and 1268 into a -single paper. -

-
- - - -

Proposed resolution:

-

-Resolved 2011-03 Madrid meeting by paper -N3278 -

- - - - - -
-

965. Various threading bugs #15

-

Section: 30.5.1 [thread.condition.condvar] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar]: the constructor for -condition_variable throws an exception with error code -device_or_resource_busy "if attempting to initialize a -previously-initialized but as of yet undestroyed condition_variable." -How can this occur? -

- -

[ -Summit: -]

- -
-

-Move to review. Proposed resolution: strike the device_or_resource_busy -error condition from the constructor of condition_variable. -

-
    -
  • -This is a POSIX error that cannot occur in this interface because the -C++ interface does not separate declaration from initialization. -
    • -
-
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 30.5.1 [thread.condition.condvar] p3: -

- -
-
    -
  • ...
    • -
  • -device_or_resource_busy -- if attempting to initialize a -previously-initialized but as of yet undestroyed -condition_variable. -
    • -
-
- - - - - -
-

966. Various threading bugs #16

-

Section: 30.5.1 [thread.condition.condvar] Status: Resolved - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar]: -condition_variable::wait and -condition_variable::wait_until both have a postcondition that -lock is locked by the calling thread, and a throws clause that -requires throwing an exception if this postcondition cannot be achieved. -How can the implementation detect that this lock can never be -obtained? -

- -

[ -Summit: -]

- - -

-Move to open. Requires wording. Agreed this is an issue, and the -specification should not require detecting deadlocks. -

- -

[ -2009-08-01 Howard provides wording. -]

- - -
-

-The proposed wording is inspired by the POSIX spec which says: -

- -
-
-
[EINVAL]
-
The value specified by cond or mutex is invalid.
-
[EPERM]
-
The mutex was not owned by the current thread at the time of the call.
-
-
- -

-I do not believe [EINVAL] is possible without memory corruption (which we don't -specify). [EPERM] is possible if this thread doesn't own the mutex, which is -listed as a precondition. "May" is used instead of "Shall" because not all -OS's are POSIX. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave open, Detlef to provide improved wording. -

- -

[ -2009-10-23 Detlef Provided wording. -]

- - -
-

-Detlef's wording put in Proposed resolution. Original wording here: -

-
-

-Change 30.5.1 [thread.condition.condvar] p12, p19 and -30.5.2 [thread.condition.condvarany] p10, p16: -

- -

-Throws: May throw std::system_error - -if a precondition is not met. - -when the effects or postcondition -cannot be achieved. -

-
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Leave open, Detlef to provide improved wording. -

- -

[ -2009-11-18 Anthony adds: -]

- - -
-

-condition_variable::wait takes a unique_lock<mutex>. We -know whether or not a unique_lock owns a lock, through use of its -owns_lock() member. -

- -

-I would like to propose the following resolution: -

- -
-

-Modify the first sentence of 30.5.1 [thread.condition.condvar] p9: -

- -
-void wait(unique_lock<mutex>& lock);
-
-

-9 Precondition: lock is locked by the calling thread -lock.owns_lock() is true, and either -

...

-
-
- -

-Replace 30.5.1 [thread.condition.condvar] p11-13 with: -

- -
-void wait(unique_lock<mutex>& lock);
-
-
-

...

-

-11 Postcondition: lock is locked by the calling -thread lock.owns_lock() is true. -

- -

-12 Throws: std::system_error when the effects or -postcondition cannot be achieved if the implementation detects that -the preconditions are not met or the effects cannot be achieved. Any exception -thrown by lock.lock() or lock.unlock(). -

- -

-13 Error Conditions: The error conditions are implementation -defined. -

- -
    -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
- -
-
-
-
- -

[ -2010 Pittsburgh: -]

- - -
-

-There are heavy conflicts with adopted papers. -

-

-This issue is dependent on LWG 1268. -

-

-Leave open pending outstanding edits to the working draft. Detlef will provide -wording. -

-

-Possibly related to 964. -

- -
- -

[2011-03-24 Madrid]

- -

Rationale:

-

-This has been resolved since filing, with the introduction of system_error to the thread specification. -

- - - - -

Proposed resolution:

-

-Replace 30.5.1 [thread.condition.condvar] p12, p19 and -30.5.2 [thread.condition.condvarany] p10, p16: -

- -
-

-Throws: std::system_error when the effects or -postcondition cannot be achieved. -

-

-Error conditions: -

-
    -
  • -equivalent error condition from lock.lock() or lock.unlock(). -
    • -
- -

-Throws: It is implementation-defined whether a std::system_error -with implementation-defined error condition is thrown if the -precondition is not met. -

-
- - - - - - -
-

967. Various threading bugs #17

-

Section: 30.3.1.2 [thread.thread.constr] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-the error handling for the constructor for condition_variable -distinguishes lack of memory from lack of other resources, but the error -handling for the thread constructor does not. Is this difference -intentional? -

- -

[ -Beman has volunteered to provide proposed wording. -]

- - -

[ -2009-09-25 Beman provided proposed wording. -]

- - -

-The proposed resolution assumes 962 has been accepted and -its proposed resolution applied to the working paper. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- - -

Change Mutex requirements 30.4.1 [thread.mutex.requirements], -paragraph 4, as indicated:

-
- -

Error conditions:

-
- -
    -
  • not_enough_memory — if there is not enough memory to construct -the mutex object.
    • - -
  • resource_unavailable_try_again — if any native handle type -manipulated is not available.
    • - -
  • operation_not_permitted — if the thread does not have the -necessary permission to change the state of the mutex object.
    • - -
  • device_or_resource_busy — if any native handle type -manipulated is already locked.
    • - -
  • invalid_argument — if any native handle type manipulated as -part of mutex construction is incorrect.
    • -
-
-
- -

Change Class condition_variable 30.5.1 [thread.condition.condvar], -default constructor, as indicated:

-
-

condition_variable();

-
-

Effects: Constructs an object of type condition_variable.

-

Throws: std::system_error when an exception is required (30.2.2 [thread.req.exception]).

-

Error conditions:

-
-
    -
  • not_enough_memory — if a memory limitation prevents - initialization.
    • -
  • resource_unavailable_try_again — if some non-memory - resource limitation prevents initialization.
    • -
  • device_or_resource_busy — if attempting to initialize a - previously-initialized but as of yet undestroyed condition_variable.
    • -
-
-
-
- - - - - -
-

968. Various threading bugs #18

-

Section: 30.4.1 [thread.mutex.requirements] Status: C++11 - Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2015-04-08

-

View other active issues in [thread.mutex.requirements].

-

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-

View all issues with C++11 status.

-

Discussion:

-

-30.4.1 [thread.mutex.requirements]: several functions are -required to throw exceptions "if the thread does not have the necessary -permission ...". "The necessary permission" is not defined. -

- -

[ -Summit: -]

- -

-Move to open. -

- - -

[ -Beman has volunteered to provide proposed wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready with minor word-smithing in the example. -

- - - -

Proposed resolution:

- - -

Change Exceptions 30.2.2 [thread.req.exception] as indicated:

-
-

Some functions described in this Clause are -specified to throw exceptions of type system_error (19.5.5). Such exceptions -shall be thrown if any of the Error conditions are detected or a call to an operating system or other underlying API -results in an error that prevents the library function from meeting its specifications. -[Note: See 17.6.5.12 [res.on.exception.handling] for exceptions thrown to report -storage allocation failures. —end -note]

- -

[Example:

- -
- -

Consider a function in this clause that is specified to throw exceptions of type -system_error and specifies Error conditions that include -operation_not_permitted for a thread that does not have the privilege to -perform the operation. Assume that, during the execution of this function, an errno -of EPERM is reported by a POSIX API call used by the -implementation. Since POSIX specifies an errno of EPERM -when "the caller does not have the privilege to perform the operation", -the implementation maps EPERM  to an error_condition -of operation_not_permitted (19.5 [syserr]) and an exception of type -system_error is thrown.

- -
- -

—end example]

- -

Editorial note: For the sake of exposition, -the existing text above is shown with the changes proposed in issues 962 and 967. The -proposed additional example is independent of whether or not the 962 and 967 -proposed resolutions are accepted.

- -
- -

Change Mutex requirements 30.4.1 [thread.mutex.requirements], -paragraph 4, as indicated:

- -
- -

— operation_not_permitted — if the thread does not have the -necessary permission to change the state of the mutex object privilege to perform the operation.

- -
- -

Change Mutex requirements 30.4.1 [thread.mutex.requirements], -paragraph 12, as indicated:

- -
- -

— operation_not_permitted — if the thread does not have the -necessary permission to change the state of the mutex privilege to perform the operation.

- -
- - - - - - -
-

970. addressof overload unneeded

-

Section: 20.7.12.1 [specialized.addressof] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-01-16 Last modified: 2015-04-08

-

View all other issues in [specialized.addressof].

-

View all issues with C++11 status.

-

Discussion:

-

-20.7.12.1 [specialized.addressof] specifies: -

- -
-template <ObjectType T> T* addressof(T& r);
-template <ObjectType T> T* addressof(T&& r);
-
- -

-The two signatures are ambiguous when the argument is an lvalue. The -second signature seems not useful: what does it mean to take the -address of an rvalue? -

- -

[ -Post Summit: -]

- - -

-Recommend Review. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-11-18 Moved from Pending WP to WP. Confirmed in -N3000. -]

- - - -

Proposed resolution:

-

-Change 20.7.12.1 [specialized.addressof]: -

- -
-template <ObjectType T> T* addressof(T& r);
-template <ObjectType T> T* addressof(T&& r);
-
- - - - - - -
-

974. duration<double> should not implicitly convert to duration<int>

-

Section: 20.12.5.1 [time.duration.cons] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-01-21 Last modified: 2015-04-08

-

View all other issues in [time.duration.cons].

-

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-

Discussion:

-

-The following code should not compile because it involves implicit truncation -errors (against the design philosophy of the duration library). -

- -
-duration<double> d(3.5);
-duration<int> i = d;  // implicit truncation, should not compile
-
- -

-This intent was codified in the example implementation which drove this proposal -but I failed to accurately translate the code into the specification in this -regard. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -improved for enable_if type constraining, possibly following Robert's -formula. -

- -

[ -2009-08-01 Howard adds: -]

- - -

-Addressed by 1177. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Not completely addressed by 1177. Move to Ready. -

- - - -

Proposed resolution:

-

-Change 20.12.5.1 [time.duration.cons], p4: -

- -
-
-template <class Rep2, class Period2> 
-  duration(const duration<Rep2, Period2>& d);
-
-

--4- Requires: treat_as_floating_point<rep>::value -shall be true or both ratio_divide<Period2, -period>::type::den shall be 1 -and treat_as_floating_point<Rep2>::value -shall be false. -Diagnostic required. -[Note: This requirement prevents implicit truncation error when -converting between integral-based duration types. Such a -construction could easily lead to confusion about the value of the -duration. — end note] -

-
- - - - - -
-

975. is_convertible cannot be instantiated for non-convertible types

-

Section: 20.10.6 [meta.rel] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-01-25 Last modified: 2015-04-08

-

View all other issues in [meta.rel].

-

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-

Discussion:

-

Addresses UK 206

- -

-Related to 1114. -

- -

-The current specification of std::is_convertible (reference is draft -N2798) -is basically defined by 20.10.6 [meta.rel] p.4: -

- -
-

-In order to instantiate the template is_convertible<From, -To>, the following code shall be well formed: -

- -
-template <class T>
-  typename add_rvalue_reference<T>::type create();
-
-To test() {
-  return create<From>();
-}
-
- -

-[Note: This requirement gives well defined results for reference -types, void types, array types, and function types. — end note] -

-
- -

-The first sentence can be interpreted, that e.g. the expression -

- -
-std::is_convertible<double, int*>::value
-
- -

-is ill-formed because std::is_convertible<double, int*> could not be -instantiated, or in more general terms: The wording requires that -std::is_convertible<X, Y> cannot be instantiated for otherwise valid -argument types X and Y if X is not convertible to Y. -

- -

-This semantic is both unpractical and in contradiction to what the last type -traits paper -N2255 -proposed: -

- -
-

-If the following test function is well formed code b -is true, else it is false. -

- -
-template <class T>
-  typename add_rvalue_reference<T>::type create();
-
-To test() {
-  return create<From>();
-}
-
- -

-[Note: This definition gives well defined results for reference -types, void types, array types, and function types. — end note] -

-
- -

[ -Post Summit: -]

- - -
-

-Jens: Checking that code is well-formed and then returning true/false -sounds like speculative compilation. John Spicer would really dislike -this. Please find another wording suggesting speculative compilation. -

-

-Recommend Open. -

-
- -

[ -Post Summit, Howard adds: -]

- - -
-

-John finds the following wording clearer: -

-
- - - - - - - - - - -
TemplateConditionComments
template <class From, class To>
struct is_convertible;		see belowFrom and To shall be complete types, arrays of unknown bound, -or (possibly cv-qualified) void types.
- -

-Given the following function prototype: -

- -
-template <class T>
-  typename add_rvalue_reference<T>::type create();
-
- -

-is_convertible<From, To>::value shall be true if the -return expression in the following code would be well-formed, including -any implicit conversions to the return type of the function, else -is_convertible<From, To>::value shall be false. -

- -
-To test() {
-  return create<From>();
-}
-
- -
- -
-

-Original proposed wording: -

-

-In 20.10.6 [meta.rel]/4 change: -

- -

-In order to instantiate the template is_convertible<From, To>, the -following code shall be well formed If the following code -is well formed is_convertible<From, To>::value is true, otherwise -false:[..] -

- -

Revision 2

- -
- -

-In 20.10.6 [meta.rel] change: -

- -
- - - - - - - - - - - -
TemplateConditionComments
.........
template <class From, class To>
struct is_convertible;		 -The code set out below shall be well formed. -see belowFrom and To shall be complete types, arrays of unknown bound, -or (possibly cv-qualified) void types.
- -

--4- In order to instantiate the template is_convertible<From, To>, the -following code shall be well formed: -Given the following function prototype: -

- -
-template <class T> 
-  typename add_rvalue_reference<T>::type create();
-
- -

-is_convertible<From, To>::value inherits either directly or -indirectly from true_type if the -return expression in the following code would be well-formed, including -any implicit conversions to the return type of the function, else -is_convertible<From, To>::value inherits either directly or -indirectly from false_type. -

- -
-To test() { 
-  return create<From>(); 
-}
-
- -

-[Note: This requirement gives well defined results for reference types, -void types, array types, and function types. -- end note] -

- -
-
- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

- -

-In 20.10.6 [meta.rel] change: -

- -
- - - - - - - - - - - -
TemplateConditionComments
.........
template <class From, class To>
struct is_convertible;		 -The code set out below shall be well formed. -see belowFrom and To shall be complete types, arrays of unknown bound, -or (possibly cv-qualified) void types.
- -

--4- In order to instantiate the template is_convertible<From, To>, the -following code shall be well formed: -Given the following function prototype: -

- -
-template <class T> 
-  typename add_rvalue_reference<T>::type create();
-
- -

-the predicate condition for a template specialization -is_convertible<From, To> shall be satisfied, if and only -if the return expression in the following code would be well-formed, -including any implicit conversions to the return type of the -function. -

- -
-To test() { 
-  return create<From>(); 
-}
-
- -

-[Note: This requirement gives well defined results for reference types, -void types, array types, and function types. — end note] -

- -
- - - - - -
-

976. Class template std::stack should be movable

-

Section: 23.6.5.2 [stack.defn] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-02-01 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-The synopsis given in 23.6.5.2 [stack.defn] does not show up -

- -
-requires MoveConstructible<Cont> stack(stack&&);
-requires MoveAssignable<Cont> stack& operator=(stack&&);
-
- -

-although the other container adaptors do provide corresponding members. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-08-18 Daniel updates the wording and Howard sets to Review. -]

- - -

[ -2009-08-23 Howard adds: -]

- - -

-1194 also adds these move members using an editorially different style. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark NAD EditorialResolved, addressed by issue 1194. -

- - - -

Proposed resolution:

-

-In the class stack synopsis of 23.6.5.2 [stack.defn] insert: -

- -
-template <class T, class Container = deque<T> >
-class stack {
-  [..]
-  explicit stack(const Container&);
-  explicit stack(Container&& = Container());
-  stack(stack&& s) : c(std::move(s.c)) {}
-  stack& operator=(stack&& s) { c = std::move(s.c); return *this; }
-  [..]
-};
-
- - - - - - - - -
-

978. Hashing smart pointers

-

Section: 20.9.13 [unord.hash] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-02-02 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

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-

Discussion:

-

Addresses UK 208

-

-I don't see an open issue on supporting std::hash for smart pointers -(unique_ptr and shared_ptr at least). -

-

-It seems reasonable to at least expect support for the smart -pointers, especially as they support comparison for use in ordered -associative containers. -

- -

[ -Batavia (2009-05): -]

- -
-

-Howard points out that the client can always supply a custom hash function. -

-

-Alisdair replies that the smart pointer classes are highly likely -to be frequently used as hash keys. -

-

-Bill would prefer to be conservative. -

-

-Alisdair mentions that this issue may also be viewed as a subissue or -duplicate of issue 1025. -

-

-Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -

-
- -

[ -2009-05-31 Peter adds: -]

- - -
-

-Howard points out that the client can always supply a custom hash function. -

-

-Not entirely true. The client cannot supply the function that hashes the -address of the control block (the equivalent of the old operator<, now -proudly carrying the awkward name of 'owner_before'). Only the -implementation can do that, not necessarily via specializing hash<>, of -course. -

-

-This hash function makes sense in certain situations for shared_ptr -(when one needs to switch from set/map using ownership ordering to -unordered_set/map) and is the only hash function that makes sense for -weak_ptr. -

-
- -

[ -2009-07-28 Alisdair provides wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2009-11-16 Moved from Ready to Open: -]

- - -
-

-Pete writes: -

-
-

-As far as I can see, "...suitable for using this type as key in unordered -associative containers..." doesn't define any semantics. It's advice to the -reader, and if it's present at all it should be in a note. But we have far too -much of this sort of editorial commentary as it is. -

-

-And in the resolution of 978 it's clearly wrong: it says that if there is no -hash specialization available for D::pointer, the implementation may provide -hash<unique_ptr<T,D>> if the result is not suitable for use in unordered -containers. -

-
- -

-Howard writes: -

- -

-Is this a request to pull 978 from Ready? -

- -

-Barry writes: -

-
-

-I read this as more than a request. The PE says it's wrong, so it can't be -Ready. -

-
- -
- -

[ -2010-01-31 Alisdair: related to 1245 and 1182. -]

- - -

[ -2010-02-08 Beman updates wording. -]

- - -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -

Add the following declarations to the synopsis of <memory> in -20.7 [memory]

- -
-
// [util.smartptr.hash] hash support
-template <class T> struct hash;
-template <class T, class D> struct hash<unique_ptr<T,D>>;
-template <class T> struct hash<shared_ptr<T>>;
-
- -

Add a new subclause under 20.8.2 [util.smartptr] called hash support

- -
-

hash support [util.smartptr.hash]

- -
template <class T, class D> struct hash<unique_ptr<T,D>>;
- -
-

-Specialization meeting the requirements of class template hash (20.9.13 [unord.hash]). For an object p of type UP, where -UP is a type unique_ptr<T,D>, -hash<UP>()(p) shall evaluate to the same value as -hash<typename UP::pointer>()(p.get()). The specialization -hash<typename UP::pointer> is required to be well-formed. -

-
- -
template <class T> struct hash<shared_ptr<T>>;
- -
-

-Specialization meeting the requirements of class template hash (20.9.13 [unord.hash]). For an object p of type -shared_ptr<T>, hash<shared_ptr<T>>()(p) -shall evaluate to the same value as hash<T*>()(p.get()). -

-
-
- - - - - - -
-

981. Unordered container requirements should add initializer_list support

-

Section: 23.2.5 [unord.req] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-02-08 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

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-

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-

Discussion:

-

-Refering to -N2800 -all container requirements tables (including those for -associative containers) provide useful member function overloads -accepting std::initializer_list as argument, the only exception is -Table 87. There seems to be no reason for not providing them, because 23.5 [unord] -is already initializer_list-aware. For the sake of -library interface consistency and user-expectations corresponding -overloads should be added to the table requirements of unordered -containers as well. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

- -

-In 23.2.5 [unord.req]/9 insert: -

- -

-... [q1, q2) is a valid range in a, il -designates an object of type initializer_list<value_type>, t is a value of type -X::value_type, ... -

- -

-In 23.2.5 [unord.req], Table 87 insert: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 87 - Unordered associative container requirements (in addition to container)
Expression Return type Assertion/note
pre-/post-condition		 Complexity
X(i, j)
X a(i, j)		 X ... ...
X(il) XSame as X(il.begin(), il.end()).Same as X(il.begin(), il.end()).
... ... ... ...
a = b X ... ...
a = il X&a = X(il); return *this;Same as a = X(il).
... ... ... ...
a.insert(i, j) void ... ...
a.insert(il) voidSame as a.insert(il.begin(), il.end()).Same as a.insert(il.begin(), il.end()).
-
- - - - - - -
-

982. Wrong complexity for initializer_list assignment in Table 85

-

Section: 23.2.4 [associative.reqmts] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-02-08 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

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-

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-

Discussion:

-

-According to -N2800, -the associative container requirements table 85 says - that assigning an initializer_list to such a container is of - constant complexity, which is obviously wrong. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

- -

-In 23.2.4 [associative.reqmts], Table 85 change: -

- -
- - - - - - - - - -
Table 85 - Associative container requirements (in addition to container)
Expression Return type Assertion/note
pre-/post-condition		 Complexity
a = il X& a = X(il);
return *this;		constantSame as a = X(il).
-
- - - - - - -
-

983. unique_ptr reference deleters should not be moved from

-

Section: 20.8.1.2 [unique.ptr.single] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-02-10 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single].

-

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-

Discussion:

-

-Dave brought to my attention that when a unique_ptr has a non-const reference -type deleter, move constructing from it, even when the unique_ptr containing -the reference is an rvalue, could have surprising results: -

- -
-D d(some-state);
-unique_ptr<A, D&> p(new A, d);
-unique_ptr<A, D> p2 = std::move(p);
-// has d's state changed here?
-
- -

-I agree with him. It is the unique_ptr that is the rvalue, not the -deleter. When the deleter is a reference type, the unique_ptr should -respect the "lvalueness" of the deleter. -

- -

-Thanks Dave. -

- -

[ -Batavia (2009-05): -]

- -

-Seems correct, but complicated enough that we recommend moving to Review. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2010-03-14 Howard adds: -]

- - -

-We moved -N3073 -to the formal motions page in Pittsburgh which should obsolete this issue. I've -moved this issue to NAD Editorial, solved by N3073. -

- - - -

Rationale:

-

-Solved by N3073. -

- - -

Proposed resolution:

-

-Change 20.8.1.2.1 [unique.ptr.single.ctor], p20-21 -

- -
-
-template <class U, class E> unique_ptr(unique_ptr<U, E>&& u);
-
- -
- -

--20- Requires: If D E is not a reference type, -construction of the deleter D from an rvalue of type E -shall be well formed and shall not throw an exception. - -Otherwise E is a reference type and construction of the deleter -D from an lvalue of type E shall be well formed and -shall not throw an exception. - -If D is -a reference type, then E shall be the same type as D -(diagnostic required). unique_ptr<U, E>::pointer shall be -implicitly convertible to pointer. [Note: These -requirements imply that T and U are complete types. -— end note] -

- -

--21- Effects: Constructs a unique_ptr which owns the -pointer which u owns (if any). If the deleter -E is not a reference type, it this -deleter is move constructed from u's deleter, otherwise -the reference this deleter is copy constructed -from u.'s deleter. After the construction, u no longer -owns a pointer. [Note: The deleter constructor can be implemented -with std::forward<DE>. — end -note] -

- -
-
- -

-Change 20.8.1.2.3 [unique.ptr.single.asgn], p1-3 -

- -
-
-unique_ptr& operator=(unique_ptr&& u);
-
-
- -

--1- Requires: If the deleter D is not a reference type, -Aassignment of the deleter D from an rvalue D shall not throw an exception. - -Otherwise the deleter D is a reference type, -and assignment of the deleter D from an lvalue D shall not throw an exception. -

- -

--2- Effects: reset(u.release()) followed by -an move assignment from u's deleter to this deleter -std::forward<D>(u.get_deleter()). -

- -

--3- Postconditions: This unique_ptr now owns the pointer -which u owned, and u no longer owns it. [Note: If -D is a reference type, then the referenced lvalue deleters are -move assigned. — end note] -

-
-
- -

-Change 20.8.1.2.3 [unique.ptr.single.asgn], p6-7 -

- -
-
-template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u);
-
-
- -

-Requires: If the deleter E is not a reference type, -Aassignment of the deleter D from an rvalue -DE shall not throw an exception. - -Otherwise the deleter E is a reference type, -and assignment of the deleter D from an lvalue E shall not throw an exception. -unique_ptr<U, E>::pointer shall be implicitly convertible to pointer. -[Note: These requirements imply that T and U> -are complete types. — end note] -

- -

-Effects: reset(u.release()) followed by -an move assignment from u's deleter to this deleter -std::forward<E>(u.get_deleter()). -If either -D or E is a reference type, then the referenced lvalue -deleter participates in the move assignment. -

- -
-
- - - - - - -
-

984. Does <cinttypes> have macro guards?

-

Section: 27.9.2 [c.files] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-02-12 Last modified: 2015-04-08

-

View all other issues in [c.files].

-

View all issues with C++11 status.

-

Discussion:

-

-The C standard says about <inttypes.h>: -

- -

-C++ implementations should define these macros only when __STDC_FORMAT_MACROSis defined -before <inttypes.h> is included. -

- -

-The C standard has a similar note about <stdint.h>. For <cstdint> -we adopted a "thanks but no thanks" policy and documented that fact in 18.4.1 [cstdint.syn]: -

- -

-... [Note: The macros defined by <stdint> are -provided unconditionally. In particular, the symbols -__STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS -(mentioned in C99 footnotes 219, 220, and 222) play no role in C++. -— end note] -

- -

-I recommend we put a similar note in 27.9.2 [c.files] regarding <cinttypes>. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Add to 27.9.2 [c.files]: -

- -

-Table 112 describes header <cinttypes>. - -[Note: The macros defined by <cintypes> are -provided unconditionally. In particular, the symbol -__STDC_FORMAT_MACROS -(mentioned in C99 footnote 182) plays no role in C++. -— end note] - -

- - - - - -
-

985. Allowing throwing move

-

Section: 23.2.1 [container.requirements.general] Status: Resolved - Submitter: Rani Sharoni Opened: 2009-02-12 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

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-

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-

Discussion:

-

-Introduction -

- -

This proposal is meant to resolve potential regression of the -N2800 -draft, see -next section, and to relax the requirements for containers of types with -throwing move constructors.

- -

The basic problem is that some containers operations, like push_back, -have a strong exception safety -guarantee (i.e. no side effects upon exception) that are not achievable when -throwing move constructors are used since there is no way to guarantee revert -after partial move. For such operations the implementation can at most provide -the basic guarantee (i.e. valid but unpredictable) as it does with multi -copying operations (e.g. range insert).

- -

For example, vector<T>::push_back() (where T has a move -constructor) might resize the vector and move the objects to the new underlying -buffer. If move constructor throws it might -not be possible to recover the throwing object or to move the old objects back to -the original buffer.

- -

The current draft is explicit by disallowing throwing move -for some operations (e.g. vector<>::reserve) and not clear about other -operations mentioned in 23.2.1 [container.requirements.general]/10 -(e.g. single element insert): it guarantees strong exception -safety without explicitly disallowing a throwing move constructor. -

- -

-Regression -

- -

This section only refers to cases in which the contained object -is by itself a standard container.

- -

Move constructors of standard containers are allowed to throw and therefore -existing operations are broken, compared with C++03, due to move optimization. -(In fact existing implementations like Dinkumware are actually throwing).

- -

For example, vector< list<int> >::reserve yields -undefined behavior since list<int>'s move constructor is allowed to throw. -On the other hand, the same operation has strong exception safety guarantee in -C++03.

- -

There are few options to solve this regression:

- -
    -
  1. -Disallow throwing move and throwing default constructor -
    2. - -
  2. -Disallow throwing move but disallowing usage after move -
    3. - -
  3. -Special casing -
    4. - -
  4. -Disallow throwing move and making it optional -
    5. - -
- -

Option 1 is suggested by proposal -N2815 -but it might not be applicable for existing implementations for which -containers default constructors are throwing.

- -

Option 2 limits the usage significantly and it's error prone -by allowing zombie objects that are nothing but destructible (e.g. no clear() -is allowed after move). It also potentially complicates the implementation by -introducing special state.

- -

Option 3 is possible, for example, using default -construction and swap instead of move for standard containers case. The -implementation is also free to provide special hidden operation for non -throwing move without forcing the user the cope with the limitation of option-2 -when using the public move.

- -

Option 4 impact the efficiency in all use cases due to rare throwing move.

- -

The proposed wording will imply option 1 or 3 though option 2 is also -achievable using more wording. I personally oppose to option 2 that has impact -on usability.

- -

-Relaxation for user types -

- -

Disallowing throwing move constructors in general seems very restrictive -since, for example, common implementation of move will be default construction -+ swap so move will throw if the -default constructor will throw. This is currently the case with the Dinkumware -implementation of node based containers (e.g. std::list) -though this section doesn't refer to standard types.

- -

For throwing move constructors it seem that the implementation should have -no problems to provide the basic guarantee instead of the strong one. It's -better to allow throwing move constructors with basic guarantee than to -disallow it silently (compile and run), via undefined behavior.

- -

There might still be cases in which the relaxation will break existing generic -code that assumes the strong guarantee but it's broken either way given a -throwing move constructor since this is not a preserving optimization.

- -

[ -Batavia (2009-05): -]

- -
-

-Bjarne comments (referring to his draft paper): -"I believe that my suggestion simply solves that. Thus, we don't need a throwing move." -

-

-Move to Open and recommend it be deferred until after the next -Committee Draft is issued. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Should wait to get direction from Dave/Rani -(N2983). -

- -

[ -2010-03-28 Daniel updated wording to sync with N3092. -]

- - -
-

-The suggested change of 23.3.3.4 [deque.modifiers]/2 should be removed, -because the current wording does say more general things: -

- -

-2 Remarks: If an exception is thrown other than by the copy constructor, -move constructor, assignment operator, or move assignment operator of T -there are no effects. If an exception is thrown by the move constructor of a -non-CopyConstructible T, the effects are unspecified. -

- -

-The suggested change of 23.3.6.3 [vector.capacity]/2 should be removed, -because the current wording does say more general things: -

- -

-2 Effects: A directive that informs a vector of a planned change -in size, so that it can manage the storage allocation accordingly. After -reserve(), capacity() is greater or equal to the argument of -reserve if reallocation happens; and equal to the previous value of -capacity() otherwise. Reallocation happens at this point if and only if -the current capacity is less than the argument of reserve(). If an -exception is thrown other than by the move constructor of a -non-CopyConstructible type, there are no effects. -

- -
- -

[2011-03-15: Daniel updates wording to sync with N3242 and comments]

- - -

-The issue has nearly been resolved by previous changes to the working paper, in -particular all suggested changes for deque and vector are no -longer necessary. The still remaining parts involve the unordered associative containers. -

- -

[2011-03-24 Madrid meeting]

- - -

It looks like this issue has been resolved already by noexcept paper N3050

- - -

Rationale:

-Resolved by N3050 -

- -

Proposed resolution:

- -

-23.2.1 [container.requirements.general] paragraph 10 add footnote: -

- -
-

--10- Unless otherwise specified (see 23.2.4.1 [associative.reqmts.except], 23.2.5.1 [unord.req.except], -23.3.3.4 [deque.modifiers], and 23.3.6.5 [vector.modifiers]) all container types defined in this -Clause meet the following additional requirements: -

-
    -
  • …
    • -
- -

-[Note: for compatibility with C++ 2003, when "no effect" is required, standard containers should not use the -value_type's throwing move constructor when the contained object is by itself a standard container. — end note] -

- -
- -

23.2.5.1 [unord.req.except] change paragraph 2+4 to say:

- -
-

--2- For unordered associative containers, if an exception is -thrown by any operation other than the container's hash function from within an -insert() function inserting a single element, the insert() -function has no effect unless the exception is thrown by the contained -object move constructor. -

-[…] -

--4- For unordered associative containers, if an exception is -thrown from within a rehash() function other than by the container's hash -function or comparison function, the rehash() function has no effect -unless the exception is thrown by the contained -object move constructor.

- -
- -

-Keep 23.3.3.4 [deque.modifiers] paragraph 2 unchanged [Drafting note: The originally -proposed wording did suggest to add a last sentence as follows: -

-

-If an exception is thrown by push_back() or emplace_back() -function, that function has no effects unless the exception is thrown by -the move constructor of T. -

-

— end drafting note ]

- -

--2- Remarks: If an exception is thrown other than by -the copy constructor, move constructor, assignment operator, -or move assignment operator of T there are no effects. -If an exception is thrown by the move constructor of a non-CopyInsertable -T, the effects are unspecified. -

- -

-Keep 23.3.6.3 [vector.capacity] paragraph 2 unchanged [Drafting note: The originally -proposed wording did suggest to change the last sentence as follows: -

-

-If an exception is thrown, there are no effects unless the exception is thrown by the -contained object move constructor. -

-

— end drafting note ]

- -

--2- Effects: A directive that informs a vector -of a planned change in size, so -that it can manage the storage allocation accordingly. After reserve(), -capacity() is greater or equal to the argument of reserve -if reallocation happens; and equal -to the previous value of capacity() -otherwise. Reallocation happens at this point if and only if the current -capacity is less than the argument of reserve(). -If an exception is thrown other than by the move constructor of a -non-CopyInsertable type, there are no effects. -

- -

-Keep 23.3.6.3 [vector.capacity] paragraph 12 unchanged [Drafting note: The originally -proposed wording did suggest to change the old paragraph as follows: -

-

--12- Requires: If value_type has a move constructor, -that constructor shall not throw any exceptions. -If an exception is thrown, there are no effects unless the exception is thrown by -the contained object move constructor. -

-

— end drafting note ]

- -

--12- Requires: If an exception is thrown other than by the move constructor of a non-CopyInsertable -T there are no effects. -

- -

-Keep 23.3.6.5 [vector.modifiers] paragraph 1 unchanged [Drafting note: The originally -proposed wording did suggest to change the old paragraph as follows: -

-

--1- Requires: If value_type has a move constructor, -that constructor shall not throw any exceptions. -Remarks: If an exception is thrown by push_back() -or emplace_back() function, that function has no effect unless the -exception is thrown by the move constructor of T. -

-

— end drafting note ]

- -

--1- Remarks: Causes reallocation if the new size is greater than the old capacity. If no reallocation happens, -all the iterators and references before the insertion point remain valid. If an exception is thrown other -than by the copy constructor, move constructor, assignment operator, or move assignment operator -of T or by any InputIterator operation there are no effects. If an exception is thrown by the move -constructor of a non-CopyInsertable T, the effects are unspecified. -

- - - - - - -
-

986. Generic try_lock contradiction

-

Section: 30.4.3 [thread.lock.algorithm] Status: C++11 - Submitter: Chris Fairles Opened: 2009-02-14 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-In 30.4.3 [thread.lock.algorithm], the generic try_lock effects (p2) say that a failed -try_lock is when it either returns false or throws an exception. In -the event a call to try_lock does fail, by either returning false or -throwing an exception, it states that unlock shall be called for all -prior arguments. Then the returns clause (p3) goes on to state -in a note that after returning, either all locks are locked or none -will be. So what happens if multiple locks fail on try_lock? -

- -

-Example: -

- -
-#include <mutex>
-
-int main() {
- std::mutex m0, m1, m2;
- std::unique_lock<std::mutex> l0(m0, std::defer_lock);
- std::unique_lock<std::mutex> l1(m1); //throws on try_lock
- std::unique_lock<std::mutex> l2(m2); //throws on try_lock
-
- int result = std::try_lock(l0, l1, l2);
-
- assert( !l0.owns_lock() );
- assert( l1.owns_lock() ); //??
- assert( l2.owns_lock() ); //??
-}
-
- -

-The first lock's try_lock succeeded but, being a prior argument to a -lock whose try_lock failed, it gets unlocked as per the effects clause -of 30.4.3 [thread.lock.algorithm]. However, 2 locks remain locked in this case but the return -clause states that either all arguments shall be locked or none will -be. This seems to be a contradiction unless the intent is for -implementations to make an effort to unlock not only prior arguments, -but the one that failed and those that come after as well. Shouldn't -the note only apply to the arguments that were successfully locked? -

- -

-Further discussion and possible resolutions in c++std-lib-23049. -

- -

[ -Summit: -]

- -

-Move to review. Agree with proposed resolution. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

- -

-Change 30.4.3 [thread.lock.algorithm], p2: -

- -

--2- Effects: Calls try_lock() for each argument in order -beginning with the first until all arguments have been processed or a -call to try_lock() fails, either by returning false or by throwing an -exception. If a call to try_lock() fails, unlock() shall be called for -all prior arguments and there shall be no further calls to try_lock(). -

- -

-Delete the note from 30.4.3 [thread.lock.algorithm], p3 -

- -

--3- Returns: -1 if all calls to try_lock() returned true, -otherwise a 0-based index value that indicates -the argument for which try_lock() returned false. [Note: -On return, either all arguments will be -locked or none will be locked. -- end note] -

- - - - - -
-

987. reference_wrapper and function types

-

Section: 20.9.4 [refwrap] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-02-18 Last modified: 2015-04-08

-

View all other issues in [refwrap].

-

View all issues with C++11 status.

-

Discussion:

-

-The synopsis in 20.9.4 [refwrap] says: -

- -
-template <ObjectType T> class reference_wrapper
-...
-
- -

-And then paragraph 3 says: -

- -
-

-The template instantiation reference_wrapper<T> shall be -derived from std::unary_function<T1, R> only if the type -T is any of the following: -

- -
    -
  • -a function type or a pointer to function type taking one argument of -type T1 and returning R -
    • -
-
- -

-But function types are not ObjectTypes. -

- -

-Paragraph 4 contains the same contradiction. -

- -

[ -Post Summit: -]

- - -
-

-Jens: restricted reference to ObjectType -

-

-Recommend Review. -

-
- -

[ -Post Summit, Peter adds: -]

- - -
-

-In https://svn.boost.org/trac/boost/ticket/1846 -however Eric Niebler makes the very reasonable point that reference_wrapper<F>, -where F is a function type, represents a reference to a function, -a legitimate entity. So boost::ref was changed to allow it. -

-

-http://svn.boost.org/svn/boost/trunk/libs/bind/test/ref_fn_test.cpp -

-

-Therefore, I believe an alternative proposed resolution for issue 987 could simply -allow reference_wrapper to be used with function types. -

-
- -

[ -Post Summit, Howard adds: -]

- - -
-

-I agree with Peter (and Eric). I got this one wrong on my first try. Here -is code that demonstrates how easy (and useful) it is to instantiate -reference_wrapper with a function type: -

- -
-#include <functional>
-
-template <class F>
-void test(F f);
-
-void f() {}
-
-int main()
-{
-    test(std::ref(f));
-}
-
- -

-Output (link time error shows type of reference_wrapper instantiated -with function type): -

- -
-Undefined symbols:
-  "void test<std::reference_wrapper<void ()()> >(std::reference_wrapper<void ()()>)",...
-
- -

-I've taken the liberty of changing the proposed wording to allow function types -and set to Open. I'll also freely admit that I'm not positive ReferentType -is the correct concept. -

- -
- - - -

[ -Batavia (2009-05): -]

- -
-

-Howard observed that FunctionType, -a concept not (yet?) in the Working Paper, -is likely the correct constraint to be applied. -However, the proposed resolution provides an adequate approximation. -

-

-Move to Review. -

-
- -

[ -2009-05-23 Alisdair adds: -]

- - -
-

-By constraining to PointeeType we rule out the ability for T to be a -reference, and call in reference-collapsing. I'm not sure if this is -correct and intended, but would like to be sure the case was considered. -

-

-Is dis-allowing reference types and the -implied reference collapsing the intended result? -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Review to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-10-14 Daniel provided de-conceptified wording. -]

- - -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change 20.9.4 [refwrap]/1 as indicated: -

- -

-reference_wrapper<T> is a CopyConstructible and -CopyAssignable wrapper around a -reference to an object or function of type T. -

- - - - - - - - -
-

990. monotonic_clock::is_monotonic must be true

-

Section: X [time.clock.monotonic] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-03-09 Last modified: 2015-04-08

-

View all other issues in [time.clock.monotonic].

-

View all issues with C++11 status.

-

Discussion:

-

-There is some confusion over what the value of monotonic_clock::is_monotonic -when monotonic_clock is a synonym for system_clock. The -intent is that if monotonic_clock exists, then monotonic_clock::is_monotonic -is true. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-Change X [time.clock.monotonic], p1: -

- -

--1- Objects of class monotonic_clock represent clocks for which -values of time_point never decrease as physical time advances. -monotonic_clock may be a synonym for system_clock -if and only if system_clock::is_monotonic is -true. -

- - - - - -
-

991. Provide allocator for wstring_convert

-

Section: 22.3.3.2.2 [conversions.string] Status: C++11 - Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2015-04-08

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-50 [CD1]

-

-Add custom allocator parameter to wstring_convert, since we cannot -allocate memory for strings from a custom allocator. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 22.3.3.2.2 [conversions.string]: -

- -
-template<class Codecvt, class Elem = wchar_t,
-         class Wide_alloc = std::allocator<Elem>,
-         class Byte_alloc = std::allocator<char> > class wstring_convert {
-  public:
-    typedef std::basic_string<char, char_traits<char>, Byte_alloc> byte_string;
-    typedef std::basic_string<Elem, char_traits<Elem>, Wide_alloc> wide_string;
-     ...
-
- -

-Change 22.3.3.2.2 [conversions.string], p3: -

- -

--3- The class template describes an ob ject that controls conversions -between wide string ob jects of class -std::basic_string<Elem, char_traits<Elem>, Wide_alloc> -and byte string objects of class -std::basic_string<char, char_traits<char>, Byte_alloc> -(also known as std::string). -

- - - - - - -
-

993. _Exit needs better specification

-

Section: 18.5 [support.start.term] Status: C++11 - Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2015-04-08

-

View all other issues in [support.start.term].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK-188 [CD1]

-

-The function _Exit does not appear to be defined in this standard. -Should it be added to the table of functions included-by-reference to -the C standard? -

- -

[ -2009-05-09 Alisdair fixed some minor issues in the wording. -]

- - -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Add to 18.5 [support.start.term] Table 20 (Header -<cstdlib> synopsis) Functions: -

- -
-_Exit
-
- -

-Add before the description of abort(void): -

- -
-void _Exit [[noreturn]] (int status)
-
- -
-

-The function _Exit(int status) has additional behavior in this -International Standard: -

-
    -
  • -The program is terminated without executing destructors for objects of -automatic, thread, or static storage duration and without calling the -functions passed to atexit() (3.6.3 [basic.start.term]). -
    • -
-
-
- - - - - - -
-

994. quick_exit should terminate well-defined

-

Section: 18.6.2.3 [new.handler] Status: C++11 - Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK-193 [CD1]

-

-quick_exit has been added as a new valid way to terminate a program in a -well defined way. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 18.6.2.3 [new.handler], p2: -

- -
-

--2- Required behavior: ... -

-
    -
  • ...
    • -
  • -call either abort() or exit(); -terminate execution of the program without returning to the caller -
    • -
-
- - - - - - - -
-

997. "Effects: Equivalent to" is underspecified

-

Section: 17.5.1.4 [structure.specifications] Status: C++11 - Submitter: Thomas Plum Opened: 2009-03-03 Last modified: 2015-04-08

-

View all other issues in [structure.specifications].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK-163 [CD1]

-

-Many functions are defined as "Effects: Equivalent to a...", which seems -to also define the preconditions, effects, etc. But this is not made -clear. -

- -

-After studying the occurrences of "Effects: Equivalent to", I agree with -the diagnosis but disagree with the solution. In 21.4.2 [string.cons] -we find -

- -
-

-14 Effects: If InputIterator is an integral type, equivalent to -basic_string(static_cast<size_type>(begin), static_cast<value_type>(end), a) -

-

-15 Otherwise constructs a string from the values in the range [begin, -end), as indicated in the Sequence Requirements table (see 23.1.3). -

-
- -

-This would be devishly difficult to re-write with an explicit -"Equivalent to:" clause. Instead, I propose the following, which will -result in much less editorial re-work. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -

-This issue is related to 492. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Add a new paragraph after 17.5.1.4 [structure.specifications], p3: -

- -
-

--3- Descriptions of function semantics contain the following elements (as appropriate):154 -

- -
    -
  • -Requires: the preconditions for calling the function -
    • -
  • -Effects: the actions performed by the function -
    • -
  • -Postconditions: the observable results established by the function -
    • -
  • -Returns: a description of the value(s) returned by the function -
    • -
  • -Throws: any exceptions thrown by the function, and the conditions that would cause the exception -
    • -
  • -Complexity: the time and/or space complexity of the function -
    • -
  • -Remarks: additional semantic constraints on the function -
    • -
  • -Error conditions: the error conditions for error codes reported by the function. -
    • -
  • -Notes: non-normative comments about the function -
    • -
- -

-Whenever the Effects element specifies that the semantics of some -function F are Equivalent to some code-sequence, then -the various elements are interpreted as follows. If F's -semantics specifies a Requires element, then that requirement is -logically imposed prior to the equivalent-to semantics. Then, -the semantics of the code-sequence are determined by the -Requires, Effects, Postconditions, Returns, -Throws, Complexity, Remarks, Error -Conditions and Notes specified for the (one or more) function -invocations contained in the code-sequence. The value returned from -F is specified by F's Returns element, or -if F has no Returns element, a non-void return from F is specified -by the Returns elements in code-sequence. If -F's semantics contains a Throws (or -Postconditions, or Complexity) element, then that -supersedes any occurrences of that element in the code-sequence. -

-
- - - - - - -
-

998. Smart pointer referencing its owner

-

Section: 20.8.1.2.5 [unique.ptr.single.modifiers] Status: C++11 - Submitter: Pavel Minaev Opened: 2009-02-26 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.modifiers].

-

View all issues with C++11 status.

-

Discussion:

-

-Consider the following (simplified) implementation of -std::auto_ptr<T>::reset(): -

- -
-void reset(T* newptr = 0) { 
-   if (this->ptr && this->ptr != newptr) { 
-     delete this->ptr; 
-   } 
-   this->ptr = newptr; 
-} 
-
- -

-Now consider the following code which uses the above implementation: -

- -
-struct foo { 
-   std::auto_ptr<foo> ap; 
-   foo() : ap(this) {} 
-   void reset() { ap.reset(); } 
-}; 
-int main() { 
-   (new foo)->reset(); 
-} 
-
- -

-With the above implementation of auto_ptr, this results in U.B. at the -point of auto_ptr::reset(). If this isn't obvious yet, let me explain -how this goes step by step: -

- -
    -
  1. -foo::reset() entered -
    2. -
  2. -auto_ptr::reset() entered -
    3. -
  3. -auto_ptr::reset() tries to delete foo -
    4. -
  4. -foo::~foo() entered, tries to destruct its members -
    5. -
  5. -auto_ptr::~auto_ptr() executed - auto_ptr is no longer a valid object! -
    6. -
  6. -foo::~foo() left -
    7. -
  7. -auto_ptr::reset() sets its "ptr" field to 0 <- U.B.! auto_ptr -is not a valid object here already! -
    8. -
- -

[ -Thanks to Peter Dimov who recognized the connection to unique_ptr and -brought this to the attention of the LWG, and helped with the solution. -]

- - -

[ -Howard adds: -]

- - -

-To fix this behavior reset must be specified such that deleting the -pointer is the last action to be taken within reset. -

- -

[ -Alisdair adds: -]

- - -
-

-The example providing the rationale for LWG 998 is poor, as it relies on -broken semantics of having two object believing they are unique owners of a -single resource. It should not be surprising that UB results from such -code, and I feel no need to go out of our way to support such behaviour. -

-

-If an example is presented that does not imply multiple ownership of a -unique resource, I would be much more ready to accept the proposed -resolution. -

-
- -

[ -Batavia (2009-05): -]

- -
-

-Howard summarizes: -

-

-This issue has to do with circular ownership, -and affects auto_ptr, too (but we don't really care about that). -It is intended to spell out the order in which operations must be performed -so as to avoid the possibility -of undefined behavior in the self-referential case. -

-

-Howard points to message c++std-lib-23175 for another example, -requested by Alisdair. -

-

-We agree with the issue and with the proposed resolution. -Move to Tentatively Ready. -

-
- - - -

Proposed resolution:

-

-Change 20.8.1.2.5 [unique.ptr.single.modifiers], p5 (Effects clause for reset), and p6: -

- -
-

--5- Effects: If get() == nullptr there are no effects. Otherwise get_deleter()(get()). -Assigns p to the stored pointer, and then if the old value of the pointer is not -equal to nullptr, calls get_deleter()(the old value of the pointer). -[Note: The order of these operations is significant because the call to get_deleter() -may destroy *this. -- end note] -

- -

--6- Postconditions: get() == p. -[Note: The postcondition does not hold if the call to -get_deleter() destroys *this since this->get() is no longer a valid -expression. -- end note] -

-
- - - - - -
-

999. Taking the address of a function

-

Section: 20.7.12 [specialized.algorithms] Status: C++11 - Submitter: Peter Dimov Opened: 2009-03-09 Last modified: 2015-04-08

-

View all other issues in [specialized.algorithms].

-

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-

Discussion:

-

-The same fix (reference 987) may be applied to addressof, which is also constrained to -ObjectType. (That was why boost::ref didn't work with functions - it -tried to apply boost::addressof and the reinterpret_cast<char&> -implementation of addressof failed.) -

- - - -

[ -Batavia (2009-05): -]

- -
-

-We agree. -

-

-Move to Tentatively Ready. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-10-10 Daniel updates wording to concept-free. -]

- - -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

-

[ -The resolution assumes that addressof is reintroduced as described in -n2946 -]

- - -

-In 20.7.12 [specialized.algorithms] change as described: -

- -
-template <class T> T* addressof(T& r);
-
-

-Returns: The actual address of the object or function -referenced by r, even in the presence of an overloaded operator&. -

-
- - - - - - - -
-

1004. Clarify "throws an exception"

-

Section: 17.6.4.8 [res.on.functions] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [res.on.functions].

-

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-

Discussion:

- -

Addresses UK 179

- -

-According to the 4th bullet there is a problem if "if any replacement -function or handler function or destructor operation throws an -exception". There should be no problem throwing exceptions so long as -they are caught within the function. -

- -

[ -Batavia (2009-05): -]

- -

-The phrasing "throws an exception" is commonly used elsewhere -to mean "throws or propagates an exception." -Move to Open pending a possible more general resolution. -

- -

[ -2009-07 Frankfurt: -]

- - -

-Replace "propagates" in the proposed resolution with the phrase "exits -via" and move to Ready. -

- - - -

Proposed resolution:

-

-Change the 4th bullet of 17.6.4.8 [res.on.functions], p2: -

- -
-
    -
  • -if any replacement function or handler function or destructor operation -throws exits via an exception, unless specifically -allowed in the applicable Required behavior: paragraph. -
    • -
-
- - - - - - -
-

1006. operator delete in garbage collected implementation

-

Section: 18.6.1 [new.delete] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [new.delete].

-

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-

Discussion:

- -

Addresses UK 190

- -

-It is not entirely clear how the current specification acts in the -presence of a garbage collected implementation. -

- -

[ -Summit: -]

- - -

-Agreed. -

- -

[ -2009-05-09 Alisdair adds: -]

- - -

-Proposed wording is too strict for implementations that do not support -garbage collection. Updated wording supplied. -

- -

[ -Batavia (2009-05): -]

- -

-We recommend advancing this to Tentatively Ready -with the understanding that it will not be moved for adoption -unless and until the proposed resolution to Core issue #853 is adopted. -

- - -

Proposed resolution:

- -

-(Editorial note: This wording ties into the proposed -resolution for Core #853) -

- -

-Add paragraphs to 18.6.1.1 [new.delete.single]: -

- -
-void operator delete(void* ptr) throw();
-void operator delete(void* ptr, const std::nothrow_t&) throw();
-
- -

[ -The second signature deletion above is editorial. -]

- - -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-10- ...

-
- -
-void operator delete(void* ptr, const std::nothrow_t&) throw();
-
- -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-15- ...

-
- -
- -

-Add paragraphs to 18.6.1.2 [new.delete.array]: -

- -
-void operator delete[](void* ptr) throw();
-void operator delete[](void* ptr, const std::nothrow_t&) throw();
-
- -

[ -The second signature deletion above is editorial. -]

- - -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-9- ...

-
- -
-void operator delete[](void* ptr, const std::nothrow_t&) throw();
-
- -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-13- ...

-
- -
- - -

-Add paragraphs to 18.6.1.3 [new.delete.placement]: -

- -
-void operator delete(void* ptr, void*) throw();
-
- -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-7- ...

-
- -
-void operator delete[](void* ptr, void*) throw();
-
- -
-

-Requires: If an implementation has strict pointer safety -(3.7.4.3 [basic.stc.dynamic.safety]) then ptr shall -be a safely-derived pointer. -

- -

-9- ...

-
- -
- - - - - - -
-

1011. next/prev wrong iterator type

-

Section: 24.4.4 [iterator.operations] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [iterator.operations].

-

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-

Discussion:

- -

Addresses UK 271

- -

-next/prev return an incremented iterator without changing the value of -the original iterator. However, even this may invalidate an -InputIterator. A ForwardIterator is required to guarantee the -'multipass' property. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-10-14 Daniel provided de-conceptified wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

- - -
    -
  1. -

    -Change header <iterator> synopsis 24.3 [iterator.synopsis] as indicated: -

    - -
    -// 24.4.4, iterator operations:
-...
-template <class InputForwardIterator>
-  InputForwardIterator
-  next(InputForwardIterator x, typename std::iterator_traits<InputForwardIterator>::difference_type n = 1);
-
    -
    2. - -
  2. -

    -Change 24.4.4 [iterator.operations] before p.6 as indicated: -

    - -
    -template <class InputForwardIterator>
-  InputForwardIterator
-  next(InputForwardIterator x, typename std::iterator_traits<InputForwardIterator>::difference_type n = 1);
-
    -
    3. -
- - - - - - -
-

1012. reverse_iterator default ctor should value initialize

-

Section: 24.5.1.3.1 [reverse.iter.cons] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 277

- -

-The default constructor default-initializes current, rather than -value-initializes. This means that when Iterator corresponds to a -trivial type, the current member is left un-initialized, even when the -user explictly requests value intialization! At this point, it is not -safe to perform any operations on the reverse_iterator other than assign -it a new value or destroy it. Note that this does correspond to the -basic definition of a singular iterator. -

- -

[ -Summit: -]

- - -

-Agree with option i. -

- -

-Related issue: 408 -

- -

[ -Batavia (2009-05): -]

- -

-We believe this should be revisited -in conjunction with issue 408, -which nearly duplicates this issue. -Move to Open. -

- -

[ -2009-07 post-Frankfurt: -]

- - -
-

-Change "constructed" to "initialized" in two places in the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- -

[ -2009 Santa Cruz: -]

- - -

-Moved to Ready for this meeting. -

- - - -

Proposed resolution:

-

-Change [reverse.iter.con]: -

- -
-reverse_iterator();
-
-

--1- Effects: Default Value initializes current. Iterator -operations applied to the resulting iterator have defined behavior if and -only if the corresponding operations are defined on a default constructed -value initialized -iterator of type Iterator. -

-
- -

-Change 24.5.3.3.1 [move.iter.op.const]: -

- -
-move_iterator();
-
-

--1- Effects: Constructs a move_iterator, default value -initializing current. -Iterator -operations applied to the resulting iterator have defined behavior if and -only if the corresponding operations are defined on a -value initialized -iterator of type Iterator. -

-
- - - - - - -
-

1014. basic_regex should be created/assigned from initializer lists

-

Section: 28.8.2 [re.regex.construct] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [re.regex.construct].

-

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-

Discussion:

- -

Addresses UK 317 and JP 74

- -

-UK 317: -

- -

-basic_string has both a constructor and an assignment operator that -accepts an initializer list, basic_regex should have the same. -

- -

-JP 74: -

- -

-basic_regex & operator= (initializer_list<T>); is not defined. -

- -

[ -Batavia (2009-05): -]

- -

-UK 317 asks for both assignment and constructor, -but the requested constructor is already present in the current Working Paper. -We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 28.8 [re.regex]: -

- -
-template <class charT,
-          class traits = regex_traits<charT> >
-class basic_regex {
-  ...
-  basic_regex& operator=(const charT* ptr);
-  basic_regex& operator=(initializer_list<charT> il);
-  template <class ST, class SA>
-    basic_regex& operator=(const basic_string<charT, ST, SA>& p);
-  ...
-};
-
- -

-Add in 28.8.2 [re.regex.construct]: -

- -
-

--20- ... -

-
-basic_regex& operator=(initializer_list<charT> il);
-
-

--21- Effects: returns assign(il.begin(), il.end()); -

-
- - - - - - -
-

1019. Make integral_constant objects useable in integral-constant-expressions

-

Section: 20.10.3 [meta.help] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [meta.help].

-

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-

Discussion:

- -

Addresses UK 205 [CD1]

- -

-integral_constant objects should be usable in integral-constant-expressions. -The addition to the language of literal types and the enhanced rules for -constant expressions make this possible. -

- -

[ -Batavia (2009-05): -]

- -

-We agree that the static data member -ought be declared constexpr, -but do not see a need for the proposed operator value_type(). -(A use case would be helpful.) -Move to Open. -

- -

[ -2009-05-23 Alisdair adds: -]

- - -
-

-The motivating case in my mind is that we can then use -true_type and false_type as integral Boolean expressions, for example inside -a static_assert declaration. In that sense it is purely a matter of style. -

-

-Note that Boost has applied the non-explicit conversion operator for many -years as it has valuable properties for extension into other metaprogramming -libraries, such as MPL. If additional rationale is desired I will poll the -Boost lists for why this extension was originally applied. I would argue -that explicit conversion is more appropriate for 0x though. -

-
- -

[ -2009-07-04 Howard adds: -]

- - -
-

-Here's a use case which demonstrates the syntactic niceness which Alisdair describes: -

- -
-#define requires(...) class = typename std::enable_if<(__VA_ARGS__)>::type
-
-template <class T, class U,
-    requires(!is_lvalue_reference<T>() ||
-              is_lvalue_reference<T>() && is_lvalue_reference<U>()),
-    requires(is_same<typename base_type<T>::type,
-                     typename base_type<U>::type>)>
-inline
-T&&
-forward(U&& t)
-{
-    return static_cast<T&&>(t);
-}
-
-
- -

[ -2009-07 post-Frankfurt: -]

- - -

-Move to Tentatively Ready. -

- -

[ -2009 Santa Cruz: -]

- - -

-Moved to Ready for this meeting. -

- - - -

Proposed resolution:

-

-Add to the integral_constant struct definition in 20.10.3 [meta.help]: -

- -
-template <class T, T v>
-struct integral_constant {
-  static constexpr T value = v;
-  typedef T value_type;
-  typedef integral_constant<T,v> type;
-  constexpr operator value_type() { return value; }
-};
-
- - - - - -
-

1021. Allow nullptr_t assignments to unique_ptr

-

Section: 20.8.1.2.3 [unique.ptr.single.asgn] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.asgn].

-

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-

Discussion:

- -

Addresses UK 211 [CD1]

- -

-The nullptr_t type was introduced to resolve the null pointer literal -problem. It should be used for the assignment operator, as with the -constructor and elsewhere through the library. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change the synopsis in 20.8.1.2 [unique.ptr.single]: -

- -
-unique_ptr& operator=(unspecified-pointer-type nullptr_t);
-
- -

-Change 20.8.1.2.3 [unique.ptr.single.asgn]: -

- -
-unique_ptr& operator=(unspecified-pointer-type nullptr_t);
-
-

-Assigns from the literal 0 or NULL. [Note: The -unspecified-pointer-type is often implemented as a pointer to a -private data member, avoiding many of the implicit conversion pitfalls. -— end note] -

-
- - - - - -
-

1030. Missing requirements for smart-pointer safety API

-

Section: 20.8.2.6 [util.smartptr.shared.atomic] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.atomic].

-

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-

Discussion:

- -

Addresses JP 44 [CD1]

- -

-The 1st parameter p and 2nd parameter v is now -shared_ptr<T>*. -

-

-It should be shared_ptr<T>&, or if these are -shared_ptr<T>* then add the "p shall not be a -null pointer" at the requires. -

- -

[ -Summit: -]

- - -

-Agree. All of the functions need a requirement that p (or -v) is a pointer to a valid object. -

- -

[ -2009-07 post-Frankfurt: -]

- - -
-

-Lawrence explained that these signatures match the regular atomics. The -regular atomics must not use references because these signatures are -shared with C. The decision to pass shared_ptrs by pointer rather than -by reference was deliberate and was motivated by the principle of least -surprise. -

-

-Lawrence to write wording that requires that the pointers not be null. -

-
- -

[ -2009-09-20 Lawrence provided wording: -]

- - -
-

-The parameter types for atomic shared pointer access -were deliberately chosen to be pointers -to match the corresponding parameters of the atomics chapter. -Those in turn were deliberately chosen -to match C functions, -which do not have reference parameters. -

-

-We adopt the second suggestion, -to require that such pointers not be null. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-In section "shared_ptr atomic access" -20.8.2.6 [util.smartptr.shared.atomic], add to each function the -following clause. -

-

-Requires: p shall not be null. -

- - - - - -
-

1033. thread::join() effects?

-

Section: 30.3.1.5 [thread.thread.member] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [thread.thread.member].

-

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-

Discussion:

- -

-While looking at thread::join() I think I spotted a couple of -possible defects in the specifications. I could not find a previous -issue or NB comment about that, but I might have missed it. -

- -

-The postconditions clause for thread::join() is: -

- -

-Postconditions: If join() throws an exception, the value -returned by get_id() is unchanged. Otherwise, get_id() == id(). -

- -

-and the throws clause is: -

- -

-Throws: std::system_error when the postconditions cannot be achieved. -

- -

-Now... how could the postconditions not be achieved? -It's just a matter of resetting the value of get_id() or leave it -unchanged! I bet we can always do that. Moreover, it's a chicken-and-egg -problem: in order to decide whether to throw or not I depend on the -postconditions, but the postconditions are different in the two cases. -

- -

-I believe the throws clause should be: -

- -

-Throws: std::system_error when the effects or postconditions -cannot be achieved. -

- -

-as it is in detach(), or, even better, as the postcondition is -trivially satisfiable and to remove the circular dependency: -

- - -

-Throws: std::system_error if the effects cannot be achieved. -

- -

-Problem is that... ehm... join() has no "Effects" clause. Is that intentional? -

- -

[ -See the thread starting at c++std-lib-23204 for more discussion. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Pete believes there may be some more general language (in frontmatter) -that can address this and related issues such as 962. -

-

-Move to Open. -

-
- -

[ -2009-11-18 Anthony provides wording. -]

- - - -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

Proposed resolution:

-

-Edit 30.3.1.5 [thread.thread.member] as indicated: -

- -
-void join();
-
-
-

-5 Precondition: joinable() is true. -

-

-Effects: Blocks until the thread represented by *this has completed. -

- -

-6 Synchronization: The completion of the thread represented by -*this happens before (1.10 [intro.multithread]) -join() returns. [Note: Operations on *this are not -synchronized. — end note] -

- -

-7 Postconditions: If join() throws an exception, the value -returned by get_id() is unchanged. Otherwise, The thread -represented by *this has completed. get_id() == id(). -

- -

-8 ... -

- - -
-
- - - - - - -
-

1034. Clarify generality of Container Requirement tables

-

Section: 23.2.1 [container.requirements.general] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 222 [CD1]

- -

-It is not clear what purpose the Requirement tables serve in the -Containers clause. Are they the definition of a library Container? Or -simply a conventient shorthand to factor common semantics into a single -place, simplifying the description of each subsequent container? This -becomes an issue for 'containers' like array, which does not meet the -default-construct-to-empty requirement, or forward_list which does not -support the size operation. Are these components no longer containers? -Does that mean the remaining requirements don't apply? Or are these -contradictions that need fixing, despite being a clear design decision? -

- -

-Recommend: -

- -

-Clarify all the tables in 23.2 [container.requirements] are -there as a convenience for documentation, rather than a strict set of -requirements. Containers should be allowed to relax specific -requirements if they call attention to them in their documentation. The -introductory text for array should be expanded to mention a -default constructed array is not empty, and -forward_list introduction should mention it does not provide -the required size operation as it cannot be implemented -efficiently. -

- -

[ -Summit: -]

- - -

-Agree in principle. -

- -

[ -2009-07 post-Frankfurt: -]

- - -

-We agree in principle, but we have a timetable. This group feels that -the issue should be closed as NAD unless a proposed resolution is -submitted prior to the March 2010 meeting. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Looked at this and still intend to close as NAD in March -2010 unless there is proposed wording that we like. -

- -

[ -2010-02-02 Nicolai M. Josuttis updates proposed wording and adds: -]

- - -
-

-I just came across issue #1034 (response to UK 222), -which covers the role of container requirements. -The reason I found this issue was that I am wondering why -array<> is specified to be a sequence container. -For me, currently, this follows from -Sequence containers 23.2.3 [sequence.reqmts] -saying: -

-

-The library provides five basic kinds of sequence containers: array, -vector, forward_list, list, and deque. while -later on in Table 94 "Sequence container requirements" are defined. -

- -

-IMO, you can hardly argue that this is NAD. -We MUST say somewhere that either array is not a sequence container -or does not provide all operations of a sequence container -(even not all requirements of a container in general). -

-

-Here is the number of requirements array<> does not meet -(AFAIK): -

-

-general container requirements: -

-
    -
  • -a default constructed array is not empty -
    • -
  • -swap has no constant complexity -
    • -
- -

- Note also that swap not only has linear complexity - it also invalidates iterators (or to be more precise, - assigns other values to the elements), which - is different from the effect swap has for other containers. - For this reason, I must say that i tend to propose to - remove swap() for arrays. -

- -

-sequence container requirements: -

- -
    -
  • -There is no constructor and assignment for a range -
    • -
  • -There is no constructor and assignment for n copies of t -
    • -
  • - There are no emplace, insert, erase, clear, - assign operations -
    • -
- -

-In fact, out of all sequence container requirements array<> only -provides the following operations: -from sequence requirements (Table 94): -

-
-X(il);
-a = il;
-
-

-and from optional requirements (Table 95): -

-
-[], at(), front(), back()
-
-

-This is almost nothing! -

- -

-Note in addition, that due to the fact that -array is an aggregate and not a container with -initializer_lists -a construction or assignment with an initializer list is valid -for all sequence containers but not valid for array: -

- -
-vector<int>  v({1,2,3});   // OK
-v = {4,5,6};               // OK
-
-array<int,3> a({1,2,3});   // Error
-array<int,3> a = {1,2,3};  // OK
-a = {4,5,6};               // Error
-
- -

-BTW, for this reason, I am wondering, why <array> includes -<initializer_list>. -

- -

-IMO, we can't really say that array is a sequence container. -array is special. -As the solution to this issue seemed to miss some proposed wording -where all could live with, let me try to suggest some. -

- -
- -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: Ok with move to Ready except for "OPEN:" part. -]

- - - - -

Proposed resolution:

- -

In Sequence containers 23.2.3 [sequence.reqmts] modify paragraph 1 as -indicated:

-
-

1 A sequence container organizes a finite set of objects, all of the same - type, into a strictly linear arrangement. The library provides five - four basic kinds of sequence containers: array, - vector, forward_list, list, and deque. - In addition, array is provided as a sequence container that - only provides limited sequence operations because it has a fixed number of - elements. It The library also provides container adaptors that make it easy to - construct abstract data types, such as stacks or queues, out - of the basic sequence container kinds (or out of other kinds of sequence - containers that the user might define).

-
-

Modify paragraph 2 as follows (just editorial):

-
-

2 The five basic sequence - containers offer the programmer different complexity trade-offs and should be - used accordingly. vector or array is the type of sequence - container that should be used by default. list or forward_list - should be used when there are frequent insertions and deletions from the - middle of the sequence. deque is the data structure of choice when - most insertions and deletions take place at the beginning or at the end of the - sequence.

-
-

In Class template array 23.3.2 [array] modify paragraph 3 as indicated: -

-
-

3 Unless otherwise specified, all array operations are as - described in 23.2. An array satisfies all of the requirements of a - container and of a reversible container (given in two tables in 23.2 [container.requirements]) - except that a default constructed array is not empty, swap - does not have constant complexity, and swap may throw exceptions. An array satisfies some of the requirements of a - sequence container (given in 23.2.3 [sequence.reqmts]). Descriptions are - provided here only for operations on array that are not described - in that Clause in one of these tables or for operations - where there is additional semantic information.

-
-

In array specialized algorithms 23.3.2.3 [array.special] add to the -specification of swap():

-
- 
template <class T, size_t N> void swap(array<T,N>& x, array<T,N>& y);
-
-
-

1 Effects: ...

-

Complexity: Linear in N.

-
-
- - - - - - - - - -
-

1037. Unclear status of match_results as library container

-

Section: 23.2.3 [sequence.reqmts] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 232 [CD1]

- -

-match_results may follow the requirements but is not listed a general -purpose library container. -

- -

-Remove reference to match_results against a[n] operation. -

- -

[ -Summit: -]

- - -

-Agree. operator[] is defined elsewhere. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-In 23.2.3 [sequence.reqmts] Table 84, remove reference to -match_results in the row describing the a[n] operation. -

- - - - - -
-

1038. Sequence requirement table needs to reference several new containers

-

Section: 23.2.3 [sequence.reqmts] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

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-

Discussion:

- -

Addresses UK 233 [CD1]

- -

-Table 84 is missing references to several new container types. -

- -

[ -Summit: -]

- - -

-Agree. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-In 23.2.3 [sequence.reqmts] Table 84, Add reference to listed -containers to the following rows: -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 84 -- Optional sequence container operations
ExpressionReturn typeOperational semanticsContainer
a.front()......vector, list, deque, basic_string, array, forward_list
a.back()......vector, list, deque, basic_string, array
a.emplace_front(args)......list, deque, forward_list
a.push_front(t)......list, deque, forward_list
a.push_front(rv)......list, deque, forward_list
a.pop_front()......list, deque, forward_list
a[n]......vector, deque, basic_string, array
a.at(n)......vector, deque, basic_string, array
-
- - - - - -
-

1039. Sequence container back function should also support const_iterator

-

Section: 23.2.3 [sequence.reqmts] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

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-

Discussion:

- -

Addresses UK 234 [CD1]

- -

-The reference to iterator in semantics for back should -also allow for const_iterator when called on a const-qualified -container. This would be ugly to specify in the 03 standard, but is -quite easy with the addition of auto in this new standard. -

- -

[ -Summit: -]

- - -

-Agree. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-In 23.2.3 [sequence.reqmts] Table 84, replace iterator with auto in semantics for back: -

- -
- - - - - - - - - - - - - - -
Table 84 — Optional sequence container operations
ExpressionReturn typeOperational semanticsContainer
a.back()reference; const_reference for constant a{ iterator auto tmp = a.end();
--tmp;
return *tmp; }		vector, list, deque, basic_string
-
- - - - - -
-

1040. Clarify possible sameness of associative container's iterator and const_iterator

-

Section: 23.2.4 [associative.reqmts] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

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-

Discussion:

- -

Addresses UK 238 [CD1]

- -

-Leaving it unspecified whether or not iterator and const_iterator are the -same type is dangerous, as user code may or may not violate the One -Definition Rule by providing overloads for -both types. It is probably too late to specify a single behaviour, but -implementors should document what to expect. Observing that problems can be -avoided by users restricting themselves to using const_iterator, add a note to that effect. -

-

-Suggest Change 'unspecified' to 'implementation defined'. -

- -

[ -Summit: -]

- - -

-Agree with issue. Agree with adding the note but not with changing the -normative text. We believe the note provides sufficient guidance. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-In 23.2.4 [associative.reqmts] p6, add: -

- -

--6- iterator of an associative container meets the requirements -of the BidirectionalIterator concept. For associative -containers where the value type is the same as the key type, both -iterator and const_iterator are constant iterators. It -is unspecified whether or not iterator and -const_iterator are the same type. -[Note: iterator and const_iterator have identical semantics in -this case, and iterator is convertible to const_iterator. Users can avoid -violating the One Definition Rule by always using const_iterator -in their function parameter lists -- end note] -

- - - - - -
-

1043. Clarify that compare_exchange is not a read-modify-write operation

-

Section: 29.6 [atomics.types.operations] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

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-

Discussion:

- -

Addresses US 91 [CD1]

- -

-It is unclear whether or not a failed compare_exchange is a RMW operation -(as used in 1.10 [intro.multithread]). -

- -

-Suggested solution: -

- -

-Make failing compare_exchange operations not be RMW. -

- -

[ -Anthony Williams adds: -]

- - -

-In 29.6 [atomics.types.operations] p18 it says that "These -operations are atomic read-modify-write operations" (final sentence). -This is overly restrictive on the implementations of -compare_exchange_weak and compare_exchange_strong on platforms without a -native CAS instruction. -

- - -

[ -Summit: -]

- - -

-Group agrees with the resolution as proposed by Anthony Williams in the attached note. -

- -

[ -Batavia (2009-05): -]

- -

-We recommend the proposed resolution be reviewed -by members of the Concurrency Subgroup. -

- -

[ -2009-07 post-Frankfurt: -]

- - -

-This is likely to be addressed by Lawrence's upcoming paper. He will -adopt the proposed resolution. -

- -

[ -2009-08-17 Handled by -N2925. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

-

-Change 29.6 [atomics.types.operations] p18: -

- -

--18- Effects: Atomically, compares the value pointed to by -object or by this for equality with that in -expected, and if true, replaces the value pointed to by -object or by this with desired, and if false, updates -the value in expected with the value pointed to by -object or by this. Further, if the comparison is true, -memory is affected according to the value of success, and if the -comparison is false, memory is affected according to the value of -failure. When only one memory_order argument is -supplied, the value of success is order, and the value -of failure is order except that a value of -memory_order_acq_rel shall be replaced by the value -memory_order_acquire and a value of -memory_order_release shall be replaced by the value -memory_order_relaxed. If the comparison is true, -Tthese operations are atomic -read-modify-write operations (1.10). -If the comparison is false, these -operations are atomic load operations. -

- - - - - - -
-

1044. Empty tag types should be constexpr literals

-

Section: 30.4 [thread.mutex] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [thread.mutex].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 325 [CD1]

- -

-We believe constexpr literal values should be a more natural expression -of empty tag types than extern objects as it should improve the -compiler's ability to optimize the empty object away completely. -

- -

[ -Summit: -]

- - -

-Move to review. The current specification is a "hack", and the proposed -specification is a better "hack". -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change the synopsis in 30.4 [thread.mutex]: -

- -
-struct defer_lock_t {};
-struct try_to_lock_t {};
-struct adopt_lock_t {};
-
-extern constexpr defer_lock_t defer_lock {};
-extern constexpr try_to_lock_t try_to_lock {};
-extern constexpr adopt_lock_t adopt_lock {};
-
- - - - - - -
-

1045. Remove unnecessary preconditions from unique_lock constructor

-

Section: 30.4.2.2.1 [thread.lock.unique.cons] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 326 [CD1]

- -

-The precondition that the mutex is not owned by this thread offers -introduces the risk of unnecessary undefined behaviour into the -program. The only time it matters whether the current thread owns the -mutex is in the lock operation, and that will happen subsequent to -construction in this case. The lock operation has the identical -pre-condition, so there is nothing gained by asserting that precondition -earlier and denying the program the right to get into a valid state -before calling lock. -

- -

[ -Summit: -]

- - -

-Agree, move to review. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Strike 30.4.2.2.1 [thread.lock.unique.cons] p7: -

- -
-unique_lock(mutex_type& m, defer_lock_t);
-
-

--7- Precondition: If mutex_type is not a recursive mutex -the calling thread does not own the mutex. -

-
- - - - - - -
-

1046. Provide simple facility to start asynchronous operations

-

Section: 30.6 [futures] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [futures].

-

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-

Discussion:

- -

Addresses UK 329 [CD1]

- -

-future, promise and packaged_task provide a -framework for creating future values, but a simple function to tie all -three components together is missing. Note that we only need a simple -facility for C++0x. Advanced thread pools are to be left for TR2. -

- -

-Simple Proposal: -

- -

-Provide a simple function along the lines of: -

-
-template< typename F, typename ... Args >
-  requires Callable< F, Args... >
-    future< Callable::result_type > async( F&& f, Args && ... ); 
-
- -

-Semantics are similar to creating a thread object with a packaged_task -invoking f with forward<Args>(args...) -but details are left unspecified to allow different scheduling and thread -spawning implementations. -

-

-It is unspecified whether a task submitted to async is run on its own thread -or a thread previously used for another async task. If a call to async -succeeds, it shall be safe to wait for it from any thread. -

-

-The state of thread_local variables shall be preserved during async calls. -

-

-No two incomplete async tasks shall see the same value of -this_thread::get_id(). -

-

-[Note: this effectively forces new tasks to be run on a new thread, or a -fixed-size pool with no queue. If the -library is unable to spawn a new thread or there are no free worker threads -then the async call should fail. --end note] -

- -

[ -Summit: -]

- - -
-

-The concurrency subgroup has revisited this issue and decided that it -could be considered a defect according to the Kona compromise. A task -group was formed lead by Lawrence Crowl and Bjarne Stroustrup to write a -paper for Frankfort proposing a simple asynchronous launch facility -returning a future. It was agreed that the callable must be run on a -separate thread from the caller, but not necessarily a brand-new thread. -The proposal might or might not allow for an implementation that uses -fixed-size or unlimited thread pools. -

-

-Bjarne in c++std-lib-23121: I think that what we agreed was that to -avoid deadlock async() would almost certainly be specified to launch in -a different thread from the thread that executed async(), but I don't -think it was a specific design constraint. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Proposed resolution: see -N2996 -(Herb's and Lawrence's paper on Async). Move state to NAD editorialResolved. -

- - - -

Proposed resolution:

- - - - - -
-

1047. Ensure that future's get() blocks when not ready

-

Section: 30.6.6 [futures.unique_future] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 334 [CD1]

- -

-Behaviour of get() is undefined if calling get() while -not is_ready(). The intent is that get() is a blocking -call, and will wait for the future to become ready. -

- -

[ -Summit: -]

- - -
-

-Agree, move to Review. -

-
- -

[ -2009-04-03 Thomas J. Gritzan adds: -]

- - -
-

-This issue also applies to shared_future::get(). -

- -

-Suggested wording: -

- -

-Add a paragraph to 30.6.7 [futures.shared_future]: -

- -
-void shared_future<void>::get() const;
-
-

-Effects: If is_ready() would return false, block on the asynchronous -result associated with *this. -

-
-
- -

[ -Batavia (2009-05): -]

- -

-It is not clear to us that this is an issue, -because the proposed resolution's Effects clause seems to duplicate -information already present in the Synchronization clause. -Keep in Review status. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

-

-Add a paragraph to 30.6.6 [futures.unique_future]: -

- -
-R&& unique_future::get(); 
-R& unique_future<R&>::get(); 
-void unique_future<void>::get();
-
-
-

Note:...

-

-Effects: If is_ready() would return false, -block on the asynchronous result associated with *this. -

-

-Synchronization: if *this is associated with a -promise object, the completion of set_value() or -set_exception() to that promise happens before (1.10) -get() returns. -

-
-
- - - - - -
-

1048. Provide empty-state inspection for std::unique_future

-

Section: 30.6.6 [futures.unique_future] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 335 [CD1]

- -

-std::unique_future is MoveConstructible, so you can transfer the -association with an asynchronous result from one instance to another. -However, there is no way to determine whether or not an instance has -been moved from, and therefore whether or not it is safe to wait for it. -

- -
-std::promise<int> p;
-std::unique_future<int> uf(p.get_future());
-std::unique_future<int> uf2(std::move(uf));
-uf.wait(); // oops, uf has no result to wait for. 
-
- -

-Suggest we add a waitable() function to unique_future -(and shared_future) akin to std::thread::joinable(), -which returns true if there is an associated result to wait for -(whether or not it is ready). -

- -

-Then we can say: -

- -
-if(uf.waitable()) uf.wait();
-
- -

[ -Summit: -]

- - -
-

-Create an issue. Requires input from Howard. Probably NAD. -

-
- -

[ -Post Summit, Howard throws in his two cents: -]

- - -
-

-Here is a copy/paste of my last prototype of unique_future which was -several years ago. At that time I was calling unique_future future: -

- -
-template <class R>
-class future
-{
-public:
-    typedef R result_type;
-private:
-    future(const future&);// = delete;
-    future& operator=(const future&);// = delete;
-
-    template <class R1, class F1> friend class prommise;
-public:
-    future();
-    ~future();
-
-    future(future&& f);
-    future& operator=(future&& f);
-
-    void swap(future&& f);
-
-    bool joinable() const;
-    bool is_normal() const;
-    bool is_exceptional() const;
-    bool is_ready() const;
-
-    R get();
-
-    void join();
-    template <class ElapsedTime>
-        bool timed_join(const ElapsedTime&);
-};
-
- -

-shared_future had a similar interface. I intentionally reused -the thread interface where possible to lessen the learning -curve std::lib clients will be faced with. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1049. Move assignment of promise inverted

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

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-

Discussion:

- -

Addresses UK 339 [CD1]

- -

-Move assignment is going in the wrong direction, assigning from -*this to the passed rvalue, and then returning a reference to -an unusable *this. -

- -

[ -Summit: -]

- - -
-

-Agree, move to Review. -

-
- -

[ -Batavia (2009-05): -]

- -

-We recommend deferring this issue until after Detlef's paper (on futures) -has been issued. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

-

-Strike 30.6.5 [futures.promise] p6 and change p7: -

- -
-promise& operator=(promise&& rhs);
-
-
-

--6- Effects: move assigns its associated state to rhs. -

-

--7- Postcondition: *this has no associated -state. associated state of *this is the same as the -associated state of rhs before the call. rhs has no -associated state. -

-
-
- - - - - - -
-

1050. Clarify postconditions for get_future()

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 340 [CD1]

- -

-There is an implied postcondition for get_future() that the state of the -promise is transferred into the future leaving the promise with no -associated state. It should be spelled out. -

- -

[ -Summit: -]

- - -
-

-Agree, move to Review. -

-
- -

[ -2009-04-03 Thomas J. Gritzan adds: -]

- - -
-

-promise::get_future() must not invalidate the state of the promise object. -

-

-A promise is used like this: -

-
-promise<int> p; 
-unique_future<int> f = p.get_future(); 
-// post 'p' to a thread that calculates a value 
-// use 'f' to retrieve the value. 
-
-

-So get_future() must return an object that shares the same associated -state with *this. -

-

-But still, this function should throw an future_already_retrieved error -when it is called twice. -

-

-packaged_task::get_future() throws std::bad_function_call if its future -was already retrieved. It should throw -future_error(future_already_retrieved), too. -

-

-Suggested resolution: -

-

-Replace p12/p13 30.6.5 [futures.promise]: -

-
-

--12- Throws: future_error if *this has no associated state -the future has already been retrieved. -

-

--13- Error conditions: future_already_retrieved if *this -has no associated state -the future associated with -the associated state has already been retrieved. -

-

-Postcondition: The returned object and *this share the associated state. -

-
-

-Replace p14 30.6.9 [futures.task]: -

-
-

--14- Throws: std::bad_function_call future_error if the future associated with -the task has already been retrieved. -

- -

-Error conditions: future_already_retrieved if the future associated with -the task has already been retrieved. -

-

-Postcondition: The returned object and *this share the associated task. -

-
-
- -

[ -Batavia (2009-05): -]

- -

-Keep in Review status pending Detlef's forthcoming paper on futures. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

-

-Add after p13 30.6.5 [futures.promise]: -

- -
-unique_future<R> get_future();
-
-
-

--13- ... -

-

-Postcondition: *this has no associated state. -

-
-
- - - - - - -
-

1054. forward broken

-

Section: 20.2.4 [forward] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-03-13 Last modified: 2015-04-08

-

View all other issues in [forward].

-

View all issues with Resolved status.

-

Discussion:

- -

-This is a placeholder issue to track the fact that we (well I) put the standard -into an inconsistent state by requesting that we accept -N2844 -except for the proposed changes to [forward]. -

- -

-There will exist in the post meeting mailing -N2835 -which in its current state reflects the state of affairs prior to the Summit -meeting. I hope to update it in time for the post Summit mailing, but as I write -this issue I have not done so yet. -

- -

[ -Batavia (2009-05): -]

- - -

-Move to Open, awaiting the promised paper. -

- -

[ -2009-08-02 Howard adds: -]

- - -
-

-My current preferred solution is: -

- -
-template <class T>
-struct __base_type
-{
-   typedef typename remove_cv<typename remove_reference<T>::type>::type type;
-};
-
-template <class T, class U,
-   class = typename enable_if<
-       !is_lvalue_reference<T>::value ||
-        is_lvalue_reference<T>::value &&
-        is_lvalue_reference<U>::value>::type,
-   class = typename enable_if<
-        is_same<typename __base_type<T>::type,
-                typename __base_type<U>::type>::value>::type>
-inline
-T&&
-forward(U&& t)
-{
-   return static_cast<T&&>(t);
-}
-
- -

-This has been tested by Bill, Jason and myself. -

- -

-It allows the following lvalue/rvalue casts: -

- -
    -
  1. -Cast an lvalue t to an lvalue T (identity). -
    2. -
  2. -Cast an lvalue t to an rvalue T. -
    3. -
  3. -Cast an rvalue t to an rvalue T (identity). -
    4. -
- -

-It disallows: -

- -
    -
  1. -Cast an rvalue t to an lvalue T. -
    2. -
  2. -Cast one type t to another type T (such as int to double). -
    3. -
- -

-"a." is disallowed as it can easily lead to dangling references. -"b." is disallowed as this function is meant to only change the lvalue/rvalue -characteristic of an expression. -

- -

-Jason has expressed concern that "b." is not dangerous and is useful in contexts -where you want to "forward" a derived type as a base type. I find this use case -neither dangerous, nor compelling. I.e. I could live with or without the "b." -constraint. Without it, forward would look like: -

- -
-template <class T, class U,
-   class = typename enable_if<
-       !is_lvalue_reference<T>::value ||
-        is_lvalue_reference<T>::value &&
-        is_lvalue_reference<U>::value>::type>
-inline
-T&&
-forward(U&& t)
-{
-   return static_cast<T&&>(t);
-}
-
- -

-Or possibly: -

- -
-template <class T, class U,
-   class = typename enable_if<
-       !is_lvalue_reference<T>::value ||
-        is_lvalue_reference<T>::value &&
-        is_lvalue_reference<U>::value>::type,
-   class = typename enable_if<
-        is_base_of<typename __base_type<U>::type,
-                   typename __base_type<T>::type>::value>::type>
-inline
-T&&
-forward(U&& t)
-{
-   return static_cast<T&&>(t);
-}
-
- - -

-The "promised paper" is not in the post-Frankfurt mailing only because I'm waiting -for the non-concepts draft. But I'm hoping that by adding this information here -I can keep people up to date. -

-
- -

[ -2009-08-02 David adds: -]

- - -
-

-forward was originally designed to do one thing: perfect forwarding. -That is, inside a function template whose actual argument can be a const -or non-const lvalue or rvalue, restore the original "rvalue-ness" of the -actual argument: -

- -
-template <class T>
-void f(T&& x)
-{
-    // x is an lvalue here.  If the actual argument to f was an
-    // rvalue, pass static_cast<T&&>(x) to g; otherwise, pass x.
-    g( forward<T>(x) );
-}
-
- -

-Attempting to engineer forward to accomodate uses other than perfect -forwarding dilutes its idiomatic meaning. The solution proposed here -declares that forward<T>(x) means nothing more than static_cast<T&&>(x), -with a patchwork of restrictions on what T and x can be that can't be -expressed in simple English. -

- -

-I would be happy with either of two approaches, whose code I hope (but -can't guarantee) I got right. -

- -
    -
  1. -

    -Use a simple definition of forward that accomplishes its original -purpose without complications to accomodate other uses: -

    - -
    -template <class T, class U>
-T&& forward(U& x)
-{
-    return static_cast<T&&>(x);
-}
-
    -
    2. - -
  2. -

    -Use a definition of forward that protects the user from as many -potential mistakes as possible, by actively preventing all other -uses: -

    - -
    -template <class T, class U>
-boost::enable_if_c<
-    // in forward<T>(x), x is a parameter of the caller, thus an lvalue
-    is_lvalue_reference<U>::value
-    // in caller's deduced T&& argument, T can only be non-ref or lvalue ref
-    && !is_rvalue_reference<T>::value
-    // Must not cast cv-qualifications or do any type conversions
-    && is_same<T&,U&>::value
-    , T&&>::type forward(U&& a)
-{
-    return static_cast<T&&>(a);
-}
-
    -
    3. -
- -
- -

[ -2009-09-27 Howard adds: -]

- - -

-A paper, -N2951, -is available which compares several implementations (including David's) with respect to several -use cases (including Jason's) and provides wording for one implementation. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2951. -

- - - -

Proposed resolution:

- - - - - -
-

1055. Provide a trait that returns the underlying type of an enumeration type

-

Section: 20.10.7.6 [meta.trans.other] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

- -

Addresses UK 98 [CD1]

- -

-It would be useful to be able to determine the underlying -type of an arbitrary enumeration type. This would allow -safe casting to an integral type (especially needed for -scoped enums, which do not promote), and would allow -use of numeric_limits. In general it makes generic -programming with enumerations easier. -

- -

[ -Batavia (2009-05): -]

- -

-Pete observes (and Tom concurs) -that the proposed resolution seems to require compiler support -for its implementation, -as it seems necessary to look at the range of values -of the enumerated type. -To a first approximation, -a library solution could give an answer based on the size of the type. -If the user has specialized numeric_limits for the enumerated type, -then the library might be able to do better, -but there is no such requirement. -Keep status as Open -and solicit input from CWG. -

- -

[ -2009-05-23 Alisdair adds: -]

- - -

-Just to confirm that the BSI originator of this comment assumed it did -indeed imply a compiler intrinsic. Rather than request a Core extension, it -seemed in keeping with that the type traits interface provides a library API -to unspecified compiler features - where we require several other traits -(e.g. has_trivial_*) to get the 'right' answer now, unlike in TR1. -

- -

[ -Addressed in N2947. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2984. -

- - - -

Proposed resolution:

-

-Add a new row to the table in 20.10.7.6 [meta.trans.other]: -

- -
- - - - - - - - - - - - -
Table 41 -- Other transformations
TemplateConditionComments
-template< class T > struct enum_base; - -T shall be an enumeration type (7.2 [dcl.enum]) - -The member typedef type shall name the underlying type -of the enum T. -
-
- - - - - -
-

1065. Allow inline namespaces within namespace std for implementations

-

Section: 17.6.1.1 [contents] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-03-15 Last modified: 2015-04-08

-

View all other issues in [contents].

-

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-

Discussion:

-

Addresses UK 168 [CD1]

-

-We should make it clear (either by note or normatively) that namespace -std may contain inline namespaces, and that entities specified to be -defined in std may in fact be defined in one of these inline namespaces. -(If we're going to use them for versioning, eg when TR2 comes along, -we're going to need that.) -

- -

-Replace "namespace std or namespaces nested within namespace std" with -"namespace std or namespaces nested within namespace std or inline -namespaces nested directly or indirectly within namespace std" -

- -

[ -Summit: -]

- -

-adopt UK words (some have reservations whether it is correct) -

- -

[ -2009-05-09 Alisdair improves the wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Bill believes there is strictly speaking no need to say that -because no portable test can detect the difference. -However he agrees that it doesn't hurt to say this. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-Change 17.6.1.1 [contents] p2: -

- -

-All library entities except macros, operator new and -operator delete are defined within the namespace std or -namespaces nested within namespace std. -It is unspecified whether names declared in a specific namespace -are declared directly in that namespace, or in an inline namespace inside -that namespace. [Footnote: This gives implementers freedom to support -multiple configurations of the library.] -

- - - - - -
-

1066. Use [[noreturn]] attribute in the library

-

Section: 18 [language.support] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-03-15 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK 189 and JP 27 [CD1]

-

-The addition of the [[noreturn]] attribute to the language will be an -important aid for static analysis tools. -

- -

-The following functions should be declared in C++ with the -[[noreturn]] attribute: abort exit -quick_exit terminate unexpected -rethrow_exception throw_with_nested. -

- -

[ -Summit: -]

- -

-Agreed. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 18.5 [support.start.term] p3: -

- -
-

-2- ...

-
-void abort [[noreturn]] (void)
-
-

-3- ...

-

-6- ...

-
-void exit [[noreturn]] (int status)
-
-

-7- ...

-

-11- ...

-
-void quick_exit [[noreturn]] (int status)
-
-

-12- ...

-
- -

-Change the <exception> synopsis in 18.8 [support.exception]: -

- -
-void unexpected [[noreturn]] ();
-...
-void terminate [[noreturn]] ();
-...
-void rethrow_exception [[noreturn]] (exception_ptr p);
-...
-template <class T> void throw_with_nested [[noreturn]] (T&& t); // [[noreturn]]
-
- -

-Change D.8.4 [unexpected]: -

- -
-void unexpected [[noreturn]] ();
-
- -

-Change 18.8.3.4 [terminate]: -

- -
-void terminate [[noreturn]] ();
-
- -

-Change 18.8.5 [propagation]: -

- -
-void rethrow_exception [[noreturn]] (exception_ptr p);
-
- -

-In the synopsis of 18.8.6 [except.nested] and the definition area change: -

- -
-template <class T> void throw_with_nested [[noreturn]] (T&& t); // [[noreturn]]
-
- - - - - -
-

1070. Ambiguous move overloads in function

-

Section: 20.9.12.2 [func.wrap.func] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-03-19 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The synopsis in 20.9.12.2 [func.wrap.func] says: -

- -
-template<Returnable R, CopyConstructible... ArgTypes> 
-class function<R(ArgTypes...)>
-{
-    ...
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function(F); 
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function(F&&);
-    ...
-    template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F); 
-    template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F&&);
-    ...
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes..> 
-            && Convertible<Callable<F, ArgTypes...>::result_type 
-      function& operator=(F); 
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function& operator=(F&&);
-    ...
-};
-
- -

-Each of the 3 pairs above are ambiguous. We need only one of each pair, and we -could do it with either one. If we choose the F&& version we -need to bring decay into the definition to get the pass-by-value behavior. -In the proposed wording I've gotten lazy and just used the pass-by-value signature. -

- -

[ -2009-05-01 Daniel adds: -]

- - -

-1024 modifies the second removed constructor. -

- -

[ -Batavia (2009-05): -]

- -
-

-We briefly discussed whether we ought support moveable function objects, -but decided that should be a separate issue if someone cares to propose it. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-Change the synopsis of 20.9.12.2 [func.wrap.func], and remove the associated definitions in -20.9.12.2.1 [func.wrap.func.con]: -

- -
-template<Returnable R, CopyConstructible... ArgTypes> 
-class function<R(ArgTypes...)>
-{
-    ...
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function(F); 
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function(F&&);
-    ...
-    template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F); 
-    template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F&&);
-    ...
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes..> 
-            && Convertible<Callable<F, ArgTypes...>::result_type 
-      function& operator=(F); 
-    template<class F> 
-      requires CopyConstructible<F> && Callable<F, ArgTypes...> 
-            && Convertible<Callable<F, ArgTypes...>::result_type, R> 
-      function& operator=(F&&);
-    ...
-};
-
- - - - - - -
-

1071. is_bind_expression should derive from integral_constant<bool>

-

Section: 20.9.10.1 [func.bind.isbind] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-Class template is_bind_expression 20.9.10.1 [func.bind.isbind]: -

- -
-namespace std {
-  template<class T> struct is_bind_expression {
-    static const bool value = see below;
-  };
-}
-
-

-is_bind_expression should derive from std::integral_constant<bool> like -other similar trait types. -

- -

[ -Daniel adds: -]

- -

-We need the same thing for the trait is_placeholder as well. -

-

[ -2009-03-22 Daniel provided wording. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-We recommend this be deferred until after the next Committee Draft is issued. -

-

-Move to Open. -

-
- -

[ -2009-05-31 Peter adds: -]

- - -
-

-I am opposed to the proposed resolution and to the premise of the issue -in general. The traits's default definitions should NOT derive from -integral_constant, because this is harmful, as it misleads people into -thinking that is_bind_expression<E> always derives from -integral_constant, whereas it may not. -

-

-is_bind_expression and is_placeholder allow user -specializations, and in fact, this is their primary purpose. Such user -specializations may not derive from integral_constant, and the -places where is_bind_expression and is_placeholder are -used intentionally do not require such derivation. -

-

-The long-term approach here is to switch to -BindExpression<E> and Placeholder<P> -explicit concepts, of course, but until that happens, I say leave them -alone. -

-
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. We are comfortable with requiring user specializations -to derive from integral_constant. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 20.9.10.1 [func.bind.isbind] change as indicated: -

    -
    -namespace std {
- template<class T> struct is_bind_expression : integral_constant<bool, see below> { };{
-   static const bool value = see below;
- };
-}
-
    -
    2. -
  2. -

    -In 20.9.10.1 [func.bind.isbind]/2 change as indicated: -

    -
    -static const bool value;
-
    -

    --2- true if T is a type returned from bind, false otherwise. - If T is a type returned from bind, is_bind_expression<T> shall -be publicly derived from - integral_constant<bool, true>, otherwise it shall be -publicly derived from - integral_constant<bool, false>. -

    -
    -
    3. -
  3. -

    -In 20.9.10.2 [func.bind.isplace] change as indicated: -

    -
    -namespace std {
- template<class T> struct is_placeholder : integral_constant<int, see below> { };{
-   static const int value = see below;
- };
-}
-
    -
    4. -
  4. -

    -In 20.9.10.2 [func.bind.isplace]/2 change as indicated: -

    -
    -static const int value;
-
    -

    --2- value is J if T is the type of std::placeholders::_J, 0 otherwise. - If T is the type of std::placeholders::_J, is_placeholder<T> -shall be publicly - derived from integral_constant<int, J> otherwise it shall -be publicly derived - from integral_constant<int, 0>. -

    -
    -
    5. -
- - - - - -
-

1073. Declaration of allocator_arg should be constexpr

-

Section: 20.7 [memory] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

- -

-Declaration of allocator_arg should be constexpr to ensure constant -initialization. -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. Move to Tentatively Ready. -

- - -

Proposed resolution:

-

-Change 20.7 [memory] p2: -

- -
-// 20.8.1, allocator argument tag
-struct allocator_arg_t { };
-constexpr allocator_arg_t allocator_arg = allocator_arg_t();
-
- - - - - - -
-

1075. Scoped allocators are too complex

-

Section: 20 [utilities], 23 [containers] Status: Resolved - Submitter: Alan Talbot Opened: 2009-03-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US 65 and US 74.1 [CD1]

- -

US 65:

- -

-Scoped allocators and allocator propagation traits add a small amount of -utility at the cost of a great deal of machinery. The machinery is user -visible, and it extends to library components that don't have any -obvious connection to allocators, including basic concepts and simple -components like pair and tuple. -

- -

Suggested resolution:

- -

-Sketch of proposed resolution: Eliminate scoped allocators, replace -allocator propagation traits with a simple uniform rule (e.g. always -propagate on copy and move), remove all mention of allocators from -components that don't explicitly allocate memory (e.g. pair), and adjust -container interfaces to reflect this simplification. -

-

-Components that I propose eliminating include HasAllocatorType, -is_scoped_allocator, allocator_propagation_map, scoped_allocator_adaptor, -and ConstructibleAsElement. -

-
- -

US 74.1:

- -
-

-Scoped allocators represent a poor trade-off for standardization, since -(1) scoped-allocator--aware containers can be implemented outside the -C++ standard library but used with its algorithms, (2) scoped -allocators only benefit a tiny proportion of the C++ community -(since few C++ programmers even use today's allocators), and (3) all C++ -users, especially the vast majority of the C++ community that won't ever -use scoped allocators are forced to cope with the interface complexity -introduced by scoped allocators. -

-

-In essence, the larger community will suffer to support a very small -subset of the community who can already implement their own -data structures outside of the standard library. Therefore, scoped -allocators should be removed from the working paper. -

-

-Some evidence of the complexity introduced by scoped allocators: -

-
-

-20.3 [pairs], 20.4 [tuple]: Large increase in the -number of pair and tuple constructors. -

-

-23 [containers]: Confusing "AllocatableElement" requirements throughout. -

-
-

Suggested resolution:

- -

-Remove support for scoped allocators from the working paper. This -includes at least the following changes: -

- -
-

-Remove X [allocator.element.concepts] -

-

-Remove 20.13 [allocator.adaptor] -

-

-Remove [construct.element] -

-

-In Clause 23 [containers]: replace requirements naming the -AllocatableElement concept with requirements naming CopyConstructible, -MoveConstructible, DefaultConstructible, or Constructible, as -appropriate. -

-
- -
- -

[ -Post Summit Alan moved from NAD to Open. -]

- - -

[ -2009-05-15 Ganesh adds: -]

- - -
-

-The requirement AllocatableElement should not be replaced with -Constructible on the emplace_xxx() functions as suggested. In the -one-parameter case the Constructible requirement is not satisfied when -the constructor is explicit (as per [concept.map.fct], twelfth -bullet) but we do want to allow explicit constructors in emplace, as the -following example shows: -

- -
-vector<shared_ptr<int>> v;
-v.emplace_back(new int); // should be allowed
-
- -

-If the issue is accepted and scoped allocators are removed, I suggest to -add a new pair of concepts to [concept.construct], namely: -

- -
-auto concept HasExplicitConstructor<typename T, typename... Args> {
- explicit T::T(Args...);
-}
-
-auto concept ExplicitConstructible<typename T, typename... Args>
- : HasExplicitConstructor<T, Args...>, NothrowDestructible<T>
-{ }
-
- -

-We should then use ExplicitConstructible as the requirement for all -emplace_xxx() member functions. -

-

-For coherence and consistency with the similar concepts -Convertible/ExplicitlyConvertible, we might also consider changing -Constructible to: -

- -
-auto concept Constructible<typename T, typename... Args>
- : HasConstructor<T, Args...>, ExplicitConstructible<T, Args...>
-{ }
-
- -

-Moreover, all emplace-related concepts in [container.concepts] -should also use ExplicitConstructible instead of Constructible in the -definitions of their axioms. In fact the concepts in [container.concepts] should be -corrected even if the issue is not accepted. -

-

-On the other hand, if the issue is not accepted, the scoped allocator -adaptors should be fixed because the following code: -

- -
-template <typename T> using scoped_allocator = scoped_allocator_adaptor<allocator<T>>;
-
-vector<shared_ptr<int>, scoped_allocator<shared_ptr<int>>> v;
-v.emplace_back(new int); // ops! doesn't compile
-
- -

-doesn't compile, as the member function construct() of the scoped -allocator requires non-explicit constructors through concept -ConstructibleWithAllocator. Fixing that is not difficult but probably -more work than it's worth and is therefore, IMHO, one more reason in -support of the complete removal of scoped allocators. -

-
- -

[ -2009-06-09 Alan adds: -]

- - -
-

-I reopened this issue because I did not think that these National Body -comments were adequately addressed by marking them NAD. My understanding -is that something can be marked NAD if it is clearly a misunderstanding -or trivial, but a substantive issue that has any technical merit -requires a disposition that addresses the concerns. -

-

-The notes in the NB comment list (US 65 & US 74.1) say that: -

-
    -
  1. -this issue has not introduced any new arguments not previously discussed, -
    2. -
  2. -the vote (4-9-3) was not a consensus for removing scoped allocators, -
    3. -
  3. -the issue is resolved by -N2840. -
    4. -
-

-My opinion is: -

-
    -
  1. -there are new arguments in both comments regarding concepts (which were -not present in the library when the scoped allocator proposal was voted -in), -
    2. -
  2. -the vote was clearly not a consensus for removal, but just saying there -was a vote does not provide a rationale, -
    3. -
  3. -I do not believe that N2840 addresses these comments (although it does -many other things and was voted in with strong approval). -
    4. -
- -

-My motivation to open the issue was to ensure that the NB comments were -adequately addressed in a way that would not risk a "no" vote on our -FCD. If there are responses to the technical concerns raised, then -perhaps they should be recorded. If the members of the NB who authored -the comments are satisfied with N2840 and the other disposition remarks -in the comment list, then I am sure they will say so. In either case, -this issue can be closed very quickly in Frankfurt, and hopefully will -have helped make us more confident of approval with little effort. If in -fact there is controversy, my thought is that it is better to know now -rather than later so there is more time to deal with it. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2982. -

- - - -

Proposed resolution:

- - -

Rationale:

-

-Scoped allocators have been revised significantly. -

- - - - - -
-

1079. UK-265: RandomAccessIterator's operator- has nonsensical effects clause

-

Section: 24.2.7 [random.access.iterators] Status: C++11 - Submitter: Doug Gregor Opened: 2009-03-20 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses UK 265

- -

UK-265:

-

-This effects clause is nonesense. It looks more like an axiom stating -equivalence, and certainly an effects clause cannot change the state of -two arguments passed by const reference -

- -

[ -2009-09-18 Alisdair adds: -]

- - -
-

-For random access iterators, the definitions of (b-a) and -(a<b) are circular: -

- -

-From table Table 104 -- Random access iterator requirements: -

- -
-b - a :==>  (a < b) ? distance(a,b) : -distance(b,a)
-
-a < b :==>  b - a > 0
-
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- -

[ -2010-02-13 Alisdair opens. -]

- - -
-

-Looking again at LWG 1079, the wording in the issue no longer exists, and -appears to be entirely an artefact of the concepts wording. -

- -

-This issue is currently on our Ready list (not even Tentative!) but I think it -has to be pulled as there is no way to apply the resolution. -

- -

-Looking at the current paper, I think this issue is now "NAD, solved by the -removal of concepts". Unfortunately it is too late to poll again, so we will -have to perform that review in Pittsburgh. -

-
- -

[ -2010-02-13 Daniel updates the wording to address the circularity problem. -]

- - -
-

[ -The previous wording is preserved here: -]

- -
- -

Modify 24.2.7 [random.access.iterators]p7-9 as follows:

- -
-difference_type operator-(const X& a, const X& b);
-
-

- -7- Precondition: there exists a value n of - difference_type such that a == b + n. -

- -8- Effects: b == a + (b - a) -

- -9- Returns: (a < b) ? distance(a,b) : - -distance(b,a)n -

-
- -
-
- -

[ -2010 Pittsburgh: -]

- - -

-Moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

-

-Modify Table 105 in 24.2.7 [random.access.iterators]: -

- -
- - - - - - - - - - - - - - - - - -
Table 105 — Random access iterator requirements (in addition to -bidirectional iterator)
ExpressionReturn typeOperational semanticsAssertion/note
pre-/post-condition
b - aDistancedistance(a,b) -return npre: there exists a value n of Distance such that a + -n == b. b == a + (b - a).
-
- - - - - -
-

1088. std::promise should provide non-member swap overload

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses UK 342 [CD1]

- -

-std::promise is missing a non-member overload of swap. This is -inconsistent with other types that provide a swap member function. -

- -

-Add a non-member overload void swap(promise&& x,promise&& y){ x.swap(y); } -

- -

[ -Summit: -]

- -

-Create an issue. Move to review, attention: Howard. Detlef will also look into it. -

- -

[ -Post Summit Daniel provided wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

-
    -
  1. -

    -In 30.6.5 [futures.promise], before p.1, immediately after class template -promise add: -

    -
    -
-template <class R>
-void swap(promise<R>& x, promise<R>& y);
-
-
    -
    2. -
  2. -

    -Change 30.6.5 [futures.promise]/10 as indicated (to fix a circular definition): -

    -
    -

    --10- Effects: swap(*this, other)Swaps the associated state -of *this and other -

    -

    -Throws: Nothing. -

    -
    -
    3. -
  3. -

    -After the last paragraph in 30.6.5 [futures.promise] add the following -prototype description: -

    -
    -
-template <class R>
-void swap(promise<R>& x, promise<R>& y);
-
    -
    -

    -Effects: x.swap(y) -

    -

    -Throws: Nothing. -

    -
    -
    -
    4. - -
- - - - - - -
-

1089. Unify "Throws: Nothing." specifications

-

Section: 30 [thread] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [thread].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP 76 [CD1]

- -

-A description for "Throws: Nothing." are not unified. -

- -

-At the part without throw, "Throws: Nothing." should be described. -

- -

-Add "Throws: Nothing." to the following. -

- -
    -
  • -30.3.1.6 [thread.thread.static] p1 -
    • -
  • -30.4.2.1 [thread.lock.guard] p4 -
    • -
  • -30.4.2.2.1 [thread.lock.unique.cons] p6 -
    • -
  • -30.5.1 [thread.condition.condvar] p7 and p8 -
    • -
  • -30.5.2 [thread.condition.condvarany] p6, p7, p19, p21 and p25 -
    • -
- -

[ -Summit: -]

- -

-Pass on to editor. -

- -

[ -Post Summit: Editor declares this non-editorial. -]

- - -

[ -2009-08-01 Howard provided wording: -]

- - -
- -

-The definition of "Throws: Nothing." that I added is probably going to -be controversial, but I beg you to consider it seriously. -

- -
-

-In C++ there are three "flow control" options for a function: -

- -
    -
  1. -It can return, either with a value, or with void. -
    2. -
  2. -It can call a function which never returns, such as std::exit or -std::terminate. -
    3. -
  3. -It can throw an exception. -
    4. -
-

-The above list can be abbreviated with: -

-
    -
  1. Returns.
    2. -
  2. Ends program.
    3. -
  3. Throws exception.
    4. -
- -

-In general a function can have the behavior of any of these 3, or any combination -of any of these three, depending upon run time data. -

- -
    -
  1. R
    2. -
  2. E
    3. -
  3. T
    4. -
  4. RE
    5. -
  5. RT
    6. -
  6. ET
    7. -
  7. RET
    8. -
- -

-A function with no throw spec, and no documentation, is in general a RET -function. It may return, it may end the program, or it may throw. When we -specify a function with an empty throw spec: -

- -
-void f() throw();
-
- -

-We are saying that f() is an RE function: It may return or end -the program, but it will not throw. -

- -

-I posit that there are very few places in the library half of the standard -where we intend for functions to be able to end the program (call terminate). -And none of those places where we do say terminate could be called, -do we currently say "Throws: Nothing.". -

- -

-I believe that if we define "Throws: Nothing." to mean R, -we will both clarify many, many places in the standard, and give us a -good rationale for choosing between "Throws: Nothing." (R) -and throw() (RE) in the future. Indeed, this may give us motivation -to change several throw()s to "Throws: Nothing.". -

-
- -

-I did not add the following changes as JP 76 requested as I believe we want to -allow these functions to throw: -

- -
-

-Add a paragraph under 30.4.2.1 [thread.lock.guard] p4: -

- -
-explicit lock_guard(mutex_type& m);
-
- -

-Throws: Nothing. -

-
- -

-Add a paragraph under 30.4.2.2.1 [thread.lock.unique.cons] p6: -

- -
-explicit unique_lock(mutex_type& m);
-
- -

-Throws: Nothing. -

-
- -

-Add a paragraph under 30.5.2 [thread.condition.condvarany] p19, p21 and p25: -

- -
-template <class Lock, class Rep, class Period> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
- -

-Throws: Nothing. -

-
- -
-template <class Lock, class Duration, class Predicate> 
-  bool wait_until(Lock& lock, const chrono::time_point<Clock, Duration>& rel_time, Predicate pred);
-
- -

-Throws: Nothing. -

-
- -
-template <class Lock, class Rep, class Period, class Predicate> 
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
-
- -

-Throws: Nothing. -

-
- -
- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-Defer pending further developments with exception restriction annotations. -

- -

[ -2010-02-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-24 Pete moved to Open: -]

- - -

-A "Throws: Nothing" specification is not the place to say that a function -is not allowed to call exit(). While I agree with the thrust of the -proposed resolution, "doesn't throw exceptions" is a subset of "always returns -normally". If it's important to say that most library functions don't call -exit(), say so. -

- -

[ -2010 Pittsburgh: -]

- - -

-Move to Ready except for the added paragraph to 17.5.1.4 [structure.specifications]. -

- - - -

Proposed resolution:

- - -

-Add a paragraph under 30.3.1.6 [thread.thread.static] p1: -

- -
-unsigned hardware_concurrency();
-
- -

--1- Returns: ... -

- -

-Throws: Nothing. -

-
- -

-Add a paragraph under 30.5.1 [thread.condition.condvar] p7 and p8: -

- -
-

-[Informational, not to be incluced in the WP: The POSIX spec allows only: -

-
-
[EINVAL]
-
The value cond does not refer to an initialized condition variable. — end informational]
-
- -
-void notify_one();
-
- -

--7- Effects: ... -

- -

-Throws: Nothing. -

-
- -
-void notify_all();
-
- -

--8- Effects: ... -

- -

-Throws: Nothing. -

-
- - -

-Add a paragraph under 30.5.2 [thread.condition.condvarany] p6 and p7: -

- -
-
-void notify_one();
-
- -

--6- Effects: ... -

- -

-Throws: Nothing. -

-
- -
-void notify_all();
-
- -

--7- Effects: ... -

- -

-Throws: Nothing. -

-
- - - - - - - -
-

1090. Missing description of packaged_task member swap, missing non-member swap

-

Section: 30.6.9 [futures.task] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [futures.task].

-

View all issues with Resolved status.

-

Discussion:

-

-Class template packaged_task in 30.6.9 [futures.task] shows a member swap -declaration, but misses to document it's effects (No prototype provided). Further on this class -misses to provide a non-member swap. -

- -

[ -Batavia (2009-05): -]

- -
-

-Alisdair notes that paragraph 2 of the proposed resolution has already been -applied in the current Working Draft. -

-

-We note a pending future-related paper by Detlef; -we would like to wait for this paper before proceeding. -

-

-Move to Open. -

-
- -

[ -2009-05-24 Daniel removed part 2 of the proposed resolution. -]

- - -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready, removing bullet 3 from the proposed -resolution but keeping the other two bullets. -

- -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-
    -
  1. -

    -In 30.6.9 [futures.task], immediately after the definition of class -template packaged_task add: -

    -
    -
-template<class R, class... Argtypes>
-void swap(packaged_task<R(ArgTypes...)>&, packaged_task<R(ArgTypes...)>&);
-
-
    -
    2. -
  2. -

    -At the end of 30.6.9 [futures.task] (after p. 20), add the following -prototype description: -

    - -
    -
-template<class R, class... Argtypes>
-void swap(packaged_task<R(ArgTypes...)>& x, packaged_task<R(ArgTypes...)>& y);
-
    -
    -

    -Effects: x.swap(y) -

    -

    -Throws: Nothing. -

    -
    -
    -
    3. -
- - - - - -
-

1093. Multiple definitions for random_shuffle algorithm

-

Section: 25.3.12 [alg.random.shuffle] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-03-22 Last modified: 2015-04-08

-

View all other issues in [alg.random.shuffle].

-

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-

Discussion:

- -

-There are a couple of issues with the declaration of the random_shuffle -algorithm accepting a random number engine. -

- -
    -
  1. -The Iterators must be shuffle iterators, yet this requirement is missing. -
    2. -
  2. -The RandomNumberEngine concept is now provided by the random number -library -(n2836) -and the placeholder should be removed. -
    3. -
- -

[ -2009-05-02 Daniel adds: -]

- - -
-

-this issue completes adding necessary requirement to the -third new random_shuffle overload. The current suggestion is: -

- -
-template<RandomAccessIterator Iter, UniformRandomNumberGenerator Rand>
-requires ShuffleIterator<Iter>
-void random_shuffle(Iter first, Iter last, Rand&& g);
-
- -

-IMO this is still insufficient and I suggest to add the requirement -

-
-Convertible<Rand::result_type, Iter::difference_type>
-
-

-to the list (as the two other overloads already have). -

- -

-Rationale: -

- -
-

-Its true that this third overload is somewhat different from the remaining -two. Nevertheless we know from UniformRandomNumberGenerator, that -it's result_type is an integral type and that it satisfies -UnsignedIntegralLike<result_type>. -

-

-To realize it's designated task, the algorithm has to invoke the -Callable aspect of g and needs to perform some algebra involving -it's min()/max() limits to compute another index value that -at this point is converted into Iter::difference_type. This is so, -because 24.2.7 [random.access.iterators] uses this type as argument -of it's algebraic operators. Alternatively consider the equivalent -iterator algorithms in 24.4.4 [iterator.operations] with the same result. -

-

-This argument leads us to the conclusion that we also need -Convertible<Rand::result_type, Iter::difference_type> here. -

-
- -
- -

[ -Batavia (2009-05): -]

- -
-

-Alisdair notes that point (ii) has already been addressed. -

-

-We agree with the proposed resolution to point (i) -with Daniel's added requirement. -

-

-Move to Review. -

-
- -

[ -2009-06-05 Daniel updated proposed wording as recommended in Batavia. -]

- - -

[ -2009-07-28 Alisdair adds: -]

- - -

-Revert to Open, with a note there is consensus on direction but the -wording needs updating to reflect removal of concepts. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Leave Open, Walter to work on it. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved, addressed by -N3056. -]

- - - - -

Rationale:

-

-Solved by -N3056. -

- - -

Proposed resolution:

-

-Change in [algorithms.syn] and 25.3.12 [alg.random.shuffle]: -

- -
-concept UniformRandomNumberGenerator<typename Rand> { }
-template<RandomAccessIterator Iter, UniformRandomNumberGenerator Rand>
-  requires ShuffleIterator<Iter> &&
-  Convertible<Rand::result_type, Iter::difference_type>
-  void random_shuffle(Iter first, Iter last, Rand&& g);
-
- - - - - - -
-

1094. Replace "unspecified-bool-type" by "explicit operator bool() const" in I/O library

-

Section: 27.5.5.4 [iostate.flags] Status: C++11 - Submitter: P.J. Plauger Opened: 2009-03-24 Last modified: 2015-04-08

-

View all other issues in [iostate.flags].

-

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-

Discussion:

-

Addresses JP 65 and JP 66 [CD1]

- -

-Switch from "unspecified-bool-type" to "explicit operator bool() const". -

- -

-Replace operator unspecified-bool-type() const;" with explicit operator bool() const; -

- -

[ -Batavia (2009-05): -]

- -

-We agree with the proposed resolution. -Move to Review. -

- -

[ -2009 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-Change the synopis in 27.5.5 [ios]: -

- -
-explicit operator unspecified-bool-type bool() const;
-
- -

-Change 27.5.5.4 [iostate.flags]: -

- -
-explicit operator unspecified-bool-type bool() const;
-
- -
-

--1- Returns: !fail() If fail() then a value that will evaluate -false in a boolean context; otherwise a value that will evaluate true in -a boolean context. The value type returned shall not be convertible to -int. -

-

-[Note: This conversion can be used in contexts where a bool is expected -(e.g., an if condition); however, implicit conversions (e.g., -to int) that can occur with bool are not allowed, -eliminating some sources of user error. One possible implementation -choice for this type is pointer-to-member. -- end note] -

-
-
- - - - - - - -
-

1095. Shared objects and the library wording unclear

-

Section: 17.6.4.10 [res.on.objects] Status: C++11 - Submitter: Beman Dawes Opened: 2009-03-27 Last modified: 2015-04-08

-

View all other issues in [res.on.objects].

-

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-

Discussion:

-

-N2775, -Small library thread-safety revisions, among other changes, removed a note from -17.6.4.10 [res.on.objects] that read: -

- -

-[Note: This prohibition against concurrent non-const access means that -modifying an object of a standard library type shared between threads -without using a locking mechanism may result in a data race. --end note.] -

- -

-That resulted in wording which is technically correct but can only be -understood by reading the lengthy and complex 17.6.5.9 [res.on.data.races] -Data race avoidance. This has the effect of making -17.6.4.10 [res.on.objects] unclear, and has already resulted in a query -to the LWG reflector. See c++std-lib-23194. -

- -

[ -Batavia (2009-05): -]

- -
-

-The proposed wording seems to need a bit of tweaking -("really bad idea" isn't quite up to standardese). -We would like feedback -as to whether the original Note's removal was intentional. -

-

-Change the phrase "is a really bad idea" -to "risks undefined behavior" and -move to Review status. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Note: Change to read: "Modifying...", Delete 'thus', move to Ready -

- - - -

Proposed resolution:

-

-Change 17.6.4.10 [res.on.objects] as indicated: -

- -
-

-The behavior of a program is undefined if calls to standard library -functions from different threads may introduce a data race. The -conditions under which this may occur are specified in 17.6.4.7. -

-

-[Note: Modifying an object of a standard library type shared between -threads risks undefined behavior unless objects of the type are explicitly -specified as being sharable without data races or the user supplies a -locking mechanism. --end note] -

-
- - - - - -
-

1097. #define __STDCPP_THREADS

-

Section: 18.2 [support.types] Status: C++11 - Submitter: Jens Maurer Opened: 2009-04-03 Last modified: 2015-04-08

-

View all other issues in [support.types].

-

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-

Discussion:

-

Addresses DE 18

- -

-Freestanding implementations do not (necessarily) have - support for multiple threads (see 1.10 [intro.multithread]). - Applications and libraries may want to optimize for the - absence of threads. I therefore propose a preprocessor - macro to indicate whether multiple threads can occur. -

- -

-There is ample prior implementation experience for this - feature with various spellings of the macro name. For - example, gcc implicitly defines _REENTRANT - if multi-threading support is selected on the compiler - command-line. -

- -

-While this is submitted as a library issue, it may be more - appropriate to add the macro in 16.8 cpp.predefined in the - core language. -

- -

-See also -N2693. -

- -

[ -Batavia (2009-05): -]

- -
-

-We agree with the issue, and believe it is properly a library issue. -

-

-We prefer that the macro be conditionally defined -as part of the <thread> header. -

-

-Move to Review. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2010-02-25 Pete moved to Open: -]

- - -
-

-The proposed resolution adds a feature-test macro named -__STDCPP_THREADS, described after the following new text: -

- -

-The standard library defines the following macros; no explicit prior inclusion -of any header file is necessary. -

- -

-The correct term here is "header", not "header file". But that's minor. The real -problem is that library entities are always defined in headers. If -__STDCPP_THREADS is defined without including any header it's part of -the language and belongs with the other predefined macros in the Preprocessor -clause. -

- -

-Oddly enough, the comments from Batavia say "We prefer that the macro be -conditionally defined as part of the <thread> header." There's no -mention of a decision to change this. -

-
- -

[ -2010-02-26 Ganesh updates wording. -]

- - -

[ -2010 Pittsburgh: Adopt Ganesh's wording and move to Review. -]

- - -

[ -2010-03-08 Pete adds: -]

- - -

-Most macros we have begin and end with with double underbars, this one -only begins with double underbars. -

- -

[ -2010 Pittsburgh: Ganesh's wording adopted and moved to Ready for Pittsburgh. -]

- - - - -

Proposed resolution:

- -

-Change 17.6.1.3 [compliance]/3: -

- -

-3 The supplied version of the header <cstdlib> shall -declare at least the functions abort(), atexit(), and -exit() (18.5). The supplied version of the header -<thread> either shall meet the same requirements as for a -hosted implementation or including it shall have no effect. The -other headers listed in this table shall meet the same requirements as -for a hosted implementation. -

- -

-Add the following line to table 15: -

- -
- - - - - - - - - - - - - - - - - -
Table 15 — C++ headers for freestanding implementations
SubclauseHeader(s)
...
30.3 [thread.threads] Threads<thread>
- -
- -

-Add to the <thread> synopsis in 30.3 [thread.threads]/1 the line: -

- -
-namespace std {
-
-#define __STDCPP_THREADS __cplusplus
-
-  class thread;
-  ...
-
- - - - - - - - - -
-

1098. definition of get_pointer_safety()

-

Section: 20.7.4 [util.dynamic.safety] Status: C++11 - Submitter: Jens Maurer Opened: 2009-04-03 Last modified: 2015-04-08

-

View all other issues in [util.dynamic.safety].

-

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-

Discussion:

-

Addresses DE 18

- -

- In 20.7.4 [util.dynamic.safety], get_pointer_safety() purports -to define behavior for - non-safely derived pointers (3.7.4.3 [basic.stc.dynamic.safety]). However, - the cited core-language section in paragraph 4 specifies undefined behavior - for the use of such pointer values. This seems an unfortunate near-contradiction. - I suggest to specify the term relaxed pointer safety in - the core language section and refer to it from the library description. - This issue deals with the library part, the corresponding core issue (c++std-core-13940) - deals with the core modifications. -

- -

-See also -N2693. -

- -

[ -Batavia (2009-05): -]

- -
-

-We recommend if this issue is to be moved, -the issue be moved concurrently with the cited Core issue. -

-

-We agree with the intent of the proposed resolution. -We would like input from garbage collection specialists. -

-

-Move to Open. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-The core issue is 853 and is in Ready status. -

- - - -

Proposed resolution:

-

-In 20.7.4 [util.dynamic.safety] p16, replace the description of -get_pointer_safety() with: -

- -
-

-pointer_safety get_pointer_safety(); -

-
-

-Returns: an enumeration value indicating the implementation's treatment -of pointers that are not safely derived (3.7.4.3). Returns -pointer_safety::relaxed if pointers that are not safely derived will be -treated the same as pointers that are safely derived for the duration of -the program. Returns pointer_safety::preferred if pointers that are not -safely derived will be treated the same as pointers that are safely -derived for the duration of the program but allows the implementation to -hint that it could be desirable to avoid dereferencing pointers that are -not safely derived as described. [Example: pointer_safety::preferred -might be returned to detect if a leak detector is running to avoid -spurious leak reports. -- end note] Returns pointer_safety::strict if -pointers that are not safely derived might be treated differently than -pointers that are safely derived. -

-

-Returns: Returns pointer_safety::strict if the implementation has - strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]). It is - implementation-defined whether get_pointer_safety returns - pointer_safety::relaxed or pointer_safety::preferred if the - implementation has relaxed pointer safety - (3.7.4.3 [basic.stc.dynamic.safety]).Footnote -

- -

-Throws: nothing -

- -

-Footnote) pointer_safety::preferred might be returned to indicate to the - program that a leak detector is running so that the program can avoid - spurious leak reports. - -

- -
-
- - - - - -
-

1100. auto_ptr to unique_ptr conversion

-

Section: 20.8.1.2.1 [unique.ptr.single.ctor] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.ctor].

-

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-

Discussion:

-

-Message c++std-lib-23182 led to a discussion in which several people -expressed interest in being able to convert an auto_ptr to a -unique_ptr without the need to call release. Below is -wording to accomplish this. -

- -

[ -Batavia (2009-05): -]

- -
-

-Pete believes it not a good idea to separate parts of a class's definition. -Therefore, if we do this, -it should be part of unique-ptr's specification. -

-

-Alisdair believes the lvalue overload may be not necessary. -

-

-Marc believes it is more than just sugar, -as it does ease the transition to unique-ptr. -

-

-We agree with the resolution as presented. -Move to Tentatively Ready. -

-
- -

[ -2009-07 Frankfurt -]

- - -

-Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -

- -

[ -2009-08-01 Howard deconceptifies wording: -]

- - -

-I also moved the change from X [depr.auto.ptr] -to 20.8.1.2 [unique.ptr.single] per the Editor's request -in Batavia (as long as I was making changes anyway). Set back -to Review. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- -

[ -2010-03-14 Howard adds: -]

- - -

-We moved -N3073 -to the formal motions page in Pittsburgh which should obsolete this issue. I've -moved this issue to NAD Editorial, solved by N3073. -

- - - -

Rationale:

-

-Solved by N3073. -

- - -

Proposed resolution:

-

-Add to 20.8.1.2 [unique.ptr.single]: -

- -
-template <class T, class D>
-class unique_ptr
-{
-public:
-    template <class U>
-      unique_ptr(auto_ptr<U>& u);
-    template <class U>
-      unique_ptr(auto_ptr<U>&& u);
-};
-
- -

-Add to 20.8.1.2.1 [unique.ptr.single.ctor]: -

- -
-template <class U>
-  unique_ptr(auto_ptr<U>& u);
-template <class U>
-  unique_ptr(auto_ptr<U>&& u);
-
-
-

-Effects: Constructs a unique_ptr with u.release(). -

- -

-Postconditions: get() == the value u.get() had before -the construciton, modulo any required offset adjustments resulting from the cast from -U* to T*. u.get() == nullptr. -

- -

-Throws: nothing. -

- -

-Remarks: U* shall be implicitly convertible to T* and -D shall be the same type as default_delete<T>, else these -constructors shall not participate in overload resolution. -

-
-
- - - - - - -
-

1103. system_error constructor postcondition overly strict

-

Section: 19.5.6.2 [syserr.syserr.members] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-19.5.6.2 [syserr.syserr.members] says: -

- -
-system_error(error_code ec, const string& what_arg);
-
-
-

-Effects: Constructs an object of class system_error. -

-

-Postconditions: code() == ec and strcmp(runtime_error::what(), what_arg.c_str()) == 0. -

-
-
- -

-However the intent is for: -

- -
-std::system_error se(std::errc::not_a_directory, "In FooBar");
-...
-se.what();  // returns something along the lines of:
-            //   "In FooBar: Not a directory"
-
- -

-The way the constructor postconditions are set up now, to achieve both -conformance, and the desired intent in the what() string, the -system_error constructor must store "In FooBar" in the base class, -and then form the desired output each time what() is called. Or -alternatively, store "In FooBar" in the base class, and store the desired -what() string in the derived system_error, and override -what() to return the string in the derived part. -

- -

-Both of the above implementations seem suboptimal to me. In one I'm computing -a new string every time what() is called. And since what() -can't propagate exceptions, the client may get a different string on different -calls. -

- -

-The second solution requires storing two strings instead of one. -

- -

-What I would like to be able to do is form the desired what() string -once in the system_error constructor, and store that in the -base class. Now I'm: -

- -
    -
  1. Computing the desired what() only once.
    2. -
  2. The base class what() definition is sufficient and nothrow.
    3. -
  3. I'm not storing multiple strings.
    4. -
- -

-This is smaller code, smaller data, and faster. -

- -

-ios_base::failure has the same issue. -

- -

[ -Comments about this change received favorable comments from the system_error -designers. -]

- - -

[ -Batavia (2009-05): -]

- - -
-

-We agree with the proposed resolution. -

-

-Move to Tentatively Ready. -

-
- - -

Proposed resolution:

-

-In 19.5.6.2 [syserr.syserr.members], change the following constructor postconditions: -

- -
-
-system_error(error_code ec, const string& what_arg);
-
-

--2- Postconditions: code() == ec -and strcmp(runtime_error::what(), what_arg.c_str()) == 0 -string(what()).find(what_arg) != string::npos. -

- -
-system_error(error_code ec, const char* what_arg);
-
-

--4- Postconditions: code() == ec -and strcmp(runtime_error::what(), what_arg) == 0 -string(what()).find(what_arg) != string::npos. -

- -
-system_error(error_code ec);
-
-

--6- Postconditions: code() == ec -and strcmp(runtime_error::what(), "". -

- -
-system_error(int ev, const error_category& ecat, const string& what_arg);
-
-

--8- Postconditions: code() == error_code(ev, ecat) -and strcmp(runtime_error::what(), what_arg.c_str()) == 0 -string(what()).find(what_arg) != string::npos. -

- -
-system_error(int ev, const error_category& ecat, const char* what_arg);
-
-

--10- Postconditions: code() == error_code(ev, ecat) -and strcmp(runtime_error::what(), what_arg) == 0 -string(what()).find(what_arg) != string::npos. -

- -
-system_error(int ev, const error_category& ecat);
-
-

--12- Postconditions: code() == error_code(ev, ecat) -and strcmp(runtime_error::what(), "") == 0. -

- -
- -

-In 19.5.6.2 [syserr.syserr.members], change the description of what(): -

- -
-
-const char *what() const throw();
-
-
-

--14- Returns: An NTBS incorporating runtime_error::what() and -code().message() the arguments supplied in the constructor. -

-

-[Note: One possible implementation would be: -The return NTBS might take the form: what_arg + ": " + code().message() -

-

-if (msg.empty()) { 
-  try { 
-    string tmp = runtime_error::what(); 
-    if (code()) { 
-      if (!tmp.empty()) 
-        tmp += ": "; 
-      tmp += code().message(); 
-    } 
-    swap(msg, tmp); 
-  } catch(...) { 
-    return runtime_error::what(); 
-  } 
-return msg.c_str();
-
-

-— end note] -

-
-
- -

-In 27.5.3.1.1 [ios::failure], change the synopsis: -

- -
-namespace std { 
-  class ios_base::failure : public system_error { 
-  public: 
-    explicit failure(const string& msg, const error_code& ec = io_errc::stream); 
-    explicit failure(const char* msg, const error_code& ec = io_errc::stream); 
-    virtual const char* what() const throw();
-  }; 
-}
-
- -

-In 27.5.3.1.1 [ios::failure], change the description of the constructors: -

- -
- -
-explicit failure(const string& msg, , const error_code& ec = io_errc::stream);
-
-
-

--3- Effects: Constructs an object of class failure -by constructing the base class with msg and ec. -

-

--4- Postcondition: code() == ec and strcmp(what(), msg.c_str()) == 0 -

-
- -
-explicit failure(const char* msg, const error_code& ec = io_errc::stream);
-
-
-

--5- Effects: Constructs an object of class failure -by constructing the base class with msg and ec. -

-

--6- Postcondition: code() == ec and strcmp(what(), msg) == 0 -

-
- -
- -

-In 27.5.3.1.1 [ios::failure], remove what (the base class definition -need not be repeated here). -

- -
-
-const char* what() const;
-
-

--7- Returns: The message msg with which the exception was created. -

- -
- - - - - - -
-

1104. basic_ios::move should accept lvalues

-

Section: 27.5.5.3 [basic.ios.members] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

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-

Discussion:

-

-With the rvalue reference changes in -N2844 -basic_ios::move no longer has the most convenient signature: -

- -
-void move(basic_ios&& rhs);
-
- -

-This signature should be changed to accept lvalues. It does not need to be -overloaded to accept rvalues. This is a special case that only derived clients -will see. The generic move still needs to accept rvalues. -

- -

[ -Batavia (2009-05): -]

- -
-

-Tom prefers, on general principles, to provide both overloads. -Alisdair agrees. -

-

-Howard points out that there is no backward compatibility issue -as this is new to C++0X. -

-

-We agree that both overloads should be provided, -and Howard will provide the additional wording. -Move to Open. -

-
- -

[ -2009-05-23 Howard adds: -]

- - -

-Added overload, moved to Review. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add a signature to the existing prototype in the synopsis of 27.5.5 [ios] -and in 27.5.5.3 [basic.ios.members]: -

- -
-void move(basic_ios& rhs);
-void move(basic_ios&& rhs);
-
- - - - - -
-

1106. Multiple exceptions from connected shared_future::get()?

-

Section: 30.6.7 [futures.shared_future] Status: Resolved - Submitter: Thomas J. Gritzan Opened: 2009-04-03 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

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-

Discussion:

-

-It is not clear, if multiple threads are waiting in a -shared_future::get() call, if each will rethrow the stored exception. -

-

-Paragraph 9 reads: -

-

-Throws: the stored exception, if an exception was stored and not -retrieved before. -

-

-The "not retrieved before" suggests that only one exception is thrown, -but one exception for each call to get() is needed, and multiple calls -to get() even on the same shared_future object seem to be allowed. -

-

-I suggest removing "and not retrieved before" from the Throws paragraph. -I recommend adding a note that explains that multiple calls on get() are -allowed, and each call would result in an exception if an exception was -stored. -

- -

[ -Batavia (2009-05): -]

- -
-

-We note there is a pending paper by Detlef -on such future-related issues; -we would like to wait for his paper before proceeding. -

-

-Alisdair suggests we may want language to clarify that this -get() function can be called from several threads -with no need for explicit locking. -

-

-Move to Open. -

-
- -

[ -2010-01-23 Moved to Tentatively NAD Editorial after 5 positive votes on c++std-lib. -]

- - - - -

Rationale:

-

-Resolved by paper -N2997. -

- - -

Proposed resolution:

-

-Change 30.6.7 [futures.shared_future]: -

- -
-const R& shared_future::get() const; 
-R& shared_future<R&>::get() const; 
-void shared_future<void>::get() const;
-
-
-

...

-

--9- Throws: the stored exception, if an exception was stored and not retrieved before. - -[Note: Multiple calls on get() are allowed, and each call would result in an exception -if an exception was stored. — end note] - -

-
-
- - - - - - -
-

1108. thread.req.exception overly constrains implementations

-

Section: 30.2.2 [thread.req.exception] Status: C++11 - Submitter: Christopher Kohlhoff Opened: 2009-04-25 Last modified: 2015-04-08

-

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-

Discussion:

-

-The current formulation of 30.2.2 [thread.req.exception]/2 reads: -

-

-The error_category of the error_code reported by such an -exception's code() member function is as specified in the error -condition Clause. -

-

-This constraint on the code's associated error_categor means an -implementation must perform a mapping from the system-generated -error to a generic_category() error code. The problems with this -include: -

- -
    -
  • -The mapping is always performed, even if the resultant value is - never used. -
    • -
  • -

    -The original error produced by the operating system is lost. -

    -
    • -
-

-The latter was one of Peter Dimov's main objections (in a private -email discussion) to the original error_code-only design, and led to -the creation of error_condition in the first place. Specifically, -error_code and error_condition are intended to perform -the following roles: -

-
    -
  • -error_code holds the original error produced by the operating - system. -
    • -
  • -error_condition and the generic category provide a set of well - known error constants that error codes may be tested against. -
    • -
-

-Any mapping determining correspondence of the returned error code to -the conditions listed in the error condition clause falls under the -"latitude" granted to implementors in 19.5.1.5 [syserr.errcat.objects]. -(Although obviously their latitude is restricted a little by the -need to match the right error condition when returning an error code -from a library function.) -

-

-It is important that this error_code/error_condition usage is done -correctly for the thread library since it is likely to set the pattern for future -TR libraries that interact with the operating system. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

-

-Change 30.2.2 [thread.req.exception] p.2: -

- -
-

--2- The error_category (19.5.1.1) of the error_code reported by -such an exception's code() member function -is as specified in the error condition Clause. - -The error_code reported by such an exception's code() member -function shall compare equal to one of the conditions specified in -the function's error condition Clause. [Example: When the thread -constructor fails: - -

-

-ec.category() == implementation-defined // probably system_category
-ec == errc::resource_unavailable_try_again // holds true
-
- -

-— end example] -

- -
- - - - - - -
-

1110. Is for_each overconstrained?

-

Section: 25.2.4 [alg.foreach] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-04-29 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Quoting working paper for reference (25.2.4 [alg.foreach]): -

- -
-
-template<InputIterator Iter, Callable<auto, Iter::reference> Function>
-  requires CopyConstructible<Function>
-  Function for_each(Iter first, Iter last, Function f);
-
-
-

-1 Effects: Applies f to the result of dereferencing every iterator in the - range [first,last), starting from first and proceeding to last - 1. -

-

-2 Returns: f. -

-

-3 Complexity: Applies f exactly last - first times. -

-
-
- -

-P2 implies the passed object f should be invoked at each stage, rather than -some copy of f. This is important if the return value is to usefully -accumulate changes. So the requirements are an object of type Function can -be passed-by-value, invoked multiple times, and then return by value. In -this case, MoveConstructible is sufficient. This would open support for -move-only functors, which might become important in concurrent code as you -can assume there are no other references (copies) of a move-only type and so -freely use them concurrently without additional locks. -

- -

[ -See further discussion starting with c++std-lib-23686. -]

- - -

[ -Batavia (2009-05): -]

- -
-

-Pete suggests we may want to look at this in a broader context -involving other algorithms. -We should also consider the implications of parallelism. -

-

-Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -

-
- -

[ -2009-10-14 Daniel de-conceptified the proposed resolution. -]

- - -
-

-The note in 25.1 [algorithms.general]/9 already says the right thing: -

-

-Unless otherwise specified, algorithms that take function objects -as arguments are permitted to copy those function objects freely. -

-

-So we only need to ensure that the wording for for_each is sufficiently -clear, which is the intend of the following rewording. -

-
- -

[ -2009-10-15 Daniel proposes: -]

- - -
-
    -
  • -

    -Add a new Requires clause just after the prototype declaration (25.2.4 [alg.foreach]): -

    -
    -

    -Requires: Function shall be MoveConstructible -( [moveconstructible]), CopyConstructible is not required. -

    -
    -
    • -
  • -

    -Change 25.2.4 [alg.foreach]/2 as indicated: -

    - -

    -Returns: std::move(f). -

    -
    • -
-
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready, using Daniel's wording without the portion -saying "CopyConstructible is not required". -

- -

[ -2009-10-27 Daniel adds: -]

- - -
-

-I see that during the Santa Cruz meeting the originally proposed addition -

- -

-, CopyConstructible is not required. -

- -

-was removed. I don't think that this removal was a good idea. The combination -of 25.1 [algorithms.general] p.9 -

- -

-[Note: Unless otherwise specified, algorithms that take function objects -as arguments are permitted to copy those function objects freely.[..] -

- -

-with the fact that CopyConstructible is a refinement MoveConstructible -makes it necessary that such an explicit statement is given. Even the -existence of the usage of std::move in the Returns clause doesn't -help much, because this would still be well-formed for a CopyConstructible -without move constructor. Let me add that the originally proposed -addition reflects current practice in the standard, e.g. 25.3.9 [alg.unique] p.5 -usages a similar terminology. -

- -

-For similar wording need in case for auto_ptr see 973. -

- -

[ -Howard: Moved from Tentatively Ready to Open. -]

- -
- -

[ -2009-11-20 Howard restores "not CopyConstructible" to the spec. -]

- - -

[ -2009-11-22 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-
    -
  • -

    -Add a new Requires clause just after the prototype declaration (25.2.4 [alg.foreach]): -

    -
    -

    -Requires: Function shall meet the requirements of -MoveConstructible ( [moveconstructible]). -Function need not meet the requirements of -CopyConstructible ( [copyconstructible]). -

    -
    -
    • -
  • -

    -Change 25.2.4 [alg.foreach]/2 as indicated: -

    - -

    -Returns: std::move(f). -

    -
    • -
- - - - - - - - -
-

1113. bitset::to_string could be simplified

-

Section: 20.6 [template.bitset] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-05-09 Last modified: 2015-04-08

-

View other active issues in [template.bitset].

-

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-

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-

Discussion:

-

-In 853 our resolution is changing the signature by adding two -defaulting arguments to 3 calls. In principle, this means that ABI breakage -is not an issue, while API is preserved. -

-

-With that observation, it would be very nice to use the new ability to -supply default template parameters to function templates to collapse all 3 -signatures into 1. In that spirit, this issue offers an alternative resolution -than that of 853. -

- -

[ -Batavia (2009-05): -]

- -

-Move to Open, -and look at the issue again after 853 has been accepted. -We further recommend this be deferred until after the next Committee Draft. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

- -
    -
  1. -

    -In 20.6 [template.bitset]/1 (class bitset) ammend: -

    -
    -template <class charT = char,
-            class traits = char_traits<charT>,
-            class Allocator = allocator<charT>> 
-  basic_string<charT, traits, Allocator>
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-template <class charT, class traits> 
-  basic_string<charT, traits, allocator<charT> > to_string() const; 
-template <class charT> 
-  basic_string<charT, char_traits<charT>, allocator<charT> > to_string() const; 
-basic_string<char, char_traits<char>, allocator<char> > to_string() const;
-
    -
    2. -
  2. -

    -In 20.6.2 [bitset.members] prior to p35 ammend: -

    -
    -template <class charT = char,
-            class traits = char_traits<charT>,
-            class Allocator = allocator<charT>> 
-  basic_string<charT, traits, Allocator>
-  to_string(charT zero = charT('0'), charT one = charT('1')) const;
-
    -
    3. -
  3. -Strike 20.6.2 [bitset.members] paragraphs 37 -> 39 (including signature -above 37) -
    4. -
- - - - - - -
-

1114. Type traits underspecified

-

Section: 20.10 [meta] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-05-12 Last modified: 2015-04-08

-

View other active issues in [meta].

-

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-

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-

Discussion:

- -

-Related to 975 and 1023. -

- -

-The current wording in 20.10.1 [meta.rqmts] is still unclear concerning -it's requirements on the type traits classes regarding ambiguities. -Specifically it's unclear -

- -
    -
  • -if a predicate trait (20.10.4 [meta.unary], 20.10.6 [meta.rel]) could derive from both -true_type/false_type. -
    • -
  • -if any of the type traits (20.10.1 [meta.rqmts], 20.10.4 [meta.unary], 20.10.6 [meta.rel]) could ambiguously derive -from the same specified result type. -
    • -
  • -if any of the type traits (20.10.1 [meta.rqmts], 20.10.4 [meta.unary], 20.10.6 [meta.rel]) could derive from other -integral_constant types making the contained names ambiguous -
    • -
  • -if any of the type traits (20.10.1 [meta.rqmts], 20.10.4 [meta.unary], 20.10.6 [meta.rel]) could have other base -classes that contain members hiding the name of the result type members -or make the contained member names ambiguous. -
    • -
- -

[ -Batavia (2009-05): -]

- -
-

-Alisdair would prefer to factor some of the repeated text, -but modulo a corner case or two, -he believes the proposed wording is otherwise substantially correct. -

-

-Move to Open. -

-
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

-

[ -The usage of the notion of a BaseCharacteristic below might be -useful in other places - e.g. to define the base class relation in 20.9.4 [refwrap], 20.9.11 [func.memfn], or 20.9.12.2 [func.wrap.func]. In this case it's definition should probably -be moved to Clause 17 -]

- - -
    -
  1. -

    -Change 20.10.1 [meta.rqmts] p.1 as indicated: -

    -

    -[..] It shall be DefaultConstructible, CopyConstructible, and publicly -and unambiguously derived, directly or indirectly, from -its BaseCharacteristic, which is a specialization of the -template integral_constant (20.6.3), with the arguments to the template -integral_constant determined by the requirements for the particular -property being described. The member names of the -BaseCharacteristic shall be unhidden and unambiguously -available in the UnaryTypeTrait. -

    -
    2. -
  2. -

    -Change 20.10.1 [meta.rqmts] p.2 as indicated: -

    -

    -[..] It shall be DefaultConstructible, CopyConstructible, and publicly -and unambiguously derived, directly or indirectly, from -an instance its BaseCharacteristic, which is a -specialization of the template integral_constant (20.6.3), with -the arguments to the template integral_constant determined by the -requirements for the particular relationship being described. The -member names of the BaseCharacteristic shall be unhidden -and unambiguously available in the BinaryTypeTrait. -

    -
    3. -
  3. -

    -Change 20.10.4 [meta.unary] p.2 as indicated: -

    -

    -Each of these templates shall be a UnaryTypeTrait (20.6.1), -publicly derived directly or indirectly from true_type if the -corresponding condition is true, otherwise from false_type -where its BaseCharacteristic shall be true_type if the -corresponding condition is true, otherwise false_type. -

    -
    4. -
  4. -

    -Change 20.10.6 [meta.rel] p.2 as indicated: -

    - -

    -Each of these templates shall be a BinaryTypeTrait (20.6.1), -publicly derived directly or indirectly from true_type if the -corresponding condition is true, otherwise from false_type -where its BaseCharacteristic shall be true_type if the -corresponding condition is true, otherwise false_type. -

    -
    5. -
- - - - - - -
-

1116. Literal constructors for tuple

-

Section: 20.4.2 [tuple.tuple] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-05-23 Last modified: 2015-04-08

-

View all other issues in [tuple.tuple].

-

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-

Discussion:

-

-It is not currently possible to construct tuple literal values, -even if the elements are all literal types. This is because parameters -are passed to constructor by reference. -

-

-An alternative would be to pass all constructor arguments by value, where it -is known that *all* elements are literal types. This can be determined with -concepts, although note that the negative constraint really requires -factoring out a separate concept, as there is no way to provide an 'any of -these fails' constraint inline. -

-

-Note that we will have similar issues with pair (and -tuple constructors from pair) although I am steering -clear of that class while other constructor-related issues settle. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2994. -

- - -

Proposed resolution:

-

-Ammend the tuple class template declaration in 20.4.2 [tuple.tuple] as -follows -

- -
-

-Add the following concept: -

- -
-auto concept AllLiteral< typename ... Types > {
-  requires LiteralType<Types>...;
-}
-
- -

-ammend the constructor -

- -
-template <class... UTypes>
-  requires AllLiteral<Types...>
-        && Constructible<Types, UTypes>...
-  explicit tuple(UTypes...);
-
-template <class... UTypes>
-  requires !AllLiteral<Types...>
-        && Constructible<Types, UTypes&&>...
-  explicit tuple(UTypes&&...);
-
- -

-ammend the constructor -

- -
-template <class... UTypes>
-  requires AllLiteral<Types...>
-        && Constructible<Types, UTypes>...
-  tuple(tuple<UTypes...>);
-
-template <class... UTypes>
-  requires !AllLiteral<Types...>
-        && Constructible<Types, const UTypes&>...
-  tuple(const tuple<UTypes...>&);
-
- -
- -

-Update the same signatures in 20.4.2.1 [tuple.cnstr], paras 3 and 5. -

- - - - - -
-

1117. tuple copy constructor

-

Section: 20.4.2.1 [tuple.cnstr] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-05-23 Last modified: 2015-04-08

-

View other active issues in [tuple.cnstr].

-

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-

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-

Discussion:

-

-The copy constructor for the tuple template is constrained. This seems an -unusual strategy, as the copy constructor will be implicitly deleted if the -constraints are not met. This is exactly the same effect as requesting an -=default; constructor. The advantage of the latter is that it retains -triviality, and provides support for tuples as literal types if issue -1116 is also accepted. -

-

-Actually, it might be worth checking with core if a constrained copy -constructor is treated as a constructor template, and as such does not -suppress the implicit generation of the copy constructor which would hide -the template in this case. -

- -

[ -2009-05-27 Daniel adds: -]

- - -

-This would solve one half of the suggested changes in 801. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2994. -

- - -

Proposed resolution:

-

-Change 20.4.2 [tuple.tuple] and 20.4.2.1 [tuple.cnstr] p4: -

- -
-requires CopyConstructible<Types>... tuple(const tuple&) = default;
-
- - - - - -
-

1118. tuple query APIs do not support cv-qualification

-

Section: 20.4.2.5 [tuple.helper] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-05-23 Last modified: 2015-04-08

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-

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-

Discussion:

-

-The APIs tuple_size and tuple_element do not support -cv-qualified tuples, pairs or arrays. -

-

-The most generic solution would be to supply partial specializations once -for each cv-type in the tuple header. However, requiring this header for -cv-qualified pairs/arrays seems unhelpful. The BSI editorial -suggestion (UK-198/US-69, -N2533) -to merge tuple into <utility> would help with pair, -but not array. That might be resolved by making a dependency between the -<array> header and <utility>, or simply recognising -the dependency be fulfilled in a Remark. -

- -

[ -2009-05-24 Daniel adds: -]

- - -
-

-All tuple_size templates with a base class need to derive publicly, e.g. -

- -
-template <IdentityOf T> class tuple_size< const T > :
-   public tuple_size<T> {};
-
- -

-The same applies to the tuple_element class hierarchies. -

-

-What is actually meant with the comment -

-

-this solution relies on 'metafunction forwarding' to inherit the -nested typename type -

-

-? -

-

-I ask, because all base classes are currently unconstrained and their -instantiation is invalid in the constrained context of the tuple_element partial -template specializations. -

-
- -

[ -2009-05-24 Alisdair adds: -]

- - -
-

-I think a better solution might be to ask Pete editorially to change all -declarations of tupling APIs to use the struct specifier instead of class. -

-

-"metafunction forwarding" refers to the MPL metafunction protocol, where a -metafunction result is declared as a nested typedef with the name "type", -allowing metafunctions to be chained by means of inheritance. It is a -neater syntax than repeatedly declaring a typedef, and inheritance syntax is -slightly nicer when it comes to additional typename keywords. -

-

-The constrained template with an unconstrained base is a good observation -though. -

-
- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Open, Alisdair to provide wording. Once wording is -provided, Howard will move to Review. -

- -

[ -2010-03-28 Daniel deconceptified wording. -]

- - -

[ -Post-Rapperswil - Daniel provides wording: -]

- - -

-The below given P/R reflects the discussion from the Rapperswil meeting that the wording should not constrain -implementation freedom to realize the actual issue target. Thus the original code form was replaced by -normative words. -

-

-While preparing this wording it turned out that several tuple_size specializations as -that of pair and array are underspecified, because the underlying type of the member -value is not specified except that it is an integral type. For the specializations we could introduce a -canonical one - like size_t - or we could use the same type as the specialization of the -unqualified type uses. The following wording follows the second approach. -

-

-The wording refers to N3126. -

- -

-Moved to Tentatively Ready after 6 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -
    -
  1. Change 20.4.1 [tuple.general] p.2, header <tuple> synopsis, as indicated: -
    -// 20.4.2.5, tuple helper classes:
-template <class T> class tuple_size; // undefined
-template <class T> class tuple_size<const T>;
-template <class T> class tuple_size<volatile T>;
-template <class T> class tuple_size<const volatile T>;
-
-template <class... Types> class tuple_size<tuple<Types...> >;
-	
-template <size_t I, class T> class tuple_element; // undefined
-template <size_t I, class T> class tuple_element<I, const T>;
-template <size_t I, class T> class tuple_element<I, volatile T>;
-template <size_t I, class T> class tuple_element<I, const volatile T>;
-
-template <size_t I, class... Types> class tuple_element<I, tuple<Types...> >;
-
    -
    2. -
  2. Add the end of subclause 20.4.2.5 [tuple.helper] insert the following two paragraphs: -
    -template <class T> class tuple_size<const T>;
-template <class T> class tuple_size<volatile T>;
-template <class T> class tuple_size<const volatile T>;
-

    -Let TS denote tuple_size<T> of the cv-unqualified type T. -Then each of the three templates shall meet the UnaryTypeTrait requirements (20.7.1) with a BaseCharacteristic of -integral_constant<remove_cv<decltype(TS::value)>::type, TS::value>. -

    - -
    -template <size_t I, class T> class tuple_element<I, const T>;
-template <size_t I, class T> class tuple_element<I, volatile T>;
-template <size_t I, class T> class tuple_element<I, const volatile T>;
-

    -Let TE denote tuple_element<I, T> of the cv-unqualified type T. Then each of the -three templates shall meet the TransformationTrait requirements (20.7.1) with a member typedef type that shall name the -same type as the following type:

    -
      -
    • for the first specialization, the type add_const<TE::type>::type,
      • -
    • for the second specialization, the type add_volatile<TE::type>::type, and
      • -
    • for the third specialization, the type add_cv<TE::type>::type
      • -
    -
    -
    3. -
- - - - - - -
-

1122. Ratio values should be constexpr

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Section: 20.11.3 [ratio.ratio] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-05-25 Last modified: 2015-04-08

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Discussion:

-

-The values num and den in the ratio template -should be declared constexpr. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2994. -

- - -

Proposed resolution:

-

-20.11.3 [ratio.ratio] -

- -
-namespace std {
-  template <intmax_t N, intmax_t D = 1>
-  class ratio {
-  public:
-    static constexpr intmax_t num;
-    static constexpr intmax_t den;
-  };
-}
-
- - - - - - -
-

1123. No requirement that standard streams be flushed

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Section: 27.5.3.1.6 [ios::Init] Status: C++11 - Submitter: James Kanze Opened: 2009-05-14 Last modified: 2015-04-08

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Discussion:

-

-As currently formulated, the standard doesn't require that there -is ever a flush of cout, etc. (This implies, for example, that -the classical hello, world program may have no output.) In the -current draft -(N2798), -there is a requirement that the objects -be constructed before main, and before the dynamic -initialization of any non-local objects defined after the -inclusion of <iostream> in the same translation unit. The only -requirement that I can find concerning flushing, however, is in -27.5.3.1.6 [ios::Init], where the destructor of the last -std::ios_base::Init object flushes. But there is, as far as I -can see, no guarantee that such an object ever exists. -

-

-Also, the wording in [iostreams.objects] says that: -

-

-The objects -are constructed and the associations are established at some -time prior to or during the first time an object of class -ios_base::Init is constructed, and in any case before the body -of main begins execution. -

-

-In 27.5.3.1.6 [ios::Init], however, as an -effect of the constructor, it says that -

-

-If init_cnt is zero, -the function stores the value one in init_cnt, then constructs -and initializes the objects cin, cout, cerr, clog -wcin, wcout, wcerr, and wclog" -

- -

-which seems to forbid earlier -construction. -

- -

-(Note that with these changes, the exposition only "static -int init_cnt" in ios_base::Init can be dropped.) -

-

-Of course, a determined programmer can still inhibit the -flush with things like: -

-
-new std::ios_base::Init ;       //  never deleted 
-
-

-or (in a function): -

-
-std::ios_base::Init ensureConstruction ; 
-//  ... 
-exit( EXIT_SUCCESS ) ; 
-
-

-Perhaps some words somewhere to the effect that all -std::ios_base::Init objects should have static lifetime -would be in order. -

- -

[ -2009 Santa Cruz: -]

- - -

-Moved to Ready. Some editorial changes are expected (in addition to the -proposed wording) to remove init_cnt from Init. -

- - - -

Proposed resolution:

-

-Change 27.4 [iostream.objects]/2: -

- -

--2- The objects are constructed and the associations are established at -some time prior to or during the first time an object of class -ios_base::Init is constructed, and in any case before the body -of main begins execution.292 The objects are not destroyed -during program execution.293 -If a translation unit includes -<iostream> or explicitly constructs an -ios_base::Init object, these stream objects shall be -constructed before dynamic initialization of non-local objects defined -later in that translation unit. -The results of including <iostream> in a translation -unit shall be as if <iostream> defined an instance of -ios_base::Init with static lifetime. Similarly, the entire -program shall behave as if there were at least one instance of -ios_base::Init with static lifetime. -

- -

-Change 27.5.3.1.6 [ios::Init]/3: -

- -
-
-Init();
-
-

--3- Effects: Constructs an object of class Init. -If init_cnt is zero, the function stores the value one in -init_cnt, then constructs and initializes the objects -cin, cout, cerr, clog (27.4.1), -wcin, wcout, wcerr, and wclog -(27.4.2). In any case, the function then adds one to the value stored in -init_cnt. -Constructs and initializes the objects cin, cout, -cerr, clog, wcin, wcout, -wcerr and wclog if they have not already been -constructed and initialized. -

-
- -

-Change 27.5.3.1.6 [ios::Init]/4: -

- -
-
-~Init();
-
-

--4- Effects: Destroys an object of class Init. -The function subtracts one from the value stored in init_cnt and, -if the resulting stored value is one, -If there are no other instances of the class still in -existance, -calls cout.flush(), -cerr.flush(), clog.flush(), wcout.flush(), -wcerr.flush(), wclog.flush(). -

-
- - - - - - -
-

1126. istreambuff_iterator::equal needs a const & parameter

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Section: 24.6.3.5 [istreambuf.iterator::equal] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2015-04-08

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-

Discussion:

-

-The equal member function of istreambuf_iterator is -declared const, but takes its argument by non-const reference. -

-

-This is not compatible with the operator== free function overload, which is -defined in terms of calling equal yet takes both arguments by reference to -const. -

- -

[ -The proposed wording is consistent with 110 with status TC1. -]

- - -

[ -2009-11-02 Howard adds: -]

- - -

-Set to Tentatively Ready after 5 positive votes on c++std-lib. -

- - - -

Proposed resolution:

-

-Ammend in both:
-24.6.3 [istreambuf.iterator]
-24.6.3.5 [istreambuf.iterator::equal]
-

- -
-bool equal(const istreambuf_iterator& b) const;
-
- - - - - - -
-

1129. istream(buf)_iterator should support literal sentinel value

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Section: 24.6.1.1 [istream.iterator.cons], 24.6.3 [istreambuf.iterator] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-05-30 Last modified: 2015-04-08

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-

Discussion:

-

-istream_iterator and istreambuf_iterator should support literal sentinel -values. The default constructor is frequently used to terminate ranges, and -could easily be a literal value for istreambuf_iterator, and -istream_iterator when iterating value types. A little more work using a -suitably sized/aligned char-array for storage (or an updated component like -boost::optional proposed for TR2) would allow istream_iterator to support -constexpr default constructor in all cases, although we might leave this -tweak as a QoI issue. Note that requiring constexpr be supported also -allows us to place no-throw guarantees on this constructor too. -

- -

[ -2009-06-02 Daniel adds: -]

- - -
-

-I agree with the usefulness of the issue suggestion, but we need -to ensure that istream_iterator can satisfy be literal if needed. -Currently this is not clear, because 24.6.1 [istream.iterator]/3 declares -a copy constructor and a destructor and explains their semantic in -24.6.1.1 [istream.iterator.cons]/3+4. -

-

-The prototype semantic specification is ok (although it seems -somewhat redundant to me, because the semantic doesn't say -anything interesting in both cases), but for support of trivial class -types we also need a trivial copy constructor and destructor as of -9 [class]/6. The current non-informative specification of these -two special members suggests to remove their explicit declaration -in the class and add explicit wording that says that if T is -trivial a default constructed iterator is also literal, alternatively it -would be possible to mark both as defaulted and add explicit -(memberwise) wording that guarantees that they are trivial. -

-

-Btw.: I'm quite sure that the istreambuf_iterator additions to -ensure triviality are not sufficient as suggested, because the -library does not yet give general guarantees that a defaulted -special member declaration makes this member also trivial. -Note that e.g. the atomic types do give a general statement! -

-

-Finally there is a wording issue: There does not exist something -like a "literal constructor". The core language uses the term -"constexpr constructor" for this. -

-

-Suggestion: -

-
    -
  1. -

    -Change 24.6.1 [istream.iterator]/3 as indicated: -

    -
    -constexpr istream_iterator();
-istream_iterator(istream_type& s);
-istream_iterator(const istream_iterator<T,charT,traits,Distance>& x) = default;
-~istream_iterator() = default;
-
    -
    2. -
  2. -

    -Change 24.6.1.1 [istream.iterator.cons]/1 as indicated: -

    -
    -constexpr istream_iterator();
-
    -

    --1- Effects: Constructs the end-of-stream iterator. If T is a literal type, -then this constructor shall be a constexpr constructor. -

    -
    -
    3. -
  3. -

    -Change 24.6.1.1 [istream.iterator.cons]/3 as indicated: -

    -
    -istream_iterator(const istream_iterator<T,charT,traits,Distance>& x) = default;
-
    -

    --3- Effects: Constructs a copy of x. If T is a literal type, then -this constructor shall be a trivial copy constructor. -

    -
    -
    4. -
  4. -

    -Change 24.6.1.1 [istream.iterator.cons]/4 as indicated: -

    - -
    -~istream_iterator() = default;
-
    -

    --4- Effects: The iterator is destroyed. If T is a literal type, then -this destructor shall be a trivial -destructor. -

    -
    -
    5. -
  5. -

    -Change 24.6.3 [istreambuf.iterator] before p. 1 as indicated: -

    - -
    -constexpr istreambuf_iterator() throw();
-istreambuf_iterator(const istreambuf_iterator&)  throw() = default;
-~istreambuf_iterator()  throw() = default;
-
    -
    6. -
  6. -

    -Change 24.6.3 [istreambuf.iterator]/1 as indicated: -

    -

    -[..] The default constructor istreambuf_iterator() and the constructor -istreambuf_iterator(0) both construct an end of stream iterator object -suitable for use as an end-of-range. All specializations of -istreambuf_iterator shall have a trivial copy constructor, a constexpr -default constructor and a trivial destructor. -

    -
    7. -
-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2994. -

- - - -

Proposed resolution:

-

-24.6.1 [istream.iterator] para 3 -

- -
-constexpr istream_iterator();
-
- -

-24.6.1.1 [istream.iterator.cons] -

- -
-constexpr istream_iterator();
-
-

--1- Effects: Constructs the end-of-stream iterator. -If T is a literal type, then this constructor shall -be a literal constructor. -

-
- -

-24.6.3 [istreambuf.iterator] -

- -
-constexpr istreambuf_iterator() throw();
-
- - - - - - -
-

1130. copy_exception name misleading

-

Section: 18.8.5 [propagation] Status: C++11 - Submitter: Peter Dimov Opened: 2009-05-13 Last modified: 2015-04-08

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-

Discussion:

-

-The naming of std::copy_exception misleads almost everyone -(experts included!) to think that it is the function that copies an -exception_ptr: -

- -
-exception_ptr p1 = current_exception();
-exception_ptr p2 = copy_exception( p1 );
-
- -

-But this is not at all what it does. The above actually creates an -exception_ptr p2 that contains a copy of p1, not of -the exception to which p1 refers! -

-

-This is, of course, all my fault; in my defence, I used copy_exception -because I was unable to think of a better name. -

-

-But I believe that, based on what we've seen so far, any other name would be better. -

-

-Therefore, I propose copy_exception to be renamed to -create_exception: -

- -
-template<class E> exception_ptr create_exception(E e);
-
- -

-with the following explanatory paragraph after it: -

- -

-Creates an exception_ptr that refers to a copy of e. -

- -

[ -2009-05-13 Daniel adds: -]

- - -
-

-What about -

-
-make_exception_ptr
-
-

-in similarity to make_pair and make_tuple, make_error_code and -make_error_condition, or make_shared? Or, if a stronger symmetry to -current_exception is preferred: -

- -
-make_exception
-
-

-We have not a single create_* function in the library, it was always -make_* used. -

-
- -

[ -2009-05-13 Peter adds: -]

- - -

-make_exception_ptr works for me. -

- -

[ -2009-06-02 Thomas J. Gritzan adds: -]

- - -
-

-To avoid surprises and unwanted recursion, how about making a call to -std::make_exception_ptr with an exception_ptr illegal? -

-

-It might work like this: -

-
-template<class E>
-exception_ptr make_exception_ptr(E e);
-template<>
-exception_ptr make_exception_ptr<exception_ptr>(exception_ptr e) = delete;
-
-
- -

[ -2009 Santa Cruz: -]

- - -

-Move to Review for the time being. The subgroup thinks this is a good -idea, but doesn't want to break compatibility unnecessarily if someone -is already shipping this. Let's talk to Benjamin and PJP tomorrow to -make sure neither objects. -

- -

[ -2009-11-16 Jonathan Wakely adds: -]

- - -

-GCC 4.4 shipped with copy_exception but we could certainly keep that -symbol in the library (but not the headers) so it can still be found -by any apps foolishly relying on the experimental C++0x mode being ABI -stable. -

- -

[ -2009-11-16 Peter adopts wording supplied by Daniel. -]

- - -

[ -2009-11-16 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 18.8 [support.exception]/1, header <exception> -synopsis as indicated: -

    - -
    -exception_ptr current_exception();
-void rethrow_exception [[noreturn]] (exception_ptr p);
-template<class E> exception_ptr copy_exceptionmake_exception_ptr(E e);
-
    -
    2. - -
  2. -

    -Change 18.8.5 [propagation]: -

    - -
    -
    -template<class E> exception_ptr copy_exceptionmake_exception_ptr(E e);
-
    - -
    -

    --11- Effects: Creates an exception_ptr that refers -to a copy of e, as if -

    - -
    -try {
-  throw e;
-} catch(...) {
-  return current_exception();
-}
-
    - -

    ...

    -
    - -
    -
    3. - -
  3. -

    -Change 30.6.5 [futures.promise]/7 as indicated: -

    - -

    -Effects: if the associated state of *this is not ready, stores an exception -object of type future_error with an error code of broken_promise as if by -this->set_exception(copy_exceptionmake_exception_ptr( -future_error(future_errc::broken_promise)). Destroys ... -

    -
    4. -
- - - - - - -
-

1131. C++0x does not need alignment_of

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++11 - Submitter: Niels Dekker Opened: 2009-06-01 Last modified: 2015-04-08

-

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-

Discussion:

-

-The alignment_of template is no longer necessary, now that the -core language will provide alignof. Scott Meyers raised this -issue at comp.std.c++, -C++0x: alignof vs. alignment_of, -May 21, 2009. In a reply, Daniel Krügler pointed out that -alignof was added to the working paper after -alignment_of. So it appears that alignment_of is only -part of the current Working Draft -(N2857) -because it is in TR1. -

-

-Having both alignof and alignment_of would cause -unwanted confusion. In general, I think TR1 functionality should not be -brought into C++0x if it is entirely redundant with other C++0x language -or library features. -

- -

[ -2009-11-16 Chris adds: -]

- - -
-

-I would like to suggest the following new wording for this issue, based on -recent discussions. Basically this doesn't delete alignment_of, it just -makes it clear that it is just a wrapper for alignof. This deletes the -first part of the proposed resolution, changes the second part by leaving in -alignof(T) but changing the precondition and leaves the 3rd part -unchanged. -

- -

-Suggested Resolution: -

- -
-

-Change the first row of Table 44 ("Type property queries"), from Type properties -20.10.4.3 [meta.unary.prop]: -

- -
- - - - - - - -
Table 44 — Type property queries
-template <class T> struct alignment_of; - -alignof(T).
-Precondition: T shall be a complete type, a reference type, -or an array of unknown bound, but shall not be a function type or (possibly -cv-qualified) void. alignof(T) shall be defined -
-
- -

-Change text in Table 51 ("Other transformations"), from Other transformations -20.10.7.6 [meta.trans.other], as follows: -

- -
- - - - - - - -
Table 51 — Other transformations
…aligned_storage; -Len shall not be zero. Align shall be equal to -alignment_of<T>::value alignof(T) for some -type T or to default-alignment. -…
-
-
-
- -

[ -2010-01-30 Alisdair proposes that Chris' wording be moved into the proposed wording -section and tweaks it on the way. -]

- - -
-

-Original proposed wording saved here: -

-
-

-Remove from Header <type_traits> synopsis 20.10.2 [meta.type.synop]: -

-
-template <class T> struct alignment_of;
-
- -

-Remove the first row of Table 44 ("Type property queries"), from -Type properties 20.10.4.3 [meta.unary.prop]: -

-
- - - - - - -
Table 44 — Type property queries
template <class T> struct alignment_of;alignof(T).
-Precondition: T shall be a complete type, a reference -type, or an array of unknown bound, but shall not be a function type or -(possibly cv-qualified) void. -
-
- -

-Change text in Table 51 ("Other transformations"), from Other -transformations 20.10.7.6 [meta.trans.other], as follows: -

-
- - - - - - - -
Table 51 — Other transformations
…aligned_storage; -Len shall not be zero. Align shall be equal to -alignment_of<T>::value alignof(T) for some -type T or to default-alignment. -…
-
-
-
- -

[ -2010-01-30 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -

-Change the first row of Table 43 ("Type property queries"), from Type properties -20.10.4.3 [meta.unary.prop]: -

- -
- - - - - - - -
Table 43 — Type property queries
-template <class T> struct alignment_of; - -alignof(T).
-Precondition: T shall be a complete type, a reference type, -or an array of unknown bound, but shall not be a function type or (possibly -cv-qualified) void. alignof(T) is a valid -expression (5.3.6 [expr.alignof]) -
-
- -

-Change text in Table 51 ("Other transformations"), from Other transformations -20.10.7.6 [meta.trans.other], as follows: -

- -
- - - - - - - -
Table 51 — Other transformations
…aligned_storage; -Len shall not be zero. Align shall be equal to -alignment_of<T>::value alignof(T) for some -type T or to default-alignment. -…
-
- - - - - - -
-

1133. Does N2844 break current specification of list::splice?

-

Section: 23.3.4.6 [forwardlist.ops], 23.3.5.5 [list.ops] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-05-09 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-IIUC, -N2844 -means that lvalues will no longer bind to rvalue references. -Therefore, the current specification of list::splice (list -operations 23.3.5.5 [list.ops]) will be a breaking change of behaviour for existing -programs. That is because we changed the signature to swallow via an rvalue -reference rather than the lvalue reference used in 03. -

-

-Retaining this form would be safer, requiring an explicit move when splicing -from lvalues. However, this will break existing programs. -We have the same problem with forward_list, although without the risk of -breaking programs so here it might be viewed as a positive feature. -

-

-The problem signatures: -

-
-void splice_after(const_iterator position, forward_list<T,Alloc>&& x);
-void splice_after(const_iterator position, forward_list<T,Alloc>&& x,
-                  const_iterator i);
-void splice_after(const_iterator position, forward_list<T,Alloc>&& x,
-                  const_iterator first, const_iterator last);
-
-void splice(const_iterator position, list<T,Alloc>&& x);
-void splice(const_iterator position, list<T,Alloc>&& x,
-            const_iterator i);
-void splice(const_iterator position, list<T,Alloc>&& x,
-            const_iterator first, const_iterator last);
-
- -

-Possible resolutions: -

- -

-Option A. Add an additional (non-const) lvalue-reference -overload in each case -

-

-Option B. Change rvalue reference back to (non-const) -lvalue-reference overload in each case -

-

-Option C. Add an additional (non-const) lvalue-reference -overload in just the std::list cases -

-

-I think (B) would be very unfortunate, I really like the forward_list -behaviour in (C) but feel (A) is needed for consistency. -

-

-My actual preference would be NAD, ship with this as a breaking change as it -is a more explicit interface. I don't think that will fly though! -

- -

-See the thread starting with c++std-lib-23725 for more discussion. -

- -

[ -2009-10-27 Christopher Jefferson provides proposed wording for Option C. -]

- - -

[ -2009-12-08 Jonathan Wakely adds: -]

- - -
-

-As Bill Plauger pointed out, list::merge needs similar treatment. -

-

[ -Wording updated. -]

- -
- -

[ -2009-12-13 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-In 23.3.5 [list] -

- -

-Add lvalue overloads before rvalue ones: -

- -
-void splice(const_iterator position, list<T,Allocator>& x);
-void splice(const_iterator position, list<T,Allocator>&& x);
-void splice(const_iterator position, list<T,Allocator>& x, const_iterator i);
-void splice(const_iterator position, list<T,Allocator>&& x, const_iterator i);
-void splice(const_iterator position, list<T,Allocator>& x,
-            const_iterator first, const_iterator last);
-void splice(const_iterator position, list<T,Allocator>&& x,
-            const_iterator first, const_iterator last);
-void merge(list<T,Allocator>& x);
-template <class Compare> void merge(list<T,Allocator>& x, Compare comp);
-void merge(list<T,Allocator>&& x);
-template <class Compare> void merge(list<T,Allocator>&& x, Compare comp);
-
-
- -

-In 23.3.5.5 [list.ops], similarly add lvalue overload before each rvalue one: -

-

-(After paragraph 2) -

- -
-void splice(const_iterator position, list<T,Allocator>& x);
-void splice(const_iterator position, list<T,Allocator>&& x);
-
- -

-(After paragraph 6) -

- -
-void splice(const_iterator position, list<T,Allocator>& x, const_iterator i);
-void splice(const_iterator position, list<T,Allocator>&& x, const_iterator i);
-
- -

-(After paragraph 10) -

- -
-void splice(const_iterator position, list<T,Allocator>& x,
-            const_iterator first, const_iterator last);
-void splice(const_iterator position, list<T,Allocator>&& x,
-            const_iterator first, const_iterator last);
-
- -

-In 23.3.5.5 [list.ops], after paragraph 21 -

- -
-void merge(list<T,Allocator>& x);
-template <class Compare> void merge(list<T,Allocator>& x, Compare comp);
-void merge(list<T,Allocator>&& x);
-template <class Compare> void merge(list<T,Allocator>&& x, Compare comp);
-
- - - - - - -
-

1134. Redundant specification of <stdint.h>, <fenv.h>, <tgmath.h>, - and maybe <complex.h>

-

Section: X [stdinth], X [fenv], 26.8 [c.math], X [cmplxh] Status: C++11 - Submitter: Robert Klarer Opened: 2009-05-26 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-This is probably editorial. -

-

-The following items should be removed from the draft, because they're -redundant with Annex D, and they arguably make some *.h headers -non-deprecated: -

-

-X [stdinth] (regarding <stdint.h>) -

-

-X [fenv] (regarding <fenv.h> -

-

-Line 3 of 26.8 [c.math] (regarding <tgmath.h>) -

-

-X [cmplxh] (regarding <complex.h>, though the note in this subclause is not redundant) -

- -

[ -2009-06-10 Ganesh adds: -]

- - -

-While searching for stdint in the CD, I found that <stdint.h> is also -mentioned in 3.9.1 [basic.fundamental] p.5. I guess it should refer to -<cstdint> instead. -

- -

[ -2009 Santa Cruz: -]

- - -

-Real issue. Maybe just editorial, maybe not. Move to Ready. -

- - - -

Proposed resolution:

-

-Remove the section X [stdinth]. -

-

-Remove the section X [fenv]. -

-

-Remove 26.8 [c.math], p3: -

- -

--3- The header <tgmath.h> effectively includes the headers <complex.h> -and <math.h>. -

-

-Remove the section X [cmplxh]. -

- - - - - -
-

1135. exception_ptr should support contextual conversion to bool

-

Section: 18.8.5 [propagation] Status: Resolved - Submitter: Daniel Krügler Opened: 2007-06-06 Last modified: 2015-04-08

-

View all other issues in [propagation].

-

View all issues with Resolved status.

-

Discussion:

-

-As of -N2857 -18.8.5 [propagation] p.5, the implementation-defined type -exception_ptr does provide the following ways to check whether -it is a null value: -

-
-void f(std::exception_ptr p) {
-  p == nullptr;
-  p == 0;
-  p == exception_ptr();
-}
-
-

-This is rather cumbersome way of checking for the null value -and I suggest to require support for evaluation in a boolean -context like so: -

- -
-void g(std::exception_ptr p) {
-  if (p) {}
-  !p;
-}
-
- -

[ -2009 Santa Cruz: -]

- - -

-Move to Ready. Note to editor: considering putting in a cross-reference -to 4 [conv], paragraph 3, which defines the phrase -"contextually converted to bool". -

- -

[ -2010-03-14 Howard adds: -]

- - -

-We moved -N3073 -to the formal motions page in Pittsburgh which should obsolete this issue. I've -moved this issue to NAD Editorial, solved by N3073. -

- - - -

Rationale:

-

-Solved by N3073. -

- - -

Proposed resolution:

-

-In section 18.8.5 [propagation] insert a new paragraph between p.5 and p.6: -

- -

- -An object e of type exception_ptr can be contextually converted to bool. -The effect shall be as if e != exception_ptr() had been evaluated in place -of e. There shall be no implicit conversion to arithmetic type, to -enumeration type or to pointer type. - -

- - - - - -
-

1136. Incomplete specification of nested_exception::rethrow_nested()

-

Section: 18.8.6 [except.nested] Status: C++11 - Submitter: Daniel Krügler Opened: 2007-06-06 Last modified: 2015-04-08

-

View other active issues in [except.nested].

-

View all other issues in [except.nested].

-

View all issues with C++11 status.

-

Discussion:

-

-It was recently mentioned in a newsgroup article -http://groups.google.de/group/comp.std.c++/msg/f82022aff68edf3d -that the specification of the member function rethrow_nested() of the -class nested_exception is incomplete, specifically it remains unclear -what happens, if member nested_ptr() returns a null value. In -18.8.6 [except.nested] we find only the following paragraph related to that: -

-
-void rethrow_nested() const; // [[noreturn]]
-
-

--4- Throws: the stored exception captured by this nested_exception object. -

-
-

-This is a problem, because it is possible to create an object of -nested_exception with exactly such a state, e.g. -

-
-#include <exception>
-#include <iostream>
-
-int main() try {
-  std::nested_exception e; // OK, calls current_exception() and stores it's null value
-  e.rethrow_nested(); // ?
-  std::cout << "A" << std::endl;
-}
-catch(...) {
-  std::cout << "B" << std::endl;
-}
-
-

-I suggest to follow the proposal of the reporter, namely to invoke -terminate() if nested_ptr() return a null value of exception_ptr instead -of relying on the fallback position of undefined behavior. This would -be consistent to the behavior of a throw; statement when no -exception is being handled. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Change around 18.8.6 [except.nested] p.4 as indicated: -

-
-

--4- Throws: the stored exception captured by this nested_exception -object, if nested_ptr() != nullptr -

-

-- Remarks: If nested_ptr() == nullptr, terminate() -shall be called. -

-
- - - - - -
-

1137. Return type of conj and proj

-

Section: 26.4.9 [cmplx.over] Status: C++11 - Submitter: Marc Steinbach Opened: 2009-06-11 Last modified: 2015-04-08

-

View all other issues in [cmplx.over].

-

View all issues with C++11 status.

-

Discussion:

-

-In clause 1, the Working Draft -(N2857) -specifies overloads of the -functions -

-
-arg, conj, imag, norm, proj, real
-
-

-for non-complex arithmetic types (float, double, -long double, and integers). -The only requirement (clause 2) specifies effective type promotion of arguments. -

-

-I strongly suggest to add the following requirement on the return types: -

-

-All the specified overloads must return real (i.e., non-complex) values, -specifically, the nested value_type of effectively promoted arguments. -

- -

-(This has no effect on arg, imag, norm, real: -they are real-valued anyway.) -

-

Rationale:

-

-Mathematically, conj() and proj(), like the transcendental functions, are -complex-valued in general but map the (extended) real line to itself. -In fact, both functions act as identity on the reals. -A typical user will expect conj() and proj() to preserve this essential -mathematical property in the same way as exp(), sin(), etc. -A typical use of conj(), e.g., is the generic scalar product of n-vectors: -

- -
-template<typename T>
-inline T
-scalar_product(size_t n, T const* x, T const* y) {
-  T result = 0;
-  for (size_t i = 0; i < n; ++i)
-    result += x[i] * std::conj(y[i]);
-  return result;
-}
-
-

-This will work equally well for real and complex floating-point types T if -conj() returns T. It will not work with real types if conj() -returns complex values. -

-

-Instead, the implementation of scalar_product becomes either less efficient -and less useful (if a complex result is always returned), or unnecessarily -complicated (if overloaded versions with proper return types are defined). -In the second case, the real-argument overload of conj() cannot be used. -In fact, it must be avoided. -

-

-Overloaded conj() and proj() are principally needed in generic programming. -All such use cases will benefit from the proposed return type requirement, -in a similar way as the scalar_product example. -The requirement will not harm use cases where a complex return value -is expected, because of implicit conversion to complex. -Without the proposed return type guarantee, I find overloaded versions -of conj() and proj() not only useless but actually troublesome. -

- - -

[ -2009-11-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Insert a new paragraph after 26.4.9 [cmplx.over]/2: -

- -

- -All of the specified overloads shall have a return type which is the nested value_type of -the effectively cast arguments. - -

- - - - - -
-

1138. Unusual return value for operator+

-

Section: 21.4.8.1 [string::op+] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-06-12 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Many of the basic_string operator+ overloads return an rvalue-reference. Is -that really intended? -

-

-I'm considering it might be a mild performance tweak to avoid making -un-necessary copies of a cheaply movable type, but it opens risk to dangling -references in code like: -

- -
-auto && s = string{"x"} + string{y};
-
- -

-and I'm not sure about: -

- -
-auto s = string{"x"} + string{y};
-
- -

[ -2009-10-11 Howard updated Returns: clause for each of these. -]

- - -

[ -2009-11-05 Howard adds: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - -

Proposed resolution:

-

-Strike the && from the return type in the following function -signatures: -

- -
-

-21.3 [string.classes] p2 Header Synopsis -

- -
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              const basic_string<charT,traits,Allocator>& rhs);
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(const basic_string<charT,traits,Allocator>& lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(const charT* lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(charT lhs, basic_string<charT,traits,Allocator>&& rhs);
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              const charT* rhs);
-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs, charT rhs);
-
- -

-21.4.8.1 [string::op+] -

- -
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              const basic_string<charT,traits,Allocator>& rhs);
-
-

-Returns: std::move(lhs.append(rhs)) -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(const basic_string<charT,traits,Allocator>& lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-

-Returns: std::move(rhs.insert(0, lhs)) -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-

-Returns: std::move(lhs.append(rhs)) [Note: Or equivalently -std::move(rhs.insert(0, lhs)) — end note] -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(const charT* lhs,
-              basic_string<charT,traits,Allocator>&& rhs);
-
-

-Returns: std::move(rhs.insert(0, lhs)). -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(charT lhs, basic_string<charT,traits,Allocator>&& rhs);
-
-

-Returns: std::move(rhs.insert(0, 1, lhs)). -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs,
-              const charT* rhs);
-
-

-Returns: std::move(lhs.append(rhs)). -

-
-template<class charT, class traits, class Allocator>
-  basic_string<charT,traits,Allocator>&&
-    operator+(basic_string<charT,traits,Allocator>&& lhs, charT rhs);
-
-

-Returns: std::move(lhs.append(1, rhs)). -

-
- -
- - - - - - -
-

1143. Atomic operations library not concept enabled

-

Section: 29 [atomics] Status: Resolved - Submitter: LWG Opened: 2009-06-15 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 87, UK 311

- -

-The atomics chapter is not concept enabled. -

- -

-Needs to also consider issues 923 and 924. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

- - - - - -
-

1144. "thread safe" is undefined

-

Section: 18.5 [support.start.term] Status: C++11 - Submitter: LWG Opened: 2009-06-16 Last modified: 2015-04-08

-

View all other issues in [support.start.term].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 187

- -

-The term "thread safe" is not defined nor used in this context -anywhere else in the standard. -

- -

Suggested action:

-

-Clarify the meaning of "thread safe". -

- -

[ -2009 Santa Cruz: -]

- - -
-

-The "thread safe" language has already been change in the WP. It was -changed to "happen before", but the current WP text is still a little -incomplete: "happen before" is binary, but the current WP text only -mentions one thing. -

-

-Move to Ready. -

-
- - - -

Proposed resolution:

-

-For the following functions in 18.5 [support.start.term]. -

-

-extern "C" int at_quick_exit(void (*f)(void));
-extern "C++" int at_quick_exit(void (*f)(void));
-
- -

-Edit paragraph 10 as follows. -The intent is -to provide the other half of the happens before relation; -to note indeterminate ordering; -and to clean up some formatting. -

-

-Effects: -The at_quick_exit() functions -register the function pointed to by f -to be called without arguments when quick_exit is called. -It is unspecified whether a call to at_quick_exit() -that does not happen-before happen before (1.10) -all calls to quick_exit -will succeed. -[Note: -the at_quick_exit() functions -shall not introduce a data race (17.6.4.7). -exitnote -—end note] - -[Note: -The order of registration may be indeterminate -if at_quick_exit was called from more than one thread. -—end note] - -[Note: The at_quick_exit registrations -are distinct from the atexit registrations, -and applications may need to call both registration functions -with the same argument. -—end note] -

- -

-For the following function. -

-

-void quick_exit [[noreturn]] (int status)
-
- -

-Edit paragraph 13 as follows. -The intent is to note that thread-local variables may be different. -

-

-Effects: -Functions registered by calls to at_quick_exit -are called in the reverse order of their registration, -except that a function shall be called -after any previously registered functions -that had already been called at the time it was registered. -Objects shall not be destroyed as a result of calling quick_exit. -If control leaves a registered function called by quick_exit -because the function does not provide a handler for a thrown exception, -terminate() shall be called. - -[Note: -Functions registered by one thread may be called by any thread, -and hence should not rely on the identity of thread-storage-duration objects. -—end note] - -After calling registered functions, -quick_exit shall call _Exit(status). -[Note: -The standard file buffers are not flushed. -See: ISO C 7.20.4.4. -—end note] -

- - - - - -
-

1145. Inappropriate headers for atomics

-

Section: 29 [atomics] Status: Resolved - Submitter: LWG Opened: 2009-06-16 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 312

- -

-The contents of the <stdatomic.h> header are not listed anywhere, -and <cstdatomic> is listed as a C99 header in chapter 17. -If we intend to use these for compatibility with a future C standard, -we should not use them now. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2992. -

- - - -

Proposed resolution:

-

-Remove <cstdatomic> from the C99 headers in table 14. -Add a new header <atomic> to the headers in table 13. -Update chapter 29 to remove reference to <stdatomic.h> -and replace the use of <cstdatomic> with <atomic>. -

-

[ -If and when WG14 adds atomic operations to C -we can add corresponding headers to table 14 with a TR. -]

- - - - - - -
-

1146. "lockfree" does not say enough

-

Section: 29.4 [atomics.lockfree] Status: Resolved - Submitter: Jeffrey Yasskin Opened: 2009-06-16 Last modified: 2015-04-08

-

View all other issues in [atomics.lockfree].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 88

- -

-The "lockfree" facilities do not tell the programmer enough. -

- -

-There are 2 problems here. -First, at least on x86, -it's less important to me whether some integral types are lock free -than what is the largest type I can pass to atomic and have it be lock-free. -For example, if long longs are not lock-free, -ATOMIC_INTEGRAL_LOCK_FREE is probably 1, -but I'd still be interested in knowing whether longs are always lock-free. -Or if long longs at any address are lock-free, -I'd expect ATOMIC_INTEGRAL_LOCK_FREE to be 2, -but I may actually care whether I have access to -the cmpxchg16b instruction. -None of the support here helps with that question. -(There are really 2 related questions here: -what alignment requirements are there for lock-free access; -and what processor is the program actually running on, -as opposed to what it was compiled for?) -

- -

-Second, having atomic_is_lock_free only apply to individual objects -is pretty useless -(except, as Lawrence Crowl points out, -for throwing an exception when an object is unexpectedly not lock-free). -I'm likely to want to use its result to decide what algorithm to use, -and that algorithm is probably going to allocate new memory -containing atomic objects and then try to act on them. -If I can't predict the lock-freedom of the new object -by checking the lock-freedom of an existing object, -I may discover after starting the algorithm that I can't continue. -

- -

[ -2009-06-16 Jeffrey Yasskin adds: -]

- - -
-

-To solve the first problem, I think 2 macros would help: -MAX_POSSIBLE_LOCK_FREE_SIZE and MAX_GUARANTEED_LOCK_FREE_SIZE, -which expand to the maximum value of sizeof(T) for which atomic may -(or will, respectively) use lock-free operations. -Lawrence points out that this -"relies heavily on implementations -using word-size compare-swap on sub-word-size types, -which in turn requires address modulation." -He expects that to be the end state anyway, so it doesn't bother him much. -

- -

-To solve the second, -I think one could specify that equally aligned objects of the same type -will return the same value from atomic_is_lock_free(). -I don't know how to specify "equal alignment". -Lawrence suggests an additional function, atomic_is_always_lock_free(). -

-
- -

[ -2009-10-22 Benjamin Kosnik: -]

- - -
-

-In the evolution discussion of N2925, "More Collected Issues with -Atomics," there is an action item with respect to -LWG 1146, US 88 -

- -

-This is stated in the paper as: -

-

-Relatedly, Mike Sperts will create an issue to propose adding a traits -mechanism to check the compile-time properties through a template -mechanism rather than macros -

- -

-Here is my attempt to do this. I don't believe that a separate trait is -necessary for this, and that instead atomic_integral::is_lock_free can -be re-purposed with minimal work as follows. -

- -

[ -Howard: Put Benjamin's wording in the proposed wording section. -]

- - -
- -

[ -2009-10-22 Alberto Ganesh Barbati: -]

- - -
-

-Just a thought... wouldn't it be better to use a scoped enum instead of -plain integers? For example: -

- -
-enum class is_lock_free
-{
-    never = 0, sometimes = 1, always = 2;
-};
-
- -

-if compatibility with C is deemed important, we could use an unscoped -enum with suitably chosen names. It would still be more descriptive -than 0, 1 and 2. -

- -
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2992. -

- - - -

Proposed resolution:

-

-Header <cstdatomic> synopsis [atomics.synopsis] -

- -

-Edit as follows: -

- -
-namespace std {
-...
-// 29.4, lock-free property
-#define ATOMIC_INTEGRAL_LOCK_FREE unspecified
-#define ATOMIC_CHAR_LOCK_FREE unspecified
-#define ATOMIC_CHAR16_T_LOCK_FREE unspecified
-#define ATOMIC_CHAR32_T_LOCK_FREE unspecified
-#define ATOMIC_WCHAR_T_LOCK_FREE unspecified
-#define ATOMIC_SHORT_LOCK_FREE unspecified
-#define ATOMIC_INT_LOCK_FREE unspecified
-#define ATOMIC_LONG_LOCK_FREE unspecified
-#define ATOMIC_LLONG_LOCK_FREE unspecified
-#define ATOMIC_ADDRESS_LOCK_FREE unspecified
-
- -

-Lock-free Property 29.4 [atomics.lockfree] -

- -

-Edit the synopsis as follows. -

- -
-namespace std {
-   #define ATOMIC_INTEGRAL_LOCK_FREE unspecified
-   #define ATOMIC_CHAR_LOCK_FREE unspecified
-   #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
-   #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
-   #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
-   #define ATOMIC_SHORT_LOCK_FREE unspecified
-   #define ATOMIC_INT_LOCK_FREE unspecified
-   #define ATOMIC_LONG_LOCK_FREE unspecified
-   #define ATOMIC_LLONG_LOCK_FREE unspecified
-   #define ATOMIC_ADDRESS_LOCK_FREE unspecified
-}
-
- -

-Edit paragraph 1 as follows. -

- -

-The ATOMIC_...._LOCK_FREE macros ATOMIC_INTEGRAL_LOCK_FREE and ATOMIC_ADDRESS_LOCK_FREE indicate the general lock-free -property of integral and address atomic the corresponding atomic integral types, with the -signed and unsigned variants grouped together. -The properties also apply to the corresponding specializations of the atomic template. -A value of 0 -indicates that the types are never lock-free. A value of 1 -indicates that the types are sometimes lock-free. A value of 2 -indicates that the types are always lock-free. -

- -

-Operations on Atomic Types 29.6 [atomics.types.operations] -

- -

-Edit as follows. -

- -
-void static constexpr bool A::is_lock_free() const volatile;
-
-

-Returns: True if the object's types's operations are lock-free, false -otherwise. - -[Note: In the same way that <limits> -std::numeric_limits<short>::max() is related to <limits.h> -__LONG_LONG_MAX__, <atomic> std::atomic_short::is_lock_free is related to -<stdatomic.h> and ATOMIC_SHORT_LOCK_FREE — end note] - -

-
- - - - - - -
-

1147. Non-volatile atomic functions

-

Section: 29.6 [atomics.types.operations] Status: Resolved - Submitter: Jeffrey Yasskin Opened: 2009-06-16 Last modified: 2015-04-08

-

View all other issues in [atomics.types.operations].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 90

- -

-The C++0X draft declares all of the functions dealing with atomics -(section 29.6 [atomics.types.operations]) to take volatile -arguments. Yet it also says (29.4-3), -

- -
-

-[ Note: Many operations are volatile-qualified. -The "volatile as device register" semantics have not changed in the standard. -This qualification means that volatility is preserved -when applying these operations to volatile objects. -It does not mean that operations on non-volatile objects become volatile. -Thus, volatile qualified operations on non-volatile objects -may be merged under some conditions. — end note ] -

-
- -

-I was thinking about how to implement this in gcc, -and I believe that we'll want to overload most of the functions -on volatile and non-volatile. -Here's why: -

- -

-To let the compiler take advantage of the permission -to merge non-volatile atomic operations and reorder atomics in certain, -we'll need to tell the compiler backend -about exactly which atomic operation was used. -So I expect most of the functions of the form atomic_<op>_explicit() -(e.g. atomic_load_explicit, atomic_exchange_explicit, -atomic_fetch_add_explicit, etc.) -to become compiler builtins. -A builtin can tell whether its argument was volatile or not, -so those functions don't really need extra explicit overloads. -However, I don't expect that we'll want to add builtins -for every function in chapter 29, -since most can be implemented in terms of the _explicit free functions: -

- -
class atomic_int {
-  __atomic_int_storage value;
- public:
-  int fetch_add(int increment, memory_order order = memory_order_seq_cst) volatile {
-    // &value has type "volatile __atomic_int_storage*".
-    atomic_fetch_add_explicit(&value, increment, order);
-  }
-  ...
-};
-
- -

-But now this always calls -the volatile builtin version of atomic_fetch_add_explicit(), -even if the atomic_int wasn't declared volatile. -To preserve volatility and the compiler's permission to optimize, -I'd need to write: -

- -
class atomic_int {
-  __atomic_int_storage value;
- public:
-  int fetch_add(int increment, memory_order order = memory_order_seq_cst) volatile {
-    atomic_fetch_add_explicit(&value, increment, order);
-  }
-  int fetch_add(int increment, memory_order order = memory_order_seq_cst) {
-    atomic_fetch_add_explicit(&value, increment, order);
-  }
-  ...
-};
-
- -

-But this is visibly different from the declarations in the standard -because it's now overloaded. -(Consider passing &atomic_int::fetch_add as a template parameter.) -

- -

-The implementation may already have permission to add overloads -to the member functions: -

- -
-

-17.6.5.5 [member.functions] An implementation may declare additional non-virtual -member function signatures within a class:
-... -

-
    -
  • by adding a member function signature for a member function name.
    • -
-
- -

-but I don't see an equivalent permission to add overloads to the free functions. -

- -

[ -2009-06-16 Lawrence adds: -]

- - -
-

-I recommend allowing non-volatile overloads. -

-
- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2992. -

- - - -

Proposed resolution:

- - - - - -
-

1151. Behavior of the library in the presence of threads is incompletely specified

-

Section: 17 [library] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US 63

- -

Description

-

The behavior of the library in the presence of threads - is incompletely specified.

-

For example, if thread 1 assigns to X, then writes data - to file f, which is read by thread 2, and then accesses - variable X, is thread 2 guaranteed to be able to see the - value assigned to X by thread 1? In other words, does the - write of the data "happen before" the read?

-

Another example: does simultaneous access using operator - at() to different characters in the same non-const string - really introduce a data race?

-

Suggestion

-

Notes

17 SG: should go to threads group; misclassified in document -

- -

Concurrency SG: Create an issue. Hans will look into it.

- -

[ -2009 Santa Cruz: -]

- - -

-Move to "Open". Hans and the rest of the concurrency working group will -study this. We can't make progress without a thorough review and a -paper. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3069. -

- - -

Proposed resolution:

- - - - - -
-

1152. Expressions parsed differently than intended

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: C++11 - Submitter: Seungbeom Kim Opened: 2009-06-27 Last modified: 2015-04-08

-

View all other issues in [facet.num.put.virtuals].

-

View all issues with C++11 status.

-

Discussion:

-

-In Table 73 — Floating-point conversions, 22.4.2.2.2 [facet.num.put.virtuals], -in -N2914, -we have the following entries: -

- - - - - - - - - - - - - - -
Table 73 — Floating-point conversions
State stdio equivalent
floatfield == ios_base::fixed | ios_base::scientific && !uppercase%a
floatfield == ios_base::fixed | ios_base::scientific%A
- -

-These expressions are supposed to mean: -

- -
-floatfield == (ios_base::fixed | ios_base::scientific) && !uppercase 
-floatfield == (ios_base::fixed | ios_base::scientific) 
-
-

-but technically parsed as: -

-
-((floatfield == ios_base::fixed) | ios_base::scientific) && (!uppercase) 
-((floatfield == ios_base::fixed) | ios_base::scientific) 
-
-

-and should be corrected with additional parentheses, as shown above. -

- -

[ -2009-10-28 Howard: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - - -

Proposed resolution:

-

-Change Table 83 — Floating-point conversions in 22.4.2.2.2 [facet.num.put.virtuals]: -

- - - - - - - - - - - - - - - -
Table 83 — Floating-point conversions
State stdio equivalent
floatfield == (ios_base::fixed | ios_base::scientific) && !uppercase%a
floatfield == (ios_base::fixed | ios_base::scientific)%A
- - - - - -
-

1157. Local types can now instantiate templates

-

Section: 17.6.4.2.1 [namespace.std] Status: C++11 - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [namespace.std].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 175

- -

Description

-

Local types can - now be used to instantiate templates, but don't have - external linkage.

-

Suggestion

-

Remove the reference to external linkage.

- -

Notes

-

We accept the proposed solution. Martin will draft an issue.

- -

[ -2009-07-28 Alisdair provided wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-17.6.4.2.1 [namespace.std] -

-

-Strike "of external linkage" in p1 and p2: -

- -
-

--1- The behavior of a C++ program is undefined if it adds declarations or -definitions to namespace std or to a namespace within namespace std -unless otherwise specified. A program may add a concept map for any -standard library concept or a template specialization for any standard -library template to namespace std only if the declaration depends on a -user-defined type of external linkage and the specialization meets the -standard library requirements for the original template and is not -explicitly prohibited.179 -

- -

--2- The behavior of a C++ program is undefined if it declares -

-
    -
  • -an explicit specialization of any member function of a standard library -class template, or -
    • -
  • -an explicit specialization of any member function template of a standard -library class or class template, or -
    • -
  • -an explicit or partial specialization of any member class template of a -standard library class or class template. -
    • -
-

-A program may explicitly instantiate a template defined in the standard -library only if the declaration depends on the name of a user-defined -type of external linkage and the instantiation meets the standard -library requirements for the original template. -

-
- - - - - - -
-

1158. Encouragement to use monotonic clock

-

Section: 30.2.4 [thread.req.timing] Status: C++11 - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [thread.req.timing].

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 322, US 96

- -

Description

-

Not all systems - can provide a monotonic clock. How are they expected to - treat a _for function?

-

Suggestion

-

Add at least a note explaining the intent - for systems that do not support a monotonic clock.

- -

Notes

-

Create an issue, together with UK 96. Note that the specification as is - already allows a non-monotonic clock due to the word “should” rather than - “shall”. If this wording is kept, a footnote should be added to make the - meaning clear.

- -

[ 2009-06-29 Beman provided a proposed resolution. ]

- -

[ -2009-10-31 Howard adds: -]

- - -

-Set to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -2010-02-24 Pete moved to Open: -]

- - -

-LWG 1158's proposed resolution replaces the ISO-specified normative term -"should" with "are encouraged but not required to", which presumably means the -same thing, but has no ISO normative status. The WD used the latter formulation -in quite a few non-normative places, but only three normative ones. I've changed -all the normative uses to "should". -

- -

[ -2010-03-06 Beman updates wording. -]

- - -

[ -2010 Pittsburgh: Moved to Ready. -]

- - - - -

Proposed resolution:

- -

Change Timing specifications 30.2.4 [thread.req.timing] as indicated:

- -

-The member functions whose names end in _for take an argument that -specifies a relative time. Implementations should use a monotonic clock to -measure time for these functions. [Note: Implementations are not -required to use a monotonic clock because such a clock may be unavailable. -— end note] -

- - - - - - -
-

1159. Unclear spec for resource_deadlock_would_occur

-

Section: 30.4.2.2.2 [thread.lock.unique.locking] Status: C++11 - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [thread.lock.unique.locking].

-

View all issues with C++11 status.

-

Duplicate of: 1219

-

Discussion:

- -

Addresses UK 327, UK 328

- -

UK 327 Description

-

Not clear what - the specification for error condition - resource_deadlock_would_occur means. It is perfectly - possible for this thread to own the mutex without setting - owns to true on this specific lock object. It is also - possible for lock operations to succeed even if the thread - does own the mutex, if the mutex is recursive. Likewise, if - the mutex is not recursive and the mutex has been locked - externally, it is not always possible to know that this - error condition should be raised, depending on the host - operating system facilities. It is possible that 'i.e.' was - supposed to be 'e.g.' and that suggests that recursive - locks are not allowed. That makes sense, as the - exposition-only member owns is boolean and not a integer to - count recursive locks.

- -

UK 327 Suggestion

-

Add a precondition !owns. Change the 'i.e.' - in the error condition to be 'e.g.' to allow for this - condition to propogate deadlock detection by the host OS.

-

UK 327 Notes

-

Create an issue. Assigned to Lawrence Crowl. Note: not sure what try_lock - means for recursive locks when you are the owner. POSIX has language on - this, which should ideally be followed. Proposed fix is not quite right, for - example, try_lock should have different wording from lock.

- -

UK 328 Description

- -

There is a missing precondition that owns - is true, or an if(owns) test is missing from the effect - clause

-

UK 328 Suggestion

-

Add a - precondition that owns == true. Add an error condition to - detect a violation, rather than yield undefined behaviour.

-

UK 328 Notes

-

Handle in same issue as UK 327. Also uncertain that the proposed resolution - is the correct one.

- -

[ -2009-11-11 Alisdair notes that this issue is very closely related to 1219, -if not a dup. -]

- - -

[ -2010-02-12 Anthony provided wording. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Wording updated and moved to Ready for Pittsburgh. -

- - - -

Proposed resolution:

-

-Modify 30.4.2.2.2 [thread.lock.unique.locking] p3 to say: -

- -
-
void lock();
-
-

...

-

-3 Throws: Any exception thrown by pm->lock(). -std::system_error if an exception is required (30.2.2 [thread.req.exception]). -std::system_error with an error condition of -operation_not_permitted if pm is 0. -std::system_error with an error condition of -resource_deadlock_would_occur if on entry owns is true. -std::system_error when the -postcondition cannot be achieved. -

-
-
- -

-Remove 30.4.2.2.2 [thread.lock.unique.locking] p4 (Error condition clause). -

- -

-Modify 30.4.2.2.2 [thread.lock.unique.locking] p8 to say: -

- -
-
bool try_lock();
-
-

...

-

-8 Throws: Any exception thrown by pm->try_lock(). -std::system_error if an exception is required (30.2.2 [thread.req.exception]). -std::system_error with an error condition of -operation_not_permitted if pm is 0. -std::system_error with an error condition of -resource_deadlock_would_occur if on entry owns is true. -std::system_error when the -postcondition cannot be achieved. -

-
-
- -

-Remove 30.4.2.2.2 [thread.lock.unique.locking] p9 (Error condition clause). -

- -

-Modify 30.4.2.2.2 [thread.lock.unique.locking] p13 to say: -

- -
-
template <class Clock, class Duration>
-  bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
-
-

...

-

-13 Throws: Any exception thrown by pm->try_lock_until(). -std::system_error if an exception is required (30.2.2 [thread.req.exception]). -std::system_error with an error condition of -operation_not_permitted if pm is 0. -std::system_error with an error condition of -resource_deadlock_would_occur if on entry owns is true. -std::system_error when the -postcondition cannot be achieved. -

-
-
- -

-Remove 30.4.2.2.2 [thread.lock.unique.locking] p14 (Error condition clause). -

- -

-Modify 30.4.2.2.2 [thread.lock.unique.locking] p18 to say: -

- -
-
template <class Rep, class Period>
-  bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
-
-

...

-

-18 Throws: Any exception thrown by pm->try_lock_for(). -std::system_error if an exception is required (30.2.2 [thread.req.exception]). -std::system_error with an error condition of -operation_not_permitted if pm is 0. -std::system_error with an error condition of -resource_deadlock_would_occur if on entry owns is true. -std::system_error when the -postcondition cannot be achieved. -

-
-
- -

-Remove 30.4.2.2.2 [thread.lock.unique.locking] p19 (Error condition clause). -

- - - - - - -
-

1160. future_error public constructor is 'exposition only'

-

Section: 30.6.3 [futures.future_error] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 331

- -

Description

-

Not clear what - it means for a public constructor to be 'exposition only'. - If the intent is purely to support the library calling this - constructor then it can be made private and accessed - through friendship. Otherwise it should be documented for - public consumption.

-

Suggestion

-

Declare the constructor as private with a - note about intended friendship, or remove the - exposition-only comment and document the semantics.

-

Notes

-

Create an issue. Assigned to Detlef. Suggested resolution probably makes - sense.

- -

[ -2009-07 Frankfurt -]

- - -

-Pending a paper from Anthony Williams / Detlef Vollmann. -

- -

[ -2009-10-14 Pending paper: -N2967. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1161. Unnecessary unique_future limitations

-

Section: 30.6.6 [futures.unique_future] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 336

- -

Description

- -

It is possible - to transfer ownership of the asynchronous result from one - unique_future instance to another via the move-constructor. - However, it is not possible to transfer it back, and nor is - it possible to create a default-constructed unique_future - instance to use as a later move target. This unduly limits - the use of unique_future in code. Also, the lack of a - move-assignment operator restricts the use of unique_future - in containers such as std::vector - vector::insert requires - move-assignable for example.

-

Suggestion

-

Add a default constructor with the - semantics that it creates a unique_future with no - associated asynchronous result. Add a move-assignment - operator which transfers ownership.

-

Notes

-

Create an issue. Detlef will look into it.

- -

[ -2009-07 Frankfurt -]

- - -

-Pending a paper from Anthony Williams / Detlef Vollmann. -

- -

[ -2009-10-14 Pending paper: -N2967. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1162. shared_future should support an efficient move constructor

-

Section: 30.6.7 [futures.shared_future] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 337

- -

Description

-

shared_future - should support an efficient move constructor that can avoid - unnecessary manipulation of a reference count, much like - shared_ptr

-

Suggestion

-

Add a move constructor

-

Notes

-

Create an issue. Detlef will look into it.

- -

[ -2009-07 Frankfurt -]

- - -

-Pending a paper from Anthony Williams / Detlef Vollmann. -

- -

[ -2009-10-14 Pending paper: -N2967. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1163. shared_future is inconsistent with shared_ptr

-

Section: 30.6.7 [futures.shared_future] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 338

- -

Description

- -

shared_future is currently - CopyConstructible, but not CopyAssignable. This is - inconsistent with shared_ptr, and will surprise users. - Users will then write work-arounds to provide this - behaviour. We should provide it simply and efficiently as - part of shared_future. Note that since the shared_future - member functions for accessing the state are all declared - const, the original usage of an immutable shared_future - value that can be freely copied by multiple threads can be - retained by declaring such an instance as "const - shared_future".

-

Suggestion

-

Remove "=delete" - from the copy-assignment operator of shared_future. Add a - move-constructor shared_future(shared_future&& - rhs), and a move-assignment operator shared_future& - operator=(shared_future&& rhs). The postcondition - for the copy-assignment operator is that *this has the same - associated state as rhs. The postcondition for the - move-constructor and move assignment is that *this has the - same associated as rhs had before the - constructor/assignment call and that rhs has no associated - state.

-

Notes

-

Create an issue. Detlef will look into it.

- -

[ -2009-07 Frankfurt -]

- - -

-Pending a paper from Anthony Williams / Detlef Vollmann. -

- -

[ -2009-10-14 Pending paper: -N2967. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Adressed by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1165. Unneeded promise move constructor

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses UK 343

- -

Description

-

The move constructor of a std::promise - object does not need to allocate any memory, so the - move-construct-with-allocator overload of the constructor - is superfluous.

-

Suggestion

-

Remove the constructor with the signature template <class - Allocator> promise(allocator_arg_t, const Allocator& - a, promise& rhs);

-

Notes

-

Create an issue. Detlef will look into it. Will solicit feedback from Pablo. - Note that "rhs" argument should also be an rvalue reference in any case.

- -

[ -2009-07 Frankfurt -]

- - -

-Pending a paper from Anthony Williams / Detlef Vollmann. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Adressed by -N2997. -

- - - -

Proposed resolution:

- - - - - -
-

1166. Allocator-specific move/copy break model of move-constructor and - move-assignment

-

Section: X [allocator.propagation], X [allocator.propagation.map], 23 [containers] Status: Resolved - Submitter: LWG Opened: 2009-06-28 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 77

- -

Description

-

Allocator-specific move and copy behavior for containers - (N2525) complicates a little-used and already-complicated - portion of the standard library (allocators), and breaks - the conceptual model of move-constructor and - move-assignment operations on standard containers being - efficient operations. The extensions for allocator-specific - move and copy behavior should be removed from the working - paper.

-

With the introduction of rvalue references, we are teaching - programmers that moving from a standard container (e.g., a - vector<string>) is an efficient, constant-time - operation. The introduction of N2525 removed that - guarantee; depending on the behavior of four different - traits (20.8.4), the complexity of copy and move operations - can be constant or linear time. This level of customization - greatly increases the complexity of standard containers, - and benefits only a tiny fraction of the C++ community.

-

Suggestion

- -

Remove 20.8.4.

- -

Remove 20.8.5.

- -

Remove all references to the facilities in - 20.8.4 and 20.8.5 from clause 23.

-

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2982. -

- - - -

Proposed resolution:

- - - - - -
-

1170. String char-like types no longer PODs

-

Section: 21.1 [strings.general] Status: C++11 - Submitter: Beman Dawes Opened: 2009-06-22 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

- -

Addresses UK 218

- -

Prior to the introduction of constant expressions into the library, -basic_string elements had to be POD types, and thus had to be both trivially -copyable and standard-layout. This ensured that they could be memcpy'ed and -would be compatible with other libraries and languages, particularly the C -language and its library.

-

-N2349, -Constant Expressions in the Standard Library Revision 2, changed the -requirement in 21/1 from "POD type" to "literal type". That change had the -effect of removing the trivially copyable and standard-layout requirements from -basic_string elements.

-

This means that basic_string elements no longer are guaranteed to be -memcpy'able, and are no longer guaranteed to be standard-layout types:

-
-

3.9/p2 and 3.9/p3 both make it clear that a "trivially copyable type" is - required for memcpy to be guaranteed to work.

-

Literal types (3.9p12) may have a non-trivial copy assignment operator, and - that violates the trivially copyable requirements given in 9/p 6, bullet item - 2.

-

Literal types (3.9p12) have no standard-layout requirement, either.

-
-

This situation probably arose because the wording for "Constant Expressions -in the Standard Library" was in process at the same time the C++ POD -deconstruction wording was in process.

-

Since trivially copyable types meet the C++0x requirements for literal types, -and thus work with constant expressions, it seems an easy fix to revert the -basic_string element wording to its original state.

- -

[ - 2009-07-28 Alisdair adds: - ]

- - -

-When looking for any resolution for this issue, consider the definition of -"character container type" in 17.3 [defns.character.container]. This -does require the character type to be a POD, and this term is used in a -number of places through clause 21 and 28. This suggests the PODness -constraint remains, but is much more subtle than before. Meanwhile, I -suspect the change from POD type to literal type was intentional with -the assumption that trivially copyable types with -non-trivial-but-constexpr constructors should serve as well. I don't -believe the current wording offers the right guarantees for either of -the above designs. -

- -

[ -2009-11-04 Howard modifies proposed wording to disallow array types as -char-like types. -]

- - -

[ -2010-01-23 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -

Change General 21.1 [strings.general] as indicated:

-
-

This Clause describes components for manipulating sequences of any -literal non-array POD (3.9) type. In this Clause -such types are called char-like types, and objects of char-like -types are called char-like objects or simply -characters.

-
- - - - - - -
-

1171. duration types should be literal

-

Section: 20.12.5 [time.duration] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-07-06 Last modified: 2015-04-08

-

View all other issues in [time.duration].

-

View all issues with C++11 status.

-

Discussion:

-

-The duration types in 20.12.5 [time.duration] are exactly the sort of type -that should be "literal types" in the new standard. Likewise, -arithmetic operations on durations should be declared constexpr. -

- -

[ -2009-09-21 Daniel adds: -]

- - -

-An alternative (and possibly preferable solution for potentially -heap-allocating big_int representation types) would be to ask the core -language to allow references to const literal types as feasible -arguments for constexpr functions. -

- -

[ -2009-10-30 Alisdair adds: -]

- - -
-

-I suggest this issue moves from New to Open. -

- -

-Half of this issue was dealt with in paper -n2994 -on constexpr constructors. -

- -

-The other half (duration arithmetic) is on hold pending Core support for -const & in constexpr functions. -

- -
- -

[ -2010-03-15 Alisdair updated wording to be consistent with -N3078. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-This issue was the motivation for Core adding the facility for constexpr -functions to take parameters by const &. - -Move to Tentatively Ready. -

- -

[ -Adopted at 2010-11 Batavia. -]

- - - - -

Proposed resolution:

-

-Add constexpr to declaration of following functions and constructors: -

-

-Modify p1 20.12 [time], and the prototype definitions in 20.12.5.5 [time.duration.nonmember], 20.12.5.6 [time.duration.comparisons], -and 20.12.5.7 [time.duration.cast]: -

- -
-

-Header <chrono> synopsis -

- -
-// duration arithmetic
-template <class Rep1, class Period1, class Rep2, class Period2>
-   typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
-   constexpr operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
-   constexpr operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period, class Rep2>
-   duration<typename common_type<Rep1, Rep2>::type, Period>
-   constexpr operator*(const duration<Rep1, Period>& d, const Rep2& s);
-template <class Rep1, class Period, class Rep2>
-   duration<typename common_type<Rep1, Rep2>::type, Period>
-   constexpr operator*(const Rep1& s, const duration<Rep2, Period>& d);
-template <class Rep1, class Period, class Rep2>
-   duration<typename common_type<Rep1, Rep2>::type, Period>
-   constexpr operator/(const duration<Rep1, Period>& d, const Rep2& s);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   typename common_type<Rep1, Rep2>::type
-   constexpr operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-
-// duration comparisons
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator==(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator< (const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator<=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator> (const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-template <class Rep1, class Period1, class Rep2, class Period2>
-   constexpr bool operator>=(const  duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-
-// duration_cast
-template <class ToDuration, class Rep, class Period>
-   constexpr ToDuration duration_cast(const duration<Rep, Period>& d);
-
- -
- -

-Change 20.12.5 [time.duration]: -

- -
- -
-template <class Rep, class Period = ratio<1>>
-class duration {
-  ...
-public:
-  ...
-  constexpr duration(const duration&) = default;
-  ...
-
-};
-
-
-

[ -Note - this edit already seems assumed by definition of the duration static members -zero/min/max. They cannot meaningfully be constexpr without -this change. -]

- - - - - - -
-

1172. select_on_container_(copy|move)_construction over-constrained

-

Section: X [allocator.concepts.members] Status: Resolved - Submitter: Alberto Ganesh Barbati Opened: 2009-07-08 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-I believe the two functions -select_on_container_(copy|move)_construction() are over-constrained. For -example, the return value of the "copy" version is (see -X [allocator.concepts.members]/21): -

-

-Returns: x if the allocator should propagate from the existing -container to the new container on copy construction, otherwise X(). -

-

-Consider the case where a user decides to provide an explicit concept -map for Allocator to adapt some legacy allocator class, as he wishes to -provide customizations that the LegacyAllocator concept map template -does not provide. Now, although it's true that the legacy class is -required to have a default constructor, the user might have reasons to -prefer a different constructor to implement -select_on_container_copy_construction(). However, the current wording -requires the use of the default constructor. -

-

-Moreover, it's not said explicitly that x is supposed to be the -allocator of the existing container. A clarification would do no harm. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Addressed by -N2982. -

- - - -

Proposed resolution:

-

-Replace X [allocator.concepts.members]/21 with: -

- -
-X select_on_container_copy_construction(const X& x);
-
-

--21- Returns: x if the allocator should propagate from the existing -container to the new container on copy construction, otherwise X(). -an allocator object to be used by the new container on copy -construction. [Note: x is the allocator of the existing container that -is being copied. The most obvious choices for the return value are x, if -the allocator should propagate from the existing container, and X(). -— end note] -

-
- -

-Replace X [allocator.concepts.members]/25 with: -

- -
-X select_on_container_move_construction(X&& x);
-
-

--25- Returns: move(x) if the allocator should propagate from the existing -container to the new container on move construction, otherwise X(). -an allocator object to be used by the new container on move -construction. [Note: x is the allocator of the existing container that -is being moved. The most obvious choices for the return value are move(x), if -the allocator should propagate from the existing container, and X(). -— end note] -

-
- - - - - - -
-

1174. Type property predicates

-

Section: 20.10.4.3 [meta.unary.prop] Status: Resolved - Submitter: Jason Merrill Opened: 2009-07-16 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with Resolved status.

-

Discussion:

-

-I've been implementing compiler support for is_standard_layout, and -noticed a few nits about 20.10.4.3 [meta.unary.prop]: -

- -
    -
  1. -There's no trait for "trivially copyable type", which is now the -property that lets you do bitwise copying of a type, and therefore seems -useful to be able to query. has_trivial_assign && -has_trivial_copy_constructor && has_trivial_destructor -is similar, but -not identical, specifically with respect to const types. -
    2. -
  2. -has_trivial_copy_constructor and has_trivial_assign lack the "or an -array of such a class type" language that most other traits in that -section, including has_nothrow_copy_constructor and has_nothrow_assign, -have; this seems like an oversight. -
    3. -
- -

[ -See the thread starting with c++std-lib-24420 for further discussion. -]

- - -

[ -Addressed in N2947. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-NAD EditorialResolved. Solved by -N2984. -

- - - -

Proposed resolution:

-

-

- - - - - -
-

1177. Improve "diagnostic required" wording

-

Section: 20.12.5 [time.duration] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-07-18 Last modified: 2015-04-08

-

View all other issues in [time.duration].

-

View all issues with C++11 status.

-

Discussion:

-

-"diagnostic required" has been used (by me) for code words meaning "use -enable_if to constrain templated functions. This needs to be -improved by referring to the function signature as not participating in -the overload set, and moving this wording to a Remarks paragraph. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- -

[ -2009-11-19 Pete opens: -]

- - -
-

-Oh, and speaking of 1177, most of the changes result in rather convoluted prose. -Instead of saying -

- -

-A shall be B, else C -

- -

-it should be -

- -

-C if A is not B -

- -

-That is: -

- -

-Rep2 shall be implicitly convertible to CR(Rep1, Rep2), else -this signature shall not participate in overload resolution. -

- -

-should be -

- -

-This signature shall not participate in overload resolution if Rep2 is -not implicitly convertible to CR(Rep1, Rep2). -

- -

-That is clearer, and eliminates the false requirement that Rep2 "shall -be" convertible. -

- -
- -

[ -2009-11-19 Howard adds: -]

- - -

-I've updated the wording to match Pete's suggestion and included bullet 16 -from 1195. -

- -

[ -2009-11-19 Jens adds: -]

- - -
-

-Further wording suggestion using "unless": -

- -

-This signature shall not participate in overload resolution unless Rep2 -is implicitly convertible to CR(Rep1, Rep2). -

-
- -

[ -2009-11-20 Howard adds: -]

- - -

-I've updated the wording to match Jens' suggestion. -

- -

[ -2009-11-22 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

[ -This proposed resolution addresses 947 and 974. -]

- - -
    -
  1. -

    -Change 20.12.5.1 [time.duration.cons] (and reorder the Remarks -paragraphs per 17.5.1.4 [structure.specifications]): -

    - -
    -
    -template <class Rep2> 
-  explicit duration(const Rep2& r);
-
    -
    -

    -Requires: Remarks: This constructor shall not -participate in overload resolution unless Rep2 shall be -is implicitly convertible to rep and -

    -
      -
    • -treat_as_floating_point<rep>::value shall be -is true, or -
      • -
    • -treat_as_floating_point<Rep2>::value shall be -is false. -
      • -
    -

    -Diagnostic required [Example: -

    -
    -duration<int, milli> d(3); // OK 
-duration<int, milli> d(3.5); // error 
-
    - -

    -— end example] -

    - -

    -Effects: Constructs an object of type duration. -

    - -

    -Postcondition: count() == static_cast<rep>(r). -

    - -
    - -
    -template <class Rep2, class Period2>
-  duration(const duration<Rep2, Period2>& d);
-
    -
    -

    -Requires: Remarks: This constructor shall not -participate in overload resolution unless -treat_as_floating_point<rep>::value shall be -is true or ratio_divide<Period2, -period>::type::den shall be is 1. Diagnostic -required. [Note: This requirement prevents implicit truncation -error when converting between integral-based duration types. Such a construction -could easily lead to confusion about the value of the duration. — end -note] [Example: -

    - -
    -duration<int, milli> ms(3); 
-duration<int, micro> us = ms; // OK 
-duration<int, milli> ms2 = us; // error 
-
    - -

    -— end example] -

    - -

    -Effects: Constructs an object of type duration, constructing -rep_ from -duration_cast<duration>(d).count(). -

    - -
    - - -
    -
    2. - -
  2. -

    -Change the following paragraphs in 20.12.5.5 [time.duration.nonmember]: -

    - -
    -
    -template <class Rep1, class Period, class Rep2> 
-  duration<typename common_type<Rep1, Rep2>::type, Period> 
-  operator*(const duration<Rep1, Period>& d, const Rep2& s);
-
    -

    -Requires Remarks: This operator shall not -participate in overload resolution unless Rep2 shall -be is implicitly convertible to CR(Rep1, Rep2). -Diagnostic required. -

    - -
    -template <class Rep1, class Period, class Rep2> 
-  duration<typename common_type<Rep1, Rep2>::type, Period> 
-  operator*(const Rep1& s, const duration<Rep2, Period>& d);
-
    -

    -Requires Remarks: This operator shall not -participate in overload resolution unless Rep1 shall -be is implicitly convertible to CR(Rep1, Rep2). -Diagnostic required. -

    - -
    -template <class Rep1, class Period, class Rep2> 
-  duration<typename common_type<Rep1, Rep2>::type, Period> 
-  operator/(const duration<Rep1, Period>& d, const Rep2& s);
-
    -

    -Requires Remarks: This operator shall not -participate in overload resolution unless Rep2 shall -be is implicitly convertible to CR(Rep1, Rep2) and -Rep2 shall not be is not an instantiation of -duration. Diagnostic required. -

    - -
    -template <class Rep1, class Period, class Rep2> 
-  duration<typename common_type<Rep1, Rep2>::type, Period> 
-  operator%(const duration<Rep1, Period>& d, const Rep2& s);
-
    -

    -Requires Remarks: This operator shall not -participate in overload resolution unless Rep2 shall -be is implicitly convertible to CR(Rep1, Rep2) and -Rep2 shall not be is not an instantiation of -duration. Diagnostic required. -

    - -
    -
    3. - -
  3. -

    -Change the following paragraphs in 20.12.5.7 [time.duration.cast]: -

    - -
    -template <class ToDuration, class Rep, class Period> 
-  ToDuration duration_cast(const duration<Rep, Period>& d);
-
    - -

    -Requires Remarks: This function shall not -participate in overload resolution unless ToDuration shall -be is an instantiation of duration. Diagnostic -required. -

    -
    -
    4. - -
  4. -

    -Change 20.12.6.1 [time.point.cons]/3 as indicated: -

    - -
    -

    -Requires: Duration2 shall be implicitly convertible to duration. -Diagnostic required. -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless Duration2 is implicitly convertible to -duration. -

    -
    - -
    5. - -
  5. -

    -Change the following paragraphs in 20.12.6.7 [time.point.cast]: -

    - -
    -template <class ToDuration, class Clock, class Duration> 
-  time_point<Clock, ToDuration> time_point_cast(const time_point<Clock, Duration>& t);
-
    - -

    -Requires Remarks: This function shall not -participate in overload resolution unless ToDuration shall -be is an instantiation of duration. Diagnostic -required. -

    -
    -
    6. -
- - - - - - -
-

1178. Header dependencies

-

Section: 17.6.5.2 [res.on.headers] Status: C++11 - Submitter: Beman Dawes Opened: 2009-07-18 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-See Frankfurt notes of 1001. -

- - -

Proposed resolution:

-

Change 17.6.5.2 [res.on.headers], Headers, paragraph 1, as indicated:

- -
- -

-A C++ header may include other C++ -headers.[footnote] A C++ header shall provide -the declarations and definitions that appear in its synopsis -(3.2 [basic.def.odr]). A C++ header shown in its synopsis as including -other C++ headers shall provide the declarations and definitions that appear in -the synopses of those other headers. -

- -

[footnote] C++ headers must include a C++ header that contains - any needed definition (3.2).

-
- - - - - - -
-

1180. Missing string_type member typedef in class sub_match

-

Section: 28.9.1 [re.submatch.members] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-07-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-The definition of class template sub_match is strongly dependent -on the type basic_string<value_type>, both in interface and effects, -but does not provide a corresponding typedef string_type, as e.g. -class match_results does, which looks like an oversight to me that -should be fixed. -

- -

[ -2009-11-15 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

- -
    -
  1. -

    -In the class template sub_match synopsis 28.9 [re.submatch]/1 -change as indicated: -

    - -
    -template <class BidirectionalIterator>
-class sub_match : public std::pair<BidirectionalIterator, BidirectionalIterator> {
-public:
-  typedef typename iterator_traits<BidirectionalIterator>::value_type value_type;
-  typedef typename iterator_traits<BidirectionalIterator>::difference_type difference_type;
-  typedef BidirectionalIterator iterator;
-  typedef basic_string<value_type> string_type;
-
-  bool matched;
-
-  difference_type length() const;
-  operator basic_string<value_type>string_type() const;
-  basic_string<value_type>string_type str() const;
-  int compare(const sub_match& s) const;
-  int compare(const basic_string<value_type>string_type& s) const;
-  int compare(const value_type* s) const;
-};
-
    -
    2. - -
  2. -

    -In 28.9.1 [re.submatch.members]/2 change as indicated: -

    - -
    -operator basic_string<value_type>string_type() const;
-
    - -

    -Returns: matched ? basic_string<value_type> -string_type(first, second) : basic_string<value_type> -string_type(). -

    -
    -
    3. - -
  3. -

    -In 28.9.1 [re.submatch.members]/3 change as indicated: -

    - -
    -basic_string<value_type>string_type str() const;
-
    - -

    -Returns: matched ? basic_string<value_type> -string_type(first, second) : basic_string<value_type> -string_type(). -

    -
    -
    4. - -
  4. -

    -In 28.9.1 [re.submatch.members]/5 change as indicated: -

    - -
    -int compare(const basic_string<value_type>string_type& s) const;
-
    -
    5. -
- - - - - - -
-

1181. Invalid sub_match comparison operators

-

Section: 28.9.2 [re.submatch.op] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-07-25 Last modified: 2015-04-08

-

View all other issues in [re.submatch.op].

-

View all issues with C++11 status.

-

Discussion:

-

-Several heterogeneous comparison operators of class template -sub_match are specified by return clauses that are not valid -in general. E.g. 28.9.2 [re.submatch.op]/7: -

- -
-template <class BiIter, class ST, class SA>
-bool operator==(
-  const basic_string<
-    typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-  const sub_match<BiIter>& rhs);
-
-

-Returns: lhs == rhs.str(). -

-
- -

-The returns clause would be ill-formed for all cases where -ST != std::char_traits<iterator_traits<BiIter>::value_type> -or SA != std::allocator<iterator_traits<BiIter>::value_type>. -

-

-The generic character of the comparison was intended, so -there are basically two approaches to fix the problem: The -first one would define the semantics of the comparison -using the traits class ST (The semantic of basic_string::compare -is defined in terms of the compare function of the corresponding -traits class), the second one would define the semantics of the -comparison using the traits class -

- -
-std::char_traits<iterator_traits<BiIter>::value_type>
-
- -

-which is essentially identical to -

- -
-std::char_traits<sub_match<BiIter>::value_type>
-
- -

-I suggest to follow the second approach, because -this emphasizes the central role of the sub_match -object as part of the comparison and would also -make sure that a sub_match comparison using some -basic_string<char_t, ..> always is equivalent to -a corresponding comparison with a string literal -because of the existence of further overloads (beginning -from 28.9.2 [re.submatch.op]/19). If users really want to -take advantage of their own traits::compare, they can -simply write a corresponding compare function that -does so. -

- -

[ -Post-Rapperswil -]

- - -

-The following update is a result of the discussion during the Rapperswil meeting, the P/R expresses all comparisons by -delegating to sub_match's compare functions. The processing is rather mechanical: Only == and < -where defined by referring to sub_match's compare function, all remaining ones where replaced by the canonical -definitions in terms of these two. -

- -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-The wording refers to N3126. -

- -
    -
  1. Change 28.9.2 [re.submatch.op]/7 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator==(
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-   const sub_match<BiIter>& rhs);
-

    -7 Returns: lhs == rhs.str()rhs.compare(lhs.c_str()) == 0. -

    -
    2. -
  2. Change 28.9.2 [re.submatch.op]/8 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator!=(
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-   const sub_match<BiIter>& rhs);
-

    -8 Returns: lhs != rhs.str()!(lhs == rhs). -

    -
    3. -
  3. Change 28.9.2 [re.submatch.op]/9 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator<(
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-   const sub_match<BiIter>& rhs);
-

    -9 Returns: lhs < rhs.str()rhs.compare(lhs.c_str()) > 0. -

    -
    4. -
  4. Change 28.9.2 [re.submatch.op]/10 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator>(
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-   const sub_match<BiIter>& rhs);
-

    -10 Returns: lhs > rhs.str()rhs < lhs. -

    -
    5. -
  5. Change 28.9.2 [re.submatch.op]/11 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator>=(
-   const basic_string<
-   typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
- const sub_match<BiIter>& rhs);
-

    -11 Returns: lhs >= rhs.str()!(lhs < rhs). -

    -
    6. -
  6. Change 28.9.2 [re.submatch.op]/12 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator<=(
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-   const sub_match<BiIter>& rhs);
-

    -12 Returns: lhs <= rhs.str()!(rhs < lhs). -

    -
    7. -
  7. Change 28.9.2 [re.submatch.op]/13 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator==(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -13 Returns: lhs.str() == rhslhs.compare(rhs.c_str()) == 0. -

    -
    8. -
  8. Change 28.9.2 [re.submatch.op]/14 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator!=(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -14 Returns: lhs.str() != rhs!(lhs == rhs). -

    -
    9. -
  9. Change 28.9.2 [re.submatch.op]/15 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator<(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -15 Returns: lhs.str() < rhslhs.compare(rhs.c_str()) < 0. -

    -
    10. -
  10. Change 28.9.2 [re.submatch.op]/16 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator>(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -16 Returns: lhs.str() > rhsrhs < lhs. -

    -
    11. -
  11. Change 28.9.2 [re.submatch.op]/17 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator>=(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -17 Returns: lhs.str() >= rhs!(lhs < rhs). -

    -
    12. -
  12. Change 28.9.2 [re.submatch.op]/18 as indicated: -
    -template <class BiIter, class ST, class SA>
- bool operator<=(const sub_match<BiIter>& lhs,
-   const basic_string<
-     typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-

    -18 Returns: lhs.str() <= rhs!(rhs < lhs). -

    -
    13. -
  13. Change 28.9.2 [re.submatch.op]/19 as indicated: -
    -template <class BiIter>
- bool operator==(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -19 Returns: lhs == rhs.str()rhs.compare(lhs) == 0. -

    -
    14. -
  14. Change 28.9.2 [re.submatch.op]/20 as indicated: -
    -template <class BiIter>
- bool operator!=(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -20 Returns: lhs != rhs.str()!(lhs == rhs). -

    -
    15. -
  15. Change 28.9.2 [re.submatch.op]/21 as indicated: -
    -template <class BiIter>
- bool operator<(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -21 Returns: lhs < rhs.str()rhs.compare(lhs) > 0. -

    -
    16. -
  16. Change 28.9.2 [re.submatch.op]/22 as indicated: -
    -template <class BiIter>
- bool operator>(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -22 Returns: lhs > rhs.str()rhs < lhs. -

    -
    17. -
  17. Change 28.9.2 [re.submatch.op]/23 as indicated: -
    -template <class BiIter>
- bool operator>=(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -23 Returns: lhs >= rhs.str()!(lhs < rhs). -

    -
    18. -
  18. Change 28.9.2 [re.submatch.op]/24 as indicated: -
    -template <class BiIter>
- bool operator<=(typename iterator_traits<BiIter>::value_type const* lhs,
-   const sub_match<BiIter>& rhs);
-

    -24 Returns: lhs <= rhs.str()!(rhs < lhs). -

    -
    19. -
  19. Change 28.9.2 [re.submatch.op]/25 as indicated: -
    -template <class BiIter>
- bool operator==(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -25 Returns: lhs.str() == rhslhs.compare(rhs) == 0. -

    -
    20. -
  20. Change 28.9.2 [re.submatch.op]/26 as indicated: -
    -template <class BiIter>
- bool operator!=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -26 Returns: lhs.str() != rhs!(lhs == rhs). -

    -
    21. -
  21. Change 28.9.2 [re.submatch.op]/27 as indicated: -
    -template <class BiIter>
- bool operator<(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -27 Returns: lhs.str() < rhslhs.compare(rhs) < 0. -

    -
    22. -
  22. Change 28.9.2 [re.submatch.op]/28 as indicated: -
    -template <class BiIter>
- bool operator>(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -28 Returns: lhs.str() > rhsrhs < lhs. -

    -
    23. -
  23. Change 28.9.2 [re.submatch.op]/29 as indicated: -
    -template <class BiIter>
- bool operator>=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -29 Returns: lhs.str() >= rhs!(lhs < rhs). -

    -
    24. -
  24. Change 28.9.2 [re.submatch.op]/30 as indicated: -
    -template <class BiIter>
- bool operator<=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const* rhs);
-

    -30 Returns: lhs.str() <= rhs!(rhs < lhs). -

    -
    25. -
  25. Change 28.9.2 [re.submatch.op]/31 as indicated: -
    -template <class BiIter>
- bool operator==(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -31 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) == rhs.str().
    -31 Returns: rhs.compare(typename sub_match<BiIter>::string_type(1, lhs)) == 0. -

    -
    26. -
  26. Change 28.9.2 [re.submatch.op]/32 as indicated: -
    -template <class BiIter>
- bool operator!=(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -32 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) != -rhs.str()!(lhs == rhs). -

    -
    27. -
  27. Change 28.9.2 [re.submatch.op]/33 as indicated: -
    -template <class BiIter>
- bool operator<(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -33 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) < rhs.str().
    -33 Returns: rhs.compare(typename sub_match<BiIter>::string_type(1, lhs)) > 0. -

    -
    28. -
  28. Change 28.9.2 [re.submatch.op]/34 as indicated: -
    -template <class BiIter>
- bool operator>(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -34 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) > rhs.str()rhs < lhs. -

    -
    29. -
  29. Change 28.9.2 [re.submatch.op]/35 as indicated: -
    -template <class BiIter>
- bool operator>=(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -35 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) >= rhs.str()!(lhs < rhs). -

    -
    30. -
  30. Change 28.9.2 [re.submatch.op]/36 as indicated: -
    -template <class BiIter>
- bool operator<=(typename iterator_traits<BiIter>::value_type const& lhs,
-   const sub_match<BiIter>& rhs);
-

    -36 Returns: basic_string<typename iterator_traits<BiIter>::value_type>(1, lhs) <= rhs.str()!(rhs < lhs). -

    -
    31. -
  31. Change 28.9.2 [re.submatch.op]/37 as indicated: -
    -template <class BiIter>
- bool operator==(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -37 Returns: lhs.str() == basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs).
    -37 Returns: lhs.compare(typename sub_match<BiIter>::string_type(1, rhs)) == 0. -

    -
    32. -
  32. Change 28.9.2 [re.submatch.op]/38 as indicated: -
    -template <class BiIter>
- bool operator!=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -38 Returns: lhs.str() != basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs)!(lhs == rhs). -

    -
    33. -
  33. Change 28.9.2 [re.submatch.op]/39 as indicated: -
    -template <class BiIter>
- bool operator<(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -39 Returns: lhs.str() < basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs).
    -39 Returns: lhs.compare(typename sub_match<BiIter>::string_type(1, rhs)) < 0. -

    -
    34. -
  34. Change 28.9.2 [re.submatch.op]/40 as indicated: -
    -template <class BiIter>
- bool operator>(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -40 Returns: lhs.str() > basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs)rhs < lhs. -

    -
    35. -
  35. Change 28.9.2 [re.submatch.op]/41 as indicated: -
    -template <class BiIter>
- bool operator>=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -41 Returns: lhs.str() >= basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs)!(lhs < rhs). -

    -
    36. -
  36. Change 28.9.2 [re.submatch.op]/42 as indicated: -
    -template <class BiIter>
- bool operator<=(const sub_match<BiIter>& lhs,
-   typename iterator_traits<BiIter>::value_type const& rhs);
-

    -42 Returns: lhs.str() <= basic_string<typename iterator_traits<BiIter>::value_type>(1, rhs)!(rhs < lhs). -

    -
    37. -
- - - - - - -
-

1182. Unfortunate hash dependencies

-

Section: 20.9.13 [unord.hash] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-07-28 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK 324

- -

-The implied library dependencies created by spelling out all the hash -template specializations in the <functional> synopsis are unfortunate. -The potential coupling is greatly reduced if the hash specialization is -declared in the appropriate header for each library type, as it is much -simpler to forward declare the primary template and provide a single -specialization than it is to implement a hash function for a string or -vector without providing a definition for the whole string/vector -template in order to access the necessary bits. -

- -

-Note that the proposed resolution purely involves moving the -declarations of a few specializations, it specifically does not make any -changes to 20.9.13 [unord.hash]. -

- -

[ -2009-09-15 Daniel adds: -]

- - -

-I suggest to add to the current existing -proposed resolution the following items. -

- -
    -
  • -

    -Add to the very first strike-list of the currently suggested resolution -the following lines: -

    - -
    -template <> struct hash<std::error_code>;
-template <> struct hash<std::thread::id>;
-
    -
    • - -
  • -

    -Add the following declarations to 19.5 [syserr], header -<system_error> synopsis after // 19.5.4: -

    - -
    -
-// 19.5.x hash support
-template <class T> struct hash;
-template <> struct hash<error_code>;
-
-
    -
    • - -
  • -

    -Add a new clause 19.5.X (probably after 19.5.4): -

    - -
    -

    -19.5.X Hash support [syserr.hash] -

    - -
    
-template <> struct hash<error_code>;
-
    - -

    -An explicit specialization of the class template hash (20.9.13 [unord.hash]) -shall be provided -for the type error_code suitable for using this type as key in -unordered associative -containers (23.5 [unord]). -

    -
    -
    • - -
  • -

    -Add the following declarations to 30.3.1.1 [thread.thread.id] just after the -declaration of -the comparison operators: -

    - -
    -
-template <class T> struct hash;
-template <> struct hash<thread::id>;
-
    -
    • - -
  • -

    -Add a new paragraph at the end of 30.3.1.1 [thread.thread.id]: -

    - -
    -
    
-template <> struct hash<thread::id>;
-
    - -

    -An explicit specialization of the class template hash (20.9.13 [unord.hash]) -shall be provided -for the type thread::id suitable for using this type as key in -unordered associative -containers (23.5 [unord]). -

    -
    -
    • - -
  • -Issue 889 independently suggests moving the specialization -std::hash<std::thread::id> to header <thread>. -
    • -
- -

[ -2009-11-13 Alisdair adopts Daniel's suggestion and the extended note from -889. -]

- - -

[ -2010-01-31 Alisdair: related to 1245 and 978. -]

- - -

[ -2010-02-07 Proposed wording updated by Beman, Daniel, Alisdair and Ganesh. -]

- - -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

Strike the following specializations declared in the <functional> -synopsis p2 20.9 [function.objects]

-
-template <> struct hash<std::string>;
-template <> struct hash<std::u16string>;
-template <> struct hash<std::u32string>;
-template <> struct hash<std::wstring>;
-
-template <> struct hash<std::error_code>;
-template <> struct hash<std::thread::id>;
-template <class Allocator> struct hash<std::vector<bool, Allocator> >;
-template <std::size_t N> struct hash<std::bitset<N> >;
-
-

Add the following at the end of 20.9.13 [unord.hash]:

-
-template <> struct hash<bool>;
-template <> struct hash<char>;
-template <> struct hash<signed char>;
-template <> struct hash<unsigned char>;
-template <> struct hash<char16_t>;
-template <> struct hash<char32_t>;
-template <> struct hash<wchar_t>;
-template <> struct hash<short>;
-template <> struct hash<unsigned short>;
-template <> struct hash<int>;
-template <> struct hash<unsigned int>;
-template <> struct hash<long>;
-template <> struct hash<long long>;
-template <> struct hash<unsigned long>;
-template <> struct hash<unsigned long long>;
-template <> struct hash<float>;
-template <> struct hash<double>;
-template <> struct hash<long double>;
-template<class T> struct hash<T*>;
-

- Specializations meeting the requirements of class template hash 20.9.13 [unord.hash].

-
-

Add the following declarations to 19.5 [syserr], header <system_error> -synopsis after // 19.5.4:

-
- 
// [syserr.hash] hash support
-template <class T> struct hash;
-template <> struct hash<error_code>;
-
-

Add a new clause 19.5.X (probably after 19.5.4):

-
-

19.5.X Hash support [syserr.hash]

- 
template <> struct hash<error_code>;
-

Specialization meeting the requirements of class template hash 20.9.13 [unord.hash].

-
-

Add the following declarations to the synopsis of <string> in 21.3 [string.classes] - -

-
-// [basic.string.hash] hash support
-template <class T> struct hash;
-template <> struct hash<string>;
-template <> struct hash<u16string>;
-template <> struct hash<u32string>;
-template <> struct hash<wstring>;
-
-

Add a new clause 21.4.X

-
-

21.4.X Hash support [basic.string.hash]>

- 
template <> struct hash<string>;
-template <> struct hash<u16string>;
-template <> struct hash<u32string>;
-template <> struct hash<wstring>;
-

Specializations meeting the requirements of class template hash 20.9.13 [unord.hash].

-
-

Add the following declarations to the synopsis of <vector> in -23.3 [sequences]

-
-// 21.4.x hash support
-template <class T> struct hash;
-template <class Allocator> struct hash<vector<bool, Allocator>>;
-
-

Add a new paragraph to the end of 23.3.7 [vector.bool]

-
- 
template <class Allocator> struct hash<vector<bool, Allocator>>;
-

Specialization meeting the requirements of class template hash 20.9.13 [unord.hash].

-
-

Add the following declarations to the synopsis of <bitset> in 20.6 [template.bitset]

-
- 
// [bitset.hash] hash support
-template <class T> struct hash;
-template <size_t N> struct hash<bitset<N> >;
-
-

Add a new subclause 20.3.7.X [bitset.hash]

-
-

20.3.7.X bitset hash support [bitset.hash]

- 
template <size_t N> struct hash<bitset<N> >;
-

Specialization meeting the requirements of class template hash 20.9.13 [unord.hash].

-
-

Add the following declarations to 30.3.1.1 [thread.thread.id] synopsis just after the -declaration of the comparison operators:

-
- 
template <class T> struct hash;
-template <> struct hash<thread::id>;
-
-

Add a new paragraph at the end of 30.3.1.1 [thread.thread.id]:

-
- 
template <> struct hash<thread::id>;
-

Specialization meeting the requirements of class template hash 20.9.13 [unord.hash].

-
- -

Change Header <typeindex> synopsis 20.14.1 [type.index.synopsis] as -indicated:

-
-
namespace std {
-class type_index;
-  // [type.index.hash] hash support
-  template <class T> struct hash;
-  template<> struct hash<type_index>;  : public unary_function<type_index, size_t> {
-    size_t operator()(type_index index) const;
-  }
-}
-
- -

Change Template specialization hash<type_index> [type.index.templ] - as indicated:

- -
- -

20.11.4 Template specialization hash<type_index> [type.index.templ] - Hash support [type.index.hash]

- - 
size_t operator()(type_index index) const;
-
-

Returns: index.hash_code()

-
- - 
template<> struct hash<type_index>;
-

Specialization meeting the requirements of class template hash [unord.hash]. - For an object index of type type_index, hash<type_index>()(index) - shall evaluate to the same value as index.hash_code().

- -
- - - - - - -
-

1183. basic_ios::set_rdbuf may break class invariants

-

Section: 27.5.5.3 [basic.ios.members] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-07-28 Last modified: 2015-04-08

-

View all other issues in [basic.ios.members].

-

View all issues with C++11 status.

-

Discussion:

-

-The protected member function set_rdbuf had been added during the -process of adding move and swap semantics to IO classes. A relevant -property of this function is described by it's effects in -27.5.5.3 [basic.ios.members]/19: -

- -

-Effects: Associates the basic_streambuf object pointed to by sb with -this stream without calling clear(). -

- -

-This means that implementors of or those who derive from existing IO classes -could cause an internal state where the stream buffer could be 0, but the -IO class has the state good(). This would break several currently existing -implementations which rely on the fact that setting a stream buffer via the -currently only ways, i.e. either by calling -

- -
-void init(basic_streambuf<charT,traits>* sb);
-
- -

-or by calling -

- -
-basic_streambuf<charT,traits>* rdbuf(basic_streambuf<charT,traits>* sb);
-
- -

-to set rdstate() to badbit, if the buffer is 0. This has the effect that many -internal functions can simply check rdstate() instead of rdbuf() for being 0. -

- -

-I therefore suggest that a requirement is added for callers of set_rdbuf to -set a non-0 value. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Open. Martin volunteers to provide new wording, where -set_rdbuf() sets the badbit but does not cause an -exception to be thrown like a call to clear() would. -

- -

[ -2009-10-20 Martin provides wording: -]

- - -

-Change 27.5.5.3 [basic.ios.members] around p. 19 as indicated: -

- -
-void set_rdbuf(basic_streambuf<charT, traits>* sb);
-
- -
-

-Effects: Associates the basic_streambuf object pointed -to by sb with this stream without calling clear(). -Postconditions: rdbuf() == sb. -

- -

-Effects: As if: -

- -

-iostate state = rdstate();
-try { rdbuf(sb); }
-catch(ios_base::failure) {
-   if (0 == (state & ios_base::badbit))
-       unsetf(badbit);
-}
-
- -

-Throws: Nothing. -

- -
-
- -

Rationale:

-We need to be able to call set_rdbuf() on stream objects -for which (rdbuf() == 0) holds without causing ios_base::failure to -be thrown. We also don't want badbit to be set as a result of -setting rdbuf() to 0 if it wasn't set before the call. This changed -Effects clause maintains the current behavior (as of N2914) without -requiring that sb be non-null. -

- -

[ -Post-Rapperswil -]

- - -

-Several reviewers and the submitter believe that the best solution would be to add a pre-condition that the -buffer shall not be a null pointer value. -

- -

-Moved to Tentatively Ready with revised wording provided by Daniel after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-
    -
  1. Add a new pre-condition just before 27.5.4.2 [basic.ios.members]/23 as indicated: -
    -void set_rdbuf(basic_streambuf<charT, traits>* sb);
-
    -

    -?? Requires: sb != nullptr. -

    -23 Effects: Associates the basic_streambuf object pointed to by sb with this stream without calling clear(). -

    -

    -24 Postconditions: rdbuf() == sb. -

    -

    -25 Throws: Nothing. -

    -
    -
    2. -
- - -

Rationale:

-We believe that setting a nullptr stream buffer can be prevented. -

- - - - -
-

1185. Iterator categories and output iterators

-

Section: 24.2 [iterator.requirements] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-07-31 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

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-

Discussion:

-

-(wording relative to -N2723 -pending new working paper) -

- -

-According to p3 24.2 [iterator.requirements], Forward iterators, -Bidirectional iterators and Random Access iterators all satisfy the -requirements for an Output iterator: -

- -

-XXX iterators satisfy all the requirements of the input and output iterators -and can be used whenever either kind is specified ... -

- -

-Meanwhile, p4 goes on to contradict this: -

- -

-Besides its category, a forward, bidirectional, or random access -iterator can also be mutable or constant... -

- -

-... Constant iterators do not satisfy the requirements for output iterators -

- -

-The latter seems to be the overriding concern, as the iterator tag -hierarchy does not define forward_iterator_tag as multiply derived from -both input_iterator_tag and output_iterator_tag. -

- -

-The work on concepts for iterators showed us that output iterator really -is fundamentally a second dimension to the iterator categories, rather -than part of the linear input -> forward -> bidirectional -> -random-access sequence. It would be good to clear up these words to -reflect that, and separately list output iterator requirements in the -requires clauses for the appropriate algorithms and operations. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

- - - - - -
-

1187. std::decay

-

Section: 20.10.7.6 [meta.trans.other] Status: C++11 - Submitter: Jason Merrill Opened: 2009-08-07 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

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-

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-

Discussion:

-

-I notice that std::decay is specified to strip the cv-quals from -anything but an array or pointer. This seems incorrect for values of -class type, since class rvalues can have cv-qualified type (3.10 [basic.lval]/9). -

- -

[ -2009-08-09 Howard adds: -]

- - -

-See the thread starting with c++std-lib-24568 for further discussion. And -here is a convenience link to the -original proposal. -Also see the closely related issue 705. -

- -

[ -2010 Pittsburgh: Moved to Ready. -]

- - - - -

Proposed resolution:

- -

-Add a note to decay in 20.10.7.6 [meta.trans.other]: -

- -

-[Note: This behavior is similar to the lvalue-to-rvalue (4.1), -array-to-pointer (4.2), and function-to-pointer (4.3) conversions -applied when an lvalue expression is used as an rvalue, but also strips -cv-qualifiers from class types in order to more closely model by-value -argument passing. — end note] -

- - - - - - - - -
-

1189. Awkward interface for changing the number of buckets in an unordered associative container

-

Section: 23.2.5 [unord.req], 23.5 [unord] Status: C++11 - Submitter: Matt Austern Opened: 2009-08-10 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

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-

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-

Discussion:

-

-Consider a typical use case: I create an unordered_map and then start -adding elements to it one at a time. I know that it will eventually need -to store a few million elements, so, for performance reasons, I would -like to reserve enough capacity that none of the calls to insert will -trigger a rehash. -

- -

-Unfortunately, the existing interface makes this awkward. The user -naturally sees the problem in terms of the number of elements, but the -interface presents it as buckets. If m is the map and n is the expected -number of elements, this operation is written m.rehash(n / -m.max_load_factor()) — not very novice friendly. -

- -

[ -2009-09-30 Daniel adds: -]

- - -

-I recommend to replace "resize" by a different name like -"reserve", because that would better match the intended -use-case. Rational: Any existing resize function has the on-success -post-condition that the provided size is equal to size(), which -is not satisfied for the proposal. Reserve seems to fit the purpose of -the actual renaming suggestion. -

- -

[ -2009-10-28 Ganesh summarizes alternative resolutions and expresses a -strong preference for the second (and opposition to the first): -]

- - -
-
    -
  1. -

    -In the unordered associative container requirements (23.2.5 [unord.req]), -remove the row for -rehash and replace it with: -

    - -
    - - - - - - - - - - - - - -
    Table 87 — Unordered associative container requirements -(in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    a.rehashreserve(n)void -Post: a.bucket_count > max(a.size(), n) -/ a.max_load_factor() and a.bucket_count() ->= n. - -Average case linear in a.size(), worst case quadratic. -
    -
    - -

    -Make the corresponding change in the class synopses in 23.5.4 [unord.map], 23.5.5 [unord.multimap], 23.5.6 [unord.set], and 23.5.7 [unord.multiset]. -

    -
    2. -
  2. - -

    -In 23.2.5 [unord.req]/9, table 98, append a new row after the last one: -

    - -
    - - - - - - - - - - - - - - - - - - - -
    Table 87 — Unordered associative container requirements -(in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    a.rehash(n)void -Post: a.bucket_count > a.size() -/ a.max_load_factor() and a.bucket_count() ->= n. - -Average case linear in a.size(), worst case quadratic. -
    -a.reserve(n) - -void - -Same as a.rehash(ceil(n / a.max_load_factor())) - -Average case linear in a.size(), worst case quadratic. -
    -
    - -

    -In 23.5.4 [unord.map]/3 in the definition of class template unordered_map, in -23.5.5 [unord.multimap]/3 in the definition of class template unordered_multimap, in -23.5.6 [unord.set]/3 in the definition of class template unordered_set and in -23.5.7 [unord.multiset]/3 in the definition of class template unordered_multiset, add the -following line after member function rehash(): -

    - -
    -void reserve(size_type n);
-
    - -
    3. -
-
- -

[ -2009-10-28 Howard: -]

- - -
-

-Moved to Tentatively Ready after 5 votes in favor of Ganesh's option 2 above. -The original proposed wording now appears here: -

- -
-

-Informally: instead of providing rehash(n) provide resize(n), with the -semantics "make the container a good size for n elements". -

- -

-In the unordered associative container requirements (23.2.5 [unord.req]), -remove the row for -rehash and replace it with: -

- -
- - - - - - - - - - - - - -
Table 87 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
a.rehashresize(n)void -Post: a.bucket_count > max(a.size(), n) -/ a.max_load_factor() and a.bucket_count() ->= n. - -Average case linear in a.size(), worst case quadratic. -
-
- -

-Make the corresponding change in the class synopses in 23.5.4 [unord.map], 23.5.5 [unord.multimap], 23.5.6 [unord.set], and 23.5.7 [unord.multiset]. -

- -
-
- - -

Proposed resolution:

-

-In 23.2.5 [unord.req]/9, table 98, append a new row after the last one: -

- -
- - - - - - - - - - - - - - - - - - - -
Table 87 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
a.rehash(n)void -Post: a.bucket_count > a.size() -/ a.max_load_factor() and a.bucket_count() ->= n. - -Average case linear in a.size(), worst case quadratic. -
-a.reserve(n) - -void - -Same as a.rehash(ceil(n / a.max_load_factor())) - -Average case linear in a.size(), worst case quadratic. -
-
- -

-In 23.5.4 [unord.map]/3 in the definition of class template unordered_map, in -23.5.5 [unord.multimap]/3 in the definition of class template unordered_multimap, in -23.5.6 [unord.set]/3 in the definition of class template unordered_set and in -23.5.7 [unord.multiset]/3 in the definition of class template unordered_multiset, add the -following line after member function rehash(): -

- -
-void reserve(size_type n);
-
- - - - - -
-

1191. tuple get API should respect rvalues

-

Section: 20.4.2.6 [tuple.elem] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-08-18 Last modified: 2015-04-08

-

View all other issues in [tuple.elem].

-

View all issues with C++11 status.

-

Discussion:

-

-The tuple get API should respect rvalues. This would allow for moving a -single element out of a tuple-like type. -

- -

[ -2009-10-30 Alisdair adds: -]

- - -
-

-The issue of rvalue overloads of get for tuple-like types was briefly -discussed in Santa Cruz. -

- -

-The feedback was this would be welcome, but we need full wording for the -other types (pair and array) before advancing. -

- -

-I suggest the issue moves to Open from New as it has been considered, -feedback given, and it has not (yet) been rejected as NAD. -

-
- - -

[ -2010 Rapperswil: -]

- - -

-Note that wording has been provided, and this issue becomes more important -now that we have added a function to support forwarding argument lists as -tuples. - -Move to Tentatively Ready. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Add the following signature to p2 20.4.1 [tuple.general] -

- -

-template <size_t I, class ... Types>
-typename tuple_element<I, tuple<Types...> >::type&& get(tuple<Types...> &&);
-
- -

-And again to 20.4.2.6 [tuple.elem]. -

- -

-template <size_t I, class ... Types>
-typename tuple_element<I, tuple<Types...> >::type&& get(tuple<Types...>&& t);
-
- -
-

-Effects: Equivalent to return std::forward<typename tuple_element<I, tuple<Types...> >::type&&>(get<I>(t)); -

- - -

-[Note: If a T in Types is some reference type X&, -the return type is X&, not X&&. -However, if the element type is non-reference type T, -the return type is T&&. — end note] -

- -
-
- -

-Add the following signature to p1 20.2 [utility] -

- -

-template <size_t I, class T1, class T2>
-typename tuple_element<I, pair<T1,T2> >::type&& get(pair<T1, T2>&&);
-
- -

-And to p5 20.3.4 [pair.astuple] -

- -

-template <size_t I, class T1, class T2>
-typename tuple_element<I, pair<T1,T2> >::type&& get(pair<T1, T2>&& p);
-
- -
-

-Returns: If I == 0 returns std::forward<T1&&>(p.first); -if I == 1 -returns std::forward<T2&&>(p.second); otherwise the program is ill-formed. -

- -

-Throws: Nothing. -

- -
- -
- -

-Add the following signature to 23.3 [sequences] <array> synopsis -

- -
template <size_t I, class T, size_t N>
-T&& get(array<T,N> &&);
-
- -

-And after p8 23.3.2.9 [array.tuple] -

- -
-template <size_t I, class T, size_t N>
-T&& get(array<T,N> && a);
-
- -

-Effects: Equivalent to return std::move(get<I>(a)); -

-
- - - - - - -
-

1192. basic_string missing definitions for cbegin / cend / crbegin / crend

-

Section: 21.4.3 [string.iterators] Status: C++11 - Submitter: Jonathan Wakely Opened: 2009-08-14 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-Unlike the containers in clause 23, basic_string has definitions for -begin() and end(), but these have not been updated to include cbegin, -cend, crbegin and crend. -

- -

[ -2009-10-28 Howard: -]

- - -

-Moved to Tentatively NAD after 5 positive votes on c++std-lib. Added -rationale. -

- -

[ -2009-10-28 Alisdair disagrees: -]

- - -
-

-I'm going to have to speak up as the dissenting voice. -

- -

-I agree the issue could be handled editorially, and that would be my -preference if Pete feels this is appropriate. Failing that, I really -think this issue should be accepted and moved to ready. The other -begin/end functions all have a semantic definition for this template, -and it is confusing if a small few are missing. -

- -

-I agree that an alternative would be to strike all the definitions for -begin/end/rbegin/rend and defer completely to the requirements tables in -clause 23. I think that might be confusing without a forward reference -though, as those tables are defined in a later clause than the -basic_string template itself. If someone wants to pursue this I would -support it, but recommend it as a separate issue. -

- -

-So my preference is strongly to move Ready over NAD, and a stronger -preference for NAD Editorial if Pete is happy to make these changes. -

- -
- -

[ -2009-10-29 Howard: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. Removed -rationale to mark it NAD. :-) -

- - - -

Proposed resolution:

-

-Add to 21.4.3 [string.iterators] -

- -
-iterator       begin();
-const_iterator begin() const;
-const_iterator cbegin() const;
-
- -

...

- -
-iterator       end();
-const_iterator end() const;
-const_iterator cend() const;
-
- -

...

- -
-reverse_iterator       rbegin();
-const_reverse_iterator rbegin() const;
-const_reverse_iterator crbegin() const;
-
- -

...

- -
-reverse_iterator       rend();
-const_reverse_iterator rend() const;
-const_reverse_iterator crend() const;
-
- -
- - - - - -
-

1193. default_delete cannot be instantiated with incomplete types

-

Section: 20.8.1.1 [unique.ptr.dltr] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-08-18 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-According to the general rules of 17.6.4.8 [res.on.functions] p 2 b 5 the effects -are undefined, if an incomplete type is used to instantiate a library template. But neither in -20.8.1.1 [unique.ptr.dltr] nor -in any other place of the standard such explicit allowance is given. -Since this template is intended to be instantiated with incomplete -types, this must be fixed. -

- -

[ -2009-11-15 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2009-11-17 Alisdair Opens: -]

- - -
-

-LWG 1193 tries to support unique_ptr for incomplete types. I believe the -proposed wording goes too far: -

- -

-The template parameter T of default_delete may be an -incomplete type. -

- -

-Do we really want to support cv-void? Suggested ammendment: -

- -

-The template parameter T of default_delete may be an -incomplete type other than cv-void. -

- -

-We might also consider saying something about arrays of incomplete types. -

- -

-Did we lose support for unique_ptr<function-type> when the -concept-enabled work was shelved? If so, we might want a -default_delete partial specialization for function types that does -nothing. Alternatively, function types should not be supported by -default, but there is no reason a user cannot support them via their own -deletion policy. -

- -

-Function-type support might also lead to conditionally supporting a -function-call operator in the general case, and that seems way too inventive at -this stage to me, even if we could largely steal wording directly from -reference_wrapper. shared_ptr would have similar problems -too. -

- -
- -

[ -2010-01-24 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Add two new paragraphs directly to 20.8.1.1 [unique.ptr.dltr] (before -20.8.1.1.2 [unique.ptr.dltr.dflt]) with the following -content: -

- -
-

-The class template default_delete serves as the default deleter (destruction policy) for -the class template unique_ptr. -

- -

-The template parameter T of default_delete may be an incomplete type. -

-
- - - - - -
-

1194. Unintended queue constructor

-

Section: 23.6 [container.adaptors] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-08-20 Last modified: 2015-04-08

-

View all other issues in [container.adaptors].

-

View all issues with C++11 status.

-

Discussion:

-

-23.6.3.1 [queue.defn] has the following queue constructor: -

- -
-template <class Alloc> explicit queue(const Alloc&);
-
- -

-This will be implemented like so: -

- -
-template <class Alloc> explicit queue(const Alloc& a) : c(a) {}
-
- -

-The issue is that Alloc can be anything that a container will construct -from, for example an int. Is this intended to compile? -

- -
-queue<int> q(5);
-
- -

-Before the addition of this constructor, queue<int>(5) would not compile. -I ask, not because this crashes, but because it is new and appears to be -unintended. We do not want to be in a position of accidently introducing this -"feature" in C++0X and later attempting to remove it. -

- -

-I've picked on queue. priority_queue and stack have -the same issue. Is it useful to create a priority_queue of 5 -identical elements? -

- -

[ -Daniel, Howard and Pablo collaborated on the proposed wording. -]

- - -

[ -2009-10 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- -

[ -This resolution includes a semi-editorial clean up, giving definitions to members -which in some cases weren't defined since C++98. -This resolution also offers editorially different wording for 976, -and it also provides wording for 1196. -]

- - -

-Change container.adaptors, p1: -

- -

-The container adaptors each take a Container template parameter, and -each constructor takes a Container reference argument. This container is -copied into the Container member of each adaptor. If the container takes -an allocator, then a compatible allocator may be passed in to the -adaptor's constructor. Otherwise, normal copy or move construction is -used for the container argument. [Note: it is not necessary for an -implementation to distinguish between the one-argument constructor that -takes a Container and the one- argument constructor that takes an -allocator_type. Both forms use their argument to construct an instance -of the container. — end note] -

- -

-Change queue.defn, p1: -

- -
-template <class T, class Container = deque<T> >
-class queue {
-public:
-  typedef typename Container::value_type      value_type;
-  typedef typename Container::reference       reference;
-  typedef typename Container::const_reference const_reference;
-  typedef typename Container::size_type       size_type;
-  typedef Container                           container_type;
-protected:
-  Container c;
-
-public:
-  explicit queue(const Container&);
-  explicit queue(Container&& = Container());
-  queue(queue&& q); : c(std::move(q.c)) {}
-  template <class Alloc> explicit queue(const Alloc&);
-  template <class Alloc> queue(const Container&, const Alloc&);
-  template <class Alloc> queue(Container&&, const Alloc&);
-  template <class Alloc> queue(queue&&, const Alloc&);
-  queue& operator=(queue&& q); { c = std::move(q.c); return *this; }
-
-  bool empty() const          { return c.empty(); }
-  ...
-};
-
- -

-Add a new section after 23.6.3.1 [queue.defn], [queue.cons]: -

- -
-

queue constructors [queue.cons]

- -
-explicit queue(const Container& cont);
-
- -
- -

-Effects: Initializes c with cont. -

- -
- -
-explicit queue(Container&& cont = Container());
-
- -
- -

-Effects: Initializes c with std::move(cont). -

- -
- -
-queue(queue&& q)
-
- -
- -

-Effects: Initializes c with std::move(q.c). -

- -
- -

-For each of the following constructors, -if uses_allocator<container_type, Alloc>::value is false, -then the constructor shall not participate in overload resolution. -

- -
-template <class Alloc> 
-  explicit queue(const Alloc& a);
-
- -
- -

-Effects: Initializes c with a. -

- -
- -
-template <class Alloc> 
-  queue(const container_type& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with cont as the first -argument and a as the second argument. -

- -
- -
-template <class Alloc> 
-  queue(container_type&& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(cont) as the -first argument and a as the second argument. -

- -
- -
-template <class Alloc> 
-  queue(queue&& q, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(q.c) as the -first argument and a as the second argument. -

- -
- -
-queue& operator=(queue&& q);
-
- -
- -

-Effects: Assigns c with std::move(q.c). -

- -

-Returns: *this. -

- -
- - - -
- -

-Add to 23.6.4.1 [priqueue.cons]: -

- -
- -
-priority_queue(priority_queue&& q);
-
- -
- -

-Effects: Initializes c with std::move(q.c) and -initializes comp with std::move(q.comp). -

- -
- -

-For each of the following constructors, -if uses_allocator<container_type, Alloc>::value is false, -then the constructor shall not participate in overload resolution. -

- -
-template <class Alloc>
-  explicit priority_queue(const Alloc& a);
-
- -
- -

-Effects: Initializes c with a and value-initializes comp. -

- -
- -
-template <class Alloc>
-  priority_queue(const Compare& compare, const Alloc& a);
-
- -
- -

-Effects: Initializes c with a and initializes comp -with compare. -

- -
- -
-template <class Alloc>
-  priority_queue(const Compare& compare, const Container& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with cont as the first argument -and a as the second argument, -and initializes comp with compare. -

- -
- -
-template <class Alloc>
-  priority_queue(const Compare& compare, Container&& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(cont) as -the first argument and a as the second argument, -and initializes comp with compare. -

- -
- -
-template <class Alloc>
-  priority_queue(priority_queue&& q, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(q.c) as the -first argument and a as the second argument, -and initializes comp with std::move(q.comp). -

- -
- -
-priority_queue& operator=(priority_queue&& q);
-
- -
- -

-Effects: Assigns c with std::move(q.c) and -assigns comp with std::move(q.comp). -

- -

-Returns: *this. -

- -
- -
- - - - -

-Change 23.6.5.2 [stack.defn]: -

- -
-template <class T, class Container = deque<T> >
-class stack {
-public:
-  typedef typename Container::value_type      value_type;
-  typedef typename Container::reference       reference;
-  typedef typename Container::const_reference const_reference;
-  typedef typename Container::size_type       size_type;
-  typedef Container                           container_type;
-protected:
-  Container c;
-
-public:
-  explicit stack(const Container&);
-  explicit stack(Container&& = Container());
-  stack(stack&& s);
-  template <class Alloc> explicit stack(const Alloc&);
-  template <class Alloc> stack(const Container&, const Alloc&);
-  template <class Alloc> stack(Container&&, const Alloc&);
-  template <class Alloc> stack(stack&&, const Alloc&);
-  stack& operator=(stack&& s);
-
-  bool empty() const          { return c.empty(); }
-  ...
-};
-
- -

-Add a new section after 23.6.5.2 [stack.defn], [stack.cons]: -

- -
-

stack constructors [stack.cons]

- -
-stack(stack&& s);
-
- -
- -

-Effects: Initializes c with std::move(s.c). -

- -
- -

-For each of the following constructors, -if uses_allocator<container_type, Alloc>::value is false, -then the constructor shall not participate in overload resolution. -

- -
-template <class Alloc> 
-  explicit stack(const Alloc& a);
-
- -
- -

-Effects: Initializes c with a. -

- -
- -
-template <class Alloc> 
-  stack(const container_type& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with cont as the -first argument and a as the second argument. -

- -
- -
-template <class Alloc> 
-  stack(container_type&& cont, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(cont) as the -first argument and a as the second argument. -

- -
- -
-template <class Alloc> 
-  stack(stack&& s, const Alloc& a);
-
- -
- -

-Effects: Initializes c with std::move(s.c) as the -first argument and a as the second argument. -

- -
- -
-stack& operator=(stack&& s);
-
- -
- -

-Effects: Assigns c with std::move(s.c). -

- -

-Returns: *this. -

- -
- -
- - - - - - -
-

1195. "Diagnostic required" wording is insufficient to prevent UB

-

Section: 17 [library] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-08-18 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

View all issues with C++11 status.

-

Discussion:

-

-Several parts of the library use the notion of "Diagnostic required" -to indicate that -in the corresponding situation an error diagnostic should occur, e.g. -20.8.1.1.2 [unique.ptr.dltr.dflt]/2 -

-
-void operator()(T *ptr) const;
-
- -

-Effects: calls delete on ptr. A diagnostic is required if T is an -incomplete type. -

-
- -

-The problem with this approach is that such a requirement is -insufficient to prevent undefined behavior, if this situation occurs. -According to 1.3 [defns.diagnostic] -a diagnostic message is defined as -

- -

-a message belonging to an implementation-defined subset of the -implementation's output messages. -

- -

-which doesn't indicate any relation to an ill-formed program. In fact, -"compiler warnings" are a typical expression of such diagnostics. This means -that above wording can be interpreted by compiler writers that they satisfy -the requirements of the standard if they just produce such a "warning", if -the compiler happens to compile code like this: -

- -
-#include <memory>
-
-struct Ukn; // defined somewhere else
-Ukn* create_ukn(); // defined somewhere else
-
-int main() {
- std::default_delete<Ukn>()(create_ukn());
-}
-
- -

-In this and other examples discussed here it was the authors intent to -guarantee that the -program is ill-formed with a required diagnostic, therefore such -wording should be used instead. -According to the general rules outlined in 1.4 [intro.compliance] it -should be sufficient -to require that these situations produce an ill-formed program and the -"diagnostic -required" part should be implied. The proposed resolution also -suggests to remove -several redundant wording of "Diagnostics required" to ensure that -the absence of -such saying does not cause a misleading interpretation. -

- -

[ -2009 Santa Cruz: -]

- - -
-

-Move to NAD. -

-

-It's not clear that there's any important difference between -"ill-formed" and "diagnostic required". From 1.4 [intro.compliance], -1.3 [defns.ill.formed], and 1.3 [defns.well.formed] -it appears that an ill-formed program is one that is not correctly constructed -according to the syntax rules and diagnosable semantic rules, which means -that... "a conforming implementation shall issue at least one diagnostic message." The -author's intent seems to be that we should be requiring a fatal error -instead of a mere warning, but the standard just doesn't have language -to express that distinction. The strongest thing we can ever require is -a "diagnostic". -

-

-The proposed rewording may be a clearer way of expressing the same thing -that the WP already says, but such a rewording is editorial. -

-
- -

[ -2009 Santa Cruz: -]

- - -

-Considered again. Group disagrees that the change is technical, but likes -it editorially. Moved to NAD Editorial. -

- -

[ -2009-11-19: Moved from NAD Editorial to Open. Please see the thread starting -with Message c++std-lib-25916. -]

- - -

[ -2009-11-20 Daniel updated wording. -]

- - -
-

-The following resolution differs from the previous one by avoiding the unusual -and misleading term "shall be ill-formed", which does also not follow the core -language style. This resolution has the advantage of a minimum impact on the -current wording, but I would like to mention that a more intrusive solution -might be preferrable - at least as a long-term solution: Jens Maurer suggested -the following approach to get rid of the usage of the term "ill-formed" from the -library by introducing a new category to existing elements to the list of 17.5.1.4 [structure.specifications]/3, e.g. "type requirements" or "static -constraints" that define conditions that can be checked during compile-time and -any violation would make the program ill-formed. As an example, the currently -existing phrase 20.4.2.5 [tuple.helper]/1 -

- -

-Requires: I < sizeof...(Types). The program is ill-formed if -I is out of bounds. -

- -

-could then be written as -

- -

-Static constraints: I < sizeof...(Types). -

- -
- -

[ -2009-11-21 Daniel updated wording. -]

- - -

[ -2009-11-22 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-
    -
  1. -

    -Change 20.11 [ratio]/2 as indicated: -

    - -

    -Throughout this subclause, if the template argument types R1 -and R2 shall be are not specializations of the -ratio template, the program is ill-formed. Diagnostic -required. -

    -
    2. - -
  2. -

    -Change 20.11.3 [ratio.ratio]/1 as indicated: -

    - -

    -If tThe template argument D shall not -be is zero, and or the absolute values of -the template arguments N and D shall be are -not representable by type intmax_t, the program is -ill-formed. Diagnostic required. [..] -

    - -
    3. - -
  3. -

    -Change 20.11.4 [ratio.arithmetic]/1 as indicated: -

    - -

    -Implementations may use other algorithms to compute these values. If overflow -occurs, the program is ill-formed a diagnostic shall be -issued. -

    - -
    4. - -
  4. -

    -Change 20.11.5 [ratio.comparison]/2 as indicated: -

    - -

    -[...] Implementations may use other algorithms to compute this relationship to -avoid overflow. If overflow occurs, the program is ill-formed a -diagnostic is required. -

    - -
    5. - -
  5. -

    -Change 20.8.1.1.2 [unique.ptr.dltr.dflt]/2 as indicated: -

    - -
    -

    -Effects: calls delete on ptr. A diagnostic is -required if T is an incomplete type. -

    - -

    -Remarks: If T is an incomplete type, the program is -ill-formed. -

    -
    - -
    6. - -
  6. -

    -Change 20.8.1.1.3 [unique.ptr.dltr.dflt1]/1 as indicated: -

    - -
    -void operator()(T* ptr) const;
-
    -
    -

    -Effects: operator() calls -delete[] on ptr. A diagnostic is required if T -is an incomplete type. -

    -

    -Remarks: If T is an incomplete type, the program is -ill-formed. -

    -
    -
    - -
    7. - -
  7. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor] as indicated: [Note: This -editorially improves the currently suggested wording of 932 by -replacing -

    -

    -"shall be ill-formed" by "is ill-formed"] -

    - -

    -[If -N3025 -is accepted this bullet is applied identically in that paper as well.] -

    - -
    -

    --1- Requires: D shall be default constructible, and that -construction shall not throw an exception. D shall not be a -reference type or pointer type (diagnostic required). -

    - -

    ...

    - -

    -Remarks: If this constructor is instantiated with a pointer type -or reference type for the template argument D, the program is -ill-formed. -

    -
    - -
    8. - -
  8. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor]/8 as indicated: [Note: This -editorially improves the currently suggested wording of 932 by -replacing -

    -

    -"shall be ill-formed" by "is ill-formed"] -

    - -

    -[If -N3025 -is accepted this bullet is applied identically in that paper as well.] -

    - -
    -unique_ptr(pointer p);
-
    -
    -

    ...

    -

    -Remarks: If this constructor is instantiated with a pointer type -or reference type for the template argument D, the program is -ill-formed. -

    -
    -
    - -
    9. - -
  9. -

    -Change 20.8.1.2.1 [unique.ptr.single.ctor]/13 as indicated: -

    - -

    -[..] If d is an rvalue, it will bind to the second constructor of this -pair and the program is ill-formed. That constructor shall emit -a diagnostic. [Note: The diagnostic could be implemented using a -static_assert which assures that D is not a reference type. -— end note] Else d is an lvalue and will bind to the first -constructor of this pair. [..] -

    - -
    10. - -
  10. -20.8.1.2.1 [unique.ptr.single.ctor]/20: Solved by 950. -
    11. - -
  11. -

    -Change 20.8.1.3 [unique.ptr.runtime]/1 as indicated: -

    - -
    -

    -A specialization for array types is provided with a slightly altered interface. -

    -
      -
    • -Conversions among different types of unique_ptr<T[], D> or to or -from the non-array forms of unique_ptr are disallowed (diagnostic -required) produce an ill-formed program. -
      • -
    • ...
      • -
    -
    - -
    12. - -
  12. -

    -Change 20.12.5 [time.duration]/2-4 as indicated: -

    - -
    -

    -2 Requires: Rep shall be an arithmetic type or a class emulating -an arithmetic type. If a program instantiates duration with a -duration type for the template argument Rep a diagnostic is -required. -

    -

    -3 Remarks: If duration is instantiated with a -duration type for the template argument Rep, the program is -ill-formed. -

    - -

    -3 4 Requires Remarks: -If Period shall be is not a -specialization of ratio, diagnostic required the -program is ill-formed. -

    - -

    -4 5 Requires Remarks: -If Period::num shall be is not -positive, diagnostic required the program is ill-formed. -

    -
    - -
    13. - -
  13. -20.12.5.1 [time.duration.cons]/1+4: Apply 1177 -
    14. - -
  14. -20.12.5.5 [time.duration.nonmember]/4+6+8+11: Apply 1177 -
    15. - -
  15. -20.12.5.7 [time.duration.cast]/1: Apply 1177 -
    16. - -
  16. -

    -Change 20.12.6 [time.point]/2 as indicated: -

    -

    -If Duration shall be is not an -instance of duration, the program is ill-formed. -Diagnostic required. -

    -
    17. - -
  17. -20.12.6.1 [time.point.cons]/3: Apply 1177 -
    18. - -
  18. -20.12.6.7 [time.point.cast]/1: Apply 1177 -
    19. - -
- - - - - - -
-

1196. move semantics undefined for priority_queue

-

Section: 23.6.4.1 [priqueue.cons] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-08-19 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-The class template priority_queue declares signatures for a move -constructor and move assignment operator in its class definition. -However, it does not provide a definition (unlike std::queue, and -proposed resolution for std::stack.) Nor does it provide a text clause -specifying their behaviour. -

- -

[ -2009-08-23 Daniel adds: -]

- - -

-1194 provides wording that solves this issue. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Mark NAD EditorialResolved, solved by issue 1194. -

- - - -

Proposed resolution:

- - - - - -
-

1197. Can unordered containers have bucket_count() == 0?

-

Section: 23.2.5 [unord.req] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-08-24 Last modified: 2015-04-08

-

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-

View all other issues in [unord.req].

-

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-

Discussion:

-

-Table 97 "Unordered associative container requirements" in -23.2.5 [unord.req] says: -

- -
- - - - - - - - - - - - - - - - - -
Table 97 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
b.bucket(k)size_typeReturns the index of the bucket in which elements with keys -equivalent to k would be found, -if any such element existed. -Post: the return value shall be -in the range [0, -b.bucket_count()).Constant
-
- -

-What should b.bucket(k) return if b.bucket_count() == 0? -

- -

-I believe allowing b.bucket_count() == 0 is important. It is a -very reasonable post-condition of the default constructor, or of a moved-from -container. -

- -

-I can think of several reasonable results from b.bucket(k) when -b.bucket_count() == 0: -

- -
    -
  1. -Return 0. -
    2. -
  2. -Return numeric_limits<size_type>::max(). -
    3. -
  3. -Throw a domain_error. -
    4. -
  4. -Requires: b.bucket_count() != 0. -
    5. -
- -

[ -2009-08-26 Daniel adds: -]

- - -
-

-A forth choice would be to add the pre-condition "b.bucket_count() != 0" -and thus imply undefined behavior if this is violated. -

- -

[ -Howard: I like this option too, added to the list. -]

- - -

-Further on here my own favorite solution (rationale see below): -

- -

Suggested resolution:

- -

-[Rationale: I suggest to follow choice (1). The main reason is -that all associative container functions which take a key argument, -are basically free of pre-conditions and non-disrupting, therefore -excluding choices (3) and (4). Option (2) seems a bit unexpected -to me. It would be more natural, if several similar functions -would exist which would also justify the existence of a symbolic -constant like npos for this situation. The value 0 is both simple -and consistent, it has exactly the same role as a past-the-end -iterator value. A typical use-case is: -

- -
-size_type pos = m.bucket(key);
-if (pos != m.bucket_count()) {
- ...
-} else {
- ...
-}
-
- -

— end Rationale]

- -

-- Change Table 97 in 23.2.5 [unord.req] as follows (Row b.bucket(k), Column "Assertion/..."): -

- -
- - - - - - - - - - - - - - - - - -
Table 97 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
b.bucket(k)size_typeReturns the index of the bucket in which elements with keys -equivalent to k would be found, -if any such element existed. -Post: if b.bucket_count() != 0, the return value shall be -in the range [0, -b.bucket_count()), otherwise 0.Constant
-
- -
- -

[ -2010-01-25 Choice 4 put into proposed resolution section. -]

- - -

[ -2010-01-31 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change Table 97 in 23.2.5 [unord.req] as follows (Row b.bucket(k), Column -"Assertion/..."): -

- -
- - - - - - - - - - - - - - - - - -
Table 97 — Unordered associative container requirements -(in addition to container)
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
b.bucket(k)size_typePre: b.bucket_count() > 0 Returns the index of the -bucket in which elements with keys equivalent to k would be found, if -any such element existed. Post: the return value shall be in the range [0, -b.bucket_count()).Constant
-
- - - - - - -
-

1198. Container adaptor swap: member or non-member?

-

Section: 23.6 [container.adaptors] Status: C++11 - Submitter: Pablo Halpern Opened: 2009-08-26 Last modified: 2015-04-08

-

View all other issues in [container.adaptors].

-

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-

Discussion:

-

-Under 23.6 [container.adaptors] of -N2914 -the member function of swap of queue and stack call: -

- -
-swap(c, q.c);
-
- -

-But under 23.6 [container.adaptors] of -N2723 -these members are specified to call: -

- -
-c.swap(q.c);
-
- -

-Neither draft specifies the semantics of member swap for -priority_queue though it is declared. -

- -

-Although the distinction between member swap and non-member -swap is not important when these adaptors are adapting standard -containers, it may be important for user-defined containers. -

-

-We (Pablo and Howard) feel that -it is more likely for a user-defined container to support a namespace scope -swap than a member swap, and therefore these adaptors -should use the container's namespace scope swap. -

- -

[ -2009-09-30 Daniel adds: -]

- - -

-The outcome of this issue should be considered with the outcome of 774 both in style and in content (e.g. 774 bullet 9 -suggests to define the semantic of void -priority_queue::swap(priority_queue&) in terms of the member -swap of the container). -

- -

[ -2010-03-28 Daniel update to diff against N3092. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-Preference to move the wording into normative text, rather than inline function definitions in the class synopsis. - -Move to Tenatively Ready. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

-Change 23.6.3.1 [queue.defn]: -

- -
-template <class T, class Container = deque<T> > 
-class queue {
-   ...
-   void swap(queue& q) { using std::swap;
-                          c.swap(c, q.c); }
-   ...
-};
-
- -

-Change 23.6.4 [priority.queue]: -

- -
-template <class T, class Container = vector<T>, 
-          class Compare = less<typename Container::value_type> > 
-class priority_queue { 
-    ...
-    void swap(priority_queue& q); { using std::swap;
-                                     swap(c, q.c);
-                                     swap(comp, q.comp); }
-    ...
-};
-
- -

-Change 23.6.5.2 [stack.defn]: -

- -
-template <class T, class Container = deque<T> > 
-class stack {
-   ...
-   void swap(stack& s) { using std::swap;
-                          c.swap(c, s.c); }
-   ...
-};
-
- - - - - - -
-

1199. Missing extended copy constructor in container adaptors

-

Section: 23.6 [container.adaptors] Status: C++11 - Submitter: Pablo Halpern Opened: 2009-08-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-queue has a constructor: -

- -
-template <class Alloc>
-  queue(queue&&, const Alloc&);
-
- -

-but it is missing a corresponding constructor: -

- -
-template <class Alloc>
-  queue(const queue&, const Alloc&);
-
- -

-The same is true of priority_queue, and stack. This -"extended copy constructor" is needed for consistency and to ensure that the -user of a container adaptor can always specify the allocator for his adaptor. -

- -

[ -2010-02-01 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

[ -This resolution has been harmonized with the proposed resolution to issue -1194 -]

- - -

Change 23.6.3.1 [queue.defn], p1:

- -
-template <class T, class Container = deque<T> >
-class queue {
-public:
-  typedef typename Container::value_type      value_type;
-  typedef typename Container::reference       reference;
-  typedef typename Container::const_reference const_reference;
-  typedef typename Container::size_type       size_type;
-  typedef Container                           container_type;
-protected:
-  Container c;
-
-public:
-  explicit queue(const Container&);
-  explicit queue(Container&& = Container());
-  queue(queue&& q);
-
-  template <class Alloc> explicit queue(const Alloc&);
-  template <class Alloc> queue(const Container&, const Alloc&);
-  template <class Alloc> queue(Container&&, const Alloc&);
-  template <class Alloc> queue(const queue&, const Alloc&);
-  template <class Alloc> queue(queue&&, const Alloc&);
-  queue& operator=(queue&& q);
-
-  bool empty() const          { return c.empty(); }
-  ...
-};
-
- -

-To the new section 23.6.3.2 [queue.cons], introduced -in 1194, add: -

- -
- -
-template <class Alloc> 
-  queue(const queue& q, const Alloc& a);
-
- -

-Effects: Initializes c with q.c as the -first argument and a as the second argument. -

- -
- -

Change 23.6.4 [priority.queue] as follows (I've an included an editorial change to - move the poorly-placed move-assignment operator):

- -
-template <class T, class Container = vector<T>,
-          class Compare = less<typename Container::value_type> >
-class priority_queue {
-public:
-  typedef typename Container::value_type      value_type;
-  typedef typename Container::reference       reference;
-  typedef typename Container::const_reference const_reference;
-  typedef typename Container::size_type       size_type;
-  typedef          Container                  container_type;
-protected:
-  Container c;
-  Compare comp;
-
-public:
-  priority_queue(const Compare& x, const Container&);
-  explicit priority_queue(const Compare& x = Compare(), Container&& = Container());
-  template <class InputIterator>
-    priority_queue(InputIterator first, InputIterator last,
-                   const Compare& x, const Container&);
-  template <class InputIterator>
-    priority_queue(InputIterator first, InputIterator last,
-                   const Compare& x = Compare(), Container&& = Container());
-  priority_queue(priority_queue&&);
-  priority_queue& operator=(priority_queue&&);
-  template <class Alloc> explicit priority_queue(const Alloc&);
-  template <class Alloc> priority_queue(const Compare&, const Alloc&);
-  template <class Alloc> priority_queue(const Compare&,
-                                        const Container&, const Alloc&);
-  template <class Alloc> priority_queue(const Compare&,
-                                        Container&&, const Alloc&);
-  template <class Alloc> priority_queue(const priority_queue&, const Alloc&);
-  template <class Alloc> priority_queue(priority_queue&&, const Alloc&);
-
-  priority_queue& operator=(priority_queue&&);
-  ...
-};
-
- -

-Add to 23.6.4.1 [priqueue.cons]: -

- -
- -
-template <class Alloc>
-  priority_queue(const priority_queue& q, const Alloc& a);
-
- -

-Effects: Initializes c with q.c as the -first argument and a as the second argument, -and initializes comp with q.comp. -

- -
- -

-Change 23.6.5.2 [stack.defn]: -

- -
-template <class T, class Container = deque<T> >
-class stack {
-public:
-  typedef typename Container::value_type      value_type;
-  typedef typename Container::reference       reference;
-  typedef typename Container::const_reference const_reference;
-  typedef typename Container::size_type       size_type;
-  typedef Container                           container_type;
-protected:
-  Container c;
-
-public:
-  explicit stack(const Container&);
-  explicit stack(Container&& = Container());
-  stack(stack&& s);
-
-  template <class Alloc> explicit stack(const Alloc&);
-  template <class Alloc> stack(const Container&, const Alloc&);
-  template <class Alloc> stack(Container&&, const Alloc&);
-  template <class Alloc> stack(const stack&, const Alloc&);
-  template <class Alloc> stack(stack&&, const Alloc&);
-  stack& operator=(stack&& s);
-
-  bool empty() const          { return c.empty(); }
-  ...
-};
-
- -

-To the new section 23.6.5.3 [stack.cons], introduced -in 1194, add: -

- -
- -
-template <class Alloc> 
-  stack(const stack& s, const Alloc& a);
-
- -

-Effects: Initializes c with s.c as the -first argument and a as the second argument. -

-
- - - - - - -
-

1204. Global permission to move

-

Section: 17.6.4.9 [res.on.arguments] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-09-12 Last modified: 2015-04-08

-

View all other issues in [res.on.arguments].

-

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-

Discussion:

-

-When a library function binds an rvalue reference parameter to an argument, the -library must be able to assume that the bound argument is a temporary, and not -a moved-from lvalue. The reason for this is that the library function must be -able to modify that argument without concern that such modifications will corrupt -the logic of the calling code. For example: -

- -
-template <class T, class A>
-void
-vector<T, A>::push_back(value_type&& v)
-{
-    // This function should move from v, potentially modifying
-    // the object v is bound to.
-}
-
- -

-If v is truly bound to a temporary, then push_back has the -only reference to this temporary in the entire program. Thus any -modifications will be invisible to the rest of the program. -

- -

-If the client supplies std::move(x) to push_back, the onus is -on the client to ensure that the value of x is no longer important to -the logic of his program after this statement. I.e. the client is making a statement -that push_back may treat x as a temporary. -

- -

-The above statement is the very foundation upon which move semantics is based. -

- -

-The standard is currently lacking a global statement to this effect. I propose -the following addition to 17.6.4.9 [res.on.arguments]: -

- -
-

-Each of the following statements applies to all arguments to functions -defined in the C++ standard library, unless explicitly stated otherwise. -

-
    -
  • -If an argument to a function has an invalid value (such as a value -outside the domain of the function, or a pointer invalid for its -intended use), the behavior is undefined. -
    • -
  • -If a function argument is described as being an array, the pointer -actually passed to the function shall have a value such that all address -computations and accesses to objects (that would be valid if the pointer -did point to the first element of such an array) are in fact valid. -
    • -
  • -If a function argument binds to an rvalue reference parameter, the C++ -standard library may assume that this parameter is a unique reference -to this argument. If the parameter is a generic parameter of the -form T&&, and an lvalue of type A is bound, -then the binding is considered to be to an lvalue reference -(14.8.2.1 [temp.deduct.call]) and thus not covered by this clause. -[Note: -If a program casts an lvalue to an rvalue while passing that lvalue to -a library function (e.g. move(x)), then the program is effectively -asking the library to treat that lvalue as a temporary. The library is at -liberty to optimize away aliasing checks which might be needed if the argument -were an lvalue. -— end note] -
    • -
- -
- -

-Such a global statement will eliminate the need for piecemeal statements such as -23.2.1 [container.requirements.general]/13: -

- -

-An object bound to an rvalue reference parameter of a member function of -a container shall not be an element of that container; no diagnostic -required. -

- -

-Additionally this clarifies that move assignment operators need not perform the -traditional if (this != &rhs) test commonly found (and needed) in -copy assignment operators. -

- -

[ -2009-09-13 Niels adds: -]

- - -

-Note: This resolution supports the change of 27.9.1.3 [filebuf.assign]/1, -proposed by LWG 900. -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add a bullet to 17.6.4.9 [res.on.arguments]: -

- -
-

-Each of the following statements applies to all arguments to functions -defined in the C++ standard library, unless explicitly stated otherwise. -

-
    -
  • -If an argument to a function has an invalid value (such as a value -outside the domain of the function, or a pointer invalid for its -intended use), the behavior is undefined. -
    • -
  • -If a function argument is described as being an array, the pointer -actually passed to the function shall have a value such that all address -computations and accesses to objects (that would be valid if the pointer -did point to the first element of such an array) are in fact valid. -
    • -
  • -If a function argument binds to an rvalue reference parameter, the C++ -standard library may assume that this parameter is a unique reference -to this argument. If the parameter is a generic parameter of the -form T&&, and an lvalue of type A is bound, -then the binding is considered to be to an lvalue reference -(14.8.2.1 [temp.deduct.call]) and thus not covered by this clause. -[Note: -If a program casts an lvalue to an rvalue while passing that lvalue to -a library function (e.g. move(x)), then the program is effectively -asking the library to treat that lvalue as a temporary. The library is at -liberty to optimize away aliasing checks which might be needed if the argument -were an lvalue. -— end note] -
    • -
-
- -

-Delete 23.2.1 [container.requirements.general]/13: -

- -

-An object bound to an rvalue reference parameter of a member function of -a container shall not be an element of that container; no diagnostic -required. -

- - - - - - -
-

1205. Some algorithms could more clearly document their handling of empty ranges

-

Section: 25 [algorithms] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-09-13 Last modified: 2015-04-08

-

View other active issues in [algorithms].

-

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-

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-

Discussion:

-

-There are a number of algorithms whose result might depend on the -handling of an empty range. In some cases the result is not clear, -while in others it would help readers to clearly mention the result -rather than require some subtle intuition of the supplied wording. -

- -

-25.2.1 [alg.all_of] -

- -

-Returns: true if pred(*i) is true for every -iterator i in the range [first,last), ... -

- -

-What does this mean if the range is empty? -

- -

-I believe that we intend this to be true and suggest a -non-normative note to clarify: -

- -

-Add to p1 25.2.1 [alg.all_of]: -

- -

-[Note: Returns true if [first,last) is empty. -— end note] -

- -

-25.2.3 [alg.none_of] -

- -

-Returns: true if pred(*i) is false for every -iterator i in the range [first,last), ... -

- -

-What does this mean if the range empty? -

- -

-I believe that we intend this to be true and suggest a -non-normative note to clarify: -

- -

-Add to p1 25.2.3 [alg.none_of]: -

- -

-[Note: Returns true if [first,last) is empty. -— end note] -

- -

-25.2.2 [alg.any_of] -

- -

-The specification for an empty range is actually fairly clear in this -case, but a note wouldn't hurt and would be consistent with proposals -for all_of/none_of algorithms. -

- -

-Add to p1 25.2.2 [alg.any_of]: -

- -

-[Note: Returns false if [first,last) is empty. -— end note] -

- -

-25.2.6 [alg.find.end] -

- -

-what does this mean if [first2,last2) is empty? -

- -

-I believe the wording suggests the algorithm should return -last1 in this case, but am not 100% sure. Is this in fact the -correct result anyway? Surely an empty range should always match and the -naive expected result would be first1? -

- -

-My proposed wording is a note to clarify the current semantic: -

- -

-Add to p2 25.2.6 [alg.find.end]: -

- -

-[Note: Returns last1 if [first2,last2) is -empty. — end note] -

- -

-I would prefer a normative wording treating empty ranges specially, but -do not believe we can change semantics at this point in the process, -unless existing implementations actually yield this result: -

- -

-Alternative wording: (NOT a note) -

-

-Add to p2 25.2.6 [alg.find.end]: -

-

-Returns first1 if [first2,last2) is empty. -

- -

-25.2.7 [alg.find.first.of] -

- -

-The phrasing seems precise when [first2, last2) is empty, but a small -note to confirm the reader's understanding might still help. -

- -

-Add to p2 25.2.7 [alg.find.first.of] -

-

-[Note: Returns last1 if [first2,last2) is -empty. — end note] -

- -

-25.2.13 [alg.search] -

- -

-What is the expected result if [first2, last2) is empty? -

- -

-I believe the wording suggests the algorithm should return last1 in this -case, but am not 100% sure. Is this in fact the correct result anyway? -Surely an empty range should always match and the naive expected result -would be first1? -

- -

-My proposed wording is a note to clarify the current semantic: -

- -

-Add to p2 25.2.13 [alg.search]: -

- -

-[Note: Returns last1 if [first2,last2) is -empty. — end note] -

- -

-Again, I would prefer a normative wording treating empty ranges -specially, but do not believe we can change semantics at this point in -the process, unless existing implementations actually yield this result: -

- -

-Alternative wording: (NOT a note) -

-

-Add to p2 25.2.13 [alg.search]: -

- -

-Returns first1 if [first2,last2) is empty. -

- -

-25.3.13 [alg.partitions] -

- -

-Is an empty range partitioned or not? -

- -

-Proposed wording: -

- -

-Add to p1 25.3.13 [alg.partitions]: -

- -

-[Note: Returns true if [first,last) is empty. -— end note] -

- -

-25.4.5.1 [includes] -

- -

-Returns: true if every element in the range -[first2,last2) is contained in the range -[first1,last1). ... -

- -

-I really don't know what this means if [first2,last2) is empty. -I could loosely guess that this implies empty ranges always match, and -my proposed wording is to clarify exactly that: -

- -

-Add to p1 25.4.5.1 [includes]: -

- -

-[Note: Returns true if [first2,last2) is empty. -— end note] -

- -

-25.4.6.2 [pop.heap] -

- -

-The effects clause is invalid if the range [first,last) is empty, unlike -all the other heap alogorithms. The should be called out in the -requirements. -

- -

-Proposed wording: -

-

-Revise p2 25.4.6.2 [pop.heap] -

- -

-Requires: The range [first,last) shall be a valid -non-empty heap. -

- -

-[Editorial] Reverse order of 25.4.6.2 [pop.heap] p1 and p2. -

- -

-25.4.7 [alg.min.max] -

- -

-minmax_element does not clearly specify behaviour for an empty -range in the same way that min_element and max_element do. -

- -

-Add to p31 25.4.7 [alg.min.max]: -

- -

-Returns make_pair(first, first) if first == last. -

- -

-25.4.8 [alg.lex.comparison] -

- -

-The wording here seems quite clear, especially with the sample algorithm -implementation. A note is recommended purely for consistency with the -rest of these issue resolutions: -

- -

-Add to p1 25.4.8 [alg.lex.comparison]: -

- -

-[Note: An empty sequence is lexicographically less than any other -non-empty sequence, but not to another empty sequence. — end note] -

- -

[ -2009-11-11 Howard changes Notes to Remarks and changed search to -return first1 instead of last1. -]

- - -

[ -2009-11-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Add to 25.2.1 [alg.all_of]: -

-

-Remarks: Returns true if [first,last) is empty. -

- -

-Add to 25.2.2 [alg.any_of]: -

- -

-Remarks: Returns false if [first,last) is empty. -

- -

-Add to 25.2.3 [alg.none_of]: -

-

-Remarks: Returns true if [first,last) is empty. -

- -

-Add to 25.2.6 [alg.find.end]: -

-

-Remarks: Returns last1 if [first2,last2) is -empty. -

- -

-Add to 25.2.7 [alg.find.first.of] -

-

-Remarks: Returns last1 if [first2,last2) is -empty. -

- -

-Add to 25.2.13 [alg.search]: -

-

-Remarks: Returns first1 if [first2,last2) is -empty. -

- -

-Add to 25.3.13 [alg.partitions]: -

-

-Remarks: Returns true if [first,last) is empty. -

- -

-Add to 25.4.5.1 [includes]: -

-

-Remarks: Returns true if [first2,last2) is empty. -

- -

-Revise p2 25.4.6.2 [pop.heap] -

-

-Requires: The range [first,last) shall be a valid -non-empty heap. -

- -

-[Editorial] -

-

-Reverse order of 25.4.6.2 [pop.heap] p1 and p2. -

- -

-Add to p35 25.4.7 [alg.min.max]: -

-
-template<class ForwardIterator, class Compare>
-  pair<ForwardIterator, ForwardIterator>
-    minmax_element(ForwardIterator first, ForwardIterator last, Compare comp);
-
-

-Returns: make_pair(m, M), where m is the first iterator in -[first,last) such that no iterator in the range refers to a smaller -element, and where M is the last iterator in [first,last) such that no -iterator in the range refers to a larger element. -Returns make_pair(first, first) if first == last. -

-
- -

-Add to 25.4.8 [alg.lex.comparison]: -

-

-Remarks: An empty sequence is lexicographically less than any other -non-empty sequence, but not less than another empty sequence. -

- - - - - - -
-

1206. Incorrect requires for move_backward and copy_backward

-

Section: 25.3.2 [alg.move] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-09-13 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-25.3.2 [alg.move], p6 says: -

- -
-
-template<class BidirectionalIterator1, class BidirectionalIterator2>
-  BidirectionalIterator2
-    move_backward(BidirectionalIterator1 first,
-                  BidirectionalIterator1 last,
-                  BidirectionalIterator2 result);
-
-
-

...

-

-Requires: result shall not be in the range -[first,last). -

-
-
- -

-This is essentially an "off-by-one" error. -

- -

-When result == last, which -is allowed by this specification, then the range [first, last) -is being move assigned into the range [first, last). The move -(forward) algorithm doesn't allow self move assignment, and neither should -move_backward. So last should be included in the range which -result can not be in. -

- -

-Conversely, when result == first, which is not allowed by this -specification, then the range [first, last) -is being move assigned into the range [first - (last-first), first). -I.e. into a non-overlapping range. Therefore first should -not be included in the range which result can not be in. -

- -

-The same argument applies to copy_backward though copy assigning elements -to themselves (result == last) should be harmless (though is disallowed -by copy). -

- -

[ -2010 Pittsburgh: Moved to Ready. -]

- - - - -

Proposed resolution:

-

-Change 25.3.2 [alg.move], p6: -

- -
-
-template<class BidirectionalIterator1, class BidirectionalIterator2>
-  BidirectionalIterator2
-    move_backward(BidirectionalIterator1 first,
-                  BidirectionalIterator1 last,
-                  BidirectionalIterator2 result);
-
-
-

...

-

-Requires: result shall not be in the range -[(first,last]). -

-
-
- -

-Change 25.3.1 [alg.copy], p13: -

- -
-
-template<class BidirectionalIterator1, class BidirectionalIterator2>
-  BidirectionalIterator2
-    copy_backward(BidirectionalIterator1 first,
-                  BidirectionalIterator1 last,
-                  BidirectionalIterator2 result);
-
-
-

...

-

-Requires: result shall not be in the range -[(first,last]). -

-
-
- - - - - -
-

1207. Underspecified std::list operations?

-

Section: 23.3.5.5 [list.ops] Status: C++11 - Submitter: Loïc Joly Opened: 2009-09-13 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with C++11 status.

-

Discussion:

-

-It looks to me like some operations of std::list -(sort, reverse, remove, unique & -merge) do not specify the validity of iterators, pointers & -references to elements of the list after those operations. Is it implied -by some other text in the standard? -

- -

-I believe sort & reverse do not invalidating -anything, remove & unique only invalidates what -refers to erased elements, merge does not invalidate anything -(with the same precision as splice for elements who changed of -container). Are those assumptions correct ? -

- -

[ -2009-12-08 Jonathan Wakely adds: -]

- - -
-

-23.2.1 [container.requirements.general] paragraph 11 says iterators -aren't invalidated unless specified, so I don't think it needs to be repeated on -every function that doesn't invalidate iterators. list::unique says it -"eliminates" elements, that should probably be "erases" because IMHO that term -is used elsewhere and so makes it clearer that iterators to the erased elements -are invalidated. -

- -

-list::merge coud use the same wording as list::splice w.r.t -iterators and references to moved elements. -

- -

-Suggested resolution: -

- -

-In 23.3.5.5 [list.ops] change paragraph 19 -

- -
-                                 void unique();
-template <class BinaryPredicate> void unique(BinaryPredicate binary_pred);
-
-

-Effects: Eliminates Erases all but the first -element from every consecutive group ... -

-
- -

-Add to the end of paragraph 23 -

- -
-void                          merge(list<T,Allocator>&& x);
-template <class Compare> void merge(list<T,Allocator>&& x, Compare comp);
-
-
-

...

-

-Effects: ... that is, for every iterator i, in the range other -than the first, the condition comp(*i, *(i - 1) will be false. -Pointers and references to the moved elements of x now refer to -those same elements but as members of *this. Iterators referring to the -moved elements will continue to refer to their elements, but they now behave as -iterators into *this, not into x. -

-
-
-
- -

[ -2009-12-12 Loïc adds wording. -]

- - -

[ -2010-02-10 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-10 Alisdair opens: -]

- - -
-

-I object to the current resolution of #1207. I believe it is overly strict with -regard to list end iterators, being the only mutating operations to -require such stability. -

- -

-More importantly, the same edits need to be applied to forward_list, -which uses slightly different words to describe some of these operations so may -require subtly different edits (not checked.) -

- -

-I am prepared to pick up the end() iterator as a separate (new) issue, -as part of the FCD ballot review (BSI might tell me 'no' first ;~) but I do want -to see forward_list adjusted at the same time. -

-
- -

[ -2010-03-28 Daniel adds the first 5 bullets in an attempt to address Alisdair's -concerns. -]

- - - -

[ -2010 Rapperswil: -]

- - -

-The wording looks good. - -Move to Tentatively Ready. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -
    - -
  1. -

    -Change 23.3.4.6 [forwardlist.ops]/12 as indicated: -

    - -
    -void remove(const T& value);
-template <class Predicate> void remove_if(Predicate pred);
-
    - -

    -12 Effects: Erases all the elements in the list referred by a list -iterator i for which the following conditions hold: *i == value -(for remove()), pred(*i) is true (for remove_if()). This operation -shall be stable: the relative order of the elements that are not removed is the -same as their relative order in the original list. Invalidates only the -iterators and references to the erased elements. -

    -
    -
    2. - -
  2. -

    -Change 23.3.4.6 [forwardlist.ops]/15 as indicated: -

    - -
    -template <class BinaryPredicate> void unique(BinaryPredicate pred);
-
    - -

    -15 Effects:: EliminatesErases all but the first -element from every consecutive group of equal elements referred to by the -iterator i in the range [first + 1,last) for which *i == -*(i-1) (for the version with no arguments) or pred(*i, *(i - 1)) -(for the version with a predicate argument) holds. Invalidates only the -iterators and references to the erased elements. -

    -
    -
    3. - -
  3. -

    -Change 23.3.4.6 [forwardlist.ops]/19 as indicated: -

    - -
    -void merge(forward_list<T,Allocator>&& x);
-template <class Compare> void merge(forward_list<T,Allocator>&& x, Compare comp)
-
    - -
    -

    -[..] -

    - -

    -19 Effects:: Merges x into *this. This operation shall -be stable: for equivalent elements in the two lists, the elements from -*this shall always precede the elements from x. x is -empty after the merge. If an exception is thrown other than by a comparison -there are no effects. Pointers and references to the moved elements of -x now refer to those same elements but as members of *this. -Iterators referring to the moved elements will continue to refer to their -elements, but they now behave as iterators into *this, not into -x. -

    -
    -
    -
    4. - -
  4. -

    -Change 23.3.4.6 [forwardlist.ops]/22 as indicated: -

    - -
    -void sort();
-template <class Compare> void sort(Compare comp);
-
    - -
    -

    -[..] -

    - -

    -22 Effects:: Sorts the list according to the operator< or the -comp function object. This operation shall be stable: the relative -order of the equivalent elements is preserved. If an exception is thrown the -order of the elements in *this is unspecified. Does not affect the -validity of iterators and references. -

    -
    -
    -
    5. - -
  5. -

    -Change 23.3.4.6 [forwardlist.ops]/24 as indicated: -

    - -
    -void reverse();
-
    - -

    -24 Effects:: Reverses the order of the elements in the list. Does -not affect the validity of iterators and references. -

    -
    -
    6. - -
  6. -

    -Change 23.3.5.5 [list.ops], p15: -

    - -
    -                           void remove(const T& value);
-template <class Predicate> void remove_if(Predicate pred);
-
    -

    -Effects: Erases all the elements in the list referred by a list iterator -i for which the following conditions hold: *i == value, pred(*i) != -false. Invalidates only the iterators and references to the erased -elements. -

    -
    -
    7. - -
  7. -

    -Change 23.3.5.5 [list.ops], p19: -

    - -
    -                                 void unique();
-template <class BinaryPredicate> void unique(BinaryPredicate binary_pred);
-
    -

    -Effects: Eliminates Erases all but the first -element from every consecutive group of equal elements referred to by the -iterator i in the range [first + 1,last) for which *i == -*(i-1) (for the version of unique with no arguments) or -pred(*i, *(i - 1)) (for the version of unique with a predicate -argument) holds. Invalidates only the iterators and references to the -erased elements. -

    -
    -
    8. - -
  8. -

    -Change 23.3.5.5 [list.ops], p23: -

    - -
    -void                          merge(list<T,Allocator>&& x);
-template <class Compare> void merge(list<T,Allocator>&& x, Compare comp);
-
    -

    -Effects: If (&x == this) does nothing; otherwise, merges the -two sorted ranges [begin(), end()) and [x.begin(), x.end()). -The result is a range in which the elements will be sorted in non-decreasing -order according to the ordering defined by comp; that is, for every -iterator i, in the range other than the first, the condition -comp(*i, *(i - 1) will be false. -Pointers and references to the moved elements of x now refer to -those same elements but as members of *this. Iterators referring to the -moved elements will continue to refer to their elements, but they now behave as -iterators into *this, not into x. -

    -
    -
    9. - -
  9. -

    -Change 23.3.5.5 [list.ops], p26: -

    - -
    -void reverse();
-
    -

    -Effects: Reverses the order of the elements in the list. -Does not affect the validity of iterators and references. -

    -
    -
    10. - -
  10. -

    -Change 23.3.5.5 [list.ops], p30: -

    - -
    -                         void sort();
-template <class Compare> void sort(Compare comp);
-
    -

    -Effects: Sorts the list according to the operator< or a -Compare function object. -Does not affect the validity of iterators and references. -

    -
    -
    11. - -
- - - - - - -
-

1208. valarray initializer_list constructor has incorrect effects

-

Section: 26.6.2.2 [valarray.cons] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-09-23 Last modified: 2015-04-08

-

View all other issues in [valarray.cons].

-

View all issues with C++11 status.

-

Discussion:

-

-26.6.2.2 [valarray.cons] says: -

- -
-
-valarray(initializer_list<T> il);
-
-

-Effects: Same as valarray(il.begin(), il.end()). -

-
- -

-But there is no valarray constructor taking two const T*. -

- -

[ -2009-10-29 Howard: -]

- - -

-Moved to Tentatively Ready after 6 positive votes on c++std-lib. -

- - -

Proposed resolution:

-

-Change 26.6.2.2 [valarray.cons]: -

- -
-
-valarray(initializer_list<T> il);
-
-

-Effects: Same as valarray(il.begin(), il.endsize()). -

-
- - - - - -
-

1209. match_results should be moveable

-

Section: 28.10.1 [re.results.const] Status: C++11 - Submitter: Stephan T. Lavavej Opened: 2009-09-15 Last modified: 2015-04-08

-

View other active issues in [re.results.const].

-

View all other issues in [re.results.const].

-

View all issues with C++11 status.

-

Discussion:

-

-In Working Draft -N2914, -match_results lacks a move constructor and move -assignment operator. Because it owns dynamically allocated memory, it -should be moveable. -

- -

-As far as I can tell, this isn't tracked by an active issue yet; Library -Issue 723 doesn't talk about match_results. -

- -

[ -2009-09-21 Daniel provided wording. -]

- - -

[ -2009-11-18: Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-
    -
  1. -

    -Add the following member declarations to 28.10 [re.results]/3: -

    - -
    -// 28.10.1, construct/copy/destroy:
-explicit match_results(const Allocator& a = Allocator());
-match_results(const match_results& m);
-match_results(match_results&& m);
-match_results& operator=(const match_results& m);
-match_results& operator=(match_results&& m);
-~match_results();
-
    -
    2. - -
  2. -

    -Add the following new prototype descriptions to 28.10.1 [re.results.const] -using the table numbering of -N3000 -(referring to the table titled "match_results assignment operator effects"): -

    - -
    -
    -match_results(const match_results& m);
-
    - -

    -4 Effects: Constructs an object of class match_results, as a -copy of m. -

    - -
    -match_results(match_results&& m);
-
    - -
    -

    -5 Effects: Move-constructs an object of class match_results -from m satisfying the same postconditions as Table 131. Additionally -the stored Allocator value is move constructed from m.get_allocator(). -After the initialization of *this sets m to an unspecified but valid -state. -

    - -

    -6 Throws: Nothing if the allocator's move constructor throws nothing. -

    -
    - -
    -match_results& operator=(const match_results& m);
-
    - -

    -7 Effects: Assigns m to *this. The postconditions of this function are -indicated in Table 131. -

    - -
    -match_results& operator=(match_results&& m);
-
    - -
    -

    -8 Effects: Move-assigns m to *this. The postconditions of this -function are indicated in Table 131. After the assignment, m is in -a valid but unspecified state. -

    - -

    -9 Throws: Nothing. -

    -
    -
    -
    3. - -
- - - - - -
-

1210. Iterator reachability should not require a container

-

Section: 24.2 [iterator.requirements] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-09-18 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

View all issues with Resolved status.

-

Discussion:

-

-p6 Iterator requirements 24.2 [iterator.requirements] -

- -

-An iterator j is called reachable from an iterator i if and only if -there is a finite sequence of applications of the expression ++i that -makes i == j. If j is reachable from i, they refer to the same -container. -

- -

-A good example would be stream iterators, which do not refer to a -container. Typically, the end iterator from a range of stream iterators -will compare equal for many such ranges. I suggest striking the second -sentence. -

- -

-An alternative wording might be: -

- -

-If j is reachable from i, and both i and -j are dereferencable iterators, then they refer to the same -range. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

-

-Change 24.2 [iterator.requirements], p6: -

- -

-An iterator j is called reachable from an iterator -i if and only if there is a finite sequence of applications of -the expression ++i that makes i == j. If -j is reachable from i, they refer to the same -container. -

- - - - - -
-

1211. Move iterators should be restricted as input iterators

-

Section: 24.5.3.1 [move.iterator] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-09-18 Last modified: 2015-04-08

-

View all other issues in [move.iterator].

-

View all issues with Resolved status.

-

Discussion:

-

-I contend that while we can support both bidirectional and random access -traversal, the category of a move iterator should never be better than -input_iterator_tag. -

- -

-The contentious point is that you cannot truly have a multipass property -when values are moved from a range. This is contentious if you view a -moved-from object as still holding a valid value within the range. -

- -

-The second reason comes from the Forward Iterator requirements table: -

- -
-

-Forward iterators 24.2.5 [forward.iterators] -

- -

-Table 102 — Forward iterator requirements -

- -

-For expression *a the return type is: -"T& if X is mutable, otherwise const T&" -

-
- -

-There is a similar constraint on a->m. -

- -

-There is no support for rvalue references, nor do I believe their should -be. Again, opinions may vary but either this table or the definition of -move_iterator need updating. -

- -

-Note: this requirement probably need updating anyway if we wish to -support proxy iterators but I am waiting to see a new working paper -before filing that issue. -

- -

[ -2009-10 post-Santa Cruz: -]

- - -

-Move to Open. Howard to put his rationale mentioned above into the issue -as a note. -

- -

[ -2009-10-26 Howard adds: -]

- - -
-

-vector::insert(pos, iter, iter) is significantly more effcient when -iter is a random access iterator, as compared to when it is an -input iterator. -

- -

-When iter is an input iterator, the best algorithm -is to append the inserted range to the end of the vector using -push_back. This may involve several reallocations before the input -range is exhausted. After the append, then one can use std::rotate -to place the inserted range into the correct position in the vector. -

- -

-But when iter is a random access iterator, the best algorithm -is to first compute the size of the range to be inserted (last - first), -do a buffer reallocation if necessary, scoot existing elements in the vector -down to make the "hole", and then insert the new elements directly to their correct -place. -

- -

-The insert-with-random-access-iterators algorithm is considerably more efficient -than the insert-with-input-iterators algorithm -

- -

-Now consider: -

- -
-vector<A> v;
-//  ... build up a large vector of A ...
-vector<A> temp;
-//  ... build up a large temporary vector of A to later be inserted ...
-typedef move_iterator<vector<A>::iterator> MI;
-//  Now insert the temporary elements:
-v.insert(v.begin() + N, MI(temp.begin()), MI(temp.end()));
-
- -

-A major motivation for using move_iterator in the above example is the -expectation that A is cheap to move but expensive to copy. I.e. the -customer is looking for high performance. If we allow vector::insert -to subtract two MI's to get the distance between them, the customer enjoys -substantially better performance, compared to if we say that vector::insert -can not subtract two MI's. -

- -

-I can find no rationale for not giving this performance boost to our customers. -Therefore I am strongly against restricting move_iterator to the -input_iterator_tag category. -

- -

-I believe that the requirement that forward -iterators have a dereference that returns an lvalue reference to cause unacceptable -pessimization. For example vector<bool>::iterator also does not return -a bool& on dereference. Yet I am not aware of a single vendor that -is willing to ship vector<bool>::iterator as an input iterator. -Everyone classifies it as a random access iterator. Not only does this not -cause any problems, it prevents significant performance problems. -

- -
- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

-

-Class template move_iterator 24.5.3.1 [move.iterator] -

- -
-namespace std {
-template <class Iterator>
-class move_iterator {
-public:
- ...
- typedef typename iterator_traits<Iterator>::iterator_category input_iterator_tag iterator_category;
-
- - - - - -
-

1212. result of post-increment/decrement operator

-

Section: 24.2 [iterator.requirements] Status: Resolved - Submitter: Alisdair Meredith Opened: 2009-09-18 Last modified: 2015-04-08

-

View all other issues in [iterator.requirements].

-

View all issues with Resolved status.

-

Discussion:

-

-Forward iterator and bidirectional iterator place different requirements on the result of post-increment/decrement operator. -The same form should be used in each case. -

- -

-Merging row from: -

- -
-Table 102 -- Forward iterator requirements
-Table 103 -- Bidirectional iterator requirements
-
-    r++ : convertible to const X&
-    r-- : convertible to const X&
-    
-    *r++ : T& if X is mutable, otherwise const T&
-    *r-- : convertible to T
-
- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

- - - - - -
-

1214. Insufficient/inconsistent key immutability requirements for associative containers

-

Section: 23.2.4 [associative.reqmts] Status: C++14 - Submitter: Daniel Krügler Opened: 2009-09-20 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Scott Meyers' mentions on a recent posting on c.s.c++ -some arguments that point to an incomplete resolution -of 103 and to an inconsistency of requirements on keys in ordered and -unordered associative -containers: -

- -
-

-1) 103 introduced the term immutable without defining it in a unique manner in -23.2.4 [associative.reqmts]/5: -

- -

-[..] Keys in an associative container are immutable. -

- -

-According to conventional dictionaries immutable is an unconditional way of -saying that something cannot be changed. So without any further explicit -allowance a user always runs into undefined behavior if (s)he attempts -to modify such a key. IMO this was not the intend of the committee to resolve -103 in that way because the comments suggest an interpretation that -should give any user the freedom to modify the key in an explicit way -provided it would not affect the sort order in that container. -

- -

-2) Another observation was that surprisingly no similar 'safety guards' -exists against unintentional key changes for the unordered associative -containers, specifically there is no such requirement as in -23.2.4 [associative.reqmts]/6 that "both iterator and const_iterator are constant -iterators". But the need for such protection against unintentional -changes as well as the constraints in which manner any explicit -changes may be performed are both missing and necessary, because -such changes could potentially change the equivalence of keys that -is measured by the hasher and key_equal. -

- -

-I suggest to fix the unconditional wording involved with "immutable keys" -by at least adding a hint for the reader that users may perform such -changes in an explicit manner and to perform similar wording changes -as 103 did for the ordered associative containers also for the unordered -containers. -

-
- -

[ -2010-03-27 Daniel provides wording. -]

- - -

-This update attempts to provide normative wording that harmonizes the key and -function object constraints of associative and unordered containers. -

- -

[ -2010 Batavia: -]

- - -

-We're uncomfortable with the first agenda item, and we can live with the second agenda -item being applied before or after Madrid. -

- -

[ -2011 Bloomington -]

- - -

-Further discussion persuades us this issue is Ready (and so moved). -We may need a further issue clarifying the notion of key value -vs. key object, as object identity appears to be important -to this wording. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 23.2.4 [associative.reqmts]/2 as indicated: [This ensures that -associative containers make better clear what this "arbitrary" type is, as the -unordered containers do in 23.2.5 [unord.req]/3] -

    - -

    -2 Each associative container is parameterized on Key and an ordering -relation Compare that induces a strict weak ordering (25.4) on elements -of Key. In addition, map and multimap associate an -arbitrary mapped typetype T with the -Key. The object of type Compare is called the comparison -object of a container. -

    -
    2. - -
  2. -

    -Change 23.2.4 [associative.reqmts]/5 as indicated: [This removes the -too strong requirement that keys must not be changed at all and brings this line -in sync with 23.2.5 [unord.req]/7. We take care about the real -constraints by the remaining suggested changes. The rationale provided by LWG -103 didn't really argue why that addition is necessary, and I -believe the remaining additions make it clear that any user changes have strong -restrictions]: -

    - -

    -5 For set and multiset the value type is the same as the key -type. For map and multimap it is equal to pair<const -Key, T>. Keys in an associative container are immutable. -

    -
    3. - -
  3. -

    -Change 23.2.5 [unord.req]/3+4 as indicated: [The current sentence of -p.4 has doesn't say something really new and this whole subclause misses to -define the concepts of the container-specific hasher object and predicate -object. We introduce the term key equality predicate which is -already used in the requirements table. This change does not really correct part -of this issue, but is recommended to better clarify the nomenclature and the -difference between the function objects and the function object types, -which is important, because both can potentially be stateful.] -

    - -
    -

    -3 Each unordered associative container is parameterized by Key, by a -function object type Hash that meets the Hash requirements -(20.2.4) and acts as a hash function for argument values of type Key, -and by a binary predicate Pred that induces an equivalence relation on -values of type Key. Additionally, unordered_map and -unordered_multimap associate an arbitrary mapped type -T with the Key. -

    - -

    -4 The container's object of type Hash - denoted by -hash - is called the hash function of the container. -The container's object of type Pred - denoted by -pred - is called the key equality predicate of the -container.A hash function is a function object that takes a single -argument of type Key and returns a value of type -std::size_t. -

    -
    -
    4. - -
  4. -

    -Change 23.2.5 [unord.req]/5 as indicated: [This adds a similar -safe-guard as the last sentence of 23.2.4 [associative.reqmts]/3] -

    - -

    -5 Two values k1 and k2 of type Key are considered -equivalent if the container's key equality -predicatekey_equal function object returns -true when passed those values. If k1 and k2 are -equivalent, the container's hash function shall return the same value -for both. [Note: thus, when an unordered associative container is -instantiated with a non-default Pred parameter it usually needs a -non-default Hash parameter as well. — end note] For -any two keys k1 and k2 in the same container, calling -pred(k1, k2) shall always return the same value. For any key k -in a container, calling hash(k) shall always return the same -value. -

    -
    5. - -
  5. -

    -After 23.2.5 [unord.req]/7 add the following new paragraph: [This -ensures the same level of compile-time protection that we already require for -associative containers. It is necessary for similar reasons, because any change -in the stored key which would change it's equality relation to others or would -change it's hash value such that it would no longer fall in the same bucket, -would break the container invariants] -

    - -
    -

    -7 For unordered_set and unordered_multiset the value type is -the same as the key type. For unordered_map and -unordered_multimap it is std::pair<const Key, T>. -

    -

    -For unordered containers where the value type is the same as the key type, -both iterator and const_iterator are constant iterators. It is -unspecified whether or not iterator and const_iterator are the -same type. [Note: iterator and const_iterator have -identical semantics in this case, and iterator is convertible to -const_iterator. Users can avoid violating the One Definition Rule by -always using const_iterator in their function parameter lists. — -end note] -

    -
    -
    6. - -
- - - - - - -
-

1215. list::merge with unequal allocators

-

Section: 23.3.5.5 [list.ops] Status: C++11 - Submitter: Pablo Halpern Opened: 2009-09-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In Bellevue (I think), we passed -N2525, -which, among other things, specifies that the behavior of -list::splice is undefined if the allocators of the two lists -being spliced do not compare equal. The same rationale should apply to -list::merge. The intent of list::merge (AFAIK) is to -move nodes from one sorted list into another sorted -list without copying the elements. This is possible only if the -allocators compare equal. -

- - -

Proposed resolution:

-

-Relative to the August 2009 WP, -N2857, -change 23.3.5.5 [list.ops], -paragraphs 22-25 as follows: -

- -
-
-void merge(list&& x);
-template <class Compare> void merge(list&& x, Compare comp);
-
-
-

-Requires: both the list and the argument list shall be sorted -according to operator< or comp. -

-

-Effects: If (&x == this) does nothing; otherwise, merges the -two sorted ranges [begin(), end()) and [x.begin(), -x.end()). The result is a range in which the elements will be -sorted in non-decreasing order according to the ordering defined by -comp; that is, for every iterator i, in the range other than the -first, the condition comp(*i, *(i - 1)) will be -false. -

-

-Remarks: Stable. If (&x != this) the range [x.begin(), x.end()) is -empty after the merge. No elements are copied by this operation. -The behavior is undefined if this->get_allocator() != -x.get_allocator(). -

-

-Complexity: At most size() + x.size() - 1 applications of comp -if (&x != this); otherwise, no applications of comp are performed. If an -exception is thrown other than by a comparison there are no effects. -

-
-
- - - - - -
-

1216. LWG 1066 Incomplete?

-

Section: 18.8.6 [except.nested] Status: C++11 - Submitter: Pete Becker Opened: 2009-09-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-LWG 1066 adds [[noreturn]] to a bunch of things. -It doesn't add it to rethrow_nested(), which seems like an obvious -candidate. I've made the changes indicated in the issue, and haven't -changed rethrow_nested(). -

- -

[ -2009 Santa Cruz: -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

-Add [[noreturn]] to rethrow_nested() in 18.8.6 [except.nested]. -

- - - - - -
-

1218. mutex destructor synchronization

-

Section: 30.4.1 [thread.mutex.requirements] Status: C++11 - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-If an object *o contains a mutex mu and a -correctly-maintained reference count c, is the following code -safe? -

- -
-o->mu.lock();
-bool del = (--(o->c) == 0);
-o->mu.unlock();
-if (del) { delete o; }
-
- -

-If the implementation of mutex::unlock() can touch the mutex's -memory after the moment it becomes free, this wouldn't be safe, and -"Construction and destruction of an object of a Mutex type need not be -thread-safe" 30.4.1 [thread.mutex.requirements] may imply that -it's not safe. Still, it's useful to allow mutexes to guard reference -counts, and if it's not allowed, users are likely to write bugs. -

- -

[ -2009-11-18: Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-
    -
  • -

    -Add a new paragraph after 30.4.1.2.1 [thread.mutex.class] p1: -

    -
    -

    -1 The class mutex provides a non-recursive mutex ... -

    -

    -[Note: After a thread A has called unlock(), releasing -the mutex, it is possible for another thread B to lock the same mutex, -observe that it is no longer in use, unlock and destroy it, before thread -A appears to have returned from its unlock call. Implementations are -required to handle such scenarios correctly, as long as thread A -doesn't access the mutex after the unlock call returns. These cases typically -occur when a reference-counted object contains a mutex that is used to protect -the reference count. — end note] -

    -
    -
    • - -
- - - - - -
-

1220. What does condition_variable wait on?

-

Section: 30.5 [thread.condition] Status: C++11 - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-"Class condition_variable provides a condition variable that can only -wait on an object of type unique_lock" should say "...object of type -unique_lock<mutex>" -

- -

[ -2009-11-06 Howard adds: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - - -

Proposed resolution:

-

-Change 30.5 [thread.condition], p1: -

- -

-Condition variables provide synchronization primitives used to block a -thread until notified by some other thread that some condition is met or -until a system time is reached. Class condition_variable -provides a condition variable that can only wait on an object of type -unique_lock<mutex>, allowing maximum -efficiency on some platforms. Class condition_variable_any -provides a general condition variable that can wait on objects of -user-supplied lock types. -

- - - - - -
-

1221. condition_variable wording

-

Section: 30.5.1 [thread.condition.condvar] Status: C++11 - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar] says: -

- -
-
-~condition_variable();
-
-

-Precondition: There shall be no thread blocked on *this. -[Note: That is, all threads shall have been notified; they may -subsequently block on the lock specified in the wait. Beware that -destroying a condition_variable object while the corresponding -predicate is false is likely to lead to undefined behavior. -— end note] -

-
- -

-The text hasn't introduced the notion of a "corresponding predicate" -yet. -

- -

[ -2010-02-11 Anthony provided wording. -]

- - -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Modify 30.5.1 [thread.condition.condvar]p4 as follows: -

- -
-
~condition_variable();
-

-4 Precondition: There shall be no thread blocked on *this. -[Note: That is, all threads shall have been notified; they may -subsequently block on the lock specified in the wait. Beware that -destroying a condition_variable object while the corresponding -predicate is false is likely to lead to undefined behavior. The user -must take care to ensure that no threads wait on *this once the -destructor has been started, especially when the waiting threads are calling the -wait functions in a loop or using the overloads of wait, -wait_for or wait_until that take a predicate. — -end note] -

-
- - - - - -
-

1222. condition_variable incorrect effects for exception safety

-

Section: 30.5 [thread.condition] Status: C++11 - Submitter: Jeffrey Yasskin Opened: 2009-09-30 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

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-

Discussion:

-

-30.5.1 [thread.condition.condvar] says: -

- -
-
-void wait(unique_lock<mutex>& lock);
-
-
-

...

-

-Effects: -

-
    -
  • ...
    • -
  • -If the function exits via an exception, lock.unlock() shall be -called prior to exiting the function scope. -
    • -
-
-
- -

-Should that be lock.lock()? -

- -

[ -2009-11-17 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

- -

-Change 30.5.1 [thread.condition.condvar] p10: -

- -
-
-void wait(unique_lock<mutex>& lock);
-
-
-

...

-

-Effects: -

-
    -
  • ...
    • -
  • -If the function exits via an exception, lock.unlock() shall be -called prior to exiting the function scope. -
    • -
-
-
- -

-And make a similar change in p16, and in 30.5.2 [thread.condition.condvarany], -p8 and p13. -

- - - - - - -
-

1225. C++0x result_of issue

-

Section: X [func.ret] Status: Resolved - Submitter: Sebastian Gesemann Opened: 2009-10-05 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-I think the text about std::result_of could be a little more precise. -Quoting from -N2960... -

- -
-

-X [func.ret] Function object return types -

- -
-template<class> class result_of;
-
-template<class Fn, class... ArgTypes>
-class result_of<Fn(ArgTypes...)> {
-public:
-  typedef see below type;
-};
-
- -

-Given an rvalue fn of type Fn and values t1, t2, -..., tN of types T1, T2, ... TN in ArgTypes -respectivly, the type member is the result type of the -expression fn(t1,t2,...,tN). the values ti are lvalues -when the corresponding type Ti is an lvalue-reference type, and -rvalues otherwise. -

-
- -

-This text doesn't seem to consider lvalue reference types for Fn. -Also, it's not clear whether this class template can be used for -"SFINAE" like std::enable_if. Example: -

- -
-template<typename Fn, typename... Args>
-typename std::result_of<Fn(Args...)>::type
-apply(Fn && fn, Args && ...args)
-{
-  // Fn may be an lvalue reference, too
-  return std::forward<Fn>(fn)(std::forward<Args>(args)...);
-}
-
- -

-Either std::result_of<...> can be instantiated and simply may not have -a typedef "type" (-->SFINAE) or instantiating the class template for -some type combinations will be a "hard" compile-time error. -

- -

[ -2010-02-14 Daniel adds: -]

- - -

-This issue should be considered resolved by 1255 and 1270. The wish to change result_of into a compiler-support -trait was beyond the actual intention of the submitter Sebastian. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved, rationale added below. -]

- - - - -

Rationale:

-

-Solved by 1270. -

- - -

Proposed resolution:

- -

[ -These changes will require compiler support -]

- - -

-Change X [func.ret]: -

- -
-template<class> class result_of; // undefined
-
-template<class Fn, class... ArgTypes>
-class result_of<Fn(ArgTypes...)> {
-public:
-  typedef see below type;
-};
-
- -

-Given an rvalue fn of type Fn and values t1, t2, -..., tN of types T1, T2, ... TN in ArgTypes -respectivly, the type member is the result type of the -expression fn(t1,t2,...,tN). the values ti are lvalues -when the corresponding type Ti is an lvalue-reference type, and -rvalues otherwise. -

- -

-The class template result_of shall meet the requirements of a -TransformationTrait: Given the types Fn, T1, T2, ..., TN every -template specialization result_of<Fn(T1,T2,...,TN)> shall define the -member typedef type equivalent to decltype(RE) if and only if -the expression RE -

- -

-value<Fn>() ( value<T1>(), value<T2>(), ... value<TN>()  )
-
- -

-would be well-formed. Otherwise, there shall be no member typedef -type defined. -

- -
- -

[ -The value<> helper function is a utility Daniel Krügler -proposed in -N2958. -]

- - - - - - -
-

1226. Incomplete changes of #890

-

Section: 30.6.2 [futures.errors] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-10-05 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-Defect issue 890 overlooked to adapt the future_category from -30.6.1 [futures.overview] and 30.6.2 [futures.errors]: -

- -
-extern const error_category* const future_category;
-
- -

-which should be similarly transformed into function form. -

- -

[ -2009-10-27 Howard: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -2009-11-11 Daniel adds: -]

- - -
-

-I just observe that the proposed resolution of this issue -is incomplete and needs to reworded. The problem is that the -corresponding declarations -

- -
-constexpr error_code make_error_code(future_errc e);
-constexpr error_condition make_error_condition(future_errc e);
-
- -

-as constexpr functions are incompatible to the requirements of constexpr -functions given their specified implementation. Note that the incompatibility -is not a result of the modifications proposed by the issue resolution, -but already existed within the -N2960 -state where we have -

- -
-extern const error_category* const future_category;
-
- -

-combined with -

- -
-constexpr error_code make_error_code(future_errc e);
-
-

-3 Returns: error_code(static_cast<int>(e), *future_category). -

- -
-constexpr error_code make_error_condition(future_errc e);
-
-

-4 Returns: error_condition(static_cast<int>(e), *future_category). -

-
- -

-Neither is any of the constructors of error_code and error_condition -constexpr, nor does the expression *future_category satisfy the -requirements for a constant expression (5.20 [expr.const]/2 bullet 6 in -N3000). -

- -

-The simple solution is just to remove the constexpr qualifiers for both -functions, which makes sense, because none of the remaining make_error_* -overloads in the library is constexpr. One might consider to realize that -those make_* functions could satisfy the constexpr requirements, but this -looks not like an easy task to me, because it would need to rely on a not -yet existing language feature. If such a change is wanted, a new issue -should be opened after the language extension approval (if at all) [1]. -

- -

-If no-one complaints I would like to ask Howard to add the following -modifications to this issue, alternatively a new issue could be opened but I -don't know what the best solution is that would cause as little overhead -as possible. -

-

-What-ever the route is, the following is my proposed resolution for this issue -interaction part of the story: -

- -
-

-In 30.6.1 [futures.overview]/1, Header <future> synopsis and -in 30.6.2 [futures.errors]/3+4 -change as indicated: -

- -
-constexpr error_code make_error_code(future_errc e);
-constexpr error_condition make_error_condition(future_errc e);
-
-
- -

-[1] Let me add that we have a related NAD issue here: 832 -so the chances for realization are little IMO. -

- -

[ -Howard: I've updated the proposed wording as Daniel suggests and set to Review. -]

- -
- -

[ -2009-11-13 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-
    -
  1. -

    -Change in 30.6.1 [futures.overview], header <future> synopsis: -

    - -
    -extern const error_category&* const future_category();
-
    -
    2. - -
  2. -

    -In 30.6.1 [futures.overview]/1, Header <future> synopsis -change as indicated: -

    - -
    -constexpr error_code make_error_code(future_errc e);
-constexpr error_condition make_error_condition(future_errc e);
-
    -
    3. - -
  3. -

    -Change in 30.6.2 [futures.errors]: -

    - -
    -extern const error_category&* const future_category();
-
    - -
    -

    -1- future_category shall point to a statically initialized object -of a type derived from class error_category. -

    -

    -1- Returns: A reference to an object of a type -derived from class error_category. -

    -
    - -
    -constexpr error_code make_error_code(future_errc e);
-
    - -

    -3 Returns: error_code(static_cast<int>(e), -*future_category()). -

    - -
    -constexpr error_codecondition make_error_condition(future_errc e);
-
    - -

    -4 Returns: error_condition(static_cast<int>(e), -*future_category()). -

    -
    -
    4. -
- - - - - -
-

1227. <bitset> synopsis overspecified

-

Section: 20.6 [template.bitset] Status: C++11 - Submitter: Bo Persson Opened: 2009-10-05 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The resolutions to some library defect reports, like 1178 -requires that #includes in each synopsis should be taken -literally. This means that the <bitset> header now -must include <stdexcept>, even though none of the -exceptions are mentioned in the <bitset> header. -

-

-Many other classes are required to throw exceptions like -invalid_argument and out_of_range, without explicitly -including <stdexcept> in their synopsis. It is totally -possible for implementations to throw the needed exceptions from utility -functions, whose implementations are not visible in the headers. -

-

-I propose that <stdexcept> is removed from the -<bitset> header. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

-Change 20.6 [template.bitset]: -

- -
-#include <cstddef>        // for size_t
-#include <string>
-#include <stdexcept>      // for invalid_argument,
-                          // out_of_range, overflow_error
-#include <iosfwd>         // for istream, ostream
-namespace std {
-...
-
- - - - - -
-

1229. error_code operator= typo

-

Section: 19.5.2.3 [syserr.errcode.modifiers] Status: Resolved - Submitter: Stephan T. Lavavej Opened: 2009-10-08 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-N2960 -19.5.2.1 [syserr.errcode.overview] and 19.5.2.3 [syserr.errcode.modifiers] say: -

- -
 
-template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type&
-    operator=(ErrorCodeEnum e);
-
- -

-They should say: -

- -
 
-template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value, error_code>::type&
-    operator=(ErrorCodeEnum e);
-
- -

-Or (I prefer this form): -

- -
 
-template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value, error_code&>::type
-    operator=(ErrorCodeEnum e);
-
- -

-This is because enable_if is declared as (20.10.7.6 [meta.trans.other]): -

- -
 
-template <bool B, class T = void> struct enable_if;
-
- -

-So, the current wording makes operator= return -void&, which is not good. -

- -

-19.5.2.3 [syserr.errcode.modifiers]/4 says -

- -

-Returns: *this. -

-

-which is correct. -

- -

-Additionally, -

- -

-19.5.3.1 [syserr.errcondition.overview]/1 says: -

- -
 
-template<typename ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>, error_code>::type &
-    operator=( ErrorConditionEnum e );
-
- -

-Which contains several problems (typename versus class -inconsistency, lack of ::value, error_code instead of -error_condition), while 19.5.3.3 [syserr.errcondition.modifiers] says: -

- -
 
-template <class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value>::type&
-    operator=(ErrorConditionEnum e);
-
- -

-Which returns void&. They should both say: -

- -
 
-template <class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value, 
-  error_condition>::type&
-    operator=(ErrorConditionEnum e);
-
- -

-Or (again, I prefer this form): -

- -
 
-template <class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value, 
-  error_condition&>::type
-    operator=(ErrorConditionEnum e);
-
- -

-Additionally, 19.5.3.3 [syserr.errcondition.modifiers] lacks a -"Returns: *this." paragraph, which is presumably -necessary. -

- -

[ -2009-10-18 Beman adds: -]

- - -

-The proposed resolution for issue 1237 makes this issue -moot, so it should become NAD. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-NADResolved, solved by 1237. -

- - - -

Proposed resolution:

- -

-Change 19.5.2.1 [syserr.errcode.overview] and 19.5.2.3 [syserr.errcode.modifiers]: -

- -
-template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value, 
-  error_code&>::type&
-    operator=(ErrorCodeEnum e);
-
- -

-Change 19.5.3.1 [syserr.errcondition.overview]: -

- -
-template<typename class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value, 
-  error_conditionde&>::type &
-    operator=( ErrorConditionEnum e );
-
- -

-Change 19.5.3.3 [syserr.errcondition.modifiers]: -

- -
-template <class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value, 
-  error_condition&>::type&
-    operator=(ErrorConditionEnum e);
-
-
-

-Postcondition: *this == make_error_condition(e). -

-

-Returns: *this. -

-

-Throws: Nothing. -

-
-
- - - - - - -
-

1231. weak_ptr comparisons incompletely resolved

-

Section: 20.8.2.3.5 [util.smartptr.weak.obs] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-10-10 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.weak.obs].

-

View all issues with C++11 status.

-

Discussion:

-

-The -n2637 -paper suggested several updates of the ordering semantics of shared_ptr -and weak_ptr, among those the explicit comparison operators of weak_ptr were -removed/deleted, instead a corresponding functor owner_less was added. -The problem is that -n2637 -did not clearly enough specify, how the previous wording parts describing -the comparison semantics of weak_ptr should be removed. -

- -

[ -2009-11-06 Howard adds: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Change 20.8.2.3 [util.smartptr.weak]/2 as described, the intention is to fix -the now no longer valid requirement that weak_ptr is LessComparable -[Note the deleted comma]: -

    - -

    -Specializations of weak_ptr shall be CopyConstructible, -and CopyAssignable, and LessThanComparable, -allowing their use in standard containers. -

    -
    2. - -
  2. -

    -In 20.8.2.3.5 [util.smartptr.weak.obs] remove the paragraphs 9-11 including prototype: -

    - -

    -template<class T, class U> bool operator<(const weak_ptr<T>& a, const weak_ptr<U>& b); - -

    -Returns: an unspecified value such that -

    -
      -
    • -operator< is a strict weak ordering as described in 25.4; -
      • -
    • -under the equivalence relation defined by operator<, !(a -< b) && !(b < a), two weak_ptr instances are -equivalent if and only if they share ownership or are both empty. -
      • -
    - -

    -Throws: nothing. -

    - -

    -[Note: Allows weak_ptr objects to be used as keys in associative -containers. — end note] -

    -
    -
    3. -
- - - - - -
-

1234. "Do the right thing" and NULL

-

Section: 23.2.3 [sequence.reqmts] Status: C++11 - Submitter: Matt Austern Opened: 2009-10-09 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with C++11 status.

-

Discussion:

-

-On g++ 4.2.4 (x86_64-linux-gnu), the following file gives a compile error: -

- -
-#include <vector>
-void foo() { std::vector<int*> v(500L, NULL); }
-
- -

-Is this supposed to work? -

- -

-The issue: if NULL happens to be defined as 0L, this is an invocation of -the constructor with two arguments of the same integral type. -23.2.3 [sequence.reqmts]/14 -(N3035) -says that this will behave as if the overloaded constructor -

- -
-X(size_type, const value_type& = value_type(),
-  const allocator_type& = allocator_type())
-
- -

-were called instead, with the arguments -static_cast<size_type>(first), last and -alloc, respectively. However, it does not say whether this -actually means invoking that constructor with the exact textual form of -the arguments as supplied by the user, or whether the standard permits -an implementation to invoke that constructor with variables of the same -type and value as what the user passed in. In most cases this is a -distinction without a difference. In this particular case it does make a -difference, since one of those things is a null pointer constant and the -other is not. -

- -

-Note that an implementation based on forwarding functions will use the -latter interpretation. -

- -

[ -2010 Pittsburgh: Moved to Open. -]

- - -

[ -2010-03-19 Daniel provides wording. -]

- - -
-
    -
  • -Adapts the numbering used in the discussion to the recent working paper -N3035. -
    • - -
  • -Proposes a resolution that requires implementations to use sfinae-like means to -possibly filter away the too generic template c'tor. In fact this resolution is -equivalent to that used for the pair-NULL problem (811), -the only difference is, that issue 1234 was already a C++03 problem. -
    • -
- -

-This issue can be considered as a refinement of 438. -

- -
- -

[ -Post-Rapperswil -]

- - -

-Wording was verified to match with the most recent WP. Jonathan Wakely and Alberto Barbati observed that the current -WP has a defect that should be fixed here as well: The functions signatures fx1 and fx3 are -incorrectly referring to iterator instead of const_iterator. -

- -

-Moved to Tentatively Ready with revised wording after 7 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- - -

-Change 23.2.3 [sequence.reqmts]/14+15 as indicated: -

- -
-

-14 For every sequence container defined in this Clause and in Clause 21: -

- -
    -
  • -

    -If the constructor -

    - -
    -template <class InputIterator>
-X(InputIterator first, InputIterator last,
-  const allocator_type& alloc = allocator_type())
-
    - -

    -is called with a type InputIterator that does not qualify as an input -iterator, then the constructor shall not participate in overload -resolution.will behave as if the overloaded constructor: -

    - -
    
-X(size_type, const value_type& = value_type(),
-  const allocator_type& = allocator_type())
-
    - -

    -were called instead, with the arguments static_cast<size_type>(first), -last and alloc, respectively. -

    -
    • - -
  • - -

    -If the member functions of the forms: -

    - -
    -template <class InputIterator> // such as insert()
-rt fx1(const_iterator p, InputIterator first, InputIterator last);
-
-template <class InputIterator> // such as append(), assign()
-rt fx2(InputIterator first, InputIterator last);
-
-template <class InputIterator> // such as replace()
-rt fx3(const_iterator i1, const_iterator i2, InputIterator first, InputIterator last);
-
    - -

    -are called with a type InputIterator that does not qualify as an input -iterator, then these functions shall not participate in overload -resolution.will behave as if the overloaded member functions: -

    - -
    -rt fx1(iterator, size_type, const value_type&);
-
-rt fx2(size_type, const value_type&);
-
-rt fx3(iterator, iterator, size_type, const value_type&);
-
    - -

    -were called instead, with the same arguments. -

    -
    • - -
- -

-15 In the previous paragraph the alternative binding will fail if first -is not implicitly convertible to X::size_type or if last is -not implicitly convertible to X::value_type. -

-
- - - - - - -
-

1237. Constrained error_code/error_condition members

-

Section: 19.5 [syserr] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-10-14 Last modified: 2015-04-08

-

View all other issues in [syserr].

-

View all issues with C++11 status.

-

Discussion:

-

-I'm just reflecting on the now SFINAE-constrained constructors -and assignment operators of error_code and error_condition: -

-

-These are the only library components that are pro-actively -announcing that they are using std::enable_if as constraining tool, -which has IMO several disadvantages: -

- -
    -
  1. -

    -With the availability of template default arguments and -decltype, using enable_if in the C++0x standard library, seems -unnecessary restricting implementation freedom. E.g. there -should be no need for a useless specification of a dummy -default function argument, which only confuses the reader. -A more reasonable implementation could e.g. be -

    - -
    -template <class ErrorCodeEnum
- class = typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type>
-error_code(ErrorCodeEnum e);
-
    - -

    -As currently specified, the function signatures are so unreadable, -that errors quite easily happen, see e.g. 1229. -

    -
    2. - -
  2. -

    -We have a lot of constrained functions in other places, that -now have a standard phrase that is easily understandable: -

    - -

    -Remarks: This constructor/function shall participate in overload -resolution if and only if X. -

    - -

    -where X describes the condition. Why should these components deviate? -

    -
    3. - -
  3. -

    -If enable_if would not be explicitly specified, the standard library -is much better prepared for the future. It would also be possible, that -libraries with partial support for not-yet-standard-concepts could provide -a much better diagnostic as is possible with enable_if. This again -would allow for experimental concept implementations in the wild, -which as a result would make concept standardization a much more -natural thing, similar to the way as templates were standardized -in C++. -

    - -

    -In summary: I consider it as a library defect that error_code and -error_condition explicitly require a dependency to enable_if and -do limit implementation freedom and I volunteer to prepare a -corresponding resolution. -

    -
    4. -
- -

[ -2009-10-18 Beman adds: -]

- - -

-I support this proposed resolution, and thank Daniel for writing it up. -

- -

[ -2009-10 Santa Cruz: -]

- - -

-Moved to Ready. -

- - - -

Proposed resolution:

-

[ -Should this resolution be accepted, I recommend to resolve 1229 as NAD -]

- - -
    -
  1. -

    -In 19.5.2.1 [syserr.errcode.overview]/1, class error_code, -change as indicated: -

    - -
    -// 19.5.2.2 constructors:
-error_code();
-error_code(int val, const error_category& cat);
-template <class ErrorCodeEnum>
-  error_code(ErrorCodeEnum e,
-    typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type * = 0);
-
-// 19.5.2.3 modifiers:
-void assign(int val, const error_category& cat);
-template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::typeerror_code&
-    operator=(ErrorCodeEnum e);
-void clear();
-
    -
    2. - -
  2. -

    -Change 19.5.2.2 [syserr.errcode.constructors] around the prototype before p. 7: -

    - -
    -template <class ErrorCodeEnum>
-error_code(ErrorCodeEnum e,
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type * = 0);
-
    -
    -

    -Remarks: This constructor shall not participate in overload -resolution, unless -is_error_code_enum<ErrorCodeEnum>::value == true. -

    -
    -
    -
    3. - -
  3. -

    -Change 19.5.2.3 [syserr.errcode.modifiers] around the prototype before p. 3: -

    - -
    -template <class ErrorCodeEnum>
-  typename enable_if<is_error_code_enum<ErrorCodeEnum>::value>::typeerror_code&
-    operator=(ErrorCodeEnum e);
-
    - -

    -Remarks: This operator shall not participate in overload resolution, unless -is_error_code_enum<ErrorCodeEnum>::value == true. -

    -
    -
    4. - -
  4. -

    -In 19.5.3.1 [syserr.errcondition.overview]/1, class error_condition, change -as indicated: -

    - -
    -// 19.5.3.2 constructors:
-error_condition();
-error_condition(int val, const error_category& cat);
-template <class ErrorConditionEnum>
-  error_condition(ErrorConditionEnum e,
-    typename enable_if<is_error_condition_enum<ErrorConditionEnum>::type* = 0);
-
-// 19.5.3.3 modifiers:
-void assign(int val, const error_category& cat);
-template<typenameclass ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>, error_code>::typeerror_condition &
-    operator=( ErrorConditionEnum e );
-void clear();
-
    -
    5. - -
  5. -

    -Change 19.5.3.2 [syserr.errcondition.constructors] around the -prototype before p. 7: -

    - -
    -template <class ErrorConditionEnum>
-  error_condition(ErrorConditionEnum e,
-    typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value>::type* = 0);
-
    -

    -Remarks: This constructor shall not participate in overload -resolution, unless -is_error_condition_enum<ErrorConditionEnum>::value == true. -

    -
    -
    6. - -
  6. -

    -Change 19.5.3.3 [syserr.errcondition.modifiers] around the -prototype before p. 3: -

    - -
    -template <class ErrorConditionEnum>
-  typename enable_if<is_error_condition_enum<ErrorConditionEnum>::value>::typeerror_condition&
-    operator=(ErrorConditionEnum e);
-
    - -
    -

    -Remarks: This operator shall not participate in overload resolution, unless -is_error_condition_enum<ErrorConditionEnum>::value == true. -

    - -

    -Postcondition: *this == make_error_condition(e). -

    - -

    -Returns: *this -

    -
    -
    - -
    7. -
- - - - - - -
-

1240. Deleted comparison functions of std::function not needed

-

Section: 20.9.12.2 [func.wrap.func] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-10-18 Last modified: 2015-04-08

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

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-

Discussion:

-

-The class template std::function contains the following member -declarations: -

- -
-// deleted overloads close possible hole in the type system
-template<class R2, class... ArgTypes2>
-  bool operator==(const function<R2(ArgTypes2...)>&) = delete;
-template<class R2, class... ArgTypes2>
-  bool operator!=(const function<R2(ArgTypes2...)>&) = delete;
-
- -

-The leading comment here is part of the history of std::function, which -was introduced with -N1402. -During that time no explicit conversion functions existed, and the -"safe-bool" idiom (based on pointers-to-member) was a popular -technique. The only disadvantage of this idiom was that given two -objects f1 and f2 of type std::function the expression -

- -
-f1 == f2;
-
- -

-was well-formed, just because the built-in operator== for pointer to member -was considered after a single user-defined conversion. To fix this, an -overload set of undefined comparison functions was added, -such that overload resolution would prefer those ending up in a linkage error. -The new language facility of deleted functions provided a much better -diagnostic mechanism to fix this issue. -

- -

-The central point of this issue is, that with the replacement of the -safe-bool idiom by explicit conversion to bool the original "hole in the -type system" does no longer exist and therefore the comment is wrong and -the superfluous function definitions should be removed as well. An -explicit conversion function is considered in direct-initialization -situations only, which indirectly contain the so-called "contextual -conversion to bool" (4 [conv]/3). These conversions are not considered for -== or != as defined by the core language. -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-In 20.9.12.2 [func.wrap.func]/1, class function change as indicated: -

- -
-// 20.7.15.2.3, function capacity:
-explicit operator bool() const;
-
-// deleted overloads close possible hole in the type system
-template<class R2, class... ArgTypes2>
-  bool operator==(const function<R2(ArgTypes2...)>&) = delete;
-template<class R2, class... ArgTypes2>
-  bool operator!=(const function<R2(ArgTypes2...)>&) = delete;
-
- - - - - -
-

1241. unique_copy needs to require EquivalenceRelation

-

Section: 25.3.9 [alg.unique] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-10-17 Last modified: 2015-04-08

-

View all other issues in [alg.unique].

-

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-

Discussion:

-

-A lot of fixes were silently applied during concept-time and we should -not lose them again. The Requires clause of 25.3.9 [alg.unique]/5 -doesn't mention that == and the predicate need to satisfy an -EquivalenceRelation, as it is correctly said for unique. -This was intentionally fixed during conceptification, were we had: -

- -
-template<InputIterator InIter, class OutIter>
-  requires OutputIterator<OutIter, RvalueOf<InIter::value_type>::type>
-        && EqualityComparable<InIter::value_type>
-        && HasAssign<InIter::value_type, InIter::reference>
-        && Constructible<InIter::value_type, InIter::reference>
-  OutIter unique_copy(InIter first, InIter last, OutIter result);
-
-template<InputIterator InIter, class OutIter,
-         EquivalenceRelation<auto, InIter::value_type> Pred>
-  requires OutputIterator<OutIter, RvalueOf<InIter::value_type>::type>
-        && HasAssign<InIter::value_type, InIter::reference>
-        && Constructible<InIter::value_type, InIter::reference>
-        && CopyConstructible<Pred>
-  OutIter unique_copy(InIter first, InIter last, OutIter result, Pred pred);
-
- -

-Note that EqualityComparable implied an equivalence relation. -

- -

[ -N.B. adjacent_find was also specified to require -EquivalenceRelation, but that was considered as a defect in -concepts, see 1000 -]

- - -

[ -2009-10-31 Howard adds: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- - - -

Proposed resolution:

-

-Change 25.3.9 [alg.unique]/5 as indicated: -

- -
-template<class InputIterator, class OutputIterator>
-  OutputIterator
-    unique_copy(InputIterator first, InputIterator last, OutputIterator result);
-
-template<class InputIterator, class OutputIterator, class BinaryPredicate>
-  OutputIterator
-    unique_copy(InputIterator first, InputIterator last,
-                OutputIterator result, BinaryPredicate pred);
-
-

-Requires: The comparison function shall be an equivalence -relation. The ranges [first,last) and -[result,result+(last-first)) shall not overlap. The expression -*result = *first shall be valid. If neither -InputIterator nor OutputIterator meets the -requirements of forward iterator then the value type of -InputIterator shall be CopyConstructible (34) and -CopyAssignable (table 36). Otherwise CopyConstructible -is not required. -

-
- - - - - -
-

1244. wait_*() in *future for synchronous functions

-

Section: 30.6 [futures] Status: Resolved - Submitter: Detlef Vollmann Opened: 2009-10-22 Last modified: 2015-04-08

-

View all other issues in [futures].

-

View all issues with Resolved status.

-

Discussion:

-

-With the addition of async(), a future might be -associated with a function that is not running in a different thread but -is stored to by run synchronously on the get() call. It's not -clear what the wait() functions should do in this case. -

- -

-Suggested resolution: -

- -

-Throw an exception. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

- - - - - -
-

1245. std::hash<string> & co

-

Section: 20.9.13 [unord.hash] Status: C++11 - Submitter: Paolo Carlini Opened: 2009-10-22 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

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-

Discussion:

-

-In 20.9.13 [unord.hash], operator() is specified as -taking the argument by value. Moreover, it is said that operator() shall -not throw exceptions. -

- -

-However, for the specializations for class types, like string, -wstring, etc, the former requirement seems suboptimal from the -performance point of view (a specific PR has been filed about this in the GCC Bugzilla) -and, together with the latter requirement, hard if not impossible to -fulfill. It looks like pass by const reference should be allowed in such -cases. -

- -

[ -2009-11-18: Ganesh updates wording. -]

- - -

-I've removed the list of types for which hash shall be instantiated -because it's already explicit in the synopsis of header -<functional> in 20.9 [function.objects]/2. -

- -

[ -2009-11-18: Original wording here: -]

- - -
-

-Add to 20.9.13 [unord.hash]/2: -

- -
-
-namespace std {
-  template <class T>
-  struct hash : public std::unary_function<T, std::size_t> {
-    std::size_t operator()(T val) const;
-  };
-}
-
- -

-The return value of operator() is unspecified, except that -equal arguments shall yield the same result. operator() shall -not throw exceptions. It is also unspecified whether -operator() of std::hash specializations for class -types takes its argument by value or const reference. -

-
-
- -

[ -2009-11-19 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2009-11-24 Ville Opens: -]

- - -

-I have received community requests to ask for this issue to be reopened. -Some users feel that mandating the inheritance is overly constraining. -

- -

[ -2010-01-31 Alisdair: related to 978 and 1182. -]

- - -

[ -2010-02-07 Proposed resolution updated by Beman, Daniel and Ganesh. -]

- - -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

Insert a new subclause either before or after the current 17.6.3.5 [allocator.requirements]:

-
- -

Hash Requirements [hash.requirements]

- -

This subclause defines the named requirement Hash, - used in several clauses of the C++ standard library. A type H meets the Hash requirement if

- -
    -
  • - -

    it is a function object type (20.9 [function.objects]).

    - -
    • -
  • - -

    it satisfies the requirements of CopyConstructible, and - Destructible (17.6.3.1 [utility.arg.requirements]),

    - -
    • -
  • - -

    the expressions shown in the following table are valid and have the - indicated semantics, and

    - -
    • -
  • - -

    it satisfies all other requirements of this subclause.

    - -
    • -
- -

Given Key is an argument type for function objects of - type H, in the table below h is a value of type (possibly const) - H, u is an lvalue of type Key,  and - k - is a value of a type convertible to (possibly const) Key:

- - - - - - - - - - - - - - - - - - -
Table ? — Hash requirements
ExpressionReturn typeRequirement
h(k)size_tShall not throw exceptions. The value returned shall depend only on -the argument k. [Note: Thus all evaluations of the expression - h(k) with the - same value for k yield the same result. — end note] [Note: - For t1 and t2 of different values, the probability that - h(t1) - and h(t2) compare equal should be very small, approaching (1.0/numeric_limits<size_t>::max()). - — end note] Comment - (not to go in WP): The wording for the second note is based on a similar - note in 22.4.4.1.2 [locale.collate.virtuals]/3
h(u)size_tShall not modify u.
- -
- -

Change 20.9.13 [unord.hash] as indicated: -

-
-

1 The unordered associative containers defined in Clause 23.5 [unord] use - specializations of the class template hash as the default - hash function. For all object types T for which there exists a - specialization hash<T>, the instantiation hash<T> shall:

-
    -
  • satisfy the Hash requirements([hash.requirements]), with T as the - function call argument type, the - DefaultConstructible requirements ([defaultconstructible]), the CopyAssignable - requirements ([copyassignable]), and the - Swappable requirements ([swappable]), -
    • -
  • provide two nested types result_type and argument_type which shall - be synonyms for size_t and T, respectively,
    • -
  • satisfy the - requirement that if k1 == k2 is true, h(k1) == h(k2) - is true, where h is an object of type hash<T>, and - k1, k2 are objects of type T.
    • -
-

This class template is only required to be instantiable - for integer types (3.9.1 [basic.fundamental]), floating-point types (3.9.1 [basic.fundamental]), - pointer types (8.3.1 [dcl.ptr]), and std::string, std::u16string, - std::u32string, std::wstring, std::error_code, - std::thread::id, std::bitset, and std::vector<bool>.

-
- 
namespace std {
-  template <class T>
-  struct hash : public std::unary_function<T, std::size_t> {
-    std::size_t operator()(T val) const;
-  };
-}
-
-

2 The return value of operator() is unspecified, except that - equal arguments shall yield the same result. operator() shall not - throw exceptions.

- -
- -

Change Unordered associative containers 23.2.5 [unord.req] as indicated:

-
-

Each unordered associative container is parameterized by Key, by a - function object type Hash([hash.requirements]) that acts as a hash - function for argument values of type Key, - and by a binary predicate Pred that induces an equivalence relation - on values of type Key. Additionally, unordered_map and - unordered_multimap associate an arbitrary mapped type T with the - Key.

-

A hash function is a function object that takes a single argument of type - Key and returns a value of type std::size_t.

-

Two values k1 and k2 of type Key are considered -equal if the container's equality function object returns true when passed those -values. If k1 and k2 are equal, the hash function shall return -the same value for both. [Note: Thus supplying a non-default Pred -parameter usually implies the need to supply a non-default Hash -parameter. — end note]

- -
- - - - - - -
-

1247. auto_ptr is overspecified

-

Section: X [auto.ptr] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-10-24 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-This issue is extracted as the ongoing point-of-interest from earlier -issue 463. -

- -

-auto_ptr is overspecified as the auto_ptr_ref -implementation detail is formally specified, and the technique is -observable so workarounds for compiler defects can cause a working -implementation of the primary auto_ptr template become -non-conforming. -

- -

-auto_ptr_ref is a documentation aid to describe a possible -mechanism to implement the class. It should be marked exposition only, -as per similar classes, e.g., istreambuf_iterator::proxy -

- -

[ -2009-10-25 Daniel adds: -]

- - -
-

-I wonder, whether the revised wording shouldn't be as straight as -for istream_buf by adding one further sentence: -

- -

-An implementation is permitted to provide equivalent functionality without -providing a class with this name. -

-
- -

[ -2009-11-06 Alisdair adds Daniel's suggestion to the proposed wording. -]

- - -

[ -2009-11-06 Howard moves issue to Review. -]

- - -

[ -2009-11-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Add the term "exposition only" in the following two places: -

- -

-Ammend X [auto.ptr]p2: -

- -
-

-The exposition only class Ttemplate auto_ptr_ref -holds a reference to an auto_ptr. It is used by the -auto_ptr conversions to allow auto_ptr objects to be -passed to and returned from functions. -An implementation is permitted to provide equivalent functionality -without providing a class with this name. -

- -
-namespace std {
- template <class Y> struct auto_ptr_ref { }; // exposition only
-
-
- - - - - -
-

1248. Equality comparison for unordered containers

-

Section: 23.5 [unord] Status: Resolved - Submitter: Herb Sutter Opened: 2009-10-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-See -N2986. -

- -

[ -2010-01-22 Alisdair Opens. -]

- - -

[ -2010-01-24 Alisdair provides wording. -]

- - -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3068. -

- - -

Proposed resolution:

-

-Apply paper -N2986. -

- - - - - -
-

1249. basic_ios default ctor

-

Section: 27.5.5.2 [basic.ios.cons] Status: C++11 - Submitter: Martin Sebor Opened: 2009-10-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The basic_ios default ctor is required to leave the objects members -uninitialized (see below). The paragraph says the object must be -initialized by calling basic_ios::init() before it's destroyed but -I can't find a requirement that it be initialized before calling -any of the class other member functions. Am I not looking in the -right place or that an issue? -

- -

[ -2009-10-25 Daniel adds: -]

- - -
-

-I agree, that your wording makes that clearer, but suggest to write -

- -

-... calling basic_ios::init() before ... -

- -

-Doing so, I recommend to adapt that of ios_base(); as well, where -we have: -

- -

-Effects: Each ios_base member has an indeterminate value -after construction. These members shall be initialized by calling -basic_ios::init. If an ios_base object is destroyed -before these initializations have taken place, the behavior is -undefined. -

-
- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 27.5.3.7 [ios.base.cons] p1: -

- -
-ios_base();
-
-

-Effects: Each ios_base member has an indeterminate value -after construction. These The object's members shall be initialized by calling -basic_ios::init before the object's first use or before - it is destroyed, whichever comes first; otherwise the behavior - is undefined.. If an ios_base object is destroyed -before these initializations have taken place, the behavior is -undefined. -

-
- -

-Change 27.5.5.2 [basic.ios.cons] p2: -

- -
-basic_ios();
-
-

-Effects: Constructs an object of class basic_ios -(27.5.2.7) leaving its member objects uninitialized. The object shall be -initialized by calling its -basic_ios::init before its first -use or before it is destroyed, whichever comes first; otherwise the -behavior is undefined. member function. If it is destroyed -before it has been initialized the behavior is undefined. -

-
- - - - - -
-

1250. <bitset> still overspecified

-

Section: 20.6 [template.bitset] Status: C++11 - Submitter: Martin Sebor Opened: 2009-10-29 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Issue 1227 — <bitset> synopsis overspecified makes the observation -that std::bitset, and in fact the whole library, may be implemented -without needing to #include <stdexcept> in any library header. The -proposed resolution removes the #include <stdexcept> directive from -the header. -

- -

-I'd like to add that the <bitset> header (as well as the rest of -the library) has also been implemented without #including the -<cstddef> header in any library header. In the case of std::bitset, -the template is fully usable (i.e., it may be instantiated and all -its member functions may be used) without ever mentioning size_t. -In addition, just like no library header except for <bitset> -#includes <stdexcept> in its synopsis, no header but <bitset> -#includes <cstddef> either. -

- -

-Thus I suggest that the #include <cstddef> directive be similarly -removed from the synopsis of <bitset>. -

- -

[ -2010-02-08 Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Change 20.6 [template.bitset]: -

- -
-#include <cstddef>        // for size_t
-#include <string>
-#include <iosfwd>         // for istream, ostream
-namespace std {
-...
-
- - - - - -
-

1252. wbuffer_convert::state_type inconsistency

-

Section: 22.3.3.2.3 [conversions.buffer] Status: C++11 - Submitter: Bo Persson Opened: 2009-10-21 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The synopsis for wbuffer_convert 22.3.3.2.3 [conversions.buffer]/2 contains -

- -
-typedef typename Tr::state_type   state_type; 
-
- -

-making state_type a synonym for (possibly) some -char_traits<x>::state_type. -

- -

-However, in paragraph 9 of the same section, we have -

- -
-typedef typename Codecvt::state_type state_type;
-
- -

-The type shall be a synonym for Codecvt::state_type. -

-
- -

-From what I can see, it might be hard to implement wbuffer_convert if -the types were not both std::mbstate_t, but I cannot find a requirement -that they must be the same type. -

- -

[ -Batavia 2010: -]

- - -

-Howard to draft wording, move to Review. Run it by Bill. Need to move this in Madrid. -

- -

[2011-03-06: Howard drafts wording]

- - -

[2011-03-24 Madrid meeting]

- - -

Moved to Immediate

- - -

Proposed resolution:

-

Modify the state_type typedef in the synopsis of 22.3.3.2.3 [conversions.buffer] p.2 as shown -[This makes the synopsis consistent with 22.3.3.2.3 [conversions.buffer] p.9]:

- -
-namespace std {
-template<class Codecvt,
-  class Elem = wchar_t,
-  class Tr = std::char_traits<Elem> >
-class wbuffer_convert
-  : public std::basic_streambuf<Elem, Tr> {
-public:
-  typedef typename TrCodecvt::state_type state_type;
-  […]
-};
-}
-
- - - - - -
-

1253. invalidation of iterators and emplace vs. insert inconsistence in assoc. containers

-

Section: 23.2.4 [associative.reqmts] Status: C++11 - Submitter: Boris Dušek Opened: 2009-10-24 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-In the latest published draft -N2960, -section 23.2.4 [associative.reqmts], paragraph 8, it is specified -that that insert does not invalidate any iterators. As per -23.2.1 [container.requirements.general], paragraph 12, this holds -true not only for insert, but emplace as well. This -gives the insert member a special treatment w.r.t. -emplace member in 23.2.4 [associative.reqmts], par. 8, -since both modify the container. For the sake of consistency, in 23.2.4 [associative.reqmts], par. 8: either reference to insert -should be removed (i.e. count on 23.2.1 [container.requirements.general], -par. 12), or reference to emplace be added (i.e. mention all -members of assoc. containers that modify it). -

- -

[ -2009-11-18 Chris provided wording. -]

- - -

-This suggested wording covers both the issue discussed, and a number of other -identical issues (namely insert being discussed without emplace). I'm happy to -go back and split and introduce a new issue if appropriate, but I think the -changes are fairly mechanical and obvious. -

- -

[ -2010-01-23 Daniel Krügler and J. Daniel García updated wording to -make the use of hint consistent with insert. -]

- - -

[ -2011-02-23 Daniel Krügler adapts wording to numbering changes to match the N3225 draft. During this -action it was found that 23.2.5 [unord.req] had been changed considerably -due to acceptance of N3068 -during the Pittsburgh meeting, such that the suggested wording change to -p. 6 can no longer be applied. The new wording is more general and should -now include insert() and emplace() calls as well ("mutating operations"). -]

- - -

[2011-03-06 Daniel Krügler adapts wording to numbering changes to match the N3242 draft]

- - - - -

Proposed resolution:

-
    -
  1. -

    -Modify bullet 1 of 23.2.1 [container.requirements.general], p. 10: -

    - -

    -10 Unless otherwise specified (see [associative.reqmts.except], [unord.req.except], [deque.modifiers], and [vector.modifiers]) -all container types defined in this Clause meet the following additional -requirements: -

    - -
      -
    • -if an exception is thrown by an insert() or -emplace() function while inserting a single element, that -function has no effects. -
      • -
    • ...
      • -
    - -
    2. - -
  2. -

    -Modify 23.2.4 [associative.reqmts], p. 4: -

    - -

    -4 An associative container supports unique keys if it may contain at most -one element for each key. Otherwise, it supports equivalent keys. The -set and map classes support unique keys; the multiset -and multimap classes support equivalent keys. For multiset and -multimap, insert, emplace, and -erase preserve the relative ordering of equivalent elements. -

    - -
    3. - -
  3. -

    -Modify Table 102 — Associative container requirements in -23.2.4 [associative.reqmts]: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note
    pre-/post-condition    		Complexity
    […]
    a_eq.emplace(args)iterator[…] Effects: Inserts a T object t constructed with -std::forward<Args>(args)... and returns the iterator pointing to -the newly inserted element. If a range containing elements equivalent to -t exists in a_eq, t is inserted at the end of that -range.logarithmic
    a.emplace_hint(p, args)iteratorequivalent to a.emplace(std::forward<Args>(args)...). Return -value is an iterator pointing to the element with the key equivalent to the -newly inserted element. The const_iterator p is a hint pointing to -where the search should start. The element is inserted as close as -possible to the position just prior to p. Implementations -are permitted to ignore the hint.logarithmic in general, but amortized constant if the element is inserted -right after before p
    […]
    -
    - -
    4. - -
  4. -

    -Modify 23.2.4 [associative.reqmts], p. 9: -

    - -

    -9 The insert and emplace members shall not affect -the validity of iterators and references to the container, and the -erase members shall invalidate only iterators and references to the -erased elements. -

    - -
    5. - -
  5. -

    -Modify 23.2.4.1 [associative.reqmts.except], p. 2: -

    - -

    -2 For associative containers, if an exception is thrown by any operation from -within an insert() or emplace() function inserting -a single element, the insert() function insertion -has no effect. -

    - -
    6. - -
  6. -

    -Modify 23.2.5 [unord.req], p. 13 and p. 14: -

    - -
    -

    -6 An unordered associative container supports unique keys if it may -contain at most one element for each key. Otherwise, it supports equivalent -keys. unordered_set and unordered_map support unique keys. -unordered_multiset and unordered_multimap support equivalent -keys. In containers that support equivalent keys, elements with equivalent keys -are adjacent to each other in the iteration order of the container. Thus, although -the absolute order of elements in an unordered container is not specified, its -elements are grouped into equivalent-key groups such that all elements of each -group have equivalent keys. Mutating operations on unordered containers shall -preserve the relative order of elements within each equivalent-key group unless -otherwise specified. -

    - -

    […]

    - -

    -13 The insert and emplace members shall not affect -the validity of references to container elements, but may invalidate all -iterators to the container. The erase members shall invalidate only iterators -and references to the erased elements. -

    - -

    -14 The insert and emplace members shall not affect -the validity of iterators if (N+n) < z * B, where N is the -number of elements in the container prior to the insert operation, n is -the number of elements inserted, B is the container's bucket count, and -z is the container's maximum load factor. -

    -
    - -
    7. - -
  7. -

    -Modify 23.2.5.1 [unord.req.except], p. 2: -

    - -

    -2 For unordered associative containers, if an exception is thrown by any -operation other than the container's hash function from within an -insert() or emplace() function inserting a single -element, the insert() insertion -function has no effect. -

    - -
    8. -
- - - - - - -
-

1254. Misleading sentence in vector<bool>::flip

-

Section: 23.3.7 [vector.bool] Status: C++11 - Submitter: Christopher Jefferson Opened: 2009-11-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The effects of vector<bool>::flip has the line: -

- -

-It is unspecified whether the function has any effect on allocated but -unused bits. -

- -

-While this is technically true, it is misleading, as any member function -in any standard container may change unused but allocated memory. Users -can never observe such changes as it would also be undefined behaviour -to read such memory. -

- -

[ -2009-11-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Strike second sentence from the definition of vector<bool>::flip(), -23.3.7 [vector.bool], paragraph 5. -

- -

-Effects: Replaces each element in the container with its complement. -It is unspecified whether the function has any effect on allocated -but unused bits. -

- - - - - -
-

1255. declval should be added to the library

-

Section: 20.2 [utility] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-11-03 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-During the Santa Cruz meeting it was decided to split off the provision -of the library utility value() proposed in -N2979 -from the concrete request of the -UK 300 -comment. -The provision of a new library component that allows the production of -values in unevaluated expressions is considered as important -to realize constrained templates in C++0x where concepts are not -available. -

- -

-The following proposed resolution is an improvement over that suggested in -N2958, -because the proposed component can now be defined without loss of -general usefulness and any use by user-code will make the program ill-formed. -A possible prototype implementation that satisfies the core language -requirements can be written as: -

- -
-template<class T>
-  struct declval_protector {
-    static const bool stop = false;
-    static typename std::add_rvalue_reference<T>::type delegate(); // undefined
-  };
-
-template<class T>
-typename std::add_rvalue_reference<T>::type declval() {
-  static_assert(declval_protector<T>::stop, "declval() must not be used!");
-  return declval_protector<T>::delegate();
-}
-
- -

-Further-on the earlier suggested name value() has been changed to declval() -after discussions with committee members. -

- -

-Finally the suggestion shown below demonstrates that it can simplify -existing standard wording by directly using it in the library -specification, and that it also improves an overlooked corner case for -common_type by adding support for cv void. -

- -

[ -2009-11-19 Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

[ -The proposed resolution has been updated to -N3000 -numbering and wording -]

- - -
    -
  1. -

    -Change 20.2 [utility], header <utility> synopsis -as indicated: -

    - -
    -// 20.3.3, forward/move:
-template <class T> struct identity;
-template <class T, class U> T&& forward(U&&);
-template <class T> typename remove_reference<T>::type&& move(T&&);
-
-// 20.3.4, declval:
-template <class T> typename add_rvalue_reference<T>::type declval(); // as unevaluated operand
-
    -
    2. - -
  2. -

    -Immediately after the current section 20.2.4 [forward] insert a -new section: -

    -

    -20.3.4 Function template declval [declval] -

    -

    -The library provides the function template declval to simplify -the definition of expressions which occur as -unevaluated operands (5 [expr]). The -template parameter T of declval may -be an incomplete type. -

    - -
    -template <class T> typename add_rvalue_reference<T>::type declval(); // as unevaluated operand
-
    - -
    -

    -Remarks: If this function is used according to 3.2 [basic.def.odr], -the program is ill-formed. -

    - -

    -[Example: -

    - -
    
-template<class To, class From>
-decltype(static_cast<To>(declval<From>())) convert(From&&);
-
    - -

    - -declares a function template convert, which only participates in -overloading if the type From can be explicitly cast to type To. -For another example see class template common_type -(20.10.7.6 [meta.trans.other]). -— end example] -

    -
    - -
    3. - -
  3. -

    -This bullet just makes clear that after applying -N2984, -the changes in 20.10.4.3 [meta.unary.prop], before -table Type property queries should not use declval, -because the well-formedness requirement of the specification of -is_constructible would become more complicated, because we -would need to make sure that the expression CE is checked in an -unevaluated context. -

    -
    4. - -
  4. -

    -Also 20.10.6 [meta.rel]/4 is not modified similar to the previous bullet, -because with the stricter requirements of not using declval() the well-formedness condition -would be harder to specify. The following changes are only editorial ones (e.g. -the removal of the duplicate declaration of create()): -

    - -
    -

    -Given the following function prototype: -

    - -
    -template <class T>
-  typename add_rvalue_reference<T>::type create();
-
    - -

    -the predicate condition for a template specialization -is_convertible<From, To> shall be satisfied if and only -if the return expression in the following code would be well-formed, -including any -implicit conversions to the return type of the function: -

    - -
    -template <class T>
-typename add_rvalue_reference<T>::type create();
-To test() {
-  return create<From>();
-}
-
    -
    -
    5. - -
  5. -

    -Change the entry in column "Comments" for common_type in Table 51 — -Other transformations (20.10.7.6 [meta.trans.other]): -

    - -

    [ -NB: This wording change extends the type domain of common_type for cv -void => cv void transformations and thus makes common_type usable for -all binary type combinations that are supported by is_convertible -]

    - - -

    -The member typedef type shall be defined as set out below. All -types in the parameter pack T shall be complete or -(possibly cv-qualified) void. A program may specialize -this trait if at least one template parameter in the specialization is a -user-defined type. [Note: Such specializations are needed when -only explicit conversions are desired among the template arguments. -— end note] -

    -
    6. - -
  6. -

    -Change 20.10.7.6 [meta.trans.other]/3 as indicated: -

    - -

    [ -NB: This wording change is more than an editorial simplification of -the definition of common_type: It also extends its usefulness for cv -void types as outlined above -]

    - - -
    -

    -The nested typedef common_type::type shall be defined as follows: -

    - -
    -

    -[..] -

    -
    -template <class T, class U>
-struct common_type<T, U> {
-private:
-  static T&& __t();
-  static U&& __u();
-public:
-  typedef decltype(true ? __tdeclval<T>() : __udeclval<U>()) type;
-};
-
    -
    -
    -
    7. - -
  7. -

    -Change X [func.ret]/1 as indicated -[This part solves some main aspects of issue 1225]: -

    - -
    -namespace std {
-  template <class> class result_of; // undefined
-
-  template <class Fn, class... ArgTypes>
-  class result_of<Fn(ArgTypes...)> {
-  public :
-    // types
-    typedef see belowdecltype(declval<Fn>() ( declval<ArgTypes>()... )) type;
-  };
-}
-
    -

    -1 Given an rvalue fn of type Fn and values t1, t2, ..., tN of -types T1, T2, ..., TN in ArgTypes, -respectively, the type member is the result type of the expression -fn(t1, t2, ...,tN). The values ti -are lvalues when the corresponding type Ti is an lvalue-reference -type, and rvalues otherwise. -

    -
    -
    8. -
- - - - - - -
-

1256. weak_ptr comparison functions should be removed

-

Section: 20.8.2.3 [util.smartptr.weak] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-11-04 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.weak].

-

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-

Discussion:

-

-Additional to the necessary cleanup of the description of the the -weak_ptr component from 20.8.2.3 [util.smartptr.weak] -described in 1231 it turns out that the currently deleted -comparison functions of weak_ptr are not needed at all: There -is no safe-bool conversion from weak_ptr, and it won't silently -chose a conversion to shared_ptr. -

- -

[ -2009-11-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 20.8.2.3 [util.smartptr.weak]/1 as indicated: -

- -
-namespace std {
-template<class T> class weak_ptr {
-public:
-...
-  // comparisons
-  template<class Y> bool operator<(weak_ptr<Y> const&) const = delete;
-  template<class Y> bool operator<=(weak_ptr<Y> const&) const = delete;
-  template<class Y> bool operator>(weak_ptr<Y> const&) const = delete;
-  template<class Y> bool operator>=(weak_ptr<Y> const&) const = delete;
-};
-...
-
- - - - - -
-

1257. Header <ios> still contains a concept_map

-

Section: 27.5 [iostreams.base] Status: C++11 - Submitter: Beman Dawes Opened: 2009-11-04 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The current WP still contains a concept_map. -

- -

[ -2009-11-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change Iostreams base classes 27.5 [iostreams.base], Header <ios> synopsis, -as indicated: -

- -
-concept_map ErrorCodeEnum<io_errc> { };
-template <> struct is_error_code_enum<io_errc> : true_type { }
-error_code make_error_code(io_errc e);
-error_condition make_error_condition(io_errc e);
-const error_category& iostream_category();
-
- - - - - - -
-

1258. std::function Effects clause impossible to satisfy

-

Section: 20.9.12.2.2 [func.wrap.func.mod] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-11-05 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-As of 20.9.12.2.2 [func.wrap.func.mod]/2+ we have the following -prototype description: -

- -
-template<class F, Allocator Alloc>
-  void assign(F, const Alloc&);
-
-

-Effects: function(f, a).swap(*this) -

-
- -

-Two things: First the concept debris needs to be removed, second and -much more importantly, the effects clause is now impossible to satisfy, -because there is no constructor that would match the parameter sequence -(FunctionObject, Allocator) [plus the fact that no -f and no a is part of the signature]. The most -probable candidate is -

- -
-template<class F, class A> function(allocator_arg_t, const A&, F);
-
- -

-and the effects clause needs to be adapted to use this signature. -

- -

[ -2009-11-13 Daniel brought wording up to date. -]

- - -

[ -2009-11-15 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-11 Moved to Tentatively NAD Editorial after 5 positive votes on -c++std-lib. It was noted that this issue was in partial conflict with 1288, and the two issues were merged in 1288. -]

- - -

Rationale:

-

-Addressed by 1288. -

- - - - -

Proposed resolution:

-

-Change in 20.9.12.2.2 [func.wrap.func.mod] the complete prototype description as -indicated -

-

[ -Question to -the editor: Shouldn't there a paragraph number in front of the Effects clause? -]

- - -
-template<class F, Allocator Allocclass A>
-  void assign(F f, const Alloc& a);
-
-

-3 Effects: function(f, aallocator_arg, a, -f).swap(*this) -

-
- - - - - -
-

1260. is_constructible<int*,void*> reports true

-

Section: 20.10.4.3 [meta.unary.prop] Status: Resolved - Submitter: Peter Dimov Opened: 2009-11-07 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The specification of is_constructible<T,Args...> in -N3000 -uses -

- -
-static_cast<T>(create<Args>()...)
-
- -

-for the one-argument case, but static_cast also permits -unwanted conversions such as void* to T* and -Base* to Derived*. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to NAD EditorialResolved, this issue is addressed by paper -n3047 -

- - - -

Proposed resolution:

-

-Change 20.10.4.3 [meta.unary.prop], p6: -

- -
-

-the predicate condition for a template specialization -is_constructible<T, Args> shall be satisfied, if and only -if the following expression CE variable -definition would be well-formed: -

- -
    -
  • -

    -if sizeof...(Args) == 0 1, the expression: -

    -
    -static_cast<T>(create<Args>()...)
-T t;
-
    -
    • -
  • -

    -otherwise the expression: -

    -
    -T t(create<Args>()...);
-
    -
    • -
-
- - - - - -
-

1261. Insufficent overloads for to_string / to_wstring

-

Section: 21.5 [string.conversions] Status: C++11 - Submitter: Christopher Jefferson Opened: 2009-11-10 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Reported on the gcc mailing list. -

- -

-The code "int i; to_string(i);" fails to compile, as -'int' is ambiguous between 'long long' and 'long -long unsigned'. It seems unreasonable to expect users to cast -numbers up to a larger type just to use to_string. -

- -

[ -2009-11-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-21.3 [string.classes], change to_string and -to_wstring to: -

- -
-string to_string(int val);
-string to_string(unsigned val);
-string to_string(long val);
-string to_string(unsigned long val);
-string to_string(long long val); 
-string to_string(unsigned long long val); 
-string to_string(float val);
-string to_string(double val);
-string to_string(long double val);
-
-wstring to_wstring(int val);
-wstring to_wstring(unsigned val);
-wstring to_wstring(long val);
-wstring to_wstring(unsigned long val);
-wstring to_wstring(long long val); 
-wstring to_wstring(unsigned long long val); 
-wstring to_wstring(float val);
-wstring to_wstring(double val);
-wstring to_wstring(long double val);
-
- -

-In 21.5 [string.conversions], paragraph 7, change to: -

- -
-string to_string(int val);
-string to_string(unsigned val);
-string to_string(long val);
-string to_string(unsigned long val);
-string to_string(long long val); 
-string to_string(unsigned long long val); 
-string to_string(float val);
-string to_string(double val);
-string to_string(long double val);
-
- -

-7 Returns: each function returns a string object holding -the character representation of the value of its argument that would be -generated by calling sprintf(buf, fmt, val) with a format -specifier of "%d", "%u", "%ld", -"%lu", "%lld", "%llu", -"%f", "%f", or "%Lf", respectively, -where buf designates an internal character buffer of sufficient -size. -

-
- -

-In 21.5 [string.conversions], paragraph 14, change to: -

- -
-wstring to_wstring(int val);
-wstring to_wstring(unsigned val);
-wstring to_wstring(long val);
-wstring to_wstring(unsigned long val);
-wstring to_wstring(long long val); 
-wstring to_wstring(unsigned long long val); 
-wstring to_wstring(float val);
-wstring to_wstring(double val);
-wstring to_wstring(long double val);
-
- -

-14 Returns: Each function returns a wstring object -holding the character representation of the value of its argument that -would be generated by calling swprintf(buf, buffsz, fmt, val) -with a format specifier of L"%d", L"%u", -L"%ld", L"%lu", L"%lld", -L"%llu", L"%f", L"%f", or -L"%Lf", respectively, where buf designates an internal -character buffer of sufficient size buffsz. -

-
- - - - - -
-

1262. std::less<std::shared_ptr<T>> is underspecified

-

Section: 20.8.2.2.7 [util.smartptr.shared.cmp] Status: C++11 - Submitter: Jonathan Wakely Opened: 2009-11-10 Last modified: 2015-04-08

-

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-

Discussion:

-

-20.8.2.2.7 [util.smartptr.shared.cmp]/5 says: -

- -

-For templates greater, less, greater_equal, and less_equal, the -partial specializations for shared_ptr shall yield a total order, even if -the built-in operators <, >, <=, and >= do not. -Moreover, less<shared_ptr<T> >::operator()(a, b) shall return -std::less<T*>::operator()(a.get(), b.get()). -

- -

-This is necessary in order to use shared_ptr as the key in associate -containers because -n2637 -changed operator< on shared_ptrs to be -defined in terms of operator< on the stored pointers (a mistake IMHO -but too late now.) By 5.9 [expr.rel]/2 the result of comparing builtin -pointers is unspecified except in special cases which generally do not -apply to shared_ptr. -

- -

-Earlier versions of the WP -(n2798, -n2857) -had the following note on that paragraph: -

- -

-[Editor's note: It's not clear to me whether the first sentence is a requirement -or a note. The second sentence seems to be a requirement, but it doesn't really belong -here, under operator<.] -

- -

-I agree completely - if partial specializations are needed they should -be properly specified. -

- -

-20.8.2.2.7 [util.smartptr.shared.cmp]/6 has a note saying the comparison operator -allows shared_ptr objects to be used as keys in associative -containers, which is misleading because something else like a -std::less partial specialization is needed. If it is not correct that -note should be removed. -

- -

-20.8.2.2.7 [util.smartptr.shared.cmp]/3 refers to 'x' and -'y' but the prototype has parameters 'a' and -'b' - that needs to be fixed even if the rest of the issue is -NAD. -

- -

-I see two ways to fix this, I prefer the first because it removes the -need for any partial specializations and also fixes operator> and -other comparisons when defined in terms of operator<. -

- -
    -
  1. -

    -Replace 20.8.2.2.7 [util.smartptr.shared.cmp]/3 with the following and -remove p5: -

    - -
    -template<class T, class U> bool operator<(const shared_ptr<T>& a, const shared_ptr<U>& b);
-
    -
    -

    -3 Returns: x.get() < y.get(). -std::less<V>()(a.get(), b.get()), where V is the -composite pointer type (5.9 [expr.rel]). -

    - -

    -4 Throws: nothing. -

    - -

    -5 For templates greater, less, greater_equal, and less_equal, the -partial specializations for shared_ptr shall yield a total order, even if -the built-in operators <, >, -<=, and >= do not. Moreover, -less<shared_ptr<T> >::operator()(a, b) shall return -std::less<T*>::operator()(a.get(), b.get()). -

    -

    -6 [Note: Defining a comparison operator allows -shared_ptr objects to be used as keys in associative -containers. — end note] -

    -
    -
    -
    2. - - -
  2. -

    -Add to 20.8.2.2 [util.smartptr.shared]/1 (after the shared_ptr comparisons) -

    - -
    -template<class T> struct greater<shared_ptr<T>>;
-template<class T> struct less<shared_ptr<T>>;
-template<class T> struct greater_equal<shared_ptr<T>>;
-template<class T> struct less_equal<shared_ptr<T>>;
-
    - -

    -Remove 20.8.2.2.7 [util.smartptr.shared.cmp]/5 and /6 and replace with: -

    - -
    -template<class T, class U> bool operator<(const shared_ptr<T>& a, const shared_ptr<U>& b);
-
    -
    -

    -3 Returns: xa.get() < yb.get(). -

    - -

    -4 Throws: nothing. -

    - -

    -5 For templates greater, less, greater_equal, and less_equal, the -partial specializations for shared_ptr shall yield a total order, even if -the built-in operators <, >, -<=, and >= do not. Moreover, -less<shared_ptr<T> >::operator()(a, b) shall return -std::less<T*>::operator()(a.get(), b.get()). -

    -

    -6 [Note: Defining a comparison operator allows -shared_ptr objects to be used as keys in associative -containers. — end note] -

    -
    - -
    
-template<class T> struct greater<shared_ptr<T>> :
-binary_function<shared_ptr<T>, shared_ptr<T>, bool> {
-  bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const;
-};
-
    - -

    -operator() returns greater<T*>()(a.get(), b.get()). -

    - -
    
-template<class T> struct less<shared_ptr<T>> :
-binary_function<shared_ptr<T>, shared_ptr<T>, bool> {
-  bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const;
-};
-
    - -

    -operator() returns less<T*>()(a.get(), b.get()). -

    - -
    
-template<class T> struct greater_equal<shared_ptr<T>> :
-binary_function<shared_ptr<T>, shared_ptr<T>, bool> {
-  bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const;
-};
-
    - -

    -operator() returns greater_equal<T*>()(a.get(), b.get()). -

    - -
    
-template<class T> struct less_equal<shared_ptr<T>> :
-binary_function<shared_ptr<T>, shared_ptr<T>, bool> {
-  bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const;
-};
-
    - -

    -operator() returns less_equal<T*>()(a.get(), b.get()). -

    - -
    -
    3. -
- -

[ -2009-11-18: Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Replace 20.8.2.2.7 [util.smartptr.shared.cmp]/3 with the following and -remove p5: -

- -
-template<class T, class U> bool operator<(const shared_ptr<T>& a, const shared_ptr<U>& b);
-
-
-

-3 Returns: x.get() < y.get(). -less<V>()(a.get(), b.get()), where V is the -composite pointer type (5.9 [expr.rel]) of T* and U*. -

- -

-4 Throws: nothing. -

- -

-5 For templates greater, less, greater_equal, and less_equal, the -partial specializations for shared_ptr shall yield a total order, even if -the built-in operators <, >, -<=, and >= do not. Moreover, -less<shared_ptr<T> >::operator()(a, b) shall return -std::less<T*>::operator()(a.get(), b.get()). -

-

-6 [Note: Defining a comparison operator allows -shared_ptr objects to be used as keys in associative -containers. — end note] -

-
-
- - - - - - -
-

1264. quick_exit support for freestanding implementations

-

Section: 17.6.1.3 [compliance] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-11-12 Last modified: 2015-04-08

-

View all other issues in [compliance].

-

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-

Discussion:

-

Addresses UK 172

- -

-This issue is a response to NB comment UK-172 -

- -

-The functions quick_exit and at_quick_exit should be -added to the required features of <cstdlib> in a -freestanding implementation. -

- -

-This comment was rejected in Summit saying neither at_exit nor -at_quick_exit should be required. This suggests the comment was -misread, as atexit is already required to be supported. If the LWG -really did wish to not require the registration functions be supported, -then a separate issue should be opened to change the current standard. -

- -

-Given both exit and atexit are required, the UK panel feels it is -appropriate to require the new quick_exit facility is similarly -supported. -

- -

[ -2009-12-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Ammend p3 Freestanding implementations 17.6.1.3 [compliance] -

- -

-3 The supplied version of the header <cstdlib> shall -declare at least the functions abort(), atexit(), -at_quick_exit, and exit(), and -quick_exit(18.5 [support.start.term]). The other -headers listed in this table shall meet the same requirements as for a -hosted implementation. -

- - - - - - -
-

1266. shared_future::get and deferred async functions

-

Section: 30.6.7 [futures.shared_future] Status: Resolved - Submitter: Anthony Williams Opened: 2009-11-17 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

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-

Discussion:

-

-If a shared_future is constructed with the result of an async call with a -deferred function, and two or more copies of that shared_future are created, -with multiple threads calling get(), it is not clear which thread runs the -deferred function. 30.6.7 [futures.shared_future]p22 from -N3000 -says (minus editor's note): -

- -

-Effects: if the associated state contains a deferred function, executes -the deferred function. Otherwise, blocks until the associated state is ready. -

- -

-In the absence of wording to the contrary, this implies that every thread that -calls wait() will execute the deferred function. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

-

-Replace 30.6.7 [futures.shared_future]p22 with the following: -

- -
-

-Effects: If the associated state -contains a deferred function, executes the deferred function. Otherwise, -blocks until the associated state is ready. -was created by a promise or packaged_task object, block -until the associated state is ready. If the associated state is associated with -a thread created for an async call (30.6.8 [futures.async]), as -if associated-thread.join(). -

- -

-If the associated state contains a deferred function, calls to wait() -on all shared_future objects that share the same associated state are -serialized. The first call to wait() that shares a given associated -state executes the deferred function and stores the return value or exception in -the associated state. -

- -

-Synchronization: if the associated state was created by a -promise object, the completion of set_value() or -set_exception() to that promise happens before (1.10 [intro.multithread]) wait() returns. If the associated state -was created by a packaged_task object, the completion of the associated -task happens before wait() returns. If the associated state is -associated with a thread created for an async call (30.6.8 [futures.async]), the completion of the associated thread happens-before -wait() returns. -

- -

-If the associated state contained a deferred function, the invocation of the -deferred function happens-before any call to wait() on a -future that shares that state returns. -

-
- - - - - -
-

1267. Incorrect wording for condition_variable_any::wait_for

-

Section: 30.5.2 [thread.condition.condvarany] Status: C++11 - Submitter: Anthony Williams Opened: 2009-11-17 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvarany].

-

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-

Discussion:

-

-30.5.2 [thread.condition.condvarany]p18 and 30.5.2 [thread.condition.condvarany]p27 specify incorrect preconditions for -condition_variable_any::wait_for. The stated preconditions require that -lock has a mutex() member function, and that this produces the -same result for all concurrent calls to wait_for(). This is -inconsistent with wait() and wait_until() which do not impose -such a requirement. -

- -

[ -2009-12-24 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Remove 30.5.2 [thread.condition.condvarany]p18 and 30.5.2 [thread.condition.condvarany]p27. -

-
-
-template <class Lock, class Rep, class Period>
-  cv_status wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
-
-

-18 Precondition: lock is locked by the calling thread, and either -

-
    -
  • -no other thread is waiting on this condition_variable object or -
    • -
  • -lock.mutex() returns the same value for each of the lock arguments -supplied by all concurrently waiting (via wait, wait_for, or -wait_until) threads. -
    • -
-
- -

...

- -
-template <class Lock, class Rep, class Period, class Predicate>
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
-
- -
- -

-27 Precondition: lock is locked by the calling thread, and either -

-
    -
  • -no other thread is waiting on this condition_variable object or -
    • -
  • -lock.mutex() returns the same value for each of the lock arguments -supplied by all concurrently waiting (via wait, wait_for, or -wait_until) threads. -
    • -
- -
- -
- - - - - - -
-

1268. The Mutex requirements in 30.4.1 and 30.4.2 are wrong

-

Section: 30.4 [thread.mutex] Status: Resolved - Submitter: Anthony Williams Opened: 2009-11-17 Last modified: 2015-04-08

-

View all other issues in [thread.mutex].

-

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-

Discussion:

-

-The Mutex requirements in 30.4.1 [thread.mutex.requirements] and -30.4.1.3 [thread.timedmutex.requirements] confuse the requirements on the -behaviour of std::mutex et al with the requirements on -Lockable types for use with std::unique_lock, -std::lock_guard and std::condition_variable_any. -

- -

[ -2010 Pittsburgh: -]

- - -
-

-Concepts of threads chapter and issue presentation are: Lockable < Mutex < -TimedMutex and Lockable < TimedLockable < TimedMutex. -

-

-Typo in failed deletion of Mutex in 30.4.4 p4 edits. -

-

-Lockable requirements are too weak for condition_variable_any, but the Mutex -requirements are too strong. -

-

-Need subset of Lockable requirements for condition_variable_any that does not -include try_lock. E.g. CvLockable < Lockable. -

-

-Text needs updating to recent draft changes. -

-

-Needs to specify exception behavior in Lockable. -

-

-The current standard is fine for what it says, but it places requirements that -are too strong on authors of mutexes and locks. -

-

-Move to open status. Suggest Anthony look at condition_variable_any -requirements. Suggest Anthony refine requirements/concepts categories. -

-

-Related to 964 and 966 -

-
- -

[ -2010-03-28 Daniel synced with N3092. -]

- - -

[ -2010-10-25 Daniel adds: -]

- - -

-Accepting n3130 -would solve this issue. -

- -

[ -2010-11 Batavia: -]

- - -

-Resolved by adopting n3197. -

- - - - -

Proposed resolution:

-

-Add a new section to 30.2 [thread.req] after 30.2.4 [thread.req.timing] -as follows: -

- -
-

-30.2.5 Requirements for Lockable types -

- -

-The standard library templates unique_lock (30.4.2.2 [thread.lock.unique]), lock_guard (30.4.2.1 [thread.lock.guard]), lock, try_lock (30.4.3 [thread.lock.algorithm]) and condition_variable_any (30.5.2 [thread.condition.condvarany]) all operate on user-supplied -Lockable objects. Such an object must support the member functions -specified for either the Lockable Requirements or the -TimedLockable requirements as appropriate to acquire or release -ownership of a lock by a given thread. [Note: the -nature of any lock ownership and any synchronization it may entail are not part -of these requirements. — end note] -

- -

-30.2.5.1 Lockable Requirements -

- -

-In order to qualify as a Lockable type, the following expressions must -be supported, with the specified semantics, where m denotes a value of -type L that supports the Lockable: -

- -

-The expression m.lock() shall be well-formed and have the following -semantics: -

- -
-
Effects:
Block until a lock can be acquired for the current thread.
-
Return type:
void
-
- -

-The expression m.try_lock() shall be well-formed and have the -following semantics: -

- -
-
Effects:
Attempt to acquire a lock for the current thread without blocking.
-
Return type:
bool
-
Returns:
true if the lock was - acquired, false otherwise.
-
- -

-The expression m.unlock() shall be well-formed and have the -following semantics: -

- -
-
Effects:
Release a lock on m held by the current thread.
-
Return type:
void
-
Throws:
Nothing if the current thread holds a lock on m.
-
- -

-30.2.5.2 TimedLockable Requirements -

- -

-For a type to qualify as TimedLockable it must meet the -Lockable requirements, and additionally the following -expressions must be well-formed, with the specified semantics, -where m is an instance of a type TL that supports -the TimedLockable requirements, rel_time denotes -instantiation of duration (20.12.5 [time.duration]) and abs_time -denotes an instantiation of time_point (20.12.6 [time.point]) - -

- -

-The expression m.try_lock_for(rel_time) shall be well-formed and have the -following semantics: -

- -
-
Effects:
Attempt to acquire a lock for the current - thread within the specified time period.
-
Return type:
bool
-
Returns:
true if the lock was - acquired, false otherwise.
-
- -

-The expression m.try_lock_until(abs_time) shall be well-formed and have the -following semantics: -

- -
-
Effects:
Attempt to acquire a lock for the current - thread before the specified point in time.
-
Return type:
bool
-
Returns:
true if the lock was - acquired, false otherwise.
-
-
- -

-Replace 30.4.1 [thread.mutex.requirements] paragraph 2 with the -following: -

- -

-2 This section describes requirements on template argument types -used to instantiate templates defined in the mutex types -supplied by the C++ standard library. The template -definitions in the C++ standard library refer These types shall -conform to the named Mutex requirements whose details are set -out below. In this description, m is an object -of a Mutex type -one of the standard library mutex types std::mutex, -std::recursive_mutex, std::timed_mutex or -std::recursive_timed_mutex.. -

- -

-Add the following paragraph after 30.4.1 [thread.mutex.requirements] -paragraph 2: -

- -

-A Mutex type shall conform to the Lockable -requirements (30.2.5.1). -

- -

-Replace 30.4.1.3 [thread.timedmutex.requirements] paragraph 1 with the -following: -

- -

-The C++ standard library TimedMutex types std::timed_mutex - and std::recursive_timed_mutex -A TimedMutex type shall meet the requirements for -a Mutex type. In addition, itthey shall -meet the requirements set out in this Clause 30.4.2below, -where rel_time denotes an instantiation of duration -(20.12.5 [time.duration]) and abs_time denotes an instantiation -of time_point (20.12.6 [time.point]). -

- -

-Add the following paragraph after 30.4.1.3 [thread.timedmutex.requirements] paragraph 1: -

- -

-A TimedMutex type shall conform to the TimedLockable -requirements (30.2.5.1). -

- - -

-Add the following paragraph following 30.4.2.1 [thread.lock.guard] -paragraph 1: -

- -

-The supplied Mutex type shall meet the Lockable -requirements (30.2.5.1). -

- -

-Add the following paragraph following 30.4.2.2 [thread.lock.unique] -paragraph 1: -

- -

-The supplied Mutex type shall meet the Lockable -requirements -(30.2.5.1). unique_lock<Mutex> meets the Lockable -requirements. If Mutex meets the TimedLockable -requirements -(30.2.5.2) then unique_lock<Mutex> also meets the -TimedLockable requirements. -

- -

-Replace the use of "mutex" or "mutex object" with "lockable object" -throughout clause 30.4.2 [thread.lock] paragraph 1: -

- -

-1 A lock is an object that holds a reference to -a mutexlockable object and may unlock -the mutexlockable object during the lock's -destruction (such as when leaving block scope). A thread of execution -may use a lock to aid in managing mutex ownership of a -lockable object in an exception safe manner. A lock is said to -own a mutexlockable object if it is currently -managing the ownership of that mutexlockable -object for a thread of execution. A lock does not manage the -lifetime of the mutexlockable object it -references. [ Note: Locks are intended to ease the burden of -unlocking the mutexlockable object under both -normal and exceptional circumstances. — end note ] -

- -

30.4.2 [thread.lock] paragaph 2:

- -

-2 Some lock constructors take tag types which describe what should be -done with the mutexlockable object during the -lock's constuction. -

- -

30.4.2.1 [thread.lock.guard] paragaph 1:

- -

-1 An object of type lock_guard controls the ownership of a - mutexlockable object within a scope. A -lock_guard object maintains ownership of -a mutexlockable object throughout -the lock_guard object's lifetime. The behavior of a program -is undefined if the mutexlockable object -referenced by pm does not exist for the entire lifetime (3.8) -of the lock_guard object. Mutex shall meet - the Lockable requirements (30.2.5.1). -

- -

30.4.2.2 [thread.lock.unique] paragaph 1:

- -

-1 An object of type unique_lock controls the ownership of -a mutexlockable object within a -scope. Mutex oOwnership of the -lockable object may be acquired at construction or after -construction, and may be transferred, after acquisition, to -another unique_lock object. Objects of -type unique_lock are not copyable but are movable. The -behavior of a program is undefined if the contained -pointer pm is not null and the mutex pointed to -by pm does not exist for the entire remaining lifetime (3.8) -of the unique_lock object. Mutex shall meet -the Lockable requirements (30.2.5.1). -

- - -

-Add the following to the precondition of unique_lock(mutex_type& -m, const chrono::time_point<Clock, Duration>& abs_time) in -30.4.2.2.1 [thread.lock.unique.cons] paragraph 18: -

- -
template <class Clock, class Duration>
-  unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time);
-
- -

-18 Requires: If mutex_type is not a recursive mutex -the calling thread does not own the mutex. The supplied mutex_type -type shall meet the TimedLockable requirements (30.2.5.2). -

-
- -

-Add the following to the precondition of unique_lock(mutex_type& - m, -const chrono::duration<Rep, Period>& rel_time) in -30.4.2.2.1 [thread.lock.unique.cons] -paragraph 22 -

- -

-22 Requires: If mutex_type is not a recursive mutex - the -calling thread does not own the mutex. The supplied mutex_type -type shall meet the TimedLockable requirements (30.2.5.2). -

- -

-Add the following as a precondition of bool try_lock_until(const -chrono::time_point<Clock, Duration>& abs_time) before -30.4.2.2.2 [thread.lock.unique.locking] paragraph 8 -

- -
template <class Clock, class Duration>
-  bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
-
-

-Requires: The supplied mutex_type type shall meet the -TimedLockable requirements (30.2.5.2). -

-
- -

-Add the following as a precondition of bool try_lock_for(const -chrono::duration<Rep, Period>& rel_time) before -30.4.2.2.2 [thread.lock.unique.locking] paragraph 12 -

- -
template <class Rep, class Period>
-  bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
-
-

-Requires: The supplied mutex_type type shall meet the -TimedLockable requirements (30.2.5.2). -

-
- -

-Replace 30.4.3 [thread.lock.algorithm] p1 with the following: -

- -
template <class L1, class L2, class... L3> int try_lock(L1&, L2&, L3&...);
-
-

-1 Requires: Each template parameter type shall meet the -Mutex Lockable requirements -(30.2.5.1)., except that a call to try_lock() -may throw an exception. [Note: The unique_lock class -template meets these requirements when suitably instantiated. — end note] -

-
- -

-Replace 30.4.3 [thread.lock.algorithm] p4 with the following: -

- -
template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...);
-
-

-4 Requires: Each template parameter type shall meet the -MutexMutex Lockable -requirements (30.2.5.1)., except that a call to -try_lock() may throw an exception. [Note: The -unique_lock class template meets these requirements when -suitably instantiated. — end note] -

-
- -

-Replace 30.5.2 [thread.condition.condvarany] paragraph 1 with: -

- -

-1 A Lock type shall meet the requirements for a Mutex -type Lockable requirements (30.2.5.1), except -that try_lock is not required. [Note: All of the standard -mutex types meet this requirement. — end note] -

- - - - - - -
-

1269. Associated state doesn't account for async

-

Section: 30.6.4 [futures.state] Status: Resolved - Submitter: Anthony Williams Opened: 2009-11-18 Last modified: 2015-04-08

-

View all other issues in [futures.state].

-

View all issues with Resolved status.

-

Discussion:

-

-The current description of the associated state in 30.6.4 [futures.state] -does not allow for futures created by an async call. The description -therefore needs to be extended to cover that. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

-

-Add a new sentence to 30.6.4 [futures.state] p2: -

- -

-2 This associated state consists of some state information and some -(possibly not yet evaluated) result, which can be a (possibly -void) value or an exception. If the associated state was created -by a call to async (30.6.8 [futures.async]) then it may also -contain a deferred function or an associated thread. -

- -

-Add an extra bullet to 30.6.4 [futures.state] p3: -

- -
-

-The result of an associated state can be set by calling: -

-
    -
  • -promise::set_value, -
    • -
  • -promise::set_exception, or -
    • -
  • -packaged_task::operator()., or -
    • -
  • -a call to async (30.6.8 [futures.async]). -
    • -
-
- - - - - -
-

1270. result_of should be moved to <type_traits>

-

Section: X [func.ret] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-11-19 Last modified: 2015-04-08

-

View all other issues in [func.ret].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses UK 198

- -

-NB Comment: UK-198 makes this request among others. It refers to a more -detailed issue that BSI did not manage to submit by the CD1 ballot deadline -though. -

- -

-result_of is essentially a metafunction to return the type of an -expression, and belongs with the other library metafunctions in -<type_traits> rather than lurking in <functional>. - The current definition in <functional> made sense when -result_of was nothing more than a protocol to enable several components -in <functional> to provide their own result types, but it has -become a more general tool. For instance, result_of is now used in the -threading and futures components. -

- -

-Now that <type_traits> is a required header for free-standing -implementations it will be much more noticeable (in such environments) that a -particularly useful trait is missing, unless that implementation also chooses to -offer <functional> as an extension. -

- -

-The simplest proposal is to simply move the wording (editorial direction below) -although a more consistent form for type_traits would reformat this as a table. -

- -

-Following the acceptance of 1255, result_of now -depends on the declval function template, tentatively provided -in <utility> which is not (yet) required of a -free-standing implementation. -

- -

-This dependency is less of an issue when result_of continues to -live in <functional>. -

- -

-Personally, I would prefer to clean up the dependencies so both -result_of and declval are available in a free-standing -implementation, but that would require slightly more work than suggested -here. A minimal tweak would be to require <utility> in a -free-standing implementation, although there are a couple of subtle -issues with make_pair, which uses reference_wrapper in -its protocol and that is much harder to separate cleanly from -<functional>. -

- -

-An alternative would be to enact the other half of -N2979 -and create a new minimal header for the new C++0x library facilities to -be added to the freestanding requirements (plus swap.) -

- -

-I have a mild preference for the latter, although there are clearly -reasons to consider better library support for free-standing in general, -and adding the whole of <utility> could be considered a step in that -direction. See NB comment -JP-23 -for other suggestions (array, ratio) -

- -

[ -2010-01-27 Beman updated wording. -]

- - -
-

-The original wording is preserved here: -

-
- -

-Move X [func.ret] to a heading below 20.10 [meta]. Note -that in principle we should not change the tag, although this is a new tag for -0x. If it has been stable since TR1 it is clearly immutable though. -

- -

-This wording should obviously adopt any other changes currently in (Tentatively) -Ready status that touch this wording, such as 1255. -

- -
-
- -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

From Function objects 20.9 [function.objects], Header <functional> -synopsis, remove:

-
- 
// 20.7.4 result_of:
-template <class> class result_of; // undefined
-template <class F, class... Args> class result_of<F(ArgTypes...)>;
-
- -

Remove Function object return types X [func.ret] in its entirety. -This sub-section reads:

-
- 
namespace std {
-  template <class> class result_of; // undefined
-
-  template <class Fn, class... ArgTypes>
-  class result_of<Fn(ArgTypes...)> {
-  public :
-    // types
-    typedef see below type;
-  };
-}
-

Given an rvalue fn of type Fn and values - t1, t2, ..., tN of types T1, T2, ..., TN in ArgTypes, - respectively, the type member is the result type of the expression - fn(t1, t2, ...,tN). The values ti are lvalues when the - corresponding type Ti is an lvalue-reference type, and rvalues - otherwise.

-
-

To Header <type_traits> synopsis 20.10.2 [meta.type.synop], add at -the indicated location:

-
- 
template <class T> struct underlying_type;
-template <class T> struct result_of; // not defined
-template <class Fn, class... ArgTypes> struct result_of<Fn(ArgTypes...)>;
-
-

To Other transformations 20.10.7.6 [meta.trans.other], Table 51 — -Other transformations, add:

-
- - - - - - - - - - - - - - - - -
TemplateConditionComments
template <class T>
- struct underlying_type;		T shall be an enumeration type - (7.2)The member typedef type shall - name the underlying type of T.
template <class Fn, class... ArgTypes> - struct result_of<Fn(ArgTypes...)>;Fn shall be a function object type - 20.9 [function.objects], reference to function, or reference to - function object type. - decltype(declval<Fn>()(declval<ArgTypes>()...)) shall - be well formed.The member typedef type - shall name the type decltype(declval<Fn>()(declval<ArgTypes>()...)).
-
-

At the end of Other transformations 20.10.7.6 [meta.trans.other] add:

- -
-

[Example: Given these definitions:

- - 
typedef bool(&PF1)();
-typedef short(*PF2)(long);
-
-struct S {
-  operator PF2() const;
-  double operator()(char, int&);
- };
-

the following assertions will hold:

- 
static_assert(std::is_same<std::result_of<S(int)>::type, short>::value, "Error!");
-static_assert(std::is_same<std::result_of<S&(unsigned char, int&)>::type, double>::value, "Error!");
-static_assert(std::is_same<std::result_of<PF1()>::type, bool>::value, "Error!");
-

 — end example]

-
- - - - - -
-

1271. CR undefined in duration operators

-

Section: 20.12.5.5 [time.duration.nonmember] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-11-21 Last modified: 2015-04-08

-

View all other issues in [time.duration.nonmember].

-

View all issues with C++11 status.

-

Discussion:

-

-IMO CR alone is not really defined (it should be CR(Rep1, -Rep2)). -

- -

[ -2009-12-24 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 20.12.5.5 [time.duration.nonmember] paragraphs 9 and 12: -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator/(const duration<Rep1, Period>& d, const Rep2& s);
-
-

-9 Returns: duration<CR(Rep1, Rep2), Period>(d) /= s. -

- -
-template <class Rep1, class Period, class Rep2>
-  duration<typename common_type<Rep1, Rep2>::type, Period>
-  operator%(const duration<Rep1, Period>& d, const Rep2& s);
-
-

-12 Returns: duration<CR(Rep1, Rep2), Period>(d) %= s. -

- -
- - - - - -
-

1272. confusing declarations of promise::set_value

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-11-22 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with Resolved status.

-

Discussion:

-

-The definitions of promise::set_value need tidying up, the -synopsis says: -

- -
-// setting the result
-void set_value(const R& r);
-void set_value(see below);
-
- -

-Why is the first one there? It implies it is always present for all -specialisations of promise, which is not true. -

- -

-The definition says: -

- -
-void set_value(const R& r);
-void promise::set_value(R&& r);
-void promise<R&>::set_value(R& r);
-void promise<void>::set_value();
-
- -

-The lack of qualification on the first one again implies it's present -for all specialisations, again not true. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

-

-Change the synopsis in 30.6.5 [futures.promise]: -

- -
-// setting the result
-void set_value(const R& r);
-void set_value(see below);
-
- -

-And the definition be changed by qualifying the first signature: -

- -
-void promise::set_value(const R& r);
-void promise::set_value(R&& r);
-void promise<R&>::set_value(R& r);
-void promise<void>::set_value();
-
- - - - - -
-

1273. future::valid should be callable on an invalid future

-

Section: 30.6.6 [futures.unique_future] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-11-22 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with Resolved status.

-

Discussion:

-

-30.6.6 [futures.unique_future]/3 says: -

- -

-The effect of calling any member function other than the destructor or -the move-assignment operator on a future object for which -valid() == false is undefined. -

- -

-This means calling future::valid() is undefined unless it will -return true, so you can only use it if you know the answer! -

- -

[ -2009-12-08 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-

-Change 30.6.6 [futures.unique_future]/3: -

- -

-The effect of calling any member function other than the -destructor, or the move-assignment operator, or -valid, on a future object for which valid() -== false is undefined. -

- - - - - - -
-

1274. atomic_future constructor

-

Section: X [futures.atomic_future] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-11-22 Last modified: 2015-04-08

-

View all other issues in [futures.atomic_future].

-

View all issues with Resolved status.

-

Discussion:

-

-In X [futures.atomic_future] this constructor: -

- -
-atomic_future(future<R>&&);
-
- -

-is declared in the synopsis, but not defined. Instead -n2997 -defines: -

- -
-atomic_future(const future<R>&& rhs);
-
- -

-and -n3000 -defines -

- -
-atomic_future(atomic_future<R>&& rhs);
-
- -

-both of which are wrong. The constructor definition should be changed -to match the synopsis. -

- -

[ -2009-12-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-

-Adjust the signature above X [futures.atomic_future]/6 like so: -

- -
-atomic_future(atomic_future<R>&& rhs);
-
- - - - - -
-

1275. Creating and setting futures

-

Section: 30.6 [futures] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-11-22 Last modified: 2015-04-08

-

View all other issues in [futures].

-

View all issues with Resolved status.

-

Discussion:

-

-30.6.6 [futures.unique_future]/1 should be updated to mention -async. -

- -

-30.6.7 [futures.shared_future]/1 should also be updated for -async. That paragraph also says -

- -

-... Its value or exception can be set by use of a -shared_future, promise (30.6.5 [futures.promise]), or packaged_task (30.6.9 [futures.task]) object that shares the same associated state. -

- -

-How can the value be set by a shared_future? -

- -

-X [futures.atomic_future]/1 says -

- -

-An atomic_future object can only be created by use of a -promise (30.6.5 [futures.promise]) or -packaged_task (30.6.9 [futures.task]) object. -

- -

-which is wrong, it's created from a std::future, which could -have been default-constructed. That paragraph should be closer to the -text of 30.6.7 [futures.shared_future]/1, and should also mention -async. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

- - - - - -
-

1276. forwardlist missing allocator constructors

-

Section: 23.3.4 [forwardlist] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-12-12 Last modified: 2015-04-08

-

View all other issues in [forwardlist].

-

View all issues with C++11 status.

-

Discussion:

-

-I found that forward_list has only -

- -
-forward_list(const forward_list<T,Allocator>& x);
-forward_list(forward_list<T,Allocator>&& x);
-
- -

-but misses -

- -
-forward_list(const forward_list& x, const Allocator&);
-forward_list(forward_list&& x, const Allocator&);
-
- -

-Note to other reviewers: I also checked the container adaptors for similar -inconsistencies, but as far as I can see these are already handled by the -current active issues 1194 and 1199. -

- -

[ -2010-01-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-In 23.3.4 [forwardlist]/3, class template forward_list synopsis change as -indicated: -

- -
-forward_list(const forward_list<T,Allocator>& x);
-forward_list(forward_list<T,Allocator>&& x);
-forward_list(const forward_list&, const Allocator&);
-forward_list(forward_list&&, const Allocator&);
-
- - - - - - -
-

1277. std::thread::id should be trivially copyable

-

Section: 30.3.1.1 [thread.thread.id] Status: C++11 - Submitter: Anthony Williams Opened: 2009-11-24 Last modified: 2015-04-08

-

View all other issues in [thread.thread.id].

-

View all issues with C++11 status.

-

Discussion:

-

-The class definition of std::thread::id in -N3000 -is: -

- -
-class thread::id {
-public:
-  id();
-};
-
- -

-Typically, I expect that the internal data members will either be -pointers or integers, so that in practice the class will be trivially -copyable. However, I don't think the current wording guarantees it, and -I think it would be useful. In particular, I can see a use for -std::atomic<std::thread::id> to allow a thread -to claim ownership of a data structure atomicly, and -std::atomic<T> requires that T is trivially -copyable. -

- -

[ -2010-02-12 Moved to Tentatively Ready after 7 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Add a new sentence to 30.3.1.1 [thread.thread.id] p1: -

- -

-1 An object of type thread::id provides a unique identifier for -each thread of execution and a single distinct value for all -thread objects that do not represent a thread of execution -(30.3.1 [thread.thread.class]). Each thread of execution has an -associated thread::id object that is not equal to the -thread::id object of any other thread of execution and that is -not equal to the thread::id object of any std::thread -object that does not represent threads of execution. The library may -reuse the value of a thread::id of a terminated thread that can -no longer be joined. thread::id shall be a trivially -copyable class (9 [class]). -

- - - - - - -
-

1278. Inconsistent return values for forward_list::insert_after

-

Section: 23.3.4.5 [forwardlist.modifiers] Status: C++11 - Submitter: Bo Persson Opened: 2009-11-25 Last modified: 2015-04-08

-

View all other issues in [forwardlist.modifiers].

-

View all issues with C++11 status.

-

Discussion:

-

-After applying LDR149, forward_list now has 5 -overloads of insert_after, all returning an iterator. -

- -

-However, two of those - inserting a single object - return "An iterator -pointing to a copy of x [the inserted object]" while the other -three - inserting zero or more objects - return an iterator equivalent -to the position parameter, pointing before any possibly inserted -objects. -

- -

-Is this the intended change? -

- -

-I don't really know what insert_after(position, empty_range) -should really return, but always returning position seems less -than useful. -

- -

[ -2010-02-04 Howard adds: -]

- - -
-

-I agree this inconsistency will be error prone and needs to be fixed. -Additionally emplace_after's return value is unspecified. -

-
- -

[ -2010-02-04 Nico provides wording. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-We prefer to return an iterator to the last inserted element. Modify the -proposed wording and then set to Ready. -

- -

[ -2010-03-15 Howard adds: -]

- - -

-Wording updated and set to Ready. -

- - - -

Proposed resolution:

-

-In forward_list modifiers 23.3.4.5 [forwardlist.modifiers] -make the following modifications: -

- -
-
-iterator insert_after(const_iterator position, size_type n, const T& x);
-
-
-

...

-

-10 Returns: position. An iterator pointing to the last -inserted copy of x or position if n == 0. -

-
- -
-template <class InputIterator>
-  iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
-
-
-

...

- -

-13 Returns: position. An iterator pointing to the last -inserted element or position if first == last. -

-
- -
-iterator insert_after(const_iterator position, initializer_list<T> il);
-
-
-

...

- -

-15 Returns: position. An iterator pointing to the last -inserted element or position if il is empty. -

-
- -
-template <class... Args>
-  iterator emplace_after(const_iterator position, Args&&... args);
-
-
-

...

-

17 ...

- -

-Returns: An iterator pointing to the new constructed element from -args. -

-
- -
- - - - - - -
-

1279. forbid [u|bi]nary_function specialization

-

Section: X [depr.base] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2009-11-30 Last modified: 2015-04-08

-

View all other issues in [depr.base].

-

View all issues with C++11 status.

-

Discussion:

-

-A program should not be allowed to add specialization of class templates -unary_function and binary_function, in force of 17.6.4.2.1 [namespace.std]/1. -If a program were allowed to specialize these templates, the library could no -longer rely on them to provide the intended typedefs or there might be other -undesired interactions. -

- -

[ -2010-03-27 Daniel adds: -]

- - -

-Accepting issue 1290 would resolve this issue as NAD editorial. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3145 would resolve this issue as NAD editorial. -

- -

[ -2010 Batavia: -]

- - -

-Pete: Is this issue actually addressed by N3198, or did deprecating unary/binary_function? -

-We determined that this issue is NOT resolved and that it must be resolved or else -N3198 could break code that does specialize unary/binary function. -

-Matt: don't move to NAD -

-Howard: I suggest we go further and move 1279 to ready for Madrid. -

-Group: Agrees move 1279 to ready for Madrid -

- -

-Previous proposed resolution: -

- -

-1 The following classes class templates are provided to -simplify the typedefs of the argument and result types:. A -program shall not declare specializations of these templates. -

- -

[2011-03-06 Daniel comments]

- - -

-This meeting outcome was not properly reflected in the proposed resolution. I -also adapted the suggested wording to the N3242 numbering and content state. -During this course of action it turned out that the first suggested wording -change has already been applied. -

- - - -

Proposed resolution:

-

-Change paragraph X [depr.base]/1 as follows: -

- -

-1 The class templates unary_function and binary_function are deprecated. -A program shall not declare specializations of these templates. -

- - - - - -
-

1280. Initialization of stream iterators

-

Section: 24.6.1.1 [istream.iterator.cons], 24.6.2.1 [ostream.iterator.cons.des] Status: C++11 - Submitter: Jonathan Wakely Opened: 2009-12-04 Last modified: 2015-04-08

-

View all other issues in [istream.iterator.cons].

-

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-

Discussion:

-

-24.6.1.1 [istream.iterator.cons] describes the effects in terms of: -

- -
-basic_istream<charT,traits>* in_stream; // exposition only
-
- -

-3 Effects: Initializes in_stream with s. -

-
- -

-That should be &s and similarly for 24.6.2.1 [ostream.iterator.cons.des]. -

- -

[ -2009-12-23 Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 24.6.1.1 [istream.iterator.cons] like so: -

- -
-istream_iterator(istream_type& s);
-
-

-3 Effects: Initializes in_stream with &s. -value ... -

-
- -

-And 24.6.2.1 [ostream.iterator.cons.des] like so: -

- -
-ostream_iterator(ostream_type& s);
-
-

-1 Effects: Initializes out_stream with &s -and delim with null. -

- -
-ostream_iterator(ostream_type& s, const charT* delimiter);
-
-

-2 Effects: Initializes out_stream with &s -and delim with delimiter. -

-
- - - - - - -
-

1281. CopyConstruction and Assignment between ratios having the same normalized form

-

Section: 20.11.3 [ratio.ratio] Status: Resolved - Submitter: Vicente Juan Botet Escribá Opened: 2009-12-07 Last modified: 2015-04-08

-

View all other issues in [ratio.ratio].

-

View all issues with Resolved status.

-

Discussion:

-

-CopyConstruction and Assignment between ratios having the same -normalized form. Current -N3000 -do not allows to copy-construct or assign ratio instances of -ratio classes having the same normalized form. -

- -

-Two ratio classes ratio<N1,D1> and -ratio<N2,D2> have the same normalized form if -

- -
-ratio<N1, D1>::num == ratio<N2, D2>::num &&
-ratio<N1, D1>::den == ratio<N2, D2>::den
-
- -

-This simple example -

- -
-ratio<1,3> r1;
-ratio<3,9> r2;
-r1 = r2; // (1)
-
- -

-fails to compile in (1). Other example -

- -
-ratio<1,3> r1;
-ratio_subtract<ratio<2,3>, ratio<1,3>>::type r2;
-r1 = r2;  
-
- -

-The nested type of ratio_subtract<ratio<2,3>, -ratio<1,3>> could be ratio<3,9> so the compilation -could fail. It could also be ratio<1,3> and the compilation -succeeds. -

- -

-In 20.11.4 [ratio.arithmetic] 3 and similar clauses -

- -

-3 The nested typedef type shall be a synonym for ratio<T1, -T2> where T1 has the value R1::num * R2::den - R2::num * -R1::den and T2 has the value R1::den * R2::den. -

- -

-the meaning of synonym let think that the result shall be a normalized -ratio equivalent to ratio<T1, T2>, but there is not an -explicit definition of what synonym means in this context. -

- -

-Additionally we should add a typedef for accessing the normalized -ratio, and change 20.11.4 [ratio.arithmetic] to return only this -normalized result. -

- -

[ -2010 Pittsburgh: -]

- - -
-

-There is no consensus to add the converting copy constructor or converting copy -assignment operator. However there was consensus to add the typedef. -

- -

-Proposed wording modified. Original proposed wording preserved here. Moved to -Review. -

- -
-

-Make ratio default constructible, copy-constructible and assignable -from any ratio which has the same reduced form. -

- -

-Add to 20.11.3 [ratio.ratio] synopsis -

- -
-template <intmax_t N, intmax_t D = 1>
-class ratio {
-public:
-  static constexpr intmax_t num;
-  static constexpr intmax_t den;
-
-  typedef ratio<num, den> type;
-
-  ratio() = default;
-  template <intmax_t N2, intmax_t D2>
-    ratio(const ratio<N2, D2>&);
-  template <intmax_t N2, intmax_t D2>
-    ratio& operator=(const ratio<N2, D2>&);
-};
-
- -

-Add to 20.11.3 [ratio.ratio]: -

- -
-

-Two ratio classes ratio<N1,D1> and ratio<N2,D2> -have the same reduced form if ratio<N1,D1>::type is the same -type as ratio<N2,D2>::type -

- -
- -

-Add a new section: [ratio.cons] -

- -
-

-Construction and assignment [ratio.cons] -

- -
-template <intmax_t N2, intmax_t D2>
-  ratio(const ratio<N2, D2>& r);
-
- -
-

-Effects: Constructs a ratio object. -

-

-Remarks: This constructor shall not participate in overload resolution -unless r has the same reduced form as *this. -

-
- -
-template <intmax_t N2, intmax_t D2>
-  ratio& operator=(const ratio<N2, D2>& r);
-
- -
-

-Effects: None. -

-

-Returns: *this. -

-

-Remarks: This operator shall not participate in overload resolution -unless r has the same reduced form as *this. -

-
- -
- -

-Change 20.11.4 [ratio.arithmetic] -

- -
-

-Implementations may use other algorithms to compute these values. If overflow -occurs, a diagnostic shall be issued. -

- -
-template <class R1, class R2> struct ratio_add {
-  typedef see below type;
-};
-
- -

-The nested typedef type shall be a synonym for ratio<T1, -T2>::type where T1 has the value R1::num * -R2::den + R2::num * R1::den and T2 has the value R1::den * -R2::den. -

- -
-template <class R1, class R2> struct ratio_subtract {
-  typedef see below type;
-};
-
- -

-The nested typedef type shall be a synonym for ratio<T1, -T2>::type where T1 has the value R1::num * -R2::den - R2::num * R1::den and T2 has the value R1::den * -R2::den. -

- -
-template <class R1, class R2> struct ratio_multiply {
-  typedef see below type;
-};
-
- -

-The nested typedef type shall be a synonym for ratio<T1, -T2>::type where T1 has the value R1::num * -R2::num and T2 has the value R1::den * R2::den. -

- -
-template <class R1, class R2> struct ratio_divide {
-  typedef see below type;
-};
-
- -

-The nested typedef type shall be a synonym for ratio<T1, -T2>::type where T1 has the value R1::num * -R2::den and T2 has the value R1::den * R2::num. -

- -
- -
- -
- -

[ -2010-03-27 Howard adds: -]

- - -
-

-Daniel brought to my attention the recent addition of the typedef type -to the FCD -N3092: -

- -
-typedef ratio type;
-
- -

-This issue was discussed in Pittsburgh, and the decision there was to accept the -typedef as proposed and move to Review. Unfortunately the issue was accidently -applied to the FCD, and incorrectly. The FCD version of the typedef refers to -ratio<N, D>, but the typedef is intended to refer to -ratio<num, den> which in general is not the same type. -

- -

-I've updated the wording to diff against -N3092. -

- -
- -

[Batavia: NAD EditorialResolved - see rationale below]

- - - - -

Rationale:

Already fixed in working draft

- -

Proposed resolution:

-

-Add to 20.11.3 [ratio.ratio] synopsis -

- -
-template <intmax_t N, intmax_t D = 1>
-class ratio {
-public:
-  static constexpr intmax_t num;
-  static constexpr intmax_t den;
-
-  typedef ratio<num, den> type;
-};
-
- - - - - - -
-

1283. MoveConstructible and MoveAssignable need clarification -of moved-from state

-

Section: 17.6.3.1 [utility.arg.requirements] Status: Resolved - Submitter: Howard Hinnant Opened: 2009-12-12 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

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-

Discussion:

-

Addresses UK 150

- -

-There is on going confusion over what one can and can not do with a moved-from -object (e.g. -UK 150, -910). -This issue attempts to clarify that moved-from objects are valid objects with an -unknown state. -

- -

[ -2010-01-22 Wording tweaked by Beman. -]

- - -

[ -2010-01-22 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-01-23 Alisdair opens: -]

- - -
-

-I'm afraid I must register an objection. -

- -

-My primary objection is that I have always been opposed to this kind of a -resolution as over-constraining. My preferred example is a call implementing -the pImpl idiom via unique_ptr. Once the pImpl has been moved from, it -is no longer safe to call the vast majority of the object's methods, yet I see -no reason to make such a type unusable in the standard library. I would prefer -a resolution along the lines suggested in the UK comment, which only requires -that the object can be safely destroyed, and serve as the target of an -assignment operator (if supported.) -

- -

-However, I will not hold the issue up if I am a lone dissenting voice on this -(yes, that is a call to hear more support, or I will drop that objection in -Pittsburgh) -

- -

-With the proposed wording, I'm not clear what the term 'valid object' means. In -my example above, is a pImpl holding a null pointer 'valid'? What about a float -holding a signalling NaN? What determines if an object is valid? Without a -definition of a valid/invalid object, I don't think this wording adds anything, -and this is an objection that I do want resolved. -

- -

[ -2010-01-24 Alisdair removes his objection. -]

- - -

[ -2010-01-24 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -
- -

[ -2010-02-10 Reopened. The wording here has been merged into 1309. -]

- - -

[ -2010-02-10 Moved to Tentatively NAD EditorialResolved after 5 postive votes on -c++std-lib. Rationale added below. -]

- - - - -

Rationale:

-

-This issue is now addressed by 1309. -

- - -

Proposed resolution:

-

-Change the follwing tables in 17.6.3.1 [utility.arg.requirements] as shown: -

- -
- - - - - - - - - - - - - - -
Table 33 — MoveConstructible requirements [moveconstructible]
ExpressionPost-condition
-T t(rv) - -t is equivalent to the value of rv before the construction. -
-[Note: -There is no requirement on the value of rv after the -construction. -rv remains a valid object. Its state is unspecified. -— end note] -
- -
-
- - - - - - - - - - - - - - - - - - -
Table 35 — MoveAssignable requirements [moveassignable]
ExpressionReturn typeReturn valuePost-condition
-t = rv - -T& - -t - -t is equivalent to the value of rv before the assigment. -
-[Note: -There is no requirement on the value of rv after the -assignment. -rv remains a valid object. Its state is unspecified. -— end note] -
- -
- - - - - -
-

1284. vector<bool> initializer_list constructor missing an allocator argument

-

Section: 23.3.7 [vector.bool] Status: C++11 - Submitter: Bo Persson Opened: 2009-12-09 Last modified: 2015-04-08

-

View all other issues in [vector.bool].

-

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-

Discussion:

-

-The specialization for vector<bool> (23.3.7 [vector.bool]) -has a constructor -

- -
-vector(initializer_list<bool>);
-
- -

-which differs from the base template's constructor (and other containers) in -that it has no allocator parameter. -

- -

[ -2009-12-16 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change the signature in the synopsis of 23.3.7 [vector.bool] to -

- -
-vector(initializer_list<bool>, const Allocator& = Allocator());
-
- - - - - -
-

1285. allocator_traits call to new

-

Section: 20.7.8.2 [allocator.traits.members] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-12-10 Last modified: 2015-04-08

-

View all other issues in [allocator.traits.members].

-

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-

Discussion:

-

-LWG issue 402 added "::" to the call to new -within allocator::construct. I suspect we want to retain that fix. -

- -

[ -2009-12-13 Moved to Tentatively Ready after 7 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 17.6.3.5 [allocator.requirements], table 40 "Allocator requirements": -

- -
- - - - - - - - - - - - - - -
Table 40 — Allocator requirements
ExpressionReturn typeAssertion/note
pre-/post-condition		Default
-a.construct(c,args) - -(not used) - -Effect: Constructs an object of type C at c - -::new ((void*)c) C(forward<Args>(args)...) -
-
- -

-Change 20.7.8.2 [allocator.traits.members], p4: -

- -
-template <class T, class... Args>
-  static void construct(Alloc& a, T* p, Args&&... args);
-
-

-4 Effects: calls a.construct(p, -std::forward<Args>(args)...) if that call is well-formed; otherwise, -invokes ::new (static_cast<void*>(p)) -T(std::forward<Args>(args)...). -

-
- - - - - -
-

1286. allocator_traits::select_on_container_copy_construction type-o

-

Section: 20.7.8.2 [allocator.traits.members] Status: C++11 - Submitter: Howard Hinnant Opened: 2009-12-10 Last modified: 2015-04-08

-

View all other issues in [allocator.traits.members].

-

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-

Discussion:

-

-allocator_traits::select_on_container_copy_construction refers to an -unknown "a": -

- -
-static Alloc select_on_container_copy_construction(const Alloc& rhs);
-
- -

-7 Returns: rhs.select_on_container_copy_construction(a) if that -expression is well-formed; otherwise, rhs. -

-
- -

[ -2009-12-13 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Change 20.7.8.2 [allocator.traits.members], p7: -

- -
-static Alloc select_on_container_copy_construction(const Alloc& rhs);
-
- -

-7 Returns: -rhs.select_on_container_copy_construction(a) if that -expression is well-formed; otherwise, rhs. -

-
- - - - - -
-

1287. std::function requires CopyConstructible target object

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: C++11 - Submitter: Jonathan Wakely Opened: 2009-12-13 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.con].

-

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-

Discussion:

-

-I think std::function should require CopyConstructible for the -target object. -

- -

-I initially thought that MoveConstructible was enough, but it's not. If -F is move-only then function's copy constructor cannot be called, but -because function uses type erasure, F is not known and so the copy -constructor cannot be disabled via enable_if. One option would be to -throw an exception if you try to copy a function with a non-copyable target -type, but I think that would be a terrible idea. -

- -

-So although the constructors require that the target be initialised by -std::move(f), that's only an optimisation, and a copy constructor is -required. -

- -

[ -2009-12-24 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Add to 20.9.12.2.1 [func.wrap.func.con] paragraph 9: -

- -
-template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
- -

-9 Requires: F shall be CopyConstructible. -f shall be callable for argument types ArgTypes and return -type R. The copy constructor and destructor of A shall not -throw exceptions. -

-
- - - - - - -
-

1288. std::function assignment from rvalues

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: C++11 - Submitter: Jonathan Wakely Opened: 2009-12-13 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.con].

-

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-

Discussion:

-

-In 20.9.12.2.1 [func.wrap.func.con] -

- -
-template<class F> function& operator=(F f);
-
-
-

-20 Effects: function(f).swap(*this); -

-

-21 Returns: *this -

-
-
- -

-This assignment operator can be called such that F is an rvalue-reference e.g. -

- -
-func.operator=<F&&>(f);
-
- -

-There are two issues with this. -

- -
    -
  1. -the effects mean that f is passed as an lvalue and so there will be an -unnecessary copy. The argument should be forwarded, so that the copy can be -avoided. -
    2. -
  2. -It should not be necessary to use that syntax to pass an rvalue. As F -is a deduced context it can be made to work with either lvalues or rvalues. -
    3. -
- -

-The same issues apply to function::assign. -

- -

-N.B. this issue is not related to 1287 and applies whether that -issue is resolved or not. The wording below assumes the resolution of LWG 1258 has been applied. -

- -

[ -2009-12-16 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -201002-11 Opened by Alisdair for the purpose of merging 1258 into -this issue as there is a minor conflict. -]

- - -

[ -2010-02-11 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-In 20.9.12.2.1 [func.wrap.func.con] -

- -
-template<class F> function& operator=(F&& f);
-
-
-

-20 Effects: -function(std::forward<F>(f)).swap(*this); -

-

-21 Returns: *this -

-
-
- -

-In 20.9.12.2.2 [func.wrap.func.mod] -

- -
-template<class F, Allocator Allocclass A>
-  void assign(F&& f, const Alloc& a);
-
-
-

-3 Effects: function(f, aallocator_arg, a, -std::forward<F>(f)).swap(*this); -

-
-
- -

-Update member function signature for class template in 20.9.12.2 [func.wrap.func] -

- -
-template<class F> function& operator=(F&&);
-
-template<class F, class A> void assign(F&&, const A&);
-
- - - - - - - -
-

1290. Don't require [u|bi]nary_function inheritance

-

Section: 20.9 [function.objects] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-12-14 Last modified: 2015-04-08

-

View all other issues in [function.objects].

-

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-

Discussion:

-

-This issue is a follow-up of the discussion on issue 870 during -the 2009 Santa Cruz meeting. -

- -

-The class templates unary_function and binary_function are -actually very simple typedef providers, -

- -
-namespace std {
-
-template <class Arg, class Result>
-struct unary_function {
- typedef Arg argument_type;
- typedef Result result_type;
-};
-
-template <class Arg1, class Arg2, class Result>
-struct binary_function {
- typedef Arg1 first_argument_type;
- typedef Arg2 second_argument_type;
- typedef Result result_type;
-};
-
-}
-
- -

-which may be used as base classes (similarly to the iterator template), -but were originally not intended as a customization point. The SGI -documentation introduced the concept -Adaptable Unary -Function as function objects "with nested typedefs that define its argument -type and result type" and a similar definition for -Adaptable Binary -Function related to binary_function. But as of TR1 a protocol was -introduced that relies on inheritance relations based on these types. 20.9.4 [refwrap]/3 b. 3 requires that a specialization of -reference_wrapper<T> shall derive from unary_function, -if type T is "a class type that is derived from -std::unary_function<T1, R>" and a similar inheritance-based rule -for binary_function exists as well. -

- -

-As another disadvantage it has been pointed out in the TR1 issue list, N1837 -(see section 10.39), that the requirements of mem_fn 20.9.11 [func.memfn]/2+3 to derive from -std::unary_function/std::binary_function under circumstances, where the -provision of corresponding typedefs would be sufficient, unnecessarily prevent -implementations that take advantage of empty-base-class optimizations. -

- -

-Both requirements should be relaxed in the sense that the -reference_wrapper should provide typedef's argument_type, -first_argument_type, and second_argument_type based on similar -rules as the weak result type rule (20.9.2 [func.require]/3) does -specify the presence of result_type member types. -

- -

-For a related issue see also 1279. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3145 -would resolve this issue as NAD editorial. -

- - - -

[ -2010-11 Batavia: Solved by N3198 -]

- -

-Resolved by adopting n3198. -

- -

-Previous proposed resolution: -

-

[ -The here proposed resolution is an attempt to realize the common denominator of -the reflector threads c++std-lib-26011, c++std-lib-26095, and c++std-lib-26124. -]

- -
-
    -
  1. -

    -Change [base]/1 as indicated: [The intend is to provide an -alternative fix for issue 1279 and some editorial harmonization -with existing wording in the library, like 24.4.2 [iterator.basic]/1] -

    - -
    -

    -1 The following class templates are provided to simplify the -definition of typedefs of the argument and result types for -function objects. The behavior of a program that adds specializations for any of -these templates is undefined.: -

    - -
    -namespace std {
- template <class Arg, class Result>
- struct unary_function {
-   typedef Arg argument_type;
-   typedef Result result_type;
- };
-}
-
-namespace std {
- template <class Arg1, class Arg2, class Result>
- struct binary_function {
-   typedef Arg1 first_argument_type;
-   typedef Arg2 second_argument_type;
-   typedef Result result_type;
- };
-}
-
    -
    -
    2. - -
  2. -

    -Change 20.9.4 [refwrap], class template reference_wrapper -synopsis as indicated: [The intent is to remove the requirement that -reference_wrapper derives from unary_function or -binary_function if the situation requires the definition of the -typedefs argument_type, first_argument_type, or -second_argument_type. This change is suggested, because the new way of -definition uses the same strategy as the weak result type specification -applied to argument types, which provides the following advantages: It creates -less potential conflicts between [u|bi]nary_function bases and typedefs -in a function object and it ensures that user-defined function objects which -provide typedefs but no such bases are handled as first class citizens.] -

    - -
    -namespace std {
- template <class T> class reference_wrapper
-   : public unary_function<T1, R> // see below
-   : public binary_function<T1, T2, R> // see below
- {
- public :
-   // types
-   typedef T type;
-   typedef see below result_type; // not always defined
-   typedef see below argument_type; // not always defined
-   typedef see below first_argument_type; // not always defined
-   typedef see below second_argument_type; // not always defined
-
-   // construct/copy/destroy
-   ...
- };
-
    -
    3. - -
  3. -

    -Change 20.9.4 [refwrap]/3 as indicated: [The intent is to remove the -requirement that reference_wrapper derives from unary_function -if the situation requires the definition of the typedef argument_type -and result_type. Note that this clause does concentrate on -argument_type alone, because the result_type is already ruled -by p. 2 via the weak result type specification. The new way of -specifying argument_type is equivalent to the weak result type -specification] -

    - -
    -

    -3 The template instantiation reference_wrapper<T> shall be -derived from std::unary_function<T1, R>define a nested -type named argument_type as a synonym for T1 only if the -type T is any of the following: -

    -
      -
    • a function type or a pointer to function type taking one argument -of type T1 and returning R -
      • -
    • a pointer to member function R T0::f cv (where -cv represents the member function's cv-qualifiers); -the type T1 is cv T0* -
      • -
    • a class type that is derived from -std::unary_function<T1, R>with a member type -argument_type; - the type T1 is T::argument_type -
      • -
    -
    -
    4. - -
  4. -

    -Change 20.9.4 [refwrap]/4 as indicated: [The intent is to remove the -requirement that reference_wrapper derives from -binary_function if the situation requires the definition of the typedef -first_argument_type, second_argument_type, and -result_type. Note that this clause does concentrate on -first_argument_type and second_argument_type alone, because -the result_type is already ruled by p. 2 via the weak result -type specification. The new way of specifying first_argument_type -and second_argument_type is equivalent to the weak result type -specification] -

    - -
    -

    -The template instantiation reference_wrapper<T> shall be -derived from std::binary_function<T1, T2, R>define two -nested types named first_argument_type and -second_argument_type as a synonym for T1 and T2, -respectively, only if the type T is any of the following: -

    -
      -
    • a function type or a pointer to function type taking two arguments -of types T1 and T2 and returning -R -
      • -
    • a pointer to member function R T0::f(T2) cv -(where cv represents the member function's cv-qualifiers); - the type T1 is cv T0* -
      • -
    • a class type that is derived from -std::binary_function<T1, T2, R>with member -types first_argument_type - and second_argument_type; the type T1 is -T::first_argument_type and the type T2 is - T::second_argument_type -
      • -
    -
    -
    5. - -
  5. -

    -Change 20.9.11 [func.memfn]/2+3 as indicated: [The intent is to remove -the requirement that mem_fn's return type has to derive -from [u|bi]nary_function. The reason for suggesting the -change here is to better support empty-base-class optimization -choices as has been pointed out in -N1837] -

    - -
    -

    -2 The simple call wrapper shall be derived from -std::unary_function<cv T*, Ret>define -two nested types named argument_type and result_type as a -synonym for cv T* and Ret, respectively, -when pm is a pointer to member function with cv-qualifier cv -and taking no arguments, where Ret is pm's return type. -

    -

    -3 The simple call wrapper shall be derived from -std::binary_function<cv T*, T1, -Ret>define three nested types named -first_argument_type, second_argument_type, and -result_type as a synonym for cv T*, T1, and -Ret, respectively, when pm is a pointer to member -function with cv-qualifier cv and taking one argument of type -T1, where Ret is pm's return type. -

    -
    -
    6. - -
-
- -

Proposed resolution:

-Addressed by paper n3198. -

- - - -
-

1291. Exceptions thrown during promise::set_value

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-12-18 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

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-

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-

Discussion:

-

-In 30.6.5 [futures.promise] -

- -

-Does promise<R>::set_value return normally if the copy/move -constructor of R throws? -

- -

-The exception could be caught and set using -promise<R>::set_exception, or it could be allowed to leave the -set_value call, but it's not clear which is intended. I suggest the -exception should not be caught. -

- -

-N.B. This doesn't apply to promise<R&>::set_value or -promise<void>::set_value because they don't construct a new -object. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

-

-Change 30.6.5 [futures.promise]/18: -

- -

-18 Throws: future_error if its associated state is already -ready or, for the first version an exception thrown by the copy constructor -of R, or for the second version an exception thrown by the move -constructor of R. -

- - - - - -
-

1292. std::function should support all callable types

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-12-19 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Some parts of the specification of std::function is unnecessarily -restricted to a subset of all callable types (as defined in 20.9.1 [func.def]/3), even though the intent clearly is to be usable for -all of them as described in 20.9.12.2 [func.wrap.func]/1. This -argument becomes strengthened by the fact that current C++0x-compatible -compilers work fine with them: -

- -
-#include <functional>
-#include <iostream>
-
-struct A
-{
-  int foo(int i) const {return i+1;}
-};
-
-struct B
-{
-  int mem;
-};
-
-int main()
-{
-  std::function<int(const A&, int)> f(&A::foo);
-  A a;
-  std::cout << f(a, 1) << '\n';
-  std::cout << f.target_type().name() << '\n';
-  typedef int (A::* target_t)(int) const;
-  target_t* p = f.target<target_t>();
-  std::cout << (p != 0) << '\n';
-  std::function<int(B&)> f2(&B::mem);
-  B b = { 42 };
-  std::cout << f2(b) << '\n';
-  std::cout << f2.target_type().name() << '\n';
-  typedef int (B::* target2_t);
-  target2_t* p2 = f2.target<target2_t>();
-  std::cout << (p2 != 0) << '\n';
-}
-
- -

-The problematic passages are 20.9.12.2.1 [func.wrap.func.con]/10: -

- -
-template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
-
-

...

-

-10 Postconditions: !*this if any of the following hold: -

-
    -
  • -f is a NULL function pointer. -
    • -
  • -f is a NULL member function pointer. -
    • -
  • -F is an instance of the function class template, and !f -
    • -
-
-
- -

-because it does not consider pointer to data member and all constraints based on -function objects which like 20.9.12.2 [func.wrap.func]/2 or 20.9.12.2.5 [func.wrap.func.targ]/3. The latter two will be resolved by the proposed -resolution of 870 and are therefore not handled here. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 20.9.12.2.1 [func.wrap.func.con]/10+11 as indicated: -

- -
-template<class F> function(F f);
-template <class F, class A> function(allocator_arg_t, const A& a, F f);
-
-
-

...

-

-10 Postconditions: !*this if any of the following hold: -

-
    -
  • -f is a NULL function pointer. -
    • -
  • -f is a NULL pointer to member function pointer. -
    • -
  • -F is an instance of the function class template, and !f -
    • -
- -

-11 Otherwise, *this targets a copy of f or, -initialized with std::move(f) if f is not a pointer -to member function, and targets a copy of mem_fn(f) if f is a -pointer to member function. [Note: implementations are encouraged -to avoid the use of dynamically allocated memory for small function objects, for -example, where f's target is an object holding only a pointer or -reference to an object and a member function pointer. — end note] -

- -
-
- - - - - -
-

1293. unique_ptr<T[], D> needs to get rid of unspecified-pointer-type

-

Section: 20.8.1.3 [unique.ptr.runtime] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-12-20 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.runtime].

-

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-

Discussion:

-

Addresses UK 211

- -

-As a response to UK 211 LWG issue 1021 has replaced the -unspecified-pointer-type by nullptr_t to allow assignment of -type-safe null-pointer literals in the non-array form of -unique_ptr::operator=, but did not the same for the specialization for -arrays of runtime length. But without this parallel change of the signature we -have a status quo, where unique_ptr<T[], D> declares a member -function which is completely unspecified. -

- -

[ -2009-12-21 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-03-14 Howard adds: -]

- - -

-We moved -N3073 -to the formal motions page in Pittsburgh which should obsolete this issue. I've -moved this issue to NAD Editorial, solved by N3073. -

- - - -

Rationale:

-

-Solved by N3073. -

- - -

Proposed resolution:

-

-In 20.8.1.3 [unique.ptr.runtime], class template unique_ptr<T[], -D> synopsis, change as indicated: -

- -
-// assignment
-unique_ptr& operator=(unique_ptr&& u);
-unique_ptr& operator=(unspecified-pointer-typenullptr_t);
-
- - - - - - -
-

1294. Difference between callable wrapper and forwarding call wrapper unclear

-

Section: 20.9.2 [func.require] Status: C++11 - Submitter: Jens Maurer Opened: 2009-12-21 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-The current wording in the standard makes it hard to discriminate the difference -between a "call wrapper" as defined in 20.9.1 [func.def]/5+6: -

- -
-

-5 A call wrapper type is a type that holds a callable object and supports -a call operation that forwards to that object. -

-

-6 A call wrapper is an object of a call wrapper type. -

-
- -

-and a "forwarding call wrapper" as defined in 20.9.2 [func.require]/4: -

- -
-

-4 [..] A forwarding call wrapper is a call wrapper that can be called -with an argument list. [Note: in a typical implementation forwarding call -wrappers have an overloaded function call operator of the form -

- -
-template<class... ArgTypes>
-R operator()(ArgTypes&&... args) cv-qual;
-
- -

-— end note] -

-
- -

-Reason for this lack of clear difference seems to be that the wording adaption -to variadics and rvalues that were applied after it's original proposal in N1673: -

- -
-

-[..] A forwarding call wrapper is a call wrapper that can be called -with an argument list t1, t2, ..., tN where each ti is an lvalue. -The effect of calling a forwarding call wrapper with one or more -arguments that are rvalues is implementation defined. [Note: in -a typical implementation forwarding call wrappers have overloaded -function call operators of the form -

- -
-template<class T1, class T2, ..., class TN>
-R operator()(T1& t1, T2& t2, ..., TN& tN) cv-qual;
-
- -

-— end note] -

-
- -

-combined with the fact that the word "forward" has two different meanings in -this context. This issue attempts to clarify the difference better. -

- -

[ -2010-09-14 Daniel provides improved wording and verified that it is correct against N3126. Previous resolution is shown here: -]

- - -
-

-4 [..] A forwarding call wrapper is a call wrapper that can be called -with an arbitrary argument list and uses perfect forwarding to -deliver the arguments to the wrapped callable object. [Note: in a -typical implementation forwarding call wrappers have an overloaded function call -operator of the form -

- -
-template<class... ArgTypes>
-R operator()(ArgTypes&&... args) cv-qual;
-
- -

-— end note] -

-
- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 20.9.2 [func.require]/4 as indicated: -

- -

-[..] A forwarding call wrapper is a call wrapper that can be called with an arbitrary argument -list and delivers the arguments as references to the wrapped callable object. This forwarding step shall ensure -that rvalue arguments are delivered as rvalue-references and lvalue arguments are delivered as lvalue-references. -[Note: in a typical implementation forwarding call wrappers have an overloaded function call operator of the -form -

- -
-template<class... UnBoundArgs>
-R operator()(UnBoundArgs&&... unbound_args) cv-qual;
-
-

-— end note ] -

-
- - - - - - -
-

1295. Contradictory call wrapper requirements

-

Section: 20.9.2 [func.require] Status: C++11 - Submitter: Daniel Krügler Opened: 2009-12-22 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-20.9.2 [func.require]/3 b 1 says -

- -
-

-3 If a call wrapper (20.9.1 [func.def]) has a weak result type the -type of its member type result_type is based on the type T of -the wrapper's target object (20.9.1 [func.def]): -

- -
    -
  • -if T is a function, reference to function, or pointer to function type, -result_type shall be a synonym for the return type of T; -
    • -
  • -[..] -
    • -
-
- -

-The first two enumerated types (function and reference to function) -can never be valid types for T, because -

- -

-20.9.1 [func.def]/7 -

- -

-7 A target object is the callable object held by a call wrapper. -

- -

-and 20.9.1 [func.def]/3 -

- -

-3 A callable type is a pointer to function, a pointer to member function, -a pointer to member data, or a class type whose objects can appear immediately -to the left of a function call operator. -

- -

-exclude functions and references to function as "target objects". -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 20.9.2 [func.require]/3 b 1 as indicated: -

- -
-

-3 If a call wrapper (20.9.1 [func.def]) has a weak result type the -type of its member type result_type is based on the type T of -the wrapper's target object (20.9.1 [func.def]): -

- -
    -
  • -if T is a function, reference to function, or pointer to -function type, result_type shall be a synonym for the return type of -T; -
    • -
  • -[..] -
    • -
-
- - - - - - -
-

1297. unique_ptr's relational operator functions should induce a total order

-

Section: 20.8.1.5 [unique.ptr.special] Status: Resolved - Submitter: Daniel Krügler Opened: 2009-12-23 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-The comparison functions of unique_ptr currently directly delegate to -the underlying comparison functions of unique_ptr<T, D>::pointer. -This is disadvantageous, because this would not guarantee to induce a total -ordering for native pointers and it is hard to define a total order for mixed -types anyway. -

-

-The currently suggested resolution for shared_ptr comparison as of -1262 uses a normalization strategy: They perform the comparison on -the composite pointer type (5.9 [expr.rel]). This is not -exactly possible for unique_ptr in the presence of user-defined -pointer-like types but the existing definition of std::duration -comparison as of 20.12.5.6 [time.duration.comparisons] via -common_type of both argument types demonstrates a solution of this -problem. The approach can be seen as the general way to define a composite -pointer type and this is the approach which is used for here suggested -wording change. -

-

-For consistency reasons I would have preferred the same normalization strategy -for == and !=, but Howard convinced me not to do so (now). -

- -

[ -2010-11-03 Daniel comments and adjustes the currently proposed wording changes: -]

- - -

-Issue 1401 is remotely related. Bullet A of its proposed resolution -provides an alternative solution for issue discussed here and addresses NB comment GB-99. -Additionally I updated the below suggested wording in regard to the following: -It is an unncessary requirement that the below defined effective composite pointer-like -type CT satisfies the LessThanComparable requirements. All what is -needed is, that the function object type less<CT> induces a strict -weak ordering on the pointer values. -

- -

[2011-03-24 Madrid meeting]

- - -

Resolved by 1401

- - - -

Proposed resolution:

- -

-Change 20.8.1.5 [unique.ptr.special]/4-7 as indicated: [The implicit -requirements and remarks imposed on the last three operators are the same as for -the first one due to the normative "equivalent to" usage within a Requires -element, see 17.5.1.4 [structure.specifications]/4. The effects of this -change are that all real pointers wrapped in a unique_ptr will order -like shared_ptr does.] -

- -
-template <class T1, class D1, class T2, class D2>
-  bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
- -
-

-? Requires: Let CT be common_type<unique_ptr<T1, -D1>::pointer, unique_ptr<T2, D2>::pointer>::type. Then -the specialization less<CT> shall be a function object type ([function.objects]) -that induces a strict weak ordering ([alg.sorting]) on the pointer values. -

- -

-4 Returns: less<CT>()(x.get(), y.get())x.get() -< y.get(). -

- -

-? Remarks: If unique_ptr<T1, D1>::pointer is not -implicitly convertible to CT or unique_ptr<T2, -D2>::pointer is not implicitly convertible to CT, the program -is ill-formed. -

-
- -
-template <class T1, class D1, class T2, class D2>
-  bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
- -

-5 Effects: Equivalent to return !(y < x) -Returns: x.get() <= y.get(). -

- -
-template <class T1, class D1, class T2, class D2>
-  bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
- -

-6 Effects: Equivalent to return (y < x) -Returns: x.get() > y.get(). -

- -
-template <class T1, class D1, class T2, class D2>
-  bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
- -

-7 Effects: Equivalent to return !(x < y) -Returns: x.get() >= y.get(). -

-
- - - - - - -
-

1298. Missing specialization of ctype_byname<char>

-

Section: 22.2 [locale.syn] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-12-25 Last modified: 2015-04-08

-

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-

Discussion:

-

-The <locale> synopsis in 22.2 [locale.syn] calls out an -explicit specialization for ctype_byname<char>, however no such -specialization is defined in the standard. The only reference I can find to -ctype_byname<char> is 22.3.1.1.2 [locale.facet]:Table 77 -— Required specializations (for facets) which also refers to -ctype_byname<wchar_t> which has no special consideration. -

- -

-Is the intent an explicit instantiation which would use a slightly -different syntax? Should the explicit specialization simply be struck? -

- -

[ -2010-01-31 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-22.2 [locale.syn] -

- -
-

-Strike the explicit specialization for ctype_byname<char> from -the <locale> synopsis -

-
-...
-template <class charT> class ctype_byname;
-template <>            class ctype_byname<char>;  // specialization
-...
-
-
- - - - - -
-

1299. Confusing typo in specification for get_time

-

Section: 27.7.5 [ext.manip] Status: C++11 - Submitter: Alisdair Meredith Opened: 2009-12-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Extended Manipulators 27.7.5 [ext.manip] p8 defines the semantics of -get_time in terms of a function f. -

- -
-template <class charT, class traits>
-void f(basic_ios<charT, traits>& str, struct tm* tmb, const charT* fmt) {
-   typedef istreambuf_iterator<charT, traits> Iter;
-   typedef time_get<charT, Iter> TimeGet;
-
-   ios_base::iostate err = ios_base::goodbit;
-   const TimeGet& tg = use_facet<TimeGet>(str.getloc());
-
-   tm.get(Iter(str.rdbuf()), Iter(), str, err, tmb, fmt, fmt + traits::length(fmt));
-
-   if (err != ios_base::goodbit)
-       str.setstate(err):
-}
-
- -

-Note the call to tm.get. This is clearly an error, as tm is a -type and not an object. I believe this should be tg.get, rather than -tm, but this is not my area of expertise. -

- -

[ -2010-01-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - -

Proposed resolution:

-

-Change 27.7.5 [ext.manip] p8: -

- -
-template <class charT, class traits>
-void f(basic_ios<charT, traits>& str, struct tm* tmb, const charT* fmt) {
-   typedef istreambuf_iterator<charT, traits> Iter;
-   typedef time_get<charT, Iter> TimeGet;
-
-   ios_base::iostate err = ios_base::goodbit;
-   const TimeGet& tg = use_facet<TimeGet>(str.getloc());
-
-   tgm.get(Iter(str.rdbuf()), Iter(), str, err, tmb, fmt, fmt + traits::length(fmt));
-
-   if (err != ios_base::goodbit)
-       str.setstate(err):
-}
-
- - - - - -
-

1300. Circular definition of promise::swap

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: Jonathan Wakely Opened: 2009-12-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-30.6.5 [futures.promise]/12 defines the effects of -promise::swap(promise&) as -

- -
-void swap(promise& other);
-
-

-12 Effects: swap(*this, other) -

-
- -

-and 30.6.5 [futures.promise]/25 defines swap(promise<R&>, -promise<R>&) as -

- -
-template <class R>
-  void swap(promise<R>& x, promise<R>& y);
-
-

-25 Effects: x.swap(y). -

-
- -

[ -2010-01-13 Daniel added "Throws: Nothing." -]

- - -

[ -2010-01-14 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-

-Change 30.6.5 [futures.promise] paragraph 12 -

- -
-void swap(promise& other);
-
-
-

-12 Effects: swap(*this, other) Exchanges the -associated -states of *this and other. -

-

-13 ... -

-

-Throws: Nothing. -

-
-
- - - - - - -
-

1303. shared_ptr, unique_ptr, and rvalue references v2

-

Section: 20.8.1.2 [unique.ptr.single], 20.8.2.2 [util.smartptr.shared] Status: C++11 - Submitter: Stephan T. Lavavej Opened: 2010-01-23 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single].

-

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-

Discussion:

-

-N3000 -20.8.2.2 [util.smartptr.shared]/1 still says: -

- -
-template <class Y, class D> explicit shared_ptr(const unique_ptr<Y, D>& r) = delete;
-template <class Y, class D> shared_ptr& operator=(const unique_ptr<Y, D>& r) = delete;
-
- -

-I believe that this is unnecessary now that "rvalue references v2" -prevents rvalue references from binding to lvalues, and I didn't -see a Library Issue tracking this. -

- -

[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -

-Strike from 20.8.1.2 [unique.ptr.single]: -

- -
-template <class T, class D = default_delete<T>> class unique_ptr {
-  ...
-  unique_ptr(const unique_ptr&) = delete;
-  template <class U, class E> unique_ptr(const unique_ptr<U, E>&) = delete;
-  unique_ptr& operator=(const unique_ptr&) = delete;
-  template <class U, class E> unique_ptr& operator=(const unique_ptr<U, E>&) = delete;
-};
-
- -

-Strike from 20.8.2.2 [util.smartptr.shared]: -

- -
-template<class T> class shared_ptr {
-  ...
-  template <class Y, class D> explicit shared_ptr(const unique_ptr<Y, D>& r) = delete;
-  ...
-  template <class Y, class D> shared_ptr& operator=(const unique_ptr<Y, D>& r) = delete;
-  ...
-};
-
- - - - - - -
-

1304. Missing preconditions for shared_future

-

Section: 30.6.7 [futures.shared_future] Status: Resolved - Submitter: Alisdair Meredith Opened: 2010-01-23 Last modified: 2015-04-08

-

View all other issues in [futures.shared_future].

-

View all issues with Resolved status.

-

Discussion:

- -

-The revised futures package in the current working paper simplified the -is_ready/has_exception/has_value set of APIs, replacing them with a -single 'valid' method. This method is used in many places to signal pre- and -post- conditions, but that edit is not complete. Each method on a -shared_future that requires an associated state should have a -pre-condition that valid() == true. -

- -

[ -2010-01-28 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010 Pittsburgh: -]

- - -

-Moved to NAD EditorialResolved. Rationale added below. -

- - - -

Rationale:

-

-Solved by N3058. -

- - -

Proposed resolution:

-

-Insert the following extra paragraphs: -

- -

-In 30.6.7 [futures.shared_future] -

- -
-shared_future();
-
-
-

-4 Effects: constructs ... -

- -

-Postcondition: valid() == false. -

- -

-Throws: nothing. -

-
-
- -
-void wait() const;
-
-
- -

-Requires: valid() == true. -

- -

-22 Effects: if the associated ... -

-
-
- -
-template <class Rep, class Period>
-  bool wait_for(const chrono::duration<Rep, Period>& rel_time) const;
-
-
- -

-Requires: valid() == true. -

- -

-23 Effects: if the associated ... -

-
-
- -
-template <class Clock, class Duration>
-  bool wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
-
-
- -

-Requires: valid() == true. -

- -

-25 Effects: blocks until ... -

-
-
- - - - - - -
-

1305. preconditions for atomic_future

-

Section: X [futures.atomic_future] Status: Resolved - Submitter: Alisdair Meredith Opened: 2010-01-23 Last modified: 2015-04-08

-

View all other issues in [futures.atomic_future].

-

View all issues with Resolved status.

-

Discussion:

- -

-The revised futures package in the current working paper simplified the -is_ready/has_exception/has_value set of APIs, replacing them with a -single 'valid' method. This method is used in many places to signal pre- and -post- conditions, but that edit is not complete. -

- -

-Atomic future retains the extended earlier API, and provides defined, -synchronized behaviour for all calls. However, some preconditions and throws -clauses are missing, which can easily be built around the new valid() -api. Note that for consistency, I suggest is_ready/has_exception/has_value -throw an exception if valid() is not true, rather than -return false. I think this is implied by the existing pre-condition on -is_ready. -

- -

[ -2010-01-23 See discussion starting with Message c++std-lib-26666. -]

- - -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3058. -

- - -

Proposed resolution:

-

-Insert the following extra paragraphs: -

- -

-In X [futures.atomic_future] -

- -
-bool is_ready() const;
-
-
-

-17 Precondition Requires: valid() == true. -

- -

-18 Returns: true only if the associated state is ready. -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- -
-bool has_exception() const;
-
-
- -

-Requires: valid() == true. -

- -

-19 Returns: true only if the associated state is ready and -contains an exception. -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- -
-bool has_value() const;
-
-
- -

-Requires: valid() == true. -

- -

-20 Returns: true only if the associated state is ready and -contains a value. -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- -
-void wait() const;
-
-
- -

-Requires: valid() == true. -

- -

-22 Effects: blocks until ... -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- -
-template <class Rep, class Period>
-  bool wait_for(const chrono::duration<Rep, Period>& rel_time) const;
-
-
- -

-Requires: valid() == true. -

- -

-23 Effects: blocks until ... -

- -

-24 Returns: true only if ... -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- -
-template <class Clock, class Duration>
-  bool wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
-
-
- -

-Requires: valid() == true. -

- -

-25 Effects: blocks until ... -

- -

-26 Returns: true only if ... -

- -

-Throws: future_error with an error condition of -no_state if the precondition is not met. -

- -
-
- - - - - - -
-

1306. pointer and const_pointer for <array>

-

Section: 23.3.2 [array] Status: C++11 - Submitter: Nicolai Josuttis Opened: 2010-01-24 Last modified: 2015-04-08

-

View other active issues in [array].

-

View all other issues in [array].

-

View all issues with C++11 status.

-

Discussion:

-

-Class <array> is the only sequence container class that has no -types pointer and const_pointer defined. You might argue that -this makes no sense because there is no allocator support, but on the other -hand, types reference and const_reference are defined for -array. -

- -

[ -2010-02-11 Moved to Tentatively Ready after 6 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-Add to Class template array 23.3.2 [array]: -

- -
-namespace std {
-  template <class T, size_t N >
-  struct array {
-    ...
-    typedef T value_type;
-    typedef T * pointer;
-    typedef const T * const_pointer;
-    ...
-  };
-}
-
- - - - - -
-

1307. exception_ptr and allocator pointers don't understand !=

-

Section: 18.8.5 [propagation] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-01-26 Last modified: 2015-04-08

-

View all other issues in [propagation].

-

View all issues with Resolved status.

-

Discussion:

-

-The current requirements for a conforming implementation of -std::exception_ptr (18.8.5 [propagation]/1-6) does not clarify -whether the expression -

- -
-e1 != e2
-e1 != nullptr
-
- -

-with e1 and e2 being two values of type -std::exception_ptr are supported or not. Reason for this oddity is that -the concept EqualityComparable does not provide operator !=. -

- -

-For the same reason programmers working against the types X::pointer, -X::const_pointer, X::void_pointer, and -X::const_void_pointer of any allocator concept X (17.6.3.5 [allocator.requirements]/4 + Table 40) in a generic context can not rely -on the availability of the != operation, which is rather unnatural and -error-prone. -

- -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3073. -

- - -

Proposed resolution:

- - - - - -
-

1309. Missing expressions for Move/CopyConstructible

-

Section: 17.6.3.1 [utility.arg.requirements] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-02-03 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with C++11 status.

-

Discussion:

-

-Table 33 — MoveConstructible requirements [moveconstructible] and -Table 34 — CopyConstructible requirements [copyconstructible] support -solely the following expression: -

- -
-T t(rv)
-
- -

-where rv is defined to be as "non-const rvalue of type T" and -t as a "modifiable lvalue of type T" in 17.6.3.1 [utility.arg.requirements]/1. -

- -

-This causes two different defects: -

- -
    -
  1. -

    -We cannot move/copy-initialize a const lvalue of type T as in: -

    - -
    -int get_i();
-
-const int i1(get_i());
-
    - -

    -both in Table 33 and in Table 34. -

    -
    2. - -
  2. -

    -The single support for -

    - -
    -T t(rv)
-
    - -

    -in case of CopyConstructible means that we cannot provide an -lvalue as a source of a copy as in -

    - -
    -const int& get_lri();
-
-int i2(get_lri());
-
    -
    3. -
- -

-I believe this second defect is due to the fact that this single -expression supported both initialization situations according -to the old (implicit) lvalue reference -> rvalue reference -conversion rules. -

- -

-Finally [copyconstructible] refers to some name u which is not part of -the expression, and both [copyconstructible] and [moveconstructible] should -support construction expressions from temporaries - this would be a stylistic -consequence in the light of the new DefaultConstructible requirements -and compared with existing requirements (see e.g. Container requirements or the -output/forward iterator requirements).. -

- -

[ -2010-02-09 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - -

[ -2010-02-10 Reopened. The proposed wording of 1283 has been -merged here. -]

- - -

[ -2010-02-10 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

- -
    - -
  1. -

    -Change 17.6.3.1 [utility.arg.requirements]/1 as indicated: [This change -suggestion is motivated to make type descriptions clearer: First, a, -b, and c may also be non-const T. Second, u -is described in a manner consistent with the container requirements tables.] -

    - -

    -1 The template definitions in the C++ standard library refer to various named -requirements whose details are set out in tables 31-38. In these tables, -T is an object or reference type to be supplied by a C++ -program instantiating a template; a, b, and c are -values of type (possibly const) T; s and -t are modifiable lvalues of type T; u denotes an -identifier; is a value of type (possibly const) T; -and rv is an non-const rvalue of type -T; and v is an lvalue of type (possibly const) -T or an rvalue of type const T. -

    -
    2. - -
  2. -

    -In 17.6.3.1 [utility.arg.requirements] Table 33 ([moveconstructible]) -change as indicated [Note: The symbol u is defined to be either a -const or a non-const value and is the right one we need here]: -

    - -
    - - - - - - - - - - - - - - - - - - - - - -
    Table 33 — MoveConstructible requirements [moveconstructible]
    ExpressionPost-condition
    -T tu(rv); - -tu is equivalent -to the value of rv before the construction -
    T(rv)T(rv) is equivalent to the value of rv before the -construction
    [Note: -There is no requirement on the value of rv after the -construction. -rv remains a valid object. Its state is unspecified. -— end note]
    -
    -
    3. - -
  3. -

    -In 17.6.3.1 [utility.arg.requirements] Table 34 ([copyconstructible]) -change as indicated [Note: The symbol u is defined to be either a -const or a non-const value and is the right one we need here. The expressions -using a are recommended to ensure that lvalues are supported as sources -of the copy expression]: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 34 — CopyConstructible requirements [copyconstructible]
    -(in addition to MoveConstructible)
    ExpressionPost-condition
    -T tu(rv); - -the value of uv -is unchanged and is equivalent to tu -
    -T(v) -the value of v is unchanged and is equivalent to T(v) -
    [Note: A type that satisfies the -CopyConstructible requirements also satisfies the MoveConstructible -requirements. — end note]
    -
    - -
    4. - -
  4. -

    -In Table 35 — MoveAssignable requirements [moveassignable] change as -indicated: -

    - -
    - - - - - - - - - - - - - - - - - - -
    Table 35 — MoveAssignable requirements [moveassignable]
    ExpressionReturn typeReturn valuePost-condition
    -t = rv - -T& - -t - -t is equivalent to the value of rv before the assigment. -
    -[Note: -There is no requirement on the value of rv after the -assignment. -rv remains a valid object. Its state is unspecified. -— end note] -
    - -
    -
    5. - -
  5. -

    -In 17.6.3.1 [utility.arg.requirements] change Table 36 as indicated: -

    - -
    - - - - - - - - - - - - - - - - - - - - - -
    Table 36 — CopyAssignable requirements -[copyassignable]
    (in addition to MoveAssignable)
    ExpressionReturn typeReturn valuePost-condition
    t = uvT&tt is equivalent to uv, the value of -uv is unchanged
    [Note: A type that satisfies the CopyAssignable -requirements also satisfies the MoveAssignable requirements. — -end note]
    -
    -
    6. -
- - - - - - -
-

1310. forward_list splice_after from lvalues

-

Section: 23.3.4.6 [forwardlist.ops] Status: C++11 - Submitter: Howard Hinnant Opened: 2010-02-05 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with C++11 status.

-

Discussion:

-

-We've moved 1133 to Tentatively Ready and I'm fine with that. -

- -

-1133 adds lvalue-references to the splice signatures for list. So now -list can splice from lvalue and rvalue lists (which was the intent of the -original move papers btw). During the discussion of this issue it was mentioned -that if we want to give the same treatment to forward_list, that should be a -separate issue. -

- -

-This is that separate issue. -

- -

-Consider the following case where you want to splice elements from one place in -a forward_list to another. Currently this must be coded like so: -

- -
-fl.splice_after(to_here, std::move(fl), from1, from2);
-
- -

-This looks pretty shocking to me. I would expect to be able to code instead: -

- -
-fl.splice_after(to_here, fl, from1, from2);
-
- -

-but we currently don't allow it. -

- -

-When I say move(fl), I consider that as saying that I don't care about -the value of fl any more (until I assign it a new value). But in the -above example, this simply isn't true. I do care about the value of fl -after the move, and I'm not assigning it a new value. I'm merely permuting its -current value. -

- -

-I propose adding forward_list& overloads to the 3 -splice_after members. For consistency's sake (principal of least -surprise) I'm also proposing to overload merge this way as well. -

- - -

Proposed resolution:

-

-Add to the synopsis of 23.3.4.1 [forwardlist.overview]: -

- -
-template <class T, class Allocator = allocator<T> >
-class forward_list {
-public:
-  ...
-  // [forwardlist.ops], forward_list operations:
-  void splice_after(const_iterator p, forward_list& x);
-  void splice_after(const_iterator p, forward_list&& x);
-  void splice_after(const_iterator p, forward_list& x, const_iterator i);
-  void splice_after(const_iterator p, forward_list&& x, const_iterator i);
-  void splice_after(const_iterator p, forward_list& x,
-                    const_iterator first, const_iterator last);
-  void splice_after(const_iterator p, forward_list&& x,
-                    const_iterator first, const_iterator last);
-  ...
-  void merge(forward_list& x);
-  void merge(forward_list&& x);
-  template <class Compare> void merge(forward_list& x, Compare comp);
-  template <class Compare> void merge(forward_list&& x, Compare comp);
-  ...
-};
-
- -

-Add to the signatures of 23.3.4.6 [forwardlist.ops]: -

- -
-
-void splice_after(const_iterator p, forward_list& x);
-void splice_after(const_iterator p, forward_list&& x);
-
-
-

1 ...

-
- -
-void splice_after(const_iterator p, forward_list& x, const_iterator i);
-void splice_after(const_iterator p, forward_list&& x, const_iterator i);
-
-
-

4 ...

-
- -
-void splice_after(const_iterator p, forward_list& x,
-                const_iterator first, const_iterator last);
-void splice_after(const_iterator p, forward_list&& x,
-                const_iterator first, const_iterator last);
-
-
-

7 ...

-
- -
-void merge(forward_list& x);
-void merge(forward_list&& x);
-template <class Compare> void merge(forward_list& x, Compare comp);
-template <class Compare> void merge(forward_list&& x, Compare comp);
-
-
-

16 ...

-
- -
- - - - - - -
-

1311. multi-pass property of Forward Iterator underspecified

-

Section: 24.2.5 [forward.iterators] Status: Resolved - Submitter: Alisdair Meredith Opened: 2010-02-07 Last modified: 2015-04-08

-

View all other issues in [forward.iterators].

-

View all issues with Resolved status.

-

Discussion:

-

-The following example demonstrates code that would meet the guarantees of a -Forward Iterator, but only permits a single traversal of the underlying -sequence: -

- -
-template< typename ForwardIterator>
-struct bad_iterator {
-  shared_ptr<ForwardIterator> impl;
-
-  bad_iterator( ForwardIterator iter ) {
-     : impl{new ForwardIterator{iter} } 
-     {
-  }
-
-  auto operator*() const -> decltype(*ForwardIterator{}) {
-     return **impl;
-  }
-
-  auto operator->() const -> ForwardIterator {
-     return *impl;
-  }
-
-  auto operator==(bad_iterator const & rhs) const -> bool {
-     return impl == rhs.impl;
-  }
-
-  auto operator++() -> bad_iterator& {
-     ++(*impl);
-     return *this;
-  }
-  // other operations as necessary...
-};
-
- -

-Here, we use shared_ptr to wrap a forward iterator, so all iterators -constructed from the same original iterator share the same 'value', and -incrementing any one copy increments all others. -

- -

-There is a missing guarantee, expressed by the following code sequence -

- -
-FwdIter x = seq.begin();  // obtain forward iterator from a sequence
-FwdIter y = x;            // copy the iterator
-assert(x == y);           // iterators must be the same
-++x;                      // increment *just one* iterator
-assert(x != y);           // iterators *must now be different*
-++y;                      // increment the other iterator
-assert(x == y);           // now the iterators must be the same again
-
- -

-That inequality in the middle is an essential guarantee. Note that this list is -simplified, as each assertion should also note that they refer to exactly the -same element (&*x == &*y) but I am not complicating the issue -with tests to support proxy iterators, or value types overloading unary -operator+. -

- -

-I have not yet found a perverse example that can meet this additional -constraint, and not meet the multi-pass expectations of a Forward Iterator -without also violating other Forward Iterator requirements. -

- -

-Note that I do not yet have standard-ready wording to resolve the problem, as -saying this neatly and succinctly in 'standardese' is more difficult. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3066. -

- - -

Proposed resolution:

- - - - - -
-

1312. vector::data no longer returns a raw pointer

-

Section: 23.3.6.4 [vector.data] Status: C++11 - Submitter: Alisdair Meredith Opened: 2010-02-07 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-The original intent of vector::data was to match array::data -in providing a simple API with direct access to the contiguous buffer of -elements that could be passed to a "classic" C API. At some point, the return -type became the 'pointer' typedef, which is not derived from the -allocator via allocator traits - it is no longer specified to precisely -T *. The return type of this function should be corrected to no longer -use the typedef. -

- -

[ -2010-02-10 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]

- - - - -

Proposed resolution:

-

-23.3.6 [vector] -

- -

-Update the class definition in p2: -

- -
-// 23.3.6.3 data access
-pointerT * data();
-const_pointerconst T * data() const;
-
- -

-23.3.6.4 [vector.data] -

- -

-Adjust signatures: -

- -
-pointerT * data();
-const_pointerconst T * data() const;
-
- - - - - -
-

1316. scoped_allocator_adaptor operator== has no definition

-

Section: 20.13 [allocator.adaptor] Status: C++11 - Submitter: Pablo Halpern Opened: 2009-02-11 Last modified: 2015-04-08

-

View all other issues in [allocator.adaptor].

-

View all issues with C++11 status.

-

Discussion:

-

-The WP -(N3000) -contains these declarations: -

- -
-
template <class OuterA1, class OuterA2, class... InnerAllocs>
-  bool operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
-                  const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b);
-template <class OuterA1, class OuterA2, class... InnerAllocs>
-  bool operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
-                  const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b);
-
- -

-But does not define what the behavior of these operators are. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Add a new section after 20.13.4 [allocator.adaptor.members]: -

- -
-

Scoped allocator operators [scoped.adaptor.operators]

- -
template <class OuterA1, class OuterA2, class... InnerAllocs>
-  bool operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
-                  const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b);
- -

-Returns: a.outer_allocator() == b.outer_allocator() -if sizeof...(InnerAllocs) is zero; otherwise, -a.outer_allocator() == b.outer_allocator() && -a.inner_allocator() == b.inner_allocator(). -

- -
template <class OuterA1, class OuterA2, class... InnerAllocs>
-  bool operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
-                  const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b);
- -

-Returns: !(a == b). -

- -
- - - - - - -
-

1319. Containers should require an iterator that is at least a Forward Iterator

-

Section: 23.2.1 [container.requirements.general] Status: C++11 - Submitter: Alisdair Meredith Opened: 2010-02-16 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++11 status.

-

Discussion:

-

-The requirements on container iterators are spelled out in -23.2.1 [container.requirements.general], table 91. -

- -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 91 — Container requirements
ExpressionReturn typeOperational semanticsAssertion/note
pre-/post-condition		Complexity
...
X::iteratoriterator type whose value type is Tany iterator category except output iterator. Convertible to -X::const_iterator.compile time
X::const_iteratorconstant iterator type whose value type is Tany iterator category except output iteratorcompile time
...
-
- -

-As input iterators do not have the multi-pass guarantee, they are not suitable -for iterating over a container. For example, taking two calls to -begin(), incrementing either iterator might invalidate the other. -While data structures might be imagined where this behaviour produces -interesting and useful results, it is very unlikely to meet the full set of -requirements for a standard container. -

- -

[ -Post-Rapperswil: -]

- - -

-Daniel notes: I changed the currently suggested P/R slightly, because it is not robust in regard to new fundamental iterator -catagories. I recommend to say instead that each container::iterator shall satisfy (and thus may refine) the forward -iterator requirements. -

- -

-Moved to Tentatively Ready with revised wording after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -
    -
  1. Change Table 93 — Container requirements in [container.requirements.general] as indicated: -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 93 — Container requirements
    ExpressionReturn typeOperational
    semantics    		Assertion/note
    pre-/post-condition    		Complexity
    ...
    X::iteratoriterator type
    whose value
    type is T    		any iterator category
    except output iterator
    that -meets the forward iterator requirements    . convertible
    to
    X::const_iterator    		compile time
    X::const_iteratorconstant iterator type
    whose value
    type is T    		any iterator category
    except output iterator
    that -meets the forward iterator requirements    .    		compile time
    ...
    -
    - -
    2. -
- - - - - - -
-

1321. scoped_allocator_adaptor construct and destroy don't -use allocator_traits

-

Section: 20.13.4 [allocator.adaptor.members] Status: Resolved - Submitter: Howard Hinnant Opened: 2010-02-16 Last modified: 2015-04-08

-

View all other issues in [allocator.adaptor.members].

-

View all issues with Resolved status.

-

Discussion:

-

-20.13.4 [allocator.adaptor.members] p8-9 says: -

- -
- -
-template <class T, class... Args>
-  void construct(T* p, Args&&... args);
-
-
-

-8 Effects: let OUTERMOST(x) be x if x -does not have an outer_allocator() function and -OUTERMOST(x.outer_allocator()) otherwise. -

- -
    -
  • -If uses_allocator<T, inner_allocator_type>::value is -false and is_constructible<T, Args...>::value is -true, calls OUTERMOST(*this).construct(p, -std::forward<Args>(args)...). -
    • - -
  • -Otherwise, if uses_allocator<T, inner_allocator_type>::value is -true and is_constructible<T, allocator_arg_t, -inner_allocator_type, Args...>::value is true, calls -OUTERMOST(*this).construct(p, allocator_arg, -inner_allocator(),std::forward<Args>(args)...). -
    • - -
  • -Otherwise, if uses_allocator<T, inner_allocator_type>::value is -true and is_constructible<T, Args..., -inner_allocator_type>::value is true, calls -OUTERMOST(*this).construct(p, std::forward<Args>(args)..., -inner_allocator()). -
    • - -
  • -Otherwise, the program is ill-formed. [Note: an error will result if -uses_allocator evaluates to true but the specific constructor -does not take an allocator. This definition prevents a silent failure to pass an -inner allocator to a contained element. — end note] -
    • -
- -
- -
-template <class T>
-  void destroy(T* p);
-
-

-9 Effects: calls outer_allocator().destroy(p). -

- -
- -

-In all other calls where applicable scoped_allocator_adaptor does not -call members of an allocator directly, but rather does so indirectly via -allocator_traits. For example: -

- -
-
-size_type max_size() const;
-
-

-7 Returns: -allocator_traits<OuterAlloc>::max_size(outer_allocator()). -

-
- -

-Indeed, without the indirection through allocator_traits the -definitions for construct and destroy are likely to fail at -compile time since the outer_allocator() may not have the members -construct and destroy. -

- -

[ -The proposed wording is a product of Pablo, Daniel and Howard. -]

- - -

[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3059. -

- - -

Proposed resolution:

-

-In 20.13.4 [allocator.adaptor.members] move and change p8 -as indicated, and change p9 as indicated: -

- -
- -

-Let OUTERMOST(x) be x if x -does not have an outer_allocator() member function and -OUTERMOST(x.outer_allocator()) otherwise. Let -OUTERMOST_ALLOC_TRAITS(x) be -allocator_traits<decltype(OUTERMOST(x))>. -[Note: OUTERMOST(x) and -OUTERMOST_ALLOC_TRAITS(x) are recursive operations. It is -incumbent upon the definition of outer_allocator() to ensure that the -recursion terminates. It will terminate for all instantiations -of scoped_allocator_adaptor. — end note] - -

- -
-template <class T, class... Args>
-  void construct(T* p, Args&&... args);
-
-
- -

-8 Effects: let OUTERMOST(x) be x if -x does not have an outer_allocator() function and -OUTERMOST(x.outer_allocator()) otherwise. -

- -
    -
  • -If uses_allocator<T, inner_allocator_type>::value is -false and is_constructible<T, Args...>::value is -true, calls OUTERMOST(*this). -OUTERMOST_ALLOC_TRAITS(outer_allocator())::construct( -OUTERMOST(outer_allocator()), p, -std::forward<Args>(args)... ). -
    • - -
  • -Otherwise, if uses_allocator<T, inner_allocator_type>::value is -true and is_constructible<T, allocator_arg_t, -inner_allocator_type, Args...>::value is true, calls -OUTERMOST(*this). -OUTERMOST_ALLOC_TRAITS(outer_allocator())::construct( -OUTERMOST(outer_allocator()), p, allocator_arg, -inner_allocator(), std::forward<Args>(args)... ). -
    • - -
  • -Otherwise, if uses_allocator<T, inner_allocator_type>::value is -true and is_constructible<T, Args..., -inner_allocator_type>::value is true, calls -OUTERMOST(*this). -OUTERMOST_ALLOC_TRAITS(outer_allocator())::construct( -OUTERMOST(outer_allocator()), p, -std::forward<Args>(args)..., inner_allocator() ). -
    • - -
  • -Otherwise, the program is ill-formed. [Note: an error will result if -uses_allocator evaluates to true but the specific constructor -does not take an allocator. This definition prevents a silent failure to pass an -inner allocator to a contained element. — end note] -
    • -
- -
- -
-template <class T>
-  void destroy(T* p);
-
-

-9 Effects: calls outer_allocator(). -OUTERMOST_ALLOC_TRAITS(outer_allocator())::destroy( -OUTERMOST(outer_allocator()), p). -

- -
- - - - - - -
-

1322. Explicit CopyConstructible requirements are insufficient

-

Section: 17.6.3.1 [utility.arg.requirements] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-02-16 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with Resolved status.

-

Discussion:

-

-With the acceptance of library defect 822 only -direct-initialization is supported, and not copy-initialization in the -requirement sets MoveConstructible and CopyConstructible. This -is usually a good thing, if only the library implementation needs to obey these -restrictions, but the Empire strikes back quickly: -

- -
    -
  1. -

    -Affects user-code: std::exception_ptr is defined purely via -requirements, among them CopyConstructible. A strict reading of the -standard would make implementations conforming where std::exception_ptr -has an explicit copy-c'tor and user-code must code defensively. This is a very -unwanted effect for such an important component like -std::exception_ptr. -

    -
    2. - -
  2. -

    -Wrong re-use: Recently proposed requirement sets -(NullablePointer as of -N3025, -Hash) or cleanup of existing requirement sets (e.g. iterator requirements as of -N3046) -tend to reuse existing requirement sets, so reusing CopyConstructible -is attempting, even in cases, where the intend is to support copy-initialization -as well. -

    -
    3. - -
  3. -

    -Inconsistency: The current iterator requirements set Table 102 (output -iterator requirements) and Table 103 (forward iterator requirements) demonstrate -quite clearly a strong divergence of copy-semantics: The specified semantics of -

    - -
    -X u(a);
-X u = a;
-
    - -

    -are underspecified compared to the most recent clarifications of the -CopyConstructible requirements, c.f. issue 1309 which is -very unsatisfactory. This will become worse for each further issue that involves -the CopyConstructible specification (for possible directions see 1173). -

    -
    4. -
- -

-The suggested resolution is to define two further requirements -implicit-MoveConstructible and implicit-CopyConstructible (or -any other reasonable name like MoveConvertible and -CopyConvertible) each with a very succinct but precise meaning solving -all three problems mentioned above. -

- -

[Batavia: Resolved by accepting n3215.]

- - - - - - - -

Proposed resolution:

-
    -
  1. -

    -Add the following new table ?? after Table 34 — MoveConstructible -requirements [moveconstructible]: -

    - -
    - - - - - - - - - - - - - - -
    Table ?? — Implicit MoveConstructible requirements -[implicit.moveconstructible] (in addition to -MoveConstructible)
    ExpressionOperational Semantics
    T u = rv;Equivalent to: T u(rv);
    -
    - -
    2. - -
  2. -

    -Add the following new table ?? after Table 35 — CopyConstructible -requirements [copyconstructible]: -

    - -
    - - - - - - - - - - - - - - -
    Table ?? — Implicit CopyConstructible requirements -[implicit.copyconstructible] (in addition to -CopyConstructible)
    ExpressionOperational Semantics
    T u = v;Equivalent to: T u(v);
    -
    - -
    3. - -
  3. -

    -Change 17.6.3.3 [nullablepointer.requirements]/1 as follows: -

    - -
    -

    -A NullablePointer type is a pointer-like type that supports null -values. A type P meets the requirements of NullablePointer if: -

    - -
      -
    • -P satisfies the requirements of EqualityComparable, -DefaultConstructible, implicit CopyConstructible, -CopyAssignable, and Destructible, -
      • - -
    • [..]
      • -
    -
    -
    4. - -
  4. -

    -Change 17.6.3.4 [hash.requirements]/1 as indicated: [explicit -copy-constructible functors could not be provided as arguments -to any algorithm that takes these by value. Also a typo is fixed.] -

    - -
    -

    -1 A type H meets the Hash requirements if: -

    -
      -
    • -it is a function object type (20.8), -
      • -
    • -it satisfiesifes the requirements of -implicit CopyConstructible and Destructible -(20.2.1), -
      • -
    • -[..] -
      • -
    - -
    - -
    5. - -
  5. -

    -Change 20.10.1 [meta.rqmts]/1+2 as indicated: -

    - -
    -

    -1 A UnaryTypeTrait describes a property of a type. It shall be a class -template that takes one template type argument and, optionally, additional -arguments that help define the property being described. It shall be -DefaultConstructible, implicit CopyConstructible, -[..] -

    - -

    -2 A BinaryTypeTrait describes a relationship between two types. It -shall be a class template that takes two template type arguments and, -optionally, additional arguments that help define the relationship being -described. It shall be DefaultConstructible, -implicit CopyConstructible, and [..] -

    - -
    - -
    6. - -
  6. -

    -Change 20.9.2 [func.require]/4 as indicated: [explicit -copy-constructible functors could not be provided as arguments to any algorithm -that takes these by value] -

    - -

    -4 Every call wrapper (20.8.1) shall be implicit -MoveConstructible. A simple call wrapper is a call wrapper that is -implicit CopyConstructible and CopyAssignable and -whose copy constructor, move constructor, and assignment operator do not throw -exceptions. [..] -

    -
    7. - -
  7. -

    -Change 20.9.4 [refwrap]/1 as indicated: -

    - -

    -1 reference_wrapper<T> is an implicit -CopyConstructible and CopyAssignable wrapper around a -reference to an object or function of type T. -

    -
    8. - -
  8. -

    -Change 20.9.10.3 [func.bind.bind]/5+9 as indicated: -

    - -
    -

    -5 Remarks: The return type shall satisfy the requirements of -implicit MoveConstructible. If all of FD and -TiD satisfy the requirements of CopyConstructible, then the -return type shall satisfy the requirements of implicit -CopyConstructible. [Note: this implies that all of FD and -TiD are MoveConstructible. — end note] -

    - -

    -[..] -

    - -

    -9 Remarks: The return type shall satisfy the requirements of -implicit MoveConstructible. If all of FD and -TiD satisfy the requirements of CopyConstructible, then the -return type shall satisfy the requirements of implicit -CopyConstructible. [Note: this implies that all of FD and -TiD are MoveConstructible. — end note] -

    -
    - -
    9. - -
  9. -

    -Change 20.9.10.4 [func.bind.place] as indicated: -

    - -

    -1 All placeholder types shall be DefaultConstructible and -implicit CopyConstructible, and [..] -

    -
    10. - -
  10. -

    -Change 20.8.1 [unique.ptr]/5 as indicated: -

    - -

    -5 Each object of a type U instantiated form the unique_ptr -template specified in this subclause has the strict ownership semantics, -specified above, of a unique pointer. In partial satisfaction of these -semantics, each such U is implicit -MoveConstructible and MoveAssignable, but is not -CopyConstructible nor CopyAssignable. The template parameter -T of unique_ptr may be an incomplete type. -

    -
    11. - -
  11. -

    -Change 20.8.2.2 [util.smartptr.shared]/2 as indicated: -

    - -

    -2 Specializations of shared_ptr shall be -implicit CopyConstructible, CopyAssignable, and -LessThanComparable, [..] -

    -
    12. - -
  12. -

    -Change 20.8.2.3 [util.smartptr.weak]/2 as indicated: -

    - -

    -2 Specializations of weak_ptr shall be implicit -CopyConstructible and CopyAssignable, allowing their use in -standard containers. The template parameter T of weak_ptr may -be an incomplete type. -

    -
    13. - -
  13. -

    -Change 24.2.2 [iterator.iterators]/2 as indicated: [This fixes a -defect in the Iterator requirements. None of the usual algorithms accepting -iterators would be usable with iterators with explicit copy-constructors] -

    - -
    -

    -2 A type X satisfies the Iterator requirements if: -

    - -
      -
    • -X satisfies the implicit CopyConstructible, -CopyAssignable, and Destructible requirements (20.2.1) -and lvalues of type X are swappable (20.2.2), and [..] -
      • -
    • ...
      • -
    - -
    - -
    14. - -
  14. -

    -Change X [auto.ptr]/3 as indicated: -

    - -

    -3 [..] Instances of auto_ptr meet the requirements of -implicit MoveConstructible and MoveAssignable, but -do not meet the requirements of CopyConstructible and -CopyAssignable. — end note] -

    -
    15. - -
- - - - - - -
-

1323. basic_string::replace should use const_iterator

-

Section: 21.4.6.6 [string::replace] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-02-19 Last modified: 2015-04-08

-

View all other issues in [string::replace].

-

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-

Discussion:

- -

-In contrast to all library usages of purely positional iterator values several -overloads of std::basic_string::replace still use iterator instead of -const_iterator arguments. The paper -N3021 -quite nicely visualizes the purely positional responsibilities of the function -arguments. -

- -

-This should be fixed to make the library consistent, the proposed changes are -quite mechanic. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-
    - -
  1. -

    -In 21.4 [basic.string], class template basic_string synopsis -change as indicated: -

    - -
    -// 21.4.6 modifiers:
-...
-basic_string& replace(const_iterator i1, const_iterator i2,
-                      const basic_string& str);
-basic_string& replace(const_iterator i1, const_iterator i2,
-                      const charT* s, size_type n);
-basic_string& replace(const_iterator i1, const_iterator i2,
-                      const charT* s);
-basic_string& replace(const_iterator i1, const_iterator i2,
-                      size_type n, charT c);
-template<class InputIterator>
-  basic_string& replace(const_iterator i1, const_iterator i2,
-                        InputIterator j1, InputIterator j2);
-basic_string& replace(const_iterator, const_iterator,
-                      initializer_list<charT>);
-
    -
    2. - -
  2. -

    -In 21.4.6.6 [string::replace] before p.18, change the following signatures -as indicated: -

    - -
    -basic_string& replace(const_iterator i1, const_iterator i2, const basic_string& str);
-
    -
    3. - -
  3. -

    -In 21.4.6.6 [string::replace] before p.21, change the following signatures -as indicated: -

    - -
    -basic_string&
-  replace(const_iterator i1, const_iterator i2, const charT* s, size_type n);
-
    -
    4. - -
  4. -

    -In 21.4.6.6 [string::replace] before p.24, change the following signatures -as indicated: -

    - -
    -basic_string& replace(const_iterator i1, const_iterator i2, const charT* s);
-
    -
    5. - -
  5. -

    -In 21.4.6.6 [string::replace] before p.27, change the following signatures -as indicated: -

    - -
    -basic_string& replace(const_iterator i1, const_iterator i2, size_type n,
-                      charT c);
-
    -
    6. - -
  6. -

    -In 21.4.6.6 [string::replace] before p.30, change the following signatures -as indicated: -

    - -
    -template<class InputIterator>
-  basic_string& replace(const_iterator i1, const_iterator i2,
-                        InputIterator j1, InputIterator j2);
-
    -
    7. - -
  7. -

    -In 21.4.6.6 [string::replace] before p.33, change the following signatures -as indicated: -

    - -
    -basic_string& replace(const_iterator i1, const_iterator i2,
-                      initializer_list<charT> il);
-
    -
    8. - -
- - - - - - -
-

1324. Still too many implicit conversions for pair and tuple

-

Section: 20.3.2 [pairs.pair], 20.4.2.1 [tuple.cnstr] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-03-20 Last modified: 2015-04-08

-

View all other issues in [pairs.pair].

-

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-

Discussion:

-

-In analogy to library defect 811, tuple's variadic constructor -

- -
-template <class... UTypes>
-explicit tuple(UTypes&&... u);
-
- -

-creates the same problem as pair: -

- -
-#include <tuple>
-
-int main()
-{
-  std::tuple<char*> p(0);
-}
-
- -

-produces a similar compile error for a recent gcc implementation. -

- -

-I suggest to follow the same resolution path as has been applied to -pair's corresponding c'tor, that is require that these c'tors should -not participate in overload resolution, if the arguments are not implicitly -convertible to the element types. -

- -

-Further-on both pair and tuple provide converting constructors -from different pairs/tuples that should be not available, if -the corresponding element types are not implicitly convertible. It seems -astonishing that in the following example -

- -
-struct A {
-  explicit A(int);
-};
-
-A  a = 1; // Error
-
-std::tuple<A> ta = std::make_tuple(1); // # OK?
-
- -

-the initialization marked with # could be well-formed. -

- -

[ -Only constraints on constructors are suggested. Adding similar constraints on -assignment operators is considered as QoI, because the assigments wouldn't be -well-formed anyway. -]

- - -
    - -
  1. -

    -Following 20.3.2 [pairs.pair]/5 add a new Remarks element: -

    - -
    -template<class U, class V> pair(const pair<U, V>& p);
-
    - -
    -

    -5 Effects: Initializes members from the corresponding members of the -argument, performing implicit conversions as needed. -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless U is implicitly convertible to first_type -and V is implicitly convertible to second_type. -

    -
    -
    - -
    2. - -
  2. -

    -Following 20.3.2 [pairs.pair]/6 add a new Remarks element: -

    - -
    -template<class U, class V> pair(pair<U, V>&& p);
-
    - -
    -

    -6 Effects: The constructor initializes first with -std::move(p.first) and second with std::move(p.second). -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless U is implicitly convertible to first_type -and V is implicitly convertible to second_type. -

    -
    -
    -
    3. - -
  3. -

    -Following 20.4.2.1 [tuple.cnstr]/7 add a new Remarks element: -

    - -
    -template <class... UTypes>
-explicit tuple(UTypes&&... u);
-
    - -
    -

    -6 Requires: Each type in Types shall satisfy the requirements of -MoveConstructible (Table 33) from the corresponding type in -UTypes. sizeof...(Types) == sizeof...(UTypes). -

    - -

    -7 Effects: Initializes the elements in the tuple with the -corresponding value in std::forward<UTypes>(u). -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless each type in UTypes is implicitly convertible to its -corresponding type in Types. -

    -
    -
    -
    4. - -
  4. -

    -Following 20.4.2.1 [tuple.cnstr]/13 add a new Remarks element: -

    - -
    -template <class... UTypes> tuple(const tuple<UTypes...>& u);
-
    - -
    -

    -12 Requires: Each type in Types shall be constructible from the -corresponding type in UTypes. sizeof...(Types) == -sizeof...(UTypes). -

    - -

    -13 Effects: Constructs each element of *this with the -corresponding element of u. -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless each type in UTypes is implicitly convertible to its -corresponding type in Types. -

    - -

    -14 [Note: enable_if can be used to make the converting -constructor and assignment operator exist only in the cases where the source and -target have the same number of elements. — end note] -

    -
    -
    -
    5. - -
  5. -

    -Following 20.4.2.1 [tuple.cnstr]/16 add a new Remarks element: -

    - -
    -template <class... UTypes> tuple(tuple<UTypes...>&& u);
-
    - -
    -

    -15 Requires: Each type in Types shall shall satisfy the -requirements of MoveConstructible (Table 33) from the corresponding -type in UTypes. sizeof...(Types) == sizeof...(UTypes). -

    - -

    -16 Effects: Move-constructs each element of *this with the -corresponding element of u. -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless each type in UTypes is implicitly convertible to its -corresponding type in Types. -

    - -

    -[Note: enable_if can be used to make the converting constructor -and assignment operator exist only in the cases where the source and target have -the same number of elements. — end note] -

    -
    -
    -
    6. - -
  6. -

    -Following 20.4.2.1 [tuple.cnstr]/18 add a new Remarks element: -

    - -
    -template <class U1, class U2> tuple(const pair<U1, U2>& u);
-
    - -
    -

    -17 Requires: The first type in Types shall be constructible from -U1 and the second type in Types shall be constructible from -U2. sizeof...(Types) == 2. -

    - -

    -18 Effects: Constructs the first element with u.first and the -second element with u.second. -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless U1 is implicitly convertible to the first type in -Types and U2 is implicitly convertible to the second type in -Types. -

    -
    -
    -
    7. - -
  7. -

    -Following 20.4.2.1 [tuple.cnstr]/20 add a new Remarks element: -

    - -
    -template <class U1, class U2> tuple(pair<U1, U2>&& u);
-
    - -
    -

    -19 Requires: The first type in Types shall shall satisfy the -requirements of MoveConstructible(Table 33) from U1 and the -second type in Types shall be move-constructible from U2. -sizeof...(Types) == 2. -

    - -

    -20 Effects: Constructs the first element with std::move(u.first) -and the second element with std::move(u.second) -

    - -

    -Remarks: This constructor shall not participate in overload -resolution unless U1 is implicitly convertible to the first type in -Types and U2 is implicitly convertible to the second type in -Types. -

    -
    -
    -
    8. - -
-

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting -n3140 -would solve this issue. -

- - -

Proposed resolution:

-See n3140. -

- - - - -
-

1325. bitset

-

Section: 20.6.1 [bitset.cons] Status: C++11 - Submitter: Christopher Jefferson Opened: 2010-03-07 Last modified: 2015-04-08

-

View all other issues in [bitset.cons].

-

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-

Discussion:

-

-As mentioned on the boost mailing list: -

- -

-The following code, valid in C++03, is broken in C++0x due to ambiguity -between the "unsigned long long" and "char*" -constructors. -

- -
-#include <bitset>
-std::bitset<10> b(0);
-
- -

[ -The proposed resolution has been reviewed by Stephan T. Lavavej. -]

- - -

[ -Post-Rapperswil -]

- - -

-The proposed resolution has two problems: -

-
    -
  • -

    it fails to provide support for non-terminated strings, which -could be easily added and constitutes an important use-case. For -example, the following code would invoke UB with the current -P/R:

    -
    -
    -char s[4] = { '0', '1', '0', '1' }; // notice: not null-terminated!
-bitset<4> b(s, 0, 4);
-
    -because it requires the evaluation (under the as-if rule, to be fair, -but it doesn't matter) of basic_string<char>(s) -
    • -
  • -

    it promotes a consistency between the two bitset -constructors that take a const std::string& and a -const char*, respectively, while practice established by -std::basic_string would recommend a different set of -parameters. In particular, the constructor of -std::basic_string that takes a const char* does -not have a pos parameter

    -
    • -
- -

-Moved to Tentatively Ready with revised wording provided by Alberto -Ganesh Babati after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- - -
    -
  1. In the synopsis of header <bitset> in -20.6 [template.bitset]/1, replace the fourth bitset constructor: -
    -
    -explicit bitset(const char *str);
-template <class charT>
-  explicit bitset(
-    const charT *str,
-    typename basic_string<charT>::size_type n = basic_string<charT>::npos,
-    charT zero = charT('0'), charT one = charT('1'));
-
    -
    2. -
  2. In 20.6.1 [bitset.cons]/8: -
    -
    -explicit bitset(const char *str);
-template <class charT>
-explicit
-bitset(const charT *str,
-       typename basic_string<charT>::size_type n = basic_string<charT>::npos,
-       charT zero = charT('0'), charT one = charT('1'));
-
    -

    -Effects: Constructs an object of class -bitset<N> as if by -bitset(string(str)). -

    -
    
-bitset(
-  n == basic_string<charT>::npos
-    ? basic_string<charT>(str)
-    : basic_string<charT>(str, n),
-  0, n, zero, one)
-
    -
    3. -
- - - - - - -
-

1326. Missing/wrong preconditions for pair and tuple functions

-

Section: 20.3.2 [pairs.pair], 20.4.2.1 [tuple.cnstr] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-03-07 Last modified: 2015-04-08

-

View all other issues in [pairs.pair].

-

View all issues with Resolved status.

-

Discussion:

-

-There are several constructors and creation functions of std::tuple -that impose requirements on it's arguments, that are unnecessary -restrictive and don't match the intention for the supported argument -types. This is related to the fact that tuple is supposed to accept both -object types and lvalue-references and the usual MoveConstructible and -CopyConstructible requirements are bad descriptions for non-const -references. Some examples: -

- -
    -
  1. -

    -20.4.2.1 [tuple.cnstr] before p.4 and p.8, resp.: -

    - -
    -explicit tuple(const Types&...);
-
    -

    -4 Requires: Each type in Types shall be copy constructible. -

    - -
    -tuple(const tuple& u) = default;
-
    -

    -8 Requires: Each type in Types shall satisfy the requirements of -CopyConstructible (Table 34). -

    -
    - -

    -A tuple that contains lvalue-references to non-const can never -satisfy the CopyConstructible requirements. CopyConstructible -requirements refine the MoveConstructible requirements and -this would require that these lvalue-references could bind -rvalues. But the core language does not allow that. Even, if we -would interpret that requirement as referring to the underlying -non-reference type, this requirement would be wrong as well, -because there is no reason to disallow a type such as -

    - -
    -struct NoMoveNoCopy {
-  NoMoveNoCopy(NoMoveNoCopy&&) = delete;
-  NoMoveNoCopy(const NoMoveNoCopy&) = delete;
-  ...
-}:
-
    - -

    -for the instantiation of std::tuple<NoMoveNoCopy&> and -that of it's copy constructor. -

    - -

    -A more reasonable requirement for this example would be to require that -"is_constructible<Ti, const Ti&>::value shall -evaluate to true for all Ti in Types". In this case -the special reference-folding and const-merging rules of references -would make this well-formed in all cases. We could also add the further -constraint "if Ti is an object type, it shall satisfy the -CopyConstructible requirements", but this additional -requirement seems not really to help here. Ignoring it would only mean -that if a user would provide a curious object type C that -satisfies the std::is_constructible<C, const C&> -test, but not the "C is CopyConstructible" test would -produce a tuple<C> that does not satisfy the -CopyConstructible requirements as well. -

    -
    2. - -
  2. -

    -20.4.2.1 [tuple.cnstr] before p.6 and p.10, resp.: -

    - -
    -template <class... UTypes>
-explicit tuple(UTypes&&... u);
-
    - -

    -6 Requires: Each type in Types shall satisfy the -requirements of MoveConstructible (Table 33) from the -corresponding type in UTypes. sizeof...(Types) == -sizeof...(UTypes). -

    - -
    -tuple(tuple&& u);
-
    -

    -10 Requires: Each type in Types shall shall -satisfy the requirements of MoveConstructible (Table 33). -

    -
    - -

    -We have a similar problem as in (a): Non-const lvalue-references -are intended template arguments for std::tuple, but cannot satisfy -the MoveConstructible requirements. In this case the correct -requirements would be -

    - -

    -is_constructible<Ti, Ui>::value shall evaluate to true -for all Ti in Types and for all Ui in -UTypes -

    - -

    -and -

    - -

    -is_constructible<Ti, Ti>::value shall evaluate to true -for all Ti in Types -

    - -

    -respectively. -

    -
    3. -
- -

-Many std::pair member functions do not add proper requirements, e.g. -the default c'tor does not require anything. This is corrected within the -suggested resolution. Further-on the P/R has been adapted to the FCD numbering. -

- -

[ -2010-03-25 Daniel updated wording: -]

- - -

-The issue became updated to fix some minor inconsistencies and to ensure a -similarly required fix for std::pair, which has the same specification -problem as std::tuple, since pair became extended to support -reference members as well. -

- -

[Original proposed resolution:]

- -
    - -
  1. -

    -Change 20.3.2 [pairs.pair]/1 as indicated [The changes for the effects -elements are not normative changes, they just ensure -harmonization with existing wording style]: -

    - -
    -constexpr pair();
-
    - -
    -

    -Requires: first_type and second_type shall satisfy -the DefaultConstructible requirements. -

    - -

    -1 Effects: Value-initializes first and -second.Initializes its members as if implemented: pair() -: first(), second() { }. -

    - -
    -
    - -
    2. - -
  2. -

    -Change 20.3.2 [pairs.pair]/2 as indicated: -

    - -
    -pair(const T1& x, const T2& y);
-
    - -
    -

    -Requires: is_constructible<T1, const T1&>::value -is true and is_constructible<T2, const T2&>::value -is true. -

    - -

    -2 Effects: The constructor initializes first with x and -second with y. -

    - -
    -
    - -
    3. - -
  3. -

    -Change 20.3.2 [pairs.pair]/3 as indicated: -

    - -
    -template<class U, class V> pair(U&& x, V&& y);
-
    - -
    -

    -Requires: is_constructible<first_type, U>::value is -true and is_constructible<second_type, V>::value is -true. -

    - -

    -3 Effects: The constructor initializes first with -std::forward<U>(x) and second with -std::forward<V>(y). -

    - -

    -4 Remarks: If U is not implicitly convertible to -first_type or V is not implicitly convertible to -second_type this constructor shall not participate in overload -resolution. -

    - -
    -
    - -
    4. - -
  4. -

    -Change 20.3.2 [pairs.pair]/5 as indicated [The change in the effects -element should be non-normatively and is in compatible to the change suggestion -of 1324]: -

    - -
    -template<class U, class V> pair(const pair<U, V>& p);
-
    - -
    -

    -Requires: is_constructible<first_type, const -U&>::value is true and is_constructible<second_type, -const V&>::value is true. -

    - -

    -5 Effects: Initializes members from the corresponding members of the -argument, performing implicit conversions as needed. -

    - -
    -
    - -
    5. - -
  5. -

    -Change 20.3.2 [pairs.pair]/6 as indicated: -

    - -
    -template<class U, class V> pair(pair<U, V>&& p);
-
    - -
    -

    -Requires: is_constructible<first_type, U>::value is -true and is_constructible<second_type, V>::value is -true. -

    - -

    -6 Effects: The constructor initializes first with -std::moveforward<U>(p.first) and -second with -std::moveforward<V>(p.second). -

    -
    -
    -
    6. - -
  6. -

    -Change 20.3.2 [pairs.pair]/7+8 as indicated [The deletion in the effects -element should be non-normatively]: -

    - -
    -template<class... Args1, class... Args2>
-  pair(piecewise_construct_t,
-       tuple<Args1...> first_args, tuple<Args2...> second_args);
-
    - -
    -

    -7 Requires: is_constructible<first_type, -Args1...>::value is true and -is_constructible<second_type, Args2...>::value is -true. All the types in Args1 and Args2 -shall be CopyConstructible (Table 35). T1 shall be -constructible from Args1. T2 shall be constructible from -Args2. -

    - -

    -8 Effects: The constructor initializes first with arguments of -types Args1... obtained by forwarding the elements of -first_args and initializes second with arguments of types -Args2... obtained by forwarding the elements of second_args. -(Here, forwarding an element x of type U within a -tuple object means calling std::forward<U>(x).) -This form of construction, whereby constructor arguments for first and -second are each provided in a separate tuple object, is called -piecewise construction. -

    - -
    -
    - -
    7. - -
  7. -

    -Change 20.3.2 [pairs.pair] before 12 as indicated: -

    - -
    -pair& operator=(pair&& p);
-
    - -
    -

    -Requires: first_type and second_type shall satisfy -the MoveAssignable requirements. -

    - -

    -12 Effects: Assigns to first with std::move(p.first) -and to second with std::move(p.second). -

    - -

    -13 Returns: *this. -

    - -
    -
    - -
    8. - -
  8. -

    -Change [pairs.pair] before 14 as indicated: [The heterogeneous usage -of MoveAssignable is actually not defined, -but the library uses it at several places, so we follow this tradition -until a better term has been agreed on. One -alternative could be to write "first_type shall be assignable from an -rvalue of U [..]"] -

    - -
    -template<class U, class V> pair& operator=(pair<U, V>&& p);
-
    - -
    - -

    -Requires: first_type shall be MoveAssignable from -U and second_type shall be MoveAssignable from -V. -

    - -

    -14 Effects: Assigns to first with std::move(p.first) -and to second with std::move(p.second). -

    - -

    -15 Returns: *this. -

    - -
    -
    - -
    9. - -
  9. -

    -Change 20.4.2.1 [tuple.cnstr]/4+5 as indicated: -

    - -
    -explicit tuple(const Types&...);
-
    - -
    -

    -4 Requires: is_constructible<Ti, const -Ti&>::value == true for eEach type -Ti in Types shall be copy -constructible. -

    - -

    -5 Effects: Copy iInitializes each element with the -value of the corresponding parameter. -

    - -
    -
    - -
    10. - -
  10. -

    -Change 20.4.2.1 [tuple.cnstr]/6 as indicated: -

    - -
    -template <class... UTypes>
-explicit tuple(UTypes&&... u);
-
    - -
    -

    -6 Requires: is_constructible<Ti, Ui>::value == -true for eEach type Ti in -Types shall satisfy the requirements of -MoveConstructible (Table 33) fromand for the -corresponding type Ui in UTypes. -sizeof...(Types) == sizeof...(UTypes). -

    - -

    -7 Effects: Initializes the elements in the tuple with the -corresponding value in std::forward<UTypes>(u). -

    - -
    -
    -
    11. - -
  11. -

    -Change 20.4.2.1 [tuple.cnstr]/8+9 as indicated: -

    - -
    -tuple(const tuple& u) = default;
-
    - -
    -

    -8 Requires: is_constructible<Ti, const -Ti&>::value == true for eEach type -Ti in Types shall satisfy the -requirements of CopyConstructible(Table 34). -

    - -

    -9 Effects: InitializesCopy constructs each element -of *this with the corresponding element of u. -

    - -
    -
    -
    12. - -
  12. -

    -Change 20.4.2.1 [tuple.cnstr]/10+11 as indicated: -

    - -
    -tuple(tuple&& u);
-
    - -
    -

    -10 Requires: Let i be in [0, sizeof...(Types)) and -let Ti be the ith type in Types. -Then is_constructible<Ti, Ti>::value shall be true for -all i. Each type in Types shall shall satisfy the -requirements of MoveConstructible (Table 34). -

    - -

    -11 Effects: For each Ti in Types, initializes the -ith Move-constructs each element of -*this with the corresponding element of -std::forward<Ti>(get<i>(u)). -

    -
    -
    -
    13. - -
  13. -

    -Change 20.4.2.1 [tuple.cnstr]/15+16 as indicated: -

    - -
    -template <class... UTypes> tuple(tuple<UTypes...>&& u);
-
    - -
    -

    -15 Requires: Let i be in [0, sizeof...(Types)), -Ti be the ith type in Types, and -Ui be the ith type in UTypes. Then -is_constructible<Ti, Ui>::value shall be true for all -i. Each type in Types shall shall satisfy the -requirements of MoveConstructible (Table 34) from the corresponding -type in UTypes. sizeof...(Types) == sizeof...(UTypes). -

    - -

    -16 Effects: For each type Ti, initializes the -ith Move-constructs each element of -*this with the corresponding element of -std::forward<Ui>(get<i>(u)). -

    - -
    -
    - -
    14. - -
  14. -

    -Change 20.4.2.1 [tuple.cnstr]/19+20 as indicated: -

    - -
    -template <class U1, class U2> tuple(pair<U1, U2>&& u);
-
    - -
    -

    -19 Requires: is_constructible<T1, U1>::value == -true for tThe first type -T1 in Types shall shall satisfy the -requirements of MoveConstructible(Table 33) from -U1 and is_constructible<T2, U2>::value == -true for the second type T2 in -Types shall be move-constructible from U2. -sizeof...(Types) == 2. -

    - -

    -20 Effects: InitializesConstructs the first -element with -std::forward<U1>move(u.first) and -the second element with -std::forward<U2>move(u.second). -

    - -
    -
    -
    15. - -
  15. -

    -Change 20.4.2.4 [tuple.creation]/9-16 as indicated: -

    - -
    -template <class... TTypes, class... UTypes>
-tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
    - -
    -

    -9 Requires: is_constructible<Ti, const -Ti&>::value == true for each type TiAll -the types in TTypes shall be -CopyConstructible (Table 34). -is_constructible<Ui, const Ui&>::value == true -for each type UiAll the types in -UTypes shall be CopyConstructible (Table -34). -

    - -

    -10 Returns: A tuple object constructed by -initializingcopy constructing its first -sizeof...(TTypes) elements from the corresponding elements of -t and initializingcopy constructing its -last sizeof...(UTypes) elements from the corresponding elements -of u. -

    -
    - -
    -template <class... TTypes, class... UTypes>
-tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&& t, const tuple<UTypes...>& u);
-
    - -
    -

    -11 Requires: Let i be in [0, sizeof...(TTypes)), -Ti be the ith type in Types, -j be in [0, sizeof...(UTypes)), and Uj be the -jth type in UTypes. -is_constructible<Ti, Ti>::value shall be true for each -type Ti and is_constructible<Uj, const Uj&>::value -shall be true for each type Uj All the types in -TTypes shall be MoveConstructible (Table 34). All the types in -UTypes shall be CopyConstructible (Table 35). -

    - -

    -12 Returns: A tuple object constructed by initializing the -ith element with -std::forward<Ti>(get<i>(t)) for all Ti in -TTypes and initializing the -(j+sizeof...(TTypes))th element with -get<j>(u) for all Uj in UTypes. move -constructing its first sizeof...(TTypes) elements from the -corresponding elements of t and copy constructing its last -sizeof...(UTypes) elements from the corresponding elements of -u. -

    -
    - -
    -template <class... TTypes, class... UTypes>
-tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>& t, tuple<UTypes...>&& u);
-
    - -
    -

    -13 Requires: Let i be in [0, sizeof...(TTypes)), -Ti be the ith type in Types, -j be in [0, sizeof...(UTypes)), and Uj be the -jth type in UTypes. -is_constructible<Ti, const Ti&>::value shall be true -for each type Ti and is_constructible<Uj, Uj>::value -shall be true for each type Uj All the types in -TTypes shall be CopyConstructible (Table 35). All the types in -UTypes shall be MoveConstructible (Table 34). -

    - -

    -14 Returns: A tuple object constructed by initializing the -ith element with get<i>(t) for each -type Ti and initializing the -(j+sizeof...(TTypes))th element with -std::forward<Uj>(get<j>(u)) for each type Uj -copy constructing its first sizeof...(TTypes) elements from the -corresponding elements of t and move constructing its last -sizeof...(UTypes) elements from the corresponding elements of -u. -

    -
    - -
    -template <class... TTypes, class... UTypes>
-tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&& t, tuple<UTypes...>&& u);
-
    - -
    -

    -15 Requires: Let i be in [0, sizeof...(TTypes)), -Ti be the ith type in Types, -j be in [0, sizeof...(UTypes)), and Uj be the -jth type in UTypes. -is_constructible<Ti, Ti>::value shall be true for each -type Ti and is_constructible<Uj, Uj>::value shall be -true for each type Uj All the types in -TTypes shall be MoveConstructible (Table 34). All the types in -UTypes shall be MoveConstructible (Table 34). -

    - -

    -16 Returns: A tuple object constructed by initializing the -ith element with -std::forward<Ti>(get<i>(t)) for each type Ti and -initializing the (j+sizeof...(TTypes))th element with -std::forward<Uj>(get<j>(u)) for each type Uj -move constructing its first sizeof...(TTypes) elements from the -corresponding elements of t and move constructing its last -sizeof...(UTypes) elements from the corresponding elements of -u. -

    -
    -
    -
    16. -
- - -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 -would solve this issue. -

- - -

Proposed resolution:

-

-See n3140. -

- - - - - -
-

1327. templates defined in <cmath> replacing C macros with the same name

-

Section: 26.8 [c.math] Status: Resolved - Submitter: Michael Wong Opened: 2010-03-07 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

View all other issues in [c.math].

-

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-

Discussion:

-

-In 26.8 [c.math]p12 -The templates defined in <cmath> replace the C99 macros -with the same names. The templates have the following declarations: -

- -
-namespace std {
-template <class T> bool signbit(T x);
-template <class T> int fpclassify(T x);
-template <class T> bool isfinite(T x);
-template <class T> bool isinf(T x);
-template <class T> bool isnan(T x);
-template <class T> bool isnormal(T x);
-template <class T> bool isgreater(T x, T y);
-template <class T> bool isgreaterequal(T x, T y);
-template <class T> bool isless(T x, T y);
-template <class T> bool islessequal(T x, T y);
-template <class T> bool islessgreater(T x, T y);
-template <class T> bool isunordered(T x, T y);
-}
-
- -

-and p13: -

- -

-13 The templates behave the same as the C99 macros with corresponding -names defined in C99 7.12.3, Classification macros, and C99 7.12.14, -Comparison macros in the C standard. -

- -

-The C Std versions look like this: -

- -
-

-7.12.14.1/p1: -

-
-

-Synopsis -

-

-1 #include <math.h> -

-
-int isgreaterequal(real-floating x, real-floating y);
-
-
-
- -

-which is not necessarily the same types as is required by C++ since the -two parameters may be different. Would it not be better if it were truly -aligned with C? -

- -

[ -2010 Pittsburgh: Bill to ask WG-14 if heterogeneous support for the -two-parameter macros is intended. -]

- - -

[ -2010-09-13 Daniel comments: -]

- - -

-I recommend to resolve this issue as NAD Editorial because -the accepted resolution for NB comment US-136 -by motion 27 does address this. -

- -

[ -2010-09-14 Bill comments: -]

- - -

-Motion 27 directly addresses LWG 1327 and solves the problem -presented there. Moreover, the solution has been aired before -WG14 with no dissent. These functions now behave the same for -mixed-mode calls in both C and C++ -

- - - -

Proposed resolution:

-Apply proposed resolution for -US-136 -

- - - - -
-

1328. istream extractors not setting failbit if eofbit is already set

-

Section: 27.7.2.1.3 [istream::sentry] Status: Resolved - Submitter: Paolo Carlini Opened: 2010-02-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Basing on the recent discussion on the library reflector, see c++std-lib-27728 -and follow ups, I hereby formally ask for LWG 419 to be re-opened, the rationale -being that according to the current specifications, per -n3000, -it seems actually impossible to seek away from end of file, contrary to the -rationale which led 342 to its closure as NAD. My request is also -supported by Martin Sebor, and I'd like also to add, as tentative proposed -resolution for the re-opened issue, the wording suggested by Sebor, thus, change -the beginning of 27.7.2.1.3 [istream::sentry]/2, to: -

- -

-2 Effects: If (!noskipws && !is.good()) is -false true, calls is.setstate(failbit). -Otherwise prepares for formatted or unformatted input. ... -

- -

[ -2010-10 Batavia -]

- - -

-Resolved by adopting -n3168. -

- -

-Previous proposed resolution: -

-Change 27.7.2.1.3 [istream::sentry] p.2: -

- -

-2 Effects: If (!noskipws && !is.good()) is -false true, calls is.setstate(failbit). -Otherwise prepares for formatted or unformatted input. ... -

- - -

Proposed resolution:

-Addressed by paper -n3168. -

- - - - -
-

1329. Data races on vector<bool>

-

Section: 23.2.2 [container.requirements.dataraces] Status: Resolved - Submitter: Jeffrey Yaskin Opened: 2010-03-09 Last modified: 2015-04-08

-

View all other issues in [container.requirements.dataraces].

-

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-

Discussion:

-

-The common implementation of vector<bool> is as an -unsynchronized bitfield. The addition of 23.2.2 [container.requirements.dataraces]/2 would require either a -change in representation or a change in access synchronization, both of -which are undesireable with respect to compatibility and performance. -

- -

[ -2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below. -]

- - - - -

Rationale:

-

-Solved by -N3069. -

- - -

Proposed resolution:

-

-Container data races 23.2.2 [container.requirements.dataraces] -

- -

-Paragraph 1 is unchanged as follows: -

- -

-1 For purposes of avoiding data races (17.6.4.8), implementations shall -consider the following functions to be const: -begin, end, rbegin, -rend, front, back, -data, find, lower_bound, -upper_bound, equal_range, and, except in -associative containers, operator[]. -

- -

-Edit paragraph 2 as follows: -

- -

-2 Notwithstanding (17.6.4.8), implementations are required to avoid data -races when the contents of the contained object in different elements in -the same sequence, excepting vector<bool>, -are modified concurrently. -

- -

-Edit paragraph 3 as follows: -

- -

-3 [Note: -For a vector<int> x with a size greater than one, -x[1] = 5 and *x.begin() = 10 -can be executed concurrently without a data race, -but x[0] = 5 and *x.begin() = 10 -executed concurrently may result in a data race. -As an exception to the general rule, -for a vector<bool> y, -y[i] = true may race with y[j] = true. -—end note] -

- - - - - - -
-

1332. Let Hash objects throw!

-

Section: 17.6.3.4 [hash.requirements] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-03-26 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-The currently added Hash requirements demand in Table 40 — Hash -requirements [hash]: -

- -
- - - - - - - - - - - - - - - - -
Table 40 — Hash requirements [hash]
ExpressionReturn typeRequirement
h(k)size_tShall not throw exceptions. [..]
-
- -

-While it surely is a generally accepted idea that hash function objects -should not throw exceptions, this basic constraint for such a fundamental -requirement set does neither match the current library policy nor real world -cases: -

- -
    -
  1. -There are little known situations where a swap or move operation may throw an -exception and in some popular domains such functions are required not -to throw. But the library invested already efforts for good reasons to require -"working" container implementations in the presence of throwing move or swap -operations, see e.g. 23.2.4.1 [associative.reqmts.except], 23.2.5.1 [unord.req.except]. -
    2. - -
  2. -The container library is already specified to cope with potentially throwing -comparers, predicates, and hash function objects, see above. -
    3. - -
  3. -

    -The new definition goes beyond the original hash requirements as specified -by SGI library in regard to the exception requirement: -

    -

    -http://www.sgi.com/tech/stl/HashFunction.html -

    -
    4. - -
  4. -There are indeed real-world examples of potentially throwing hash functions, -typically when the proxy pattern is used and when the to-be hashed proxied -instance is some volatile object, e.g. a file or internet resource, that -might suddenly be unavailable at the time of hashing. -
    5. - -
  5. -With the new noexcept language facility libraries can still take -advantage of no-throw guarantees of hasher functions with stricter guarantees. -
    6. -
- -

-Even though the majority of all known move, swap, and hash functions won't throw -and in some cases must not throw, it seems like unnecessary -over-constraining the definition of a Hash functor not to propagate exceptions -in any case and it contradicts the general principle of C++ to impose such a -requirement for this kind of fundamental requirement. -

- -

[ -2010-11-11 Daniel asks the working group whether they would prefer a replacement -for the second bullet of the proposed resolution (a result of discussing this -with Alberto) of the form: -]

- - -

-Add to 20.9.13 [unord.hash]/1 a new bullet: -

- -
-

-1 The unordered associative containers defined in Clause 23.5 use -specializations of the class template hash -as the default hash function. For all object types Key for which there -exists a specialization hash<Key>, the -instantiation hash<Key> shall: -

-
    -
  • -satisfy the Hash requirements (20.2.4), with Key as the -function call argument type, the DefaultConstructible requirements -(33), the CopyAssignable requirements (37), -
    • -
  • -be swappable (20.2.2) for lvalues, -
    • -
  • -provide two nested types result_type and argument_type which -shall be synonyms for size_t and Key, respectively, -
    • -
  • -satisfy the requirement that if k1 == k2 is true, h(k1) == -h(k2) is also true, where h is an object of type -hash<Key> and k1 and k2 are objects of type -Key,. -
    • -
  • -satisfy the requirement noexcept(h(k)) == true, where h is an object -of type hash<Key> and k is an object of type Key, unless -hash<Key> is a user-defined specialization that depends on at least one user-defined type. -
    • -
-
- - - -

[Batavia: Closed as NAD Future, then reopened. See the wiki for Tuesday.]

- - -

Proposed resolution:

-
    -
  1. -

    -Change Table 26 — Hash requirements [tab:hash] as indicated: -

    - -
    - - - - - - - - - - - - - - - - -
    Table 26 — Hash requirements [tab:hash]
    ExpressionReturn typeRequirement
    h(k)size_tShall not throw exceptions. […]
    -
    -
    2. - -
  2. -

    -Add to 20.9.13 [unord.hash] p. 1 a new bullet: -

    - -
    -

    -1 The unordered associative containers defined in Clause 23.5 [unord] use -specializations of the class template hash -as the default hash function. For all object types Key for which there -exists a specialization hash<Key>, the -instantiation hash<Key> shall: -

    -
      -
    • -satisfy the Hash requirements ([hash.requirements]), with Key as the -function call argument type, the DefaultConstructible requirements -(Table [defaultconstructible]), the CopyAssignable requirements (Table [copyassignable]), -
      • -
    • -be swappable ([swappable.requirements]) for lvalues, -
      • -
    • -provide two nested types result_type and argument_type which -shall be synonyms for size_t and Key, respectively, -
      • -
    • -satisfy the requirement that if k1 == k2 is true, h(k1) == -h(k2) is also true, where h is an object of type -hash<Key> and k1 and k2 are objects of type -Key,. -
      • -
    • -satisfy the requirement that the expression h(k), where h -is an object of type hash<Key> and k is an object of -type Key, shall not throw an exception, unless -hash<Key> is a user-defined specialization that depends on at -least one user-defined type. -
      • -
    -
    -
    3. -
- - - - - - -
-

1333. Missing forwarding during std::function invocation

-

Section: 20.9.12.2.4 [func.wrap.func.inv] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-03-26 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.inv].

-

View all issues with C++11 status.

-

Discussion:

-

-The current wording of 20.9.12.2.4 [func.wrap.func.inv]/1: -

- -
-R operator()(ArgTypes... args) const
-
- -

-Effects: INVOKE(f, t1, t2, ..., tN, R) (20.8.2), where -f is the target object (20.8.1) of *this and t1, t2, ..., -tN are the values in args.... -

-
- -

-uses an unclear relation between the actual args and the used variables -ti. It should be made clear, that std::forward has to be used -to conserve the expression lvalueness. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 20.9.12.2.4 [func.wrap.func.inv]/1+2 as indicated: -

- -
-R operator()(ArgTypes... args) const
-
- -
-

-1 Effects:: INVOKE(f, -std::forward<ArgTypes>(args)...t1, t2, ..., tN, -R) (20.8.2), where f is the target object (20.8.1) of -*this and t1, t2, ..., tN are the values in -args.... -

- -

-2 Returns: Nothing if R is void, otherwise the return -value of INVOKE(f, -std::forward<ArgTypes>(args)...t1, t2, ..., tN, -R). -

- -

-3 Throws: bad_function_call if !*this; otherwise, any -exception thrown by the wrapped callable object. -

-
-
- - - - - - -
-

1334. Insert iterators are broken for some proxy containers compared to C++03

-

Section: 24.5.2.2.2 [back.insert.iter.op=], 24.5.2.4.2 [front.insert.iter.op=], X [insert.insert.iter.op=] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-03-28 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-In C++03 this was valid code: -

- -
-#include <vector>
-#include <iterator>
-
-int main() {
-  typedef std::vector<bool> Cont;
-  Cont c;
-  std::back_insert_iterator<Cont> it = std::back_inserter(c);
-  *it = true;
-}
-
- -

-In C++0x this code does no longer compile because of an ambiguity error for this -operator= overload pair: -

- -
-back_insert_iterator<Container>&
-operator=(typename Container::const_reference value);
-
-back_insert_iterator<Container>&
-operator=(typename Container::value_type&& value);
-
- -

-This is so, because for proxy-containers like std::vector<bool> -the const_reference usually is a non-reference type and in this case -it's identical to Container::value_type, thus forming the ambiguous -overload pair -

- -
-back_insert_iterator<Container>&
-operator=(bool value);
-
-back_insert_iterator<Container>&
-operator=(bool&& value);
-
- -

-The same problem exists for std::back_insert_iterator, -std::front_insert_iterator, and std::insert_iterator. -

- -

-One possible fix would be to require that const_reference of a proxy -container must not be the same as the value_type, but this would break -earlier valid code. The alternative would be to change the first signature to -

- -
-back_insert_iterator<Container>&
-operator=(const typename Container::const_reference& value);
-
- -

-This would have the effect that this signature always expects an lvalue -or rvalue, but it would not create an ambiguity relative to the second form with -rvalue-references. [For all non-proxy containers the signature will be the same -as before due to reference-collapsing and const folding rules] -

- - -

[ -Post-Rapperswil -]

- - -

-This problem is not restricted to the unspeakable vector<bool>, but is already existing for other proxy -containers like gcc's rope class. The following code does no longer work ([Bug libstdc++/44963]): -

-
-#include <iostream>
-#include <ext/rope>
-
-using namespace std;
-
-int main()
-{
-     __gnu_cxx::crope line("test");
-     auto ii(back_inserter(line));
-
-     *ii++ = 'm'; // #1
-     *ii++ = 'e'; // #2
-
-     cout << line << endl;
-}
-
-

-Both lines marked with #1 and #2 issue now an error because the library has properly implemented the current -wording state (Thanks to Paolo Calini for making me aware of this real-life example). -

-

-The following P/R is a revision of the orignal P/R and was initially suggested by Howard -Hinnant. Paolo verified that the approach works in gcc. -

- -

-Moved to Tentatively Ready with revised wording after 6 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

The wording refers to N3126.

- -
    -
  1. Change [back.insert.iterator], class back_insert_iterator synopsis as indicated: -
    -template <class Container>
-class back_insert_iterator :
- public iterator<output_iterator_tag,void,void,void,void> {
-protected:
- Container* container;
-public:
- [..]
- back_insert_iterator<Container>&
-   operator=(const typename Container::const_referencevalue_type& value);
- back_insert_iterator<Container>&
-   operator=(typename Container::value_type&& value);
- [..]
-};
-
    -
    2. -
  2. Change [back.insert.iter.op=] before p. 1 as indicated: -
    -back_insert_iterator<Container>&
-   operator=(const typename Container::const_referencevalue_type& value);
-
    -

    -1 Effects: container->push_back(value);
    -2 Returns: *this. -

    -
    3. -
  3. Change [front.insert.iterator], class front_insert_iterator synposis as indicated: -
    -template <class Container>
-class front_insert_iterator :
- public iterator<output_iterator_tag,void,void,void,void> {
-protected:
- Container* container;
-public:
- [..]
- front_insert_iterator<Container>&
-   operator=(const typename Container::const_referencevalue_type& value);
- front_insert_iterator<Container>&
-   operator=(typename Container::value_type&& value);
- [..]
-};
-
    -
    4. -
  4. Change [front.insert.iter.op=] before p.1 as indicated: -
    -front_insert_iterator<Container>&
-   operator=(const typename Container::const_referencevalue_type& value);
-
    -

    -1 Effects: container->push_front(value);
    -2 Returns: *this. -

    -
    5. -
  5. Change [insert.iterator], class insert_iterator synopsis as indicated: -
    -template <class Container>
-   class insert_iterator :
-     public iterator<output_iterator_tag,void,void,void,void> {
-   protected:
-     Container* container;
-     typename Container::iterator iter;
-   public:
-     [..]
-     insert_iterator<Container>&
-       operator=(const typename Container::const_referencevalue_type& value);
-     insert_iterator<Container>&
-       operator=(typename Container::value_type&& value);
-     [..]
-   };
-
    -
    6. -
  6. Change [insert.iter.op=] before p. 1 as indicated: -
    -insert_iterator<Container>&
-    operator=(const typename Container::const_referencevalue_type& value);
-
    -

    -1 Effects: -

    -  iter = container->insert(iter, value);
-  ++iter;
-

    -2 Returns: *this. -

    -
    7. -
- - - - - - -
-

1335. Insufficient requirements for tuple::operator<()

-

Section: 20.4.2.7 [tuple.rel] Status: C++11 - Submitter: Joe Gottman Opened: 2010-05-15 Last modified: 2015-04-08

-

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-

View all other issues in [tuple.rel].

-

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-

Discussion:

-

-The requirements section for std::tuple says the following: -

- -

-Requires: For all i, where 0 <= i and i < -sizeof...(Types), get<i>(t) < get<i>(u) is a valid -expression returning a type that is convertible to bool. -sizeof...(TTypes) == sizeof...(UTypes). -

- -

-This is necessary but not sufficient, as the algorithm for comparing -tuples also computes get<i>(u) < get<i>(t) -(note the order) -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready with updated wording correcting change-bars after 6 -positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -
    -
  1. Change [tuple.rel] before p. 4 as indicated [Remark to the editor: This paragraph doesn't have a number yet, -but it seems to me as if it should have one]: -
    -template<class... TTypes, class... UTypes>
-bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
-
    -

    -Requires: For all i, where 0 <= i and i < sizeof...(Types), -get<i>(t) < get<i>(u) and get<i>(u) < get<i>(t)is -a valid expression returning a type that is are valid expressions returning types that -are convertible to bool. sizeof...(TTypes) == sizeof...(UTypes). -

    -
    2. -
- - - - - - -
-

1337. Swapped arguments in regex_traits::isctype

-

Section: 28.7 [re.traits] Status: C++11 - Submitter: Howard Hinnant Opened: 2010-06-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-28.7 [re.traits]/12 describes regex_traits::isctype in terms -of ctype::is(c, m), where c is a charT and m -is a ctype_base::mask. Unfortunately 22.4.1.1.1 [locale.ctype.members] -specifies this function as ctype::is(m, c) -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 28.7 [re.traits] p.12: -

- -
-bool isctype(charT c, char_class_type f) const;
-
-
-

-11 ... -

-

-12 Returns: Converts f into a value m of type -std::ctype_base::mask in an unspecified manner, and returns -true if use_facet<ctype<charT> ->(getloc()).is(cm, mc) is -true. Otherwise returns true if f bitwise or'ed with -the result of calling lookup_classname with an iterator pair that -designates the character sequence "w" is not equal to 0 and c == -'_', or if f bitwise or'ed with the result of calling -lookup_classname with an iterator pair that designates the character -sequence "blank" is not equal to 0 and c is one of an -implementation-defined subset of the characters for which isspace(c, -getloc()) returns true, otherwise returns false. -

-
-
- - - - - -
-

1338. LWG 1205 incorrectly applied

-

Section: 25.2.13 [alg.search] Status: C++11 - Submitter: Howard Hinnant Opened: 2010-06-25 Last modified: 2015-04-08

-

View all other issues in [alg.search].

-

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-

Discussion:

-

-LWG 1205 (currently in WP) clarified the return value of several -algorithms when dealing with empty ranges. In particular it recommended for -25.2.13 [alg.search]: -

- -
-template<class ForwardIterator1, class ForwardIterator2>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2);
-
-template<class ForwardIterator1, class ForwardIterator2,
-         class BinaryPredicate>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2,
-           BinaryPredicate pred);
-
-
-

-1 Effects: ... -

-

-2 Returns: ... Returns last1 if no such iterator is found. -

-

-3 Remarks: Returns first1 if [first2,last2) is empty. -

-
-
- -

-Unfortunately this got translated to an incorrect specification for what gets -returned when no such iterator is found (N3092): -

- -
-template<class ForwardIterator1, class ForwardIterator2>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2);
-
-template<class ForwardIterator1, class ForwardIterator2,
-         class BinaryPredicate>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2,
-           BinaryPredicate pred);
-
-
-

-1 Effects: ... -

-

-2 Returns: ... Returns first1 if [first2,last2) is -empty or if no such iterator is found. -

-
-
- -

-LWG 1205 is correct and N3092 is not equivalent nor correct. -

- -

-I have not reviewed the other 10 recommendations of 1205. -

- -

[ -Post-Rapperswil -]

- - -

-It was verified that none of the remaining possibly affected algorithms does -have any similar problems and a concrete P/R was added that used a similar -style as has been applied to the other cases. -

- -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-
    -
  1. Change [alg.search] p.2 as indicated: -
    -template<class ForwardIterator1, class ForwardIterator2>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2);
-
-template<class ForwardIterator1, class ForwardIterator2,
-            class BinaryPredicate>
-  ForwardIterator1
-    search(ForwardIterator1 first1, ForwardIterator1 last1,
-           ForwardIterator2 first2, ForwardIterator2 last2,
-           BinaryPredicate pred);
-
    -

    -1 - [...] -

    -2 - Returns: The first iterator i in the range [first1,last1 - (last2-first2)) such that for any nonnegative -integer n less than last2 - first2 the following corresponding conditions hold: *(i + n) == *(first2 + n), -pred(*(i + n), *(first2 + n)) != false. Returns first1 if [first2,last2) is empty or, otherwise - returns last1 if no such iterator is found. -

    -
    2. -
- - - - - -
-

1339. uninitialized_fill_n should return the end of its range

-

Section: 20.7.12.4 [uninitialized.fill.n] Status: C++11 - Submitter: Jared Hoberock Opened: 2010-07-14 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-N3092's -specification of uninitialized_fill_n discards useful information and -is inconsistent with other algorithms such as fill_n which accept an -iterator and a size. As currently specified, unintialized_fill_n -requires an additional linear traversal to find the end of the range. -

- -

-Instead of returning void, unintialized_fill_n should return -one past the last iterator it dereferenced. -

- -

[ -Post-Rapperswil: -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-In section 20.7 [memory] change:, -

- -
-template <class ForwardIterator, class Size, class T>
-  void ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x);
-
- - -

-In section 20.7.12.4 [uninitialized.fill.n] change, -

- -
-template <class ForwardIterator, class Size, class T>
-  void ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x);
-
-
-

-1 Effects: -

-
-for (; n--; ++first)
-  ::new (static_cast<void*>(&*first))
-    typename iterator_traits<ForwardIterator>::value_type(x);
-return first;
-
-
-
- - - - - - -
-

1340. Why does forward_list::resize take the object to be copied by value?

-

Section: 23.3.4.5 [forwardlist.modifiers] Status: C++11 - Submitter: James McNellis Opened: 2010-07-16 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In -N3092 -23.3.4.5 [forwardlist.modifiers], the resize() member function is -declared as: -

- -
-void resize(size_type sz, value_type c); 
-
- -

-The other sequence containers (list, deque, and -vector) take 'c' by const reference. -

- -

-Is there a reason for this difference? If not, then resize() should -be declared as: -

- -
-void resize(size_type sz, const value_type& c); 
-
- -

-The declaration would need to be changed both at its declaration in the class -definition at 23.3.4 [forwardlist]/3 and where its behavior is specified -at 23.3.4.5 [forwardlist.modifiers]/22. -

- -

-This would make forward_list consistent with the CD1 issue 679. -

- -

[ -Post-Rapperswil -]

- - -

-Daniel changed the P/R slightly, because one paragraph number has been changed since the issue -had been submitted. He also added a similar Requires element that exists in all other containers with -a resize member function. He deliberately did not touch the wrong usage of "default-constructed" because that -will be taken care of by LWG issue 868. -

- -

-Moved to Tentatively Ready with revised wording after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- - -
    -
  1. Change [forwardlist]/3, class template forward_list synopsis, as indicated: -
    -...
-void resize(size_type sz);
-void resize(size_type sz, const value_type& c);
-void clear();
-...
-
    -
    2. -
  2. Change [forwardlist.modifiers]/27 as indicated: -
    	
-void resize(size_type sz);
-void resize(size_type sz, const value_type& c);
-
    -

    -27 Effects: If sz < distance(begin(), end()), erases the last distance(begin(), end()) - sz elements -from the list. Otherwise, inserts sz - distance(begin(), end()) elements at the end of the list. For the first -signature the inserted elements are default constructed, and for the second signature they are copies of c. -

    -28 - Requires: T shall be DefaultConstructible for the first form and it shall be CopyConstructible - for the second form. -

    -
    3. -
- - - - - - -
-

1344. Replace throw() with noexcept

-

Section: 17 [library] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [library].

-

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-

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-

Duplicate of: 1351

-

Discussion:

-

Addresses GB-60, CH-16

-

-Dynamic exception specifications are deprecated; the -library should recognise this by replacing all non-throwing -exception specifications of the form throw() with the -noexcept form. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Replace all non-throwing exception specifications -of the form 'throw()' with the 'noexcept' form. -

- -

[ -2010-10-31 Daniel comments: -]

- - -

-The proposed resolution of n3148 -would satisfy this request. -

- -

[ -2010-Batavia: -]

- - -

-Resolved by adopting n3148. -

- - - -

Proposed resolution:

-

-See n3148 -See n3150 -See n3195 -See n3155 -See n3156 -

- - - - - -
-

1345. Library classes should have noexcept move operations

-

Section: 17 [library] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

View all other issues in [library].

-

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-

Discussion:

-

Addresses GB-61

-

-All library types should have non-throwing move -constructors and move-assignment operators unless -wrapping a type with a potentially throwing move operation. -When such a type is a class-template, these -operations should have a conditional noexcept -specification. -

-

-There are many other places where a noexcept -specification may be considered, but the move operations -are a special case that must be called out, to effectively -support the move_if_noexcept function template. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Review every class and class template in the library. If noexcept -move constructor/assignment operators can be implicitly declared, then they -should be implicitly declared, or explicitly defaulted. Otherwise, a move -constructor/move assignment operator with a noexcept exception -specification should be provided. -

- -

[ -2010-10-31 Daniel comments: -]

- - -

-The proposed resolution of n3157 -would satisfy this request. -

- -

[2011-03-24 Madrid meeting]

- - -

Resolved by papers to be listed later

- - - -

Proposed resolution:

-

-See n3157 -

- - - - - -
-

1346. Apply noexcept where library specification does not permit exceptions

-

Section: 17 [library] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

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-

Duplicate of: 1352

-

Discussion:

-

Addresses GB-62, CH-17

-

-Issues with efficiency and unsatisfactory semantics mean -many library functions document they do not throw -exceptions with a Throws: Nothing clause, but do not -advertise it with an exception specification. The semantic -issues are largely resolved with the new 'noexcept' -specifications, and the noexcept operator means we will -want to detect these guarantees programatically in order -to construct programs taking advantage of the guarantee. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Add a noexcept exception specification on each -libary API that offers an unconditional Throws: -Nothing guarantee. Where the guarantee is -conditional, add the appropriate -noexcept(constant-expression) if an appropriate -constant expression exists. -

- -

[ -2010-10-31 Daniel comments: -]

- - -

-The proposed resolution of n3149 -would satisfy this request. -

- -

[ -2010-Batavia: -]

- - -

-Resolved by adopting n3149. -

- - - -

Proposed resolution:

-This issue is resolved by the adoption of n3195 -

- - - - -
-

1347. Apply noexcept judiciously throughout the library

-

Section: 17 [library] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [library].

-

View all other issues in [library].

-

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-

Discussion:

-

Addresses GB-63, US-80

-

-Since the newly introduced operator noexcept makes it -easy (easier than previously) to detect whether or not a -function has been declared with the empty exception -specification (including noexcept) library functions that -cannot throw should be decorated with the empty -exception specification. Failing to do so and leaving it as a -matter of QoI would be detrimental to portability and -efficiency. -

- -

[ -Resolution proposed by ballot comment -]

- - -

-Review the whole library, and apply the noexcept -specification where it is appropriate. -

- -

[ -2010-10-31 Daniel comments: -]

- - -

-The proposed resolution of the combination of n3155, -n3156, -n3157, -n3167 -would satisfy this request. The paper n3150 is related -to this as well. -

- -

[ -2010 Batavia: -]

- -

-While the LWG expects to see further papers in this area, sufficient action was taken in Batavia to close the issue as Resolved by the listed papers. -

- - - -

Proposed resolution:

-See n3155, -n3156, -n3157, -n3167 and remotely -n3150 -

- - - - -
-

1349. swap should not throw

-

Section: 17 [library] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses GB-65

-

-Nothrowing swap operations are key to many C++ idioms, -notably the common copy/swap idiom to provide the -strong exception safety guarantee. -

- -

[ -Resolution proposed by ballot comment -]

- - -

-Where possible, all library types should provide a -swap operation with an exception specification -guaranteeing no exception shall propagate. -Where noexcept(true) cannot be guaranteed to -not terminate the program, and the swap in -questions is a template, an exception specification -with the appropriate conditional expression could -be specified. -

- -

[2011-03-13: Daniel comments and drafts wording]

- - -

During a survey of the library some main categories for -potential noexcept swap function could be isolated:

- -
    -
  1. Free swap functions that are specified in terms of already -noexcept swap member functions, like that of valarray.
    2. - -
  2. Free swap of std::function, and member and free swap -functions of stream buffers and streams where considered but rejected as good candidates, -because of the danger to potentially impose requirements of existing implementations. -These functions could be reconsidered as candidates in the future.
    3. -
- -

Negative list:

- -
    -
  1. Algorithms related to swap, like iter_swap, have not been touched, -because there are no fundamental exceptions constraints on iterator operations in general -(only for specific types, like library container iterators)
    2. -
- -

While evaluating the current state of swap functions -of library components it was observed that several conditional noexcept -functions have turned into unconditional ones, e.g. in the -header <utility> synopsis:

- -
-template<class T> void swap(T& a, T& b) noexcept;
-
- -

The suggested resolution shown below also attempts to fix -these cases.

- -

[2011-03-22 Daniel redrafts to satisfy new criteria for applying noexcept. -Parts resolved by N3263-v2 and D3267 are not added here.]

- - - - -

Proposed resolution:

-
    -

  1. Edit 20.2 [utility] p. 2, header <utility> synopsis and -20.2.2 [utility.swap] before p. 1, as indicated (The intent is to fix an editorial -omission):

    - -
    -template<class T> void swap(T& a, T& b) noexcept(see below);
-
    -
    2. - -

  2. Edit the prototype declaration in 20.3.2 [pairs.pair] before p. 34 as indicated (The intent -is to fix an editorial omission):

    - -
    -void swap(pair& p) noexcept(see below);
-
    -
    3. - -

  3. Edit 20.4.1 [tuple.general] p. 2 header <tuple> synopsis and -20.4.2.9 [tuple.special] before p. 1 as indicated (The intent is to fix an editorial omission):

    - -
    -template <class... Types>
-void swap(tuple<Types...>& x, tuple<Types...>& y) noexcept(see below);
-
    -
    4. - -

  4. Edit 20.4.2 [tuple.tuple], class template tuple synopsis and -20.4.2.3 [tuple.swap] before p. 1 as indicated (The intent is to fix an editorial omission):

    - -
    -void swap(tuple&) noexcept(see below);
-
    -
    5. - -

  5. Edit 20.7.2 [memory.syn] p. 1, header <memory> synopsis as indicated (The -intent is to fix an editorial omission of the proposing paper N3195).

    - -
    -template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b) noexcept;
-
    -
    6. - -

  6. Edit header <valarray> synopsis, 26.6.1 [valarray.syn] and -26.6.3.4 [valarray.special] before p. 1 as indicated -[Drafting comment: The corresponding member swap is already noexcept]:

    - -
    -template<class T> void swap(valarray<T>&, valarray<T>&) noexcept;
-
    -
    7. - -
- - - - - -
-

1353. Clarify the state of a moved-from object

-

Section: 17 [library] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses CH-18

-

-The general approach on moving is that a library object -after moving out is in a "valid but unspecified state". But -this is stated at the single object specifications, which is -error prone (especially if the move operations are implicit) -and unnecessary duplication. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Consider putting a general statement to the same -effect into clause 17. -

- -

[2010-11-05 Beman provides exact wording. -The wording was inspired by Dave Abrahams' -message c++std-lib-28958, and refined with help from Alisdair, Daniel, and Howard. -]

- - -

[2011-02-25 P/R wording superseded by N3241. -]

- - - - -

Proposed resolution:

-

Resolved by N3241

- - - - - -
-

1354. The definition of deadlock excludes cases involving a single thread

-

Section: 17.3 [defns.deadlock] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-52

-

-The definition of deadlock in 17.3.7 excludes cases -involving a single thread making it incorrect. -

- -

[ -Resolution proposed by ballot comment -]

- -

-The definition should be corrected. -

- -

[ -2010 Batavia Concurrency group provides a Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 17.3 [defns.deadlock] as indicated: -

-

-deadlock -

-twoone or more threads are unable to continue execution because each is blocked waiting for one or more of the -others to satisfy some condition. -

- - - - - -
-

1355. The definition of move-assignment operator is redundant

-

Section: X [defns.move.assign.op] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-50

-

-This definition of move-assignment operator is redundant -and confusing now that the term move-assignment -operator is defined by the core language in subclause -12.8p21. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3142 -provides a superior resolution. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Strike subclause X [defns.move.assign.op]. -Add a cross-reference to (12.8) to 17.3.12. -

- - - -

Proposed resolution:

-Resolved by paper n3142. -

- - - - -
-

1356. The definition of move-constructor is redundant

-

Section: X [defns.move.ctor] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-51

-

-This definition of move-constructor is redundant and -confusing now that the term constructor is defined by the -core language in subclause 12.8p3. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3142 provides a superior resolution. -

- -

[ -2010 Batavia: resolved as NAD Editorial by adopting paper n3142. -]

- -

-Original proposed resolution preserved for reference: -

-
-

-Strike subclause 17.3.14, [defns.move.ctor] -

- -

-17.3.14 [defns.move.ctor]
-move constructor a constructor which accepts only an rvalue argument of the type being constructed and might modify the argument as a side effect during construction. -

-
- - - -

Proposed resolution:

-Resolved by paper n3142. -

- - - - -
-

1357. Library bitmask types to not satisfy the bimask type requirements

-

Section: 17.5.2.1.3 [bitmask.types] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-53

-

-The bitmask types defined in 27.5.2 and 28.5 contradict -the bitmask type requirements in 17.5.2.1.3, and have -missing or incorrectly defined operators. -

- -

[ -Resolution proposed by ballot comment -]

- -

-See Appendix 1 - Additional Details -

- -

[ -2010 - Rapperswil -]

- -

-The paper n3110 -was made available during the meeting to resolve this comment, but withdrawn from formal motions -to give others time to review the document. There was no technical objection, and it is expected -that this paper will go forward at the next meeting. -

- - - -

Proposed resolution:

-See n3110. -

- - - - -
-

1360. Add <atomic> to free-standing implementations

-

Section: 17.6.1.3 [compliance] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-57

-

-The atomic operations facility is closely tied to clause 1 -and the memory model. It is not easily supplied as an -after-market extension, and should be trivial to implement -of a single-threaded serial machine. The consequence of -not having this facility will be poor interoperability with -future C++ libraries that memory model concerns -seriously, and attempt to treat them in a portable way. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Add <atomic> to table 15, headers required for a -free-standing implementation. -

- - - - -
-

1362. Description of binding to rvalue-references should use the new 'xvalue' vocabulary

-

Section: 17.6.4.9 [res.on.arguments] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-82

-

-17.6.4.9 [res.on.arguments] p.1. b.3: The second Note can benefit by adopting recent nomenclature. -

- - -

[ -Resolution proposed by the ballot comment: -]

- -

-Rephrase the Note in terms of xvalue. -

- -

[ -Pre-Batavia: -]

- -

-Walter Brown provides wording. -

- -

[Batavia: Immediate]

- - -

[ -Adopted at 2010-11 Batavia -]

- - -

Proposed resolution:

- -

-Amend the note in 17.6.3.9 [res.on.arguments] p1 bullet 3. -

-

-[ Note: If a program casts an lvalue to an rvaluexvalue while -passing that lvalue to a library function (e.g. by calling the function with the argument -move(x)), the program is effectively asking that function to treat that lvalue as -a temporary. The implementation is free to optimize away aliasing checks which might be -needed if the argument was anlvalue. — end note] -

- - - - - - -
-

1363. offsetof should be marked noexcept

-

Section: 18.2 [support.types] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-68

- -

-There is no reason for the offsetof macro to invoke -potentially throwing operations, so the result of -noexcept(offsetof(type,member-designator)) should be -true. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add to the end of 18.2p4:

-

-No operation invoked by the offsetof macro shall -throw an exception, and -noexcept(offsetof(type,member-designator)) shall -be true. -

- - - - - -
-

1364. It is not clear how exception_ptr is synchronized

-

Section: 18.8.5 [propagation] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses CH-19

-

-It is not clear how exception_ptr is synchronized. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Make clear that accessing in different threads -multiple exception_ptr objects that all refer to the -same exception introduce a race. -

- -

[2011-03-08: Lawrence comments and drafts wording]

- - -

I think fundamentally, this issue is NAD, but clarification would not hurt.

- -
-

Proposed resolution

-

Add a new paragraph to 18.8.5 [propagation] after paragraph 6 as follows:

- -

-[Note: Exception objects have no synchronization requirements, and expressions -using them may conflict (1.10 [intro.multithread]). — end note] -

-
- - - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1365. Thread-safety of handler functions

-

Section: 18.6.2 [alloc.errors] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-71

-

-The thread safety of std::set_new_handler(), -std::set_unexpected(), std::set_terminate(), is -unspecified making the the functions impossible to use in a thread -safe manner. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-The thread safety guarantees for the functions -must be specified and new interfaces should be -provided to make it possible to query and install -handlers in a thread safe way. -

- -

[ -2010-10-31 Daniel comments: -]

- - -

-The proposed resolution of n3122 -partially addresses this request. This issue is related to 1366. -

- - -

[ -2010-Batavia: -]

- -

-Resolved by adopting n3189. -

- - - -

Proposed resolution:

-Resolved in Batavia by accepting n3189. -

- - - - -
-

1366. New-handler and data races

-

Section: 18.6.1.4 [new.delete.dataraces] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses DE-14

-

-It is unclear how a user replacement function can -simultaneously satisfy the race-free conditions imposed in -this clause and query the new-handler in case of a failed -allocation with the only available, mutating interface -std::set_new_handler. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Offer a non-mutating interface to query the current new-handler. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3122 would solve this issue. -This issue is related to 1365. -

- -

[ -2010-Batavia: -]

- -

-Resolved by adopting n3189. -

- - - -

Proposed resolution:

-Resolved in Batavia by accepting n3189. -

- - - - -
-

1367. Deprecate library support for checking dynamic exception specifications

-

Section: D.8 [exception.unexpected] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-72

-

-Dynamic exception specifications are deprecated, so -clause 18.8.2 that describes library support for this facility -should move to Annex D, with the exception of the -bad_exception class which is retained to indicate other -failures in the exception dispatch mechanism (e.g. calling -current_exception()). -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-With the exception of 18.8.2.1 [bad.exception], -move clause 18.8.2 directly to Annex D. -[bad.exception] should simply become the new -18.8.2. -

- - - - -
-

1368. Thread safety of std::uncaught_exception()

-

Section: X [uncaught] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-73

-

-The thread safety std::uncaught_exception() and the -result of the function when multiple threads throw -exceptions at the same time are unspecified. To make the -function safe to use in the presence of exceptions in -multiple threads the specification needs to be updated. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Update this clause to support safe calls from -multiple threads without placing synchronization -requirements on the user. -

- -

[ -2010 Batavia Concurrency group provides a Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

Change X [uncaught] p. 1 as follows:

-

-Returns: true after the current thread has initialized initializing - an exception object (15.1) until a handler for the exception (including unexpected() or terminate()) - is activated (15.3). [ Note: This includes stack unwinding (15.2). — end note ] -

- - - - - - -
-

1370. throw_with_nested should not use perfect forwarding

-

Section: 18.8.6 [except.nested] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-84

-

-The throw_with_nested specification passes in its argument as -T&& (perfect forwarding pattern), but then discusses -requirements on T without taking into account that T -may be an lvalue-reference type. It is also not clear in the spec that -t is intended to be perfectly forwarded. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Patch [except.nested] p6-7 to match the intent with regards to -requirements on T and the use of -std::forward<T>(t). -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3144 would solve this issue. -

- -

[2010-11-10 Batavia: LWG accepts Howard's updated wording with -corrected boo boos reported by Sebastian Gesemann and Pete Becker, -which is approved for Immediate adoption this meeting.]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

Change 18.8.7 nested_exception [except.nested] as indicated:

-
- 
[[noreturn]] template <class T> void throw_with_nested(T&& t);
-
-
-

Let U be remove_reference<T>::type

-

6 Requires: T U shall be - CopyConstructible.

-

7 Throws: If T U is a non-union - class type not derived from nested_exception, an exception of - unspecified type that is publicly derived from both T U - and nested_exception and constructed from std::forward<T>(t), - otherwise throws std::forward<T>(t). -

-
-
- - - - - -
-

1372. Adopt recommended practice for standard error categories

-

Section: 19.5.1.5 [syserr.errcat.objects] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-76

- -

-The C++0x FCD recommends, in a note (see 19.5.1.1/1), that users -create a single error_category object for each user defined error -category and specifies error_category equality comparsions based on -equality of addresses (19.5.1.3). The Draft apparently ignores this -when specifying standard error category objects in section 19.5.1.5, -by allowing the generic_category() and system_category() -functions to return distinct objects for each invocation. -

-

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-Append a new sentence to 19.5.1.5 [syserr.errcat.objects]/1, and append -the same sentence to 19.5.1.5/3. -

-

-All calls of this function return references to the same object. -

- - - - - -
-

1377. The revised forward is not compatible with access-control

-

Section: 20.2 [utility] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-90

-

-In n3090, at variance with previous iterations of the idea -discussed in papers and incorporated in WDs, -std::forward is constrained via std::is_convertible, -thus is not robust wrt access control. This causes problems in -normal uses as implementation detail of member -functions. For example, the following snippet leads to a -compile time failure, whereas that was not the case for an -implementation along the lines of n2835 (using enable_ifs -instead of concepts for the constraining, of course) -

-
-#include <utility>
-struct Base { Base(Base&&); };
-
-struct Derived
-  : private Base
-{
-  Derived(Derived&& d)
-    : Base(std::forward<Base>(d)) { }
-};
-
-

-In other terms, LWG 1054 can be resolved in a better -way, the present status is not acceptable. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3143 would solve this issue. -

- - - -

Proposed resolution:

-Resolved as NAD Editorial by paper n3143. -

- - - - -
-

1378. pair and tuple have too many conversions

-

Section: 20.3 [pairs] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses DE-15

-

-Several function templates of pair and tuple allow for too -many implicit conversions, for example: -

-
-#include <tuple>
-std::tuple<char*> p(0); // Error?
-
-struct A { explicit A(int){} };
-A a = 1; // Error
-std::tuple<A> ta = std::make_tuple(1); // OK?
-
- -

[ -Resolution proposed by ballot comment -]

- -

-Consider to add wording to constrain these function templates. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 would solve this issue. -

- - - - -

Proposed resolution:

-See n3140. -

- - - - -
-

1379. pair copy-assignment not consistent for references

-

Section: 20.3.2 [pairs.pair] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-95

-

-Copy-assignment for pair is defaulted and does not work -for pairs with reference members. This is inconsistent with -conversion-assignment, which deliberately succeeds even -if one or both elements are reference types, just as for -tuple. The copy-assignment operator should be -consistent with the conversion-assignment operator and -with tuple's assignment operators. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 would provide a superior resolution, -because pair does not depend on the semantic requirements of CopyAssignable. -

- -

[ -2010-11 Batavia -]

- -

-Resolved by adopting n3140. -

- - - -

Proposed resolution:

-

Add to pair synopsis:

-

-pair& operator=(const pair& p); -

-

-Add before paragraph 9: -

-

-pair& operator=(const pair& p); -

-

-Requires: T1 and T2 shall satisfy the -requirements of CopyAssignable. -

-

-Effects: Assigns p.first to first and p.second to -second. -Returns: *this. -

-
-
- - - - - -
-

1380. pair and tuple of references need to better specify move-semantics

-

Section: 20.3 [pairs] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses DE-16

-

-Several pair and tuple functions in regard to move -operations are incorrectly specified if the member types -are references, because the result of a std::move cannot -be assigned to lvalue-references. In this context the usage -of the requirement sets MoveConstructible and -CopyConstructible also doesn't make sense, because -non-const lvalue-references cannot satisfy these requirements. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Replace the usage of std::move by that of -std::forward and replace MoveConstructible and -CopyConstructible requirements by other requirements. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 would solve this issue. -

- -

[ -2010-11 Batavia: -]

- - -

-Resolved by adopting n3140. -

- - - -

Proposed resolution:

-See n3140. -

- - - - -
-

1381. Replace pair's range support by proper range facility

-

Section: X [pair.range] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-85

-

-While std::pair may happen to hold a pair of iterators -forming a valid range, this is more likely a coincidence -than a feature guaranteed by the semantics of the pair -template. A distinct range-type should be supplied to -enable the new for-loop syntax rather than overloading an -existing type with a different semantic. -

- -

-If a replacement facility is required for C++0x, consider n2995. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Strike 20.3.5.4 and the matching declarations in 20.3 header synopsis. -

- - - - -
-

1382. pair and tuple constructors should forward arguments

-

Section: 20.3 [pairs] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-96

-

-pair and tuple constructors and assignment operators use -std::move when they should use std::forward. This -causes lvalue references to be erroneously converted to -rvalue references. Related requirements clauses are also -wrong. -

- -

[ -Resolution proposed by ballot comment -]

- -

-See Appendix 1 - Additional Details -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 would solve this issue. -

- -

[ -2010-11 Batavia -]

- -

-Resolved by adopting n3140. -

- - - -

Proposed resolution:

-See n3140. -

- - - - -
-

1383. Inconsistent defaulted move/copy members in pair and tuple

-

Section: 20.3 [pairs], 20.4 [tuple] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [pairs].

-

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-

Discussion:

-

Addresses US-97

-

-pair's class definition in N3092 20.3.2 [pairs.pair] -contains "pair(const pair&) = default;" and -"pair& operator=(pair&& p);". The latter is described by -20.3.2 [pairs.pair] p.12-13. -

-"pair(const pair&) = default;" is a user-declared explicitly defaulted -copy constructor. According to 12.8 [class.copy]/10, this inhibits -the implicitly-declared move constructor. pair should be move constructible. -(12.8 [class.copy]/7 explains that "pair(pair<U, V>&& p)" -will never be instantiated to move pair<T1, T2> to pair<T1, T2>.)
-"pair& operator=(pair&& p);" is a user-provided move -assignment operator (according to 8.4.2 [dcl.fct.def.default]/4: "A -special member function is user-provided if it is user-declared and not explicitly defaulted -on its first declaration."). According to 12.8 [class.copy]/20, this inhibits -the implicitly-declared copy assignment operator. pair -should be copy assignable, and was in C++98/03. (Again, -12.8 [class.copy]/7 explains that "operator=(const pair<U, V>& p)" -will never be instantiated to copy pair<T1, T2> to pair<T1, T2>.)
-Additionally, "pair& operator=(pair&& p);" is -unconditionally defined, whereas according to 12.8 [class.copy]/25, -defaulted copy/move assignment operators are defined as -deleted in several situations, such as when non-static data -members of reference type are present. -

-If "pair(const pair&) = default;" and "pair& operator=(pair&& p);" -were removed from pair's class definition in 20.3.2 [pairs.pair] and from -20.3.2 [pairs.pair]/12-13, pair would -receive implicitly-declared copy/move constructors and -copy/move assignment operators, and 12.8 [class.copy]/25 would -apply. The implicitly-declared copy/move constructors -would be trivial when T1 and T2 have trivial copy/move -constructors, according to 12.8 [class.copy]/13, and similarly for the -assignment operators, according to12.8 [class.copy]/27. Notes could -be added as a reminder that these functions would be -implicitly-declared, but such notes would not be necessary -(the Standard Library specification already assumes a -high level of familiarity with the Core Language, and -casual readers will simply assume that pair is copyable -and movable). -

-Alternatively, pair could be given explicitly-defaulted -copy/move constructors and copy/move assignment -operators. This is a matter of style. -

-tuple is also affected. tuple's class definition in 20.4 [tuple] contains: -

-
-tuple(const tuple&) = default;
-tuple(tuple&&);
-tuple& operator=(const tuple&);
-tuple& operator=(tuple&&);
-
-

-They should all be removed or all be explicitly-defaulted, -to be consistent with pair. Additionally, 20.4.2.1 [tuple.cnstr]/8-9 specifies the -behavior of an explicitly defaulted function, which is currently inconsistent with -pair. -

-

[ -Resolution proposed by ballot comment: -]

- -

-Either remove "pair(const pair&) = default;" and -"pair& operator=(pair&& p);" from pair's class -definition in 20.3.2 [pairs.pair] and from 20.3.2 [pairs.pair] p.12-13, or -give pair explicitly-defaulted copy/move constructors and copy/move assignment operators.
-Change tuple to match. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3140 would solve this issue: -The move/copy constructor will be defaulted, but the corresponding assignment operators need a non-default implementation -because they are supposed to work for references as well. -

- - - -

Proposed resolution:

-See n3140. -

- - - - -
-

1384. Function pack_arguments is poorly named

-

Section: 20.4.2.4 [tuple.creation] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [tuple.creation].

-

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-

Discussion:

-

Addresses US-98

-

-pack_arguments is poorly named. It does not reflect the -fact that it is a tuple creation function and that it forwards -arguments. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Rename pack_arguments to forward_as_tuple throughout the standard. -

- - - - -
-

1385. tuple_cat should be a single variadic signature

-

Section: 20.4.2.4 [tuple.creation] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-88

-

-The tuple_cat template consists of four overloads and that -can concatenate only two tuples. A single variadic -signature that can concatenate an arbitrary number of -tuples would be preferred. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Adopt a simplified form of the proposal in n2975, -restricted to tuples and neither requiring nor outlawing support for other tuple-like types. -

- -

[ -2010 Rapperswil: Alisdair to provide wording. -]

- - -

[ -2010-11-06: Daniel comments and proposes some alternative wording: -]

- - -

-There are some problems in the wording: First, even though the result type tuple<see below> -implies it, the specification of the contained tuple element types is missing. Second, the term "tuple -protocol" is not defined anywhere and I see no reason why this normative wording should not be a non-normative -note. We could at least give a better approximation, maybe "tuple-like protocol" as indicated from header -<utility> synopsis. Further, it seems to me that the effects need to contain a combination of std::forward -with the call of get. Finally I suggest to replace the requirements Move/CopyConstructible -by proper usage of is_constructible, as indicated by n3140. -

- -

[ -2010 Batavia -]

- -

-Moved to Ready with Daniel's improved wording. -

- - -

Proposed resolution:

-

Note: This alternate proposed resolution works only if 1191 has been accepted.

- -
    -
  1. Change 20.4.1 [tuple.general] p. 2, header <tuple> synopsis, as indicated: -
    -namespace std {
-
-...
-
-// 20.4.2.4, tuple creation functions:
-const unspecified ignore;
-
-template <class... Types>
-  tuple<VTypes...> make_tuple(Types&&...);
-  template <class... Types>
-  tuple<ATypes...> forward_as_tuple(Types&&...);
-  
-template<class... Types>
-  tuple<Types&...> tie(Types&...);
-  
-template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>&, const tuple<UTypes...>&);
-template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&&, const tuple<UTypes...>&);
-template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>&, tuple<UTypes...>&&);
-template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&&, tuple<UTypes...>&&);
-template <class... Tuples>
-  tuple<CTypes...> tuple_cat(Tuples&&...);
-
-...
-
-
    -
    2. -
  2. Change 20.4.2.4 [tuple.creation] as indicated: -
    -
    template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
    -

    -8 Requires: All the types in TTypes shall be CopyConstructible (Table 35). All the types in -UTypes shall be CopyConstructible (Table 35). -

    -

    -9 Returns: A tuple object constructed by copy constructing its first sizeof...(TTypes) elements -from the corresponding elements of t and copy constructing its last sizeof...(UTypes) elements from the -corresponding elements of u. -

    -
    template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&& t, const tuple<UTypes...>& u);
    -

    -10 Requires: All the types in TTypes shall be MoveConstructible (Table 34). All the types in -UTypes shall be CopyConstructible (Table 35). -

    -

    -11 Returns: A tuple object constructed by move constructing its first sizeof...(TTypes) elements -from the corresponding elements of t and copy constructing its last sizeof...(UTypes) elements from the -corresponding elements of u. -

    -
    template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(const tuple<TTypes...>& t, tuple<UTypes...>&& u);
    -

    -12 Requires: All the types in TTypes shall be CopyConstructible (Table 35). All the types in -UTypes shall be MoveConstructible (Table 34). -

    -

    -13 Returns: A tuple object constructed by copy constructing its first sizeof...(TTypes) elements -from the corresponding elements of t and move constructing its last sizeof...(UTypes) elements from the -corresponding elements of u. -

    -
    template <class... TTypes, class... UTypes>
-  tuple<TTypes..., UTypes...> tuple_cat(tuple<TTypes...>&& t, tuple<UTypes...>&& u);
    -

    -14 Requires: All the types in TTypes shall be MoveConstructible (Table 34). All the types in -UTypes shall be MoveConstructible (Table 34). -

    -

    -15 Returns: A tuple object constructed by move constructing its first sizeof...(TTypes) elements -from the corresponding elements of t and move constructing its last sizeof...(UTypes) elements from the -corresponding elements of u. -

    -
    template <class... Tuples>
-  tuple<CTypes...> tuple_cat(Tuples&&... tpls);
-
    -

    -8 Let Ti be the ith type in Tuples, Ui be remove_reference<Ti>::type, -and tpi be the ith parameter in the function parameter pack tpls, where all -indexing is zero-based in the following paragraphs of this sub-clause [tuple.creation]. -

    -

    -9 Requires: For all i, Ui shall be the type cvi tuple<Argsi...>, -where cvi is the (possibly empty) ith cv-qualifier-seq, and -Argsi is the parameter pack representing the element types in Ui. Let Aik be the -kith type in Argsi, then for all Aik the following -requirements shall be satisfied: If Ti is deduced as an lvalue reference type, then -is_constructible<Aik, cvi Aik&>::value == true, otherwise -is_constructible<Aik, cvi Aik&&>::value == true. -

    -

    -10 Remarks: The types in CTypes shall be equal to the ordered sequence of the expanded types -Args0..., Args1..., Argsn-1..., where n equals -sizeof...(Tuples). Let ei... be the ith ordered -sequence of tuple elements of the result tuple object corresponding to the type sequence -Argsi. -

    -

    -11 Returns: A tuple object constructed by initializing -the kith type element eik in ei... -with get<ki>(std::forward<Ti>(tpi)) -for each valid ki and each element group ei in order. -

    -

    -12 [Note: An implementation may support additional types in the parameter pack Tuples, such as -pair and array that support the tuple-like protocol. — end note] -

    -
    -
    3. -
- - - - - - -
-

1386. pack_arguments overly complex

-

Section: 20.4.2.4 [tuple.creation] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-99

-

-pack_arguments is overly complex. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-This issue resulted from a lack of understanding of -how references are forwarded. The definition of -pack_arguments should be simply:
-template <class... Types> -tuple<ATypes&&> -pack_arguments(Types&&...t);
-Types: Let Ti be each type in Types....
-Effects: ...
-Returns:
-tuple<ATypes&&...>(std::forward<Types>(t)...)
-The synopsis should also change to reflect this simpler signature. -

- - - - -
-

1387. Range support by tuple should be removed

-

Section: X [tuple.range] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-87

-

-There is no compelling reason to assume a -heterogeneous tuple of two elements holds a pair of -iterators forming a valid range. Unlike std::pair, there are -no functions in the standard library using this as a return -type with a valid range, so there is even less reason to try -to adapt this type for the new for-loop syntax. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Strike 20.4.2.10 and the matching declarations in -the header synopsis in 20.4. -

- - - - -
-

1388. LWG 1281 incorrectly accepted

-

Section: 20.11.3 [ratio.ratio] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-100

-

-LWG 1281 was discussed in Pittsburgh, and the decision -there was to accept the typedef as proposed and move to -Review. Unfortunately the issue was accidentally applied -to the FCD, and incorrectly. The FCD version of the -typedef refers to ratio<N, D>, but the typedef is intended -to refer to ratio<num, den> which in general is not the -same type. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Accept the current proposed wording of LWG 1281 which adds:
-typedef ratio<num, den> type; -

- - - - -
-

1389. Compile-time rational arithmetic and overflow

-

Section: 20.11.4 [ratio.arithmetic] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-89

-

-The alias representations of the ratio arithmetic templates -do not allow implementations to avoid overflow, since they -explicitly specify the form of the aliased template -instantiation. For example -ratio_multiply, ratio<2, LLONG_MAX> is required to -alias ratio<2*LLONG_MAX, LLONG_MAX*2>, which -overflows, so is ill-formed. However, this is trivially equal -to ratio<1, 1>. It also contradicts the opening statement of -20.11.4 [ratio.arithmetic] p. 1 "implementations may use other algorithms to -compute these values". -

- -

[ -2010-10-25 Daniel adds: -]

- - -

-Accepting n3131 would solve this issue. -

- -

[Batavia: Resolved by accepting -n3210.]

- - - - -

Proposed resolution:

-

Change the wording in 20.11.4 [ratio.arithmetic] p. 2-5 as follows:

-
-template <class R1, class R2> using ratio_add = see below;
-

-2 The type ratio_add<R1, R2> shall be a synonym for ratio<T1, T2> -ratio<U, V> such that ratio<U, V>::num and ratio<U, V>::den -are the same as the corresponding members of ratio<T1, T2> would be in the absence of -arithmetic overflow where T1 has the value R1::num * R2::den + R2::num * R1::den -and T2 has the value R1::den * R2::den. If the required values of ratio<U, V>::num -and ratio<U, V>::den cannot be represented in intmax_t then the program is ill-formed. -

-
-template <class R1, class R2> using ratio_subtract = see below;
-

-3 The type ratio_subtract<R1, R2> shall be a synonym for ratio<T1, T2> -ratio<U, V> such that ratio<U, V>::num and ratio<U, V>::den -are the same as the corresponding members of ratio<T1, T2> would be in the absence of -arithmetic overflow where T1 has the value R1::num * R2::den - R2::num * R1::den -and T2 has the value R1::den * R2::den. If the required values of ratio<U, V>::num -and ratio<U, V>::den cannot be represented in intmax_t then the program is ill-formed. -

-
-template <class R1, class R2> using ratio_multiply = see below;
-

-4 The type ratio_multiply<R1, R2> shall be a synonym for ratio<T1, T2> -ratio<U, V> such that ratio<U, V>::num and ratio<U, V>::den -are the same as the corresponding members of ratio<T1, T2> would be in the absence of -arithmetic overflow where T1 has the value R1::num * R2::num and T2 -has the value R1::den * R2::den. If the required values of ratio<U, V>::num -and ratio<U, V>::den cannot be represented in intmax_t then the program is ill-formed. -

-
-template <class R1, class R2> using ratio_divide = see below;
-

-5 The type ratio_divide<R1, R2> shall be a synonym for ratio<T1, T2> -ratio<U, V> such that ratio<U, V>::num and ratio<U, V>::den -are the same as the corresponding members of ratio<T1, T2> would be in the absence of -arithmetic overflow where T1 has the value R1::num * R2::den and T2 -has the value R1::den * R2::num. If the required values of ratio<U, V>::num -and ratio<U, V>::den cannot be represented in intmax_t then the program is ill-formed. -

- - - - - -
-

1390. Limit speculative compilation for constructible/convertible traits

-

Section: 20.10 [meta] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses DE-17

-

-Speculative compilation for std::is_constructible and -std::is_convertible should be limited, similar to the core -language (see 14.8.2 paragraph 8). -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3142 would solve this issue. -

- - - -

Proposed resolution:

-Resolved by paper n3142. -

- - - - -
-

1391. constructible/convertible traits and access control

-

Section: 20.10 [meta] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses DE-18

-

-Several type traits require compiler support, e.g. -std::is_constructible or std::is_convertible. -Their current specification seems to imply, that the corresponding -test expressions should be well-formed, even in absense of access: -

-
-class X { X(int){} };
-constexpr bool test = std::is_constructible<X, int>::value;
-
-

-The specification does not clarify the context of this test -and because it already goes beyond normal language -rules, it's hard to argue by means of normal language -rules what the context and outcome of the test should be. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Specify that std::is_constructible and -std::is_convertible will return true only for -public constructors/conversion functions. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3142 would solve this issue. -

- - - -

Proposed resolution:

-Resolved by paper n3142. -

- - - - -
-

1392. result_of should support pointer-to-data-member

-

Section: 20.10.4 [meta.unary] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-102

-

-Despite Library Issue 520's ("result_of and pointers to -data members") resolution of CD1, the FCD's result_of -supports neither pointers to member functions nor -pointers to data members. It should. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Ensure result_of supports pointers to member -functions and pointers to data members. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3123 would solve this issue. -

- - - -

Proposed resolution:

-Resolved by n3123. -

- - - - -
-

1393. Trivial traits imply noexcept

-

Section: 20.10.4.3 [meta.unary.prop] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses GB-92

-

-Trivial functions implicitly declare a noexcept exception -specification, so the references to has_trivial_* traits in the -has_nothrow_* traits are redundant, and should be struck for clarity. -

- -

[ -Resolution proposed by ballot comment -]

- -

-For each of the has_nothrow_something traits, -remove all references to the matching has_trivial_something traits. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3142 would solve this issue. -

- - - -

Proposed resolution:

-Resolved by n3142. -

- - - - -
-

1394. is_constructible reports false positives

-

Section: 20.10.4.3 [meta.unary.prop] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses DE-19

-

-The fundamental trait is_constructible reports false -positives, e.g. -

-
-is_constructible<char*, void*>::value
-
-

-evaluates to true, even though a corresponding variable initialization would be ill-formed. -

-

[ -Resolved in Rapperswil by paper N3047. -]

- - - - -

Proposed resolution:

-Remove all false positives from the domain of is_constructible. -

- - - - -
-

1397. Deprecate '98 binders

-

Section: 20.9 [function.objects] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-95

-

-The adaptable function protocol supported by -unary_function/binary_function has been superceded by -lambda expressions and std::bind. Despite the name, the -protocol is not very adaptable as it requires intrusive -support in the adaptable types, rather than offering an -external traits-like adaption mechanism. This protocol and -related support functions should be deprecated, and we -should not make onerous requirements for the -specification to support this protocol for callable types -introduced in this standard revision, including those -adopted from TR1. It is expected that high-quality -implementations will provide such support, but we should -not have to write robust standard specifications mixing this -restricted support with more general components such as -function, bind and reference_wrapper. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Move clauses 20.8.3, 20.8.9, 20.8.11 and 20.8.12 -to Annex D. -

-Remove the requirements to conditionally derive from -unary/binary_function from function, -reference_wrapper, and the results of calling mem_fn -and bind. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3145 would solve this issue. -

- - - -

Proposed resolution:

-Resolved by paper N3198. -

- - - - -
-

1399. function does not need an explicit default constructor

-

Section: 20.9.12.2 [func.wrap.func] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses JP-3

-

-explicit default contructor is defined in std::function. -Although it is allowed according to 12.3.1, it seems -unnecessary to qualify the constructor as explicit. -If it is explicit, there will be a limitation in initializer_list. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Remove explicit.

-
-namespace std {
-template<class> class function;
-// undefined
-template<class R, class... ArgTypes>
-class function<R(ArgTypes...)>
-: public unary_function<T1, R>
-// iff sizeof...(ArgTypes) == 1 and ArgTypes contains T1
-: public binary_function<T1, T2, R>
-// iff sizeof...(ArgTypes) == 2 and ArgTypes contains T1 andT2
-{
-public:typedef R result_type;
-// 20.8.14.2.1, construct/copy/destroy:
-  explicit function();
-
- - - - - -
-

1400. FCD function does not need an explicit default constructor

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses JP-4

-

-Really does the function require that default constructor is explicit? -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Remove explicit.

-
-function();
-template <class A>
-function(allocator_arg_t, const A& a);
-
- - - - - -
-

1401. Provide support for unique_ptr<T> == nullptr

-

Section: 20.7 [memory] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-99

-

-One reason that the unique_ptr constructor taking a -nullptr_t argument is not explicit is to allow conversion -of nullptr to unique_ptr in contexts like equality -comparison. Unfortunately operator== for unique_ptr is a -little more clever than that, deducing template parameters for both -arguments. This means that nullptr does not get deduced -as unique_ptr type, and there are no other comparison -functions to match. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Add the following signatures to 20.7 [memory] p.1, <memory> -header synopsis: -

-template<typename T, typename D>
-bool operator==(const unique_ptr<T, D> & lhs, nullptr_t);
-template<typename T, typename D>
-bool operator==(nullptr_t, const unique_ptr<T, D> & rhs);
-template<typename T, typename D>
-bool operator!=(const unique_ptr<T, D> & lhs, nullptr_t);
-template<typename T, typename D>
-bool operator!=(nullptr_t, const unique_ptr<T, D> & rhs);
-
-
- -

[ -2010-11-02 Daniel comments and provides a proposed resolution: -]

- - -

-The same problem applies to shared_ptr as well: In both cases there are no -conversions considered because the comparison functions are templates. I agree with -the direction of the proposed resolution, but I believe it would be very surprising -and inconsistent, if given a smart pointer object p, the expression -p == nullptr would be provided, but not p < nullptr and the -other relational operators. According to 5.9 [expr.rel] they are defined -if null pointer values meet other pointer values, even though the result is unspecified -for all except some trivial ones. But null pointer values are nothing special here: -The Library already defines the relational operators for both unique_ptr and -shared_ptr and the outcome of comparing non-null pointer values will be equally -unspecified. If the idea of supporting nullptr_t arguments for relational -operators is not what the committee prefers, I suggest at least to consider to remove -the existing relational operators for both unique_ptr and shared_ptr -for consistency. But that would not be my preferred resolution of this issue. -

-The number of overloads triple the current number, but I think it is much clearer to -provide them explicitly instead of adding wording that attempts to say that "sufficient overloads" are -provided. The following proposal makes the declarations explicit. -

-Additionally, the proposal adds the missing declarations for some shared_ptr -comparison functions for consistency. -

- -

[ -2010-11-03 Daniel adds: -]

- - -

-Issue 1297 is remotely related. The following proposed resolution splits -this bullet into sub-bullets A and B. Sub-bullet A would -also solve 1297, but sub-bullet B would not. -

-A further remark in regard to the proposed semantics of the ordering of nullptr -against other pointer(-like) values: One might think that the following definition might -be superior because of simplicity: -

-
-template<class T>
-bool operator<(const shared_ptr<T>& a, nullptr_t);
-template<class T>
-bool operator>(nullptr_t, const shared_ptr<T>& a);
-

-Returns: false. -

-

-The underlying idea behind this approach is the assumption that nullptr corresponds -to the least ordinal pointer value. But this assertion does not hold for all supported -architectures, therefore this approach was not followed because it would lead to -the inconsistency, that the following assertion could fire: -

-
-shared_ptr<int> p(new int);
-shared_ptr<int> null;
-bool v1 = p < nullptr;
-bool v2 = p < null;
-assert(v1 == v2);
-
- -

[2011-03-06: Daniel comments]

- - -

The current issue state is not acceptable, because the Batavia meeting -did not give advice whether choice A or B of bullet 3 should be applied. -Option B will now be removed and if this resolution is accepted, issue -1297 should be declared as resolved by 1401. -This update also resyncs the wording with N3242.

- - - -

Proposed resolution:

-

-Wording changes are against N3242. -

-
    -
  1. Change 20.7.2 [memory.syn] p. 1, header <memory> synopsis as indicated. -noexcept specifications are only added, where the guarantee exists, that the function -shall no throw an exception (as replacement of "Throws: Nothing". Note that -the noexcept additions to the shared_ptr comparisons are editorial, because -they are already part of the accepted paper n3195: -
    -namespace std {
-  […]
-  // [unique.ptr] Class unique_ptr:
-  template <class T> class default_delete;
-  template <class T> class default_delete<T[]>;
-  template <class T, class D = default_delete<T>> class unique_ptr;
-  template <class T, class D> class unique_ptr<T[], D>;
-
-  template <class T1, class D1, class T2, class D2>
-  bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
-  template <class T, class D>
-  bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-  template <class T, class D>
-  bool operator==(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-  template <class T, class D>
-  bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-  template <class T, class D>
-  bool operator!=(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-  template <class T, class D>
-  bool operator<(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator<(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator<=(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator>(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator>(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator>=(nullptr_t, const unique_ptr<T, D>& x);
-  
-  // [util.smartptr.weakptr], Class bad_weak_ptr:
-  class bad_weak_ptr;
-
-  // [util.smartptr.shared], Class template shared_ptr:
-  template<class T> class shared_ptr;
-
-  // [util.smartptr.shared.cmp], shared_ptr comparisons:
-  template<class T, class U>
-  bool operator==(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-  template<class T, class U>
-  bool operator!=(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-  template<class T, class U>
-  bool operator<(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-  template<class T, class U>
-  bool operator>(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-  template<class T, class U>
-  bool operator<=(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-  template<class T, class U>
-  bool operator>=(shared_ptr<T> const& a, shared_ptr<U> const& b)  noexcept;
-
-  template<class T>
-  bool operator==(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator==(nullptr_t, shared_ptr<T> const& a) noexcept;
-  template<class T>
-  bool operator!=(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator!=(nullptr_t, shared_ptr<T> const& a) noexcept;
-  template<class T>
-  bool operator<(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator<(nullptr_t, shared_ptr<T> const& a) noexcept;
-  template>class T>
-  bool operator>(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template>class T>
-  bool operator>(nullptr_t, shared_ptr<T> const& a) noexcept;
-  template<class T>
-  bool operator<=(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator<=(nullptr_t, shared_ptr<T> const& a) noexcept;
-  template>class T>
-  bool operator>=(shared_ptr<T> const& a, nullptr_t) noexcept;
-  template>class T>
-  bool operator>=(nullptr_t, shared_ptr<T> const& a) noexcept;
-
-  […]
-}
-
    -
    2. -
  2. Change the synopsis just after 20.8.1 [unique.ptr] p. 6 as indicated: -
    -namespace std {
-  […]
-  
-  template <class T1, class D1, class T2, class D2>
-  bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-  template <class T1, class D1, class T2, class D2>
-  bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
-  template <class T, class D>
-  bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-  template <class T, class D>
-  bool operator==(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-  template <class T, class D>
-  bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-  template <class T, class D>
-  bool operator!=(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-  template <class T, class D>
-  bool operator<(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator<(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator<=(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator>(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator>(nullptr_t, const unique_ptr<T, D>& x);
-  template <class T, class D>
-  bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
-  template <class T, class D>
-  bool operator>=(nullptr_t, const unique_ptr<T, D>& x);
-
-}
-
    -
    3. -
  3. This bullet does now only suggest the first approach: -

    Change 20.8.1.5 [unique.ptr.special] p. 4-7 as indicated and add a series of prototype -descriptions:

    -
    -template <class T1, class D1, class T2, class D2>
-  bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -
    -

    -? Requires: Let CT be common_type<unique_ptr<T1, -D1>::pointer, unique_ptr<T2, D2>::pointer>::type. Then -the specialization less<CT> shall be a function object type ([function.objects]) -that induces a strict weak ordering ([alg.sorting]) on the pointer values. -

    - -

    -4 Returns: less<CT>()(x.get(), y.get())x.get() -< y.get(). -

    - -

    -? Remarks: If unique_ptr<T1, D1>::pointer is not -implicitly convertible to CT or unique_ptr<T2, -D2>::pointer is not implicitly convertible to CT, the program -is ill-formed. -

    -
    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -

    -5 Returns: !(y < x)x.get() <= y.get(). -

    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -

    -6 Returns: (y < x)x.get() > y.get(). -

    - -
    -template <class T1, class D1, class T2, class D2>
-  bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
-
    - -

    -7 Returns: !(x < y)x.get() >= y.get(). -

    -
    - -
    -template <class T, class D>
-bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-template <class T, class D>
-bool operator==(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-

    -? Returns: !x. -

    - -
    -template <class T, class D>
-bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
-template <class T, class D>
-bool operator!=(nullptr_t, const unique_ptr<T, D>& x) noexcept;
-

    -? Returns: (bool) x. -

    - -
    -template <class T, class D>
-bool operator<(const unique_ptr<T, D>& x, nullptr_t);
-template <class T, class D>
-bool operator>(nullptr_t, const unique_ptr<T, D>& x);
-
    -

    -? Requires: The specialization less<unique_ptr<T, D>::pointer> -shall be a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) -on the pointer values. -

    -

    -? Returns: less<unique_ptr<T, D>::pointer>()(x.get(), nullptr). -

    - -
    -template <class T, class D>
-bool operator<(nullptr_t, const unique_ptr<T, D>& x);
-template <class T, class D>
-bool operator>(const unique_ptr<T, D>& x, nullptr_t);
-
    -

    -? Requires: The specialization less<unique_ptr<T, D>::pointer> -shall be a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) -on the pointer values. -

    -

    -? Returns: less<unique_ptr<T, D>::pointer>()(nullptr, x.get()). -

    - -
    -template <class T, class D>
-bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
-template <class T, class D>
-bool operator>=(nullptr_t, const unique_ptr<T, D>& x);
-

    -? Returns: !(nullptr < x). -

    - -
    -template <class T, class D>
-bool operator<=(nullptr_t, const unique_ptr<T, D>& x);
-template <class T, class D>
-bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
-

    -? Returns: !(x < nullptr). -

    - - -
    4. -

  4. Change 20.8.2.2 [util.smartptr.shared] p. 1, class template shared_ptr -synopsis as indicated. For consistency reasons the remaining normal relation -operators are added as well: -

    -
    -namespace std {
-
-  […]
-
-  // [util.smartptr.shared.cmp], shared_ptr comparisons:
-  template<class T, class U>
-  bool operator==(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-  template<class T, class U>
-  bool operator!=(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-  template<class T, class U>
-  bool operator<(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-  template<class T, class U>
-  bool operator>(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-  template<class T, class U>
-  bool operator<=(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-  template<class T, class U>
-  bool operator>=(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
-
-  template<class T>
-  bool operator==(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator==(nullptr_t, const shared_ptr<T>& a) noexcept;
-  template<class T>
-  bool operator!=(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator!=(nullptr_t, const shared_ptr<T>& a) noexcept;
-  template<class T>
-  bool operator<(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator<(nullptr_t, const shared_ptr<T>& a) noexcept;
-  template>class T>
-  bool operator>(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template>class T>
-  bool operator>(nullptr_t, const shared_ptr<T>& a) noexcept;
-  template<class T>
-  bool operator<=(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template<class T>
-  bool operator<=(nullptr_t, const shared_ptr<T>& a) noexcept;
-  template>class T>
-  bool operator>=(const shared_ptr<T>& a, nullptr_t) noexcept;
-  template>class T>
-  bool operator>=(nullptr_t, const shared_ptr<T>& a) noexcept;
-
-  […]
-}
-
    -
    5. -
  5. Add the following series of prototype specifications at the very end of 20.8.2.2.7 [util.smartptr.shared.cmp]. -For mixed comparison the general "generation" rule of 20.2.1 [operators] p. 10 does not apply, -therefore all of them are defined. Below wording takes advantage of the simplified definition of the -composite pointer type if one partner is a null pointer constant: -
    -template<class T>
-bool operator==(const shared_ptr<T>& a, nullptr_t) noexcept;
-template<class T>
-bool operator==(nullptr_t, const shared_ptr<T>& a) noexcept;
-

    -? Returns: !a. -

    - -
    -template<class T>
-bool operator!=(const shared_ptr<T>& a, nullptr_t) noexcept;
-template<class T>
-bool operator!=(nullptr_t, const shared_ptr<T>& a) noexcept;
-

    -? Returns: (bool) a. -

    - -
    -template<class T>
-bool operator<(const shared_ptr<T>& a, nullptr_t) noexcept;
-template<class T>
-bool operator>(nullptr_t, const shared_ptr<T>& a) noexcept;
-

    -? Returns: less<T*>()(a.get(), nullptr). -

    - -
    -template<class T>
-bool operator<(nullptr_t, const shared_ptr<T>& a) noexcept;
-template<class T>
-bool operator>(const shared_ptr<T>& a, nullptr_t) noexcept;
-

    -? Returns: less<T*>()(nullptr, a.get()). -

    - -
    -template<class T>
-bool operator<=(const shared_ptr<T>& a, nullptr_t) noexcept;
-template<class T>
-bool operator>=(nullptr_t, const shared_ptr<T>& a) noexcept;
-

    -? Returns: !(nullptr < a). -

    - -
    -template<class T>
-bool operator<=(nullptr_t, const shared_ptr<T>& a) noexcept;
-template<class T>
-bool operator>=(const shared_ptr<T>& a, nullptr_t) noexcept;
-

    -? Returns: !(a < nullptr). -

    - -
    6. -
- - - - - -
-

1402. nullptr constructors for smart pointers should be constexpr

-

Section: 20.7 [memory] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [memory].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-100

-

-The unique_ptr and shared_ptr constructors taking -nullptr_t delegate to a constexpr constructor, and could be -constexpr themselves. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-In the 20.8.1.2 [unique.ptr.single] synopsis add -"constexpr" to unique_ptr(nullptr_t).
-In the 20.8.1.3 [unique.ptr.runtime] synopsis add -"constexpr" to unique_ptr(nullptr_t).
-In the 20.8.2.2 [util.smartptr.shared] synopsis -add "constexpr" to shared_ptr(nullptr_t). -

- - - - - -
-

1403. Inconsistent definitions for allocator_arg

-

Section: 20.7.6 [allocator.tag] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-85

-

-There are inconsistent definitions for allocator_arg. -In 20.7 [memory] paragraph 1, -

-
-constexpr allocator_arg_t allocator_arg = allocator_arg_t();
-
-

-and in 20.9.1, -

-
-const allocator_arg_t allocator_arg = allocator_arg_t();
-
- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Change "const" to "constexpr" in 20.9.1 as follows.

-
-constexpr allocator_arg_t allocator_arg = allocator_arg_t();
-
- - - - - -
-

1404. pointer_traits should have a size_type member

-

Section: 20.7.3 [pointer.traits] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-106

-

-pointer_traits should have a size_type member for completeness. -

-

-Add typedef see below size_type; to the generic -pointer_traits template and typedef size_t -size_type; to pointer_traits<T*>. Use -pointer_traits::size_type and -pointer_traits::difference_type as the defaults for -allocator_traits::size_type and -allocator_traits::difference_type. -

-

-See Appendix 1 - Additional Details -

- -

[ -Post-Rapperswil, Pablo provided wording: -]

- - -

-The original ballot comment reads simply: "pointer_traits should have a -size_type for completeness." The additional details reveal, however, -that the desire for a size_type is actually driven by the needs -of allocator_traits. The allocator_traits template should get its -default difference_type from pointer_traits but if it did, -it should get its size_type from the same source. Unfortunately, -there is no obvious meaning for size_type in pointer_traits. -

-

-Alisdair suggested, however, that the natural relationship between -difference_type and size_type can be expressed simply by the -std::make_unsigned<T> metafunction. Using this metafunction, -we can easily define size_type for allocator_traits without -artificially adding size_type to pointer_traits. -

- -

-Moved to Tentatively Ready after 6 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - - -

Proposed resolution:

-

-In [allocator.requirements], Table 42, change two rows as follows: -

-
- - - - - - - - - - - - - -
X::size_typeunsigned integral typea type that can represent the size of the largest object in the - allocation model - size_t - make_unsigned<X::difference_type>::type -
X::difference_typesigned integral typea type that can represent the difference between any two pointers in - the allocation model - ptrdiff_t - pointer_traits<X::pointer>::difference_type -
-
-

-In [allocator.traits.types], Change the definition of difference_type and -size_type as follows: -

-

- typedef see below difference_type; -

- Type: Alloc::difference_type if such a type exists, - else ptrdiff_t - pointer_traits<pointer>::difference_type. -

-

- typedef see below size_type; -

- Type: Alloc::size_type if such a type exists, - else size_t - make_unsigned<difference_type>::type. -

-
- - - - - -
-

1405. Move scoped_allocator_adaptor into separate header

-

Section: 20.13 [allocator.adaptor] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [allocator.adaptor].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-107

-

-scoped_allocator_adaptor should have its own header. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-See Appendix 1 - Additional Details -

- - - - -
-

1407. Synch shared_ptr constructors taking movable types

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-108

- -

-shared_ptr should have the same policy for constructing -from auto_ptr as unique_ptr. Currently it does not. -

- -

[ -Resolved in Rapperswil by paper N3109. -]

- - - - -

Proposed resolution:

-

-Add -

-template <class Y> explicit shared_ptr(auto_ptr<Y>&); 
-

-to [util.smartptr.shared.const] (and to the synopsis). -

- - - - -
-

1408. Allow recycling of pointers after undeclare_no_pointers

-

Section: 20.7.4 [util.dynamic.safety] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [util.dynamic.safety].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-103

-

-The precondition to calling declare_no_pointers is that no -bytes in the range "have been previously registered" with -this call. As written, this precondition includes bytes in -ranges, even after they have been explicitly unregistered -with a later call to undeclare_no_pointers. -

- - -

Proposed resolution:

-

-Update 20.7.4 [util.dynamic.safety] p.9: -

-
-void declare_no_pointers(char *p, size_t n);
-

-9 Requires: No bytes in the specified range have been -previously registeredare currently registered with declare_no_pointers(). -If the specified range is in an allocated object, then it must be entirely within a single allocated object. -The object must be live until the corresponding undeclare_no_pointers() call. [..] -

- - - - - -
-

1409. Specify whether monotonic_clock is a distinct type or a typedef

-

Section: X [time.clock.monotonic] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [time.clock.monotonic].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-111

-

-What it means for monotonic_clock to be a synonym is -undefined. If it may or may not be a typedef, then certain -classes of programs become unportable. -

- -

[ -Resolution proposed in ballot comment: -]

- -

-Require that it be a distinct class type. -

- -

[ -2010-11-01 Daniel comments: -]

- -

-Paper n3128 addresses -this issue by replacing monotonic_clock with steady_clock, which is not a typedef. -

- - - -

Proposed resolution:

-

-This is resolved by n3191. -

- - - - - -
-

1410. Add a feature-detect macro for monotonic_clock

-

Section: X [time.clock.monotonic] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [time.clock.monotonic].

-

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-

Duplicate of: 1411

-

Discussion:

-

Addresses GB-107, DE-20

-

-1.4 [intro.compliance] p.9 states that which conditionally -supported constructs are available should be provided in the -documentation for the implementation. This doesn't help programmers trying -to write portable code, as they must then rely on -implementation-specific means to determine the -availability of such constructs. In particular, the presence -or absence of std::chrono::monotonic_clock may require -different code paths to be selected. This is the only -conditionally-supported library facility, and differs from the -conditionally-supported language facilities in that it has -standard-defined semantics rather than implementation-defined -semantics. -

- -

[ -Resolution proposed in ballot comment: -]

- -

-Provide feature test macro for determining the -presence of std::chrono::monotonic_clock. Add -_STDCPP_HAS_MONOTONIC_CLOCK to the -<chrono> header, which is defined if -monotonic_clock is present, and not defined if it is -not present. -

- -

[ -2010-11-01 Daniel comments: -]

- -

-Paper n3128 addresses -this issue by replacing monotonic_clock with steady_clock, which is not conditionally supported, -so there is no need to detect it. -

- - - -

Proposed resolution:

-This is resolved by n3191. -

- - - - -
-

1412. Make monotonic clocks mandatory

-

Section: X [time.clock.monotonic] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [time.clock.monotonic].

-

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-

Discussion:

-

Addresses CH-21

-

-Monotonic clocks are generally easy to provide on all -systems and are implicitely required by some of the library -facilities anyway. -

- -

[ -2010-11-01 Daniel comments: -]

- -

-Paper n3128 addresses -this issue by replacing monotonic_clock with steady_clock, which is mandatory. -

- -

[ -2010-11-13 Batavia meeting: -]

- -

-This is resolved by adopting n3191. -The original resolution is preserved for reference: -

-
-

Make monotonic clocks mandatory.

-

Strike X [time.clock.monotonic] p.2

-

-2 The class monotonic_clock is conditionally supported. -

- -

Change 30.2.4 [thread.req.timing] p.2 accordingly

-

-The member functions whose names end in _for take an argument that -specifies a relative time. Implementations should use a monotonic clock to -measure time for these functions. [ Note: Implementations are not -required to use a monotonic clock because such a clock may not be available. -— end note ] -

-
- - - -

Proposed resolution:

-This is resolved by n3191. -

- - - - -
-

1414. Fixing remaining dead links to POS_T and OFF_T

-

Section: 21.2.3.2 [char.traits.specializations.char16_t] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Duplicate of: 1444

-

Discussion:

-

Addresses GB-109, GB-123

- -

-It is not clear what the specification means for -u16streampos, u32streampos or wstreampos when they -refer to the requirements for POS_T in 21.2.2, as there -are no longer any such requirements. Similarly the annex -D.7 refers to the requirements of type POS_T in 27.3 that -no longer exist either. -

-

-Clarify the meaning of all cross-reference to the -removed type POS_T. -

- - -

[ -Post-Rapperswil, Daniel provides the wording. -]

- - -

-When preparing the wording for this issue I first thought about adding both u16streampos and u32streampos -to the [iostream.forward] header <iosfwd> synopsis similar to streampos and wstreampos, -but decided not to do so, because the IO library does not yet actively support the char16_t and char32_t -character types. Adding those would misleadingly imply that they would be part of the iostreams. Also, the addition -would make them also similarly equal to a typedef to fpos<mbstate_t>, as for streampos and -wstreampos, so there is no loss for users that would like to use the proper fpos instantiation for -these character types. -

-

-Additionally the way of referencing was chosen to follow the style suggested by NB comment -GB 108. -

- -

-Moved to Tentatively Ready with proposed wording after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-The following wording changes are against N3126. -

- -
    -

  1. Change [char.traits.specializations.char16_t]p.1 as indicated:

    -

    -1 - The type u16streampos shall be an implementation-defined type that satisfies the requirements -for POS_T in 21.2.2pos_type in [iostreams.limits.pos]. -

    -
    2. -

  2. Change [char.traits.specializations.char32_t]p.1 as indicated:

    -

    -1 - The type u32streampos shall be an implementation-defined type that satisfies the requirements -for POS_T in 21.2.2pos_type in [iostreams.limits.pos]. -

    -
    3. -

  3. Change [char.traits.specializations.wchar.t]p.2 as indicated:

    -

    -2 - The type wstreampos shall be an implementation-defined type that satisfies the requirements -for POS_T in 21.2.2pos_type in [iostreams.limits.pos]. -

    -
    4. -

  4. Change [fpos.operations], Table 124 — Position type requirements as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 124 — Position type requirements
    ExpressionReturn type...
    .........
    O(p)OFF_Tstreamoff...
    .........
    o = p - qOFF_Tstreamoff...
    streamsize(o)
    O(sz)    		streamsize
    OFF_Tstreamoff    		...
    -
    -
    5. -

  5. Change [depr.ios.members]p.1 as indicated:

    -
    -namespace std {
- class ios_base {
- public:
-   typedef T1 io_state;
-   typedef T2 open_mode;
-   typedef T3 seek_dir;
-   typedef OFF_Timplementation-defined streamoff;
-   typedef POS_Timplementation-defined streampos;
-   // remainder unchanged
- };
-}
-
    -
    6. -

  6. Change [depr.ios.members]p.5+6 as indicated:

    -

    -5 - The type streamoff is an implementation-defined type that satisfies the requirements -of type OFF_T (27.5.1)off_type in [iostreams.limits.pos]. -

    -

    -6 - The type streampos is an implementation-defined type that satisfies the requirements -of type POS_T (27.3)pos_type in [iostreams.limits.pos]. -

    -
    7. -
- - - - - - -
-

1416. forward_list::erase_after should not be allowed to throw

-

Section: 23.2 [container.requirements] Status: C++11 - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [container.requirements].

-

View all other issues in [container.requirements].

-

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-

Discussion:

-

Addresses DE-21

- -

-23.2.1/11 provides a general no-throw guarantee for -erase() container functions, exceptions from this are -explicitly mentioned for individual containers. Because of -its different name, forward_list's erase_after() function is -not ruled by this but should so. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

-Add a "Throws: Nothing" clause to both -erase_after overloads in 23.3.3.4, [forwardlist.modifiers]. -

- - - - - -
-

1417. front/back on a zero-sized array should be undefined

-

Section: 23.3.2.8 [array.zero] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [array.zero].

-

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-

Discussion:

-

Addresses GB-112

- -

-Should the effect of calling front/back on a zero-sized -array really be implementation defined i.e. require the -implementor to define behaviour? -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Change "implementation defined" to "undefined" -

- - - - -
-

1418. Effects of resize(size()) on a deque

-

Section: 23.3.3.3 [deque.capacity] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [deque.capacity].

-

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-

Discussion:

-

Addresses GB-113

-

-There is no mention of what happens if sz==size(). While -it obviously does nothing I feel a standard needs to say -this explicitely. -

- - -

[ -2010 Batavia -]

- -

-Accepted with a simplified resolution turning one of the < -comparisons into <=. -

- -

Proposed resolution:

-

Ammend [deque.capacity]

-

void resize(size_type sz);

-

-Effects: If sz <= size(), equivalent to erase(begin() + -sz, end());. If size() < sz, appends sz - size() default -constructedvalue initialized elements to the sequence. -

- - - - - -
-

1420. Effects of resize(size()) on a list

-

Section: 23.3.5.3 [list.capacity] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [list.capacity].

-

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-

Discussion:

-

Addresses GB-115

-

-There is no mention of what happens if sz==size(). While -it obviously does nothing I feel a standard needs to say -this explicitely. -

- -

[ -Resolution proposed in ballot comment -]

- -

-Express the semantics as pseudo-code similarly -to the way it is done for the copying overload that -follows (in p3). Include an else clause that does -nothing and covers the sz==size() case. -

- -

[ -2010 Batavia -]

- -

-Accepted with a simplified resolution turning one of the < -comparisons into <=. -

- - - - -

Proposed resolution:

-

-Ammend [list.capacity] p1: -

-
-

void resize(size_type sz);

-

-Effects: If sz <= size(), equivalent to list<T>::iterator -it = begin(); advance(it, sz); erase(it, end());. If -size() < sz, appends sz - size() default constructed -value initialized elements to the sequence. -

-
- - - - - - -
-

1421. Accidental move-only library types due to new core language rules

-

Section: 23.6 [container.adaptors] Status: Resolved - Submitter: DIN Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [container.adaptors].

-

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-

Duplicate of: 1350

-

Discussion:

- -

Addresses DE-22, CH-15

-

-With the final acceptance of move operations as special -members and introduction of corresponding suppression -rules of implicitly generated copy operations the some -library types that were copyable in C++03 are no longer -copyable (only movable) in C++03, among them queue, -priority_queue, and stack. -

- -

[ -2010-10-26: Daniel comments: -]

- - -

-Accepting n3112 should fix this. -

- -

[2011-02-17: Lawrence comments:]

- - -

-The only open issue in CH 15 with respect to the concurrency group -was the treatment of atomic_future. Since we removed atomic_future -in Batavia, I think all that remains is to remove the open issue from -N3112 and adopt it. -

- -

[2011-03-23 Madrid meeting]

- - -

Resolved by N3264

- - - -

Proposed resolution:

-

-See n3112 -

- - - - - -
-

1423. map constructor accepting an allocator as single parameter should be explicit

-

Section: 23.4.4 [map] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses JP-6

- -

-Constructor accepting an allocator as a single parameter should be qualified as explicit.

-
-namespace std {
-template <class Key, class T, class Compare =
-less<Key>,
-class Allocator = allocator<pair<const Key, T> > >
-class map {
-public:
-...
-map(const Allocator&);
-
- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key, class T, class Compare =
-less<Key>,
-class Allocator = allocator<pair<const Key, T> > >
-class map {
-public:
-...
-explicit map(const Allocator&);
-
- - - - - -
-

1424. multimap constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.4.5 [multimap] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-7

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key, class T, class Compare =
-less<Key>,
-class Allocator = allocator<pair<const Key, T> > >
-class multimap {
-public:
-...
-explicit multimap(const Allocator&);
-
- - - - - -
-

1425. set constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.4.6 [set] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [set].

-

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-

Discussion:

-

Addresses JP-8

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key, class Compare = less<Key>,
-class Allocator = allocator<Key> >
-class set {
-public:
-...
-explicit set(const Allocator&);
-
- - - - - -
-

1426. multiset constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.4.7 [multiset] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-9

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key, class Compare = less<Key>,
-class Allocator = allocator<Key> >
-class multiset {
-public:
-...
-explicit multiset(const Allocator&);
-
- - - - - -
-

1427. unordered_map constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.5.4 [unord.map] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [unord.map].

-

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-

Discussion:

-

Addresses JP-10

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key,
-template <class Key,
-class T,
-class Hash = hash<Key>,
-class Pred = std::equal_to<Key>,
-class Alloc = std::allocator<std::pair<const Key,
-T> > >
-class unordered_map
-{
-public:
-...
-explicit unordered_map(const Allocator&);
-
- - - - - -
-

1428. unordered_multimap constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.5.5 [unord.multimap] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-11

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key,
-class T,
-class Hash = hash<Key>,
-class Pred = std::equal_to<Key>,
-class Alloc = std::allocator<std::pair<const Key,
-T> > >
-class unordered_multimap
-{
-public:
-...
-explicit unordered_multimap(const Allocator&);
-
- - - - - -
-

1429. unordered_set constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.5.6 [unord.set] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-12

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key,
-class Hash = hash<Key>,
-class Pred = std::equal_to<Key>,
-class Alloc = std::allocator<Key> >
-class unordered_set
-{
-public:
-...
-explicit unordered_set(const Allocator&);
-
- - - - - -
-

1430. unordered_multiset constructor accepting an allocator as a single parameter should be explicit

-

Section: 23.5.7 [unord.multiset] Status: C++11 - Submitter: Japan Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses JP-13

- -

-Constructor accepting an allocator as a single parameter -should be qualified as explicit. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

Add explicit.

-
-namespace std {
-template <class Key,
-class Hash = hash<Key>,
-class Pred = std::equal_to<Key>,
-class Alloc = std::allocator<Key> >
-class unordered_multiset
-{
-public:
-...
-explicit unordered_multiset(const Allocator&);
-
- - - - - -
-

1431. is_permutation must be more restrictive

-

Section: 25.2.12 [alg.is_permutation] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-120

- -

-is_permutation is underspecified for anything but the -simple case where both ranges have the same value type -and the comparison function is an equivalence relation. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-Restrict is_permutation to the case where it is well -specified. See Appendix 1 - Additional Details -

- - - - -
-

1432. random_shuffle signatures are inconsistent

-

Section: 25.3.12 [alg.random.shuffle] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [alg.random.shuffle].

-

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-

Duplicate of: 1433

-

Discussion:

- -

Addresses US-121, GB-119

- -

-random_shuffle and shuffle should be consistent in how -they accept their source of randomness: either both by rvalue reference or -both by lvalue reference. -

- -

[ -Post-Rapperswil, Daniel provided wording -]

- - -

-The signatures of the shuffle and random_shuffle algorithms are different -in regard to the support of rvalues and lvalues of the provided generator: -

- -
-template<class RandomAccessIterator, class RandomNumberGenerator>
-void random_shuffle(RandomAccessIterator first,
-RandomAccessIterator last,
-RandomNumberGenerator&& rand);
-
- -
-template<class RandomAccessIterator, class UniformRandomNumberGenerator>
-void shuffle(RandomAccessIterator first,
-RandomAccessIterator last,
-UniformRandomNumberGenerator& g);
-
- -

-The first form uses the perfect forwarding signature and that change compared to -C++03 was done intentionally as shown in the first rvalue proposal -papers. -

- -

-While it is true, that random generators are excellent examples of stateful -functors, there still exist good reasons to support rvalues as arguments: -

- -
    -
  1. If one of the shuffle algorithms is called with the intention to shuffle items with a reproducible ordering - from a given generator class, it makes sense to create a generator exactly at the call point. -
    2. -
  2. Other algorithms with similar need for stateful functors (like std::generate and std::generate_n) - accept both rvalues and lvalues as well. -
    3. -
  3. Given the deduction rules for perfect forwarding it is hard for a user to produce code that does the wrong thing -unintentionally. Any lvalue generator will deduce an lvalue-reference and behave as in C++03. In the specific -cases, where rvalues are provided, the argument will be accepted instead of being rejected. -
    4. -
- -

-Arguments have been raised that accepting rvalues is error-prone or even fundamentally wrong. The author of this -proposal disagrees with that position for two additional reasons: -

- -
    -
  1. Enforcing lvalues as arguments won't prevent user code to enforce what they -want. So given -
    -my_generator get_generator(int size);
-
    -instead of writing -
    -std::vector<int> v = ...;
-std::shuffle(v.begin(), v.end(), get_generator(v.size()));
-
    -they will just write -
    -std::vector<int> v = ...;
-auto gen = get_generator(v.size());
-std::shuffle(v.begin(), v.end(), gen);
-
    -and feel annoyed about the need for it. -
    2. -
  2. Generators may be copyable and movable, and random number engines are required to be CopyConstructible -and this is obviously a generally useful property for such objects. It is also useful and sometimes necessary to start a -generator with exactly a specific seed again and again and thus to provide a new generator (or a copy) for each call. The -CopyConstructible requirements allow providing rvalues of generators and thus this idiom must be useful as well. -Therefore preventing [random_]shuffle to accept rvalues is an unnecessary restriction which doesn't prevent any -user-error, if there would exist one. -
    3. -
- -

-Thus this proposal recommends to make both shuffle functions consistent and perfectly forward-able. -

- -

-Moved to Tentatively Ready after 6 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -
    -
  1. Change [algorithms.general], header <algorithm> synopsis as indicated: -
    -template<class RandomAccessIterator, class UniformRandomNumberGenerator>
-void shuffle(RandomAccessIterator first, RandomAccessIterator last,
-UniformRandomNumberGenerator&& rand);
-
    -
    2. -
  2. Change the prototype description of [alg.random.shuffle] as indicated: -
    -template<class RandomAccessIterator, class UniformRandomNumberGenerator>
-void shuffle(RandomAccessIterator first, RandomAccessIterator last,
-UniformRandomNumberGenerator&& rand);
-
    -
    3. -
- - - - - - -
-

1435. Unclear returns specifications for C99 complex number functions

-

Section: 26.4.7 [complex.value.ops] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [complex.value.ops].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-120

- -

-The complex number functions added for compatibility -with the C99 standard library are defined purely as a -cross-reference, with no hint of what they should return. -This is distinct from the style of documentation for the -functions in the earlier standard. In the case of the -inverse-trigonometric and hyperbolic functions, a -reasonable guess of the functionality may be made from -the name, this is not true of the cproj function, which -apparently returns the projection on the Reimann Sphere. -A single line description of each function, associated with -the cross-reference, will greatly improve clarity. -

- -

[2010-11-06 Beman provides proposed resolution wording.]

- - -

[ -2010 Batavia: The working group concurred with the issue's Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

Change 26.4.7 complex value operations [complex.value.ops] as indicated:

-
-

template<class T> complex<T> proj(const complex<T>& x);

-
-

Returns: the projection of x onto the Riemann - sphere.

-

Effects: Remarks: Behaves the same as the C function cproj, - defined in 7.3.9.4.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> acos(const complex<T>& x);

-
-

Returns:  the complex arc cosine of x.

-

Effects: Remarks: Behaves the same as the C function cacos, - defined in 7.3.5.1.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> asin(const complex<T>& x);

-
-

Returns:  the complex arc sine of x.

-

Effects: Remarks: Behaves the same as the C function casin, - defined in 7.3.5.2.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> atan(const complex<T>& x);

-
-

Returns:  the complex arc tangent of x.

-

Effects: Remarks: Behaves the same as the C function catan, - defined in 7.3.5.3.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> acosh(const complex<T>& x);

-
-

Returns:  the complex arc hyperbolic cosine of - x.

-

Effects: Remarks: Behaves the same as the C function cacosh, - defined in 7.3.6.1.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> asinh(const complex<T>& x);

-
-

Returns:  the complex arc hyperbolic sine of - x.

-

Effects: Remarks: Behaves the same as the C function casinh, - defined in 7.3.6.2.

-
-
- -

Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:

-
-

template<class T> complex<T> atanh(const complex<T>& x);

-
-

Returns:  the complex arc hyperbolic tangent of - x.

-

Effects: Remarks: Behaves the same as the C function catanh, - defined in 7.3.6.2.

-
-
- - - - - - - -
-

1436. Random number engine constructor concerns

-

Section: 26.5.3 [rand.eng] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [rand.eng].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-121

- -

-All the random number engine types in this clause have a -constructor taking an unsigned integer type, and a -constructor template for seed sequences. This means that -an attempt to create a random number engine seeded by -an integer literal must remember to add the appropriate -unsigned suffix to the literal, as a signed integer will -attempt to use the seed sequence template, yielding -undefined behaviour, as per 26.5.1.1p1a. It would be -helpful if at least these anticipated cases produced a -defined behaviour, either an erroneous program with -diagnostic, or a conversion to unsigned int forwarding to -the appropriate constructor. -

- -

[ -2010-11-03 Daniel comments and provides a proposed resolution: -]

- - -

-I suggest to apply a similar solution as recently suggested for 1234. -It is basically a requirement for an implementation to constrain the template. -

- -

[ -2010-11-04 Howard suggests to use !is_convertible<Sseq, result_type>::value -as minimum requirement instead of the originally proposed !is_scalar<Sseq>::value. -This would allow for a user-defined type BigNum, that is convertible to result_type, -to be used as argument for a seed instead of a seed sequence. The wording has been updated to -reflect this suggestion. -]

- - -

[ -2010 Batavia: There were some initial concerns regarding the portability and reproducibility of results -when seeded with a negative signed value, but these concerns were allayed after discussion. Thus, after -reviewing the issue, the working group concurred with the issue's Proposed Resolution. -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Add the following paragraph at the end of 26.5.3 [rand.eng]: -

-
-

-5 Each template specified in this section [rand.eng] requires one or more relationships, involving the value(s) of -its non-type template parameter(s), to hold. A program instantiating any of these templates is ill-formed if -any such required relationship fails to hold. -

- -

-? For every random number engine and for every random number engine adaptor X defined in this sub-clause -[rand.eng] and in sub-clause [rand.adapt]:

-
    -
  • If the constructor -
    -template<class Sseq> explicit X(Sseq& q);
-

    -is called with a type Sseq that does not qualify as a seed sequence, then this constructor -shall not participate in overload resolution. -

    -
    • -
  • If the member function -
    -template<class Sseq> void seed(Sseq& q);
-

    -is called with a type Sseq that does not qualify as a seed sequence, then this function -shall not participate in overload resolution. -

    -
    • -
-

-The extent to which an implementation determines that a type cannot be a seed sequence is unspecified, -except that as a minimum a type shall not qualify as seed sequence, if it is implicitly convertible -to X::result_type. -

-
- -
- - - - - -
-

1437. Mersenne twister meaningless for word sizes less than two

-

Section: 26.5.3.2 [rand.eng.mers] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [rand.eng.mers].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-124

- -

-The Mersenne twister algorithm is meaningless for word -sizes less than two, as there are then insufficient bits -available to be “twisted”. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Insert the following among the relations that are required to hold: 2u < w. -

- -

[ -2010 Batavia: The working group concurred with the issue's Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Change 26.5.3.2 [rand.eng.mers] p. 4 as indicated: -

-

-4 The following relations shall hold: 0 < m, m <= n, 2u < w, -r <= w, u <= w, s <= w, t <= w, -l <= w, w <= numeric_limits<UIntType>::digits, -a <= (1u<<w) - 1u, b <= (1u<<w) - 1u, -c <= (1u<<w) - 1u, d <= (1u<<w) - 1u, -and f <= (1u<<w) - 1u. -

- - - - - -
-

1438. No definition for base()

-

Section: 26.5.4.2 [rand.adapt.disc] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [rand.adapt.disc].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-126

- -

Each adaptor has a member function called base() which has no definition.

- -

[ -Resolution proposed by ballot comment: -]

- -

-Give it the obvious definition. -

- -

[ -2010-11-03 Daniel comments and provides a proposed resolution: -]

- - -

The following proposal adds noexcept specifiers to the declarations of -the base() functions as replacement for a "Throws: Nothing" element. -

- -

[ -2010 Batavia: The working group reviewed this issue, and recommended to add the following to the Proposed Resolution. -]

- -
  • -Append to paragraph 1 of [rand.req.adapt] (or at the Editor's discretion insert as a new paragraph following that paragraph): -The expression a.base() shall be valid and shall return a const reference to a's base engine. -
    • -
-

-After further review, the working group concurred with the Proposed Resolution. -

- - -

[Batavia: waiting for WEB to review wording]

- - - - -

Proposed resolution:

-
    -
  1. -Add the following sentence to the end of 26.5.1.5 [rand.req.adapt]/1: -

    -A random number engine adaptor (commonly shortened to adaptor) a of type A is a -random number engine that takes values produced by some other random number engine, and applies an algorithm to -those values in order to deliver a sequence of values with different randomness properties. An engine b -of type B adapted in this way is termed a base engine in this context. The expression -a.base() shall be valid and shall return a const reference to a's base engine. -

    -
    2. -
  2. Change in [rand.adapt.disc]/3, class template discard_block_engine synopsis, the following declaration: -
    -// property functions
-const Engine& base() const noexcept;
-
    -
    3. -
  3. Add the following new prototype description at the end of sub-clause 26.5.4.2 [rand.adapt.disc]: -
    -
    const Engine& base() const noexcept;
-
    -

    -? Returns: e. -

    -
    -
    4. -
  4. Change in [rand.adapt.ibits]/4, class template independent_bits_engine synopsis, the following declaration: -
    -// property functions
-const Engine& base() const noexcept;
-
    -
    5. -
  5. Add the following new prototype description at the end of sub-clause 26.5.4.3 [rand.adapt.ibits]: -
    -
    const Engine& base() const noexcept;
-
    -

    -? Returns: e. -

    -
    -
    6. -
  6. Change in 26.5.4.4 [rand.adapt.shuf]/3, class template shuffle_order_engine synopsis, the following declaration: -
    -// property functions
-const Engine& base() const noexcept;
-
    -
    7. -
  7. Add the following new prototype description at the end of sub-clause 26.5.4.4 [rand.adapt.shuf]: -
    -
    const Engine& base() const noexcept;
-
    -

    -? Returns: e. -

    -
    -
    8. -
- - - - - -
-

1439. Return from densities() functions?

-

Section: 26.5.8.6.2 [rand.dist.samp.pconst] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [rand.dist.samp.pconst].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-134

- -

-These two distributions have a member function called -densities() which returns a vector<double>. The -distribution is templated on RealType. The distribution -also has another member called intervals() which returns -a vector<RealType>. Why doesn't densities return -vector<RealType> as well? If RealType is long double, -the computed densities property isn't being computed to -the precision the client desires. If RealType is float, the -densities vector is taking up twice as much space as the client desires. -

- -

[ -Resolution proposed by ballot comment: -]

- -
-

-Change the piecewise constant and linear -distributions to hold / return the densities in a -vector<result_type>. -

-If this is not done, at least correct 26.5.8.6.2 [rand.dist.samp.pconst] p. 13 which describes -the return of densities as a vector<result_type>. -

- -

[ -Batavia 2010: After reviewing this issue, the working group concurred with the first of the -suggestions proposed by the NB comment: "Change the piecewise constant and linear distributions -to hold/return the densities in a vector. " -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-
    -
  1. Change 26.5.8.6.2 [rand.dist.samp.pconst] p. 2, class template piecewise_constant_distribution synopsis -and the prototype description 26.5.8.6.2 [rand.dist.samp.pconst] before p. 13 as indicated: -
    -vector<doubleresult_type> densities() const;
-
    -
    2. - -
  2. Change 26.5.8.6.3 [rand.dist.samp.plinear] p. 2, class template piecewise_linear_distribution synopsis -and the prototype description 26.5.8.6.3 [rand.dist.samp.plinear] before p. 13 as indicated: -
    -vector<doubleresult_type> densities() const;
-
    -
    3. -
- - - - - -
-

1440. Incorrect specification for piecewise_linear_distribution

-

Section: 26.5.8.6.3 [rand.dist.samp.plinear] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-135

- -

-This paragraph says: Let bk = xmin+k·δ for k = 0,...,n, -and wk = fw(bk +δ) for k = 0,...,n. -However I believe that fw(bk) would be far more desirable. -I strongly suspect that this is nothing but a type-o. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Change p. 10 to read:
-Let bk = xmin+k·δ for k = 0,...,n, and wk = fw(bk) -for k = 0,...,n. -

- -

[ -2010-11-02 Daniel translates into a proposed resolution -]

- - -

[ -2010 Batavia: The working group concurred with the issue's Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

Change 26.5.8.6.3 [rand.dist.samp.plinear] p. 10 as indicated:

-

-10 Effects: Constructs a piecewise_linear_distribution object with parameters taken or calculated -from the following values: Let bk = xmin+k·δ for -k = 0, . . . , n, and wk = fw(bk +δ) -for k = 0, . . . , n. -

- - - - - -
-

1441. Floating-point test functions are incorrectly specified

-

Section: 26.8 [c.math] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

View all other issues in [c.math].

-

View all issues with C++11 status.

-

Discussion:

-

Addresses US-136

- -

-Floating-point test functions are incorrectly specified. -

- -

[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]

- - - - -

Proposed resolution:

-

See Appendix 1 - Additional Details

- - - - - -
-

1445. Several iostreams member functions incorrectly specified

-

Section: 27.7 [iostream.format] Status: Resolved - Submitter: INCITS/PJ Plauger Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [iostream.format].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-137

- -

-Several iostreams member functions are incorrectly -specified. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-See Appendix 1 - Additional Details -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3168 would solve this issue. -

- - - -

Proposed resolution:

-Addressed by paper n3168. -

- - - - -
-

1447. Request to resolve issue LWG 1328

-

Section: 27.7 [iostream.format] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [iostream.format].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-139

- -

-Resolve issue LWG 1328 one way or the other, but -preferably in the direction outlined in the proposed -resolution, which, however, is not complete as-is: in any -case, the sentry must not set ok_ = false if is.good() == false, -otherwise istream::seekg, being an unformatted -input function, does not take any action because the -sentry object returns false when converted to type bool. -Thus, it remains impossible to seek away from end of file. -

- - -

Proposed resolution:

-Addressed by paper n3168. -

- - - - -
-

1448. Concerns about basic_stringbuf::str(basic_string) postconditions

-

Section: 27.8.2.3 [stringbuf.members] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-124

- -

-N3092 27.8.2.3 [stringbuf.members] contains this text specifying the postconditions of -basic_stringbuf::str(basic_string): -

-

-Postconditions: If mode & ios_base::out is true, -pbase() points to the first underlying character and epptr() >= -pbase() + s.size() holds; in addition, if mode & ios_base::in -is true, pptr() == pbase() + s.data() holds, otherwise -pptr() == pbase() is true. [...] -

-

-Firstly, there's a simple mistake: It should be pbase() + s.length(), -not pbase() + s.data(). -

-

-Secondly, it doesn't match existing implementations. As far as I can tell, -GCC 4.5 does not test for mode & ios_base::in in the second part -of that sentence, but for mode & (ios_base::app | ios_base_ate), -and Visual C++ 9 for mode & ios_base::app. Besides, the wording of -the C++0x draft doesn't make any sense to me. I suggest changing the second part -of the sentence to one of the following: -

-

-Replace ios_base::in with (ios_base::ate | ios_base::app), -but this would require Visual C++ to change (replacing only with -ios_base::ate would require GCC to change, and would make -ios_base::app completely useless with stringstreams): -

-

-in addition, if mode & (ios_base::ate | ios_base::app) is true, -pptr() == pbase() + s.length() holds, otherwise pptr() == pbase() -is true. -

-

-Leave pptr() unspecified if mode & ios_base::app, but not -mode & ios_base::ate (implementations already differ in this case, and it -is always possible to use ios_base::ate to get the effect of appending, so it -is not necessary to require any implementation to change): -

-

-in addition, if mode & ios_base::ate is true, -pptr() == pbase() + s.length() holds, if neither mode & ios_base::ate -nor mode & ios_base::app is true, pptr() == pbase() holds, -otherwise pptr() >= pbase() && pptr() <= pbase() + s.length() -(which of the values in this range is unspecified). -

-

-Slightly stricter: -

-

-in addition, if mode & ios_base::ate is true, -pptr() == pbase() + s.length() holds, if neither -mode & ios_base::ate nor mode & ios_base::app is true, -pptr() == pbase() holds, otherwise pptr() == pbase() || pptr() == pbase() + s.length() -(which of these two values is unspecified). A small table might help to better explain the three cases. -BTW, at the end of the postconditions is this text: "egptr() == eback() + s.size() hold". -Is there a perference for basic_string::length or basic_string::size? It doesn't really -matter, but it looks a bit inconsistent. -

- -

[2011-03-09: Nicolai Josuttis comments and drafts wording]

- - -

First, it seems the current wording is just an editorial mistake. -When we added issue 432 -to the draft standard (in n1733), -the wording in the issue: -

- -

-If mode & ios_base::out is true, initializes the output sequence -such that pbase() points to the first underlying character, epptr() -points one past the last underlying character, and if (mode & ios_base::ate) is true, -pptr() is set equal to epptr() else pptr() is set equal to -pbase(). -

- -

became:

- -

-If mode & ios_base::out is true, initializes the output sequence -such that pbase() points to the first underlying character, epptr() -points one past the last underlying character, and pptr() is equal to epptr() -if mode & ios_base::in is true, otherwise pptr() is equal to -pbase(). -

- -

-which beside some changes of the order of words changed -

-
-ios_base::ate
-
-

-into -

-
-ios_base::in
-
-

-So, from this point of view, clearly mode & ios_base::ate was meant. -

- -

-Nevertheless, with this proposed resolution we'd have no wording regarding ios_base::app. -Currently the only statements about app in the Standard are just in two tables: -

-
    -
  • Table 125 — "openmode effects" says that the effect of -app is "seek to end before each write" -
    • - -
  • Table 132 — "File open modes" says that the stdio equivalent -for app is "a" -
    • -
-

-Indeed we seem to have different behavior currently in respect to app: For -

- -
-stringstream s2(ios_base::out|ios_base::in|ios_base::app);
-s2.str("s2 hello");
-s1 << "more";
-
- -
    -
  • Visual C++ 10 does overwrite (=> "moreello")
    • -
  • G++ 4.5 does append (=> "s2 hellomore")
    • -
- -

BTW, for fstreams, both implementations append when app is set: -If f2.txt has contents "xy",

- -
-fstream f2("f2.txt",ios_base::out|ios_base::in|ios_base::app);
-f1 << "more";
-
- -

appends "more" so that the contents is "xymore".

- -

So IMO app should set the write pointer to the end so that each writing -appends. -

-I don't know whether what the standard says is enough. You can argue the -statement in Table 125 clearly states that such a buffer should always append, -which of course also applies to str() of stringbuffer. -

-Nevertheless, it doesn't hurt IMO if we clarify the behavior of str() -here in respect to app. -

- -

[2011-03-10: P.J.Plauger comments:]

- - -

I think we should say nothing special about app at construction -time (thus leaving the write pointer at the beginning of the buffer). -Leave implementers wiggle room to ensure subsequent append writes as they see -fit, but don't change existing rules for initial seek position.

- -

[Madrid meeting: It was observed that a different issue should be opened that -clarifies the meaning of app for stringstream]

- - - -

Proposed resolution:

- -

Change 27.8.2.3 [stringbuf.members] p. 3 as indicated:

- -
-void str(const basic_string<charT,traits,Allocator>& s);
-
-

-2 Effects: Copies the content of s into the basic_stringbuf -underlying character sequence and initializes the input and output sequences according -to mode. -

-3 Postconditions: If mode & ios_base::out is true, pbase() -points to the first underlying character and epptr() >= pbase() + s.size() -holds; in addition, if mode & ios_base::inios_base::ate -is true, pptr() == pbase() + s.data()s.size() holds, -otherwise pptr() == pbase() is true. If mode & ios_base::in -is true, eback() points to the first underlying character, and both -gptr() == eback() and egptr() == eback() + s.size() -hold. -

-
- - - - - -
-

1449. Incomplete specification of header <cinttypes>

-

Section: 27.8.3 [istringstream] Status: C++11 - Submitter: Canada Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses CA-4

- -

-Subclause 27.9.2 [c.files] specifies that <cinttypes> has -declarations for abs() and div(); however, the signatures -are not present in this subclause. The signatures -proposed under TR1 ([tr.c99.inttypes]) are not present in -FCD (unless if intmax_t happened to be long long). It is -unclear as to which, if any of the abs() and div() functions -in [c.math] are meant to be declared by <cinttypes>. This -subclause mentions imaxabs() and imaxdiv(). These -functions, among other things, are not specified in FCD to -be the functions from Subclause 7.8 of the C Standard. -Finally, <cinttypes> is not specified in FCD to include -<cstdint> (whereas <inttypes.h> includes <stdint.h> in C). -

- -

[ -Post-Rapperswil, Daniel provides wording -]

- - -

-Subclause [c.files] specifies that <cinttypes> has declarations for abs() and div(); -however, the signatures are not present in this subclause. The signatures proposed under TR1 ([tr.c99.inttypes]) are not -present in FCD (unless if intmax_t happened to be long long). It is unclear as to which, if any of the -abs() and div() functions in [c.math] are meant to be declared by <cinttypes>. This -subclause mentions imaxabs() and imaxdiv(). These functions, among other things, are not specified in -FCD to be the functions from subclause 7.8 of the C Standard. Finally, <cinttypes> is not specified -in FCD to include <cstdint> (whereas <inttypes.h> includes <stdint.h> in C). -

- -

-Moved to Tentatively Ready with proposed wording after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-The wording refers to N3126. -

-
    -
  1. Add the following series of new paragraphs following [c.files] p.1: -

    -Table 132 describes header <cinttypes>. [Note: The macros defined by <cinttypes> are provided unconditionally. -In particular, the symbol __STDC_FORMAT_MACROS, mentioned in footnote 182 of the C standard, plays no role in C++. -— end note ] -

    -2 - The contents of header <cinttypes> are the same as the Standard C library header <inttypes.h>, -with the following changes: -

    -3 - The header <cinttypes> includes the header <cstdint> instead of <stdint.h>. -

    -4 - If and only if the type intmax_t designates an extended integer type ([basic.fundamental]), the following function -signatures are added: -

    -
    -intmax_t abs(intmax_t);
-imaxdiv_t div(intmax_t, intmax_t);
-
    -

    -which shall have the same semantics as the function signatures intmax_t imaxabs(intmax_t) and -imaxdiv_t imaxdiv(intmax_t, intmax_t), respectively. -

    -
    -
    2. -
- - - - - -
-

1450. Contradiction in regex_constants

-

Section: 28.5.2 [re.matchflag] Status: C++14 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

Addresses GB-127

- -

-The Bitmask Type requirements in 17.5.2.1.3 [bitmask.types] p.3 say that -all elements on a bitmask type have distinct values, but -28.5.2 [re.matchflag] defines regex_constants::match_default and -regex_constants::format_default as elements of the -bitmask type regex_constants::match_flag_type, both with -value 0. This is a contradiction. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-One of the bitmask elements should be removed -from the declaration and should be defined -separately, in the same manner as -ios_base::adjustfield, ios_base::basefield and -ios_base::floatfield are defined by 27.5.3.1.2 [ios::fmtflags] p.2 -and Table 120. These are constants of a bitmask -type, but are not distinct elements, they have -more than one value set in the bitmask. -regex_constants::format_default should be -specified as a constant with the same value as -regex_constants::match_default. -

- -

[ -2010-10-31 Daniel comments: -]

- -

-Strictly speaking, a bitmask type cannot have any element of value 0 at all, because -any such value would contradict the requirement expressed in 17.5.2.1.3 [bitmask.types] p. 3: -

-

-for any pair Ci and Cj, Ci & Ci is nonzero -

-

-So, actually both regex_constants::match_default and -regex_constants::format_default are only constants of the type -regex_constants::match_flag_type, and no bitmask elements. -

- -

[ -2010-11-03 Daniel comments and provides a proposed resolution: -]

- - -

The proposed resolution is written against N3126 and considered as a further improvement -of the fixes suggested by n3110. -

- -
-

-Add the following sentence to 28.5.2 [re.matchflag] paragraph 1: -

-

-1 The type regex_constants::match_flag_type is an implementation-defined bitmask type (17.5.2.1.3). -Matching a regular expression against a sequence of characters [first,last) proceeds according to the -rules of the grammar specified for the regular expression object, modified according to the effects listed in -Table 136 for any bitmask elements set. Type regex_constants::match_flag_type also defines the -constants regex_constants::match_default and regex_constants::format_default. -

-
- -

[ -2011 Bloomington -]

- - -

-It appears the key problem is the phrasing of the bitmask requirements. Jeremiah supplies updated wording. -

- -

-Pete Becker has also provided an alternative resolution. -

- -

-Ammend 17.5.2.1.3 [bitmask.types]: -

-

-Change the list of values for "enum bit mask" in p2 from -

-

-V0 = 1 << 0, V1 = 1 << 1, V2 = 1 << 2, V3 = 1 << 3, .... -

-

-to -

-

-V0 = 0, V1 = 1 << 0, V2 = 1 << 1, V3 = 1 << 2, .... -

-

-Here, the names C0, C1, etc. represent bitmask elements for this particular -bitmask type. All such non-zero elements have distinct values such that, for any pair -Ci and Cj where i != j, Ci & Ci is nonzero -and Ci & Cj is zero. -

-

-Change bullet 3 of paragraph 4: -

-

-TheA non-zero value Y is set in the object X if the expression X & Y is nonzero. -

- -

[2014-02-13 Issaquah:]

- - - - -

Proposed resolution:

-

-Ammend 17.5.2.1.3 [bitmask.types] p3: -

-

-Here, the names C0, C1, etc. represent bitmask elements for this particular -bitmask type. All such elements have distinct, nonzero values such that, for any pair -Ci and Cj where i != j, Ci & Ci is nonzero -and Ci & Cj is zero. Additionally, the value 0 is used to represent an -empty bitmask, in which no bitmask elements are set. -

- -

-Add the following sentence to 28.5.2 [re.matchflag] paragraph 1: -

-

-1 The type regex_constants::match_flag_type is an implementation-defined bitmask type (17.5.2.1.3). -The constants of that type, except for match_default and format_default, are bitmask -elements. The match_default and format_default constants are empty bitmasks. Matching -a regular expression against a sequence of characters [first,last) proceeds according to the rules of the -grammar specified for the regular expression object, modified according to the effects listed in Table 136 -for any bitmask elements set. -

- - - - - -
-

1453. Default constructed match_results behavior for certain operations

-

Section: 28.10.4 [re.results.acc] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [re.results.acc].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses GB-126

- -

-It's unclear how match_results should behave if it has -been default-constructed. The sub_match objects -returned by operator[], prefix and suffix cannot point to the -end of the sequence that was searched if no search was -done. The iterators held by unmatched sub_match objects -might be singular. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Add to match_results::operator[], -match_results::prefix and match_results::suffix:
-Requires: !empty() -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3158 would solve this issue. -

- - - -

Proposed resolution:

-Addressed by paper n3158. -

- - - - -
-

1455. C language compatibility for atomics

-

Section: 29 [atomics] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

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-

Duplicate of: 1454

-

Discussion:

-

Addresses CH-22, GB-128

- -

-WG14 currently plans to introduce atomic facilities that are -intended to be compatible with the facilities of clause 29. -They should be compatible. -

- -

[ -Resolution proposed by ballot comment -]

- -

-Make sure the headers in clause 29 are defined in -a way that is compatible with the planned C -standard. -

- -

[ -2010 Batavia -]

- -

-Resolved by adoption of n3193. -

- - -

Proposed resolution:

-Solved by n3193. -

- - - - -
-

1457. Splitting lock-free properties

-

Section: 29.2 [atomics.syn] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.syn].

-

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-

Discussion:

-

Addresses GB-130

- -

-The synopsis for the <atomic> header lists the macros -ATOMIC_INTEGRAL_LOCK_FREE and ATOMIC_ADDRESS_LOCK_FREE. -

-

-The ATOMIC_INTEGRAL_LOCK_FREE macro has been replaced with a set of macros -for each integral type, as listed in 29.4 [atomics.lockfree]. -

- -

[Proposed resolution as of comment]

- - -
-

-Against FCD, N3092: -

-

-In [atomics.syn], header <atomic> synopsis replace as indicated: -

-
-// 29.4, lock-free property
-#define ATOMIC_INTEGRAL_LOCK_FREE unspecified
-#define ATOMIC_CHAR_LOCK_FREE implementation-defined
-#define ATOMIC_CHAR16_T_LOCK_FREE implementation-defined
-#define ATOMIC_CHAR32_T_LOCK_FREE implementation-defined
-#define ATOMIC_WCHAR_T_LOCK_FREE implementation-defined
-#define ATOMIC_SHORT_LOCK_FREE implementation-defined
-#define ATOMIC_INT_LOCK_FREE implementation-defined
-#define ATOMIC_LONG_LOCK_FREE implementation-defined
-#define ATOMIC_LLONG_LOCK_FREE implementation-defined
-#define ATOMIC_ADDRESS_LOCK_FREE unspecified
-
-
- -

[ -2010-10-26: Daniel adds: -]

- - -

-The proposed resolution below is against the FCD working draft. After application -of the editorial issues US-144 -and US-146 the remaining difference -against the working draft is the usage of implementation-defined instead of unspecified, effectively -resulting in this delta: -

- -
-// 29.4, lock-free property
-#define ATOMIC_CHAR_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_CHAR16_T_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_CHAR32_T_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_WCHAR_T_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_SHORT_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_INT_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_LONG_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_LLONG_LOCK_FREE unspecifiedimplementation-defined
-#define ATOMIC_ADDRESS_LOCK_FREE unspecified
-
- -

-It is my understanding that the intended wording should be unspecified as for ATOMIC_ADDRESS_LOCK_FREE -but if this is right, we need to use the same wording in 29.4 [atomics.lockfree], which consequently uses -the term implementation-defined. I recommend to keep 29.2 [atomics.syn] as it currently is and to -fix 29.4 [atomics.lockfree] instead as indicated: -

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- -

[2011-02-20: Daniel adapts the proposed wording to N3225 and fixes an editorial omission of -applying N3193]

- - -

[2011-03-06: Daniel adapts the wording to N3242]

- - -

[Proposed Resolution]

- -
-

-Change 29.4 [atomics.lockfree] as indicated: -

-
-#define ATOMIC_CHAR_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_CHAR16_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_CHAR32_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_WCHAR_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_SHORT_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_INT_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_LONG_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_LLONG_LOCK_FREE implementation-definedunspecified
-
-
- - - - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1460. Missing lock-free property for type bool should be added

-

Section: 29.4 [atomics.lockfree] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.lockfree].

-

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-

Discussion:

-

Addresses US-154

- -

There is no ATOMIC_BOOL_LOCK_FREE macro.

- -

Proposed resolution suggested by the NB comment:

- -

-Add ATOMIC_BOOL_LOCK_FREE to 29.4 [atomics.lockfree] and to 29.2 [atomics.syn]: -

-
-[..]
-#define ATOMIC_BOOL_LOCK_FREE unspecified
-#define ATOMIC_CHAR_LOCK_FREE unspecified
-#define ATOMIC_CHAR16_T_LOCK_FREE unspecified
-#define ATOMIC_CHAR32_T_LOCK_FREE unspecified
-[..]
-
- - -

[2011-03-12: Lawrence comments and drafts wording]

- - -

Point: We were missing a macro test for bool.

- -

Comment: The atomic<bool> type is the easiest to make lock-free. -There is no harm in providing a macro.

- -

Action: Add an ATOMIC_BOOL_LOCK_FREE.

- -

Point: We were missing a macro test for pointers.

- -

Comment: The national body comment noting the missing macro -for bool did not note the lack of a macro for pointers because -ATOMIC_ADDRESS_LOCK_FREE was present at the time of the comment. -Its removal appears to be an overzealous consequence of removing -atomic_address.

- -

Action: Add an ATOMIC_POINTER_LOCK_FREE.

- -

Point: Presumably atomic_is_lock_free() will be an inline function -producing a constant in those cases in which the macros are useful.

- -

Comment: The point is technically correct, but could use some -exposition. Systems providing forward binary compatibility, e.g. -mainstream desktop and server systems, would likely have these -functions as inline constants only when the answer is true. -Otherwise, the function should defer to a platform-specific dynamic -library to take advantage of future systems that do provide lock-free -support.

- -

Comment: Such functions are not useful in the preprocessor, and not -portably useful in static_assert.

- -

Action: Preserve the macros.

- -

Point: The required explicit instantiations are atomic<X> for each -of the types X in Table 145. Table 145 does not list bool, so -atomic<bool> is not a required instantiation.

- -

Comment: I think specialization was intended in the point instead of -instantiation. In any event, 29.5 [atomics.types.generic] paragraph 5 does -indirectly require a specialization for atomic<bool>. Confusion -arises because the specialization for other integral types have a -wider interface than the generic atomic<T>, but -atomic<bool> does not.

- -

Action: Add clarifying text.

- -

Point: The name of Table 145, "atomic integral typedefs", is perhaps -misleading, since the types listed do not contain all of the -"integral" types.

- -

Comment: Granted, though the table describe those with extra operations.

- -

Action: Leave the text as is.

- -

Point: The macros correspond to the types in Table 145, "with the -signed and unsigned variants grouped together". That's a rather -inartful way of saying that ATOMIC_SHORT_LOCK_FREE applies to -signed short and unsigned short. Presumably this also means that -ATOMIC_CHAR_LOCK_FREE applies to all three char types.

- -

Comment: Yes, it is inartful.

- -

Comment: Adding additional macros to distinguish signed and unsigned -would provide no real additional information given the other -constraints in the language.

- -

Comment: Yes, it applies to all three char types.

- -

Action: Leave the text as is.

- -

Point: The standard says that "There are full specializations over the -integral types (char, signed char, ...)" bool -is not in the list. But this text is not normative. It simply tells you -that "there are" specializations, not "there shall be" specializations, which would -impose a requirement. The requirement, to the extent that there is -one, is in the header synopsis, which, in N3242, sort of pulls in the -list of types in Table 145.

- -

Comment: The intent was for the specializations to be normative. -Otherwise the extra member functions could not be present.

- -

Action: Clarify the text.

- -

[Proposed Resolution]

- -
-
    -

  1. Edit header <atomic> synopsis 29.2 [atomics.syn]:

    - -
    -namespace std {
-  // 29.3, order and consistency
-  enum memory_order;
-  template <class T>
-  T kill_dependency(T y);
-
-  // 29.4, lock-free property
-  #define ATOMIC_BOOL_LOCK_FREE unspecified
-  #define ATOMIC_CHAR_LOCK_FREE unspecified
-  #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
-  #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
-  #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
-  #define ATOMIC_SHORT_LOCK_FREE unspecified
-  #define ATOMIC_INT_LOCK_FREE unspecified
-  #define ATOMIC_LONG_LOCK_FREE unspecified
-  #define ATOMIC_LLONG_LOCK_FREE unspecified
-  #define ATOMIC_POINTER_LOCK_FREE unspecified
-  
-  // 29.5, generic types
-  template<class T> struct atomic;
-  template<> struct atomic<integral>;
-  template<class T> struct atomic<T*>;
-
-  // 29.6.1, general operations on atomic types
-  // In the following declarations, atomic_type is either
-  // atomic<T> or a named base class for T from
-  // Table 145 or inferred from
-  // Table 146 or from bool. 
-
-  […]
-}
-
    -
    2. - -

  2. Edit the synopsis of 29.4 [atomics.lockfree] and paragraph 1 as follows:

    - -
    -#define ATOMIC_BOOL_LOCK_FREE unspecified
-#define ATOMIC_CHAR_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_CHAR16_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_CHAR32_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_WCHAR_T_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_SHORT_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_INT_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_LONG_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_LLONG_LOCK_FREE implementation-definedunspecified
-#define ATOMIC_POINTER_LOCK_FREE unspecified
-
    -

    -1 The ATOMIC_…_LOCK_FREE macros indicate the lock-free property of the corresponding atomic types, with -the signed and unsigned variants grouped together. The properties also apply to the corresponding (partial) -specializations of the atomic template. A value of 0 indicates that the types are never lock-free. A value of 1 -indicates that the types are sometimes lock-free. A value of 2 indicates that the types are always lock-free. -

    -
    -
    3. - -

  3. Edit 29.5 [atomics.types.generic] paragraph 3, 4, and 6-8 as follows:

    - -

    -2 The semantics of the operations on specializations of atomic are defined in 29.6 [atomics.types.operations]. -

    -3 Specializations and instantiations of the atomic template shall have a deleted copy constructor, -a deleted copy assignment operator, and a constexpr value constructor. -

    -4 There areshall be full specializations overfor the integral types ( -char, signed char, unsigned char, short, unsigned short, int, -unsigned int, long, unsigned long, long long, unsigned long long, -char16_t, char32_t, and wchar_t, and any other types needed by the typedefs in the header -<cstdint>) on the atomic class -template. For each integral type integral, the specialization atomic<integral> provides additional atomic -operations appropriate to integral types. [Editor's note: I'm guessing that this is the correct rendering of -the text in the paper; if this sentence was intended to impose a requirement, rather than a description, it -will have to be changed.] There shall be a specialization atomic<bool> which provides -the general atomic operations as specified in 29.6.1 [atomics.types.operations.general]. -

    -5 The atomic integral specializations and the specialization atomic<bool> shall have standard layout. They -shall each have a trivial default constructor and a trivial destructor. They shall each support aggregate -initialization syntax. -

    -6 There areshall be pointer partial specializations onof the atomic -class template. These specializations shall have trivial default constructors and trivial destructors. -

    -7 There areshall be named types corresponding to the integral specializations of atomic, as -specified in Table 145. In addition, there shall be named type atomic_bool corresponding to the specialization -atomic<bool>. Each named type is either a typedef to the corresponding specialization -or a base class of the corresponding specialization. If it is a base class, it shall support the same member functions -as the corresponding specialization. -

    -8 There areshall be atomic typedefs corresponding to the typedefs in the header <inttypes.h> -as specified in Table 146. -

    -
    -
    4. -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1462. Ambiguous value assignment to atomic_bool

-

Section: X [atomics.types.integral] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.integral].

-

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-

Duplicate of: 1463

-

Discussion:

-

Addresses GB-132, US-157

- -

-The atomic_itype types and atomic_address have two -overloads of operator=; one is volatile qualified, and the -other is not. atomic_bool only has the volatile qualified -version: -

-
-bool operator=(bool) volatile;
-
-

-On a non-volatile-qualified object this is ambiguous with -the deleted copy-assignment operator -

-
-atomic_bool& operator=(atomic_bool const&) = delete;
-
-

-due to the need for a single standard conversion in each -case when assigning a bool to an atomic_bool as in: -

-
-atomic_bool b;
-b = true;
-
-

-The conversions are: -

-
-atomic_bool& → atomic_bool volatile&
-
-

- vs -

-
-bool → atomic_bool
-
- -

[ -Proposed resolution as of NB comment: -]

- - -

-Change X [atomics.types.integral] as indicated: -

-
-namespace std {
-  typedef struct atomic_bool {
-    [..]
-    bool operator=(bool) volatile;
-    bool operator=(bool);
-  } atomic_bool;
-  [..]
-}
-
- -

[ -2010-10-27 Daniel adds: -]

- - -

-Accepting n3164 would solve this issue -by replacing atomic_bool by atomic<bool>. -

- -

[ -2010 Batavia -]

- -

-Resolved by adoption of n3193. -

- - -

Proposed resolution:

-Solved by n3193. -

- - - - -
-

1464. Underspecified typedefs for atomic integral types

-

Section: X [atomics.types.integral] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.integral].

-

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-

Discussion:

-

Addresses US-160

- -

-The last sentence of X [atomics.types.integral] p.1 says: -

-

-Table 143 shows typedefs to atomic integral classes and the corresponding <cstdint> typedefs. -

-

-That's nice, but nothing says these are supposed to be part of the implementation, and -they are not listed in the synopsis. -

- -

[ -Proposed resolution as of NB comment -]

- - -
    -
  1. Remove Table 143 — Atomics for standard typedef types. -

    -

    -
    2. -
  2. Change X [atomics.types.integral] p.1 as indicated: -

    -1 The name atomic_itype and the functions operating on it in the preceding synopsis are placeholders for a -set of classes and functions. Throughout the preceding synopsis, atomic_itype should be replaced by each -of the class names in Table 142 and integral should be replaced by the integral type corresponding to the -class name. Table 143 shows typedefs to atomic integral classes and the corresponding <cstdint> typedefs. -

    -
    3. -
- -

[ -2010-10-27 Daniel adds: -]

- - -

-Accepting n3164 would solve this issue. -

- -

[ -2010-11 Batavia -]

- -

-Resolved by adopting n3193. -

- - - -

Proposed resolution:

-Solved by n3193. -

- - - - -
-

1465. Missing arithmetic operators for atomic_address

-

Section: X [atomics.types.address] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.address].

-

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-

Discussion:

-

Addresses US-161

- -

-atomic_address has operator+= and operator-=, but no -operator++ or operator--. The template specialization -atomic<Ty*> has all of them. -

- -

[ -2010-10-27 Daniel adds: -]

- - -

-Accepting n3164 would solve this issue by -replacing atomic_address by atomic<void*>. -

- -

[ -Resolved in Batavia by accepting -n3193. -]

- - - - -

Proposed resolution:

-

Change X [atomics.types.address], class atomic_address synopsis, as indicated:

-
-namespace std {
-  typedef struct atomic_address {
-    […]
-    void* operator=(const void*) volatile;
-    void* operator=(const void*);
-    void* operator++(int) volatile;
-    void* operator++(int);
-    void* operator--(int) volatile;
-    void* operator--(int);
-    void* operator++() volatile;
-    void* operator++();
-    void* operator--() volatile;
-    void* operator--();
-    void* operator+=(ptrdiff_t) volatile;
-    void* operator+=(ptrdiff_t);
-    void* operator-=(ptrdiff_t) volatile;
-    void* operator-=(ptrdiff_t);
-  } atomic_address;
-  […]
-}
-
- - - - - - -
-

1466. Silent const breakage by compare_exchange_* member functions

-

Section: X [atomics.types.address] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-162

- -

-The compare_exchange_weak and compare_exchange_strong member functions that take -const void* arguments lead to a silent removal of const, because the load -member function and other acessors return the stored value as a void*. -

- -

[ -Proposed resolution as of NB comment: -]

- - -

-Change X [atomics.types.address], class atomic_address synopsis, as indicated: -

-
-namespace std {
-  typedef struct atomic_address {
-    [..]
-    bool compare_exchange_weak(const void*&, const void*,
-      memory_order, memory_order) volatile;
-    bool compare_exchange_weak(const void*&, const void*,
-      memory_order, memory_order);
-    bool compare_exchange_strong(const void*&, const void*,
-      memory_order, memory_order) volatile;
-    bool compare_exchange_strong(const void*&, const void*,
-      memory_order, memory_order);
-    bool compare_exchange_weak(const void*&, const void*,
-      memory_order = memory_order_seq_cst) volatile;
-    bool compare_exchange_weak(const void*&, const void*,
-      memory_order = memory_order_seq_cst);
-    bool compare_exchange_strong(const void*&, const void*,
-      memory_order = memory_order_seq_cst) volatile;
-    bool compare_exchange_strong(const void*&, const void*,
-      memory_order = memory_order_seq_cst);
-    [..]
-  } atomic_address;
-  [..]
-}
-
- -

[ -2010-10-27 Daniel adds: -]

- - -

-Accepting n3164 -would solve this issue by replacing atomic_address by atomic<void*>. -

- -

[ -Resolved in Batavia by accepting -n3193. -]

- - - - -

Proposed resolution:

-Solved by n3193. -

- - - - -
-

1467. Deriving atomic<T*> from atomic_address breaks type safety

-

Section: X [atomics.types.address] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.address].

-

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-

Discussion:

-

Addresses US-163

- -

-Requiring atomic<T*> to be derived from atomic_address breaks type safety: -

-
-atomic<double*> ip;
-char ch;
-atomic_store(&ip, &ch);
-*ip.load() = 3.14159;
-
-

-The last line overwrites ch with a value of type double. -

- -

[ -2010-10-27 Daniel adds: -]

- - -
-

-Resolving this issue will also solve 1469 -

-Accepting n3164 would solve this issue by -removing atomic_address. -

-
- -

[ -Resolved in Batavia by accepting -n3193. -]

- - - -

Proposed resolution:

-
    -
  1. Change 29.5 [atomics.types.generic], class template specialization atomic<T*> synopsis, as indicated: -
    -namespace std {
-  template <class T> struct atomic<T*> : atomic_address {
-    [..]
-  };
-  [..]
-}
-
    -
    2. -
  2. Change 29.5 [atomics.types.generic] p. 4 as indicated: -

    -4 There are pointer partial specializations on the atomic class template. These specializations shall be publicly -derived from atomic_address. The unit of addition/subtraction for these specializations shall be the size -of the referenced type. These specializations shall have trivial default constructors and trivial destructors. -

    -
    3. -
- - - - - - -
-

1468. atomic_address::compare_exchange_* member functions should match atomic_compare_exchange_* free functions

-

Section: X [atomics.types.address] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [atomics.types.address].

-

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-

Discussion:

-

Addresses US-164

- -

-atomic_address has member functions compare_exchange_weak and -compare_exchange_strong that take arguments of type const void*, -in addition to the void* versions. If these member functions survive, -there should be corresponding free functions. -

- -

[ -2010-10-27 Daniel adds: -]

- - -

-Accepting n3164 would solve this issue -differently by removing the overloads with const void* arguments, because they break type-safety. -

-

[ -Resolved in Batavia by accepting -n3193. -]

- - - -

Proposed resolution:

-

-Extend the synopsis around atomic_address in X [atomics.types.address] -as indicated: -

-
-namespace std {
-  [..]
-  bool atomic_compare_exchange_weak(volatile atomic_address*, void**, void*);
-  bool atomic_compare_exchange_weak(atomic_address*, void**, void*);
-  bool atomic_compare_exchange_strong(volatile atomic_address*, void**, void*);
-  bool atomic_compare_exchange_strong(atomic_address*, void**, void*);
-  bool atomic_compare_exchange_weak_explicit(volatile atomic_address*, void**, void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_weak_explicit(atomic_address*, void**, void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_strong_explicit(volatile atomic_address*, void**, void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_strong_explicit(atomic_address*, void**, void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_weak(volatile atomic_address*, const void**, const void*);
-  bool atomic_compare_exchange_weak(atomic_address*, const void**, const void*);
-  bool atomic_compare_exchange_strong(volatile atomic_address*, const void**, const void*);
-  bool atomic_compare_exchange_strong(atomic_address*, const void**, const void*);
-  bool atomic_compare_exchange_weak_explicit(volatile atomic_address*, const void**, const void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_weak_explicit(atomic_address*, const void**, const void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_strong_explicit(volatile atomic_address*, const void**, const void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_strong_explicit(volatile atomic_address*, const void**, const void*,
-    memory_order, memory_order);
-  bool atomic_compare_exchange_strong_explicit(atomic_address*, const void**, const void*,
-    memory_order, memory_order);
-  [..]
-}
-
- - - - - - -
-

1469. atomic<T*> inheritance from atomic_address breaks type safety

-

Section: 29.5 [atomics.types.generic] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [atomics.types.generic].

-

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-

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-

Discussion:

-

Addresses GB-133

- -

-The free functions that operate on atomic_address can be -used to store a pointer to an unrelated type in an atomic<T*> -without a cast. e.g. -

-
-int i;
-atomic<int*> ai(&i);
-string s;
-atomic_store(&ai,&s);
-
-

-Overload the atomic_store, atomic_exchange and -atomic_compare_exchange_[weak/strong] operations for -atomic<T*> to allow storing only pointers to T. -

- -

[ -2010-10-27 Daniel adds: -]

- - -
-

-Resolving this issue will also solve 1467 -

-Accepting n3164 would solve this issue by -removing atomic_address. -

-
- -

[Resolved in Batavia by accepting -n3193. -]

- - - -

Proposed resolution:

-

Add the following overloads to 29.5 [atomics.types.generic], the synopsis around the specialization -atomic<T*>, as indicated:

-
-namespace std {
-  [..]
-  template <class T> struct atomic<T*> : atomic_address {
-    [..]
-  };
-
-  template<typename T>
-  void atomic_store(atomic<T*>&,T*);
-  template<typename T>
-  void atomic_store(atomic<T*>&,void*) = delete;
-  template<typename T>
-  void atomic_store_explicit(atomic<T*>&,T*,memory_order);
-  template<typename T>
-  void atomic_store_explicit(atomic<T*>&,void*,memory_order) = delete;
-  template<typename T>
-  T* atomic_exchange(atomic<T*>&,T*);
-  template<typename T>
-  T* atomic_exchange(atomic<T*>&,void*) = delete;
-  template<typename T>
-  T* atomic_exchange_explicit(atomic<T*>&,T*,memory_order);
-  template<typename T>
-  T* atomic_exchange_explicit(atomic<T*>&,void*,memory_order) = delete;
-  template<typename T>
-  T* atomic_compare_exchange_weak(atomic<T*>&,T**,T*);
-  template<typename T>
-  T* atomic_compare_exchange_weak(atomic<T*>&,void**,void*) = delete;
-  template<typename T>
-  T* atomic_compare_exchange_weak_explicit(atomic<T*>&,T**,T*,memory_order);
-  template<typename T>
-  T* atomic_compare_exchange_weak_explicit(atomic<T*>&,void**,void*,memory_order) = delete;
-  template<typename T>
-  T* atomic_compare_exchange_strong(atomic<T*>&,T**,T*);
-  template<typename T>
-  T* atomic_compare_exchange_strong(atomic<T*>&,void**,void*) = delete;
-  template<typename T>
-  T* atomic_compare_exchange_strong_explicit(atomic<T*>&,T**,T*,memory_order);
-  template<typename T>
-  T* atomic_compare_exchange_strong_explicit(atomic<T*>&,void**,void*,memory_order) = delete;
-
-}
-
- - - - - -
-

1474. weak compare-and-exchange confusion

-

Section: 29.6.5 [atomics.types.operations.req] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Duplicate of: 1470, 1475, 1476, 1477

-

Discussion:

- - - -

Addresses US-175, US-165, CH-23, GB-135

-

-29.6.5 [atomics.types.operations.req] p. 25: The first sentence is grammatically incorrect. -

-

[ -2010-10-28 Daniel adds: -]

- -

-Duplicate issue 1475 also has a proposed resolution, but both issues are resolved with -below proposed resolution. -

- -

[ -2011-02-15 Howard fixes numbering, Hans improves the wording -]

- - -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 6 votes. -

- - -

Proposed resolution:

-
    -
  1. -

    Change 29.6.5 [atomics.types.operations.req] p. 23 as indicated:

    - -

    -[ Note: For example, tThe effect of -the compare-and-exchange operationsatomic_compare_exchange_strong is -

    -if (memcmp(object, expected, sizeof(*object)) == 0)
-  memcpy(object, &desired, sizeof(*object));
-else
-  memcpy(expected, object, sizeof(*object));
-
    -

    — end note ] [..]

    -
    -
    2. - -
  2. -

    Change 29.6.5 [atomics.types.operations.req] p. 25 as indicated:

    -

    -25 Remark: The weak compare-and-exchange operations may fail spuriously, that is, return false while -leaving the contents of memory pointed to by expected before the operation is the same that same -as that of the object and the same as that of expected after the operationA weak -compare-and-exchange operation may fail spuriously. That is, even when the contents of memory referred to by -expected and object are equal, it may return false and store back to expected the same -memory contents that were originally there.. [ Note: This spurious -failure enables implementation of compare-and-exchange on a broader class of machines, e.g., loadlocked -store-conditional machines. A consequence of spurious failure is that nearly all uses of weak -compare-and-exchange will be in a loop. -

    -When a compare-and-exchange is in a loop, the weak version will yield better performance on some -platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the -strong one is preferable. — end note ] -

    -
    -
    3. -
- - - - - -
-

1478. Clarify race conditions in atomics initialization

-

Section: 29.6 [atomics.types.operations] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-136

-

-GB requests normative clarification in 29.6 [atomics.types.operations] p.4 that -concurrent access constitutes a race, as already done on p.6 and p.7. -

-

[ -Resolution proposed in ballot comment: -]

- - -

-Initialisation of atomics: -

-We believe the intent is that for any atomics there is a distinguished -initialisation write, but that this need not happens-before all the -other operations on that atomic - specifically so that the -initialisation write might be non-atomic and hence give rise to a data -race, and hence undefined behaviour, in examples such as this (from -Hans): -

-
-atomic<atomic<int> *> p
-f()                      |
-{ atomic<int>x;          | W_na x
-  p.store(&x,mo_rlx);    | W_rlx p=&x
-}                        |
-

-(where na is nonatomic and rlx is relaxed). We suspect also that no -other mixed atomic/nonatomic access to the same location is intended -to be permitted. Either way, a note would probably help. -

- -

[2011-02-26: Hans comments and drafts wording]

- - -

I think the important point here is to clarify that races on atomics -are possible, and can be introduced as a result of non-atomic -initialization operations. There are other parts of this that remain unclear -to me, such as whether there are other ways to introduce data races on atomics, -or whether the races with initialization also introduce undefined behavior -by the 3.8 lifetime rules. But I don't think that it is necessary to resolve -those issues before releasing the standard. That's particularly true -since we've introduced atomic_init, which allows easier ways to -construct initialization races. -

- -

[2011-03 Madrid]

- -

Accepted to be applied immediately to the WP

- - - -

Proposed resolution:

-
    -

  1. Update 29.6.5 [atomics.types.operations.req] p. 5 as follows:

    - -
    -constexpr A::A(C desired);
-

    -5 Effects: Initializes the object with the value desired. [ Note: -Construction is not atomic. — end note ] Initialization is not an -atomic operation (1.10) [intro.multithread]. [Note: It is possible to have an -access to an atomic object A race with its construction, for example -by communicating the address of the just-constructed object A to another thread -via memory_order_relaxed atomic operations on a suitable atomic pointer variable, -and then immediately accessing A in the receiving thread. This results in undefined -behavior. — end note] -

    -
    2. - -

  2. In response to the editor comment to 29.6.5 [atomics.types.operations.req] p. 8: -The first Effects element is the correct and intended one:

    - -
    -void atomic_init(volatile A *object, C desired);
-void atomic_init(A *object, C desired);
-

    -8 Effects: Non-atomically initializes *object with value desired. -This function shall only be applied to objects that have been default constructed, and then only once. -[ Note: these semantics ensure compatibility with C. — end note ] [ Note: -Concurrent access from another thread, even via an atomic operation, constitutes a data -race. — end note ] [Editor's note: The preceding text is from the WD as -amended by N3196. N3193 makes different changes, marked up in the paper as follows:] -Effects: Dynamically initializes an atomic variable. Non-atomically That is, non-atomically assigns the -value desired to *object. [ Note: this operation may need to initialize -locks. — end note ] Concurrent access from another thread, even via an atomic -operation, constitutes a data race. -

    -
    3. -
- - - - - -
-

1479. Fence functions should be extern "C"

-

Section: 29.8 [atomics.fences] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-179

-

-The fence functions (29.8 [atomics.fences] p.5 + p.6) should be extern "C", for C compatibility. -

- -

[2011-02-16 Reflector discussion]

- -

-Moved to Tentatively Ready after 6 votes. -

- - - -

Proposed resolution:

-
    -
  1. Change 29.2 [atomics.syn], header <atomic> synopsis as indicated: -
    -namespace std {
-  [..]
-  // 29.8, fences
-  extern "C" void atomic_thread_fence(memory_order);
-  extern "C" void atomic_signal_fence(memory_order);  
-}
-
    -
    2. -

  2. Change 29.8 [atomics.fences], p. 5 and p. 6 as indicated:

    -
    -extern "C" void atomic_thread_fence(memory_order);
-

    -5 Effects: depending on the value of order, this operation: [..] -

    -
    -extern "C" void atomic_signal_fence(memory_order);  
-

    -6 Effects: equivalent to atomic_thread_fence(order), except that synchronizes with relationships are -established only between a thread and a signal handler executed in the same thread. -

    -
    3. -
- - - - - -
-

1480. Atomic fences don't have synchronizes with relation

-

Section: 29.8 [atomics.fences] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses GB-137

-

-Thread fence not only establish synchronizes with relationships, -there are semantics of fences that are expressed not in -terms of synchronizes with relationships (for example see 29.3 [atomics.order] p.5). -These semantics also need to apply to the use of -atomic_signal_fence in a restricted way. -

-

[Batavia: Concurrency group discussed issue, and is OK with the proposed resolution.]

- - -

[2011-02-26 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

Change 29.8 [atomics.fences] p. 6 as indicated:

-
-void atomic_signal_fence(memory_order);  
-

-6 Effects: equivalent to atomic_thread_fence(order), except that synchronizes -with relationshipsthe resulting ordering constraints are established only between a -thread and a signal handler executed in the same thread. -

- - - - - -
-

1481. Missing Lockable requirements

-

Section: 30.2 [thread.req] Status: Resolved - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

Discussion:

-

Addresses GB-138

- -

-The FCD combines the requirements for lockable objects -with those for the standard mutex objects. These should -be separate. This is LWG issue 1268. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-See attached Appendix 1 - Additional Details -

- -

[ -2010-11-01 Daniel comments: -]

- -

-Paper n3130 addresses -this issue. -

- - - -

Proposed resolution:

-

Resolved by n3197.

- - - - - -
-

1482. Timeout operations are under-specified

-

Section: 30.2.4 [thread.req.timing] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-181

- -

-The timeout operations are under-specified. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Define precise semantics for timeout_until and timeout_for. See -n3141 page 193 - Appendix 1 - Additional Details -

- -

[ -2010-11-01 Daniel comments: -]

- - -

-Accepting n3128 would solve this issue. -

- - -

Proposed resolution:

-Resolved by n3191. -

- - - - -
-

1487. Clock related operations exception specifications conflict

-

Section: 30.3.2 [thread.thread.this] Status: C++11 - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses CH-25

-

-Clock related operations are currently not required not to -throw. So "Throws: Nothing." is not always true. -

-

[ -Resolution proposed by ballot comment: -]

- -

-Either require clock related operations not to throw -(in 20.10) or change the Throws clauses in 30.3.2. -Also possibly add a note that abs_time in the past -or negative rel_time is allowed. -

- -

[2011-02-10: Howard Hinnant provides a resolution proposal]

- - -

[Previous proposed resolution:]

- -
    -
  1. -

    Change the Operational semantics of C1::now() in 20.12.3 [time.clock.req], -Table 59 — Clock requirements as follows: -

    - -
    - - - - - - - - - - - - - - - - - - - -
    Table 59 — Clock requirements
    -Expression - -Return type - -Operational semantics -
    C1::now()C1::time_pointReturns a time_point object
    -representing the current point in time.
    -Shall not throw an exception.
    -
    - - -
    2. -
- -

[2011-02-19: Daniel comments and suggests an alternative wording]

- - -

Imposing the no-throw requirement on C1::now() of any clock time -is an overly radical step: It has the indirect consequences that representation -types for C1::rep can never by types with dynamic memory managment, -e.g. my big_int, which are currently fully supported by the time -utilities. Further-on this strong constraint does not even solve the problem -described in the issue, because we are still left with the fact that any -of the arithmetic operations of C1::rep, C1::duration, -and C1::time_point may throw exceptions. -

-

The alternative proposal uses the following strategy: The general Clock -requirements remain untouched, but we require that any functions of the library-provided -clocks from sub-clause 20.12.7 [time.clock] and their associated types shall not -throw exceptions. Second, we replace existing noexcept specifications of -functions from Clause 30 that depend on durations, clocks, or time points by wording that -clarifies that these functions can only throw, if the operations of user-provided durations, -clocks, or time points used as arguments to these functions throw exceptions. -

- -

[2011-03-23 Daniel and Peter check and simplify the proposed resolution resulting in this paper]

- - -

There is an inherent problem with std::time_point that it doesn't seem to have an equivalent value -for ((time_t)-1) that gets returned by C's time() function to signal a problem, e.g., because -the underlying hardware is unavailable. After a lot of thinking and checks we came to the resolution that -timepoint::max() should be the value to serve as a value signaling errors in cases where we -prefer to stick with no-throw conditions. Of-course, user-provided representation types don't need to -follow this approach if they prefer exceptions to signal such failures. -

-the functions now() and from_time_t() can remain noexcept with the solution to -return timepoint::max() in case the current time cannot be determined or (time_t)-1 is passed -in, respectively. -

-Based on the previous proposed solution to LWG 1487 we decided that the new TrivialClock requirements -should define that now() mustn't throw and return timepoint::max() to signal a problem. That -is in line with the C standard where (time_t)-1 signals a problem. Together with a fix to a - we assumed - -buggy specifcation in 20.11.3 p2 which uses "happens-before" relationship with something that isn't any action: -

-

-2 In Table 59 C1 and C2 denote clock types. t1 and t2 are values returned by -C1::now() where the call returning t1 happens before (1.10) the call returning t2 and -both of these calls happen before C1::time_point::max(). -

- -

[2011-03-23 Review with Concurrency group suggested further simplifications and Howard pointed out, that -we do not need time_point::max() as a special value.]

- - -

also the second "happens before" will be changed to "occurs before" in the english meaning. this is -to allow a steady clock to wrap. -

-Peter updates issue accordingly to discussion. -

- -

[Note to the editor: we recommend removal of the following redundant paragraphs in - 30.5.2 [thread.condition.condvarany] p. 18 to p. 21, p. 27, p. 28, p. 30, and p. 31 that are -defining details for the wait functions that are given by the Effects element. -]

- - -

[Note to the editor: we recommend removal of the following redundant paragraphs in -30.5.1 [thread.condition.condvar]: p24-p26, p33-p34, and p36-p37 that are defining details for the -wait_for functions. We believe these paragraphs are redundant with respect to the Effects clauses that -define semantics based on wait_until. An example of such a specification is the wait() with a predicate. -]

- - - -

Proposed resolution:

- -
    -

  1. Change p2 in 20.11.3 [time.clock.req] as follows

    -

    -2 In Table 59 C1 and C2 denote clock types. t1 and -t2 are values returned by C1::now() where the call returning t1 -happens before (1.10) the call returning t2 and both of these calls happen -occur before C1::time_point::max(). -[ Note: This means C1 didn't wrap around between t1 and t2 — end note ] -

    -
    2. - -

  2. Add the following new requirement set at the end of sub-clause 20.12.3 [time.clock.req]: [Comment: -This requirement set is intentionally incomplete. The reason for -this incompleteness is the based on the fact, that if we would make it right for C++0x, we would end up defining -something like a complete ArithmeticLike concept for TC::rep, TC::duration, and TC::time_point. -But this looks out-of scope for C++0x to me. The effect is that we essentially do not exactly say, which arithmetic -or comparison operations can be used in the time-dependent functions from Clause 30, even though I expect that -all declared functions of duration and time_point are well-formed and well-defined. — end comment]

    -

    -3 [ Note: the relative difference in durations between those reported by a given clock and the SI definition is -a measure of the quality of implementation. — end note ] -

    - -

    -? A type TC meets the TrivialClock requirements if: -

    -
      -

    • -TC satisfies the Clock requirements (20.12.3 [time.clock.req]), -

      • -

    • -the types TC::rep, TC::duration, and TC::time_point satisfy -the requirements of EqualityComparable ( [equalitycomparable]), LessThanComparable -( [lessthancomparable]), DefaultConstructible ( [defaultconstructible]), -CopyConstructible ( [copyconstructible]), CopyAssignable ( [copyassignable]), -Destructible ( [destructible]), and of numeric types ([numeric.requirements]) [Note: This means in -particular, that operations of these types will not throw exceptions — end note ], -

      • -

    • -lvalues of the types TC::rep, TC::duration, and TC::time_point are swappable -(17.6.3.2 [swappable.requirements]), -

      • -

    • -the function TC::now() does not throw exceptions, and -

      • -

    • -the type TC::time_point::clock meets the TrivialClock requirements, recursively. -

      • -
    -
    -
    3. - -
  3. -

    Modify 20.12.7 [time.clock] p. 1 as follows:

    - -

    -1 - The types defined in this subclause shall satisfy the TrivialClock requirements (20.11.1). -

    -
    4. - -
  4. -

    Modify 20.12.7.1 [time.clock.system] p. 1, class system_clock synopsis, as follows:

    - -
    -class system_clock {
-public:
-  typedef see below rep;
-  typedef ratio<unspecified , unspecified > period;
-  typedef chrono::duration<rep, period> duration;
-  typedef chrono::time_point<system_clock> time_point;
-  static const bool is_monotonic is_steady = unspecified;
-  static time_point now() noexcept;
-  // Map to C API
-  static time_t to_time_t (const time_point& t) noexcept;
-  static time_point from_time_t(time_t t) noexcept;
-};
-
    - -
    5. - -
  5. -

    Modify the prototype declarations in 20.12.7.1 [time.clock.system] p. 3 + p. 4 as indicated (This -edit also fixes the miss of the static specifier in these prototype declarations):

    - -
    -static time_t to_time_t(const time_point& t) noexcept;
-
    - -
    -static time_point from_time_t(time_t t) noexcept;
-
    -
    - -
    6. - -
  6. -

    Modify 20.12.7.2 [time.clock.steady] p. 1, class steady_clock synopsis, as follows:

    - -
    -class steady_clock {
-public:
-  typedef unspecified rep;
-  typedef ratio<unspecified , unspecified > period;
-  typedef chrono::duration<rep, period> duration;
-  typedef chrono::time_point<unspecified, duration> time_point;
-  static const bool is_monotonic is_steady = true;
-
-  static time_point now() noexcept;
-};
-
    - -
    7. - -
  7. -

    Modify 20.12.7.3 [time.clock.hires] p. 1, class high_resolution_clock synopsis, as follows:

    - -
    -class high_resolution_clock {
-public:
-  typedef unspecified rep;
-  typedef ratio<unspecified , unspecified > period;
-  typedef chrono::duration<rep, period> duration;
-  typedef chrono::time_point<unspecified, duration> time_point;
-  static const bool is_monotonic is_steady = unspecified;
-
-  static time_point now() noexcept;
-};
-
    - -
    8. - -

  8. Add a new paragraph at the end of 30.2.4 [thread.req.timing]:

    - -

    -6 The resolution of timing provided by an implementation depends on both operating system and hardware. -The finest resolution provided by an implementation is called the native resolution. -

    - -

    -? Implementation-provided clocks that are used for these functions shall meet the TrivialClock -requirements (20.12.3 [time.clock.req]). -

    -
    9. - -
  9. -

    Edit the synopsis of 30.3.2 [thread.thread.this] before p. 1. -[Note: this duplicates edits also in D/N3267]: -

    - -
    -template <class Clock, class Duration>
-void sleep_until(const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-template <class Rep, class Period>
-void sleep_for(const chrono::duration<Rep, Period>& rel_time) noexcept;
-
    -
    10. - -
  10. -

    Modify the prototype specifications in 30.3.2 [thread.thread.this] before p. 4 and p. 6 and -re-add a Throws element following the Synchronization elements at p. 5 and p. 7:

    - -
    -template <class Clock, class Duration>
-void sleep_until(const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-

    -4 - [...] -

    -5 - Synchronization: None. -

    -? - Throws: Nothing if Clock satisfies the TrivialClock requirements (20.12.3 [time.clock.req]) and -operations of Duration do not throw exceptions. -[Note: Instantiations of time point types and clocks supplied by the implementation as specified in 20.12.7 [time.clock] -do not throw exceptions. — end note] -

    -
    - -
    -template <class Rep, class Period>
-void sleep_for(const chrono::duration<Rep, Period>& rel_time) noexcept;
-

    -6 [...] -

    -7 Synchronization: None. -

    -? Throws: Nothing if operations of chrono::duration<Rep, Period> do not throw exceptions. -[Note: Instantiations of duration types supplied by the implementation as specified in 20.12.7 [time.clock] -do not throw exceptions. — end note] -

    -
    -
    11. - -

  11. Fix a minor incorrectness in p. 5: Duration types need to compare against duration<>::zero(), -not 0:

    - -

    -3 The expression m.try_lock_for(rel_time) shall be well-formed and have the following semantics: -

    -[...] -

    -5 Effects: The function attempts to obtain ownership of the mutex within the relative timeout (30.2.4) -specified by rel_time. If the time specified by rel_time is less than or equal to 0rel_time.zero(), -the function attempts to obtain ownership without blocking (as if by calling try_lock()). The function shall return -within the timeout specified by rel_time only if it has obtained ownership of the mutex object. -[ Note: As with try_lock(), there is no guarantee that ownership will be obtained if the lock is -available, but implementations are expected to make a strong effort to do so. — end note ] -

    -
    -
    12. - -

  12. Modify the class timed_mutex synopsis in 30.4.1.3.1 [thread.timedmutex.class] as indicated: -[Note: this duplicates edits also in D/N3267]: -

    - -
    -class timed_mutex {
-public:
-  [...]
-  template <class Rep, class Period>
-    bool try_lock_for(const chrono::duration<Rep, Period>& rel_time) noexcept;
-  template <class Clock, class Duration>
-    bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-  [...]
-};
-
    -
    13. - -

  13. Modify the class recursive_timed_mutex synopsis in 30.4.1.3.2 [thread.timedmutex.recursive] as indicated: -[Note: this duplicates edits also in D/N3267]: -

    - -
    -class recursive_timed_mutex {
-public:
-  [...]
-  template <class Rep, class Period>
-    bool try_lock_for(const chrono::duration<Rep, Period>& rel_time) noexcept;
-  template <class Clock, class Duration>
-    bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-  [...]
-};
-
    -
    14. - -

  14. Modify the class template unique_lock synopsis in 30.4.2.2 [thread.lock.unique] as indicated. -[Note: this duplicates edits also in D/N3267]: -

    - -
    -template <class Mutex>
-class unique_lock {
-public:
-  [...]
-  template <class Clock, class Duration>
-    unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-  template <class Rep, class Period>
-    unique_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time) noexcept;
-  [...]
-};
-
    -
    15. - -

  15. Modify the constructor prototypes in 30.4.2.2.1 [thread.lock.unique.cons] before p. 14 and p. 17 -[Note: this duplicates edits also in D/N3267]: -

    - -
    -template <class Clock, class Duration>
-  unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time) noexcept;
-
    - -
    -template <class Rep, class Period>
-  unique_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time) noexcept;
-
    -
    16. - - -
- - - - - - -
-

1490. Mutex requirements too stringent

-

Section: 30.4.1 [thread.mutex.requirements] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [thread.mutex.requirements].

-

View all other issues in [thread.mutex.requirements].

-

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-

Discussion:

-

Addresses CH-27

- -

-The mutex requirements force try_lock to be -noexcept(true). However, where they are used by the -generic algorithms, those relax this requirement and say -that try_lock may throw. This means the requirement is -too stringent, also a non-throwing try_lock does not allow -for a diagnostic such as system_error that lock() -will give us. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-delete p18, adjust 30.4.4 p1 and p4 accordingly -

- -

[ -2010-11-01 Daniel comments: -]

- - -

-Accepting n3130 would solve this issue. -

- - -

Proposed resolution:

-Resolved by n3197. -

- - - - -
-

1491. try_lock does not guarantee forward progress

-

Section: 30.4.1 [thread.mutex.requirements] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [thread.mutex.requirements].

-

View all other issues in [thread.mutex.requirements].

-

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-

Discussion:

-

Addresses US-186

- -

-try_lock does not provide a guarantee of forward progress -because it is allowed to spuriously fail. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-The standard mutex types must not fail spuriously -in try_lock. See n3141 -page 205 - Appendix 1 - Additional Details -

- -

[ -2010-11-01 Daniel comments: -]

- -

-Paper n3152 addresses -this issue. -

- - - -

Proposed resolution:

-Resolved by n3209. -

- - - - -
-

1492. Mutex requirements should not be bound to threads

-

Section: 30.4.1 [thread.mutex.requirements] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View other active issues in [thread.mutex.requirements].

-

View all other issues in [thread.mutex.requirements].

-

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-

Discussion:

-

Addresses US-188

- -

-Mutex requirements should not be bound to threads. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-See Appendix 1 of n3141 - Additional Details, p. 208. -

- -

[ -2010-10-24 Daniel adds: -]

- - -

-Accepting n3130 would solve this issue. -

- - -

Proposed resolution:

-Resolved by n3197. -

- - - - -
-

1494. Term "are serialized" not defined

-

Section: 30.4.4.2 [thread.once.callonce] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.once.callonce].

-

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-

Discussion:

-

Addresses US-190

-

-The term "are serialized" is never defined (30.4.4.2 [thread.once.callonce] p. 2). -

-

[ -Resolution proposed by ballot comment: -]

- -

-Remove the sentence with "are serialized" from -paragraph 2. Add "Calls to call_once on the same -once_flag object shall not introduce data races -(17.6.4.8)." to paragraph 3. -

- -

[ -2010-11-01 Daniel translates NB comment into wording -]

- - - -

[ -2011-02-17: Hans proposes an alternative resolution -]

- - -

[ -2011-02-25: Hans, Clark, and Lawrence update the suggested wording -]

- - -

[2011-02-26 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

Change 30.4.4.2 [thread.once.callonce] p.2+3 as indicated:

- -
-template<class Callable, class ...Args>
-void call_once(once_flag& flag, Callable&& func, Args&&... args);
-

-[..] -

-2 Effects: Calls to call_once on the same once_flag object are serialized. -If there has been a prior effective call to call_once on the same once_flag object, the call to call_once -returns without invoking func. If there has been no prior effective call to call_once -on the same once_flag object, INVOKE(decay_copy( std::forward<Callable>(func)), -decay_copy(std::forward<Args>(args))...) is executed. The call to call_once is effective -if and only if INVOKE(decay_copy( std::forward<Callable>(func)), decay_copy(std::forward<Args>(args))...) -returns without throwing an exception. If an exception is thrown it is propagated to the caller. -An execution of call_once that does not call its func is a passive execution. -An execution of call_once that calls its func is an active execution. -An active execution shall call INVOKE(decay_copy(std::forward<Callable>(func)), -decay_copy(std::forward<Args>(args))...). If such a call to func throws an exception, -the execution is exceptional, otherwise it is returning. -An exceptional execution shall propagate the exception to the caller of call_once. -Among all executions of call_once for any given once_flag: at most one shall be a -returning execution; if there is a returning execution, it shall be the last active execution; and -there are passive executions only if there is a returning execution. -[Note: Passive executions allow other threads to reliably observe the results produced by the -earlier returning execution. — end note] -

-3 Synchronization: The completion of an effective call to call_once on a once_flag -object synchronizes with (1.10 [intro.multithread]) all subsequent calls to call_once -on the same once_flag object.For any given once_flag: all active executions occur in a total -order; completion of an active execution synchronizes with (1.10 [intro.multithread]) the start of -the next one in this total order; and the returning execution synchronizes with the return from all passive -executions. -

- - - - - - -
-

1497. lock() postcondition can not be generally achieved

-

Section: 30.5 [thread.condition] Status: C++11 - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

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-

Discussion:

-

Addresses CH-30

-

-If lock.lock() throws an exception, the postcondition can not be generally achieved. -

-

[ -Resolution proposed by ballot comment: -]

- -

-Either state that the postcondition might not be achieved, depending on the error condition, or -state that terminate() is called in this case. -

- -

[ -2010-08-13 Peter Sommerlad comments and provides wording -]

- - -

-30.5.1 [thread.condition.condvar], 30.5.2 [thread.condition.condvarany] -

-p. 13, last bullet, and corresponding paragraphs in all wait functions -

-Problem:
-Condition variable wait might fail, because the lock cannot be acquired when notified. -CH-30 says: "If lock.lock() throws an exception, the postcondition can not be generally achieved." -CH-30 proposes: "Either state that the postcondition might not be achieved, depending on the error -condition, or state that terminate() is called in this case." -

-The discussion in Rapperswil concluded that calling terminate() might be too drastic in -this case and a corresponding exception should be thrown/passed on and one should use a lock type -that allows querying its status, which unique_lock allows for std::condition_variable -

-We also had some additional observations while discussing in Rapperswil: -

-
    -
  • in 30.5.1 [thread.condition.condvar] wait with predicate and wait_until with -predicate lack the precondition, postcondition and Error conditions sections. the lack of the precondition -would allow to call pred() without holding the lock. -
    • -
  • in 30.5.1 [thread.condition.condvar] wait_until and wait_for and -30.5.2 [thread.condition.condvarany] wait_for still specify an -error condition for a violated precondition. This should be removed. -
    • -
-

-and add the following proposed solution: -

-
- -

[2011-02-27: Daniel adapts numbering to n3225]

- - - -

Proposed resolution:

-
    -
  1. Change 30.5.1 [thread.condition.condvar] as indicated: -
    -void wait(unique_lock<mutex>& lock);
-
    -

    - 9 Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait or timed_wait) threads. -
      • -
    -
    -[..] -

    -11 Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    -[..] -
    -template <class Predicate>
-void wait(unique_lock<mutex>& lock, Predicate pred);
-
    -

    -?? Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait or timed_wait) threads. -
      • -
    -
    -

    -14 Effects: -

    -while (!pred())
-  wait(lock);
-
    -
    - -

    -?? Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    -

    -?? Throws: std::system_error when an exception is required (30.2.2). -

    -

    -?? Error conditions: -

    -
      -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    - -
    -template <class Clock, class Duration>
-cv_status wait_until(unique_lock<mutex>& lock,
-  const chrono::time_point<Clock, Duration>& abs_time);
-
    -

    -15 Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait, wait_for, or wait_until) threads. -
      • -
    -

    -[..] -

    -17 Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    -[..] -

    -20 Error conditions: -

    -
      -
    • operation_not_permitted — if the thread does not own the lock. -
      • -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    -
    -template <class Rep, class Period>
-cv_status wait_for(unique_lock<mutex>& lock,
-  const chrono::duration<Rep, Period>& rel_time);
-
    -

    -21 Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait, wait_for, or wait_until) threads. -
      • -
    -

    -[..] -

    -24 Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    -[..] -

    -26 Error conditions: -

    -
      -
    • operation_not_permitted — if the thread does not own the lock. -
      • -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    -
    -template <class Clock, class Duration, class Predicate>
-bool wait_until(unique_lock<mutex>& lock,
-  const chrono::time_point<Clock, Duration>& abs_time,
-    Predicate pred);
-
    -

    -?? Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait or timed_wait) threads. -
      • -
    -
    -

    -27 Effects: -

    -while (!pred())
-  if (wait_until(lock, abs_time) == cv_status::timeout)
-    return pred();
-return true;
-
    -
    -

    -28 Returns: pred() -

    - -

    -?? Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    - -

    -29 [ Note: The returned value indicates whether the predicate evaluates to true regardless of whether the -timeout was triggered. — end note ] -

    - -

    -?? Throws: std::system_error when an exception is required (30.2.2). -

    -

    -?? Error conditions: -

    -
      -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    - -
    -template <class Rep, class Period, class Predicate>
-bool wait_for(unique_lock<mutex>& lock,
-  const chrono::duration<Rep, Period>& rel_time,
-    Predicate pred);
-
    -

    -30 Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either -

    -
      -
    • no other thread is waiting on this condition_variable object or -
      • -
    • lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait, wait_for, or wait_until) threads. -
      • -
    -

    -[..] -

    -33 Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread. -

    -[..] -

    -37 Error conditions: -

    -
      -
    • operation_not_permitted — if the thread does not own the lock. -
      • -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    - -
    2. - -
  2. Change 30.5.2 [thread.condition.condvarany] as indicated: -

    -[..] -

    -template <class Lock, class Predicate>
-void wait(Lock& lock, Predicate pred);
-
    -

    -[Note: if any of the wait functions exits with an exception it is indeterminate if the Lock is held. -One can use a Lock type that allows to query that, such as the unique_lock wrapper. — end note] -

    -

    -11 Effects: -

    -while (!pred())
-  wait(lock);
-
    -

    -[..] -

    -31 Error conditions: -

    -
      -
    • operation_not_permitted — if the thread does not own the lock. -
      • -
    • equivalent error condition from lock.lock() or lock.unlock(). -
      • -
    -
    -
    3. - -
- - - - - -
-

1498. Unclear specification for [thread.condition]

-

Section: 30.5 [thread.condition] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses CH-29

- -

-It is unclear if a spurious wake-up during the loop and reentering -of the blocked state due to a repeated execution -of the loop will adjust the timer of the blocking with the -respect to the previously specified rel_time value. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Make it clear (e.g. by a note) that when reexecuting -the loop the waiting time when blocked -will be adjusted with respect to the elapsed time of -the previous loop executions. -

- -

[ -2010-08-13 Peter Sommerlad comments and provides wording: -]

- - -

-Problem: It is unclear if a spurious wake-up during the loop and re-entering of the blocked state due -to a repeated execution of the loop will adjust the timer of the blocking with the respect to the -previously specified rel_time value. -

-Proposed Resolution from CH29: -

-Make it clear (e.g. by a note) that when re-executing the loop the waiting time when blocked will be -adjusted with respect to the elapsed time of the previous loop executions. -

-Discussion in Rapperswil: -

-Assuming the introduction of a mandatory steady_clock proposed by US-181 to the FCD the -specification of condition_variable::wait_for can be defined in terms of wait_until -using the steady_clock. This is also interleaving with US-181, because that touches the -same paragraph (30.5.1 p 25, p34 and 30.5.2 p 20, p 28 in n3092.pdf) -

-(The "as if" in the proposed solutions should be confirmed by the standardization terminology experts) -

- -

[ -2010-11 Batavia: Resolved by applying n3191 -]

- - -
-
    -
  1. Change 30.5.1 [thread.condition.condvar] paragraph 25, wait_for Effects as indicated: -
    -template <class Rep, class Period>
-cv_status wait_for(unique_lock<mutex>& lock,
-  const chrono::duration<Rep, Period>& rel_time);
-
    -

    -[..] -

    -25 Effects: as if -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time);
-
    -
      -
    • Atomically calls lock.unlock() and blocks on *this. -
      • -
    • When unblocked, calls lock.lock() (possibly blocking on the lock), then returns. -
      • -
    • The function will unblock when signaled by a call to notify_one() or a call to notify_all(), -by the elapsed time rel_time passing (30.2.4), or spuriously. -
      • -
    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function scope. -
      • -
    -
    -
    2. -
  2. Change 30.5.1 [thread.condition.condvar] paragraph 34, wait_for with predicate Effects as indicated: -
    -template <class Rep, class Period, class Predicate>
-bool wait_for(unique_lock<mutex>& lock,
-  const chrono::duration<Rep, Period>& rel_time,
-  Predicate pred);
-
    -

    -[..] -

    -34 Effects: as if -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time, std::move(pred));
-
    -
      -
    • Executes a loop: Within the loop the function first evaluates pred() and exits the loop if the -result is true. -
      • - -
    • Atomically calls lock.unlock() and blocks on *this. -
      • - -
    • When unblocked, calls lock.lock() (possibly blocking on the lock). -
      • - -
    • The function will unblock when signaled by a call to notify_one() or a call to notify_all(), -by the elapsed time rel_time passing (30.2.4), or spuriously. -
      • - -
    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function -scope. -
      • - -
    • The loop terminates when pred() returns true or when the time duration specified by rel_time -has elapsed. -
      • - -
    -
    -
    3. - -
  3. Change 30.5.2 [thread.condition.condvarany] paragraph 20, wait_for Effects as indicated: -
    -template <class Lock, class Rep, class Period>
-cv_status wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
    -

    -20 Effects: as if -

    -return wait_until(lock, chrono::steady_clock::now() + rel_time);
-
    -
      -
    • Atomically calls lock.unlock() and blocks on *this. -
      • - -
    • When unblocked, calls lock.lock() (possibly blocking on the lock), then returns. -
      • - -
    • The function will unblock when signaled by a call to notify_one() or a call to notify_all(), -by the elapsed time rel_time passing (30.2.4), or spuriously. -
      • - -
    • If the function exits via an exception, lock.unlock() shall be called prior to exiting the function -scope. -
      • -
    -
    -
    4. - -
  4. Change 30.5.2 [thread.condition.condvarany] paragraph 28, wait_for with predicate Effects as indicated: -
    -template <class Lock, class Rep, class Period, class Predicate>
-bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
-
    -

    -28 Effects: as if -

    -return wait_until(lock, chrono::steady_clock::now() + rel_time, std::move(pred));
-
    -
      -
    • Executes a loop: Within the loop the function first evaluates pred() and exits the loop if the -result is true. -
      • - -
    • Atomically calls lock.unlock() and blocks on *this. -
      • - -
    • When unblocked, calls lock.lock() (possibly blocking on the lock). -
      • - -
    • The function will unblock when signaled by a call to notify_one() or a call to notify_all(), -by the elapsed time rel_time passing (30.2.4), or spuriously. -
      • - -
    • If the function exits via an exception, lock.unlock() shall be called prior to exiting the function -scope. -
      • - -
    • The loop terminates when pred() returns true or when the time duration specified by rel_time -has elapsed. -
      • -
    -
    -
    5. - -
- -
- - -

Proposed resolution:

-Resolved by n3191. -

- - - - -
-

1501. Specification for managing associated asynchronous state has problems

-

Section: 30.6 [futures] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [futures].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-194

- -

-The specification for managing associated asynchronous -state is confusing, sometimes omitted, and redundantly -specified. -

- -

[ -Resolution proposed by ballot comment: -]

- - -

-Define terms-of-art for releasing, making ready, -and abandoning an associated asynchronous -state. Use those terms where appropriate. See -Appendix 1 - Additional Details -

- - -

Proposed resolution:

-Resolved in Batavia by accepting -n3192. -

- - - - -
-

1502. Specification of [futures.state] unclear

-

Section: 30.6.4 [futures.state] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [futures.state].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses US-195

- -

The intent and meaning of 30.6.4 [futures.state] p10 is not apparent.

- -

-10 Accesses to the same shared state conflict (1.10). -

- -

[ -2011-03-07 Jonathan Wakely adds: -]

- -

-It's not clear which paragraph this refers to, I had to go to the -ballot comments where US-195 reveals it's para 8, which in the FCD -(N3092) says: -

- Accesses to the same associated asynchronous state conflict (1.10). -

-

This is now para 10 in N3242:

-

- Accesses to the same shared state conflict (1.10). -

-
- -

[2011-03-07: Lawrence comments and drafts wording]

- - -

The intent of this paragraph is to deal with operations, -such as shared_future::get(), that return a reference -to a value held in the shared state. User code could potentially -conflict when accessing that value.

- -

Lawrence proposed resolution:

- -

Modify 30.6.4 [futures.state] p10 as follows:

- -

-10 Accesses to the same shared state conflict (1.10 [intro.multithread]).Some - operations, e.g. shared_future::get() - (30.6.7 [futures.shared_future]), may return a reference to a - value held in their shared state. Accesses and modifications through - those references by concurrent threads to the same - shared state may potentially conflict (1.10 [intro.multithread]). - [Note: As a consequence, accesses must either use - read-only operations or provide additional synchronization. - — end note] -

- -

[2011-03-19: Detlef suggests an alternative resolution, shown below.]

- - -
-

Proposed Resolution

-

Modify 30.6.4 [futures.state] p10 as follows:

- -

-10 Accesses to the same shared state conflict (1.10 [intro.multithread]). [Note: -This explicitely specifies that the shared state is visible in the objects that reference this state -in the sense of data race avoidance 17.6.5.9 [res.on.data.races]. — end note] -

-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1504. Term "are serialized" is not defined

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-196

-

-The term "are serialized" is not defined (30.6.5 [futures.promise] p. 21, 25). -

-

[ -Resolution proposed by ballot comment: -]

- -

-Replace "are serialized" with "shall not introduce a data race (17.6.4.8)". -

- -

[ -2010-11-02 Daniel translates proposal into proper wording changes -]

- - -

[2011-03-19: Detlef comments]

- - -

The proposed resolution for 1507 would cover this issue as well.

- -

[Proposed Resolution]

- -
-
    -
  1. Change 30.6.5 [futures.promise] p. 21 as indicated: -

    -21 Synchronization: calls to set_value and set_exception on a single -promise object are serializedshall not introduce a data race ([res.on.data.races]). -[ Note: and they synchronize and serialize with other functions through the referred associated asynchronous -state. — end note ] -

    -
    2. -
  2. Change 30.6.5 [futures.promise] p. 25 as indicated: -

    -25 Synchronization: calls to set_value and set_exception on a single -promise object are serializedshall not introduce a data race ([res.on.data.races]). -[ Note: and they synchronize and serialize with other functions through the referred associated asynchronous -state. — end note ] -

    -
    3. -
-
- - -

Proposed resolution:

-Resolved 2001-03 Madrid by issue 1507. -

- - - -
-

1505. Synchronization between promise::set_value and future::get

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-197

-

-There is no defined synchronization between promise::set_value and future::get -(30.6.5 [futures.promise] p. 21, 25). -

-

[ -Resolution proposed by ballot comment: -]

- -

-Replace "[Note: and they synchronize and -serialize with other functions through the referred -associated asynchronous state. — end note]" with -the normative "They synchronize with (1.10) any -operation on a future object with the same -associated asynchronous state marked ready." -

- -

[ -2010-11-02 Daniel translates proposal into proper wording changes -]

- - -

[2011-03-19: Detlef comments]

- - -

The proposed resolution for 1507 would cover this issue as well. -Effectively it will reject the request but a clarification is added that the -normative wording is already in 30.6.4 [futures.state].

- -
-
    -
  1. Change 30.6.5 [futures.promise] p. 21 as indicated: -

    -21 Synchronization: calls to set_value and set_exception on a single -promise object are serialized. -[ Note: and they synchronize and serialize with other functions through the referred associated asynchronous -state. — end note ]They synchronize with ([intro.multithread]) any -operation on a future object with the same associated asynchronous state marked ready. -

    -
    2. -
  2. Change 30.6.5 [futures.promise] p. 25 as indicated: -

    -25 Synchronization: calls to set_value and set_exception on a single -promise object are serialized. -[ Note: and they synchronize and serialize with other functions through the referred associated asynchronous -state. — end note ]They synchronize with ([intro.multithread]) any -operation on a future object with the same associated asynchronous state marked ready. -

    -
    3. -
-
- - -

Proposed resolution:

-Resolved 2001-03 Madrid by issue 1507. -

- - - -
-

1507. promise::XXX_at_thread_exit functions have no -synchronization requirements

-

Section: 30.6.5 [futures.promise] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

Addresses US-199

-

-promise::XXX_at_thread_exit functions have no -synchronization requirements. Specifying synchronization -for these member functions requires coordinating with the -words in 30.6.5 [futures.promise]/21 and 25, which give synchronization -requirements for promise::set_value and -promise::set_exception (30.6.5 [futures.promise] p. 26 ff., p. 29 ff.). -

-

[ -Resolution proposed by ballot comment: -]

- -

-Change 30.6.5 [futures.promise]/21 to mention set_value_at_thread_exit and -set_exception_at_thread_exit; with this text, replace 30.6.5 [futures.promise]/25 -and add two new paragraphs, after 30.6.5 [futures.promise]/28 and 30.6.5 [futures.promise]/31. -

- -

[2011-03-8: Lawrence comments and drafts wording]

- - -

This comment applies as well to other *_at_thread_exit -functions. The following resolution adds synchronization paragraphs -to all of them and edits a couple of related synchronization -paragraphs.

- -

[2011-03-09: Hans and Anthony add some improvements]

- - -

[2011-03-19: Detlef comments]

- - -

In regard to the suggested part:

- -

-These operations do not provide any ordering guarantees with -respect to other operations, except through operations on futures -that reference the same shared state. -

- -

I would like this to change to:

- -

-These operations do not provide any ordering guarantees with -respect to other operations on the same promise object. -[Note: They synchronize with calls to operations on -objects that refer to the same shared state according to -30.6.4 [futures.state]. — end note] -

- -

The current proposed resolution has exactly the same paragraph at -for places. I propose to have it only once as new paragraph 2.

- -

This also covers 1504 (US-196) and 1505 (US-197). -US-197 is essentially rejected with this resolution, but a clarification is added -that the normative wording is already in 30.6.4 [futures.state].

- -
-

Proposed Resolution

-
    -

  1. Edit 30.4.1.2 [thread.mutex.requirements.mutex] paragraph 5 as follows:

    - -

    -5 The implementation shall provide lock and unlock operations, as described below. The implementation -shall serialize those operations.For purposes of determining the existence of a data race, these -behave as atomic operations (1.10 [intro.multithread]). The lock and unlock operations on -a single mutex shall appear to occur in a single total order. [Note: this can be viewed as the -modification order (1.10 [intro.multithread]) of the mutex. — end note] [ Note: -Construction and destruction of an object of a mutex type need not be thread-safe; other synchronization -should be used to ensure that mutex objects are initialized and visible to other threads. — end note ] -

    -
    2. - -

  2. Edit 30.5 [thread.condition] paragraphs 6-9 as follows:

    - -
    -void notify_all_at_thread_exit(condition_variable& cond, unique_lock<mutex> lk);
-
    -
    -

    --6- Requires: lk is locked by the calling thread and either -

    -
      -
    • no other thread is waiting on cond, or
      • -
    • lk.mutex() returns the same value for each of the lock arguments supplied by all concurrently -waiting (via wait, wait_for, or wait_until) threads.
      • -
    -

    --7- Effects: transfers ownership of the lock associated with lk into internal storage and schedules -cond to be notified when the current thread exits, after all objects of thread storage duration -associated with the current thread have been destroyed. This notification shall be as if -

    -
    -lk.unlock();
-cond.notify_all();
-
    -

    --?- Synchronization: The call to notify_all_at_thread_exit -and the completion of the destructors for all the current thread's variables of -thread storage duration synchronize with (1.10 [intro.multithread]) calls -to functions waiting on cond. -

    --8- Note: The supplied lock will be held until the thread exits, and care must be taken to ensure that -this does not cause deadlock due to lock ordering issues. After calling notify_all_at_thread_exit -it is recommended that the thread should be exited as soon as possible, and that no blocking or -time-consuming tasks are run on that thread. -

    --9- Note: It is the user's responsibility to ensure that waiting threads do not erroneously -assume that the thread has finished if they experience spurious wakeups. This typically requires -that the condition being waited for is satisfied while holding the lock on lk, and that -this lock is not released and reacquired prior to calling notify_all_at_thread_exit. -

    -
    -
    3. - -

  3. Edit 30.6.5 [futures.promise], paragraphs 14-27 as follows:

    - -
    -void promise::set_value(const R& r);
-void promise::set_value(R&& r);
-void promise<R&>::set_value(R& r);
-void promise<void>::set_value();
-
    -
    -

    --14- Effects: atomically stores the value r in the shared state and makes that state -ready (30.6.4 [futures.state]). -

    --15- Throws: -

    -
      -
    • future_error if its shared state already has a stored value or exception, or
      • -
    • for the first version, any exception thrown by the copy constructor of R, or
      • -
    • for the second version, any exception thrown by the move constructor of R.
      • -
    -

    --16- Error conditions: -

    -
      -
    • promise_already_satisfied if its shared state already has a stored value or exception.
      • -
    • no_state if *this has no shared state.
      • -
    -

    --17- Synchronization: calls to set_value and set_exception on a single -promise object are serialized. [ Note: And they synchronize and serialize with other functions -through the referred shared state. — end note ]For purposes of determining the -existence of a data race, set_value, set_exception, set_value_at_thread_exit, -and set_exception_at_thread_exit behave as atomic operations (1.10 [intro.multithread]) on -the memory location associated with the promise. Calls to these operations on a single promise shall -appear to occur in a single total order. [Note: this can be viewed as the modification order -(1.10 [intro.multithread]) of the promise. — end note] These operations do not -provide any ordering guarantees with respect to other operations, except through operations on futures -that reference the same shared state. -

    -
    - -
    -void set_exception(exception_ptr p);
-
    -
    -

    --18- Effects: atomically stores the exception pointer p in the shared state and makes that -state ready (30.6.4 [futures.state]). -

    - -

    --19- Throws: future_error if its shared state already has a stored value or exception. -

    - -

    --20- Error conditions: -

    -
      -
    • promise_already_satisfied if its shared state already has a stored value or exception.
      • -
    • no_state if *this has no shared state.
      • -
    - -

    --21- Synchronization: calls to set_value and set_exception on a single -promise object are serialized. [ Note: And they synchronize and serialize with -other functions through the referred shared state. — end note ]For purposes of determining the -existence of a data race, set_value, set_exception, set_value_at_thread_exit, -and set_exception_at_thread_exit behave as atomic operations (1.10 [intro.multithread]) on -the memory location associated with the promise. Calls to these operations on a single promise shall -appear to occur in a single total order. [Note: this can be viewed as the modification order -(1.10 [intro.multithread]) of the promise. — end note] These operations do not -provide any ordering guarantees with respect to other operations, except through operations on futures -that reference the same shared state. -

    -
    - -
    -void promise::set_value_at_thread_exit(const R& r);
-void promise::set_value_at_thread_exit(R&& r);
-void promise<R&>::set_value_at_thread_exit(R& r);
-void promise<void>::set_value_at_thread_exit();
-
    -
    -

    --22- Effects: Stores the value r in the shared state without making that state -ready immediately. Schedules that state to be made ready when the current thread exits, after -all objects of thread storage duration associated with the current thread have been destroyed. -

    --23- Throws: future_error if an error condition occurs. -

    --24- Error conditions: -

    -
      -
    • promise_already_satisfied if its shared state already has a stored value or exception.
      • -
    • no_state if *this has no shared state.
      • -
    -

    --??- Synchronization: For purposes of determining the existence of a data race, set_value, -set_exception, set_value_at_thread_exit, and set_exception_at_thread_exit behave as -atomic operations (1.10 [intro.multithread]) on the memory location associated with the promise. -Calls to these operations on a single promise shall appear to occur in a single total order. [Note: -this can be viewed as the modification order (1.10 [intro.multithread]) of the promise. — -end note] These operations do not provide any ordering guarantees with respect to other operations, -except through operations on futures that reference the same shared state. -

    -
    - -
    -void promise::set_exception_at_thread_exit(exception_ptr p);
-
    -
    -

    --25- Effects: Stores the exception pointer p in the shared state without -making that state ready immediately. Schedules that state to be made ready when the current -thread exits, after all objects of thread storage duration associated with the current -thread have been destroyed. -

    --26- Throws: future_error if an error condition occurs. -

    --27- Error conditions: -

    -
      -
    • promise_already_satisfied if its shared state already has a stored value or exception.
      • -
    • no_state if *this has no shared state.
      • -
    -

    --??- Synchronization: For purposes of determining the existence of a data race, set_value, -set_exception, set_value_at_thread_exit, and set_exception_at_thread_exit behave as -atomic operations (1.10 [intro.multithread]) on the memory location associated with the promise. -Calls to these operations on a single promise shall appear to occur in a single total order. [Note: -this can be viewed as the modification order (1.10 [intro.multithread]) of the promise. — -end note] These operations do not provide any ordering guarantees with respect to other operations, -except through operations on futures that reference the same shared state. -

    -
    -
    4. - -

  4. Edit 30.6.9.1 [futures.task.members], paragraph 15-21 as follows:

    - -
    -void operator()(ArgTypes... args);
-
    -
    -

    --15- Effects: INVOKE(f, t1, t2, ..., tN, R), where f is the stored task -of *this and t1, t2, ..., tN are the values in -args.... If the task returns normally, the return value is stored as the asynchronous -result in the shared state of *this, otherwise the exception thrown by the task is -stored. The shared state of *this is made ready, and any threads blocked in a function -waiting for the shared state of *this to become ready are unblocked. -

    --16- Throws: a future_error exception object if there is no shared state or the stored -task has already been invoked. -

    --17- Error conditions: -

    -
      -
    • promise_already_satisfied if the shared state is already ready.
      • -
    • no_state if *this has no shared state.
      • -
    -

    --18- Synchronization: a successful call to operator() synchronizes with (1.10 [intro.multithread]) -a call to any member function of a future or shared_future object that shares the -shared state of *this. The completion of the invocation of the stored task and the storage -of the result (whether normal or exceptional) into the shared state synchronizes with (1.10 [intro.multithread]) -the successful return from any member function that detects that the state is set to ready. [ Note: -operator() synchronizes and serializes with other functions through the shared state. — end note ] -

    -
    - -
    -void make_ready_at_thread_exit(ArgTypes... args);
-
    -
    -

    --19- Effects: INVOKE(f, t1, t2, ..., tN, R), where f is the -stored task and t1, t2, ..., tN are the values in args.... -If the task returns normally, the return value is stored as the asynchronous result in the shared -state of *this, otherwise the exception thrown by the task is stored. In either case, -this shall be done without making that state ready (30.6.4 [futures.state]) immediately. -Schedules the shared state to be made ready when the current thread exits, after all objects of -thread storage duration associated with the current thread have been destroyed. -

    --20- Throws: future_error if an error condition occurs. -

    --21- Error conditions: -

    -
      -
    • promise_already_satisfied if the shared state already has a stored value or exception.
      • -
    • no_state if *this has no shared state.
      • -
    -

    --??- Synchronization: a successful call to make_ready_at_thread_exit -synchronizes with (1.10 [intro.multithread]) a call to any member function of -a future or shared_future object that shares the shared state of -*this. The completion of -

    -
      -

    • the invocation of the stored task and the storage of the result (whether normal or -exceptional) into the shared state

      • -

    • the destructors for all the current thread's variables of thread storage duration

      • -
    -

    -synchronize with (1.10 [intro.multithread]) the successful return from any member function -that detects that the state is set to ready. [Note: make_ready_at_thread_exit -synchronizes and serializes with other functions through the shared state. — end note] -

    -
    - -
    5. -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1508. Rename packaged_task::operator bool()

-

Section: 30.6.9 [futures.task] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-201

-

-packaged_task provides operator bool() to check whether -an object has an associated asynchronous state. The various future -types provide a member function valid() that does the same thing. -The names of these members should be the same. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Replaced the name packaged_task::operator bool() with packaged_task::valid() in the synopsis -(30.6.9 [futures.task]/2) and the member function specification (before 30.6.9.1 [futures.task.members]/15). -

- -

[ -2010-11-02 Daniel translates proposed wording changes into a proper proposed resolution -and verified that no other places implicitly take advantage of packaged_task -conversion to bool. -]

- - -

[Resolved in Batavia by accepting -n3194. -]

- - - - -

Proposed resolution:

-
    -
  1. Change 30.6.9 [futures.task]/2, class template packaged_task synopsis as indicated: -
    -template<class R, class... ArgTypes>
-class packaged_task<R(ArgTypes...)> {
-public:
-  typedef R result_type;
-  [..]
-  explicit operator bool valid() const;
-  [..]
-};
-
    -
    2. -
  2. Change 30.6.9 [futures.task] before p. 15 as indicated: -
    -explicit operator bool valid() const;
-

    -15 Returns: true only if *this has an associated asynchronous state. -

    -16 Throws: nothing. -

    -
    3. -
- - - - - -
-

1513. 'launch' enum too restrictive

-

Section: 30.6 [futures] Status: Resolved - Submitter: Switzerland Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [futures].

-

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-

Discussion:

-

Addresses CH-36

-

-Providing only three different possible values for the enum -launch and saying that launch::any means either -launch::sync or launch::async is very restricting. This -hinders future implementors to provide clever -infrastructures that can simply by used by a call to -async(launch::any,...). Also there is no hook for an -implementation to provide additional alternatives to launch -enumeration and no useful means to combine those (i.e. -interpret them like flags). We believe something like -async(launch::sync | launch::async, ...) should be allowed -and can become especially useful if one could say also -something like async(launch::any & ~launch::sync, ....) -respectively. This flexibility might limit the features usable -in the function called through async(), but it will allow a -path to effortless profit from improved hardware/software -without complicating the programming model when just -using async(launch::any,...) -

-

[ -Resolution proposed by ballot comment: -]

- -

-Change in 30.6.1 [futures.overview] 'enum class launch' to allow -further implementation defined values and provide -the following bit-operators on the launch values -(operator|, operator&, operator~ delivering a -launch value). -

-Note: a possible implementation might use an -unsigned value to represent the launch enums, -but we shouldn't limit the standard to just 32 or 64 -available bits in that case and also should keep -the launch enums in their own enum namespace. -

-Change [future.async] p3 according to the -changes to enum launch. change --launch::any to -"the implementation may choose any of the -policies it provides." Note: this can mean that an -implementation may restrict the called function to -take all required information by copy in case it will -be called in a different address space, or even, on -a different processor type. To ensure that a call is -either performed like launch::async or -launch::sync describe one should call -async(launch::sync|launch::async,...) -

- -

[ -2010-11-02 Daniel comments: -]

- - -

-The new paper n3113 provides concrete wording. -

- - -

Proposed resolution:

-

-Resolved by n3188. -

- - - - - -
-

1514. packaged_task constructors need review

-

Section: 30.6.9.1 [futures.task.members] Status: C++11 - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

Addresses US-207

-

-The constructor that takes R(*)(ArgTypes...) is not -needed; the constructor that takes a callable type works -for this argument type. More generally, the constructors -for packaged_task should parallel those for function. -

-

[ -US-207 Suggested Resolution: -]

- - -

-Review the constructors for packaged_task and -provide the same ones as function, except where -inappropriate. -

- -

[ -2010-10-22 Howard provides wording, as requested by the LWG in Rapperswil. -]

- - -

[2011-02-10 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

-Alter the list of constructors in both 30.6.9 [futures.task] and in 30.6.9.1 [futures.task.members] as indicated: -

-
-
template <class F>
-explicit packaged_task(F f);
-template <class F, class Allocator>
-explicit packaged_task(allocator_arg_t, const Allocator& a, F f);
-explicit packaged_task(R(*f)(ArgTypes...));
-template <class F>
-explicit packaged_task(F&& f);
-template <class F, class Allocator>
-explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
-
-
- - - - - -
-

1515. packaged_task::make_ready_at_thread_exit has no synchronization requirements

-

Section: 30.6.9.1 [futures.task.members] Status: Resolved - Submitter: INCITS Opened: 2010-08-25 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

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-

Discussion:

-

Addresses US-208

- -

-packaged_task::make_ready_at_thread_exit has no synchronization requirements. -

- -

[ -Resolution proposed by ballot comment: -]

- -

-Figure out what the synchronization requirements -should be and write them. -

- -

[2011-02-09 Anthony provides a proposed resolution]

- - -

[2011-02-19 Additional edits by Hans, shown in the proposed resolution section]

- - -

[2011-02-22 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- -
-

Proposed Resolution

- -

Add a new paragraph following 30.6.9.1 [futures.task.members] p. 19:

- -
-void make_ready_at_thread_exit(ArgTypes... args);
-
-
-

-19 - ... -

-

-?? - Synchronization: Following a successful call to make_ready_at_thread_exit, the -destruction of all objects with thread storage duration associated with -the current thread happens before the associated asynchronous state is -made ready. The marking of the associated asynchronous state as ready -synchronizes with (1.10 [intro.multithread]) the successful return from any function that -detects that the state is set to ready. -

-
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

1516. No specification for which header contains auto_ptr

-

Section: X [depr.auto.ptr] Status: C++11 - Submitter: BSI Opened: 2010-08-25 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

Addresses GB-142

-

-auto_ptr does not appear in the <memory> synopsis and -[depr.auto.ptr] doesn't say which header declares it. -Conversely, the deprecated binders bind1st etc. are in the -<functional> synopsis, this is inconsistent -

-

-Either auto_ptr should be declared in the -<memory> synopsis, or the deprecated binders -should be removed from the <functional> synopsis -and appendix D should say which header declares -the binders and auto_ptr. -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

Add the following lines to the synopsis of header <memory> -in [memory]/1:

-
-
-// [depr.auto.ptr], Class auto_ptr (deprecated):
-template <class X> class auto_ptr;

-
- - - - - -
-

1517. default_delete's default constructor should be trivial

-

Section: 20.8.1.1.2 [unique.ptr.dltr.dflt] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-09-12 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.dltr.dflt].

-

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-

Discussion:

-

-The current working draft does specify the default c'tor of default_delete in a manner -to guarantee static initialization for default-constructed objects of static storage duration -as a consequence of the acceptance of the proposal n2976 -but this paper overlooked the fact that the suggested declaration does not ensure that the type -will be a trivial type. The type default_delete was always considered as a simple wrapper for -calling delete or delete[], respectivly and should be a trivial type. -

-

-In agreement with the new settled core language rules this easy to realize by just changing the declaration to -

-
-constexpr default_delete() = default;
-
-

-This proposal also automatically solves the problem, that the semantics of the default constructor of the -partial specialization default_delete<T[]> is not specified at all. By defaulting its default constructor -as well, the semantics are well-defined. -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

The following wording changes are against N3126.

- -
    -
  1. Change the synopsis of the primary template definition of default_delete in [unique.ptr.dltr.dflt] as indicated: -
    -namespace std {
-  template <class T> struct default_delete {
-    constexpr default_delete() = default;
-    template <class U> default_delete(const default_delete<U>&);
-    void operator()(T*) const;
-  };
-}
-
    -
    2. -
  2. -Remove the prototype specification of the default_delete default constructor in [unique.ptr.dltr.dflt]/1. This -brings it in harmony with the style used in the partial specialization default_delete<T[]>. Since there are -neither implied nor explicit members, there is no possibility to misinterpret what the constructor does: -
    -constexpr default_delete();
-

    -1 Effects: Default constructs a default_delete object. -

    -
    3. -
  3. Change the synopsis of the partial specialization of default_delete in [unique.ptr.dltr.dflt1] as indicated: -
    -namespace std {
-  template <class T> struct default_delete<T[]> {
-    constexpr default_delete() = default;
-    void operator()(T*) const;
-    template <class U> void operator()(U*) const = delete;
-  };
-}
    -
    4. -
- - - - - -
-

1518. Waiting for deferred functions

-

Section: 30.6 [futures] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2010-09-14 Last modified: 2015-04-08

-

View all other issues in [futures].

-

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-

Discussion:

-

The current WP N3126 contains ambiguous statements about the -behaviour of functions wait_for/wait_until in -case the future refers to a deferred function. Moreover, I believe -it describes a disputable intent, different from the one contained -in the original async proposals, that may have been introduced -inadvertently during the "async cleanup" that occurred recently. -Consider the following case:

-
-
-int f();  
-future<int> x = async(launch::deferred, f);
-future_status s = x.wait_for(chrono::milliseconds(100));
-
-

This example raises two questions:

-
    -
  1. is f invoked?
    2. -
  2. what is the value of s?
    3. -
-

According to the current WP, the answer to question 1 is yes, -because 30.6.9/3 says "The first call to a function waiting for the -associated asynchronous state created by this async call to become -ready shall invoke the deferred function in the thread that called -the waiting function". The answer to question 2, however, is not as -clear. According to 30.6.6/23, s should be -future_status::deferred because x refers to a -deferred function that is not running, but it should also be -future_status::ready because after executing f -(and we saw that f is always executed) the state becomes -ready. By the way, the expression "deferred function that is not -running" is very unfortunate in itself, because it may apply to -both the case where the function hasn't yet started, as well as the -case where it was executed and completed.

-

While we clearly have a defect in the WP answering to question -2, it is my opinion that the answer to question 1 is wrong, which -is even worse. Consider that the execution of the function -f can take an arbitrarily long time. Having -wait_for() invoke f is a potential violation of -the reasonable expectation that the execution of -x.wait_for(chrono::milliseconds(100)) shall take at most -100 milliseconds plus a delay dependent on the quality of implementation -and the quality of management (as described in paper N3128). -In fact, previous versions of the WP -clearly specified that only function wait() is required to -execute the deferred function, while wait_for() and -wait_until() shouldn't.

-

The proposed resolution captures the intent that -wait_for() and wait_until() should never attempt -to invoke the deferred function. In other words, the P/R provides -the following answers to the two questions above:

-
    -
  1. no
    2. -
  2. future_status::deferred
    3. -
-

In order to simplify the wording, the definition of deferred -function has been tweaked so that the function is no longer -considered deferred once its evaluation has started, as suggested -by Howard.

-

Discussions in the reflector questioned whether -wait_for() and wait_until() should return -immediately or actually wait hoping for a second thread to execute -the deferred function. I believe that waiting could be useful only -in a very specific scenario but detrimental in the general case and -would introduce another source of ambiguity: should -wait_for() return future_status::deferred or -future_status::timeout after the wait? Therefore the P/R -specifies that wait_for/wait_until shall return -immediately, which is simpler, easier to explain and more useful in -the general case.

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

The proposed wording changes are relative to the Final Committee Draft, -N3126.

-

Note to the editor: the proposed wording is meant not be in conflict -with any change proposed by paper N3128 "C++ Timeout Specification". -Ellipsis are deliberately used to avoid any unintended overlapping.

-
    -
  1. -

    In [futures.unique_future] 30.6.6/22:

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    2. -
  2. -

    In [futures.unique_future] 30.6.6/23 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    3. -
  3. -

    In [futures.unique_future] 30.6.6/25:

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    4. -
  4. -

    In [futures.unique_future] 30.6.6/26 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    5. -
  5. -

    In [futures.shared_future] 30.6.7/27

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    6. -
  6. -

    In [futures.unique_future] 30.6.7/28 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    7. -
  7. -

    In [futures.shared_future] 30.6.6/30:

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    8. -
  8. -

    In [futures.unique_future] 30.6.7/31 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    9. -
  9. -

    In [futures.atomic_future] 30.6.8/23

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    10. -
  10. -

    In [futures.unique_future] 30.6.8/24 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    11. -
  11. -

    In [futures.atomic_future] 30.6.8/27:

    -

    Effects: none if the associated asynchronous state contains -a deferred function (30.6.9), otherwise blocks until the -associated asynchronous state is ready or [...].

    -
    12. -
  12. -

    In [futures.unique_future] 30.6.8/28 first bullet:

    -

    — future_status::deferred if the associated asynchronous -state contains a deferred function that is not -running.

    -
    13. -
  13. -

    In [futures.async] 30.6.9/3 second bullet:

    -

    [...] The first call to a function -waitingrequiring a non-timed wait for the -associated asynchronous state created by this async call to become -ready shall invoke the deferred function in the thread that called -the waiting function; once evaluation of INVOKE(g, -xyz) begins, the function is no longer considered -deferred all other calls waiting for the same associated -asynchronous state to become ready shall block until the deferred -function has completed.

    -
    14. -
- - - - - - -
-

1519. bucketsize() const only for unordered set

-

Section: 23.5.4 [unord.map], 23.5.5 [unord.multimap], 23.5.7 [unord.multiset] Status: C++11 - Submitter: Nicolai Josuttis Opened: 2010-10-09 Last modified: 2015-04-08

-

View all other issues in [unord.map].

-

View all issues with C++11 status.

-

Discussion:

-

-While bucket_size() is const for unordered_set, for all other unordered containers it is not defined as -constant member function. -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

The wording refers to N3126.

- -
    -
  1. Change 23.7.1 Class template unordered_map [unord.map]/3, as indicated: -
    -  namespace std {
-    template <class Key,
-      class T,
-      class Hash = hash<Key>,
-      class Pred = std::equal_to<Key>,
-      class Alloc = std::allocator<std::pair<const Key, T> > >
-    class unordered_map
-    {
-    public:
-      [..]
-      // bucket interface
-      size_type bucket_count() const;
-      size_type max_bucket_count() const;
-      size_type bucket_size(size_type n) const;
-      [..]
-
    -
    2. -
  2. Change 23.7.2 Class template unordered_multimap [unord.multimap]/3, as indicated: -
    -  namespace std {
-    template <class Key,
-      class T,
-      class Hash = hash<Key>,
-      class Pred = std::equal_to<Key>,
-      class Alloc = std::allocator<std::pair<const Key, T> > >
-    class unordered_multimap
-    {
-    public:
-      [..]
-      // bucket interface
-      size_type bucket_count() const;
-      size_type max_bucket_count() const;
-      size_type bucket_size(size_type n) const;
-      [..]
-
    -
    3. -
  3. Change 23.7.4 Class template unordered_multiset [unord.multiset]/3, as indicated: -
    -  namespace std {
-    template <class Key,
-      class Hash = hash<Key>,
-      class Pred = std::equal_to<Key>,
-      class Alloc = std::allocator<Key> >
-    class unordered_multiset
-    {
-    public:
-      [..]
-      // bucket interface
-      size_type bucket_count() const;
-      size_type max_bucket_count() const;
-      size_type bucket_size(size_type n) const;
-      [..]
-
    -
    4. -
- - - - - - -
-

1520. INVOKE on member data pointer with too many arguments

-

Section: 20.9.2 [func.require] Status: C++11 - Submitter: Howard Hinnant Opened: 2010-10-10 Last modified: 2015-04-08

-

View other active issues in [func.require].

-

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-

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-

Discussion:

- -

-20.8.2 [func.require] p1 says: -

- -
-

-1 Define INVOKE(f, t1, t2, ..., tN) as follows: -

- -
    -
  • -(t1.*f)(t2, ..., tN) when f is a pointer to a member function -of a class T and t1 is an object of type T or a -reference to an object of type T or a reference to an object of a type -derived from T; -
    • -
  • -((*t1).*f)(t2, ..., tN) when f is a pointer to a member -function of a class T and t1 is not one of the types described -in the previous item; -
    • -
  • -t1.*f when f is a pointer to member data of a class T -and t1 is an object of type T or a reference to an object of -type T or a reference to an object of a type derived from T; -
    • -
  • -(*t1).*f when f is a pointer to member data of a class -T and t1 is not one of the types described in the previous -item; -
    • -
  • -f(t1, t2, ..., tN) in all other cases. -
    • -
-
- -

-The question is: What happens in the 3rd and -4th bullets when N > 1? -

- -

-Does the presence of t2, ..., tN get ignored, or does it make the -INVOKE ill formed? -

- -

-Here is sample code which presents the problem in a concrete example: -

- -
-#include <functional>
-#include <cassert>
-
-struct S {
-   char data;
-};
-
-typedef char S::*PMD;
-
-int main()
-{
-   S s;
-   PMD pmd = &S::data;
-   std::reference_wrapper<PMD> r(pmd);
-   r(s, 3.0) = 'a';  // well formed?
-   assert(s.data == 'a');
-}
-
- -

-Without the "3.0" the example is well formed. -

-

-[Note: Daniel provided wording to make it explicit that the above example is ill-formed. — end note ] -

- -

[ -Post-Rapperswil -]

- - -

-Moved to Tentatively Ready after 5 positive votes on c++std-lib. -

- -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

- -

The wording refers to N3126.

- -

-Change 20.8.2 [func.require]/1 as indicated: -

-
-

-1 Define INVOKE(f, t1, t2, ..., tN) as follows: -

- -
    -
  • -... -
    • -
  • -... -
    • -
  • -t1.*f when N == 1 and f is a pointer to -member data of a class T and t1 is an object of type -T or a reference to an object of type T or a reference to an -object of a type derived from T; -
    • -
  • -(*t1).*f when N == 1 and f is a pointer to -member data of a class T and t1 is not one of the types -described in the previous item; -
    • -
  • -... -
    • -
-
- - - - - - -
-

1522. conj specification is now nonsense

-

Section: 26.4.9 [cmplx.over] Status: C++11 - Submitter: P.J. Plauger Opened: 2010-10-14 Last modified: 2015-04-08

-

View all other issues in [cmplx.over].

-

View all issues with C++11 status.

-

Discussion:

-

-In Pittsburgh, we accepted the resolution of library issue 1137, to add -a sentence 3 to [cmplx.over]: -

-

-All the specified overloads shall have a return type which is the nested -value_type of the effectively cast arguments. -

-

-This was already true for four of the six functions except conj and -proj. It is not completely unreasonable to make proj return -the real value only, but the IEC specification does call for an imaginary part -of -0 in some circumstances. The people who care about these distinctions really -care, and it is required by an international standard. -

-

-Making conj return just the real part breaks it horribly, however. It is -well understood in mathematics that conj(re + i*im) is (re - i*im), -and it is widely used. The accepted new definition makes conj useful only -for pure real operations. This botch absolutely must be fixed. -

- -

[ -2010 Batavia: The working group concurred with the issue's Proposed Resolution -]

- - -

[ -Adopted at 2010-11 Batavia -]

- - - - -

Proposed resolution:

-

-Remove the recently added paragraph 3 from [cmplx.over]: -

-

-3 All the specified overloads shall have a return type which is the nested -value_type of the effectively cast arguments. -

- - - - - -
-

1523. noexcept for Clause 29

-

Section: 29 [atomics] Status: Resolved - Submitter: Hans Boehm Opened: 2010-11-13 Last modified: 2015-04-08

-

View all other issues in [atomics].

-

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-

Discussion:

-

Addresses GB-63 for Clause 29

- -

Clause 29 does not specify noexcept for any of the atomic operations. -It probably should, though that's not completely clear. -In particular, atomics may want to throw in implementations that support transactional memory. -

- - -

Proposed resolution:

-

-Apply paper N3251, -noexcept for the Atomics Library. -

- - - - - -
-

1524. Allocation functions are missing happens-before requirements and guarantees

-

Section: 18.6.1.4 [new.delete.dataraces] Status: C++11 - Submitter: Hans Boehm Opened: 2011-02-26 Last modified: 2015-04-08

-

View all other issues in [new.delete.dataraces].

-

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-

Discussion:

-

Addresses US-34

- -

Technical details: -

-When the same unit of storage is allocated and deallocated repeatedly, operations on it can't be allowed to -race between the allocator and the user program. But I don't see any mention of happens-before in the -descriptions of allocation and deallocation functions. -

-Proposed resolution (not wording yet): -

-
    -

  • The call to an allocation function returning a pointer P must happen-before the matching -deallocation call with P as a parameter. Otherwise the behavior is undefined. I don't know whether -receiving P with memory_order_consume fits this requirement. memory_order_relaxed does not.

    -
    • -

  • If some memory is passed to a deallocation function, the implementation must ensure that the -deallocation call happens-before any allocation call that returns the same memory address.

    -
    • -
- -

[2011-02-26: Hans comments and drafts wording]

- - -

The second requirement already exists, almost verbatim, as 18.6.1.4 [new.delete.dataraces] p. 1. -I think this is where the statement belongs. However, this paragraph requires work to correctly address -the first part of the issue. -

- -

[Adopted at Madrid, 2011-03]

- - - - -

Proposed resolution:

-

Change 18.6.1.4 [new.delete.dataraces] p. 1 as follows:

- -

-1 The library versions of operator new and operator delete, user replacement versions of global -operator new and operator delete, and the C standard library functions calloc, malloc, -realloc, and free shall not introduce data races (1.10 [intro.multithread]) as a result -of concurrent calls from different threads. For purposes of determining the existence of data races, -the library versions of operator new, user replacement versions of global operator new, and the C -standard library functions calloc and malloc shall behave as though they accessed and modified only -the storage referenced by the return value. The library versions of operator delete, user replacement -versions of operator delete, and the C standard library function free shall behave as though they -accessed and modified only the storage referenced by their first argument. The C standard library realloc -function shall behave as though it accessed and modified only the storage referenced by its first argument and by -its return value. Calls to these functions that allocate or deallocate a particular unit of storage -shall occur in a single total order, and each such deallocation call shall happen before the next allocation -(if any) in this order. -

- - - - - -
-

1525. Effects of resize(size()) on a vector

-

Section: 23.3.6.3 [vector.capacity] Status: C++11 - Submitter: BSI Opened: 2011-03-24 Last modified: 2015-04-08

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

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-

Discussion:

-

Addresses GB-117

- -

23.3.6.3 [vector.capacity] p. 9 (Same as for 23.3.3.3 [deque.capacity] p. 1 i.e. -deque::resize). There is no mention of what happens if sz==size(). While -it obviously does nothing I feel a standard needs to say this explicitely.

-

Suggested resolution:

-

Append "If sz == size(), does nothing" to the effects.

- -

[2011-03-24 Daniel comments]

- - -

During the edit of this issue some non-conflicting overlap with 2033 became obvious. -CopyInsertable should be MoveInsertable and there is missing the DefaultConstructible -requirements, but this should be fixed by 2033.

- - -

Proposed resolution:

-

Change 23.3.6.3 [vector.capacity] p. 9 as follows:

- -
-void resize(size_type sz);
-
-

-9 Effects: If sz <= size(), equivalent to erase(begin() + sz, end());. -If size() < sz, appends sz - size() value-initialized elements to the sequence. -

-10 Requires: T shall be CopyInsertable into *this. -

- - - - - -
-

1526. C++ should not impose thread safety requirements on C99 library implementations

-

Section: 17.6.5.9 [res.on.data.races] Status: Resolved - Submitter: BSI Opened: 2011-03-24 Last modified: 2015-05-22

-

View all issues with Resolved status.

-

Discussion:

-

Addresses GB-111

- -

Section 17.6.5.9 [res.on.data.races], Data Race Avoidance, requires the C++ Standard Library to avoid data races -that might otherwise result from two threads making calls to C++ Standard Library functions on -distinct objects. The C standard library is part of the C++ Standard Library and some C++ Standary library -functions (parts of the Localization library, as well as Numeric Conversions in 21.5), are specified -to make use of the C standard library. Therefore, the C++ standard indirectly imposes a requirement -on the thread safety of the C standard library. However, since the C standard does not address the -concept of thread safety conforming C implementations exist that do no provide such guarantees. -This conflict needs to be reconciled.

- -

Suggested resolution by national body comment:

- -

-remove the requirement to make use of strtol() and sprintf() since these functions depend on the -global C locale and thus cannot be made thread safe. -

- -

[2011-03-24 Madrid meeting]

- - -

Deferred

- -

[ -2011 Bloomington -]

- -

-Alisdair: PJ, does this cause a problem in C? -

-

-PJ: Every implementation know of is thread safe. -

-

-Pete: There a couple of effects that are specified on strtol() and sprintf() which is a problem. -

-

-PJ: When C++ talks about C calls it should be "as if" calling the function. -

-

-Pete: Culprit is to string stuff. My fault. -

-

-PJ: Not your fault. You did what you were told. Distinct resolution to change wording. -

-

-Dietmar: What would we break if we change it back? -

-

-Pete: Nothing. If implemented on top of thread safe C library you are just fine. -

-

-Alisdair: Anyone want to clean up wording and put it back to what Pete gave us? -

-

-Alisdair: No volunteers. Do we want to mark as NAD? We could leave it as deferred. -

-

-Stefanus: Did original submitter care about this? -

-

-Lawrence: There is some work to make local calls thread safe. The resolution would be to call those thread safe version. -

-

-Pete: "As if called under single threaded C program" -

-

-Action Item (Alisdair): Write wording for this issue. -

- -

[2012, Kona]

- -

-Re-opened at the request of the concurrency subgroup, who feel there is an issue that needs -clarifying for the (planned) 2017 standard. -

- -

Rationale:

No consensus to make a change at this time

- -

[2012, Portland]

- -

-The concurrency subgroup decided to encourage the LWG to consider a change to 17.2 [library.c] or thereabouts -to clarify that we are requiring C++-like thread-safety for setlocale, so that races are not introduced -by C locale accesses, even when the C library allows it. This would require e.g. adding "and data race avoidance" -at the end of 17.2 [library.c] p1: -

-

-"The C++ standard library also makes available the facilities of the C standard library, suitably adjusted to -ensure static type safety and data race avoidance.", -

-

-with some further clarifications in the sections mentioned in 1526. -

-

-This seems to be consistent with existing implementations. This would technically not be constraining C implementation, -but it would be further constraining C libraries used for both C and C++. -

- -

[Lenexa 2015-05-05: Move to Resolved]

- -

JW: it's a bit odd that the issue title says sould not impose requirements on C libs, then the P/R does exactly that. Does make sense though, previously we imposed an implicit requirement which would not have been met. Now we say it explicitly and require it is met.

-

STL: I think this is Resolved, it has been fixed in the working paper [support.runtime]/6 is an example where we call out where things can race. That implies that for everything else they don't create races.

-

JW: I'm not sure, I think we still need the "and data race avoidance" to clarify that the features from C avoid races, even though C99 says no such thing.

-

STL: [library.c] says that something like sqrt is part of the C++ Standard LIbrary. [res.on.data.races] then applies to them. Would be OK with a note there, but am uncomfortable with "and data race avoidance" which sounds like it's making a very strong guarantee.

-

ACTION ITEM JW to editorially add note to [library.c] p1: "Unless otherwise specified, the C Standard Library functions shall meet the requirements for data race avoidance (xref [res.on.data.races])"

-

Move to Resolved?

-

10 in favor, 0 opposed, 3 abstentions

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 17.2 [library.c] p1 as indicated:

    - -

    --1- The C++ standard library also makes available the facilities of the C standard library, suitably adjusted to -ensure static type safety and data race avoidance. -

    -
    2. -
- - - - - - -
-

2000. Missing definition of packaged_task specialization of uses_allocator

-

Section: 30.6.9.2 [futures.task.nonmembers] Status: C++11 - Submitter: Howard Hinnant Opened: 2010-08-29 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

-[futures.task.nonmembers]/3 says: -

-
-   template <class R, class Alloc>
-     struct uses_allocator<packaged_task<R>, Alloc>;
-
-

-This is a declaration, but should be a definition. -

- - -

Proposed resolution:

-

-Change [futures.task.nonmembers]/3: -

- -
-   template <class R, class Alloc>
-     struct uses_allocator<packaged_task<R>, Alloc>;
-        : true_type {};
-
- - - - - -
-

2001. Class template basic_regex uses non existent string_type

-

Section: 28.8.3 [re.regex.assign] Status: C++11 - Submitter: Volker Lukas Opened: 2010-10-21 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-In working draft N3126, subclause 28.8.3 [re.regex.assign], paragraphs 12, 13 and 19, -the name string_type is used. This is presumably a typedef for basic_string<value_type>, where -value_type is the character type used by basic_regex. The basic_regex -template however defines no such typedef, and neither does the <regex> -header or the <initializer_list> header included by <regex>. -

- -

[ -2010-11-03 Daniel comments and suggests alternative wording: -]

- -

-The proposed resolution needs to use basic_string<charT> instead of basic_string<char> -

- -

-Previous Proposed Resolution: -

-Make the following changes to [re.regex.assign]: -

-
-
-basic_regex& assign(const charT* ptr, flag_type f = regex_constants::ECMAScript);
-
-

-12 Returns: assign(string_typebasic_string<charT>(ptr), f). -

- -
-basic_regex& assign(const charT* ptr, size_t len,
-  flag_type f = regex_constants::ECMAScript);
-
-

-13 Returns: assign(string_typebasic_string<charT>(ptr, len), f). -

- -
-[..]
-
-template <class InputIterator> 
-  basic_regex& assign(InputIterator first, InputIterator last, 
-                          flag_type f = regex_constants::ECMAScript);
-
- -

-18 Requires: The type InputIterator shall satisfy the requirements for an Input Iterator (24.2.3). -

- -

-19 Returns: assign(string_typebasic_string<charT>(first, last), f). -

- -
- -

[ -2010 Batavia -]

- - -

-Unsure if we should just give basic_regex a string_type typedef. Looking for when string_type was -introduced into regex. Howard to draft wording for typedef typename traits::string_type string_type, then move to Review. -

- -

[ -2011-02-16: Daniel comments and provides an alternative resolution. -]

- - -

-I'm strongly in favour with the Batavia idea to provide a separate string_type within -basic_regex, but it seems to me that the issue resultion should add one more -important typedef, namely that of the traits type! Currently, basic_regex is the -only template that does not publish the type of the associated traits type. Instead -of opening a new issue, I added this suggestion as part of the proposed wording. -

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 6 votes. -

- - -

Proposed resolution:

-

-Change the class template basic_regex synopsis, 28.8 [re.regex] p. 3, as indicated:

- -
-namespace std {
-  template <class charT,
-            class traits = regex_traits<charT> >
-  class basic_regex {
-  public:
-    // types:
-    typedef charT value_type;
-    typedef traits traits_type;
-    typedef typename traits::string_type string_type;
-    typedef regex_constants::syntax_option_type flag_type;
-    typedef typename traits::locale_type locale_type;
-
-    [..]
-  };
-}
-
- - - - - - -
-

2002. Class template match_results does not specify the semantics of operator==

-

Section: 28.10.8 [re.results.nonmember] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-10-24 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-The Returns element of operator== says: -

- -

-true only if the two objects refer to the same match -

- -

-It is not really clear what this means: The current specification would allow for an -implementation to return true, only if the address values of m1 and -m2 are the same. While this approach is unproblematic in terms of used operations -this is also a bit unsatisfactory. With identity equality alone there seems to be no convincing -reason to provide this operator at all. It could for example also refer to an comparison based -on iterator values. In this case a user should better know that this will be done, because -there is no guarantee at all that inter-container comparison of iterators -is a feasible operation. This was a clear outcome of the resolution provided in -N3066 -for LWG issue 446. -It could also mean that a character-based comparison of the individual sub_match -elements should be done - this would be equivalent to applying operator== to -the subexpressions, prefix and suffix. -

- - - -

Proposed resolution:

-

Addressed by paper n3158.

- - - - - -
-

2003. String exception inconsistency in erase.

-

Section: 21.4.1 [string.require] Status: C++14 - Submitter: José Daniel García Sánchez Opened: 2010-10-21 Last modified: 2015-04-08

-

View all other issues in [string.require].

-

View all issues with C++14 status.

-

Discussion:

-

-Clause 21.4.1 [string.require]p3 states: -

-

-No erase() or pop_back() member function shall throw -any exceptions. -

-

-However in 21.4.6.5 [string::erase] p2 the first version of erase has -

-

-Throws: out_of_range if pos > size(). -

- -

[2011-03-24 Madrid meeting]

- - -

-Beman: Don't want to just change this, can we just say "unless otherwise specified"? -

-Alisdair: Leave open, but update proposed resolution to say something like "unless otherwise specified". -

-General agreement that it should be corrected but not a stop-ship. -

-Action: Update proposed wording for issue 2003 as above, but leave Open. -

- -

[2014-02-12 Issaquah meeting]

- - -

-Jeffrey: Madrid meeting's proposed wording wasn't applied, and it's better than the original proposed wording. -However, this sentence is only doing 3 functions' worth of work, unlike the similar paragraphs in 23.2.1 [container.requirements.general]. -Suggest just putting "Throws: Nothing" on the 3 functions. -

- -

[2014-02-13 Issaquah meeting]

- -

-Move as Immmediate -

- - - -

Proposed resolution:

-

-Remove [string.require]p/3: -

-

-3 No erase() or pop_back() member function shall throw any exceptions. -

- -

-Add to the specifications of iterator erase(const_iterator p);, iterator erase(const_iterator first, const_iterator last);, - and void pop_back(); in 21.4.6.5 [string::erase]: -

-

Throws: Nothing

- - - - - -
-

2004. duration::operator* has template parameters in funny order

-

Section: 20.12.5.5 [time.duration.nonmember] Status: C++11 - Submitter: P.J. Plauger Opened: 2010-10-14 Last modified: 2015-04-08

-

View all other issues in [time.duration.nonmember].

-

View all issues with C++11 status.

-

Discussion:

-

-In [time] and [time.duration.nonmember] we have: -

-
-template <class Rep1, class Period, class Rep2>
-    duration<typename common_type<Rep1, Rep2>::type, Period>
-        operator*(const Rep1& s, const duration<Rep2, Period>& d);
-
-

-Everywhere else, we always have <rep, period> in that order for a given -type. But here, we have Period and Rep2 in reverse order for -<Rep2, Period>. This is probably of little importance, since the -template parameters are seldom spelled out for a function like this. But changing it -now will eliminate a potential source of future errors and confusion. -

- - -

Proposed resolution:

-

-Change the signature in [time] and [time.duration.nonmember] to: -

-
-template <class Rep1, class PeriodRep2, class Rep2Period>
-    duration<typename common_type<Rep1, Rep2>::type, Period>
-        operator*(const Rep1& s, const duration<Rep2, Period>& d);
-
- - - - - -
-

2005. unordered_map::insert(T&&) protection should apply to map too

-

Section: 23.4.4.4 [map.modifiers], 23.4.5.3 [multimap.modifiers], 23.5.4.4 [unord.map.modifiers], 23.5.5.3 [unord.multimap.modifiers] Status: C++14 - Submitter: P.J. Plauger Opened: 2010-10-14 Last modified: 2015-04-08

-

View all other issues in [map.modifiers].

-

View all issues with C++14 status.

-

Discussion:

-

-In [unord.map.modifiers], the signature: -

-
-template <class P>
-    pair<iterator, bool> insert(P&& obj);
-
-

-now has an added Remarks paragraph: -

-

-Remarks: This signature shall not participate in overload resolution unless P -is implicitly convertible to value_type. -

-

-The same is true for unordered_multimap. -

-But neither map nor multimap have this constraint, even though it is a -Good Thing(TM) in those cases as well. -

- -

[ -The submitter suggests: Add the same Remarks clause to [map.modifiers] and [multimap.modifiers]. -]

- - -

[ -2010-10-29 Daniel comments: -]

- - -

-I believe both paragraphs need more cleanup: First, the current Requires element conflict with the Remark; -second, it seems to me that the whole single Requires element is intended to be split into a Requires -and an Effects element; third, the reference to tuple is incorrect (noticed by Paolo Carlini); -fourth, it refers to some non-existing InputIterator parameter relevant for a completely different -overload; sixth, the return type of the overload with hint is wrong. -The following proposed resolution tries to solve these issues as well and uses similar wording as for -the corresponding unordered containers. Unfortunately it has some redundancy over Table 99, but I did -not remove the specification because of the more general template parameter P - the Table 99 -requirements apply only for an argument identical to value_type. -

-Daniel's Proposed resolution (not current): -

- -
-
    -
  1. Change 23.4.4.4 [map.modifiers] around p. 1 as indicated: -
    -template <class P> pair<iterator, bool> insert(P&& x);
-template <class P> pair<iterator, bool> insert(const_iterator position, P&& x);
-

    -1 Requires: P shall be convertible to value_type is constructible -from std::forward<P>(x).. -

    -If P is instantiated as a reference type, then the argument x is copied from. Otherwise x is considered -to be an rvalue as it is converted to value_type and inserted into the map. Specifically, in -such cases CopyConstructible is not required of key_type or mapped_type unless the conversion -from P specifically requires it (e.g., if P is a tuple<const key_type, mapped_type>, then key_type -must be CopyConstructible). The signature taking InputIterator parameters does not require -CopyConstructible of either key_type or mapped_type if the dereferenced InputIterator returns a -non-const rvalue pair<key_type,mapped_type>. Otherwise CopyConstructible is required for both -key_type and mapped_type.
    -? Effects: Inserts x converted to value_type if and only if there is no element in the container with -key equivalent to the key of value_type(x). For the second form, the iterator position is a hint pointing to where the -search should start. -

    -? Returns: For the first form, the bool component of the returned pair object indicates whether the -insertion took place and the iterator component - or for the second form the returned iterator - points to the element with key equivalent -to the key of value_type(x). -

    -? Complexity: Logarithmic in general, but amortized constant if x is inserted right before position. -

    -? Remarks: These signatures shall not participate in overload resolution unless P -is implicitly convertible to value_type. -

    -
    -
    2. -
  2. Change 23.4.5.3 [multimap.modifiers] around p. 1 as indicated: -
    -template <class P> iterator insert(P&& x);
-template <class P> iterator insert(const_iterator position, P&& x);
-

    -1 Requires: P shall be convertible to value_type is constructible from -std::forward<P>(x). -

    -If P is instantiated as a reference type, then the argument x is copied from. Otherwise -x is considered to be an rvalue as it is converted to value_type and inserted into the map. -Specifically, in such cases CopyConstructible is not required of key_type or mapped_type -unless the conversion from P specifically requires it (e.g., if P is a tuple<const key_type, mapped_type>, -then key_type must be CopyConstructible). The signature taking InputIterator parameters -does not require CopyConstructible of either key_type or mapped_type if the dereferenced -InputIterator returns a non-const rvalue pair<key_type, mapped_type>. Otherwise CopyConstructible -is required for both key_type and mapped_type.
    -? Effects: Inserts x converted to value_type. For the second form, the iterator position -is a hint pointing to where the search should start. -

    -? Returns: An iterator that points to the element with key equivalent to the key of value_type(x). -

    -? Complexity: Logarithmic in general, but amortized constant if x is inserted right before position. -

    -? Remarks: These signatures shall not participate in overload resolution unless P -is implicitly convertible to value_type. -

    -
    -
    3. -
- -
- -

[ -2010 Batavia: -]

- - -

-We need is_convertible, not is_constructible, both in ordered and unordered containers. -

- -

[ -2011 Bloomington -]

- - -

-The effects of these inserts can be concisely stated in terms of emplace(). -Also, the correct term is "EmplaceConstructible", not "constructible". -

- -

-New wording by Pablo, eliminating duplicate requirements already implied by the effects clause. Move to Review. -

- -

[ -2011-10-02 Daniel comments and refines the proposed wording -]

- - -

-Unfortunately the template constraints expressed as "P is implicitly convertible to value_type" -reject the intended effect to support move-only key types, which was the original intention when -the library became move-enabled through the rvalue-reference proposals by Howard (This can clearly be deduced -from existing carefully selected wording that emphasizes that CopyConstructible is only required -for special situations involving lvalues or const rvalues as arguments). The root of the problem is based -on current core rules, where an "implicitly converted" value has copy-initialization semantics. Consider -a move-only key type KM, some mapped type T, and a source value p of type P -equal to std::pair<KM, T>, this is equivalent to: -

-
-std::pair<const KM, T> dest = std::move(p);
-
-

-Now 8.5 [dcl.init] p16 b6 sb2 says that the effects of this heterogeneous copy-initialization (p -has a different type than dest) are as-if a temporary of the target type std::pair<const KM, T> -is produced from the rvalue p of type P (which is fine), and this temporary is used to initialize -dest. This second step cannot succeed, because we cannot move from const KM to const KM. This -means that std::is_convertible<P, std::pair<const KM, T>>::value is false. -

-But the actual code that is required (with the default allocator) is simply a direct-initialization -from P to value_type, so imposing an implicit conversion is more than necessary. Therefore -I strongly recommend to reduce the "overload participation" constraint to -std::is_constructible<std::pair<const KM, T>, P>::value instead. This change is the -only change that has been performed to the previous proposed wording from Pablo shown below. -

- -

[2012, Kona]

- -

-Moved to Tentatively Ready by the post-Kona issues processing subgroup, after much discussion -on Daniel's analysis of Copy Initialization and move semantics, which we ultimately agreed with. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

- -
    -
  1. Change 23.4.4.4 [map.modifiers] around p. 1 as indicated: -
    -template <class P> pair<iterator, bool> insert(P&& x);
-template <class P> pair<iterator, bool> insert(const_iterator position, P&& x);
-
    -1 Requires: P shall be convertible to value_type. -

    -If P is instantiated as a reference type, then the argument x is copied from. Otherwise x is considered -to be an rvalue as it is converted to value_type and inserted into the map. Specifically, in -such cases CopyConstructible is not required of key_type or mapped_type unless the conversion -from P specifically requires it (e.g., if P is a tuple<const key_type, mapped_type>, then key_type -must be CopyConstructible). The signature taking InputIterator parameters does not require -CopyConstructible of either key_type or mapped_type if the dereferenced InputIterator returns a -non-const rvalue pair<key_type,mapped_type>. Otherwise CopyConstructible is required for both -key_type and mapped_type.
    -? Effects: The first form is equivalent to -return emplace(std::forward<P>(x)). -The second form is equivalent to -return emplace_hint(position, std::forward<P>(x)). -

    -? Remarks: These signatures shall not participate in overload resolution unless -std::is_constructible<value_type, P&&>::value is true. -

    -

    -
    2. -
  2. Change 23.4.5.3 [multimap.modifiers] around p. 1 as indicated: -
    -template <class P> iterator insert(P&& x);
-template <class P> iterator insert(const_iterator position, P&& x);
-
    -1 Requires: P shall be convertible to value_type. -

    -If P is instantiated as a reference type, then the argument x is copied from. Otherwise -x is considered to be an rvalue as it is converted to value_type and inserted into the map. -Specifically, in such cases CopyConstructible is not required of key_type or mapped_type -unless the conversion from P specifically requires it (e.g., if P is a tuple<const key_type, mapped_type>, -then key_type must be CopyConstructible). The signature taking InputIterator parameters -does not require CopyConstructible of either key_type or mapped_type if the dereferenced -InputIterator returns a non-const rvalue pair<key_type, mapped_type>. Otherwise CopyConstructible -is required for both key_type and mapped_type.
    -? Effects: The first form is equivalent to -return emplace(std::forward<P>(x)). -The second form is equivalent to -return emplace_hint(position, std::forward<P>(x)). -

    -? Remarks: These signatures shall not participate in overload resolution unless -std::is_constructible<value_type, P&&>::value is true. -

    -

    -
    3. -
  3. Change [unord.map.modifers] around p. 1 as indicated: -
    -template <class P>
-pair<iterator, bool> insert(P&& obj);
-
    -
    -1 Requires: value_type is constructible from std::forward<P>(obj). -

    -2 Effects: -equivalent to return emplace(std::forward<P>(obj)). -Inserts obj converted to value_type if and only if there is no element in the container with -key equivalent to the key of value_type(obj). -

    -3 Returns: The bool component of the returned pair object indicates whether the insertion took place -and the iterator component points to the element with key equivalent to the key of value_type(obj). -

    -4 Complexity: Average case O(1), worst case O(size()). -

    -53 Remarks: This signature shall not participate in overload resolution unless -P is implicitly convertible to value_typestd::is_constructible<value_type, -P&&>::value is true. -

    -

    -
    template <class P>
-iterator insert(const_iterator hint, P&& obj);
-
    -
    -6 Requires: value_type is constructible from std::forward<P>(obj). -

    -7? Effects: -equivalent to return emplace_hint(hint, std::forward<P>(obj)). -Inserts obj converted to value_type if and only if there is no element in the container with -key equivalent to the key of value_type(obj). The iterator hint is a hint pointing to where the -search should start. -

    -8 Returns: An iterator that points to the element with key equivalent to the key of -value_type(obj). -

    -9 Complexity: Average case O(1), worst case O(size()). -

    -10? Remarks: This signature shall not participate in overload resolution unless -P is implicitly convertible to value_typestd::is_constructible<value_type, -P&&>::value is true. -

    -
    4. -
  4. Change [unord.multimap.modifers] around p. 1 as indicated: -
    -template <class P>
-iterator insert(P&& obj);
-
    -
    -1 Requires: value_type is constructible from std::forward<P>(obj). -

    -2 Effects: -equivalent to return emplace(std::forward<P>(obj)). -Inserts obj converted to value_type. -

    -3 Returns: An iterator that points to the element with key equivalent to the key of value_type(obj). -

    -4 Complexity: Average case O(1), worst case O(size()). -

    -53 Remarks: This signature shall not participate in overload resolution -unless P is implicitly convertible to value_typestd::is_constructible<value_type, -P&&>::value is true. -

    -
    -template <class P>
-iterator insert(const_iterator hint, P&& obj);
-
    -
    -6 Requires: value_type is constructible from std::forward<P>(obj). -

    -7? Effects: -equivalent to return emplace_hint(hint, std::forward<P>(obj)). -Inserts obj converted to value_type. The iterator hint is a hint pointing to where the search -should start. -

    -8 Returns: An iterator that points to the element with key equivalent to the key of value_type(obj). -

    -9 Complexity: Average case O(1), worst case O(size()). -

    -10? Remarks: This signature shall not participate in overload resolution -unless P is implicitly convertible to value_typestd::is_constructible<value_type, -P&&>::value is true. -

    -
    5. -
- - - - - - -
-

2007. Incorrect specification of return value for map<>::at()

-

Section: 23.4.4.3 [map.access] Status: C++11 - Submitter: Matt Austern Opened: 2010-11-01 Last modified: 2015-04-08

-

View all other issues in [map.access].

-

View all issues with C++11 status.

-

Discussion:

-

-In [map.access]/9, the Returns clause for map<Key, T>::at(x) says -that it returns "a reference to the element whose key is equivalent to x." That can't be right. -The signature for at() says that its return type is T, but the elements -of map<Key, T> have type pair<const K, T>. (I checked [unord.map.elem] -and found that its specification of at() is correct. This is a problem for map only.) -

- - -

Proposed resolution:

-

-Change the wording in [map.access]/9 so it's identical to what we already say for operator[], -which is unambiguous and correct. -

-

-Returns: A reference to the element whose key is equivalentmapped_type -corresponding to x in *this. -

- - - - - -
-

2008. Conflicting Error Conditions for packaged_task::operator()

-

Section: 30.6.9.1 [futures.task.members] Status: C++11 - Submitter: Pete Becker Opened: 2010-06-21 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

View all issues with C++11 status.

-

Discussion:

-

-The Throws clause for packaged_task::operator() says that it throws "a -future_error exception object if there is no associated asynchronous -state or the stored task has already been invoked." However, the Error -Conditions clause does not define an error condition when the stored task has -already been invoked, only when the associated state is already ready (i.e. the -invocation has completed). -

- -

[2011-02-17 Anthony provides an alternative resolution]

- - -

Previous proposed resolution:

- -

-Change the first bullet item in 30.6.9.1 [futures.task.members] /22: -

- -
-void operator()(ArgTypes... args);
-
-
-

-20 ... -

-

-21 ... -

-

-22 Error conditions: -

-
    -
  • -promise_already_satisfied if the associated asynchronous state is -already ready operator() has already been called. -
    • -
  • -no_state if *this has no associated asynchronous state. -
    • -
-
-
- -

[Adopted at Madrid, 2011-03]

- - - - -

Proposed resolution:

-
    -
  1. -

    -Change the first bullet item in 30.6.9.1 [futures.task.members] p. 17: -

    - -
    -void operator()(ArgTypes... args);
-
    -
    -

    -15 ... -

    -

    -16 ... -

    -

    -17 Error conditions: -

    -
      -
    • -promise_already_satisfied if the associated asynchronous state is already -readystored task has already been invoked. -
      • -
    • -no_state if *this has no associated asynchronous state. -
      • -
    -
    -
    -
    2. - -
  2. -

    -Change the first bullet item in 30.6.9.1 [futures.task.members] p. 21: -

    - -
    -void make_ready_at_thread_exit(ArgTypes... args);
-
    -
    -

    -19 ... -

    -

    -20 ... -

    -

    -21 Error conditions: -

    -
      -
    • -promise_already_satisfied if the associated asynchronous state already has a stored value or -exceptionstored task has already been invoked. -
      • -
    • -no_state if *this has no associated asynchronous state. -
      • -
    -
    -
    - -
    3. -
- - - - - - -
-

2009. Reporting out-of-bound values on numeric string conversions

-

Section: 21.5 [string.conversions] Status: C++14 - Submitter: Alisdair Meredith Opened: 2010-07-19 Last modified: 2015-04-08

-

View all other issues in [string.conversions].

-

View all issues with C++14 status.

-

Discussion:

-

-The functions (w)stoi and (w)stof -are specified in terms of calling C library APIs for potentially wider -types. The integer and floating-point versions have subtly different -behaviour when reading values that are too large to convert. The -floating point case will throw out_of_bound if the read value -is too large to convert to the wider type used in the implementation, -but behaviour is undefined if the converted value cannot narrow to a -float. The integer case will throw out_of_bounds if the -converted value cannot be represented in the narrower type, but throws -invalid_argument, rather than out_of_range, if the -conversion to the wider type fails due to overflow. -

- -

-Suggest that the Throws clause for both specifications should be -consistent, supporting the same set of fail-modes with the matching set -of exceptions. -

- - - -

Proposed resolution:

-

-21.5p3 [string.conversions] -

- -
-int stoi(const string& str, size_t *idx = 0, int base = 10);
-long stol(const string& str, size_t *idx = 0, int base = 10);
-unsigned long stoul(const string& str, size_t *idx = 0, int base = 10);
-long long stoll(const string& str, size_t *idx = 0, int base = 10);
-unsigned long long stoull(const string& str, size_t *idx = 0, int base = 10);
-
- -
-

-... -

-

-3 Throws: invalid_argument if strtol, -strtoul, strtoll, or strtoull reports that no -conversion could be performed. Throws out_of_range if -strtol, strtoul, strtoll or -strtoull sets errno to ERANGE, or if -the converted value is outside the range of representable values for the -return type. -

-
-
- -

-21.5p6 [string.conversions] -

- -
-float stof(const string& str, size_t *idx = 0);
-double stod(const string& str, size_t *idx = 0);
-long double stold(const string& str, size_t *idx = 0);
-
- -
-

-... -

-

-6 Throws: invalid_argument if strtod or -strtold reports that no conversion could be performed. Throws -out_of_range if strtod or strtold sets -errno to ERANGE or if the converted value is -outside the range of representable values for the return type. -

-
-
- - - - - - -
-

2010. is_* traits for binding operations can't be meaningfully specialized

-

Section: 20.9.10.1 [func.bind.isbind] Status: C++14 - Submitter: Sean Hunt Opened: 2010-07-19 Last modified: 2015-04-08

-

View all other issues in [func.bind.isbind].

-

View all issues with C++14 status.

-

Discussion:

-

-20.9.10.1 [func.bind.isbind] says for is_bind_expression: -

- -

-Users may specialize this template to indicate that a type should be -treated as a subexpression in a bind call. -

- -

-But it also says: -

- -

-If T is a type returned from bind, -is_bind_expression<T> shall be publicly derived from -integral_constant<bool, true>, otherwise from -integral_constant<bool, false>. -

- -

-This means that while the user is free to specialize, any specialization -would have to be false to avoid violating the second -requirement. A similar problem exists for is_placeholder. -

- -

[ -2010 Batavia (post meeting session) -]

- -

-Alisdair recognises this is clearly a bug introduced by some wording he -wrote, the sole purpose of this metafunction is as a customization point -for users to write their own bind-expression types that participate -in the standard library bind protocol. The consensus was that this -should be fixed in Madrid, moved to Open. -

- -

[2011-05-13 Jonathan Wakely comments and provides proposed wording]

- - -

-The requirements are that is_bind_expression<T>::value is true when T -is a type returned from bind, false for any other type, except when -there's a specialization involving a user-defined type (N.B. 17.6.4.2.1 [namespace.std] -means we don't need to say e.g. is_bind_expression<string> is false.) -

-The obvious way to meet the requirements is for the primary template -to derive from integral_constant<bool, false> and for implementations -to provide specializations for the unspecified types returned from -bind. User-defined specializations can do whatever they like, as long -as is_bind_expression::value is sane. There's no reason to forbid -users from defining is_bind_expression<user_defined_type>::value=false -if that's what they want to do. -

-Similar reasoning applies to is_placeholder, but a further issue is -that 20.9.10.1 [func.bind.isbind] contains wording for is_placeholder but -contains no definition of it and the sub-clause name only refers to -is_bind_expression. The wording below proposes splitting paragraphs 3 -and 4 of 20.9.10.1 [func.bind.isbind] into a new sub-clause covering -is_placeholder. -

-If the template specializations added by the proposed wording are too -vague then they could be preceded by "for exposition only" comments -

- -

[2011-05-18 Daniel comments and provides some refinements to the P/R]

- - -

-Both bind-related type traits should take advantage of the -UnaryTypeTrait requirements. Additionally, the updated wording does not -imply that the implementation provides several specializations. Wording was -used similar to the specification of the uses_allocator type trait -(which unfortunately is not expressed in terms of BinaryTypeTrait requirements). -

- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Change 20.9.10.1 [func.bind.isbind] to:

    - -
    -namespace std {
-  template<class T> struct is_bind_expression; // see below
-    : integral_constant<bool, see below> { };
-}
-

    --1- is_bind_expression can be used to detect function objects generated by bind. bind -uses is_bind_expression to detect subexpressions. Users may specialize this template to indicate -that a type should be treated as a subexpression in a bind call. -

    --2- If T is a type returned from bind, is_bind_expression<T> shall -be publicly derived from integral_constant<bool, true>, otherwise from -integral_constant<bool, false>Instantiations of the is_bind_expression template -shall meet the UnaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition -that has a BaseCharacteristic of true_type if T is a type returned from bind, otherwise -it shall have a BaseCharacteristic of false_type. A program may specialize this template for a user-defined -type T to have a BaseCharacteristic of true_type to indicate that T should be treated -as a subexpression in a bind call.. -

    --3- is_placeholder can be used to detect the standard placeholders _1, _2, and so on. -bind uses is_placeholder to detect placeholders. Users may specialize this template to indicate -a placeholder type. -

    --4- If T is the type of std::placeholders::_J, is_placeholder<T> shall be -publicly derived from integral_constant<int, J>, otherwise from integral_constant<int, 0>. -

    -
    2. -

  2. Insert a new sub-clause immediately following sub-clause 20.9.10.1 [func.bind.isbind], the suggested -sub-clause tag is [func.bind.isplace]: -

    -

    20.8.9.1.? Class template is_placeholder [func.bind.isplace]

    -
    -namespace std {
-  template<class T> struct is_placeholder; // see below
-}
-

    --?- is_placeholder can be used to detect the standard placeholders _1, _2, and so on. -bind uses is_placeholder to detect placeholders. -

    --?- Instantiations of the is_placeholder template shall meet the UnaryTypeTrait requirements ([meta.rqmts]). -The implementation shall provide a definition that has a BaseCharacteristic of integral_constant<int, J> -if T is the type of std::placeholders::_J, otherwise it shall have a BaseCharacteristic of -integral_constant<int, 0>. A program may specialize this template for a user-defined type T -to have a BaseCharacteristic of integral_constant<int, N> with N > 0 -to indicate that T should be treated as a placeholder type. -

    -
    3. -
- - - - - -
-

2011. Unexpected output required of strings

-

Section: 21.4.8.9 [string.io] Status: C++14 - Submitter: James Kanze Opened: 2010-07-23 Last modified: 2015-04-08

-

View all other issues in [string.io].

-

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-

Discussion:

-

-What should the following code output? -

- -
-#include <string>
-#include <iostream>
-#include <iomanip>
-
-int main() 
-{ 
-   std::string test("0X1Y2Z"); 
-   std::cout.fill('*'); 
-   std::cout.setf(std::ios::internal, std::ios::adjustfield); 
-   std::cout << std::setw(8) << test << std::endl; 
-} 
-
- -

-I would expect "**0X1Y2Z", and this is what the compilers I have access -to (VC++, g++ and Sun CC) do. But according to the standard, it should be -"0X**1Y2Z": -

- -

-21.4.8.9 [string.io]/5: -

- -
-template<class charT, class traits, class Allocator>
-  basic_ostream<charT, traits>&
-    operator<<(basic_ostream<charT, traits>& os, const basic_string<charT,traits,Allocator>& str);
-

-Effects: Behaves as a formatted output function (27.7.3.6.1 [ostream.formatted.reqmts]). After constructing -a sentry object, if this object returns true when converted to a value of type bool, -determines padding as described in 22.4.2.2.2 [facet.num.put.virtuals], then inserts the resulting sequence of -characters seq as if by calling os.rdbuf()->sputn(seq, n), where n is the larger of -os.width() and str.size(); then calls os.width(0). -

-
- -

-22.4.2.2.2 [facet.num.put.virtuals]/5: -

- -
-

-[…] -

- -

-Stage 3: A local variable is initialized as -

- -
-fmtflags adjustfield= (flags & (ios_base::adjustfield));
-
- -

-The location of any padding is determined according to Table 88. -

- -

-If str.width() is nonzero and the number of charT's in the -sequence after stage 2 is less than str.width(), then enough fill -characters are added to the sequence at the position indicated for padding to -bring the length of the sequence to str.width(). str.width(0) -is called. -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Table 88 — Fill padding
StateLocation
adjustfield == ios_base::leftpad after
adjustfield == ios_base::rightpad before
adjustfield == internal and a sign occurs in the representationpad after the sign
adjustfield == internal and representation after stage 1 began with 0x or 0Xpad after x or X
otherwisepad before
- -
- -

-Although it's not 100% clear what "the sequence after stage 2" should mean here, -when there is no stage 2, the only reasonable assumption is that it is the -contents of the string being output. In the above code, the string being output -is "0X1Y2Z", which starts with "0X", so the padding should be -inserted "after x or X", and not before the string. I believe that this is a -defect in the standard, and not in the three compilers I tried. -

- -

[ -2010 Batavia (post meeting session) -]

- -

-Consensus that all known implementations are consistent, and disagree with the -standard. Preference is to fix the standard before implementations start trying -to conform to the current spec, as the current implementations have the preferred -form. Howard volunteered to drught for Madrid, move to Open. -

- -

[2011-03-24 Madrid meeting]

- - -

-Daniel Krügler volunteered to provide wording, interacting with Dietmar and -Bill. -

- -

[2011-06-24 Daniel comments and provides wording]

- - -

-The same problem applies to the output provided by const char* and similar -character sequences as of 27.7.3.6.4 [ostream.inserters.character] p. 5. and even for -single character output (!) as described in 27.7.3.6.4 [ostream.inserters.character] p. 1, -just consider the character value '-' where '-' is the sign character. In this case -Table 91 — "Fill padding" requires to pad after the sign, i.e. the output -for the program -

-
-#include <iostream>
-#include <iomanip>
-
-int main() 
-{ 
-   char c = '-'; 
-   std::cout.fill('*'); 
-   std::cout.setf(std::ios::internal, std::ios::adjustfield); 
-   std::cout << std::setw(2) << c << std::endl; 
-} 
-
- -

-According to the current wording this program should output "-*", but -all tested implementations output "*-" instead. - -

-I suggest to replace the reference to 22.4.2.2.2 [facet.num.put.virtuals] in all three places. -It is not very complicated to describe the padding rules for simple character sequences "inline". -A similar approach is used as for the money_put functions. -

- -

[ -2011 Bloomington -]

- - -

-Move to Review, the resolution seems correct but it would be nice if some factoring of the -common words were proposed. -

- -

[2012, Kona]

- -

-Moved to Tentatively Ready by the post-Kona issues processing subgroup. -

-

-While better factoring of the common words is desirable, it is also editorial and -should not hold up the progress of this issue. As the edits impact two distinct -clauses, it is not entirely clear what a better factoring should look like. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

-The new wording refers to the FDIS numbering. -

-
    -

  1. Change 21.4.8.9 [string.io]/5 as indicated:

    -
    -template<class charT, class traits, class Allocator>
-  basic_ostream<charT, traits>&
-    operator<<(basic_ostream<charT, traits>& os,
-               const basic_string<charT,traits,Allocator>& str);
-

    --5- Effects: Behaves as a formatted output function ([ostream.formatted.reqmts]). After constructing a sentry object, -if this object returns true when converted to a value of type bool, determines padding as described -in [facet.num.put.virtuals],follows: A charT character sequence is produced, initially consisting of -the elements defined by the range [str.begin(), str.end()). If str.size() is less than os.width(), -then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() -characters. If (os.flags() & ios_base::adjustfield) == ios_base::left is true, the fill characters -are placed after the character sequence; otherwise, they are placed before the character sequence. Tthen -inserts the resulting sequence of characters seq as if by calling os.rdbuf()->sputn(seq, n), where -n is the larger of os.width() and str.size(); then calls os.width(0). -

    -
    2. - -

  2. Change 27.7.3.6.4 [ostream.inserters.character]/1 as indicated (An additional editorial -fix is suggested for the first prototype declaration):

    -
    -template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          charT c});
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          char c);
-// specialization
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         char c);
-// signed and unsigned
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         signed char c);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         unsigned char c);
-

    --1- Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out. -After a sentry object is constructed it inserts characters. In case c has type char and the -character type of the stream is not char, then the character to be inserted is out.widen(c); -otherwise the character is c. Padding is determined as described in [facet.num.put.virtuals]follows: -A character sequence is produced, initially consisting of the insertion character. If out.width() is greater -than one, then enough copies of out.fill() are added to this sequence as necessary to pad to a width of -out.width() characters. If (out.flags() & ios_base::adjustfield) == ios_base::left is true, -the fill characters are placed after the insertion character; otherwise, they are placed before the insertion -character. width(0) is called. The insertion character and any required padding are -inserted into out; then calls os.width(0). -

    -
    3. - -

  3. Change 27.7.3.6.4 [ostream.inserters.character]/5 as indicated:

    -
    -template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          const charT* s);
-template<class charT, class traits>
-  basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
-                                          const char* s);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const char* s);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const signed char* s);
-template<class traits>
-  basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
-                                         const unsigned char* s);
-

    -[…] -

    --5- Padding is determined as described in [facet.num.put.virtuals]. The n characters starting at s -are widened using out.widen ([basic.ios.members])follows: A character sequence is produced, initially -consisting of the elements defined by the n characters starting at s widened using -out.widen ([basic.ios.members]). If n is less than out.width(), then enough copies of -out.fill() are added to this sequence as necessary to pad to a width of out.width() characters. -If (out.flags() & ios_base::adjustfield) == ios_base::left is true, the fill characters are -placed after the character sequence; otherwise, they are placed before the character sequence. The -widened characters and any required padding are inserted into out. Calls width(0). -

    -
    4. -
- - - - - - -
-

2012. Associative maps should insert pair, not tuple

-

Section: 23.4 [associative] Status: Resolved - Submitter: Paolo Carlini Opened: 2010-10-29 Last modified: 2015-04-08

-

View other active issues in [associative].

-

View all other issues in [associative].

-

View all issues with Resolved status.

-

Discussion:

-

-I'm seeing something strange in the paragraphs 23.4.4.4 [map.modifiers] and 23.4.5.3 [multimap.modifiers]: -they both talk about tuple<const key_type, mapped_type> but I think they -should be talking about pair<const key_type, mapped_type> because, among -other reasons, a tuple is not convertible to a pair. If I replace tuple -with pair everything makes sense to me. -

-The proposed resolution is obvious. -

- -

[ -2010-11-07 Daniel comments -]

- - -

-This is by far not the only necessary fix within both sub-clauses. For details see the 2010-10-29 comment in -2005. -

- -

[2011-03-24 Madrid meeting]

- - -

-Paolo: Don't think we can do it now. -

-Daniel K: Agrees. -

- -

[ -2011 Bloomington -]

- - -

-Consensus that this issue will be resolved by 2005, but held open until that issue is resolved. -

- - - -

Proposed resolution:

-

-Apply the resolution proposed by the 2010-10-29 comment in 2005. -

- - - - - -
-

2013. Do library implementers have the freedom to add constexpr?

-

Section: 17.6.5.6 [constexpr.functions] Status: C++14 - Submitter: Matt Austern Opened: 2010-11-12 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

Suppose that a particular function is not tagged as constexpr in the standard, -but that, in some particular implementation, it is possible to write it within -the constexpr constraints. If an implementer tags such a function as constexpr, -is that a violation of the standard or is it a conforming extension?

- -

There are two questions to consider. First, is this allowed under the -as-if rule? Second, if it does not fall under as-if, is there -(and should there be) any special license granted to implementers -to do this anyway, sort of the way we allow elision of copy constructors -even though it is detectable by users?

- -

I believe that this does not fall under "as-if", so implementers -probably don't have that freedom today. I suggest changing the WP -to grant it. Even if we decide otherwise, however, I suggest that -we make it explicit.

- -

[ -2011 Bloomington -]

- - -

-General surprise this was not already in 'Ready' status, and so moved. -

- -

[ -2012 Kona -]

- - -

-Some concern expressed when presented to full committee for the vote to WP status -that this issue had been resolved without sufficient thought of the consequences -for diverging library implementations, as users may use SFINAE to observe -different behavior from otherwise identical code. Issue moved back to Review -status, and will be discussed again in Portland with a larger group. - -Note for Portland: John Spicer has agreed to represent Core's concerns during -any such discussion within LWG. -

- -

[2013-09 Chicago]

- - -

-Straw poll: LWG strongly favoured to remove from implementations the freedom to add constexpr. -

-

-Matt provides new wording. -

- -

[2013-09 Chicago]

- - -

-Move to Immediate after reviewing Matt's new wording, apply the new wording to the Working Paper. -

- - - -

Proposed resolution:

-

In 17.6.5.6 [constexpr.functions], change paragraph 1 to:

- -

-This standard explicitly requires that certain standard library functions -are constexpr [dcl.constexpr]. -An implementation shall not declare any standard library function signature as constexpr -except for those where it is explicitly required. -Within any header that provides any non-defining declarations of constexpr -functions or constructors an implementation shall provide corresponding definitions. -

- - - - - - -
-

2014. More restrictions on macro names

-

Section: 17.6.4.3.1 [macro.names] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2010-11-16 Last modified: 2015-04-08

-

View all other issues in [macro.names].

-

View all issues with C++11 status.

-

Discussion:

-

-A program is currently forbidden to use keywords as macro names. This restriction should be strengthened to include all identifiers -that could be used by the library as attribute-tokens (for example noreturn, which is used by header <cstdlib>) -and the special identifiers introduced recently for override control (these are not currently used in the library public interface, -but could potentially be used by the implementation or in future revisions of the library). -

-

[2011-02-10 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

Modify 17.6.4.3.1 [macro.names] paragraph 2 as follows:

- -

-A translation unit shall not #define or #undef names -lexically identical to keywords, to the identifiers listed in Table -X [Identifiers with special meaning], or to the attribute-tokens -described in clause 7.6 [dcl.attr]. -

- - - - - - -
-

2015. Incorrect pre-conditions for some type traits

-

Section: 20.10.4 [meta.unary] Status: C++14 - Submitter: Nikolay Ivchenkov Opened: 2010-11-08 Last modified: 2015-04-08

-

View all other issues in [meta.unary].

-

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-

Discussion:

-

According to N3126 ‑ 3.9/9,

- -

"Scalar types, trivial class types (Clause 9), arrays of such types -and cv‑qualified versions of these types (3.9.3) are collectively -called trivial types."

- -

Thus, an array (possibly of unknown bound) can be trivial type, non‑trivial type, -or an array type whose triviality cannot be determined because its element type is incomplete.

- -

According to N3126 ‑ Table 45, preconditions for std::is_trivial are -defined as follows:

- -

"T shall be a complete type, (possibly cv-qualified) void, -or an array of unknown bound"

- -

It seems that "an array of unknown bound" should be changed to "an -array of unknown bound of a complete element type". Preconditions for -some other templates (e.g., std::is_trivially_copyable, -std::is_standard_layout, std::is_pod, and std::is_literal_type) should -be changed similarly.

- -

On the other hand, some preconditions look too restrictive. For -example, std::is_empty and std::is_polymorphic might accept any -incomplete non‑class type.

- -

[2011-02-18: Daniel provides wording proposal]

- - -

-While reviewing the individual preconditions I could find three different groups of -either too weakening or too strengthening constraints: -

-
    -
  1. is_empty/is_polymorphic/is_abstract/has_virtual_destructor:
    - -

    These traits can only apply for non‑union class types, otherwise the result must -always be false

    -
    2. - -
  2. is_base_of:
    - -

    Similar to the previous bullet, but the current wording comes already near to that ideal, -it only misses to add the non‑union aspect.

    -
    3. - -
  3. is_trivial/is_trivially_copyable/is_standard_layout/is_pod/is_literal_type:
    - -

    These traits always require that std::remove_all_extents<T>::type to be cv void or -a complete type.

    -
    4. -
- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

-
    -
  1. -

    -Modify the pre-conditions of the following type traits in 20.10.4.3 [meta.unary.prop], Table 48 — Type property predicates: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 48 — Type property predicates
    TemplateConditionPreconditions
    ...
    template <class T>
    -struct is_trivial;    		T is a trivial type (3.9)remove_all_extents<T>::type
    -shall be a complete type, or (possibly
    -cv-qualified) void, or an array of
    -unknown bound    .
    template <class T>
    -struct is_trivially_copyable;    		T is a trivially copyable
    -type (3.9)    		remove_all_extents<T>::type
    -shall be a complete type, or (possibly
    -cv-qualified) void, or an array of
    -unknown bound    .
    template <class T>
    -struct is_standard_layout;    		T is a standard-layout
    -type (3.9)    		remove_all_extents<T>::type
    -shall be a complete type, or (possibly
    -cv-qualified) void, or an array of
    -unknown bound    .
    template <class T>
    -struct is_pod;    		T is a POD type (3.9)remove_all_extents<T>::type
    -shall be a complete type, or (possibly
    -cv-qualified) void, or an array of
    -unknown bound    .
    template <class T>
    -struct is_literal_type;    		T is a literal type (3.9)remove_all_extents<T>::type
    -shall be a complete type, or (possibly
    -cv-qualified) void, or an array of
    -unknown bound    .
    template <class T>
    -struct is_empty;    		T is a class type, but not a
    -union type, with no
    -non-static data members
    -other than bit-fields of
    -length 0, no virtual
    -member functions, no
    -virtual base classes, and
    -no base class B for which
    -is_empty<B>::value is
    -false.    		T shall be a complete type,
    -(possibly cv-qualified) void, or
    -an array of unknown bound    If T
    -is a non‑union class type, T
    -shall be a complete type    .
    template <class T>
    -struct is_polymorphic;    		T is a polymorphic
    -class (10.3)    		T shall be a complete type,
    -type, (possibly cv-qualified) void, or
    -an array of unknown bound    If T
    -is a non‑union class type, T
    -shall be a complete type    .
    template <class T>
    -struct is_abstract;    		T is an abstract
    -class (10.4)    		T shall be a complete type,
    -type, (possibly cv-qualified) void, or
    -an array of unknown bound    If T
    -is a non‑union class type, T
    -shall be a complete type    .
    ...
    template <class T>
    -struct has_virtual_destructor;    		T has a virtual
    -destructor (12.4)    		T shall be a complete type,
    -(possibly cv-qualified) void, or
    -an array of unknown bound    If T
    -is a non‑union class type, T
    -shall be a complete type    .
    -
    - -
    2. - -
  2. -

    -Modify the pre-conditions of the following type traits in 20.10.6 [meta.rel], Table 50 — Type relationship predicates: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 50 — Type relationship predicates
    TemplateConditionComments
    ...
    template <class Base, class
    -Derived>
    -struct is_base_of;    		Base is a base class of
    -Derived (10) without
    -regard to cv-qualifiers
    -or Base and Derived
    -are not unions and
    -name the same class
    -type without regard to
    -cv-qualifiers    		If Base and Derived are
    -non‑union class types
    -and are different types
    -(ignoring possible cv-qualifiers)
    -then Derived shall be a complete
    -type. [ Note: Base classes that
    -are private, protected, or
    -ambigious are, nonetheless, base
    -classes. — end note ]
    ...
    -
    -
    3. -
- - - - - -
-

2016. Allocators must be no-throw swappable

-

Section: 17.6.3.5 [allocator.requirements] Status: WP - Submitter: Daniel Krügler Opened: 2010-11-17 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

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-

Discussion:

-

-During the Batavia meeting it turned out that there is a definition -hole for types satisfying the Allocators requirements: The problem -became obvious when it was discussed whether all swap functions -of Containers with internal data handles can be safely tagged -with noexcept or not. While it is correct that the implicit -swap function of an allocator is required to be a no-throw -operation (because move/copy-constructors and assignment operators are -required to be no-throw functions), there are no such requirements -for specialized swap overloads for a particular allocator. -

-But this requirement is essential because the Containers are -required to support swappable Allocators, when the value -allocator_traits<>::propagate_on_container_swap evaluates -to true. -

-

[2011-02-10 Alberto, Daniel, and Pablo collaborated on the proposed wording]

- -

-The proposed resolution (based on N3225) attempts to solve the following problems: -

-
    -
  1. Table 44 — Allocator requirements, expression rows -X::propagate_on_container_copy_assignment, X::propagate_on_container_move_assignment, and -X::propagate_on_container_swap only describe operations, but no requirements. In fact, if and only -if these compile-time predicates evaluate to true, the additional requirements -CopyAssignable, no-throw MoveAssignable, and no-throw lvalue Swappable, -respectively, are imposed on the allocator types.
    2. -
  2. 23.2.1 [container.requirements.general] p. 9 misses to refer to the correct swap conditions: The current wording does not relate to -17.6.3.2 [swappable.requirements] as it should and omits to mention that lvalues shall be swapped. Additional there is one -situation described twice in p. 8 and p. 9 (undefined behaviour unless a.get_allocator() == b.get_allocator() -or allocator_traits<allocator_type>::propagate_on_container_swap::value == true), which should be cleaned up.
    3. -
- -

[2011-04-08 Pablo comments]

- -

-I'm implementing a version of list now and I actually do find it impossible to write an exception-safe assignment -operator unless I can assume that allocator assignment does not throw. (The problem is that I use a sentinel node -and I need to allocate a new sentinel using the new allocator without destroying the old one -- then swap the -allocator and sentinel pointer in atomically, without risk of an exception leaving one inconsistent with the other. -

-Please update the proposed resolution to add the nothrow requirement to copy-assignment. -

- -

[2014-02-14 Issaquah: Move to Ready]

- -

-Fix a couple of grammar issues related to calling swap and move to Ready. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Adapt the following three rows from Table 44 — Allocator requirements: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 44 — Allocator requirements
    -Expression - -Return type - -Assertion/note
    pre-/post-condition -    		 -Default -
    X::propagate_on_container_copy_assignmentIdentical to or derived from true_type
    -or false_type    		true_type only if an allocator of type X should be copied
    -when the client container is copy-assigned. See Note B, below.    		false_type
    X::propagate_on_container_move_assignmentIdentical to or derived from true_type
    -or false_type    		true_type only if an allocator of type X should be moved
    -when the client container is move-assigned. See Note B, below.    		false_type
    X::propagate_on_container_swapIdentical to or derived from true_type
    -or false_type    		true_type only if an allocator of type X should be swapped
    -when the client container is swapped. See Note B, below.    		false_type
    -
    - - -
    2. - -
  2. -

    Following 17.6.3.5 [allocator.requirements] p. 3 insert a new normative paragraph:

    - -

    -Note B: If X::propagate_on_container_copy_assignment::value is true, X shall -satisfy the CopyAssignable requirements (Table 39 [copyassignable]) and the copy -operation shall not throw exceptions. If X::propagate_on_container_move_assignment::value is -true, X shall satisfy the MoveAssignable requirements (Table 38 [moveassignable]) -and the move operation shall not throw exceptions. If X::propagate_on_container_swap::value is -true, lvalues of X shall be swappable (17.6.3.2 [swappable.requirements]) and the swap -operation shall not throw exceptions. -

    -
    3. - -
  3. -

    Modify 23.2.1 [container.requirements.general] p. 8 and p. 9 as indicated:

    - -

    -8 - [..] The allocator may be replaced only via assignment or swap(). Allocator replacement is -performed by copy assignment, move assignment, or swapping of the allocator only if -allocator_traits<allocator_type>::propagate_on_container_copy_assignment::value, -allocator_traits<allocator_type>::propagate_on_container_move_assignment::value, -or allocator_traits<allocator_type>::propagate_on_container_swap::value is true -within the implementation of the corresponding container operation. The behavior of a call to -a container's swap function is undefined unless the objects being swapped have allocators that compare -equal or allocator_traits<allocator_type>::propagate_on_container_swap::value is true. In all -container types defined in this Clause, the member get_allocator() returns a copy of the allocator -used to construct the container or, if that allocator has been replaced, a copy of the most recent replacement. -

    -9 - The expression a.swap(b), for containers a and b of a standard container type -other than array, shall exchange the values of a and b without invoking any move, -copy, or swap operations on the individual container elements. Lvalues of aAny Compare, -Pred, or Hash objectstypes belonging to a and b shall be swappable -and shall be exchanged by unqualified calls to non-member calling swap -as described in 17.6.3.2 [swappable.requirements]. If allocator_traits<allocator_type>::propagate_on_container_swap::value -is true, then lvalues of allocator_type shall be swappable and the allocators of a and -b shall also be exchanged using an unqualified call to non-memberby calling -swap as described in 17.6.3.2 [swappable.requirements]. Otherwise, -theythe allocators shall not be swapped, and the behavior is undefined unless -a.get_allocator() == b.get_allocator(). Every iterator referring to an element in one container before -the swap shall refer to the same element in the other container after the swap. It is unspecified whether an -iterator with value a.end() before the swap will have value b.end() after the swap. -

    -
    4. -
- - - - - - -
-

2017. std::reference_wrapper makes incorrect usage of std::result_of

-

Section: 20.9.4 [refwrap] Status: C++11 - Submitter: Nikolay Ivchenkov Opened: 2010-11-15 Last modified: 2015-04-08

-

View all other issues in [refwrap].

-

View all issues with C++11 status.

-

Discussion:

-

-std::reference_wrapper's function call operator uses wrong -type encoding for rvalue-arguments. An rvalue-argument of type T must -be encoded as T&&, not as just T. -

-
-#include <functional>
-#include <iostream>
-#include <string>
-#include <type_traits>
-#include <utility>
-
-template <class F, class... Types>
-     typename std::result_of<F (Types...)>::type
-         f1(F f, Types&&... params)
-{
-     return f(std::forward<Types...>(params...));
-}
-
-template <class F, class... Types>
-     typename std::result_of<F (Types&&...)>::type
-         f2(F f, Types&&... params)
-{
-     return f(std::forward<Types...>(params...));
-}
-
-struct Functor
-{
-     template <class T>
-         T&& operator()(T&& t) const
-     {
-         return static_cast<T&&>(t);
-     }
-};
-
-int main()
-{
-     typedef std::string const Str;
-     std::cout << f1(Functor(), Str("1")) << std::endl; // (1)
-     std::cout << f2(Functor(), Str("2")) << std::endl; // (2)
-}
-
-

-Lets consider the function template f1 (which is similar to -std::reference_wrapper's function call operator). In the invocation -(1) F is deduced as 'Functor' and Types is deduced as type sequence -which consists of one type 'std::string const'. After the substitution -we have the following equivalent: -

-
-template <>
-    std::result_of<F (std::string const)>::type
-        f1<Functor, std::string const>(Functor f, std::string const && params)
-{
-    return f(std::forward<const std::string>(params));
-}
-
-

-The top-level cv-qualifier in the parameter type of 'F (std::string const)' is removed, so we have -

-
-template <>
-    std::result_of<F (std::string)>::type
-        f1<Functor, std::string const>(Functor f, std::string const && params)
-{
-    return f(std::forward<const std::string>(params));
-}
-
-

-Let r be an rvalue of type 'std::string' and cr be an rvalue of type -'std::string const'. The expression Str("1") is cr. The corresponding -return type for the invocation -

-
-Functor().operator()(r)
-
-

-is 'std::string &&'. The corresponding return type for the invocation -

-
-Functor().operator()(cr)
-
-

-is 'std::string const &&'. -

-std::result_of<Functor (std::string)>::type is the same type as the -corresponding return type for the invocation Functor().operator()(r), -i.e. it is 'std::string &&'. As a consequence, we have wrong reference -binding in the return statement in f1. -

-Now lets consider the invocation (2) of the function template f2. When -the template arguments are substituted we have the following equivalent: -

-
-template <>
-    std::result_of<F (std::string const &&)>::type
-        f2<Functor, std::string const>(Functor f, std::string const && params)
-{
-    return f(std::forward<const std::string>(params));
-}
-
-

-std::result_of<F (std::string const &&)>::type is the same type as -'std::string const &&'. This is correct result. -

-

[ -2010-12-07 Jonathan Wakely comments and suggests a proposed resolution -]

- - -

-I agree with the analysis and I think this is a defect in the -standard, it would be a shame if it can't be fixed. -

-In the following example one would expect f(Str("1")) and -std::ref(f)(Str("2")) to be equivalent but the current wording makes -the invocation through reference_wrapper ill-formed: -

-
-#include <functional>
-#include <string>
-
-struct Functor
-{
-   template <class T>
-       T&& operator()(T&& t) const
-       {
-           return static_cast<T&&>(t);
-       }
-};
-
-int main()
-{
-   typedef std::string const Str;
-   Functor f;
-   f( Str("1") );
-   std::ref(f)( Str("2") );  // error
-}
-
- -

[ -2010-12-07 Daniel comments and refines the proposed resolution -]

- - -

-There is one further defect in the usage of result_of within -reference_wrapper's function call operator: According to 20.9.4.4 [refwrap.invoke] p. 1 -the invokable entity of type T is provided as lvalue, but -result_of is fed as if it were an rvalue. This does not only lead to -potentially incorrect result types, but it will also have the effect that -we could never use the function call operator with a function type, -because the type encoding used in result_of would form an invalid -function type return a function type. The following program demonstrates -this problem: -

-
-#include <functional>
-
-void foo(int) {}
-
-int main()
-{
-   std::ref(foo)(0);  // error
-}
-

-The correct solution is to ensure that T becomes T& -within result_of, which solves both problems at once. -

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-
    -
  1. -

    -Change the synopsis in 20.9.4 [refwrap] paragraph 1: -

    - -
    -namespace std {
-  template <class T> class reference_wrapper
-  {
-  public :
-    [...]
-    // invocation
-    template <class... ArgTypes>
-    typename result_of<T&(ArgTypes&&...)>::type
-    operator() (ArgTypes&&...) const;
-  };
-}
-
    -
    2. - -
  2. -

    -Change the signature in 20.9.4.4 [refwrap.invoke] before paragraph 1 -

    - -
    -template <class... ArgTypes>
-typename result_of<T&(ArgTypes&&... )>::type
-operator()(ArgTypes&&... args) const;
-

    -1 Returns: INVOKE(get(), std::forward<ArgTypes>(args)...). (20.8.2) -

    -
    3. -
- - - - - -
-

2018. [CD] regex_traits::isctype Returns clause is wrong

-

Section: 28.7 [re.traits] Status: C++14 - Submitter: Jonathan Wakely Opened: 2010-11-16 Last modified: 2015-04-08

-

View all other issues in [re.traits].

-

View all issues with C++14 status.

-

Discussion:

- -

Addresses GB 10

- -

28.7 [re.traits] p. 12 says:

- -

-returns true if f bitwise or'ed with the result of calling -lookup_classname with an iterator pair that designates the character -sequence "w" is not equal to 0 and c == '_' -

- -

-If the bitmask value corresponding to "w" has a non-zero value (which -it must do) then the bitwise or with any value is also non-zero, and -so isctype('_', f) returns true for any f. Obviously this is wrong, -since '_' is not in every ctype category. -

- -

-There's a similar problem with the following phrases discussing the -"blank" char class. -

- -

[2011-05-06: Jonathan Wakely comments and provides suggested wording]

- - -

-DR 2019 added isblank support to <locale> which simplifies the -definition of regex_traits::isctype by removing the special case for the "blank" class. -

-My suggestion for 2018 is to add a new table replacing the lists of -recognized names in the Remarks clause of regex_traits::lookup_classname. -I then refer to that table in the Returns clause of regex_traits::isctype -to expand on the "in an unspecified manner" wording which is too vague. The conversion -can now be described using the "is set" term defined by 17.5.2.1.3 [bitmask.types] and -the new table to convey the intented relationship between e.g. -[[:digit:]] and ctype_base::digit, which is not actually stated in the -FDIS. -

-The effects of isctype can then most easily be described in code, -given an "exposition only" function prototype to do the not-quite-so-unspecified conversion -from char_class_type to ctype_base::mask. -

-The core of LWG 2018 is the "bitwise or'ed" wording which gives the -wrong result, always evaluating to true for all values of f. That is -replaced by the condition (f&x) == x where x is the result of calling -lookup_classname with "w". I believe that's necessary, because the -"w" class could be implemented by an internal "underscore" class i.e. -x = _Alnum|_Underscore in which case (f&x) != 0 would give the wrong -result when f==_Alnum. -

-The proposed resolution also makes use of ctype::widen which addresses -the problem that the current wording only talks about "w" and '_' which assumes -charT is char. There's still room for improvement here: -the regex grammar in 28.13 [re.grammar] says that the class names in the -table should always be recognized, implying that e.g. U"digit" should -be recognized by regex_traits<char32_t>, but the specification of -regex_traits::lookup_classname doesn't cover that, only mentioning -char and wchar_t. Maybe the table should not distinguish narrow and -wide strings, but should just have one column and add wording to say -that regex_traits widens the name as if by using use_facet<ctype<charT>>::widen(). -

-Another possible improvement would be to allow additional -implementation-defined extensions in isctype. An implementation is -allowed to support additional class names in lookup_classname, e.g. -[[:octdigit:]] for [0-7] or [[:bindigit:]] for [01], but the current -definition of isctype provides no way to use them unless ctype_base::mask -also supports them. -

- -

[2011-05-10: Alberto and Daniel perform minor fixes in the P/R]

- - -

[ -2011 Bloomington -]

- - -

-Consensus that this looks to be a correct solution, and the presentation as a table is a big improvement. -

- -

-Concern that the middle section wording is a little muddled and confusing, Stefanus volunteered to reword. -

- -

[ -2013-09 Chicago -]

- - -

-Stefanus provides improved wording (replaced below) -

- -

[ -2013-09 Chicago -]

- - -

-Move as Immediate after reviewing Stefanus's revised wording, apply the new wording to the Working Paper. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Modify 28.7 [re.traits] p. 10 as indicated:

    -
    -template <class ForwardIterator>
-  char_class_type lookup_classname(
-    ForwardIterator first, ForwardIterator last, bool icase = false) const;
-

    --9- Returns: an unspecified value that represents the character classification named by the character -sequence designated by the iterator range [first,last). If the parameter icase is true then the -returned mask identifies the character classification without regard to the case of the characters being -matched, otherwise it does honor the case of the characters being matched.(footnote 335) The value returned shall -be independent of the case of the characters in the character sequence. If the name is not recognized -then returns a value that compares equal to 0. -

    --10- Remarks: For regex_traits<char>, at least the names "d", "w", "s", "alnum", "alpha", "blank", -"cntrl", "digit", "graph", "lower", "print", "punct", "space", "upper" and "xdigit"narrow character -names in Table X shall be recognized. For regex_traits<wchar_t>, at least the names L"d", L"w", -L"s", L"alnum", L"alpha", L"blank", L"cntrl", L"digit", L"graph", L"lower", L"print", L"punct", L"space", L"upper" and -L"xdigit"wide character names in Table X shall be recognized. -

    -
    2. - -

  2. Modify 28.7 [re.traits] p. 12 as indicated:

    -
    -bool isctype(charT c, char_class_type f) const;
-

    --11- Effects: Determines if the character c is a member of the character classification represented by f. -

    --12- Returns: Converts f into a value m of type std::ctype_base::mask in an - unspecified manner, and returns true if use_facet<ctype<charT> >(getloc()).is(m, c) is true. Otherwise - returns true if f bitwise or'ed with the result of calling lookup_classname with an iterator pair that - designates the character sequence "w" is not equal to 0 and c == '_', or if f bitwise or'ed - with the result of calling lookup_classname with an iterator pair that designates the character sequence "blank" - is not equal to 0 and c is one of an implementation-defined subset of the characters for - which isspace(c, getloc()) returns true, otherwise returns false. -Given an exposition-only function prototype

    -
    -
-  template<class C>
-   ctype_base::mask convert(typename regex_traits<C>::char_class_type f);
-
-
    -

    -that returns a value in which each ctype_base::mask value corresponding to a value in f named in Table X is set, -then the result is determined as if by: -

    -
    -
-ctype_base::mask m = convert<charT>(f);
-const ctype<charT>& ct = use_facet<ctype<charT>>(getloc());
-if (ct.is(m, c)) {
-  return true;
-} else if (c == ct.widen('_')) {
-  charT w[1] = { ct.widen('w') };
-  char_class_type x = lookup_classname(w, w+1);
-  
-  return (f&x) == x;
-} else {
-  return false;
-} 
-
-
    -

    [Example:

    - -
    
-regex_traits<char> t;
-string d("d");
-string u("upper");
-regex_traits<char>::char_class_type f;
-f = t.lookup_classname(d.begin(), d.end());
-f |= t.lookup_classname(u.begin(), u.end());
-ctype_base::mask m = convert<char>(f); // m == ctype_base::digit|ctype_base::upper
-
    -

    — end example]

    -

    [Example:

    -
    
-regex_traits<char> t;
-string w("w");
-regex_traits<char>::char_class_type f;
-f = t.lookup_classname(w.begin(), w.end());
-t.isctype('A', f); // returns true
-t.isctype('_', f); // returns true
-t.isctype(' ', f); // returns false
-
    -

    — end example]

    -
    -
    3. - -

  3. At the end of 28.7 [re.traits] add a new "Table X — Character class names and corresponding ctype masks":

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table X — Character class names and corresponding ctype masks
    Narrow character nameWide character nameCorresponding ctype_base::mask value
    "alnum"L"alnum"ctype_base::alnum
    "alpha"L"alpha"ctype_base::alpha
    "blank"L"blank"ctype_base::blank
    "cntrl"L"cntrl"ctype_base::cntrl
    "digit"L"digit"ctype_base::digit
    "d"L"d"ctype_base::digit
    "graph"L"graph"ctype_base::graph
    "lower"L"lower"ctype_base::lower
    "print"L"print"ctype_base::print
    "punct"L"punct"ctype_base::punct
    "space"L"space"ctype_base::space
    "s"L"s"ctype_base::space
    "upper"L"upper"ctype_base::upper
    "w"L"w"ctype_base::alnum
    "xdigit"L"xdigit"ctype_base::xdigit
    -
    -
    4. -
- - - - - - -
-

2019. isblank not supported by std::locale

-

Section: 22.3.3.1 [classification] Status: C++11 - Submitter: Jonathan Wakely Opened: 2010-11-16 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

C99 added isblank and iswblank to <locale.h> but <locale> does not -provide any equivalent.

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 6 votes. -

- - -

Proposed resolution:

-

Add to 22.3.3.1 [classification] synopsis:

-
-template <class charT> bool isgraph (charT c, const locale& loc);
-template <class charT> bool isblank (charT c, const locale& loc);
-
- -

Add to 22.4.1 [category.ctype] synopsis:

- -
-static const mask xdigit = 1 << 8;
-static const mask blank = 1 << 9;
-static const mask alnum = alpha | digit;
-static const mask graph = alnum | punct;
-
- - - - - - -
-

2020. Time utility arithmetic constexpr functions have invalid effects

-

Section: 20.12.5.5 [time.duration.nonmember] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-12-06 Last modified: 2015-04-08

-

View all other issues in [time.duration.nonmember].

-

View all issues with C++11 status.

-

Discussion:

-

-As of issue 1171 several time-utility functions have been marked constexpr. -Alas this was done without adapting the corresponding return elements, which has the effect that -none of current arithmetic functions of class template duration marked as constexpr -can ever be constexpr functions (which makes them ill-formed, no diagnostics required as -of recent core rules), because they invoke a non-constant expression, e.g. 20.12.5.5 [time.duration.nonmember]/2: -

-
-template <class Rep1, class Period1, class Rep2, class Period2>
-constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>{>}::type
-operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-
-2 Returns: CD(lhs) += rhs.
-
-

-The real problem is, that we cannot defer to as-if rules here: The returns element -specifies an indirect calling contract of a potentially user-defined function. This cannot be -the += assignment operator of such a user-defined type, but must be the corresponding -immutable binary operator+ (unless we require that += shall be an immutable function -which does not really makes sense). -

-

[2011-02-17 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - - -

Proposed resolution:

-

-The suggested wording changes are against the working draft N3242. Additional to the normative wording -changes some editorial fixes are suggested. -

-
    -
  1. -

    In 20.12.5.5 [time.duration.nonmember], change the following arithmetic function specifications as follows:

    -
    -template <class Rep1, class Period1, class Rep2, class Period2>
-constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>{>}::type
-operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-

    -2 Returns: CD(lhs) += rhsCD(CD(lhs).count() + CD(rhs).count()). -

    - -
    -template <class Rep1, class Period1, class Rep2, class Period2>
-constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>{>}::type
-operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-

    -3 Returns: CD(lhs) -= rhsCD(CD(lhs).count() - CD(rhs).count()). -

    - -
    -template <class Rep1, class Period, class Rep2>
-constexpr duration<typename common_type<Rep1, Rep2>::type, Period>
-operator*(const duration<Rep1, Period>& d, const Rep2& s);
-

    -4 Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible -to CR(Rep1, Rep2). -

    -5 Returns: duration<CR(Rep1, Rep2), Period>(d) *= sCD(CD(d).count() * s). -

    - -

    -[...] -

    - -
    -template <class Rep1, class Period, class Rep2>
-constexpr duration<typename common_type<Rep1, Rep2>::type, Period>
-operator/(const duration<Rep1, Period>& d, const Rep2& s);
-

    -8 Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible -to CR(Rep1, Rep2) and Rep2 is not an instantiation of duration. -

    -9 Returns: duration<CR(Rep1, Rep2), Period>(d) /= sCD(CD(d).count() / s). -

    - -

    -[...] -

    - -
    -template <class Rep1, class Period, class Rep2>
-constexpr duration<typename common_type<Rep1, Rep2>::type, Period>
-operator%(const duration<Rep1, Period>& d, const Rep2& s);
-

    -11 Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible -to CR(Rep1, Rep2) and Rep2 is not an instantiation of duration. -

    -12 Returns: duration<CR(Rep1, Rep2), Period>(d) %= sCD(CD(d).count() % s) -

    - -
    -template <class Rep1, class Period1, class Rep2, class Period2>
-constexpr typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
-operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
-

    -13 Returns: common_type<duration<Rep1, Period1>, duration<Rep2, Period2> >::type(lhs) - %= rhsCD(CD(lhs).count() % CD(rhs).count()). -

    -
    2. -
- - - - - -
-

2021. Further incorrect usages of result_of

-

Section: 20.9.10.3 [func.bind.bind], 30.6.1 [futures.overview], 30.6.8 [futures.async] Status: C++14 - Submitter: Daniel Krügler Opened: 2010-12-07 Last modified: 2015-04-08

-

View all other issues in [func.bind.bind].

-

View all issues with C++14 status.

-

Discussion:

-

-Issue 2017 points out some incorrect usages of result_of in the -declaration of the function call operator overload of reference_wrapper, -but there are more such specification defects: -

-
    -
  1. According to 20.9.10.3 [func.bind.bind] p. 3: -

    -[..] The effect of g(u1, u2, ..., uM) shall be INVOKE(fd, v1, v2, ..., vN, result_of<FD cv (V1, V2, ..., VN)>::type) [..] -

    -

    -but fd is defined as "an lvalue of type FD constructed from std::forward<F>(f)". This means that -the above usage must refer to result_of<FD cv & (V1, V2, ..., VN)> instead. -

    -
    2. -

  2. -Similar in 20.9.10.3 [func.bind.bind] p. 10 bullet 2 we have: -

    -

    -if the value of is_bind_expression<TiD>::value is true, the argument is tid(std::forward<Uj>(uj)...) -and its type Vi is result_of<TiD cv (Uj...)>::type -

    -

    -Again, tid is defined as "lvalue of type TiD constructed from std::forward<Ti>(ti)". This means that -the above usage must refer to result_of<TiD cv & (Uj...)> instead. We also have similar defect as in -2017 in regard to the argument types, this leads us to the further corrected form -result_of<TiD cv & (Uj&&...)>. This is not the end: Since the Vi -are similar sensitive to the argument problem, the last part must say: -

    -"[..] its type Vi is result_of<TiD cv & (Uj&&...)>::type &&" -

    -(The bound arguments Vi can never be void types, therefore we don't need -to use the more defensive std::add_rvalue_reference type trait) -

    -
    3. -

  3. The function template async is declared as follows (the other overload has the same problem):

    -
    -template <class F, class... Args>
-future<typename result_of<F(Args...)>::type>
-async(F&& f, Args&&... args);
-

    -This usage has the some same problems as we have found in reference_wrapper (2017) and more: According to -the specification in 30.6.8 [futures.async] the effective result type is that of the call of -

    -INVOKE(decay_copy(std::forward<F>(f)), decay_copy(std::forward<Args>(args))...)
-

    -First, decay_copy potentially modifies the effective types to decay<F>::type and decay<Args>::type.... -Second, the current specification is not really clear, what the value category of callable type or the arguments shall be: According -to the second bullet of 30.6.8 [futures.async] p. 3: -

    -

    -Invocation of the deferred function evaluates INVOKE(g, xyz) where g is the stored value of -decay_copy(std::forward<F>(f)) and xyz is the stored copy of -decay_copy(std::forward<Args>(args)).... -

    -This seems to imply that lvalues are provided in contrast to the direct call expression of 30.6.8 [futures.async] p. 2 -which implies rvalues instead. The specification needs to be clarified. -

    -
    4. -
- -

[2011-06-13: Daniel comments and refines the proposed wording changes]

- - -

The feedback obtained following message c++std-lib-30745 and follow-ups point to the intention, that -the implied provision of lvalues due to named variables in async should be provided as rvalues to support -move-only types, but the functor type should be forwarded as lvalue in bind. -

-If bind were newly invented, the value strategy could be improved, because now we have a preference of -ref & qualified function call operator overloads. But such a change seems to be too late now. -User-code that needs to bind a callable object with an ref && qualified function call -operator (or conversion function to function pointer) needs to use a corresponding wrapper similar to reference_wrapper -that forwards the reference as rvalue-reference instead. -

-The wording has been adapted to honor these observations and to fit to FDIS numbering as well. -

- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

-The suggested wording changes are against the FDIS. -

-
    -
  1. -

    Change 20.9.10.3 [func.bind.bind] p. 3 as indicated:

    - -
    -template<class F, class... BoundArgs>
-  unspecified bind(F&& f, BoundArgs&&... bound_args);
-

    --2- Requires: is_constructible<FD, F>::value shall be true. For each Ti in BoundArgs, -is_constructible<TiD, Ti>::value shall be true. INVOKE(fd, w1, w2, ..., wN) (20.8.2) shall -be a valid expression for some values w1, w2, ..., wN, where N == sizeof...(bound_args). -

    --3- Returns: A forwarding call wrapper g with a weak result type (20.8.2). The effect of -g(u1, u2, ..., uM) shall be INVOKE(fd, std::forward<V1>(v1), -std::forward<V2>(v2), ..., std::forward<VN>(vN), -result_of<FD cv & (V1, V2, ..., VN)>::type), where cv represents -the cv-qualifiers of g and the values and types of the bound arguments v1, -v2, ..., vN are determined as specified below. […] -

    - -
    2. - -
  2. -

    Change 20.9.10.3 [func.bind.bind] p. 7 as indicated:

    - -
    -template<class R, class F, class... BoundArgs>
-   unspecified bind(F&& f, BoundArgs&&... bound_args);
-

    --6- Requires: is_constructible<FD, F>::value shall be true. For each Ti in BoundArgs, -is_constructible<TiD, Ti>::value shall be true. INVOKE(fd, w1, w2, ..., wN) shall be a valid -expression for some values w1, w2, ..., wN, where N == sizeof...(bound_args). -

    --7- Returns: A forwarding call wrapper g with a nested type result_type defined as a synonym for -R. The effect of g(u1, u2, ..., uM) shall be INVOKE(fd, std::forward<V1>(v1), -std::forward<V2>(v2), ..., std::forward<VN>(vN), R), where -the values and types of the bound arguments v1, v2, ..., vN are determined as specified below. […] -

    - -
    3. - -
  3. -

    Change 20.9.10.3 [func.bind.bind] p. 10 as indicated:

    - -

    --10- The values of the bound arguments v1, v2, ..., vN and their corresponding types V1, -V2, ..., VN depend on the types TiD derived from the call to bind and the cv-qualifiers -cv of the call wrapper g as follows:

    -
      -
    • if TiD is reference_wrapper<T>, the argument is tid.get() and its type Vi -is T&;
      • -
    • if the value of is_bind_expression<TiD>::value is true, the argument is -tid(std::forward<Uj>(uj)...) and its type Vi is -result_of<TiD cv & (Uj&&...)>::type&&;
      • -
    • if the value j of is_placeholder<TiD>::value is not zero, the argument is -std::forward<Uj>(uj) and its type Vi is Uj&&;
      • -
    • otherwise, the value is tid and its type Vi is TiD cv &.
      • -
    -
    - -
    4. - -
  4. -

    -This resolution assumes that the wording of 30.6.8 [futures.async] is intended to provide rvalues -as arguments of INVOKE. -

    - -

    -Change the function signatures in header <future> synopsis 30.6.1 [futures.overview] p. 1 -and in 30.6.8 [futures.async] p. 1 as indicated: -

    - -
    -template <class F, class... Args>
-future<typename result_of<typename decay<F>::type(typename decay<Args>::type...)>::type>
-async(F&& f, Args&&... args);
-template <class F, class... Args>
-future<typename result_of<typename decay<F>::type(typename decay<Args>::type...)>::type>
-async(launch policy, F&& f, Args&&... args);
-
    -
    5. - -
  5. -

    Change 30.6.8 [futures.async] as indicated: (Remark: There is also a tiny editorial correction -in p. 4 that completes one :: scope specifier) -

    - -

    --3- Effects: […] -

    -
      -
    • […]
      • -
    • if policy & launch::deferred is non-zero — Stores DECAY_COPY(std::forward<F>(f)) -and DECAY_COPY(std::forward<Args>(args))... in the shared state. These copies of f and -args constitute a deferred function. Invocation of the deferred function evaluates -INVOKE(std::move(g), std::move(xyz)) -where g is the stored value of DECAY_COPY(std::forward<F>(f)) and xyz is the -stored copy of DECAY_COPY(std::forward<Args>(args)).... The shared state is not made ready -until the function has completed. The first call to a non-timed waiting function (30.6.4) on an asynchronous -return object referring to this shared state shall invoke the deferred function in the thread that -called the waiting function. Once evaluation of INVOKE(std::move(g), -std::move(xyz)) begins, the function is no longer considered deferred. [ Note: If -this policy is specified together with other policies, such as when using a policy value of -launch::async | launch::deferred, implementations should defer invocation or the selection of -the policy when no more concurrency can be effectively exploited. — end note ]
      • -
    -
    - -

    --4- Returns: an object of type -future<typename result_of<typename decay<F>::type(typename decay<Args>::type...)>::type> -that refers to the associated asynchronous state created by this call to async. -

    -
    6. -
- - - - - -
-

2022. reference_wrapper<T>::result_type is underspecified

-

Section: 20.9.4 [refwrap] Status: C++11 - Submitter: Daniel Krügler Opened: 2010-12-08 Last modified: 2015-04-08

-

View all other issues in [refwrap].

-

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-

Discussion:

-

-Issue 1295 correctly removed function types and references to function types from the -bullet 1 of 20.9.2 [func.require] p. 3 because neither function types nor function references -satisfy the requirements for a target object which is defined to be an object of a callable -type. This has the effect that the reference in 20.9.4 [refwrap] p. 2 -

-

-reference_wrapper has a weak result type (20.8.2). -

-

-is insufficient as a reference to define the member type result_type when the template argument -T is a function type. -

-There are basically two approaches to solve the problem: -

-
    -

  1. Extend the definition of a weak result type in 20.9.2 [func.require] p. 3 to both -function types and references thereof. This extension must be specified independend from the concept -of a call wrapper, though.

    -
    2. -

  2. Add one extra sentence to 20.9.4 [refwrap] p. 2 that simply defines the member type -result_type for reference_wrapper<T>, when T is a function type.

    -
    3. -
-

-I checked the current usages of weak result type to have a base to argue for one or the other -approach. It turns out, that there is no further reference to this definition in regard to -function types or references thereof. The only other reference can be found in -20.9.10.3 [func.bind.bind] p. 3, where g is required to be a class type. -

- -

[2011-02-23 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

-The suggested wording changes are against the working draft N3242. -

- -
    -
  1. -

    Change 20.9.4 [refwrap] p. 2 as indicated:

    - -

    -2 reference_wrapper<T> has a weak result type (20.8.2). If T is a function type, -result_type shall be a synonym for the return type of T. -

    - -
    2. - -
- - - - - -
-

2023. Incorrect requirements for lock_guard and unique_lock

-

Section: 30.4.2.1 [thread.lock.guard], 30.4.2.2 [thread.lock.unique] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-12-08 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-There are two different *Lockable requirements imposed on template arguments -of the class template lock_guard as of 30.4.2.1 [thread.lock.guard] p. 1+2: -

-

-1 [..] The supplied Mutex type shall meet the BasicLockable requirements (30.2.5.2). -

- -

-2 The supplied Mutex type shall meet the Lockable requirements (30.2.5.3). -

-

-The Lockable requirements include the availability of a member function try_lock(), -but there is no operational semantics in the specification of lock_guard that would rely -on such a function. It seems to me that paragraph 2 should be removed. -

-Similarly, 30.4.2.2 [thread.lock.unique] p. 1+2 refer to exactly the same two requirements. -In this case it seems as if the intention was that the template arguement Mutex should -always provide the try_lock() member function, because several member functions of -unique_lock (unique_lock(mutex_type& m, try_to_lock_t) or bool try_lock()) -take advantage of such a function without adding extra requirements for this. -It seems that the requirement subset BasicLockable should be removed. -

-I searched for further possible misusages of the *Lockable requirements, but could not -find any more. -

- -

[2011-02-23]

- - -

Howard suggests an alternative approach in regard to unique_lock: The current -minimum requirements on its template argument should better be reduced to BasicLockable -instead of the current Lockable, including ammending member-wise constraints where required. -This suggestions was supported by Anthony, Daniel, and Pablo. -

-Daniel drafts wording that follows this separation strategy. -

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- -
-

-The suggested wording changes are against the working draft N3242. -

- -
    -
  1. -

    Remove 30.4.2.1 [thread.lock.guard] p. 2 completely:

    - -

    -2 The supplied Mutex type shall meet the Lockable requirements (30.2.5.3). -

    - -
    2. - -
  2. -

    Change 30.4.2.2 [thread.lock.unique] p. 1-3 as indicated. The intend is to make BasicLockable -the fundamental requirement for unique_lock. We also update the note to reflect these changes and -synchronize one remaining reference of 'mutex' by the proper term 'lockable object' in sync -to the wording changes of lock_guard:

    - -

    -1 [..] The behavior of a program is undefined if the contained pointer pm is not null -and the mutexlockable object pointed to by pm does not exist for the entire remaining lifetime (3.8) -of the unique_lock object. The supplied Mutex type shall meet the -BasicLockable requirements (30.2.5.2). [Editor's note: -BasicLockable is redundant, since the following additional paragraph requires Lockable.] -

    - -

    -2 The supplied Mutex type shall meet the Lockable requirements (30.2.5.3). -

    - -

    -3 [ Note: unique_lock<Mutex> meets the BasicLockable requirements. If -Mutex meets the Lockable requirements ([thread.req.lockable.req]), unique_lock<Mutex> -also meets the Lockable requirements and if Mutex meets the TimedLockable -requirements (30.2.5.4), unique_lock<Mutex> also meets the TimedLockable -requirements. — end note ] -

    - -
    3. - -

  3. Modify 30.4.2.2.1 [thread.lock.unique.cons] to add the now necessary member-wise -additional constraints for Lockable:

    - -
    -unique_lock(mutex_type& m, try_to_lock_t) noexcept;
-

    -8 Requires: The supplied Mutex type shall meet the Lockable requirements ([thread.req.lockable.req]). -If mutex_type is not a recursive mutex the calling thread does not own the mutex. -

    -9 Effects: Constructs an object of type unique_lock and calls m.try_lock(). -

    -
    4. - -

  4. Modify 30.4.2.2.2 [thread.lock.unique.locking] to add the now necessary member-wise -additional constraints for Lockable:

    - -
    -bool try_lock();
-

    -? Requires: The supplied Mutex type shall meet the Lockable requirements ([thread.req.lockable.req]). -

    -4 Effects: pm->try_lock() -

    -
    5. -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

2024. Inconsistent implementation requirements for atomic<integral> and atomic<T*>

-

Section: 29.5 [atomics.types.generic] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-12-08 Last modified: 2015-04-08

-

View other active issues in [atomics.types.generic].

-

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-

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-

Discussion:

-

-Paragraph 5 and 6 of 29.5 [atomics.types.generic] impose different requirements on implementations for -specializations of the atomic class template for integral types and for pointer types: -

-

-5 The atomic integral specializations and the specialization atomic<bool> shall have standard layout. -They shall each have a trivial default constructor and a trivial destructor. They shall each support aggregate -initialization syntax. -

- -

-6 There are pointer partial specializations on the atomic class template. These specializations shall have -trivial default constructors and trivial destructors. -

- -

-It looks like an oversight to me, that for pointer specializations the requirements for standard layout and -support for aggregate initialization syntax are omitted. In fact, this been confirmed by the -N3193 proposal author. I suggest -to impose the same implementation requirements for pointer types as for integral types, this should not impose -unrealistic requirements on implementations. -

- -

[2011-02-10 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- -
-

Proposed Resolution

-

-The suggested wording changes are against the working draft N3242. -

- -
    -
  1. -

    Change 29.5 [atomics.types.generic] p. 6 as indicated:

    - -

    -6 There are pointer partial specializations on the atomic class template. These specializations shall have -standard layout, trivial default constructors, and trivial destructors. They shall each -support aggregate initialization syntax. -

    - -
    2. -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

2025. Incorrect semantics of move assignment operator of packaged_task

-

Section: 30.6.9.1 [futures.task.members] Status: Resolved - Submitter: Daniel Krügler Opened: 2010-12-08 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

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-

Discussion:

-

-According to 30.6.9.1 [futures.task.members] p. 7 bullet 2: -

-
-packaged_task& operator=(packaged_task&& other);
-

-7 Effects:
-

-
    -

  • [...]

    • -

  • packaged_task<R, ArgTypes...>(other).swap(*this).

    • -
-
-

-The argument other given to the move constructor is an lvalue and must be converted into -an rvalue via appropriate usage of std::move. -

- -
-

Proposed Resolution

-

-The suggested wording changes are against the working draft N3242. -

- -
    -
  1. -

    Change 30.6.9.1 [futures.task.members] p. 7 bullet 2 as indicated:

    - -
    -packaged_task& operator=(packaged_task&& other);
-

    -7 Effects:
    -

    -
      -

    • [...]

      • -

    • packaged_task(std::move(other)).swap(*this).

      • -
    -
    - -
    2. -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

2027. Initialization of the stored task of a packaged_task

-

Section: 30.6.9.1 [futures.task.members] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2011-02-09 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

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-

Discussion:

-

-Related with LWG issue 1514. -

- -

-The move constructor of packaged_task does not specify how the stored task is constructed. -The obvious way is to move-construct it using the task stored in the argument. Moreover, the -constructor should be provided with a throws clause similar to one used for the other constructors, -as the move constructor of the stored task is not required to be nothrow.

- -

-As for the other constructors, the terms "stores a copy of f" do not reflect the intent, which is -to allow f to be moved when possible. -

- -

[2011-02-25: Alberto updates wording]

- - -

[2011-02-26 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

(wording written assuming LWG 1514 is also accepted)

- -
    -
  1. -

    Change 30.6.9.1 [futures.task.members] paragraph 3:

    - -

    -3 Effects: constructs a new packaged_task object with an associated asynchronous state and stores a -copy of f as the object's stored taskinitializes the object's stored task with std::forward<F>(f). -The constructors that take an Allocator argument use it to allocate memory needed to store the internal data structures. -

    - -
    2. - -
  2. -

    Change 30.6.9.1 [futures.task.members] paragraph 5:

    - -

    -5 Effects: constructs a new packaged_task object and transfers ownership of other's associated asynchronous -state to *this, leaving other with no associated asynchronous state. Moves the stored task from other -to *this. -

    - -
    3. - -
- - - - - - -
-

2028. messages_base::catalog overspecified

-

Section: 22.4.7.1 [locale.messages] Status: C++14 - Submitter: Howard Hinnant Opened: 2011-02-14 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-In 22.4.7.1 [locale.messages], messages_base::catalog is specified to be a typedef to int. -This type is subsequently used to open, access and close catalogs. -

- -

-However, an OS may have catalog/messaging services that are indexed and managed by types other than int. -For example POSIX, publishes the following messaging API: -

- -
-typedef unspecified nl_catd;
-
-nl_catd catopen(const char* name , int oflag);
-char*   catgets(nl_catd catd, int set_id, int msg_id, const char* s);
-int     catclose(nl_catd catd);
-
- -

-I.e., the catalog is managed with an unspecified type, not necessarily an int. -Mac OS uses a void* for nl_catd (which is conforming to the POSIX standard). -The current messages_base spec effectively outlaws using the built-in OS messaging service -supplied for this very purpose! -

- -

[2011-02-24: Chris Jefferson updates the proposed wording, changing unspecified to unspecified signed integral type]

- - -

[2011-03-02: Daniel updates the proposed wording, changing unspecified signed integral type to - unspecified signed integer type (We don't want to allow for bool or char)]

- - -

[2011-03-24 Madrid meeting]

- - -

-Consensus that this resolution is the direction we would like to see. -

- - - -

Proposed resolution:

-
    -
  1. -

    Modify 22.4.7.1 [locale.messages]:

    - -
    -namespace std {
-  class messages_base {
-  public:
-    typedef intunspecified signed integer type catalog;
-  };
-  ...
-}
-
    - -
    2. - -
- - - - - - -
-

2029. Missing 'noexcept' on basic_regex move-assignment operator

-

Section: 28.8 [re.regex] Status: C++11 - Submitter: Jonathan Wakely Opened: 2011-02-16 Last modified: 2015-04-08

-

View all other issues in [re.regex].

-

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-

Discussion:

-

-N3149 replaced -the "Throws: nothing" clause on basic_regex::assign(basic_regex&&) with -the noexcept keyword. The effects of the move-assignment operator are defined in terms of -the assign() function, so the "Throws: nothing" applied there too, and a -noexcept-specification should be added there too. -

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 7 votes. -

- - -

Proposed resolution:

- -
    -
  1. -

    Modify the basic_regex synopsis in 28.8 [re.regex] p. 3:

    - -
    -namespace std {
-  template <class charT,
-            class traits = regex_traits<charT> >
-  class basic_regex {
-  public:
-    ...
-    basic_regex& operator=(const basic_regex&);
-    basic_regex& operator=(basic_regex&&) noexcept;
-    basic_regex& operator=(const charT* ptr);
-    ...
-  };
-}
-
    - -
    2. - -
  2. -

    Modify 28.8.3 [re.regex.assign] p. 2:

    - -
    -basic_regex& operator=(basic_regex&& e) noexcept;
-
    -

    -2 Effects: returns assign(std::move(e)). -

    -
    -
    3. -
- - - - - - -
-

2030. packaged_task::result_type should be removed

-

Section: 30.6.9 [futures.task] Status: C++11 - Submitter: Anthony Williams Opened: 2010-11-12 Last modified: 2015-04-08

-

View all other issues in [futures.task].

-

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-

Discussion:

-

-packaged_task::operator() always returns void, regardless of the return -type of the wrapped task. However, packaged_task::result_type is a -typedef to the return type of the wrapped task. This is inconsistent -with other uses of result_type in the standard, where it matches the -return type of operator() (e.g. function, owner_less). This is confusing. -

- -

-It also violates the TR1 result_of protocol, and thus makes -packaged_task harder to use with anything that respects that protocol. -

- -

-Finally, it is of little use anyway. -

- -

packaged_task::result_type should therefore be removed.

- -

[2011-02-24 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

Alter the class definition of packaged_task in 30.6.9 [futures.task] p. 2 as follows:

-
-template<class R, class... ArgTypes>
-class packaged_task<R(ArgTypes...)> {
-public:
-  typedef R result_type;
-  [...]
-};
-
- - - - - -
-

2031. std::future<>::share() only applies to rvalues

-

Section: 30.6.6 [futures.unique_future] Status: C++11 - Submitter: Anthony Williams Opened: 2011-02-17 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

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-

Discussion:

-

-As specified, future<>::share() has the signature -

- -
-shared_future<R> share() &&;
-
- -

-This means that it can only be applied to rvalues. One of the key benefits of share() is -that it can be used with the new auto facility: -

- -
-std::promise<some_long_winded_type_name> some_promise;
-auto f = some_promise.get_future(); // std::future
-auto sf = std::move(f).share();
-
- -

-share() is sufficiently explicit that the move should not be required. We should be able to write: -

- -
-auto sf = f.share();
-
- -

[2011-02-22 Reflector discussion]

- -

-Moved to Tentatively Ready after 5 votes. -

- - -

Proposed resolution:

-

Alter the declaration of share() to remove the "&&" rvalue qualifier in -30.6.6 [futures.unique_future] p. 3, and 30.6.6 [futures.unique_future] p. 11:

- -
-shared_future<R> share() &&;
-
- - - - - - -
-

2032. Incorrect synchronization clause of async function

-

Section: 30.6.8 [futures.async] Status: C++11 - Submitter: Alberto Ganesh Barbati Opened: 2011-02-17 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

-Clause 30.6.8 [futures.async] has undergone significant rewording -in Batavia. Due to co-presence of at least three different sources -of modification there is a part where changes have overlapped -(marked by an Editor's note), which should be reconciled. Moreover, -I believe that a few non-overlapping sentences are now incorrect -and should be fixed, so the problem cannot be handled editorially. -(See c++std-lib-29667.) -

- -

[Adopted in Madrid, 2011-03]

- - - - -

Proposed resolution:

-
    -
  1. -

    -Edit 30.6.4 [futures.state], paragraph 3 as follows. -

    - -
    -

    -An asynchronous return object -is an object that reads results from an associated asynchronous state. -A waiting function of an asynchronous return object -is one that potentially blocks -to wait for the associated asynchronous state to be made ready. -If a waiting function can return -before the state is made ready because of a timeout (30.2.5), -then it is a timed waiting function, -otherwise it is a non-timed waiting function. -

    -
    -
    2. - -
  2. -

    -Edit within 30.6.8 [futures.async] paragraph 3 bullet 2 as follows. -

    - -
    -

    -Effects: -[...] -

    -
    • if policy & launch::deferred is non-zero — [...] -The associated asynchronous state is not made ready -until the function has completed. -The first call to a non-timed waiting function -(30.6.4 [futures.state]) -requiring a non-timed wait -on an asynchronous return object -referring to the this -associated asynchronous state -created by this async call to become ready -shall invoke the deferred function -in the thread that called the waiting function;. -once Once evaluation of -INVOKE(g, xyz) begins, -the function is no longer considered deferred. -[...] -
    -
    -
    3. - -
  3. -

    -Edit 30.6.8 [futures.async] paragraph 5 as follows. -

    - -
    -

    -Synchronization: -Regardless of the provided policy argument, -

    -
      -
    • -the invocation of async synchronizes with (1.10) -the invocation of f. -[Note: -this statement applies even when the corresponding future object -is moved to another thread. -—end note]; -and -
      • -
    • -the completion of the function f -is sequenced before (1.10) the associated asynchronous state is made ready. -[Note: -f might not be called at all, -so its completion might never happen. -—end note] -
      • -
    - -

    -If policy & launch::async is non-zero, -If the implementation chooses the launch::async policy, -

    -
      -
    • -a call to a waiting function on an asynchronous return object -that shares the associated asynchronous state -created by this async call -shall block until the associated thread has completed, -as if joined (30.3.1.5); -
      • -
    • -the join() on the created thread object -the associated thread completion -synchronizes with (1.10) -the return from the first function -that successfully detects the ready status of the associated asynchronous state -or with the return from the last function that -releases the associated asynchronous state returns, -whichever happens first. -[Editor's note: -N3196 changes the following sentence as indicated. -N3188 removes the sentence. -Please pick one.] -If the invocation is deferred, -the completion of the invocation of the deferred function -synchronizes with the successful return -from a call to a waiting function on the associated asynchronous state. -
      • -
    -
    - -
    4. -
- - - - - - -
-

2033. Preconditions of reserve, shrink_to_fit, and resize functions

-

Section: 23.3.6.3 [vector.capacity], 23.3.3.3 [deque.capacity] Status: C++14 - Submitter: Nikolay Ivchenkov Opened: 2011-02-20 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-I have several questions with regard to the working paper N3225 (C++0x working draft): -

-
    -

  1. -Where the working draft specifies preconditions for shrink_to_fit -member function of std::vector and std::deque? -

    2. -

  2. -Where the working draft specifies preconditions for 'void reserve(size_type n)' -member function of std::vector? -

    3. -

  3. -Does a call to 'void resize(size_type sz)' of std::vector require -the element type to be DefaultConstructible? If yes, why such -requirement is not listed in the Requires paragraph? -

    4. -

  4. -Does a call to 'void resize(size_type sz)' of std::vector require -the element type to be MoveAssignable because the call erase(begin() + sz, end()) -mentioned in the Effects paragraph would require the element type to be MoveAssignable? -

    5. -

  5. -Why CopyInsertable requirement is used for 'void resize(size_type sz)' of std::vector -instead of MoveInsertable requirement? -

    6. -
- -

[2011-06-12: Daniel comments and provides wording]

- -

According to my understanding of the mental model of vector (and to some parts for deque) the -some requirements are missing in the standard as response to above questions:

-
    -
  1. The preconditions of shrink_to_fit for both std::vector and std::deque -should impose the MoveInsertable requirements. The reason for this is, that these containers -can host move-only types. For a container type X the C++03 idiom X(*this).swap(*this) -imposes the CopyInsertable requirements which would make the function call ill-formed, -which looks like an unacceptable restriction to me. Assuming the committee decides to support the -move-only case, further wording has to be added for the situation where such a move-only type could -throw an exception, because this can leave the object in an unspecified state. This seems consistent -with the requirements of reserve, which seems like a very similar function to me (for -vector). And this brings us smoothly to the following bullet: -
    2. - -

  2. I agree that we are currently missing to specify the preconditions of the reserve function. -My interpretation of the mental model of this function is that it should work for move-only types, which -seems to be supported by the wording used in 23.3.6.3 [vector.capacity] p2: -

    -

    -[…] If an exception is thrown other than by the move constructor of a non-CopyInsertable type, -there are no effects. -

    -

    -Given this statement, the appropriate requirement is MoveInsertable into the vector. -

    -
    3. - -
  3. I agree that vector::resize(size_type) misses to list the DefaultConstructible -requirements. -
    4. - -
  4. Unfortunately the current specification in terms of erase implies the MoveAssignable -requirements. I don't think that this implication is intended. This function requires "append" and -"pop-back" effects, respectively, where the former can be realized in terms of MoveInsertable -requirements. The same fix in regard to using pop_back instead of erase is necessary -for the two argument overload of resize as well (no MoveAssignable is required). -
    5. - -
  5. The CopyInsertable requirement is incorrect and should be MoveInsertable instead.
    6. -
- -

In addition to above mentioned items, the proposed resolution adds a linear complexity bound for -shrink_to_fit and attempts to resolve the related issue 2066.

- -

[ -2011 Bloomington -]

- - -

-Move to Ready. -

- -

-Note for editor: we do not normally refer to 'linear time' for complexity requirements, but there -is agreement that any clean-up of such wording is editorial. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Edit 23.3.3.3 [deque.capacity] as indicated [Remark: The suggested change of p4 is -not redundant, because CopyInsertable is not necessarily a refinement of MoveInsertable -in contrast to the fact that CopyConstructible is a refinement of MoveConstructible]:

    - -
    -void resize(size_type sz);
-

    --1- Effects: If sz <= size(), equivalent to erase(begin() + sz, -end());calling pop_back() size() - sz times. If -size() < sz, appends sz - size() value-initialized elements to the sequence. -

    --2- Requires: T shall be MoveInsertable into *this and DefaultConstructible. -

    - -
    -void resize(size_type sz, const T& c);
-

    --3- Effects: If sz <= size(), equivalent to calling pop_back() -size() - sz times. If size() < sz, appends sz - size() copies of c -to the sequence. -

    -if (sz > size())
-  insert(end(), sz-size(), c);
-else if (sz < size())
-  erase(begin()+sz, end());
-else
-  ; // do nothing
-
    -

    --4- Requires: T shall be MoveInsertable into *this and -CopyInsertable into *this. -

    - -
    -void shrink_to_fit();
-

    --?- Requires: T shall be MoveInsertable into *this. -

    --?- Complexity: Takes at most linear time in the size of the sequence. -

    --5- Remarks: shrink_to_fit is a non-binding request to reduce memory use but does -not change the size of the sequence. [ Note: The request is non-binding to allow latitude -for implementation-specific optimizations. — end note ] -

    -
    2. - -

  2. Edit 23.3.6.3 [vector.capacity] as indicated including edits that also resolve 2066 -[Remark: The combined listing of MoveInsertable and CopyInsertable before p12 is not redundant, -because CopyInsertable is not necessarily a refinement of MoveInsertable in contrast to the -fact that CopyConstructible is a refinement of MoveConstructible]:

    - -

    […]

    - -
    -void reserve(size_type n);
-

    --?- Requires: T shall be MoveInsertable into *this. -

    --2- Effects: A directive that informs a vector of a planned change in size, so that it can manage the storage -allocation accordingly. After reserve(), capacity() is greater or equal to the argument of reserve if -reallocation happens; and equal to the previous value of capacity() otherwise. Reallocation happens -at this point if and only if the current capacity is less than the argument of reserve(). If an exception -is thrown other than by the move constructor of a non-CopyInsertable type, there are no effects. -

    --3- Complexity: It does not change the size of the sequence and takes at most linear time in the size of -the sequence. -

    --4- Throws: length_error if n > max_size().[footnote 266] -

    --5- Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements -in the sequence. It is guaranteed that no reallocation takes place during insertions that happen after -a call to reserve() until the time when an insertion would make the size of the vector greater than -the value of capacity(). -

    - -
    -void shrink_to_fit();
-

    --?- Requires: T shall be MoveInsertable into *this. -

    --?- Complexity: Takes at most linear time in the size of the sequence. -

    --6- Remarks: shrink_to_fit is a non-binding request to reduce capacity() to size(). -[ Note: The request is non-binding to allow latitude for implementation-specific optimizations. — end note ] -If an exception is thrown other than by the move constructor of a non-CopyInsertable T there -are no effects. -

    - -

    […]

    - -
    -void resize(size_type sz);
-

    --9- Effects: If sz <= size(), equivalent to erase(begin() + sz, end());calling -pop_back() size() - sz times. If size() < sz, appends sz - size() -value-initialized elements to the sequence. -

    --10- Requires: T shall be CopyMoveInsertable into *this -and DefaultConstructible. -

    --??- Remarks: If an exception is thrown other than by the move constructor of a non-CopyInsertable -T there are no effects. -

    - -
    -void resize(size_type sz, const T& c);
-

    --11- Effects: If sz <= size(), equivalent to calling pop_back() -size() - sz times. If size() < sz, appends sz - size() copies of c -to the sequence. -

    -if (sz > size())
-  insert(end(), sz-size(), c);
-else if (sz < size())
-  erase(begin()+sz, end());
-else
-  ; // do nothing
-

    --??- Requires: T shall be MoveInsertable into *this and -CopyInsertable into *this. -

    --12- RequiresRemarks: If an exception is thrown other than by the move constructor of a -non-CopyInsertable T there are no effects. -

    - -
    3. - -
- - - - - -
-

2034. Initialization of atomics is misspecified so that it doesn't preserve sequential consistency

-

Section: 29.3 [atomics.order] Status: Resolved - Submitter: Hans Boehm Opened: 2011-02-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-This violates the core intent of the memory model, as stated in the note in 1.10 [intro.multithread] p. 21. -

- -

-This was discovered by Mark Batty, and pointed out in their POPL 2011 paper, "Mathematizing C++ Concurrency", -section 4, "Sequential consistency of SC atomics". The problem is quite technical, but well-explained in that paper. -

- -

-This particular issue was not understood at the time the FCD comments were generated. But it is closely related -to a number of FCD comments. It should have arisen from -US-171, though that's not -the actual history. -

- -

This issue has been under discussion for several months in a group that included a half dozen or so of the -most interested committee members. The P/R represents a well-considered consensus among us:

- -

[2011-03-16: Jens updates wording]

- - -
-

Modify 29.3 [atomics.order] p.3, so that the normative part reads:

- -

-3 There shall be a single total order S on all memory_order_seq_cst operations, consistent -with the "happens before" order and modification orders for all affected locations, such that each -memory_order_seq_cst operation that loads a value observes either the last -preceding modification according to this order S, A (if any), or the result of an operation -X that is notdoes not happen before A and that is not memory_order_seq_cst. -[ Note: Although it is not explicitly required that S include locks, it can always be extended -to an order that does include lock and unlock operations, since the ordering between those is already included -in the "happens before" ordering. — end note ] -

- -
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

2037. atomic free functions incorrectly specified

-

Section: 29.2 [atomics.syn] Status: Resolved - Submitter: Pete Becker Opened: 2011-03-01 Last modified: 2015-04-08

-

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-

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-

Discussion:

-

In earlier specifications of atomics the template specialization atomic<integer> -was derived from atomic_integer (e.g. atomic<int> was derived from atomic_int), -and the working draft required free functions such as

- -
-int atomic_load(const atomic_int*)
-
- -

for each of the atomic_integer types. This worked fine with normal function overloading.

- -

For the post-Batavia working draft, N3193 removed the requirement that atomic<integer> -be derived from atomic_integer and replaced the free functions taking pointers to -atomic_integer with template functions taking atomic_type*, such as

- -
-template <class T> T atomic_load(const atomic_type*);
-
- -

and a code comment explaining that atomic_type can be either atomic<T> or a -named base class of atomic<T>. The latter possibility is supposed to allow existing -implementations based on the previous specification to continue to conform.

- -

From history, this allowance seems to imply that functions like atomic_load can be non-template -free functions, as they were before. The explicit requirements do not allow this, and, by requiring that -they be templates, make them far more complicated. As the specification is currently written, code that -uses an implementation that uses a base class would have to provide an explicit template type:

- -
-atomic<int> my_atomic_int;
-atomic_load<int>(&my_atomic_int);
-
- -

That type argument isn't needed when atomic_type is atomic<T>, but cautious -users would always provide it to make their code portable across different implementations of the -standard library.

- -

One possibility for the implementor would be to do some template meta-programming to infer the type -T when there are no function parameters of type T, but without running afoul of the -prohibition on adding parameters with default values (17.6.5.4 [global.functions]/3).

- -

So the promise that implementations of the previous specification continue to conform has not been -met. The specification of these free functions should be rewritten to support library code written to -the previous specification or the vacuous promise should be removed. -

- -

[2011-03-08: Lawrence comments and drafts wording:]

- - -

One of the goals is to permit atomics code to compile under both C and C++. Adding explicit -template arguments would defeat that goal. -

-The intent was to permit the normal function overloads for atomic_int when atomic_int -is distinct from atomic<int>. That intent was not reflected in the wording. -

- -
-

Proposed Resolution

-

Explicitly permit free functions.

- -
    -
  1. -

    Edit within the header <atomic> synopsis 29.2 [atomics.syn] as follows:

    - -
    -// 29.6.1, general operations on atomic types
-// In the following declarations, atomic_type is either
-// atomic<T> or a named base class for T from
-// Table 145 or inferred from
-// Table 146.
-// In the following declarations, atomic-type is either 
-// atomic<T> or a named base class for T from
-// Table 145 or inferred from
-// Table 146.
-// If it is atomic<T>, then the declaration is a template
-// declaration prefixed with template <class T>
-template <class T>
-bool atomic_is_lock_free(const volatile atomic_typeatomic-type*);
-template <class T>
-bool atomic_is_lock_free(const atomic_typeatomic-type*);
-template <class T>
-void atomic_init(volatile atomic_typeatomic-type*, T);
-template <class T>
-void atomic_init(atomic_typeatomic-type*, T);
-template <class T>
-void atomic_store(volatile atomic_typeatomic-type*, T);
-template <class T>
-void atomic_store(atomic_typeatomic-type*, T);
-template <class T>
-void atomic_store_explicit(volatile atomic_typeatomic-type*, T, memory_order);
-template <class T>
-void atomic_store_explicit(atomic_typeatomic-type*, T, memory_order);
-template <class T>
-T atomic_load(const volatile atomic_typeatomic-type*);
-template <class T>
-T atomic_load(const atomic_typeatomic-type*);
-template <class T>
-T atomic_load_explicit(const volatile atomic_typeatomic-type*, memory_order);
-template <class T>
-T atomic_load_explicit(const atomic_typeatomic-type*, memory_order);
-template <class T>
-T atomic_exchange(volatile atomic_typeatomic-type*, T);
-template <class T>
-T atomic_exchange(atomic_typeatomic-type*, T);
-template <class T>
-T atomic_exchange_explicit(volatile atomic_typeatomic-type*, T, memory_order);
-template <class T>
-T atomic_exchange_explicit(atomic_typeatomic-type*, T, memory_order);
-template <class T>
-bool atomic_compare_exchange_weak(volatile atomic_typeatomic-type*, T*, T);
-template <class T>
-bool atomic_compare_exchange_weak(atomic_typeatomic-type*, T*, T);
-template <class T>
-bool atomic_compare_exchange_strong(volatile atomic_typeatomic-type*, T*, T);
-template <class T>
-bool atomic_compare_exchange_strong(atomic_typeatomic-type*, T*, T);
-template <class T>
-bool atomic_compare_exchange_weak_explicit(volatile atomic_typeatomic-type*, T*, T,
-  memory_order, memory_order);
-template <class T>
-bool atomic_compare_exchange_weak_explicit(atomic_typeatomic-type*, T*, T.
-  memory_order, memory_order);
-template <class T>
-bool atomic_compare)exchange_strong_explicit(volatile atomic_typeatomic-type*, T*, T,
-  memory_order, memory_order);
-template <class T>
-bool atomic_compare_exchange_strong_explicit(atomic_typeatomic-type*, T*, T,
-  memory_order, memory_order);
-  
-// 29.6.2, templated operations on atomic types
-// In the following declarations, atomic_type is either
-// atomic<T> or a named base class for T from
-// Table 145 or inferred from
-// Table 146.
-template <class T>
-T atomic_fetch_add(volatile atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_add(atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_add_explicit(volatile atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_add_explicit(atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_sub(volatile atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_sub(atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_sub_explicit(volatile atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_sub_explicit(atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_and(volatile atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_and(atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_and_explicit(volatile atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_and_explicit(atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_or(volatile atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_or(atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_or_explicit(volatile atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_or_explicit(atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_xor(volatile atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_xor(atomic-typeatomic<T>*, T);
-template <class T>
-T atomic_fetch_xor_explicit(volatile atomic-typeatomic<T>*, T, memory_order);
-template <class T>
-T atomic_fetch_xor_explicit(atomic-typeatomic<T>*, T, memory_order);
-
-// 29.6.3, arithmetic operations on atomic types
-// In the following declarations, atomic-integral is either 
-// atomic<T> or a named base class for T from 
-// Table 145 or inferred from 
-// Table 146.
-// If it is atomic<T>,
-// then the declaration is a template specialization declaration prefixed with
-// template <>
-template <>
-integral atomic_fetch_add(volatile atomic-integral*, integral);
-template <>
-integral atomic_fetch_add(atomic-integral*, integral);
-template <>
-integral atomic_fetch_add_explicit(volatile atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_add_explicit(atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_sub(volatile atomic-integral*, integral);
-template <>
-integral atomic_fetch_sub(atomic-integral*, integral);
-template <>
-integral atomic_fetch_sub_explicit(volatile atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_sub_explicit(atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_and(volatile atomic-integral*, integral);
-template <>
-integral atomic_fetch_and(atomic-integral*, integral);
-template <>
-integral atomic_fetch_and_explicit(volatile atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_and_explicit(atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_or(volatile atomic-integral*, integral);
-template <>
-integral atomic_fetch_or(atomic-integral*, integral);
-template <>
-integral atomic_fetch_or_explicit(atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_or_explicit(atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_xor(volatile atomic-integral*, integral);
-template <>
-integral atomic_fetch_xor(atomic-integral*, integral);
-template <>
-integral atomic_fetch_xor_explicit(volatile atomic-integral*, integral, memory_order);
-template <>
-integral atomic_fetch_xor_explicit(atomic-integral*, integral, memory_order);
-
    -
    2. - -

  2. Edit 29.6.1 [atomics.types.operations.general] paragraph 1+2 as follows:

    - -

    --1- The implementation shall provide the functions and function templates identified as -"general operations on atomic types" in 29.2 [atomics.syn]. -

    --2- In the declarations of these functions and function templates, the name atomic-type -refers to either atomic<T> or to a named base class for T from Table 145 or -inferred from Table 146. -

    -
    -
    3. - -

  3. In 29.6.2 [atomics.types.operations.templ] delete paragraph 2:

    - -

    --1- The implementation shall declare but not define the function templates identified as -"templated operations on atomic types" in 29.2 [atomics.syn]. -

    --2- In the declarations of these templates, the name atomic-type refers to either -atomic<T> or to a named base class for T from Table 145 or -inferred from Table 146. -

    -
    -
    4. - -

  4. Edit 29.6.3 [atomics.types.operations.arith] paragraph 1+2 as follows:

    - -

    --1- The implementation shall provide the functions and function template -specializations identified as "arithmetic operations on atomic types" in -29.2 [atomics.syn]. -

    --2- In the declarations of these functions and function template specializations, -the name integral refers to an integral type and the name atomic-integral -refers to either atomic<integral> or to a named base class for -integral from Table 145 or inferred from Table 146. -

    -
    -
    5. - -
-
- - -

Proposed resolution:

-Resolved 2011-03 Madrid meeting by paper N3278 -

- - - - -
-

2039. Issues with std::reverse and std::copy_if

-

Section: 25.3.1 [alg.copy], 25.3.10 [alg.reverse] Status: C++14 - Submitter: Nikolay Ivchenkov Opened: 2011-03-02 Last modified: 2015-04-08

-

View other active issues in [alg.copy].

-

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-

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-

Discussion:

- -
    -

  1. In the description of std::reverse

    -

    -Effects: For each non-negative integer i <= (last - first)/2, applies iter_swap -to all pairs of iterators first + i, (last - i) - 1. -

    -

    -should be changed to -

    -Effects: For each non-negative integer i < (last - first)/2, applies iter_swap -to all pairs of iterators first + i, (last - i) - 1. -

    -Here i shall be strictly less than (last - first)/2. -

    -
    2. -

  2. In the description of std::copy_if Returns paragraph is missing.

    3. -
- -

[2011-03-02: Daniel drafts wording]

- - - -

Proposed resolution:

-
    -

  1. Modify 25.3.10 [alg.reverse] p. 1 as indicated:

    - -

    -1 Effects: For each non-negative integer i <= (last - first)/2, applies iter_swap -to all pairs of iterators first + i, (last - i) - 1. -

    -
    2. - -

  2. Add the following Returns element after 25.3.1 [alg.copy] p. 9:

    - -
    -template<class InputIterator, class OutputIterator, class Predicate>
-OutputIterator copy_if(InputIterator first, InputIterator last,
-   OutputIterator result, Predicate pred);
-

    -8 Requires: The ranges [first,last) and [result,result + (last - first)) shall not overlap. -

    -9 Effects: Copies all of the elements referred to by the iterator i in the range [first,last) -for which pred(*i) is true. -

    -?? Returns: The end of the resulting range. -

    -10 Complexity: Exactly last - first applications of the corresponding predicate. -

    -11 Remarks: Stable. -

    -
    3. -
- - - - - -
-

2041. Stage 2 accumulate incompatibilty

-

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: C++11 - Submitter: Howard Hinnant Opened: 2011-03-09 Last modified: 2015-04-08

-

View other active issues in [facet.num.get.virtuals].

-

View all other issues in [facet.num.get.virtuals].

-

View all issues with C++11 status.

-

Discussion:

-

num_get Stage 2 accumulation changed between C++03 and the current C++0x working draft. The sentences:

- -

-If it is not discarded, then a check is made to determine if c is allowed as the -next character of an input field of the conversion specifier returned by stage 1. -If so it is accumulated. -

- -

have been dropped from 22.4.2.1.2 [facet.num.get.virtuals], Stage 2, paragraph 3 that begins:

- -

-If discard is true, […] -

- -

Consider this code:

- -
-#include <sstream>
-#include <iostream>
-
-int main(void)
-{
-   std::istringstream s("8cz");
-   long i = 0;
-   char c;
-   s >> i;
-   if (!s.fail())
-       std::cout << "i = " << i << '\n';
-   else
-   {
-       std::cout << "s >> i failed\n";
-       s.clear();
-   }
-   s >> c;
-   if (!s.fail())
-       std::cout << "c = " << c << '\n';
-   else
-       std::cout << "s >> c failed\n";
-}
-
- -

C++0x currently prints out:

- -
-s >> i failed
-c = z
-
- -

However C++03 conforming implementations will output:

- -
-i = 8
-c = c
-
- -

I believe we need to restore C++03 compatibility.

- - - -

Proposed resolution:

- -

Add to 22.4.2.1.2 [facet.num.get.virtuals], Stage 2:

- -

-If discard is true, then if '.' has not yet been accumulated, then the position of the character -is remembered, but the character is otherwise ignored. Otherwise, if '.' has already been -accumulated, the character is discarded and Stage 2 terminates. If it is not discarded, then a -check is made to determine if c is allowed as the next character of an input field of the -conversion specifier returned by stage 1. If so it is accumulated. -

-If the character is either discarded or accumulated then in is advanced by ++in and processing -returns to the beginning of stage 2. -

- - - - - -
-

2042. Comparing forward_list::before_begin() to forward_list::end()

-

Section: 23.3.4.3 [forwardlist.iter] Status: C++11 - Submitter: Joe Gottman Opened: 2011-03-13 Last modified: 2015-04-08

-

View all issues with C++11 status.

-

Discussion:

-

For an object c of type forward_list<X, Alloc>, the iterators -c.before_begin() and c.end() are part of the same underlying sequence, -so the expression c.before_begin() == c.end() must be well-defined. -But the standard says nothing about what the result of this expression -should be. The forward iterator requirements says no dereferenceable -iterator is equal to a non-dereferenceable iterator and that two -dereferenceable iterators are equal if and only if they point to the -same element. But since before_begin() and end() are both -non-dereferenceable, neither of these rules applies. -

- -

-Many forward_list methods, such as insert_after(), have a -precondition that the iterator passed to them must not be equal to -end(). Thus, user code might look like the following: -

-
-void foo(forward_list<int>& c, forward_list<int>::iterator it)
-{
-  assert(it != c.end());
-  c.insert_after(it, 42);
-}
-
- -

-Conversely, before_begin() was specifically designed to be used with -methods like insert_after(), so if c.before_begin() is passed to -this function the assertion must not fail. -

- -

[2011-03-14: Daniel comments and updates the suggested wording]

- - -

The suggested wording changes are necessary but not sufficient. Since there -does not exist an equivalent semantic definition of cbefore_begin() as -we have for cbegin(), this still leaves the question open whether -the normative remark applies to cbefore_begin() as well. A simple fix -is to define the operational semantics of cbefore_begin() in terms of -before_begin().

- -

[2011-03-24 Madrid meeting]

- - -

-General agreement that this is a serious bug. -

-Pablo: Any objections to moving 2042 to Immediate? -

-No objections. -

- - - -

Proposed resolution:

- -

Add to the definition of forward_list::before_begin() 23.3.4.3 [forwardlist.iter] -the following:

- -
-iterator before_begin();
-const_iterator before_begin() const;
-const_iterator cbefore_begin() const;
-

--1- Returns: A non-dereferenceable iterator that, when incremented, is equal to the iterator returned by begin(). -

--?- Effects: cbefore_begin() is equivalent to const_cast<forward_list const&>(*this).before_begin(). -

--?- Remarks: before_begin() == end() shall equal false. -

- - - - - -
-

2044. No definition of "Stable" for copy algorithms

-

Section: 17.6.5.7 [algorithm.stable] Status: C++14 - Submitter: Pablo Halpern Opened: 2011-03-24 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

- -

-17.6.5.7 [algorithm.stable] specified the meaning of "stable" when applied to -the different types of algorithms. The second bullet says: -

-

-— For the remove algorithms the relative order of the elements that are not removed is preserved. -

- -

-There is no description of what "stable" means for copy algorithms, even though the term is -applied to copy_if (and perhaps others now or in the future). Thus, copy_if -is using the term without a precise definition. -

- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  1. In 17.6.5.7 [algorithm.stable] p. 1 change as indicated:

    - -

    -When the requirements for an algorithm state that it is “stable” without further elaboration, it means: -

    -
      -
    • For the sort algorithms the relative order of equivalent elements is preserved.
      • -
    • For the remove and copy algorithms the relative order of the elements that are -not removed is preserved.
      • -
    • For the merge algorithms, for equivalent elements in the original two ranges, the elements from the -first range precede the elements from the second range.
      • -
    -
    - -
    2. - -
- - - - - - -
-

2045. forward_list::merge and forward_list::splice_after with unequal allocators

-

Section: 23.3.4.6 [forwardlist.ops] Status: C++14 - Submitter: Pablo Halpern Opened: 2011-03-24 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with C++14 status.

-

Discussion:

- -

-See also: 1215 -

- -

-list::merge and list::splice have the requirement that the two lists being merged or -spliced must use the same allocator. Otherwise, moving list nodes from one container to the other would -corrupt the data structure. The same requirement is needed for forward_list::merge and -forward_list::splice_after. -

- -

[ -2011 Bloomington -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  1. In 23.3.4.6 [forwardlist.ops] p. 1 change as indicated:

    - -
    -void splice_after(const_iterator position, forward_list<T,Allocator>& x);
-void splice_after(const_iterator position, forward_list<T,Allocator>&& x);
-

    -1 - Requires: position is before_begin() or is a dereferenceable -iterator in the range [begin(),end()). get_allocator() == x.get_allocator(). -&x != this. -

    - -
    2. - -

  2. In 23.3.4.6 [forwardlist.ops] p. 5 change as indicated:

    - -
    -void splice_after(const_iterator position, forward_list<T,Allocator>& x, const_iterator i);
-void splice_after(const_iterator position, forward_list<T,Allocator>&& x, const_iterator i);
-

    -5 - Requires: position is before_begin() or is a dereferenceable -iterator in the range [begin(),end()). The iterator following i is a -dereferenceable iterator in x. get_allocator() == x.get_allocator(). -

    - -
    3. - -

  3. In 23.3.4.6 [forwardlist.ops] p. 9 change as indicated:

    - -
    -void splice_after(const_iterator position, forward_list<T,Allocator>& x, 
-                  const_iterator first, const_iterator last);
-void splice_after(const_iterator position, forward_list<T,Allocator>&& x, 
-                  const_iterator first, const_iterator last);
-

    -9 - Requires: position is before_begin() or is a dereferenceable -iterator in the range [begin(),end()). (first,last) is a valid range -in x, and all iterators in the range (first,last) are dereferenceable. -position is not an iterator in the range (first,last). -get_allocator() == x.get_allocator(). -

    - -
    4. - -

  4. In 23.3.4.6 [forwardlist.ops] p. 18 change as indicated:

    - -
    -void merge(forward_list<T,Allocator>& x);
-void merge(forward_list<T,Allocator>&& x);
-template <class Compare> void merge(forward_list<T,Allocator>& x, Compare comp);
-template <class Compare> void merge(forward_list<T,Allocator>&& x, Compare comp);
-

    -18 - Requires: comp defines a strict weak ordering ([alg.sorting]), and *this -and x are both sorted according to this ordering. get_allocator() == x.get_allocator(). -

    - -
    5. - -
- - - - - - -
-

2047. Incorrect "mixed" move-assignment semantics of unique_ptr

-

Section: 20.8.1.2.3 [unique.ptr.single.asgn] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-04-16 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.asgn].

-

View all issues with C++14 status.

-

Discussion:

-

The semantics described in 20.8.1.2.3 [unique.ptr.single.asgn] p. 6

-

-Effects: Transfers ownership from u to *this as if […] followed -by an assignment from std::forward<D>(u.get_deleter()). -

-

-contradicts to the pre-conditions described in p. 4: -

-

-Requires: If E is not a reference type, assignment of the deleter from an rvalue of type E shall be -well-formed and shall not throw an exception. Otherwise, E is a reference type and assignment of the -deleter from an lvalue of type E shall be well-formed and shall not throw an exception. -

-

-Either the pre-conditions are incorrect or the semantics should be an assignment from -std::forward<E>(u.get_deleter()), instead. -

-

It turns out that this contradiction is due to an incorrect transcription from the proposed -resolution of 983 to the finally accepted proposal -n3073 (see -bullet 12) as confirmed by Howard Hinnant, thus the type argument provided to std::forward -must be fixed as indicated. -

- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  1. Edit 20.8.1.2.3 [unique.ptr.single.asgn] p. 6 as indicated:

    - -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
-

    -4 - Requires: If E is not a reference type, assignment of the deleter from an rvalue -of type E shall be well-formed and shall not throw an exception. Otherwise, E is a -reference type and assignment of the deleter from an lvalue of type E shall be well-formed and -shall not throw an exception. -

    -5 - Remarks: This operator shall not participate in overload resolution unless:

    -
      -
    • unique_ptr<U, E>::pointer is implicitly convertible to pointer and
      • -
    • U is not an array type.
      • -
    -

    -6 - Effects: Transfers ownership from u to *this as if by calling -reset(u.release()) followed by an assignment from std::forward<DE>(u.get_deleter()). -

    -7 - Returns: *this. -

    -
    -
    - -
    2. -
- - - - - - -
-

2048. Unnecessary mem_fn overloads

-

Section: 20.9 [function.objects], 20.9.11 [func.memfn] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-04-18 Last modified: 2015-04-08

-

View all other issues in [function.objects].

-

View all issues with C++14 status.

-

Discussion:

-

-The mem_fn overloads for member functions are redundant and misleading -and should be removed from the post-C++11 WP. -

-I believe the history of the overloads is as follows: -

-In TR1 and in C++0x prior to the N2798 draft, mem_fn was specified by -a single signature: -

-
-template<class R, class T> unspecified mem_fn(R T::* pm);
-
-

-and was accompanied by the remark "Implementations may implement mem_fn -as a set of overloaded function templates." This remark predates variadic templates -and was presumably to allow implementations to provide overloads for a limited -number of function parameters, to meet the implementation-defined limit on numbers of -template parameters. -

-N2770 "Concepts for the C++0x Standard Library: Utilities" added -separate overloads for pointers to member functions, apparently so -that function parameters would require the CopyConstructible concept -(those overloads first appeared in N2322.) The overloads failed to -account for varargs member functions (i.e. those declared with an -ellipsis in the parameter-declaration-clause) e.g. -

-
-struct S {
- int f(int, ...);
-};
-
-

-Syntactically such a function would be handled by the original -mem_fn(R T::* pm) signature, the only minor drawback being that there -would be no CopyConstructible requirement on the parameter list. (Core -DR 547 clarifies that partial specializations can be written to match -cv-qualified and ref-qualified functions to support the case where R T::* -matches a pointer to member function type.) -

-LWG issue 920 pointed out that additional overloads were missing for -member functions with ref-qualifiers. These were not strictly -necessary, because such functions are covered by the mem_fn(R T::* pm) signature. -

-Concepts were removed from the draft and N3000 restored the original -single signature and accompanying remark. -

-LWG 1230 was opened to strike the remark again and to add an overload -for member functions (this overload was unnecessary for syntactic reasons and -insufficient as it didn't handle member functions with cv-qualifiers and/or -ref-qualifiers.) -

-920 (and 1230) were resolved by restoring a full set of -(non-concept-enabled) overloads for member functions with cv-qualifiers and ref-qualifiers, -but as in the concept-enabled draft there were no overloads for member functions with -an ellipsis in the parameter-declaration-clause. This is what is present in the FDIS. -

-Following the thread beginning with message c++std-lib-30675, it is my -understanding that all the mem_fn overloads for member functions are -unnecessary and were only ever added to allow concept requirements. -I'm not aware of any reason implementations cannot implement mem_fn as -a single function template. Without concepts the overloads are -redundant, and the absence of overloads for varargs functions can be -interpreted to imply that varargs functions are not intended to work -with mem_fn. Clarifying the intent by adding overloads for varargs -functions would expand the list of 12 redundant overloads to 24, it -would be much simpler to remove the 12 redundant overloads entirely. -

- -

[Bloomington, 2011]

- -

-Move to Review. -

- -

-The issue and resolution appear to be correct, but there is some concern that the wording of INVOKE may be different depending on whether you pass a pointer-to-member-data or pointer-to-member-function. That might make the current wording necessary after all, and then we might need to add the missing elipsis overloads. -

- -

-There was some concern that the Remark confirming implementors had freedom to implement this as a set of overloaded functions may need to be restored if we delete the specification for these overloads. -

- -

[2012, Kona]

- -

-Moved to Tentatively Ready by the post-Kona issues processing subgroup. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  1. Change the <functional> synopsis 20.9 [function.objects] p. 2 as follows:

    - -
    -namespace std {
-  […]
-  // [func.memfn], member function adaptors:
-  template<class R, class T> unspecified mem_fn(R T::*);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...));
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) volatile);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const volatile);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) &);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const &);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) volatile &);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const volatile &);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) &&);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const &&);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) volatile &&);
-  template<class R, class T, class... Args>
-  unspecified mem_fn(R (T::*)(Args...) const volatile &&);
-
-  […]
-}
-
    -
    2. - -

  2. Change 20.9.11 [func.memfn] as follows:

    - -
    -template<class R, class T> unspecified mem_fn(R T::*);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...));
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) volatile);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const volatile);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) &);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const &);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) volatile &);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const volatile &);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) &&);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const &&);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) volatile &&);
-template<class R, class T, class... Args>
-unspecified mem_fn(R (T::*)(Args...) const volatile &&);
-
    -
    3. - -
- - - - - - -
-

2049. is_destructible is underspecified

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-04-18 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with C++14 status.

-

Discussion:

-

The conditions for the type trait is_destructible to be true -are described in Table 49 — Type property predicates:

-

-For a complete type T and given
-template <class U> -struct test { U u; };,
-test<T>::~test() is not deleted. -

- -

This specification does not say what the result would be for function -types or for abstract types:

-
    -
  1. For an abstract type X the instantiation test<X> -is already ill-formed, so we cannot say anything about whether the destructor -would be deleted or not.
    2. -
  2. In regard to function types, there exists a special rule in the core language, 14.3.1 [temp.arg.type] p. 3, -which excludes member functions to be declared via the type of the template parameter: -

    -If a declaration acquires a function type through a type dependent on a template-parameter -and this causes a declaration that does not use the syntactic form of a function declarator -to have function type, the program is ill-formed. -

    -[ Example:

    -
    -template<class T> struct A {
-  static T t;
-};
-typedef int function();
-A<function> a; // ill-formed: would declare A<function>::t
-               // as a static member function
-
    -

    -— end example ] -

    -which has the same consequence as for abstract types, namely that the corresponding -instantiation of test is already ill-formed and we cannot say anything -about the destructor. -
    3. -
-

To solve this problem, I suggest to specify function types as trivially and nothrowing -destructible, because above mentioned rule is very special for templates. For non-templates, -a typedef can be used to introduce a member as member function as clarified in 8.3.5 [dcl.fct] -p. 10.

-

For abstract types, two different suggestions have been brought to my attention: -Either declare them as unconditionally non-destructible or check whether the expression -

-
-std::declval<T&>().~T()
-
-

is well-formed in an unevaluated context. The first solution is very easy to specify, -but the second version has the advantage for providing more information to user-code. This -information could be quite useful, if generic code is supposed to invoke the destructor -of a reference to a base class indirectly via a delete expression, as suggested by -Howard Hinnant:

-
-template <class T>
-my_pointer<T>::~my_pointer() noexcept(is_nothrow_destructible<T>::value)
-{
-   delete ptr_;
-}
-
-

Additional to the is_destructible traits, its derived forms is_trivially_destructible -and is_nothrow_destructible are similarly affected, because their wording refers to "the indicated -destructor" and probably need to be adapted as well.

- -

[ -2011 Bloomington -]

- - -

-After discussion about to to handle the exceptional cases of reference types, function types (available by defererencing a function pointer) -and void types, Howard supplied proposed wording. -

- -

[ -2011-08-20 Daniel comments and provides alternatives wording -]

- - -

-The currently proposed wording would have the consequence that -every array type is not destructible, because the pseudo-destructor -requires a scalar type with the effect that the expression -

-std::declval<T&>().~T()
-

-is not well-formed for e.g. T equal to int[3]. The intuitive -solution to fix this problem would be to adapt the object type case to refer to -the expression -

-std::declval<U&>().~U()
-

-with U equal to remove_all_extents<T>::type, but that -would have the effect that arrays of unknown bounds would be destructible, if -the element type is destructible, which was not the case before (This was -intentionally covered by the special "For a complete type T" rule in -the FDIS). -

-Suggestion: Use the following definition instead: -

-

-Let U be remove_all_extents<T>::type.
-For incomplete types and function types, is_destructible<T>::value is false.
-For object types, if the expression std::declval<U&>().~U() is well-formed
-when treated as an unevaluated operand (Clause 5), then is_destructible<T>::value
-is true, otherwise it is false.
-For reference types, is_destructible<T>::value is true. -

-

-This wording also harmonizes with the "unevaluated operand" phrase -used in other places, there does not exist the definition of an -"unevaluated context" -

-Note: In the actually proposed wording this wording has been slightly reordered with the same effects. -

- -

Howard's (old) proposed resolution:

-
-

-Update 20.10.4.3 [meta.unary.prop], table 49: -

- - - - - - - -
template <class T> -struct is_destructible; -For a complete type T and given template <class U> struct test { U u; };, test<T>::~test() is not deleted. - -
- -For object types, if the expression: std::declval<T&>().~T() is well-formed in an unevaluated context then -is_destructible<T>::value is true, otherwise it is false. -
-For void types, is_destructible<T>::value is false. -
-For reference types, is_destructible<T>::value is true. -
-For function types, is_destructible<T>::value is false. - -		T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
-
-

-

- -

[2012, Kona]

- -

-Moved to Tentatively Ready by the post-Kona issues processing subgroup. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

- -

-Update 20.10.4.3 [meta.unary.prop], table 49: -

- - - - - - - -
template <class T> -struct is_destructible; -For a complete type T and given template <class U> struct test { U u; };, test<T>::~test() is not deleted. - -
- -For reference types, is_destructible<T>::value is true.
-For incomplete types and function types, is_destructible<T>::value is false.
-For object types and given U equal to remove_all_extents<T>::type,
-if the expression std::declval<U&>().~U() is well-formed when treated as an
-unevaluated operand (Clause 5 [expr]), then is_destructible<T>::value is true,
-otherwise it is false.
- -		T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
- - - - - - -
-

2050. Unordered associative containers do not use allocator_traits to define member types

-

Section: 23.5 [unord] Status: C++14 - Submitter: Tom Zieberman Opened: 2011-04-29 Last modified: 2015-04-08

-

View all other issues in [unord].

-

View all issues with C++14 status.

-

Discussion:

-

The unordered associative containers define their member types reference, -const_reference, pointer, const_pointer in terms of -their template parameter Allocator (via allocator_type typedef). As -a consequence, only the allocator types, that provide sufficient typedefs, are usable -as allocators for unordered associative containers, while other containers do not have -this deficiency. In addition to that, the definitions of said typedefs are different -from ones used in the other containers. This is counterintuitive and introduces a certain -level of confusion. These issues can be fixed by defining pointer and -const_pointer typedefs in terms of allocator_traits<Allocator> -and by defining reference and const_reference in terms of -value_type as is done in the other containers. -

- -

[ -2011 Bloomington. -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

- -

This wording is relative to the FDIS.

- -
    -

  • Change 23.5.4.1 [unord.map.overview] paragraph 3 as indicated:

    - -
    -namespace std {
-  template <class Key,
-            class T,
-            class Hash = hash<Key>,
-            class Pred = std::equal_to<Key>,
-            class Allocator = std::allocator<std::pair<const Key, T> > >
-  class unordered_map
-  {
-  public:
-    // types
-    typedef Key key_type;
-    typedef std::pair<const Key, T> value_type;
-    typedef T mapped_type;
-    typedef Hash hasher;
-    typedef Pred key_equal;
-    typedef Allocator allocator_type;
-    typedef typename allocator_typeallocator_traits<Allocator>::pointer pointer;
-    typedef typename allocator_typeallocator_traits<Allocator>::const_pointer const_pointer;
-    typedef typename allocator_type::referencevalue_type& reference;
-    typedef typename allocator_type::const_referenceconst value_type& const_reference;
-    typedef implementation-defined size_type;
-    typedef implementation-defined difference_type;
-
-    […]
-  };
-}
-
    -
    • - -

  • Change 23.5.5.1 [unord.multimap.overview] paragraph 3 as indicated:

    - -
    -namespace std {
-  template <class Key,
-            class T,
-            class Hash = hash<Key>,
-            class Pred = std::equal_to<Key>,
-            class Allocator = std::allocator<std::pair<const Key, T> > >
-  class unordered_multimap
-  {
-  public:
-    // types
-    typedef Key key_type;
-    typedef std::pair<const Key, T> value_type;
-    typedef T mapped_type;
-    typedef Hash hasher;
-    typedef Pred key_equal;
-    typedef Allocator allocator_type;
-    typedef typename allocator_typeallocator_traits<Allocator>::pointer pointer;
-    typedef typename allocator_typeallocator_traits<Allocator>::const_pointer const_pointer;
-    typedef typename allocator_type::referencevalue_type& reference;
-    typedef typename allocator_type::const_referenceconst value_type& const_reference;
-    typedef implementation-defined size_type;
-    typedef implementation-defined difference_type;
-
-    […]
-  };
-}
-
    -
    • - -

  • Change 23.5.6.1 [unord.set.overview] paragraph 3 as indicated:

    - -
    -namespace std {
-  template <class Key,
-            class Hash = hash<Key>,
-            class Pred = std::equal_to<Key>,
-            class Allocator = std::allocator<Key> >
-  class unordered_set
-  {
-  public:
-    // types
-    typedef Key key_type;
-    typedef Key value_type;
-    typedef Hash hasher;
-    typedef Pred key_equal;
-    typedef Allocator allocator_type;
-    typedef typename allocator_typeallocator_traits<Allocator>::pointer pointer;
-    typedef typename allocator_typeallocator_traits<Allocator>::const_pointer const_pointer;
-    typedef typename allocator_type::referencevalue_type& reference;
-    typedef typename allocator_type::const_referenceconst value_type& const_reference;
-    typedef implementation-defined size_type;
-    typedef implementation-defined difference_type;
-
-    […]
-  };
-}
-
    -
    • - -

  • Change 23.5.7.1 [unord.multiset.overview] paragraph 3 as indicated:

    - -
    -namespace std {
-  template <class Key,
-            class Hash = hash<Key>,
-            class Pred = std::equal_to<Key>,
-            class Allocator = std::allocator<Key> >
-  class unordered_multiset
-  {
-  public:
-    // types
-    typedef Key key_type;
-    typedef Key value_type;
-    typedef Hash hasher;
-    typedef Pred key_equal;
-    typedef Allocator allocator_type;
-    typedef typename allocator_typeallocator_traits<Allocator>::pointer pointer;
-    typedef typename allocator_typeallocator_traits<Allocator>::const_pointer const_pointer;
-    typedef typename allocator_type::referencevalue_type& reference;
-    typedef typename allocator_type::const_referenceconst value_type& const_reference;
-    typedef implementation-defined size_type;
-    typedef implementation-defined difference_type;
-
-    […]
-  };
-}
-
    -
    • - -
- - - - - - -
-

2052. Mixup between mapped_type and value_type for associative containers

-

Section: 23.2.4 [associative.reqmts] Status: Resolved - Submitter: Marc Glisse Opened: 2011-05-04 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with Resolved status.

-

Discussion:

-

-(this is basically reopening the first part of issue 2006, as discussed in the thread -starting at c++std-lib-30698 ) -

-Section 23.2.4 [associative.reqmts] -

-In Table 102, several uses of T (which means mapped_type here) should -be value_type instead. This is almost editorial. For instance: -

-
-a_uniq.emplace(args)
-

-Requires: T shall be EmplaceConstructible into X from args. -

-Effects: Inserts a T object t constructed with -std::forward<Args>(args)... if and only if there is no element in the -container with key equivalent to the key of t. The bool component of -the returned pair is true if and only if the insertion takes place, and the iterator component -of the pair points to the element with key equivalent to the key of t. -

- -

[ -2011 Bloomington -]

- - -

-Not even an exhaustive list of problem locations. No reason to doubt issue. -

-

-Pablo agrees to provide wording. -

- -

[ -2011-09-04 Pablo Halpern provides improved wording -]

- - -

[2014-02-15 post-Issaquah session : move to Resolved]

- -

-AJM to replace this note with a 'Resolved By...' after tracking down the exact sequence of events, but clearly resolved in C++14 DIS. -

- - - -

Proposed resolution:

-

-In both section 23.2.4 [associative.reqmts] Table 102 and 23.2.5 [unord.req], Table 103, make the following text replacements: -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Original text, in FDIS Replacement text
T is CopyInsertable into X and CopyAssignable.value_type is CopyInsertable into X, key_type is CopyAssignable, and -mapped_type is CopyAssignable (for containers having a mapped_type)
T is CopyInsertablevalue_type is CopyInsertable
T shall be CopyInsertablevalue_type shall be CopyInsertable
T shall be MoveInsertablevalue_type shall be MoveInsertable
T shall be EmplaceConstructiblevalue_type shall be EmplaceConstructible
T objectvalue_type object
- -

[ -Notes to the editor: The above are carefully selected -phrases that can be used for global search-and-replace within -the specified sections without accidentally making changes to -correct uses T. -]

- - - - - - -
-

2053. Errors in regex bitmask types

-

Section: 28.5 [re.const] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-05-09 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-When N3110 -was applied to the WP some redundant "static" keywords were added and one form of initializer -which isn't valid for enumeration types was replaced with another form of invalid initializer. -

- -

[ -2011 Bloomington. -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Change 28.5.1 [re.synopt] as indicated:

    -
    -namespace std {
-  namespace regex_constants {
-    typedef T1 syntax_option_type;
-    static constexpr syntax_option_type icase = unspecified ;
-    static constexpr syntax_option_type nosubs = unspecified ;
-    static constexpr syntax_option_type optimize = unspecified ;
-    static constexpr syntax_option_type collate = unspecified ;
-    static constexpr syntax_option_type ECMAScript = unspecified ;
-    static constexpr syntax_option_type basic = unspecified ;
-    static constexpr syntax_option_type extended = unspecified ;
-    static constexpr syntax_option_type awk = unspecified ;
-    static constexpr syntax_option_type grep = unspecified ;
-    static constexpr syntax_option_type egrep = unspecified ;
-  }
-}
-
    -
    2. - -

  2. Change 28.5.2 [re.matchflag] as indicated:

    -
    -namespace std {
-  namespace regex_constants {
-    typedef T2 match_flag_type;
-    static constexpr match_flag_type match_default = 0{};
-    static constexpr match_flag_type match_not_bol = unspecified ;
-    static constexpr match_flag_type match_not_eol = unspecified ;
-    static constexpr match_flag_type match_not_bow = unspecified ;
-    static constexpr match_flag_type match_not_eow = unspecified ;
-    static constexpr match_flag_type match_any = unspecified ;
-    static constexpr match_flag_type match_not_null = unspecified ;
-    static constexpr match_flag_type match_continuous = unspecified ;
-    static constexpr match_flag_type match_prev_avail = unspecified ;
-    static constexpr match_flag_type format_default = 0{};
-    static constexpr match_flag_type format_sed = unspecified ;
-    static constexpr match_flag_type format_no_copy = unspecified ;
-    static constexpr match_flag_type format_first_only = unspecified ;
-  }
-}
-
    -
    3. - -

  3. Change 28.5.3 [re.err] as indicated:

    -
    -namespace std {
-  namespace regex_constants {
-    typedef T3 error_type;
-    static constexpr error_type error_collate = unspecified ;
-    static constexpr error_type error_ctype = unspecified ;
-    static constexpr error_type error_escape = unspecified ;
-    static constexpr error_type error_backref = unspecified ;
-    static constexpr error_type error_brack = unspecified ;
-    static constexpr error_type error_paren = unspecified ;
-    static constexpr error_type error_brace = unspecified ;
-    static constexpr error_type error_badbrace = unspecified ;
-    static constexpr error_type error_range = unspecified ;
-    static constexpr error_type error_space = unspecified ;
-    static constexpr error_type error_badrepeat = unspecified ;
-    static constexpr error_type error_complexity = unspecified ;
-    static constexpr error_type error_stack = unspecified ;
-  }
-}
-
    -
    4. -
- - - - - -
-

2054. time_point constructors need to be constexpr

-

Section: 20.12.6 [time.point] Status: Resolved - Submitter: Anthony Williams Opened: 2011-05-13 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-In 20.12.6 [time.point], time_point::min() and time_point::max() -are listed as constexpr. However, time_point has no constexpr constructors, -so is not a literal type, and so these functions cannot be constexpr without adding a -constexpr constructor for implementation purposes. -

-Proposed resolution: Add constexpr to the constructors of time_point. The effects of -the constructor template basically imply that the member function time_since_epoch() is -intended to be constexpr as well. -

- -

[2012, Portland]

- -

-Resolved by adopting paper n3469. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Alter the class template definition in 20.12.6 [time.point] as follows:

    -
    -template <class Clock, class Duration = typename Clock::duration>
-class time_point {
-  […]
-public:
-  // 20.11.6.1, construct:
-  constexpr time_point(); // has value epoch
-  constexpr explicit time_point(const duration& d); // same as time_point() + d
-  template <class Duration2>
-    constexpr time_point(const time_point<clock, Duration2>& t);
-
-  // 20.11.6.2, observer:
-  constexpr duration time_since_epoch() const;
-  […]
-};
-
    -
    2. - -

  2. Alter the declarations in 20.12.6.1 [time.point.cons]:

    -
    -constexpr time_point();
-

    --1- Effects: Constructs an object of type time_point, initializing d_ with duration::zero(). Such a -time_point object represents the epoch. -

    -
    -constexpr explicit time_point(const duration& d);
-

    --2- Effects: Constructs an object of type time_point, initializing d_ with d. Such a -time_point object represents the epoch + d. -

    -
    -template <class Duration2>
-  constexpr time_point(const time_point<clock, Duration2>& t);
-

    --3- Remarks: This constructor shall not participate in overload resolution unless Duration2 is implicitly -convertible to duration. -

    --4- Effects: Constructs an object of type time_point, initializing d_ with t.time_since_epoch(). -

    -
    3. - -

  3. Alter the declaration in 20.12.6.2 [time.point.observer]:

    -
    -constexpr duration time_since_epoch() const;
-

    --1- Returns: d_. -

    -
    4. -
- - - - - -
-

2056. future_errc enums start with value 0 (invalid value for broken_promise)

-

Section: 30.6.1 [futures.overview] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2011-05-18 Last modified: 2015-04-08

-

View all other issues in [futures.overview].

-

View all issues with C++14 status.

-

Discussion:

-

-In 30.6.1 [futures.overview] enum class future_errc is defined as follows: -

-enum class future_errc {
-  broken_promise,
-  future_already_retrieved,
-  promise_already_satisfied,
-  no_state
-};
-

-With this declaration broken_promise has value 0, which means that -for a future_error f with this code -

-f.code().operator bool()
-

-yields false, which makes no sense. 0 has to be reserved for "no error". -So, the enums defined here have to start with 1. -

-Howard, Anthony, and Jonathan have no objections. -

-

[Discussion in Bloomington 2011-08-16] -

-

-Previous resolution: -

-
-

This wording is relative to the FDIS.

-
    -

  1. In 30.6.1 [futures.overview], header <future> synopsis, fix -the declaration of future_errc as follows:

    -
    -namespace std {
-  enum class future_errc {
-    broken_promise,
-    future_already_retrieved = 1,
-    promise_already_satisfied,
-    no_state,
-    broken_promise
-  };
-  […]
-}
-
    -
    2. -
-
-

-Is this resolution overspecified? These seem to be all implementation-defined. How do users add new values and not conflict with established error codes? -

-PJP proxy says: over-specified. boo. -

-Other error codes: look for is_error_code_enum specializations. Only one exists io_errc -

-Peter: I don't see any other parts of the standard that specify error codes where we have to do something similar. -

-Suggest that for every place where we add an error code, the following: -

-
    -
  1. no zero values -
  2. all implementation defined values, so future_already_retrieved = implementation_defined -
  3. values are distinct -
- -

[2012, Kona]

- -

-Moved to Tentatively Ready by the post-Kona issues processing subgroup. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-

In 30.6.1 [futures.overview], header <future> synopsis, fix -the declaration of future_errc as follows:

- -
-namespace std {
-  enum class future_errc {
-    broken_promise = implementation defined,
-    future_already_retrieved = implementation defined,
-    promise_already_satisfied = implementation defined,
-    no_state = implementation defined
-  };
-  […]
-}
-
-

In 30.6.1 [futures.overview], header <future> synopsis, add a paragraph after paragraph 2 as follows:

- -The enum values of future_errc are distinct and not zero. - - - - -
-

2057. time_point + duration semantics should be made constexpr conforming

-

Section: 20.12.6.5 [time.point.nonmember] Status: Resolved - Submitter: Daniel Krügler Opened: 2011-05-21 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

-It has been observed by LWG 2054 that the specification of some time_point member functions -already imply that time_point needs to be a literal type and suggests to specify the constructors -and the member function time_since_epoch() as constexpr functions at the -minimum necessary. Adding further constexpr specifier to other operations should -clearly be allowed and should probably be done as well. But to allow for further constexpr -functions in the future requires that their semantics is compatible to operations allowed in constexpr -functions. This is already fine for all operations, except this binary plus operator: -

-
-template <class Clock, class Duration1, class Rep2, class Period2>
-time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2>>::type>
-operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
-

--1- Returns: CT(lhs) += rhs, where CT is the type of the return value. -

-

-for similar reasons as those mentioned in 2020. The semantics should be fixed to allow -for making them constexpr. This issue should also be considered as a placeholder for a request -to make the remaining time_point operations similarly constexpr as had been done for -duration. -

- - -

[2012, Portland]

- -

-Resolved by adopting paper n3469. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. In 20.12.6.5 [time.point.nonmember], p.1 change the Returns element semantics as indicated:

    -
    -template <class Clock, class Duration1, class Rep2, class Period2>
-time_point<Clock, typename common_type<Duration1, duration<Rep2, Period2>>::type>
-operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
-

    --1- Returns: CT(lhs) += rhsCT(lhs.time_since_epoch() + rhs), where CT -is the type of the return value. -

    -
    2. -
- - - - - -
-

2058. valarray and begin/end

-

Section: 26.6 [numarray] Status: C++14 - Submitter: Gabriel Dos Reis Opened: 2011-05-17 Last modified: 2015-04-08

-

View all other issues in [numarray].

-

View all issues with C++14 status.

-

Discussion:

-

-It was just brought to my attention that the pair of functions -begin/end were added to valarray component. -Those additions strike me as counter to the long standing agreement -that valarray<T> is not yet another container. Valarray values -are in general supposed to be treated as a whole, and as such -has a loose specification allowing expression template techniques. -

-The addition of these functions sound to me as making it much harder -(or close to impossible) to effectively use expression templates -as implementation techniques, for no clear benefits. -

-My recommendation would be to drop begin/end - or at least for the -const valarray<T>& version. I strongly believe those -are defects. -

-

[This issue was discussed on the library reflector starting from c++std-lib-30761. -Some of the key conclusions of this discussion were:]

- -
    -
  1. The begin/end members were added to allow valarray to participate -in the new range-based for-loop by n2930 -and not to make them container-like.
    2. -
  2. It is currently underspecified when the iterator values returned from -begin/end become invalidated. To fix this, these invalidation rules need at -least to reflect the invalidation rules of the references returned by the -operator[] overloads of valarray (26.6.2.4 [valarray.access]). -
    3. -
  3. A further problem is that the requirements expressed in 26.6.1 [valarray.syn] p.3-5 -enforce an implementation to provide further overloads of begin/end, if the -replacement type technique is used (which was clearly part of the design of valarray). -Providing such additional overloads would also lead to life-time problems in examples like -begin(x + y) where x and y are expressions involving valarray -objects. To fix this, the begin/end overloads could be explicitly excluded from the -general statements of 26.6.1 [valarray.syn] p.3-5. This would make it unspecified -whether the expression begin(x + y) would be well-formed, portable code would -need to write this as begin(std::valarray<T>(x + y)).
    4. -
- -

[ -2011 Bloomington -]

- - -

-The intent of these overloads is entirely to support the new for syntax, and not to create -new containers. -

- -

-Stefanus provides suggested wording. -

- - -

[2012, Kona]

- -

-Moved to Tenatively Ready by post-meeting issues processing group, after confirmation -from Gaby. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

-In 26.6.1 [valarray.syn]/4, make the following insertion: -

- -

-4 Implementations introducing such replacement types shall provide additional functions and operators as -follows: -

-
    -
  • for every function taking a const valarray<T>& other than begin and end -(26.6.10 [valarray.range]), identical functions taking the replacement types shall be added; -
    • -
  • -for every function taking two const valarray<T>& arguments, identical functions taking every combination -of const valarray<T>& and replacement types shall be added. -
    • -
- -

-In 26.6.10 [valarray.range], make the following insertion: -

-

-1 In the begin and end function templates that follow, unspecified1 is a type that meets -the requirements of a mutable random access iterator (24.2.7) whose value_type is the template parameter -T and whose reference type is T&. unspecified2 is a type that meets the -requirements of a constant random access iterator (24.2.7) whose value_type is the template parameter -T and whose reference type is const T&. -

-

-2 The iterators returned by begin and end for an array are guaranteed to be valid until the -member function resize(size_t, T) (26.6.2.8 [valarray.members]) is called for that array or until -the lifetime of that array ends, whichever happens first. -

- - - - - -
-

2059. C++0x ambiguity problem with map::erase

-

Section: 23.4.4 [map] Status: WP - Submitter: Christopher Jefferson Opened: 2011-05-18 Last modified: 2015-05-22

-

View all other issues in [map].

-

View all issues with WP status.

-

Discussion:

-

-map::erase (and several related methods) took an iterator in C++03, but take a const_iterator -in C++0x. This breaks code where the map's key_type has a constructor which accepts an iterator -(for example a template constructor), as the compiler cannot choose between erase(const key_type&) -and erase(const_iterator).

-
-#include <map>
-
-struct X
-{
-  template<typename T>
-  X(T&) {}
-};
-
-bool operator<(const X&, const X&) { return false; }
-
-void erasor(std::map<X,int>& s, X x)
-{
-  std::map<X,int>::iterator it = s.find(x);
-  if (it != s.end())
-    s.erase(it);
-}
-
- -

[ -2011 Bloomington -]

- - -

-This issue affects only associative container erase calls, and is not more general, as these are the -only functions that are also overloaded on another single arguement that might cause confusion - the erase -by key method. The complete resolution should simply restore the iterator overload in addition to the -const_iterator overload for all eight associative containers. -

- -

-Proposed wording supplied by Alan Talbot, and moved to Review. -

- - -

[2012, Kona]

- -

-Moved back to Open by post-meeting issues processing group. -

-

-Pablo very unhappy about case of breaking code with ambiguous conversion between both iterator types. -

-

-Alisdair strongly in favor of proposed resolution, this change from C++11 bit Chris in real code, -and it took a while to track down the cause. -

-

-Move to open, bring in front of a larger group -

-

-Proposed wording from Jeremiah: - -erase(key) shall not participate in overload resolution if iterator is -convertible to key. - -Note that this means making erase(key) a template-method -

-

-Poll Chris to find out if he already fixed his code, or fixed his library -

-

-Jeremiah - allow both overloads, but enable_if the const_iterator form as -a template, requiring is_same to match only const_iterator. -

-

-Poll PJ to see if he has already applied this fix? -

- -

[2015-02 Cologne]

- -

-AM: To summarize, we changed a signature and code broke. At what point do we stop and accept breakage in increasingly obscure code? -VV: libc++ is still broken, but libstdc++ works, so they've fixed this — perhaps using this PR? [Checks] Yes, libstdc++ -uses this solution, and has a comment pointing to LWG 2059. AM: This issue hasn't been looked at since Kona. In any case, we -already have implementation experience now. -

-AM: I'd say let's ship it. We already have implementation experience (libstdc++ and MSVS). MC: And "tentatively ready" lets me -try to implement this and see how it works. -

- - -

Proposed resolution:

-

-Editorial note: The following things are different between 23.2.4 [associative.reqmts] p.8 and -23.2.5 [unord.req] p.10. These should probably be reconciled. -

-
-
    -
  1. First uses the convention "denotes"; second uses the convention "is".
    2. -
  2. First redundantly says: "If no such element exists, returns a.end()." in erase table entry, second does not.
    3. -
-
- -

-23.2.4 [associative.reqmts] Associative containers -

-

-8 In Table 102, X denotes an associative container class, a denotes a value of X, a_uniq -denotes a value of X when X supports unique keys, a_eq denotes a value of X when -X supports multiple keys, u denotes an identifier, i and j satisfy input iterator -requirements and refer to elements implicitly convertible to value_type, [i,j) denotes a valid range, -p denotes a valid const iterator to a, q denotes a valid dereferenceable const iterator to a, -r denotes a valid dereferenceable iterator to a, [q1, q2) denotes a valid range of const iterators -in a, il designates an object of type initializer_list<value_type>, t denotes a value of -X::value_type, k denotes a value of X::key_type and c denotes a value of type -X::key_compare. A denotes the storage allocator used by X, if any, or -std::allocator<X::value_type> otherwise, and m denotes an allocator of a type convertible to A. -

- -

-23.2.4 [associative.reqmts] Associative containers Table 102 -

-

-Add row: -

- - - - - - - - -
a.erase(r)iterator -erases the element pointed to by r. Returns an iterator pointing to the element immediately following r -prior to the element being erased. If no such element exists, returns a.end(). -amortized constant
- - -

-23.2.5 [unord.req] Unordered associative containers

-

-10 In table 103: X is an unordered associative container class, a is an object of type X, -b is a possibly const object of type X, a_uniq is an object of type X when -X supports unique keys, a_eq is an object of type X when X supports equivalent keys, -i and j are input iterators that refer to value_type, [i, j) is a valid range, -p and q2 are valid const iterators to a, q and q1 are valid dereferenceable -const iterators to a, r is a valid dereferenceable iterator to a, [q1,q2) is a -valid range in a, il designates an object of type initializer_list<value_type>, -t is a value of type X::value_type, k is a value of type key_type, hf is a -possibly const value of type hasher, eq is a possibly const value of type key_equal, -n is a value of type size_type, and z is a value of type float. -

- -

-23.2.5 [unord.req] Unordered associative containers Table 103 -

-

-Add row: -

- - - - - - - - -
a.erase(r)iterator -Erases the element pointed to by r. Returns the iterator immediately following r prior to the erasure. -Average case O(1), worst case O(a.size()).
- - -

-23.4.4.1 [map.overview] Class template map overview p. 2 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.4.5.1 [multimap.overview] Class template multimap overview p. 2 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.4.6.1 [set.overview] Class template set overview p. 2 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.4.7.1 [multiset.overview] Class template multiset overview -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.5.4.1 [unord.map.overview] Class template unordered_map overview p. 3 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.5.5.1 [unord.multimap.overview] Class template unordered_multimap overview p. 3 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-23.5.6.1 [unord.set.overview] Class template unordered_set overview p. 3 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- - -

-23.5.7.1 [unord.multiset.overview] Class template unordered_multiset overview p. 3 -

-
-iterator erase(iterator position);
-iterator erase(const_iterator position);
-size_type erase(const key_type& x);
-iterator erase(const_iterator first, const_iterator last);
-
- -

-C.2.13 [diff.cpp03.containers] C.2.12 Clause 23: containers library -

-

-23.2.3, 23.2.4 -

-

-Change: Signature changes: from iterator to const_iterator parameters -

-

-Rationale: Overspecification. Effects: The signatures of the following member functions changed from -taking an iterator to taking a const_iterator: -

-
    -
  • insert(iter, val) for vector, deque, list, set, multiset, map, multimap
    • -
  • insert(pos, beg, end) for vector, deque, list, forward_list
    • -
  • erase(iter) for set, multiset, map, multimap
    • -
  • erase(begin, end) for set, multiset, map, multimap
    • -
  • all forms of list::splice
    • -
  • all forms of list::merge
    • -
-

-Valid C++ 2003 code that uses these functions may fail to compile with this International Standard. -

- - - - - -
-

2061. make_move_iterator and arrays

-

Section: 24.3 [iterator.synopsis], 24.5.3 [move.iterators] Status: C++14 - Submitter: Marc Glisse Opened: 2011-05-28 Last modified: 2015-04-08

-

View all other issues in [iterator.synopsis].

-

View all issues with C++14 status.

-

Discussion:

-

-The standard library always passes template iterators by value and never by reference, -which has the nice effect that an array decays to a pointer. There is one exception: -make_move_iterator. -

-
-#include <iterator>
-int main(){
-  int a[]={1,2,3,4};
-  std::make_move_iterator(a+4);
-  std::make_move_iterator(a); // fails here
-}
-
- -

[ -2011 Bloomington. -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Modify the header <iterator> synopsis in 24.3 [iterator.synopsis]:

    -
    -namespace std {
-  […]
-  template <class Iterator>
-  move_iterator<Iterator> make_move_iterator(const Iterator&Iterator i);
-
-  […]
-}
-
    -
    2. - -

  2. Modify the class template move_iterator synopsis in 24.5.3.1 [move.iterator]:

    -
    -namespace std {
-  […]
-  template <class Iterator>
-  move_iterator<Iterator> make_move_iterator(const Iterator&Iterator i);
-}
-
    -
    3. - -

  3. Modify 24.5.3.3.14 [move.iter.nonmember]:

    -
    -template <class Iterator>
-move_iterator<Iterator> make_move_iterator(const Iterator&Iterator i);
-

    --3- Returns: move_iterator<Iterator>(i). -

    -
    4. -
- - - - - -
-

2063. Contradictory requirements for string move assignment

-

Section: 21.4 [basic.string] Status: WP - Submitter: Howard Hinnant Opened: 2011-05-29 Last modified: 2015-05-22

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with WP status.

-

Discussion:

-

-21.4.1 [string.require]/p4 says that basic_string is an "allocator-aware" -container and behaves as described in 23.2.1 [container.requirements.general]. -

-23.2.1 [container.requirements.general] describes move assignment in p7 and Table 99. -

-If allocator_traits<allocator_type>::propagate_on_container_move_assignment::value -is false, and if the allocators stored in the lhs and rhs sides are not equal, then move -assigning a string has the same semantics as copy assigning a string as far as resources are -concerned (resources can not be transferred). And in this event, the lhs may have to acquire -resources to gain sufficient capacity to store a copy of the rhs. -

-However 21.4.2 [string.cons]/p22 says: -

-basic_string<charT,traits,Allocator>&
-operator=(basic_string<charT,traits,Allocator>&& str) noexcept;
-

-Effects: If *this and str are not the same object, modifies *this -as shown in Table 71. [Note: A valid implementation is swap(str). — end note ] -

-These two specifications for basic_string::operator=(basic_string&&) are in conflict with -each other. It is not possible to implement a basic_string which satisfies both requirements. -

-Additionally assign from an rvalue basic_string is defined as: -

-basic_string& assign(basic_string&& str) noexcept;
-

-Effects: The function replaces the string controlled by *this with a string of length -str.size() whose elements are a copy of the string controlled by str. [ Note: A valid -implementation is swap(str). — end note ] -

-It seems contradictory that this member can be sensitive to propagate_on_container_swap instead -of propagate_on_container_move_assignment. Indeed, there is a very subtle chance for undefined -behavior here: If the implementation implements this in terms of swap, and if -propagate_on_container_swap is false, and if the two allocators are unequal, the behavior -is undefined, and will likely lead to memory corruption. That's a lot to go wrong under a member -named "assign". -

- -

[ -2011 Bloomington -]

- - -

-Alisdair: Can this be conditional noexcept? -

-

-Pablo: We said we were not going to put in many conditional noexcepts. Problem is not allocator, but non-normative definition. It says swap is a valid operation which it is not. -

-

-Dave: Move assignment is not a critical method. -

-

-Alisdair: Was confusing assignment and construction. -

-

-Dave: Move construction is critical for efficiency. -

-

-Kyle: Is it possible to test for noexcept. -

-

-Alisdair: Yes, query the noexcept operator. -

-

-Alisdair: Agreed there is a problem that we cannot unconditionally mark these operations as noexcept. -

-

-Pablo: How come swap is not defined in alloc -

-

-Alisdair: It is in utility. -

-

-Pablo: Swap has a conditional noexcept. Is no throw move constructable, is no throw move assignable. -

-

-Pablo: Not critical for strings or containers. -

-

-Kyle: Why? -

-

-Pablo: They do not use the default swap. -

-

-Dave: Important for deduction in other types. -

-

-Alisdair: Would change the policy we adopted during FDIS mode. -

-

-Pablo: Keep it simple and get some vendor experience. -

-

-Alisdair: Is this wording correct? Concerned with bullet 2. -

-

-Pablo: Where does it reference containers section. -

-

-Alisdair: String is a container. -

-

-Alisdair: We should not remove redundancy piecemeal. -

-

-Pablo: I agree. This is a deviation from rest of string. Missing forward reference to containers section. -

-

-Pablo: To fix section 2. Only the note needs to be removed. The rest needs to be a forward reference to containers. -

-

-Alisdair: That is a new issue. -

-

-Pablo: Not really. Talking about adding one sentence, saying that basic string is a container. -

-

-Dave: That is not just a forward reference, it is a semantic change. -

-

-PJ: We intended to make it look like a container, but it did not satisfy all the requirements. -

-

-Pablo: Clause 1 is correct. Clause 2 is removing note and noexcept (do not remove the rest). Clause 3 is correct. -

-

-Alisdair: Not sure data() is correct (in clause 2). -

-

-Conclusion: Move to open, Alisdair and Pablo volunteered to provide wording -

- -

[ -originally proposed wording: -]

- - -

This wording is relative to the FDIS.

-
    -

  1. Modify the class template basic_string synopsis in 21.4 [basic.string]:

    -
    -namespace std {
-  template<class charT, class traits = char_traits<charT>,
-    class Allocator = allocator<charT> >
-  class basic_string {
-  public:
-    […]
-    basic_string& operator=(basic_string&& str) noexcept;
-    […]
-    basic_string& assign(basic_string&& str) noexcept;
-    […]
-  };
-}
-
    -
    2. - -

  2. Remove the definition of the basic_string move assignment operator from 21.4.2 [string.cons] -entirely, including Table 71 — operator=(const basic_string<charT, traits, Allocator>&&). -This is consistent with how we define move assignment for the containers in Clause 23:

    -
    -basic_string<charT,traits,Allocator>&
-operator=(basic_string<charT,traits,Allocator>&& str) noexcept;
-

    --22- Effects: If *this and str are not the same object, modifies *this as shown -in Table 71. [ Note: A valid implementation is swap(str). — end note ] -

    --23- If *this and str are the same object, the member has no effect. -

    --24- Returns: *this -

    -
    - - - - - - - - - - - - - - - - - - - - - - - -
    Table 71 — operator=(const basic_string<charT, traits, Allocator>&&)
    ElementValue
    data()points at the array whose first element was pointed -at by str.data()
    size()previous value of str.size()
    capacity()a value at least as large as size()
    -
    -
    3. - -

  3. Modify the paragraphs prior to 21.4.6.3 [string::assign] p.3 as indicated (The -first insertion recommends a separate paragraph number for the indicated paragraph):

    -
    -basic_string& assign(basic_string&& str) noexcept;
-

    --?- Effects: Equivalent to *this = std::move(str). -The function replaces the string controlled by *this with a string of length -str.size() whose elements are a copy of the string controlled by str. -[ Note: A valid implementation is swap(str). — end note ] -

    --3- Returns: *this -

    - -
    4. -
- -

[ -2012-08-11 Joe Gottman observes: -]

- - -
-

-One of the effects of basic_string's move-assignment operator (21.4.2 [string.cons], Table 71) is -

-
- - - - - - - - - - - - - -
ElementValue
data()points at the array whose first element was pointed at by str.data()
- -
-

-If a string implementation uses the small-string optimization and the input string str is small enough -to make use of it, this effect is impossible to achieve. To use the small string optimization, a string has to -be implemented using something like -

-
-union
-{
-   char buffer[SMALL_STRING_SIZE];
-   char *pdata;
-};
-
-

-When the string is small enough to fit inside buffer, the data() member function returns -static_cast<const char *>(buffer), and since buffer is an array variable, there -is no way to implement move so that the moved-to string's buffer member variable is equal to -this->buffer. -

-Resolution proposal: -

-Change Table 71 to read: -

-
- - - - - - - - - - - - - -
ElementValue
data()points at the array whose first element was pointed at by str.data() -that contains the same characters in the same order as str.data() contained before -operator=() was called
- -
-
-
-
- -

[2015-05-07, Lenexa]

- -

-Howard suggests improved wording -

-Move to Immediate -

- - - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Modify the class template basic_string synopsis in 21.4 [basic.string]:

    -
    -namespace std {
-  template<class charT, class traits = char_traits<charT>,
-    class Allocator = allocator<charT> >
-  class basic_string {
-  public:
-    […]
-    basic_string& assign(basic_string&& str) noexcept(
-         allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
-           allocator_traits<Allocator>::is_always_equal::value);
-    […]
-  };
-}
-
    -
    2. - -

  2. Change 21.4.2 [string.cons]/p21-23:

    -
    -basic_string&
-operator=(basic_string&& str) noexcept(
-         allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
-           allocator_traits<Allocator>::is_always_equal::value);
-

    --21- Effects: If *this and str are not the same object, modifies *this as shown -in Table 71. [ Note: A valid implementation is swap(str). — end note ] -Move assigns as a sequence container ([container.requirements]), except that iterators, pointers and references may be invalidated. -

    --22- If *this and str are the same object, the member has no effect. -

    --23- Returns: *this -

    -
    - - - - - - - - - - - - - - - - - - - - - - - -
    Table 71 — operator=(basic_string&&) effects
    ElementValue
    data()points at the array whose first element was pointed -at by str.data()
    size()previous value of str.size()
    capacity()a value at least as large as size()
    -
    -
    3. - -

  3. Modify the paragraphs prior to 21.4.6.3 [string::assign] p.3 as indicated

    -
    -basic_string& assign(basic_string&& str) noexcept(
-         allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
-           allocator_traits<Allocator>::is_always_equal::value);
-

    --3- Effects: Equivalent to *this = std::move(str). -The function replaces the string controlled by *this with a string of length -str.size() whose elements are a copy of the string controlled by str. -[ Note: A valid implementation is swap(str). — end note ] -

    --4- Returns: *this -

    - -
    4. -
- - - - - -
-

2064. More noexcept issues in basic_string

-

Section: 21.4 [basic.string] Status: C++14 - Submitter: Howard Hinnant Opened: 2011-05-29 Last modified: 2015-04-08

-

View other active issues in [basic.string].

-

View all other issues in [basic.string].

-

View all issues with C++14 status.

-

Discussion:

-

-The following inconsistencies regarding noexcept for basic_string are noted. -

-Member swap is not marked noexcept: -

-void swap(basic_string& str);
-

-But the global swap is marked noexcept: -

-template<class charT, class traits, class Allocator>
-void swap(basic_string<charT,traits,Allocator>& lhs,
-          basic_string<charT,traits,Allocator>& rhs) noexcept;
-

-But only in the definition, not in the synopsis. -

-All comparison operators are marked noexcept in their definitions, but not in the synopsis. -

-The compare function that takes a pointer: -

-int compare(const charT *s) const;
-

-is not marked noexcept. But some of the comparison functions which are marked noexcept -(only in their definition) are specified to call the throwing compare operator: -

-template<class charT, class traits, class Allocator>
-bool operator==(const basic_string<charT,traits,Allocator>& lhs,
-                const charT* rhs) noexcept;
-

-Returns: lhs.compare(rhs) == 0. -

-

-All functions with a narrow contract should not be declared as noexcept according to -the guidelines presented in n3279. -Among these narrow contract functions are the swap functions (23.2.1 [container.requirements.general] p. 8) -and functions with non-NULL const charT* parameters. -

-

[2011-06-08 Daniel provides wording]

- - -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS. Both move-assignment operator and the moving assign -function are not touched by this issue, because they are handled separately by issue 2063.

-
    -

  1. Modify the header <string> synopsis in 21.3 [string.classes] as -indicated (Rationale: Adding noexcept to these specific overloads is in sync with -applying the same rule to specific overloads of the member functions find, compare, etc. -This approach deviates from that taken in n3279, -but seems more consistent given similar application for comparable member functions):

    - -
    -#include <initializer_list>
-
-namespace std {
-
-  […]
-  template<class charT, class traits, class Allocator>
-    bool operator==(const basic_string<charT,traits,Allocator>& lhs,
-                    const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-  template<class charT, class traits, class Allocator>
-    bool operator!=(const basic_string<charT,traits,Allocator>& lhs,
-                    const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-
-  template<class charT, class traits, class Allocator>
-    bool operator<(const basic_string<charT,traits,Allocator>& lhs,
-                   const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-  template<class charT, class traits, class Allocator>
-    bool operator>(const basic_string<charT,traits,Allocator>& lhs,
-                   const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-
-  template<class charT, class traits, class Allocator>
-    bool operator<=(const basic_string<charT,traits,Allocator>& lhs,
-                    const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-  template<class charT, class traits, class Allocator>
-    bool operator>=(const basic_string<charT,traits,Allocator>& lhs,
-                    const basic_string<charT,traits,Allocator>& rhs) noexcept;
-  […]
-}
-
    -
    2. - -

  2. Modify the class template basic_string synopsis in 21.4 [basic.string] as -indicated (Remark 1: The noexcept at the move-constructor is fine, because even for a -small-object optimization there is no problem here, because basic_string::value_type -is required to be a non-array POD as of 21.1 [strings.general] p1, Remark 2: This -proposal removes the noexcept at single character overloads of find, rfind, -etc. because they are defined in terms of potentially allocating functions. It seems like -an additional issue to me to change the semantics in terms of non-allocating functions and -adding noexcept instead):

    - -
    -namespace std {
-  template<class charT, class traits = char_traits<charT>,
-    class Allocator = allocator<charT> >
-  class basic_string {
-  public:
-    […]
-    // [string.ops], string operations:
-    […]
-    size_type find (charT c, size_type pos = 0) const noexcept;
-    […]
-    size_type rfind(charT c, size_type pos = npos) const noexcept;
-    […]
-    size_type find_first_of(charT c, size_type pos = 0) const noexcept;
-    […]
-    size_type find_last_of (charT c, size_type pos = npos) const noexcept;
-    […]
-    size_type find_first_not_of(charT c, size_type pos = 0) const noexcept;
-    […]
-    size_type find_last_not_of (charT c, size_type pos = npos) const noexcept;
-    […]
-  };
-}
-
    - -
    3. - -

  3. Modify 21.4.7.2 [string::find] before p5 and before p7 as indicated:

    - -
    -size_type find(const charT* s, size_type pos = 0) const noexcept;
-[…]
-size_type find(charT c, size_type pos = 0) const noexcept;
-

    --7- Returns: find(basic_string<charT,traits,Allocator>(1,c), pos). -

    - -
    4. - -

  4. Modify 21.4.7.3 [string::rfind] before p7 as indicated:

    - -
    -size_type rfind(charT c, size_type pos = npos) const noexcept;
-

    --7- Returns: rfind(basic_string<charT,traits,Allocator>(1,c),pos). -

    - -
    5. - -

  5. Modify 21.4.7.4 [string::find.first.of] before p7 as indicated:

    - -
    -size_type find_first_of(charT c, size_type pos = 0) const noexcept;
-

    --7- Returns: find_first_of(basic_string<charT,traits,Allocator>(1,c), pos). -

    - -
    6. - -

  6. Modify 21.4.7.5 [string::find.last.of] before p7 as indicated:

    - -
    -size_type find_last_of(charT c, size_type pos = npos) const noexcept;
-

    --7- Returns: find_last_of(basic_string<charT,traits,Allocator>(1,c),pos). -

    - -
    7. - -

  7. Modify 21.4.7.6 [string::find.first.not.of] before p7 as indicated:

    - -
    -size_type find_first_not_of(charT c, size_type pos = 0) const noexcept;
-

    --7- Returns: find_first_not_of(basic_string(1, c), pos). -

    - -
    8. - -

  8. Modify 21.4.7.7 [string::find.last.not.of] before p7 as indicated:

    - -
    -size_type find_last_not_of(charT c, size_type pos = npos) const noexcept;
-

    --7- Returns: find_last_not_of(basic_string(1, c), pos). -

    - -
    9. - -

  9. Modify 21.4.8.2 [string::operator==] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator==(const charT* lhs,
-                const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator==(const basic_string<charT,traits,Allocator>& lhs,
-                const charT* rhs) noexcept;
-
    - -
    10. - -

  10. Modify 21.4.8.3 [string::op!=] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator!=(const charT* lhs,
-                const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator!=(const basic_string<charT,traits,Allocator>& lhs,
-                const charT* rhs) noexcept;
-
    - -
    11. - -

  11. Modify 21.4.8.4 [string::op<] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator<(const charT* lhs,
-               const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator<(const basic_string<charT,traits,Allocator>& lhs,
-               const charT* rhs) noexcept;
-
    - -
    12. - -

  12. Modify 21.4.8.5 [string::op>] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator>(const charT* lhs,
-               const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator>(const basic_string<charT,traits,Allocator>& lhs,
-               const charT* rhs) noexcept;
-
    - -
    13. - -

  13. Modify 21.4.8.6 [string::op<=] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator<=(const charT* lhs,
-                const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator<=(const basic_string<charT,traits,Allocator>& lhs,
-                const charT* rhs) noexcept;
-
    - -
    14. - -

  14. Modify 21.4.8.7 [string::op>=] before p2+p3 as indicated:

    - -
    -template<class charT, class traits, class Allocator>
-bool operator>=(const charT* lhs,
-                const basic_string<charT,traits,Allocator>& rhs) noexcept;
-
-[…]
-				
-template<class charT, class traits, class Allocator>
-bool operator>=(const basic_string<charT,traits,Allocator>& lhs,
-                const charT* rhs) noexcept;
-
    - -
    15. - -

  15. Modify 21.4.8.8 [string.special] as indicated (Remark: The change of -the semantics guarantees as of 17.5.1.4 [structure.specifications] p4 that -the "Throws: Nothing" element of member swap is implied):

    - -
    -template<class charT, class traits, class Allocator>
-  void swap(basic_string<charT,traits,Allocator>& lhs,
-    basic_string<charT,traits,Allocator>& rhs) noexcept;
-

    --1- Effects: Equivalent to lhs.swap(rhs); -

    - -
    16. -
- - - - - -
-

2065. Minimal allocator interface

-

Section: 17.6.3.5 [allocator.requirements] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-06-06 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with C++14 status.

-

Discussion:

-

-The example in 17.6.3.5 [allocator.requirements] says SimpleAllocator satisfies -the requirements of Table 28 — Allocator requirements, but it doesn't support comparison -for equality/inequality. -

- -

[Bloomington, 2011]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Modify the example in 17.6.3.5 [allocator.requirements] p5 as indicated:

    -

    --5- […] -

    -[ Example: the following is an allocator class template supporting the minimal interface -that satisfies the requirements of Table 28: -

    -template <class Tp>
-struct SimpleAllocator {
-  typedef Tp value_type;
-  SimpleAllocator(ctor args);
-  template <class T> SimpleAllocator(const SimpleAllocator<T>& other);
-  Tp *allocate(std::size_t n);
-  void deallocate(Tp *p, std::size_t n);
-};
-
-template <class T, class U>
-bool operator==(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
-template <class T, class U>
-bool operator!=(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
-

    -— end example ] -

    -
    2. -
- - - - - -
-

2066. Missing specification of vector::resize(size_type)

-

Section: 23.3.6.3 [vector.capacity] Status: Resolved - Submitter: Rani Sharoni Opened: 2011-03-29 Last modified: 2015-04-08

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

View all issues with Resolved status.

-

Discussion:

-

-In C++1x (N3090) there are two version of vector::resize — 23.3.6.3 [vector.capacity]: -

-
-void resize(size_type sz);
-void resize(size_type sz, const T& c);
-
-

-The text in 23.3.6.3 [vector.capacity]/12 only mentions "no effects on throw" for the -two args version of resize: -

-Requires: If an exception is thrown other than by the move constructor -of a non-CopyConstructible T there are no effects. -

-This seems like unintentional oversight since resize(size) is -semantically the same as resize(size, T()). -Additionally, the C++03 standard only specify single version of resize -with default for the second argument - 23.2.4: -

-
-void resize(size_type sz, T c = T());
-
-

-Therefore not requiring same guarantees for both version of resize is -in fact a regression. -

- -

[2011-06-12: Daniel comments]

- - -

The proposed resolution for issue 2033 should solve this issue as well.

- -

[ -2011 Bloomington -]

- - -

-This issue will be resolved by issue 2033, and closed when this issue is applied. -

- -

[2012, Kona]

- -

-Resolved by adopting the resolution in issue 2033 at this meeting. -

- - - -

Proposed resolution:

-

Apply the proposed resolution of issue 2033

- - - - - -
-

2067. packaged_task should have deleted copy c'tor with const parameter

-

Section: 30.6.9 [futures.task] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-06-16 Last modified: 2015-04-08

-

View all other issues in [futures.task].

-

View all issues with C++14 status.

-

Discussion:

-

-Class template packaged_task is a move-only type with the following form of the -deleted copy operations: -

-
-packaged_task(packaged_task&) = delete;
-packaged_task& operator=(packaged_task&) = delete;
-
-

-Note that the argument types are non-const. This does not look like a typo to me, -this form seems to exist from the very first proposing paper on -N2276. -Using either of form of the copy-constructor did not make much difference before the -introduction of defaulted special member functions, but it makes now an observable -difference. This was brought to my attention by a question on a German C++ newsgroup -where the question was raised why the following code does not compile on a recent -gcc: -

-
-#include <utility>
-#include <future>
-#include <iostream>
-#include <thread>
-
-int main(){
-  std::packaged_task<void()> someTask([]{ std::cout << std::this_thread::get_id() << std::endl; });
-  std::thread someThread(std::move(someTask)); // Error here
-  // Remainder omitted
-}
-
-

-It turned out that the error was produced by the instantiation of some return type -of std::bind which used a defaulted copy-constructor, which leads to a -const declaration conflict with [class.copy] p8. -

-Some aspects of this problem are possibly core-language related, but I consider it -more than a service to programmers, if the library would declare the usual form of -the copy operations (i.e. those with const first parameter type) as deleted for -packaged_task to prevent such problems. -

-A similar problem exists for class template basic_ostream in 27.7.3.1 [ostream]: -

-
-namespace std {
-  template <class charT, class traits = char_traits<charT> >
-  class basic_ostream : virtual public basic_ios<charT,traits> {
-    […]
-
-    // 27.7.3.3 Assign/swap
-    basic_ostream& operator=(basic_ostream& rhs) = delete;
-    basic_ostream& operator=(const basic_ostream&& rhs);
-    void swap(basic_ostream& rhs);
-};
-
-

-albeit this could be considered as an editorial swap of copy and move -assignment operator, I suggest to fix this as part of this issue as well. -

- -

[ -2011 Bloomington. -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

-
    -

  1. Modify the class template basic_ostream synopsis in 27.7.3.1 [ostream] -as indicated (Note: The prototype signature of the move assignment operator in 27.7.3.3 [ostream.assign] -is fine):

    - -
    -namespace std {
-  template <class charT, class traits = char_traits<charT> >
-  class basic_ostream : virtual public basic_ios<charT,traits> {
-    […]
-
-    // 27.7.3.3 Assign/swap
-    basic_ostream& operator=(const basic_ostream& rhs) = delete;
-    basic_ostream& operator=(const basic_ostream&& rhs);
-    void swap(basic_ostream& rhs);
-};
-
    -
    2. - -

  2. Modify the class template packaged_task synopsis in 30.6.9 [futures.task] p2 -as indicated:

    - -
    -namespace std {
-  template<class> class packaged_task; // undefined
-
-  template<class R, class... ArgTypes>
-  class packaged_task<R(ArgTypes...)> {
-  public:
-    […]
-  
-    // no copy
-    packaged_task(const packaged_task&) = delete;
-    packaged_task& operator=(const packaged_task&) = delete;
-    
-    […]
-  };
-  […]
-}
-
    -
    3. -
- - - - - -
-

2069. Inconsistent exception spec for basic_string move constructor

-

Section: 21.4.2 [string.cons] Status: C++14 - Submitter: Bo Persson Opened: 2011-07-01 Last modified: 2015-04-08

-

View all other issues in [string.cons].

-

View all issues with C++14 status.

-

Discussion:

-

-Sub-clause 21.4.2 [string.cons] contains these constructors in paragraphs 2 and 3: -

-
-basic_string(const basic_string<charT,traits,Allocator>& str);
-basic_string(basic_string<charT,traits,Allocator>&& str) noexcept;
-
-

-[…] -

--3- Throws: The second form throws nothing if the allocator's move constructor throws nothing. -

-

-How can it ever throw anything if it is marked noexcept? -

-

[2011-07-11: Daniel comments and suggests wording changes]

- -

-Further, according to paragraph 18 of the same sub-clause: -

-
-basic_string(const basic_string& str, const Allocator& alloc);
-basic_string(basic_string&& str, const Allocator& alloc);
-
-

-[…] -

--18- Throws: The second form throws nothing if alloc == str.get_allocator() -unless the copy constructor for Allocator throws. -

-
-

-The constraint "unless the copy constructor for Allocator throws" -is redundant, because according to Table 28 — Allocator requirements, the expressions -

-
-X a1(a);
-X a(b);
-
-

-impose the requirement: "Shall not exit via an exception". -

- -

[ -2011 Bloomington. -]

- - -

-Move to Ready. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change 21.4.2 [string.cons] p3 as indicated (This move constructor has a wide -contract and is therefore safely marked as noexcept):

    - -
    -basic_string(const basic_string<charT,traits,Allocator>& str);
-basic_string(basic_string<charT,traits,Allocator>&& str) noexcept;
-
    -

    --2- Effects: Constructs an object of class basic_string as indicated in Table 64. -In the second form, str is left in a valid state with an unspecified value. -

    --3- Throws: The second form throws nothing if the allocator's move constructor throws nothing. -

    -
    -
    2. - -

  2. Change 21.4.2 [string.cons] p18 as indicated (This move-like constructor may throw, -if the allocators don't compare equal, but not because of a potentially throwing allocator -copy constructor, only because the allocation attempt may fail and throw an exception):

    - -
    -basic_string(const basic_string& str, const Allocator& alloc);
-basic_string(basic_string&& str, const Allocator& alloc);
-
    -

    -[…] -

    --18- Throws: The second form throws nothing if alloc == str.get_allocator() -unless the copy constructor for Allocator throws. -

    -
    -
    3. - -
- - - - - - -
-

2071. std::valarray move-assignment

-

Section: 26.6.2.3 [valarray.assign] Status: C++14 - Submitter: Paolo Carlini Opened: 2011-05-05 Last modified: 2015-04-08

-

View all other issues in [valarray.assign].

-

View all issues with C++14 status.

-

Discussion:

- -

-Yesterday I noticed that the language we have in the FDIS about std::valarray move assignment -is inconsistent with the resolution of LWG 675. Indeed, we guarantee constant complexity (vs linear -complexity). We also want it to be noexcept, that is more subtle, but again it's at variance with all -the containers. -

-Also, even if we suppose that LWG 675 applies only to the containers proper, I don't think the current -"as if by calling resize(v.size())" is internally consistent with the noexcept requirement. -

-So, what do we really want for std::valarray? Shall we maybe just strike or fix the as-if, consider it -some sort of pasto from the copy-assignment text, thus keep the noexcept and constant complexity requirements -(essentially the whole operation would boild down to a swap of POD data members). Or LWG 675 should be -explicitly extended to std::valarray too? In that case both noexcept and constant complexity -would go, I think, and the operation would boil down to the moral equivalent of clear() (which -doesn't really exist in this case) + swap? -

- -

-Howard: I agree the current wording is incorrect. The complexity should be linear in size() (not -v.size()) because the first thing this operator needs to do is resize(0) (or clear() -as you put it). -

-I think we can keep the noexcept. -

-As for proper wording, here's a first suggestion: -

-Effects: *this obtains the value of v. The value of v after the assignment -is not specified. -

-Complexity: linear. -

-

- -

-See also reflector discussion starting with c++std-lib-30690. -

- -

[2012, Kona]

- -

-Move to Ready. -

-

-Some discussion on the types supported by valarray concludes that the wording is -trying to say something similar to the core wording for trivial types, but significantly -predates it, and does allow for types with non-trivial destructors. Howard notes that -the only reason for linear complexity, rather than constant, is to support types with -non-trivial destructors. -

-

-AJM suggests replacing the word 'value' with 'state', but straw poll prefers moving -forward with the current wording, 5 to 2. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

In 26.6.2.3 [valarray.assign] update as follows:

- -
-valarray<T>& operator=(valarray<T>&& v) noexcept;
-

-3 Effects: *this obtains the value of v. If the length of v -is not equal to the length of *this, resizes *this to make the two arrays the -same length, as if by calling resize(v.size()), before performing the assignment.The -value of v after the assignment is not specified. -

-4 Complexity: ConstantLinear. -

- - - - - - -
-

2074. Off by one error in std::reverse_copy

-

Section: 25.3.10 [alg.reverse] Status: C++14 - Submitter: Peter Miller Opened: 2011-08-17 Last modified: 2015-04-08

-

View all other issues in [alg.reverse].

-

View all issues with C++14 status.

-

Discussion:

- -

-The output of the program below should be: -

-
-"three two one null \n"
-
-

-But when std::reverse_copy is implemented as described in N3291 25.3.10 [alg.reverse] -it's: -

-
-"null three two one \n"
-
-

-because there's an off by one error in 25.3.10 [alg.reverse]/4; the definition should read: -

-
-*(result + (last - first) - 1 - i) = *(first + i)
-
-

-Test program: -

-
-#include <algorithm>
-#include <iostream>
-
-template <typename BiIterator, typename OutIterator>
-auto
-reverse_copy_as_described_in_N3291(
-  BiIterator first, BiIterator last, OutIterator result )
--> OutIterator
-{
-  // 25.3.10/4 [alg.reverse]:
-  // "...such that for any non-negative integer i < (last - first)..."
-  for ( unsigned i = 0; i < ( last - first ); ++i )
-    // "...the following assignment takes place:"
-    *(result + (last - first) - i) = *(first + i);
-
-  // 25.3.10/6
-  return result + (last - first);
-}
-
-int main()
-{
-  using std::begin;
-  using std::end;
-  using std::cout;
-
-  static const char*const in[3]  { "one", "two", "three" };
-  const char*             out[4] { "null", "null", "null", "null" };
-
-  reverse_copy_as_described_in_N3291( begin( in ), end( in ), out );
-
-  for ( auto s : out )
-    cout << s << ' ';
-
-  cout << std::endl;
-
-  return 0;
-}
-
- -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

-Change 25.3.10 [alg.reverse] p4 as follows: -

-
-template<class BidirectionalIterator, class OutputIterator>
-  OutputIterator
-    reverse_copy(BidirectionalIterator first,
-                 BidirectionalIterator last, OutputIterator result);
-

--4- Effects: Copies the range [first,last) to the range [result,result+(last-first)) -such that for any non-negative integer i < (last - first) the following assignment takes place: -*(result + (last - first) - 1 - i) = *(first + i). -

--5- Requires: The ranges [first,last) and [result,result+(last-first)) shall not overlap. -

--6- Returns: result + (last - first). -

--7- Complexity: Exactly last - first assignments. -

- - - - - -
-

2075. Progress guarantees, lock-free property, and scheduling assumptions

-

Section: 1.10 [intro.multithread], 29.4 [atomics.lockfree], 29.6.5 [atomics.types.operations.req] Status: Resolved - Submitter: Torvald Riegel Opened: 2011-08-18 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

- -

-According to 1.10 [intro.multithread] p2: -

-

-"Implementations should ensure that all unblocked threads eventually make progress." -

-
    -
  • If taken literally, this cannot be achieved with lock-free atomics in - general because they only guarantee that some thread makes progress - (i.e., minimal progress, whereas 1.10 [intro.multithread] p2 seems to - require maximal progress). -
    • -
  • What does it mean precisely to "make progress"? Does "unblocked - threads" exclude live-locked threads (if so, lock-free atomics would - be sufficient I suppose)? -
    • -

  • Which assumptions can an implementation make about the thread - scheduling? This is relevant for how implementations implement - compare-exchange with load-linked / store conditional (LL-SC), and - atomic read-modifiy-write operations with load...compare-exchange-weak - loops. -

    -
      -
    • Do threads run long enough without being descheduled (e.g., - OS timeslices are long enough, interrupt frequency is not too - high, etc.)? -
      • -
    • Or is this implementation-defined, and the sentence is just about - stating that the progress guarantees will not hold on, for example, - systems with unfair scheduling or thread priorities? -
      • -
    -
    • -
- -

-29.4 [atomics.lockfree] p2 declares the lock-free property for a -particular object. However, "lock-free" is never defined, and in discussions -that I had with committee members it seemed as if the standard's lock-free would be -different from what lock-free means in other communities (eg, research, -text books on concurrent programming, etc.). -

-
    -
  • Originally, lock-freedom for an object requires minimal progress (ie, - some thread makes progress, but other threads might never do) without - any assumptions about the scheduling (threads could be stopped - executing (so it is "nonblocking"), and threads are not guaranteed to - execute in isolation, even for very small intervals of cycles). -
    • -
  • In contrast, obstruction-freedom, another nonblocking progress - condition, guarantees progress for all threads that eventually get - executed long enough in isolation (ie, without interference by other - threads). -
    • -
  • Simple load...compare-exchange-weak loops (or LL-SC loops) to - implement atomic read-modify-write operations can be just - obstruction-free but not lock-free because they can livelock - (depending on the hardware's LL-SC implementation, though). However, - they effectively guarantee the same as lock-free iff threads will - eventually run in isolation for long enough (that can be an assumption - about the OS scheduler), or if the implementation adds this (e.g., - probabilistically by employing randomized exponential back-off when - contention is detected, in all operations that can create contention). -
    • -
  • Does the particular object has to be lock-free, or is it only required - that threads make progress irrespective on which object? Again - considering compare-exchange-weak or LL-SC here, what happens if the - compare-exchange object shares a cacheline with an integer counter - object that is constantly updated by other threads? The - compare-exchange-weak can always fail, so the object would not be - lock-free. However, if we consider progress to be overall progress for - threads, it would be lock-free because other threads succeed updating - the integer counter. I would have assumed the lock-free property is - strictly about the atomic object, but in discussions with committee - members it seemed as if progress for any object could be the intended - guarantee. -
    • -
- -

-Following 29.6.5 [atomics.types.operations.req] p7 is_lock_free() -returns "true if the object is lock-free". What is returned if the object is only -sometimes lock-free? -

- -

-Basically, I would like to see clarifications for the progress -guarantees so that users know what they can expect from implementations -(and what they cannot expect!), and to give implementors a clearer -understanding of which user expectations they have to implement. -

-
    -

  1. Elaborate on the intentions of the progress guarantee in -1.10 [intro.multithread] p2. As I don't know about your intentions, -it's hard to suggest a resolution. -

    -
      -
    • Is it for straightforward, non-synchronizing code only?
      • -
    • Is it for blocking code only? (Is "unblocked" more than blocked on - external I/O or on deadlocks?) -
      • -
    • What does it mean to "make progress"?
      • -
    • Is this meant to only waive any progress guarantees if there are - thread priorities? -
      • -
    • Can an implementation make any assumptions about thread scheduling? -
      • -
    -
    2. -

  2. Define the lock-free property. The definition should probably include -the following points: -

    -
      -
    • Is it just nonblocking, or what is the distinction to just being nonblocking?
      • -
    • Does it make any assumptions about the scheduler?
      • -
    • What are the progress guarantees, minimal or maximal (some or all threads finish eventually).
      • -
    • Is progress guaranteed for all operations on the particular object, or - do operations on other objects also count as "making progress"? -
      • -
    -
    3. -
  3. Add a note explaining that compare-exchange-weak is not necessarily -lock-free (but is nonblocking)? Or is it indeed intended to be lock-free -(only allowed to fail spuriously but guaranteed to not fail eventually)? -Implementing the latter might be a challenge on LL-SC machines or lead -to space overheads I suppose, see the cacheline sharing example above. -
    4. -
- -

[2011-12-01: Hans comments]

- - -

-1.10 [intro.multithread] p2 was an intentional compromise, and it was understood at the -time that it was not a precise statement. The wording was introduced by -N3209, which -discusses some of the issues. There were additional reflector discussions. -

-This is somewhat separable from the question of what lock-free means, which is probably a more -promising question to focus on. -

- -

[2012, Kona]

- -

-General direction: lock-free means obstruction-free. Leave the current "should" recommendation -for progress. It would take a lot of effort to try to do better. -

- - -

[2012, Portland: move to Open]

- -

-The current wording of 1.10 [intro.multithread] p2 doesn't really say very much. -As far as we can tell the term lock-free is nowhere defined in the standard. -

-

-James: we would prefer a different way to phrase it. -

-

-Hans: the research literature includes the term abstraction-free which might be a better fit. -

-

-Detlef: does Posix define a meaning for blocking (or locking) that we could use? -

-

-Hans: things like compare-exchange-strong can wait indefinitely. -

-

-Niklas: what about spin-locks -- still making no progress. -

-

-Hans: suspect we can only give guidance, at best. The lock-free meaning from the theoretical commmunity (forard progress will be made) is probably too strong here. -

-

-Atrur: what about livelocks? -

-

-Hans: each atomic modification completes, even if the whole thing is blocked. -

-

-Moved to open. -

- -

[2013-11-06: Jason Hearne-McGuiness comments]

- - -

-Related to this issue, the wording in 29.4 [atomics.lockfree] p2, -

-

-In any given program execution, the result of the lock-free query -shall be consistent for all pointers of the same type. -

-

-should be made clearer, because the object-specific (non-static) nature of the is_lock_free() functions -from 29.5 [atomics.types.generic] and 29.6 [atomics.types.operations] imply that for different -instances of pointers of the same type the returned value could be different. -

- - - -

Proposed resolution:

- -

[2014-02-16 Issaquah: Resolved by paper n3927]

- - - - - - - -
-

2076. Bad CopyConstructible requirement in set constructors

-

Section: 23.4.6.2 [set.cons] Status: WP - Submitter: Jens Maurer Opened: 2011-08-20 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

- -

-23.4.6.2 [set.cons] paragraph 4 says: -

- -

-Requires: If the iterator's dereference operator returns an lvalue or a non-const rvalue, -then Key shall be CopyConstructible. -

- -

-I'm confused why a "non-const rvalue" for the return value of the iterator -would require CopyConstructible; isn't that exactly the situation -when you'd want to apply the move constructor? -

-The corresponding requirement for multimap seems better in that regard -([multimap.cons] paragraph 3): -

-

-Requires: If the iterator's dereference operator returns an lvalue or a const rvalue -pair<key_type, mapped_type>, then both key_type and mapped_type -shall be CopyConstructible. -

-

-Obviously, if I have a const rvalue, I can't apply the move constructor (which will -likely attempt modify its argument). -

-Dave Abrahams: -

-I think you are right. -Proposed resolution: drop "non-" from 23.4.6.2 [set.cons] paragraph 3. -

- -

[2012, Kona]

- -

-The wording is in this area will be affected by Pablo's paper being adopted at this meeting. -Wait for that paper to be applied before visiting this issue - deliberately leave in New -status until the next meeting. -

- -

Proposed resolution from Kona 2012:

-
-

This wording is relative to the FDIS.

- -

-Change 23.4.6.2 [set.cons] p3 as follows: -

-
-template <class InputIterator>
-  set(InputIterator first, InputIterator last,
-    const Compare& comp = Compare(), const Allocator& = Allocator());
-

--3- Effects: Constructs an empty set using the specified comparison object and allocator, and inserts -elements from the range [first,last). -

--4- Requires: If the iterator's dereference operator returns an lvalue or a non-const rvalue, -then Key shall be CopyConstructible. -

--5- Complexity: Linear in N if the range [first,last) is already sorted using -comp and otherwise N logN, where N is last - first. -

-
- -

[2014-05-18, Daniel comments]

- -

-According to Pablo, the current P/R correctly incorporates the changes from his paper (which was adopted in Kona) -

- -

[2014-06-10, STL comments and suggests better wording]

- -

-N1858 was voted into WP -N2284 but was -"(reworded)", introducing the "non-const" damage. -

-N1858 wanted to add this for map: -

-

-Requires: Does not require CopyConstructible of either key_type or mapped_type if the dereferenced -InputIterator returns a non-const rvalue pair<key_type, mapped_type>. Otherwise CopyConstructible -is required for both key_type and mapped_type. -

-

-And this for set: -

-

-Requires: Key must be CopyConstructible only if the dereferenced InputIterator returns an lvalue -or const rvalue. -

-

-(And similarly for multi.) -

-This was reworded to N2284 23.3.1.1 [map.cons]/3 and N2284 23.3.3.1 [set.cons]/4, and it slightly changed over the years into -N3936 23.4.4.2 [map.cons]/3 and N3936 23.4.6.2 [set.cons]/4. -

-In 2005/2007, this was the best known way to say "hey, we should try to move this stuff", as the fine-grained element requirements -were taking shape. -

-Then in 2010, N3173 was -voted into WP -N3225, adding the definition of -EmplaceConstructible and modifying the container requirements tables to make the range constructors require -EmplaceConstructible. -

-After looking at this history and double-checking our implementation (where map/set range construction goes through -emplacement, with absolutely no special-casing for map's pairs), I am convinced that N3173 superseded N1858 here. -(Range-insert() and the unordered containers are unaffected.) -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to the N3936.

- -

-Change 23.4.6.2 [set.cons] p4 as follows: -

-
-template <class InputIterator>
-  set(InputIterator first, InputIterator last,
-    const Compare& comp = Compare(), const Allocator& = Allocator());
-

--3- Effects: Constructs an empty set using the specified comparison object and allocator, and inserts -elements from the range [first,last). -

--4- Requires: If the iterator's indirection operator returns an lvalue or a non-const rvalue, -then Key shall be CopyInsertible into *this. -

--5- Complexity: Linear in N if the range [first,last) is already sorted using -comp and otherwise N logN, where N is last - first. -

-
- -

[2015-02 Cologne]

- -

-GR: Do requirements supersede rather than compose [container requirements and per-function requirements]? AM: Yes, they supersede. -

-AM: This looks good. Ready? Agreement. -

- - -

Proposed resolution:

-

This wording is relative to the N4296.

- -
    -

  1. -Remove 23.4.4.2 [map.cons] p3: -

    -
    -template <class InputIterator>
-  map(InputIterator first, InputIterator last,
-      const Compare& comp = Compare(), const Allocator& = Allocator());
-
    -

    --3- Requires: If the iterator's indirection operator returns an lvalue or a const rvalue -pair<key_type, mapped_type>, then both key_type and mapped_type shall be -CopyInsertible into *this. -

    -[…] -

    -
    2. - -

  2. -Remove 23.4.5.2 [multimap.cons] p3: -

    -
    -template <class InputIterator>
-  multimap(InputIterator first, InputIterator last,
-           const Compare& comp = Compare(), 
-           const Allocator& = Allocator());
-
    -

    --3- Requires: If the iterator's indirection operator returns an lvalue or a const rvalue -pair<key_type, mapped_type>, then both key_type and mapped_type shall be -CopyInsertible into *this. -

    -[…] -

    -
    -
    3. - -

  3. -Remove 23.4.6.2 [set.cons] p4: -

    -
    -template <class InputIterator>
-  set(InputIterator first, InputIterator last,
-      const Compare& comp = Compare(), const Allocator& = Allocator());
-
    -

    -[…] -

    --4- Requires: If the iterator's indirection operator returns an lvalue or a non-const rvalue, then -Key shall be CopyInsertible into *this. -

    -
    4. - -

  4. -Remove 23.4.7.2 [multiset.cons] p3: -

    -
    -template <class InputIterator>
-  multiset(InputIterator first, InputIterator last,
-           const Compare& comp = Compare(), 
-           const Allocator& = Allocator());
-
    -

    --3- Requires: If the iterator's indirection operator returns an lvalue or a const rvalue, then -Key shall be CopyInsertible into *this. -

    -[…] -

    -
    5. -
- - - - - -
-

2078. Throw specification of async() incomplete

-

Section: 30.6.8 [futures.async] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2011-08-29 Last modified: 2015-04-08

-

View all other issues in [futures.async].

-

View all issues with C++14 status.

-

Discussion:

- -

-The current throw specification of async() does state: -

-

--6- Throws: system_error if policy is launch::async and -the implementation is unable to start a new thread. -

-

-First it seems not clear whether this only applies if policy equals -launch::async of if the async launch mode flag is set -(if policy|launch::async!=0) -

-In the discussion Lawrence Crowl also wrote: -

-

- More generally, I think what we want to say is that if the - implementation cannot successfully execute on one of the policies - allowed, then it must choose another. The principle would apply - to implementation-defined policies as well. -

- -

-Peter Sommerlad: -

-

-Should not throw. That was the intent. "is async" meat exactly. -

- -

[2012, Portland: move to Tentatively NAD Editorial]

- -

-If no launch policy, it is undefined behavior. -

-

-Agree with Lawrence, should try all the allowed policies. We will rephrase so that -the policy argument should be lauch::async. Current wording seems good enough. -

-

-We believe this choice of policy statement is really an editorial issue. -

- -

[2013-09 Chicago]

- -

-If all the implementors read it and can't get it right - it is not editorial. Nico to provide wording -

-

-No objections to revised wording, so moved to Immediate. -

-

-Accept for Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 30.6.8 [futures.async] p6, p7 as indicated:

    - -
    -

    --6- Throws: system_error if policy is == launch::async -and the implementation is unable to start a new thread. -

    -

    --7- Error conditions: -

    -
      -

    • resource_unavailable_try_again — if policy is == launch::async -and the system is unable to start a new thread.

      -
      • -
    -
    -
    2. -
- - - - - - -
-

2080. Specify when once_flag becomes invalid

-

Section: 30.4.4 [thread.once] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2011-08-30 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

- -

-In function call_once 30.4.4.2 [thread.once.callonce] -paragraph 4 and 5 specify for call_once(): -

- -
-

-Throws: system_error when an exception is required (30.2.2 [thread.req.exception]), -or any exception thrown by func. -

-Error conditions: -

-
    -
  • invalid_argument — if the once_flag object is no longer valid.
    • -
-
- -

-However, nowhere in 30.4.4 [thread.once] is specified, when a once-flag becomes invalid. -

-As far as I know this happens if the flag is used for different functions. So we either have to have -to insert a sentence/paragraph in -

-

-30.4.4.2 Function call_once [thread.once.callonce] -

-

-or -

-

-30.4.4 Call once [thread.once] -

-

-explaining when a once_flag becomes invalidated or we should state as error condition something like: -

- -
    -
  • invalid_argument — if the func used in combination with the once_flag is different -from a previously passed func for the same once_flag -
    • -
- -

-Anthony Williams: -

-
-

-A once_flag is invalidated if you destroy it (e.g. it is an automatic object, or heap -allocated and deleted, etc.) -

-If the library can detect that this is the case then it will throw this exception. If it cannot -detect such a case then it will never be thrown. -

-
- -

-Jonathan Wakely: -

-
-

-I have also wondered how that error can happen in C++, where the type -system will reject a non-callable type being passed to call_once() and -should prevent a once_flag being used after its destructor runs. -

-If a once_flag is used after its destructor runs then it is indeed -undefined behaviour, so implementations are already free to throw any -exception (or set fire to a printer) without the standard saying so. -

-My assumption was that it's an artefact of basing the API on pthreads, -which says: -

-
-

-The pthread_once() function may fail if: -

-[EINVAL] If either once_control or init_routine is invalid. -

-
-
- -

-Pete Becker: -

-

-Yes, probably. We had to clean up several UNIXisms that were in the original design. -

- -

[2012, Kona]

- -

-Remove error conditions, move to Review. -

- -

[2012, Portland: move to Tentatively Ready]

- -

-Concurrency move to Ready, pending LWG review. -

- -

-LWG did not have time to perform the final review in Portland, so moving to -tentatively ready to reflect the Concurrency belief that the issue is -ready, but could use a final inspection from library wordsmiths. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

- -

This wording is relative to N3337.

- -
    -

  1. Change 30.4.4.2 [thread.once.callonce] as indicated:

    -
    -template<class Callable, class ...Args>
-void call_once(once_flag& flag, Callable&& func, Args&&... args);
-
    -

    -[…] -

    --4- Throws: system_error when an exception is required (30.2.2), or any exception thrown by func. -

    --5- Error conditions: -

    -
      -
    • invalid_argument — if the once_flag object is no longer valid.
      • -
    -
    -
    2. -
- - - - - -
-

2081. Allocator requirements should include CopyConstructible

-

Section: 17.6.3.5 [allocator.requirements] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-08-30 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

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-

Discussion:

- -

-As discussed in c++std-lib-31054 and c++std-lib-31059, the Allocator -requirements implicitly require CopyConstructible because -a.select_on_container_copy_construction() and -container.get_allocator() both return a copy by value, but the -requirement is not stated explicitly anywhere. -

-In order to clarify that allocators cannot have 'explicit' copy -constructors, the requirements should include CopyConstructible. -

- -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change Table 28 — Allocator requirements in 17.6.3.5 [allocator.requirements]:

    - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements
    ExpressionReturn typeAssertion/note pre-/post-conditionDefault
    -X a1(a);
    -X a1 = a;     -    		 - -Shall not exit via an exception.
    -post: a1 == a -    		 -
    -… -
    -X a1(move(a));
    -X a1 = move(a);     -    		 - -Shall not exit via an exception.
    -post: a1 equals the prior value
    -of a. -    		 -
    - -
    2. - -

  2. Change 17.6.3.5 [allocator.requirements] paragraph 4:

    - -

    -An allocator type X shall satisfy the requirements of CopyConstructible -(17.6.3.1 [utility.arg.requirements]). The X::pointer, X::const_pointer, -X::void_pointer, and X::const_void_pointer types shall satisfy the requirements of -NullablePointer (17.6.3.3 [nullablepointer.requirements]). No constructor, comparison -operator, copy operation, move operation, or swap operation on these types shall exit via an -exception. X::pointer and X::const_pointer shall also satisfy the requirements -for a random access iterator (24.2 [iterator.requirements]). -

    -
    3. -
- - - - - -
-

2083. const-qualification on weak_ptr::owner_before

-

Section: 20.8.2.3 [util.smartptr.weak], 20.8.2.3.5 [util.smartptr.weak.obs] Status: C++14 - Submitter: Ai Azuma Opened: 2011-09-06 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.weak].

-

View all issues with C++14 status.

-

Discussion:

- -

-Is there any reason why weak_ptr::owner_before member function templates are not const-qualified? -

- -

-Daniel Krügler: -

-

-I don't think so. To the contrary, without these to be const member function templates, the -semantics of the specializations owner_less<weak_ptr<T>> and -owner_less<shared_ptr<T>> described in 20.8.2.4 [util.smartptr.ownerless] -is unclear. -

-It is amusing to note that this miss has remain undetected from the accepted paper -n2637 -on. For the suggested wording changes see below. -

- - -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change the class template weak_ptr synopsis in 20.8.2.3 [util.smartptr.weak] -as indicated:

    -
    -namespace std {
-  template<class T> class weak_ptr {
-  public:
-    typedef T element_type;
-    […]
-    template<class U> bool owner_before(shared_ptr<U> const& b) const;
-    template<class U> bool owner_before(weak_ptr<U> const& b) const;
-  };
-  […]
-}
-
    -
    2. -

  2. Change the prototypes in 20.8.2.3.5 [util.smartptr.weak.obs] before p6 as indicated:

    -
    -template<class U> bool owner_before(shared_ptr<U> const& b) const;
-template<class U> bool owner_before(weak_ptr<U> const& b) const;
-
    -
    3. -
- - - - - -
-

2085. Wrong description of effect 1 of basic_istream::ignore

-

Section: 27.7.2.3 [istream.unformatted] Status: C++14 - Submitter: Krzysztof Zelechowski Opened: 2011-09-11 Last modified: 2015-04-08

-

View other active issues in [istream.unformatted].

-

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-

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-

Discussion:

- -

-27.7.2.3 [istream.unformatted] in N3242 currently has the following to say about the -semantics of basic_istream::ignore: -

- -

-[..]. Characters are extracted until any of the following occurs: -

-
    -
  • if n != numeric_limits<streamsize>::max() (18.3.2), n characters are extracted -
    • -
-
- -

-This statement, apart from being slightly ungrammatical, indicates that if -(n == numeric_limits<streamsize>::max()), the method returns without -extracting any characters. -

-The description intends to describe the observable behaviour of an -implementation in terms of logical assertions. Logical assertions are not -"bullets" that can be "entered" but need not; they are predicates that can -evaluate to true or false. -

-The description contains two predicates, either of them causes extraction to -terminate. In the incriminated case, the first predicate is evaluates to -true because its premise is false, therefore no characters will be -extracted. -

-The intended semantics would be described by the following statement: -

- -

-[..]. Characters are extracted until any of the following occurs: -

-
    -
  • (n != numeric_limits<streamsize>::max()) (18.3.2) and (n) characters -have been extracted so far. -
    • -
-
- -

[2013-04-20, Bristol]

- - -

-Resolution: Ready. -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 27.7.2.3 [istream.unformatted] p25 as indicated:

- -
-basic_istream<charT,traits>&
-  ignore(streamsize n = 1, int_type delim = traits::eof());
-

--25- Effects: Behaves as an unformatted input function (as described in 27.7.2.3 [istream.unformatted], paragraph 1). After -constructing a sentry object, extracts characters and discards them. Characters are extracted until -any of the following occurs: -

-
    -
  • if n != numeric_limits<streamsize>::max() (18.3.2.1 [limits.numeric]),and -n characters arehave been extracted so far -
    • -
  • end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), -which may throw ios_base::failure (27.5.5.4 [iostate.flags])); -
    • -
  • traits::eq_int_type(traits::to_int_type(c), delim) for the next available input character c -(in which case c is extracted). -
    • -
-
- - - - - -
-

2086. Overly generic type support for math functions

-

Section: 26.8 [c.math] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-09-22 Last modified: 2015-04-08

-

View other active issues in [c.math].

-

View all other issues in [c.math].

-

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-

Discussion:

- -

-26.8 [c.math] ends with a description of a rule set for "sufficient overloads" -in p11: -

- -
-

Moreover, there shall be additional overloads sufficient to ensure:

-
    -
  1. -If any argument corresponding to a double parameter has type long double, then all arguments -corresponding to double parameters are effectively cast to long double. -
    2. -
  2. -Otherwise, if any argument corresponding to a double parameter has type double or an integer type, -then all arguments corresponding to double parameters are effectively cast to double. -
    3. -
  3. -Otherwise, all arguments corresponding to double parameters are effectively cast to float. -
    4. -
-
- -

-My impression is that this rule set is probably more generic as intended, my assumption is that it is written -to mimic the C99/C1x rule set in 7.25 p2+3 in the "C++" way: -

- -
-

--2- Of the <math.h> and <complex.h> functions without an -f (float) or l (long double) suffix, several have -one or more parameters whose corresponding real type is double. For each such -function, except modf, there is a corresponding type-generic macro. (footnote 313) -The parameters whose corresponding real type is double in the function -synopsis are generic parameters. Use of the macro invokes a function whose -corresponding real type and type domain are determined by the arguments for the generic -parameters. (footnote 314) -

--3- Use of the macro invokes a function whose generic parameters have the corresponding -real type determined as follows: -

-
    -
  • -First, if any argument for generic parameters has type long double, the type -determined is long double. -
    • -
  • -Otherwise, if any argument for generic parameters has type double or is of integer -type, the type determined is double. -
    • -
  • -Otherwise, the type determined is float. -
    • -
-
- -

-where footnote 314 clarifies the intent: -

- -
-

-If the type of the argument is not compatible with the type of the parameter for the selected function, -the behavior is undefined. -

-
- -

-The combination of the usage of the unspecific term "cast" with otherwise no further constraints -(note that C constraints the valid set to types that C++ describes as arithmetic types, but see below -for one important difference) has the effect that it requires the following examples to be well-formed -and well-defined: -

- -
-#include <cmath>
-
-enum class Ec { };
-
-struct S { explicit operator long double(); };
-
-void test(Ec e, S s) {
- std::sqrt(e); // OK, behaves like std::sqrt((float) e);
- std::sqrt(s); // OK, behaves like std::sqrt((float) s);
-}
-
-

-GCC 4.7 does not accept any of these examples. -

-I found another example where the C++ rule differs from the C set, -but in this case I'm not so sure, which direction C++ should follow. -The difference is located in the fact, that in C enumerated types are -integer types as described in 6.2.5 p17 (see e.g. n1569 or n1256): -

-"The type char, the signed and unsigned integer types, and -the enumerated types are collectively called integer types. The -integer and real floating types are collectively called real types." -

-This indicates that in C the following code -

-
-#include <math.h>
-
-enum E { e };
-
-void test(void) {
-  sqrt(e); // OK, behaves like sqrt((double) e);
-}
-
-

-seems to be well-defined and e is cast to double, but in C++ -referring to -

-
-#include <cmath>
-
-enum E { e };
-
-void test() {
-  std::sqrt(e); // OK, behaves like sqrt((float) e);
-}
-
- -

-is also well-defined (because of our lack of constraints) but we -must skip bullet 2 (because E is not an integer type) and effectively -cast e to float. Accepting this, we would introduce -a silent, but observable runtime difference for C and C++. -

-GCC 4.7 does not accept this example, but causes an ambiguity -error among the three floating point overloads of sqrt. -

-My current suggestion to fix these problems would be to constrain the -valid argument types of these functions to arithmetic types. -

- -

-Howard provided wording to solve the issue. -

- -

[2012, Kona]

- -

-Moved to Ready. The proposed wording reflects both original intent from -TR1, and current implementations. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 26.8 [c.math] p11 as indicated:

- -
-

Moreover, there shall be additional overloads sufficient to ensure:

-
    -
  1. -If any arithmetic argument corresponding to a double parameter has -type long double, then all arithmetic arguments corresponding to -double parameters are effectively cast to long double. -
    2. -
  2. -Otherwise, if any arithmetic argument corresponding to a double -parameter has type double or an integer type, then all arithmetic -arguments corresponding to double parameters are effectively cast to double. -
    3. -
  3. -Otherwise, all arithmetic arguments corresponding to double parameters -are effectively cast tohave type float. -
    4. -
-
- - - - - - -
-

2087. iostream_category() and noexcept

-

Section: 27.5 [iostreams.base] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2011-09-22 Last modified: 2015-04-08

-

View all other issues in [iostreams.base].

-

View all issues with C++14 status.

-

Discussion:

- -

-In <system_error> we have: -

- -
-const error_category& generic_category() noexcept;
-const error_category& system_category() noexcept;
-
- -

-In <future> we have: -

- -
-const error_category& future_category() noexcept;
-
- -

-But in <ios> we have: -

- -
-const error_category& iostream_category();
-
- -

-Is there any reason that iostream_category() is not declared with -noexcept or is this an oversight? -

- -

-Daniel: -

-This looks like an oversight to me. We made the above -mentioned changes as part of noexcept-ifying the thread -library but iostream_category() was skipped, so it seems -to be forgotten. There should be no reason, why it cannot -be noexcept. When doing so, we should also make these functions -noexcept (similar to corresponding overloads): -

-
-error_code make_error_code(io_errc e);
-error_condition make_error_condition(io_errc e);
-
- -

-Suggested wording provided by Daniel. -

- -

[2013-04-20, Bristol]

- - -

-Unanimous. -

-Resolution: move to tentatively ready. -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
  1. -

    Change 27.5.1 [iostreams.base.overview], header <ios> synopsis -as indicated: -

    -
    -#include <iosfwd>
-namespace std {
-  […]
-  error_code make_error_code(io_errc e) noexcept;
-  error_condition make_error_condition(io_errc e) noexcept;
-  const error_category& iostream_category() noexcept;
-}
-
    - -
    2. -
  2. -

    Change the prototype declarations in 27.5.6.5 [error.reporting] as indicated: -

    -
    -error_code make_error_code(io_errc e) noexcept;
-
    -

    --1- Returns: error_code(static_cast<int>(e), iostream_category()). -

    -
    -error_condition make_error_condition(io_errc e) noexcept;
-
    -

    --2- Returns: error_condition(static_cast<int>(e), iostream_category()). -

    -
    -const error_category& iostream_category() noexcept;
-
    -

    --3- Returns: A reference to an object of a type derived from class error_category. -

    --4- The objectÂ’s default_error_condition and equivalent virtual functions shall behave as specified -for the class error_category. The objectÂ’s name virtual function shall return a pointer to the string -"iostream". -

    -
    -
    3. -
- - - - - - -
-

2091. Misplaced effect in m.try_lock_for()

-

Section: 30.4.1.3 [thread.timedmutex.requirements] Status: C++14 - Submitter: Pete Becker Opened: 2011-10-18 Last modified: 2015-04-08

-

View all other issues in [thread.timedmutex.requirements].

-

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-

Discussion:

- -

-30.4.1.3 [thread.timedmutex.requirements]/4 says, in part, -

-"Requires: If the tick period of [the argument] is not exactly -convertible … [it] shall be rounded up …" -

-

-This doesn't belong in the requires clause. It's an effect. It belongs in paragraph 5. -Nitpickingly, this would be a technical change: as written it imposes an obligation on -the caller, while moving it imposes an obligation on the callee. Although that's certainly -not what was intended. -

-Peter Dimov comments: -

-Not to mention that it should round down, not up. :-) -

-Incidentally, I see that the wrong try_lock requirement that the caller shall not own -the mutex has entered the standard, after all. Oh well. Let's hope that the real world -continues to ignore it. -

- -

[2012, Kona]

- -

-Remove the offending sentence from the requirements clause. Do not add it back -anywhere else. The implementation already must have license to wake up late, so the -rounding is invisible. -

-Move to Review. -

- -

[2012, Portland]

- -

-Concurrency move to Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3337.

- -
    -

  1. Change 30.4.1.3 [thread.timedmutex.requirements]/4 as indicated:

    - -

    --3- The expression m.try_lock_for(rel_time) shall be well-formed and have the following semantics: -

    --4- Requires: If the tick period of rel_time is not exactly convertible to the native tick period, the -duration shall be rounded up to the nearest native tick period. If m is of type std::timed_mutex, -the calling thread does not own the mutex. -

    - -
    2. -
- - - - - - -
-

2092. Vague Wording for condition_variable_any

-

Section: 30.5.2 [thread.condition.condvarany] Status: C++14 - Submitter: Pete Becker Opened: 2011-10-20 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvarany].

-

View all issues with C++14 status.

-

Discussion:

- -

-30.5.2 [thread.condition.condvarany]/4 says, in part, that -condition_variable_any() throws an exception -"if any native handle type manipulated is not available". -

-I don't know what that means. Is this intended to say something different -from the analogous words for condition_variable() [30.5.1 [thread.condition.condvar]/4], -"if some non-memory resource limitation prevents initialization"? If not, -it should be worded the same way. -

- -

[2012, Kona]

- -

-Copy the corresponding wording from the condition_variable constructor in 30.5.1 [thread.condition.condvar] p4. -

-Move to Review. -

- -

[2012, Portland]

- -

-Concurrency move to Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3337.

- -
    -

  1. Change 30.4.1.3 [thread.timedmutex.requirements]/4 as indicated:

    - -
    -condition_variable_any();
-
    -

    -[…] -

    --4- Error conditions: -

    -
      -
    • resource_unavailable_try_again — if any native handle type manipulated is not available -if some non-memory resource limitation prevents initialization.
      • -
    • operation_not_permitted — if the thread does not have the privilege to perform the operation.
      • -
    -
    - -
    2. -
- - - - - - -
-

2093. Throws clause of condition_variable::wait with predicate

-

Section: 30.5.1 [thread.condition.condvar] Status: C++14 - Submitter: Alberto Ganesh Barbati Opened: 2011-10-27 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

View all issues with C++14 status.

-

Discussion:

- -

-the Throws: clause of condition_variable::wait/wait_xxx functions that -take a predicate argument is: -

-

-Throws: system_error when an exception is required (30.2.2 [thread.req.exception]). -

-

-If executing the predicate throws an exception, I would expect such exception to propagate unchanged -to the caller, but the throws clause seems to indicate that it gets mutated into a system_error. T -hat's because of 17.5.1.4 [structure.specifications]/4: -

-"If FÂ’s semantics contains a Throws:, Postconditions:, or Complexity: element, then that supersedes -any occurrences of that element in the code sequence." -

-Is my interpretation correct? Does it match the intent? -

-Daniel comments: -

-I don't think that this interpretation is entirely correct, the wording does not say that -std::system_error or a derived class must be thrown, it simply is underspecified -in this regard (The extreme interpretation is that the behaviour would be undefined, but -that would be too far reaching I think). We have better wording for this in -30.4.4.2 [thread.once.callonce] p4, where it says: -

-"Throws: system_error when an exception is required (30.2.2 [thread.req.exception]), -or any exception thrown by func." -

-or in 30.3.2 [thread.thread.this] p6/p9: -

-"Throws: Nothing if Clock satisfies the TrivialClock requirements -(20.12.3 [time.clock.req]) and operations of Duration do not throw exceptions. -[ Note: instantiations of time point types and clocks supplied by the implementation -as specified in 20.12.7 [time.clock] do not throw exceptions. — end note ]" -

-So, the here discussed Throws elements should add lines along the lines of -

-"Any exception thrown by operations of pred." -

-and similar wording for time-related operations: -

-"Any exception thrown by operations of Duration", -

-"Any exception thrown by operations of chrono::duration<Rep, Period>" -

- -

[2011-11-28: Ganesh comments and suggests wording]

- - -

-As for the discussion about the exception thrown by the manipulation of time-related objects, -I believe the argument applies to all functions declared in 30 [thread]. Therefore, -instead of adding wording to each member, I would simply move those requirements from -30.3.2 [thread.thread.this] p6/p9 to a new paragraph in 30.2.4 [thread.req.timing]. -

-As for 30.5.2 [thread.condition.condvarany], the member functions wait() and -wait_until() are described only in terms of the Effects: clause (so strictly speaking, -they need no changes), however, wait_for() is described with a full set of clauses -including Throws: and Error conditions:. Either we should add those clauses to wait/wait_until -with changes similar to the one above, or remove paragraphs 29 to 34 entirely. By the way, -even paragraph 26 could be removed IMHO. -

- -

[2012, Kona]

- -

-We like the idea behind the proposed resolution. -

-Modify the first addition to read instead: "Functions that specify a timeout, will throw if an operation -on a clock, time point, or time duration throws an exception." -

-In the note near the bottom change "even if the timeout has already expired" to "or if the timeout has -already expired". (This is independent, but the original doesn't seem to make sense.) -

-Move to Review. -

- -

[2012, Portland]

- -

-Concurrency move to Ready with slightly ammended wording. -

- -

[2013-04-20 Bristol]

- - - -

Proposed resolution:

-

This wording is relative to N3337.

- -
    -

  1. Add a new paragraph at the end of 30.2.4 [thread.req.timing]:

    - -
    -

    -[…] -

    --6- The resolution of timing provided by an implementation depends on both operating system and hardware. -The finest resolution provided by an implementation is called the native resolution. -

    --7- Implementation-provided clocks that are used for these functions shall meet the TrivialClock -requirements (20.12.3 [time.clock.req]). -

    - --?- Functions that specify a timeout, will throw if, during the execution of this function, -a clock, time point, or time duration throws an exception. [ Note: instantiations of clock, -time point and duration types supplied by the implementation as specified in 20.12.7 [time.clock] -do not throw exceptions. — end note] -

    -
    -
    2. - - -

  2. Change 30.3.2 [thread.thread.this] as indicated:

    - -
    -template <class Clock, class Duration>
-  void sleep_until(const chrono::time_point<Clock, Duration>& abs_time);;
-
    -

    --4- Effects: Blocks the calling thread for the absolute timeout (30.2.4 [thread.req.timing]) specified by abs_time. -

    --5- Synchronization: None. -

    --6- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]).Nothing if -Clock satisfies the TrivialClock requirements (20.12.3 [time.clock.req]) and -operations of Duration do not throw exceptions. [ Note: instantiations of time point types -and clocks supplied by the implementation as specified in 20.12.7 [time.clock] do not throw -exceptions. — end note] -

    -
    - -
    -template <class Rep, class Period>
-  void sleep_for(const chrono::duration<Rep, Period>& rel_time);;
-
    -

    --7- Effects: Blocks the calling thread for the relative timeout (30.2.4 [thread.req.timing]) specified by rel_time. -

    --8- Synchronization: None. -

    --9- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]).Nothing -if operations of chrono::duration<Rep, Period> do not throw exceptions. -[ Note: instantiations of time point types and clocks supplied by the implementation -as specified in 20.12.7 [time.clock] do not throw exceptions. — end note] -

    -
    - -
    3. - -

  3. Change 30.4.1.3 [thread.timedmutex.requirements] as indicated:

    - -

    --3- The expression m.try_lock_for(rel_time) shall be well-formed and have the following semantics: -

    -[…] -

    --5- Effects: The function attempts to obtain ownership of the mutex within the relative timeout (30.2.4 [thread.req.timing]) -specified by rel_time. If the time specified by rel_time is less than or equal to rel_time.zero(), the -function attempts to obtain ownership without blocking (as if by calling try_lock()). The function -shall return within the timeout specified by rel_time only if it has obtained ownership of the mutex -object. [Note: As with try_lock(), there is no guarantee that ownership will be obtained if the lock -is available, but implementations are expected to make a strong effort to do so. — end note] -

    -[…] -

    --8- Synchronization: If try_lock_for() returns true, prior unlock() operations on the same object -synchronize with (1.10 [intro.multithread]) this operation. -

    --9- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]).Nothing. -

    --10- The expression m.try_lock_until(abs_time) shall be well-formed and have the following semantics: -

    -[…] -

    --12- Effects: The function attempts to obtain ownership of the mutex. If abs_time has already passed, the -function attempts to obtain ownership without blocking (as if by calling try_lock()). The function -shall return before the absolute timeout (30.2.4 [thread.req.timing]) specified by abs_time only -if it has obtained ownership of the mutex object. [Note: As with try_lock(), there is no guarantee -that ownership will be obtained if the lock is available, but implementations are expected to make a strong effort -to do so. — end note] -

    -[…] -

    --15- Synchronization: If try_lock_until() returns true, prior unlock() operations on the same object -synchronize with (1.10 [intro.multithread]) this operation. -

    --16- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]).Nothing. -

    -
    4. - -

  4. Change 30.5.1 [thread.condition.condvar] as indicated:

    - -
    -template <class Predicate>
-  void wait(unique_lock<mutex>& lock, Predicate pred);
-
    -

    -[…] -

    --15- Effects: Equivalent to: -

    -
    -while (!pred())
-  wait(lock);
-
    -

    -[…] -

    --17- Throws: std::system_error when an exception is required (30.2.2 [thread.req.exception]), -timeout-related exceptions (30.2.4 [thread.req.timing]), or any exception thrown by pred. -

    -[…] -

    -
    - -
    -template <class Clock, class Duration>
-  cv_status wait_until(unique_lock<mutex>& lock,
-                       const chrono::time_point<Clock, Duration>& abs_time);
-
    -

    -[…] -

    --23- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]) -or timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -[…] -

    -
    - -
    -template <class Rep, class Period>
-  cv_status wait_for(unique_lock<mutex>& lock,
-                     const chrono::duration<Rep, Period>& rel_time);
-
    -

    -[…] -

    --26- Effects: as ifEquivalent to: -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time);
-
    -

    -[…] -

    --29- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]) -or timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -[…] -

    -
    - -
    -template <class Clock, class Duration, class Predicate>
-  bool wait_until(unique_lock<mutex>& lock,
-                  const chrono::time_point<Clock, Duration>& abs_time,
-                  Predicate pred);
-
    -

    -[…] -

    --32- Effects: Equivalent to: -

    -
    -while (!pred())
-  if (wait_until(lock, abs_time) == cv_status::timeout)
-    return pred();
-return true;
-
    -

    --33- Returns: pred() -

    -[…] -

    --36- Throws: std::system_error when an exception is required (30.2.2 [thread.req.exception]), -timeout-related exceptions (30.2.4 [thread.req.timing]), or any exception thrown by pred. -

    -[…] -

    -
    - -
    -template <class Rep, class Period, class Predicate>
-  bool wait_for(unique_lock<mutex>& lock,
-                const chrono::duration<Rep, Period>& rel_time,
-                Predicate pred);
-
    -

    -[…] -

    --39- Effects: as ifEquivalent to: -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time, std::move(pred));
-
    -

    -[…] -

    --42- Returns: pred() -

    -[…] -

    --44- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]), -timeout-related exceptions (30.2.4 [thread.req.timing]), or any exception thrown by pred. -

    -[…] -

    -
    - -
    5. - -

  5. Change 30.5.2 [thread.condition.condvarany] as indicated:

    - -
    -template <class Lock, class Predicate>
-  void wait(Lock& lock, Predicate pred);
-
    -

    --14- Effects: Equivalent to: -

    -
    -while (!pred())
-  wait(lock);
-
    -
    - -
    -template <class Lock, class Clock, class Duration>
-  cv_status wait_until(Lock& lock, const chrono::time_point<Clock, Duration>& abs_time);
-
    -

    -[…] -

    --18- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]) -or any timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -[…] -

    -
    - -
    -template <class Lock, class Rep, class Period>
-  cv_status wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
    -

    -[…] -

    --20- Effects: as ifEquivalent to: -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time);
-
    -

    -[…] -

    --23- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]) -or any timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -[…] -

    -
    - -
    -template <class Lock, class Clock, class Duration, class Predicate>
-  bool wait_until(Lock& lock, const chrono::time_point<Clock, Duration>& abs_time, Predicate pred);
-
    -

    --25- Effects: Equivalent to: -

    -
    -while (!pred())
-  if (wait_until(lock, abs_time) == cv_status::timeout)
-    return pred();
-return true;
-
    -

    --26- Returns: pred()[Note: There is no blocking if pred() is initially true, -or if the timeout has already expired. — end note] -

    --27- [Note: The returned value indicates whether the predicate evaluates to true regardless of whether the -timeout was triggered. end note] -

    -
    - -
    -template <class Lock, class Rep, class Period, class Predicate>
-  bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);
-
    -

    --28- Effects: as ifEquivalent to: -

    -
    -return wait_until(lock, chrono::steady_clock::now() + rel_time, std::move(pred));
-
    -

    --29- [Note: There is no blocking if pred() is initially true, -even if the timeout has already expired. — end note] --30- Postcondition: lock is locked by the calling thread. -

    --31- Returns: pred() -

    --32- [Note: The returned value indicates whether the predicate evaluates to true -regardless of whether the timeout was triggered. — end note] -

    --33- Throws: system_error when an exception is required (30.2.2 [thread.req.exception]). -

    --34- Error conditions: -

    -
      -
    • equivalent error condition from lock.lock() or lock.unlock().
      • -
    -
    - -
    6. -
- - - - - -
-

2094. duration conversion overflow shouldn't participate in overload resolution

-

Section: 20.12.5.1 [time.duration.cons] Status: C++14 - Submitter: Vicente J. Botet Escriba Opened: 2011-10-31 Last modified: 2015-04-08

-

View all other issues in [time.duration.cons].

-

View all issues with C++14 status.

-

Discussion:

- -

-20.12.5.1 [time.duration.cons] says: -

-
-template <class Rep2, class Period2>
-  constexpr duration(const duration<Rep2, Period2>& d);
-
-

-Remarks: This constructor shall not participate in overload resolution unless -treat_as_floating_point<rep>::value is true or both -ratio_divide<Period2, period>::den is 1 and treat_as_floating_point<Rep2>::value -is false. -

-

-The evaluation of ratio_divide<Period2, period>::den could make -ratio_divide<Period2, period>::num overflow. -

-This occur for example when we try to create a millisecond (period=ratio<1,1000>) -from an exa-second (Period2=ratio<1018>). -

-ratio_divide<ratio<1018>, ratio<1,1000>>::num is -1021 which overflows which makes the compiler error. -

-If the function f is overloaded with milliseconds and seconds -

-
-void f(milliseconds);
-void f(seconds);
-
-

-The following fails to compile. -

-
-duration<int,exa> r(1);
-f(r);
-
-

-While the conversion to seconds work, the conversion to milliseconds make the program fail at compile time. -In my opinion, this program should be well formed and the constructor from duration<int,exa> -to milliseconds shouldn't participate in overload resolution as the result can not be represented. -

-I think the wording of the standard can be improved so no misinterpretations are possible by adding that -"no overflow is induced by the conversion". -

- -

[2012, Kona]

- -

-Move to Review. -

-

Pete: The wording is not right.

-

Howard: Will implement this to be sure it works.

-

Jeffrey: If ratio needs a new hook, should it be exposed to users for their own uses?

-

Pete: No.

- -

-Move to Review, -Howard to implement in a way that mere mortals can understand. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change the following paragraphs of 20.12.5.1 [time.duration.cons] p4 indicated:

- -
-template <class Rep2, class Period2>
-  constexpr duration(const duration<Rep2, Period2>& d);
-
-

-Remarks: This constructor shall not participate in overload resolution unless no -overflow is induced in the conversion and treat_as_floating_point<rep>::value -is true or both ratio_divide<Period2, period>::den is 1 and -treat_as_floating_point<Rep2>::value is false. [ Note: This -requirement prevents implicit truncation error when converting between integral-based duration -types. Such a construction could easily lead to confusion about the value of the -duration. — end note ] -

- - - - - - -
-

2096. Incorrect constraints of future::get in regard to MoveAssignable

-

Section: 30.6.6 [futures.unique_future] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-11-02 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with C++14 status.

-

Discussion:

- -

-30.6.6 [futures.unique_future] paragraph 15 says the following: -

-
-R future::get();
-
-

-… -

--15- Returns: -

-
    -
  • -

    future::get() returns the value stored in the objectÂ’s shared state. If the type of the value is -MoveAssignable the returned value is moved, otherwise it is copied. -

    -… -

    -
    • -
-

-There are some problems with the description: -

-"If the type of the value is MoveAssignable the returned value is moved, otherwise it is copied." -

-
    -
  1. It seems to impose unrealistic constraints on implementations, because how could an implementor -recognize whether a user-defined type satisfies the semantics of MoveAssignable? This should be -based solely on a pure expression-based requirement, if this is an requirement for implementations. -
    2. -
  2. -Reducing MoveAssignable to the plain expression part std::is_move_assignable -would solvs (1), but raises another question, namely why a move-assignment should be relevant -for a function return based on the value stored in the future state? We would better fall back to -std::is_move_constructible instead. -
    3. -

  3. The last criticism I have is about the part -

    -"the returned value is moved, otherwise it is copied" -

    -because an implementation won't be able to recognize what the user-defined type -will do during an expression that is prepared by the implementation. I think the -wording is intended to allow a move by seeding with an rvalue expression via -std::move (or equivalent), else the result will be an effective -copy construction. -

    -
    4. -
- -

[2011-11-28 Moved to Tentatively Ready after 5 positive votes on c++std-lib.]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 30.6.6 [futures.unique_future] paragraph 15 as indicated:

- -
-R future::get();
-
-

-… -

--15- Returns: -

-
    -
  • -

    future::get() returns the value v stored in the objectÂ’s shared -state as std::move(v). If the type of the value is MoveAssignable -the returned value is moved, otherwise it is copied. -

    -… -

    -
    • -
- - - - - - -
-

2097. packaged_task constructors should be constrained

-

Section: 30.6.9.1 [futures.task.members] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-11-02 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

View all issues with C++14 status.

-

Discussion:

- -

-With the proposed resolution of 2067, this no longer selects the -copy constructor: -

-
-std::packaged_task<void()> p1;
-std::packaged_task<void()> p2(p1);
-
-

-Instead this constructor is a better match: -

-
-template <class F>
- explicit packaged_task(F&& f);
-
-

-This attempts to package a packaged_task, which internally tries to -copy p2, which fails because the copy constructor is deleted. For at -least one implementation the resulting error message is much less -helpful than the expected "cannot call deleted function" because it -happens after instantiating several more templates rather than in the -context where the constructor is called. -

-I believe the solution is to constrain to the template constructors so -the template argument F cannot be deduced as (possibly cv) -packaged_task& or packaged_task. It could be argued -this constraint is already implied because packaged_task is not -copyable and the template constructors require that "invoking a copy of f -shall behave the same as invoking f". -

-Daniel points out that the variadic constructor of std::thread -described in 30.3.1.2 [thread.thread.constr] has a similar problem and -suggests a similar wording change, which has been integrated below. -

-An alternative is to declare thread(thread&) and -packaged_task(packaged_task&) as deleted. -

- -

[2012, Portland]

- -

-This issue appears to be more about library specification than technical -concurrency issues, so should be handled in LWG. -

- - -

[2013, Chicago]

- -

-Move to Immediate resolution. -

-

-Howard volunteered existing implementation experience with the first change, and saw no issue that the second would -introduce any new issue. -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Insert a new Remarks element to 30.3.1.2 [thread.thread.constr] around p3 as indicated:

    - -
    -template <class F, class ...Args> explicit thread(F&& f, Args&&... args);
-
    -

    --3- Requires: F and each Ti in Args shall satisfy the MoveConstructible -requirements. INVOKE(DECAY_COPY ( std::forward<F>(f)), DECAY_COPY (std::forward<Args>(args))...) -(20.8.2) shall be a valid expression. -

    --?- Remarks: This constructor shall not participate in overload resolution if decay<F>::type -is the same type as std::thread. -

    -
    2. - -

  2. Insert a new Remarks element to 30.6.9.1 [futures.task.members] around p2 as indicated:

    - -
    -template <class F>
-  packaged_task(F&& f);
-template <class F, class Allocator>
-  explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
-
    -

    --2- Requires: INVOKE(f, t1, t2, ..., tN, R), where t1, t2, ..., tN are values of the corresponding -types in ArgTypes..., shall be a valid expression. Invoking a copy of f shall behave the same as invoking f. -

    --?- Remarks: These constructors shall not participate in overload resolution if decay<F>::type -is the same type as std::packaged_task<R(ArgTypes...)>. -

    -
    3. - -
- - - - - - -
-

2098. Minor Inconsistency between promise::set_value and promise::set_value_at_thread_exit

-

Section: 30.6.5 [futures.promise] Status: C++14 - Submitter: Pete Becker Opened: 2011-11-14 Last modified: 2015-04-08

-

View other active issues in [futures.promise].

-

View all other issues in [futures.promise].

-

View all issues with C++14 status.

-

Discussion:

- -

-30.6.5 [futures.promise]/16 says that promise::set_value(const R&) throws any exceptions -thrown by R's copy constructor, and that promise_set_value(R&&) throws any exceptions -thrown by R's move constructor. -

-30.6.5 [futures.promise]/22 is the Throws: clause for promise::set_value_at_thread_exit. It -has no corresponding requirements, only that these functions throw "future_error if an error condition -occurs." -

-Daniel suggests wording to fix this: The approach is a bit more ambitious and also attempts to fix wording glitches -of 30.6.5 [futures.promise]/16, because it would be beyond acceptable efforts of implementations to -determine whether a constructor call of a user-defined type will indeed call a copy constructor or move constructor -(in the first case it might be a template constructor, in the second case it might also be a copy-constructor, -if the type has no move constructor). -

- -

[2012, Portland: move to Review]

- -

-Moved to Review by the concurrency working group, with no further comments. -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change 30.6.5 [futures.promise]/16 as indicated:

    -
    -void promise::set_value(const R& r);
-void promise::set_value(R&& r);
-void promise<R&>::set_value(R& r);
-void promise<void>::set_value();
-

    -[…] -

    --16- Throws: -

    -
      -
    • future_error if its shared state already has a stored value or exception, or
      • -
    • for the first version, any exception thrown by the copy constructor -ofconstructor selected to copy an object of R, or
      • -
    • for the second version, any exception thrown by the move constructor -ofconstructor selected to move an object of R.
      • -
    -
    -
    2. - -

  2. Change 30.6.5 [futures.promise]/22 as indicated:

    -
    -void promise::set_value_at_thread_exit(const R& r);
-void promise::set_value_at_thread_exit(R&& r);
-void promise<R&>::set_value_at_thread_exit(R& r);
-void promise<void>::set_value_at_thread_exit();
-

    -[…] -

    --16- Throws: future_error if an error condition occurs. -

    -
      -
    • future_error if its shared state already has a stored value or exception, or
      • -
    • for the first version, any exception thrown by the constructor selected to copy an object of R, or
      • -
    • for the second version, any exception thrown by the constructor selected to move an object of R.
      • -
    -
    -
    3. -
- - - - - - -
-

2099. Unnecessary constraints of va_start() usage

-

Section: 18.10 [support.runtime] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-11-12 Last modified: 2015-04-08

-

View other active issues in [support.runtime].

-

View all other issues in [support.runtime].

-

View all issues with C++14 status.

-

Discussion:

- -

-In 18.10 [support.runtime] p3 we find (emphasis mine): -

-

-The restrictions that ISO C places on the second parameter to the va_start() macro in header <stdarg.h> -are different in this International Standard. The parameter parmN is the identifier of the rightmost parameter -in the variable parameter list of the function definition (the one just before the ...).227 If the parameter -parmN is declared with a function, array, or reference type, -or with a type that is not compatible with the type that results when passing an argument for which there is no parameter, -the behavior is undefined. -

- -

-It seems astonishing that the constraints on function types and array types imposes these -on the declared parameter parmN, not to the adjusted one (which would -not require this extra wording, because that is implicit). This seems to say that a function -definition of the form (Thanks to Johannes Schaub for this example) -

-
-#include <stdarg.h>
-
-void f(char const paramN[], ...) {
-  va_list ap;
-  va_start(ap, paramN);
-  va_end(ap);
-}
-
-

-would produce undefined behaviour when used. -

-Similar wording exists in C99 and in the most recent C11 draft in 7.16.1.4 p4 -

-In my opinion the constraints in regard to array types and function types are -unnecessary and should be relaxed. Are there really implementations out in the -wild that would (according to my understanding incorrectly) provide the declared and -not the adjusted type of paramN as deduced type to va_start()? -

- - -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 18.10 [support.runtime] p3 as indicated:

-

-The restrictions that ISO C places on the second parameter to the va_start() macro in header <stdarg.h> -are different in this International Standard. The parameter parmN is the identifier of the rightmost parameter -in the variable parameter list of the function definition (the one just before the ...).227 If the parameter -parmN is declared withof a function, array, or reference type, or -withof a type that is not compatible with the type that results when passing an argument for -which there is no parameter, the behavior is undefined. -

- - - - - - -
-

2100. timed waiting functions cannot timeout if launch::async policy used

-

Section: 30.6.8 [futures.async] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-11-14 Last modified: 2015-04-08

-

View all other issues in [futures.async].

-

View all issues with C++14 status.

-

Discussion:

- -

-30.6.8 [futures.async] p5 says -

- -
-

-If the implementation chooses the launch::async policy, -

-
  • a call to a waiting function on an asynchronous return object that shares the -shared state created by this async call shall block until the associated thread has -completed, as if joined (30.3.1.5 [thread.thread.member]);
    • -
-
- -

-That should say a non-timed waiting function, otherwise, calling a timed waiting function -can block indefinitely waiting for the associated thread to complete, rather than timing -out after the specified time. -

-Since std::thread does not provide a timed_join() function (nor does -Pthreads, making it impossible on many platforms) there is no way for a timed waiting -function to try to join but return early due to timeout, therefore timed waiting -functions either cannot guarantee to timeout or cannot be used to meet the requirement -to block until the thread is joined. In order to allow timed waiting functions to -timeout the requirement should only apply to non-timed waiting functions. -

- -

[2012, Portland: move to Review]

- -

-Detlef: Do we actually need this fix — is it detectable? -

-

-Yes — you will never get a timeout. Should we strike the whole paragraph? -

-

-Hans: issue with thread local destruction. -

-

-Niklas: I have a strong expectation that a timed wait will respect the timeout -

-

-agreed -

-

-Detlef: we want a timed wait that does not time out to return like a non-timed wait; but is this implementable? -

-

-Pablo: Could we simply append ", or else time out" -

-

-Detlef: the time out on the shared state needs implementing anyway, even if the underlying O/S does not support a timed join. -

-

-Hans: the net effect is the timeout does not cover the thread local destruction... ah, I see what you're doing -

-

-Detlef: happy with Pablo's proposal -

-

-Wording proposed is to append after the word "joined" add ", or else time out" -

-

-Moved to review with this wording. -

- -

[2013, Bristol]

- - -

-"Non-timed" made the new wording redundant and the result overly weak. Remove it. -

-Attempted to move to add this to the working paper (Concurrency motion 2) without the addition of "non-timed". -Motion was withdrawn after Jonathan Wakely expressed implementability concerns. -

- -

[2013-09, Chicago]

- -

-Discussion of interaction with the absence of a Posix timed join. -

-Jonathan Wakely withdrew his objection, so moved to Immediate. -

-Accept for Working Paper -

- - - -

Proposed resolution:

-

[This wording is relative to the FDIS.]

- - -

Change 30.6.8 [futures.async] p5 as indicated:

- -
-

-If the implementation chooses the launch::async policy, -

-
  • a call to a waiting function on an asynchronous return object -that shares the shared state created by this async call shall block until the -associated thread has completed, as if joined, or else time out -(30.3.1.5 [thread.thread.member]);
    • -
-
- - - - - - -
-

2102. Why is std::launch an implementation-defined type?

-

Section: 30.6.1 [futures.overview] Status: C++14 - Submitter: Jonathan Wakely Opened: 2011-11-20 Last modified: 2015-04-08

-

View all other issues in [futures.overview].

-

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-

Discussion:

- -

-30.6.1 [futures.overview] says std::launch is an -implementation-defined bitmask type, which would usually mean the -implementation can choose whether to define an enumeration type, or a -bitset, or an integer type. But in the case of std::launch it's -required to be a scoped enumeration type, -

-
-enum class launch : unspecified {
-  async = unspecified,
-  deferred = unspecified,
-  implementation-defined
-};
-
-

-so what is implementation-defined about it, and what is an implementation -supposed to document about its choice? -

- -

[2011-12-02 Moved to Tentatively Ready after 6 positive votes on c++std-lib.]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 30.6.1 [futures.overview] paragraph 2 as indicated:

- -

-The enum type launch is an implementation-defineda bitmask type -(17.5.2.1.3 [bitmask.types]) with launch::async and launch::deferred -denoting individual bits. [ Note: Implementations can provide bitmasks to specify restrictions -on task interaction by functions launched by async() applicable to a corresponding subset of -available launch policies. Implementations can extend the behavior of the first overload of async() by -adding their extensions to the launch policy under the “as if” rule. — end note ] -

- - - - - - -
-

2103. std::allocator_traits<std::allocator<T>>::propagate_on_container_move_assignment

-

Section: 20.7.9 [default.allocator] Status: C++14 - Submitter: Ai Azuma Opened: 2011-11-08 Last modified: 2015-04-08

-

View all other issues in [default.allocator].

-

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-

Discussion:

- -

-"std::allocator_traits<std::allocator<T>>::propagate_on_container_move_assignment::value" -is specified as "false", according to (20.7.9 [default.allocator]) and (20.7.8.1 [allocator.traits.types]). -However, according to (23.2.1 [container.requirements.general]), this specification leads to the unneeded requirements -(MoveInsertable and MoveAssignable of the value type) on the move assignment operator of containers -with the default allocator. -

-Proposed resolution: -

-Either of the following two changes; -

-
    -
  1. -adding the nested typedef like -"typedef std::true_type propagate_on_container_move_assignment;" -in the definition of std::allocator class template, -
    2. -
  2. -adding the explicit partial specialization of -"std::allocator_traits" class template for "std::allocator" -class template, in which "propagate_on_container_move_assignment" -nested typedef is specified as "std::true_type". -
    3. -
-

-Pablo prefers the first resolution. -

- -

[2011-12-02: Pablo comments]

- - -

-This issue has potentially some overlap with 2108. Should the trait always_compare_equal -been added, this issue's resolution should be improved based on that. -

- -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 20.7.9 [default.allocator], the class template allocator synopsis as indicated:

- -
-namespace std {
-  template <class T> class allocator;
-
-  // specialize for void:
-  template <> class allocator<void> {
-  public:
-    typedef void* pointer;
-    typedef const void* const_pointer;
-    // reference-to-void members are impossible.
-    typedef void value_type;
-    template <class U> struct rebind { typedef allocator<U> other; };
-  };
-
-  template <class T> class allocator {
-  public:
-    typedef size_t size_type;
-    typedef ptrdiff_t difference_type;
-    typedef T* pointer;
-    typedef const T* const_pointer;
-    typedef T& reference;
-    typedef const T& const_reference;
-    typedef T value_type;
-    template <class U> struct rebind { typedef allocator<U> other; };
-    typedef true_type propagate_on_container_move_assignment;
-
-    […]
-  };
-}
-
- - - - - - -
-

2104. unique_lock move-assignment should not be noexcept

-

Section: 30.4.2.2 [thread.lock.unique] Status: C++14 - Submitter: Anthony Williams Opened: 2011-11-27 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

- -

-I just noticed that the unique_lock move-assignment operator is declared noexcept. This -function may call unlock() on the wrapped mutex, which may throw. -

-Suggested change: remove the noexcept specification from unique_lock::operator=(unique_lock&&) -in 30.4.2.2 [thread.lock.unique] and 30.4.2.2.1 [thread.lock.unique.cons]. -

-Daniel: -

-I think the situation is actually a bit more complex as it initially looks. -

-First, the effects of the move-assignment operator are (emphasize mine): -

-

-Effects: If owns calls pm->unlock(). -

-

-Now according to the BasicLockable requirements: -

-

-m.unlock() -

-3 Requires: The current execution agent shall hold a lock on m. -

-4 Effects: Releases a lock on m held by the current execution agent. -

-Throws: Nothing. -

-

-This shows that unlock itself is a function with narrow contract and for -this reasons no unlock function of a mutex or lock itself does have a noexcept -specifier according to our mental model. -

-Now the move-assignment operator attempts to satisfy these -requirement of the function and calls it only when it assumes that the conditions -are ok, so from the view-point of the caller of the move-assignment operator it -looks as if the move-assignment operator would in total a function with a -wide contract. -

-The problem with this analysis so far is, that it depends on the assumed -correctness of the state "owns". -

-Looking at the construction or state-changing functions, there do exist several -ones that depend on caller-code satisfying the requirements and there is one -guy, who looks most suspicious: -

-

-unique_lock(mutex_type& m, adopt_lock_t); -

-11 Requires: The calling thread own the mutex.
-[…]
-13 Postconditions: pm == &m and owns == true.
-

-

-because this function does not even call lock() (which may, but is not -required to throw an exception if the calling thread does already own the mutex). -So we have in fact still a move-assignment operator that might throw an exception, -if the mutex was either constructed or used (call of lock) incorrectly. -

-The correct fix seems to me to also add a "Throws: Nothing" element to -the move-assignment operator, because using it correctly shall not throw an -exception. -

- -

[Issaquah 20014-10-11: Move to Immediate after SG1 review]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -
  1. -

    Change 30.4.2.2 [thread.lock.unique], class template unique_lock synopsis as indicated:

    - -
    -namespace std {
-  template <class Mutex>
-  class unique_lock {
-  public:
-    typedef Mutex mutex_type;
-    […]
-    unique_lock(unique_lock&& u) noexcept;
-    unique_lock& operator=(unique_lock&& u) noexcept;
-    […]
-  };
-}
-
    -
    2. - -
  2. -

    Change 30.4.2.2.1 [thread.lock.unique.cons] around p22 as indicated:

    - -
    -unique_lock& operator=(unique_lock&& u) noexcept;
-
    -

    --22- Effects: If owns calls pm->unlock(). -

    --23- Postconditions: pm == u_p.pm and owns == u_p.owns (where u_p -is the state of u just prior to this construction), u.pm == 0 and u.owns == false. -

    --24- [Note: With a recursive mutex it is possible for both *this and u to own -the same mutex before the assignment. In this case, *this will own the mutex after the assignment -and u will not. — end note] -

    --??- Throws: Nothing. -

    -

    -
    3. - -
- - - - - - -
-

2105. Inconsistent requirements on const_iterator's value_type

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Jeffrey Yasskin Opened: 2011-11-28 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

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-

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-

Discussion:

- -

-In the FDIS, Table 96 specifies X::const_iterator as a "constant iterator type -whose value type is T". However, Table 97 specifies X::const_reverse_iterator -as an "iterator type whose value type is const T" and which is defined as -reverse_iterator<const_iterator>. But reverse_iterator::value_type is -just "typename iterator_traits<Iterator>::value_type" 24.5.1.1 [reverse.iterator], -so const_iterator and const_reverse_iterator must have the same value_type. -

-

-The resolution to issue 322 implies that -const_reverse_iterator should change. -

- -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change Table 97 — "Reversible container requirements" as indicated

- - - - - - - - - - - - - - - - - - - - - - - -
Table 97 — Reversible container requirements
ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
-X::reverse_-
-iterator -		 -iterator type whose value type
-is T -		 -reverse_iterator<iterator> - -compile time -
-X::const_-
-reverse_-
-iterator -		 -constant iterator type whose value type
-is const T -		 -reverse_iterator<const_iterator> - -compile time -
- - - - - - - -
-

2106. move_iterator wrapping iterators returning prvalues

-

Section: 24.5.3 [move.iterators] Status: WP - Submitter: Dave Abrahams Opened: 2011-11-30 Last modified: 2015-04-08

-

View all other issues in [move.iterators].

-

View all issues with WP status.

-

Discussion:

- -

-Shouldn't move_iterator be specialized so that if the iterator it wraps -returns a prvalue when dereferenced, the move_iterator also returns by -value? Otherwise, it creates a dangling reference. -

-Howard: I believe just changing move_iterator<I>::reference would do. -A direction might be testing on is_reference<iterator_traits<I>::reference>, -or is_reference<decltype(*declval<I>())>. -

-Daniel: I would prefer to use a consistent style among the iterator adaptors, so I -suggest to keep with the iterator_traits typedefs if possible. -

-
-using reference = typename conditional<
-  is_reference<typename iterator_traits<Iterator>::reference>::value,
-  value_type&&,
-  value_type
->::type;
-
-

-We might also want to ensure that if Iterator's reference type is -a reference, the referent is equal to value_type (after removal of cv-qualifiers). -In general we have no such guarantee. -

-Marc: In the default case where we don't return value_type&&, should we use -value_type or should we keep the reference type of the wrapped iterator? -

-Daniel: This suggestion looks appealing at first, but the problem here is that using this typedef -can make it impossible for move_iterator to satisfy its contract, which means returning -an rvalue of the value type (Currently it says rvalue-reference, but this must be fixed as of -this issue anyway). I think that user-code can reasonably expect that when it has constructed -an object m of move_iterator<It>, where It is a valid -mutable iterator type, the expression -

-
-It::value_type&& rv = *m;
-
-

-is well-formed. -

-Let's set R equal to iterator_traits<Iterator>::reference -in the following. We can discuss the following situations: -

-
  1. R is a reference type: We can only return the corresponding xvalue of R, -if value_type is reference-related to the referent type, else this is presumably no -forward iterator and we cannot say much about it, except that it must be convertible to -value_type, so it better should return a prvalue.
    2. -
  2. R is not a reference type: In this case we can rely on a conversion to -value_type again, but not much more. Assume we would return R directly, -this might turn out to have a conversion to an lvalue-reference type of the value type (for -example). If that is the case, this would indirectly violate the contract of -move_iterator.
    3. -
-

-In regard to the first scenario I suggest that implementations are simply required to -check that V2 = remove_cv<remove_reference<R>::type>::type is equal -to the value type V1 as a criterion to return this reference as an xvalue, in all other -cases it should return the value type directly as prvalue. -

-The additional advantage of this strategy is, that we always ensure that reference has -the correct cv-qualification, if R is a real reference. -

-It is possible to improve this a bit by indeed supporting reference-related types, -this would require to test is_same<V1, V2>::value || is_base_of<V1, V2>::value -instead. I'm unsure whether (a) this additional effort is worth it and (b) a strict reading of -the forward iterator requirements seems not to allow to return a reference-related type (Whether -this is a defect or not is another question). -

- -

[2011-12-05: Marc Glisse comments and splits into two resolution alternatives]

- - -

-I guess I am looking at the speed of: -

-
-value_type x;
-x = *m;
-
-

-(copy construction would likely trigger copy elision and thus be neutral) - -instead of the validity of: -

-
-value_type&& x = *m;
-
-

-In this sense, Daniels earlier proposition that ignored value_type and just did -switch_lvalue_ref_to_rvalue_ref<reference> was easier to understand (and it didn't -require thinking about reference related types). -

-The currently proposed resolution has been split into two alternatives. -

- - -

[2012, Kona]

- -

-Move to Review. -

-

-Alisdair: This only applies to input iterators, so keep that in mind when thinking about this. -

-

-STL: I see what B is doing, but not A. -

-

-Howard: I agree. -

-

-Alisdair: Should we use add_rvalue_reference? -

-

-STL: No, we do not want reference collapsing. -

-

-STL: Re A, messing with the CV qualification scares me. -

-

-Alisdair: Agree. That would break my intent. -

-

-STL: Actually I don't think it's actually wrong, but I still don't see what it's doing. -

-

-Alisdair: A is picking the value type, B is picking the proxy type. -

-

-Howard: I like returning the proxy type. -

-

-STL: Returning a reference (B) seems right, because the requirements say "reference". -I suspect that B works correctly if you have a move iterator wrapping a move iterator -wrapping a thing. I think that A would mess up the type in the middle. -

-

-Considerable discussion about which version is correct, checking various examples. -

-

-STL: Still think B is right. Still don't understand A. In A we are losing the proxyness. -

-

-Howard: Agree 100%. We don't want to lose the proxy. If it's const, so be it. -

-

-STL: B is also understandable by mortals. -

-

-Howard: Remove to review, keep A but move it out of the proposed resolution area -(but keep it for rational). -

-

-Alisdair: Adding an explanatory note might be a good idea, if someone wants to write one. -

-

-Walter: Concerned about losing the word "reference" in p.1. -

-

-Howard: move_iterator will return an xvalue or a prvalue, both of which are rvalues. -

- -

[Proposed resolution A, rejected in preference to the currently proposed resolution (B) - -

    -

  1. Change 24.5.3 [move.iterators] p1 as indicated:

    - -

    -Class template move_iterator is an iterator adaptor with the same behavior as the underlying iterator -except that its dereference operator implicitly converts the value returned by the underlying iterator's -dereference operator to an rvalue referenceof the value type. Some generic algorithms -can be called with move iterators to replace copying with moving. -

    -
    2. - -

  2. Change 24.5.3.1 [move.iterator], class template move_iterator synopsis, as indicated:

    - -
    -namespace std {
-  template <class Iterator>
-  class move_iterator {
-  public:
-    typedef Iterator iterator_type;
-    typedef typename iterator_traits<Iterator>::difference_type difference_type;
-    typedef Iterator pointer;
-    typedef typename iterator_traits<Iterator>::value_type value_type;
-    typedef typename iterator_traits<Iterator>::iterator_category iterator_category;
-    typedef value_type&&see below reference;
-    […]
-  };
-}
-
    - -
    3. - -

  3. Immediately following the class template move_iterator synopsis in -24.5.3.1 [move.iterator] insert a new paragraph as indicated:

    - -

    --?- Let R be iterator_traits<Iterator>::reference and -let V be iterator_traits<Iterator>::value_type. If -is_reference<R>::value is true and if -remove_cv<remove_reference<R>::type>::type is the same type as V, -the template instantiation move_iterator<Iterator> shall define the nested type -named reference as a synonym for remove_reference<R>::type&&, -otherwise as a synonym for V. -

    -
    4. -
- -]

- - -

[2012, Portland: Move to Tentatively Ready]

- -

-AJM wonders if the implied trait might be useful elsewhere, and worth adding to type traits as a -transformation type trait. -

- -

-Suspicion that the Range SG might find such a trait useful, but wait until there is clear additional -use of such a trait before standardizing. -

- -

-Minor wording tweak to use add_rvalue_reference rather than manually adding the &&, -then move to Tentatively Ready. -

- -

[2013-01-09 Howard Hinnant comments]

- - -

-I believe the P/R for LWG 2106 is incorrect (item 3). The way it currently reads, move_iterator<I>::reference -is always an lvalue reference. I.e. if R is an lvalue reference type, then reference becomes -add_rvalue_reference<R>::type which is just R. And if R is not a reference type, -then reference becomes R (which is also just R ;-)). -

- -

-I believe the correct wording is what was there previously: -

- -

--?- Let R be iterator_traits<Iterator>::reference. If is_reference<R>::value -is true, the template instantiation move_iterator<Iterator> shall define the nested type named -reference as a synonym for remove_reference<R>::type&&, otherwise as a synonym for -R. -

- -

-Additionally Marc Glisse points out that move_iterator<I>::operator*() should return -static_cast<reference>(*current), not std::move(*current). -

- -

-Previous resolution: -

-
-

This wording is relative to the FDIS.

- -
    -

  1. Change 24.5.3 [move.iterators] p1 as indicated:

    - -

    -Class template move_iterator is an iterator adaptor with the same behavior as the underlying iterator -except that its dereference operator implicitly converts the value returned by the underlying iterator's -dereference operator to an rvalue reference. Some generic algorithms -can be called with move iterators to replace copying with moving. -

    -
    2. - -

  2. Change 24.5.3.1 [move.iterator], class template move_iterator synopsis, as indicated:

    - -
    -namespace std {
-  template <class Iterator>
-  class move_iterator {
-  public:
-    typedef Iterator iterator_type;
-    typedef typename iterator_traits<Iterator>::difference_type difference_type;
-    typedef Iterator pointer;
-    typedef typename iterator_traits<Iterator>::value_type value_type;
-    typedef typename iterator_traits<Iterator>::iterator_category iterator_category;
-    typedef value_type&&see below reference;
-    […]
-  };
-}
-
    - -
    3. - -

  3. Immediately following the class template move_iterator synopsis in -24.5.3.1 [move.iterator] insert a new paragraph as indicated:

    - -

    --?- Let R be iterator_traits<Iterator>::reference. If -is_reference<R>::value is true, the template instantiation -move_iterator<Iterator> shall define the nested type named reference -as a synonym for add_rvalue_reference<R>::type, otherwise as a synonym -for R. -

    -
    4. -
-
- -

[2014-05-19, Daniel comments]

- -

-The term instantiation has been changed to specialization in the newly added paragraph as -suggested by STL and much preferred by myself. -

- -

[2014-05-19 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on five votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 24.5.3 [move.iterators] p1 as indicated:

    - -

    -Class template move_iterator is an iterator adaptor with the same behavior as the underlying iterator -except that its indirection operator implicitly converts the value returned by the underlying iterator's -indirection operator to an rvalue reference. Some generic algorithms -can be called with move iterators to replace copying with moving. -

    -
    2. - -

  2. Change 24.5.3.1 [move.iterator], class template move_iterator synopsis, as indicated:

    - -
    -namespace std {
-  template <class Iterator>
-  class move_iterator {
-  public:
-    typedef Iterator iterator_type;
-    typedef typename iterator_traits<Iterator>::difference_type difference_type;
-    typedef Iterator pointer;
-    typedef typename iterator_traits<Iterator>::value_type value_type;
-    typedef typename iterator_traits<Iterator>::iterator_category iterator_category;
-    typedef value_type&&see below reference;
-    […]
-  };
-}
-
    - -
    3. - -

  3. Immediately following the class template move_iterator synopsis in -24.5.3.1 [move.iterator] insert a new paragraph as indicated:

    - -

    --?- Let R be iterator_traits<Iterator>::reference. If -is_reference<R>::value is true, the template specialization -move_iterator<Iterator> shall define the nested type named reference -as a synonym for remove_reference<R>::type&&, otherwise as a synonym -for R. -

    -
    4. - -

  4. Edit 24.5.3.3.4 [move.iter.op.star] p1 as indicated:

    -
    -reference operator*() const;
-
    -

    --1- Returns: std::movestatic_cast<reference>(*current). -

    -
    -
    5. -
- - - - - - -
-

2108. No way to identify allocator types that always compare equal

-

Section: 17.6.3.5 [allocator.requirements] Status: Resolved - Submitter: Jonathan Wakely Opened: 2011-12-01 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with Resolved status.

-

Discussion:

- -

-Whether two allocator objects compare equal affects the complexity of -container copy and move assignments and also the possibility of an -exception being thrown by container move assignments. The latter point -means container move assignment cannot be noexcept when -propagate_on_container_move_assignment (POCMA) is false for the -allocator because there is no way to detect at compile-time if two -allocators will compare equal. LWG 2013 means this affects all -containers using std::allocator, but even if that is resolved, this -affects all stateless allocators which do not explicitly define POCMA -to true_type. -

-One solution would be to add an "always_compare_equal" trait to -allocator_traits, but that would be duplicating information that is -already defined by the type's equality operator if that operator -always returns true. Requiring users to write operator== that simply -returns true and also explicitly override a trait to repeat the same -information would be unfortunate and risk user errors that allow the -trait and actual operator== to disagree. -

-Dave Abrahams suggested a better solution in message c++std-lib-31532, -namely to allow operator== to return true_type, which is convertible -to bool but also detectable at compile-time. Adopting this as the -recommended way to identify allocator types that always compare equal -only requires a slight relaxation of the allocator requirements so -that operator== is not required to return bool exactly. -

-The allocator requirements do not make it clear that it is well-defined -to compare non-const values, that should be corrected too. -

-In message c++std-lib-31615 Pablo Halpern suggested an always_compare_equal -trait that could still be defined, but with a sensible default value rather -than requiring users to override it, and using that to set sensible values for -other allocator traits: -

-

-Do we still need always_compare_equal if we can have an operator== -that returns true_type? What would its default value be? is_empty<A> -|| is_convertible<decltype(a == a), true_type>::value, perhaps? One -benefit I see to such a definition is that stateless C++03 allocators -that don't use the true_type idiom will still benefit from the new -trait. -

-[…] -

-One point that I want to ensure doesn't get lost is that if we adopt some sort of -always_compare_equal-like trait, then propagate_on_container_swap -and propagate_on_container_move_assignment should default to -always_compare_equal. Doing this will eliminate unnecessary requirements -on the container element type, as per [LWG 2103]. -

-

-Optionally, operator== for std::allocator could be made to return -true_type, however if LWG 2103 is adopted that is less important. -

-Alberto Ganesh Barbati: Suggest either always_compare_equal, -all_objects_(are_)equivalent, or all_objects_compare_equal. -

- -

[2014-11-07 Urbana]

- -

-Resolved by N4258 -

- - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -

  1. Change Table 27 — "Descriptive variable definitions" in 17.6.3.5 [allocator.requirements]:

    - - - - - - - - - - - - - - - - - - -
    Table 27 — Descriptive variable definitions
    VariableDefinition
    -a3, a4 - -an rvalue ofvalues of (possibly const) type X -
    -b - -a value of (possibly const) type Y -
    - -
    2. - -

  2. Change Table 28 — "Allocator requirements" in 17.6.3.5 [allocator.requirements]:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements
    ExpressionReturn typeAssertion/note pre-/post-conditionDefault
    -a1 == a2a3 == a4 - -convertible to bool - -returns true only if storage
    -allocated from each can be
    -deallocated via the other.
    -operator== shall be reflexive,
    -symmetric, and transitive, and
    -shall not exit via an exception. -    		 -
    -a1 != a2a3 != a4 - -convertible to bool - -same as !(a1 == a2)!(a3 == a4) - -
    -a3 == b - -convertible to bool - -same as a3 ==
    -Y::rebind<T>::other(b)     -    		 -
    -a3 != b - -convertible to bool - -same as !(a3 == b) - -
    -[…] -
    -a.select_on_-
    -container_copy_-
    -construction()     -    		 -X - -Typically returns either a or
    -X() -    		 -return a; -
    -X::always_compares_equal - -Identical to or derived
    -from true_type or
    -false_type     -    		 -true_type if the expression x1 == x2 is
    -guaranteed to be true for any two (possibly
    -const) values x1, x2 of type X, when
    -implicitly converted to bool. See Note B, below.     -    		 -true_type, if is_empty<X>::value is true or if
    -decltype(declval<const X&>() == declval<const X&>())
    -is convertible to true_type, otherwise false_type.     -
    -[…] -
    -

    -Note A: […] -

    -Note B: If X::always_compares_equal::value or XX::always_compares_equal::value evaluate -to true and an expression equivalent to x1 == x2 or x1 != x2 for any two values -x1, x2 of type X evaluates to false or true, respectively, the behaviour -is undefined. -

    - -
    3. - -

  3. Change class template allocator_traits synopsis, 20.7.8 [allocator.traits] as indicated:

    - -
    -namespace std {
-  template <class Alloc> struct allocator_traits {
-    typedef Alloc allocator_type;
-    […]
-    typedef see below always_compares_equal;
-    typedef see below propagate_on_container_copy_assignment;
-    […]
-  };
-}
-
    -
    4. - -

  4. Insert the following between 20.7.8.1 [allocator.traits.types] p6 and p7 as indicated:

    - -
    -typedef see below always_compares_equal;
-
    -

    --?- Type: Alloc::always_compares_equal if such a type exists; otherwise, -true_type if is_empty<Alloc>::value is true or if -decltype(declval<const Alloc&>() == declval<const Alloc&>()) -is convertible to true_type; otherwise, false_type -. -

    -
    -
    -typedef see below propagate_on_container_copy_assignment;
-
    -

    --7- Type: Alloc::propagate_on_container_copy_assignment if such a type exits, -otherwise false_type. -

    -
    -
    5. - -

  5. Change class template allocator synopsis, 20.7.9 [default.allocator] as indicated:

    - -
    -namespace std {
-  template <class T> class allocator;
-
-  // specialize for void:
-  template <> class allocator<void> {
-  public:
-    typedef void* pointer;
-    typedef const void* const_pointer;
-    // reference-to-void members are impossible.
-    typedef void value_type;
-    template <class U> struct rebind { typedef allocator<U> other; };
-  };
-
-  template <class T> class allocator {
-  public:
-    typedef size_t size_type;
-    typedef ptrdiff_t difference_type;
-    typedef T* pointer;
-    typedef const T* const_pointer;
-    typedef T& reference;
-    typedef const T& const_reference;
-    typedef T value_type;
-    template <class U> struct rebind { typedef allocator<U> other; };
-    typedef true_type always_compares_equal;
-
-    […]
-  };
-}
-
    -
    6. - -
- - - - - - -
-

2109. Incorrect requirements for hash specializations

-

Section: 19.5.5 [syserr.hash], 20.8.2.7 [util.smartptr.hash], 20.9.13 [unord.hash], 20.14.1 [type.index.synopsis], 21.6 [basic.string.hash], 23.3.7 [vector.bool], 30.3.1.1 [thread.thread.id] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-12-04 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

- -

-20.8.2.7 [util.smartptr.hash] p2 is specified as follows: -

- -

-Requires: the template specializations shall meet the requirements of class template -hash (20.8.12). -

- -

-The problem here is the usage of a Requires element, which is actually a pre-condition -that a user of a component has to satisfy. But the intent of this wording is actually -to be a requirement on implementations. The Requires element should be removed here and -the wording should be improved to say what it was intended for. -

-We have similar situations in basically all other places where the specification of library-provided -hash specializations is defined. Usually, the Requires element is incorrect. In the -special case of hash<unique_ptr<T, D>> the implementation depends on -the behaviour of hash specializations, that could be user-provided. In this case -the specification needs to separate the requirements on these specializations and those -that are imposed on the implementation. -

- - -

[2012, Kona]

- -

-Update wording and move to Review. -

-

-Believe a simpler formulation is to simply string the term Requires: and leave the -current wording intact, rather than strike the whole clause and replace it. -

- -

[Originally proposed wording for reference -

    -

  1. Change 19.5.5 [syserr.hash] as indicated:

    - -
    -template <> struct hash<error_code>;
-
    -

    --1- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<system_error> provides a definition for a specialization of the -template hash<error_code>. The requirements for the members of -this specialization are given in sub-clause 20.9.13 [unord.hash]. -

    -
    -
    2. - -

  2. Change 20.6.3 [bitset.hash] as indicated:

    - -
    -template <size_t N> struct hash<bitset<N> >;
-
    -

    --1- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<bitset> provides a definition for a partial specialization of the -hash class template for specializations of class template bitset<N>. -The requirements for the members of instantiations of this specialization are given -in sub-clause 20.9.13 [unord.hash]. -

    -
    -
    3. - -

  3. Change 20.8.2.7 [util.smartptr.hash] as indicated:

    - -
    -template <class T, class D> struct hash<unique_ptr<T, D> >;
-
    -

    --1- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<memory> provides a definition for a partial specialization of the -hash class template for specializations of class template unique_ptr<T, D>. -The requirements for the members of instantiations of this specialization are given -in sub-clause 20.9.13 [unord.hash]. For an object p of type -UP, where UP is unique_ptr<T, D>, -hash<UP>()(p) shall evaluate to the same value as -hash<typename UP::pointer>()(p.get()). The specialization -hash<typename UP::pointer> shall be well-formed. -

    --?- Requires: The specialization hash<typename UP::pointer> -shall be well-formed and well-defined [Note: the general requirements -of class template hash (20.9.13 [unord.hash]) are implied — -end note]. -

    -
    - -
    -template <class T> struct hash<shared_ptr<T> >;
-
    -

    --2- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<memory> provides a definition for a partial specialization of the -hash class template for specializations of class template shared_ptr<T>. -The requirements for the members of instantiations of this specialization are given -in sub-clause 20.9.13 [unord.hash]. For an object p of type -shared_ptr<T>, hash<shared_ptr<T> >()(p) -shall evaluate to the same value as hash<T*>()(p.get()). -

    -
    -
    4. - -

  4. Change 20.9.13 [unord.hash] p2 as indicated: [Comment: For unknown -reasons the extended integer types are not mentioned here, which looks like an oversight to -me and makes also the wording more complicated. See 2119 for this part -of the problem. — end comment]

    - -
    -template <> struct hash<bool>;
-template <> struct hash<char>;
-[…]
-template <> struct hash<long double>;
-template <class T> struct hash<T*>;
-
    -

    --2- Requires: the template specializations shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<functional> provides definitions for specializations of the -hash class template for each cv-unqualified arithmetic type except -for the extended integer types. This header also provides a definition for a partial -specialization of the hash class template for any pointer type. The -requirements for the members of these specializations are given in sub-clause -20.9.13 [unord.hash]. -

    -
    -
    5. - -

  5. Change 20.14.4 [type.index.hash] p1 as indicated:

    - -
    -template <> struct hash<type_index>;
-
    -

    --1- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<typeindex> provides a definition for a specialization of the -template hash<type_index>. The requirements for the members -of this specialization are given in sub-clause 20.9.13 [unord.hash]. For -an object index of type type_index, hash<type_index>()(index) -shall evaluate to the same result as index.hash_code(). -

    -
    -
    6. - -

  6. Change 21.6 [basic.string.hash] p1 as indicated:

    - -
    -template <> struct hash<string>;
-template <> struct hash<u16string>;
-template <> struct hash<u32string>;
-template <> struct hash<wstring>;
-
    -

    --1- Requires: the template specializations shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<string> provides definitions for specializations of the -hash class template for the types string, u16string, -u32string, and wstring. The requirements for the members -of these specializations are given in sub-clause 20.9.13 [unord.hash]. -

    -
    -
    7. - -

  7. Change 23.3.7 [vector.bool] p7 as indicated:

    - -
    -template <class Allocator> struct hash<vector<bool, Allocator> >;
-
    -

    --7- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<vector> provides a definition for a partial specialization of the -hash class template for specializations of class template vector<bool, Allocator>. -The requirements for the members of instantiations of this specialization are given -in sub-clause 20.9.13 [unord.hash]. -

    -
    -
    8. - -

  8. Change 30.3.1.1 [thread.thread.id] p14 as indicated:

    - -
    -template <> struct hash<thread::id>;
-
    -

    --14- Requires: the template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash])The header -<thread> provides a definition for a specialization of the -template hash<thread::id>. The requirements for the members of this -specialization are given in sub-clause 20.9.13 [unord.hash]. -

    -
    -
    9. - -
-]

- - -

[2012, Portland: Move to Tentatively Ready]

- -

-No further wording issues, so move to Tentatively Ready (post meeting issues processing). -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

- -
    -

  1. Change 19.5.5 [syserr.hash] as indicated:

    - -
    -template <> struct hash<error_code>;
-
    -

    --1- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]. -

    -
    -
    2. - -

  2. Change 20.6.3 [bitset.hash] as indicated:

    - -
    -template <size_t N> struct hash<bitset<N> >;
-
    -

    --1- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). -

    -
    -
    3. - -

  3. Change 20.8.2.7 [util.smartptr.hash] as indicated:

    - -
    -template <class T, class D> struct hash<unique_ptr<T, D> >;
-
    -

    --1- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). For an object p of type -UP, where UP is unique_ptr<T, D>, -hash<UP>()(p) shall evaluate to the same value as -hash<typename UP::pointer>()(p.get()). The specialization -hash<typename UP::pointer> shall be well-formed. -

    --?- Requires: The specialization hash<typename UP::pointer> -shall be well-formed and well-defined, and shall meet the requirements of class template -hash (20.9.13 [unord.hash]). -

    -
    - -
    -template <class T> struct hash<shared_ptr<T> >;
-
    -

    --2- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). For an object p of type -shared_ptr<T>, hash<shared_ptr<T> >()(p) -shall evaluate to the same value as hash<T*>()(p.get()). -

    -
    -
    4. - -

  4. Change 20.9.13 [unord.hash] p2 as indicated: [Comment: For unknown -reasons the extended integer types are not mentioned here, which looks like an oversight to -me and makes also the wording more complicated. See 2119 for this part -of the problem. — end comment]

    - -
    -template <> struct hash<bool>;
-template <> struct hash<char>;
-[…]
-template <> struct hash<long double>;
-template <class T> struct hash<T*>;
-
    -

    --2- Requires: tThe template specializations shall meet the requirements -of class template hash (20.9.13 [unord.hash]). -

    -
    -
    5. - -

  5. Change 20.14.4 [type.index.hash] p1 as indicated:

    - -
    -template <> struct hash<type_index>;
-
    -

    --1- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). For -an object index of type type_index, hash<type_index>()(index) -shall evaluate to the same result as index.hash_code(). -

    -
    -
    6. - -

  6. Change 21.6 [basic.string.hash] p1 as indicated:

    - -
    -template <> struct hash<string>;
-template <> struct hash<u16string>;
-template <> struct hash<u32string>;
-template <> struct hash<wstring>;
-
    -

    --1- Requires: tThe template specializations shall meet the requirements -of class template hash (20.9.13 [unord.hash]). -

    -
    -
    7. - -

  7. Change 23.3.7 [vector.bool] p7 as indicated:

    - -
    -template <class Allocator> struct hash<vector<bool, Allocator> >;
-
    -

    --7- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). -

    -
    -
    8. - -

  8. Change 30.3.1.1 [thread.thread.id] p14 as indicated:

    - -
    -template <> struct hash<thread::id>;
-
    -

    --14- Requires: tThe template specialization shall meet the requirements -of class template hash (20.9.13 [unord.hash]). -

    -
    -
    9. - -
- - - - - - -
-

2110. remove can't swap but note says it might

-

Section: 25.3.8 [alg.remove] Status: C++14 - Submitter: Howard Hinnant Opened: 2011-12-07 Last modified: 2015-04-08

-

View all other issues in [alg.remove].

-

View all issues with C++14 status.

-

Discussion:

- -

-25.3.8 [alg.remove]/p1 says: -

- -

-1 Requires: The type of *first shall satisfy the MoveAssignable requirements (Table 22). -

- -

-This means that remove/remove_if can only use move assignment to permute the sequence. But then -25.3.8 [alg.remove]/p6 (non-normatively) contradicts p1: -

- -

-6 Note: each element in the range [ret,last), where ret is the returned value, has a valid -but unspecified state, because the algorithms can eliminate elements by swapping with or moving from elements that -were originally in that range. -

- -

[2012, Kona]

- -

-Move to Ready. -

-

-Alisdair notes we could extend permission to use swap if it is available, but there -is no interest. Accept the proposed resolution as written. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -

Change 25.3.8 [alg.remove] as indicated:

- -
-template<class ForwardIterator, class T>
-  ForwardIterator remove(ForwardIterator first, ForwardIterator last,
-                         const T& value);
-
-template<class ForwardIterator, class Predicate>
-  ForwardIterator remove_if(ForwardIterator first, ForwardIterator last,
-                            Predicate pred);
-
-

-[…] -

--6-Note: each element in the range [ret,last), where ret is the -returned value, has a valid but unspecified state, because the algorithms can eliminate -elements by swapping with or moving from elements that were originally in that range. -

-
- - - - - - -
-

2112. User-defined classes that cannot be derived from

-

Section: 17.6.5 [conforming], 20.7.8 [allocator.traits], 20.13.1 [allocator.adaptor.syn] Status: C++14 - Submitter: Daniel Krügler Opened: 2011-11-30 Last modified: 2015-04-08

-

View all other issues in [conforming].

-

View all issues with C++14 status.

-

Discussion:

- -

-It is a very established technique for implementations to derive internally from user-defined class types that are -used to customize some library component, e.g. deleters and allocators are typical candidates. The advantage of this -approach is to possibly take advantage of the empty-base-class optimization (EBCO). -

-Whether or whether not libraries did take advantage of such a detail didn't much matter in C++03. Even though there -did exist a portable idiom to prevent that a class type could be derived from, this idiom has never reached great -popularity: The technique required -to introduce a virtual base class and it did not really prevent the derivation, but only any construction of -such a type. Further, such types are not empty as defined by the std::is_empty trait, so -could easily be detected by implementations from TR1 on. -

-With the new C++11 feature of final classes and final member functions it is now very easy to define an empty, -but not derivable from class type. From the point of the user it is quite natural to use this feature for -types that he or she did not foresee to be derivable from. -

-On the other hand, most library implementations (including third-party libraries) often take advantage of EBCO -applied to user-defined types used to instantiate library templates internally. As the time of submitting this -issue the following program failed to compile on all tested library implementations: -

-
-#include <memory>
-
-struct Noop final {
- template<class Ptr>
- void operator()(Ptr) const {}
-};
-
-std::unique_ptr<int, Noop> up;
-
-

-In addition, many std::tuple implementations with empty, final classes as element types failed as well, -due to a popular inheritance-based implementation technique. EBCO has also a long tradition to be -used in library containers to efficiently store potentially stateless, empty allocators. -

-It seems that both user and library did the best they could: None of the affected types did impose explicit -requirements on the corresponding user-defined types to be derivable from (This capability was not part of -the required operations), and libraries did apply EBCO whereever possible to the convenience of the customer. -

-Nonetheless given the existence of non-derivable-from class types in C++11, libraries have to cope with -failing derivations. How should that problem be solved? -

-It would certainly be possible to add weazel wording to the allocator requirements similar to what we had -in C++03, but restricted to derivation-from requirements. I consider this as the bad solution, because it -would add new requirements that never had existed before in this explicit form onto types like allocators. -

-Existing libraries presumably will need internal traits like __is_final or __is_derivable -to make EBCO possible in the current form but excluding non-derivable class types. As of this writing this -seems to happen already. Problem is that without a std::is_derivable trait, third-party libraries -have no portable means to do the same thing as standard library implementations. This should be a good -reason to make such a trait public available soon, but seems not essential to have now. Further, this issue -should also be considered as a chance to recognice that EBCO has always been a very special corner case -(There exist parallels to the previously existing odd core language rule that did make the interplay -between std::auto_ptr and std::auto_ptr_ref possible) and that it would be better to -provide explicit means for space-efficient storage, not necessarily restricted to inheritance relations, -e.g. by marking data members with a special attribute. -

-At least two descriptions in the current standard should be fixed now for better clarification: -

-
    -

  1. As mentioned by Ganesh, 20.7.8 [allocator.traits] p1 currently contains a (non-normative) note -"Thus, it is always possible to create a derived class from an allocator." which should be removed. -

    -
    2. -

  2. As pointed out by Howard, the specification of scoped_allocator_adaptor as of -20.13.1 [allocator.adaptor.syn] already requires derivation from OuterAlloc, but -only implies indirectly the same for the inner allocators due to the exposition-only -description of member inner. This indirect implication should be normatively required for -all participating allocators. -

    3. -
- - -

[2012, Kona]

- -

-What we really need is a type trait to indicate if a type can be derived from. Howard reports -Clang and libc++ have had success with this approach. -

-

-Howard to provide wording, and AJM to alert Core that we may be wanting to add a new trait -that requires compiler support. -

- -

[2014-02, Issaquah: Howard and Daniel comment and provide wording]

- - -

-Several existing C++11 compilers do already provide an internal __is_final intrinsic (e.g. clang and gcc) and therefore -we believe that this is evidence enough that this feature is implementable today. -

-We believe that both a simple and clear definition of the is_final query should result in a true outcome -if and only if the current existing language definition holds that a complete class type (either union or non-union) -has been marked with the class-virt-specifier final — nothing more. -

-The following guidelines lead to the design decision and the wording choice given below: -

-It has been expressed several times that a high-level trait such as "is_derivable" would be preferred and -would be more useful for non-experts. One problem with that request is that it is astonishingly hard to find a common denominator -for what the precise definition of this trait should be, especially regarding corner-cases. Another example of getting very -differing points of view is to ask a bunch of C++ experts what the best definition of the is_empty trait -should be (which can be considered as a kind of higher-level trait). -

-Once we have a fundamental trait like is_final available, we can easily define higher-level traits in the future -on top of this by a proper logical combination of the low-level traits. -

-A critical question is whether providing such a low-level compile-time introspection might be considered as disadvantageous, -because it could constrain the freedom of existing implementations even further and whether a high-level trait would solve -this dilemma. We assert that since C++11 the static introspection capabilities are already very large and we believe that -making the presence or absence of the final keyword testable does not make the current situation worse. -

-Below code example demonstrates the intention and the implementability of this feature: -

-
-#include <type_traits>
-
-namespace std
-{
-
-template <class T>
-struct is_final
-  : public integral_constant<bool, __is_final(T)>
-{};
-
-}  // std
-
-// test it
-
-union FinalUnion final { };
-
-union NonFinalUnion { };
-
-class FinalClass final { };
-
-struct NonFinalClass { };
-
-class Incomplete;
-
-int main()
-{
-  using std::is_final;
-  static_assert( is_final<const volatile FinalUnion>{}, "");
-  static_assert(!is_final<FinalUnion[]>{}, "");
-  static_assert(!is_final<FinalUnion[1]>{}, "");
-  static_assert(!is_final<NonFinalUnion>{}, "");
-  static_assert( is_final<FinalClass>{}, "");
-  static_assert(!is_final<FinalClass&>{}, "");
-  static_assert(!is_final<FinalClass*>{}, "");
-  static_assert(!is_final<NonFinalClass>{}, "");
-  static_assert(!is_final<void>{}, "");
-  static_assert(!is_final<int>{}, "");
-  static_assert(!is_final<Incomplete>{}, ""); // error incomplete type 'Incomplete' used in type trait expression
-}
-
- -

[2014-02-14, Issaquah: Move to Immediate]

- -

-This is an important issue, that we really want to solve for C++14. -

- -

-Move to Immediate after polling LEWG, and then the NB heads of delegation. -

- - - -

Proposed resolution:

- -

This wording is relative to N3797.

- -
    -

  1. Change 20.10.2 [meta.type.synop], header <type_traits> synopsis, as indicated

    - -
    -namespace std {
-  […]
-  // 20.10.4.3, type properties:
-  […]
-  template <class T> struct is_empty;
-  template <class T> struct is_polymorphic;
-  template <class T> struct is_abstract;
-  template <class T> struct is_final;
-
-  […]
-}
-
    -
    2. - -

  2. Change 20.10.4.3 [meta.unary.prop], Table 49 — Type property predicates, as indicated

    - - - - - - - - - - - - - - - - - - - - -
    Table 49 — Type property predicates
    TemplateConditionPreconditions
    -template <class T>
    -struct is_abstract; -    		 -[…] - -[…] -
    -template <class T>
    -struct is_final;     -    		 -T is a class type marked with the class-virt-specifier final (9 [class]).
    -[Note: A union is a class type that can be marked with final. — end note]     -    		 -If T is a class type, T shall be a complete type -
    - -
    3. - -

  3. After 20.10.4.3 [meta.unary.prop] p5 add one further example as indicated:

    - -

    -[Example: -

    -
    -// Given:
-struct P final { };
-union U1 { };
-union U2 final { };
-
-// the following assertions hold:
-static_assert(!is_final<int>::value, "Error!");
-static_assert( is_final<P>::value, "Error!");
-static_assert(!is_final<U1>::value, "Error!");
-static_assert( is_final<U2>::value, "Error!");
-
    -

    -— end example] -

    -
    -
    4. -
- - - - - - -
-

2118. [CD] unique_ptr for array does not support cv qualification conversion of actual argument

-

Section: 20.8.1.3 [unique.ptr.runtime] Status: Resolved - Submitter: Alf P. Steinbach Opened: 2011-12-16 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.runtime].

-

View all issues with Resolved status.

-

Discussion:

- -

Addresses US 16

- -

-N3290 20.8.1.3.1 [unique.ptr.runtime.ctor] "unique_ptr constructors": -

-

-These constructors behave the same as in the primary template except that they do not accept pointer types -which are convertible to pointer. [Note: One implementation technique is to create private -templated overloads of these members. — end note] -

-

-This language excludes even pointer itself as type for the actual argument. -

-But of more practical concern is that both Visual C++ 10.0 and MinGW g++ 4.1.1 reject the code below, where -only an implicit cv qualification is needed, which cv qualification is supported by the non-array -version: -

-
-#include <memory>
-using namespace std;
-
-struct T {};
-
-T* foo() { return new T; }
-T const* bar() { return foo(); }
-
-int main()
-{
-   unique_ptr< T const >       p1( bar() );        // OK
-   unique_ptr< T const [] >    a1( bar() );        // OK
-
-   unique_ptr< T const >       p2( foo() );        // OK
-   unique_ptr< T const [] >    a2( foo() );        // ? this is line #15
-}
-
-

-The intent seems to be clearly specified in 20.8.1.3 [unique.ptr.runtime]/1 second bullet: -

-

-— Pointers to types derived from T are rejected by the constructors, and by reset. -

- -

-But the following language in 20.8.1.3.1 [unique.ptr.runtime.ctor] then rejects far too much... -

-Proposed new wording of N3290 20.8.1.3.1 [unique.ptr.runtime.ctor] "unique_ptr constructors": -

-

-These constructors behave the same as in the primary template except that actual argument pointers p -to types derived from T are rejected by the constructors. [Note: One implementation technique -is to create private templated overloads of these members. — end note] -

-

-This will possibly capture the intent better, and avoid the inconsistency between the non-array and array -versions of unique_ptr, by using nearly the exact same phrasing as for the paragraph explaining -the intent. -

- -

[2012-08-25 Geoffrey Romer comments in c++std-lib-32978]

- - -
    -

  1. -The current P/R seems to intend to support at least two different implementation techniques — additional -unusable templates that catch forbidden arguments or replacing existing constructors by templates that -ensure ill-formed code inside the template body, when the requirements are not met. It seems unclear whether -the current wording allows the second approach, though. It should be considered to allow both strategies or -if that is not possible the note should be clearer. -

    2. - -

  2. -The very same problem exists for the reset member function, but even worse, because the current -specification is more than clear that the deleted reset function will catch all cases not equal to -pointer. It seems confusing at best to have different policies for the constructor and for the reset -function. In this case, the question in regard to implementation freedom mentioned above is even more important. -

    3. - -

  3. -It's awkward to refer to "the constructors" twice in the same sentence; I suggest revising the sentence as -"...except that they do not accept argument pointers p to types derived from T" -

    4. -
- -

[2012-12-20: Geoffrey Romer comments and provides a revised resolution]

- - -

-The array specialization of unique_ptr differs from the primary template in several ways, -including the following: -

-
    -

  • -unique_ptr<T[], D> cannot be constructed from a plain pointer whose type is not -exactly unique_ptr<T[], D>::pointer or nullptr_t. -

    • -

  • -unique_ptr<T[], D> cannot be constructed from a unique_ptr<U[], E>&& -unless U is exactly T and E is exactly D. -

    • -

  • -unique_ptr<T[], D> cannot be moveassigned from a unique_ptr<U[], E>&& -unless U is exactly T and E is exactly D. -

    • -

  • -unique_ptr<T[], D>::reset cannot take an argument whose type is not exactly -unique_ptr<T[], D>::pointer or nullptr_t. -

    • -

  • -default_delete<T[]> cannot be constructed from a default_delete<U[]> unless -U is exactly T. -

    • -

  • -default_delete<T[]>::operator() cannot be called on a pointer whose type is not -exactly T*. -

    • -
-

-The common intent of all these restrictions appears to be to disallow implicit conversions from -pointer-to-derived-class to pointer-to-base-class in contexts where the pointer is known to point -to an array, because such conversions are inherently unsafe; deleting or subscripting the result -of such a conversion leads to undefined behavior (see also CWG 1504). However, these restrictions -have the effect of disallowing all implicit conversions in those contexts, including most notably -cv-qualification, but also user-defined conversions, and possibly others. This PR narrows all those -restrictions, to disallow only unsafe pointer-to-derived to pointer-to-base conversions, while -allowing all others. -

-I removed the nebulous language stating that certain functions "will not accept" certain arguments. -Instead I use explicitly deleted template functions, which participate in overload resolution only -for pointer-to-derived to pointer-to-base conversions. This is more consistent with the existing -text and easier to express correctly than an approach based on declaring certain types of calls to -be ill-formed, but may produce inferior compiler diagnostics. -

-Wherever possible, this PR defines the semantics of template specializations in terms of their -differences from the primary template. This improves clarity and minimizes the risk of -unintended differences (e.g. LWG 2169, which this PR also fixes). This PR also makes it -explicit that the specialization inherits the description of all members, not just member functions, -from the primary template and, in passing, clarifies the default definition of pointer in the -specialization. -

-This resolution only disallows pointer-to-derived to pointer-to-base conversions between -ordinary pointer types; if user-defined pointer types provide comparable conversions, it is their -responsibility to ensure they are safe. This is consistent with C++'s general preference for -expressive power over safety, and for assuming the user knows what they're doing; -furthermore, enforcing such a restriction on user-defined types appears to be impractical without -cooperation from the user. -

-The "base class without regard to cv-qualifiers" language is intended to parallel the specification -of std::is_base_of. -

-Jonathan Wakely has a working implementation of this PR patched into libstdc++. -

- -

-Previous resolution: -

-
-

This wording is relative to the FDIS.

- -

Change 20.8.1.3.1 [unique.ptr.runtime.ctor] as indicated:

- -
-explicit unique_ptr(pointer p) noexcept;
-unique_ptr(pointer p, see below d) noexcept;
-unique_ptr(pointer p, see below d) noexcept;
-
-

-These constructors behave the same as in the primary template except that they do not accept pointer -types which are convertible to pointerargument pointers p to types derived -from T are rejected by the constructors. [Note: One implementation technique is to -create private templated overloads of these members. — end note] -

-
- -

[2014-02, Issaquah]

- -

-GR: want to prevent unsafe conversions. Standard is inconsistent how it does this. for reset() has deleted function -template capturing everything except the known-safe cases. Other functions use SFINAE. Main reason this is hard is that -unique_ptr supports fancy pointers. Have to figure out how to handle them and what requirements to put on them. -Requirements are minimal, not even required to work with pointer_traits. -

-STL surprised pointer_traits doesn't work -

-GR: ways to get fancy pointers to work is to delegate responsibility for preventing unsafe conversions to the fancy pointers themselves. -Howard doesn't like that, he wants even fancy pointers to be prevented from doing unsafe conversions in unique_ptr contexts. -

-AM: Howard says unique_ptr was meant to be very very safe under all conditions, this open a hole in that. Howard wants to -eke forward and support more, but not if we open any holes in type safety. -

-GR: do we need to be typesafe even for fancy types with incorrect pointer_traits? -

-AM: that would mean it's only unsafe for people who lie by providing a broken specialization of pointer_traits -

-GR: probably can't continue with ambiguity between using SFINAE and ill-formedness. Would appreciate guidance on direction used for that. -

-STL: difference is observable in convertibility using type traits. -

-STL: for reset() which doesn't affect convertibility ill-formed allows static_assert, better diagnostic. -For assignment it's detectable and has traits, constraining them is better. -

-EN: I strongly prefer constraints than static_asserts -

-STL: if we could rely on pointer_traits that might be good. Alternatively could we add more machinery to deleter? -make deleter say conversions are allowed, otherwise we lock down all conversions. basically want to know if converting U to -T is safe. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3485.

-
    -

  1. Revise 20.8.1.1.3 [unique.ptr.dltr.dflt1] as follows

    -
    -namespace std {
-  template <class T> struct default_delete<T[]> {
-    constexpr default_delete() noexcept = default;
-    template <class U> default_delete(const default_delete<U>&) noexcept;
-    void operator()(T*) const;
-    template <class U> void operator()(U*) const = delete;
-  };
-}
-
    -

    --?- Descriptions are provided below only for member functions that have behavior different from the -primary template. -

    -
    -
    -template <class U> default_delete(const default_delete<U>&) noexcept;
-
    -

    --?- This constructor behaves the same as in the primary template except that it shall not participate -in overload resolution unless: -

    -
      -

    • -U is an array type, and -

      • -

    • -V* is implicitly convertible to T*, and -

      • -

    • -T is not a base class of V (without regard to cv-qualifiers), -

      • -
    -

    -where V is the array element type of U. -

    -
    - -
    -void operator()(T* ptr) const;
-
    -

    --1- Effects: calls delete[] on ptr. -

    --2- Remarks: If T is an incomplete type, the program is ill-formed. -

    -
    - -
    -template <class U> void operator()(U*) const = delete;
-
    -

    --?- Remarks: This function shall not participate in overload resolution unless T is a base -class of U (without regard to cv-qualifiers). -

    -
    - -
    -
    2. - -

  2. Revise 20.8.1.2 [unique.ptr.single]/3 as follows:

    -

    -If the type remove_reference<D>::type::pointer exists, then unique_ptr<T, D>::pointer -shall be a synonym for remove_reference<D>::type::pointer. Otherwise unique_ptr<T, D>::pointer -shall be a synonym for Telement_type*. The type unique_ptr<T, D>::pointer -shall satisfy the requirements of NullablePointer (17.6.3.3 [nullablepointer.requirements]). -

    -
    3. - -

  3. Revise 20.8.1.3 [unique.ptr.runtime] as follows:

    -
    -namespace std {
-  template <class T, class D> class unique_ptr<T[], D> {
-  public:
-    typedef see below pointer;
-    typedef T element_type;
-    typedef D deleter_type;
-
-    // 20.7.1.3.1, constructors
-    constexpr unique_ptr() noexcept;
-    explicit unique_ptr(pointer p) noexcept;
-    template <class U> explicit unique_ptr(U* p) = delete;
-    unique_ptr(pointer p, see below d) noexcept;
-    template <class U> unique_ptr(U* p, see below d) = delete;
-    unique_ptr(pointer p, see below d) noexcept;
-    template <class U> unique_ptr(U* p, see below d) = delete;
-    unique_ptr(unique_ptr&& u) noexcept;
-    constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
-    template <class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
-
-    // destructor
-    ~unique_ptr();
-
-    // assignment
-    unique_ptr& operator=(unique_ptr&& u) noexcept;
-    template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
-    unique_ptr& operator=(nullptr_t) noexcept;
-
-    // 20.7.1.3.2, observers
-    T& operator[](size_t i) const;
-    pointer get() const noexcept;
-    deleter_type& get_deleter() noexcept;
-    const deleter_type& get_deleter() const noexcept;
-    explicit operator bool() const noexcept;
-
-    // 20.7.1.3.3 modifiers
-    pointer release() noexcept;
-    void reset(pointer p = pointer()) noexcept;
-    void reset(nullptr_t) noexcept;
-    template <class U> void reset(U*) = delete;
-    void swap(unique_ptr& u) noexcept;
-
-    // disable copy from lvalue
-    unique_ptr(const unique_ptr&) = delete;
-    unique_ptr& operator=(const unique_ptr&) = delete;
-  };
-}
-
    -

    --1- A specialization for array types is provided with a slightly altered interface. -

    -
      -

    • -Conversions between different types of unique_ptr<T[], D>from -unique_ptr<Derived[]> to unique_ptr<Base[]>, where Base is a -base class of Derived, from auto_ptr, or to or from the non-array forms of -unique_ptr produce an ill-formed program. -

      • -

    • -Pointers to types derived from T are rejected by the constructors, and by reset. -

      • -

    • -The observers operator* and operator-> are not provided. -

      • -

    • -The indexing observer operator[] is provided. -

      • -

    • -The default deleter will call delete[]. -

      • -
    -

    --2- Descriptions are provided below only for member functions that have behavior -differentmembers that differ from the primary template. -

    --3- The template argument T shall be a complete type. -

    -
    -
    4. - -

  4. Revise 20.8.1.3.1 [unique.ptr.runtime.ctor] as follows:

    -
    -
    -explicit unique_ptr(pointer p) noexcept;
-unique_ptr(pointer p, see below d) noexcept;
-unique_ptr(pointer p, see below d) noexcept;
-template <class U> explicit unique_ptr(U* p) = delete;
-template <class U> unique_ptr(U* p, see below d) = delete;
-template <class U> unique_ptr(U* p, see below d) = delete;
-

    -These constructors behave the same as in the primary template except that they do not accept pointer -types which are convertible to pointer. [Note: One implementation technique is to create private -templated overloads of these members. — end note]These constructors shall not -participate in overload resolution unless:

    -
      -

    • pointer is a pointer type, and

      • -

    • U* is implicitly convertible to pointer, and

      • -

    • T is a base class of U (without regard to cv-qualifiers).

      • -
    -

    The type of d is determined as in the corresponding non-deleted constructors.

    -
    -
    -template <class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
-

    --?- This constructor behaves the same as in the primary template, except that it shall not participate -in overload resolution unless: -

    -
      -

    • unique_ptr<U, E>::pointer is implicitly convertible to pointer, and

      • -

    • U is an array type, and

      • -

    • either D is a reference type and E is the same type as D, or D -is not a reference type and E is implicitly convertible to D, and

      • -

    • either at least one of pointer and unique_ptr<U, E>::pointer is not a -pointer type, or T is not a base class of the array element type of U (without regard to -cv-qualifiers).

      • -
    -
    -
    5. - -

  5. Insert a new sub-clause following 20.8.1.3.1 [unique.ptr.runtime.ctor] as follows:

    - -

    ?? unique_ptr assignment [unique.ptr.runtime.asgn]

    - -
    -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
-

    --?- This operator behaves the same as in the primary template, except that it shall not participate in -overload resolution unless:

    -
      -

    • unique_ptr<U, E>::pointer is implicitly convertible to pointer, and

      • -

    • U is an array type, and

      • -

    • either D is a reference type and E is the same type as D, or D -is not a reference type and E is implicitly convertible to D, and

      • -

    • either at least one of pointer and unique_ptr<U, E>::pointer is not a -pointer type, or T is not a base class of the array element type of U (without regard to -cv-qualifiers).

      • -
    -
    -
    6. - -

  6. Revise 20.8.1.3.4 [unique.ptr.runtime.modifiers] as follows:

    - -
    -
    -void reset(pointer p = pointer()) noexcept;
-void reset(nullptr_t p) noexcept;
-template <class U> void reset(U*) = delete;
-

    --1- Effects: If get() == nullptr there are no effects. Otherwise get_deleter()(get()). -

    --2- Postcondition: get() == p. -

    --?- This function shall not participate in overload resolution unless: -

    -
      -

    • pointer is a pointer type, and

      • -

    • U* is implicitly convertible to pointer, and

      • -

    • T is a base class of U (without regard to cv-qualifiers).

      • -
    - -
    -
    7. -
-
- -

[2014-06 Rapperswil]

- -

-Discussion of N4042 and general agreement that this paper resolves the substance of this issue and should be adopted with -minor edits. Geoffrey Romer will provide an updated paper. -

- -

[2014-06 post-Rapperswil]

- -

-As described in N4089. -

- -

[2014-11-07 Urbana]

- -

-Resolved by -N4089 -

- - - -

Proposed resolution:

-

-See proposed wording in N4089. -

- - - - - -
-

2120. What should async do if neither 'async' nor 'deferred' is set in policy?

-

Section: 30.6.8 [futures.async] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-01-01 Last modified: 2015-04-08

-

View all other issues in [futures.async].

-

View all issues with C++14 status.

-

Discussion:

- -

-Implementations already disagree, one returns an invalid future with -no shared state, one chooses policy == async and one chooses policy == -deferred, see c++std-lib-30839, c++std-lib-30840 and c++std-lib-30844. -It's not clear if returning an invalid future is allowed by the current wording. -

-

-If the intention is to allow an empty future to be returned, then -30.6.8 [futures.async] p3 and p4 should be adjusted to clarify that a -shared state might not be created and an invalid future might be returned. -

-

-If the intention is that a valid future is always returned, p3 should -say something about the case where none of the conditions applies. -

- -

[2012, Portland: move to Review]

- -

-We could make it undefined if no launch policy is defined. -

-

-Hans: If no launch policy is specified the behaviour is undefined -

-

-Artur: or implementation defined? -

-

-Hans: no: we don't want people to do this -

-

[Proposed wording]

- -

-This wording is relative to N3376 -

-

-Add a third bullet to the end of the list in 30.6.8p3 -

-
-"if no valid launch policy is provided the behaviour is undefined" -
-

-Moved to review -

- -

[2013-04-19, Bristol]

- - -

Detlef provides new wording

- -

Previous wording:

- -
-

[This wording is relative to N3376]

- -

-Add a third bullet to the end of the list in 30.6.8 [futures.async]p3 -

-
-– if no valid launch policy is provided the behaviour is undefined -
-
- -

[2013-09 Chicago]

- -

-If no policy is given, it should be undefined, so moved to Immediate. -

-

-Accept for Working Paper -

- - - -

Proposed resolution:

-

[This wording is relative to N3485]

- -

-Add a third bullet to the end of the list in 30.6.8 [futures.async]p3 -

-
-– If no value is set in the launch policy, or a value is set that is -neither specified in this International Standard or by the implementation, the behaviour -is undefined. -
- - - - - - -
-

2122. merge() stability for lists versus forward lists

-

Section: 23.3.5.5 [list.ops], 23.3.4.6 [forwardlist.ops] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2012-01-15 Last modified: 2015-04-08

-

View all other issues in [list.ops].

-

View all issues with C++14 status.

-

Discussion:

- -

-forward_list::merge() is specified in 23.3.4.6 [forwardlist.ops], p19 as follows: -

-

-This operation shall be stable: for equivalent elements in the two lists, -the elements from *this shall always precede the elements from x. -

-

-But list::merge() is only specified in 23.3.5.5 [list.ops], p24 as follows: -

-

-Remarks: Stable. -

-

-Note that in general we define "stable" only for algorithms (see 17.3 [defns.stable] and -17.6.5.7 [algorithm.stable]) so for member function we should explain it everywhere we use it. -

-Thus for lists we have to add: -

-

-Stable: for equivalent elements in the two lists, the elements from the list always precede the elements -from the argument list. -

-

-This, BTW, was the specification we had with C++03. -

-In addition, I wonder whether we also have some guarantees regarding stability saying that the order -of equivalent elements of each list merged remains stable (which would be my interpretation of just -saying "stable", BTW). -

-Thus, I'd expect that for equivalent elements we guarantee that -

-
    -
  • we first have all element of *this (in the same order as on entry)
    • -
  • and then all elements of the passed argument (in the same order as on entry).
    • -
- - -

[2012, Kona]

- -

-Move to Open. -

-

-STL says we need to fix up 17.6.5.7 to be stronger, and then the remarks for merge should -just say "Remarks: Stable (see 17.6.5.7)" -

-

-Assigned to STL for word-smithing. -

- -

[ -2013-04-14 STL provides rationale and improved wording -]

- - -

Step 1: Centralize all specifications of stability to 17.6.5.7 [algorithm.stable].

-

Step 2: 17.3 [defns.stable] and 17.6.5.7 [algorithm.stable] talk about "algorithms", without mentioning -"container member functions". There's almost no potential for confusion here, but there's a simple way to increase clarity -without increasing verbosity: make the container member functions explicitly cite 17.6.5.7 [algorithm.stable]. For -consistency, we can also update the non-member functions.

-

Step 3: Fix the "so obvious, we forgot to say it" bug in 17.6.5.7 [algorithm.stable]: a "stable" merge of equivalent -elements A B C D and W X Y Z produces A B C D W X Y Z, never D C B A X W Z Y.

-

Step 3.1: Say "(preserving their original order)" to be consistent with "the relative order [...] is preserved" in -17.6.5.7 [algorithm.stable]'s other bullet points.

-

Step 4: Copy part of list::merge()'s wording to forward_list::merge(), in order to properly connect -with 17.6.5.7 [algorithm.stable]'s "first range" and "second range".

- -

[2013-04-18, Bristol]

- - -

Original wording saved here:

-
-

This wording is relative to the FDIS.

- -
    -
  1. -

    Change 23.3.5.5 [list.ops] as indicated:

    - -
    -void                          merge(list<T,Allocator>& x);
-void                          merge(list<T,Allocator>&& x);
-template <class Compare> void merge(list<T,Allocator>& x, Compare comp);
-template <class Compare> void merge(list<T,Allocator>&& x, Compare comp);
    -

    -[…] -

    --24- Remarks: StableThis operation shall be stable: for equivalent elements -in the two lists, the elements from *this shall always precede the elements from x -and the order of equivalent elements of *this and x remains stable. If -(&x != this) the range [x.begin(), x.end()) -is empty after the merge. No elements are copied by this operation. The behavior is undefined if -this->get_allocator() != x.get_allocator(). -

    -
    2. - -
  2. -

    Change 23.3.4.6 [forwardlist.ops] as indicated:

    - -
    -void merge(forward_list<T,Allocator>& x);
-void merge(forward_list<T,Allocator>&& x);
-template <class Compare> void merge(forward_list<T,Allocator>& x, Compare comp);
-template <class Compare> void merge(forward_list<T,Allocator>&& x, Compare comp);
    -

    -[…] -

    --19- Effects: Merges x into *this. This operation shall be stable: for -equivalent elements in the two lists, the elements from *this shall always precede the -elements from x and the order of equivalent elements of *this and x -remains stable. x is empty after the merge. If an exception is thrown other -than by a comparison there are no effects. Pointers and references to the moved elements of x -now refer to those same elements but as members of *this. Iterators referring -to the moved elements will continue to refer to their elements, but they now behave as iterators into -*this, not into x. -

    -
    3. -
-
- - - -

Proposed resolution:

-

This wording is relative to the N3485.

- -
    -

  1. Change 17.6.5.7 [algorithm.stable]/1 as indicated:

    -

    -When the requirements for an algorithm state that it is “stable” without further elaboration, it means: -

    -[…] -

    -
      -
    • For the merge algorithms, for equivalent elements in the original two ranges, the elements from the -first range (preserving their original order) precede the elements from the second range (preserving -their original order).
      • -
    -
    -
    2. - -

  2. Change 23.3.4.6 [forwardlist.ops] as indicated:

    -
    -
    -void remove(const T& value);
-template <class Predicate> void remove_if(Predicate pred);
-
    -
    -

    --12- Effects: Erases all the elements in the list referred by a list iterator i for which the following conditions -hold: *i == value (for remove()), pred(*i) is true (for remove_if()). This operation shall be -stable: the relative order of the elements that are not removed is the same as their relative order in the original -list. Invalidates only the iterators and references to the erased elements. -

    --13- Throws: Nothing unless an exception is thrown by the equality comparison or the predicate. -

    --??- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…] -

    -
    - -
    -void merge(forward_list& x);
-void merge(forward_list&& x);
-template <class Compare> void merge(forward_list& x, Compare comp)
-template <class Compare> void merge(forward_list&& x, Compare comp)
-
    -
    -

    -[…] -

    --19- Effects: Merges x into *thisthe two sorted ranges [begin(), end()) -and [x.begin(), x.end()). This operation shall be stable: for equivalent -elements in the two lists, the elements from *this shall always precede the elements from x. -x is empty after the merge. If an exception is thrown other than by a comparison there are no effects. Pointers and -references to the moved elements of x now refer to those same elements but as members of *this. -Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into -*this, not into x. -

    --20- Remarks: Stable (17.6.5.7 [algorithm.stable]). The behavior is undefined if -this->get_allocator() != x.get_allocator(). -

    -[…] -

    -
    -
    -void sort();
-template <class Compare> void sort(Compare comp);
-
    -

    -[…] -

    --23- Effects: Sorts the list according to the operator< or the comp function object. This -operation shall be stable: the relative order of the equivalent elements is preserved. If an exception is thrown the order -of the elements in *this is unspecified. Does not affect the validity of iterators and references. -

    --??- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…] -

    -
    -
    -
    3. - -

  3. Change 23.3.5.5 [list.ops] as indicated:

    -
    -
    -void remove(const T& value);
-template <class Predicate> void remove_if(Predicate pred);
-
    -
    -

    -[…]

    --17- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…]

    -
    - -
    -void merge(list& x);
-void merge(list&& x);
-template <class Compare> void merge(list& x, Compare comp)
-template <class Compare> void merge(list&& x, Compare comp)
-
    -
    -

    -[…] -

    --24- Remarks: Stable (17.6.5.7 [algorithm.stable]). […] -

    -[…] -

    -
    -
    -void sort();
-template <class Compare> void sort(Compare comp);
-
    -

    -[…] -

    --30- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…] -

    -
    -
    -
    4. - -

  4. Change 25.3.1 [alg.copy]/12 as indicated:

    -
    -
    -template<class InputIterator, class OutputIterator, class Predicate>
-OutputIterator 
-copy_if(InputIterator first, InputIterator last,
-        OutputIterator result, Predicate pred);
-
    -
    -

    -[…] -

    --12- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -
    -
    -
    5. - -

  5. Change 25.3.8 [alg.remove] as indicated:

    -
    -
    -template<class ForwardIterator, class T>
-ForwardIterator 
-remove(ForwardIterator first, ForwardIterator last, const T& value);
-template<class ForwardIterator, class Predicate>
-ForwardIterator 
-remove_if(ForwardIterator first, ForwardIterator last, Predicate pred);
-
    -
    -

    -[…] -

    --4- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…] -

    -
    - -
    -template<class InputIterator, class OutputIterator, class T>
-OutputIterator
-remove_copy(InputIterator first, InputIterator last,
-            OutputIterator result, const T& value);
-template<class InputIterator, class OutputIterator, class Predicate>
-OutputIterator
-remove_copy_if(InputIterator first, InputIterator last,
-               OutputIterator result, Predicate pred);
-
    -
    -

    -[…] -

    --11- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -
    -
    -
    6. - -

  6. Change 25.4.1.2 [stable.sort]/4 as indicated:

    -
    -
    -template<class RandomAccessIterator>
-void stable_sort(RandomAccessIterator first, RandomAccessIterator last);
-template<class RandomAccessIterator, class Compare>
-void stable_sort(RandomAccessIterator first, RandomAccessIterator last,
-Compare comp);
-
    -
    -

    -[…] -

    --4- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -
    -
    -
    7. - -

  7. Change 25.4.4 [alg.merge] as indicated:

    -
    -
    -template<class InputIterator1, class InputIterator2,
-         class OutputIterator>
-OutputIterator
-merge(InputIterator1 first1, InputIterator1 last1,
-      InputIterator2 first2, InputIterator2 last2,
-      OutputIterator result);
-template<class InputIterator1, class InputIterator2,
-         class OutputIterator, class Compare>
-OutputIterator
-merge(InputIterator1 first1, InputIterator1 last1,
-      InputIterator2 first2, InputIterator2 last2,
-      OutputIterator result, Compare comp);
-
    -
    -

    -[…] -

    --5- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -[…] -

    -
    - -
    -template<class BidirectionalIterator>
-void inplace_merge(BidirectionalIterator first,
-                   BidirectionalIterator middle,
-                   BidirectionalIterator last);
-template<class BidirectionalIterator, class Compare>
-void inplace_merge(BidirectionalIterator first,
-                   BidirectionalIterator middle,
-                   BidirectionalIterator last, Compare comp);
-
    -
    -

    -[…] -

    --9- Remarks: Stable (17.6.5.7 [algorithm.stable]). -

    -
    -
    -
    8. - -
- - - - - - -
-

2123. merge() allocator requirements for lists versus forward lists

-

Section: 23.3.4.6 [forwardlist.ops] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2012-01-15 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with C++14 status.

-

Discussion:

- -

-Sub-clause 23.3.5.5 [list.ops], p24 states for lists: -

-

-The behavior is undefined if this->get_allocator() != x.get_allocator(). -

-

-But there is nothing like that for forward lists in 23.3.4.6 [forwardlist.ops], -although I would expect the same undefined behavior there. -

- -

[2012, Kona]

- -

-Move to Ready. -

- -

[2012, Portland: applied to WP]

- - - - -

Proposed resolution:

-

This wording is relative to the FDIS.

- -
    -
  1. -

    Add a new paragraph after 23.3.4.6 [forwardlist.ops] p19 as indicated:

    - -
    -void merge(forward_list<T,Allocator>& x);
-void merge(forward_list<T,Allocator>&& x);
-template <class Compare> void merge(forward_list<T,Allocator>& x, Compare comp);
-template <class Compare> void merge(forward_list<T,Allocator>&& x, Compare comp);
    -

    -[…] -

    --19- Effects: […] -

    --?- Remarks: The behavior is undefined if this->get_allocator() != x.get_allocator(). -

    -
    2. -
- - - - - - -
-

2128. Absence of global functions cbegin/cend

-

Section: 24.3 [iterator.synopsis], 24.7 [iterator.range] Status: C++14 - Submitter: Dmitry Polukhin Opened: 2012-01-23 Last modified: 2015-04-08

-

View all other issues in [iterator.synopsis].

-

View all issues with C++14 status.

-

Discussion:

- -

-All standard containers support cbegin/cend member functions but corresponding global functions are -missing. Proposed resolution it to add global cbegin/cend functions by analogy with global begin/end -functions. This addition will unify things for users. -

- -

[2012, Kona]

- - -

STL: Range-based for loops do not use global begin/end (anymore).

-

Alisdair: We will have to make sure these will be available through many headers.

-

STL: Do this, including r and cr. This won't add any additional work.

-

Matt: Users will find it strange if these are not all available.

-

Alisdair: Should we have these available everywhere begin/end are available?

-

Marshall: Yes. Not any extra work.

-

Howard: Adding all of these means we need all of <iterator>.

-

STL: We already need it all.

-

Matt: We have to be careful what we are requiring if we include the r versions.

-

Jeffrey: If we include r, should they adapt if the container does not define reverse iteration?

-

STL: No. No special behavior. Should fail to compile. Up to user to add the reverse code--it's easy.

-

Howard: Anyway it will SFINAE out.

-

Alisdair: Error messages due to SFINAE are harder to understand than simple failure to compile.

-

STL: Agrees that SFINAE makes error messages much worse.

- -

-Action: STL to provide additional wording for the r variants. -Move to Review once that wording is availalbe. -

- -

[ -2013-04-14 STL provides rationale and improved wording -]

- - -

Step 1: Implement std::cbegin/cend() by calling std::begin/end(). This has numerous advantages:

-
    -
  • It automatically works with arrays, which is the whole point of these non-member functions.
    • -
  • It works with C++98/03-era user containers, written before cbegin/cend() members were invented.
    • -
  • It works with initializer_list, which is extremely minimal and lacks cbegin/cend() members.
    • -
  • 23.2.1 [container.requirements.general] guarantees that this is equivalent to calling cbegin/cend() members.
    • -
-

Step 2: Like std::begin/end(), implement std::rbegin/rend() by calling c.rbegin/rend(). -Note that C++98/03 had the Reversible Container Requirements.

-

Step 3: Also like std::begin/end(), provide overloads of std::rbegin/rend() for arrays.

-

Step 4: Provide overloads of std::rbegin/rend() for initializer_list, because it lacks -rbegin/rend() members. These overloads follow 18.9.3 [support.initlist.range]'s signatures. Note that -because these overloads return reverse_iterator, they aren't being specified in <initializer_list>.

-

Step 5: Like Step 1, implement std::crbegin/crend() by calling std::rbegin/rend().

- -

Original wording saved here:

-
-

This wording is relative to N3337.

- -
    -

  1. In 24.3 [iterator.synopsis], header iterator synopsis, add the following declarations:

    - -
    -namespace std {
-  […]
-  // 24.6.5, range access:
-  template <class C> auto begin(C& c) -> decltype(c.begin());
-  template <class C> auto begin(const C& c) -> decltype(c.begin());
-  template <class C> auto end(C& c) -> decltype(c.end());
-  template <class C> auto end(const C& c) -> decltype(c.end());
-  template <class C> auto cbegin(const C& c) -> decltype(c.cbegin());
-  template <class C> auto cend(const C& c) -> decltype(c.cend());
-  template <class T, size_t N> T* begin(T (&array)[N]);
-  template <class T, size_t N> T* end(T (&array)[N]);
-  template <class T, size_t N> const T* cbegin(T (&array)[N]);
-  template <class T, size_t N> const T* cend(T (&array)[N]);
-}
-
    -
    2. - -

  2. In 24.7 [iterator.range] after p5 add the following series of paragraphs:

    - -
    -
    -template <class C> auto cbegin(const C& c) -> decltype(c.cbegin());
-
    -
    -

    --?- Returns: c.cbegin(). -

    -
    - -
    -template <class C> auto cend(const C& c) -> decltype(c.cend());
-
    -
    -

    --?- Returns: c.cend(). -

    -
    - -
    -template <class T, size_t N> const T* cbegin(T (&array)[N]);
-
    -
    -

    --?- Returns: array. -

    -
    - -
    -template <class T, size_t N> const T* cend(T (&array)[N]);
-
    -
    -

    --?- Returns: array + N. -

    -
    -
    -
    3. -
- -
- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. In 24.3 [iterator.synopsis], header iterator synopsis, add the following declarations:

    - -
    -namespace std {
-  […]
-  // 24.6.5, range access:
-  template <class C> auto begin(C& c) -> decltype(c.begin());
-  template <class C> auto begin(const C& c) -> decltype(c.begin());
-  template <class C> auto end(C& c) -> decltype(c.end());
-  template <class C> auto end(const C& c) -> decltype(c.end());
-  template <class T, size_t N> T* begin(T (&array)[N]);
-  template <class T, size_t N> T* end(T (&array)[N]);
-  template <class C> auto cbegin(const C& c) -> decltype(std::begin(c));
-  template <class C> auto cend(const C& c) -> decltype(std::end(c));
-  template <class C> auto rbegin(C& c) -> decltype(c.rbegin());
-  template <class C> auto rbegin(const C& c) -> decltype(c.rbegin());
-  template <class C> auto rend(C& c) -> decltype(c.rend());
-  template <class C> auto rend(const C& c) -> decltype(c.rend());
-  template <class T, size_t N> reverse_iterator<T*> rbegin(T (&array)[N]);
-  template <class T, size_t N> reverse_iterator<T*> rend(T (&array)[N]);
-  template <class E> reverse_iterator<const E*> rbegin(initializer_list<E> il);
-  template <class E> reverse_iterator<const E*> rend(initializer_list<E> il);
-  template <class C> auto crbegin(const C& c) -> decltype(std::rbegin(c));
-  template <class C> auto crend(const C& c) -> decltype(std::rend(c));
-}
-
    -
    2. - -

  2. At the end of 24.7 [iterator.range], add:

    - -
    -
    -template <class C> auto cbegin(const C& c) -> decltype(std::begin(c));
-
    -
    -

    --?- Returns: std::begin(c). -

    -
    - -
    -template <class C> auto cend(const C& c) -> decltype(std::end(c));
-
    -
    -

    --?- Returns: std::end(c). -

    -
    - -
    -template <class C> auto rbegin(C& c) -> decltype(c.rbegin());
-template <class C> auto rbegin(const C& c) -> decltype(c.rbegin());
-
    -
    -

    --?- Returns: c.rbegin(). -

    -
    - -
    -template <class C> auto rend(C& c) -> decltype(c.rend());
-template <class C> auto rend(const C& c) -> decltype(c.rend());
-
    -
    -

    --?- Returns: c.rend(). -

    -
    - -
    -template <class T, size_t N> reverse_iterator<T*> rbegin(T (&array)[N]);
-
    -
    -

    --?- Returns: reverse_iterator<T*>(array + N). -

    -
    - -
    -template <class T, size_t N> reverse_iterator<T*> rend(T (&array)[N]);
-
    -
    -

    --?- Returns: reverse_iterator<T*>(array). -

    -
    - -
    -template <class E> reverse_iterator<const E*> rbegin(initializer_list<E> il);
-
    -
    -

    --?- Returns: reverse_iterator<const E*>(il.end()). -

    -
    - -
    -template <class E> reverse_iterator<const E*> rend(initializer_list<E> il);
-
    -
    -

    --?- Returns: reverse_iterator<const E*>(il.begin()). -

    -
    - -
    -template <class C> auto crbegin(const C& c) -> decltype(std::rbegin(c));
-
    -
    -

    --?- Returns: std::rbegin(c). -

    -
    - -
    -template <class C> auto crend(const C& c) -> decltype(std::rend(c));
-
    -
    -

    --?- Returns: std::rend(c). -

    -
    -
    -
    3. -
- - - - - - -
-

2129. User specializations of std::initializer_list

-

Section: 17.6.4.2.1 [namespace.std], 18.9 [support.initlist] Status: WP - Submitter: Richard Smith Opened: 2012-01-18 Last modified: 2015-04-08

-

View all other issues in [namespace.std].

-

View all issues with WP status.

-

Discussion:

- -

-Since the implementation is intended to magically synthesize instances of std::initializer_list -(rather than by a constructor call, for instance), user specializations of this type can't generally be -made to work. I can't find any wording which makes such specializations ill-formed, though, which leads -me to suspect that they're technically legal under the provisions of 17.6.4.2.1 [namespace.std] p1.

- - -

[2012, Kona]

- -

-This sounds correct, but we need wording for a resolution. -

-

-Marshall Clow volunteers to produce wording. -

- -

[2014-02-19, Jonathan Wakely provides proposed wording]

- - -

[2014-03-27, Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Add new new paragraph below 18.9 [support.initlist] p2:

    - -
    -

    --2- An object of type initializer_list<E> provides access to an array of objects of type const E. […] -

    --?- If an explicit specialization or partial specialization of initializer_list is declared, the program is ill-formed. -

    -
    -
    2. -
- - - - - -
-

2130. Missing ordering constraints

-

Section: 29.3 [atomics.order] Status: C++14 - Submitter: Mark Batty Opened: 2012-02-22 Last modified: 2015-04-08

-

View other active issues in [atomics.order].

-

View all other issues in [atomics.order].

-

View all issues with C++14 status.

-

Discussion:

-

C11 issue 407

- -

-It seems that both C11 and C++11 are missing the following two derivatives of this -rule: -

-

- For atomic modifications A and B of an atomic object M, if there is - a memory_order_seq_cst fence X such that A is sequenced before X, - and X precedes B in S, then B occurs later than A in the - modification order of M. -

-

- For atomic modifications A and B of an atomic object M, if there is - a memory_order_seq_cst fence Y such that Y is sequenced before B, - and A precedes Y in S, then B occurs later than A in the - modification order of M. -

-

-Above wording has been suggested for the Technical Corrigendum of C11 via issue 407, details can be found -here. -

- -

[2012-03-19: Daniel proposes a slightly condensed form to reduce wording duplications]

- - -

[2012-03-20: Hans comments]

- -

-The usage of the term atomic operations in 29.3 [atomics.order] p7 is actually -incorrect and should better be replaced by atomic modifications as used in the C11 -407 wording. -

-There seems to be a similar wording incorrectness used in 1.10 [intro.multithread] p17 -which should be corrected as well. -

- -

[2012, Portland: move to Review]

- -

-Olivier: does the fence really participate in the modifications? -

-

-Hans: S is the total set of all sequentially consistent operations, - and sequentially consistent fences are in S. -

-

-Olivier: this sort of combination of a pair of half-open rules seems to imply the - write must make it to main memory -

-

-But not all implementations treat a fence as a memory operation; cannot observe the half-open rule. -

-

-Hans: not sure this is actually prevented here. You could defer until the next load. - What the wording doesn't quite show is that the third bullet in the new wording - is already in the standard. -

-

-Hans: it is the interaction between fences on one side and other memory modifications - on the other that is being defined here. -

-

-Pablo: S is not directly observable; it is a hypothetic ordering. -

-

-Moved to review -

-

-Hans: to alert C liaison -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. [Drafting note: The project editor is kindly asked to consider to replace in 1.10 [intro.multithread] p17 -the phrase "before an operation B on M" by "before a modification B of M".]

    -
    2. -

  2. Change 29.3 [atomics.order] paragraph 7 as indicated: [Drafting note: Note that the -wording change intentionally does also replace the term atomic operation by atomic modification] -

    - -

    --7- For atomic operations A and B on an atomic object M, if there are -memory_order_seq_cst fences X and Y such that A is sequenced before X, -Y is sequenced before B, and X precedes Y in S, then B -occurs later than A in the modification order of M. -For atomic modifications A and B of an atomic object M, B occurs -later than A in the modification order of M if: -

      -
    • there is a memory_order_seq_cst fence X such that A is sequenced before X, -and X precedes B in S, or -
      • -
    • there is a memory_order_seq_cst fence Y such that Y is sequenced before B, -and A precedes Y in S, or -
      • -
    • there are memory_order_seq_cst fences X and Y such that A is sequenced -before X, Y is sequenced before B, and X precedes Y in S. -
      • -
    -

    --8- [ Note: memory_order_seq_cst ensures sequential consistency only for a program that is free of data races -and uses exclusively memory_order_seq_cst operations. Any use of weaker ordering will invalidate this -guarantee unless extreme care is used. In particular, memory_order_seq_cst fences ensure a total order -only for the fences themselves. Fences cannot, in general, be used to restore sequential consistency for atomic -operations with weaker ordering specifications. — end note ] -

    -
    3. -
- - - - - - -
-

2132. std::function ambiguity

-

Section: 20.9.12.2.1 [func.wrap.func.con] Status: C++14 - Submitter: Ville Voutilainen Opened: 2012-02-28 Last modified: 2015-04-08

-

View all other issues in [func.wrap.func.con].

-

View all issues with C++14 status.

-

Discussion:

-

-Consider the following: -

-
-#include <functional>
-
-void f(std::function<void()>) {}
-void f(std::function<void(int)>) {}
-
-int main() {
-  f([]{});
-  f([](int){});
-}
-
-

-The calls to f in main are ambiguous. Apparently because the -conversion sequences to std::function from the lambdas are identical. -The standard specifies that the function object given to std::function -"shall be Callable (20.8.11.2) for argument types ArgTypes and -return type R." It doesn't say that if this is not the case, the -constructor isn't part of the overload set. -

-Daniel: During the preparation of N3123 -it turned out that there are no longer reasons to refer to INVOKE as a -conceptually entity alone, its real implementation as a function template invoke -is possible but was deferred for a later point in time. Defining a type trait for -the Callable requirement would also be possible, so there seem to be no technical -reasons why the template constructor of std::function should not be -constrained. The below suggested wording does this without introducing a special -trait for this. This corresponds to the way that has been used to specify the -result_of trait. Note that the definition of the Callable -requirement is perfectly suitable for this, because it is a pure syntactically -based requirement and can be directly transformed into a constrained template. -

-The suggested resolution also applies such wording to the "perfectly forwarding" -assignment operator -

-
-template<class F> function& operator=(F&&);
-
-

-The positive side-effect of this is that it automatically implements a solution to -a problem similar to that mentioned in issue 1234. -

-It would be possible to apply similar constraints to the member signatures -

-
-template<class F> function& operator=(reference_wrapper<F>);
-
-template<class F, class A> void assign(F&&, const A&);
-
-

-as well. At this point there does not seem to be a pestering reason to do so. -

- -

[2012-10 Portland: Move to Review]

- -

-STL: This is a real issue, but does not like a resolution relying on a SFINAEable metafunction -that is not specified and available to the users. -

- -

-packaged_task has the same issue. -

- -

-STL strongly wants to see an is_callable type trait to clarify the proposed wording. -

- -

-Jeremiah concerned about holding up what appears to be a correct resolution for a hypothetical -better one later - the issue is real. -

- -

-Why must f by CopyConstructible? Surely MoveConstructible would be sufficient? -

- -

-Answer: because function is CopyConstructible, and the bound functor is type-erased -so must support all the properties of function itself. -

- -

-Replace various applications of declval in the proposed resolution with simply using -the passed functor object, f. -

- -

-Alisdair to apply similar changes to packaged_task. -

- -

[2012-11-09, Vicente J. Botet Escriba provides another example]

- - -

-Consider the following: -

-
-class AThreadWrapper {
-public:
-  explicit operator std::thread();
-  ...
-};
-std::thread th = std::thread(AThreadWrapper); // call to conversion operator intended
-
-

-The call to the conversion operator is overloaded with the thread constructor. But thread constructor requirement -makes it fail as AThreadWrapper is not a Callable and the compiler tries to instantiate the thread -constructor and fails. -

- -

[2014-02-14 Issaquah meeting: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change the following paragraphs in 20.9.12.2.1 [func.wrap.func.con]: -[Editorial comment: The removal of the seemingly additional no-throw -requirements of copy constructor and destructor of A is recommended, -because they are already part of the Allocator requirements. Similar clean-up -has been suggested by 2070 — end comment]

    - -
    -
    -template<class F> function(F f);
-template<class F, class A> function(allocator_arg_t, const A& a, F f);
-
    -
    -

    --7- Requires: F shall be CopyConstructible. f shall be Callable -(20.9.12.2 [func.wrap.func]) for argument types ArgTypes and return type R. -The copy constructor and destructor of A shall not throw exceptions. -

    --?- Remarks: These constructors shall not participate in overload resolution unless -f is Callable (20.9.12.2 [func.wrap.func]) for argument types -ArgTypes... and return type R. -

    -
    -

    -[…] -

    -
    -template<class F> function& operator=(F&& f);
-
    -
    -

    --18- Effects: function(std::forward<F>(f)).swap(*this); -

    --19- Returns: *this -

    --?- Remarks: This assignment operator shall not participate in overload resolution unless -declval<typename decay<F>::type&>() is Callable (20.9.12.2 [func.wrap.func]) -for argument types ArgTypes... and return type R. -

    -
    -
    - -
    2. -
- - - - - - -
-

2135. Unclear requirement for exceptions thrown in condition_variable::wait()

-

Section: 30.5.1 [thread.condition.condvar], 30.5.2 [thread.condition.condvarany] Status: C++14 - Submitter: Pete Becker Opened: 2012-03-06 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

View all issues with C++14 status.

-

Discussion:

- -

-condition_varible::wait() (and, presumably, condition_variable_any::wait(), although -I haven't looked at it) says that it calls lock.unlock(), and if condition_variable::wait() -exits by an exception it calls lock.lock() on the way out. But if the initial call to -lock.unlock() threw an exception, does it make sense to call lock.lock()? We simply -don't know the state of that lock object, and it's probably better not to touch it. -

-That aside, once the wait() call has been unblocked, it calls lock.lock(). If lock.lock() -throws an exception, what happens? The requirement is: -

-

-If the function exits via an exception, lock.lock() shall be called prior to exiting the function scope. -

-

-That can be read in two different ways. One way is as if it said "lock.lock() shall have been called Â…", -i.e. the original, failed, call to lock.lock() is all that's required. But a more natural reading is -that wait has to call lock.lock() again, even though it already failed. -

-I think this wording suffers from being too general. There are two possible exception sources: the initial call -to lock.unlock() and the final call to lock.lock(). Each one should have its own requirement. -Lumping them together muddles things. -

- -

[2012, Portland: move to Open]

- -

-Pablo: unlock failing is easy -- the call leaves it locked. - The second case, trying to lock fails -- what can you do? - This is an odd state as we had it locked before was called wait. - Maybe we should call terminate as we cannot meet the post-conditions. - We could throw a different exception. -

-

-Hans: calling terminate makes sense as we're likely to call it soon anyway - and at least we have some context. -

-

-Detlef: what kind of locks might be being used? -

-

-Pablo: condition variables are 'our' locks so this is less of a problem. - condition_variable_any might be more problematic. -

-

-The general direction is to call terminate if the lock cannot be reacquired. -

-

-Pablo: Can we change the wording to 'leaves the mutex locked' ? -

-

-Hans: so if the unlock throws we simply propagate the exception. -

-

-Move the issue to open and add some formal wording at a later time. -

- -

[2013-09 Chicago: Resolved]

- - -

-Detlef improves wording. Daniel suggests to introduce a Remarks element for the special -"If the function fails to meet the postcondition..." wording and applies this to the proposed -wording. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 30.5.1 [thread.condition.condvar] as indicated:

    - -
    -void wait(unique_lock<mutex>& lock);
-
    -

    -[…] -

    --10- Effects: -

    -
      -

    • Atomically calls lock.unlock() and blocks on *this.

      • -

    • When unblocked, calls lock.lock() (possibly blocking on the lock), then returns.

      • -

    • The function will unblock when signaled by a call to notify_one() or a call to notify_all(), -or spuriously.

      • -

    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function -scope.

      • -
    -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --11- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    --12- Throws: Nothingsystem_error when an exception is required (30.2.2). -

    --13- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Predicate>
-void wait(unique_lock<mutex>& lock, Predicate pred);
-
    -

    -[…] -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --16- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    --17- Throws: system_error when an exception is required (30.2.2), timeout-related exceptions -(30.2.4), or any exception thrown by pred. -

    --18- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Clock, class Duration>
-  cv_status wait_until(unique_lock<mutex>& lock,
-    const chrono::time_point<Clock, Duration>& abs_time);
-
    -

    -[…] -

    --20- Effects: -

    -
      -

    • […]

      • -

    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function -scope.

      • -
    -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --21- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    -[…] -

    --23- Throws: system_error when an exception is required (30.2.2) or timeout-related -exceptions (30.2.4). -

    --24- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Rep, class Period>
-  cv_status wait_for(unique_lock<mutex>& lock,
-    const chrono::duration<Rep, Period>& rel_time);
-
    -

    -[…] -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --28- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    -[…] -

    --29- Throws: system_error when an exception is required (30.2.2) or timeout-related -exceptions (30.2.4). -

    --30- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Clock, class Duration, class Predicate>
-  bool wait_until(unique_lock<mutex>& lock,
-    const chrono::time_point<Clock, Duration>& abs_time,
-	Predicate pred);
-
    -

    -[…] -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --33- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    -[…] -

    --35- Throws: system_error when an exception is required (30.2.2), timeout-related exceptions -(30.2.4), or any exception thrown by pred. -

    --36- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Rep, class Period, class Predicate>
-  bool wait_for(unique_lock<mutex>& lock,
-    const chrono::duration<Rep, Period>& rel_time,
-	Predicate pred);
-
    -

    -[…] -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --40- Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling -thread. -

    -[…] -

    --42- Throws: system_error when an exception is required (30.2.2), timeout-related exceptions -(30.2.4), or any exception thrown by pred. -

    --43- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    - -
    2. - -

  2. Edit 30.5.2 [thread.condition.condvarany] as indicated:

    - -
    -template<class Lock>
-void wait(Lock& lock);
-
    -

    -[…] -

    --10- Effects: -

    -
      -

    • Atomically calls lock.unlock() and blocks on *this.

      • -

    • When unblocked, calls lock.lock() (possibly blocking on the lock) and returns.

      • -

    • The function will unblock when signaled by a call to notify_one(), a call to notify_all(), -or spuriously.

      • -

    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function -scope.

      • -
    -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --11- Postcondition: lock is locked by the calling thread. -

    --12- Throws: Nothingsystem_error when an exception is required (30.2.2). -

    --13- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    - -
    - -
    -
    -template <class Lock, class Clock, class Duration>
-  cv_status wait_until(Lock& lock, const chrono::time_point<Clock, Duration>& abs_time);
-
    -

    -[…] -

    --15- Effects: -

    -
      -

    • […]

      • -

    • If the function exits via an exception, lock.lock() shall be called prior to exiting the function -scope.

      • -
    -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --16- Postcondition: lock is locked by the calling thread. -

    -[…] -

    --18- Throws: system_error when an exception is required (30.2.2) or timeout-related -exceptions (30.2.4). -

    --19- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    -
    -template <class Lock, class Rep, class Period>
-  cv_status wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
-
    -

    -[…] -

    --?- Remarks: If the function fails to meet the postcondition, std::terminate() shall be called -(15.5.1 [except.terminate]). [Note: This can happen if the re-locking of the mutex throws an -exception. — end note] -

    --22- Postcondition: lock is locked by the calling thread. -

    -[…] -

    --23- Throws: system_error when an exception is required (30.2.2) or timeout-related -exceptions (30.2.4). -

    --24- Error conditions: -

    -
      -

    • equivalent error condition from lock.lock() or lock.unlock().

      • -
    -
    - -
    - -
    3. -
- - - - - - -
-

2138. atomic_flag::clear should not accept memory_order_consume

-

Section: 29.7 [atomics.flag] Status: C++14 - Submitter: Ben Viglietta Opened: 2012-03-08 Last modified: 2015-04-08

-

View all other issues in [atomics.flag].

-

View all issues with C++14 status.

-

Discussion:

- -

-N3376 29.7 [atomics.flag]/7 says -this about atomic_flag::clear: -

-

-Requires: The order argument shall not be memory_order_acquire or memory_order_acq_rel. -

-

-In addition, memory_order_consume should be disallowed, since it doesn't meaningfully apply to store operations. -It's already disallowed on the analogous atomic<T>::store. The proposed updated text would be: -

-

-Requires: The order argument shall not be memory_order_consume, -memory_order_acquire, or memory_order_acq_rel. -

- -

[2012, Portland: move to Review]

- -

-Hans: this is a clear oversight. -

-

-Moved to review -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

[This wording is relative to N3376.]

- - -
-void atomic_flag_clear(volatile atomic_flag *object) noexcept;
-void atomic_flag_clear(atomic_flag *object) noexcept;
-void atomic_flag_clear_explicit(volatile atomic_flag *object, memory_order order) noexcept;
-void atomic_flag_clear_explicit(atomic_flag *object, memory_order order) noexcept;
-void atomic_flag::clear(memory_order order = memory_order_seq_cst) volatile noexcept;
-void atomic_flag::clear(memory_order order = memory_order_seq_cst) noexcept;
-
-

--7- Requires: The order argument shall not be memory_order_consume, -memory_order_acquire, or memory_order_acq_rel. -

--8- Effects: Atomically sets the value pointed to by object or by this to false. Memory is affected -according to the value of order. -

-
-
- - - - - - -
-

2140. Meaning of notify_all_at_thread_exit synchronization requirement?

-

Section: 30.5 [thread.condition] Status: C++14 - Submitter: Pete Becker Opened: 2012-03-06 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

View all issues with C++14 status.

-

Discussion:

- -

-notify_all_at_thread_exit has the following synchronization requirement: -

-

-Synchronization: The call to notify_all_at_thread_exit and the completion of the destructors -for all the current thread's variables of thread storage duration synchronize with (1.10 [intro.multithread]) -calls to functions waiting on cond. -

-

-The functions waiting on cond have already been called, otherwise they wouldn't be waiting. So how can a subsequent -call to notify_all_at_thread_exit synchronize with them? -

-Also, "synchronizes with" is a relationship between library calls (1.10 [intro.multithread]/8), so it's not -meaningful for completion of destructors for non-library objects. Presumably the intention wasn't so make library -destructors special here. -

- -

[2012-03-09 Jeffrey Yasskin comments:]

- - -

-I think the text should say that "notify_all_at_thread_exit and destructor calls are sequenced before -the lk.unlock()", and leave it at that, unless there's a funny implementation I haven't thought of. -

- -

[2012-03-19 Hans Boehm comments:]

- - -

-I think the synchronization clause should just be replaced with (modulo wording tweaks): -

-"The implied lk.unlock() call is sequenced after the destruction of all objects with thread storage duration -associated with the current thread." -

-as Jeffrey suggested. -

-To use this correctly, the notifying thread has to essentially acquire the lock, set a variable indicating it's done, -call notify_all_at_thread_exit(), while the waiting thread acquires the lock, and repeatedly waits on the -cv until the variable is set, and then releases the lock. That ensures that we have the proper synchronizes with -relationship as a result of the lock. -

- -

[2012, Portland: move to Review]

- -

-The lk.unlock() refers back to the wording the previous paragraph. -

-

-Moved to review -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -

  1. Modify 30.5 [thread.condition] p8 as indicated:

    - -
    -
    -void notify_all_at_thread_exit(condition_variable& cond, unique_lock<mutex> lk);
-
    -

    -[…] -

    --8- Synchronization: The call to notify_all_at_thread_exit and the completion of the destructors for -all the current thread's variables of thread storage duration synchronize with (1.10 [intro.multithread]) -calls to functions waiting on cond The implied lk.unlock() call is sequenced after the -destruction of all objects with thread storage duration associated with the current thread. -

    -
    -
    2. -
- - - - - - -
-

2141. common_type trait produces reference types

-

Section: 20.10.7.6 [meta.trans.other] Status: C++14 - Submitter: Doug Gregor Opened: 2012-03-11 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with C++14 status.

-

Discussion:

- -

-The type computation of the common_type type trait is defined as -

-
-template <class T, class U>
- struct common_type<T, U> {
-   typedef decltype(true ? declval<T>() : declval<U>()) type;
- };
-
-

-This means that common_type<int, int>::type is int&&, because -

-
    -
  • declval<int>() returns int&&
    • -
  • The conditional operator returns an xvalue when its second and third operands have the same type -and are both xvalues (5.16 [expr.cond] p4)
    • -
  • decltype returns T&& when its expression is an xvalue (7.1.6.2 [dcl.type.simple] p4)
    • -
-

-Users of common_type do not expect to get a reference type as the result; the expectation is that -common_type will return a non-reference type to which all of the types can be converted. -

-Daniel: In addition to that it should be noted that without such a fix the definition of std::unique_ptr's -operator< in 20.8.1.5 [unique.ptr.special] (around p4) is also broken: In the most typical case -(with default deleter), the determination of the common pointer type CT will instantiate -std::less<CT> which can now be std::less<T*&&>, which will -not be the specialization of pointer types that guarantess a total order. -

-Given the historic constext of common_type original specification, the proper resolution to me -seems to be using std::decay instead of std::remove_reference: -

-
-template <class T, class U>
-struct common_type<T, U> {
-  typedef typename decay<decltype(true ? declval<T>() : declval<U>())>::type type;
-};
-
-

-At that time rvalues had no identity in this construct and rvalues of non-class types have no cv-qualification. -With this change we would ensure that -

-
-common_type<int, int>::type == common_type<const int, const int>::type == int
-
-

-Note that this harmonizes with the corresponding heterogenous case, which has already the exact same effect: -

-
-common_type<int, long>::type == common_type<const int, const long>::type == long
-
- -

[2012-10-11 Daniel comments]

- -

-While testing the effects of applying the proposed resolution I noticed that this will have the effect that the unary -form of common_type, like -

-
-common_type<int>
-
-

-is not symmetric to the n-ary form (n > 1). This is unfortunate, because this difference comes especially to effect when -common_type is used with variadic templates. As an example consider the following make_array template: -

-
-#include <array>
-#include <type_traits>
-#include <utility>
-
-template<class... Args>
-std::array<typename std::common_type<Args...>::type, sizeof...(Args)>
-make_array(Args&&... args)
-{
-  typedef typename std::common_type<Args...>::type CT;
-  return std::array<CT, sizeof...(Args)>{static_cast<CT>(std::forward<Args>(args))...};
-}
-
-int main()
-{
-  auto a1 = make_array(0); // OK: std::array<int, 1>
-  auto a2 = make_array(0, 1.2); // OK: std::array<double, 2>
-  auto a3 = make_array(5, true, 3.1415f, 'c'); // OK: std::array<float, 4>
-
-  int i = 0;
-  auto a1b = make_array(i); // Error, attempt to form std::array<int&, 1>
-
-  auto a2b = make_array(i, 1.2); // OK: std::array<double, 2>
-  auto a2c = make_array(i, 0); // OK: std::array<int, 2>
-}
-
-

-The error for a1b only happens in the unary case and it is easy that it remains unnoticed -during tests. You cannot explain that reasonably to the user here. -

-Of-course it is possible to fix that in this example by applying std::decay to the result of the -std::common_type deduction. But if this is necessary here, I wonder why it should also be applied to -the binary case, where it gives the wrong illusion of a complete type decay? The other way around: Why is -std::decay not also applied to the unary case as well? -

-This problem is not completely new and was already observed for the original std::common_type specification. -At this time the decltype rules had a similar asymmetric effect when comparing -

-

-std::common_type<const int, const int>::type (equal to 'int' at this time) -

-

-with: -

-

-std::common_type<const int>::type (equal to 'const int') -

-

-and I wondered whether the unary form shouldn't also perform the same "decay" as the n-ary form. -

-This problem makes me think that the current resolution proposal might not be ideal and I expect -differences in implementations (for those who consider to apply this proposed resolution already). I -see at least three reasonable options: -

-
    -

  1. Accept the current wording suggestion for LWG 2141 as it is and explain that to users.

    2. -

  2. Keep std::common_type as currently specified in the Standard and tell users to use -std::decay where needed. Also fix other places in the library, e.g. the comparison -functions of std::unique_ptr or a most of the time library functions.

    3. -

  3. Apply std::decay also in the unary specialization of std::common_type with -the effect that std::common_type<const int&>::type returns int.

    4. -
- -

[2012-10-11 Marc Glisse comments]

- -

-If we are going with decay everywhere, I wonder whether we should also decay in the 2-argument version before -and not only after. So if I specialize common_type<mytype, double>, -common_type<const mytype, volatile double&> would automatically work. -

- -

[2012-10-11 Daniel provides wording for bullet 3 of his list:]

- - -
    -

  1. Change 20.10.7.6 [meta.trans.other] p3 as indicated:

    -
    -template <class T>
-struct common_type<T> {
-  typedef typename decay<T>::type type;
-};
-
-template <class T, class U>
-struct common_type<T, U> {
-  typedef typename decay<decltype(true ? declval<T>() : declval<U>())>::type type;
-};
-
    -
    2. -
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-Want to carefully consider the effect of decay vs. remove_reference with respect -to constness before adopting, although this proposed resolution stands for review in Bristol. -

- -

[2013-04-18, Bristol meeting]

- - -

Previous wording:

- -
-

This wording is relative to N3376.

- -

  1. In 20.10.7.6 [meta.trans.other] p3, change the common_type definition to

    -
    -template <class T, class U>
-struct common_type<T, U> {
-  typedef typename decay<decltype(true ? declval<T>() : declval<U>())>::type type;
-};
-
    -
    2. -
-
- -

[2013-04-18, Bristol]

- - -

Move to Ready

- -

[2013-09-29, Chicago]

- - -

Accepted for the working paper

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Change 20.10.7.6 [meta.trans.other] p3 as indicated:

    -
    -template <class T>
-struct common_type<T> {
-  typedef typename decay<T>::type type;
-};
-
-template <class T, class U>
-struct common_type<T, U> {
-  typedef typename decay<decltype(true ? declval<T>() : declval<U>())>::type type;
-};
-
    -
    2. -
- - - - - -
-

2142. packaged_task::operator() synchronization too broad?

-

Section: 30.6.9.1 [futures.task.members] Status: C++14 - Submitter: Pete Becker Opened: 2012-03-12 Last modified: 2015-04-08

-

View all other issues in [futures.task.members].

-

View all issues with C++14 status.

-

Discussion:

- -

-According to 30.6.9.1 [futures.task.members] p.18: -

-

-[A] successful call to [packaged_task::]operator() synchronizes with -a call to any member function of a future or shared_future object that shares -the shared state of *this. -

-

-This requires that the call to operator() synchronizes with calls to future::wait_for, -future::wait_until, shared_future::wait_for, and shared_future::wait_until, -even when these functions return because of a timeout. -

- -

[2012, Portland: move to Open]

- -

-If it said "a successful return from" (or "a return from" to cover exceptions) the problem would be more obvious. -

-

-Detlef: will ask Anthony Williams to draft some wording. -

-

-Moved to open (Anthony drafted to draft) -

- -

[2013-09, Chicago: move to Ready]

- - -

-Anthony's conclusion is that the offending paragraph is not needed. Already included in the statement -that the state is made ready. -

-Recommendation: Remove 30.6.9.1 [futures.task.members] p18 (the synchronization clause). Redundant because of -30.6.4 [futures.state] p9. -

-

-Moved to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Remove 30.6.9.1 [futures.task.members] p18 as indicated:

    - -
    -void operator()(ArgTypes... args);
-
    -

    -[…] -

    --18- Synchronization: a successful call to operator() synchronizes with (1.10) a call to any member function -of a future or shared_future object that shares the shared state of *this. The completion of -the invocation of the stored task and the storage of the result (whether normal or exceptional) into -the shared state synchronizes with (1.10) the successful return from any member function that detects -that the state is set to ready. [Note: operator() synchronizes and serializes with other functions -through the shared state. — end note] -

    -
    -
    2. -
- - - - - - -
-

2143. ios_base::xalloc should be thread-safe

-

Section: 27.5.3 [ios.base] Status: C++14 - Submitter: Alberto Ganesh Barbati Opened: 2012-03-14 Last modified: 2015-04-08

-

View all other issues in [ios.base].

-

View all issues with C++14 status.

-

Discussion:

- -

-The static function ios_base::xalloc() could be called from multiple threads and is not covered by -17.6.4.10 [res.on.objects] and 17.6.5.9 [res.on.data.races]. Adding a thread-safety requirement -should not impose a significant burden on implementations, as the function can be easily implemented with -hopefully lock-free atomics. -

- -

[2013-04-20, Bristol]

- - -

-Unanimous. -

-Resolution: move tentatively ready. (Inform Bill about this issue.) -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. In 27.5.3.5 [ios.base.storage] add a new paragraph after paragraph 1:

    - -
    -static int xalloc();
-
    -

    --1- Returns: index ++. -

    --?- Remarks: Concurrent access to this function by multiple threads shall not result in a data -race (1.10 [intro.multithread]). -

    -
    -
    2. -
- - - - - - -
-

2144. Missing noexcept specification in type_index

-

Section: 20.14 [type.index] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-03-18 Last modified: 2015-04-08

-

View all other issues in [type.index].

-

View all issues with C++14 status.

-

Discussion:

- -

-The class type type_index is a thin wrapper of type_info to -adapt it as a valid associative container element. Similar to type_info, -all member functions have an effective noexcept(true) specification, with the -exception of hash_code() and name(). The actual effects of these -functions is a direct call to type_info's hash_code() and name -function, but according to 18.7 [support.rtti] these are both noexcept -functions, so there is no reason for not declaring them as noexcept, too. In fact, -one of the suggested changes of the original proposing paper -N2530 -specifically was to ensure that type_info would get a hash_code() -function that guarantees not to throw exceptions (during that time the hash -requirements did not allow to exit with an exception). From this we can conclude that -type_index::hash_code() was intended to be nothrow. -

-It seems both consistent and technically simply to require these functions to be noexcept. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Modify the class type_index synopsis, 20.14.2 [type.index.overview] as indicated:

    - -
    -namespace std {
-  class type_index {
-  public:
-    type_index(const type_info& rhs) noexcept;
-    bool operator==(const type_index& rhs) const noexcept;
-    bool operator!=(const type_index& rhs) const noexcept;
-    bool operator< (const type_index& rhs) const noexcept;
-    bool operator<= (const type_index& rhs) const noexcept;
-    bool operator> (const type_index& rhs) const noexcept;
-    bool operator>= (const type_index& rhs) const noexcept;
-    size_t hash_code() const noexcept;
-    const char* name() const noexcept;
-  private:
-    const type_info* target; // exposition only
-    // Note that the use of a pointer here, rather than a reference,
-    // means that the default copy/move constructor and assignment
-    // operators will be provided and work as expected.
-  };
-}
-
    -
    2. -
- -
    -

  1. Modify the prototype definitions in 20.14.3 [type.index.members] as indicated:

    - -
    -size_t hash_code() const noexcept;
-
    -

    --8- Returns: target->hash_code() -

    -
    -
    -const char* name() const noexcept;
-
    -

    --9- Returns: target->name() -

    -
    -
    - -
    2. -
- - - - - - -
-

2145. error_category default constructor

-

Section: 19.5.1 [syserr.errcat] Status: C++14 - Submitter: Howard Hinnant Opened: 2012-03-21 Last modified: 2015-04-08

-

View all other issues in [syserr.errcat].

-

View all issues with C++14 status.

-

Discussion:

- -

-Should error_category have a default constructor? -

-If you look at the synopsis in 19.5.1.1 [syserr.errcat.overview], it appears the answer is no. There -is no default constructor declared and there is another constructor declared (which should inhibit a default -constructor). -

-However in paragraph 1 of the same section, descriptive text says: -

-

-Classes may be derived from error_category to support categories of errors in addition to those -defined in this International Standard. -

-

-How shall classes derived from error_category construct their base? -

-Jonathan Wakely: In N2066 -error_category was default-constructible. That is still the case in -N2241, because no other -constructor is declared. Then later N2422 -(issue 6) declares -the copy constructor as deleted, but doesn't add a default constructor, causing it to be no longer -default-constructible. That looks like an oversight to me, and I think there should be a public default -constructor. -

-Daniel: A default-constructor indeed should be provided to allow user-derived classes as described by the -standard. I suggest this one to be both noexcept and constexpr. The latter allows -user-derived non-abstract classes to take advantage of the special constant initialization rule -of 3.6.2 [basic.start.init] p2 b2 for objects with static (or thread) storage duration in namespace -scope. Note that a constexpr constructor is feasible here, even though there exists a non-trivial -destructor and even though error_category is not a literal type (see std::mutex for a similar -design choice). -

-In addition to that the proposed resolution fixes another minor glitch: According to 17.5.2.2 [functions.within.classes] -virtual destructors require a semantics description. -

-Alberto Ganesh Barbati: I would suggest to remove =default from the constructor instead. -Please consider that defaulting a constructor or destructor may actually define them as deleted under certain -conditions (see 12.1 [class.ctor]/5 and 12.4 [class.dtor]/5). Removing =default -is easier than providing wording to ensures that such conditions do not occur. -

- -

[2012-10 Portland: move to Ready]

- -

-The issue is real and the resolution looks good. -

- -

-Are there similar issues elsewhere in this clause? -

- -

-Potential to add constexpr to more constructors, but clearly a separable issue. -

- -

[2013-04-20 Bristol]

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Modify the class error_category synopsis, 19.5.1.1 [syserr.errcat.overview] as indicated: -[Drafting note: According to the general -noexcept library guidelines -destructors should not have any explicit exception specification. This destructor was overlooked during the paper -analysis — end note] -

    - -
    -namespace std {
-  class error_category {
-  public:
-    constexpr error_category() noexcept;
-    virtual ~error_category() noexcept;
-    error_category(const error_category&) = delete;
-    error_category& operator=(const error_category&) = delete;
-    virtual const char* name() const noexcept = 0;
-    virtual error_condition default_error_condition(int ev) const noexcept;
-    virtual bool equivalent(int code, const error_condition& condition) const noexcept;
-    virtual bool equivalent(const error_code& code, int condition) const noexcept;
-    virtual string message(int ev) const = 0;
-    bool operator==(const error_category& rhs) const noexcept;
-    bool operator!=(const error_category& rhs) const noexcept;
-    bool operator<(const error_category& rhs) const noexcept;
-  };
-}
-
    -
    2. - -

  2. Before 19.5.1.2 [syserr.errcat.virtuals] p1 insert a new prototype description as indicated:

    - -
    -virtual ~error_category();
-
    -

    --?- Effects: Destroys an object of class error_category. -

    -
    -
    - -
    3. - -

  3. Before 19.5.1.3 [syserr.errcat.nonvirtuals] p1 insert a new prototype description as indicated:

    - -
    -constexpr error_category() noexcept;
-
    -

    --?- Effects: Constructs an object of class error_category. -

    -
    -
    - -
    4. -
- - - - - - -
-

2147. Unclear hint type in Allocator's allocate function

-

Section: 17.6.3.5 [allocator.requirements] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-03-05 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with C++14 status.

-

Discussion:

- -

-According to Table 28 — "Allocator requirements", the expression -

-
-a.allocate(n, u)
-
-

-expects as second argument a value u that is described in Table 27 as: -

-

-a value of type YY::const_pointer obtained by calling YY::allocate, or else nullptr. -

-

-This description leaves it open, whether or whether not a value of type YY::const_void_pointer is -valid or not. The corresponding wording in C++03 is nearly the same, but in C++03 there did not exist the concept of -a general void_pointer for allocators. There is some evidence for support of void pointers because -the general allocator_traits template declares -

-
-static pointer allocate(Alloc& a, size_type n, const_void_pointer hint);
-
-

-and the corresponding function for std::allocator<T> is declared as: -

-
-pointer allocate(size_type, allocator<void>::const_pointer hint = 0);
-
-

-As an additional minor wording glitch (especially when comparing with the NullablePointer requirements imposed on -const_pointer and const_void_pointer), the wording seems to exclude lvalues of type -std::nullptr_t, which looks like an unwanted artifact to me. -

- -

[ -2012-10 Portland: Move to Ready -]

- - -

-No strong feeling that this is a big issue, but consensus that the proposed resolution is strictly -better than the current wording, so move to Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change Table 27 — "Descriptive variable definitions" in 17.6.3.5 [allocator.requirements]:

    - - - - - - - - - - - - - -
    Table 27 — Descriptive variable definitions
    VariableDefinition
    -u - -a value of type YY::const_pointer obtained by calling YY::allocate, or else -nullptrXX::const_void_pointer obtained by conversion from a result -value of YY::allocate, or else a value of type (possibly const) std::nullptr_t. -
    - -
    2. -
- - - - - - -
-

2148. Hashing enums should be supported directly by std::hash

-

Section: 20.9.13 [unord.hash] Status: C++14 - Submitter: Ville Voutilainen Opened: 2012-04-10 Last modified: 2015-04-08

-

View other active issues in [unord.hash].

-

View all other issues in [unord.hash].

-

View all issues with C++14 status.

-

Discussion:

- -

-The paper -proposes various hashing improvements. What it doesn't mention is hashing of -enums; enums are integral types, and users expect them to have built-in hashing -support, rather than having to convert enums to ints for uses with -unordered containers and other uses of hashes. Daniel Krügler explains in c++std-lib-32412 -that this is not achievable with a SFINAEd hash specialization because it would require -a partial specialization with a type parameter and a non-type parameter with a -default argument, which is currently not allowed, and hence the fixes in N3333 should be -adopted instead. -

- -

[2012-10 Portland: Move to Open]

- -

-We agree this is a real issue that should be resolved, by specifying such a hash. -

- -

-It is not clear that we should specify this as calling hash on the underlying_type, -or whether that is overspecification and we merely require that the hash be supplied. -

- -

-STL already has shipped an implementation, and is keen to provide wording. -

- -

[ -2013-04-14 STL provides rationale and improved wording -]

- - -

Rationale:

-

This can be achieved by inserting a very small tweak to the Standardese. We merely have to require that hash<Key> -be valid when Key is an "enumeration type" (which includes both scoped and unscoped enums). This permits, but does -not require, hash<Enum> to behave identically to hash<underlying_type<Enum>::type>, following -existing precedent — note that when unsigned int and unsigned long are the same size, -hash<unsigned int> is permitted-but-not-required to behave identically to hash<unsigned long>. -

-This proposed resolution doesn't specify anything else about the primary template, allowing implementations to do -whatever they want for non-enums: static_assert nicely, explode horribly at compiletime or runtime, etc. -

-While we're in the neighborhood, this proposed resolution contains an editorial fix. The 20.9 [function.objects] -synopsis says "base template", which doesn't appear anywhere else in the Standard, and could confuse users into -thinking that they need to derive from it. The proper phrase is "primary template". -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. In 20.9 [function.objects], header functional synopsis, edit as indicated:

    - -
    -namespace std {
-  […]
-  // 20.8.12, hash function baseprimary template:
-  template <class T> struct hash;
-  […]
-}
-
    -
    2. - -

  2. In 20.9.13 [unord.hash]/1 edit as indicated:

    - -

    --1- The unordered associative containers defined in 23.5 [unord] use specializations of the class template -hash as the default hash function. For all object types Key for which there exists a -specialization hash<Key>, and for all enumeration types (7.2 [dcl.enum]) Key, -the instantiation hash<Key> shall: […] -

    -
    3. -
- - - - - -
-

2149. Concerns about 20.8/5

-

Section: 20.9 [function.objects] Status: C++14 - Submitter: Scott Meyers Opened: 2012-02-15 Last modified: 2015-04-08

-

View all other issues in [function.objects].

-

View all issues with C++14 status.

-

Discussion:

- -

-20.9 [function.objects] p5 says: -

-

-To enable adaptors and other components to manipulate function objects that take one or two arguments -it is required that the function objects correspondingly provide typedefs argument_type and -result_type for function objects that take one argument and first_argument_type, -second_argument_type, and result_type for function objects that take two arguments. -

-

-I have two concerns about this paragraph. First, the wording appears to prescribe a requirement for all -function objects in valid C++ programs, but it seems unlikely that that is the intent. As such, the scope -of the requirement is unclear. For example, there is no mention of these typedefs in the specification for -closures (5.1.2), and Daniel Krügler has explained in the thread at -http://tinyurl.com/856plkn that conforming implementations can -detect the difference between closures with and without these typedefs. (Neither gcc 4.6 nor VC10 appear -to define typedefs such as result_type for closure types. I have not tested other compilers.) -

-Second, the requirement appears to be unimplementable in some cases, notably for function objects returned -from std::bind, as Howard Hinnant explains in the thread at http://tinyurl.com/6q5bos4. -

-From what I can tell, the standard already defines which adaptability typedefs must be provided by various -kinds of function objects in the specifications for those objects. Examples include the function objects -specified in 20.9.4 [refwrap]-20.9.9 [negators]. I therefore suggest that -20.9 [function.objects]/5 simply be removed from the standard. I don't think it adds anything -except opportunities for confusion. -

- -

[2012-10 Portland: Move to Open]

- -

-This wording caused confusion earlier in the week when reviewing Stefan's paper on greater<>. -

- -

-This phrasing sounds normative, but is actually descriptive but uses unfortunate wording. -

- -

-The main reason this wording exists is to document the protocol required to support the legacy binders -in Annex D. -

- -

-Stefan points out that unary_negate and binary_negate have not been deprecated and rely -on this. He plans a paper to remove this dependency. -

- -

-Consensus that this wording is inadequate, confusing, and probably should be removed. However, that -leaves a big hole in the specification for the legacy binders, that needs filling. -

- -

-While not opposed to striking this paragraph, we will need the additional wording to fix the openning -hole before this issue can move forward. -

- -

[ -2013-04-14 STL provides rationale -]

- - -

Rationale:

- -

I've concluded that Scott's original proposed resolution was correct and complete. There are two sides to this -story: the producers and the consumers of these typedefs.

- -

Producers: As Scott noted, the Standard clearly documents which function objects must provide these -typedefs. Some function objects must provide them unconditionally (e.g. plus<T> (for T != void), -20.9.5 [arithmetic.operations]/1), some conditionally (e.g. reference_wrapper<T>, -20.9.4 [refwrap]/2-4), and some don't have to provide them at all (e.g. lambdas, 5.1.2 [expr.prim.lambda]). -These requirements are clear, so we shouldn't change them or even add informative notes. Furthermore, because these -typedefs aren't needed in the C++11 world with decltype/perfect forwarding/etc., we shouldn't add more -requirements to provide them.

- -

Consumers: This is what we were concerned about at Portland. However, the consumers also clearly document -their requirements in the existing text. For example, reference_wrapper<T> is also a conditional consumer, -and 20.9.4 [refwrap] explains what typedefs it's looking for. We were especially concerned about the old negators -and the deprecated binders, but they're okay too. 20.9.9 [negators] clearly says that -unary_negate<Predicate> requires Predicate::argument_type to be a type, and -binary_negate<Predicate> requires Predicate::first_argument_type and Predicate::second_argument_type -to be types. (unary_negate/binary_negate provide result_type but they don't consume it.) -X [depr.lib.binders] behaves the same way with Fn::first_argument_type, Fn::second_argument_type, -and Fn::result_type. No additional wording is necessary.

- -

A careful reading of 20.9 [function.objects]/5 reveals that it wasn't talking about anything beyond the mere -existence of the mentioned typedefs — for example, it didn't mention that the function object's return type should be -result_type, or even convertible to result_type. As the producers and consumers are certainly talking about -the existence of the typedefs (in addition to clearly implying semantic requirements), we lose nothing by deleting the -unnecessary paragraph.

- -

[2013-04-18, Bristol]

- - -

Previous wording:

- -
-

Remove 20.9 [function.objects] p5:

- -

-To enable adaptors and other components to manipulate function objects that take one or two arguments -it is required that the function objects correspondingly provide typedefs argument_type and -result_type for function objects that take one argument and first_argument_type, -second_argument_type, and result_type for function objects that take two arguments. -

-
- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -

Edit 20.9 [function.objects] p5:

- -

-[Note:To enable adaptors and other components to manipulate function objects that take one or two arguments -it is required that the function objectsmany of the function objects in this clause correspondingly provide -typedefs argument_type and result_type for function objects that take one argument and first_argument_type, -second_argument_type, and result_type for function objects that take two arguments.— end note] -

- - - - - -
-

2150. Unclear specification of find_end

-

Section: 25.2.6 [alg.find.end] Status: C++14 - Submitter: Andrew Koenig Opened: 2012-03-28 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

- -

-25.2.6 [alg.find.end] describes the behavior of find_end as returning: -

-

-The last iterator i in the range [first1,last1 - (last2 - first2)) such that for any -nonnegative integer n < (last2 - first2), the following corresponding conditions hold: -*(i + n) == *(first2 + n), pred(*(i + n), *(first2 + n)) != false. -

-

-Does "for any" here mean "for every" or "there exists a"? I think it means the former, but it could be -interpreted either way. -

-Daniel: The same problem exists for the following specifications from Clause 25 [algorithms]: -

-
    -
  1. 25.2.13 [alg.search] p2 and p6
    2. -
  2. 25.3.10 [alg.reverse] p4
    3. -
  3. 25.3.13 [alg.partitions] p5 and p9
    4. -
  4. 25.4 [alg.sorting] p5
    5. -
  5. 25.4.2 [alg.nth.element] p1
    6. -
  6. 25.4.3.1 [lower.bound] p2
    7. -
  7. 25.4.3.2 [upper.bound] p2
    8. -
  8. 25.4.7 [alg.min.max] p21 and p23
    9. -
- -

[2013-04-20, Bristol]

- - -

-Unanimous agreement on the wording. -

-Resolution: move to tentatively ready -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -
  1. -

    Change 25.2.6 [alg.find.end] p2 as indicated:

    - -
    -template<class ForwardIterator1, class ForwardIterator2>
-ForwardIterator1 
-find_end(ForwardIterator1 first1, ForwardIterator1 last1,
-         ForwardIterator2 first2, ForwardIterator2 last2);
-template<class ForwardIterator1, class ForwardIterator2,
-         class BinaryPredicate>
-ForwardIterator1
-find_end(ForwardIterator1 first1, ForwardIterator1 last1,
-         ForwardIterator2 first2, ForwardIterator2 last2,
-         BinaryPredicate pred);
-

    -[…] -

    --2- Returns: The last iterator i in the range [first1,last1 - (last2 - first2)) such -that for anyevery nonnegative integer n < (last2 - first2), the following -corresponding conditions hold: *(i + n) == *(first2 + n), pred(*(i + n), *(first2 + n)) != false. -Returns last1 if [first2,last2) is empty or if no such iterator is found. -

    -
    2. - -
  2. -

    Change 25.2.13 [alg.search] p2 and p6 as indicated:

    - -
    -template<class ForwardIterator1, class ForwardIterator2>
-ForwardIterator1
-search(ForwardIterator1 first1, ForwardIterator1 last1,
-       ForwardIterator2 first2, ForwardIterator2 last2);
-template<class ForwardIterator1, class ForwardIterator2,
-         class BinaryPredicate>
-ForwardIterator1
-search(ForwardIterator1 first1, ForwardIterator1 last1,
-       ForwardIterator2 first2, ForwardIterator2 last2,
-       BinaryPredicate pred);
-

    -[…] -

    --2- Returns: The first iterator i in the range [first1,last1 - (last2-first2)) -such that for anyevery nonnegative integer n less than last2 - first2 -the following corresponding conditions hold: *(i + n) == *(first2 + n), pred(*(i + n), *(first2 + n)) != false. -Returns first1 if [first2,last2) is empty, otherwise returns last1 if no such iterator -is found. -

    -

    -[…] -

    -
    -template<class ForwardIterator, class Size, class T>
-ForwardIterator
-search_n(ForwardIterator first, ForwardIterator last, Size count,
-         const T& value);
-template<class ForwardIterator, class Size, class T,
-         class BinaryPredicate>
-ForwardIterator
-search_n(ForwardIterator first, ForwardIterator last, Size count,
-         const T& value, BinaryPredicate pred);
-

    -[…] -

    --6- Returns: The first iterator i in the range [first,last-count) such that -for anyevery non-negative integer n less than count the following -corresponding conditions hold: *(i + n) == value, pred(*(i + n),value) != false. Returns last -if no such iterator is found. -

    -
    3. - -
  3. -

    Change 25.3.10 [alg.reverse] p4 as indicated:

    - -
    -template<class BidirectionalIterator, class OutputIterator>
-OutputIterator
-reverse_copy(BidirectionalIterator first,
-             BidirectionalIterator last, OutputIterator result);
-

    -[…] -

    --4- Effects: Copies the range [first,last) to the range [result,result+(last-first)) -such that for anyevery non-negative integer i < (last - first) the following -assignment takes place: *(result + (last - first) - i) = *(first + i). -

    -
    4. - -
  4. -

    Change 25.3.13 [alg.partitions] p5 and p9 as indicated:

    - -
    -template<class ForwardIterator, class Predicate>
-ForwardIterator
-partition(ForwardIterator first,
-          ForwardIterator last, Predicate pred);
-

    -[…] -

    --5- Returns: An iterator i such that for anyevery iterator j -in the range [first,i) pred(*j) != false, and for anyevery iterator k -in the range [i,last), pred(*k) == false. -

    -

    -[…] -

    -
    -template<class BidirectionalIterator, class Predicate>
-BidirectionalIterator
-stable_partition(BidirectionalIterator first,
-                 BidirectionalIterator last, Predicate pred);
-

    -[…] -

    --9- Returns: An iterator i such that for anyevery iterator j -in the range [first,i), pred(*j) != false, and for anyevery iterator k -in the range [i,last), pred(*k) == false. The relative order of the elements in both groups is preserved. -

    -
    5. - -
  5. -

    Change 25.4 [alg.sorting] p5 as indicated:

    - -

    --5- A sequence is sorted with respect to a comparator comp if for anyevery iterator -i pointing to the sequence and anyevery non-negative integer n such that -i + n is a valid iterator pointing to an element of the sequence, comp(*(i + n), *i) == false. -

    -
    6. - -
  6. -

    Change 25.4.2 [alg.nth.element] p1 as indicated:

    - -
    -template<class RandomAccessIterator>
-void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                 RandomAccessIterator last);
-template<class RandomAccessIterator, class Compare>
-void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                 RandomAccessIterator last, Compare comp);
-

    --1- After nth_element the element in the position pointed to by nth is the element that would -be in that position if the whole range were sorted. Also for anyevery iterator i -in the range [first,nth) and anyevery iterator j in the range -[nth,last) it holds that: !(*i > *j) or comp(*j, *i) == false. -

    -
    7. - -
  7. -

    Change 25.4.3.1 [lower.bound] p2 as indicated:

    - -
    -template<lass ForwardIterator, class T>
-ForwardIterator
-lower_bound(ForwardIterator first, ForwardIterator last,
-            const T& value);
-template<class ForwardIterator, class T, class Compare>
-ForwardIterator
-lower_bound(ForwardIterator first, ForwardIterator last,
-            const T& value, Compare comp);
-

    -[…] -

    --2- Returns: The furthermost iterator i in the range [first,last] such that for -anyevery iterator j in the range [first,i) the following corresponding -conditions hold: *j < value or comp(*j, value) != false. -

    -
    8. - -
  8. -

    Change 25.4.3.2 [upper.bound] p2 as indicated:

    - -
    -template<lass ForwardIterator, class T>
-ForwardIterator
-upper_bound(ForwardIterator first, ForwardIterator last,
-            const T& value);
-template<class ForwardIterator, class T, class Compare>
-ForwardIterator
-upper_bound(ForwardIterator first, ForwardIterator last,
-            const T& value, Compare comp);
-

    -[…] -

    --2- Returns: The furthermost iterator i in the range [first,last] such that for -anyevery iterator j in the range [first,i) the following corresponding -conditions hold: !(value < *j) or comp(value, *j) == false. -

    -
    9. - -
  9. -

    Change 25.4.7 [alg.min.max] p21 and p23 as indicated:

    - -
    -template<class ForwardIterator>
-ForwardIterator min_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-ForwardIterator min_element(ForwardIterator first, ForwardIterator last,
-                            Compare comp);
-

    --21- Returns: The first iterator i in the range [first,last) such that for -anyevery iterator j in the range [first,last) the following -corresponding conditions hold: !(*j < *i) or comp(*j, *i) == false. Returns -last if first == last. -

    -

    -[…] -

    -
    -template<class ForwardIterator>
-ForwardIterator max_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-ForwardIterator max_element(ForwardIterator first, ForwardIterator last,
-                            Compare comp);
-

    --23- Returns: The first iterator i in the range [first,last) such that for -anyevery iterator j in the range [first,last) the following -corresponding conditions hold: !(*i < *j) or comp(*i, *j) == false. Returns -last if first == last. -

    -
    10. - -
- - - - - - -
-

2159. atomic_flag initialization

-

Section: 29.7 [atomics.flag] Status: C++14 - Submitter: Alberto Ganesh Barbati Opened: 2012-05-24 Last modified: 2015-04-08

-

View all other issues in [atomics.flag].

-

View all issues with C++14 status.

-

Discussion:

- -

-29.7 [atomics.flag]/4 describes the ATOMIC_FLAG_INIT, but it's not quite clear about a -couple of points: -

-
    -

  1. -it's said that ATOMIC_FLAG_INIT "can be used to initialize an object of type atomic_flag" -and the following example: -

    -
    -std::atomic_flag guard = ATOMIC_FLAG_INIT;
-
    -

    -is presented. It's not clear whether the macro can also be used in the other initialization contexts: -

    -
    -std::atomic_flag guard ATOMIC_FLAG_INIT; 
-std::atomic_flag guard {ATOMIC_FLAG_INIT};
-
-struct A { std::atomic_flag flag; A(); };
-A::A() : flag (ATOMIC_FLAG_INIT); 
-A::A() : flag {ATOMIC_FLAG_INIT};
-
    -

    -Please also note that examples are non-normative, according to the ISO directives, meaning that the wording -presents no normative way to use the macro. -

    -
    2. - -

  2. -it's said that "It is unspecified whether an uninitialized atomic_flag object has an initial state -of set or clear.". I believe the use of "uninitialized" is inappropriate. First of all, if an object is -uninitialized it is obvious that we cannot assert anything about its state. Secondly, it doesn't address the -following cases: -

    -
    -std::atomic_flag a; // object is "initialized" by trivial default constructor
-std::atomic_flag a {}; // object is value-initialized
-static std::atomic_flag a; // object is zero-initialized
-
    -

    -strictly speaking a trivial constructor "initializes" the object, although it doesn't actually initialize the -sub-objects. -

    3. - -

  3. it's said that "For a static-duration object, that initialization shall be static.". Considering -the following example:

    -
    -struct A
-{
-  A(); // user-provided, not constexpr
-
-  std::atomic_flag flag = ATOMIC_FLAG_INIT;
-  // possibly other non-static data members
-};
-
-static A a;
-
    -

    -The object a.flag (as a sub-object of the object a) has static-duration, yet the initialization -has to be dynamic because A::A is not constexpr. -

    - -
    4. -
- -

[2012, Portland]

- -

-We would like to be able to allow more initialisation contexts for example: -

-
    -
  1. C struct
    2. -
  2. C++ constructor initializer-list
    3. -
-

-However we need further input from experts with implementation specific knowledge -to identify which additional contexts (if any) would be universally valid. -

-

-Moved to open -

- -

[2013, Chicago]

- -

-Move to Immediate, following review. -

-

-Some discussion over the explicit use of only copy initialization, and not direct initialization. This is necessary to -allow the implementation of atomic_flag as an aggregate, and may be further reviewed in the future. -

-

-Accept for Working Paper -

- - - -

Proposed resolution:

-

[This wording is relative to N3376.]

- - -

Change 29.7 [atomics.flag]/4 as follows:

- -

-The macro ATOMIC_FLAG_INIT shall be defined in such a way that it can be used to initialize an object of -type atomic_flag to the clear state. The macro can be used in the form: -

-
-atomic_flag guard = ATOMIC_FLAG_INIT;
-
-

-It is unspecified whether the macro can be used in other initialization contexts. For a complete -static-duration object, that initialization shall be static. It is unspecified whether an uninitialized -Unless initialized with ATOMIC_FLAG_INIT, it is unspecified whether an atomic_flag -object has an initial state of set or clear. [ Example: -

-
-atomic_flag guard = ATOMIC_FLAG_INIT;
-
-

-— end example ] -

-
- - - - - - -
-

2160. Unintended destruction ordering-specification of resize

-

Section: 23.3.6.3 [vector.capacity] Status: WP - Submitter: Daniel Krügler Opened: 2012-06-07 Last modified: 2015-05-22

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

View all issues with WP status.

-

Discussion:

- -

-As part of resolving LWG issue 2033 a wording change was done for resize() to -respect the problem mentioned in the question: -

-

-Does a call to 'void resize(size_type sz)' of std::vector require the element type to be -MoveAssignable because the call erase(begin() + sz, end()) mentioned in the Effects -paragraph would require the element type to be MoveAssignable? -

-

-The wording change was to replace in 23.3.3.3 [deque.capacity] and 23.3.6.3 [vector.capacity]: -

-

--1- Effects: If sz <= size(), equivalent to erase(begin() + sz, end()); […] -

-

-by: -

-

--1- Effects: If sz <= size(), equivalent to calling pop_back() size() - sz times. […] -

-

-The overlooked side-effect of this wording change is that this implies a destruction order -of the removed elements to be in reverse order of construction, but the previous version -did not impose any specific destruction order due to the way how the semantics of erase -is specified in Table 100. -

-Given the program: -

-
-#include <vector>
-#include <iostream>
-
-struct Probe {
-  int value;
-  Probe() : value(0) {}
-  Probe(int value) : value(value) {}
-  ~Probe() { std::cout << "~Probe() of " << value << std::endl; }
-};
-
-int main() {
-  std::vector<Probe> v;
-  v.push_back(Probe(1));
-  v.push_back(Probe(2));
-  v.push_back(Probe(3));
-  std::cout << "---" << std::endl;
-  v.resize(0);
-}
-
-

-the last three lines of the output for every compiler I tested was: -

-
-~Probe() of 1
-~Probe() of 2
-~Probe() of 3
-
-

-but a conforming implementation would now need to change this order to -

-
-~Probe() of 3
-~Probe() of 2
-~Probe() of 1
-
-

-This possible stringent interpretation makes sense, because one can argue that sequence containers -(or at least std::vector) should have the same required destruction order of it's elements, -as elements of a C array or controlled by memory deallocated with an array delete have. -I also learned that libc++ does indeed implement std::vector::resize in a way that the -second output form is observed. -

-While I agree that required reverse-destruction would better mimic the natural behaviour of -std::vector this was not required in C++03 and this request may be too strong. My current -suggestion would be to restore the effects of the previous wording in regard to the destruction order, -because otherwise several currently existing implementations would be broken just because of this -additional requirement. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Jonathan says that he believes this is a valid issue. -

-

-Walter wonders if this was intended when we made the previous change - if so, this would be NAD. -

-

-Jonathan said that Issue 2033 doesn't mention ordering. -

-

-Walter then asked if anyone is really unhappy that we're destroying items in reverse order of construction. -

-

-Jonathan points out that this conflicts with existing practice (libstc++, but not libc++). -

-

-Jonathan asked for clarification as to whether this change was intended by 2033. -

- -

[2014-06 Rapperswil]

- -

-Daniel points out that the ordering change was not intended. -

-General agreement that implementations should not be required to change. -

- -

[2014-06-28 Daniel provides alternative wording]

- - -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 23.3.3.3 [deque.capacity] as indicated: [Drafting note: The chosen wording form is similar to that for -forward_list. Note that the existing Requires element already specifies the necessary operational requirements -on the value type. — end drafting note]

    - -
    -
    -void resize(size_type sz);
-
    -
    -

    --1- Effects: If sz <= size(), erases the last size() - sz elements from the -sequenceequivalent to calling pop_back() size() - sz times. OtherwiseIf size() -<= sz, appends sz - size() default-inserted elements to the sequence. -

    -[…] -

    -
    -
    -void resize(size_type sz, const T& c);
-
    -
    -

    --3- Effects: If sz <= size(), erases the last size() - sz elements from the -sequenceequivalent to calling pop_back() size() - sz times. OtherwiseIf size() -< sz, appends sz - size() copies of c to the sequence. -

    -[…] -

    -
    -
    -
    2. - -

  2. Change 23.3.6.3 [vector.capacity] as indicated: [Drafting note: See deque for the rationale of the -used wording. — end drafting note]

    - -
    -
    -void resize(size_type sz);
-
    -
    -

    --12- Effects: If sz <= size(), erases the last size() - sz elements from the -sequenceequivalent to calling pop_back() size() - sz times. OtherwiseIf size() -< sz, appends sz - size() default-inserted elements to the sequence. -

    -[…] -

    -
    -
    -void resize(size_type sz, const T& c);
-
    -
    -

    --15- Effects: If sz <= size(), erases the last size() - sz elements from the -sequenceequivalent to calling pop_back() size() - sz times. OtherwiseIf size() -< sz, appends sz - size() copies of c to the sequence. -

    -[…] -

    -
    -
    -
    3. -
- - - - - - -
-

2162. allocator_traits::max_size missing noexcept

-

Section: 17.6.3.5 [allocator.requirements], 20.7.8.2 [allocator.traits.members], 20.7.8 [allocator.traits] Status: C++14 - Submitter: Bo Persson Opened: 2012-07-03 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with C++14 status.

-

Discussion:

- -

-N3376 describes in 20.7.8.2 [allocator.traits.members]/7 -

-
-static size_type max_size(Alloc& a);
-
-

-Returns: a.max_size() if that expression is well-formed; otherwise, numeric_limits<size_type>::max(). -

-
-

-The max_size function is supposed to call one of two functions that are both noexcept. -To make this intermediate function useful for containers, it should preserve the noexcept attribute. -

-Proposed changes: -

-In 20.7.8 [allocator.traits] and 20.7.8.2 [allocator.traits.members]/7, change the function signature to -

-
-static size_type max_size(Alloc& a) noexcept;
-
- -

[2012-08-05 Daniel comments]

- -

-On the first sight this does not seem like a defect of the specification, because the Allocator requirements in -17.6.3.5 [allocator.requirements] (Table 28) do not impose a no-throw requirement onto max_size(); -the table just describes the fall-back implementation for max_size() if a given allocator does -not provide such a function. -

-std::allocator as a special model of this concept and is allowed to increase the exception-guarantees -for max_size(), but this does not imply a corresponding rules for other allocators. -

-Furthermore, max_size() of Containers is not specified in terms of -Allocator::max_size(), so again this is not a real contradiction. -

-Nonetheless I think that the following stronger decision should be considered: -

-
    -

  1. -Require that for all Allocators (as specified in 17.6.3.5 [allocator.requirements]) max_size() -never throws an exception. This would it make much more useful to call this function in situations where no -exception should leave the context. -

    2. -

  2. -Require that for all Allocators (as specified in 17.6.3.5 [allocator.requirements]) max_size() -can be called on const allocator object. Together with the previous item this would allow an implementation -of a container's max_size() function to delegate to the allocator's max_size() function. -

    3. -
-

-In regard to the second statement it should be mentioned that there are two current specification -deviations from that in the draft: -

-
    -

  1. -The synopsis of 20.7.8 [allocator.traits] uses a const allocator argument as part of the signature -of the max_size function. -

    2. - -

  2. -Both the synopsis of 20.13.1 [allocator.adaptor.syn] and the member specification in -20.13.4 [allocator.adaptor.members] p8 declare scoped_allocator_adaptor::max_size -as const member function, but this function delegates to -

    -
    -allocator_traits<OuterAlloc>::max_size(outer_allocator())
-
    -

    -where outer_allocator() resolves to the member function overload returning a -const outer_allocator_type&. -

    -
    3. -
- -

-The question arises whether these current defects actually point to a defect in the Allocator -requirements and should be fixed there. -

- -

[ -2012-10 Portland: Move to Review -]

- - -

-Consensus that the change seems reasonable, and that for any given type the template is intantiated -with the contract should be 'wide' so this meets the guidelines we agreed in Madrid for C++11. -

- -

-Some mild concern that while we don't imagine many allocator implementations throwing on this method, -it is technically permited by current code that we would not be breaking, by turning throw -expressions into disguised terminate calls. In this case, an example might be an -instrumented 'logging' allocator that writes every function call to a log file or database, and might -throw if that connection/file were no longer available. -

- -

-Another option would be to make exception spefication a conditional no-except, much like we do for -some swap functions and assignment operators. However, this goes against the intent of the -Madrid adoption of noexcept which is that vendors are free to add such extensions, but we -look for a clear line in the library specification, and do not want to introduce conditional-noexcept -piecemeal. A change in our conventions here would require a paper addressing the library specification -as a whole. -

- -

-Consensus was to move forward, but move the issue only to Review rather than Ready to allow time -for further comments. This issue should be considered 'Ready' next time it is reviewed unless -we get such comments in the meantime. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

-In 20.7.8 [allocator.traits] and 20.7.8.2 [allocator.traits.members]/7, change the function signature to -

-
-static size_type max_size(Alloc& a) noexcept;
-
- - - - - -
-

2163. nth_element requires inconsistent post-conditions

-

Section: 25.4.2 [alg.nth.element] Status: C++14 - Submitter: Peter Sommerlad Opened: 2012-07-06 Last modified: 2015-04-08

-

View all other issues in [alg.nth.element].

-

View all issues with C++14 status.

-

Discussion:

- -

-The specification of nth_element refers to operator< whereas all sorting without a compare function is based on -operator<. While it is true that for all regular types both operators should be defined accordingly, all other -sorting algorithms only rely on existence of operator<. So I guess the paragraph p1 -

-

-After nth_element the element in the position pointed to by nth is the element that would be in that -position if the whole range were sorted. Also for any iterator i in the range [first,nth) and any -iterator j in the range [nth,last) it holds that: !(*i > *j) or comp(*j, *i) == false. -

-

-should read -

-

-After nth_element the element in the position pointed to by nth is the element that would be in that -position if the whole range were sorted. Also for any iterator i in the range [first,nth) and any -iterator j in the range [nth,last) it holds that: !(*j < *i) or comp(*j, *i) == false. -

-

-Note only "!(*i > *j)" was changed to "!(*j < *i)" and it would be more symmetric with -comp(*j, *i) as well. -

-In theory this might be a semantic change to the spec, but I believe the mistake is unintended. -

- -

[ -2012-10 Portland: Move to Ready -]

- - -

-This is clearly correct by inspection, moved to Ready by unanimous consent. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 25.4.2 [alg.nth.element] p1 as indicated:

    - -
    -template<class RandomAccessIterator>
-void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                 RandomAccessIterator last);
-template<class RandomAccessIterator, class Compare>
-void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                 RandomAccessIterator last, Compare comp);
-
    -

    --1- After nth_element the element in the position pointed to by nth is the element that would be in that -position if the whole range were sorted. Also for any iterator i in the range [first,nth) and any -iterator j in the range [nth,last) it holds that: !(*i > *j)!(*j < *i) -or comp(*j, *i) == false. -

    -
    -
    2. -
- - - - - - -
-

2168. Inconsistent specification of uniform_real_distribution constructor

-

Section: 26.5.8.2.2 [rand.dist.uni.real] Status: WP - Submitter: Marshall Clow Opened: 2012-07-14 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

- -

-uniform_real says in 26.5.8.2.2 [rand.dist.uni.real] p1: -

-

-A uniform_real_distribution random number distribution produces random numbers x, a ≤ x < b, -

-

-but also that (26.5.8.2.2 [rand.dist.uni.real] p2): -

-
-explicit uniform_real_distribution(RealType a = 0.0, RealType b = 1.0);
-

--2- Requires: a ≤ b and b - a ≤ numeric_limits<RealType>::max(). -

-
-

-If you construct a uniform_real_distribution<RealType>(a, b) where there are no representable -numbers between 'a' and 'b' (using RealType's representation) then you cannot satisfy -26.5.8.2.2 [rand.dist.uni.real]. -

-An obvious example is when a == b. -

- -

[2014-11-04 Urbana]

- -

-Jonathan provides wording. -

- -

[2014-11-08 Urbana]

- -

-Moved to Ready with the note. -

-

-There remains concern that the constructors are permitting -values that may (or may not) be strictly outside the domain -of the function, but that is a concern that affects the -design of the random number facility as a whole, and should -be addressed by a paper reviewing and addressing the whole -clause, not picked up in the issues list one distribution -at a time. It is still not clear that such a paper would be -uncontroversial. -

- - - -

Proposed resolution:

-

-This wording is relative to N4140. -

- -
    -

  1. Add a note after paragraph 1 before the synopsis in 26.5.8.2.2 [rand.dist.uni.real]:

    - -

    --1- A uniform_real_distribution random number distribution produces random numbers - -x -, - -a≤x<b -, -distributed according to the constant probability density function -

    -
    -

    - -p(x|a,b) -= - -1∕(b-a) - - -. -

    -
    -

    -[Note: This implies that -p(x|a,b) - is undefined when a == b. — end note] -

    -
    -

    -Drafting note: -p(x|a,b) - should be in math font, and a == b should be in code font. -

    -
    -
    2. -
- - - - - -
-

2169. Missing reset() requirements in unique_ptr specialization

-

Section: 20.8.1.3.4 [unique.ptr.runtime.modifiers] Status: C++14 - Submitter: Geoffrey Romer Opened: 2012-07-16 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.runtime.modifiers].

-

View all issues with C++14 status.

-

Discussion:

- -

-In 20.8.1.3.4 [unique.ptr.runtime.modifiers]/p1-2 of N3376, the description of reset() in the -array specialization of unique_ptr partially duplicates the description of the base template method -(as specified in 20.8.1.2.5 [unique.ptr.single.modifiers]/p3-5), but lacks some significant requirements. -Specifically, the text introduced in LWG 998, and item 13 of LWG 762, is present -only in the base template, not the specialization. -

-This gives the appearance that these requirements specifically do not apply to the specialization, which I -don't believe is correct or intended: the issue of reset() operation order addressed by LWG 998 -applies just as much to the derived template as to the base template, and the derived template has just as -much need to rely on get_deleter()(get()) being well-defined, well-formed, and not throwing exceptions -(arguably some of those properties follow from the fact that T is required to be a complete type, but -not all). -

-Assuming the derived template's reset() semantics are intended to be identical to the base template's, -there is no need to explicitly specify the semantics of reset(pointer p) at all (since -20.8.1.3 [unique.ptr.runtime]/3 specifies "Descriptions are provided below only for member functions that -have behavior different from the primary template."), and reset(nullptr_t p) can be specified by -reference to the 'pointer' overload. This is more concise, and eliminates any ambiguity about intentional vs. -accidental discrepancies. -

- -

[2012-10 Portland: Move to Ready]

- -

-This resolution looks blatantly wrong, as it seems to do nothing but defer to primary template -where we should describe the contract here. -

- -

-Ongoing discussion points out that the primary template has a far more carefully worded semantic -for reset(p) that we would want to copy here. -

- -

-STL points out that we need the nullptr overload for this dynamic-array form, as there is -a deleted member function template that exists to steal overloads of pointer-to-derived, avoiding -undifined behavior, so we need the extra overload. -

- -

-Finally notice that there is blanket wording further up the clause saying we describe only changes -from the primary template, so the proposed wording is in fact exactly correct. Move to Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -

Change 20.8.1.3.4 [unique.ptr.runtime.modifiers] as indicated:

- -
-void reset(pointer p = pointer()) noexcept;
-void reset(nullptr_t p) noexcept;
-
-

--1- Effects: If get() == nullptr there are no effects. Otherwise get_deleter()(get()) -Equivalent to reset(pointer()). -

--2- Postcondition: get() == p. -

-
- - - - - - -
-

2170. Aggregates cannot be DefaultConstructible

-

Section: 17.6.3.1 [utility.arg.requirements] Status: WP - Submitter: Daniel Krügler Opened: 2012-07-19 Last modified: 2015-04-08

-

View all other issues in [utility.arg.requirements].

-

View all issues with WP status.

-

Discussion:

- -

-The lack of the definition of the DefaultConstructible requirements in C++03 was fixed -by LWG 724 at a time where the core rules of list-initialization were slightly -different than today, at that time value-initialization (shortly) was the primary rule for -class types, i.e. just before applying CWG 1301, -CWG 1324, and -CWG 1368. -

-The order in 8.5.4 [dcl.init.list] p3 was changed to respect aggregate initialization, but that -had the side-effect that formally aggregate types cannot satisfy the DefaultConstructible -requirements anymore, because we require that -

-
-T u{};
-
-

-value-initializes the object u. -

-Of-course exclusion of aggregates was not intended, therefore I suggest to extend the requirements -in Table 19 (17.6.3.1 [utility.arg.requirements]) for empty aggregate-initialization as well. -

- -

[ -2012-10 Portland: Move to Core -]

- - -

-We are not qualified to pick apart the Core rules quickly at this point, but the consensus is -that if the core language has changed in this manner, then the fix should similarly be applied -in Core - this is not something that we want users of the language to have to say every time -they want to Value initialize (or aggregate initialize) an object. -

- -

-More to Open until we get a clear response from Core, Alisdair to file an issue with Mike. -

- -

[2013-04 Bristol: Back to Library]

- - -

-The Core Working group opened, discussed, and resolved CWG 1578 -as NAD for this library-related problem: Empty aggregate initialization and value-initialization are different core language concepts, -and this difference can be observed (e.g. for a type with a deleted default-constructor). -

- -

[2014-02-15 Issaquah: Move to Ready]

- -

-AM: core says still LWG issue, wording has been non-controversial, move to ready? -

-

-NJ: what about durations? think they are ok -

-

-Ville: pair and a few other have value initialize -

-

-AM: look at core 1578 -

-

-AM: value initialize would require (), remove braces from third row? -

-

-STL: no -

-

-PH: core has new issue on aggregates and non-aggregates. -

-

-AM: right, they said does not affect this issue -

-

-NJ: why ok with pair and tuple? -

-

-STL: will use (), tuple of aggregates with deleted constructor is ill-formed -

-

-Ville: aggregate with reference can't have () -

-

-STL: {} would be an issue too -

-

-Ville: aggregate with reference will have () deleted implicitly -

-

-Move to Ready. -

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -

Change Table 19 in 17.6.3.1 [utility.arg.requirements] as indicated:

- - - - - - - - - - - - - - - - - - - - - - - - -
Table 19 — DefaultConstructible requirements [defaultconstructible]
ExpressionPost-condition
-T t; - -object t is default-initialized -
-T u{}; - -object u is value-initialized or aggregate-initialized -
-T()
-T{} -		 -a temporary object of type T is value-initialized or aggregate-initialized -
- - - - - - -
-

2172. Does atomic_compare_exchange_* accept v == nullptr arguments?

-

Section: 20.8.2.6 [util.smartptr.shared.atomic] Status: C++14 - Submitter: Howard Hinnant Opened: 2012-07-28 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.atomic].

-

View all issues with C++14 status.

-

Discussion:

- -

-Looking at 20.8.2.6 [util.smartptr.shared.atomic]/p31 -

-
-template<class T>
-  bool
-  atomic_compare_exchange_strong_explicit(shared_ptr<T>* p,
-                                          shared_ptr<T>* v,
-                                          shared_ptr<T> w,
-                                          memory_order success, memory_order failure);
-

--31- Requires: p shall not be null. -

-

-What about v? Can it be null? And if so, what happens? -

-This looks closely related to C++11 issue LWG 1030, where we gave every signature in this section a: -

-

-Requires: p shall not be null. -

-

-It looks like a simple oversight to me that we did not add for the atomic_compare_exchange_*: -

-

-Requires: p shall not be null and v shall not be null. -

- -

[2012-10 Portland: Move to Ready]

- -

-This is clearly the right thing to do, and Lawrence concurs. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -

Change 20.8.2.6 [util.smartptr.shared.atomic] as indicated:

- -
-template<class T>
-  bool atomic_compare_exchange_weak(
-    shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
-

--27- Requires: p shall not be null and v shall not be null. -

-[…] -

-
-
-template<class T>
-  bool atomic_compare_exchange_weak_explicit(
-    shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-    memory_order success, memory_order failure);
-template<class T>
-  bool atomic_compare_exchange_strong_explicit(
-    shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-    memory_order success, memory_order failure);
-

--31- Requires: p shall not be null and v shall not be null. -

-[…] -

-
- - - - - - -
-

2174. wstring_convert::converted() should be noexcept

-

Section: 22.3.3.2.2 [conversions.string] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-08-02 Last modified: 2015-04-08

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with C++14 status.

-

Discussion:

- -

-There is no reason wstring_convert::converted() shouldn't be noexcept. -

-It might be possible for wstring_convert::state() and wbuffer_convert::state() -to be noexcept too, depending on the requirements on mbstate_t. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

-

-Defer the separate discsussion of state() to another issue, if anyone is ever motivated -to file one. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Edit in the class template wstring_convert synopsis 22.3.3.2.2 [conversions.string] p2:

    - -
    -size_t converted() const noexcept;
-
    -
    2. - -

  2. Edit the signature before 22.3.3.2.2 [conversions.string] p6:

    - -
    -size_t converted() const noexcept;
-
    -
    3. -
- - - - - -
-

2175. wstring_convert and wbuffer_convert validity

-

Section: 22.3.3.2.2 [conversions.string], 22.3.3.2.3 [conversions.buffer] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-08-02 Last modified: 2015-04-08

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with C++14 status.

-

Discussion:

- -

-See discussion following c++std-lib-32710. -

-It's not specified what happens if wstring_convert and wbuffer_convert objects are constructed -with null Codecvt pointers. -

-Should the constructors have preconditions that the pointers are not null? If not, are conversions expected to -fail, or is it undefined to attempt conversions if the pointers are null? -

-There are no observer functions to check whether objects were constructed with valid Codecvt pointers. -If the types are made movable such observers would be necessary even if the constructors require non-null -pointers (see also LWG 2176). -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Insert a new paragraph before 22.3.3.2.2 [conversions.string] paragraph 16:

    - -
    -wstring_convert(Codecvt *pcvt = new Codecvt);
-wstring_convert(Codecvt *pcvt, state_type state);
-wstring_convert(const byte_string& byte_err,
-  const wide_string& wide_err = wide_string());
-
    -
    -

    --?- Requires: For the first and second constructors pcvt != nullptr. -

    --16- Effects: The first constructor shall store pcvt in cvtptr and default values in -cvtstate, byte_err_string, and wide_err_string. The second constructor shall -store pcvt in cvtptr, state in cvtstate, and default values in -byte_err_string and wide_err_string; moreover the stored state shall be retained between -calls to from_bytes and to_bytes. The third constructor shall store new Codecvt -in cvtptr, state_type() in cvtstate, byte_err in byte_err_string, -and wide_err in wide_err_string. -

    -
    -
    2. - -

  2. Insert a new paragraph before 22.3.3.2.3 [conversions.buffer] paragraph 10:

    - -
    -wbuffer_convert(std::streambuf *bytebuf = 0,
-  Codecvt *pcvt = new Codecvt, state_type state = state_type());
-
    -

    --?- Requires: pcvt != nullptr. -

    --10- Effects: The constructor constructs a stream buffer object, initializes bufptr to bytebuf, -initializes cvtptr to pcvt, and initializes cvtstate to state. -

    -
    - -
    3. - -
- - - - - -
-

2176. Special members for wstring_convert and wbuffer_convert

-

Section: 22.3.3.2.2 [conversions.string], 22.3.3.2.3 [conversions.buffer] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-08-02 Last modified: 2015-04-08

-

View other active issues in [conversions.string].

-

View all other issues in [conversions.string].

-

View all issues with C++14 status.

-

Discussion:

- -

-See discussion following c++std-lib-32699. -

-The constructors for wstring_convert and wbuffer_convert should be explicit, to avoid -implicit conversions which take ownership of a Codecvt pointer and delete it unexpectedly. -

-Secondly, 22.3.3.2.3 [conversions.buffer] p11 describes a destructor which is not declared in the class -synopsis in p2. -

-Finally, and most importantly, the definitions in 22.3.3.2.2 [conversions.string] and -22.3.3.2.3 [conversions.buffer] imply implicitly-defined copy constructors and assignment operators, which -would do shallow copies of the owned Codecvt objects and result in undefined behaviour in the -destructors. -

-Codecvt is not required to be CopyConstructible, so deep copies are not possible. -The wstring_convert and wstring_buffer types could be made move-only, but the proposed -resolution below doesn't do so because of the lack of preconditions regarding null Codecvt pointers -and the absence of observer functions that would allow users to check preconditions (see also LWG 2175). -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-Jonathan pointed out that you can have an implicit constructor that takes ownership of a heap reference, -which would result an unexpected deletion. -

-

-No-one really likes the 'naked new' in the interface here, either. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Edit the class template wstring_convert synopsis in 22.3.3.2.2 [conversions.string] p2:

    - -
    -explicit wstring_convert(Codecvt *pcvt = new Codecvt);
-wstring_convert(Codecvt *pcvt, state_type state);
-explicit wstring_convert(const byte_string& byte_err,
-                         const wide_string& wide_err = wide_string());
-~wstring_convert();
-
-wstring_convert(const wstring_convert&) = delete;
-wstring_convert& operator=(const wstring_convert&) = delete;
-				 
-
    -
    2. - -

  2. Edit the signatures before 22.3.3.2.2 [conversions.string] p16:

    - -
    -explicit wstring_convert(Codecvt *pcvt = new Codecvt);
-wstring_convert(Codecvt *pcvt, state_type state);
-explicit wstring_convert(const byte_string& byte_err,
-    const wide_string& wide_err = wide_string());
-
    -
    3. - -

  3. Edit the class template wbuffer_convert synopsis in 22.3.3.2.3 [conversions.buffer] p2:

    - -
    -explicit wbuffer_convert(std::streambuf *bytebuf = 0,
-                         Codecvt *pcvt = new Codecvt,
-                         state_type state = state_type());
-
-~wbuffer_convert();
-
-wbuffer_convert(const wbuffer_convert&) = delete;
-wbuffer_convert& operator=(const wbuffer_convert&) = delete;
-						 
-
    -
    4. - -

  4. Edit the signature before 22.3.3.2.3 [conversions.buffer] p10:

    - -
    -explicit wbuffer_convert(std::streambuf *bytebuf = 0,
-    Codecvt *pcvt = new Codecvt, state_type state = state_type());
-
    -
    5. - -
- - - - - -
-

2177. Requirements on Copy/MoveInsertable

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Loïc Joly Opened: 2012-08-10 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++14 status.

-

Discussion:

- -

-See also discussion following c++std-lib-32883 -and c++std-lib-32897. -

-The requirements on CopyInsertable and MoveInsertable are either incomplete, or complete but hard to -figure out. -

-From e-mail c++std-lib-32897: -

-Pablo Halpern: -

-I agree that we need semantic requirements for all of the *Insertable concepts analogous to the requirements -we have on similar concepts. -

-Howard Hinnant: -

-I've come to believe that the standard is actually correct as written in this area. But it is really hard -to read. I would have no objection whatsoever to clarifications to CopyInsertable as you suggest (such as the -post-conditions on v). And I do agree with you that the correct approach to the clarifications is to -confirm that CopyInsertable implies MoveInsertable. -

- -

[2012, Portland: Move to Tentatively Ready]

- -

-Move to Tentatively Ready by unanimous consent. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Edit 23.2.1 [container.requirements.general] p13 as indicated:

    - -

    --13- […] Given a container type X having an allocator_type identical to A and -a value_type identical to T and given an lvalue m of type A, a pointer p -of type T*, an expression v of type (possibly const) T, and an rvalue rv -of type T, the following terms are defined. If X is not allocator-aware, the terms below are -defined as if A were std::allocator<T> — no allocator object needs to be created and -user specializations of std::allocator<T> are not instantiated: -

    -
      -

    • T is DefaultInsertable into X means that the following expression is -well-formed:

      -
      -allocator_traits<A>::construct(m, p);
-
      -
      • - -

    • An element of X is default-inserted if it is initialized by evaluation of the expression

      -
      -allocator_traits<A>::construct(m, p);
-
      -

      -where p is the address of the uninitialized storage for the element allocated within X. -

      -
      • - -

    • T is CopyMoveInsertable into X means that -the following expression is well-formed:

      -
      -allocator_traits<A>::construct(m, p, rv);
-
      -

      -and when evaluated the following postconditions hold: The value of *p is equivalent to the value of -rv before the evaluation. [Note: rv remains a valid object. Its state is unspecified — -end note] -

      -
      • - -

    • T is MoveCopyInsertable into X means -that, in addition to satisfying the MoveInsertable requirements, the following expression is -well-formed:

      -
      -allocator_traits<A>::construct(m, p, rv);
-
      -

      -and when evaluated the following postconditions hold: The value of v is unchanged and is equivalent -to *p. -

      -
      • - -

    • T is EmplaceConstructible into X from args, for zero or more arguments -args, means that the following expression is well-formed:

      -
      -allocator_traits<A>::construct(m, p, args);
-
      -
      • - -

    • T is Erasable from X means that the following expression is well-formed:

      -
      -allocator_traits<A>::destroy(m, p);
-
      -
      • - -
    -

    -[Note: A container calls allocator_traits<A>::construct(m, p, args) to construct an element -at p using args. The default construct in std::allocator will call -::new((void*)p) T(args), but specialized allocators may choose a different definition. — end note] -

    -
    -
    2. - -
- - - - - - -
-

2180. Exceptions from std::seed_seq operations

-

Section: 26.5.7.1 [rand.util.seedseq] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-08-18 Last modified: 2015-04-08

-

View all other issues in [rand.util.seedseq].

-

View all issues with C++14 status.

-

Discussion:

- -

-26.5.7.1 [rand.util.seedseq] p1 says upfront: -

-

-No function described in this section 26.5.7.1 [rand.util.seedseq] throws an exception. -

-

-This constraint seems non-implementable to me when looking especially at the members -

-
-template<class T>
-seed_seq(initializer_list<T> il);
-
-template<class InputIterator>
-seed_seq(InputIterator begin, InputIterator end);
-
-

-which have the effect of invoking v.push_back() for the exposition-only member of -type std::vector (or its equivalent) over all elements of the provided range, so -out-of-memory exceptions are always possible and the seed_seq object doesn't seem -to be constructible this way. -

-In addition to the potential lack-of-resources problem, the operations of InputIterator -might also throw exceptions. -

-Aside to that it should me mentioned, that a default constructor of vector<uint_least32_t> -in theory can also throw exceptions, even though this seems less of a problem to me in this context, because -such an implementation could easily use a different internal container in seed_seq that can hold -this no-throw exception guarantee. -

-Secondly, a slightly different problem category related to exceptions occurs for the member templates -

-
-template<class RandomAccessIterator>
-void generate(RandomAccessIterator begin, RandomAccessIterator end);
-
-template<class OutputIterator>
-void param(OutputIterator dest) const;
-
-

-where the actual operations performed by the implementation would never need to throw, but since they invoke -operations of a user-provided customization point, the overall operation, like for example -

-
-copy(v.begin(), v.end(), dest);
-
-

-could also throw exceptions. In this particular example we can just think of a std::back_insert_iterator -applied to a container that needs to allocate its elements used as the type for OutputIterator. -

-Even though Clause 26 [numerics] has mostly stronger exception constraints than other parts of the -library the here discussed are overrestrictive, especially since no operation of std::seed_seq -except the template generate is actually needed within the library implementation, as mentioned in the -discussion of LWG 2124. -

-I suggest to remove the general no-exception constraints for operations of std::seed_seq except for -member size() and the default constructor and to provide specific wording for generate() and -param() to ensure that the algorithm itself is a nothrow operation, which is especially for -generate() important, because the templates specified in 26.5.3 [rand.eng] and -26.5.4 [rand.adapt] also depend on this property indirectly, which is further discussed in LWG -2181. -

-Howard: -

-I suggest to use a different form for the exception specification, something similar to -20.9.10.3 [func.bind.bind] p4: -

-

-Throws: Nothing unless an operation on RandomAccessIterator throws an exception. -

-

-Daniel: -

-The currently suggested "what and when" form seems a bit more specific and harmonizes with the form used for -function template generate_canonical from 26.5.7.2 [rand.util.canonical]. -

- -

[2013-04-20, Bristol]

- - -

-Open an editorial issue on the exception wording ("Throws: What and when"). -

-Solution: move to tentatively ready. -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Edit 26.5.7.1 [rand.util.seedseq] p1 as indicated:

    - -
    -

    --1- No function described in this section 26.5.7.1 [rand.util.seedseq] throws an exception. -

    -
    -
    2. - -

  2. Edit 26.5.7.1 [rand.util.seedseq] around p2 as indicated:

    - -
    -seed_seq();
-
    -

    --2- Effects: Constructs a seed_seq object as if by default-constructing its member v. -

    --?- Throws: Nothing. -

    -
    -
    3. - -

  3. Edit 26.5.7.1 [rand.util.seedseq] around p7 as indicated:

    - -
    -template<class RandomAccessIterator>
-  void generate(RandomAccessIterator begin, RandomAccessIterator end);
-
    -

    --7- Requires: RandomAccessIterator shall meet the requirements of a mutable random access iterator -(Table 111) type. Moreover, iterator_traits<class RandomAccessIterator>::value_type shall denote -an unsigned integer type capable of accommodating 32-bit quantities. -

    --8- Effects: Does nothing if begin == end. Otherwise, with s = v.size() and -n = end - begin, fills the supplied range [begin, end) according to the following algorithm […] -

    --?- Throws: What and when RandomAccessIterator operations of begin and end throw. -

    -
    -
    4. - -

  4. Edit 26.5.7.1 [rand.util.seedseq] around p9 as indicated:

    - -
    -size_t size() const;
-
    -

    --9- Returns: The number of 32-bit units that would be returned by a call to param(). -

    --??- Throws: Nothing. -

    --10- Complexity: constant time. -

    -
    -
    5. - -

  5. Edit 26.5.7.1 [rand.util.seedseq] around p11 as indicated:

    - -
    -template<class OutputIterator>
-  void param(OutputIterator dest) const;
-
    -

    --11- Requires: OutputIterator shall satisfy the requirements of an output iterator (Table 108) type. -Moreover, the expression *dest = rt shall be valid for a value rt of type result_type. -

    --12- Effects: Copies the sequence of prepared 32-bit units to the given destination, as if by executing the -following statement: -

    -
    -copy(v.begin(), v.end(), dest);
-
    -

    --??- Throws: What and when OutputIterator operations of dest throw. -

    -
    -
    6. - -
- - - - - - -
-

2182. Container::[const_]reference types are misleadingly specified

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-08-20 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++14 status.

-

Discussion:

- -

-According to Table 96 (Container requirements) the return type of X::reference and -X::const_reference is "lvalue of T" and "const lvalue of T", -respectively. This does not make much sense, because an lvalue is an expression category, not a type. -It could also refer to an expression that has a type, but this doesn't make sense either in this -context, because obviously X::[const_]reference are intended to refer to types. -

-Given the fact that vector<bool> has no real reference type for X::[const_]reference -and this definition presumably is intended to cover such situations as well, one might think that the wording is -just a sloppy form of "type that represents a [const] lvalue of T". But this is also problematic, -because basically all proxy reference expressions are rvalues. -

-It is unclear what the intention is. A straightward way of fixing this wording could make -X::[const_]reference identical to [const] T&. This holds for all Library containers -except for vector<bool>. -

-Another way of solving this definition problem would be to impose a requirement that holds for both -references and reference-like proxies. Both X::reference and X::const_reference -would need to be convertible to const T&. Additionally X::reference would need to -support for a mutable container an assignment expression of the form -declval<X::reference>() = declval<T>() (this presentation intentionally does not require -declval<X::reference&>() = declval<T>()). -

-Further, the Table 96 does not impose any relations between X::reference and X::const_reference. -It seems that at least X::reference needs to be convertible to X::const_reference. -

-A related question is whether X::reference is supposed to be a mutable reference-like type, -irrespective of whether the container is an immutable container or not. The way, type match_results -defines reference identical to const_reference indicates one specific interpretation (similarly, -the initializer_list template also defines member type reference equal to const value_type&). -Note that this can be a different decision as that for iterator and const_iterator, -e.g. for sets the type X::reference still is a mutable reference, even though iterator -is described as constant iterator. -

-The proposed resolution is incomplete in regard to the last question. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-Alisdair notes that this looks like wording in the right direction. Wonders about congruence of these -typedefs and the similar ones for iterators. -

- -

[2013-09 Chicago]

- -

-Moved to Ready. -

-

-Consensus that the requirements should require real references, just like iterators, as containers are -required to support at least ForwardIterators, which have the same restriction on references. -

- -

-Matt will file a new issue for some additional concerns with regex match_results. -

- -

[2014-02-10, Daniel comments]

- - -

-The new issue opened by Matt is LWG 2306. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- -

-Issue should have been Ready in pre-meeting mailing. -

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change Table 96 — "Container requirements" as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table p6 — Container requirements
    ExpressionReturn typeOperational
    Semantics    		Assertion/note
    pre-/post-condition    		Complexity
    -X::reference - -lvalue of T& - -  - - -compile time -
    -X::const_reference - -const lvalue ofconst T& - -  - - -compile time -
    - -
    2. -
- - - - - -
-

2185. Missing throws clause for future/shared_future::wait_for/wait_until

-

Section: 30.6.6 [futures.unique_future], 30.6.7 [futures.shared_future] Status: C++14 - Submitter: Vicente J. Botet Escriba Opened: 2012-09-20 Last modified: 2015-04-08

-

View all other issues in [futures.unique_future].

-

View all issues with C++14 status.

-

Discussion:

- -

-The functions future::wait_for, future::wait_until, shared_future::wait_for, and -shared_future::wait_for can throw any timeout-related exceptions. It would be better if the wording -could be more explicit. This is in line with the changes proposed in LWG 2093's Throws element -of condition_variable::wait with predicate. -

- -

[2012, Portland: move to Review]

- -

-The phrase timeout-related exception does not exist. -

-

2093 was put in review, and there is some dependency here with this issue. -

-

If you provide a user-defined clock that throws, we need to put back an exception to allow that to be done. -

-

-We will put this in review and say that this cannot go in before 2093. -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

[This resolution should not be adopted before resolving 2093]

- - -

[This wording is relative to N3376.]

- - -
    -

  1. Change 30.6.6 [futures.unique_future] as indicated:

    -
    -template <class Rep, class Period>
-future_status wait_for(const chrono::duration<Rep, Period>& rel_time) const;
-

    --21- Effects: none if the shared state contains a deferred function (30.6.8 [futures.async]), otherwise -blocks until the shared state is ready or until the relative timeout (30.2.4 [thread.req.timing]) specified by -rel_time has expired. -

    --22- Returns: […] -

    --??- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -template <class Clock, class Duration>
-future_status wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
-

    --23- Effects: none if the shared state contains a deferred function (30.6.8 [futures.async]), otherwise -blocks until the shared state is ready or until the absolute timeout (30.2.4 [thread.req.timing]) specified by -abs_time has expired. -

    --24- Returns: […] -

    --??- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -
    2. - -

  2. Change 30.6.7 [futures.shared_future] as indicated:

    -
    -template <class Rep, class Period>
-future_status wait_for(const chrono::duration<Rep, Period>& rel_time) const;
-

    --23- Effects: none if the shared state contains a deferred function (30.6.8 [futures.async]), otherwise -blocks until the shared state is ready or until the relative timeout (30.2.4 [thread.req.timing]) specified by -rel_time has expired. -

    --24- Returns: […] -

    --??- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -template <class Clock, class Duration>
-future_status wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
-

    --25- Effects: none if the shared state contains a deferred function (30.6.8 [futures.async]), otherwise -blocks until the shared state is ready or until the absolute timeout (30.2.4 [thread.req.timing]) specified by -abs_time has expired. -

    --26- Returns: […] -

    --??- Throws: timeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -
    3. - -
- - - - - - -
-

2186. Incomplete action on async/launch::deferred

-

Section: 30.6.8 [futures.async] Status: C++14 - Submitter: Vicente J. Botet Escriba Opened: 2012-09-20 Last modified: 2015-04-08

-

View all other issues in [futures.async].

-

View all issues with C++14 status.

-

Discussion:

- -

-The description of the effects of async when the launch policy is launch::deferred doesn't -state what is done with the result of the deferred function invocation and the possible exceptions as it is done -for the asynchronous function when the policy is launch::async. -

- -

[2012, Portland: move to Open]

- -

-Detlef: agree with the problem but not with the resolution. The wording should be applied to all launch policies - rather than having to be separately specified for each one. -

-

-Hans: we should redraft to factor out the proposed text outside the two bullets. Needs to be carefully worded to - be compatible with the resolution of 2120 (see above). -

-

-Moved to open -

- -

[Issaquah 20014-10-11: Move to Immediate after SG1 review]

- - - - -

Proposed resolution:

-

[This wording is relative to N3376.]

- - -
    -

  1. Change 30.6.8 [futures.async] p3 bullet 2 as indicated:

    -
    -template <class F, class... Args>
-future<typename result_of<typename decay<F>::type(typename decay<Args>::type...)>::type>
-async(F&& f, Args&&... args);
-template <class F, class... Args>
-future<typename result_of<typename decay<F>::type(typename decay<Args>::type...)>::type>
-async(launch policy, F&& f, Args&&... args);
-

    --2- Requires: […] -

    --3- Effects:: The first function behaves the same as a call to the second function with a policy argument of -launch::async | launch::deferred and the same arguments for F and Args. […] The further -behavior of the second function depends on the policy argument as follows (if more than one of these conditions -applies, the implementation may choose any of the corresponding policies): -

    -
      -

    • if policy & launch::async is non-zero […]

      • -

    • if policy & launch::deferred is non-zero — Stores DECAY_COPY(std::forward<F>(f)) -and DECAY_COPY(std::forward<Args>(args))... in the shared state. These copies of f and args -constitute a deferred function. Invocation of the deferred function evaluates INVOKE(std::move(g), std::move(xyz)) -where g is the stored value of DECAY_COPY(std::forward<F>(f)) and xyz is -the stored copy of DECAY_COPY(std::forward<Args>(args)).... Any return value is stored as the -result in the shared state. Any exception propagated from the execution of the deferred function is stored as the -exceptional result in the shared state. The shared state is not made ready until the function has completed. -The first call to a non-timed waiting function (30.6.4 [futures.state]) on an asynchronous return object referring -to this shared state shall invoke the deferred function in the thread that called the waiting function. Once evaluation -of INVOKE(std::move(g), std::move(xyz)) begins, the function is no longer considered deferred. -[Note: If this policy is specified together with other policies, such as when using a policy value of -launch::async | launch::deferred, implementations should defer invocation or the selection of the policy -when no more concurrency can be effectively exploited. — end note] -

      • -
    -
    -
    2. -
- - - - - - -
-

2187. vector<bool> is missing emplace and emplace_back member functions

-

Section: 23.3.7 [vector.bool] Status: C++14 - Submitter: Nevin Liber Opened: 2012-09-21 Last modified: 2015-04-08

-

View all other issues in [vector.bool].

-

View all issues with C++14 status.

-

Discussion:

- -

-It should have them so that it more closely matches the vector<T> interface, as this helps when -writing generic code. -

- -

[2012, Portland: Move to Tentatively Ready]

- -

-Question on whether the variadic template is really needed, but it turns out to be needed to support -emplace of no arguments. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change the class template vector<bool> synopsis, 23.3.7 [vector.bool] p1, as indicated:

    -
    -namespace std {
-  template <class Allocator> class vector<bool, Allocator> {
-  public:
-    […]
-    // modifiers:
-    template <class... Args> void emplace_back(Args&&... args);
-    void push_back(const bool& x);
-    void pop_back();
-    template <class... Args> iterator emplace(const_iterator position, Args&&... args);
-    iterator insert(const_iterator position, const bool& x);
-    […]
-  };
-}
-
    -
    2. -
- - - - - - -
-

2188. Reverse iterator does not fully support targets that overload operator&

-

Section: 24.5.1.3.5 [reverse.iter.opref] Status: C++14 - Submitter: Alisdair Meredith Opened: 2012-09-23 Last modified: 2015-04-08

-

View all other issues in [reverse.iter.opref].

-

View all issues with C++14 status.

-

Discussion:

-

-The specification for reverse_iterator::operator-> -returns the address of the object yielded by dereferencing -with operator*, but does not have the usual -wording about returning the true address of the object. As -reverse_iterator requires the adapted iterator have -at least the bidirectional iterator category, we know that -the returned reference is a true reference, and not a proxy, -hence we can use std::addressof on the reference -to get the right answer. -

-

-This will most likely show itself as an issue with a list -or vector of a type with such an overloaded operator, -where algorithms are likely to work with a forward iteration, but -not with reverse iteration. -

- -

[2013-04-20, Bristol]

- - -

-Resolution: Goes to open now and move to review as soon as Daniel proposes a new wording. -

- -

[2014-02-12 Issaquah meeting]

- -

-Use std::addressof as the library uses elsewhere, then move as Immediate. -

- - - -

Proposed resolution:

-

-Revise 24.5.1.3.5 [reverse.iter.opref] p1, as indicated: -

-

-Returns: addressof&(operator*()). -

- - - - - -
-

2190. Condition variable specification

-

Section: 30.5 [thread.condition] Status: C++14 - Submitter: Hans Boehm Opened: 2012-09-25 Last modified: 2015-04-08

-

View all other issues in [thread.condition].

-

View all issues with C++14 status.

-

Discussion:

- -

-The condition variable specification possibly leaves it unclear whether the effect of a notify_one() -call can effectively be delayed, so that a call unblocks a wait() call that happens after the -notify_one call. (For notify_all() this is not detectable, since it only results in spurious -wake-ups.) Although this may at first glance seem like a contrived interpretation, it gains relevance since -glibc in fact allows the analogous behavior (see here) -and it is currently controversial whether this is correct and the Posix specification allows it (see -here). -

-

-The following proposed resolution disallows the glibc implementation, remaining consistent with the believed intent of C++11. -To make that clear, we require that the "unspecified total order" O from 30.5 [thread.condition] p4 be -consistent with happens-before. We also intend that the 3 components of a wait occur in order in O, -but stating that explicitly seems too pedantic. Since they are numbered, it appears clear enough that they are -sequenced one after the other. -

-

-Another uncertainty with the current phrasing is whether there is a single total order that includes all c.v. -accesses, or one total order per c.v. We believe it actually doesn't matter, because there is no way to tell the -difference, but this requires a bit more thought. We resolved it one way, just to remove the potential ambiguity. -

- -

[2012, Portland: Move to Review]

- -

-This is linked to a glibc issue, and -a POSIX specification issue. -

- -

-We believe the proposed wording fixes the ambiguity in C++ and is compatible with the proposed resolution -for Posix (which confirms the glibc behaviour as illegal). -

- -

-Moved to review (Detlef hopes to send some improved wording to the reflector). -

- -

[2013-04-20, Bristol]

- -

Accepted for the working paper

- - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 30.5 [thread.condition] p4 as indicated:

    -

    --4- The implementation shall behave as if all executions of notify_one, notify_all, -and each part of the wait, wait_for, and wait_until executions are executed in -somea single unspecified total order consistent with the "happens before" order. -

    -
    2. -
- - - - - -
-

2193. Default constructors for standard library containers are explicit

-

Section: 23 [containers] Status: C++14 - Submitter: Richard Smith Opened: 2012-10-04 Last modified: 2015-04-08

-

View other active issues in [containers].

-

View all other issues in [containers].

-

View all issues with C++14 status.

-

Discussion:

- -

-Most (all?) of the standard library containers have explicit default constructors. Consequently: -

-
-std::set<int> s1 = { 1, 2 }; // ok
-std::set<int> s2 = { 1 }; // ok
-std::set<int> s3 = {}; // ill-formed, copy-list-initialization selected an explicit constructor
-
-

-Note that Clang + libc++ rejects the declaration of s3 for this reason. This cannot possibly match the intent. -

-

-Suggested fix: apply this transformation throughout the standard library: -

-
-set() : set(Compare()) {}
-explicit set(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
- -

[ -2012-10-06: Daniel adds concrete wording. -]

- - -

[2012, Portland: Move to Open]

- -

-This may be an issue better solved by a core language tweak. Throw the issue over to EWG and see whether they -believe the issue is better resolved in Core or Library. -

- -

-AJM suggest we spawn a new status of 'EWG' to handle such issues - and will move this issue appropriately when -the software can record such resolutions. -

- -

[2013-08-27, Joaquín M López Muñoz comments:]

- - -

-For the record, I'd like to point out that the resolution proposed by the submitter, namely replacing -

- -
-explicit basic_string(const Allocator& a = Allocator());
-
- -

-by -

- -
-basic_string() : basic_string(Allocator()) {}
-explicit basic_string(const Allocator& a);
-
- -

-(and similarly for other container and container-like classes) might introduce a potential -backwards-compatibility problem related with explicit instantiation. Consider for instance -

- -
-struct my_allocator
-{
-  my_allocator(...); // no default ctor
-  ...
-};
-
-template class std::basic_string<char, std::char_traits<char>, my_allocator<char>>;
-
- -

-This (which I understand is currently a valid explicit instantiation of std::basic_string) will break if -std::basic_string ctors are modified as proposed by this issue, since my_allocator doesn't have -a default ctor. -

- -

[2013-10-06, Daniel comments:]

- - -

-Issue 2303 describes the more general problem related to explicit instantiation requests in the current -library and may help to solve this problem here as well. -

- -

[2014-02-13, Issaquah, Jonathan revises wording]

- - -

Previous resolution from Daniel [SUPERSEDED]:

- -
- -

This wording is relative to N3376.

- -

The more general criterion for performing the suggested transformation was: Any type with an initializer-list -constructor that also has an explicit default constructor.

- -
    -

  1. Change class template basic_string synopsis, 21.4 [basic.string] p5 as indicated:

    -
    -basic_string() : basic_string(Allocator()) {}
-explicit basic_string(const Allocator& a = Allocator());
-
    -
    2. - -

  2. Change 21.4.2 [string.cons] before p1 as indicated:

    -
    -explicit basic_string(const Allocator& a = Allocator());
-
    -
    3. - -

  3. Change class template deque synopsis, 23.3.3.1 [deque.overview] p2 as indicated:

    -
    -deque() : deque(Allocator()) {}
-explicit deque(const Allocator& = Allocator());
-
    -
    4. - -

  4. Change 23.3.3.2 [deque.cons] before p1 as indicated:

    -
    -explicit deque(const Allocator& = Allocator());
-
    -
    5. - -

  5. Change class template forward_list synopsis, 23.3.4.1 [forwardlist.overview] p3 as indicated:

    -
    -forward_list() : forward_list(Allocator()) {}
-explicit forward_list(const Allocator& = Allocator());
-
    -
    6. - -

  6. Change 23.3.4.2 [forwardlist.cons] before p1 as indicated:

    -
    -explicit forward_list(const Allocator& = Allocator());
-
    -
    7. - -

  7. Change class template list synopsis, 23.3.5.1 [list.overview] p2 as indicated:

    -
    -list() : list(Allocator()) {}
-explicit list(const Allocator& = Allocator());
-
    -
    8. - -

  8. Change 23.3.5.2 [list.cons] before p1 as indicated:

    -
    -explicit list(const Allocator& = Allocator());
-
    -
    9. - -

  9. Change class template vector synopsis, 23.3.6.1 [vector.overview] p2 as indicated:

    -
    -vector() : vector(Allocator()) {}
-explicit vector(const Allocator& = Allocator());
-
    -
    10. - -

  10. Change 23.3.6.2 [vector.cons] before p1 as indicated:

    -
    -explicit vector(const Allocator& = Allocator());
-
    -
    11. - -

  11. Change class template specialization vector<bool> synopsis, 23.3.7 [vector.bool] p1 as indicated:

    -
    -vector() : vector(Allocator()) {}
-explicit vector(const Allocator& = Allocator());
-
    -
    12. - -

  12. Change class template map synopsis, 23.4.4.1 [map.overview] p2 as indicated:

    -
    -map() : map(Compare()) {}
-explicit map(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    13. - -

  13. Change 23.4.4.2 [map.cons] before p1 as indicated:

    -
    -explicit map(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    14. - -

  14. Change class template multimap synopsis, 23.4.5.1 [multimap.overview] p2 as indicated:

    -
    -multimap() : multimap(Compare()) {}
-explicit multimap(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    15. - -

  15. Change 23.4.5.2 [multimap.cons] before p1 as indicated:

    -
    -explicit multimap(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    16. - -

  16. Change class template set synopsis, 23.4.6.1 [set.overview] p2 as indicated:

    -
    -set() : set(Compare()) {}
-explicit set(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    17. - -

  17. Change 23.4.6.2 [set.cons] before p1 as indicated:

    -
    -explicit set(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    18. - -

  18. Change class template multiset synopsis, 23.4.7.1 [multiset.overview] p2 as indicated:

    -
    -multiset() : multiset(Compare()) {}
-explicit multiset(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    19. - -

  19. Change 23.4.7.2 [multiset.cons] before p1 as indicated:

    -
    -explicit multiset(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    20. - -

  20. Change class template unordered_map synopsis, 23.5.4.1 [unord.map.overview] p3 as indicated:

    -
    -unordered_map() : unordered_map(see below) {}
-explicit unordered_map(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    21. - -

  21. Change 23.5.4.2 [unord.map.cnstr] before p1 as indicated:

    -
    -unordered_map() : unordered_map(see below) {}
-explicit unordered_map(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    22. - -

  22. Change class template unordered_multimap synopsis, 23.5.5.1 [unord.multimap.overview] p3 as indicated:

    -
    -unordered_multimap() : unordered_multimap(see below) {}
-explicit unordered_multimap(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    23. - -

  23. Change 23.5.5.2 [unord.multimap.cnstr] before p1 as indicated:

    -
    -unordered_multimap() : unordered_multimap(see below) {}
-explicit unordered_multimap(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    24. - -

  24. Change class template unordered_set synopsis, 23.5.6.1 [unord.set.overview] p3 as indicated:

    -
    -unordered_set() : unordered_set(see below) {}
-explicit unordered_set(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    25. - -

  25. Change 23.5.6.2 [unord.set.cnstr] before p1 as indicated:

    -
    -unordered_set() : unordered_set(see below) {}
-explicit unordered_set(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    26. - -

  26. Change class template unordered_multiset synopsis, 23.5.7.1 [unord.multiset.overview] p3 as indicated:

    -
    -unordered_multiset() : unordered_multiset(see below) {}
-explicit unordered_multiset(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    27. - -

  27. Change 23.5.7.2 [unord.multiset.cnstr] before p1 as indicated:

    -
    -unordered_multiset() : unordered_multiset(see below) {}
-explicit unordered_multiset(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    28. -
- -
- -

[Issaquah 20014-10-11: Move to Immediate after final review]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -

The more general criterion for performing the suggested transformation was: Any type with an initializer-list -constructor that also has an explicit default constructor.

- -
    -

  1. Change class template basic_string synopsis, 21.4 [basic.string] p5 as indicated:

    -
    -basic_string() : basic_string(Allocator()) { }
-explicit basic_string(const Allocator& a = Allocator());
-
    -
    2. - -

  2. Change 21.4.2 [string.cons] before p1 as indicated:

    -
    -explicit basic_string(const Allocator& a = Allocator());
-
    -
    3. - -

  3. Change class template deque synopsis, 23.3.3.1 [deque.overview] p2 as indicated:

    -
    -deque() : deque(Allocator()) { }
-explicit deque(const Allocator& = Allocator());
-
    -
    4. - -

  4. Change 23.3.3.2 [deque.cons] before p1 as indicated:

    -
    -explicit deque(const Allocator& = Allocator());
-
    -
    5. - -

  5. Change class template forward_list synopsis, 23.3.4.1 [forwardlist.overview] p3 as indicated:

    -
    -forward_list() : forward_list(Allocator()) { }
-explicit forward_list(const Allocator& = Allocator());
-
    -
    6. - -

  6. Change 23.3.4.2 [forwardlist.cons] before p1 as indicated:

    -
    -explicit forward_list(const Allocator& = Allocator());
-
    -
    7. - -

  7. Change class template list synopsis, 23.3.5.1 [list.overview] p2 as indicated:

    -
    -list() : list(Allocator()) { }
-explicit list(const Allocator& = Allocator());
-
    -
    8. - -

  8. Change 23.3.5.2 [list.cons] before p1 as indicated:

    -
    -explicit list(const Allocator& = Allocator());
-
    -
    9. - -

  9. Change class template vector synopsis, 23.3.6.1 [vector.overview] p2 as indicated:

    -
    -vector() : vector(Allocator()) { }
-explicit vector(const Allocator& = Allocator());
-
    -
    10. - -

  10. Change 23.3.6.2 [vector.cons] before p1 as indicated:

    -
    -explicit vector(const Allocator& = Allocator());
-
    -
    11. - -

  11. Change class template specialization vector<bool> synopsis, 23.3.7 [vector.bool] p1 as indicated:

    -
    -vector() : vector(Allocator()) { }
-explicit vector(const Allocator& = Allocator());
-
    -
    12. - -

  12. Change class template map synopsis, 23.4.4.1 [map.overview] p2 as indicated:

    -
    -map() : map(Compare()) { }
-explicit map(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    13. - -

  13. Change 23.4.4.2 [map.cons] before p1 as indicated:

    -
    -explicit map(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    14. - -

  14. Change class template multimap synopsis, 23.4.5.1 [multimap.overview] p2 as indicated:

    -
    -multimap() : multimap(Compare()) { }
-explicit multimap(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    15. - -

  15. Change 23.4.5.2 [multimap.cons] before p1 as indicated:

    -
    -explicit multimap(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    16. - -

  16. Change class template set synopsis, 23.4.6.1 [set.overview] p2 as indicated:

    -
    -set() : set(Compare()) { }
-explicit set(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    17. - -

  17. Change 23.4.6.2 [set.cons] before p1 as indicated:

    -
    -explicit set(const Compare& comp = Compare(),
-             const Allocator& = Allocator());
-
    -
    18. - -

  18. Change class template multiset synopsis, 23.4.7.1 [multiset.overview] p2 as indicated:

    -
    -multiset() : multiset(Compare()) { }
-explicit multiset(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    19. - -

  19. Change 23.4.7.2 [multiset.cons] before p1 as indicated:

    -
    -explicit multiset(const Compare& comp = Compare(),
-                  const Allocator& = Allocator());
-
    -
    20. - -

  20. Change class template unordered_map synopsis, 23.5.4.1 [unord.map.overview] p3 as indicated:

    -
    -unordered_map();
-explicit unordered_map(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    21. - -

  21. Change 23.5.4.2 [unord.map.cnstr] before p1 as indicated:

    -
    -unordered_map() : unordered_map(size_type(see below)) { }
-explicit unordered_map(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    - --1- Effects: Constructs an empty unordered_map using the specified hash function, key equality func-
    -tion, and allocator, and using at least n buckets. If n is not provided, For the default constructor
    -the number of buckets is implementation-defined. max_load_factor() returns 1.0. -
    - -
    22. - -

  22. Change class template unordered_multimap synopsis, 23.5.5.1 [unord.multimap.overview] p3 as indicated:

    -
    -unordered_multimap();
-explicit unordered_multimap(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    23. - -

  23. Change 23.5.5.2 [unord.multimap.cnstr] before p1 as indicated:

    -
    -unordered_multimap() : unordered_multimap(size_type(see below)) { }
-explicit unordered_multimap(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    - --1- Effects: Constructs an empty unordered_multimap using the specified hash function, key equality
    -function, and allocator, and using at least n buckets. If n is not provided, For the default constructor
    -the number of buckets is implementation-defined. max_load_factor() returns 1.0. - -
    -
    24. - -

  24. Change class template unordered_set synopsis, 23.5.6.1 [unord.set.overview] p3 as indicated:

    -
    -unordered_set();
-explicit unordered_set(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    -
    25. - -

  25. Change 23.5.6.2 [unord.set.cnstr] before p1 as indicated:

    -
    -unordered_set() : unordered_set(size_type(see below)) { }
-explicit unordered_set(size_type n = see below,
-                       const hasher& hf = hasher(),
-                       const key_equal& eql = key_equal(),
-                       const allocator_type& a = allocator_type());
-
    - --1- Effects: Constructs an empty unordered_set using the specified hash function, key equality func-
    -tion, and allocator, and using at least n buckets. If n is not provided, For the default constructor
    -the number of buckets is implementation-defined. max_load_factor() returns 1.0. - -
    -
    26. - -

  26. Change class template unordered_multiset synopsis, 23.5.7.1 [unord.multiset.overview] p3 as indicated:

    -
    -unordered_multiset();
-explicit unordered_multiset(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    -
    27. - -

  27. Change 23.5.7.2 [unord.multiset.cnstr] before p1 as indicated:

    -
    -unordered_multiset() : unordered_multiset(size_type(see below)) { }
-explicit unordered_multiset(size_type n = see below,
-                            const hasher& hf = hasher(),
-                            const key_equal& eql = key_equal(),
-                            const allocator_type& a = allocator_type());
-
    - --1- Effects: Constructs an empty unordered_multiset using the specified hash function, key equality
    -function, and allocator, and using at least n buckets. If n is not provided, For the default constructor
    -the number of buckets is implementation-defined. max_load_factor() returns 1.0. - -
    -
    28. -
- - - - - - -
-

2194. Impossible container requirements for adaptor types

-

Section: 23.6 [container.adaptors] Status: C++14 - Submitter: Sebastian Mach Opened: 2012-10-05 Last modified: 2015-04-08

-

View all other issues in [container.adaptors].

-

View all issues with C++14 status.

-

Discussion:

- -

-The stack class template does not have an member type iterator, and therefore instantiations do not -meet the general container requirements as described in 23.2.1 [container.requirements.general]. But -23.6.1 [container.adaptors.general] p1 says: -

-

-The headers <queue> and <stack> define the container adaptors queue, -priority_queue, and stack. These container adaptors meet the requirements for sequence containers. -

-

-Since sequence containers is a subset of general containers, this imposes requirements on the container adaptors that -are not satisfied. -

-

-Daniel Krügler: The wording change was performed as an editorial reorganization as requested -by GB 116 occuring first in -N3242, as a side-effect it -does now make the previous implicit C++03 classification to [lib.sequences]/1 more obvious. As the NB comment -noticed, the adaptors really are not sequences nor containers, so this wording needs to be fixed. -The most simple way to realize that is to strike the offending sentence. -

- -

[ -Daniel adds concrete wording. -]

- - -

[2013-04-20, Bristol]

- - -

-Unanimous consensus that queue and stack are not meant to be sequences. -

-Decision: move to tentatively ready -

- -

[2013-09-29, Chicago]

- - -

-Apply to Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 23.6.1 [container.adaptors.general] p1 as indicated:

    -

    --1- The headers <queue> and <stack> define the container adaptors queue, -priority_queue, and stack. These container adaptors meet the requirements for sequence containers. -

    -
    2. -
- - - - - - -
-

2196. Specification of is_*[copy/move]_[constructible/assignable] unclear for non-referencable types

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-10-06 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

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-

Discussion:

- -

-The pre-conditions for the type is_copy_constructible allow for template argument types were the language forbids -forming a reference, namely void types and function types that have cv-qualifiers or a ref-qualifier. -

-But the current wording in Table 49 defining the predicate condition, -

-

-is_constructible<T, const T&>::value is true. -

-

-leaves it open whether such argument types would (a) create a well-formed instantiation of the trait template or if so (b) what -the outcome of the trait evaluation would be, as an example consider std::is_copy_constructible<void>. -

-Current implementations differ, e.g. gcc accepts the instantiation and returns a false result, VS 2012 -also accepts the instantiation but returns true. -

-I would suggest that the wording clarifies that the instantiation would be valid for these types and I also would strongly -prefer the outcome that the trait would always return false for these types. The latter seems rather natural -to me, because there is no way to define a variable of void type or of function type at all, so it would be surprising -to return a positive result for copy or move construction if no other construction could succeed. It is also not -possible to assign to a any of these values (because there is no way to form lvalues of them), so the same argumentation -can be applied to the is_copy/move_assignable traits as well. -

-To reduce the amount of wording changes and repetitions, I suggest to define the term referenceable type in -sub-clause 17.3 [definitions] or alternatively in the core language to describe types to which references -can be created via a typedef name. This definition corresponds to what the support concept ReferentType intended -to describe during concept time. -

-In addition, LWG issue 2101 can also take advantage of the definition of a referenceable type. -

-If the proposed resolution for LWG issue 2101 would be accepted, there is an alternative solution possible -with the same effects. Now we would be able to use the now always well-formed instantiation of -std::add_lvalue_reference to modify the current definition of is_copy_constructible to -

-

-is_constructible<T,
- typename add_lvalue_reference<
- typename add_const<T>::type>::type>::value is true. -

-

-and similar changes for the other affected traits. -

- -

[2012-10 Portland: Move to Open]

- -

-Referencable-type should be defined as "something that can be bound into a reference" or similar, -rather than a list of types where that is true today. We can then provide the list of known types -that cannot be bound as examples that do not qualify in a note. -

- -

-Otherwise we are happy with the wording. AJM to redraft the definition and move to Review. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Add the following new definition to 17.3 [definitions] as indicated:

    -

    referenceable type [defns.referenceable]

    -

    -An object type, a function type that does not have cv-qualifiers or a ref-qualifier, or a reference type. -[Note: The term describes a type to which a reference can be created, including reference types. — end note] -

    -
    2. - -

  2. Change Table 49 as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 49 — Type property predicates
    TemplateConditionPreconditions
    -template <class T>
    -struct is_copy_constructible; -    		 -For a referenceable type T, the same result as
    -is_constructible<T,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_move_constructible; -    		 -For a referenceable type T, the same result as
    -is_constructible<T,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -… -
    -template <class T>
    -struct is_copy_assignable; -    		 -For a referenceable type T, the same result as
    -is_assignable<T&,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_move_assignable; -    		 -For a referenceable type T, the same result as
    -is_assignable<T&,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -… -
    -template <class T>
    -struct is_trivially_copy_constructible; -    		 -For a referenceable type T, the same result as
    -is_trivially_constructible<T,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_trivially_move_constructible; -    		 -For a referenceable type T, the same result as
    -is_trivially_constructible<T,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -… -
    -template <class T>
    -struct is_trivially_copy_assignable; -    		 -For a referenceable type T, the same result as
    -is_trivially_assignable<T&,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_trivially_move_assignable; -    		 -For a referenceable type T, the same result as
    -is_trivially_assignable<T&,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -… -
    -template <class T>
    -struct is_nothrow_copy_constructible; -    		 -For a referenceable type T, the same result as
    -is_nothrow_constructible<T,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_nothrow_move_constructible; -    		 -For a referenceable type T, the same result as
    -is_nothrow_constructible<T,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -… -
    -template <class T>
    -struct is_nothrow_copy_assignable; -    		 -For a referenceable type T, the same result as
    -is_nothrow_assignable<T&,
    -const T&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    -template <class T>
    -struct is_nothrow_move_assignable; -    		 -For a referenceable type T, the same result as
    -is_nothrow_assignable<T&,
    -T&&>::value is true, otherwise false. -    		 -T shall be a complete type,
    -(possibly cv-qualified) void, or an
    -array of unknown bound. -
    - -
    3. -
- - - - - - -
-

2197. Specification of is_[un]signed unclear for non-arithmetic types

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++14 - Submitter: Daniel Krügler Opened: 2012-10-07 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with C++14 status.

-

Discussion:

- -

-The pre-conditions for the trait is_signed allow for any types as template arguments, -including non-arithmetic ones. -

-But the current wording in Table 49 defining the predicate condition, -

-
-is_arithmetic<T>::value && T(-1) < T(0)
-
-

-looks like real code and so leaves it open whether such argument types would create a well-formed -instantiation of the trait template or not. As written this definition would lead to a hard -instantiation error for a non-arithmetic type like e.g. -

-
-struct S {};
-
-

-I would suggest that the wording clarifies that the instantiation would be valid for such types as well, -by means of a specification that is not an exact code pattern. This also reflects how existing -implementations behave. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change Table 49 as indicated:

    - - - - - - - - - - - - - - - - - - - - - -
    Table 49 — Type property predicates
    TemplateConditionPreconditions
    -template <class T>
    -struct is_signed; -    		 -If is_arithmetic<T>::value && is true, the same result as
    -integral_constant<bool, T(-1) < T(0)>::value;
    -otherwise, false.     -    		 -  -
    -template <class T>
    -struct is_unsigned; -    		 -If is_arithmetic<T>::value && is true, the same result as
    -integral_constant<bool, T(0) < T(-1)>::value;
    -otherwise, false.     -    		 -  -
    - -
    2. -
- - - - - - -
-

2200. Data race avoidance for all containers, not only for sequences

-

Section: 23.2.2 [container.requirements.dataraces] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-10-17 Last modified: 2015-04-08

-

View all other issues in [container.requirements.dataraces].

-

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-

Discussion:

- -

-23.2.2 [container.requirements.dataraces]/2 says "[…] implementations are -required to avoid data races when the contents of the contained object in different -elements in the same sequence, excepting vector<bool>, are modified -concurrently." -

-

-This should say "same container" instead of "same sequence", to avoid -the interpretation that it only applies to sequence containers. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 23.2.2 [container.requirements.dataraces]/2 as indicated:

    -

    --2- Notwithstanding (17.6.5.9 [res.on.data.races]), implementations are required to avoid data races when -the contents of the contained object in different elements in the same sequencecontainer, -excepting vector<bool>, are modified concurrently. -

    --3- [Note: For a vector<int> x with a size greater than one, x[1] = 5 and -*x.begin() = 10 can be executed concurrently without a data race, but x[0] = 5 and -*x.begin() = 10 executed concurrently may result in a data race. As an exception to the general -rule, for a vector<bool> y, y[0] = true may race with y[1] = true. — end note ] -

    -
    2. -
- - - - - -
-

2203. scoped_allocator_adaptor uses wrong argument types for piecewise construction

-

Section: 20.13.4 [allocator.adaptor.members] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-10-19 Last modified: 2015-04-08

-

View all other issues in [allocator.adaptor.members].

-

View all issues with C++14 status.

-

Discussion:

- -

-In 20.13.4 [allocator.adaptor.members] paragraph 11 the effects -clause says a tuple should be constructed with inner_allocator_type(), -but that creates an rvalue which cannot bind to inner_allocator_type&, -and would also be wrong if this->inner_allocator() != inner_allocator_type(). -This could be considered editorial, since the current wording doesn't even compile. -

-

-Secondly, in the same paragraph, the tuple objects xprime and yprime -seem to be lvalues and might be constructed by copying x and y. This -prevents using scoped_allocator to construct pairs from arguments of -move-only types. I believe the tuple_cast() expressions should use -std::move(x) and std::move(y) to move from the incoming arguments -(which are passed by value to candidates for moving) and the final sentence of the paragraph -should be: -

-

-then calls OUTERMOST_ALLOC_TRAITS(*this)::construct(OUTERMOST (*this), p, piecewise_construct, -std::move(xprime), std::move(yprime)). -

-

-so that the objects are passed to std::pair's piecewise constructor as rvalues and -are eligible for moving into the constructor arguments. This could also be considered editorial, -as the current wording prevents certain uses which were intended to be supported. -

-I've implemented these changes and can confirm they allow code to work that can't be compiled -according to the current wording. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-The resolution looks good, with wording provided by a recent implementer. However, it will take more -time than the telecon allows to review with confidence, and we would like Pablo to at least take a -look over the resolution and confirm that it matches the design intent. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change 20.13.4 [allocator.adaptor.members] paragraph 11 as indicated:

    - -
    -

    --11- Effects: Constructs a tuple object xprime from x by the following rules: -

    -
      -

    • -If uses_allocator<T1, inner_allocator_type>::value is false and -is_constructible<T1, Args1...>::value is true, then xprime is x. -

      • - -

    • -Otherwise, if uses_allocator<T1, inner_allocator_type>::value is true and -is_constructible<T1, allocator_arg_t, inner_allocator_type, Args1...>::value is true, -then xprime is tuple_cat(tuple<allocator_arg_t, inner_allocator_type&>( allocator_arg, -inner_allocator_type()), std::move(x)). -

      • - -

    • -Otherwise, if uses_allocator<T1, inner_allocator_type>::value is true and -is_constructible<T1, Args1..., inner_allocator_type>::value is true, then xprime -is tuple_cat(std::move(x), -tuple<inner_allocator_type&>(inner_allocator_type())). -

      • - -

    • -Otherwise, the program is ill-formed. -

      • -
    -

    -and constructs a tuple object yprime from y by the following rules: -

    -
      -

    • -If uses_allocator<T2, inner_allocator_type>::value is false and -is_constructible<T2, Args2...>::value is true, then yprime is y. -

      • - -

    • -Otherwise, if uses_allocator<T2, inner_allocator_type>::value is true and -is_constructible<T2, allocator_arg_t, inner_allocator_type, Args2...>::value is true, -then yprime is tuple_cat(tuple<allocator_arg_t, inner_allocator_type&>( allocator_arg, -inner_allocator_type()), std::move(y)). -

      • - -

    • -Otherwise, if uses_allocator<T2, inner_allocator_type>::value is true and -is_constructible<T2, Args2..., inner_allocator_type>::value is true, then yprime -is tuple_cat(std::move(y), -tuple<inner_allocator_type&>(inner_allocator_type())). -

      • - -

    • -Otherwise, the program is ill-formed. -

      • -
    -

    -then calls OUTERMOST_ALLOC_TRAITS(*this)::construct(OUTERMOST(*this), p, -piecewise_construct, std::move(xprime), std::move(yprime)). -

    -
    -
    2. -
- - - - - -
-

2205. Problematic postconditions of regex_match and regex_search

-

Section: 28.11.2 [re.alg.match], 28.11.3 [re.alg.search] Status: C++14 - Submitter: Pete Becker Opened: 2012-10-24 Last modified: 2015-04-08

-

View all other issues in [re.alg.match].

-

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-

Discussion:

- -

-Table 142 lists post-conditions on the match_results object when a call to regex_match succeeds. -regex_match is required to match the entire target sequence. The post-condition for m[0].matched -is "true if a full match was found." Since these are conditions for a successful search which is, by definition, -a full match, the post-condition should be simply "true". -

-

-There's an analogous probem in Table 143: the condition for m[0].matched is "true if a match was found, -false otherwise." But Table 143 gives post-conditions for a successful match, so the condition should be simply -"true". -

-

-Furthermore, they have explicit requirements for m[0].first, m[0].second, and m[0].matched. -They also have requirements for the other elements of m, described as m[n].first, m[n].second, -and m[n].matched, in each case qualifying the value of n as "for n < m.size()". Since -there is an explicit description for n == 0, this qualification should be "for 0 < n < m.size()" -in all 6 places. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Change Table 142 as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 142 — Effects of regex_match algorithm
    ElementValue
    -… -
    -m[0].first - -first -
    -m[0].second - -last -
    -m[0].matched - -true if a full match was found. -
    -m[n].first - -For all integers 0 < n < m.size(), the start of the sequence -that matched sub-expression n.
    -Alternatively, if subexpression n did not participate in the match, then last. -
    -m[n].second - -For all integers 0 < n < m.size(), the end of the sequence that -matched sub-expression n.
    -Alternatively, if sub-expression n did not participate in the match, then last. -
    -m[n].matched - -For all integers 0 < n < m.size(), true if sub-expression -n participated in the match, false otherwise. -
    -
    2. - -

  2. Change Table 143 as indicated:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 143 — Effects of regex_search algorithm
    ElementValue
    -… -
    -m[0].first - -The start of the sequence of characters that matched the regular expression -
    -m[0].second - -The end of the sequence of characters that matched the regular expression -
    -m[0].matched - -true if a match was found, and false otherwise. -
    -m[n].first - -For all integers 0 < n < m.size(), the start of the sequence -that matched sub-expression n.
    -Alternatively, if subexpression n did not participate in the match, then last. -
    -m[n].second - -For all integers 0 < n < m.size(), the end of the sequence that -matched sub-expression n.
    -Alternatively, if sub-expression n did not participate in the match, then last. -
    -m[n].matched - -For all integers 0 < n < m.size(), true if sub-expression -n participated in the match, false otherwise. -
    -
    3. - -
- - - - - -
-

2207. basic_string::at should not have a Requires clause

-

Section: 21.4.5 [string.access] Status: C++14 - Submitter: Nevin Liber Opened: 2012-10-26 Last modified: 2015-04-08

-

View all other issues in [string.access].

-

View all issues with C++14 status.

-

Discussion:

- -

-basic_string::at() has a wide contract and should not have a "Requires" clause on it. -

- -

[2013-01-17, Juan Soulie comments]

- - -

This issue would also apply to every member function of basic_string that throws -out_of_range, and to some cases where a length_error can be thrown.

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-While this could simply move to Ready on inspection, there is concern that this will not be the -only such case. Alisdair volunteers to review clause 21/23 for more of such issues for Bristol, -and update the proposed resolution as necessary. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Remove 21.4.5 [string.access] p5:

    - -
    -const_reference at(size_type pos) const;
-reference at(size_type pos);
-
    -

    --5- Requires: pos < size() -

    --6- Throws: out_of_range if pos >= size(). -

    --7- Returns: operator[](pos). -

    -
    - -
    2. -
- - - - - - -
-

2209. assign() overspecified for sequence containers

-

Section: 23.3 [sequences] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-10-31 Last modified: 2015-04-08

-

View all other issues in [sequences].

-

View all issues with C++14 status.

-

Discussion:

- -

-DR 704 ensures allocator-aware containers can reuse existing -elements during copy/move assignment, and sequence containers can do -the same for assign(). -

-But apart from std::list (which was changed by DR 320) the sequence -containers define the Effects of assign() in terms of clear() followed -by insert. A user-defined allocator can easily tell whether all old -elements are cleared and then new elements inserted or whether existing elements are assigned -to, so those Effects clauses cannot be ignored via the as-if rule. -

-The descriptions of the assign() members for deque, forward_list and -vector should be removed. Their intended effects are entirely described by the -sequence container requirements table, and the specific definitions of them are worse than -redundant, they're contradictory (if the operations are defined in terms of erase and -insert then there's no need for elements to be assignable.) The descriptions of -assign() for list are correct but redundant, so should be removed too. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3376.

- -
    -

  1. Edit 23.3.3.2 [deque.cons] to remove everything after paragraph 10:

    - -
    -
    -template <class InputIterator>
-void assign(InputIterator first, InputIterator last);
-
    -
    -

    --11- Effects: -

    -
    -erase(begin(), end());
-insert(begin(), first, last);
-
    -
    - -
    -void assign(size_type n, const T& t);
-
    -
    -

    --12- Effects: -

    -
    -erase(begin(), end());
-insert(begin(), n, t);
-
    -
    -
    - -
    2. - -

  2. Edit 23.3.4.2 [forwardlist.cons] to remove everything after paragraph 10:

    - -
    -
    -template <class InputIterator>
-void assign(InputIterator first, InputIterator last);
-
    -
    -

    --11- Effects: clear(); insert_after(before_begin(), first, last); -

    -
    - -
    -void assign(size_type n, const T& t);
-
    -
    -

    --12- Effects: clear(); insert_after(before_begin(), n, t); -

    -
    -
    - -
    3. - -

  3. Edit 23.3.5.2 [list.cons] to remove everything after paragraph 10:

    - -
    -
    -template <class InputIterator>
-void assign(InputIterator first, InputIterator last);
-
    -
    -

    --11- Effects: Replaces the contents of the list with the range [first, last). -

    -
    - -
    -void assign(size_type n, const T& t);
-
    -
    -

    --12- Effects: Replaces the contents of the list with n copies of t. -

    -
    -
    - -
    4. - -

  4. Edit 23.3.6.2 [vector.cons] to remove everything after paragraph 10:

    - -
    -
    -template <class InputIterator>
-void assign(InputIterator first, InputIterator last);
-
    -
    -

    --11- Effects: -

    -
    -erase(begin(), end());
-insert(begin(), first, last);
-
    -
    - -
    -void assign(size_type n, const T& t);
-
    -
    -

    --12- Effects: -

    -
    -erase(begin(), end());
-insert(begin(), n, t);
-
    -
    -
    - -
    5. - -
- - - - - - -
-

2210. Missing allocator-extended constructor for allocator-aware containers

-

Section: 23.3 [sequences], 23.4 [associative], 23.5 [unord] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-11-01 Last modified: 2015-04-08

-

View all other issues in [sequences].

-

View all issues with C++14 status.

-

Discussion:

- -

-The forward_list(size_type) constructor has no allocator-extended -equivalent, preventing the following code from compiling: -

-
-#include <forward_list>
-#include <vector>
-#include <scoped_allocator>
-
-using namespace std;
-
-int main()
-{
-  using list = forward_list<int>;
-  vector<list, scoped_allocator_adaptor<list::allocator_type>> v;
-  v.emplace_back(1u);
-}
-
-

-The very same problem exists for all allocator-aware sequence containers. -

-In addition it exists for associative containers. For example, it's possible to construct -std::set<int>{0, 1, 2} but not std::set<int>{{0, 1, 2}, alloc}, -and possible to construct std::set<int>{begin, end} but not -std::set<int>{begin, end, alloc}. -

-This makes the following program fail when SCOPED is defined: -

-
-#include <set>
-#include <vector>
-#include <scoped_allocator>
-
-#if SCOPED
-using A = std::scoped_allocator_adaptor<std::allocator<int>>;
-#else
-using A = std::allocator<int>;
-#endif
-
-int main()
-{
-  int values[] = {0, 1, 2};
-  std::vector<std::set<int>, A> v;
-  v.emplace_back(std::begin(values), std::end(values));
-}
-
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-Jonathan: There are lots of places where this is missing. -

-

-Howard: We should ping Pablo, this might be a deliberate design decision. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit the synopsis in 23.3.3.1 [deque.overview]/2:

    - -
    -
    -namespace std {
-  template <class T, class Allocator = allocator<T> >
-  class deque {
-  public:
-    […]
-    explicit deque(const Allocator& = Allocator());
-    explicit deque(size_type n, const Allocator& = Allocator());
-    […]
-  };
-}
-
    -
    -
    2. - -

  2. Edit 23.3.3.2 [deque.cons]/2:

    - -
    -
    -explicit deque(size_type n, const Allocator& = Allocator());
-
    -
    -

    --3- Effects: Constructs a deque with n default-inserted elements -using the specified allocator. -

    -
    -
    -
    3. - -

  3. Edit the synopsis in 23.3.4.1 [forwardlist.overview]/3:

    - -
    -
    -namespace std {
-  template <class T, class Allocator = allocator<T> >
-  class forward_list {
-  public:
-    […]
-    explicit forward_list(const Allocator& = Allocator());
-    explicit forward_list(size_type n, const Allocator& = Allocator());
-    […]
-  };
-}
-
    -
    -
    4. - -

  4. Edit 23.3.4.2 [forwardlist.cons]/3:

    - -
    -
    -explicit forward_list(size_type n, const Allocator& = Allocator());
-
    -
    -

    --3- Effects: Constructs a forward_list object with n default-inserted elements -using the specified allocator. -

    -
    -
    -
    5. - -

  5. Edit the synopsis in 23.3.5.1 [list.overview]/2:

    - -
    -
    -namespace std {
-  template <class T, class Allocator = allocator<T> >
-  class list {
-  public:
-    […]
-    explicit list(const Allocator& = Allocator());
-    explicit list(size_type n, const Allocator& = Allocator());
-    […]
-  };
-}
-
    -
    -
    6. - -

  6. Edit 23.3.5.2 [list.cons]/3:

    - -
    -
    -explicit list(size_type n, const Allocator& = Allocator());
-
    -
    -

    --3- Effects: Constructs a list with n default-inserted elements -using the specified allocator. -

    -
    -
    -
    7. - -

  7. Edit the synopsis in 23.3.6.1 [vector.overview]/2:

    - -
    -
    -namespace std {
-  template <class T, class Allocator = allocator<T> >
-  class vector {
-  public:
-    […]
-    explicit vector(const Allocator& = Allocator());
-    explicit vector(size_type n, const Allocator& = Allocator());
-    […]
-  };
-}
-
    -
    -
    8. - -

  8. Edit 23.3.6.2 [vector.cons]/3:

    - -
    -
    -explicit vector(size_type n, const Allocator& = Allocator());
-
    -
    -

    --3- Effects: Constructs a vector with n default-inserted elements -using the specified allocator. -

    -
    -
    -
    9. - -

  9. Edit the synopsis in 23.3.7 [vector.bool]/1:

    - -
    -
    -namespace std {
-  template <class Allocator> class vector<bool, Allocator> {
-  class vector {
-  public:
-    […]
-    explicit vector(const Allocator& = Allocator());
-    explicit vector(size_type n, const Allocator& = Allocator());
-    explicit vector(size_type n, const bool& value = bool(),
-                    const Allocator& = Allocator());
-    […]
-  };
-}
-
    -
    -
    10. - -

  10. Add to the synopsis in 23.4.4.1 [map.overview] p2:

    - -
    -
    -namespace std {
-  template <class Key, class T, class Compare = less<Key>,
-    class Allocator = allocator<pair<const Key, T> > > {
-  class map {
-  public:
-    […]
-    map(initializer_list<value_type>,
-      const Compare& = Compare(),
-      const Allocator& = Allocator());
-    template <class InputIterator>
-    map(InputIterator first, InputIterator last, const Allocator& a)
-      : map(first, last, Compare(), a) { }
-    map(initializer_list<value_type> il, const Allocator& a)
-      : map(il, Compare(), a) { }
-    ~map();
-    […]
-  };
-}
-
    -
    -
    11. - -

  11. Add to the synopsis in 23.4.5.1 [multimap.overview] p2:

    - -
    -
    -namespace std {
-  template <class Key, class T, class Compare = less<Key>,
-    class Allocator = allocator<pair<const Key, T> > > {
-  class multimap {
-  public:
-    […]
-    multimap(initializer_list<value_type>,
-      const Compare& = Compare(),
-      const Allocator& = Allocator());
-    template <class InputIterator>
-    multimap(InputIterator first, InputIterator last, const Allocator& a)
-      : multimap(first, last, Compare(), a) { }
-    multimap(initializer_list<value_type> il, const Allocator& a)
-      : multimap(il, Compare(), a) { }
-    ~multimap();
-    […]
-  };
-}
-
    -
    -
    12. - -

  12. Add to the synopsis in 23.4.6.1 [set.overview] p2:

    - -
    -
    -namespace std {
-  template <class Key, class Compare = less<Key>,
-    class Allocator = allocator<Key> > {
-  class set {
-  public:
-    […]
-    set(initializer_list<value_type>,
-      const Compare& = Compare(),
-      const Allocator& = Allocator());
-    template <class InputIterator>
-    set(InputIterator first, InputIterator last, const Allocator& a)
-      : set(first, last, Compare(), a) { }
-    set(initializer_list<value_type> il, const Allocator& a)
-      : set(il, Compare(), a) { }
-    ~set();
-    […]
-  };
-}
-
    -
    -
    13. - -

  13. Add to the synopsis in 23.4.7.1 [multiset.overview] p2:

    - -
    -
    -namespace std {
-  template <class Key, class Compare = less<Key>,
-    class Allocator = allocator<Key> > {
-  class multiset {
-  public:
-    […]
-    multiset(initializer_list<value_type>,
-      const Compare& = Compare(),
-      const Allocator& = Allocator());
-    template <class InputIterator>
-    multiset(InputIterator first, InputIterator last, const Allocator& a)
-      : multiset(first, last, Compare(), a) { }
-    multiset(initializer_list<value_type> il, const Allocator& a)
-      : multiset(il, Compare(), a) { }
-    ~multiset();
-    […]
-  };
-}
-
    -
    -
    14. - -

  14. Add to the synopsis in 23.5.4.1 [unord.map.overview] p3:

    - -
    -
    -namespace std {
-  template <class Key, class T,
-    class Hash = hash<Key>,
-    class Pred = std::equal_to<Key>,
-    class Allocator = std::allocator<std::pair<const Key, T> > > {
-  class unordered_map {
-  public:
-    […]
-    unordered_map(initializer_list<value_type>,
-      size_type = see below,
-      const hasher& hf = hasher(),
-      const key_equal& eql = key_equal(),
-      const allocator_type& a = allocator_type());
-    unordered_map(size_type n, const allocator_type& a)
-      : unordered_map(n, hasher(), key_equal(), a) { }
-    unordered_map(size_type n, const hasher& hf, const allocator_type& a)
-      : unordered_map(n, hf, key_equal(), a) { }
-    template <class InputIterator>
-      unordered_map(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
-      : unordered_map(f, l, n, hasher(), key_equal(), a) { }
-    template <class InputIterator>
-      unordered_map(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
-	    const allocator_type& a)
-      : unordered_map(f, l, n, hf, key_equal(), a) { }
-    unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a)
-      : unordered_map(il, n, hasher(), key_equal(), a) { }
-    unordered_map(initializer_list<value_type> il, size_type n, const hasher& hf, 
-	  const allocator_type& a)
-      : unordered_map(il, n, hf, key_equal(), a) { }
-    ~unordered_map();
-    […]
-  };
-}
-
    -
    -
    15. - -

  15. Add to the synopsis in 23.5.5.1 [unord.multimap.overview] p3:

    - -
    -
    -namespace std {
-  template <class Key, class T,
-    class Hash = hash<Key>,
-    class Pred = std::equal_to<Key>,
-    class Allocator = std::allocator<std::pair<const Key, T> > > {
-  class unordered_multimap {
-  public:
-    […]
-    unordered_multimap(initializer_list<value_type>,
-      size_type = see below,
-      const hasher& hf = hasher(),
-      const key_equal& eql = key_equal(),
-      const allocator_type& a = allocator_type());
-    unordered_multimap(size_type n, const allocator_type& a)
-      : unordered_multimap(n, hasher(), key_equal(), a) { }
-    unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
-      : unordered_multimap(n, hf, key_equal(), a) { }
-    template <class InputIterator>
-      unordered_multimap(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
-      : unordered_multimap(f, l, n, hasher(), key_equal(), a) { }
-    template <class InputIterator>
-      unordered_multimap(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
-	    const allocator_type& a)
-      : unordered_multimap(f, l, n, hf, key_equal(), a) { }
-    unordered_multimap(initializer_list<value_type> il, size_type n, const allocator_type& a)
-      : unordered_multimap(il, n, hasher(), key_equal(), a) { }
-    unordered_multimap(initializer_list<value_type> il, size_type n, const hasher& hf, 
-	  const allocator_type& a)
-      : unordered_multimap(il, n, hf, key_equal(), a) { }
-    ~unordered_multimap();
-    […]
-  };
-}
-
    -
    -
    16. - -

  16. Add to the synopsis in 23.5.6.1 [unord.set.overview] p3:

    - -
    -
    -namespace std {
-  template <class Key,
-    class Hash = hash<Key>,
-    class Pred = std::equal_to<Key>,
-    class Allocator = std::allocator<Key> > {
-  class unordered_set {
-  public:
-    […]
-    unordered_set(initializer_list<value_type>,
-      size_type = see below,
-      const hasher& hf = hasher(),
-      const key_equal& eql = key_equal(),
-      const allocator_type& a = allocator_type());
-    unordered_set(size_type n, const allocator_type& a)
-      : unordered_set(n, hasher(), key_equal(), a) { }
-    unordered_set(size_type n, const hasher& hf, const allocator_type& a)
-      : unordered_set(n, hf, key_equal(), a) { }
-    template <class InputIterator>
-      unordered_set(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
-      : unordered_set(f, l, n, hasher(), key_equal(), a) { }
-    template <class InputIterator>
-      unordered_set(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
-	    const allocator_type& a)
-      : unordered_set(f, l, n, hf, key_equal(), a) { }
-    unordered_set(initializer_list<value_type> il, size_type n, const allocator_type& a)
-      : unordered_set(il, n, hasher(), key_equal(), a) { }
-    unordered_set(initializer_list<value_type> il, size_type n, const hasher& hf, 
-	  const allocator_type& a)
-      : unordered_set(il, n, hf, key_equal(), a) { }
-    ~unordered_set();
-    […]
-  };
-}
-
    -
    -
    17. - -

  17. Add to the synopsis in 23.5.7.1 [unord.multiset.overview] p3:

    - -
    -
    -namespace std {
-  template <class Key,
-    class Hash = hash<Key>,
-    class Pred = std::equal_to<Key>,
-    class Allocator = std::allocator<Key> > {
-  class unordered_multiset {
-  public:
-    […]
-    unordered_multiset(initializer_list<value_type>,
-      size_type = see below,
-      const hasher& hf = hasher(),
-      const key_equal& eql = key_equal(),
-      const allocator_type& a = allocator_type());
-    unordered_multiset(size_type n, const allocator_type& a)
-      : unordered_multiset(n, hasher(), key_equal(), a) { }
-    unordered_multiset(size_type n, const hasher& hf, const allocator_type& a)
-      : unordered_multiset(n, hf, key_equal(), a) { }
-    template <class InputIterator>
-      unordered_multiset(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
-      : unordered_multiset(f, l, n, hasher(), key_equal(), a) { }
-    template <class InputIterator>
-      unordered_multiset(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
-	    const allocator_type& a)
-      : unordered_multiset(f, l, n, hf, key_equal(), a) { }
-    unordered_multiset(initializer_list<value_type> il, size_type n, const allocator_type& a)
-      : unordered_multiset(il, n, hasher(), key_equal(), a) { }
-    unordered_multiset(initializer_list<value_type> il, size_type n, const hasher& hf, 
-	  const allocator_type& a)
-      : unordered_multiset(il, n, hf, key_equal(), a) { }
-    ~unordered_multiset();
-    […]
-  };
-}
-
    -
    -
    18. -
- - - - - - -
-

2211. Replace ambiguous use of "Allocator" in container requirements

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-11-07 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++14 status.

-

Discussion:

- -

-23.2.1 [container.requirements.general]/7 says: -

-

-All other constructors for these container types take an Allocator& argument -(17.6.3.5 [allocator.requirements]), an allocator whose value type is the same as the -container's value type. -

-

-This is a strange place to state the requirement on the allocator's -value_type, because the allocator is a property (and template -parameter) of the container type not of some of its constructors. -It's also unclear whether "Allocator&" refers to the concept (as -implied by the cross-reference to the allocator requirements in Clause 17) -or to the container's template parameter (as implied by the fact -it's shown as an lvalue-reference type.) I believe the latter is -intended, because those constructors can't take any model of the -allocator concept, they can only take the container's allocator_type. -

-I think it would be clearer to remove the value type requirement earlier -in the paragraph (Table 99 already imposes that requirement) and to make it clear -the constructor arguments are the container's allocator_type. There is -already a cross-reference to the allocator requirements earlier in the paragraph, -so it doesn't need to be repeated in another place where it causes confusion. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 23.2.1 [container.requirements.general] paragraph 7:

    - -
    -

    -Unless otherwise specified, all containers defined in this clause obtain memory using an allocator -(see 17.6.3.5 [allocator.requirements]). Copy constructors for these container types obtain an -allocator by calling allocator_traits<allocator_type>::select_on_container_copy_construction -on their first parameters. Move constructors obtain an allocator by move construction from the allocator -belonging to the container being moved. Such move construction of the allocator shall not exit via -an exception. All other constructors for these container types take an Allocator& argument -(17.6.3.5 [allocator.requirements]), an allocator whose value type is the same as the container's value -typea const allocator_type& argument. [Note: If an invocation of a -constructor uses the default value of an optional allocator argument, then the Allocator type -must support value initialization. — end note] A copy of this allocator is used for any -memory allocation performed, by these constructors and by all member functions, during the lifetime of each -container object or until the allocator is replaced. […] -

    -
    -
    2. -
- - - - - - -
-

2212. tuple_size for const pair request <tuple> header

-

Section: 20.2 [utility] Status: WP - Submitter: Alisdair Meredith Opened: 2012-11-09 Last modified: 2015-04-08

-

View other active issues in [utility].

-

View all other issues in [utility].

-

View all issues with WP status.

-

Discussion:

-

-The <utility> header declares sufficient of the tuple API to specialize -the necessary templates for pair, notably tuple_size and -tuple_element. However, it does not make available the partial specializations -that support cv-qualified template arguments, so while I can write the following after -including only <utility>: -

-
-#include <utility>
-
-using TestType = std::pair<int, int>;
-static_assert(2 == std::tuple_size<TestType>(), "Pairs have two elements");
-std::tuple_element<0, TestType>::type var{1};
-
-

-the following may fail to compile unless I also include <tuple>: -

-
-#include <utility>
-
-using TestType = const std::pair<int, int>;
-static_assert(2 == std::tuple_size<TestType>(), "Pairs have two elements");
-std::tuple_element<0, TestType>::type var{1};
-
-

-Note, however, that the latter may compile with some standard library implementations -but not others, leading to subtle portability issues. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Howard notes that we have the same issue with array, so any resolution should apply to that header too. -

- -

[2013-10-18 Daniel provides wording]

- - -

-The suggested wording uses a similar approach as we already have in 24.7 [iterator.range] to -ensure that the range access templates are available when at least one of an enumerated list of header files is -included. -

-I also think that the restricted focus on tuple_size of this issue is too narrow and should be extended to -the similar partial template specializations of tuple_element as well. Therefore the suggested wording -ensures this as well. -

- -

[2014-03-27 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on eight votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.4.2.5 [tuple.helper] as indicated:

    - -
    -template <class T> class tuple_size<const T>;
-template <class T> class tuple_size<volatile T>;
-template <class T> class tuple_size<const volatile T>;
-
    -

    --3- Let TS denote tuple_size<T> of the cv-unqualified type T. Then -each of the three templates shall meet the UnaryTypeTrait requirements (20.10.1) with a BaseCharacteristic of -

    -
    -integral_constant<size_t, TS::value>
-
    -

    --?- In addition to being available via inclusion of the <tuple> header, each of the three templates are -available when any of the headers <array> or <utility> are included. -

    -
    - -
    -template <size_t I, class T> class tuple_element<I, const T>;
-template <size_t I, class T> class tuple_element<I, volatile T>;
-template <size_t I, class T> class tuple_element<I, const volatile T>;
-
    -

    --?- Let TE denote tuple_element<I, T> of the cv-unqualified type T. -Then each of the three templates shall meet the TransformationTrait requirements (20.10.1) with a member typedef -type that names the following type: -

    -
      -

    • -for the first specialization, add_const<TE::type>::type, -

      • -

    • -for the second specialization, add_volatile<TE::type>::type, and -

      • -

    • -for the third specialization, add_cv<TE::type>::type. -

      • -
    -

    --?- In addition to being available via inclusion of the <tuple> header, each of the three templates are -available when any of the headers <array> or <utility> are included. -

    -
    -
    2. -
- - - - - - -
-

2213. Return value of std::regex_replace

-

Section: 28.11.4 [re.alg.replace] Status: C++14 - Submitter: Pete Becker Opened: 2012-11-08 Last modified: 2015-04-08

-

View all other issues in [re.alg.replace].

-

View all issues with C++14 status.

-

Discussion:

-

-In 28.11.4 [re.alg.replace], the first two variants of std::regex_replace take an output iterator named -"out" as their first argument. Paragraph 2 of that section says that the functions return "out". When I first implemented -this, many years ago, I wrote it to return the value of the output iterator after all the insertions (cf. std::copy), -which seems like the most useful behavior. But looking at the requirement now, it like the functions should return the -original value of "out" (i.e. they have to keep a copy of the iterator for no reason except to return it). Is that -really what was intended? -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 28.11.4 [re.alg.replace] as indicated:

    -
    -template <class OutputIterator, class BidirectionalIterator,
-  class traits, class charT, class ST, class SA>
-OutputIterator
-regex_replace(OutputIterator out, BidirectionalIterator first, BidirectionalIterator last,
-  const basic_regex<charT, traits>& e, const basic_string<charT, ST, SA>& fmt,
-  regex_constants::match_flag_type flags = regex_constants::match_default);
-template <class OutputIterator, class BidirectionalIterator,
-  class traits, class charT>
-OutputIterator
-regex_replace(OutputIterator out, BidirectionalIterator first, BidirectionalIterator last,
-  const basic_regex<charT, traits>& e, const charT* fmt,
-  regex_constants::match_flag_type flags = regex_constants::match_default);
-
    -

    --1- Effects: Constructs a regex_iterator object i as if by -regex_iterator<BidirectionalIterator, charT, traits> i(first, last, e, flags), -and uses i to enumerate through all of the matches m of type -match_results<BidirectionalIterator> that occur within the sequence [first, last). -If no such matches are found and !(flags & regex_constants ::format_no_copy) then calls -out = std::copy(first, last, out). If any matches are found then, for each such match, if -!(flags & regex_constants::format_no_copy), calls out = std::copy(m.prefix().first, -m.prefix().second, out), and then calls out = m.format(out, fmt, flags) -for the first form of the function and out = m.format(out, fmt, fmt + -char_traits<charT>::length(fmt), flags) for the second. Finally, if such a match is found -and !(flags & regex_constants ::format_no_copy), calls -out = std::copy(last_m.suffix().first, last_m.suffix().second, out) where -last_m is a copy of the last match found. If flags & regex_constants::format_first_only -is non-zero then only the first match found is replaced. -

    --2- Returns: out. -

    -
    -
    2. -
- - - - - - -
-

2217. operator==(sub_match, string) slices on embedded '\0's

-

Section: 28.9.2 [re.submatch.op] Status: WP - Submitter: Jeffrey Yasskin Opened: 2012-11-26 Last modified: 2015-04-08

-

View all other issues in [re.submatch.op].

-

View all issues with WP status.

-

Discussion:

- -
-template <class BiIter, class ST, class SA>
-  bool operator==(
-    const basic_string<
-      typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-    const sub_match<BiIter>& rhs);
-
-

-is specified as: -

-

-Returns: rhs.compare(lhs.c_str()) == 0. -

-

-This is odd because sub_match::compare(basic_string) is defined to -honor embedded '\0' characters. This could allow a sub_match to == or -!= a std::string unexpectedly. -

- -

[Daniel:]

- -

-This wording change was done intentionally as of LWG 1181, but the here mentioned slicing -effect was not considered at that time. It seems best to use another overload of compare to fix this problem: -

-

-Returns: rhs.str().compare(0, rhs.length(), lhs.data(), lhs.size()) == 0. -

-

-or -

-

-Returns: rhs.compare(sub_match<BiIter>::string_type(lhs.data(), lhs.size())) == 0. -

- -

[2013-10-17: Daniel provides concrete wording]

- - -

-The original wording was suggested to reduce the need to allocate memory during comparisons. The specification would be -very much easier, if sub_match would provide an additional compare overload of the form: -

-
-int compare(const value_type* s, size_t n) const;
-
-

-But given the fact that currently all of basic_string's compare overloads are defined in terms -of temporary string constructions, the following proposed wording does follow the same string-construction route as -basic_string does (where needed to fix the embedded zeros issue) and to hope that existing implementations -ignore to interpret this semantics in the literal sense. -

-I decided to use the second replacement form -

-
-Returns: rhs.compare(sub_match<BiIter>::string_type(lhs.data(), lhs.size())) == 0.
-
-

-because it already reflects the existing style used in 28.9.2 [re.submatch.op] p31. -

- - -

[2014-02-15 post-Issaquah session : move to Tentatively Ready]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 28.9.2 [re.submatch.op] as indicated:

    - -
    -template <class BiIter, class ST, class SA>
-  bool operator==(
-    const basic_string<
-      typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-    const sub_match<BiIter>& rhs);
-
    -

    --7- Returns: rhs.compare(lhs.c_str()typename sub_match<BiIter>::string_type(lhs.data(), lhs.size())) == 0. -

    -
    -

    -[…] -

    -
    -template <class BiIter, class ST, class SA>
-  bool operator<(
-    const basic_string<
-      typename iterator_traits<BiIter>::value_type, ST, SA>& lhs,
-    const sub_match<BiIter>& rhs);
-
    -

    --9- Returns: rhs.compare(lhs.c_str()typename sub_match<BiIter>::string_type(lhs.data(), lhs.size())) > 0. -

    -
    -

    -[…] -

    -
    -template <class BiIter, class ST, class SA>
-  bool operator==(const sub_match<BiIter>& lhs,
-                  const basic_string<
-                    typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-
    -

    --13- Returns: lhs.compare(rhs.c_str()typename sub_match<BiIter>::string_type(rhs.data(), rhs.size())) == 0. -

    -
    -

    -[…] -

    -
    -template <class BiIter, class ST, class SA>
-  bool operator<(const sub_match<BiIter>& lhs,
-                 const basic_string<
-                   typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);
-
    -

    --15- Returns: lhs.compare(rhs.c_str()typename sub_match<BiIter>::string_type(rhs.data(), rhs.size())) < 0. -

    -
    - -
    -
    -

    -

    -
    - -
    -
    -

    -

    -
    - -
    -
    -

    -

    -
    - -
    -
    -

    -

    -
    -
    2. -
- - - - - - -
-

2222. Inconsistency in description of forward_list::splice_after single-element overload

-

Section: 23.3.4.6 [forwardlist.ops] Status: C++14 - Submitter: Edward Catmur Opened: 2012-12-11 Last modified: 2015-04-08

-

View all other issues in [forwardlist.ops].

-

View all issues with C++14 status.

-

Discussion:

- -

-23.3.4.6 [forwardlist.ops] p6 has -

-
-void splice_after(const_iterator position, forward_list& x, const_iterator i);
-void splice_after(const_iterator position, forward_list&& x, const_iterator i);
-

-Effects: Inserts the element following i into *this, following position, -and removes it from x. The result is unchanged if position == i or position == ++i. -Pointers and references to *i continue to refer to the same element but as a member of *this. -Iterators to *i (including i itself) continue to refer to the same element, but now behave -as iterators into *this, not into x. -

-
-

-This overload splices the element following i from x to *this, so the -language in the two latter sentences should refer to ++i: -

-

-Pointers and references to *++i continue to refer to the same element but as a member of -*this. Iterators to *++i continue to refer to the same element, but now behave as iterators -into *this, not into x. -

-

-

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 23.3.4.6 [forwardlist.ops] p6 as indicated:

    -
    -void splice_after(const_iterator position, forward_list& x, const_iterator i);
-void splice_after(const_iterator position, forward_list&& x, const_iterator i);
-
    -

    --5- Requires: position is before_begin() or is a dereferenceable iterator -in the range [begin(),end()). The iterator following i is a dereferenceable iterator -in x. get_allocator() == x.get_allocator(). -

    --6- Effects: Inserts the element following i into *this, following position, -and removes it from x. The result is unchanged if position == i or position == ++i. -Pointers and references to *++i continue to refer to the same element but as a member of -*this. Iterators to *++i (including i itself) continue to -refer to the same element, but now behave as iterators into *this, not into x. -

    -
    2. -
- - - - - - -
-

2225. Unrealistic header inclusion checks required

-

Section: 17.6.2.2 [using.headers] Status: C++14 - Submitter: Richard Smith Opened: 2012-12-18 Last modified: 2015-04-08

-

View all other issues in [using.headers].

-

View all issues with C++14 status.

-

Discussion:

- -

-17.6.2.2 [using.headers]/3 says: -

-A translation unit shall include a header only outside of any external declaration or definition, and shall -include the header lexically before the first reference in that translation unit to any of the entities -declared in that header. -

-Per 1.4 [intro.compliance]/1, programs which violate this rule are ill-formed, and a conforming -implementation is required to produce a diagnostic. This does not seem to match reality. Presumably, this -paragraph is missing a "no diagnostic is required". -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Edit 17.6.2.2 [using.headers] p3 as indicated:

    -

    -3- A translation unit shall include a header only outside of any external declaration or definition, and shall -include the header lexically before the first reference in that translation unit to any of the entities declared -in that header. No diagnostic is required.

    -
    2. -
- - - - - - -
-

2228. Missing SFINAE rule in unique_ptr templated assignment

-

Section: 20.8.1.2.3 [unique.ptr.single.asgn] Status: Resolved - Submitter: Geoffrey Romer Opened: 2012-12-20 Last modified: 2015-05-06

-

View all other issues in [unique.ptr.single.asgn].

-

View all issues with Resolved status.

-

Discussion:

- -

-20.8.1.2.3 [unique.ptr.single.asgn]/5 permits unique_ptr's templated assignment operator to participate -in overload resolution even when incompatibilities between D and E will render the result ill-formed, -but the corresponding templated copy constructor is removed from the overload set in those situations (see the third -bullet point of 20.8.1.2.1 [unique.ptr.single.ctor]/19). This asymmetry is confusing, and presumably unintended; -it may lead to situations where constructing one unique_ptr from another is well-formed, but assigning from -the same unique_ptr would be ill-formed. -

-There is a slight coupling between this and LWG 2118, in that my PR for LWG 2118 incorporates -equivalent wording in the specification of the templated assignment operator for the array specialization; the two PRs -are logically independent, but if my PR for 2118 is accepted but the above PR is not, the discrepancy -between the base template and the specialization could be confusing. -

- -

-Previous resolution [SUPERSEDED]: -

-
-

This wording is relative to N3485.

-
    -

  1. Revise 20.8.1.2.3 [unique.ptr.single.asgn] p5 as follows:

    - -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
-
    -

    --4- Requires: If E is not a reference type, assignment of the deleter from an rvalue of type E -shall be well-formed and shall not throw an exception. Otherwise, E is a reference type and assignment of the -deleter from an lvalue of type E shall be well-formed and shall not throw an exception. -

    --5- Remarks: This operator shall not participate in overload resolution unless: -

    -
      -

    • unique_ptr<U, E>::pointer is implicitly convertible to pointer and

      • -

    • U is not an array type., and

      • -

    • either D is a reference type and E is the same type as D, or D is -not a reference type and E is implicitly convertible to D.

      • -
    -

    --6- Effects: Transfers ownership from u to *this as if by calling reset(u.release()) -followed by an assignment from std::forward<E>(u.get_deleter()). -

    --7- Returns: *this. -

    -
    - -
    2. -
- -
- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-The wording looks good, but we want a little more time than the telecon permits to be truly comfortable. -We expect this issue to resolve fairly easily in Bristol. -

- -

[2015-05-18, Howard comments]

- -

-Updated proposed wording has been provided in N4366. -

- -

[2015-05, Lenexa]

- -

-Straw poll: send N4366 to full committee, -with both fixes from the sections "What is the correct fix?" and "unique_ptr<T[]> needs the correct fix too" -

- - - -

Proposed resolution:

-

-Resolved by accepting N4366. -

- - - - - -
-

2229. Standard code conversion facets underspecified

-

Section: 22.5 [locale.stdcvt] Status: C++14 - Submitter: Beman Dawes Opened: 2012-12-30 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

The only specification for the non-inherited members of classes codecvt_utf8, -codecvt_utf16, and codecvt_utf8_utf16 is a comment line in the synopsis -that says // unspecified. There is no further indication of functionality, -so a user does not know if one of these classes can be constructed or destroyed.

- -

The proposed resolution adds a constructor that mimics the class codecvt -constructor, and also adds a destructor. Following the practice of class codecvt, -the semantics are not specified.

- -

The only existing implementation I could find was libc++, and it does supply the -proposed constructor and destructor for each of the three classes.

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-There was concern about the unspecified semantics - but that matches what is done in codecvt. -

-

-Jonathan: Should these constructor/destructors be public? Proposed wording is private. -Base class constructor is public. -

-

-Howard noted that other facets do not have specified constructors. -

-

-Alisdair noted that this whole section was new in C++11. -

-

-Howard suggested looking at section 22.3.1.1.2 [locale.facet]p2/p3 for more info. -

- -

[2013-04-18, Bristol]

- - - - -

Proposed resolution:

-

In [locale.stdcvt] paragraph 2, Header codecvt synopsis:

-
- 
template<class Elem, unsigned long Maxcode = 0x10ffff,
-  codecvt_mode Mode = (codecvt_mode)0>
-class codecvt_utf8
-  : public codecvt<Elem, char, mbstate_t> {
-  // unspecified
-public:
-  explicit codecvt_utf8(size_t refs = 0);
-  ~codecvt_utf8();
-  };
-
-template<class Elem, unsigned long Maxcode = 0x10ffff,
-  codecvt_mode Mode = (codecvt_mode)0>
-class codecvt_utf16
-  : public codecvt<Elem, char, mbstate_t> {
-  // unspecified
-public:
-  explicit codecvt_utf16(size_t refs = 0);
-  ~codecvt_utf16();
-  };
-
-template<class Elem, unsigned long Maxcode = 0x10ffff,
-  codecvt_mode Mode = (codecvt_mode)0>
-class codecvt_utf8_utf16
-  : public codecvt<Elem, char, mbstate_t> {
-  // unspecified
-public:
-  explicit codecvt_utf8_utf16(size_t refs = 0);
-  ~codecvt_utf8_utf16();
-  };
-
- - - - - -
-

2230. "see below" for initializer-list constructors of unordered containers

-

Section: 23.5 [unord] Status: WP - Submitter: Jonathan Wakely Opened: 2013-01-06 Last modified: 2015-04-08

-

View all other issues in [unord].

-

View all issues with WP status.

-

Discussion:

-

-The unordered_map class definition in 23.5.4.1 [unord.map.overview] declares an -initializer-list constructor that says "see below": -

- -
-unordered_map(initializer_list<value_type>,
-    size_type = see below,
-    const hasher& hf = hasher(),
-    const key_equal& eql = key_equal(),
-    const allocator_type& a = allocator_type());
-
- -

-But that constructor isn't defined below. The same problem exists for the other unordered associative containers. -

- -

[2013-09 Chicago]

- -

-STL: ordered are also missing declarations, but issue is forthcoming -

-Walter: how does adding a signature address issue? — nevermind -

-Jayson: in his wording, isn't he just dropping the size_type? -

-Walter: partial fix is to introduce the name -

-Stefanus: explanation of requiring name because of n buckets -

-STL: solution for his issue satisfies both ordered and unordered and is simplier than provided wording -

-STL: patches general table instead -

-STL: proposes adding extra rows instead of extra declarations -

-Stefanus: clarify n in the synopsis -

-Walter: general rule, name is optional in declaration -

-Stefanus: how to proceed -

-Walter: significant overlap with forthcoming issue, suggestion to defer -

- -

[2014-02-20 Re-open Deferred issues as Priority 4]

- - -

[2014-03-27 Jonathan improves proposed wording]

- - -

[2014-05-20 STL and Jonathan communicate]

- - -

-STL: With 2322 resolved, is there anything left for this issue to fix? -

-Jonathan: The synopsis still says "see below" and it's not immediately clear -that "see below" means "see the definition of a different constructor, -which defines the behaviour of this one due to a table defined much earlier". -

- -

[2014-05-23 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on five votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Edit 23.5.4.1 [unord.map.overview], class template unordered_map synopsis, as follows:

    - -
    -[…]
-unordered_map(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-[…]
-
    -
    2. - -

  2. Edit 23.5.4.2 [unord.map.cnstr] as follows:

    -
    -template <class InputIterator>
-unordered_map(InputIterator f, InputIterator l,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-unordered_map(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-
    -

    --3- Effects: Constructs an empty unordered_map using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -implementation-defined. Then inserts elements from the range [f, l) for the first form, or from the range -[il.begin(), il.end()) for the second form. max_load_factor() returns 1.0. -

    -
    -
    3. - -

  3. Edit 23.5.5.1 [unord.multimap.overview], class template unordered_multimap synopsis, as follows:

    - -
    -[…]
-unordered_multimap(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-[…]
-
    -
    4. - -

  4. Edit 23.5.5.2 [unord.multimap.cnstr] as follows:

    -
    -template <class InputIterator>
-unordered_multimap(InputIterator f, InputIterator l,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-unordered_multimap(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-
    -

    --3- Effects: Constructs an empty unordered_multimap using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -implementation-defined. Then inserts elements from the range [f, l) for the first form, or from the range -[il.begin(), il.end()) for the second form. max_load_factor() returns 1.0. -

    -
    -
    5. - -

  5. Edit 23.5.6.1 [unord.set.overview], class template unordered_set synopsis, as follows:

    - -
    -[…]
-unordered_set(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-[…]
-
    -
    6. - -

  6. Edit 23.5.6.2 [unord.set.cnstr] as follows:

    -
    -template <class InputIterator>
-unordered_set(InputIterator f, InputIterator l,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-unordered_set(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-
    -

    --3- Effects: Constructs an empty unordered_set using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -implementation-defined. Then inserts elements from the range [f, l) for the first form, or from the range -[il.begin(), il.end()) for the second form. max_load_factor() returns 1.0. -

    -
    -
    7. - -

  7. Edit 23.5.7.1 [unord.multiset.overview], class template unordered_multiset synopsis, as follows:

    - -
    -[…]
-unordered_multiset(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-[…]
-
    -
    8. - -

  8. Edit 23.5.7.2 [unord.multiset.cnstr] as follows:

    -
    -template <class InputIterator>
-unordered_multiset(InputIterator f, InputIterator l,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-unordered_multiset(initializer_list<value_type> il,
-  size_type n = see below,
-  const hasher& hf = hasher(),
-  const key_equal& eql = key_equal(),
-  const allocator_type& a = allocator_type());
-
    -

    --3- Effects: Constructs an empty unordered_multiset using the specified hash function, key equality function, -and allocator, and using at least n buckets. If n is not provided, the number of buckets is -implementation-defined. Then inserts elements from the range [f, l) for the first form, or from the range -[il.begin(), il.end()) for the second form. max_load_factor() returns 1.0. -

    -
    -
    9. -
- - - - - - -
-

2231. DR 704 removes complexity guarantee for clear()

-

Section: 23.2.3 [sequence.reqmts] Status: C++14 - Submitter: Jonathan Wakely Opened: 2012-12-30 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

View all issues with C++14 status.

-

Discussion:

-

-From the question at stackoverflow. -

- -

-Were we aware that the resolution to LWG 704 means there is no complexity guarantee for -clear() on most sequence containers? Previously it was implied by defining it in terms of -erase(begin(), end()) but we no longer do that. -

- -

-There are explicit complexity requirements for std::list::clear(), but not the other sequence containers. -

- -

Daniel:

- -

-The idea was that the notion of "destroys all elements in a" would imply a linear complexity, but the wording -needs to be clearer, because this doesn't say that this step is the actual complexity bound. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Tentatively Ready. -

- -

[2013-04-20 Bristol]

- - - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Change Table 100 as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 100 — Sequence container requirements (in addition to container) (continued)
    ExpressionReturn typeAssertion/note pre-/post-condition
    -… -
    -a.clear() - -void - -Destroys all elements in a. Invalidates all
    -references, pointers, and iterators referring to
    -the elements of a and may invalidate the
    -past-the-end iterator.
    -post: a.empty() returns true
    -complexity: linear -
    -… -
    -
    -
    2. - -
- - - - - - -
-

2233. bad_function_call::what() unhelpful

-

Section: 20.9.12.1 [func.wrap.badcall] Status: WP - Submitter: Jonathan Wakely Opened: 2013-01-05 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

-A strict reading of the standard implies std::bad_function_call{}.what() returns the same string as -std::exception{}.what() which doesn't help to know what happened if you catch an exception by reference -to std::exception. -

- -

-For consistency with bad_weak_ptr::what() it should return "bad_function_call". -

- -

-See c++std-lib-33515 for other details. -

- -

-There was a considerable support on the reflector to instead change the specification of both bad_weak_ptr::what() -and bad_function_call::what() to return an implementation-defined string instead. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Open. -

-

-Consensus that we want consistency in how this is treated. Less consensus on what the common -direction should be. -

-

-Alisdair to provide wording proposing that all string literals held by standard exception objects are -either unspecified, or implmentation defined. -

- -

[2014-02-15 Issauqah]

- -

-STL: I think it should be an implementation-defined NTBS, same on bad_weak_ptr. I will write a PR. -

- -

[2014-03-27, STL provides improved wording]

- - -

-The new wording reflects better the general agreement of the committee, see also issue 2376 for similar wording. -

- -

[2014-03-28 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on five votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Edit 20.9.12.1.1 [func.wrap.badcall.const]:

    -
    -bad_function_call() noexcept;
-
    -

    --1- Effects: constructs a bad_function_call object. -

    --?- Postconditions: what() returns an implementation-defined NTBS. -

    -
    -
    2. -
- - - - - - -
-

2235. Undefined behavior without proper requirements on basic_string constructors

-

Section: 21.4.2 [string.cons] Status: C++14 - Submitter: Juan Soulie Opened: 2013-01-17 Last modified: 2015-04-08

-

View all other issues in [string.cons].

-

View all issues with C++14 status.

-

Discussion:

-

-In 21.4.2 [string.cons], I believe tighter requirements should be imposed on basic_string's constructors -taking an s argument (or, a behavior should be provided for the undefined cases). -These requirements are properly stated in the other members functions taking s arguments (append, -assign, insert,...). -

- -
-basic_string(const charT* s, size_type n, const Allocator& a = Allocator());
-
- -

-Relative to N3485, 21.4.2 [string.cons]/6 says "Requires: s shall not be a null pointer and n < npos", -where it should say: "Requires: s points to an array of at least n elements of charT" -

- -
-basic_string(const charT* s, const Allocator& a = Allocator());
-
- -

-21.4.2 [string.cons]/8 says "Requires: s shall not be a null pointer.", where it should say: -"Requires: s points to an array of at least traits::length(s) + 1 elements of charT" -

- -

Daniel:

-

-I think that 17.6.4.9 [res.on.arguments] p1 b2 basically requires this already, but the wording is indeed worth -improving it. -

- -

[2013-03-15 Issues Teleconference]

- -

-Moved to Review. -

-

-The resolution could be worded more cleanly, and there is some concern about redundancy between -Requirements and Effects clauses. Consensus that we do want to say something like -this for the Requirements though. -

- -

[2013-04-18, Bristol]

- - -

Move to Ready

- -

[2013-09-29, Bristol]

- - -

Apply to the Working Paper

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -

  1. Change 21.4.2 [string.cons]/6 as indicated:

    - -
    -basic_string(const charT* s, size_type n, const Allocator& a = Allocator());
-
    -

    --6- Requires: s shall not be a null pointer and n < npospoints to an array -of at least n elements of charT. -

    -
    - -
    2. - -

  2. Change 21.4.2 [string.cons]/8 as indicated:

    - -
    -basic_string(const charT* s, const Allocator& a = Allocator());
-
    -

    --8- Requires: s shall not be a null pointerpoints to an array -of at least traits::length(s) + 1 elements of charT. -

    -
    - -
    3. -
- - - - - -
-

2239. min/max/minmax requirements

-

Section: 25.4.7 [alg.min.max] Status: WP - Submitter: Juan Soulie Opened: 2013-01-26 Last modified: 2015-05-22

-

View all other issues in [alg.min.max].

-

View all issues with WP status.

-

Discussion:

-

-25.4.7 [alg.min.max] requires type T in min, max, and minmax to be -LessThanComparable, but I don't believe this should be required for the versions that take a Compare -argument. -

-Paragraphs 1 to 4 of 25.4 [alg.sorting] should apply anyway, although I'm not sure about Compare -being required to induce a strict weak ordering here. -

-Further, min and max also lack formal complexity guarantees. -

- -

[2014-06-07 Daniel comments and provides wording]

- - -

-Certainly, the functions with Compare should not impose LessThanComparable requirements. -

-In regard to the question whether a strict weak ordering should be required as implied by the Compare -requirements, I would like to point out that this is requirement is in fact needed, because the specification of -the normative Remarks elements (e.g. "Returns the first argument when the arguments are equivalent.") do depend -on the existence of a equivalence relation that can be relied on and this is also consistent with the same -strict weak ordering requirement that is indirectly imposed by the LessThanComparable requirement set for -functions referring to operator< (Let me note that the very same StrictWeakOrder language -concept had intentionally been required for similar reasons during "concept-time" in -N2914). -

- -

[2015-02 Cologne]

- -

-JY: We have library-wide requirements that Comp induce a strict weak ordering. -

-JY/MC: The un-marked-up "Complexity" (p16) is wrong. DK: I'll fix that. -

-DK will update the wording for Lenexa. -

- -

[2015-03-30 Daniel comments]

- -

-The Complexity element of p16 is correct, but some others involving initializer_list arguments are wrong. -

- -

[2015-04-02 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 25.4.7 [alg.min.max] as indicated: -

    - -
    -
    -template<class T> constexpr const T& min(const T& a, const T& b);
-template<class T, class Compare>
-  constexpr const T& min(const T& a, const T& b, Compare comp);
-
    -
    -

    --1- Requires: For the first form, type T shall beType T is LessThanComparable -(Table 18). -

    --2- Returns: The smaller value. -

    --3- Remarks: Returns the first argument when the arguments are equivalent. -

    --?- Complexity: Exactly one comparison. -

    -
    - -
    -template<class T>
-  constexpr T min(initializer_list<T> t);
-template<class T, class Compare>
-  constexpr T min(initializer_list<T> t, Compare comp);
-
    -
    -

    --4- Requires: T is LessThanComparable andshall be CopyConstructible and -t.size() > 0. For the first form, type T shall be LessThanComparable. -

    --5- Returns: […] -

    --6- Remarks: […] -

    --?- Complexity: Exactly t.size() - 1 comparisons. -

    -
    - -
    -template<class T> constexpr const T& max(const T& a, const T& b);
-template<class T, class Compare>
-  constexpr const T& max(const T& a, const T& b, Compare comp);
-
    -
    -

    --7- Requires: For the first form, type T shall beType T is LessThanComparable -(Table 18). -

    --8- Returns: […] -

    --9- Remarks: […] -

    --?- Complexity: Exactly one comparison. -

    -
    - -
    -template<class T>
-  constexpr T max(initializer_list<T> t);
-template<class T, class Compare>
-  constexpr T max(initializer_list<T> t, Compare comp);
-
    -
    -

    --10- Requires: T is LessThanComparable andshall be CopyConstructible and -t.size() > 0. For the first form, type T shall be LessThanComparable. -

    --11- Returns: […] -

    --12- Remarks: […] -

    --?- Complexity: Exactly t.size() - 1 comparisons. -

    -
    - -
    -template<class T> constexpr pair<const T&, const T&> minmax(const T& a, const T& b);
-template<class T, class Compare>
-  constexpr pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
-
    -
    -

    --13- Requires: For the first form, tType T shall be LessThanComparable -(Table 18). -

    --14- Returns: […] -

    --15- Remarks: […] -

    --16- Complexity: Exactly one comparison. -

    -
    - -
    -template<class T>
-  constexpr pair<T, T> minmax(initializer_list<T> t);
-template<class T, class Compare>
-  constexpr pair<T, T> minmax(initializer_list<T> t, Compare comp);
-
    -
    -

    --17- Requires: T is LessThanComparable andshall be CopyConstructible and -t.size() > 0. For the first form, type T shall be LessThanComparable. -

    --18- Returns: […] -

    --19- Remarks: […] -

    --20- Complexity: At most (3/2) * t.size() applications of the corresponding predicate. -

    -
    - -
    -
    2. - -
- - - - - -
-

2240. Probable misuse of term "function scope" in [thread.condition]

-

Section: 30.5.1 [thread.condition.condvar], 30.5.2 [thread.condition.condvarany] Status: Resolved - Submitter: FrankHB1989 Opened: 2013-02-03 Last modified: 2015-04-08

-

View all other issues in [thread.condition.condvar].

-

View all issues with Resolved status.

-

Discussion:

-

-All usages of "function scope" in 30.5.1 [thread.condition.condvar] and 30.5.2 [thread.condition.condvarany], -such as 30.5.1 [thread.condition.condvar] p10 b4: -

- -

-If the function exits via an exception, lock.lock() shall be called prior to exiting the function scope. -

- -

-seem to be inappropriate compared to the actual core language definition of 3.3.5 [basic.funscope]: -

- -

-Labels (6.1) have function scope and may be used anywhere in the function in which they are declared. Only -labels have function scope. -

- -

-Probably the intended meaning is "outermost block scope of the function". -

- -

[2013-09 Chicago: Resolved by proposed resolution of LWG 2135]

- - - - -

Proposed resolution:

- -

-Resolved by proposed resolution of LWG 2135. -

- - - - - - -
-

2246. unique_ptr assignment effects w.r.t. deleter

-

Section: 20.8.1.2.3 [unique.ptr.single.asgn] Status: C++14 - Submitter: Jonathan Wakely Opened: 2013-03-13 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single.asgn].

-

View all issues with C++14 status.

-

Discussion:

- -

-The Effects clauses for unique_ptr assignment don't make sense, what -is the target of "an assignment from std::forward<D>(u.get_deleter())"? -

-Obviously it's intended to be the deleter, but that isn't stated clearly. -

- -

[2013-04-20, Bristol]

- -

Move to Ready

- -

[2013-09-29, Chicago]

- -

Apply to Working Paper

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -
  1. -

    -Edit 20.8.1.2.3 [unique.ptr.single.asgn] paragraph 2: -

    -
    -unique_ptr& operator=(unique_ptr&& u) noexcept;
-
    -

    -[…] -

    --2- Effects: Transfers ownership from u to *this as if by calling -reset(u.release()) followed by an assignment fromget_deleter() = std::forward<D>(u.get_deleter()). -

    -
    -
    2. - -
  2. -

    -Edit 20.8.1.2.3 [unique.ptr.single.asgn] paragraph 6: -

    -
    -template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
-
    -

    -[…] -

    --6- Effects: Transfers ownership from u to *this as if by calling -reset(u.release()) followed by an assignment fromget_deleter() = std::forward<E>(u.get_deleter()). -

    -
    -
    3. - -
- - - - - - -
-

2247. Type traits and std::nullptr_t

-

Section: 20.10.4.1 [meta.unary.cat] Status: C++14 - Submitter: Joe Gottman Opened: 2013-03-15 Last modified: 2015-05-22

-

View all issues with C++14 status.

-

Discussion:

- -

-According to 20.10.4.1 [meta.unary.cat], for every type T, exactly one of the primary type traits is true. -So which is true for the type std::nullptr_t? By 2.13.7 [lex.nullptr] std::nullptr_t is not a -pointer type or a pointer-to-member type, so is_pointer, is_member_object_pointer and -is_member_function_pointer can't be true for std::nullptr_t, and none of the other primary type traits -seem to apply. -

- -

[2013-04-20, Bristol]

- -

Rename to is_null_pointer, move to Ready

- -

Previous wording:

- -
-

This wording is relative to N3485.

- -
    -
  1. -

    -Edit 20.10.2 [meta.type.synop], header <type_traits> synopsis: -

    -
    -namespace std {
-  […]
-  // 20.9.4.1, primary type categories:
-  template <class T> struct is_void;
-  template <class T> struct is_nullptr;
-  template <class T> struct is_integral;
-  template <class T> struct is_floating_point;
-  […]
-}
-
    -
    2. - -
  2. -

    -Edit Table 47 — "Primary type category predicates" as indicated: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 47 — Primary type category predicates
    TemplateConditionComments
    -… -
    -template <class T>
    -struct is_nullptr;     -    		 -T is std::nullptr_t ([basic.fundamental]) - -  -
    -… -
    -
    - -
    3. - -
-
- -

[2013-09-29, Chicago]

- - -

Apply to the Working Paper

- - - -

Proposed resolution:

-

This wording is relative to N3485.

- -
    -
  1. -

    -Edit 20.10.2 [meta.type.synop], header <type_traits> synopsis: -

    -
    -namespace std {
-  […]
-  // 20.9.4.1, primary type categories:
-  template <class T> struct is_void;
-  template <class T> struct is_null_pointer;
-  template <class T> struct is_integral;
-  template <class T> struct is_floating_point;
-  […]
-}
-
    -
    2. - -
  2. -

    -Edit Table 47 — "Primary type category predicates" as indicated: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 47 — Primary type category predicates
    TemplateConditionComments
    -… -
    -template <class T>
    -struct is_null_pointer;     -    		 -T is std::nullptr_t ([basic.fundamental]) - -  -
    -… -
    -
    - -
    3. - -
- - - - - - -
-

2249. [CD] Remove gets from <cstdio>

-

Section: 27.9.2 [c.files] Status: Resolved - Submitter: Jonathan Wakely Opened: 2013-04-17 Last modified: 2015-04-08

-

View all other issues in [c.files].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses GB 9

- -

-In 27.9.2 [c.files] the current C++ standard claims that <cstdio> defines a -function called "gets" but it has no declaration or semantics, because it was removed from C11, -having been deprecated since C99. We should remove it for C++14. -

- -

[2013-09 Chicago]

- -

-Will resolve with the wording in the NB comment. -

- - - -

Proposed resolution:

- -

Resolved by resolution as suggested by NB comment GB 9

- - - - - - -
-

2252. Strong guarantee on vector::push_back() still broken with C++11?

-

Section: 23.3.6.5 [vector.modifiers] Status: C++14 - Submitter: Nicolai Josuttis Opened: 2013-04-21 Last modified: 2015-04-08

-

View other active issues in [vector.modifiers].

-

View all other issues in [vector.modifiers].

-

View all issues with C++14 status.

-

Discussion:

- -

-According to my understanding, the strong guarantee of push_back() led to the introduction of noexcept -and to the typical implementation that vectors usually copy their elements on reallocation unless the move operations of -their element type guarantees not to throw. -

-However, if I read the standard correctly, we still don't give the strong guarantee any more: -Yes, 23.2.1 [container.requirements.general]/10 specifies: -

-
-

-Unless otherwise specified (see 23.2.4.1, 23.2.5.1, 23.3.3.4, and 23.3.6.5) all container types defined in this -Clause meet the following additional requirements: -

-
    -
  • […]
    • -
  • if an exception is thrown by a push_back() or push_front() function, that function has no effects.
    • -
-
-

-However, 23.3.6.5 [vector.modifiers] specifies for vector modifiers, including push_back(): -

-
-

-If an exception is thrown other than by the copy constructor, move constructor, assignment operator, or move -assignment operator of T or by any InputIterator operation there are no effects. If an exception -is thrown by the move constructor of a non-CopyInsertable T, the effects are unspecified. -

-
-

-I would interpret this as an "otherwise specified" behavior for push_back(), saying that the strong guarantee -is only given if constructors and assignments do not throw. -

-That means, the strong guarantee of C++03 is broken with C++11. -

-In addition to all that 23.2.1 [container.requirements.general] p10 b2 doesn't mention the corresponding functions -emplace_back() and emplace_front(). These are similar single-element additions and should provide the same -strong guarantee. -

-Daniel adds: -

-It seems the error came in when N2350 -and N2345 became accepted and where -integrated into the working draft N2369. -The merge resulted in a form that changed the previous meaning and as far as I understand it, this effect was not intended. -

- -

[2013-09-16, Nico provides concrete wording]

- - -

[2013-09-26, Nico improves wording]

- - -

-The new proposed resolution is driven as follows: -

-
    -

  • In the container requirements section, there shall be general statements that single element insertions - and push_back(), pop_back, emplace_front(), and emplace_back() have no effect - on any exception. -

    - That is: we extend the first two statements by adding emplace_front() and emplace_back(), which - are missing. -

    -
    • -

  • Formulate only the exceptions from that (or where other general statements might - lead to the impression, that the blanket statement no longer applies):

    -
      -

    • remove the statement in list::push_back() saying again that exceptions have to effect.

      • -

    • Clarify that all single-element insertions at either end of a deque have the strong guarantee.

      • -

    • Clarify that all single-element insertions at the end of a vector have the strong guarantee.

      • -
    -
    • -
- - - - -

Proposed resolution:

- -

This wording is relative to N3691.

- -
    -

  1. Edit 23.2.1 [container.requirements.general] p10 b2 as indicated:

    - -
      -

    • -if an exception is thrown by an insert() or emplace() function while inserting a single element, that -function has no effects. -

      • -

    • -if an exception is thrown by a push_back() or, push_front(), emplace_back(), or -emplace_front() function, that function has no effects. -

      • -
    - -
    2. - -

  2. Edit 23.3.3.4 [deque.modifiers] as indicated:

    - -
    -
    iterator insert(const_iterator position, const T& x);
-iterator insert(const_iterator position, T&& x);
-iterator insert(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-  iterator insert(const_iterator position,
-                  InputIterator first, InputIterator last);
-iterator insert(const_iterator position, initializer_list<T>);
-template <class... Args> void emplace_front(Args&&... args);
-template <class... Args> void emplace_back(Args&&... args);
-template <class... Args> iterator emplace(const_iterator position, Args&&... args);
-void push_front(const T& x);
-void push_front(T&& x);
-void push_back(const T& x);
-void push_back(T&& x);
-
    -
    -

    --1- Effects: An insertion in the middle of the deque invalidates all the iterators and references to elements -of the deque. An insertion at either end of the deque invalidates all the iterators to the deque, but has -no effect on the validity of references to elements of the deque. -

    --2- Remarks: -If an exception is thrown other than by the copy constructor, move constructor, assignment -operator, or move assignment operator of T there are no effects. - -If an exception is thrown while inserting a single element at either end, there are no effects. - -IfOtherwise, if an exception is thrown by the move -constructor of a non-CopyInsertable T, the effects are unspecified. -

    --3- Complexity: The complexity is linear in the number of elements inserted plus the lesser of the distances -to the beginning and end of the deque. Inserting a single element either at the beginning or end of a -deque always takes constant time and causes a single call to a constructor of T. -

    -
    -
    3. - -

  3. Edit 23.3.6.5 [vector.modifiers] as indicated:

    - -
    -
    iterator insert(const_iterator position, const T& x);
-iterator insert(const_iterator position, T&& x);
-iterator insert(const_iterator position, size_type n, const T& x);
-template <class InputIterator>
-  iterator insert(const_iterator position, InputIterator first, InputIterator last);
-iterator insert(const_iterator position, initializer_list<T>);
-template <class... Args> void emplace_back(Args&&... args);
-template <class... Args> iterator emplace(const_iterator position, Args&&... args);
-void push_back(const T& x);
-void push_back(T&& x);
-
    -
    -

    --1- Remarks: Causes reallocation if the new size is greater than the old capacity. If no reallocation happens, -all the iterators and references before the insertion point remain valid. -If an exception is thrown other -than by the copy constructor, move constructor, assignment operator, or move assignment operator -of T or by any InputIterator operation there are no effects. - -If an exception is thrown while inserting a single element at the end and T is CopyInsertable -or is_nothrow_move_constructible<T>::value is true, there are no effects. - -IfOtherwise, if an exception is thrown by the move -constructor of a non-CopyInsertable T, the effects are unspecified. -

    --2- Complexity: The complexity is linear in the number of elements inserted plus the distance to the end -of the vector. -

    -
    -
    4. -
- - - - - - -
-

2257. Simplify container requirements with the new algorithms

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Marshall Clow Opened: 2013-05-29 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

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-

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-

Discussion:

-

-Currently (n3690) Table 96 says, in the row for "a == b", that the -Operational semantics are: -

-
- == is an equivalence relation.
- distance(a.begin(), a.end()) == distance(b.begin(), b.end()) && equal(a.begin(), a.end(),b.begin()) -
-

-Given the extension of equal for C++14, this can be simplified to: -

-
- == is an equivalence relation.
- equal(a.begin(), a.end(), b.begin(), b.end()) -
- -

[ -Alisdair notes that a similar edit would apply to the unordered containers requirements. -]

- - -

-Previous resolution from Marshall Clow: -

-
-

-Ammend the Operational Semantics for 23.2.1 [container.requirements.general], Table 96, row "a == b" -

-
- == is an equivalence relation.
- distance(a.begin(), a.end()) == distance(b.begin(), b.end()) && equal(a.begin(), a.end(), b.begin(), b.end()) -
- -

-Ammend 23.2.5 [unord.req] p12: -

-
-Two unordered containers a and b compare equal if a.size() == b.size() -and, for every equivalent-key group [Ea1,Ea2) obtained from a.equal_range(Ea1), -there exists an equivalent-key group [Eb1,Eb2) obtained from b.equal_range(Ea1), -such that distance(Ea1, Ea2) == distance(Eb1, Eb2) and -is_permutation(Ea1, Ea2, Eb1, Eb2) -returns true. For ... -
-
- -

[2013-09 Chicago]

- - -

-Marshall improves wording -

- -

[2013-09 Chicago (evening issues)]

- -

-Moved to ready, after confirming latest wording reflects the discussion earlier in the day. -

- - - -

Proposed resolution:

-
    -
  1. -

    -Ammend 23.2.1 [container.requirements.general], Table 96 as indicated: -

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 96 — Container requirements (continued)
    ExpressionReturn typeOperational
    semantics    		Assertion/note
    pre-/post-condition    		Complexity
    -… -
    -a == b - -convertible to bool - -== is an equivalence relation.
    -distance(a.begin(),
    -a.end()) ==
    -distance(b.begin(),
    -b.end()) &&
    -equal(a.begin(),
    -a.end(),
    -b.begin(), b.end())     -    		 -Requires: T is
    -EqualityComparable -    		 -Constant if a.size() != b.size(), linear otherwise -
    -… -
    -
    - -
    2. - -
  2. -

    -Ammend 23.2.5 [unord.req] p12: -

    -
    -Two unordered containers a and b compare equal if a.size() == b.size() -and, for every equivalent-key group [Ea1,Ea2) obtained from a.equal_range(Ea1), -there exists an equivalent-key group [Eb1,Eb2) obtained from b.equal_range(Ea1), -such that distance(Ea1, Ea2) == distance(Eb1, Eb2) and -is_permutation(Ea1, Ea2, Eb1, Eb2) -returns true. For […] -
    -
    3. - -

  3. Amend 23.3.4.1 [forwardlist.overview] p2:

    -

    --2- A forward_list satisfies all of the requirements of a container (Table 96), except that the size() member -function is not provided and operator== has linear complexity. […] -

    -
    4. -
- - - - - - -
-

2258. a.erase(q1, q2) unable to directly return q2

-

Section: 23.2.4 [associative.reqmts] Status: C++14 - Submitter: Geoff Alexander Opened: 2013-05-11 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Section 23.2.4 [associative.reqmts], Table 102, page 743 of the C++ 2011 Standard states that a.erase(q1, q2) -returns q2. The problem is that a.erase(q1, q2) cannot directly return q2 as the return type, -iterator, differs from that of q2, const_iterator. -

- -

[2013-09 Chicago (evening issues group)]

- -

-The wording looks good, but is worded slightly differently to how we say the same for sequence containers, and for unordered -associative containers. We should apply consistent wording in all three cases. -

-

-Alisdair to provide the wording. -

- -

[2014-02-12 Issaquah meeting]

- -

-Move a Immediate. -

- - - -

Proposed resolution:

-
    -

  1. In the specification of a.erase(q1, q2) in sub-clause 23.2.4 [associative.reqmts], Table 102 change as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements (in addition to container) (continued)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -a.erase(q1, q2) - -iterator - -erases all the elements in the range [q1,q2). Returns q2 -an iterator pointing to the element pointed to by q2 prior to any elements -being erased. If no such element exists, a.end() is returned. - -log(a.size()) + N where N has the value distance(q1, q2). -
    -… -
    -
    -
    2. - -
- - - - - - -
-

2263. Comparing iterators and allocator pointers with different const-character

-

Section: 17.6.3.5 [allocator.requirements], 23.2 [container.requirements] Status: C++14 - Submitter: Howard Hinnant Opened: 2013-06-25 Last modified: 2015-04-08

-

View other active issues in [allocator.requirements].

-

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-

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-

Discussion:

-

-This ancient issue 179 says one ought to be able to compare iterators with const_iterators -from any given container. I'm having trouble finding words that guarantee this in C++11. This impacts not only a -container's iterators, but also the allocator requirements in allocator.requirements] surrounding -pointer, const_pointer, void_pointer and const_void_pointer. E.g. can one -compare a pointer with a const_pointer? -

-Since allocator::pointer and const_pointer are required to be random access iterators, one could -expect that the 179 guarantees apply for them as well. -

- -

[ -Daniel comments: -]

- - -

-The wording for 179 was part of several working drafts (e.g. also in -N3092) over some time and suddenly got lost -in N3242, presumably by accident. Whatever we -decide for allocator pointers, I expect that we need to restore the 179 wording as part of the overall resolution: -

- -

Reinsert after 23.2 [container.requirements] p6:

- -
-

--6- begin() returns an iterator referring to the first element in the container. end() returns an iterator which -is the past-the-end value for the container. If the container is empty, then begin() == end(); -

--?- In the expressions -

-
-i == j
-i != j
-i < j
-i <= j
-i >= j
-i > j
-i - j
-
-

-where i and j denote objects of a container's iterator type, either or both may be replaced by an object -of the container's const_iterator type referring to the same element with no change in semantics. -

-
- -

[2014-02-13 Issaquah, Daniel comments and suggests wording]

- - -

-First, I didn't originally move the seemingly lost wording to the resolution section because I wanted to ensure that the -committee double-checks the reason of this loss. -

-Second, albeit restoring this wording will restore the comparability of const_iterator and iterator of -containers specified in Clause 23, but this alone would not imply that this guarantee automatically extends to -all other iterators, simply because there is no fundamental relation between a mutable iterator and a constant -iterator by itself. This relation only exists under specific conditions, for example for containers which provide two such -typedefs of that kind. Thus the wording restoration would not ensure that allocator pointer and -const_pointer would be comparable with each other. To realize that, we would need additional guarantees added -to the allocator requirements. In fact, it is crucial to separate these things, because allocators are not -restricted to be used within containers, they have their own legitimate use for other places as well (albeit containers -presumably belong to the most important use-cases), and this is also stated in the introduction of 17.6.3.5 [allocator.requirements], -where it says: -

-

-All of the string types (Clause 21), containers (Clause 23) (except array), string buffers and string streams (Clause 27), -and match_results (Clause 28) are parameterized in terms of allocators. -

- -

[2014-02-12 Issaquah meeting]

- -

-Move a Immediate. -

- - - -

Proposed resolution:

-
    -

  1. Insert after 17.6.3.5 [allocator.requirements] p4 as indicated:

    - -

    --4- An allocator type X shall satisfy the requirements of CopyConstructible (17.6.3.1). The X::pointer, -X::const_pointer, X::void_pointer, and X::const_void_pointer types shall satisfy the requirements -of NullablePointer (17.6.3.3). No constructor, comparison operator, copy operation, move operation, or -swap operation on these types shall exit via an exception. X::pointer and X::const_pointer shall also -satisfy the requirements for a random access iterator (24.2). -

    --?- Let x1 and x2 denote objects of (possibly different) types X::void_pointer, -X::const_void_pointer, X::pointer, or X::const_pointer. Then, x1 and x2 -are equivalently-valued pointer values, if and only if both x1 and x2 can be explicitly converted -to the two corresponding objects px1 and px2 of type X::const_pointer, using a sequence of -static_casts using only these four types, and the expression px1 == px2 evaluates to true. -

    -

    -Drafting note: This wording uses the seemingly complicated route via X::const_pointer, because these are (contrary to -X::const_void_pointer) random access iterators and we can rely here for dereferenceable values on the fundamental pointee -equivalence of 24.2.5 [forward.iterators] p6: -

    -

    -If a and b are both dereferenceable, then a == b if and only if *a and *b are -bound to the same object. -

    -

    -while for null pointer values we can rely on the special equality relation induced by 17.6.3.3 [nullablepointer.requirements]. -

    -
    -

    --?- Let w1 and w2 denote objects of type X::void_pointer. Then for the expressions -

    -
    -w1 == w2
-w1 != w2
-
    -

    -either or both objects may be replaced by an equivalently-valued object of type X::const_void_pointer with no -change in semantics. -

    --?- Let p1 and p2 denote objects of type X::pointer. Then for the expressions -

    -
    -p1 == p2
-p1 != p2
-p1 < p2
-p1 <= p2
-p1 >= p2
-p1 > p2
-p1 - p2
-
    -

    -either or both objects may be replaced by an equivalently-valued object of type X::const_pointer with no -change in semantics. -

    -
    -
    2. -

  2. Reinsert after 23.2 [container.requirements] p6:

    - -

    --6- begin() returns an iterator referring to the first element in the container. end() returns an iterator which -is the past-the-end value for the container. If the container is empty, then begin() == end(); -

    --?- In the expressions -

    -
    -i == j
-i != j
-i < j
-i <= j
-i >= j
-i > j
-i - j
-
    -

    -where i and j denote objects of a container's iterator type, either or both may be replaced by an object -of the container's const_iterator type referring to the same element with no change in semantics. -

    -
    -
    3. -
- - - - - -
-

2266. vector and deque have incorrect insert requirements

-

Section: 23.2.3 [sequence.reqmts] Status: WP - Submitter: Ahmed Charles Opened: 2013-05-17 Last modified: 2015-04-08

-

View all other issues in [sequence.reqmts].

-

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-

Discussion:

-

-According to Table 100 in n3485 23.2.3 [sequence.reqmts]/4 the notes for the expression a.insert(p,i,j) -say: -

- -

-Requires: T shall be EmplaceConstructible -into X from *i. For vector, if the iterator -does not meet the forward iterator requirements (24.2.5), T shall also be -MoveInsertable into X and MoveAssignable. -

-Each iterator in the range [i,j) shall be dereferenced exactly once. -

-pre: i and j are not iterators into a. -

-Inserts copies of elements in [i, j) before p -

- -

-There are two problems with that wording: First, the special constraints for vector, that are expressed to be valid for -forward iterators only, are necessary for all iterator categories. Second, the same special constraints are needed for deque, too. -

- -

[2013-10-05, Stephan T. Lavavej comments and provides alternative wording]

- -

-In Chicago, we determined that the original proposed resolution was correct, except that it needed additional requirements. -When vector insert(p, i, j) is called with input-only iterators, it can't know how many elements will be inserted, -which is obviously problematic for insertion anywhere other than at the end. Therefore, implementations typically append elements -(geometrically reallocating), followed by rotate(). Given forward+ iterators, some implementations append and -rotate() when they determine that there is sufficient capacity. Additionally, deque insert(p, i, j) is -typically implemented with prepending/appending, with a possible call to reverse(), followed by a call to rotate(). -Note that rotate()'s requirements are strictly stronger than reverse()'s. -

-Therefore, when patching Table 100, we need to add rotate()'s requirements. Note that this does not physically affect code -(implementations were already calling rotate() here), and even in Standardese terms it is barely noticeable — if an -element is MoveInsertable and MoveAssignable then it is almost certainly MoveConstructible and swappable. -However, this patch is necessary to be strictly correct. -

- -

-Previous resolution from Ahmed Charles: -

-
-
    -

  1. Change Table 100 as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 100 — Sequence container requirements (in addition to container) (continued)
    ExpressionReturn typeAssertion/note pre-/post-condition
    -… -
    -a.insert(p,i,j) - -iterator - -Requires: T shall be EmplaceConstructible -into X from *i. For vector and deque, if the iterator -does not meet the forward iterator requirements (24.2.5), T shall also be -MoveInsertable into X and MoveAssignable.
    -Each iterator in the range [i,j) shall be dereferenced exactly once.
    -pre: i and j are not iterators into a.
    -Inserts copies of elements in [i, j) before p -
    -… -
    -
    - -
    2. -
-
- -

[2014-02-15 post-Issaquah session : move to Tentatively Ready]

- -

-Pablo: We might have gone too far with the fine-grained requirements. Typically these things come in groups. -

-

-Alisdair: I think the concepts folks assumed we would take their guidance. -

-

-Move to Tentatively Ready. -

- - - -

Proposed resolution:

- -
    -

  1. Change Table 100 as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - - -
    Table 100 — Sequence container requirements (in addition to container) (continued)
    ExpressionReturn typeAssertion/note pre-/post-condition
    -… -
    -a.insert(p,i,j) - -iterator - -Requires: T shall be EmplaceConstructible into X
    -from *i. For vector and deque, if the iterator
    -does not meet the forward iterator requirements (24.2.5), T shall also be
    -MoveInsertable into X, MoveConstructible,
    -and MoveAssignable, and swappable (17.6.3.2 [swappable.requirements]).
    -Each iterator in the range [i,j) shall be dereferenced exactly once.
    -pre: i and j are not iterators into a.
    -Inserts copies of elements in [i, j) before p -
    -… -
    -
    - -
    2. -
- - - - - - -
-

2268. Setting a default argument in the declaration of a member function assign of std::basic_string

-

Section: 21.4 [basic.string] Status: C++14 - Submitter: Vladimir Grigoriev Opened: 2013-06-26 Last modified: 2015-04-08

-

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-

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-

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-

Discussion:

-

-Constructors and member functions assign of class std::basic_string have one to one relation (except the -explicit constructor that creates an empty string). The following list shows this relation: -

- -
-explicit basic_string(const Allocator& a = Allocator());
-
-basic_string(const basic_string& str);
-basic_string& assign(const basic_string& str);
-
-basic_string(basic_string&& str) noexcept;
-basic_string& assign(basic_string&& str) noexcept;
-
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-  const Allocator& a = Allocator());
-basic_string& assign(const basic_string& str, size_type pos,
-  size_type n);
-
-basic_string(const charT* s,
-  size_type n, const Allocator& a = Allocator());
-basic_string& assign(const charT* s, size_type n);
-
-basic_string(const charT* s, const Allocator& a = Allocator());
-basic_string& assign(const charT* s);
-
-basic_string(size_type n, charT c, const Allocator& a = Allocator());
-basic_string& assign(size_type n, charT c);
-
-template<class InputIterator>
-basic_string(InputIterator begin, InputIterator end,
-  const Allocator& a = Allocator());
-template<class InputIterator>
-basic_string& assign(InputIterator first, InputIterator last);
-
-basic_string(initializer_list<charT>, const Allocator& = Allocator());
-basic_string& assign(initializer_list<charT>);
-
- -

-So in fact any creating of an object of type std::basic_string using any of the above constructors -except the explicit constructor can be substituted for creating a (possibly non-empty) string and -then applying to it the corresponding method assign. -

-For example these two code snippets give the same result: -

- -
-std::string s("Hello World");
-
- -

-and -

- -
-std::string s;
-s.assign("Hello World");
-
- -

-However there is one exception that has no a logical support. It is the pair of the following constructor and member function -assign -

- -
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-             const Allocator& a = Allocator());
-
-basic_string& assign(const basic_string& str, size_type pos, size_type n);
-
- -

-The third parameter of the constructor has a default argument while in the assign function it is absent. So it is impossible -one to one to substitute the following code snippet -

- -
-std::string s("Hello World");
-std::string t(s, 6);
-
- -

-by -

- -
-std::string s("Hello World");
-std::string t;
-t.assign(s, 6); // error: no such function
-
- -

-To get an equivalent result using the assign function the programmer has to complicate the code that is error-prone -

- -
-std::string s("Hello World");
-std::string t;
-t.assign(s, 6, s.size() - 6); 
-
- -

-To fix that, the declaration of the member function assign should be changed in such a way that its declaration -would be fully compatible with the declaration of the corresponding constructor, that is to specify the same default argument -for the third parameter of the assign. -

- -

-The assign function is not the only function that requires to be revised. -

-Now let include in the list of pairs constructor-assign with the modified method assign one more member function -append. We will get: -

- -
-explicit basic_string(const Allocator& a = Allocator());
-
-basic_string(const basic_string& str);
-basic_string& assign(const basic_string& str);
-basic_string& append(const basic_string& str);
-
-basic_string(basic_string&& str) noexcept;
-basic_string& assign(basic_string&& str) noexcept;
-
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-  const Allocator& a = Allocator());
-basic_string& assign(const basic_string& str, size_type pos,
-  size_type n);
-basic_string& append(const basic_string& str, size_type pos,
-  size_type n);
-
-basic_string(const charT* s,
-  size_type n, const Allocator& a = Allocator());
-basic_string& assign(const charT* s, size_type n);
-basic_string& append(const charT* s, size_type n);
-
-basic_string(const charT* s, const Allocator& a = Allocator());
-basic_string& assign(const charT* s);
-basic_string& append(const charT* s);
-
-basic_string(size_type n, charT c, const Allocator& a = Allocator());
-basic_string& assign(size_type n, charT c);
-basic_string& append(size_type n, charT c);
-
-template<class InputIterator>
-basic_string(InputIterator begin, InputIterator end,
-  const Allocator& a = Allocator());
-template<class InputIterator>
-basic_string& assign(InputIterator first, InputIterator last);
-template<class InputIterator>
-basic_string& append(InputIterator first, InputIterator last);
-
-basic_string(initializer_list<charT>, const Allocator& = Allocator());
-basic_string& assign(initializer_list<charT>);
-basic_string& append(initializer_list<charT>);
-
- -

As it seen from this record:

- -
-basic_string(const basic_string& str, size_type pos, size_type n = npos,
-  const Allocator& a = Allocator());
-basic_string& assign(const basic_string& str, size_type pos,
-  size_type n);
-basic_string& append(const basic_string& str, size_type pos,
-  size_type n);
-
- -

-it is obvious that the function append also should have the default argument that is that it should be declared as: -

- -
-basic_string& append(const basic_string& str, size_type pos,
-  size_type n = npos);
-
- -

-In fact there is no a great difference in using assign or append especially when the string is empty: -

- -
-std::string s("Hello World");
-std::string t;
-t.assign(s, 6);
- 
-std::string s("Hello World");
-std::string t;
-t.append(s, 6);
-
- -

-In both cases the result will be the same. So the assign and append will be interchangeable from the point -of view of used arguments. -

-There are another three member functions in class std::basic_string that could be brought in conformity with considered above functions. -They are member functions insert, replace, and compare. -

-So it is suggested to substitute the following declarations of insert, replace, and compare: -

- -
-basic_string& insert(size_type pos1, const basic_string& str,
-  size_type pos2, size_type n);
-
-basic_string& replace(size_type pos1, size_type n1,
-  const basic_string& str, size_type pos2, size_type n2);
-
-int compare(size_type pos1, size_type n1,
-  const basic_string& str, size_type pos2, size_type n2) const;
-
- -

-by the declarations: -

- -
-basic_string& insert(size_type pos1, const basic_string& str,
-  size_type pos2, size_type n = npos);
-
-basic_string& replace(size_type pos1, size_type n1,
-  const basic_string& str, size_type pos2, size_type n2 = npos);
-
-int compare(size_type pos1, size_type n1,
-  const basic_string& str, size_type pos2, size_type n2 = npos) const;
-
- -

[2013-09 Chicago]

- -

-Howard: Are we positive this won't conflict with any other overloads? -

-They all appear to be unambiguous. -

-Alisdair: Ok, move to Ready. -

- - -

Proposed resolution:

- -
    -

  1. Change class template basic_string synopsis, 21.4 [basic.string] p5, as indicated:

    - -
    -namespace std {
-  template<class charT, class traits = char_traits<charT>,
-    class Allocator = allocator<charT> >
-  class basic_string {
-  public:
-    […]
-    basic_string& append(const basic_string& str, size_type pos, size_type n = npos);
-    […]
-    basic_string& assign(const basic_string& str, size_type pos, size_type n = npos);
-    […]
-    basic_string& insert(size_type pos1, const basic_string& str, size_type pos2, size_type n = npos);
-    […]
-    basic_string& replace(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos);
-    […]
-    int compare(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos) const;
-    […]
-  };
-}
-
    -
    2. - -

  2. Change 21.4.6.2 [string::append] before p3 as indicated:

    - -
    -basic_string& append(const basic_string& str, size_type pos, size_type n = npos);
-
    -
    3. - -

  3. Change 21.4.6.3 [string::assign] before p4 as indicated:

    - -
    -basic_string& assign(const basic_string& str, size_type pos, size_type n = npos);
-
    -
    4. - -

  4. Change 21.4.6.4 [string::insert] before p5 as indicated:

    - -
    -basic_string& insert(size_type pos1, const basic_string& str, size_type pos2, size_type n = npos);
-
    -
    5. - -

  5. Change 21.4.6.6 [string::replace] before p5 as indicated:

    - -
    -basic_string& replace(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos);
-
    -
    6. - -

  6. Change 21.4.7.9 [string::compare] before p4 as indicated:

    - -
    -int compare(size_type pos1, size_type n1, const basic_string& str, size_type pos2, size_type n2 = npos) const;
-
    -
    7. -
- - - - - - -
-

2271. regex_traits::lookup_classname specification unclear

-

Section: 28.7 [re.traits] Status: C++14 - Submitter: Jonathan Wakely Opened: 2013-07-02 Last modified: 2015-04-08

-

View all other issues in [re.traits].

-

View all issues with C++14 status.

-

Discussion:

-

-28.7 [re.traits] p9 says that regex_traits::lookup_classname should -return a value that compares equal to 0, but there is no requirement -that a bitmask type is equality comparable with 0, e.g. 17.5.2.1.3 [bitmask.types] says bitmask types -can be implemented using std::bitset. -

-Either there should be an additional requirement on the type or the function definition should be fixed. -

- -

[2013-09 Chicago]

- -

-Stefanus: Resolution looks good, doesn't seem to need fixing anywhere else from a quick look through the draft. -

-Any objection to Ready? -

-No objection. -

-Action: Move to Ready.

- - -

Proposed resolution:

- -

This wording is relative to N3691.

- -
    -

  1. Edit 28.7 [re.traits] p9:

    - -
    -
    -template <class ForwardIterator>
-  char_class_type lookup_classname(
-    ForwardIterator first, ForwardIterator last, bool icase = false) const;
-
    -
    -

    --9- Returns: an unspecified value that represents the character classification named by the character -sequence designated by the iterator range [first,last). If the parameter icase is true then the -returned mask identifies the character classification without regard to the case of the characters being -matched, otherwise it does honor the case of the characters being matched. The value returned shall -be independent of the case of the characters in the character sequence. If the name is not recognized -then returns a value that compares equal to 0char_class_type(). -

    -
    -
    -
    2. -
- - - - - - -
-

2272. quoted should use char_traits::eq for character comparison

-

Section: 27.7.6 [quoted.manip] Status: C++14 - Submitter: Marshall Clow Opened: 2013-07-12 Last modified: 2015-04-08

-

View all other issues in [quoted.manip].

-

View all issues with C++14 status.

-

Discussion:

-

-In 27.7.6 [quoted.manip] p2 b2: -

-
-

-— Each character in s. If the character to be output is equal to escape or delim, -as determined by operator==, first output escape. -

-
-

-In 27.7.6 [quoted.manip] p3 b1 sb1: -

-
-

-— If the first character extracted is equal to delim, as determined by operator==, […] -

-
- -

-these should both use traits::eq. -

- -

-Also, I believe that 27.7.6 [quoted.manip] p3 implies that: -

-
-
-std::ostream _stream;
-std::string _string;
-_stream << _string;
-_stream << quoted(_string);
-
-
-

-should both compile, or both fail to compile, based on whether or not their char_traits match. -But I believe that the standard should say that explicitly. -

- -

[ -2013-09 Chicago -]

- - -

-Marshall Clow improved the wording with support from Stefanus. -

- -

[ -2013-09 Chicago (late night issues) -]

- - -

-Moved to Ready, after confirming wording correctly reflects discussion earlier in the day. -

- - - -

Proposed resolution:

- -

This wording is relative to N3691.

- -
    -

  1. Change 27.7.6 [quoted.manip] p2+3 as indicated:

    - -
    -
    -template <class charT>
-  unspecified quoted(const charT* s, charT delim=charT('"'), charT escape=charT('\\'));
-template <class charT, class traits, class Allocator>
-  unspecified quoted(const basic_string<charT, traits, Allocator>& s,
-                     charT delim=charT('"'), charT escape=charT('\\'));
-
    -
    -

    --2- Returns: An object of unspecified type such that if out is an instance of basic_ostream with member -type char_type the same as charT and with member type traits_type, which in the second form is -the same as traits, then the expression -out << quoted(s, delim, escape) behaves -as if it inserts the following characters into out using character inserter function templates (27.7.3.6.4), -which may throw ios_base::failure (27.5.3.1.1): -

    -
      -

    • delim

      • -

    • Each character in s. If the character to be output is equal to escape or delim, -as determined by operator==traits_type::eq, first output escape.

      • -

    • delim

      • -
    -
    - -
    -template <class charT, class traits, class Allocator>
-  unspecified quoted(basic_string<charT, traits, Allocator>& s,
-                     charT delim=charT('"'), charT escape=charT('\\'));
-
    -
    -

    --3- Returns: An object of unspecified type such that: -

    -
      -

    • If in is an instance of basic_istream with member types char_type -and traits_type the same as charT and traits, respectively, then the -expression in >> quoted(s, delim, escape) behaves as if it extracts -the following characters from in using basic_istream::operator>> (27.7.2.2.3) which may throw -ios_base::failure (27.5.3.1.1): -

      -
        -

      • If the first character extracted is equal to delim, as determined by -operator==traits_type::eq, then: […]

        • -
      -
      • -

    • -If out is an instance of basic_ostream with member types char_type -and traits_type the same as charT and traits, respectively, -then the expression out << quoted(s, delim, escape) behaves as specified for the const -basic_string<charT, traits, Allocator>& overload of the quoted function. -

      • -
    -
    -
    -
    2. - -
- - - - - -
-

2274. Does map::operator[] value-initialize or default-insert a missing element?

-

Section: 23.4.4.3 [map.access], 23.5.4.3 [unord.map.elem] Status: Resolved - Submitter: Andrzej Krzemieński Opened: 2013-07-16 Last modified: 2015-05-22

-

View all other issues in [map.access].

-

View all issues with Resolved status.

-

Discussion:

-

-Suppose that I provide a custom allocator for type int, that renders value 1 rather than 0 in default-insertion: -

-
-
-struct Allocator1 : std::allocator<int>
-{
-  using super = std::allocator<int>;
-
-  template<typename Up, typename... Args>
-  void construct(Up* p, Args&&... args)
-  { super::construct(p, std::forward<Args>(args)...); }
-
-  template<typename Up>
-  void construct(Up* p)
-  { ::new((void*)p) Up(1); }
-};
-
-
- -

-Now, if I use this allocator with std::map, and I use operator[] to access a not-yet-existent value, -what value of the mapped_type should be created? 0 (value-initialization) or 1 (default-insertion): -

- -
-
-map<string, int, less<string>, Allocator1> map;
-cout << map["cat"];
-
-
- -

-N3960 is not very clear. 23.4.4.3 [map.access] in para 1 says: -

-
-

-"If there is no key equivalent to x in the map, inserts value_type(x, T()) into the map." -

-
-

-So, it requires value-initialization. -

-But para 2 says: -

-
-

-"mapped_type shall be DefaultInsertable into *this." -

-
-

-This implies default-insertion, because if not, why the requirement. Also similar functions like -vector::resize already require default-insertion wherever they put DefaultInsertable requirements. -

-Not to mention that default-insertion is more useful, because it allows custom allocators to "override" the -default value of mapped_type. -

- -

[2013-09 Chicago]

- -

-Alisdair: Matters only for POD or trivial types -

-Marshall: issue might show up elsewhere other than map<> -

-Alisdair: initialize elements in any containers — by calling construct on allocator traits -

-Marshall: existing wording is clear -

-Alisdair: main concern is difference in wording, discusses default initialization -

-Nico: different requirement needed -

-Alisdair: gut is issue is NAD, brings up DefaultInsertable definition — discusses definition -

-Nico: why do we have the requirement? -

-Alisdair: other containers have this requirement -

-Marshall: this applies to many other containers -

-Nico: deque<> in particular -

-Alisdair: discusses allocator construct -

-Alisdair: wording raises concerns that aren't said in existing standard -

-Nico: sees no benefit to change -

-Marshall: leery of change -

-Alisdair: can be made clearer; might need to add note to DefaultInsertable; borderline editorial, -comfortable without note, willing to wait until other issues arise. close issue as NAD -

- -

[2015-01-20: Tomasz Kamiński comments]

- -

-With the addition of the try_emplace method the behavior of the operator[] for the maps, -may be defined as follows: -

-
-
-T& operator[](const key_type& x);
-
-
-

-Effects: Equivalent to: try_emplace(x).first->second; -

-
-
-T& operator[](key_type&& x);
-
-
-

-Effects: Equivalent to try_emplace(std::move(x)).first->second; -

-
-
-

-This would simplify the wording and also after resolution of the issue 2464, this wording would -also address this issue. -

- -

[2015-02 Cologne]

- -

-Wait until 2464 and 2469 are in, which solve this. -

- -

[2015-05-06 Lenexa: This is resolved by 2469.]

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 23.4.4.3 [map.access] p1+p5 as indicated:

    - -
    -
    -T& operator[](const key_type& x);
-
    -
    -

    --1- Effects: If there is no key equivalent to x in the map, inserts value_type(x, T()) -into the mapinto the map a value with key_type initialized using expression x and mapped_type -initialized by default-insertion. -

    --2- Requires: key_type shall be CopyInsertable and mapped_type shall be -DefaultInsertable into *this. -

    -[…] -

    -
    -
    -T& operator[](key_type&& x);
-
    -
    -

    --5- Effects: If there is no key equivalent to x in the map, inserts -value_type(std::move(x), T()) into the mapinto the map a value with key_type -initialized using expression std::move(x) and mapped_type initialized by default-insertion. -

    --6- Requires: mapped_type shall be DefaultInsertable into *this. -

    -
    -
    -
    2. - -

  2. Change 23.5.4.3 [unord.map.elem] p2 as indicated:

    - -
    -
    -mapped_type& operator[](const key_type& k);
-mapped_type& operator[](key_type&& k);
-
    -
    -

    --1- Requires: mapped_type shall be DefaultInsertable into *this. -For the first operator, key_type shall be CopyInsertable into *this. For the second -operator, key_type shall be MoveConstructible. -

    --2- Effects: If the unordered_map does not already contain an element whose key is equivalent to -k, the first operator inserts the value value_type(k, mapped_type())a value with -key_type initialized using expression x and mapped_type initialized by default-insertion -and the second operator inserts the value value_type(std::move(k), mapped_type())a value -with key_type initialized using expression std::move(x) and mapped_type initialized by -default-insertion. -

    -
    -
    -
    3. -
- - - - - - -
-

2275. [CD] Why is forward_as_tuple not constexpr?

-

Section: 20.4.2.4 [tuple.creation] Status: C++14 - Submitter: Marshall Clow Opened: 2013-07-30 Last modified: 2015-04-08

-

View all other issues in [tuple.creation].

-

View all issues with C++14 status.

-

Discussion:

-

Addresses ES 11

- -

-In n3471, a bunch of routines -from header <tuple> were made constexpr. -

-make_tuple/tuple_cat/get<>(tuple)/relational operators — all these were "constexpr-ified". -

-But not forward_as_tuple. -

-Why not? -

-This was discussed in Portland, and STL opined that this was "an omission" (along with tuple_cat, which was added) -

-In discussion on c++std-lib@accu.org list, Pablo agreed that forward_as_tuple should be constexpr. -

- -

[2013-09 Chicago]

- -

-Moved to Immediate, this directly addresses an NB comment and the wording is non-controversial. -

-

-Accept for Working Paper -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change header <tuple> synopsis, 20.4.1 [tuple.general] as indicated:

    - -
    -
    -template <class... Types>
-  constexpr tuple<Types&&...> forward_as_tuple(Types&&...) noexcept;
-
    -
    -
    2. - -

  2. Change 20.4.2.4 [tuple.creation] before p5 as indicated:

    - -
    -
    -template <class... Types>
-  constexpr tuple<Types&&...> forward_as_tuple(Types&&... t) noexcept;
-
    -
    -
    3. -
- - - - - - -
-

2278. User-defined literals for Standard Library types

-

Section: 20.12.2 [time.syn], 21.3 [string.classes] Status: C++14 - Submitter: Howard Hinnant Opened: 2013-07-22 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-This paper adds user-defined literals -for string, complex and chrono types. It puts each new literal signature in an inline namespace -inside of std. Section 3.1 of the paper gives the rationale for doing this: -

- -

-As a common schema this paper proposes to put all suffixes for user defined literals in separate inline namespaces -that are below the inline namespace std::literals. [Note: This allows a user either to do a -using namespace std::literals; to import all literal operators from the standard available through header -file inclusion, or to use using namespace std::string_literals; to just obtain the literals operators -for a specific type. — end note] -

- -

This isn't how inline namespaces work.

- -

-7.3.1 [namespace.def]/p8 says in part: -

- -

-Members of an inline namespace can be used in most respects as though they were members of the enclosing namespace. -Specifically, the inline namespace and its enclosing namespace are both added to the set of associated namespaces -used in argument-dependent lookup (3.4.2) whenever one of them is, and a using- directive (7.3.4) that names the -inline namespace is implicitly inserted into the enclosing namespace as for an unnamed namespace (7.3.1.1). […] -

- -

-I.e. these literals will appear to the client to already be imported into namespace std. The rationale in -the paper appears to indicate that this is not the intended behavior, and that instead the intended behavior is -to require the user to say: -

-
-using namespace std::literals;
-
-

-or: -

-
-using namespace std::literals::string_literals;
-
-

-prior to use. To get this behavior non-inlined (normal) namespaces must be used. -

- -

-Originally proposed resolution: -

-Strike the use of "inline" from each use associated with literals, string_literals, -chrono_literals. -

-My opinion is that this must be done prior to publishing C++14, otherwise we are stuck with this -(apparently unwanted) decision forever. -

-Marshall Clow: -

-
-

-The rationale that I recall was that: -

-
    -

  1. Users could write "using namespace std::literals;" to get all the literal suffixes, or

    2. -

  2. Users could write "using namespace std::literals::string_literals;" or -"using namespace std::literals::chrono_literals;" to get a subset of the suffixes.

    3. -
-

-To accomplish that, I believe that: -

-
    -

  1. Namespace "std::literals" should not be inline

    2. -

  2. Namespaces "std::literals::string_literals" and "std::literals::chrono_literals" should -be inline

    3. -
-
-

-Further details see also reflector message c++std-lib-34256. -

- -

-Previous resolution from Marshall Clow: -

-
-
    -

  1. Modify header <chrono> synopsis, 20.12.2 [time.syn], as indicated:

    - -
    -namespace std {
-namespace chrono {
-[…]
-} // namespace chrono
-inline namespace literals {
-inline namespace chrono_literals {
-[…]
-} // namespace chrono_literals
-} // namespace literals
-} // namespace std
-
    -
    2. - -

  2. Modify header <string> synopsis, 21.3 [string.classes] p1, as indicated:

    - -
    -#include <initializer_list>
-
-namespace std {
-[…]
-inline namespace literals {
-inline namespace string_literals {
-[…]
-}
-}
-}
-
    -
    3. -
-
- -

[2013-09 Chicago]

- - -

-After a discussion about intent, the conclusion was that if you hoist a type with a "using" directive, then you should also -get the associated literal suffixes with the type. -

-This is accomplished by marking namespace std::literals as inline, but for types in their own namespace inside -std, then they will need to do this as well. The only case in the current library is chrono. -

- -

Marshall Clow provides alternative wording.

- -

[2013-09 Chicago (late night issues)]

- -

-Moved to Ready, after confirming wording reflects the intent of the earlier discussion. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Modify header <chrono> synopsis, 20.12.2 [time.syn], as indicated:

    - -
    -namespace std {
-[…]
-inline namespace literals {
-inline namespace chrono_literals {
-[…]
-constexpr chrono::duration<unspecified , nano> operator "" ns(long double);
-
-} // namespace chrono_literals
-} // namespace literals
-
-
-namespace chrono {
-    using namespace literals::chrono_literals;
-} // namespace chrono
-
-} // namespace std
-
    -
    2. - -
- - - - - -
-

2280. begin/end for arrays should be constexpr and noexcept

-

Section: 24.7 [iterator.range] Status: C++14 - Submitter: Andy Sawyer Opened: 2013-08-22 Last modified: 2015-04-08

-

View other active issues in [iterator.range].

-

View all other issues in [iterator.range].

-

View all issues with C++14 status.

-

Discussion:

-

-The array forms of std::begin and std::end should be constexpr and noexcept. -

- -

-Previous resolution from Andy Sawyer: -

-
-
    -

  1. Edit header <iterator> synopsis, 24.3 [iterator.synopsis] as indicated:

    - -
    -
    -[…]
-template <class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept;
-template <class T, size_t N> constexpr T* end(T (&array)[N]) noexcept;
-template <class C> constexpr auto cbegin(const C& c) -> decltype(std::begin(c));
-template <class C> constexpr auto cend(const C& c) -> decltype(std::end(c));
-[…]
-
    -
    -
    2. - -

  2. Edit 24.7 [iterator.range] before p4+5 as indicated:

    - -
    -
    -template <class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept;
-
    -
    -

    --4- Returns: array. -

    -
    -
    -template <class T, size_t N> constexpr T* end(T (&array)[N]) noexcept;
-
    -
    -

    --5- Returns: array + N. -

    -
    -
    -template <class C> constexpr auto cbegin(const C& c) -> decltype(std::begin(c));
-
    -
    -

    --6- Returns: std::begin(c). -

    -
    -
    -template <class C> constexpr auto cend(const C& c) -> decltype(std::end(c));
-
    -
    -

    --7- Returns: std::end(c). -

    -
    -
    -
    3. - -
-
- -

[2013-09 Chicago]

- -

-Add noexcept(noexcept(std::begin/end(c))) to cbegin and cend, move to ready -

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Edit header <iterator> synopsis, 24.3 [iterator.synopsis] as indicated:

    - -
    -
    -[…]
-template <class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept;
-template <class T, size_t N> constexpr T* end(T (&array)[N]) noexcept;
-template <class C> constexpr auto cbegin(const C& c) noexcept(noexcept(std::begin(c))) -> decltype(std::begin(c));
-template <class C> constexpr auto cend(const C& c) noexcept(noexcept(std::end(c))) -> decltype(std::end(c));
-[…]
-
    -
    -
    2. - -

  2. Edit 24.7 [iterator.range] before p4+5 as indicated:

    - -
    -
    -template <class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept;
-
    -
    -

    --4- Returns: array. -

    -
    -
    -template <class T, size_t N> constexpr T* end(T (&array)[N]) noexcept;
-
    -
    -

    --5- Returns: array + N. -

    -
    -
    -template <class C> constexpr auto cbegin(const C& c) noexcept(noexcept(std::begin(c))) -> decltype(std::begin(c));
-
    -
    -

    --6- Returns: std::begin(c). -

    -
    -
    -template <class C> constexpr auto cend(const C& c) noexcept(noexcept(std::end(c))) -> decltype(std::end(c));
-
    -
    -

    --7- Returns: std::end(c). -

    -
    -
    -
    3. - -
- - - - - -
-

2282. [fund.ts] Incorrect is_assignable constraint in optional::op=(U&&)

-

Section: X [optional.object.assign] Status: Resolved - Submitter: Howard Hinnant Opened: 2013-08-25 Last modified: 2015-04-08

-

View all other issues in [optional.object.assign].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses: fund.ts

- -

-Minor wording nit in X [optional.object.assign]/p15: -

-
-template <class U> optional<T>& operator=(U&& v);
-
-
-

--15- Requires: is_constructible<T, U>::value is true and is_assignable<U, T>::value is true. -

-
-

-Should be: -

-
-template <class U> optional<T>& operator=(U&& v);
-
-
-

--15- Requires: is_constructible<T, U>::value is true and is_assignable<T&, U>::value is true. -

-
- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as fundamentals-ts. -

- -

[2014-06-07 Daniel comments]

- -

-This issue should be set to Resolved, because the wording fix is already applied in the -last fundamentals working draft. -

- -

[2014-06-16 Rapperswill]

- -

-Confirmed that this issue is resolved in the current Library Fundamentals working paper. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit X [optional.object.assign] p15 as indicated:

    - -
    -template <class U> optional<T>& operator=(U&& v);
-
    -
    -

    --15- Requires: is_constructible<T, U>::value is true and -is_assignable<U, TT&, U>::value is true. -

    -
    -
    2. - -
- - - - - -
-

2283. [fund.ts] optional declares and then does not define an operator<()

-

Section: X [optional.comp_with_t] Status: Resolved - Submitter: Howard Hinnant Opened: 2013-08-26 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

Addresses: fund.ts

- -

-In [optional.syn] there is: -

-
-template <class T> constexpr bool operator<(const T&, const optional<T>&);
-
-

-But I can find no definition for this signature. -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as fundamentals-ts. -

- -

[2014-06-07 Daniel comments]

- -

-This issue should be set to Resolved, because the wording fix is already applied in the -last fundamentals working draft. -

- -

[2014-06-16 Rapperswill]

- -

-Confirmed that this issue is resolved in the current Library Fundamentals working paper. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Add to X [optional.comp_with_t]:

    - -
    -template <class T> constexpr bool operator<(const T& v, const optional<T>& x);
-
    -
    -

    --?- Returns: bool(x) ? less<T>{}(v, *x) : false. -

    -
    -
    2. - -
- - - - - -
-

2284. Inconsistency in allocator_traits::max_size

-

Section: 20.7.8 [allocator.traits] Status: C++14 - Submitter: Marshall Clow Opened: 2013-08-27 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-Section 20.7.8 [allocator.traits] says: -

-
-static size_type max_size(const Alloc& a) noexcept;
-
-

-Section 20.7.8.2 [allocator.traits.members] says: -

-
-static size_type max_size(Alloc& a) noexcept;
-
- -

-These should be the same. -

- -

-Discussion: -

- -

-Pablo (who I believe wrote the allocator_traits proposal) says "The function should take a const reference." -

- -

[2013-09 Chicago]

- -

-No objections, so moved to Immediate. -

-

-Accept for Working Paper -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 20.7.8.2 [allocator.traits.members] as follows:

    - -
    -static size_type max_size(const Alloc& a) noexcept;
-
    -
    -
    2. - -
- - - - - -
-

2285. make_reverse_iterator

-

Section: 24.5.1 [reverse.iterators] Status: C++14 - Submitter: Zhihao Yuan Opened: 2013-08-27 Last modified: 2015-04-08

-

View all other issues in [reverse.iterators].

-

View all issues with C++14 status.

-

Discussion:

-

-We have make_move_iterator, but not make_reverse_iterator, which -is also useful when dealing with some types without an rbegin/rend support (like, C strings). -

- -

[2013-09 Chicago]

- -

-Billy: reviewed it last night STL: has suggested prior, but denied for complexity -

-Billy: Alisdair wanted to review for reverse(reverse()); -

-STL: likes the issue, was like him -

-Stefanus: likes definitions, places where things should be -

-STL: for consistency with make_move_iterator -

-Stefanus: minor editorial issue - subdivision in these 2 sections is different from [move.iter]. -See 24.5.3.3.14 [move.iter.nonmember] -

-STL: motion to move to Ready -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change header <iterator> synopsis, 24.3 [iterator.synopsis] as indicated:

    - -
    -
    -namespace std {
-  […]
-  template <class Iterator>
-    reverse_iterator<Iterator> operator+(
-      typename reverse_iterator<Iterator>::difference_type n,
-      const reverse_iterator<Iterator>& x);
-
-  template <class Iterator>
-    reverse_iterator<Iterator> make_reverse_iterator(Iterator i);
-
-}
-
    -
    -
    2. - -

  2. Change class template reverse_iterator synopsis, 24.5.1.1 [reverse.iterator] as indicated:

    - -
    -
    -namespace std {
-  […]
-  template <class Iterator>
-    reverse_iterator<Iterator> operator+(
-      typename reverse_iterator<Iterator>::difference_type n,
-      const reverse_iterator<Iterator>& x);
-
-  template <class Iterator>
-    reverse_iterator<Iterator> make_reverse_iterator(Iterator i);
-
-}
-
    -
    -
    3. - -

  3. After 24.5.1.3.20 [reverse.iter.opsum] add the following new sub-clause to 24.5.1.3 [reverse.iter.ops]:

    - -
    -
    -
-template <class Iterator>
-  reverse_iterator<Iterator> make_reverse_iterator(Iterator i);
-
-
    -

    --?- Returns: reverse_iterator<Iterator>(i). -

    -
    -
    4. - -
- - - - - -
-

2287. [fund.ts] Incorrect exception safety for optional copy assignment operator

-

Section: X [optional.object.assign] Status: Resolved - Submitter: Howard Hinnant Opened: 2013-08-16 Last modified: 2015-04-08

-

View all other issues in [optional.object.assign].

-

View all issues with Resolved status.

-

Discussion:

-

Addresses: fund.ts

- -

-The Exception safety paragraph of X [optional.object.assign] calls out T's copy constructor when -it should refer to T's copy assignment operator. -

- -

[2013-09 Chicago:]

- -

-Move to Deferred. This feature will ship after C++14 and should be revisited then. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as fundamentals-ts. -

- -

[2014-06-07 Daniel comments]

- -

-This issue should be set to Resolved, because the wording fix is already applied in the -last fundamentals working draft. -

- -

[2014-06-16 Rapperswill]

- -

-Confirmed that this issue is resolved in the current Library Fundamentals working paper. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change X [optional.object.assign] as indicated:

    - -
    -optional<T>& operator=(const optional<T>& rhs);
-
    -
    -

    -[…] -

    --8- Exception safety: If any exception is thrown, the values of init and rhs.init remain unchanged. If -an exception is thrown during the call to T's copy constructor, no effect. If an exception is thrown -during the call to T's copy assignment, the state of its contained value is as defined by the exception -safety guarantee of T's copy constructorassignment. -

    -
    -
    2. - -
- - - - - -
-

2288. Inconsistent requirements for shared mutexes

-

Section: 30.4.1.4 [thread.sharedmutex.requirements] Status: C++14 - Submitter: Daniel Krügler Opened: 2013-08-30 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-Albeit shared mutex types refine timed mutex types, the requirements imposed on the corresponding required member function -expressions are inconsistent in several aspects, most probably because failing synchronisation with wording changes for -timed mutexes applied by some issues: -

- -
    -
  1. -

    -Due to acceptance of N3568 a wording phrase -came in 30.4.1.4 [thread.sharedmutex.requirements] p26, -

    -

    -Effects: If the tick period of rel_time is not exactly convertible to the native tick period, the -duration shall be rounded up to the nearest native tick period. […] -

    -

    -while a very similar one had been removed for 30.4.1.3 [thread.timedmutex.requirements] by LWG 2091. -

    -Having this guaranteed effect for try_lock_shared_for but not for try_lock_for seems inconsistent -and astonishing. -

    -If the actual intended restriction imposed onto the implementation is to forbid early wakeups here, we should ensure that -to hold for timed mutex's try_lock_for as well. Note that the rationale provided for LWG 2091 was -a potential late wakeup situation, but it seems that there is no implementation restriction that prevents early wakeups. -

    -
    2. - -
  2. -

    -The shared-lock requirements for any *lock*() functions don't provide the guarantee that "If an exception is thrown then -a lock shall not have been acquired for the current execution agent.". For other mutex types this guarantee can be derived from -the corresponding TimedLockable requirements, but there are no SharedLockable requirements. -

    -
    3. - -
  3. -

    -The shared-lock requirements for *lock_for/_until() functions require "Throws: Nothing." -instead of "Throws: Timeout-related exceptions (30.2.4)." which had been added by LWG 2093, because user-provided -clocks, durations, or time points may throw exceptions. -

    -
    4. - -
  4. -

    -With the addition of std::shared_mutex, the explicit lists of 30.4.1.2 [thread.mutex.requirements.mutex] p7+15, -

    -

    -Requires: If m is of type std::mutex or std::timed_mutex, the calling thread does not own the mutex. -

    -

    -and of 30.4.1.3 [thread.timedmutex.requirements] p4+11, -

    -

    -Requires: If m is of type std::timed_mutex, the calling thread does not own the mutex. -

    -

    -are incomplete and should add the non-recursive std::shared_mutex as well. -

    -
    5. -
- -

[2014-02-16: Moved as Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 30.4.1.2 [thread.mutex.requirements.mutex] p7+15 as indicated:

    - -
    -

    --6- The expression m.lock() shall be well-formed and have the following semantics: -

    -
    -

    --7- Requires: If m is of type std::mutex or, std::timed_mutex, or -std::shared_mutex, the calling thread does not own the mutex. -

    -
    -

    -[…] -

    -

    --14- The expression m.try_lock() shall be well-formed and have the following semantics: -

    -
    -

    --15- Requires: If m is of type std::mutex or, std::timed_mutex, or -std::shared_mutex, the calling thread does not own the mutex. -

    -
    -
    -
    2. - -

  2. Change 30.4.1.3 [thread.timedmutex.requirements] p4+11 as indicated:

    - -
    -

    --3- The expression m.try_lock_for(rel_time) shall be well-formed and have the following semantics: -

    -
    -

    --4- Requires: If m is of type std::timed_mutex or std::shared_mutex, -the calling thread does not own the mutex. -

    -
    -

    -[…] -

    -

    --10- The expression m.try_lock_until(abs_time) shall be well-formed and have the following semantics: -

    -
    -

    --11- Requires: If m is of type std::timed_mutex or std::shared_mutex, -the calling thread does not own the mutex. -

    -
    -
    -
    3. - -

  3. Change 30.4.1.4 [thread.sharedmutex.requirements] as indicated:

    - -
    -

    --3- The expression m.lock_shared() shall be well-formed and have the following semantics: -

    -
    -

    --4- Requires: The calling thread has no ownership of the mutex. -

    --5- Effects: Blocks the calling thread until shared ownership of the mutex can be obtained for the calling -thread. If an exception is thrown then a shared lock shall not have been acquired for the current thread. -

    -[…] -

    -
    -

    --24- The expression m.try_lock_shared_for(rel_time) shall be well-formed and have the following semantics: -

    -
    -

    --25- Requires: The calling thread has no ownership of the mutex. -

    --26- Effects: If the tick period of rel_time is not exactly convertible to the native tick period, the -duration shall be rounded up to the nearest native tick period. Attempts to obtain shared lock -ownership for the calling thread within the relative timeout (30.2.4) specified by rel_time. If the -time specified by rel_time is less than or equal to rel_time.zero(), the function attempts to obtain -ownership without blocking (as if by calling try_lock_shared()). The function shall return within -the timeout specified by rel_time only if it has obtained shared ownership of the mutex object. [Note: -As with try_lock(), there is no guarantee that ownership will be obtained if the lock is available, but -implementations are expected to make a strong effort to do so. — end note] If an exception is thrown then -a shared lock shall not have been acquired for the current thread. -

    -[…] -

    --30- Throws: NothingTimeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -

    --31- The expression m.try_lock_shared_until(abs_time) shall be well-formed and have the following semantics: -

    -
    -

    --32- Requires: The calling thread has no ownership of the mutex. -

    --33- Effects: The function attempts to obtain shared ownership of the mutex. If abs_time has already -passed, the function attempts to obtain shared ownership without blocking (as if by calling try_lock_shared()). -The function shall return before the absolute timeout (30.2.4) specified by abs_time -only if it has obtained shared ownership of the mutex object. [Note: As with try_lock(), there is no -guarantee that ownership will be obtained if the lock is available, but implementations are expected -to make a strong effort to do so. — end note] If an exception is thrown then -a shared lock shall not have been acquired for the current thread. -

    -[…] -

    --37- Throws: NothingTimeout-related exceptions (30.2.4 [thread.req.timing]). -

    -
    -
    -
    4. - -
- - - - - -
-

2291. std::hash is vulnerable to collision DoS attack

-

Section: 17.6.3.4 [hash.requirements] Status: C++14 - Submitter: Zhihao Yuan Opened: 2013-09-02 Last modified: 2015-04-08

-

View all other issues in [hash.requirements].

-

View all issues with C++14 status.

-

Discussion:

-

-For a non-cryptographic hash function, it's possible to pre-calculate massive inputs with -the same hashed value to algorithmically slow down the unordered containers, and results -in a denial-of-service attack. Many languages with built-in hash table support have fixed -this issue. For example, Perl has universal hashing, Python 3 uses salted hashes. -

-However, for C++, in 17.6.3.4 [hash.requirements] p2, Table 26: -

- -

-The value returned shall depend only on the argument k. -[Note: Thus all evaluations of the expression h(k) with the -same value for k yield the same result. — end note] -

- -

-The wording is not clear here: does that mean all the standard -library implementations must use the same hash function for a same -type? Or it is not allowed for an implementation to change its hash -function? -

-I suggest to explicitly allow the salted hash functions. -

- -

[2013-09 Chicago]

- -

-Moved to Ready. -

- -

-There is some concern that the issue of better hashing, especially standardizing any kind of -secure hashing, is a feature that deserves attention in LEWG -

- -

-The proposed resolution is much simpler than the larger issue though, merely clarifying a -permission that many implementers believe they already have, without mandating a change to -more straight forward implementations. -

- -

-Move to Ready, rather than Immediate, as even the permission has been contentious in reflector -discussion, although the consensus in Chicago is to accept as written unless we hear a further -strong objection. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 17.6.3.4 [hash.requirements] p2, Table 26, as indicated: [Editorial note: -We can consider adding some additional guideline here. Unlike -N3333, this -proposed change makes the hashing per-execution instead of per-process. The standard does not -discuss OS processes. And, practically, a per-process hashing makes a program unable to -share an unordered container to a child process. — end note ]

    - -
    - - - - - - - - - - - - - - - - - - -
    Table 26 — Hash requirements [hash]
    ExpressionReturn typeRequirement
    -h(k) - -size_t - -The value returned shall depend only on the argument k
    -for the duration of the program.
    -[Note: Thus all evaluations of the expression h(k) with the
    -same value for k yield the same result for a given
    -execution of the program    . — end note]
    -
    -… -
    -
    -
    2. -
- - - - - -
-

2293. Wrong facet used by num_put::do_put

-

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: C++14 - Submitter: Juan Soulie Opened: 2013-09-04 Last modified: 2015-04-08

-

View all other issues in [facet.num.put.virtuals].

-

View all issues with C++14 status.

-

Discussion:

-

-At the end of 22.4.2.2.2 [facet.num.put.virtuals] (in p6), the return value is said to be obtained by calling -truename or falsename on the wrong facet: ctype should be replaced by numpunct. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 22.4.2.2.2 [facet.num.put.virtuals] p6 as indicated:

    - -

    --6- Returns: If (str.flags() & ios_base::boolalpha) == 0 returns do_put(out, str, fill, (int)val), -otherwise obtains a string s as if by -

    -
    -string_type s =
-  val ? use_facet<ctypenumpunct<charT> >(loc).truename()
-      : use_facet<ctypenumpunct<charT> >(loc).falsename();
-
    -

    -and then inserts each character c of s into out via *out++ = c and returns out. -

    -
    -
    2. -
- - - - - -
-

2298. [CD] is_nothrow_constructible is always false because of create<>

-

Section: 20.10.4.3 [meta.unary.prop] Status: C++14 - Submitter: Daniel Krügler Opened: 2013-09-24 Last modified: 2015-04-08

-

View other active issues in [meta.unary.prop].

-

View all other issues in [meta.unary.prop].

-

View all issues with C++14 status.

-

Discussion:

-

Addresses US 18

- -

-The trait is_constructible<T, Args...> is defined in terms of a helper template, create<>, -that is identical to std::declval<> except for the latter's noexcept clause. -

-If the absence of noexcept is critical to this definition, insert a Note of explanation; otherwise, excise -create<> and reformulate in terms of declval<> the definition of is_constructible. -

- -

[2013-09-24 Daniel comments and provides resolution suggestion]

- - -

-Replacing create<> by std::declval<> would make the situation worse, because the definition of -is_constructible is based on a well-formed variable definition and there is no way to specify a variable definition -without odr-using its initializer arguments. It should also be added, that there is another problem with the specification of -all existing is_trivially_* traits, because neither create<> nor std::declval<> -are considered as trivial functions, but this should be solved by a different issue. -

- -

[2013-09-26 Nico improves wording]

- - -

-The additional change is just to keep both places were create() is defined consistent. -

- -

[2013-09 Chicago]

- -

-No objections, so moved to Immediate. -

-

-Accept for Working Paper -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 20.10.4.3 [meta.unary.prop] around p6 as indicated:

    - -

    --6- Given the following function prototype: -

    -
    -template <class T>
-  typename add_rvalue_reference<T>::type create() noexcept;
-
    -

    -the predicate condition for a template specialization is_constructible<T, Args...> shall be satisfied -if and only if the following variable definition would be well-formed for some invented variable t: -

    -
    -T t(create<Args>()...);
-
    -

    -[…] -

    -
    -
    2. - -

  2. Change 20.10.4.3 [meta.unary.prop] around p4 as indicated:

    - -

    --4- Given the following function prototype: -

    -
    template <class T>
-  typename add_rvalue_reference<T>::type create() noexcept;
-
    -

    -the predicate condition for a template specialization is_convertible<From, To> shall be satisfied if and -only if the return expression in the following code would be well-formed, including any implicit conversions -to the return type of the function: -

    -
    -To test() {
-  return create<From>();
-}
-
    -

    -[…] -

    -
    -
    3. - -
- - - - - -
-

2299. [CD] Effects of inaccessible key_compare::is_transparent type are not clear

-

Section: 23.2.4 [associative.reqmts] Status: C++14 - Submitter: Daniel Krügler Opened: 2013-09-24 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with C++14 status.

-

Discussion:

-

Addresses ES 16

- -

-The condition "X::key_compare::is_transparent exists" does not specify that the type be publicly accessible. -

-Consider the public accessibility of X::key_compare::is_transparent and whether its potential inaccessibility -should be banned for a compliant key_compare type. -

- -

[2013-09-24 Daniel provides resolution suggestion]

- - -

[2013-09-25 Chicago]

- -

-Daniel's wording is good, advance to Immediate to respond to NB comment. -

- -

[2013-09-26 Chicago]

- -

-Moved back to Review as Daniel would like another look at the words, and to confirm implementability. -

- -

-Previous resolution from Daniel [SUPERSEDED]: -

-
-
    - -

  1. Change 23.2.4 [associative.reqmts] p8 as indicated:

    - -

    --8- In Table 102, X denotes an associative container class, a denotes a value of X, a_uniq -denotes a value of X when X supports unique keys, a_eq denotes a value of X when X -supports multiple keys, a_tran denotes a value of X when thea publicly accessible type -X::key_compare::is_transparent exists whose name is unambiguous and not hidden, -[…] -

    -
    -
    2. - -

  2. Change 23.2.4 [associative.reqmts] p13 as indicated:

    - -

    -The member function templates find, count, lower_bound, upper_bound, and equal_range shall not -participate in overload resolution unless thea publicly accessible type -Compare::is_transparent exists whose name is unambiguous and not hidden. -

    -
    3. -
- -
- -

[2014-02-10 Daniel comments provides alternative wording]

- - -

-I could confirm that my previous concerns were unwarranted, because they turned out to be due to a compiler-bug. -Nonetheless I would suggest to replace the previously suggested replication of core-wording situations (access, ambiguity, hidden) -by a single more robust phrase based on "valid type". -

- - -

[2014-02-12 Issaquah: Move to Immediate]

- -

-STL: This uses "valid type", which is a Phrase Of Power in Core, and Daniel has a citation for the term. -

-

-Jonathan: It's nice to rely on Core. -

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    - -

  1. Change 23.2.4 [associative.reqmts] p8 as indicated:

    - -

    --8- In Table 102, X denotes an associative container class, a denotes a value of X, a_uniq -denotes a value of X when X supports unique keys, a_eq denotes a value of X when X -supports multiple keys, a_tran denotes a value of X when the typequalified-id -X::key_compare::is_transparent existsis valid and denotes a type (14.8.2 [temp.deduct]), -[…] -

    -
    -
    2. - -

  2. Change 23.2.4 [associative.reqmts] p13 as indicated:

    - -

    -The member function templates find, count, lower_bound, upper_bound, and equal_range shall not -participate in overload resolution unless the typequalified-id -Compare::is_transparent existsis valid and denotes a type (14.8.2 [temp.deduct]). -

    -
    3. -
- - - - - -
-

2300. [CD] Redundant sections for map and multimap members should be removed

-

Section: X [map.ops], X [multimap.ops] Status: C++14 - Submitter: Daniel Krügler Opened: 2013-09-25 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

Addresses ES 17

- -

-Sections are redundant with general associative container requirements at 23.2.4 [associative.reqmts], Table 102. -

-Suggested action: -

-Delete sections. -

- -

[2013-09-25 Daniel provides resolution suggestion]

- - -

[2013-09-25 Chicago]

- -

-Daniel's wording is good, move to Immediate to resolve NB comment. -

- -

[2013-09-29 Chicago]

- -

-Accept for Working Paper -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change the header <map> synopsis, 23.4.4.1 [map.overview] p2 as indicated:

    - -
    -// 23.4.4.5, map operations:
-iterator find(const key_type& x);
-const_iterator find(const key_type& x) const;
-template <class K> iterator find(const K& x);
-template <class K> const_iterator find(const K& x) const;
-
    -
    -
    2. - -

  2. Delete the complete sub-clause X [map.ops]:

    - -

    -23.4.4.5 map operations [map.ops] -

    -
    -iterator find(const key_type& x);
-const_iterator find(const key_type& x) const;
-iterator lower_bound(const key_type& x);
-const_iterator lower_bound(const key_type& x) const;
-iterator upper_bound(const key_type& x);
-const_iterator upper_bound(const key_type &x) const;
-pair<iterator, iterator>
-  equal_range(const key_type &x);
-pair<const_iterator, const_iterator>
-  equal_range(const key_type& x) const;
-
    -

    --1- The find, lower_bound, upper_bound and equal_range member functions each have two versions, -one const and the other non-const. In each case the behavior of the two functions is identical except -that the const version returns a const_iterator and the non-const version an iterator (23.2.4). -

    -
    -
    3. - -

  3. Delete the complete sub-clause X [multimap.ops]:

    - -

    -23.4.5.4 multimap operations [multimap.ops] -

    -
    -iterator find(const key_type &x);
-const_iterator find(const key_type& x) const;
-
-iterator lower_bound(const key_type& x);
-const_iterator lower_bound(const key_type& x) const;
-
-pair<iterator, iterator>
-  equal_range(const key_type &x);
-pair<const_iterator, const_iterator>
-  equal_range(const key_type& x) const;
-
    -

    --1- The find, lower_bound, upper_bound and equal_range member functions each have two versions, -one const and one non-const. In each case the behavior of the two versions is identical except -that the const version returns a const_iterator and the non-const version an iterator (23.2.4). -

    -
    -
    4. - -
- - - - - -
-

2301. Why is std::tie not constexpr?

-

Section: 20.4.2.4 [tuple.creation] Status: C++14 - Submitter: Rein Halbersma Opened: 2013-09-11 Last modified: 2015-04-08

-

View all other issues in [tuple.creation].

-

View all issues with C++14 status.

-

Discussion:

-

-In N3471, a bunch of routines from header -<tuple> were made constexpr. -

-make_tuple/tuple_cat/get<>(tuple)/relational operators — all these were "constexpr-ified". -

-But not tie. This is similar to Issue 2275, where the same observation was made about forward_as_tuple. -

- -

[2014-02-13 Issaquah: Move as Immediate]

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change the header <tuple> synopsis, 20.4.1 [tuple.general] p2 as indicated:

    - -
    -template<class... Types>
-  constexpr tuple<Types&...> tie(Types&...) noexcept;
-
    -
    -
    2. - -

  2. Change 20.4.2.4 [tuple.creation] around p7 as indicated:

    - -
    -template<class... Types>
-  constexpr tuple<Types&...> tie(Types&... t) noexcept;
-
    -
    -
    3. - -
- - - - - -
-

2304. Complexity of count in unordered associative containers

-

Section: 23.2.5 [unord.req] Status: C++14 - Submitter: Joaquín M López Muñoz Opened: 2013-09-20 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

View all other issues in [unord.req].

-

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-

Discussion:

-

-Table 103 in 23.2.5 [unord.req] states that the complexity of b.count(k) is average case 𝒪(1) rather -than linear with the number of equivalent elements, which seems to be a typo as this requires holding an internal -count of elements in each group of equivalent keys, something which hardly looks the intent of the standard and no -(known by the submitter) stdlib implementation is currently doing. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change Table 103 as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 103 — Unordered associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -b.count(k) - -size_type - -Returns the number of elements with key equivalent to k. - -Average case 𝒪(1b.count(k)), worst case 𝒪(b.size()). -
    -… -
    -
    - -
    2. -
- - - - - -
-

2306. match_results::reference should be value_type&, not const value_type&

-

Section: 28.10 [re.results] Status: C++14 - Submitter: Matt Austern Opened: 2013-09-25 Last modified: 2015-04-08

-

View all other issues in [re.results].

-

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-

Discussion:

-

-The match_results class synopsis has -

-
-typedef const value_type& const_reference;
-typedef const_reference reference;
-
-

-We're getting too enthusiastic about types here by insisting that reference is a const reference, even -though match_results is a read-only container. In the container requirements table (Table 96, in section -23.2.1 [container.requirements.general] we say that Container::reference is "lvalue of T" and -Container::const_reference is "const lvalue of T". -

-

-That phrasing in the container requirements table is admittedly a little fuzzy and ought to be clarified (as discussed in -lwg issue 2182), but in context it's clear that Container::reference ought to be a T& -even for constant containers. In the rest of Clause 23 we see that Container::reference is T&, not -const T&, even for const-qualified containers and that it's T&, not const T&, even -for containers like set and unordered_set that provide const iterators only. -

-The way we handle const containers is just that in the case of a const-qualified container (including match_results) -there are no operations that return Container::reference. That's already the case, so this issue is complaining -about an unused typedef. -

- -

[2013-10-17: Daniel comments]

- -

-The std::initializer_list synopsis, 18.9 [support.initlist] shows a similar problem: -

-
-template<class E> class initializer_list {
-public:
-  typedef E value_type;
-  typedef const E& reference;
-  typedef const E& const_reference;
-  […]
-}
-
-

-Given the fact that std::initializer_list doesn't meet the container requirements anyway (and is such a core-language related -type) I recommend to stick with the current state. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change the class template match_results header synopsis, 28.10 [re.results] p4 as indicated:

    - -
    -typedef const value_type& const_reference;
-typedef const_referencevalue_type& reference;
-
    -
    2. -
- - - - - -
-

2308. Clarify container destructor requirements w.r.t. std::array

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Jonathan Wakely Opened: 2013-09-26 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++14 status.

-

Discussion:

-

-It has been suggested that Table 96 — "Container requirements" makes -confusing requirements for the destructor of std::array: -

-"note: the destructor is applied to every element of a; all the memory is deallocated." -

-Since std::array obtains no memory, there is none to deallocate, -arguably making it unclear what the requirement means for std::array::~array(). -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change in 23.2.1 [container.requirements.general], Table 96 — "Container requirements", -the "Assertion/note/pre-/post-condition" for the expression "(&a)->~X()" as indicated:

    - -

    -note: the destructor is applied to every element of a; all theany memory -obtained is deallocated. -

    -
    2. -
- - - - - -
-

2313. tuple_size should always derive from integral_constant<size_t, N>

-

Section: 20.4.2.5 [tuple.helper] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [tuple.helper].

-

View all issues with C++14 status.

-

Discussion:

-

-In 20.4.2.5 [tuple.helper], the "primary template" is depicted as: -

-
-template <class... Types>
-class tuple_size<tuple<Types...> >
-  : public integral_constant<size_t, sizeof...(Types)> { };
-
-

-However, 20.3.4 [pair.astuple]/1-2 and 23.3.2.9 [array.tuple]/1-2 are underspecified, saying: -

-
-tuple_size<pair<T1, T2> >::value
-
-

-Returns: Integral constant expression. -

-Value: 2. -

-
-
-tuple_size<array<T, N> >::value
-
-

-Return type: integral constant expression. -

-Value: N -

-
-

-They should be required to behave like the "primary template". This is more than a stylistic decision — it allows -tuple_size to be passed to a function taking integral_constant. -

-LWG 1118 noticed this underspecification, but instead of correcting it, the resolution changed -20.4.2.5 [tuple.helper]/3 to require tuple_size<cv T> to derive from -integral_constant<remove_cv<decltype(TS::value)>::type, TS::value>. This is unnecessarily overgeneralized. -tuple_size is primarily for tuples, where it is required to be size_t, and it has been extended to handle -pairs and arrays, which (as explained above) should also be guaranteed to be size_t. tuple_size<cv T> -works with cv-qualified tuples, pairs, arrays, and user-defined types that also want to participate in the tuple_size -system. It would be far simpler and perfectly reasonable to expect that user-defined types supporting the "tuple-like protocol" -should have tuple_sizes of size_t. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 20.3.4 [pair.astuple]/1-2 as indicated:

    - -
    -tuple_size<pair<T1, T2> >::value
-template <class T1, class T2>
-struct tuple_size<pair<T1, T2>>
-  : integral_constant<size_t, 2> { };
-
    -

    --1- Returns: Integral constant expression. -

    --2- Value: 2. -

    -
    -
    2. - -

  2. Edit 23.3.2.9 [array.tuple]/1-2 as indicated:

    - -
    -tuple_size<array<T, N> >::value
-template <class T, size_t N>
-struct tuple_size<array<T, N>>
-  : integral_constant<size_t, N> { };
-
    -

    --1- Returns: Integral constant expression. -

    --2- Value: N. -

    -
    -
    3. - -

  3. Edit 20.4.2.5 [tuple.helper]/p1-p3 as indicated:

    - -
    -template <class T> struct tuple_size;
-
    -

    --?- Remarks: All specializations of tuple_size<T> shall meet the UnaryTypeTrait -requirements (20.10.1 [meta.rqmts]) with a BaseCharacteristic of integral_constant<size_t, N> -for some N. -

    -
    -
    -
    -template <class... Types>
-struct tuple_size<tuple<Types...> >
-  : integral_constant<size_t, sizeof...(Types)> { };
-  
-template <size_t I, class... Types>
-class tuple_element<I, tuple<Types...> > {
-public:
-  typedef TI type;
-};
-
    -

    --1- Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds. -

    -[…] -

    -
    -
    -template <class T> class tuple_size<const T>;
-template <class T> class tuple_size<volatile T>;
-template <class T> class tuple_size<const volatile T>;
-
    -

    --3- Let TS denote tuple_size<T> of the cv-unqualified type T. Then each of the -three templates shall meet the UnaryTypeTrait requirements (20.10.1 [meta.rqmts]) with a BaseCharacteristic of -

    -
    -integral_constant<remove_cv<decltype(TS::value)>::typesize_t, TS::value>
-
    -
    -
    -
    4. - -
- - - - - -
-

2314. apply() should return decltype(auto) and use decay_t before tuple_size

-

Section: 20.5.1 [intseq.general] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-The example in 20.5.1 [intseq.general]/2 depicts apply_impl() and apply() as returning auto. -This is incorrect because it will trigger decay and will not preserve F's return type. For example, if invoking the -functor returns const int&, apply_impl() and apply() will return int. decltype(auto) -should be used for "perfect returning". -

-

-Additionally, this depicts apply() as taking Tuple&&, then saying "std::tuple_size<Tuple>::value". -This is incorrect because when apply() is called with lvalue tuples, perfect forwarding will deduce Tuple to be cv -tuple&, but 20.4.2.5 [tuple.helper] says that tuple_size handles only cv tuple, not -references to tuples. Using remove_reference_t would avoid this problem, but so would decay_t, which has a -significantly shorter name. (The additional transformations that decay_t does are neither beneficial nor harmful here.) -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit the example code in 20.5.1 [intseq.general]/2 as indicated:

    - -
    -template<class F, class Tuple, std::size_t... I>
-  autodecltype(auto) apply_impl(F&& f, Tuple&& t, index_sequence<I...>) {
-    return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
-  }
-template<class F, class Tuple>
-  autodecltype(auto) apply(F&& f, Tuple&& t) {
-    using Indices = make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>;
-    return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
-  }
-
    -
    2. - -
- - - - - -
-

2315. weak_ptr should be movable

-

Section: 20.8.2.3 [util.smartptr.weak] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.weak].

-

View all issues with C++14 status.

-

Discussion:

-

-Like shared_ptr, weak_ptr should be movable to avoid unnecessary atomic increments/decrements of the weak refcount. -

- -

[2014-02-13 Issaquah: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 20.8.2.3 [util.smartptr.weak]/1, class template weak_ptr synopsis, as indicated:

    - -
    -namespace std {
-  template<class T> class weak_ptr {
-  public:
-    typedef T element_type;
-
-    // 20.9.2.3.1, constructors
-    constexpr weak_ptr() noexcept;
-    template<class Y> weak_ptr(shared_ptr<Y> const& r) noexcept;
-    weak_ptr(weak_ptr const& r) noexcept;
-    template<class Y> weak_ptr(weak_ptr<Y> const& r) noexcept;
-    weak_ptr(weak_ptr&& r) noexcept;
-    template<class Y> weak_ptr(weak_ptr<Y>&& r) noexcept;
-
-    […]
-
-    // 20.9.2.3.3, assignment
-    weak_ptr& operator=(weak_ptr const& r) noexcept;
-    template<class Y> weak_ptr& operator=(weak_ptr<Y> const& r) noexcept;
-    template<class Y> weak_ptr& operator=(shared_ptr<Y> const& r) noexcept;
-    weak_ptr& operator=(weak_ptr&& r) noexcept;
-    template<class Y> weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
-  };
-}
-
    -
    2. - -

  2. Add the following new paragraphs at the end of sub-clause 20.8.2.3.1 [util.smartptr.weak.const]:

    - -
    -weak_ptr(weak_ptr&& r) noexcept;
-template<class Y> weak_ptr(weak_ptr<Y>&& r) noexcept;
-
    -

    --?- Remark: The second constructor shall not participate in overload resolution unless Y* is implicitly -convertible to T*. -

    --?- Effects: Move-constructs a weak_ptr instance from r. -

    --?- Postconditions: *this shall contain the old value of r. r shall be empty. -r.use_count() == 0. -

    -
    -
    -
    3. - -

  3. Edit 20.8.2.3.3 [util.smartptr.weak.assign] as indicated:

    - -
    -weak_ptr& operator=(const weak_ptr& r) noexcept;
-template<class Y> weak_ptr& operator=(const weak_ptr<Y>& r) noexcept;
-template<class Y> weak_ptr& operator=(const shared_ptr<Y>& r) noexcept;
-
    -

    --1- Effects: […] -

    --2- Remarks: […] -

    --?- Returns: *this. -

    -
    -
    - -
    -weak_ptr& operator=(weak_ptr&& r) noexcept;
-template<class Y> weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
-
    -

    --?- Effects: Equivalent to weak_ptr(std::move(r)).swap(*this). -

    --?- Returns: *this. -

    -
    -
    -
    4. - -
- - - - - -
-

2316. weak_ptr::lock() should be atomic

-

Section: 20.8.2.3.5 [util.smartptr.weak.obs] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.weak.obs].

-

View all issues with C++14 status.

-

Discussion:

-

-20.8.2.2 [util.smartptr.shared]/4 says: "For purposes of determining the presence of a data race, member functions shall -access and modify only the shared_ptr and weak_ptr objects themselves and not objects they refer to. Changes -in use_count() do not reflect modifications that can introduce data races." This requires shared_ptr/weak_ptr -implementations to protect their strong and weak refcounts with atomic operations, without the Standardese having to say this -elsewhere. However, 20.8.2.3.5 [util.smartptr.weak.obs]/5 describes weak_ptr::lock() with -"Returns: expired() ? shared_ptr<T>() : shared_ptr<T>(*this)." -Even after considering the blanket wording about -data races, this specification is insufficient. If this conditional expression were literally implemented, the use_count() -could change from nonzero to zero after testing expired(), causing shared_ptr<T>(*this) to throw -bad_weak_ptr when the intention is for weak_ptr::lock() to return empty or nonempty without throwing — indeed, -weak_ptr::lock() is marked as noexcept.

-

-We all know what weak_ptr::lock() should do, the Standardese just doesn't say it. -shared_ptr(const weak_ptr<Y>&)'s specification is not really affected because -20.8.2.2.1 [util.smartptr.shared.const]/23-27 describes the behavior with English instead of code. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 20.8.2.3.5 [util.smartptr.weak.obs]/5 as indicated:

    - -
    -shared_ptr<T> lock() const noexcept;
-
    -
    -

    --5- Returns: expired() ? shared_ptr<T>() : shared_ptr<T>(*this), executed atomically. -

    -
    -
    -
    2. - -
- - - - - -
-

2317. The type property queries should be UnaryTypeTraits returning size_t

-

Section: 20.10.5 [meta.unary.prop.query] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-The sibling sections 20.10.4 [meta.unary], 20.10.6 [meta.rel], and 20.10.7 [meta.trans] respectively specify -UnaryTypeTraits, BinaryTypeTraits, and TransformationTraits, as stated by each /2 paragraph. However, -20.10.5 [meta.unary.prop.query] is underspecified. alignment_of, rank, and extent are said to produce -"Values", but the type of that Value is not specified, and the struct templates are not required to derive from integral_constant. -Such derivation is more than stylistic — it allows the structs to be passed to functions taking integral_constant. -

-alignment_of returns alignof(T) which is size_t (5.3.6 [expr.alignof]/2). extent returns -an array bound, which is clearly size_t. rank returns "the number of dimensions" of an array, so any type could -be chosen, with size_t being a reasonable choice. (Another choice would be unsigned int, to match extent's -template parameter I.) -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Following 20.10.5 [meta.unary.prop.query]/1 add a new paragraph as indicated:

    - -

    -Each of these templates shall be a UnaryTypeTrait (20.10.1 [meta.rqmts]) with a BaseCharacteristic of -integral_constant<size_t, Value>. -

    -
    -
    2. - -
- - - - - -
-

2319. basic_string's move constructor should not be noexcept

-

Section: 21.4.2 [string.cons] Status: Resolved - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [string.cons].

-

View all issues with Resolved status.

-

Discussion:

-

-In debugging implementations, containers (including basic_string) may need to own dynamically allocated helper objects at -all times, including in their default-constructed and moved-from states. This means that their default constructors and move -constructors may throw exceptions. Therefore, the Standard should not mark them as noexcept. (Other implementations will -still be permitted to add noexcept.) -

- -

[2014-02, Issaquah : move to Ready]

- -

-The issue discussion was highly controversial: The arguments in favour was that implementations exist that always need to allocate -memory even for the move operations (similar as for some other containers) and that this cleans up an inconsistency between std::string -and other container types. Counter arguments were that potentially throwing move operations reduce much of the advantages of move-support, -e.g. in vector<string>. -

-

-straw poll: accept wording in the issue
-SF 4 WF 4 N 0 WA 1 SA 1 -

-

-straw poll: 14 or 17?
-C++14: 4 C++17: 4 -

-

-Move to Ready for C++17, as too close to 14 DIS without strong consensus. -

-

-It was suggested to introduce a special library vocabulary that specifies a "normative encouragement to not throw exceptions" for -functions like these. -

-

-NJ: I offer to write a proposal to add encouragement for not throwing ... "noexcept in italics means should not throw" -

- - -

[2014/11 Urbana]

- -

-Resolved by paper N4258 -

- -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. In 21.4 [basic.string]/5, class template basic_string synopsis, and 21.4.2 [string.cons]/2 -change as indicated:

    - -
    -basic_string(basic_string&& str) noexcept;
-
    -
    2. - -

  2. Edit 21.4.2 [string.cons]/17 as indicated:

    - -
    -basic_string(const basic_string& str, const Allocator& alloc);
-basic_string(basic_string&& str, const Allocator& alloc);
-
    -
    -

    -[…] -

    --17- Throws: The second form throws nothing if alloc == str.get_allocator().. -

    -
    -
    -
    3. - -
- - - - - - -
-

2320. select_on_container_copy_construction() takes allocators, not containers

-

Section: 23.2.1 [container.requirements.general] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with C++14 status.

-

Discussion:

-

-23.2.1 [container.requirements.general]/7 says "Copy constructors for these container types obtain an allocator by calling -allocator_traits<allocator_type>::select_on_container_copy_construction on their first parameters." However, -20.7.8.2 [allocator.traits.members]/8 says that this takes const Alloc&, not a container. -23.2.1 [container.requirements.general]/7 goes on to say "Move constructors obtain an allocator by move construction from -the allocator belonging to the container being moved." so we can follow that wording. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. In 23.2.1 [container.requirements.general]/7 change as indicated:

    - -

    --7- Unless otherwise specified, all containers defined in this clause obtain memory using an allocator (see 17.6.3.5). -Copy constructors for these container types obtain an allocator by calling -allocator_traits<allocator_type>::select_on_container_copy_construction on their first -parametersthe allocator belonging to the container being copied. -Move constructors obtain an allocator by move construction from the allocator belonging to the container being moved. […] -

    -
    2. - -
- - - - - - -
-

2322. Associative(initializer_list, stuff) constructors are underspecified

-

Section: 23.2.4 [associative.reqmts], 23.2.5 [unord.req] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [associative.reqmts].

-

View all other issues in [associative.reqmts].

-

View all issues with C++14 status.

-

Discussion:

-

-23.2.4 [associative.reqmts] specifies both X(i,j) and X(i,j,c), but only X(il). -23.4.4.1 [map.overview] declares "map(initializer_list<value_type>, const Compare& = Compare(), -const Allocator& = Allocator());" but 23.4.4.2 [map.cons] intentionally doesn't explain it, relying -on the big table's requirements. As a result, map(il, c)'s behavior is not actually specified by the Standard. -(All of the other ordered associative containers also provide such constructors.) -

-The unordered associative containers are similarly affected, although they have more arguments. (Again, the actual -containers are correctly depicted with the desired constructors, their behavior just isn't specified.) -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 23.2.4 [associative.reqmts], Table 102 — "Associative container requirements", as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 102 — Associative container requirements (in addition to container) (continued)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -X(il); - - - -Same as X(il.begin(), il.end()). - -sSame as X(il.begin(), il.end()). -
    -X(il, c); - -  - -Same as X(il.begin(), il.end(), c). - -Same as X(il.begin(), il.end(), c). -
    -… -
    -
    -
    2. - -

  2. Edit 23.2.5 [unord.req], Table 103 "Unordered associative container requirements", as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 103 — Unordered associative container requirements (in addition to container)
    ExpressionReturn typeAssertion/note pre-/post-conditionComplexity
    -… -
    -X(il) - -X - -Same as X(il.begin(), il.end()). - -Same as X(il.begin(), il.end()). -
    -X(il, n) - -X - -Same as X(il.begin(), il.end(), n). - -Same as X(il.begin(), il.end(), n). -
    -X(il, n, hf) - -X - -Same as X(il.begin(), il.end(), n, hf). - -Same as X(il.begin(), il.end(), n, hf). -
    -X(il, n, hf, eq) - -X - -Same as X(il.begin(), il.end(), n, hf, eq). - -Same as X(il.begin(), il.end(), n, hf, eq). -
    -… -
    -
    - -
    3. - -
- - - - - - -
-

2323. vector::resize(n, t)'s specification should be simplified

-

Section: 23.3.6.3 [vector.capacity], 23.3.3.3 [deque.capacity] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [vector.capacity].

-

View all other issues in [vector.capacity].

-

View all issues with C++14 status.

-

Discussion:

-

-First, 23.3.3.3 [deque.capacity]/4 and 23.3.6.3 [vector.capacity]/16 say that resize(size_type sz, const T& c) -"Requires: T shall be MoveInsertable into *this and CopyInsertable into *this." -The CopyInsertable requirement is correct (because sz might be size() + 2 or more), but the -MoveInsertable requirement is redundant due to 23.2.1 [container.requirements.general]/13: "T is -CopyInsertable into X means that, in addition to T being MoveInsertable into X, the [...]". -(LWG 2033's resolution said that this was "not redundant, because CopyInsertable is not necessarily a refinement -of MoveInsertable" which was true at the time, but then LWG 2177's resolution made it a refinement.) -

-Second, 23.3.6.3 [vector.capacity]/17 says "Remarks: If an exception is thrown other than by the move constructor of a -non-CopyInsertable T there are no effects." This is confusing because T is required to be -CopyInsertable. (/14 says the same thing for resize(size_type sz), where it is correct because that overload -requires only MoveInsertable and DefaultInsertable.) -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 23.3.3.3 [deque.capacity]/4 as indicated:

    - -
    -void resize(size_type sz, const T& c);
-
    -

    -[…] -

    --4- Requires: T shall be MoveInsertable into *this and CopyInsertable into -*this. -

    -
    -
    2. - -

  2. Edit 23.3.6.3 [vector.capacity]/16+17 as indicated:

    - -
    -void resize(size_type sz, const T& c);
-
    -

    -[…] -

    --16- Requires: T shall be MoveInsertable into *this and CopyInsertable into -*this. -

    --17- Remarks: If an exception is thrown other than by the move constructor of a non-CopyInsertable T -there are no effects. -

    -
    -
    3. - -
- - - - - - -
-

2324. Insert iterator constructors should use addressof()

-

Section: 24.5.2.2.1 [back.insert.iter.cons], 24.5.2.4.1 [front.insert.iter.cons], 24.5.2.6.1 [insert.iter.cons] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-24.5.2.2.1 [back.insert.iter.cons]/1, 24.5.2.4.1 [front.insert.iter.cons]/1, and 24.5.2.6.1 [insert.iter.cons]/1 -say "Initializes container with &x", which doesn't defend against containers overloading operator&(). -Containers are now required to have such defenses for their elements, so we may as well be consistent here. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 24.5.2.2.1 [back.insert.iter.cons]/1 as indicated:

    - -
    -explicit back_insert_iterator(Container& x);
-
    -

    --1- Effects: Initializes container with &xstd::addressof(x). -

    -
    -
    2. - -

  2. Edit 24.5.2.4.1 [front.insert.iter.cons]/1 as indicated:

    - -
    -explicit front_insert_iterator(Container& x);
-
    -

    --1- Effects: Initializes container with &xstd::addressof(x). -

    -
    -
    3. - -

  3. Edit 24.5.2.6.1 [insert.iter.cons]/1 as indicated:

    - -
    -insert_iterator(Container& x, typename Container::iterator i);
-
    -

    --1- Effects: Initializes container with &xstd::addressof(x) and iter with i. -

    -
    -
    4. - -
- - - - - - -
-

2325. minmax_element()'s behavior differing from max_element()'s should be noted

-

Section: 25.4.7 [alg.min.max] Status: WP - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [alg.min.max].

-

View all issues with WP status.

-

Discussion:

-

-25.4.7 [alg.min.max]/23 says that max_element() finds the first biggest element, while /25 says that -minmax_element() finds the last biggest element. This significant difference is unusual — it means that -minmax_element(args) is not equivalent to make_pair(min_element(args), max_element(args)), whereas the other -major "two for one" algorithm equal_range(args) is equivalent to make_pair(lower_bound(args), upper_bound(args)). -minmax_element()'s behavior is intentional — it is a fundamental consequence of the 3N/2 algorithm — -but the Standardese does not draw attention to this in any way. This wording came from LWG 715's resolution (which -changed the semantics but didn't mention it), citing CLRS for the algorithm — but CLRS doesn't mention the behavior for -equivalent elements! The wording here deeply confused me (as an STL maintainer fixing an incorrect implementation) until I walked -through the algorithm by hand and figured out the fundamental reason. It would be really nice for the Standard to provide a hint -that something magical is happening here. -

- -

[2014-06-06 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Add a footnote to 25.4.7 [alg.min.max]/25 as indicated:

    - -
    -template<class ForwardIterator>
-  pair<ForwardIterator, ForwardIterator>
-    minmax_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-  pair<ForwardIterator, ForwardIterator>
-    minmax_element(ForwardIterator first, ForwardIterator last, Compare comp);
-
    -

    --25- Returns: make_pair(first, first) if [first,last) is empty, otherwise make_pair(m, M), where -m is the first iterator in [first,last) such that no iterator in the range refers to a smaller element, -and where M is the last iterator [Footnote: This behavior intentionally differs from max_element().] -in [first,last) such that no iterator in the range refers to a larger element. -

    -
    -
    2. - -
- - - - - - -
-

2329. regex_match()/regex_search() with match_results should forbid temporary strings

-

Section: 28.4 [re.syn] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all other issues in [re.syn].

-

View all issues with C++14 status.

-

Discussion:

-

-Consider the following code: -

-
-const regex r(R"(meow(\d+)\.txt)");
-smatch m;
-if (regex_match(dir_iter->path().filename().string(), m, r)) {
-  DoSomethingWith(m[1]);
-}
-
-

-This occasionally crashes. The problem is that dir_iter->path().filename().string() returns a temporary string, -so the match_results contains invalidated iterators into a destroyed temporary string. -

-It's fine for regex_match/regex_search(str, reg) to accept temporary strings, because they just return bool. -However, the overloads taking match_results should forbid temporary strings. -

- -

[2014-02-13 Issaquah: Move as Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 28.4 [re.syn], header <regex> synopsis, as indicated:

    - -
    -#include <initializer_list>
-
-namespace std {
-
-  […]
-  
-  // 28.11.2, function template regex_match:
-  […]
-  template <class ST, class SA, class Allocator, class charT, class traits> 
-  bool regex_match(const basic_string<charT, ST, SA>&&, 
-                   match_results<
-                     typename basic_string<charT, ST, SA>::const_iterator, 
-                     Allocator>&, 
-                   const basic_regex<charT, traits>&, 
-                   regex_constants::match_flag_type = 
-                     regex_constants::match_default) = delete;
-
-  // 28.11.3, function template regex_search:
-  […]
-  template <class ST, class SA, class Allocator, class charT, class traits> 
-  bool regex_search(const basic_string<charT, ST, SA>&&, 
-                    match_results<
-                      typename basic_string<charT, ST, SA>::const_iterator, 
-                      Allocator>&, 
-                    const basic_regex<charT, traits>&, 
-                    regex_constants::match_flag_type = 
-                      regex_constants::match_default) = delete;
-  […]
-}
-
    -
    2. -
- - - - - -
-

2330. regex("meow", regex::icase) is technically forbidden but should be permitted

-

Section: 28.5.1 [re.synopt] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View other active issues in [re.synopt].

-

View all other issues in [re.synopt].

-

View all issues with C++14 status.

-

Discussion:

-

-28.5.1 [re.synopt]/1 says "A valid value of type syntax_option_type shall have exactly one of the elements -ECMAScript, basic, extended, awk, grep, egrep, set." -

-This "exactly one" wording technically forbids passing icase by itself! Users should not be required to pass -regex::ECMAScript | regex::icase. (Note that the cost of an additional check for no grammar being explicitly requested -is completely irrelevant, as regex construction is so much more expensive.) -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Edit 28.5.1 [re.synopt] as indicated:

    - -

    --1- The type syntax_option_type is an implementation-defined bitmask type (17.5.2.1.3). Setting its elements -has the effects listed in table 138. A valid value of type syntax_option_type shall have exactlyat most -one of the grammar elements ECMAScript, basic, extended, awk, grep, -egrep, set. If no grammar element is set, the default grammar is ECMAScript. -

    -
    2. -
- - - - - -
-

2332. regex_iterator/regex_token_iterator should forbid temporary regexes

-

Section: 28.12 [re.iter] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-Users can write "for(sregex_iterator i(s.begin(), s.end(), regex("meow")), end; i != end; ++i)", binding a temporary -regex to const regex& and storing a pointer to it. This will compile silently, triggering undefined behavior -at runtime. We now have the technology to prevent this from compiling, like how reference_wrapper refuses to bind to -temporaries. -

- -

[2014-02-14 Issaquah meeting: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Change 28.12.1 [re.regiter]/1, class template regex_iterator synopsis, as indicated:

    - -
    -regex_iterator();
-regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
-  const regex_type& re,
-  regex_constants::match_flag_type m =
-    regex_constants::match_default);
-regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
-  const regex_type&& re,
-  regex_constants::match_flag_type m =
-    regex_constants::match_default) = delete;
-
    -
    2. - -

  2. Change 28.12.2 [re.tokiter]/6, class template regex_token_iterator synopsis, as indicated:

    - -
    -regex_token_iterator();
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     int submatch = 0,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     const std::vector<int>& submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     initializer_list<int> submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-template <std::size_t N>
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type& re,
-                     const int (&submatches)[N],
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default);
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type&& re,
-                     int submatch = 0,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default) = delete;
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type&& re,
-                     const std::vector<int>& submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default) = delete;
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type&& re,
-                     initializer_list<int> submatches,
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default) = delete;
-template <std::size_t N>
-regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
-                     const regex_type&& re,
-                     const int (&submatches)[N],
-                     regex_constants::match_flag_type m =
-                       regex_constants::match_default) = delete;
-
    -
    3. -
- - - - - -
-

2333. [fund.ts] Hashing disengaged optional<T> objects

-

Section: X [optional.hash] Status: Resolved - Submitter: Jonathan Wakely Opened: 2013-10-03 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

Addresses: fund.ts

- -

-The spec for hash<optional<T>> doesn't say anything about disengaged -objects, so 1.3 [defns.undefined] would imply it's undefined behaviour, -but that's very unhelpful to users. -

-If hashing disengaged optional objects is undefined there should be a Requires, otherwise -there should be some statement saying it's OK. -

-It would be possible to specify the value, e.g. saying it returns the -same value as something like std::hash<void*>()(nullptr), but leaving -it unspecified would permit users to specialize hash<optional<UserDefinedType>> so -that the hash value for a disengaged object is distinct from any value returned by -hash<UserDefinedType>. -

- -

[2014-06-06 pre-Rapperswill]

- -

-This issue has been reopened as fundamentals-ts. -

- -

[2014-06-07 Daniel comments]

- -

-This issue should be set to Resolved, because the wording fix is already applied in the -last fundamentals working draft. -

- -

[2014-06-16 Rapperswill]

- -

-Confirmed that this issue is resolved in the current Library Fundamentals working paper. -

- - - -

Proposed resolution:

-

This wording is relative to N3691.

- -
    -

  1. Add to X [optional.hash]/3

    - -
    -template <class T> struct hash<optional<T>>;
-
    -

    -[…] -

    --3- For an object o of type optional<T>, if bool(o) == true, -hash<optional<T>>()(o) shall evaluate to the same value as -hash<T>()(*o) otherwise it evaluates to an unspecified value. -

    -
    -
    2. - -
- - - - - -
-

2339. Wording issue in nth_element

-

Section: 25.4.2 [alg.nth.element] Status: C++14 - Submitter: Christopher Jefferson Opened: 2013-10-19 Last modified: 2015-04-08

-

View all other issues in [alg.nth.element].

-

View all issues with C++14 status.

-

Discussion:

-

-The wording of nth_element says: -

-
-template<class RandomAccessIterator>
-  void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                   RandomAccessIterator last);
-
-

-After nth_element the element in the position pointed to by nth is the element that would be in that -position if the whole range were sorted. Also for every iterator i in the range [first,nth) and every -iterator j in the range [nth,last) it holds that: !(*j < *i) or comp(*j, *i) == false. -

-
-

-That wording, to me, implies that there must be an element at 'nth'. -However, gcc at least accepts nth == last, and returns without effect -(which seems like the sensible option). -

-Is it intended to accept nth == last? If so, then I would suggest adding -this to the wording explicitly, say: -

-
-

-After nth_element the element in the position pointed to by nth, if any, is the element that -would be in that position if the whole range were sorted. Also for every iterator i in the range [first,nth) -and every iterator j in the range [nth,last) it holds that: !(*j < *i) or comp(*j, *i) == false. -

-
- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 25.4.2 [alg.nth.element]/1 as indicated:

    - -
    -template<class RandomAccessIterator>
-  void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                   RandomAccessIterator last);
-template<class RandomAccessIterator, class Compare>
-  void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
-                   RandomAccessIterator last, Compare comp);
-
    -

    --1- After nth_element the element in the position pointed to by nth is the element that would be in that -position if the whole range were sorted, unless nth == last. Also for every iterator i in the -range [first,nth) and every iterator j in the range [nth,last) it holds that: !(*j < *i) -or comp(*j, *i) == false. -

    -
    -
    2. - -
- - - - - -
-

2340. Replacement allocation functions declared as inline

-

Section: 17.6.4.6 [replacement.functions] Status: WP - Submitter: David Majnemer Opened: 2013-10-20 Last modified: 2015-04-08

-

View all other issues in [replacement.functions].

-

View all issues with WP status.

-

Discussion:

-

-N3290 17.6.4.6 [replacement.functions]/p3 says: -

-

-The program's definitions shall not be specified as inline. -

-

-This seems to permit declarations of replacement allocation functions that are specified as inline so long -as they aren't used. This behavior seems more like a bug than a feature, I propose that we do the following: -

-

-The program's definitionsdeclarations shall not be specified as inline. -

- -

[2014-02-15 Issaquah : Move to Ready]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 17.6.4.6 [replacement.functions]/3 as indicated:

    - -

    --3- The program's definitions are used instead of the default versions supplied by the implementation (18.6). -Such replacement occurs prior to program startup (3.2, 3.6). The program's definitionsdeclarations -shall not be specified as inline. No diagnostic is required.

    -
    -
    2. - -
- - - - - -
-

2341. Inconsistency between basic_ostream::seekp(pos) and basic_ostream::seekp(off, dir)

-

Section: 27.7.3.5 [ostream.seeks] Status: C++14 - Submitter: Marshall Clow Opened: 2013-10-21 Last modified: 2015-04-08

-

View all issues with C++14 status.

-

Discussion:

-

-In 27.7.3.5 [ostream.seeks], we have: -

-
-basic_ostream<charT,traits>& seekp(pos_type pos);
-
-

--3- Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out). In case of failure, -the function calls setstate(failbit) (which may throw ios_base::failure). -

--4- Returns: *this. -

-
-
-basic_ostream<charT,traits>& seekp(off_type off, ios_base::seekdir dir);
-
-

--5- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out). -

--6- Returns: *this. -

-
-

-The first call is required to set the failbit on failure, but the second is not -

-So (given two ostreams, os1 and os2) the following code (confusingly) works: -

-
-os1.seekp(-1);
-assert(os1.fail());
-
-os2.seekp(-1, std::ios_base::beg);
-assert(os2.good());
-
-

-Note that the description of basic_istream<charT,traits>& seekg(off_type off, ios_base::seekdir dir) in -27.7.2.3 [istream.unformatted] p43 does require setting failbit. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 27.7.3.5 [ostream.seeks]p5 as indicated:

    - -
    -basic_ostream<charT,traits>& seekp(off_type off, ios_base::seekdir dir);
-
    -

    --5- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out). -In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure). -

    --6- Returns: *this. -

    -
    -
    2. - -
- - - - - -
-

2344. quoted()'s interaction with padding is unclear

-

Section: 27.7.6 [quoted.manip] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-11-01 Last modified: 2015-04-08

-

View all other issues in [quoted.manip].

-

View all issues with C++14 status.

-

Discussion:

-

-Given this code: -

-
-cout << "[" << left << setfill('x') << setw(20) << R"("AB \"CD\" EF")" << "]" << endl;
-cout << "[" << left << setfill('y') << setw(20) << quoted(R"(GH "IJ" KL)") << "]" << endl;
-
-

-The first line prints ["AB \"CD\" EF"xxxxxx]. The second line should probably print ["GH \"IJ\" KL"yyyyyy], but -27.7.6 [quoted.manip]/2 doesn't say whether or how quoted() should interact with padding. All it says is that -

-

-"out << quoted(s, delim, escape) behaves as if it inserts the following characters into out using character -inserter function templates (27.7.3.6.4)". -

-

-27.7.3.6.4 [ostream.inserters.character] specifies both single-character and null-terminated inserters, both referring to -27.7.3.6.1 [ostream.formatted.reqmts]/3 for padding. Literally implementing quoted() with single-character inserters -would result in padding being emitted after the first character, with undesirable effects for ios_base::left. -

-It appears that 21.4.8.9 [string.io]/5 has the appropriate incantations to follow here. It says that os << str -

-

-"Behaves as a formatted output function (27.7.3.6.1) of os. Forms a character sequence seq, initially consisting of the -elements defined by the range [str.begin(), str.end()). Determines padding for seq as described in 27.7.3.6.1. -Then inserts seq as if by calling os.rdbuf()->sputn(seq, n), where n is the larger of os.width() -and str.size(); then calls os.width(0)." -

-

-Additionally, saying that it's a "formatted output function" activates 27.7.3.6.1 [ostream.formatted.reqmts]/1's wording for -sentry objects. -

- -

[2014-02-14 Issaquah meeting: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Edit 27.7.6 [quoted.manip] as follows:

    - -
    -template <class charT>
-  unspecified quoted(const charT* s, charT delim=charT('"'), charT escape=charT('\\'));
-template <class charT, class traits, class Allocator>
-  unspecified quoted(const basic_string<charT, traits, Allocator>& s,
-                     charT delim=charT('"'), charT escape=charT('\\'));
-
    -

    --2- Returns: An object of unspecified type such that if out is an instance of basic_ostream with member -type char_type the same as charT, then the expression out << quoted(s, delim, escape) behaves -as if it inserts the following characters into out using character inserter function templates (27.7.3.6.4), -which may throw ios_base::failure (27.5.3.1.1)a formatted output function (27.7.3.6.1 [ostream.formatted.reqmts]) -of out. This forms a character sequence seq, initially consisting of the following elements: -

    -
      -

    • -delim. -

      • -

    • -Each character in s. If the character to be output is equal to escape or delim, as determined by -operator==, first output escape. -

      • -

    • -delim. -

      • -
    -

    -Let x be the number of elements initially in seq. Then padding is determined for seq as described -in 27.7.3.6.1 [ostream.formatted.reqmts], seq is inserted as if by calling out.rdbuf()->sputn(seq, n), where -n is the larger of out.width() and x, and out.width(0) is called. -The expression out << quoted(s, delim, escape) shall have type basic_ostream<charT, traits>& -and value out. -

    -
    -
    2. - -
- - - - - - -
-

2346. integral_constant's member functions should be marked noexcept

-

Section: 20.10.3 [meta.help] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2013-11-05 Last modified: 2015-04-08

-

View all other issues in [meta.help].

-

View all issues with C++14 status.

-

Discussion:

-

-Obvious. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Edit 20.10.3 [meta.help] as indicated:

    - -
    -namespace std {
-  template<class T, T v>
-  struct integral_constant {
-    static constexpr T value = v;
-    typedef T value_type;
-    typedef integral_constant<T,v> type;
-    constexpr operator value_type() const noexcept { return value; }
-    constexpr value_type operator()() const noexcept { return value; }
-  };
-  […]
-}
-
    -
    2. - -
- - - - - - -
-

2350. min, max, and minmax should be constexpr

-

Section: 25.4.7 [alg.min.max] Status: C++14 - Submitter: Ville Voutilainen Opened: 2013-12-15 Last modified: 2015-04-08

-

View all other issues in [alg.min.max].

-

View all issues with C++14 status.

-

Discussion:

-

-Having min, max, and minmax constexpr -was a large part of the motivation to allow reference-to-const arguments for -constexpr functions as per -N3039. -Furthermore, initializer_lists are immutable and not-movable-from -for large part in order to allow using them in constexpr contexts -and other hoisting-optimizations. In N3797 -version of the draft none of these functions are constexpr, and they should be made -constexpr. -

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. In 25.1 [algorithms.general], header <algorithm> synopsis, and 25.4.7 [alg.min.max], -change as indicated (add constexpr to every signature before min_element):

    - -
    -template<class T> constexpr const T& min(const T& a, const T& b);
-template<class T, class Compare>
-constexpr const T& min(const T& a, const T& b, Compare comp);
-[…]
-template<class T>
-constexpr T min(initializer_list<T> t);
-template<class T, class Compare>
-constexpr T min(initializer_list<T> t, Compare comp);
-[…]
-template<class T> constexpr const T& max(const T& a, const T& b);
-template<class T, class Compare>
-constexpr const T& max(const T& a, const T& b, Compare comp);
-[…]
-template<class T>
-constexpr T max(initializer_list<T> t);
-template<class T, class Compare>
-constexpr T max(initializer_list<T> t, Compare comp);
-[…]
-template<class T> constexpr pair<const T&, const T&> minmax(const T& a, const T& b);
-template<class T, class Compare>
-constexpr pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
-[…]
-template<class T>
-constexpr pair<T, T> minmax(initializer_list<T> t);
-template<class T, class Compare>
-constexpr pair<T, T> minmax(initializer_list<T> t, Compare comp);
-
    -
    2. - -
- - - - - - -
-

2354. Unnecessary copying when inserting into maps with braced-init syntax

-

Section: 23.4.4.1 [map.overview], 23.4.5.1 [multimap.overview], 23.5.4.1 [unord.map.overview], 23.5.5.1 [unord.multimap.overview] Status: WP - Submitter: Geoffrey Romer Opened: 2014-01-08 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

-The rvalue-reference insert() members of map, multimap, unordered_map, and -unordered_multimap are specified as function templates, where the rvalue-reference parameter type -depends on the template parameter. -As a consequence, these overloads cannot be invoked via braced-initializer syntax (e.g. my_map.insert({key, value})), -because the template argument cannot be deduced from a braced-init-list. Such calls instead resolve to the -const lvalue reference overload, which forces a non-elidable copy of the argument, despite the fact that the -argument is an rvalue, and so should be eligible for moving and copy elision. -

-This leads to sub-optimal performance for copyable values, and makes this syntax unusable with noncopyable -values. This is particularly problematic because sources such as Josuttis's "C++ Standard Library" recommend -this syntax as the preferred way to insert into a map in C++11. -

-I think this can be fixed by adding an equivalent non-template value_type&& overload for each affected -member template. Simply declaring these members in the class synopses should be sufficient; their semantics are -already dictated by the container concepts (c.f. the corresponding lvalue-reference overloads, which have no -additional discussion beyond being listed in the synopsis). -

- -

[2012-02-13 Issaquah]

- -

-AJM: Is this not better solved by emplace? -

- -

-Nico: emplace was a mistake, it breaks a uniform pattern designed into the STL. -Hence, this fix is important, it should be the preferred way to do this. -

- -

-JonW: emplace is still more efficient, as this form must make a non-elidable copy. -

- -

-GeoffR: Also, cannot move from a const key, must always make a copy. -

- -

-Poll for adopting the proposed wording: -

-SF: 1 WF: 4 N: 4 WA: 1 SA: 0 -

- -

-Move to Ready, pending implementation experience. -

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Change 23.4.4.1 [map.overview], class template map synopsis, as indicated:

    - -
    -[…]
-pair<iterator, bool> insert(const value_type& x);
-pair<iterator, bool> insert(value_type&& x);
-template <class P> pair<iterator, bool> insert(P&& x);
-iterator insert(const_iterator position, const value_type& x);
-iterator insert(const_iterator position, value_type&& x);
-template <class P>
-  iterator insert(const_iterator position, P&&);
-[…]
-
    -
    2. - -

  2. Change 23.4.5.1 [multimap.overview], class template multimap synopsis, as indicated:

    - -
    -[…]
-iterator insert(const value_type& x);
-iterator insert(value_type&& x);
-template <class P> iterator insert(P&& x);
-iterator insert(const_iterator position, const value_type& x);
-iterator insert(const_iterator position, value_type&& x);
-template <class P> iterator insert(const_iterator position, P&& x);
-[…]
-
    -
    3. - -

  3. Change 23.5.4.1 [unord.map.overview], class template unordered_map synopsis, as indicated:

    - -
    -[…]
-pair<iterator, bool> insert(const value_type& obj);
-pair<iterator, bool> insert(value_type&& obj);
-template <class P> pair<iterator, bool> insert(P&& obj);
-iterator insert(const_iterator hint, const value_type& obj);
-iterator insert(const_iterator hint, value_type&& obj);
-template <class P> iterator insert(const_iterator hint, P&& obj);
-[…]
-
    -
    4. - -

  4. Change 23.5.5.1 [unord.multimap.overview], class template unordered_multimap synopsis, as indicated:

    - -
    -[…]
-iterator insert(const value_type& obj);
-iterator insert(value_type&& obj);
-template <class P> iterator insert(P&& obj);
-iterator insert(const_iterator hint, const value_type& obj);
-iterator insert(const_iterator hint, value_type&& obj);
-template <class P> iterator insert(const_iterator hint, P&& obj);
-[…]
-
    -
    5. - -
- - - - - -
-

2356. Stability of erasure in unordered associative containers

-

Section: 23.2.5 [unord.req] Status: C++14 - Submitter: Joaquín M López Muñoz Opened: 2014-01-21 Last modified: 2015-04-08

-

View other active issues in [unord.req].

-

View all other issues in [unord.req].

-

View all issues with C++14 status.

-

Discussion:

-

-Issue 518 resolution for unordered associative containers, modelled after that of issue 371, -which is related to associative containers, states that insertion, erasure and rehashing preserve the relative ordering -of equivalent elements. Unfortunately, this is not sufficient to guarantee the validity of code such as this: -

-
-std::unordered_multimap<int, int> m;
-auto i = m.begin();
-while (i != m.end()) {
-  if (pred(i))
-    m.erase(i++);
-  else
-    ++i;
-}
-
-

-(which is a direct translation from multimap to unordered_multimap of the motivating example in 371), -or even this: -

-
-std::unordered_multimap<int, int> m;
-auto p = m.equal_range(k);
-while (p.first != p.second) {
-  if (pred(p.first))
-    m.erase((p.first)++);
-  else
-    ++(p.first);
-}
-
-

-because the relative ordering of non-equivalent elements elements could potentially change after erasure (not that any actual -implementation does that, anyway). Such an underspecification does not happen for regular associative containers, where the -relative ordering of non-equivalent elements is kept by design. -

- -

[2014-02-13 Issaquah: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 23.2.5 [unord.req], p14 as indicated:

    - -

    --14- The insert and emplace members shall not affect the validity of references to container elements, but may -invalidate all iterators to the container. The erase members shall invalidate only iterators and references -to the erased elements, and preserve the relative order of the elements that are not erased. -

    -
    2. -
- - - - - -
-

2357. Remaining "Assignable" requirement

-

Section: 25.3.13 [alg.partitions] Status: C++14 - Submitter: Daniel Krügler Opened: 2014-02-01 Last modified: 2015-04-08

-

View all other issues in [alg.partitions].

-

View all issues with C++14 status.

-

Discussion:

-

-The Requires element of partition_copy says (emphasis mine): -

-

-Requires: InputIterator's value type shall be Assignable, and … -

-

-The C++03 term Assignable was replaced by CopyAssignable, remaining cleanups happened via LWG issue -972, but algorithm partition_copy was not affected at that time (during that time the requirements -of partition_copy didn't mention writable nor assignable, but I cannot track down at the moment where these requirements -had been added). Presumably this requirement should be corrected similarly to the approach used in 972. -

-Another question is whether a CopyAssignable is needed here, given the fact that we already require "writable to" an -OutputIterator which is defined in 24.2.1 [iterator.requirements.general] and does already impose the necessary -statement -

-
-*out = *in;
-
-

-Given the fact that partition_copy never touches any input value twice, there is no reason why anything more than -writable to should be necessary. -

-The below suggested primary resolution does not respond to the second part of this question. -

- -

[Issaquah 20014-10-11: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Modify 25.3.13 [alg.partitions], p12 as indicated:

    - -

    --12- Requires: InputIterator's value type shall be CopyAssignable, and shall be writable -to the out_true and out_false OutputIterators, and shall be convertible to Predicate's -argument type. The input range shall not overlap with either of the output ranges. -

    -
    2. -
- - - - - -
-

2359. How does regex_constants::nosubs affect basic_regex::mark_count()?

-

Section: 28.5.1 [re.synopt] Status: C++14 - Submitter: Jonathan Wakely Opened: 2014-02-01 Last modified: 2015-04-08

-

View other active issues in [re.synopt].

-

View all other issues in [re.synopt].

-

View all issues with C++14 status.

-

Discussion:

-

-As discussed in c++std-lib-35399 and its replies, -I can see two possible interpretations of the effects of regex_constants::nosubs: -

-
    -

  1. -The effect of nosubs only applies during matching. Parentheses are -still recognized as marking a sub-expression by the basic_regex -compiler, and basic_regex::mark_count() still returns the number of -marked sub-expressions, but anything they match is not stored in the -results. This means it is not always true that results.size() == r.mark_count() + 1 -for a successful match. -

    2. -

  2. -nosubs affects how a regular expression is compiled, altering the -state of the std::basic_regex object so that mark_count() returns -zero. This also affects any subsequent matching. -

    3. -
-

-The definition of nosubs should make this clear. -

-The wording in 28.5.1 [re.synopt]/1 seems to imply that nosubs only has -effects during matching, which is (1), but all known implementations -do (2). John Maddock confirmed that (2) was intended. -

- -

[Issaquah 2014-02-12: Move to Immediate]

- - - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Apply the following edit to the table in 28.5.1 [re.synopt]/1

    - -

    -Specifies that no sub-expressions shall be considered to be -marked, so that when a regular expression is matched against a character container -sequence, no sub-expression matches shall be stored in the supplied -match_results structure. -

    -
    2. -
- - - - - - -
-

2360. reverse_iterator::operator*() is unimplementable

-

Section: 24.5.1.1 [reverse.iterator] Status: C++14 - Submitter: Stephan T. Lavavej Opened: 2014-02-07 Last modified: 2015-04-08

-

View all other issues in [reverse.iterator].

-

View all issues with C++14 status.

-

Discussion:

-

-Previously, C++03 24.4.1.3.3 [lib.reverse.iter.op.star] required: -

-
-
-reference operator*() const;
-
-
-

-Effects: -

-
-Iterator tmp = current;
-return *--tmp;
-
-
-

-Now, N3797 24.5.1.1 [reverse.iterator] depicts: -

-
-private:
-  Iterator deref_tmp; // exposition only
-};
-
-

-And 24.5.1.3.4 [reverse.iter.op.star] requires: -

-
-
-reference operator*() const;
-
-
-

-Effects: -

-
-deref_tmp = current;
---deref_tmp;
-return *deref_tmp;
-
-

-[Note: This operation must use an auxiliary member variable rather than a temporary variable to avoid -returning a reference that persists beyond the lifetime of its associated iterator. (See 24.2.) — end note] -

-
- -

-As written, this won't compile, because operator*() is const yet it's modifying (via assignment and decrement) -the deref_tmp data member. So what happens if you say "mutable Iterator deref_tmp;"? -

-DANGER: WARP CORE BREACH IMMINENT. -

-The Standard requires const member functions to be callable from multiple threads simultaneously. This is -17.6.5.9 [res.on.data.races]/3: "A C++ standard library function shall not directly or indirectly modify objects (1.10) -accessible by threads other than the current thread unless the objects are accessed directly or indirectly via the function's -non-const arguments, including this." -

-Multiple threads simultaneously modifying deref_tmp will trigger data races, so both mutable and some form of -synchronization (e.g. mutex or atomic) are actually necessary! -

-Here's what implementations currently do: Dinkumware/VC follows C++03 and doesn't use deref_tmp (attempting to -implement it is what led me to file this issue). According to Jonathan Wakely, libstdc++ also follows C++03 (see -PR51823 which is suspended until LWG 2204 is resolved). According to -Marshall Clow, libc++ uses deref_tmp with mutable but without synchronization, so it can trigger data races. -

-This deref_tmp Standardese was added by LWG 198 "Validity of pointers and references unspecified after -iterator destruction" and is present in Working Papers going back to N1638 -on April 11, 2004, long before C++ recognized the existence of multithreading and developed the "const means simultaneously -readable" convention. -

-A related issue is LWG 1052 "reverse_iterator::operator-> should also support smart pointers" which -mentioned the need to depict mutable in the Standardese, but it was resolved NAD Future and no change was made. -

-Finally, LWG 2204 "reverse_iterator should not require a second copy of the base iterator" talked about -removing deref_tmp, but without considering multithreading. -

-I argue that deref_tmp must be removed. Its existence has highly undesirable consequences: either no synchronization -is used, violating the Standard's usual multithreading guarantees, or synchronization is used, adding further costs for all -users that benefit almost no iterators. -

-deref_tmp is attempting to handle iterators that return references to things "inside themselves", which I usually call -"stashing iterators" (as they have a secret stash). Note that these are very unusual, and are different from proxy iterators like -vector<bool>::iterator. While vector<bool>::iterator's operator*() does not return a true -reference, it refers to a bit that is unrelated to the iterator's lifetime. -

- -

[2014-02-14 Issaquah meeting: Move to Immediate]

- -

-Strike superfluous note to avoid potential confusion, and move to Immediate. -

- - - -

Proposed resolution:

-

This wording is relative to N3797.

- -
    -

  1. Change class template reverse_iterator synopsis, 24.5.1.1 [reverse.iterator], as indicated:

    - -
    -[…]
-protected:
-  Iterator current;
-private:
-  Iterator deref_tmp; // exposition only
-};
-
    -
    2. - -

  2. Change 24.5.1.3.4 [reverse.iter.op.star] as indicated:

    - -
    -reference operator*() const;
-
    -
    -

    --1- Effects: -

    -
    -deref_tmp = current;
---deref_tmp;
-return *deref_tmp;
-Iterator tmp = current;
-return *--tmp;
-
    -

    --2- [Note: This operation must use an auxiliary member variable rather than a temporary variable to -avoid returning a reference that persists beyond the lifetime of its associated iterator. (See 24.2.) — end note] -

    -
    -
    3. -
- - - - - - -
-

2361. Apply 2299 resolution throughout library

-

Section: 20.8.1.2 [unique.ptr.single], 20.7.3.1 [pointer.traits.types], 20.7.7.1 [allocator.uses.trait], 20.7.8.1 [allocator.traits.types], 23.2.3 [sequence.reqmts] Status: WP - Submitter: Jonathan Wakely Opened: 2014-02-14 Last modified: 2015-04-08

-

View all other issues in [unique.ptr.single].

-

View all issues with WP status.

-

Discussion:

-

-LWG 2299 addressed a N.B. comment pointing out that recently added -wording about a type existing was not clear what happens if the type -exists but is inaccessible. There are 16 pre-existing uses of the same -language in the library that should use the same wording used to -resolve 2299. -

- -

-The relevant paragraphs are: -

- -

-20.8.1.2 [unique.ptr.single] -

-20.7.3.1 [pointer.traits.types] -

-20.7.7.1 [allocator.uses.trait] -

-20.7.8.1 [allocator.traits.types] -

-23.2.3 [sequence.reqmts] -

- -

[2014-05-16, Daniel provides wording]

- - -

[2014-05-18 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.7.3.1 [pointer.traits.types] as indicated:

    - -
    -
    -typedef see below element_type;
-
    -
    -

    --1- Type: Ptr::element_type if such a type existsthe qualified-id Ptr::element_type is -valid and denotes a type (14.8.2 [temp.deduct]); otherwise, T if Ptr is a class template instantiation -of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the -specialization is ill-formed. -

    -
    - -
    -typedef see below difference_type;
-
    -
    -

    --2- Type: Ptr::difference_type if such a type existsthe qualified-id Ptr::difference_type is -valid and denotes a type (14.8.2 [temp.deduct]); otherwise, std::ptrdiff_t. -

    -
    - -
    -template <class U> using rebind = see below;
-
    -
    -

    --3- Alias template: Ptr::rebind<U> if such a type existsthe qualified-id -Ptr::rebind<U> is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -SomePointer<U, Args> if Ptr is a class template instantiation of the form SomePointer<T, Args>, -where Args is zero or more type arguments; otherwise, the instantiation of rebind is ill-formed. -

    -
    -
    -
    2. - -

  2. Change 20.7.7.1 [allocator.uses.trait] p1 as indicated:

    - -
    -
    -template <class T, class Alloc> struct uses_allocator;
-
    -
    -

    --1- Remarks: automatically detects whether T has a nested allocator_type that is -convertible from Alloc. Meets the BinaryTypeTrait requirements (20.10.1). The implementation shall provide a definition -that is derived from true_type if a typethe qualified-id T::allocator_type existsis -valid and denotes a type (14.8.2 [temp.deduct]) and is_convertible<Alloc, T::allocator_type>::value != false, -otherwise it shall be derived from false_type. […] -

    -
    -
    -
    3. - -

  3. Change 20.7.8.1 [allocator.traits.types] as indicated:

    - -
    -
    -typedef see below pointer;
-
    -
    -

    --1- Type: Alloc::pointer if such a type existsthe qualified-id Alloc::pointer is -valid and denotes a type (14.8.2 [temp.deduct]); otherwise, value_type*. -

    -
    - -
    -typedef see below const_pointer;
-
    -
    -

    --2- Type: Alloc::const_pointer if such a type existsthe qualified-id Alloc::const_pointer is -valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -pointer_traits<pointer>::rebind<const value_type>. -

    -
    - -
    -typedef see below void_pointer;
-
    -
    -

    --3- Type: Alloc::void_pointer if such a type existsthe qualified-id Alloc::void_pointer is -valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -pointer_traits<pointer>::rebind<void>. -

    -
    - -
    -typedef see below const_void_pointer;
-
    -
    -

    --4- Type: Alloc::const_void_pointer if such a type existsthe qualified-id -Alloc::const_void_pointer is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -pointer_traits<pointer>::rebind<const void>. -

    -
    - -
    -typedef see below difference_type;
-
    -
    -

    --5- Type: Alloc::difference_type if such a type existsthe qualified-id -Alloc::difference_type is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -pointer_traits<pointer>::difference_type. -

    -
    - -
    -typedef see below size_type;
-
    -
    -

    --6- Type: Alloc::size_type if such a type existsthe qualified-id -Alloc::size_type is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -make_unsigned_t<difference_type>. -

    -
    - -
    -typedef see below propagate_on_container_copy_assignment;
-
    -
    -

    --7- Type: Alloc::propagate_on_container_copy_assignment if such a type existsthe qualified-id -Alloc::propagate_on_container_copy_assignment is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -false_type. -

    -
    - -
    -typedef see below propagate_on_container_move_assignment;
-
    -
    -

    --8- Type: Alloc::propagate_on_container_move_assignment if such a type existsthe qualified-id -Alloc::propagate_on_container_move_assignment is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -false_type. -

    -
    - -
    -typedef see below propagate_on_container_swap;
-
    -
    -

    --9- Type: Alloc::propagate_on_container_swap if such a type existsthe qualified-id -Alloc::propagate_on_container_swap is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -false_type. -

    -
    - -
    -template <class T> using rebind_alloc = see below;
-
    -
    -

    --10- Alias template: Alloc::rebind<T>::other if such a type existsthe qualified-id -Alloc::rebind<T>::other is valid and denotes a type (14.8.2 [temp.deduct]); otherwise, -Alloc<T, Args> if Alloc is a class template instantiation of the form Alloc<U, Args>, -where Args is zero or more type arguments; otherwise, the instantiation of rebind_alloc is ill-formed. -

    -
    -
    -
    4. - -

  4. Change 20.8.1.2 [unique.ptr.single] p3 as indicated:

    - -

    --3- If the typequalified-id remove_reference_t<D>::pointer existsis -valid and denotes a type (14.8.2 [temp.deduct]), then unique_ptr<T, D>::pointer shall be a synonym -for remove_reference_t<D>::pointer. […] -

    -
    5. - -

  5. Change 23.2.3 [sequence.reqmts] p3 as indicated:

    - -

    --3- In Tables 100 and 101, X denotes a sequence container class, a denotes a value of X containing elements -of type T, A denotes X::allocator_type if it existsthe qualified-id -X::allocator_type is valid and denotes a type (14.8.2 [temp.deduct]) and std::allocator<T> -if it doesn't, […] -

    -
    6. - - -
- - - - - - -
-

2364. deque and vector pop_back don't specify iterator invalidation requirements

-

Section: 23.3.3.4 [deque.modifiers], 23.3.6.5 [vector.modifiers] Status: WP - Submitter: Deskin Miller Opened: 2014-02-17 Last modified: 2015-05-22

-

View all other issues in [deque.modifiers].

-

View all issues with WP status.

-

Discussion:

-

-I think it's obvious that vector::pop_back invalidates the path-the-end iterator, but I cannot find language that says so to -my satisfaction in the Standard. N3797 23.2.3 [sequence.reqmts] Table 101 lists a.pop_back() semantics as "Destroys the -last element", but nowhere do I see this required to invalidate the end iterator (or iterators previously referring to the last element). - [container.reqmts.general]/11 states "Unless otherwise specified (either explicitly or by defining a function in terms of -other functions), invoking a container member function or passing a container as an argument to a library function shall not -invalidate iterators to, or change the values of, objects within that container." 23.3.6.5 [vector.modifiers]/3 says that each -flavor of vector::erase "Invalidates iterators and references at or after the point of the erase", but pop_back isn't -discussed, and it wasn't specified in terms of erase. -

-

-Similarly for std::deque, 23.2.3 [sequence.reqmts] Table 101 and [container.reqmts.general]/11 both apply. -Yet 23.3.3.4 [deque.modifiers] likewise doesn't discuss pop_back nor pop_front. Furthermore paragraph 4 fails to -specify the iterator-invalidation guarantees when erasing the first element but not the last. -

-Both std::vector and std::deque are in contrast to std::list, which says in 23.3.5.4 [list.modifiers]/3 -regarding pop_back (as well as all forms of erase, pop_front, and clear) "Effects: Invalidates only -the iterators and references to the erased elements." -

- -

[2014-06-16 Jonathan comments and improves wording]

- - -

-I believe this reflects our preferred form discussed earlier, -specifically putting the signatures with the erase signatures, so that -the full specification of erase() applies to the pop_xxx() functions. -This covers the case for deque where pop_front() erases the only -element (which is both the first and last element). -

-Open question: the "erase" wording talks about "An erase operation" — -are pop_front and pop_back clearly covered by "erase operations"? I -believe so, as 23.3.3.1 [deque.overview]/1 and other places talk about "insert -and erase operations" which covers push/pop functions too. I've added -a note which could be used to clarify that if desired. -

- -Previous resolution [SUPERSEDED]: -

-

-

This wording is relative to N3936.

- -
    -

  1. Change 23.3.3.4 [deque.modifiers] as indicated:

    - -
    -
    -iterator erase(const_iterator position);
-iterator erase(const_iterator first, const_iterator last);
-
    -

    --4- Effects: An erase operation that erases the last element of a deque invalidates only the past-the-end -iterator and all iterators and references to the erased elements. An erase operation that erases the first -element of a deque but not the last element invalidates only iterators and references to the erased elements. -An erase operation that erases neither the first element nor the last element of a deque invalidates the past-the-end iterator -and all iterators and references to all the elements of the deque. -

    --5- […] -

    --6- […] -

    -
    - -
    -void pop_front();
-void pop_back();
-
    -

    --?- Effects: pop_front invalidates iterators and references to the first element of the deque. -pop_back invalidates the past-the-end iterator, and all iterators and references to the last element of the deque. -

    -
    -
    -
    2. - -

  2. Change 23.3.6.5 [vector.modifiers] as indicated:

    -
    -
    -

    --5- […] -

    -
    - -
    -void pop_back();
-
    -

    --?- Effects: Invalidates the past-the-end iterator, and iterators and references to the last element of the vector. -

    -
    -
    -
    3. -
-
- -

[2014-06-21 Rapperswil]

- -

-Tony van Eerd: Would be good to define "an erase operation is ..." somewhere. -

-AM: The containers clause is known to be suboptimal in many ways. -

-Looks good -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

- -

This wording is relative to N3936.

- -
    -

  1. Change 23.3.3.4 [deque.modifiers] as indicated:

    - -
    -
    -iterator erase(const_iterator position);
-iterator erase(const_iterator first, const_iterator last);
-void pop_front();
-void pop_back();
-
    -

    --4- Effects: An erase operation that erases the last element of a deque invalidates only the past-the-end -iterator and all iterators and references to the erased elements. An erase operation that erases the first -element of a deque but not the last element invalidates only iterators and references to the erased elements. -An erase operation that erases neither the first element nor the last element of a deque invalidates the past-the-end iterator -and all iterators and references to all the elements of the deque. [Note: pop_front and pop_back -are erase operations — end note] -

    -
    -
    -
    2. - -

  2. Change 23.3.6.5 [vector.modifiers] as indicated:

    -
    -
    -iterator erase(const_iterator position);
-iterator erase(const_iterator first, const_iterator last);
-void pop_back();
-
    -

    --3- Effects: Invalidates iterators and references at or after the point of the erase. -

    -
    -
    -
    3. -
- - - - - - -
-

2365. Missing noexcept in shared_ptr::shared_ptr(nullptr_t)

-

Section: 20.8.2.2 [util.smartptr.shared] Status: WP - Submitter: Cassio Neri Opened: 2014-02-13 Last modified: 2015-04-08

-

View other active issues in [util.smartptr.shared].

-

View all other issues in [util.smartptr.shared].

-

View all issues with WP status.

-

Discussion:

-

-The declaration and definition of shared_ptr::shared_ptr(nullptr_t), given in 20.8.2.2 [util.smartptr.shared], is -

-
-constexpr shared_ptr(nullptr_t) : shared_ptr() { }
-
-

-The intention seems clear: this constructor should have the same semantics of the default constructor. However, contrarily to the -default constructor, this one is not noexcept. In contrast, unique_ptr::unique_ptr(nullptr_t) is noexcept, -as per 20.8.1.2 [unique.ptr.single]: -

-
-constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
-
-

-Both libstdc++ and libc++ have added noexcept to shared_ptr::shared_ptr(nullptr_t). Microsoft's STL has not. -

- -

[2014-03-26 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

- -

This wording is relative to N3936.

- -
    -

  1. Change class template shared_ptr synopsis, 20.8.2.2 [util.smartptr.shared], as indicated:

    - -
    -
    -constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
-
    -
    -
    2. -
- - - - - - -
-

2369. constexpr max(initializer_list) vs max_element

-

Section: 25.4.7 [alg.min.max] Status: WP - Submitter: Marc Glisse Opened: 2014-02-21 Last modified: 2015-05-22

-

View all other issues in [alg.min.max].

-

View all issues with WP status.

-

Discussion:

-

-As part of the resolution for LWG issue 2350, max(initializer_list) was marked as constexpr. Looking -at two implementations of this function (libstdc++ and libc++), both implement it in terms of max_element, which is not -marked as constexpr. This is inconsistent and forces some small amount of code duplication in the implementation. Unless we -remove constexpr from this overload of max, I believe we should add constexpr to max_element. -

- -

[2015-02 Cologne]

- -

-AM: Can we implement this with the C++14 constexpr rules? JM: Yes. AM: Ready? [Yes] -

-Accepted. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. In 25.1 [algorithms.general], header <algorithm> synopsis, and 25.4.7 [alg.min.max], change as -indicated (add constexpr to every signature from the first min_element to the second minmax_element)::

    - -
    -
    -template<class ForwardIterator>
-constexpr ForwardIterator min_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-constexpr ForwardIterator min_element(ForwardIterator first, ForwardIterator last,
-                                      Compare comp);
-[…]
-template<class ForwardIterator>
-constexpr ForwardIterator max_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-constexpr ForwardIterator max_element(ForwardIterator first, ForwardIterator last,
-                                      Compare comp);
-[…]
-template<class ForwardIterator>
-constexpr pair<ForwardIterator, ForwardIterator>
-minmax_element(ForwardIterator first, ForwardIterator last);
-template<class ForwardIterator, class Compare>
-constexpr pair<ForwardIterator, ForwardIterator>
-minmax_element(ForwardIterator first, ForwardIterator last, Compare comp);
-
    -
    -
    2. - -
- - - - - -
-

2371. [fund.ts] No template aliases defined for new type traits

-

Section: 20.10.2 [meta.type.synop] Status: WP - Submitter: Joe Gottman Opened: 2014-03-07 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

- -

-The library fundamentals specification defines two new type trait template classes: invocation_type and raw_invocation_type. -But it does not define the corresponding template aliases. Note that both of these classes define a member typedef type and no -other public members, so according to the argument in N3887 -the template aliases should be defined. -

- -

[2013-06-21 Rapperswil]

- -

-Accept for Library Fundamentals TS Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3908.

- -
    -

  1. Add the following to section 3.3.1[meta.type.synop] of the -Library Fundamentals specification -as indicated: -

    - -
    -namespace std {
-namespace experimental {
-inline namespace fundamentals_v1 {
-  […]
-  // 3.3.2, Other type transformations
-  template <class> class invocation_type; // not defined
-  template <class F, class... ArgTypes> class invocation_type<F(ArgTypes...)>;
-  template <class> class raw_invocation_type; // not defined
-  template <class F, class... ArgTypes> class raw_invocation_type<F(ArgTypes...)>;
-  
-  template <class T> 
-    using invocation_type_t = typename invocation_type<T>::type;
-  template <class T> 
-    using raw_invocation_type_t = typename raw_invocation_type<T>::type;
-  
-} // namespace fundamentals_v1
-} // namespace experimental
-} // namespace std
-
    -
    2. - -
- - - - - -
-

2374. [fund.ts] Remarks for optional::to_value are too restrictive

-

Section: X [optional.object.observe] Status: WP - Submitter: Jonathan Wakely Opened: 2014-03-25 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

- -

-In Bristol I think I claimed that the remarks for optional::to_value() -were unimplementable and the function could only be constexpr if both -constructors that could be called were constexpr, but I was wrong. -The remarks should be reverted to the original pre-n3793 form. -

- -

[2013-06-21 Rapperswil]

- -

-Accept for Library Fundamentals TS Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N3908.

- -
    -

  1. Change [optional.object.observe] p23 of the -Library Fundamentals specification -as indicated: -

    - -
    -template <class U> constexpr T value_or(U&& v) const &;
-
    -

    -[…] -

    --23- Remarks: If both constructors of T which could be selected are constexpr constructorsthe -selected constructor of T is a constexpr constructor, this function -shall be a constexpr function. -

    -
    -
    -
    2. - -
- - - - - -
-

2376. bad_weak_ptr::what() overspecified

-

Section: 20.8.2.1 [util.smartptr.weakptr] Status: WP - Submitter: Jonathan Wakely Opened: 2014-03-27 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

-20.8.2.1 [util.smartptr.weakptr] p2 requires bad_weak_ptr to return precisely -the string "bad_weak_ptr". -

-There was general agreement on the reflector and at the Issaquah -meeting that this is over-constrained and implementation should be -free to return something more descriptive if desired. -

-The proposed resolution makes bad_weak_ptr consistent with other -exception types such as bad_alloc and bad_cast. -

-If accepted, the P/R for issue 2233, which currently uses similar -wording to bad_weak_ptr, could be updated appropriately. -

- -

[2014-03-27 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Edit 20.8.2.1 [util.smartptr.weakptr]:

    - -
    -
    -bad_weak_ptr() noexcept;
-
    -

    --2- Postconditions: what() returns "bad_weak_ptr"an implementation-defined NTBS. -

    -
    -
    -
    2. -
- - - - - - -
-

2377. std::align requirements overly strict

-

Section: 20.7.5 [ptr.align] Status: WP - Submitter: Peter Dimov Opened: 2014-03-30 Last modified: 2015-04-08

-

View all other issues in [ptr.align].

-

View all issues with WP status.

-

Discussion:

-

-std::align requires that its alignment argument shall be "a fundamental alignment value or an -extended alignment value supported by the implementation in this context". -

-This requirement is overly strict. There are use cases that require a buffer aligned at values that are not tied -to the C++ implementation, such as page size, cache line size, sector size. These come from the hardware or the -OS and are generally not known until run time. The implementation of std::align does not depend on the -requirement that alignment be a fundamental or an extended alignment value; any power of two would be handled -the same way. -

-In addition, it is not possible for the user to even determine whether a value is "a fundamental alignment value -or an extended alignment value supported by the implementation in this context". One would expect values coming -from alignof to be fine, but I'm not sure whether even that is guaranteed in the presence of alignas. -

-Therefore, I propose that -

-

-Requires: -

-
    -

  • alignment shall be a fundamental alignment value or an extended alignment value supported by -the implementation in this context

    • -
-
-

-be changed to -

-

-Requires: -

-
    -

  • alignment shall be a power of two

    • -
-
- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Edit 20.7.5 [ptr.align] p2 as indicated:

    - -
    -
    -void* align(std::size_t alignment, std::size_t size,
-  void*& ptr, std::size_t& space);
-
    -

    --1- […] -

    --2- Requires: -

    -
      -

    • -alignment shall be a fundamental alignment value or an extended alignment value supported by -the implementation in this contextpower of two -

      • -
    -
    -
    -
    2. -
- - - - - - -
-

2378. Behaviour of standard exception types

-

Section: 18.6.2.1 [bad.alloc], 18.6.2.2 [new.badlength], 18.7.2 [bad.cast], 18.7.3 [bad.typeid], 18.8.2 [bad.exception] Status: WP - Submitter: Andy Sawyer Opened: 2014-03-31 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-I think we have an issue with the specification of some of the standard exception types. -In particular, several of them have default constructors with remarks to the effect that -"The result of calling what() on the newly constructed object is implementation-defined". -(In some cases this is contradictory to a further specification of what(), which -is specified to return an implementation-defined NTBS.) -

- -

-Previous resolution from Andy [SUPERSEDED]: -

-
-

This wording is relative to N3936.

- -
    -

  1. Edit 18.6.2.1 [bad.alloc] p3 as indicated:

    - -
    -
    -bad_alloc() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is - implementation-definedwhat() returns an implementation-defined NTBS. -

    -
    -
    -
    2. - -

  2. Edit 18.6.2.2 [new.badlength] p3 as indicated: [Drafting note: Added the Postcondition, since we don't -say anything else about bad_array_new_length::what() — end of note]

    - -
    -
    -bad_array_new_length() noexcept;
-
    -

    -[…] -

    --3- RemarksPostcondition: The result of calling what() on the newly constructed object is - implementation-definedwhat() returns an implementation-defined NTBS. -

    -
    -
    -
    3. - -

  3. Edit 18.7.2 [bad.cast] p3 as indicated:

    - -
    -
    -bad_cast() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    4. - -

  4. Edit 18.7.3 [bad.typeid] p3 as indicated:

    - -
    -
    -bad_typeid() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    5. - -

  5. Edit 18.8.2 [bad.exception] p3 as indicated:

    - -
    -
    -bad_exception() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    6. -
-
- -

[2014-06-17, Rapperswil]

- -

-Jonathan provides alternative wording. -

- -

[2015-02, Cologne]

- -

-NJ: I don't know why we need the explict statement about what() here, since bad_array_new_length -already derives.
-AM: yes.
-NJ: Then "what()" is missing from the synopsis.
-AM: Yes, that's an error and it needs to be added. -

-Conclusion: Update the wording to add the missing entry in the synopsis. -

-AM: The issue needs another update; we need to add missing "Remarks". DK updates the paper.
-AM: Any objections to "tentatively ready"? No objections. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Edit 18.6.2.1 [bad.alloc] p3 as indicated:

    - -
    -
    -bad_alloc() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is - implementation-defined. -

    -
    -
    -
    2. - -

  2. Edit 18.6.2.1 [bad.alloc] p5 as indicated:

    - -
    -
    -virtual const char* what() const noexcept;
-
    -
    -

    --5- Returns: An implementation-defined NTBS. -

    --?- Remarks: The message may be a null-terminated multibyte string (17.5.2.1.4.2), suitable for conversion -and display as a wstring (21.3, 22.4.1.4). -

    -
    -
    - -
    3. - -

  3. Edit class bad_array_new_length synopsis 18.6.2.2 [new.badlength] as indicated:

    - -
    -
    -namespace std {
-  class bad_array_new_length : public bad_alloc {
-  public:
-    bad_array_new_length() noexcept;
-    virtual const char* what() const noexcept;
-  };
-}
-
    -
    -
    4. - -

  4. Edit 18.6.2.2 [new.badlength] as indicated:

    - -
    -
    -bad_array_new_length() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is - implementation-defined. -

    -
    -
    -virtual const char* what() const noexcept;
-
    -
    -

    --?- Returns: An implementation-defined NTBS. -

    --?- Remarks: The message may be a null-terminated multibyte string (17.5.2.1.4.2), suitable for conversion -and display as a wstring (21.3, 22.4.1.4). -

    -
    -
    -
    5. - -

  5. Edit 18.7.2 [bad.cast] p3 as indicated:

    - -
    -
    -bad_cast() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    6. - -

  6. Edit 18.7.3 [bad.typeid] p3 as indicated:

    - -
    -
    -bad_typeid() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    7. - -

  7. Edit 18.8.2 [bad.exception] p3 as indicated:

    - -
    -
    -bad_exception() noexcept;
-
    -

    -[…] -

    --3- Remarks: The result of calling what() on the newly constructed object is implementation-defined.. -

    -
    -
    -
    8. -
- - - - - - -
-

2387. More nested types that must be accessible and unambiguous

-

Section: 20.9.2 [func.require], 20.9.4 [refwrap] Status: WP - Submitter: Jonathan Wakely Opened: 2014-05-23 Last modified: 2015-04-08

-

View other active issues in [func.require].

-

View all other issues in [func.require].

-

View all issues with WP status.

-

Discussion:

-

-Further to 2299 and 2361, 20.9.2 [func.require] p3 and 20.9.4 [refwrap] p3 and p4 -talk about member types without any mention of being accessible and unambiguous. -

- -

[2014-06-05 Daniel provides wording]

- - -

[2014-06-06 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.9.2 [func.require] p3 as indicated:

    - -

    --3- If a call wrapper (20.9.1) has a weak result type the type of its member type result_type is based on the -type T of the wrapper's target object (20.9.1): -

    -
      -

    • if T is a pointer to function type, result_type shall be a synonym for the return type of T;

      • -

    • if T is a pointer to member function, result_type shall be a synonym for the return type of T;

      • -

    • if T is a class type and the qualified-id T::result_type is valid and denotes a type -(14.8.2 [temp.deduct])with a member type result_type, then result_type shall be a synonym for -T::result_type;

      • -

    • otherwise result_type shall not be defined.

      • -
    -
    -
    2. - -

  2. Change 20.9.4 [refwrap] p3+p4 as indicated:

    - -
    -

    --3- The template instantiation reference_wrapper<T> shall define a nested type named argument_type as a -synonym for T1 only if the type T is any of the following: -

    -
      -

    • a function type or a pointer to function type taking one argument of type T1

      • -

    • a pointer to member function R T0::f cv (where cv represents the member function_s cv-qualifiers); -the type T1 is cv T0*

      • -

    • a class type where the qualified-id T::argument_type is valid and denotes a type -(14.8.2 [temp.deduct])with a member type argument_type; the type T1 is -T::argument_type.

      • -
    -

    --4- The template instantiation reference_wrapper<T> shall define two nested types named first_argument_type -and second_argument_type as synonyms for T1 and T2, respectively, only if the type T is any of the -following: -

    -
      -

    • a function type or a pointer to function type taking two arguments of types T1 and T2

      • -

    • a pointer to member function R T0::f(T2) cv (where cv represents the member function's cv-qualifiers); -the type T1 is cv T0*

      • -

    • a class type where the qualified-ids T::first_argument_type and T::second_argument_type are both valid -and both denote types (14.8.2 [temp.deduct])with member types first_argument_type and -second_argument_type; the type T1 is T::first_argument_type. and the type T2 is -T::second_argument_type.

      • -
    -
    - -
    3. -
- - - - - -
-

2389. [fund.ts] function::operator= is over-specified and handles allocators incorrectly

-

Section: X [mods.func.wrap] Status: WP - Submitter: Pablo Halpern Opened: 2014-05-23 Last modified: 2015-04-08

-

View all other issues in [mods.func.wrap].

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

- -

-This issue against the TS is similar to LWG 2386, which is against the standard. The Effects clauses for the assignment -operator for class template function are written as code that constructs a temporary function and then swaps it -with *this. -The intention appears to be that assignment should have the strong exception guarantee, i.e., *this is not modified if -an exception is thrown. The description in the standard is incorrect when *this was originally constructed using an -allocator. The TS attempts to correct the problem, but the correction is incomplete. -

-The wording in the TS uses -get_memory_resource() to construct a temporary function object with the same allocator as the left-hand size -(lhs) of the assignment. The intended result of using this pattern was that the allocator for *this would be unchanged, -but it doesn't quite work. The problem is that the allocator returned by get_memory_resource() is not the same type as -the type-erased allocator used to construct the function object, but rather a type-erased distillation of that type that -is insufficient for making a true copy of the allocator. The rules for type-erased allocators in the TS -([memory.type.erased.allocator]) -specify that the lifetime of the object returned by get_memory_resource() is sometimes tied to the lifetime of *this, -which might cause the (single copy of) the allocator to be destroyed if the swap operation destroys and reconstructs *this, -as some implementations do (and are allowed to do). -

-The desired behavior is that assignment would leave the allocator of the lhs unchanged. The way to achieve this behavior is to -construct the temporary function using the original allocator. Unfortunately, we cannot describe the desired behavior in -pure code, because get_memory_resource() does not really name the type-erased allocator, as mentioned above. The PR below, -therefore, uses pseudo-code, inventing a fictitious ALLOCATOR_OF(f) expression that evaluates to the actual allocator -type, even if that allocator was type erased. I have implemented this PR successfully. -

- -

[2014-06-21, Rapperswil]

- -

-Apply to Library Fundamentals TS (after removing the previous "Throws: Nothing" element to prevent an editorial conflict with -2401). -

- - -

Proposed resolution:

-

This wording is relative to N3908.

- -
    -

  1. Change in [mods.func.wrap] in the Library TS -as indicated: -

    -
    -

    -In the following descriptions, let ALLOCATOR_OF(f) be the allocator specified in the construction of function -f, or allocator<char>() if no allocator was specified. -

    -
    -function& operator=(const function& f);
-
    -
    -

    --5- Effects: function(allocator_arg, get_memory_resource()ALLOCATOR_OF(*this), f).swap(*this); -

    -[…] -

    -
    -
    -function& operator=(function&& f);
-
    -
    -

    --8- Effects: function(allocator_arg, get_memory_resource()ALLOCATOR_OF(*this), std::move(f)).swap(*this); -

    -[…] -

    -
    -
    -function& operator=(nullptr_t);
-
    -
    -

    --11- Effects: If *this != NULL, destroys the target of this. -

    --12- Postconditions: !(*this). The memory resource returned by get_memory_resource() after the assignment -is equivalent to the memory resource before the assignment. [Note: the address returned by get_memory_resource() -might change — end note] -

    --13- Returns: *this -

    -
    -
    -template<class F> function& operator=(F&& f);
-
    -
    -

    --15- Effects: function(allocator_arg, get_memory_resource()ALLOCATOR_OF(*this), -std::forward<F>(f)).swap(*this); -

    -[…] -

    -
    -
    -template<class F> function& operator=(reference_wrapper<F> f);
-
    -
    -

    --18- Effects: function(allocator_arg, get_memory_resource()ALLOCATOR_OF(*this), f).swap(*this); -

    -[…] -

    -
    -
    -
    2. -
- - - - - -
-

2390. [fund.ts] Invocation types and rvalues

-

Section: X [mods.func.wrap] Status: WP - Submitter: Michael Spertus Opened: 2014-05-26 Last modified: 2015-04-08

-

View all other issues in [mods.func.wrap].

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

- -

-invocation_type falls short of its stated goals in the following case. Using the notation of -Invocation type traits, -consider -

-
-
-void f(int const& i);
-more_perfect_forwarding_async(f, int(7)); // Oops. Dangling reference because rvalue gone when async runs
-
-
-

-This was always the advertised intent of the proposal, but while the language reflects this for the first parameter in the -case of a member pointer, it failed to include corresponding language for other parameters. -

- -

[2014-06-18, Rapperswil]

- -

-Mike Spertus, Richard Smith, Jonathan Wakely, and Jeffrey Yasskin suggest improved wording. -

- -Previous resolution [SUPERSEDED]: -

-

-

This wording is relative to N3908.

- -
    -

  1. Change Table 3, [meta.trans.other] in the Library TS -as indicated: -

    -
    - - - - - - - - - - - - - - - - - - -
    Table 3 — Other type transformations
    TemplateConditionComments
    -… -
    -template <class Fn, class... ArgTypes>
    -struct invocation_type<Fn(ArgTypes...)>;     -    		 -Fn and all types in the parameter pack ArgTypes
    -shall be complete types, (possibly cv-qualified) void,
    -or arrays of unknown bound. -    		 -If A1, A2,... denotes ArgTypes... and
    -raw_invocation_type<Fn(ArgTypes...)>::type
    -is the function type R(T1, T2, ...) then let Ui be
    -decay<Ai>::type if Ai is an rvalue otherwise Ti.
    -If     and Fn is a pointer to member type and T1 is
    -an rvalue reference, then let U1 be R(decay<T1>::type,
    -T2, ...)    .
    -Otherwise, raw_invocation_type<Fn(ArgTypes...)>::type
    -The member typedef type shall equal R(U1, U2, ...). -
    -
    - -
    2. -
-
- -

[2013-06-21 Rapperswil]

- -

-Accept for Fundamentals TS Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N4023.

- -
    -

  1. Change Table 3, [meta.trans.other] in the Library TS -as indicated: -

    -
    - - - - - - - - - - - - - - - - - - -
    Table 3 — Other type transformations
    TemplateConditionComments
    -… -
    -template <class Fn, class... ArgTypes>
    -struct invocation_type<Fn(ArgTypes...)>;     -    		 -Fn and all types in the parameter pack ArgTypes
    -shall be complete types, (possibly cv-qualified) void,
    -or arrays of unknown bound. -    		 - -The nested typedef invocation_type<Fn(ArgTypes...)>::type
    -shall be defined as follows. If
    -raw_invocation_type<Fn(ArgTypes...)>::type
    -does not exist, there shall be no member typedef type. Otherwise:
    -
      -

    • Let A1, A2, … denote ArgTypes...

      • -

    • Let R(T1, T2, …) denote
      -raw_invocation_type_t<Fn(ArgTypes...)>

      • -

    • Then the member typedef type shall name the function
      -type R(U1, U2, …) where Ui is decay_t<Ai>
      -if declval<Ai>() is an rvalue otherwise Ti.

      • -
    -     -If raw_invocation_type<Fn(ArgTypes...)>::type
    -is the function type R(T1, T2, …)
    -and Fn is a pointer to member type and T1 is
    -an rvalue reference, then R(decay<T1>::type,
    -T2, …)    .
    -Otherwise, raw_invocation_type<Fn(ArgTypes...)>::type.
     -
    -
    - -
    2. -
- - - - - -
-

2395. [fund.ts] Preconditions: is defined nowhere

-

Section: X [mods.func.wrap], X [memory.resource.priv], X [memory.polymorphic.allocator.ctor], X [memory.polymorphic.allocator.mem], X [memory.resource.pool.ctor], X [memory.resource.monotonic.buffer.ctor] Status: WP - Submitter: Zhihao Yuan Opened: 2014-06-09 Last modified: 2015-04-08

-

View all other issues in [mods.func.wrap].

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

- -

-This element has been introduced by N3916, -but the standard does not define it. The standard defines Requires: to indicate a precondition -(17.5.1.4 [structure.specifications] p3). -

-Proposed wording: -

-Substitute all Preconditions: with Requires:. -

- -

[2013-06-21 Rapperswil]

- -

-Accept for Fundamentals TS Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N4023.

- -
    -

  1. Substitute all Preconditions: with Requires:.

    2. -
- - - - - -
-

2396. underlying_type doesn't say what to do for an incomplete enumeration type

-

Section: 20.10.7.6 [meta.trans.other] Status: WP - Submitter: Richard Smith Opened: 2014-06-12 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with WP status.

-

Discussion:

-

-Consider: -

-
-enum E {
-  e = std::underlying_type<E>::type(1)
-};
-
-

-Clearly this should be ill-formed, but the library section doesn't appear to ban it. Suggestion: -

-Change in 20.10.7.6 [meta.trans.other] Table 57: -

-
-

-Template: template<class T> struct underlying_type; -

-Condition: T shall be a complete an enumeration type (7.2) -

-Comments: […] -

-
- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change Table 57 — "Other transformations" as indicated:

    2. - -
    - - - - - - - - - - - - - - - - - - -
    Table 3 — Other type transformations
    TemplateConditionComments
    -… -
    -template <class T>
    -struct underlying_type;     -    		 -T shall be a complete an enumeration type (7.2) - -[…] -
    -
    - -
- - - - - -
-

2397. map<K, V>::emplace and explicit V constructors

-

Section: 20.10.7.6 [meta.trans.other] Status: Resolved - Submitter: Peter Dimov Opened: 2014-06-12 Last modified: 2015-05-05

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with Resolved status.

-

Discussion:

-

-Please consider the following example: -

-
-#include <map>
-#include <atomic>
-
-int main()
-{
-   std::map<int, std::atomic<int>> map_;
-
-   map_.emplace(1, 0);  // fail
-   map_.emplace(1);     // fail
-   map_.emplace(1, {}); // fail
-
-   map_.emplace(std::piecewise_construct,
-       std::tuple<int>(1), std::tuple<>()); // OK
-}
-
-

-The first three calls represent attempts by an ordinary programmer (in which role I appear today) to construct -a map element. Since std::atomic<int> is non-copyable and immovable, I was naturally drawn to -emplace() because it constructs in-place and hence doesn't need to copy or move. The logic behind the -attempts was that K=int would be constructed from '1', and V=std::atomic<int> would be -(directly) constructed by '0', default constructed, or constructed by '{}'. -

-Yet none of the obvious attempts worked. -

-I submit that at least two of the three ought to have worked, and that we have therefore a defect in either -map::emplace or pair. -

-Ville: -

-There exists a related EWG issue for this. -

-Daniel: -

-If the proposal N4387 would be accepted, it would solve the first problem mentioned above. -

- -

[2015-02, Cologne]

- -

-AM: I think Peter's expectation is misguided that the second and third "//fail" cases should work.
-DK: Howard's paper [note: which hasn't been written yet] will make the second case work... AM: ...but -the third one will never work without core changes. -

-Case 1 is solved by DK's paper, cases 2 and 3 are not defects; at best they are extensions. -

- -

[2015-05, Lenexa]

- -

-STL: think this is covered with N4387
-MC: this was accepted in Cologne
-STL: only want to fix the first emplace
-MC: leave alone and mark as closed by N4387
-

- - -

Proposed resolution:

-

-Resolved by acceptance of N4387. -

- - - - - -
-

2399. shared_ptr's constructor from unique_ptr should be constrained

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.shared.const].

-

View all issues with WP status.

-

Discussion:

-

-Consider the following code: -

-
-#include <iostream>
-#include <memory>
-#include <string>
-
-using namespace std;
-
-void meow(const shared_ptr<int>& sp) {
-  cout << "int: " << *sp << endl;
-}
-
-void meow(const shared_ptr<string>& sp) {
-  cout << "string: " << *sp << endl;
-}
-
-int main() {
-  meow(make_unique<int>(1729));
-  meow(make_unique<string>("kitty"));
-}
-
-

-This fails to compile due to ambiguous overload resolution, but we can easily make this work. (Note: shared_ptr's -constructor from auto_ptr is also affected, but I believe that it's time to remove auto_ptr completely.) -

- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.8.2.2.1 [util.smartptr.shared.const] around p33 as indicated:

    - -
    -
    -template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
-
    -

    --?- Remark: This constructor shall not participate in overload resolution unless unique_ptr<Y, D>::pointer -is convertible to T*. -

    --33- Effects: Equivalent to shared_ptr(r.release(), r.get_deleter()) when D is not a reference type, -otherwise shared_ptr(r.release(), ref(r.get_deleter())). -

    -
    -
    2. -
- - - - - -
-

2400. shared_ptr's get_deleter() should use addressof()

-

Section: 20.8.2.2.10 [util.smartptr.getdeleter] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-04-08

-

View all other issues in [util.smartptr.getdeleter].

-

View all issues with WP status.

-

Discussion:

-

-The Standard Library should consistently use addressof() to defend itself against overloaded operator&(). -

-While we're in the neighbourhood, we should editorially change 0 to nullptr. -

- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.8.2.2.10 [util.smartptr.getdeleter] as indicated:

    - -
    -
    -template <class D, class T> get_deleter(const shared_ptr<T>& p) noexcept;
-
    -

    --1- Returns: If p owns a deleter d of type cv-unqualified D, returns -&std::addressof(d); -otherwise returns 0nullptr. […] -

    -
    -
    2. -
- - - - - -
-

2401. std::function needs more noexcept

-

Section: 20.9.12.2 [func.wrap.func] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-04-08

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with WP status.

-

Discussion:

-

-There are two issues here: -

-
    -

  1. std::function's constructor from nullptr_t is marked as noexcept, but its assignment operator -from nullptr_t isn't. This assignment can and should be marked as noexcept.

    2. -

  2. std::function's comparisons with nullptr_t are marked as noexcept in two out of three places.

    3. -
- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.9 [function.objects] p2, header <functional> synopsis, as indicated:

    - -
    -
    -namespace std {
-  […]
-  // 20.9.11 polymorphic function wrappers:
-  […]
-  template<class R, class... ArgTypes>
-  bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
-  template<class R, class... ArgTypes>
-  bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
-  template<class R, class... ArgTypes>
-  bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
-  template<class R, class... ArgTypes>
-  bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
-  […]
-}
-
    -
    -
    2. - -

  2. Change 20.9.12.2 [func.wrap.func], class template function synopsis, as indicated:

    - -
    -
    -[…]
-// 20.9.11.2.1, construct/copy/destroy:
-[…]
-function& operator=(nullptr_t) noexcept;
-[…]
-
    -
    -
    3. - -

  3. Change 20.9.12.2.1 [func.wrap.func.con] before p16 as indicated:

    - -
    -
    -function& operator=(nullptr_t) noexcept;
-
    -
    -
    4. -
- - - - - -
-

2403. stof() should call strtof() and wcstof()

-

Section: 21.5 [string.conversions] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-05-22

-

View all other issues in [string.conversions].

-

View all issues with WP status.

-

Discussion:

-

-stof() is currently specified to call strtod()/wcstod() (which converts the given string to -double) and then it's specified to convert that double to float. This performs rounding twice, -which introduces error. Here's an example written up by James McNellis: -

-Consider the following number X: -

-
-
-1.999999821186065729339276231257827021181583404541015625 (X)
-
-
-

-This number is exactly representable in binary as: -

-
-
-1.111111111111111111111101000000000000000000000000000001
-* ^1st                  ^23rd                        ^52nd
-
-
-

-I've marked the 23rd and 52nd fractional bits. These are the least significant bits for float and double, -respectively. -

-If we convert this number directly to float, we take the 23 most significant bits: -

-
-
-1.11111111111111111111110
-
-
-

-The next bit is a one and the tail is nonzero (the 54th fractional bit is a one), so we round up. This gives us the correctly -rounded result: -

-
-
-1.11111111111111111111111
-
-
-

-So far so good. But... If we convert X to double, we take the 52 most significant bits: -

-
-
-1.1111111111111111111111010000000000000000000000000000 (Y)
-
-
-

-The next bit is a zero, so we round down (truncating the value). If we then convert Y to float, we take -its 23 most significant bits: -

-
-
-1.11111111111111111111110
-
-
-

-The next bit is a one and the tail is zero, so we round to even (leaving the value unchanged). This is off by 1ulp from the -correctly rounded result. -

- -

[2014-06 Rapperswil]

- -

-Marshall Clow will look at this. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 21.5 [string.conversions] p4+p6 as indicated:

    - -
    -
    -float stof(const string& str, size_t* idx = 0);
-double stod(const string& str, size_t* idx = 0);
-long double stold(const string& str, size_t* idx = 0);
-
    -
    -

    --4- Effects: the first twoThese functions call strtof(str.c_str(), ptr), -strtod(str.c_str(), ptr), and the third function calls strtold(str.c_str(), ptr), -respectively. Each function returns the converted result, if any. […] -

    -[…] -

    --6- Throws: invalid_argument if strtof, strtod, or strtold reports -that no conversion could be performed. Throws out_of_range if strtof, strtod, or -strtold sets errno to ERANGE or if the converted value is outside the range of representable -values for the return type. -

    -
    -
    -
    2. - -

  2. Change 21.5 [string.conversions] p11+p13 as indicated:

    - -
    -
    -float stof(const wstring& str, size_t* idx = 0);
-double stod(const wstring& str, size_t* idx = 0);
-long double stold(const wstring& str, size_t* idx = 0);
-
    -
    -

    --11- Effects: the first twoThese functions call wcstof(str.c_str(), ptr), -wcstod(str.c_str(), ptr), and the third function calls wcstold(str.c_str(), ptr), -respectively. Each function returns the converted result, if any. […] -

    -[…] -

    --13- Throws: invalid_argument if wcstof, wcstod, or wcstold -reports that no conversion could be performed. Throws out_of_range if wcstof, wcstod, -or wcstold sets errno to ERANGE. -

    -
    -
    -
    3. -
- - - - - -
-

2404. mismatch()'s complexity needs to be updated

-

Section: 25.2.10 [mismatch] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

-N3671 updated the complexities of -equal() and is_permutation(), but not mismatch(). -

- -

[2014-06-16 Rapperswil]

- -

-Move to Ready -

- - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 25.2.10 [mismatch] p3 as indicated:

    - -
    -

    --3- Complexity: At most min(last1 - first1, last2 - first2) applications of the -corresponding predicate. -

    -
    -
    2. - -
- - - - - -
-

2406. negative_binomial_distribution should reject p == 1

-

Section: 26.5.8.3.4 [rand.dist.bern.negbin] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-26.5.8.3.4 [rand.dist.bern.negbin] p2 requires "0 < p <= 1". Consider what happens when p == 1. -The discrete probability function specified by p1 involves "* p^k * (1 - p)^i". For p == 1, this is -"* 1^k * 0^i", so every integer i >= 0 is produced with zero probability. (Let's avoid thinking about -0^0.) -

-Wikipedia states that p must be within -(0, 1), exclusive on both sides. -

- -Previous resolution [SUPERSEDED]: -
-
    -

  1. Change 26.5.8.3.4 [rand.dist.bern.negbin] p2 as indicated: [Drafting note: This should be read as: Replace the -symbol "≤" by "<" — end drafting note]

    - -
    -
    -explicit negative_binomial_distribution(IntType k = 1, double p = 0.5);
-
    -
    -

    --2- Requires: 0 < p ≤< 1 and 0 < k. -

    -
    -
    -
    2. -
-
- -

[2014-11 Urbana]

- -

-SG6 suggests better wording. -

- -

[2014-11-08 Urbana]

- -

-Moved to Ready with the node. -

-

-There remains concern that the constructors are permitting -values that may (or may not) be strictly outside the domain -of the function, but that is a concern that affects the -design of the random number facility as a whole, and should -be addressed by a paper reviewing and addressing the whole -clause, not picked up in the issues list one distribution -at a time. It is still not clear that such a paper would be -uncontroversial. -

- - - -

Proposed resolution:

-

This wording is relative to N4140.

- -
    -

  1. Add a note after paragraph 1 before the synopsis in 26.5.8.3.4 [rand.dist.bern.negbin]:

    - -
    -

    -A negative_binomial_distribution random number distribution produces random integers - -i≥0 - -distributed according to the discrete probability function -

    -
    -

    - -P(i|k,p) -= - - - -k + i - 1 -i - - -· - -p -k - -· - -(1-p) -i - - - -. -

    -
    -

    -[Note: This implies that -P(i|k,p) - is undefined when p == 1. — end note] -

    -
    -
    -

    -Drafting note: -P(i|k,p) - should be in math font, and p == 1 should be in code font. -

    -
    - -
    2. - -
- - - - - -
-

2407. packaged_task(allocator_arg_t, const Allocator&, F&&) should neither be constrained nor -explicit

-

Section: 30.6.9.1 [futures.task.members] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2015-05-22

-

View all other issues in [futures.task.members].

-

View all issues with WP status.

-

Discussion:

-

-LWG 2097's resolution was slightly too aggressive. It constrained -packaged_task(allocator_arg_t, const Allocator&, F&&), but that's unnecessary because -packaged_task doesn't have any other three-argument constructors. Additionally, it's marked as -explicit (going back to WP N2798 when packaged_task first appeared) which is unnecessary. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-Back to LWG; not an SG1 issue. -

- -

[2015-05 Lenexa]

- -

-STL improves proposed wording by restoring the constraint again. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 30.6.9 [futures.task] p2, class template packaged_task as indicated:

    - -
    -
    -template <class F>
-explicit packaged_task(F&& f);
-template <class F, class Allocator>
-explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
-
    -
    -
    2. - -

  2. Change 30.6.9.1 [futures.task.members] as indicated:

    - -
    -
    -template <class F>
-packaged_task(F&& f);
-template <class F, class Allocator>
-explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
-
    -
    -

    -[…] -

    --3- Remarks: These constructors shall not participate in overload resolution if decay_t<F> -is the same type as std::packaged_task<R(ArgTypes...)>. -

    -
    -
    -
    3. -
- - - - - -
-

2408. SFINAE-friendly common_type/iterator_traits is missing in C++14

-

Section: 20.10.7.6 [meta.trans.other], 24.4.1 [iterator.traits] Status: WP - Submitter: Daniel Krügler Opened: 2014-06-19 Last modified: 2015-04-08

-

View other active issues in [meta.trans.other].

-

View all other issues in [meta.trans.other].

-

View all issues with WP status.

-

Discussion:

-

-During the Rapperswil meeting the proposal N4041 -had been discussed and there seemed to be strong consensus to apply the SFINAE-friendly definitions -that currently exist within the fundamentals-ts to the C++ Standard working draft. This issue requests this change to happen. -

- - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.10.7.6 [meta.trans.other] p3 as indicated:

    - -
    -

    --3- For the common_type trait applied to a parameter pack T of types, -the member type shall be either defined or not present as follows: -

      -

    • If sizeof...(T) is zero, there shall be no member type.

      • -

    • If sizeof...(T) is one, let T0 denote the sole type comprising T. -The member typedef type shall denote the same type as decay_t<T0>.

      • -

    • If sizeof...(T) is greater than one, let T1, T2, and R, -respectively, denote the first, second, and (pack of) remaining types comprising T. -[Note: sizeof...(R) may be zero. — end note] Finally, let C denote -the type, if any, of an unevaluated conditional expression (5.16 [expr.cond]) whose first operand is an arbitrary value -of type bool, whose second operand is an xvalue of type T1, and whose third operand is -an xvalue of type T2. If there is such a type C, the member typedef type shall -denote the same type, if any, as common_type_t<C,R...>. Otherwise, there shall be no member -type.

      • -
    -The nested typedef common_type::type shall be defined as follows: -

    -
    -
    -template <class ...T> struct common_type;
-
-template <class T>
-struct common_type<T> {
-  typedef decay_t<T> type;
-};
-
-template <class T, class U>
-struct common_type<T, U> {
-  typedef decay_t<decltype(true ? declval<T>() : declval<U>())> type;
-};
-
-template <class T, class U, class... V>
-struct common_type<T, U, V...> {
-  typedef common_type_t<common_type_t<T, U>, V...> type;
-};
-
    -
    -
    -
    2. - -

  2. Change 24.4.1 [iterator.traits] p2 as indicated:

    - -
    -

    --2- The template iterator_traits<Iterator> is defined asshall have -the following as publicly accessible members, and have no other members, if and only if -Iterator has valid (14.8.2 [temp.deduct]) member types difference_type, -value_type, pointer, reference, and iterator_category; otherwise, -the template shall have no members: -

    -
    -
    -namespace std {
-  template<class Iterator> struct iterator_traits {
-    typedef typename Iterator::difference_type difference_type;
-    typedef typename Iterator::value_type value_type;
-    typedef typename Iterator::pointer pointer;
-    typedef typename Iterator::reference reference;
-    typedef typename Iterator::iterator_category iterator_category;
-  };
-}
-
    -
    -
    -
    3. -
- - - - - -
-

2409. [fund.ts] SFINAE-friendly common_type/iterator_traits should be removed from the fundamental-ts

-

Section: X [mods.meta.trans.other], X [mods.iterator.traits] Status: WP - Submitter: Daniel Krügler Opened: 2014-06-19 Last modified: 2015-04-08

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

-

-During the Rapperswil meeting the proposal N4041 -had been discussed and there seemed to be strong consensus to apply the SFINAE-friendly definitions -that currently exist within the fundamentals-ts to the C++17 working draft. If this happens, the fundamentals-ts -needs to remove its own specification regarding these templates. This issue requests this change to happen. -

- -

[2013-06-21 Rapperswil]

- -

-Accept for Fundamentals TS Working Paper -

- - -

Proposed resolution:

-

This wording is relative to N4023 in regard to fundamental-ts changes.

- -
    -

  1. In fundamental-ts, change Table 2 — "Significant features in this technical specification" as -indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 2 — Significant features in this technical specification
    Doc.
    No.    		TitlePrimary
    Section    		Macro Name SuffixValueHeader
    -… -
    -N3843
    -    		 -A SFINAE-
    Friendly
    common_type     -    		 -2.4 [mods.meta.trans.other]
    -    		 -common_type_sfinae - -201402 - -<type_traits>
    -
    -N3843
    -    		 -A SFINAE-
    Friendly
    iterator_traits     -    		 -2.5 [mods.iterator.traits]
    -    		 -iterator_traits_sfinae - -201402 - -<iterator>
    -
    -… -
    -
    -
    2. - -

  2. In fundamental-ts, remove the existing sub-clause 2.4 [mods.meta.trans.other] in its entirety:

    - -

    -2.4 Changes to std::common_type [mods.meta.trans.other] -

    -
    -

    --1- […] -

    -
    - -
    3. - -

  3. In fundamental-ts, remove the existing sub-clause 2.5 [mods.iterator.traits] in its entirety:

    - -

    -2.5 Changes to std::iterator_traits [mods.iterator.traits] -

    -
    -

    --1- […] -

    -
    -
    4. - -
- - - - - -
-

2410. [fund.ts] shared_ptr<array>'s constructor from unique_ptr should be constrained

-

Section: X [mods.util.smartptr.shared.const] Status: WP - Submitter: Jeffrey Yasskin Opened: 2014-06-16 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

-

-The proposed resolution for LWG 2399 doesn't apply cleanly to the Fundamentals TS, but the issue is still present. -

- -

[2015-02, Cologne]

- -

-Unanimous consent. -

- - -

Proposed resolution:

-

This wording is relative to N4023 in regard to fundamental-ts changes.

- -
    -

  1. In fundamental-ts, change [mods.util.smartptr.shared.const] p34 as indicated:

    - -
    -
    -template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
-
    -
    -

    --34- RequiresRemarks: This constructor shall not participate in overload resolution -unless Y* shall beis compatible with T*. -

    --35- Effects: Equivalent to shared_ptr(r.release(), r.get_deleter()) when D is not a reference type, -otherwise shared_ptr(r.release(), ref(r.get_deleter())). -

    --36- Exception safety: If an exception is thrown, the constructor has no effect. -

    -
    -
    -
    2. - -
- - - - - -
-

2411. shared_ptr is only contextually convertible to bool

-

Section: 20.8.2.2 [util.smartptr.shared] Status: WP - Submitter: Jonathan Wakely Opened: 2014-06-21 Last modified: 2015-05-22

-

View other active issues in [util.smartptr.shared].

-

View all other issues in [util.smartptr.shared].

-

View all issues with WP status.

-

Discussion:

-

-N3920 made this edit, which is correct but unrelated to the support for arrays: -

-
-

Change 20.7.2.2 [util.smartptr.shared] p2 as follows:

-
-

-Specializations of shared_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable, -allowing their use in standard containers. Specializations of shared_ptr shall be contextually convertible to -bool, allowing their use in boolean expressions and declarations in conditions. […] -

-
-
-

-That change is actually fixing a defect in the current wording and should be applied directly to the working paper, not just to the -Library Fundamentals TS. The declarations of the conversion operator in 20.8.2.2 [util.smartptr.shared] and -20.8.2.2.5 [util.smartptr.shared.obs] are explicit which contradicts the "convertible to bool" statement. The -intention is definitely for shared_ptr to only be contextually convertible to bool. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

This wording is relative to N3936.

- -
    -

  1. Change 20.8.2.2 [util.smartptr.shared] p2 as indicated:

    - -
    -

    --2- Specializations of shared_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable, -allowing their use in standard containers. Specializations of shared_ptr shall be contextually convertible to -bool, allowing their use in boolean expressions and declarations in conditions. The template parameter T of -shared_ptr may be an incomplete type. -

    -
    -
    2. - -
- - - - - -
-

2415. Inconsistency between unique_ptr and shared_ptr

-

Section: 20.8.2.2.1 [util.smartptr.shared.const] Status: WP - Submitter: Jonathan Wakely Opened: 2014-07-03 Last modified: 2015-05-22

-

View all other issues in [util.smartptr.shared.const].

-

View all issues with WP status.

-

Discussion:

-

-unique_ptr guarantees that it will not invoke its deleter if it stores -a null pointer, which is useful for deleters that must not be called -with a null pointer e.g. -

-
-unique_ptr<FILE, int(*)(FILE*)> fptr(file, &::fclose);
-
-

-However, shared_ptr does invoke the deleter if it owns a null pointer, -which is a silent change in behaviour when transferring -ownership from unique_ptr to shared_ptr. That means the following -leads to undefined behaviour: -

-
-std:shared_ptr<FILE> fp = std::move(fptr);
-
-

-Peter Dimov's suggested fix is to construct an empty shared_ptr from a -unique_ptr that contains a null pointer. -

- -

[2015-01-18 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on eight votes in favour. -

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.8.2.2.1 [util.smartptr.shared.const] p29 as indicated:

    -
    -
    -template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
-
    -
    -

    -[…] -

    --29- Effects: If r.get() == nullptr, equivalent to shared_ptr(). Otherwise, if D is -not a reference type, equivalent to shared_ptr(r.release(), r.get_deleter()). Otherwise, equivalent to -shared_ptr(r.release(), ref(r.get_deleter()))Equivalent to shared_ptr(r.release(), -r.get_deleter()) when D is not a reference type, otherwise shared_ptr(r.release(), -ref(r.get_deleter())). -

    -
    -
    -
    2. -
- - - - - -
-

2416. [fund.ts] std::experimental::any allocator support is unimplementable

-

Section: X [any.class] Status: Resolved - Submitter: Jonathan Wakely Opened: 2014-06-16 Last modified: 2015-04-08

-

View all issues with Resolved status.

-

Discussion:

-

Addresses: fund.ts

-

-The allocator-extended copy constructor for any requires an -arbitrary template parameter to be available in a type-erased context -where the dynamic type of the contained object is known. This is not -believed to be possible in C++. -

-If the allocator-extended copy constructor cannot be defined it -questions the usefulness of the other allocator-extended constructors. -

- -

[Urbana, 2014-11]

- -

-Resolved by paper N4270. -

- - - -

Proposed resolution:

- - - - - -
-

2418. [fund.ts] apply does not work with member pointers

-

Section: X [tuple.apply] Status: WP - Submitter: Zhihao Yuan Opened: 2014-07-08 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

-

-The definition of apply present in §3.2.2 [tuple.apply] prevents this -function template to be used with pointer to members type passed as the first argument. -

-
-Effects: -

-[…] -

-return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...); -

-

-This makes this utility inconsistent with other standard library components and limits its usability. -

-We propose to define its functionally in terms of INVOKE. -

- -

[2015-02, Cologne]

- -

-DK: We should use the new std::invoke.
-TK: Is this a defect?
-AM: std::invoke goes into C++17, and this is a defect against a TS based on C++14. We can change this later, -but now leave it as INVOKE.
-GR: The TS lets you have Editor's Notes, so leave a note to make that change for C++17. -

-[…] -

-GR: I can't see how we can assume this is part of the design. I cannot believe it was ever intended for this -design to exclude function pointers.
-AM: I can give you the exact evolution: We had "apply" as an example explaining the usefulness of index_sequence. -Then someone looked at it and said, "why isn't this in the Standard". NJ to VV: Why are you against useful steps? -We are trying to converge on a consistent standard across multiple documents. The alternative is to reopen this -in a later discussion.
-VV: All I said is that this is not defect, whether or not people like it.
-AM: So you'd be fine with the issue, but not as a DR?
-Straw poll: Who's happy to make this tentatively ready as a DR against the Fundamentals TS? -Lots of agreement, no opposition, 3 neutrals -

- - -

Proposed resolution:

-

This wording is relative to N4081 -in regard to fundamental-ts changes.

- -
    -

  1. Edit §3.2.2 [tuple.apply] paragraph 2:

    - -
    -
    -template <class F, class Tuple>
-constexpr decltype(auto) apply(F&& f, Tuple&& t);
-
    -
    -

    --2- Effects: Given the exposition only function -

    -
    -
    -template <class F, class Tuple, size_t... I>
-constexpr decltype(auto) apply_impl(  // exposition only
-    F&& f, Tuple&& t, index_sequence<I...>) {
-  return INVOKE(std::forward<F>(f)(, std::get<I>(std::forward<Tuple>(t))...);
-}
-
    -

    -[…] -

    -
    -
    -
    -
    2. -
- - - - - -
-

2420. function<void(ArgTypes...)> does not discard the return value of the target object

-

Section: 20.9.12.2 [func.wrap.func] Status: WP - Submitter: Agustín Bergé Opened: 2014-07-12 Last modified: 2015-05-22

-

View other active issues in [func.wrap.func].

-

View all other issues in [func.wrap.func].

-

View all issues with WP status.

-

Discussion:

-

-function<void(ArgTypes...)> should discard the return value of the target object. This behavior was -in the original proposal, and it was removed (accidentally?) by the resolution of LWG 870. -

- -

-Previous resolution [SUPERSEDED]: -

-
-
    -

  1. Edit 20.9.12.2 [func.wrap.func] paragraph 2:

    - -
    -

    -A callable object f of type F is Callable for argument types ArgTypes and return type -R if the expression INVOKE(f, declval<ArgTypes>()..., R), considered as an unevaluated -operand (Clause 5), is well formed (20.9.2 [func.require]) and, if R is not void, implicitly -convertible to R. -

    -
    -
    2. -
-
- -

[2014-10-05 Daniel comments]

- -

-This side-effect was indeed not intended by 870. -

- -

[2015-05, Lenexa]

- -

-STL provides improved wording. It replaces the current PR, and intentionally leaves 20.9.12.2 [func.wrap.func] -unchanged. -

-Due to 5 [expr]/6, static_cast<void> is correct even when R is const void. -

- - -

Proposed resolution:

-

This wording is relative to N4431.

- -
    -

  1. Edit 20.9.2 [func.require] as depicted:

    - -
    -

    --2- Define INVOKE(f, t1, t2, ..., tN, R) as static_cast<void>(INVOKE(f, t1, t2, ..., tN)) -if R is cv void, otherwise INVOKE(f, t1, t2, ..., tN) implicitly converted -to R. -

    -
    -
    2. - -

  2. Change 20.9.12.2.4 [func.wrap.func.inv] as depicted:

    - -
    -
    -R operator()(ArgTypes... args) const;
-
    -
    -

    --1- EffectsReturns: INVOKE(f, std::forward<ArgTypes>(args)..., R) (20.9.2), -where f is the target object (20.9.1) of *this. -

    --2- Returns: Nothing if R is void, otherwise the return value of INVOKE(f, -std::forward<ArgTypes>(args)..., R). -

    -
    -
    -
    3. -
- - - - - -
-

2425. operator delete(void*, size_t) doesn't invalidate pointers sufficiently

-

Section: 18.6.1 [new.delete] Status: WP - Submitter: Richard Smith Opened: 2014-08-29 Last modified: 2015-05-22

-

View all other issues in [new.delete].

-

View all issues with WP status.

-

Discussion:

-

-18.6.1.1 [new.delete.single]/12 says: -

-

-Requires: ptr shall be a null pointer or its value shall be a value returned by an earlier call to the -(possibly replaced) operator new(std::size_t) or operator new(std::size_t,const std::nothrow_t&) -which has not been invalidated by an intervening call to operator delete(void*). -

-

-This should say: -

-

-[…] by an intervening call to operator delete(void*) or operator delete(void*, std::size_t). -

-

-Likewise at the end of 18.6.1.2 [new.delete.array]/11, operator delete[](void*, std::size_t). -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-
    -

  1. Change 18.6.1.1 [new.delete.single]p12 as indicated:

    - -
    -

    --12- Requires: ptr shall be a null pointer or its value shall be a value returned by an earlier call to the -(possibly replaced) operator new(std::size_t) or operator new(std::size_t,const std::nothrow_t&) which -has not been invalidated by an intervening call to operator delete(void*) or -operator delete(void*, std::size_t). -

    -
    -
    2. - -

  2. Change 18.6.1.2 [new.delete.array]p11 as indicated:

    - -
    -

    --11- Requires: ptr shall be a null pointer or its value shall be the value returned by an earlier call to -operator new[](std::size_t) or operator new[](std::size_t,const std::nothrow_t&) which -has not been invalidated by an intervening call to operator delete[](void*) or -operator delete[](void*, std::size_t). -

    -
    -
    3. -
- - - - - -
-

2427. Container adaptors as sequence containers, redux

-

Section: 23.3.1 [sequences.general] Status: WP - Submitter: Tim Song Opened: 2014-08-29 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-LWG 2194 removed "These container adaptors meet the requirements for sequence containers." from -23.6.1 [container.adaptors.general]. -

-However, N3936 23.3.1 [sequences.general]/p2 still says "The headers <queue> and <stack> -define container adaptors (23.6) that also meet the requirements for sequence containers." I assume this is just an oversight. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-
    -

  1. Delete paragraph 2 of 23.3.1 [sequences.general] as indicated:

    - -
    -

    --2- The headers <queue> and <stack> define container adaptors (23.6) that -also meet the requirements for sequence containers. -

    -
    -
    2. -
- - - - - -
-

2428. "External declaration" used without being defined

-

Section: 17.6.2.2 [using.headers] Status: WP - Submitter: Tim Song Opened: 2014-09-03 Last modified: 2015-05-22

-

View all other issues in [using.headers].

-

View all issues with WP status.

-

Discussion:

-

-17.6.2.2 [using.headers]/3 says -

-

-A translation unit shall include a header only outside of any external declaration or definition […] -

-

-This wording appears to be borrowed from the C standard. However, the term "external declaration" is not defined -in the C++ standard, and in fact is only used here as far as I can tell, so it is unclear what it means. The C -standard does define external declarations as (WG14 N1570 6.9 External definitions/4-5): -

-

-As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit, which consists of a -sequence of external declarations. These are described as "external" because they appear outside any function -(and hence have file scope). [...] An external definition is an external declaration that is also a definition of -a function (other than an inline definition) or an object. -

-

-The corresponding description of a translation unit in C++ is "A translation unit consists of a sequence of declarations." -(3.5 [basic.link]/3). -

-So it appears that the C++ counterpart of "external declaration" in C is simply a "declaration" at file scope. There -is no need to specifically limit the statement in 17.6.2.2 [using.headers]/3 to file-scope declarations, however, -since every non-file-scope declaration is necessarily inside a file-scope declaration, so banning including a header -inside file-scope declarations necessarily bans including one inside non-file-scope declarations as well. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

-
    -

  1. Edit 17.6.2.2 [using.headers] as indicated:

    - -
    -

    -A translation unit shall include a header only outside of any external declaration or definition, and shall -include the header lexically before the first reference in that translation unit to any of the entities declared -in that header. No diagnostic is required. -

    -
    -
    2. -
- - - - - -
-

2433. uninitialized_copy()/etc. should tolerate overloaded operator&

-

Section: 20.7.12 [specialized.algorithms] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [specialized.algorithms].

-

View all issues with WP status.

-

Discussion:

-

-This restriction isn't necessary anymore. In fact, this is the section that defines addressof(). -

-

-(Editorial note: We can depict these algorithms as calling addressof() instead of std::addressof() -thanks to 17.6.1.1 [contents]/3 "Whenever a name x defined in the standard library is mentioned, the name -x is assumed to be fully qualified as ::std::x, unless explicitly described otherwise.") -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 20.7.12 [specialized.algorithms] p1 as depicted:

    - -
    -

    --1- All the iterators that are used as formal template parameters in the following algorithms are required to -have their operator* return an object for which operator& is defined and returns a pointer to -T. In the algorithm uninitialized_copy, the formal template parameter InputIterator -is required to satisfy the requirements of an input iterator (24.2.3). In all of the following algorithms, the formal -template parameter ForwardIterator is required to satisfy the requirements of a forward iterator (24.2.5), -and is required to have the property that no exceptions are thrown from increment, assignment, comparison, or indirection -through valid iterators. In the following algorithms, if an exception is thrown there are no effects. -

    -
    -
    2. - -

  2. Change 20.7.12.2 [uninitialized.copy] p1 as depicted:

    -
    -

    --1- Effects: -

    -
    -
    -for (; first != last; ++result, ++first)
-  ::new (static_cast<void*>(addressof(&*result)))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-
    -
    -
    -
    3. - -

  3. Change 20.7.12.2 [uninitialized.copy] p3 as depicted:

    -
    -

    --3- Effects: -

    -
    -
    -for (; n > 0; ++result, ++first, --n) {
-  ::new (static_cast<void*>(addressof(&*result)))
-    typename iterator_traits<ForwardIterator>::value_type(*first);
-}
-
    -
    -
    -
    4. - -

  4. Change 20.7.12.3 [uninitialized.fill] p1 as depicted:

    -
    -

    --1- Effects: -

    -
    -
    -for (; first != last; ++first)
-  ::new (static_cast<void*>(addressof(&*first)))
-    typename iterator_traits<ForwardIterator>::value_type(x);
-
    -
    -
    -
    5. - -

  5. Change 20.7.12.4 [uninitialized.fill.n] p1 as depicted:

    -
    -

    --1- Effects: -

    -
    -
    -for (; n--; ++first)
-  ::new (static_cast<void*>(addressof(&*first)))
-    typename iterator_traits<ForwardIterator>::value_type(x);
-return first;
-
    -
    -
    -
    6. -
- - - - - - -
-

2434. shared_ptr::use_count() is efficient

-

Section: 20.8.2.2.5 [util.smartptr.shared.obs] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [util.smartptr.shared.obs].

-

View all issues with WP status.

-

Discussion:

-

-shared_ptr and weak_ptr have Notes that their use_count() might be inefficient. -This is an attempt to acknowledge reflinked implementations (which can be used by Loki smart pointers, for -example). However, there aren't any shared_ptr implementations that use reflinking, especially -after C++11 recognized the existence of multithreading. Everyone uses atomic refcounts, so use_count() -is just an atomic load. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 20.8.2.2.5 [util.smartptr.shared.obs] p7-p10 as depicted:

    - -
    -
    -long use_count() const noexcept;
-
    -
    -

    --7- Returns: the number of shared_ptr objects, *this included, that share ownership with -*this, or 0 when *this is empty. -

    --8- [Note: use_count() is not necessarily efficient. — end note] -

    -
    -
    -bool unique() const noexcept;
-
    -
    -

    --9- Returns: use_count() == 1. -

    --10- [Note: unique() may be faster than use_count(). If you are using unique() -to implement copy on write, do not rely on a specific value when get() == 0. — end note] -

    -
    -
    -
    2. - -

  2. Change 20.8.2.3.5 [util.smartptr.weak.obs] p1-p4 as depicted:

    - -
    -
    -long use_count() const noexcept;
-
    -
    -

    --1- Returns: 0 if *this is empty; otherwise, the number of shared_ptr instances -that share ownership with *this. -

    --2- [Note: use_count() is not necessarily efficient. — end note] -

    -
    -
    -bool expired() const noexcept;
-
    -
    -

    --3- Returns: use_count() == 0. -

    --4- [Note: expired() may be faster than use_count(). — end note] -

    -
    -
    -
    3. -
- - - - - - -
-

2437. iterator_traits<OutIt>::reference can and can't be void

-

Section: 24.2.2 [iterator.iterators] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [iterator.iterators].

-

View all issues with WP status.

-

Discussion:

-

-24.2.2 [iterator.iterators]/2 requires an Iterator's *r to return reference, -i.e. iterator_traits<X>::reference according to 24.2.1 [iterator.requirements.general]/11. -

-24.2.4 [output.iterators]/1 requires an OutputIterator's *r = o to do its job, -so *r clearly can't return void. -

-24.4.1 [iterator.traits]/1 says: "In the case of an output iterator, the types -

-
-iterator_traits<Iterator>::difference_type
-iterator_traits<Iterator>::value_type
-iterator_traits<Iterator>::reference
-iterator_traits<Iterator>::pointer
-
-

-may be defined as void." -

-This is contradictory. I suggest fixing this by moving the offending requirement down from Iterator to -InputIterator, and making Iterator say that *r returns an unspecified type. This will -have the following effects: -

-
    -

  • Output-only iterators will inherit Iterator's "*r returns unspecified" requirement, while -24.4.1 [iterator.traits]/1 clearly permits reference/etc. to be void.

    • -

  • Input-or-stronger iterators (whether constant or mutable) are unaffected — they still have to satisfy -"*r returns reference", they're just getting that requirement from InputIterator instead of -Iterator.

    • -
- -

[2015-02 Cologne]

- -

-EF: This is related to 2438. MC: I'd like to take up 2438 right after this. -

-AM: Does anyone think this is wrong? -

-GR: Why do we give output iterators to have reference type void? AM: we've mandated that certain output iterators -define it as void since 1998. GR: Oh OK, I'm satisfied. -

-Accepted. And 2438 is already Ready. -

- - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. In 24.2.2 [iterator.iterators] Table 106 "Iterator requirements" change as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - -
    Table 106 — Iterator requirements
    ExpressionReturn typeOperational
    semantics    		Assertion/note pre-/post-condition
    -*r - -referenceunspecified - - - -pre: r is dereferenceable. -
    -… -
    -
    2. - -

  2. In 24.2.3 [input.iterators] Table 107 "Input iterator requirements" change as indicated:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - -
    Table 107 — Input iterator requirements (in addition to Iterator)
    ExpressionReturn typeOperational
    semantics    		Assertion/note pre-/post-condition
    -… -
    -*a - -reference, convertible to T - - - -[…] -
    -… -
    -
    3. -
- - - - - - -
-

2438. std::iterator inheritance shouldn't be mandated

-

Section: 24.4.2 [iterator.basic] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-For LWG convenience, nine STL iterators are depicted as deriving from std::iterator to get their -iterator_category/etc. typedefs. Unfortunately (and unintentionally), this also mandates the -inheritance, which is observable (not just through is_base_of, but also overload resolution). -This is unfortunate because it confuses users, who can be misled into thinking that their own iterators -must derive from std::iterator, or that overloading functions to take std::iterator is -somehow meaningful. This is also unintentional because the STL's most important iterators, the container -iterators, aren't required to derive from std::iterator. (Some are even allowed to be raw pointers.) -Finally, this unnecessarily constrains implementers, who may not want to derive from std::iterator. -(For example, to simplify debugger views.) -

-We could add wording to 24.4.2 [iterator.basic] saying that any depicted inheritance is for exposition -only, but that wouldn't really solve reader confusion. Replacing the depicted inheritance with direct typedefs -will prevent confusion. Note that implementers won't be required to change their code — they are free to -continue deriving from std::iterator if they want. -

-(Editorial note: The order of the typedefs follows the order of std::iterator's template parameters.) -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 20.7.10 [storage.iterator], class template raw_storage_iterator synopsis, as depicted:

    - -
    -
    -template <class OutputIterator, class T>
-class raw_storage_iterator
-  : public iterator<output_iterator_tag,void,void,void,void> {
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-
-  explicit raw_storage_iterator(OutputIterator x);
-  […]
-};
-
    -
    2. - -

  2. Change 24.5.1.1 [reverse.iterator], class template reverse_iterator synopsis, as depicted -(editorial note: this reorders "reference, pointer" to "pointer, reference" -and aligns whitespace):

    - -
    -
    -template <class Iterator>
-class reverse_iterator : public 
-  iterator<typename iterator_traits<Iterator>::iterator_category,
-  typename iterator_traits<Iterator>::value_type,
-  typename iterator_traits<Iterator>::difference_type,
-  typename iterator_traits<Iterator>::pointer,
-  typename iterator_traits<Iterator>::reference> {
-public:
-  typedef Iterator iterator_type;
-  typedef typename iterator_traits<Iterator>::difference_type difference_type;
-  typedef typename iterator_traits<Iterator>::reference reference;
-  typedef typename iterator_traits<Iterator>::pointer pointer;
-  typedef Iterator                                              iterator_type;
-  typedef typename iterator_traits<Iterator>::iterator_category iterator_category;
-  typedef typename iterator_traits<Iterator>::value_type        value_type;
-  typedef typename iterator_traits<Iterator>::difference_type   difference_type;
-  typedef typename iterator_traits<Iterator>::pointer           pointer;
-  typedef typename iterator_traits<Iterator>::reference         reference;
-
-  reverse_iterator();
-  […]
-};
-
    -
    3. - -

  3. Change 24.5.2.1 [back.insert.iterator], class template back_insert_iterator synopsis, as depicted:

    - -
    -
    -template <class Container>
-class back_insert_iterator : 
-  public iterator<output_iterator_tag,void,void,void,void> {
-protected:
-  Container* container;
-
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-  typedef Container container_type;
-  explicit back_insert_iterator(Container& x);
-  […]
-};
-
    -
    4. - -

  4. Change 24.5.2.3 [front.insert.iterator], class template front_insert_iterator synopsis, as depicted:

    - -
    -
    -template <class Container>
-class front_insert_iterator : 
-  public iterator<output_iterator_tag,void,void,void,void> {
-protected:
-  Container* container;
-
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-  typedef Container container_type;
-  explicit front_insert_iterator(Container& x);
-  […]
-};
-
    -
    5. - -

  5. Change 24.5.2.5 [insert.iterator], class template insert_iterator synopsis, as depicted:

    - -
    -
    -template <class Container>
-class insert_iterator : 
-  public iterator<output_iterator_tag,void,void,void,void> {
-protected:
-  Container* container;
-  typename Container::iterator iter;
-
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-  typedef Container container_type;
-  insert_iterator(Container& x, typename Container::iterator i);
-  […]
-};
-
    -
    6. - -

  6. Change 24.6.1 [istream.iterator], class template istream_iterator synopsis, as depicted:

    - -
    -
    -template <class T, class charT = char, class traits = char_traits<charT>,
-  class Distance = ptrdiff_t>
-class istream_iterator : 
-  public iterator<input_iterator_tag, T, Distance, const T*, const T&> {
-public:
-  typedef input_iterator_tag iterator_category;
-  typedef T value_type;
-  typedef Distance difference_type;
-  typedef const T* pointer;
-  typedef const T& reference;
-  […]
-};
-
    -
    7. - -

  7. Change 24.6.2 [ostream.iterator], class template ostream_iterator synopsis, as depicted:

    - -
    -
    -template <class T, class charT = char, class traits = char_traits<charT>>
-class ostream_iterator : 
-  public iterator<output_iterator_tag, void, void, void, void> {
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-  […]
-};
-
    -
    8. - -

  8. Change 24.6.3 [istreambuf.iterator], class template istreambuf_iterator synopsis, as depicted:

    - -
    -
    -template <class charT = char, class traits = char_traits<charT> >
-class istreambuf_iterator : 
-  public iterator<input_iterator_tag, charT,
-                  typename traits::off_type, unspecified, charT> {
-public:
-  typedef input_iterator_tag iterator_category;
-  typedef charT value_type;
-  typedef typename traits::off_type difference_type;
-  typedef unspecified pointer;
-  typedef charT reference;
-  […]
-};
-
    -
    9. - -

  9. Change 24.6.4 [ostreambuf.iterator], class template ostreambuf_iterator synopsis, as depicted -(editorial note: this removes a redundant "public:"):

    - -
    -
    -template <class charT = char, class traits = char_traits<charT>>
-class ostreambuf_iterator : 
-  public iterator<output_iterator_tag, void, void, void, void> {
-public:
-  typedef output_iterator_tag iterator_category;
-  typedef void value_type;
-  typedef void difference_type;
-  typedef void pointer;
-  typedef void reference;
-  […]
-public:
-  […]
-};
-
    -
    10. -
- - - - - - -
-

2439. unique_copy() sometimes can't fall back to reading its output

-

Section: 25.3.9 [alg.unique] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [alg.unique].

-

View all issues with WP status.

-

Discussion:

-

-unique_copy()'s wording says that if it's given input-only and output-only iterators, it needs -the input's value type to be copyable. This is correct, because in this case the algorithm must have a -local element copy in order to detect duplicates. -

-The wording also says that if it's given an InputIterator that's forward or stronger, the input's -value type doesn't have to be copyable. This is also correct, because in this case the algorithm can reread -the input in order to detect duplicates. -

-Finally, the wording says that if it's given an input-only iterator with an OutputIterator that's -forward or stronger, the input's value type doesn't have to be copyable. This is telling the algorithm to -compare its input to its output in order to detect duplicates, but that isn't always possible! If the input -and output have the same value type, then they can be compared (as long as *result = *first behaves -sanely; see below). If they have different value types, then we can't compare them. -

-This could be resolved by requiring heterogeneous value types to be comparable in this situation, but that -would be extremely tricky to wordsmith (as it would challenge the concept of "group of equal elements" used -by the Effects). It will be vastly simpler and more effective to extend the "local element copy" requirement -to this scenario. -

-Note that the input-only, output forward-or-stronger, identical value types scenario needs a bit of work too. -We always require *result = *first to be "valid", but in this case we need to additionally require that the -assignment actually transfers the value. (Otherwise, we'd be allowing an op=() that ignores *first -and always sets *result to zero, or other unacceptable behavior.) This is just CopyAssignable. -

-(What happens when unique_copy() is given a move_iterator is a separate issue.) -

-To summarize: -

-

-input forward+: no additional requirements -

-input-only, output forward+, same value types: needs CopyAssignable -

-input-only, output forward+, different value types: needs CopyConstructible and CopyAssignable -

-input-only, output-only: needs CopyConstructible and CopyAssignable -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 25.3.9 [alg.unique] p5, as depicted:

    - -
    -
    -template<class InputIterator, class OutputIterator>
-OutputIterator
-unique_copy(InputIterator first, InputIterator last,
-            OutputIterator result);
-template<class InputIterator, class OutputIterator,
-         class BinaryPredicate>
-OutputIterator
-unique_copy(InputIterator first, InputIterator last,
-            OutputIterator result, BinaryPredicate pred);
-
    -
    -

    --5- Requires: The comparison function shall be an equivalence relation. The ranges [first,last) and -[result,result+(last-first)) shall not overlap. The expression *result = *first shall be valid. -If neither InputIterator nor OutputIterator meets the requirements of forward iterator then the -value type of InputIterator shall be CopyConstructible (Table 21) and CopyAssignable (Table 23). -Otherwise CopyConstructible is not required.Let T be the value type of InputIterator. -If InputIterator meets the forward iterator requirements, then there are no additional requirements for T. -Otherwise, if OutputIterator meets the forward iterator requirements and its value type is the same as T, -then T shall be CopyAssignable (Table 23). Otherwise, T shall be both CopyConstructible -(Table 21) and CopyAssignable. -

    -
    2. -
- - - - - - -
-

2440. seed_seq::size() should be noexcept

-

Section: 26.5.7.1 [rand.util.seedseq] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [rand.util.seedseq].

-

View all issues with WP status.

-

Discussion:

-

-Obvious. -

- -

[Urbana 2014-11-07: Move to Ready]

- - - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 26.5.7.1 [rand.util.seedseq], class seed_seq synopsis, as depicted:

    - -
    -
    -class seed_seq
-{
-public:
-  […]
-  size_t size() const noexcept;
-  […]
-};
-
    -
    2. - -

  2. Change 26.5.7.1 [rand.util.seedseq] around p10, as depicted:

    - -
    -
    -size_t size() const noexcept;
-
    -
    -

    --10- Returns: The number of 32-bit units that would be returned by a call to param(). -

    --11- Throws: Nothing. -

    --12- Complexity: Constant time. -

    -
    -
    3. -
- - - - - - -
-

2442. call_once() shouldn't DECAY_COPY()

-

Section: 30.4.4.2 [thread.once.callonce] Status: WP - Submitter: Stephan T. Lavavej Opened: 2014-10-01 Last modified: 2015-05-22

-

View all other issues in [thread.once.callonce].

-

View all issues with WP status.

-

Discussion:

-

-When LWG 891 overhauled call_once()'s specification, it used decay_copy(), following -LWG 929's overhaul of thread's constructor. -

-In thread's constructor, this is necessary and critically important. 30.3.1.2 [thread.thread.constr]/5 -"The new thread of execution executes INVOKE(DECAY_COPY(std::forward<F>(f)), -DECAY_COPY(std::forward<Args>(args))...) -with the calls to DECAY_COPY being evaluated in the constructing thread." requires the parent thread -to copy arguments for the child thread to access. -

-In call_once(), this is unnecessary and harmful. It's unnecessary because call_once() doesn't transfer -arguments between threads. It's harmful because: -

-
    -

  • decay_copy() returns a prvalue. Given meow(int&), meow(i) can be called directly, -but call_once(flag, meow, i) won't compile.

    • -

  • decay_copy() moves from modifiable rvalues. Given purr(const unique_ptr<int>&), -purr(move(up)) won't modify up. (This is observable, because moved-from unique_ptrs are -guaranteed empty.) However, call_once(flag, purr, move(up)) will leave up empty after the first active -execution. Observe the behavioral difference — if purr() is directly called like this repeatedly until it -doesn't throw an exception, each call will observe up unchanged. With call_once(), the second active -execution will observe up to be empty.

    • -
-

-call_once() should use perfect forwarding without decay_copy(), in order to avoid interfering with the call like this. -

- -

[2015-02 Cologne]

- -

-Handed over to SG1. -

- -

[2015-05 Lenexa, SG1 response]

- -

-Looks good to us, but this is really an LWG issue. -

- -

[2015-05-07 Lenexa: Move Immediate]

- -

LWG 2442 call_once shouldn't decay_copy

-

STL summarizes the SG1 minutes.

-

Marshall: Jonathan updated all the issues with SG1 status last night. Except this one.

-

STL summarizes the issue.

-

Dietmar: Of course, call_once has become useless.

-

STL: With magic statics.

-

Jonathan: Magic statics can't be per object, which I use in future.

-

Marshall: I see why you are removing the MoveConstructible on the arguments, but what about Callable?

-

STL: That's a type named Callable, which we will no longer decay_copy. We're still requiring the INVOKE expression to be valid.

-

Marshall: Okay. Basically, ripping the decay_copy out of here.

-

STL: I recall searching the Standard for other occurrences and I believe this is the only inappropriate use of decay_copy.

-

Marshall: We do the decay_copy.

-

Jonathan: Us too.

-

Marshall: What do people think?

-

Jonathan: I think STL's right. In the use I was mentioning inside futures, I actually pass them by reference_wrapper and pointers, to avoid the decay causing problems. Inside the call_once, I then extract the args. So I've had to work around this and didn't realize it was a defect.

-

Marshall: What do people think is the right resolution?

-

STL: I would like to see Immediate.

-

Hwrd: No objections to Immediate.

-

Marshall: Bill is nodding.

-

PJP: He said it. Everything STL says applies to our other customers.

-

Marshall: Any objections to Immediate?

-

Jonathan: I can't see any funky implementations where a decay_copy would be necessary?

-

Marshall: 6 votes for Immediate, 0 opposed, 0 abstaining.

- - - -

Proposed resolution:

-

-This wording is relative to N3936. -

- -
    -

  1. Change 30.4.4.2 [thread.once.callonce] p1+p2 as depicted:

    - -
    -
    -template<class Callable, class ...Args>
-  void call_once(once_flag& flag, Callable&& func, Args&&... args);
-
    -
    -

    --1- Requires: Callable and each Ti in Args shall satisfy the MoveConstructible -requirements. INVOKE(DECAY_COPY(std::forward<Callable>(func)), -DECAY_COPY(std::forward<Args>(args))...) -(20.9.2) shall be a valid expression. -

    --2- Effects; […] An active execution shall call -INVOKE(DECAY_COPY(std::forward<Callable>(func)), -DECAY_COPY(std::forward<Args>(args))...). […] -

    -
    -
    -
    2. -
- - - - - - -
-

2448. Non-normative Container destructor specification

-

Section: 23.2.1 [container.requirements.general] Status: WP - Submitter: Daniel Krügler Opened: 2014-10-18 Last modified: 2015-05-22

-

View other active issues in [container.requirements.general].

-

View all other issues in [container.requirements.general].

-

View all issues with WP status.

-

Discussion:

-

-According to Table 96 — "Container requirements" the specification: -

-

-note: the destructor is applied to every element of a; any -memory obtained is deallocated. -

-

-The initial "note:" can be read as if that part of the specification would not be normative (This note form -differs from footnotes in tables, which have normative meaning). -

-It seems that this initial part of the specification exists since C++98. But comparing with -the similar SGI Container specification there is no evidence -for that being intended to be non-normative. -

- -

[2015-02, Cologne]

- -

-NJ: If we fix this, we should also fix it elsewhere. Oh, this is the only place?
-GR: If this is intended to be different from elsewhere, we should make sure.
-AM: valarray specifies this without the "note:".
-DK: valarray requires trivially destructible types!
-GR: That's good enough for me.
-NJ: First time valarray has been useful for something! -

- - -

Proposed resolution:

-

-This wording is relative to N4140. -

- -
    -

  1. Change 23.2.1 [container.requirements.general], Table 96 — "Container requirements", as indicated:

    -
    - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 96 — Container requirements
    ExpressionReturn typeOperational
    semantics    		Assertion/note
    pre-/post-condition    		Complexity
    -… -
    -(&a)->~X() - -void - - -note: the destructor
    -is applied to every
    -element of a; any
    -memory obtained is -deallocated. -    		 -linear -
    -… -
    -
    -
    2. -
- - - - - -
-

2454. Add raw_storage_iterator::base() member

-

Section: 20.7.10 [storage.iterator] Status: WP - Submitter: Jonathan Wakely Opened: 2014-11-11 Last modified: 2015-05-22

-

View all other issues in [storage.iterator].

-

View all issues with WP status.

-

Discussion:

-

-Eric Niebler pointed out that raw_storage_iterator should give access -to the OutputIterator it wraps. -

-This helps alleviate the exception-safety issue pointed out in the -discussion of LWG 2127, as an exception can be caught and then -destructors can be run for the constructed elements in the range -[begin, raw.base()) -

- -

[2015-02 Cologne]

- -

-NJ: Is this "const" correct [in "base()"]? DK: Yes, we always do that. NJ: And the output iterator is not qualifying in any way? -AM/DK: That wouldn't make sense. NJ: OK. -

-VV: What did LEWG say about this feature request? In other words, why is this a library issue? AM: LEWG/JY thought this wouldn't -be a contentious issue. -

-NJ: I really hope the split of LEWG and LWG will be fixed soon, since it's only wasting time. VV: So you want to spend even -more of your time on discussions that LEWG has? -

-AM: I think this specified correctly. I'm not wild about it. But no longer bothered to stand in its way. -

-GR: Why do we need to repeat the type in "Returns" even though it's part of the synopsis? AM: Good point, but not worth fixing. -

-NJ: Why is "base()" for reverse_iterator commented with "// explicit"? AM: I guess in 1998 that was the -only way to say this. -

-AM: So, it's tentatively ready. -

- - -

Proposed resolution:

-

This wording is relative to N4140.

- -
    -

  1. Add a new function to the synopsis in 20.7.10 [storage.iterator] p1:

    - -
    -namespace std {
-  template <class OutputIterator, class T>
-  class raw_storage_iterator
-    : public iterator<output_iterator_tag,void,void,void,void> {
-  public:
-    explicit raw_storage_iterator(OutputIterator x);
-
-    raw_storage_iterator<OutputIterator,T>& operator*();
-    raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
-    raw_storage_iterator<OutputIterator,T>& operator++();
-    raw_storage_iterator<OutputIterator,T> operator++(int);
-    OutputIterator base() const;
-};
-}
-
    -
    2. - -

  2. Insert the new function and a new paragraph series after p7:

    - -
    -OutputIterator base() const;
-
    -

    --?- Returns: An iterator of type OutputIterator that points to the -same value as *this points to. -

    -
    -
    3. - -
- - - - - -
-

2455. Allocator default construction should be allowed to throw

-

Section: 17.6.3.5 [allocator.requirements] Status: WP - Submitter: Pablo Halpern Opened: 2014-11-11 Last modified: 2015-05-22

-

View other active issues in [allocator.requirements].

-

View all other issues in [allocator.requirements].

-

View all issues with WP status.

-

Discussion:

-

-17.6.3.5 [allocator.requirements]/4 in the 2014-10 WP (N4140), says: -

-

-An allocator type X shall satisfy the requirements of CopyConstructible (17.6.3.1). The -X::pointer, X::const_pointer, X::void_pointer, and X::const_void_pointer -types shall satisfy the requirements of NullablePointer (17.6.3.3). No constructor, comparison operator, -copy operation, move operation, or swap operation on these types shall exit via an exception. X::pointer -and X::const_pointer shall also satisfy the requirements for a random access iterator (24.2). -

-

-The words "these types" would normally apply only to the previous sentence only, i.e., only to the pointer types. -However, an alternative reading would be that the allocator constructors themselves cannot throw. The change to -the vector and string default constructors, making them unconditionally noexcept depends -on this alternative reading. -

-I believe that the wording in the standard is not intended to forbid throwing default constructors for allocators. -Indeed, I believe that allocators do not require default constructors and that if they provide a default constructor -they should be allowed to throw. -

-In addition, the noexcept specifications for the string and vector default constructors -should be changed to make them conditional. -

- -

[2015-01-18 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - - -

Proposed resolution:

- -
    -

  1. Change 17.6.3.5 [allocator.requirements] p4 as indicated:

    - -

    -An allocator type X shall satisfy the requirements of CopyConstructible (17.6.3.1). The -X::pointer, X::const_pointer, X::void_pointer, and X::const_void_pointer -types shall satisfy the requirements of NullablePointer (17.6.3.3). No constructor, comparison operator, -copy operation, move operation, or swap operation on these pointer types shall exit via an exception. -X::pointer and X::const_pointer shall also satisfy the requirements for a random access iterator (24.2). -

    -
    2. - -

  2. Change 21.4 [basic.string] following p5, class template basic_string synopsis, as indicated: -(This change assumes that N4258 has been applied, as voted on in Urbana on 2014-11-08)

    - -
    -
    -// 21.4.2, construct/copy/destroy:
-basic_string() noexcept(noexcept(Allocator())) : basic_string(Allocator()) { }
-
    -
    - -
    -

    -An alternative formulation of the above would be: -

    -
    -// 21.4.2, construct/copy/destroy:
-basic_string() noexcept(is_nothrow_default_constructible<Allocator>{}) : basic_string(Allocator()) { }
-
    -
    -
    3. - -

  3. Change 23.3.6.1 [vector.overview] following p2, class template vector synopsis, as indicated: -(This change assumes that N4258 has been applied, as voted on in Urbana on 2014-11-08)

    - -
    -
    -// 23.3.6.2, construct/copy/destroy:
-vector() noexcept(noexcept(Allocator())) : vector(Allocator()) { }
-
    -
    - -
    -

    -An alternative formulation of the above would be: -

    -
    -// 23.3.6.2, construct/copy/destroy:
-vector() noexcept(is_nothrow_default_constructible<Allocator>{}) : vector(Allocator()) { }
-
    -
    -
    4. - -
- - - - - -
-

2458. N3778 and new library deallocation signatures

-

Section: 18.6 [support.dynamic], 18.6.1.1 [new.delete.single], 18.6.1.2 [new.delete.array] Status: WP - Submitter: Richard Smith Opened: 2014-11-23 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-N3778 -added the following sized deallocation signatures to the library: -

-
-void operator delete(void* ptr, std::size_t size) noexcept;
-void operator delete[](void* ptr, std::size_t size) noexcept;
-
-void operator delete(void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-void operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-
-

-The former two are an essential part of the proposal. The latter two seem -spurious — they are not called when new (std::nothrow) X fails due to -X::X() throwing, because the core language rules for selecting a placement -deallocation function do not consider passing a size argument. Instead, the -above would be the matching deallocation functions for: -

-
-void *operator new(std::size_t size, std::size_t size_again, const std::nothrow_t&) noexcept;
-void *operator new[](std::size_t size, std::size_t size_again, const std::nothrow_t&) noexcept;
-
-

-... which don't exist. -

-Since they're not implicitly called, the only other possible use for those -functions would be to perform an explicitly non-throwing deallocation. -But... the first two overloads are already explicitly non-throwing and are -required to be semantically identical to the second two. So there's no -point in making an explicit call to the second pair of functions either. -

-It seems to me that we should remove the (void*, size_t, nothrow_t) overloads, because -the core working group decided during the Urbana 2014 meeting, that no change to the core -language was warranted. -

- -

[2014-11-23, Daniel suggests concrete wording changes]

- - -

[2015-02 Cologne]

- -

-Nobody can call those overloads, since the nothrow allocation functions cannot throw. JY: Ship it. GR: Should we do due -diligence and make sure we're deleting what we mean to be deleting? [Some checking, everything looks good.] -

-Accepted. -

- - -

Proposed resolution:

-

This wording is relative to N4140.

- -
    -

  1. Change 18.6 [support.dynamic], header <new> synopsis, as indicated:

    - -
    -[…]
-void operator delete(void* ptr, std::size_t size) noexcept;
-void operator delete(void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-[…]
-void operator delete[](void* ptr, std::size_t size) noexcept;
-void operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-[…]
-
    - -
    2. - -

  2. Change 18.6.1.1 [new.delete.single], starting before p19, as indicated:

    -
    -void operator delete(void* ptr, const std::nothrow_t&) noexcept;
-void operator delete(void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-
    -
    -

    -[…] -

    --20- Replaceable: a C++ program may define a function with signature void operator delete(void* -ptr, const std::nothrow_t&) noexcept that displaces the default version defined by the C++ standard -library. If this function (without size parameter) is defined, the program should also define -void operator delete(void* ptr, std::size_t size, const std::nothrow_t&) noexcept. If -this function with size parameter is defined, the program shall also define the version without the -size parameter. [Note: The default behavior below may change in the future, which will require -replacing both deallocation functions when replacing the allocation function. — end note] -

    -[…] -

    --22- Requires: If present, the std::size_t size argument must equal the size -argument passed to the allocation function that returned ptr. -

    --23- Required behavior: Calls to operator delete(void* ptr, std::size_t size, const std::nothrow_t&) -may be changed to calls to operator delete(void* ptr, const std::nothrow_t&) without affecting -memory allocation. [Note: A conforming implementation is for operator delete(void* ptr, std::size_t size, -const std::nothrow_t&) to simply call operator delete(void* ptr, const std::nothrow_t&). — -end note] -

    --24- Default behavior: operator delete(void* ptr, std::size_t size, const std::nothrow_t&) -calls operator delete(ptr, std::nothrow), and operator delete(void* ptr, const std::nothrow_t&) -calls operator delete(ptr). -

    -
    -
    -
    3. - -

  3. Change 18.6.1.2 [new.delete.array], starting before p16, as indicated:

    -
    -void operator delete[](void* ptr, const std::nothrow_t&) noexcept;
-void operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) noexcept;
-
    -
    -

    -[…] -

    --17- Replaceable: a C++ program may define a function with signature void operator delete[](void* -ptr, const std::nothrow_t&) noexcept that displaces the default version defined by the C++ standard -library. If this function (without size parameter) is defined, the program should also define void -operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) noexcept. If this -function with size parameter is defined, the program shall also define the version without the size -parameter. [Note: The default behavior below may change in the future, which will require replacing -both deallocation functions when replacing the allocation function. — end note] -

    -[…] -

    --19- Requires: If present, the std::size_t size argument must equal the size argument -passed to the allocation function that returned ptr. -

    --20- Required behavior: Calls to operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) -may be changed to calls to operator delete[](void* ptr, const std::nothrow_t&) without affecting memory allocation. -[Note: A conforming implementation is for operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) -to simply call operator delete[](void* ptr, const std::nothrow_t&). — end note] -

    --21- Default behavior: operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) -calls operator delete[](ptr, std::nothrow), and operator delete[](void* ptr, const std::nothrow_t&) -calls operator delete[](ptr). -

    -
    -
    -
    4. -
- - - - - -
-

2459. std::polar should require a non-negative rho

-

Section: 26.4.7 [complex.value.ops] Status: WP - Submitter: Marshall Clow Opened: 2014-10-22 Last modified: 2015-05-22

-

View all other issues in [complex.value.ops].

-

View all issues with WP status.

-

Discussion:

-

-Different implementations give different answers for the following code: -

-
-#include <iostream>
-#include <complex>
-
-int main ()
-{
-  std::cout << std::polar(-1.0, -1.0) << '\n';
-  return 0;
-}
-
-

-One implementation prints: -

-
-(nan, nan)
-
-

-Another: -

-
-(-0.243068, 0.243068)
-
-

-Which is correct? Or neither? -

-In this list, -Howard Hinnant wrote: -

-
-

-I've read this over several times. I've consulted C++11, C11, and IEC 10967-3. [snip] -

-I'm finding: -

-
    -

  1. The magnitude of a complex number == abs(c) == hypot(c.real(), c.imag()) and is always non-negative -(by all three of the above standards).

    2. -

  2. Therefore no complex number exists for which abs(c) < 0.

    3. -

  3. Therefore when the first argument to std::polar (which is called rho) is negative, no complex number -can be formed which meets the post-conidtion that abs(c) == rho.

    -
    4. -
-

-One could argue that this is already covered in 26.4 [complex.numbers]/3, but I think it's worth making explicit. -

-
- -

[2015-02, Cologne]

- -

-Discussion on whether theta should also be constrained.
-TK: infinite theta doesn't make sense, whereas infinite rho does (theta is on a compact domain, rho is on a non-compact domain).
-AM: We already have a narrow contract, so I don't mind adding further requirements. Any objections to requiring that theta be finite?
-Some more discussion, but general consensus. Agreement that if someone finds the restrictions problematic, they should write -a proper paper to address how std::polar should behave. For now, we allow infinite rho (but not NaN and not negative), -and require finite theta. -

-No objections to tentatively ready. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 26.4.7 [complex.value.ops] around p9 as indicated

    - -
    -template<class T> complex<T> polar(const T& rho, const T& theta = 0);
-
    -
    -

    --?- Requires: rho shall be non-negative and non-NaN. theta shall be finite. -

    --9- Returns: The complex value corresponding to a complex number whose magnitude is rho and whose -phase angle is theta. -

    -
    -
    -
    2. -
- - - - - -
-

2463. [fund.ts] Incorrect complexity for sample() algorithm

-

Section: X [alg.random.sample] Status: WP - Submitter: Joe Gottman Opened: 2014-12-17 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

Addresses: fund.ts

-

-According to paragraph 10.1 of the Library Fundamentals 1 draft, the complexity of the new -std::experimental::sample template function is O(n). Note that n is actually -a parameter of this function, corresponding to the sample size. But both common algorithms for -sampling, the selection algorithm and the reservoir algorithm, are linear with respect to the -population size, which is often many orders of magnitude bigger than the sample size. -

- -

[2015-02, Cologne]

- -

-AM: I suggest we make this a DR against the Fundamentals TS.
-GR: Agreed, this is a no-brainer. -

- - -

Proposed resolution:

-

This wording is relative to N4335 in regard to fundamental-ts changes.

- -
    -

  1. Change X [alg.random.sample] p5 to read:

    - -
    -

    --5- Complexity: O(nlast - first). -

    -
    -
    2. -
- - - - - -
-

2464. try_emplace and insert_or_assign misspecified

-

Section: 23.4.4.4 [map.modifiers], 23.5.4.4 [unord.map.modifiers] Status: WP - Submitter: Thomas Koeppe Opened: 2014-12-17 Last modified: 2015-05-22

-

View all other issues in [map.modifiers].

-

View all issues with WP status.

-

Discussion:

-

-The specification of the try_emplace and insert_or_assign member functions in N4279 -contains the following errors and omissions: -

-
    -

  1. In insert_or_assign, each occurrence of std::forward<Args>(args)... -should be std::forward<M>(obj); this is was a mistake introduced in editing.

    2. - -

  2. In try_emplace, the construction of the value_type is misspecified, which -is a mistake that was introduced during the evolution from a one-parameter to a variadic form. -As written, value_type(k, std::forward<Args>(args)...) does not do the right thing; -it can only be used with a single argument, which moreover must be convertible to a mapped_type. -The intention is to allow direct-initialization from an argument pack, and the correct constructor -should be value_type(piecewise_construct, forward_as_tuple(k), -forward_as_tuple(std::forward<Args>(args)...).

    3. - -

  3. Both try_emplace and insert_or_assign are missing requirements on the -argument types. Since the semantics of these functions are specified independent of other functions, -they need to include their requirements.

    4. -
- -

[2015-02, Cologne]

- -

-This issue is related to 2469. -

-AM: The repeated references to "first and third forms" and "second and fourth forms" is a bit cumbersome. -Maybe split the four functions?
-GR: We don't have precendent for "EmplaceConstructible from a, b, c". I don't like the ambiguity between code commas and -text commas.
-TK: What's the danger?
-GR: It's difficult to follow standardese.
-AM: It seems fine with code commas. What's the problem?
-GR: It will lead to difficulties when we use a similar construction that's not at the end of a sentence.
-AM: That's premature generalization. DK: When that happens, let's look at this again.
-AM: Clean up "if the map does contain"
-TK: Can we call both containers "map"? DK/GR: yes.
-TK will send updated wording to DK. -

-Conclusion: Update wording, then poll for tentatively ready -

- -

[2015-03-26, Thomas provides improved wording]

- -

-The approach is to split the descriptions of the various blocks of four functions into two blocks each so as to make -the wording easier to follow. -

- -Previous resolution [SUPERSEDED]: -
-

This wording is relative to N4296.

- -
    -

  1. Apply the following changes to section 23.4.4.4 [map.modifiers] p3:

    - -
    -
    -template <class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
-template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: For the first and third forms, value_type shall be EmplaceConstructible into map -from piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...). -For the second and fourth forms, value_type shall be EmplaceConstructible into map -from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --3- Effects: If the key k already exists in the map, there is no effect. Otherwise, inserts an element -into the map. In the first and third forms, the element is constructed from the arguments as value_type(k, -std::forward<Args>(args)...). In the second and fourth forms, the element is -constructed from the arguments as value_type(std::move(k), std::forward<Args>(args)...). -In the first two overloads, the bool component of the returned pair is true if and only if the -insertion took place. The returned iterator points to the element of the map whose key is equivalent to k -If the map does already contain an element whose key is equivalent to k, there is no effect. -Otherwise for the first and third forms inserts a value_type object t constructed with -piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...), -for the second and fourth forms inserts a value_type object t constructed with -piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first two overloads, the bool component of the returned pair is true -if and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to -k. -

    -
    -
    -
    2. - -

  2. Apply the following changes to section 23.4.4.4 [map.modifiers] p5:

    - -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
-template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -For the first and third forms, value_type shall be EmplaceConstructible into map from k, -forward<M>(obj). For the second and fourth forms, value_type shall be EmplaceConstructible -into map from move(k), forward<M>(obj). -

    --5- Effects: If the key k does not exist in the map, inserts an element into the map. In the first -and third forms, the element is constructed from the arguments as value_type(k, std::forward<Args>(args)...). -In the second and fourth forms, the element is constructed from the arguments as value_type(std::move(k), -std::forward<Args>(args)...). If the key already exists, std::forward<M>(obj) is assigned to the -mapped_type corresponding to the key. In the first two overloads, the bool component of the returned -value is true if and only if the insertion took place. The returned iterator points to the element that -was inserted or updated -If the map does already contain an element whose key is equivalent to k, -forward<M>(obj) is assigned to the mapped_type corresponding to the key. -Otherwise the first and third forms inserts a value_type object t constructed with k, -forward<M>(obj), the second and fourth forms inserts a value_type object t -constructed with move(k), forward<M>(obj). -

    --?- Returns: In the first two overloads, the bool component of the returned pair is true -if and only if the insertion took place. The returned iterator points to the element of the map whose key is equivalent to -k. -

    -
    -
    -
    3. - -

  3. Apply the following changes to section 23.5.4.4 [unord.map.modifiers] p5:

    - -
    -
    -template <class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
-template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: For the first and third forms, value_type shall be EmplaceConstructible into unordered_map -from piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...). -For the second and fourth forms, value_type shall be EmplaceConstructible into unordered_map -from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --5- Effects: If the key k already exists in the map, there is no effect. Otherwise, inserts an element -into the map. In the first and third forms, the element is constructed from the arguments as value_type(k, -std::forward<Args>(args)...). In the second and fourth forms, the element is -constructed from the arguments as value_type(std::move(k), std::forward<Args>(args)...). -In the first two overloads, the bool component of the returned pair is true if and only if the -insertion took place. The returned iterator points to the element of the map whose key is equivalent to k -If the unordered_map does already contain an element whose key is equivalent to k, there is no effect. -Otherwise for the first and third forms inserts a value_type object t constructed with -piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...), -for the second and fourth forms inserts a value_type object t constructed with -piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first two overloads, the bool component of the returned pair is true -if and only if the insertion took place. The returned iterator points to the element of the unordered_map whose key is equivalent to -k. -

    -
    -
    -
    4. - -

  4. Apply the following changes to section 23.5.4.4 [unord.map.modifiers] p7:

    - -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
-template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -For the first and third forms, value_type shall be EmplaceConstructible into unordered_map from k, -forward<M>(obj). For the second and fourth forms, value_type shall be EmplaceConstructible -into unordered_map from move(k), forward<M>(obj). -

    --7- Effects: If the key k does not exist in the map, inserts an element into the map. -In the first and third forms, the element is constructed from the arguments as value_type(k, std::forward<Args>(args)...). -In the second and fourth forms, the element is constructed from the arguments as value_type(std::move(k), -std::forward<Args>(args)...). If the key already exists, std::forward<M>(obj) is assigned to the -mapped_type corresponding to the key. In the first two overloads, the bool component of the returned -value is true if and only if the insertion took place. The returned iterator points to the element that -was inserted or updated -If the unordered_map does already contain an element whose key is equivalent to k, -forward<M>(obj) is assigned to the mapped_type corresponding to the key. -Otherwise the first and third forms inserts a value_type object t constructed with k, -forward<M>(obj), the second and fourth forms inserts a value_type object t -constructed with move(k), forward<M>(obj). -

    --?- Returns: In the first two overloads, the bool component of the returned pair is true -if and only if the insertion took place. The returned iterator points to the element of the unordered_map whose key is -equivalent to k. -

    -
    -
    -
    5. - -
-
- -

[2015-05, Lenexa]

- -

-STL: existing wording is horrible, this is Thomas' wording and his issue
-STL: already implemented the piecewise part
-MC: ok with changes
-STL: changes are mechanical
-STL: believe this is P1, it must be fixed, we have wording
-PJP: functions are sensible
-STL: has been implemented
-MC: consensus is to move to ready -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Apply the following changes to 23.4.4.4 [map.modifiers] p3+p4:

    - -
    -
    -template <class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
-template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: value_type shall be EmplaceConstructible into map from -piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...). -

    --3- Effects: If the key k already exists in the map, there is no effect. Otherwise, inserts an element -into the map. In the first and third forms, the element is constructed from the arguments as value_type(k, -std::forward<Args>(args)...). In the second and fourth forms, the element is -constructed from the arguments as value_type(std::move(k), std::forward<Args>(args)...). -In the first two overloads, the bool component of the returned pair is true if and only if the -insertion took place. The returned iterator points to the element of the map whose key is equivalent to k -If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an -object of type value_type constructed with piecewise_construct, forward_as_tuple(k), -forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and only -if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --4- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    - -
    -template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: value_type shall be EmplaceConstructible into map from -piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --?- Effects: If the map already contains an element whose key is equivalent to k, there is no effect. -Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), -forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and only -if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --?- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -
    2. - -

  2. Apply the following changes to 23.4.4.4 [map.modifiers] p5+p6:

    - -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
-template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -value_type shall be EmplaceConstructible into map from k, forward<M>(obj). -

    --5- Effects: If the key k does not exist in the map, inserts an element into the map. In the first -and third forms, the element is constructed from the arguments as value_type(k, std::forward<Args>(args)...). -In the second and fourth forms, the element is constructed from the arguments as value_type(std::move(k), -std::forward<Args>(args)...). If the key already exists, std::forward<M>(obj) is assigned to the -mapped_type corresponding to the key. In the first two overloads, the bool component of the returned -value is true if and only if the insertion took place. The returned iterator points to the element that -was inserted or updated -If the map already contains an element e whose key is equivalent to k, assigns forward<M>(obj) -to e.second. Otherwise inserts an object of type value_type constructed with k, forward<M>(obj). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and -only if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --6- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -value_type shall be EmplaceConstructible into map from move(k), forward<M>(obj). -

    --?- Effects: If the map already contains an element e whose key is equivalent to k, -assigns forward<M>(obj) to e.second. Otherwise inserts an object of type value_type -constructed with move(k), forward<M>(obj). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and only -if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --?- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -
    3. - -

  3. Apply the following changes to 23.5.4.4 [unord.map.modifiers] p5+p6:

    - -
    -
    -template <class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
-template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: value_type shall be EmplaceConstructible into unordered_map from -piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...). -

    --5- Effects: If the key k already exists in the map, there is no effect. Otherwise, inserts an element -into the map. In the first and third forms, the element is constructed from the arguments as value_type(k, -std::forward<Args>(args)...). In the second and fourth forms, the element is -constructed from the arguments as value_type(std::move(k), std::forward<Args>(args)...). -In the first two overloads, the bool component of the returned pair is true if and only if the -insertion took place. The returned iterator points to the element of the map whose key is equivalent to k -If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts -an object of type value_type constructed with piecewise_construct, forward_as_tuple(k), -forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and only -if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --6- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
-template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
-
    -
    -

    --?- Requires: value_type shall be EmplaceConstructible into unordered_map from -piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...). -

    --?- Effects: If the map already contains an element whose key is equivalent to k, there is no effect. -Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), -forward_as_tuple(forward<Args>(args)...). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if and only -if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --?- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -
    4. - -

  4. Apply the following changes to 23.5.4.4 [unord.map.modifiers] p7+p8:

    - -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
-template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -value_type shall be EmplaceConstructible into unordered_map from k, -forward<M>(obj). -

    --7- Effects: If the key k does not exist in the map, inserts an element into the map. -In the first and third forms, the element is constructed from the arguments as value_type(k, std::forward<Args>(args)...). -In the second and fourth forms, the element is constructed from the arguments as value_type(std::move(k), -std::forward<Args>(args)...). If the key already exists, std::forward<M>(obj) is assigned to the -mapped_type corresponding to the key. In the first two overloads, the bool component of the returned -value is true if and only if the insertion took place. The returned iterator points to the element that -was inserted or updated -If the map already contains an element e whose key is equivalent to k, assigns forward<M>(obj) -to e.second. Otherwise inserts an object of type value_type constructed with k, forward<M>(obj). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if -and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to k. -

    --8- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -template <class M> pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
-template <class M> iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
-
    -
    -

    --?- Requires: is_assignable<mapped_type&, M&&>::value shall be true. -value_type shall be EmplaceConstructible into unordered_map from move(k), -forward<M>(obj). -

    --?- Effects: If the map already contains an element e whose key is equivalent to k, -assigns forward<M>(obj) to e.second. Otherwise inserts an object of type value_type -constructed with move(k), forward<M>(obj). -

    --?- Returns: In the first overload, the bool component of the returned pair is true if -and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to -k. -

    --?- Complexity: The same as emplace and emplace_hint, respectively. -

    -
    -
    -
    5. - -
- - - - - -
-

2467. is_always_equal has slightly inconsistent default

-

Section: 17.6.3.5 [allocator.requirements], 20.7.8.1 [allocator.traits.types] Status: WP - Submitter: Howard Hinnant Opened: 2015-01-18 Last modified: 2015-05-22

-

View other active issues in [allocator.requirements].

-

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-

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-

Discussion:

-

-Table 28 — "Allocator requirements" says that X::is_always_equal has a default value -of is_empty<X>, and this is consistent with the return type description: -

-
-

-Identical to or derived from true_type or false_type -

-
-

-is_empty<X> is guaranteed to be derived from either true_type or false_type. -So far so good. -

-20.7.8.1 [allocator.traits.types]/p10 says: -

-
-
-typedef see below is_always_equal;
-
-
-

-Type: Alloc::is_always_equal if the qualified-id Alloc::is_always_equal is valid and denotes a -type (14.8.2); otherwise is_empty<Alloc>::type. -

-
-
-

-This is subtly different than what Table 28 says is the default: is_empty<Alloc>::type is -not is_empty<Alloc>, but is rather one of true_type or false_type. -

-There are two ways to fix this: -

-
    -
  1. -

    -Change Table 28 to say: is_empty<X>::type. -

    -or -

    2. - -

  2. Change 20.7.8.1 [allocator.traits.types]/p10:

    3. -
    -

    -Type: Alloc::is_always_equal if the qualified-id Alloc::is_always_equal is valid and denotes a -type (14.8.2); otherwise is_empty<Alloc>::type. -

    -
    -
-

-Both options are correct, and I see no reason to prefer one fix over the other. But Table 28 and -20.7.8.1 [allocator.traits.types]/p10 should be consistent with one another. -

- -

[2015-02 Cologne]

- -

-DK: We should accept the first bullet. GR: Why does is_empty even have a type member? AM: All type traits -have a type member. I agree with DK's preference for the first type. -

- - -

Proposed resolution:

-

-This wording is relative to N4296. -

- -
    -

  1. Change 17.6.3.5 [allocator.requirements], Table 28 — "Allocator requirements" as presented:

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - -
    Table 28 — Allocator requirements
    ExpressionReturn typeAssertion/note
    pre-/post-condition    		Default
    -… -
    -X::is_always_equal - -Identical to or derived
    -from true_type or
    -false_type -    		 -[…] - -is_empty<X>::type -
    -… -
    -
    - -
    2. -
- - - - - -
-

2470. Allocator's destroy function should be allowed to fail to instantiate

-

Section: 17.6.3.5 [allocator.requirements] Status: WP - Submitter: Daniel Krügler Opened: 2015-03-22 Last modified: 2015-05-22

-

View other active issues in [allocator.requirements].

-

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-

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-

Discussion:

-

-This issue is a spin-off of issue LWG 2447: It focuses on the observation that -17.6.3.5 [allocator.requirements] p9 (based on the numbering of working draft N4296) gives -the template member construct more relaxations than the template member destroy: -

-
-

-An allocator may constrain the types on which it can be instantiated and the arguments for which its -construct member may be called. If a type cannot be used with a particular allocator, the allocator class -or the call to construct may fail to instantiate. -

-
-

-Construction and destruction of a type T are usually intimately related to each other, so it -seems similarly useful to allow the destroy member to fail to instantiate for a possible sub-set -of instantiation types. -

- -

[2015-04-01 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 17.6.3.5 [allocator.requirements] p9 as indicated:

    - -

    --8- An allocator may constrain the types on which it can be instantiated and the arguments for which its -construct or destroy members may be called. If a type cannot be -used with a particular allocator, the allocator class or the call to construct or destroy -may fail to instantiate. -

    -
    2. -
- - - - - -
-

2482. [c.strings] Table 73 mentions nonexistent functions

-

Section: 21.8 [c.strings] Status: WP - Submitter: S. B.Tam Opened: 2015-01-18 Last modified: 2015-05-22

-

View other active issues in [c.strings].

-

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-

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-

Discussion:

-

-N4296 Table 73 mentions the functions mbsrtowc and wcsrtomb, which are not defined in ISO C -or ISO C++. Presumably they should be mbsrtowcs and wcsrtombs instead. -

- -

[2015-04-02 Library reflector vote]

- -

-The issue has been identified as Tentatively Ready based on six votes in favour. -

- - -

Proposed resolution:

- -

This wording is relative to N4296.

- -
    -
  1. -
    - - - - - - - - - - - - - - - -
    Table 33 — Potential mbstate_t data races
    -mbrlen - -mbrtowc - -mbsrtowcs - -mbtowc - -wcrtomb -
    -wcsrtombs - -wctomb -
    -
    -
    2. -
- - - - - - -
-

2488. Placeholders should be allowed and encouraged to be constexpr

-

Section: 20.9.10.4 [func.bind.place] Status: WP - Submitter: Stephan T. Lavavej Opened: 2015-03-27 Last modified: 2015-05-22

-

View all issues with WP status.

-

Discussion:

-

-piecewise_construct (20.3.5 [pair.piecewise]), allocator_arg (20.7.6 [allocator.tag]), -and adopt_lock/defer_lock/try_to_lock (30.4.2 [thread.lock]) are all required to be -constexpr with internal linkage. bind()'s placeholders should be allowed to follow this modern practice, -for increased consistency and reduced implementer headaches (header-only is easier than separately-compiled). -

- -

[2015-05-07 Lenexa: Move to Immediate]

- -

STL: I'd like this one immediate.

-

Jonathan: I want to think about forcing constexpr, but the current issue, I have no objections. I'd say ready, but I won't object to immediate if STL wants it.

-

Marshall: You should report in Kona how it worked out.

-

STL: We went around a bit on the reflector about how to phrase the encouragement.

-

Jonathan: I think the shall may be not quite right.

-

Marshall: I see, you can change your implementation, but you don't.

-

Jonathan: There's precedent for the shall, but it's wrong, see editorial issue 493.

-

STL: I would prefer not to ask Daniel to reword, and 493 can fix it later.

-

Marshall: I remove my objection to immediate because it doesn't force implementations to change.

-

Marshall: Any other discussion?

-

Marshall: Immediate vote: 6. Opposed, 0. Abstain, 1.

- - - -

Proposed resolution:

-

This wording is relative to N4296.

- -
    -

  1. Change 20.9 [function.objects] p2 "Header <functional> synopsis" as depicted:

    - -
    -
    -namespace placeholders {
-  // M is the implementation-defined number of placeholders
-  see belowextern unspecified _1;
-  see belowextern unspecified _2;
-  ...
-  see belowextern unspecified _M;
-}
-
    -
    -
    2. - -

  2. Change 20.9.10.4 [func.bind.place] p2 as depicted:

    - -
    -
    -namespace std::placeholders {
-  // M is the implementation-defined number of placeholders
-  see belowextern unspecified _1;
-  see belowextern unspecified _2;
-             .
-             .
-             .
-  see belowextern unspecified _M;
-}
-
    -

    --1- All placeholder types shall be DefaultConstructible and CopyConstructible, and -their default constructors and copy/move constructors shall not throw exceptions. It is -implementation-defined whether placeholder types are CopyAssignable. CopyAssignable -placeholders' copy assignment operators shall not throw exceptions. -

    --?- Placeholders should be defined as: -

    -
    -
    -constexpr unspecified _1{};
-
    -
    -

    -If they are not, they shall be declared as: -

    -
    -
    -extern unspecified _1;
-
    -
    -
    -
    3. -
- - - - - - - - diff --git a/libstdc++-v3/doc/xml/manual/intro.xml b/libstdc++-v3/doc/xml/manual/intro.xml index db6e09a7793c..b750f0a67857 100644 --- a/libstdc++-v3/doc/xml/manual/intro.xml +++ b/libstdc++-v3/doc/xml/manual/intro.xml @@ -1,3 +1,9 @@ + + +] > + @@ -208,19 +214,7 @@ requirements of the license of GCC. The links are to the specific defect reports from a partial copy of the Issues List. You can read the full version online at the ISO C++ - Committee homepage, linked to on the - GCC "Readings" - page. If - you spend a lot of time reading the issues, we recommend downloading - the ZIP file and reading them locally. - - - (NB: partial copy means that not all - links within the lwg-*.html pages will work. Specifically, - links to defect reports that have not been accorded full DR - status will probably break. Rather than trying to mirror the - entire issues list on our overworked web server, we recommend - you go to the LWG homepage instead.) + Committee homepage. If a DR is not listed here, we may simply not have gotten to @@ -228,60 +222,60 @@ requirements of the license of GCC. and src directories for appearances of _GLIBCXX_RESOLVE_LIB_DEFECTS for examples of style. Note that we usually do not make changes to the - code until an issue has reached DR status. + code until an issue has reached DR status. - 5: + 5: string::compare specification questionable This should be two overloaded functions rather than a single function. - 17: + 17: Bad bool parsing Apparently extracting Boolean values was messed up... - 19: + 19: "Noconv" definition too vague If codecvt::do_in returns noconv there are no changes to the values in [to, to_limit). - 22: + 22: Member open vs flags Re-opening a file stream does not clear the state flags. - 23: + 23: Num_get overflow result Implement the proposed resolution. - 25: + 25: String operator<< uses width() value wrong Padding issues. - 48: + 48: Use of non-existent exception constructor An instance of ios_base::failure is constructed instead. - 49: + 49: Underspecification of ios_base::sync_with_stdio The return type is the previous state of synchronization. - 50: + 50: Copy constructor and assignment operator of ios_base These members functions are declared private and are @@ -289,55 +283,55 @@ requirements of the license of GCC. "copying stream state" was deemed too complicated. - 60: + 60: What is a formatted input function? This DR made many widespread changes to basic_istream and basic_ostream all of which have been implemented. - 63: + 63: Exception-handling policy for unformatted output Make the policy consistent with that of formatted input, unformatted input, and formatted output. - 68: + 68: Extractors for char* should store null at end And they do now. An editing glitch in the last item in the list of [27.6.1.2.3]/7. - 74: + 74: Garbled text for codecvt::do_max_length The text of the standard was gibberish. Typos gone rampant. - 75: + 75: Contradiction in codecvt::length's argument types Change the first parameter to stateT& and implement the new effects paragraph. - 83: + 83: string::npos vs. string::max_size() Safety checks on the size of the string should test against max_size() rather than npos. - 90: + 90: Incorrect description of operator>> for strings The effect contain isspace(c,getloc()) which must be replaced by isspace(c,is.getloc()). - 91: + 91: Description of operator>> and getline() for string<> might cause endless loop @@ -346,7 +340,7 @@ requirements of the license of GCC. not required to set gcount). - 103: + 103: set::iterator is required to be modifiable, but this allows modification of keys. @@ -355,14 +349,14 @@ requirements of the license of GCC. are constant iterators. - 109: + 109: Missing binders for non-const sequence elements The binder1st and binder2nd didn't have an operator() taking a non-const parameter. - 110: + 110: istreambuf_iterator::equal not const This was not a const member function. Note that the DR says to @@ -370,84 +364,84 @@ requirements of the license of GCC. overloaded version with identical contents. - 117: + 117: basic_ostream uses nonexistent num_put member functions num_put::put() was overloaded on the wrong types. - 118: + 118: basic_istream uses nonexistent num_get member functions Same as 117, but for num_get::get(). - 129: + 129: Need error indication from seekp() and seekg() These functions set failbit on error now. - 130: + 130: Return type of container::erase(iterator) differs for associative containers Make member erase return iterator for set, multiset, map, multimap. - 136: + 136: seekp, seekg setting wrong streams? seekp should only set the output stream, and seekg should only set the input stream. - - 167: + 167: Improper use of traits_type::length() op<< with a const char* was calculating an incorrect number of characters to write. - 169: + 169: Bad efficiency of overflow() mandated Grow efficiently the internal array object. - 171: + 171: Strange seekpos() semantics due to joint position Quite complex to summarize... - 181: + 181: make_pair() unintended behavior This function used to take its arguments as reference-to-const, now it copies them (pass by value). - 195: + 195: Should basic_istream::sentry's constructor ever set eofbit? Yes, it can, specifically if EOF is reached while skipping whitespace. - 211: + 211: operator>>(istream&, string&) doesn't set failbit If nothing is extracted into the string, op>> now sets failbit (which can cause an exception, etc., etc.). - 214: + 214: set::find() missing const overload Both set and multiset were missing @@ -455,47 +449,47 @@ requirements of the license of GCC. for const instances. - 231: + 231: Precision in iostream? For conversion from a floating-point type, str.precision() is specified in the conversion specification. - 233: + 233: Insertion hints in associative containers Implement N1780, first check before then check after, insert as close to hint as possible. - 235: + 235: No specification of default ctor for reverse_iterator The declaration of reverse_iterator lists a default constructor. However, no specification is given what this constructor should do. - 241: + 241: Does unique_copy() require CopyConstructible and Assignable? Add a helper for forward_iterator/output_iterator, fix the existing one for input_iterator/output_iterator to not rely on Assignability. - 243: + 243: get and getline when sentry reports failure Store a null character only if the character array has a non-zero size. - 251: + 251: basic_stringbuf missing allocator_type This nested typedef was originally not specified. - 253: + 253: valarray helper functions are almost entirely useless Make the copy constructor and copy-assignment operator declarations @@ -503,60 +497,60 @@ requirements of the license of GCC. definitions. - 265: + 265: std::pair::pair() effects overly restrictive The default ctor would build its members from copies of temporaries; now it simply uses their respective default ctors. - 266: + 266: bad_exception::~bad_exception() missing Effects clause The bad_* classes no longer have destructors (they are trivial), since no description of them was ever given. - 271: + 271: basic_iostream missing typedefs The typedefs it inherits from its base classes can't be used, since (for example) basic_iostream<T>::traits_type is ambiguous. - 275: + 275: Wrong type in num_get::get() overloads Similar to 118. - 280: + 280: Comparison of reverse_iterator to const reverse_iterator Add global functions with two template parameters. (NB: not added for now a templated assignment operator) - 292: + 292: Effects of a.copyfmt (a) If (this == &rhs) do nothing. - 300: + 300: List::merge() specification incomplete If (this == &x) do nothing. - 303: + 303: Bitset input operator underspecified Basically, compare the input character to is.widen(0) and is.widen(1). - 305: + 305: Default behavior of codecvt<wchar_t, char, mbstate_t>::length() @@ -564,20 +558,20 @@ requirements of the license of GCC. mbstate_t>::do_length must return. - 328: + 328: Bad sprintf format modifier in money_put<>::do_put() Change the format string to "%.0Lf". - 365: + 365: Lack of const-qualification in clause 27 Add const overloads of is_open. - 387: + 387: std::complex over-encapsulated Add the real(T) and imag(T) @@ -586,20 +580,20 @@ requirements of the license of GCC. free functions. - 389: + 389: Const overload of valarray::operator[] returns by value Change it to return a const T&. - 396: + 396: what are characters zero and one Implement the proposed resolution. - 402: + 402: Wrong new expression in [some_]allocator::construct Replace "new" with "::new". @@ -613,7 +607,7 @@ requirements of the license of GCC. Tweak the debug-mode checks in _Safe_iterator. - 409: + 409: Closing an fstream should clear the error state Have open clear the error flags. @@ -625,57 +619,57 @@ requirements of the license of GCC. Implement Option 3, as per N1599. - 432: + 432: stringbuf::overflow() makes only one write position available Implement the resolution, beyond DR 169. - 434: + 434: bitset::to_string() hard to use Add three overloads, taking fewer template arguments. - 438: + 438: Ambiguity in the "do the right thing" clause Implement the resolution, basically cast less. - 445: + 445: iterator_traits::reference unspecified for some iterator categories Change istreambuf_iterator::reference in C++11 mode. - 453: + 453: basic_stringbuf::seekoff need not always fail for an empty stream Don't fail if the next pointer is null and newoff is zero. - 455: + 455: cerr::tie() and wcerr::tie() are overspecified Initialize cerr tied to cout and wcerr tied to wcout. - 464: + 464: Suggestion for new member functions in standard containers Add data() to std::vector and at(const key_type&) to std::map. - 467: + 467: char_traits::lt(), compare(), and memcmp() Change lt. - 508: + 508: Bad parameters for ranlux64_base_01 Fix the parameters. @@ -694,7 +688,7 @@ requirements of the license of GCC. Use &value. - 538: + 538: 241 again: Does unique_copy() require CopyConstructible and Assignable? @@ -702,7 +696,7 @@ requirements of the license of GCC. input_iterator' value_type. - 539: + 539: partial_sum and adjacent_difference should mention requirements @@ -710,250 +704,250 @@ requirements of the license of GCC. in adjacent_difference. - 541: + 541: shared_ptr template assignment and void Add an auto_ptr<void> specialization. - 543: + 543: valarray slice default constructor Follow the straightforward proposed resolution. - 550: + 550: What should the return type of pow(float,int) be? In C++11 mode, remove the pow(float,int), etc., signatures. - 586: + 586: string inserter not a formatted function Change it to be a formatted output function (i.e. catch exceptions). - 596: + 596: 27.8.1.3 Table 112 omits "a+" and "a+b" modes Add the missing modes to fopen_mode. - 630: + 630: arrays of valarray Implement the simple resolution. - 660: + 660: Missing bitwise operations Add the missing operations. - 691: + 691: const_local_iterator cbegin, cend missing from TR1 In C++11 mode add cbegin(size_type) and cend(size_type) to the unordered containers. - 693: + 693: std::bitset::all() missing Add it, consistently with the discussion. - 695: + 695: ctype<char>::classic_table() not accessible Make the member functions table and classic_table public. - 696: + 696: istream::operator>>(int&) broken Implement the straightforward resolution. - 761: + 761: unordered_map needs an at() member function In C++11 mode, add at() and at() const. - 775: + 775: Tuple indexing should be unsigned? Implement the int -> size_t replacements. - 776: + 776: Undescribed assign function of std::array In C++11 mode, remove assign, add fill. - 781: + 781: std::complex should add missing C99 functions In C++11 mode, add std::proj. - 809: + 809: std::swap should be overloaded for array types Add the overload. - 853: + 853: to_string needs updating with zero and one Update / add the signatures. - 865: + 865: More algorithms that throw away information The traditional HP / SGI return type and value is blessed by the resolution of the DR. - 1339: + 1339: uninitialized_fill_n should return the end of its range Return the end of the filled range. - 2021: + 2021: Further incorrect uses of result_of Correctly decay types in signature of std::async. - 2049: + 2049: is_destructible underspecified Handle non-object types. - 2056: + 2056: future_errc enums start with value 0 (invalid value for broken_promise) Reorder enumerators. - 2059: + 2059: C++0x ambiguity problem with map::erase Add additional overloads. - 2062: + 2062: 2062. Effect contradictions w/o no-throw guarantee of std::function swaps Add noexcept to swap functions. - 2063: + 2063: Contradictory requirements for string move assignment Respect propagation trait for move assignment. - 2064: + 2064: More noexcept issues in basic_string Add noexcept to the comparison operators. - 2067: + 2067: packaged_task should have deleted copy c'tor with const parameter Fix signatures. - 2101: + 2101: Some transformation types can produce impossible types Use the referenceable type concept. - 2106: + 2106: move_iterator wrapping iterators returning prvalues Change the reference type. - 2108: + 2108: No way to identify allocator types that always compare equal Define and use is_always_equal even for C++11. - 2118: + 2118: unique_ptr for array does not support cv qualification conversion of actual argument Adjust constraints to allow safe conversions. - 2127: + 2127: Move-construction with raw_storage_iterator Add assignment operator taking an rvalue. - 2132: + 2132: std::function ambiguity Constrain the constructor to only accept callable types. - 2141: + 2141: common_type trait produces reference types Use decay for the result type. - 2144: + 2144: Missing noexcept specification in type_index Add noexcept - 2145: + 2145: error_category default constructor Declare a public constexpr constructor. - 2162: + 2162: allocator_traits::max_size missing noexcept Add noexcept. - 2187: + 2187: vector<bool> is missing emplace and emplace_back member functions Add emplace and emplace_back member functions. - 2192: + 2192: Validity and return type of std::abs(0u) is unclear Move all declarations to a common header and remove the generic abs which accepted unsigned arguments. - 2196: + 2196: Specification of is_*[copy/move]_[constructible/assignable] unclear for non-referencable types Use the referenceable type concept. - 2212: + 2212: tuple_size for const pair request <tuple> header The tuple_size and tuple_element @@ -961,56 +955,56 @@ requirements of the license of GCC. is included by <array>. - 2296: + 2296: std::addressof should be constexpr Use __builtin_addressof and add constexpr to addressof for C++17 and later. - 2313: + 2313: tuple_size should always derive from integral_constant<size_t, N> Update definitions of the partial specializations for const and volatile types. - 2328: + 2328: Rvalue stream extraction should use perfect forwarding Use perfect forwarding for right operand. - 2329: + 2329: regex_match()/regex_search() with match_results should forbid temporary strings Add deleted overloads for rvalue strings. - 2332: + 2332: regex_iterator/regex_token_iterator should forbid temporary regexes Add deleted constructors. - 2399: + 2399: shared_ptr's constructor from unique_ptr should be constrained Constrain the constructor to require convertibility. - 2400: + 2400: shared_ptr's get_deleter() should use addressof() Use addressof. - 2401: + 2401: std::function needs more noexcept Add noexcept to the assignment and comparisons. - 2407: + 2407: packaged_task(allocator_arg_t, const Allocator&, F&&) should neither be constrained nor explicit @@ -1018,74 +1012,74 @@ requirements of the license of GCC. Remove explicit from the constructor. - 2415: + 2415: Inconsistency between unique_ptr and shared_ptr Create empty an shared_ptr from an empty unique_ptr. - 2418: + 2418: apply does not work with member pointers Use mem_fn for member pointers. - 2440: + 2440: seed_seq::size() should be noexcept Add noexcept. - 2441: + 2441: Exact-width atomic typedefs should be provided Define the typedefs. - 2442: + 2442: call_once() shouldn't DECAY_COPY() Remove indirection through call wrapper that made copies of arguments and forward arguments straight to std::invoke. - 2454: + 2454: Add raw_storage_iterator::base() member Add the base() member function. - 2455: + 2455: Allocator default construction should be allowed to throw Make noexcept specifications conditional. - 2458: + 2458: N3778 and new library deallocation signatures Remove unused overloads. - 2459: + 2459: std::polar should require a non-negative rho Add debug mode assertion. - 2466: + 2466: allocator_traits::max_size() default behavior is incorrect Divide by the object type. - 2484: + 2484: rethrow_if_nested() is doubly unimplementable @@ -1093,21 +1087,21 @@ requirements of the license of GCC. ill-formed. - 2583: + 2583: There is no way to supply an allocator for basic_string(str, pos) Add new constructor - 2684: + 2684: priority_queue lacking comparator typedef Define the value_compare typedef. - 2770: + 2770: tuple_size<const T> specialization is not SFINAE compatible and breaks decomposition declarations @@ -1116,7 +1110,7 @@ requirements of the license of GCC. only use it if valid. - 2781: + 2781: Contradictory requirements for std::function and std::reference_wrapper -- 2.43.5